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NASA/TM—2004–213550 Quartz Crystal Microbalance Operation and In Situ Calibration K.C. Albyn Marshall Space Flight Center, Marshall Space Flight Center, Alabama ERING D E IR IN E G C N T E O R C A F T S E M R EEDD E T S N E E A M R P C O H L E T EV EC D HNOL GY O November 2004

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The NASA STI Program Office…in Profile Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office is operated by Langley Research Center, the lead center for NASA’s scientific and technical information. The NASA STI Program Office provides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA’s institutional mechanism for disseminating the results of its research and development activities. These results are published by NASA in the NASA STI Report Series, which includes the following report types: • TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA’s counterpart of peerreviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations. • TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis. • CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees. • CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by NASA. • SPECIAL PUBLICATION. Scientific, technical, or historical information from NASA programs, projects, and mission, often concerned with subjects having substantial public interest. • TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA’s mission. Specialized services that complement the STI Program Office’s diverse offerings include creating custom thesauri, building customized databases, organizing and publishing research results…even providing videos. For more information about the NASA STI Program Office, see the following: • Access the NASA STI Program Home Page at http://www.sti.nasa.gov • E-mail your question via the Internet to help@sti.nasa.gov • Fax your question to the NASA Access Help Desk at 301–621–0134 • Telephone the NASA Access Help Desk at 301–621–0390 • Write to: NASA Access Help Desk NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076–1320 301–621–0390

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NASA/TM—2004–213550 Quartz Crystal Microbalance Operation and In Situ Calibration K.C. Albyn Marshall Space Flight Center, Marshall Space Flight Center, Alabama National Aeronautics and Space Administration Marshall Space Flight Center • MSFC, Alabama 35812 November 2004 i

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Available from: NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076–1320 301–621–0390 ii National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 703–487–4650

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TABLE OF CONTENTS 1. INTRODUCTION ........................................................................................................................... 1 2. QUARTZ CRYSTAL MICROBALANCE TYPES ........................................................................ 2 3. MODIFICATION OF THE MEASURED DEPOSITION RATE .................................................. 3 3.1 Dynamic Deposition Process .................................................................................................... 3 4. VERIFICATION OF SOURCE-SENSOR RELATIONSHIP ......................................................... 5 5. INDIVIDUAL SENSOR PERFORMANCE .................................................................................. 8 6. MEASUREMENT DURATION .................................................................................................... 10 7. DEPOSITION SURFACE REGENERATION ............................................................................... 12 8. CONCLUSION ............................................................................................................................... 13 APPENDIX A—CALCULATION OF THE CLAUSING FACTOR FOR AN ORIFICE OR SHORT TUBE ................................................................................................... 14 APPENDIX B—CALCULATION OF THE DWELL TIME OF CONTAMINANTS ON SURFACES ........................................................................................................ 15 APPENDIX C—NOTES ON USING THE VAN’T HOFFT RELATION TO CALCULATE THE ENTHALPY OF SUBLIMATION .................................................................. 16 REFERENCES .................................................................................................................................... 17 iii

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LIST OF FIGURES 1. Four CQCMs with a common outgassing source-to-sensor geometry. During the first 2 hr of the measurement, two of the CQCMs were warmed from –100 to –62 ºC, and this period was not included in the plot. (Adipic acid, January 27, 2004: –62 ºC deposition surface, 55 ºC effusion cell—from 2 to 24.50556 hr.) .......................................... 5 2. Another example of multiple CQCMs with a common source-to-sensor geometry. (Adipic acid, June 30, 2003: –42 ºC deposition surface, 41 ºC effusion cell—from zero to 16.25 hr.) .................................................................................................................... 6 3. The four CQCMs used to collect the data presented in figures 1 and 2 as they are mounted in the vacuum chamber. The effusion cell, in which the sample is heated, would be mounted on the bracket in the foreground ............................................................. 6 4. Linear regression analysis of frequency data collected with a CQCM. The slope for the curve is x-value multiplier (6.5341 Hz/hr) and the r2value (0.9998) is the linear regression coefficient. (Adipic acid, CQCM 2, January 24, 2004: –62 ºC deposition surface, 44 ºC effusion cell.) ................................................................................................. 10 5. Time period from 10 to 10.5 hr of the frequency data presented in figure 4. The fluctuation in the frequency data primarily comes from fluctuations in the effusion cell heater temperature and a slight fluctuation in the deposition surface temperature. (Adipic acid, CQCM 2, January 24, 2004: –62 ºC deposition surface, 44 ºC effusion cell—from 10 to 10.5 hr.) ....................................................................................................... 11 LIST OF TABLES 1. Frequency data for multiple sensors with a common source-to-sensor geometry ................. 7 2. Enthalpy of sublimation calculated from adipic acid deposition measurements .................... 9 iv

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LIST OF ACRONYMS ASTM American Society for Testing and Materials CQCM cryogenic quartz crystal microbalance QCM quartz crystal microbalance TM Technical Memorandum VCM volatile condensable material VF view factor v

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NOMENCLATURE A orifice radius Ea activation energy (cal/mole) K Clausing factor L orifice length R gas constant, 8.3144 kJ/mole-K; 1.9872 cal/K/mole r2 linear regression coefficient R1 deposition rate measured at T1 (moles/cm2-s) R2 deposition rate measured at T2 (moles/cm2-s) T surface temperature (K) T1 lower effusion cell temperature (K) T 2 higher effusion cell temperature (K) τ surface dwell time (s) τo vibration frequency (vibrations/s) vi

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TECHNICAL MEMORANDUM QUARTZ CRYSTAL MICROBALANCE OPERATION AND IN SITU CALIBRATION 1. INTRODUCTION Quartz crystal microbalances (QCMs) are commonly used to measure the rate of deposition of molecular species on a surface. The usual process is that the deposition rate for a specific material is measured and then mathematically modified to calculate a source term, or outgassing rate, for the material. The source term, which is representative of the material’s outgassing rate, can be used as input for computer programs that predict the rate of deposition of the emitted or outgassed material on another surface. The outgassing process is diffusion controlled, and the rate of release, or outgassing, is temperature dependant. Outgassing measurements are not typically used to measure the release of material due to degradation of the parent material or the material generated by the chemical interactions of the released compounds that result in the production and deposition of a different chemical species. The deposition process is temperature dependant with the efficiency of the condensation process increasing as the deposition surface temperature becomes increasingly colder than the temperature of the outgassing material. The species, molecular or atomic, released from a material during the outgassing process are typically quantified and described in two ways: (1) The total amount of material that is lost through the outgassing process is often referred to as the total mass loss for the material, and (2) material released during the outgassing process that will recondense on another surface is often identified as volatile condensable material (VCM). Both quantities can be expressed as a percentage of the original sample mass, but only VCM can also be expressed as an outgassing rate when measured with an instrument such as a QCM. 1

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1. QUARTZ CRYSTAL MICROBALANCE TYPES QCMs typically fall into two major categories and three subcategories. QCMs either have a single quartz crystal or a matched pair of quartz crystals, forming a clear distinction between the two major classes of QCMs. This Technical Memorandum (TM) will only address the QCMs that have a matched pair of quartz crystals. One of the crystals serves as a reference oscillator while the deposition of VCMs occurs on the surface of the other quartz crystal. This class of microbalances can be further subdivided into the following: • QCMs: These microbalances do not have an active mechanism to control the temperature of the deposition surface. Heating and cooling of the microbalance is typically done by controlling the temperature of the structure on which the QCM is mounted. These are the simplest of the QCMs that have a matched pair of crystals. • Temperature-controlled QCMs: The temperature of the quartz crystals in these balances is actively controlled. Both cooling and heating is controlled, often by building a Peltier device, a solid state heater/cooler, into the balance. • Cryogenic QCMs (CQCMs): These microbalances can actively heat the crystal pair, but they rely on passive cooling to control the temperature of the deposition surface. Cryogenic deposition surface temperatures are passively achieved by mounting this microbalance on a cryogen-cooled, typically liquid nitrogen, surface. Throughout the remainder of this TM, the initialism QCM will be used as the generic label for all three types of QCM. 2

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1. MODIFICATION OF THE MEASURED DEPOSITION RATE The measured deposition rate is simply a measurement of how fast the outgassed materials condense on the deposition surface of the QCM. The difference in oscillation of the reference crystal and the crystal on which material deposits is often referred to as the beat frequency. Using a sensitivity factor specific to the type of QCM being used, the measured change in frequency can be converted into a deposition rate. The sensitivity factor is normally provided by the QCM vendor. The deposition rate is typically reported in units of grams per centimeter squared-second and is calculated from the observed change in the beat frequency with time (ΔHz/s). The source term, or outgassing rate, for a material is normally different than the measured deposition rate and is arrived at mathematically. The calculation involves a view factor (VF) and is further modified by the sample surface area. The view factor is a mathematical description of the geometry between the emitting surface, the outgassing source, and the deposition surface. If the measurement system employs an effusion cell for heating the sample, then the length and radius of the effusion cell orifice along with the sample surface area must also be considered in the calculation. An additional factor, the Clausing factor, that quantifies the conductance of the orifice (app. A) must also be incorporated into the VF calculation.1 For the measurements appearing in this TM, the VF calculation presented in American Society for Testing and Materials (ASTM) method E–1559 has been used to calculate the reported source terms.2 The ASTM method E–1559 VF is not the only VF calculation employed for the calculation of source terms. The ASTM E–1559 VF method is specific to measurements in which the sample is heated in an effusion cell and should not be used to calculate surface-to-surface VFs.3 3.1 Dynamic Deposition Process A simple assumption often made is that the material being deposited on a surface remains on the surface and that all the condensed species have the same affinity for the deposition surface. This is often not the case, and some deposited material may be lost, or reevaporated, from the deposition surface while the majority of the condensate remains on the deposition surface. Often, the sticking coefficient or factor for a material is set at 1 to simplify the measurement and modeling of the deposition process. Cooling the outgassing source below the temperature of the deposition surface, effectively turning off the outgassing source, often reveals a slow loss of material from the deposition surface. Reevaporation usually occurs at a significantly lower rate than the measured deposition rate and varies with the deposition surface temperature and composition. 3

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The dwell time of a molecular species on a surface can be calculated if all the required parameters are obtained from laboratory measurements or published references (app. B). However, this level of precision is not needed for the typical applications that the outgassing rate measurements are intended to support. 4

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1. VERIFICATION OF SOURCE-SENSOR RELATIONSHIP When multiple QCMs are used to measure the outgassing from a common source, the VF for each sensor will be unique to the geometry between the source and the sensor. In some systems employing multiple sensors, a common geometry is used by design, and all the sensors have a common VF. The assumption of a common geometry can be confirmed by comparing the deposition rates that are measured by the sensors while viewing the same outgassing source. For this technique to be effective, the deposition surfaces of the sensors must all be at the same temperature and the sample/QCM geometries must be uniform. Figures 1 and 2 are frequency curves for four CQCMs viewing an effusion cell (fig. 3) containing a sample of adipic acid (Chemical Abstracts Service Registry Number: 124–04–9). The slopes for the curves presented in table 1 were obtained from a linear regression analysis of the individual frequency curves. 7,000 6,000 5,000 4,000 CQCM 1 3,000 Frequency (Hz) 2,000 1,000 CQCM 2 0 1 6 CQCM 3 CQCM 4 11 16 21 26 Time (hr) Figure 1. Four CQCMs with a common outgassing source-to-sensor geometry. During the first 2 hr of the measurement, two of the CQCMs were warmed from –100 to – 62 ºC, and this period was not included in the plot. (Adipic acid, January 27, 2004: –62 ºC deposition surface, 55 ºC effusion cell—from 2 to 24.50556 hr.) 5

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4,700 4,200 3,700 Frequency (Hz) 3,200 CQCM 4 2,700 0 2 4 6 CQCM 2 CQCM 3 CQCM 1 8 10 12 14 16 Time (hr) Figure 2. Another example of multiple CQCMs with a common source-to-sensor geometry. (Adipic acid, June 30, 2003: –42 ºC deposition surface, 41 ºC effusion cell—from zero to 16.25 hr.) Figure 3. The four CQCMs used to collect the data presented in figures 1 and 2 as they are mounted in the vacuum chamber. The effusion cell, in which the sample is heated, would be mounted on the bracket in the foreground. 6

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Table 1. Frequency data for multiple sensors with a common source-to-sensor geometry. Deposition Effusion Cell Surface Temperature Temperature Frequency Regression QCM (ºC) January 2004 CQCM 1 55 CQCM 2 55 CQCM 3 55 CQCM 4 55 June 2003 CQCM 1 42 CQCM 2 42 CQCM 3 42 CQCM 4 42 (ºC) (Hz/hr) Coefficient –62 31.99 0.9998 –62 33.904 1 –62 36.464 0.9999 –62 33.581 0.9998 –42 4.0657 0.9978 –42 4.2807 0.9977 –42 5.2736 0.9963 –42 3.5931 0.9901 In each instance, perfect agreement between the slopes of the curves was not obtained, suggesting a bias of the common geometry to one of the sensors. The amount of bias that is acceptable for the measurement being made should be taken into account when determining if further modifications to the measurement setup are required or if the measurement setup is adequate to meet the requirements for the accuracy of the data. The performance of the individual sensors can have a large influence on the perceived bias and should also be addressed in the evaluation of a multisensor system. 7

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1. INDIVIDUAL SENSOR PERFORMANCE The quality of the measurement made with each individual QCM can be assessed using deposition measurements made with the QCM to calculate the enthalpy of sublimation for a known condensate species.4A series of deposition measurements is made at a constant deposition surface temperature and several source temperatures. The quality of the individual deposition measurements is then assessed using a linear regression analysis of the data to establish the quality of the data and to obtain the slope of the frequency curve. The slope is usually measured in hertz per hour (Hz/hr) and, using the QCM sensitivity factor, converted to a deposition rate, g/cm2-s. The deposition rate is then converted to a source term, which is stated in moles/cm2-s. The material selected for the measurements must sublime as a single species and cannot degrade during the outgassing/deposition process.5Values for the enthalpy of sublimation and the molecular weight and melting point of the material can be obtained from various chemical references.6–8Melting the material is undesirable and will produce erroneous results if the enthalpy of sublimation is calculated using data obtained from a melted sample. Using the source terms measured for two different effusion cell temperatures, the enthalpy of sublimation for the material can be calculated using the van’t Hoff relation:9 Enthalpy of sublimation=R[T2–T1/T2×T1]×ln[R1/R2] , (1) where R is 8.3144 kJ/mole-K, the gas constant T1 is the lower effusion cell temperature (K) T 2 is the higher effusion cell temperature (K) 1 (moles/cm2-s) R1 is the deposition rate measured at T 2 (moles/cm2-s). R2 is the deposition rate measured at T To illustrate the process, the enthalpy of sublimation for adipic acid, 129.3±2.5 kJ-mole–1, has been calculated and is presented in table 2.8 Exact agreement between the calculated enthalpy of sublimation and published values may not always be achieved, and a decision on the accuracy needed for the measurements will have to be made by those making the measurement. Often the published values for the enthalpy of sublimation will be a value plus or minus some uncertainty, which makes exact agreement between the calculated and those published values even more difficult to achieve (app. C). The objective is to show that the data collected with each QCM as an indicator of QCM performance are accurate and reasonable over a range of source temperatures. 8

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Table 2. Enthalpy of sublimation calculated from adipic acid deposition measurements. CQCM Deposition Surface T1 T2 (moles/cm2-s) (moles/cm2-s) Sublimation (%) No. Temperature (ºC) (ºC) (ºC) 1.9×10–11 5.2×10–10 97.3 1 –62 33 55 3.47×10–11 5.2×10–10 98.7 1 –62 37 55 6.26×10–11 5.2×10–10 93.5 1 –62 40 55 9.67×10–11 5.2×10–10 102.7 1 –62 44 55 2.14×10–11 5.45×10–10 95.3 2 –62 33 55 3.72×10–11 5.45×10–10 97.6 2 –62 37 55 1.01×10–10 5.45×10–10 102.3 2 –62 44 55 2.8×10–10 5.45×10–10 91 2 –62 50 55 2.5×10–11 7.11×10–10 98.6 3 –102 33 55 3.98×10–11 7.11×10–10 105 3 –102 37 55 1.28×10–10 7.11×10–10 104.6 3 –102 44 55 2.5×10–11 4.39×10–10 107.5 3 –102 33 50 R1 R2 Enthalpy of 9

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1. MEASUREMENT DURATION The number of the data points collected during each deposition measurement should lend itself to good statistical analysis. Data collection intervals of 5 to 300 s over a period of 10 hr or more will provide an adequate amount of data with good resolution for deposition calculations (fig. 4). In addition, the random QCM frequency data variations from fluctuations in the sample temperature, small variations in the deposition surface temperature, and disturbances from cryo-panel fill cycles will have a less pronounced effect when data are collected for reasonably long periods (fig. 5). 600 y=6.5341x+270.84 r 2=0.9998 500 400 300 Frequency (Hz) 200 100 0 0 5 10 15 20 25 30 35 40 45 Time (hr) Figure 4. Linear regression analysis of frequency data collected with a CQCM. The slope for the curve is x-value multiplier (6.5341 Hz/hr) and the r 2value (0.9998) is the linear regression coefficient. (Adipic acid, CQCM 2, January 24, 2004: –62 ºC deposition surface, 44 ºC effusion cell.) Linear regression analysis is a good method for the evaluation of frequency data. It provides the slope of the frequency curve in addition to a linear regression coefficient. Typically, data with a correlation coefficient > 0.99 are of high enough quality to produce good deposition data and are adequate for the accurate calculation of the enthalpy of sublimation. 10

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340 339.5 339 338.5 338 337.5 337 Frequency (Hz)336.5 336 335.5 335 334.5 9.9 10 10.1 10.2 10.3 10.4 10.5 10.6 Time (hr) Figure 5. Time period from 10 to 10.5 hr of the frequency data presented in figure 4. The fluctuation in the frequency data primarily comes from fluctuations in the effusion cell heater temperature and a slight fluctuation in the deposition surface temperature. (Adipic acid, CQCM 2, January 24, 2004: –62 ºC deposition surface, 44 ºC effusion cell—from 10 to 10.5 hr.) 11

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1. DEPOSITION SURFACE REGENERATION The typical beat frequency observed for a clean QCM crystal pair will fall between 500 and 2,000 Hz. Condensation of material on the QCM crystal will cause a linear increase in the beat frequency until the deposition of material on the crystal begins to degrade the measurement being made. As a guideline for the user, the capacity—a maximum frequency value or microbalance loading—of each QCM is typically provided by the vendor. The deposition surface can be regenerated by raising the temperature of the crystal pair, thereby thermally reversing the deposition process. At the end of the crystal cleaning process, some historeses, or residual mass, which will be observed as a slight increase in the baseline frequency when the crystal is cooled, may remain on the crystal. Not all QCMs measure the deposition process as an increase in the beat frequency. Some QCMs measure the increase in deposited material as a decrease in the measured beat frequency. Either approach to the deposition measurement process is acceptable as long as the frequency change observed is consistent with the proper functioning of the QCM. 12

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1. CONCLUSION QCMs are widely used by the aerospace community, as well as other communities interested in the rate at which material condenses on contamination-sensitive surfaces, to measure deposition rates. Simple methods can be employed to evaluate the relation between the sensor and the source of the condensing species. The in situ assessment of individual QCM performance can be made using physical constants such as the enthalpy of sublimation, which is available in chemical handbooks and other references. This TM describes the calibration of QCMs installed in the Marshall Space Flight Center Outgassing Facility, which is operated by the Environmental Effects Group (ED31). The deposition rate measurements for a substance that sublimes as a single molecular species demonstrated that the facility provides quality outgassing measurements and that the microbalances can be monitored for both performance and sensitivity. The techniques presented in this TM are also recommended for the in situ calibration of QCMs installed in other vacuum chambers. 13

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APPENDIX A—CALCULATION OF THE CLAUSING FACTOR FOR AN ORIFICE OR SHORT TUBE The Clausing factor, K, is a unitless number that describes the conductance of material through short tubes or the orifice of an effusion cell. This factor was developed by Clausing, and a good description of the factor and the theoretical background for the calculation can be found in Dushman:1 K=1/[1+(3/8)(L/A)] , (2) where L is the orifice length and A is the orifice radius. 14

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APPENDIX B—CALCULATION OF THE DWELL TIME OF CONTAMINANTS ON SURFACES Surface dwell time, τ (s), for a contaminant can be calculated if the vibration frequency of the species, the activation energy of the species, and the temperature of the surface are known: τ =τ o exp(Ea/RT) , (3) where τo is the vibration frequency (vibrations/s) Ea is the activation energy (cal/mole) R is the gas constant (1.9872 cal/K/mole) T is the surface temperature (K). The activation energy and characteristic vibration frequency of a molecule or atom for a species can be obtained from publications, chemical handbooks and databases, or measurements made in the laboratory.8 15

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APPENDIX C—NOTES ON USING THE VAN’T HOFFT RELATION TO CALCULATE THE ENTHALPY OF SUBLIMATION Screening the measured frequency data using linear regression can quickly eliminate poor quality data and help guide the measurement process before attempting to calculate the enthalpy of sublimation. A range of acceptable error in the calculated enthalpy of sublimation; e.g., ±10 percent, should be identified as providing measurements with the accuracy required for the application that the measurements are intended to support. The efficiency of the deposition process increases as the deposition surface temperature becomes increasingly colder than the source temperature. The data collected for the hottest source temperature and not eliminated by the linear regression screening process would be a good candidate to select as one of the two data sets needed for the enthalpy of sublimation calculation. This data set can be considered to be an informal reference point for the exercise, against which the data collected at other source temperatures can be evaluated. The apparent error or disagreement between the calculated enthalpy of sublimation and the published value can become very large when using data collected at two very similar source temperatures, typically a difference of <5 ºC. Some of the error is from instabilities in the sample heater, instabilities in the temperature of the deposition surface, and the fill cycles of the cryogenic surfaces. Repeating the calculation and substituting a deposition rate measured at a slightly higher or lower source temperature than the previously selected, informal reference may reduce the error. Once the enthalpy of sublimation has been calculated for a range of source temperatures, the agreement or disagreement in the calculated values can be used to evaluate the performance of the microbalance. 16

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REFERENCES 1. Dushman, S.: Scientific Foundations of Vacuum Technique, J.M. Lafferty (ed.), John Wiley & Sons, Inc., New York, NY, p. 91, 1965. 2. “Standard Test Method for Contamination Outgassing Characteristics of Spacecraft Materials,” in Annual Book of ASTM Standards, Vol. 15.03, American Society for Testing and Materials, Philadelphia, PA, p. 9, 1993. 3. Tribbl, A.C.: The Space Environment: Implications for Spacecraft Design, Princeton University Press, Princeton, NJ, p. 272, 1995. 4. Albyn, K.C.: “Extension of the Enthalpy of Sublimation for Adaptic Acid to Temperatures Below 80 ºC,” J. Chem. and Eng. Data, Vol. 46, No. 6, p. 1416, 2001. 5. “Conformational Thermal Vacuum Stability Test Method Development,” TR–427–001, Johnson Space Center, White Sands Test Facility, p. 33, January 3, 1989. 6. CRC Handbook of Chemistry and Physics, 66th ed., R.C. Weast (ed.), Chemical Rubber Publishing, Boca Raton, FL, p. 2464, 1986. 7. Davies, M.; and Thomas, G.: “The Lattice Energies, Infra-Red Spectra, and Possible Cyclization of Some Dicarboxylic Acids,” Trans. Faraday Soc., Vol. 56, pp. 185–192, 1960. 8. Afeedy, H.Y.; Liebman, J.F.; and Stein, S.E.: “Neutral Thermochemical Data,” in NIST Chemistry WebBook, NIST Standard Reference Database No. 69 (online), W.G. Mallard and P.J. Linstrom (eds.), National Institute of Standards and Technology, Gaithersburg, MD, November 1998, URL: http://webbook.nist.gov Cited October 21, 2004. 9. Benson, S.W.: Thermochemical Kinetics, John Wiley & Sons, New York, NY, p. 1017, 1968. 17

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Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operation and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE November 2004 4. TITLE AND SUBTITLE 3. REPORT TYPE AND DATES COVERED Technical Memorandum 5. FUNDING NUMBERS Quartz Crystal Microbalance Operation and In Situ Calibration 6. AUTHORS K.C. Albyn 7. PERFORMING ORGANIZATION NAMES(S) AND ADDRESS(ES) George C. Marshall Space Flight Center Marshall Space Flight Center, AL 35812 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) National Aeronautics and Space Administration Washington, DC 20546–0001 11. SUPPLEMENTARY NOTES 8. PERFORMING ORGANIZATION REPORT NUMBER M–1125 10. SPONSORING/MONITORING AGENCY REPO NUMBER NASA/TM—2004–213550 Prepared by the Materials, Processes, and Manufacturing Department, Engineering Directorate 12a. DISTRIBUTION/AVAILABILITY STATEMENT Unclassified-Unlimited Subject Category 23 Availability: NASA CASI 301–621–0390 13. ABSTRACT (Maximum 200 words) 12b. DISTRIBUTION CODE Quartz crystal microbalances (QCMs) are commonly used to measure the rate of deposition of molecular species on a surface. The measurement is often used to select materials with a low outgassing rate for applications where the material has a line of sight to a contamination-sensitive surface. A quantitative, in situ calibration of the balance, or balances, using a pure material for which the enthalpy of sublimation is known, is described in this Technical Memorandum. Supporting calculations for surface dwell times of deposited materials and the effusion cell Clausing factor are presented along with examples of multiple QCM measurements of outgassing from a common source. 14. SUBJECT TERMS 15. NUMBER OF PAGES calibration, quartz crystal microbalance, deposition rate, effusion cell, view factor, 24 frequency, enthalpy of sublimation, volatile condensable materials, Clausing factor, 16. PRICE CODE surface dwell time, beat frequency, deposition measurement, outgassing 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION OF REPORT OF THIS PAGE Unclassified Unclassified NSN 7540-01-280-5500 18 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF ABSTRACT Unclassified Unlimited Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. 239-18 298-102