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NASA Technical Memorandum 104774 TECHNICAL UPDATE: JSC System Using a Solid Electrolytic Cell in a Remote Location to Measure Oxygen Fugacities in CO/CO2 Controlled-Atmosphere Furnaces A. J. G. Jurewicz Lockheed Engineering and Sciences Co. Houston, TX 77058 R. J. Williams NASA Space Station Program Officer Reston, VA 22091 L. Le Lockheed Engineering and Sciences Co. Houston, TX 77058 J. Wagstaff Lockheed Engineering and Sciences Co. Houston, TX 77058 NASA National Aeronautics and Space Administration G. E. Lofgren, Ph.D. Lyndon B. Johnson Space Center Houston, Texas 77058 A. Lanier Lockheed Engineering and Sciences Co. Houston, TX 77058 W. Carter Lockheed Engineering and Sciences Co. Houston, TX 77058 A. Roshko National Institute of Standards and Technology Boulder, CO 80303

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CONTENTS Section Page SUMMARY ........................................................................................................................... 1 INTRODUCTION ................................................................................................................ 1 NEW MODIFICATIONS ...................................................................................................... 1 COMPUTER SOFTWARE .................................................................................................. 3 CONCLUDING REMARKS ................................................................................................. 4 REFERENCES ..................................................................................................................... 4 APPENDIX ............................................................................................................................ A-1

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FIGURES Figure Page Schematicof the manifoldsystemusedto divertthe exhaust furnacetothe referencefurnace.......................................... 6 gasesfromthe sample 2 The differencebetweenthe oxygencontentofthe samplefurnace as measureddirectlyandthe oxygencontentof the samplefurnace calculatedfrommeasurementsinthereferencefurnace............................................ 3 A graphin T-fO2spaceshowinghowlinesof constantgas mixturesaresubparallelto solidbuffers................................................................... 4 Printoutfromthe BASICprogramthatis usedto relatethe measurementsfromthe referencefurnaceto conditionsinthe samplefurnace......................................................................................................... iv

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TECHNICAL UPDATE: JSC System Using a Solid Electrolytic Cell in a Remote Location to Measure Oxygen Fugaclties in CO/CO2 Controlled-Atmosphere Furnaces SUMMARY The CO/CO 2 controlled-atmosphere furnaces in the Johnson Space Center Experimental Petrology Laboratory have been modified so that only one solid electrolyte zirconia cell 1,2 is needed for all the furnaces running under standard operating conditions and requiring standard tolerances for deviations in oxygen fugacity. This technique relies on measuring the oxygen fugacity (fO2) in each experimental furnace using a zirconia cell in a designated reference furnace. A manifold system diverts the exhaust gas from the experimental furnace containing the sample through the reference furnace. Then, (1) the temperature and fO2 of the reference furnace are used to calculate the composition of the exhaust gases; (2) given the temperature of the sample furnace and the composition of the exhaust gas, the fO2 of the sample furnace is obtained from the Deines et al. (1974) tables. 3 This cumbersome procedure has been computerized to save time and to give added flexibility to the scientist using the system. Using a remote system for measuring fO 2 saves money by reducing the need for a zirconia cell in each furnace, as well as extending the life of the cells in use. It also widens the range of temperatures and fO2's within which the scientist can run samples. There are, however, additional errors incurred while measuring the gases outside the sample furnace. Calibration procedures can be used to show the size of the additional error for a given furnace configuration and set of experimental conditions. INTRODUCTION Williams and Mullins' (1981) NASA Technical Memorandum 58234 describes the basic system used at JSC for performing experiments and materials synthesis under controlled oxygen fugacities. 2 The system controls the partial pressure of oxygen by passing a gas comprised of a specific mixture of CO and CO2 gases over the sample slowly enough that they react to produce predictable, equilibrium amounts of CO, CO2, and 02. Using this method, very small concentrations of 02 can be controlled very precisely. For example, oxygen partial pressures of 10 "10 atm (+10 "0"2 atm) 02 are obtained routinely. There are, however, several limitations to the basic system described by Williams and Mullins (1981). That system requires that an electrolytic cell be placed within each of the furnaces, even though the cells are both fragile and expensive. Moreover, the cells are easily contaminated, and they are limited in the range of temperatures and oxygen fugacities at which they will function. So, even as Williams and Mullins (1981) was being published, new modifications were being implemented to make the systems less expensive to maintain, more flexible, and easier to operate.

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NEWMODIFICATIONS The most radical improvement to the JSC system is the implementation of a technique for remotely measuring the oxygen fugacities. The exhaust gas from each furnace is routed through a manifold having a series of T-valves (fig. 1). When all of the valves are closed, the flow of the exhaust gases are unchanged from that of the Williams and Mullins (1981) system. 2 However, to measure fO2, the exhaust gas for a given furnace is diverted by opening the appropriate valve on the manifold) through a second "reference" furnace containing a zirconia cell. The temperature and fO2 of the reference furnace and the temperature of the sample are then measured. Then, by assuming that the gas mixture is the same in both the specimen furnace and the reference furnace, the fO2 of the specimen furnace, the ambient oxygen fugacity around the sample can be calculated using the equations 3 of Deines etaL, 1981. Having the cell in a remote furnace has four major advantages. First, only one cell is required to monitor the oxygen partial pressure, or fugacity (fO2), of gases from each of a whole bank of furnaces. Second, the cells are not subject to contamination by either volatiles from the sample or by actual physical contact from the sample,* so that the life of the individual cell is increased. Third, the cell is not subjected to the heating and cooling cycles encountered while loading or changing samples. Moreover, any change in temperature required during maintenance can be done in a controlled manner; accordingly, the cell does not experience significant thermal cycling or shock, and the life of the cell is increased. Fourth, conditions can be obtained in the sample furnace that normally would be too extreme for monitoring the oxygen fugacity directly. Under extreme conditions, especially for long durations, the zirconia cell begins to be nonlinear and inaccurate. In many cases, the temperature of the reference furnace can be chosen so that, when the exhaust gas from the sample furnace is passed through the reference furnace, the reference fO 2 is within the linear range of the cell. Of course, when using the remote system for this purpose, the experimentalist must assume that the gases within the sample furnace are behaving ideally, as there is no way to measure the partial pressure of oxygen directly. Because the world is not ideal, the reference system is not a complete panacea. Potential problems are associated with this system or any system that monitors conditions remotely. For example, any leaks of oxygen into the system could swamp the small fO2s being measured and make the reference fO2 more oxidizing than the sample conditions would dictate. In theory, a physical leak of 02 into the manifold system can be circumvented by keeping the gas pressure within the furnaces and lines above one atmosphere. Carbon precipitation from the gas AFTER the gas passes through the hotspot of the furnace would also make the reference fO2 appear more oxidizing than that actually in the sample furnace. * The electrolytic cell works because the oxygen-defect concentration at a given temperature and fO2 is predictable; accordingly, even minor contamination may produce significant errors. A reaction between the cell and a sample with which it is in physical contact renders the cell completely inoperative. In the modified JSC system, the sample will clearly never come in contact with the remote solid electrolytecell. Moreover, most of the volatiles from the sample, such as iron or silica, are likely to precipitate in the cold parts of the sample furnace or in the gas lines leading to the reference furnace. Thus, they will not reach the remote cell. 2

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Severalsets of experiments have been run to quantify how large an error is incurred by sampling the gases remotely. In these experiments, the ambient fO2's in the specimen and reference furnaces were measured simultaneously over a variety of conditions. The first set of these "calibration" experiments was done by R. Williams, O. Mullins, and a then summer intern student, A. Roshko, in 1981-1982 as a part of the initial implementation of the system. Other investigators have since performed similar experiments for their particular furnaces and conditions. In 1990, L. Le performed extensive calibrations over a wide range of fO2's for a variety of furnace configurations. This was followed in 1992 by a recalibration of L. Le's most successful furnace configurations using the smaller, faster-responding Ceramic Oxide Fabricators sensors (Australian Patents #466251 and #513552). Figure 2 gives the results from one of the latest furnace calibrations. It illustrates an important point concerning the accuracy of the reference system. For the more oxidizing CO/CO2 gas mixtures, the reference system is quite accurate over a wide range of temperaturesmthe oxygen partial pressures calculated for the sample fumace are within xl0:l: 0.2 atmospheres of the actual oxygen content. Although not illustrated here, loss of accuracy can occur when the sample furnace is at a lower temperature. This loss of accuracy is explained if the reaction between the CO and CO2 gas in the sample furnace has not gone to completion. As such, this error can be a function of flow rate. There is also a loss of accuracy for the more reducing CO/CO2 gas mixtures. In these extreme cases, this loss of accuracy is explained if the exhaust gases are unstable in the temperature gradients of either the sample furnace or the reference furnace, or both. The instability could allow carbon to precipitate after the gas has passed the sample and entered the cooler regions of the furnace or exhaust line, causing measurement in the reference furnace to indicate that the sample furnace is significantly more oxidizing than it actually is. In fact, we routinely observe such carbon precipitates under certain operating conditions. In general, it has been found that the deviation in f02 between the reference furnace and the sample furnace varies with parameters such as furnace configuration, gas flow rates, and run conditions. However, these deviations are considered acceptably small by the majority of scientists using the system. The restrictions for accurate use of the remote system for all of the controlled-atmosphere furnaces now in use at JSC are (a) redox conditions well above the graphite saturation surface, (b) temperatures high enough for the initial gas mixture to react to completion, and (c) flow rates within the recommended range (cf., ref. 4). Experimental conditions characterized by C0/C02 gas mixtures near the graphite saturation surface, low temperatures, or unusual gas flow rates can be attained; however, the scientist must be aware of the potential sources of error. 3

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COMPUTERSOFTWARE When initially implemented, the remote measuring system saved laboratory costs and promoted flexibility; however, it required that the scientist spend additional time setting up each experiment. First, after a run temperature and fO2 were chosen, the appropriate gas mixture had to be found in the Deines et aL (1974) tables. Then, the gas mixture and the temperature of the reference furnace were used to calculate (a) the fO2 of the reference furnace, and (b) the EMF readout from the zirconia electrolytic cell. Because the Deines et al. (1974) tables were designed for finding a gas mixture given a temperature and fO2, but not the reverse, finding the fO2 given the gas mixture was sometimes a time-consuming process. For several years after the implementation of the reference system, many scientists used approximations to make the calculation process less cumbersome. One shortcut was to notice that in T-fO2 space, the CO/CO 2 mixing curves were similar in trajectory to standard buffer curves (fig. 3). Then, for small changes in temperature, the buffer curve was assumed to be parallel to the CO/CO 2 mixing curve on a plot of T versus fOp. If the fOp of the reference furnace were set relative to that of a standard buffer, the-fO 2 inside-the sample furnace could be computed analytically by assuming it to have the same offset from that standard buffer, although at a different temperature. If, at a later date, the assumption of parallel trajectories were deemed insufficient, then the actual fO 2 to which the sample was exposed could be calculated. Similarly, when a sample was set at a given temperature and fO 2, and then the temperature was ramped, it was generally assumed that the fO 2 staye_l constant relative to a standard buffer curve (cf., notation of fig. 2). This approximation was adequate for small changes in temperature. However, large changes in temperature at a given gas mixture produced large changes in fO 2, which had to be tediously calculated from the Deines et aL (1974)tables. 3 In 1990, A. J. G. Jurewicz developed a computer program to use with the remote measuring system based upon a preexisting BASIC program.5 The central algorithm is based upon the computations of Deines et aL (1974). This new program (a) calculates the fOpin the reference furnace and EMF measured by the zirconia cell given the T, fO 2 of the sample furnace and the temperature of the reference furnace (b) back-calculates the fO 2 in the sample furnace given the T and fO 2 (or EMF measured by the zirconia cell) in the reference furnace (c) calculates the fO 2 as a function of temperature for a given gas mixture, the situation that occurs when the furnace conditions are set, and then the temperature is ramped up or down during the run. In addition, the program calculates (1) changes in EMF with changes in both temperature and fop, (2) changes in fOp with small fluctuations in the gas composition, as well as (3) whether or not carbon will-precipitate in the hot spot of the furnace. A sample printout from version 2.2 is shown in figure 4.

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CONCLUDING REMARKS Both the network of JSC controlled-atmosphere furnaces and the applicable computer software constitute a dynamic system. Physical modifications that may increase the reliability and the ease of using the furnaces are being tested continuously. Similarly, the computer program has been modified several times as needs arise, and it will continue to grow and provide more flexibility and efficiency for the scientist. REFERENCES 1. Sato, Motoaki: Electrochemical Measurements and Control of Oxygen Fugacity and Other Gaseous Fugacities with Solid Electrolyte Sensors. Research Techniques for High Pressure and High Temperature, Gene C. Ulmer, ed., Springer-Verlag (New York), 1971, pp. 43-49. 2. Williams, R. J. and O. Mullins: JSC Systems Using Solid Ceramic Oxygen Electrolyte Cells to Measure Oxygen Fugacities in Gas-Mixing Systems. NASA TM-58234, 1981. 3. Deines, P.; Nafziger, R. H.; Ulmer, G. C.; and E. Woermann: Temperature-oxygen fugacity tables for selected gas mixtures in the system C-H-O at one atmosphere total pressure. Earth and Miner. Sci. Exper. Sta., Bull., The Penn. State Univ. College of Earth and Miner. Sci., N 88 129 pp., 1974. 4. Darkin, L. S.; and R. W. Gurry: The system iron-oxygen. I. The wustite field and related equilibria. J. Amer. Chem. Soc. V86, 1945, pp. 1398-1412. 5. Jurewicz, A. G. J.: Appendix 2: Software Used to Calculate Run Conditions for the Deltech Controlled-Atmosphere Furnace in Effect of Temperature, Pressure, Oxygen Fugacity and Composition on Calcium Partitioning, Calcium-Magnesium Distribution and the Kinetics of Cation Exchange Between Olivines and Basaltic Melts. Thesis, Geology Department, Rensselaer Polytechnic Inst. (Troy, NY, 12180), 1986, pp. 206-213 5

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furnace I_ exhaust gas (.|uml¢s 1) ..... p,- tO reference ol ................ exhaust gas (furnace 1) exhaust gas (furnace 2) NORMAL EXHAUST exhaust gas (furnace 3) exhaust gas (furnace 4) LEGEND valve, a check-valve is recommended ...... _ path and direction of gas flow Figure 1. Schematic of the manifold system used to divert the exhaust gases from the sample furnace to the reference furnace. Each valve controls the exhaust gas of a different fumace. When a valve is closed, the exhaust is unchanged from that of Williams and Mullins (1981).2 When a valve is opened, the exhaust gas is diverted through the reference furnace. Care must be taken not to open more than one valve at a time. Also, it is recommended that the valves on the manifold be check valves, although any gas-tight, two-way valve is adequate.

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0.6 - 0.4o.2o ! _ -0.4 - _o61- , , 1000 1100 IW+l IW IW-1 IW-2 [] _ - -" , , , 1200 1300 1400 TEMPERATURE (Oc) Figure 2. The difference between (1) the oxygen content of the sample fumace as measured directly and (2) the oxygen content of the sample furnace calculated from measurements in the reference furnace (e.g., log f_2 sample - log fO2 reference). Standard flow rates of CO/CO 2 gasses were used;-" the zirconia cells were calibrated for any cell-specific nonlinearities; and, prior to the calibration, the sample furnace was determined to be free of gas leaks (air leaking into the system AFTER the hot spot of the sample furnace would distort the results). For this calibration, the reference furnace was set to near 1200"C (1205"+5"C): a temperature high enough to ensure rapid gas-phase reactions. The CO/CO 2 gas mixtures were chosen so that they produced oxygen partial pressures, w_ich can be related to that of the Iron-Wuestite (IW) standard buffer assemblage.-" For example, IW+I refers to one log unit above the oxygen partial pressure produced by the IW buffer (i.e., 10 times the oxygen content), while IW-1 refers to conditions one log unit below the oxygen partial presssure produced by the IW buffer (i.e., the oxygen content divided by 10). 7

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-4 Mixed CO/CO 2 -6 gas: [] 90% CO2 -8 • lOO/oC_ _ 1 4 Solid buffers: _' m / • QFM (quartz, -18 fayalite magnetite) -20 ..... / # - _'' r. - -. ...... • _ g =p t: %, , 1000 1200 1400 1600 TEMPERATURE (°C) Figure 3. A graph in T-fO 2 space showing how lines of constant gas mixtures are subparallel to solid buffers. 8

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EXAMPLE RUN CONDITIONS SPECIMEN T(C) 1180 FURNACE REFERENCE FURNACE 1110 log (fO2/at m) -13.16 -14.18 %CO2 10.10 dlogfO2/d%CO2 +0.015 EMF (mV)* dEMF/dT(mV) dEMF/dfO2 (mV/0.1) buffer+offset IW-1.00 C in H.S.? NO 10.10 -953.9 +0.47 +6.86 NO * This number is 19 mV from the ideal Figure 4. Printout from the BASIC program, which is used to relate the measurements from the reference furnace to conditions in the sample furnace. The information printed includes the temperatures of both furnaces (T(°C)); the oxygen content of the gas in each furnace in log units (Iog(fO2/atm)); the initial CO_(CO+CO ) ratio of the gas (%CO2); the voltage in millivolts measured across the ectrolytic2cell in the reference furnace (EMF); estimates of the changes in EMF with changes in temperature (dEMF/dT) and oxygen content (dEMF/dfO2); the relationship of the specimen fO 2 to a standard buffer (buffer+offset); whether or not carbon will precipitate in the hot spots of the furnaces (C In H.S.?); and, the correction for the intrinsic error of that particular zirconia cell (*). 9

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APPENDIX SoftwareUsedalongwiththe ReferenceSystemof DeterminingFurnaceConditions. This softwareactuallyconsistsof threeseparateGWBASIC programs. The programs are: GAS.BAS, used for selecting gas mixtures to acheive specific oxygen fugacities given ideal sample furnace temperatures; GASREV2.BAS, used for calculating the true oxygen fugacity in the sample furnace, given the sample temperature and the measured conditions in the reference furnace; and RAMP.BAS, used for seeing how conditions change in the sample furnace at a given gas mix when the temperature is ramped. All three applications have been linked using the CHAIN function, and are organized by a menu program (MENU.BAS), used for selecting applications. A fourth application program, CALIB.BAS, used for calculating the ideal EMF of a zirconia cell given a chemical analysis of a calibration gas and the measured furnace temperature, is still in progress. The software is based upon the BASIC program by A. Jurewicz (1986). A-1

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Listof Variables. A. BranchingandStringVariables A$ =generalbranchvariable. B$ = YESif carbonwill precipitatein the hot spotof the furnaceand NOotherwise BUFFERS= the labelof the buffer(= NONEif Z$=N) CHANGE%= branchvariablein menu. CHOICE%= branchvariablein menu. C$ = generalbranchvariable. DECIDES= to continueor exitif carbonprecipitation. FURNACES= sampleor reference ICOUNTER= for indicatingsampleor reference J, J1 = countingvariablesforprint-outin rampingprogram. LABELS--titleforcalculation&/orprint-out. P$ = branch,askingprogramto endloop. Q$ = branchvariable. ROUND%= for checkingif printerto use(Laseror Epson)hasbeendefined. STEPFO2= counterfor iterativelycalculatingoxygenfugacity,stepwise. STEPT%= temperaturestepsoverwhichto calculateoxygenfugacityat a constantgasmixture. V$ = checksfor INKEYto endpause. Y = numberof loopstheprogramhasrun (Y>0meansheadinghasalreadybeen printed). X$,XX$ = simplebranches. Z = counterfor H= +1 or -1 (seeQ(Z)). Z$, Y = fO2 correspondsto a buffer;N = fO2 doesnot correspondto a buffer. Constants. R = empericalconstantinequationsof equilibriumequationsof Deinesetal (1974). NumericVariables. A = functionof K1and LOGFO2as listed. AA= newAfor shiftintemperature(calculatingDELEMFDELT). CORREMF= the systematicoffsetofthe EMFof the referencefurnacemeasured duringcalibration. DELEMFDELFO2=the change in ideal EMF with a small change in furnace fO2. DELEMFDELT = the change of EMF with small changes in temperature. EMF(T,K) = EMF at temperature T (celcius) and oxygen fugacity K (log units). FCO = the partial pressure of carbon monixide. FCO2 = the partial pressure of carbon dioxide. FO2OFFSET -- deviation of oxygen fugacity from that of a standard, reference buffer in sample furnace. FO2OFFSET2 -- deviation of oxygen fugacity from that of a standard, reference buffer in reference furnace. GG = new Gibbs free energy for calculating DELEMFDELT. G1 = Gibbs free energy for the reaction, CO+O 2 to CO 2 from Deines et al (1974). G2 ---Gibbs free energy for the reaction, C+O2 to CO from Deines et al (1974). H = incremental change in temperature (DELEMFDELT). IDEALEMF = EMF calculated from the Nernst Equation. K1 = equilibrium constant for the reaction CO+O2 to CO2 from Deines et al (1974). K2 = equilibrium constant for the reaction, C+O2 to CO from Deines et al (1974). KK = variable equilibrium constant (for calculating DELEMFDELT). LOGFO2 = the natural logarithm of the oxygen fugacity of interest (atmospheres). MIXRATIO = %CO2 in gas mix for both furnaces. A-2

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DELRATIO= differencein gasmix betweenwanted(MIXRATIO)andcalculatedfor calculatingoxygenfugacityof referencefurnace NEWFO2= LOGFO2afterchangingtemperature. Q(Z)= equilibriumconstantsusedfor checkingstabilityof oxygenfugacitywith temperatureandgasmix. REALEMF= EMFincludingsystematicoffset. REFFO2= oxygenfugacityof referencefurnace. RM(X,Y)= empiricalvariableusingequilibriumconstantX andoxygenfugacityY, fromDeineset al (1974). SPECFO2= "specific"oxygenfugacitywantedin thesamplefurnaceduringan experiment;the specimenfO2. TC=samplefurnacetemperature;initialtemperatureduringramp. TREF= referencefurnacetemperature. TFINAL=finaltemperatureduringramp. VOLCO2= the gas mixturein volume%CO2. W = TC+Hforcalculatingstabilityofoxygenfugacitywithtemperatureandgas mix. A-3

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MENU.BAS Thissub-programsegmentlinksallof thesub-programstogetherusingthe CHAINcommand. Essentially,it actslikea menuforselectingapplications(theothersub-programs). SelectseitherEpsonprinteror Laserprinter(autoformfeed).Seeline204. 1 ROUND%=-1:PRINTER$="EPSON" InitialTitleforProgram 2 DIMREFFO2(100),FO2OFFSET2(100) 5 DEFDBLG,A,K 10 COLOR 15,14,14:CLS 20 PRINT:PRINT:PRINT:PRINT 30 PRINT" CO/CO2GASMIXINGUTILITYPROGRAM" 32 PRINT" version3.0":PRINT:PRINT:PRINT 34 PRINT" SeeA.J.GJurewicz,if you haveanyquestions" 40 PRINT:PRINT:PRINT 41 COLOR14,15,15 42 PRINT"Pressanykey to continue..." 50 V$=INKEY$ 60 IF (LEN(V$)=0)GOTO50 ProgramMenu 70 COLOR15,9,9:CLS:PRINT:PRINT:PRINT:PRINT 75 ROUND%=ROUND%+I 80 PRINT"Do youwant to:" 90 PRINT:PRINT°' 1.Take knownsampletemperatureandoxygenfugacities" 100PRINT" anddeterminethe %CO2ofthe gas,andthe" 102PRINT °' fO2, & EMF of reference furnace" 110 PRINT:PRINT 120 PRINT" 2. Take EMF (or setpoint) and T of reference furnace and" 130 PRINT" determine fO2 of the sample" 140 PRINT:PRINT 150 PRINT" 3. Determine the range of fO2's experienced by a sample" 160 PRINT" with a fixed gas mixture, but where the temperature was" 170 PRINT" ramped" 180 PRINT:PRINT:PRINT" 4. Exit program" 185 COLOR 1,15,15 190 PRINT:PRINT:PRINT "Enter choice of 1,2, 3, or 4. ";:INPUT "",CHOICE% 200 IF (CHOICE%<1) OR (CHOICE%>4) GOTO 190 201 IF (CHOICE%=4) GOTO 211 202 IF ROUND%>0 GOTO 210 Selects either Epson printer or Laser printer. The only difference for this program is that the Laser printer requires an automatic form feed after printing. 204 COLOR 14,15,15:PRINT:PRINT:PRINT "Do you have a laser printer (Y/N)?";: 206 Q$=INPUT$(1):IF (Q$="y") OR (Q$="Y") GOTO 209 207 IF (Q$="N") OR (Q$="n") GOTO 210 208 PRINT "HUH?":GOTO 204 209 PRINTER$="LASER" A-4

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Branchtoothersub-programs,or Exit,as selectedonmenu. 210 COLOR31,1,1:CLS:PRINT:PRINT:PRINT:PRINT"LOADINGNEXT SEGMENT" 211 ON CHOICE%GOTO220,230,240,250 220CHAIN"GAS.BAS",I0,ALL 230CHAIN"GASREV2",I0,ALL 240CHAIN"RAMP",10,ALL 250 COLOR17,15,15 252PRINT:PRINT:PRINT"Areyou surethatyouwantto exit (Y/N)?";: 260 Q$=INPUT$(1):IF(Q$="y")OR (Q$="Y")GOTO290 270 IF (Q$="N")OR (Q$="n")GOTO70 280 PRINT"HUH?":GOTO240 290 PRINT"O.K.":COLOR15,0,0:CLS 300PRINT:PRINT:PRINT:PRINT 305PRINT"Atthe OKprompt,type SYSTEM" 310 PRINT"Toreturntothe operatingsystem":PRINT:PRINT:END A-5

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GAS.BAS This sub-programtakesthe sampletemperatureandoxygenfugacitywhichtheexperimentalist desires,andcalculateswhatthe gasmixtureshouldbe.Then,giventhe temperatureofthe referencefurnace,calculatesthe oxygenfugacityofthe referencefurnaceandthe EMFregistered by thezirconiacell. SetsUser-definedfunctionsas well as mainmenu. 10REM 20 REMTHIS VERSIONINCLUDESCHANGINGREFERENCEGASTO OXYGEN 30 DEFFNEMF(T,K)= .0496055*(T+273)(K+0) 40 REMDEFDBLG,K,A 50 DEFFN RM(X,Y)=(X-3X*(10^Y)- 2"((10^Y)^(3/2)))/(2"X*(10^Y)+(10^Y)+((10^Y)^(3/2))+SQR(10^Y)) 52 COLOR 15,1,1:CLS 60 PRINT:PRINT 62 PRINT" PROGRAMTO CALCULATEPARAMETERSTO BE USED WITH" 70 PRINT" NASACO/CO2GAS-MIXINGFURNACES" 72 PRINT 73 PRINT" REMINDER.... " 80 PRINT" FOREXTREMERANGES(OTHERTHAN1000C<T<1400, -6<logfO2<-16)" 90 PRINT" THEZlRCONIACELLMAYBECOMENON-IDEAL" 100COLOR6,15,15 127PRINT:PRINT"Doyouwishto continue,or returnto the mainmenu(C/R)?" 128Q$=INPUT$(1) 129 IF (Q$="c")OR (Q$="C")GOTO150 130 IF (Q$="r")OR (Q$="R")GOTO140 135 PRINT:PRINT"HUH?":PRINT:GOTO127 140CHAIN"MENU.BAS",70,ALL Selectingandchangingvariables. 150Y=0:R=1.98726E-03 200 REMVARIABLESUSEDARE: TC,TREF,FO2OFFSET2,BUFFER$,REFFO2,REALEMF,CORREMF 202 REMMOREVARIABLESUSEDARE:IDEALEMF 205 PRINT:PRINT:PRINT 210 TC=1400:TREF=1065:FO2OFFSET2=-I:BUFFER$="IW":SPECFO2=- 10.69719 215 CORREMF=26:BUFFER$="IW" 220 COLOR15,3,3:CLS:PRINT:PRINT:PRINT"Thecurrent conditions are:" 225 B$(1 )="NO":B$(2)="NO":DECIDE$="YES" 230PRINT:PRINT" 1. Sample temperature is ";TC;" degrees C" 250 PRINT" 2. Sample oxygen fugacity is ";SPECFO2;" log (/atm)" 255 IF (FO2OFFSET2--0) GOTO 265 260 PRINT" --- which is ";BUFFERS;" offset ";FO2OFFSET2;" log units":GOTO 270 265 PRINT" --- which is ";BUFFERS 270 PRINT" 3. Reference temperature is ";TREF;" degrees C" 280 PRINT" 4. The correction to the zirconia cell is ";CORREMF;" mV" 3OOPRINT" and 5. The reference buffer is ";BUFFERS A-6

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320 PRINT:PRINT:PRINT 380COLOR15,9,9:PRINT"Enterthe numberyouwishto change(1 - 5, 6 to continue;7 toexit).";: 390 INPUT.... ,CHANGE% 400 IF (CHANGE%>0)AND(CHANGE%<8)GOTO420 410 COLOR31,9,9:PRINT"Pleaseentera number,1 - 7.";:COLOR15,9,9:GOTO 390 420 CLS:ONCHANGE%GOTO430,580,440,450,487,1000,140 Changingsampletemperatureat constantfO2. 430 INPUT"Enterthe newsampletemperaturein degreesC";TC 431 IF (BUFFER$="IW")GOTO850 432 IF (BUFFER$="WM")GOTO851 433 IF (BUFFER$="MH")GOTO852 434 IF (BUFFER$="QFM")GOTO853 435 IF (BUFFER$="NNO")GOTO854 436 PRINT"ERRORIN PROGRAM/NOBUFFER":STOP Changingreferencefurnacetemperature. 440INPUT "Enter the new reference temperature in degrees C";TREF:CLS:GOTO 220 Changing the deviation of zirconia cell from the ideal (systematic offset determined by calibration at reference temperature). 450 INPUT "Enter the new correction to the zirconia celI";CORREMF:CLS:GOTO 220 Changing the oxygen fugacity of the sample furnace, as well as the reference buffer (see also 580). 460 CLS :PR INT:PR INT:PR INT 470 PRINT "The sample fO2 data will be given as relative to a buffer, as well" 480 PRINT "as in Iog(fO2/atm) units. Your choice of 'reference buffers' are:" 485 GOTO 490 487 CLS:PRINT:PRINT:PRINT:PRINT "Your choice of reference buffers are:" 490 PRINT:PRINT" 1. IW" 5OO PRINT" 2. WM" 510 PRINT" 3. MH" 520 PRINT" 4. QFM" 530 PRINT" 5. NNO" 535 PRINT:PRINT "(Your current choice is )";BUFFERS 540 PRINT:PRINT "Enter the number of your selection." 550 INPUT" ",CHANGE% 56O IF (CHANGE%<1) OR (CHANGE%>5) GOTO 460 570 ON CHANGE% GOTO 571,572,573,574,575 571 BUFFER$="IW":GOTO 850 572 BUFFER$="WM":GOTO 851 573 BUFFER$="MH":GOTO 852 574 BUFFER$="QFM":GOTO 853 575 BUFFER$="NNO":GOTO 854 A-7

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580 CLS 590 PRINT:PRINT:PRINT 600 PRINT"ThesamplefurnacefO2can be expressedas anyof threeways:" 610 PRINT:PRINT" 1.as a standardbuffer" 620PRINT" 2. as offsetfroma standardbuffer" 630 PRINT" 3. as a specificfO2 (independentof anybuffer)" 650 PRINT:PRINT"Howwould youliketo expressyour newfO2" 660PRINT" (Enter1-3,or 4 for unchanged)." 670 INPUT....,CHANGE% 680 IF (CHANGE%<1)OR (CHANGE%>4)GOTO590 690 ON CHANGE%GOTO700,700,820,692 692 CLS:GOTO220 700PRINT:PRINT"Yourchoicesof standardreferencebuffersare:":PRINT 701 PRINT" 1. IW" 702 PRINT" 2.WM" 703 PRINT"3. MH" 704 PRINT"4. QFM" 705 PRINT" 5. NNO" 706 PRINT" 6. noneabove.Returnto previousmenu." 710 PRINT:PRINT"Enterthe numberofyourselection.";: 720 INPUT.... ,CHOICE% 730 IF (CHOICE%<1)OR (CHOICE%>6)GOTO710 740 FO2OFFSET2=0:IF(CHANGE%=1)GOTO760 750 INPUT"Enterthe offsetfromthe buffer,in log(fO2/atm)units.",FO2OFFSET2 760 ON CHOICE%GOTO770,780,790,800,810,580 770 SPECFO2 = 6.57 - 27215/(TC + 273)+FO2OFFSET2:BU FFER$="IW":CLS:GOTO 220 780 SPECFO2 = 13.12 - 32730/(TC + 273)+FO2OFFSET2:BU FFER$="WM":CLS:GOTO 220 790 SPECFO2 = 13.966 - 24634/(TC + 273)+FO2OFFSET2:BU FFER$="MH":CLS:GOTO 220 800 SPECFO2 = 9! - 25738/(TC + 273)+FO2OFFSET2:BU FFER$="QFM":CLS:GOTO 220 810 SPECFO2 = 9.359999 - 24930/(TC + 273)+FO2OFFSET2:BUFFER$="N NO":CLS:GOTO 220 820 CLS:PRINT:PRINT "The current Iog(fO2) is ";SPECFO2 830 PRINT:PRINT "What is the log of the new f02 that you want? ";: 840 INPUT SPECFO2:GOTO 431 850 FO2OFFSET2=SPECFO2-(6.57 851 FO2OFFSET2=SPECFO2-(13.12 852 FO2OFFSET2=SPECFO2-(13.966 853 FO2OFFSET2=SPECFO2-(91 - 27215/(TO + 273)):CLS:GOTO 220 - 32730/(TC + 273)):CLS:GOTO 220 - 24634/(TC + 273)):CLS:GOTO 220 - 25738/(TC + 273)):CLS:GOTO 220 854 FO2OFFSET2=SPECFO2-(9.359999 - 24930/(TC + 273)):CLS:GOTO 220 Program branches to calculate the parameters of interest: the gas mix needed for the sample furnace, the oxygen fugacity of the reference furnace, the EMF of the zirconia cell in the reference furnace, and the effect of small changes in the gas mixture on the oxygen fugacity in the sample furnace and the EMF of the reference furnace• 1000 COLOR 15,0,0 1001 REM NOW FO2 HAS BEEN INPUT 1010 REM SUBROUTINE AT 1750 CALCULATES GASMIXTURES, 1830 = C STABILITY 1020 REM SUBROUTINE AT 1100 CALCULATES EMF'S A-8

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1030REMSUBROUTINEAT 1380CALCULATESDELEMFDELT;1680= DEMFDFO2 1031REMSUBROUTINEAT 1530ITERATESREFERENCEFURNACEFO2 1035CLS:PRINT:PRINT:PRiNT"WORKING.... " 1040 LOGFO2=SPECFO2:T=TC:GOSUB1760 1O5OMIXRATIO=VOLCO2:FURNACE$="SAMPLE":ICOUNTER=I:GOSUB1830 1060IF (VOLCO2>100)GOTO1290 1070IF (DECIDE$="NO")GOTO220 1080GOSUB1530 1090FURNACE$="REFERENCE":ICOUNTER=2:GOSUB1830 1100IF (DECIDE$="NO")GOTO220 1110GOSUB1680 1120GOSUB1380 1121REMCALCULATINGAPPROX.DCO2/DFO2 1125DELFO2DELCO2=0.1/(DVOLCO2) Printingroutinefor printingfinishedresultstothe screen. 1130PRINT:PRINT:PRINT"Entera labelforyourrunconditions:";:INPUTLABELS 1140CLS 1150PRINTLABELS 1160PRINT:PRINT:PRINTSPC(15);"SPECIMENFURNACE";" REFERENCE FURNACE" 1170PRINTUSING"\ \ #### ####";"T(C)";TC;TREF 1180PRINTUSING'_ \ +##.## +##.##";"Iog(fO2/atm)";SPECFO2;REFFO2 1190PRINTUSING"\ \ ###.## ###.##";"%CO2";MIXRATIO;(MIXRATIO-DELRATIO) 1195PRINTUSING'& +#.###";"dlogfO2/d%CO2";DELFO2DELCO2 1200PRINTUSING'& \ +####.#";"EMF(mV)";REALEMF 1210PRINTUSING"_ \ +##.##";"dEMF/dT(mV)";DELEMFDELT 1220PRINTUSING"\ \ +##.##";"dEMF/dfO2(mV/.1)";DELEMFDELFO2 1225 IF (FO2OFFSET2=0)GOTO1240 1230PRINTUSING'_ \ \ +#.##";"buffer+ offset";BUFFER$;FO2OFFSET2.GOTO1260 1240PRINTUSING"_ \ \ \ ";"buffer";BUFFER$ 1260PRINTUSING"Cin H.S.? \ \ \ ";B$(1);B$(2) 1270PRINT:PRINT" Thisnumberis offset";CORREMF;"mVfromthe ideal." 1272 PRINT:PRINT°'Doyouwishto Printthe results,Continuewiththisprogram," 1273PRINT" or Returnto the mainmenu?(P/C/R)" 1274P$=INPUTS(1) 1275IF (P$="r")OR(P$="R")GOTO1360 1276IF (P$="c")OR (P$="C")GOTO1350 1277IF (P$="p")OR (P$="P")GOTO1279 1278PRINT:PRINT:PRINT"Huh?":PRINT:GOTO1272 1279GOSUB2150 1280GOTO1300 1290 PRINT"Thegasmixis unrealistic(eg.,";VOLCO2;"%).Try again." 1300PRINT:PRINT"Doyouwishto continuewiththis program," 1301PRINT" or returnto themainmenu?(C/R)" 1310AS=INPUTS(1) 1320IF (A$="r")OR (A$="R")GOTO1360 1330IF (A$="c")OR (A$="C")GOTO1350 A-9

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1340PRINT:PRINT:PRINT"Huh?":PRINT:GOTO1300 1350CLS:GOTO220 1360CLS 1365CHAIN"MENU.BAS",70,ALL 1370END Sub-routineforcalculatingthedeviationsin oxygenfugacitywithtemperature.. 1380Z=I 1390RATIO= FCO2/(1-FCO2-10hREFFO2) 1400AA =(1 - 2RATIO(100/ MIXRATIO - 1))/(1 + 2"(100 / MIXRATIO - 1)) 1410PART = LOG(1 - AA)- LOG(100 / MiXRATIO - 1) 1420FOR I= 1 TO- 1 STEP -2 1430H=I 1440W=T+H 1450 GG = 62.110326# - .02144446#W + 4.720326E-07(W h 2)+(- 4.5574288#)(10h( - 12))(W h 3)- 7.343018200000001 #(10h( - 15))(W h 4) 1460 KK = EXP(- GG/(R*(W + 273.18))) 1470 Q(Z)= KK 1480 Z = Z + 1 1490 NEXT I 1500 NEWFO21 = LOG(10).5(LOG(Q(1 ))+ PART):NEWFO22 = LOG(10).5(LOG(Q(2))+ PART) 1510 DELEMFDELT =(FN EMF (TREF + 1,NEWFO21) - FN EMF (TREF - 1, NEWFO22))/2 1520 RETURN Given a gas mixture and a temperature, this sub-routine calculates the oxygen fugacity of the fumace, as well as the expected EMF of the zirconia cell. 1530 REM SUBROUTINE TO ITERATIVELY CALCULATE THE FO2 OF THE REFERENCE FURNACE 1540 STEPFO2=I !:IF (TC>TREF) GOTO 1570 1550 IF (TC=TREF) GOTO 1570 1560 STEPFO2=-STEPFO2 1570 T=TREF 1580 LOGFO2=LOGFO2-STEPFO2:GOSUB 1760 1590 DELRATIO=MIXRATIO-VOLCO2 1600 IF ABS(DELRATIO)<.001 GOTO 1660 1610 IF (TREF>TC) GOTO 1640 1620 IF (DELRATIO<0) GOTO 1580 1630 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO 1580 1640 IF (DELRATIO>0) GOTO 1580 1650 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO 1580 1660 REFFO2=LOGFO2 1665 IDEALEMF=FN EMF(TREF,REFFO2):REALEMF=IDEALEMF+CORREMF 1670 RETURN Sub-routine calculates the EMF of the zirconia cell in the reference furnace, as well as the change of EMF with small changes in temperature and oxygen fugacity. 1680 REM NOW THAT WE HAVE TEMPERATURE AND LOGFO2, WE NEED TO CALCULATE THE EMF'S AND DELTA-EMF'S 1690 IDEALEMF = FN EMF (TREF,REFFO2) A-10

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1700 DELEMFDELFO2 =( FN EMF (TREF,(REFFO2 + .1))- FN EMF (TREF,(REFFO2 - .1 )))/2 1740 RETURN Sub-routine for taking the temperature of a furnace and computing the CO/CO 2 gas mixture needed to obtain a specific oxygen fugacity. 1750 REM NOW WE WANT TO TAKE THE T, FO2 CONDITIONS & COMPUTE THE %CO2 1760 G1 = 62.110326# + T*(- .02144446#)+(Th2)(4.720326)(10h(- 7))+(Th3)(- 4.5574288#)(10h( - 12))+(Th4)(- 7.343018200000001 #)(10h( - 15)) 1770 G2 = 94.25770200000001# + T*(7.321945)(10h('4))-(Th2)(10h(- 7))(3.416474)+(Th3)(4.7858617#)(10h( - 11)) 1780 K1 = EXP(- G1 /(R(T + 273.18))): K2 = EXP(- G2 /(R*(T + 273.18))) 1790 A =(K1 "(SQR(10hLOGFO2))FN RM(K1 ,LOGFO2))/(K1 + SQR(10hLOGFO2)) 1800 FCO2 = 2"(1 - A)/(2 + A + 2FN RM(K1,LOGFO2)) 1810 VOLCO2 = 100 /(1 + FN RM(K1 ,LOG FO2)):DVOLCO2= 100/(1 +FN RM(K1 ,(LOGFO2+. 1 )))- 100/(1 +FNRM(K1 ,(LOG FO2-. 1 )))/2 1820 RETURN Sub-routine for checking whether carbon will precipitate in the hot-spot of the furnace. 1830 IF ((10 h LOGFO2)>(K2FCO2)) GOTO 1920 1840 B$(ICOUNTER)="YES": PRINT:PRINT "Carbon WILL precipitate in the ";FURNACES;" using these settings." 1850 PRINT "DO YOU WANT THE INFORMATION ANYWAY (Y/N)?" 1860 INPUT X$ 1870 IF (X$="Y") OR (X$="y") GOTO 1900 1880 IF (X$="n") OR (X$="N") GOTO 1910 1890 PRINT:PRINT: "1don't understand. Please try again.":PRINT:PRINT:GOTO 1860 1900 DECIDE$="YES":GOTO 1930 1910 DECIDE$="NO":GOTO 1930 1920 B$(ICOUNTER)="NO" 1930 RETURN Routine for printing the results to paper. 2150 LPRINT LABELS 2160 LPRINT:LPRINT:LPRINT SPC(15);"SPECIMEN FURNACE ";" REFERENCE FURNACE" 2170 LPRINT USING "\ \ #### ####";"T( C)";TC;TREF 2180 LPRINT USING "\ \ +##.## +##.##";"Iog(fO2/atm)";SPECFO2;REFFO2 2190 LPRINT USING '& \ ###.## ###.##";"%CO2";MIXRATIO;(MIXRATIO-DELRATIO) 2195 LPRINT USING '& +#.### ";"dlogfO2/d%CO2";DELFO2DELCO2 2200 LPRINT USING '& \ +####.#";"EMF(mV)";REALEMF 2210 LPRINT USING "\ \ +##.##";"dEMF/dT(mV)";DELEMFDELT 2220 LPRINT USING "\ \ +##.##";"dEMF/dfO2(mV/. 1 )";DELEMFDELFO2 2225 IF (FO2OFFSET2=0) GOTO 2240 A-11

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2230LPRINTUSING"\ \ \ +#.##";"buffer+ offset";BUFFER$;FO2OFFSET2:GOTO2260 2240LPRINTUSING"\ \ \ \ ";"buffer";BUFFER$ 2260 LPRINTUSING"Cin H.S.? \ \ \ ";B$(1);B$(2) 2270LPRINT:LPRINT"*This numberis offset";CORREMF;"mVfromthe ideal." 2275 IF (PRINTER$="EPSON")GOTO2278 2276 LPRINTCHR$(12);:GOTO2280 2278 LPRINT:LPRINT 2280 CLS 2290RETURN A-12

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GASREV2.BAS Thissub-programtakesolddata,forwhich(1)the referenceconditions(temperature,EMF)and (2)the sampletemperatureareknownandcalculateswhatthe ambientoxygenfugacitywas in the samplefurnace. SetsUser-definedfunctions,aswell as mainmenu. 1 REMVARIABLESINCLUDE:MIXRATIO,VOLCO2,G1,G2, (ALLVARIABLES 2 REMFROMDEFAULTS.BAS),DVOLCO2,FCO2,R, K1,K2,A, B$(1),B$(2), OPTIONS% 3 REMT, LOGFO2,DCO2DFO2REF 4 REMDEFDBLG,A,K 10 DEFFN RM(X,Y)=(X-3X(10^Y)- 2"((10Y)^(3/2)))/(2"X(10^Y)+(10Y)+((10Y)A(3/2))+SQR(10^Y)) 13 R=1.98726"10^(-3) 15 COLOR15,14,14:CLS:PRlNT:PRINT:PRINT 20 PRINT" PROGRAMTO TAKEDATAFROMREFERENCE FURNACE":PRINT 30 PRINT" ANDTO CALCULATETHECONDITIONSINTHESAMPLE FURNACE" 35 PRINT" FORCO/CO2GAS MIXINGSYSTEMS" 40 PRINT:PRINT:PRINT 50 COLOR15,1,1:PRINT"Doyouwishto continue,or returnto the mainmenu (C/R)?" 60 Q$=INPUT$(1 ) 70 IF (Q$="c") OR (Q$="C") GOTO 110 80 IF (Q$="R") OR (Q$="r") GOTO 100 85 PRINT "HUH?":GOTO 50 100 CHAIN "MENU.BAS",70,ALL Sets default variables, and allows them to be changed using a menu-driven system. 110 CLS 113 TC=1400:TREF--1065:FO2OFFSET=0:BU FFER$="IW":REFFO2=- 13.7706:FO2OFFSET2=0 114 IDEALEMF=-913.9486:CORREMF=26:BUFFER$="IW" 200 REM VARIABLES USED ARE: TC,TREF, FO2OFFSET,BUFFER$,REFFO2,REALEMF,CORREMF 202 REM MORE VARIABLES USED ARE: IDEALEMF 205 COLOR 15,4,4:CLS:PRINT:PRINT:PRINT:REALEMF=IDEALEMF+CORREMF 220 PRINT "The current conditions are:" 230 PRINT:PRINT" 1. Sample temperature is ";TC;" degrees C" 240 PRINT" 2. Reference temperature is ";TREF;" degrees C" 250 PRINT" 3. Reference oxygen fugacity is ";REFFO2;" log (/atm)" 255 IF (FO2OFFSET=0) GOTO 265 260 PRINT" --- which is ";BUFFERS;" offset ";FO2OFFSET;" log units":GOTO 270 265 PRINT" --- which is ";BUFFERS 270 PRINT" --- the corrected EMF is ";IDEALEMF+CORREMF;" mV" 290 PRINT" 4. The correction to the zirconia cell is ";CORREMF;" mV" 30O PRINT" and 5. The reference buffer is ";BUFFERS 320 PRINT:PRINT 330 COLOR 4,15,15 A-13

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380 PRINT "Enter the number you wish to change (or 6 to continue; 7 to exit)";: 390 INPUT .... ,CHANGE% 400 IF (CHANGE%>0) AND (CHANGE%<8) G©T© 420 410 COLOR 31,1,1 :PRINT "Please enter a number, 1 - 7.";:COLOR 15,1,1 :GOTO 390 420 ON CHANGE% GOTO 430,440,580,450,487,1000,100 Changes sample temperature at constant. 430 INPUT "Enter the new sample temperature in degrees C";TC:CLS:GOTO 205 Changes reference temperature. 440 INPUT "Enter the new reference temperature in degrees C";TREF:CLS:GOTO 845 Changes systematic deviation in the zirconia cell. 450 INPUT "Enter the new correction to the zirconia celI";CORREMF:CLS:GOTO 205 Changes the standard reference buffer used to describe the oxygen fugacity. 460 CLS:PRINT:PRINT:PRINT 470 PRINT "The sample fO2 data will be given as relative to a buffer, as well" 480 PRINT "as in Iog(fO2/atm) units. Your choice of 'reference buffers' are:" 485 GOTO 490 487 CLS:PRINT:PRINT:PRINT:PRINT "Your choice of buffers are:" 490 PRINT:PRINT" 1. IW" 500 PRINT" 2. WM" 510 PRINT" 3. MH" 520 PRINT" 4. QFM" 530 PRINT" 5. NNO" 535 PRINT:PRINT "(Your current choice is )";BUFFERS 540 PRINT:PRINT "Enter the number of your selection.";: 550 INPUT" ",CHANGE% 560 IF (CHANGE%<1) OR (CHANGE%>5) GOTO 460 570 ON CHANGE% GOTO 571,572,573,574,575 571 BUFFER$="IW":GOTO 850 572 BUFFER$="WM":GOTO 850 573 BUFFER$="MH":GOTO 850 574 BUFFER$="QFM":GOTO 850 575 BUFFER$="NNO":GOTO 850 Changes the oxygen fugacity of the reference furnace. This section allows the oxygen fugacity to be described either as a standard buffer, as an offset from a standard buffer, or in atmospheres (log units). 58O CLS 590 PRINT:PRINT:PRINT 600 PRINT "The reference furnace fO2 can be expressed as any of several ways:" 610 PRINT:PRINT" 1. as a standard buffer" 620 PRINT" 2. as offset from a standard buffer" 630 PRINT" 3. as a specific fO2 (independent of any buffer) " A-14

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640PRINT" 4. as theEMF(in mV)indicatedby the zirconiacell" 650 PRINT:PRINT"Howwouldyou liketo expressyournewfO2" 660PRINT°' Enter1-4(or 5 to continue;6 t3 exit).";: 670 INPUT .... ,CHANGE% 680 IF (CHANGE%<1) OR (CHANGE%>6) GOTO 690 ON CHANGE% GOTO 700,700,820,870,205,100 700 PRINT:PRINT "Your choices of standard reference buffers are:":PRINT 701 PRINT "1. IW" 702 PRINT "2. WM" 703 PRINT" 3. MH" 704 PRINT "4. QFM" 705 PRINT " 5. NNO" 706 PRINT" 6. none above. Return to previous menu." 710 PRINT:PRINT "Enter the number of your selection.";: 720 INPUT .... ,CHOICE% 730 IF (CHOICE%<1) OR (CHOICE%>6) GOTO 710 740 FO2OFFSET=0:IF (CHANGE%=1) GOTO 760 750 INPUT "Enter the offset from the buffer, in log (fO2/atm) units.",FO2OFFSET 760 ON CHOICE% GOTO 770,780,790,800,810,580 770 REFFO2 = 6.57 - 27215/(TREF + 273)+FO2OFFSET:IDEALEMF=0.0496055*(TREF+273)REFFO2:BU FFER$="IW":C LS:GOTO 205 780 REFFO2 = 13.12 - 32730/(TREF + 273)+FO2OFFSET:I DEALE MF=0.0496055(TREF+273)REFFO2:BU FFER$="WM": CLS:GOTO 205 790 REFFO2 = 13.966 - 24634/(TREF + 273)+FO2OFFSET:IDEALEMF=0.0496055(TREF+273)REFFO2:BUFFER$="MH": CLS:GOTO 205 800 REFFO2 = 9! - 25738/(TREF + 273)+FO2OFFSET:IDEALEMF=0.0496055(TREF+273)REFFO2:BUFFER$="QFM" :CLS:GOTO 205 810 REFFO2 = 9.359999 - 24930/(TREF + 273)+FO2OFFSET:IDEALEMF=0.0496055(TREF+273)REFFO2:BUFFER$="NNO" :CLS:GOTO 205 820 CLS 830 PRINT:PRINT "What is the log of the f02 you want? ";: 840 INPUT REFFO2 845 IDEALEMF=0.0496055(TREF+273)*REFFO2 850 IF (BUFFER$="IW") GOTO 860 852 IF (BUFFER$="WM") GOTO 862 854 IF (BUFFER$="MH") GOTO 864 856 IF (BUFFER$="QFM") GOTO 866 858 IF (BUFFER$="NNO") GOTO 868 859 PRINT "THERE IS A PROBLEM WITH THE PROGRAM!!!!!":STOP 860 FO2OFFSET=REFFO2-(6.57 - 27215/(TREF + 273)):GOTO 205 862 FO2OFFSET=REFFO2-(13.12 864 FO2OFFSET=REFFO2-(13.966 - 32730/(TREF + 273)):GOTO 205 - 24634/(TREF + 273)):GOTO 205 866 FO2OFFSET=REFFO2-(9! - 25738/(TREF + 273)):GOTO 205 868 FO2OFFSET=REFFO2-(9.359999 870 CLS 880 PRINT:PRINT:PRINT A-15 - 24930/(TREF + 273)):GOTO 205

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890PRINT"TheEMF(inmV)thatyouenteris assumedto be the" 891PRINT"correctedvalue(i.e,whatyoureadon the meter)." 892PRINT"Thecurrentcorrectionfactoris ";CORREMF;"mV." 894 PRINT"Is that O.K.(Y/N)?" 900 C$-INPUT$(1) 902 IF (C$="Y")OR (C$="y")GOTO920 904 IF (C$="N")OR (C$="n")GOTO910 906 PRINT"HUH?":GOTO870 910 INPUT"Enterthe correction,in mV(lowis +).",CORREMF 920 INPUT"Enterthe EMFin mV(eg.,-908)",REALEMF 930 IDEALEMF=REALEMF-CORREMF 940 REFFO2=IDEALEMF/(0.0496055*(TREF+273)) 950 GOTO850 At this point,thetemperatureandoxygenfugacityof the referencefurnaceis known,as is the temperatureofthe samplefurnace.Therefore,theprogramneedstocalculatethe gas mixture.Oncethe gasmixtureis known,it canbe usedto calculatethe oxygenfugacityin the samplefurnace. Calculatesgas mixturevia subroutines. 1000 REM CALCULATE THE GAS MIXTURE 1005 COLOR 20,15,0:CLS:PRINT "WORKING ... PLEASE BE PATIENT" 1010 T=TREF:LOGFO2=REFFO2:ICOUNTER=2 1020 B$(2)--"NO":GOSUB 2000 1240 MIXRATIO=VOLCO2:DCO2DFO2REF=DVOLCO2 1241 IF (MIXRATIO<100.0) GOTO 1250 1242 CLS:PRINT:PRINT:PRINT "";:COLOR 4,15,0:PRINT "The gas mixture is unrealistic" 1243 PRINT:PRINT "(i.e., ";MIXRATIO;" percent CO2)" 1244PRINT:PRINT:PRINT:PRINT "Do you want to:" 1245PRINT" 1. see your defaults" 1246PRINT" 2. continue with this unrealistic mixture, or" 1247PRINT" 3. return to the main menu":PRINT "Please enter your choice (1,2, or 3)";: 1248 INPUT OPTIONS%:IF (OPTIONS%<1) OR (OPTIONS%>3) GOTO 1242 1249 ON OPTIONS% GOTO 205,1250,100 1250 IF ((10 ^ REFFO2)>(K2FCO2)) GOTO 1300 1255 CLS:B$(2)="YES" 1260 PRINT:PRINT "*";:COLOR 4,15,0:PRINT "Carbon HAS precipitated in the reference furnace." 1270 PRINT "Accordingly, the fO2 is not what the zirconia cell suggests." 1280 PRINT "Do you wish to continue using these same parameters? (Y/N) 1282 Q$=INPUT$(1 ) 1283 IF (Q$="Y") OR (Q$="y") GOTO 1300 1285 IF (Q$="n") OR (Q$="N") GOTO 220 1287 PRINT "HUH?":GOTO 1280 Calculates oxygen fugacity of the sample furnace, given the sample temperature and the gas mixture via sub-routines. This section of the program also checks to see if carbon would have precipitated in the hot spot of the sample furnace. If so, the conditions are flagged because it is certain that the calculation of oxygen fugacity is not valid. A-16

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1300 REMWE NOWHAVETC, VOLCO2=MIXRATIO,WE NEEDFO2OF SAMPLEFURNACE 1310 ICOUNTER=I 1320 COLOR15,1,1:B$(1)="NO":GOSUB2300 1330 GOSUB2000 1340 DCO2DFO2SPEC=DVOLCO2 1350 IF ((10^ SPECFO2)>(K2FCO2))GOTO1390 1355 CLS:B$(1)="YES" 1360PRINT:PRINT.....;:COLOR4,15,0:PRINT"CarbonHASprecipitatedin the specimenfurnace." 1370PRINT"Accordingly,thefO2 is notwhatthe zirconiacellsuggests." 1380PRINT"Doyouwishto continueusingthesesameparameters?(Y/N) 1382Q$=INPUT$(1) 1383 IF (Q$="Y")OR (Q$="y")GOTO 1400 1385 IF (Q$="n")OR (Q$="N")GOTO220 1387 PRINT"HUH?":GOTO1380 1390 GOSUB2800 Printsresultsto thescreen. 1400REMEVERYTHINGISCALCULATED-- JUSTNEEDTO PRINT 1580CLS:COLOR15,4,4:PRINT:PRINT:PRINT"Entera labelfor yourrun conditions:";:INPUTLABELS 1582CLS 1585PRINTLABELS 1590PRINT:PRINT:PRINTSPC(15);"SPECIMENFURNACE";" REFERENCE FURNACE" 1595PRINTUSING"\ \ #### ####";"T(C)";TC;TREF 1600PRINTUSING'& \ +##.## +##.##";"Iog(fO2/atm)";SPECFO2;REFFO2 1605PRINTUSING"\ \ ###.## ###.##";"%CO2";MIXRATIO;(MIXRATIO-DELRATIO) 1610PRINTUSING'_ \ +####.#";"EMF(mV)";REALEMF 1619PRINTUSING"\ \ \ +#.## \ \ +#.##";"buffer+ offset";BUFFER$;FO2OFFSET2;BUFFER$;FO2OFFSET 1625PRINTUSING"C in H.S.? \ \ \ V';B$(1);B$(2) 1630 PRINT:PRINT "* This number is offset ";CORREMF;" mV from the ideal. " 1640 COLOR 15,1,1 :PRINT:PRINT:PRINT "Do you wish to: " 1645 PRINT" 1. print the results 1650 PRINT" 2. change the variables & continue, or" 1660 PRINT" 3. exitto main menu" 1670 PRINT:PRINT "Enter your choice, 1 ,2, or 3.";:INPUT OPTIONS% 1680 IF (OPTIONS%<1) OR (OPTIONS%>3) GOTO 1640 1690 ON OPTIONS% GOTO 1700,205,100 1700 GOSUB 3000 1710 STOP Sub-routine which calculates the gas mix from the reference furnace parameters. 2000 REM ROUTINE TO TAKE REFERENCE FURNACE T, FO2 AND CALCULATE THE GAS MIX 2180 G1 = 62.110326# + T*(- .02144446#)+(T^2)(4.720326)(10^( - 7))+(T"3)(- 4.5574288#)(10*(- 12))+(T^4)( - 7.343018200000001 #)(10^( - 15)) A-17

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2190 G2-- 94.25770200000001#+ T*(7.321945)(10^(-4))_(T^2)(10^(_ 7))(3.416474)+(T^3)(4.7858617#)(10^(- 11)) 2200 K1 = EXP(-G1/(R(T+ 273.18))):K2= EXP,-G2/(R*(T+ 273.18))) 2210 A =(K1 -(SQR(10^LOGFO2))FNRM(K1,LOGFO2))/(K1+ SQR(10^LOGFO2)) 2220 FCO2= 2"(1 - A)/(2+ A + 2FN RM(K1,LOGFO2)) 2230 VOLCO2= 100/(1 + FN RM(K1,LOGFO2)):DVOLCO2=100/(1+FNRM(K1,(LOGFO2+.1)))- 100/(1+FNRM(K1,(LOGFO2-.1))) 2240RETURN Sub-routinewhichcalculatesthe oxygenfugacityseenby the sample(specimen)given thegasmixcalculatedforthe referencefurnaceandthetemperatureof thesamplefurnace. 2300REM SUBROUTINETO TAKETC, GASMIXANDCALCULATESPECFO2 2370STEPFO2=I!:IF (TREF>TC)OR (TREF=TC)GOTO2385 2380STEPFO2=-STEPFO2 2385 T=TC 2390 LOGFO2=LOGFO2-STEPFO2 2391 GOSUB2000 2395 DELRATIO=MIXRATIO-VOLCO2 2400 IF (ABS(DELRATIO)<.0001)GOTO2490 2405 IF (TC>TREF)GOTO2425 2410 IF (DELRATIO<0)GOTO2390 2420 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO2390 2425 IF (DELRATIO>0)GOTO2390 2427 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO2390 2490 SPECFO2--LOGFO2 2500RETURN 2800REMCALCULATINGOFFSETFORSAMPLEFURNACE 2850IF (BUFFER$="IW")GOTO2860 2852 IF (BUFFER$="WM")GOTO2862 2854 IF (BUFFER$="MH")GOTO2864 2856 IF (BUFFER$="QFM")GOTO2866 2858 IF (BUFFER$="NNO")GOTO2868 2859PRINT"THEREISA PROBLEMWiTHTHE PROGRAM!!H!":STOP 2860FO2OFFSET2=SPECFO2-(6.57- 27215/(TC + 273)):GOTO2870 2862 FO2OFFSET2=SPECFO2-(13.12- 32730/(TC + 273)):GOTO2870 2864 FO2OFFSET2=SPECFO2-(13.966- 24634/(TC + 273)):GOTO2870 2866 FO2OFFSET2=SPECFO2-(g!- 25738/(TC + 273)):GOTO2870 2868FO2OFFSET2=SPECFO2-(9.359999- 24930/(TC + 273)):GOTO2870 2870RETURN Sub-routinefor printingthefinalresultsto paper. 3000 LPRINTLABELS 3090 LPRINT:LPRINT:LPRINTSPC(15);"SPECIMENFURNACE";" REFERENCE FURNACE" 3095 LPRINTUSING"\ \ #### ####";"T(C)";TC;TREF 3100LPRINTUSING"_ \ +##.## +##.##";"Iog(fO2/atm)";SPECFO2;REFFO2 3105 LPRINTUSING"_ \ ###.## ###.##";"%CO2";MIXRATIO;(MIXRATIO-DELRATIO) 3110LPRINTUSING'_ \ +####.#";"EMF(mV)*";REALEMF A-18

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3119LPRINTUSING"\ \ \ +#.## \ \ +#.##":"buffer+ offset";BUFFER$;FO2OFFSET2;BUFFER$;FO2OFFSET 3125LPRINTUSING"C in H.S.? \ \ _,":B$(1);B$(2) 3130 LPRINT:LPRINT"* Thisnumberis offset";CORREMF;"mVfromthe ideal." 3135 IF (PRINTER$="EPSON")GOTO3138 3137 LPRINTCHR$(12);:GOTO3140 3138LPRINT:LPRINT 3140 CLS 3150RETURN1640 A-19

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RAMP.BAS Thissub-programrampsthe temperatureof a furnaceata constantgas mixture,andcalculates the oxygenfugacityat eachtemperature.Thisoptionis a usefultoolfordesigningcooling-rate experiments. SetsUser-definedfunctionsandpresentsmainmenu. 10 REMDIMREFFO2(100),FO2OFFSET2(100) 20 REM THISVERSIONINCLUDESCHANGINGREFERENCEGASTO OXYGEN 30 DEFFNEMF(T,K)=.0496055*(T+273)(K+0) 40 REMDEFDBLG,K,A 50 DEFFNRM(X,Y)=(X-3X*(10^Y)- 2"((10^Y)^(3/2)))/(2"X*(10^Y)+(10^Y)+((10^Y)^(3/2))+SQR(10^Y)) 52 COLOR 15,6,6:CLS 60 PRINT:PRINT:PRINT" PROGRAMTHATCALCULATESFO2'S" 70 PRINT:PRINT"WHENTHETEMPERATUREIS RAMPEDINA FURNACEWITH A SETGASMIX" 72 PRINT:PRINT 100 COLOR6,15,15 127PRINT:PRINT"Doyouwishto continue,or returnto the mainmenu(C/R)?" 128Q$=INPUT$(1) 129 IF (Q$="c")OR (Q$="C")GOTO 150 130 IF (Q$="r")OR (Q$="R")GOTO 140 135 PRINT:PRINT"HUH?":PRINT:GOTO127 140CHAIN"MENU.BAS",70,ALL Sets default parameters, and allows them to be changed using a menu-driven system. 150 COLOR 15,14,14:CLS:PRINT:PRINT "If you have just run options 1 or 2 from the main menu," 151 PRINT "you can pick up your last results for this program." 152 PRINT "Do you want to pick up the new results, or set new defaults (P/D)?";: 153 C$=INPUT$(1 ) 154 IF (C$="p") OR (C$="P") GOTO 157 155 IF (C$="D") OR (C$="d") GOTO 157 156 PRINT:PRINT "HUH?":PRINT:GOTO 153 157 Y=0: R=1.98726E-03 200 REM VARIABLES USED ARE: TC,TREF,FO2OFFSET2,BUFFER$,REFFO2,REALEMF,CORREMF 202 REM MORE VARIABLES USED ARE: IDEALEMF 205 PRINT:PRINT:PRINT 207 IF (C$="p") OR (C$="P") GOTO 219 210 TC=1400:FO2OFFSET2=- 1 :BU FFER$="IW":S P EC FO2=- 10.69719 215 BUFFER$="IW" 219 TFINAL=TC-100:STEPT%=50 220 COLOR 15,3,3:CLS:PRINT:PRINT "The current conditions are:" 225 B$(1 )="NO":B$(2)="NO":DECIDE$="YES" 230 PRINT" 1. The original sample temperature is ";TC;" degrees C" 250 PRINT" 2. The original sample oxygen fugacity is ";SPECFO2;" log (/atm)" 255 IF (FO2OFFSET2=0) GOTO 265 260 PRINT" --- which is ";BUFFERS;" offset ";FO2OFFSET2;" log units":GOTO 270 A-20

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265 PRINT" ---which is ";BUFFERS 270 PRINT" 3. Final temperature is ";TFINAL;" degrees C" 280 PRINT " --- and fO2's will be printed for e,,,e_v ";STEPT%;" degrees" 300 PRINT "and 4. The reference buffer is ";BUFFERS 320 PRINT:PRINT:PRINT 380 COLOR 15,9,9:PRINT "Please enter a number: 1 - 4 for changes; 5 to continue; 6 to exit.";: 390 INPUT .... ,CHANGE% 400 IF (CHANGE%>0) AND (CHANGE%<7) GOTO 420 410 PRINT:COLOR 31,9,9:PRINT .....;:GOTO 380 420 CLS:ON CHANGE% GOTO 430,580,440,487,1000,140 430 INPUT "Enter the new sample temperature in degrees C";TC 431 IF (BUFFER$="IW") GOTO 850 432 IF (BUFFER$="WM") GOTO 851 433 IF (BUFFER$="MH") GOTO 852 434 IF (BUFFER$="QFM") GOTO 853 435 IF (BUFFER$="NNO") GOTO 854 436 PRINT "ERROR IN PROGRAM/NO BUFFER":STOP 440 INPUT "Enter the final temperature in degrees C";TFINAL 450 INPUT "Enter the interval for which you want fO2's printed ";STEPT%:CLS:GOTO 220 460 CLS:PRINT:PRINT:PRINT 470 PRINT "The sample fO2 data will be given as relative to a buffer, as well" 480 PRINT "as in Iog(fO2/atm) units. Your choice of 'reference buffers' are:" 485 GOTO 490 487 CLS:PRINT:PRINT:PRINT:PRINT "Your choice of reference buffers are:" 490 PRINT:PRINT" 1. IW" 500 PRINT" 2. WM" 510 PRINT" 3. MH" 520 PRINT" 4. QFM" 530 PRINT" 5. NNO" 535 PRINT:PRINT "(Your current choice is )";BUFFERS 540 PRINT:PRINT "Enter the number of your selection." 550 INPUT .... ,CHANGE% 560 IF (CHANGE%<1) OR (CHANGE%>5) GOTO 460 570 ON CHANGE% GOTO 571,572,573,574,575 571 BUFFER$="IW":GOTO 850 572 BUFFER$="WM":GOTO 851 573 BUFFER$--"MH":GOTO 852 574 BUFFER$="QFM":GOTO 853 575 BUFFER$="NNO":GOTO 854 580 CLS 590 PRINT:PRINT:PRINT 600 PRINT "The sample furnace fO2 can be expressed as any of three ways:" 610 PRINT:PRINT" 1. as a standard buffer" 620 PRINT" 2. as offset from a standard buffer" 630 PRINT" 3. as a specific fO2 (independent of any buffer) " 650 PRINT:PRINT "How would you like to express your new fO2" 660 PRINT" (Enter 1-3, or 4 for unchanged)." 670 INPUT .... ,CHANGE% 680 IF (CHANGE%<1) OR (CHANGE%>4) GOTO 590 690 ON CHANGE% GOTO 700,700,820,692 692 CLS:GOTO 220 700 PRINT:PRINT "Your choices of standard reference buffers are:":PRINT A-21

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701 PRINT"1. IW" 702 PRINT" 2. WM" 703 PRINT" 3. MH" 704 PRINT" 4. QFM" 705 PRINT" 5. NNO" 706 PRINT" 6. noneabove.Returnto previousmenu." 710PRINT:PRINT"Enterthe numberofyourselection.";: 720 INPUT.... ,CHOICE% 730 IF (CHOICE%<1)OR (CHOICE%>6)GOTO 710 740 FO2OFFSET2=0:IF(CHANGE%=1)GOTO760 750 INPUT"Enterthe offsetfromthe buffer,in log(fO2/atm)units.",FO2OFFSET2 760 ON CHOICE%GOTO770,780,790,800,810,580 770 SPECFO2= 6.57- 27215/(TC+ 273)+FO2OFFSET2:BUFFER$="IW":CLS:GOTO220 780 SPECFO2= 13.12- 32730/(TC+ 273)+FO2OFFSET2:BUFFER$="WM":CLS:GOTO220 790 SPECFO2= 13.966- 24634/(TC+ 273)+FO2OFFSET2:BUFFER$="MH":CLS:GOTO220 800 SPECFO2= 9! - 25738/(TC+ 273)+FO2OFFSET2:BUFFER$="QFM":CLS:GOTO220 810SPECFO2= 9.359999- 24930/(TC+ 273)+FO2OFFSET2:BUFFER$="NNO":CLS:GOTO220 820 CLS 830 PRINT:PRINT"Whatis the logof the f02 youwant?";: 840 INPUTSPECFO2:GOTO431 850 FO2OFFSET2=SPECFO2-(6.57- 27215/(TC + 273)):CLS:GOTO220 851 FO2OFFSET2=SPECFO2-(13.12- 32730/(TC + 273)):CLS:GOTO220 852 FO2OFFSET2=SPECFO2-(13.966- 24634/(TC + 273)):CLS:GOTO220 853 FO2OFFSET2=SPECFO2-(9!- 25738/(TC + 273)):CLS:GOTO220 854 FO2OFFSET2--SPECFO2-(9.359999- 24930/(TC + 273)):CLS:GOTO220 Given the initial conditions in the sample furnace, the cooling rate, and the temperature of the reference furnace, the other parameters of interest can be calculated using sub-routines. 1000 COLOR 15,6,6:CLS 1001 REM NOW TC,TFINAL,STEPT,FO2 HAS BEEN INPUT 1010 REM SUBROUTINE AT 1750 CALCULATES GASMIXTURES, 1830 = C STABILITY 1020 REM SUBROUTINE AT 1100 CALCULATES EMF'S 1030 REM SUBROUTINE AT 1380 CALCULATES DELEMFDELT; 1680 = DEMFDFO2 1031 REM SUBROUTINE AT 1530 ITERATES REFERENCE FURNACE FO2 1032 PRINT:PRINT:PRINT "Enter a label for this calculation: ";:INPUT LABELS 1034 COLOR 15,1,1 :CLS:PRINT:PRINT:PRINT "WORKING ... PLEASE BE PATIENT" 1035 PRINT:PRINT:PRINT:PRINT:PRINT:PRINT:PRINT LABELS 1040 T=TC:LOGFO2=SPECFO2:GOSUB 1760 1050 MIXRATIO=VOLCO2 1057 PRINT:PRINT "For a constant gas mix of ";:PRINT USING "###.##";MIXRATIO:PRINT:PRINT "T";SPC(5);"logfO2";SPC(2);"Buffer + offset" 1060 IF (VOLCO2>100)GOTO 1290 1070 IF (TFINAL>TC) GOTO 1075 1073 STEPT%=-STEPT% 1074 I1=0 A-22

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1075FOR I=TCTO TFINALSTEPSTEPT% 1078TREF=I:II=I1+1:GOSUB1530 1079GOSUB1830 1080PRINTUSING" #### +##.##\ +#.## ";TREF;REFFO2;BUFFER$;FO2OFFSET2 1085FO2OFFSET2(I1)=FO2OFFSET2:REFFO2(I1)=REFFO2 1090NEXTI 1100PRINT:PRINT"Doyouwishto Printthe results,Continuewiththisprogram, 1101PRINT" or Returnto the mainmenu?(P/C/R)" 1110P$= INPUTS(1) 1120IF (P$="r")OR (P$="R")GOTO1360 1130IF (P$="c")OR (P$="C")GOTO1350 1135IF (P$="P")OR (P$="p")GOTO1150 1140PRINT:PRINT:PRINT"Huh?":PRINT:GOTO1100 1150GOSUB2000 1200GOTO1300 1290PRINT"Thegasmixis unrealistic(eg.,";VOLCO2;"%).Try again." 1300PRINT:PRINT"Doyouwishto continuewiththis program,°' 1301PRINT" or returntothe mainmenu?(C/R)" 1310P$=INPUTS(1) 1320IF (P$="r")OR (P$="R")GOTO1360 1330IF (P$="c")OR (P$="C")GOTO1350 1340PRINT:PRINT:PRINT"Huh?":PRINT:GOTO1300 1350CLS:GOTO220 1360CLS 1365CHAIN"MENU.BAS",70,ALL 1370END Sub-routineforcalculatingthe changein oxygenfugacitywithchangein temperaturefor smallchangesintemperature. 1380Z = 1 1390 RATIO= FCO2/(1-FCO2-10^REFFO2) 1400AA =(1 - 2RATIO(100/ MIXRATIO - 1))/(1 + 2"(100 / MIXRATIO - 1)) 1410 PART = LOG(1 - AA)- LOG(100 / MIXRATIO - 1) 1420 FOR I= 1 TO- 1 STEP -2 1430 H = I 1440 W -- T + H 1450 GG = 62.110326# - .02144446#W + 4.720326E-07(W ^ 2)+(- 4.5574288#)(10^( - 12))(W ^ 3)- 7.343018200000001#(10^( - 15))( w^ 4) 1460 KK = EXP(- GG/(R*(W + 273.18))) 1470 Q(Z)= KK 1480 Z = Z+ 1 1490 NEXT I 1500 NEWFO21 = LOG(10).5(LOG(Q(1))+ PART):NEWFO22 = LOG(10).5(LOG(Q(2))+ PART) 1510 DELEMFDELT =(FN EMF (TREF + 1,NEWFO21) - FN EMF (TREF - 1, NEWFO22))/2 1520 RETURN Sub-routine to calculate the oxygen fugacity for the reference furnace. 1530 REM SUBROUTINE TO ITERATIVELY CALCULATE THE FO2 OF THE REFERENCE FURNACE A-23

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1540 STEPFO2=I {:IF (TC>TREF) GOTO 1570 1550 IF (TC=TREF) GOTO 1570 1560 STEPFO2=-STEPFO2 1570 T=TREF 1580 LOGFO2=LOGFO2-STEPFO2:GOSUB 1760 1590 DELRATIO=MIXRATIO-VOLCO2 1600 IF ABS(DELRATIO)<.001 GOTO 1660 1610 IF (TREF>TC) GOTO 1640 1620 IF (DELRATIO<0) GOTO 1580 1630 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO 1580 1640 IF (DELRATIO>0) GOTO 1580 1650 LOGFO2=LOGFO2+STEPFO2:STEPFO2=STEPFO2/2:GOTO 1580 1660 REFFO2=LOGFO2 1670 RETURN Sub-routine to calculate the EMF of the zirconia cell, and how it changes with small fluctuations in temperature and oxygen fugacity. 1680 REM NOW THAT WE HAVE TEMPERATURE AND LOGFO2, WE NEED TO CALCULATE THE EMF'S AND DELTA-EMF'S 1690 IDEALEMF = FN EMF (TREF,REFFO2) 1700 DELEMFDELFO2 =( FN EMF (TREF,(REFFO2 + .1))- FN EMF (TREF,(REFFO2 - .1)))/2 1740 RETURN Sub-routine for calculating the gas mixture. 1750 REM NOW WE WANT TO TAKE THE T, FO2 CONDITIONS & COMPUTE THE %CO2 1760 G 1 = 62.110326# + T*(- .02144446#)+(Th2)(4.720326)(10h( - 7))+(T^3)(- 4.5574288#)(10h(- 12))+(T4)(- 7.343018200000001#)(10h(- 15)) 1770 G2 = 94.25770200000001# + T(7.321945)(10h('4))-(Th2)(10h(- 7))(3.416474)+(T3)(4.7858617#)(10h( - 11 )) 1780 K1 = EXP(- G1/(R*(T + 273.18))): K2 = EXP(- G2/(R*(T + 273.18))) 1790 A =(K1 -(SQR(10ALOGFO2))FN RM(K1 ,LOGFO2))/(K1 + SQR(10hLOGFO2)) 1800 FCO2 = 2"(1 - A)/(2 + A + 2FN RM(K1 ,LOGFO2)) 1810 VOLCO2 = 100/(1 + FN RM(K1, LOG FO2)) :DVOLCO2= 100/(1 +FN RM(K1, (LOGFO2+. 1 )))- 100/(1 +FN R M(K 1 ,(LOGFO2-. 1))) 1820 RETURN Sub-routine for comparing the oxygen fugacities in the sample and reference furnaces with a standard buffer. 1830 REM CALCULATING FO2OFFSET 1831 IF (BUFFER$="IW") GOTO 1850 1832 IF (BUFFER$="WM") GOTO 1851 1833 IF (BUFFER$="MH") GOTO 1852 1834 IF (BUFFER$="QFM") GOTO 1853 1835 IF (BUFFER$="NNO") GOTO 1854 1850 FO2OFFSET2=REFFO2-(6.57 - 27215/(TREF + 273)):GOTO 1860 1851 FO2OFFSET2=REFFO2-(13.12 - 32730/(TREF + 273)):GOTO 1860 1852 FO2OFFSET2=REFFO2-(13.966 - 24634/(TREF + 273)):GOTO 1860 A-24

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1853FO2OFFSET2=REFFO2-(9!-25738/(TREF+ 273)):GOTO1860 1854FO2OFFSET2=REFFO2-(9.359999- 24930/(TREF+ 273)) 1860RETURN Sub-routinefor printingthe resultsto paper. 2000 REM PRINTINGSUBROUTINE 2035 LPRINTLABEL$:LPRINT:LPRINT"(atconstantgas mixof ";:LPRINTUSING "###.##";MIXRATIO;:LPRINT")":LPRINT:LPRINT "T";SPC(5);"logfO2";SPC(2);"Buffer+ offset" 2040 J1=0 2050 FORJ=TCTO TFINALSTEPSTEPT% 2060 TPRINT=J:JI=JI+I 2080 LPRINTUSING"#### +##.##\ +#.## ";TPRINT;REFFO2(J1);BUFFER$;FO2OFFSET2(J1) 2100 NEXTJ 2110 IF (PRINTER$="EPSON")GOTO2125 2120 LPRINTCHR$(12);:GOTO2127 2125LPRINT:LPRINT 2127 CLS 2130RETURN A-25

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REPORT DOCUM ENTATION PAGE OMB_o.OZO_-OTBBFormApproved PubliC reporting burden for this collection of information is estimated to average 1 hour per recjx>nse, including the trme for re_q_wmg instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information Send comments regarding 1his burden estimate or any other aspect of _his coltectlon of informatton including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations ano Reoorts, 1215 Jefferson Davis Highway, Suite 1204, Arhngton, VA 22202-4302. and to the Office of Management and Budget, paperwork Reduction Proiect {0704-0188}, Washington. DC 205G3 1, AGENCY USE ONLY (Leave blank) 2. REPORT DATE September 1993 4. TITLE AND SUBTITLE 3. REPORT TY oE AND DATES COVERED interim S. FUNDING NUMBERS Technical Update: JSC System Using a Solid ElectrolyticCell in a Remote Location to Measure Oxygen Fugacities in CO/CO2 Controlled-Atmosphere Furnaces 6 AUTHOR(S) NAS 9-11410F A. J. G. Jurewicz, R. J. Williams, L. Le, J.Wagstaff, G. Lofgren,A. Lanier, W. Carter,A. Roshko PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Lyndon B. Johnson Space Center Houston, TX 77058 SPONSORING/MONITORINGAGENCYNAME(S)AND ADDRESS(ES) National Aeronautics and Space Administration Washington. D.C. 20546 11. SUPPLEMENTARY NOTES 12a. DISTRIBUTION/AVAILABILITYSTATEMENT National Technical Informatin Service 5285 Port Royal Road Springfield,VA 22161 (703) 487-4600 8. PERFORMING ORGANIZATION REPORT NUMBER S-727 10. SPONSORING / MONITORING AGENCY REPORT NUMBER TM-104774 12b. DISTRIBUTION CODE Subject Category: 88 Space Sciences General 13. ABSTRACT (Maximum 200 words) Detailsare given forthe design and applicationof a (one atmosphere) redox-controlsystem. This system differsfrom that given in NASA Technical Memorandum 58234 in that ituses a singlesolid-electrolyticcellin a remote location tomeasure the oxygen fugacitiesof multiple CO/CO2 controlled-atmosphere furnaces. This remote measurement (1)extends the range ofsample-furnace conditionsthat can be measured using a solid-electrolyticcell,and (2)cuts costsby extending the lifeofthe sensors and by minimizing the number of sensors in use. The system consistsofa referencefurnace and an exhaust-gas manifold. The referencefurnace isdesigned according to the redox control system of NASA Technical Memorandum 58234, and any number ofCO/CO2 controlled-atmosphere furnaces can be attached to the exhaust-gas manifold. Using the manifold,the exhaust gas from individualCO/CO2 controlledatmosphere furnaces can be diverted through the referencefurnace,where a solid-electrolytecellisused to read the ambient oxygen fugacity.The oxygen fugacitymeasured in the referencefurnace can then be used to calculatethe oxygen fugacityin the individualCO/CO2 controlled-atmosphere furnace. A BASIC computer program was developed to expedite thiscalculationand isavailablefrom the firstauthor. 14. SUBJECT TERMS 15. NUMBER OF PAGES 37 furnaces,controlled-atmosphere;oxygen fugacity;electrolyticcell(solid);redox cells (controlsystem) 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION OF REPORT OF THIS PAGE Unclassified Unclassified Standard Form 298 (Ray. 2-8g) Prescribed by ANSI Std. 239-18 298-102 16. PRICE CODE 20. LIMITATION OF ABSTRACT 19. SECURITY CLASSIFICATION OF ABSTRACT Unclassified Unlimited