1、Designation: B 808 05Standard Test Method forMonitoring of Atmospheric Corrosion Chambers by QuartzCrystal Microbalances1This standard is issued under the fixed designation B 808; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method monitors the reactivity of a gaseoustest environment in which metal surfaces (for example,
3、elec-trical contacts, assembled printed wiring boards, and so forth)and other materials subject to pollutant gas attack undergoaccelerated atmospheric corrosion testing. This test method isapplicable to adherent corrosion films whose total corrosionfilm thickness ranges from a few atomic monolayers
4、toapproximately a micrometre.1.2 The test method provides a dynamic, continuous, in-situ, procedure for monitoring the corrosion rate in corrosionchambers; the uniformity of corrosion chambers; and thecorrosion rate on different surfaces. Response time in the orderof seconds is possible.1.3 With the
5、 proper samples, the quartz crystal microbal-ance (QCM) test method can also be used to monitor theweight loss from a surface as a result of the desorption ofsurface species (that is, reduction of an oxide in a reducingatmosphere). (Alternative names for QCM are quartz crystaloscillator, piezoelectr
6、ic crystal oscillator, or thin-film evapora-tion monitor.)1.4 This test method is not sufficient to specify the corrosionprocess that may be occurring in a chamber, since a variety ofpollutant gases and environments may cause similar weightgains.1.5 This test method is generally not applicable to te
7、stenvironments in which solid or liquid particles are deposited onthe surface of the quartz crystal.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to become familiarwith all hazards includ
8、ing those identified in the appropriateMaterial Safety Data Sheet for this product/material as pro-vided by the manufacturer, to establish appropriate safety andhealth practices, and determine the applicability of regulatorylimitations prior to use.1.7 The values stated in SI units are to be regarde
9、d as thestandard. The values in parentheses are for information only.2. Referenced Documents2.1 ASTM Standards:2B 810 Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-pons3. Summary of Test Method3.1 A single crystal of quartz has various natural re
10、sonantfrequencies depending on the crystals size and shape. Thedecrease in natural frequency is linearly proportional to thecrystal mass and the mass of well-bonded surface films. Forcrystals with reactive metal films on the surface (usuallydriving electrodes), the mass of the crystal/metal film inc
11、reasesas the metal oxidizes or forms other compounds with gasesadsorbed from the atmosphere.3,4Thus, by measuring the rateof resonant frequency change, a rate of corrosion is measured.Non-adherent corrosion films, particles, and droplets yieldambiguous results.Areview of theory and applications is g
12、ivenin Lu and Czanderna.5See Appendix X1 for discussion of thequantitative relationship between frequency change and masschange.3.2 The chamber environmental uniformity and corrosionrate can be measured by placing matching quartz crystals withmatching reactive metal films at various locations in the
13、chamber. If the chamber and corrosion rate have been stan-dardized, the corrosion rate on various surface materials thathave been deposited on the quartz crystal can be determined.1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct respo
14、nsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved May 1, 2005. Published June 2005. Originallyapproved in 1997. Last previous edition approved in 2003 as B 808 97 (2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
15、tomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3King, W. H. Jr., Analytical Chemistry, Vol 36, 1964, p. 173.4Karmarkar, K. H. and Guilbaut, G. G. Analytical Chemistry Acta, Vol 75, 1975,p. 111.5Lu
16、, C. and Czanderna,A. W. Eds., Applications of Piezoelectric Quartz CrystalMicrobalances, Elsevier, c1984.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 Corrosion film growth with thicknesses varying from
17、amonolayer of atoms up to 1 m can readily be measured on acontinuous, real-time, in-situ, basis with QCMs.4.2 The test results obtained for this test method areinfluenced by various factors, including geometrical effects,temperature, humidity, film thickness, film materials, electrodeconditions, gas
18、es in the corrosion chamber, atmospheric pres-sure, and so forth. Calibration of coated crystals and instru-mentation and reproducible crystal operating conditions arenecessary for consistent results.5. Apparatus5.1 Apparatus can be a simple series circuit of crystal (withelectrodes and sensing film
19、), oscillator (typically 6 MHz) andfrequency counter (610-Hz accuracy and stability), as sche-matically shown in Fig. 1.5.2 Commercial, Thin-Film Monitors,6incorporating thosefunctions that read out thicknesses or weight gain are alsoavailable and acceptable after they have been calibrated.5.3 Balan
20、ce, with an accuracy of 62 g is needed forcalibration procedures.5.4 Recording Devices or Computers are needed for real-time, continuous measurements.76. Materials6.1 Crystals shall be of the AT5cut variety with a resonantfrequency in the MHz range and matched to the frequencymeasuring apparatus use
21、d. Quartz crystal surfaces shall bepolished to a surface finish with an arithmetical mean devia-tion, Ra, of less than 0.1 m. With this surface finish, the crystalappears optically transparent to the human eye.86.2 Electrodes, used to drive the crystals resonant fre-quency, can be made from any elec
22、trically conducting materialand usually are a metal film evaporated on the quart crystalsurface. The material under study or being used to calibrate thesystem may be the same as or different than the electrodematerial. If the two materials are different, the potentialcorrosion of the electrodes shal
23、l be accounted for during thedesign and subsequent experiments. Depending on the materi-als under test, the QCMs can have copper, silver, nickel, zinc,gold, etc. electrodes. The preferred method of deposition is byevaporation for a high purity, smooth surface. If sublayers areused to enhance the adh
24、esion of the final electrode, they shouldbe covered by the final electrode material so that less than 1 %of the metallic area is of exposed sublayer material. Because ofthe fragility of the metal electrode there should be multiple(three or more), spring-loaded contacts between the crystal andelectro
25、nics.6.3 After metallization of the crystals, they should be storedin desiccators. After two years storage or if the metallizationshows discoloration or staining, the crystals shall be discarded.Crystal surfaces should not be chemically or mechanicallycleaned before use in the corrosion chamber. The
26、y should beblown clean with inert compressed gas. Chilling and conden-sation on the surface, as can occur with the use of pressurizedfluorocarbons, shall be avoided. Care shall be exercised so thatthe crystals are only handled by clean tweezers or tongs andnever touched by hands.7. Calibration7.1 QC
27、Ms and its electronics shall be calibrated initially ina given corrosion system and thereafter on an annual basis.Calibration shall be performed with the same shape and size ofcrystal holder to be used during operation. Recalibration shallbe performed if the crystal holder geometry is changed.Calibr
28、ation can be done by comparison to a standard such asactual gravimetric weighing on a microbalance (62 g). Use asample of the same material as the sensing film with aminimum area of 5 cm2and a thickness of 0.1 to 0.6 mm (seeTest Method B 810). Foil surface roughness should be within620 % of the QCM
29、sensing film roughness. The procedure forthe generation (that is, evaporation) and cleaning of thegravimetric sample should be the same as used for the sensingfilms. The age and storage of the gravimetric sample should becomparable to the age of the QCM sensing film. Allow the foilto equilibrate wit
30、h the microbalance atmosphere for 0.5 h, thenweigh the sample with 62-g accuracy before exposure.Suspend the weighed gravimetric sample between two simi-larly treated QCMs spaced 20 cm apart with the large surfacearea dimension of the samples parallel to the air flow. Aftersufficient exposure, as de
31、termined in the paragraph below,remove the sample from the corrosion chamber, equilibrate itwith the balance atmosphere, and reweigh. The gravimetricallymeasured, foil weight gain per unit area should be within610 % of the calculated weight gain, found on the active areaof the QCM.7.2 A weight gain
32、of the metal foil of 50 g is sufficient fora microbalance with 62-g reproducibility and is sufficient forcalibration. (If the reproducibility of the microbalance is poorerthan 62 g, proportionally greater weight gain shall be used.)If the sensing material was copper and the corrosion film wasCu2O, 5
33、0 g/5 cm2would correspond to a film thickness of 149nm if the density of Cu2O was 6 g/cm3and the percentage ofoxygen in the film was 11 % (16/143). For improved accuracy,greater weight gain may be used. However, the calculatedthickness of the corrosion film should not exceed 50 % of theelectrode thi
34、ckness.6Current listings of available suppliers can be found in trade publicationscovering semiconductor processing equipment including thin film depositionmonitors or by doing an internet search for QCM or thin film monitors.7Schubert, R. “ASecond GenerationAcceleratedAtmospheric Corrosion Cham-ber
35、,” ASTM STP 965, 1988, p. 374.8Most instrument suppliers of thin film monitors also sell crystals with variouscoatings and roughness. Polished and coated crystals are available from ICMOklahoma City, OK and have been found satisfactory for this purpose.FIG. 1 Schematic of QCM and Related Electronics
36、B8080528. Procedure8.1 All metal surfaces that are not being used in themeasurement should be shrouded or coated with a nonreactivematerial to protect the surfaces from unwanted corrosion (thatis, clear nail polish, Q-dope, heat shrink TFE-fluorocarbon, andso forth). It is especially important to pr
37、otect any electricalconnections that are being used for measurements or providingpower from the corrosive atmosphere under investigation.8.2 Do not handle the crystals by hand or with anything thatleaves a residue after evaporation on the crystal electrodes. Usecaution in all handling to avoid scrat
38、ching the sensing filmsurface.8.3 One QCM with a sensing film inert to the test environ-ment should be in the system to monitor changes in the amountof relative humidity in the system, adsorbed hydrocarbons, andso forth. (A gold-coated QCM is usually a good choice for thisapplication.) At the end of
39、 the chamber exposure when all thepollutant gases have been removed and the humidity has beenreturned to its initial value, the frequency of this QCM shouldstill be at its initial value. (This is not meant to replace arelative humidity meter, rather it verifies the system electronicsstability.)8.4 F
40、or determining the chambers spatial uniformity ofpollutant gas, QCMs should be located uniformly at variouslocations around a chamber to confirm that the corrosion rate isthe same (610 %) at all locations. A typical distribution is onesensor per every 7 L of volume or 4 sensors/ft3for a cubicchamber
41、 of 28-L (1-ft3) volume. See Test Method B 810 fortypical distribution schemes of QCM. This density can beincreased or decreased depending on the chamber shape,chamber loading, and chamber airflow.8.5 It is preferable that the monitoring QCMs shall beoriented with the sensing surface perpendicular t
42、o and facingthe air flow. If another orientation to the air flow is used, themonitors orientation relative to the air flow shall be reported inthe test report.9. Report9.1 Recorded data should include the following:9.1.1 Types and concentrations of the corrosive gases in thecorrosion chamber, relati
43、ve humidity, temperature, and air flowcharacteristics (for example, direction, velocity, turbulence,and exchange rate).9.1.2 Sensing material(s), weight gain(s), versus time anddate for the QCMs, and their location in the chamber.9.1.3 Description of the samples in the chamber during theexperiments,
44、 including the material, surface area, and locationin the chamber.10. Precision and Bias10.1 PrecisionThe precision of this test method has beendetermined to be 610 % using copper QCMs. This experimentis reported in the open literature.9However, as a result ofvariations in fixturing, film compositio
45、n, film smoothness, andair flow characteristics, all QCM measurements should becompared to total corrosion rates as determined by TestMethod B 810 and described previously.10.2 BiasCrystal fixturing may produce large variabilityin chamber-to-chamber results. Since there is no acceptablereference sui
46、table for determining the bias for QCMs, bias hasnot been determined.11. Keywords11.1 corrosion monitor; piezoelectric crystals, sensors, thin-film monitorAPPENDIX(Nonmandatory Information)X1. SAUERBREY EQUATION RELATING FREQUENCY CHANGE OF A QUARTZ CRYSTAL MICROBALANCE (QCM) TOMASS CHANGE IN AN ATM
47、OSPHERIC CORROSION TESTX1.1 A piezoelectric quartz crystal utilizes the ConversePiezoelectric Effect to determine mass changes as a result offrequency change of the crystal. Material such as copper iscoated onto the crystal that bonds with a material from theatmosphere. When the gaseous material bon
48、ds to the materialon the crystal surface, its added mass lowers the crystalfrequency. The Sauerbrey equation10relates the frequencychange to the mass change. One form of the Sauerbreyequation is given as follows:Df 52Dmdf2/rqvq(X1.1)where:Df = change in frequency of the crystal,Dmd= change in mass s
49、urface density (md, mass per unitof surface area),f2= square of the frequency of the crystal,rq= density of quartz (2650 kg m-3), andvq= velocity of propagation of sound inquartz (3340 m s-1).X1.1.1 For small changes in mass of the crystal and relatedsmall changes in frequency, the relation:Df 52K Dmd(X1.2)is adequate for purposes of this test method where Kincorporates the square of the initial frequency and the materialconstants. Since a frequency change of one part in 107is9Schubert, R. and Neuburger, G. G., Journal of the Electrochemical Society,Vol137, No. 4, 1990,
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