1、Designation: D2715 92 (Reapproved 2012)Standard Test Method forVolatilization Rates of Lubricants in Vacuum1This standard is issued under the fixed designation D2715; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the rates ofvolatilization of lubricants in a thermal-vacuum environment atpr
3、essures and temperatures necessary to obtain a measurablerate of evaporation, or evidence of decomposition.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concer
4、ns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E296 Practice for Ionization Gage Applica
5、tion to SpaceSimulatorsE297 Methods for Calibrating Ionization Vacuum GageTubes33. Summary of Test Method3.1 A known quantity of specimen is placed in a thermalvacuum balance system and the evaporated material is con-densed on a cold plate. The weight of the specimen iscontinually recorded as a func
6、tion of time for nominal constantsurface area.4. Significance and Use4.1 This test method provides data for comparison of theevaporation rate of lubricants used in unshielded bearings inthe space environment.5. Apparatus5.1 Recording Vacuum Microbalance , with capacity of 1 gor more, sensitivity of
7、0.01 mg or less, zero stability of 0.025mg or less for 8 h with ranges of weight change of 10 mg ormore, and 0.1 mg or less, capable of being pumped to 105Pa(107torr) or less.5.1.1 When Procedure B for the more volatile samples isused, the vacuum requirement shall be 102Pa (104torr) orless.5.2 Vacuu
8、m SystemA pumping system capable of main-taining a starting pressure of 106to 105Pa (108to 107torr)(5.1.1). An optically dense baffle system should be used toensure freedom from back-streaming. A conventional bell jarsystem with an oil diffusion pump, a mechanical back-uppump, and an optically dense
9、, liquid, nitrogen-cooled baffle hasbeen found satisfactory on the configuration as shown in Fig. 1.5.3 Furnace, with thermocouple indicator, capable of main-taining a constant sample temperature 63C. All parts of thisfurnace must be proved to be usable at the highest temperatureand vacuum contempla
10、ted.5.4 Recorder, capable of recording weight changes continu-ously with the balance used, to the performance specified in5.1.5.5 Specimen Container, made of 300 series stainless steelin the form of a straight cylinder with an aspect ratio of heightto diameter of approximately 1:14. Where chemical r
11、eactionsare experienced with the container, alternative materials maybe used.5.6 Contacting Thermocouple, touching solid or immersedin liquid specimens, with the leads brought out in such a wayas not to influence balance indication.5.7 Cold PlateA condensing shield cooled with liquidnitrogen to immo
12、bilize molecules evaporated from the lubri-cant which subtends, at least, a 160 arc from the center of thesample.5.8 Nude Ionization Gage, installed as described in PracticeE296 and calibrated as described in Methods E297.5.9 Optional Supplemental Equipment:5.9.1 Mass Spectrometer, to identify degas
13、sing products andevaporating species.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.L0.07 on Engineering Sciences of High Performance Fluids andSolids (Formally D02.1100).Current
14、 edition approved April 15, 2012. Published April 2012. Originallyapproved in 1968. Last previous edition approved in 2007 as D271592 (2007).DOI: 10.1520/D2715-92R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual B
15、ook of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
16、United StatesNOTICE: This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for the latest information15.9.2 Infrared Optical Pyrometer System, for determiningthe specimen temperature. This must be calibrated against thethermocou
17、ple for each material used, due to emissivity effects.5.9.3 Copper Tab, on a cold plate facing the specimen, forX-ray analysis of the condensate.5.9.4 Noncontact Specimen Thermocouple, calibratedagainst 5.5.5.9.5 Pressure Recording Pen, added to the recorder.5.9.6 Time Derivative Computer, to report
18、 the rate directly.6. Reagents and Materials6.1 Antiwetting AgentA low-surface tension material forcoating the specimen container and the thermocouple. Itsvolatility must be low enough to contribute less than 5 % to theevaporation rate of any sample to be tested.6.2 Calibration MaterialPure compound
19、 of suitablephysical properties to simulate the lubricant under investiga-tion. (N-heptadecane and bis m-(m-phenoxyphenoxy) phenylether have been found satisfactory. Tin provides a low evapo-ration rate material, the performance of which can be checkedby the Langmuir equation.)46.3 Liquid Nitrogen,
20、commercial grade.6.4 Helium, ACS purified grade.7. Specimen Preparation7.1 Remove dissolved gases from the bulk lot prior to testusing a separate vacuum chamber. Break the vacuum in thechamber with helium. A large enough sample of materialshould be degassed in this pretreatment so that it will suffi
21、ce forall anticipated test runs. A mass spectrometer can be used toverify complete degassing.7.2 If required as evidenced by creepage of lubricant in firstrun, coat the container and the thermocouple with the anti-wetting agent (6.1). Silicones are especially likely to requirethis precaution.4Freund
22、lich, M. M., “Microbalance for Measuring Evaporation Rates inVacuum,” Vacuum, Vol 14, 1963, pp. 293297.FIG. 1 Apparatus for Measuring Evaporation Rates in VacuumD2715 92 (2012)27.3 Add to the container the required amount of sample, 756 5 mg/cm2of area exposed for evaporation. Press solids andsemiso
23、lids into the container with sufficient pressure to assurethe apparent surface area approximates the real surface area. Ifa coherent surface cannot be achieved, note this fact in thereport.8. System Calibration8.1 Calibrate the system in the vacuum, using one of thecalibration materials, over the te
24、mperature range to be used,following the procedure shown in 9.1 9.8.8.2 The rates obtained are compared with those predicted bythe Langmuir equation:5G 5 7.77p=M/T (1)where:G = evaporation rate, g/cm2s,p = vapor pressure, Pa,M = molecular weight, andT = temperature, K.8.2.1 If the measured rates dif
25、fer by more than 620 % fromthose calculated, take all possible corrective steps to locate thesource of the discrepancy. Use of a calibration factor is notencouraged, but may be tolerated in some cases if so reported.A factor greater than 2 or less than 0.5 casts such doubt on theresults as to practi
26、cally invalidate them and require correctiveaction.9. Procedure A9.1 Immerse the thermocouple in the sample, and bring thefurnace to approximate operating temperature.9.2 Suspend the sample and the container in position overthe furnace, and tare to near the upper limit of the range.9.3 Assemble the
27、vacuum apparatus and pump the system togive a chamber pressure of 106to 105Pa (108to 107torr).9.4 Start the liquid nitrogen flowing and cool the cold plateto 143 K (200F) or lower. Stabilize the furnace temperature.9.5 Measure the pressure near the furnace position with thenude ionization gage.9.6 M
28、ove the furnace into operating position surroundingthe specimen. Start the recorder, and mark the recorder chartstart of heat.9.7 Hold the temperature constant at the required level forsufficient length of time to measure the rate of weight changeand determine constancy of this rate.NOTE 1A time der
29、ivative computer may be used to report rate ofweight change directly.9.8 Monitor pressure changes manually or by the secondpen on the recorder when available. When the test temperatureis reached, and a steady weight loss condition attained,establish the sample weight and measure the evaporation rate
30、for this percentage point of the original weight. If the materialhas uniform molecular weight throughout, the rate will notchange with progressing evaporation. If the rate changes,continue measurement until the time for a single rate determi-nation exceeds 3 h.9.9 Determine rates for several tempera
31、tures, using a freshsample for each determination. Temperature intervals of 25 K,which approximate a ten-fold increase in rate, are usuallysuitable.NOTE 2If the sample is known to be an essentially pure compound,repetitive measurements are permissible. If such purity is merelysuspected, judgment may
32、 be made on the basis that a sample is not to bereused after a determination in the course of which the rate has changedmore than 25 % at a single temperature. However, if the supply is limited,it is possible to obtain some meaningful data on a spot basis, as indicatedbelow.9.10 After primary data h
33、ave been obtained at increasingtemperature levels on a sample which meets the above criterionof less than 25 % change during any single measurement, makespot measurements at decreasing temperature levels to detectany changes in the specimen.10. Procedure B10.1 Immerse the thermocouple, suspend the s
34、ample, andposition the furnace as described in 9.1 9.3.10.2 Assemble the vacuum apparatus and pump the systemto give a chamber pressure of 103to 102Pa (105to 104torr).10.3 Conduct the rest of the test as described in 9.4 9.10.11. Calculations11.1 When the evaporation rate proves to be constant withi
35、nthe limit of a 25 % decrease during a determination, or 25 %hif the determination takes less than 1 h, the evaporation rate foreach temperature is as follows:R 5 w02 w1!/t12 t0! (2)where:R = evaporation rate, g/s,w1= weight of sample at the end of the test, g,w0= initial weight of the sample, g,t1=
36、 time at the end of the test, s, andt0= initial time of the test, s.11.2 If the sample has a changing rate, this rate is calculatedfor each of the standard degrees of evaporation required in 12.2as follows:11.2.1 The weight required at each evaporation level is:wr5 100w02 Ew0!/100 (3)where:wr= weigh
37、t at specified evaporation loss, g,w0= initial weight of sample, g, andE = evaporation loss, %.11.2.2 Draw a line tangent to the curve on the recorder chartat each weight corresponding to the evaporation loss from11.2.1 and calculate the evaporation rate as follows:R 5 wa2 wb!/tb2 ta! (4)5Buckley, D
38、. H., and Johnson, R. L., “Evaporation Rates for Various Organicand Solid Lubricants in Vacuum to 108Millimetres of Mercury at 55 to 1100F,”National Aeronautics and Space Administration Technical Note D-2081, 1963.D2715 92 (2012)3where:R = evaporation rate, g/s,wa= weight at one point on the tangent
39、 line, g,wb= weight at a second point on the tangent line, g,ta= time at a point on the tangent line corresponding to wa,s, andtb= time at a point on the tangent line corresponding to wb,s,11.3 The evaporation rate per unit area is:E 5 R/A!C (5)where:E = evaporation rate per unit area, g/cm2s,R = ev
40、aporation rate from 11.1 or 11.2, g/s,A = surface area of sample exposed for evaporation, cm2,andC = calibration factor from 8.2, if applicable.11.4 If the molecular weight of the sample is known, therates may be converted to vapor pressures by the equationgiven in 8.2.As the molecular weight enters
41、 as square root, theallowable error is twice that for the vapor pressure.12. Report12.1 For specimens of constant rate according to 11.1, thereport shall consist of the evaporation rate per unit area foreach temperature, plus a statement of any deviations incoherence of surface as in 7.3, or variati
42、on in chamber pressurebeyond the limits in 9.3, or decomposition found in 9.10.12.2 For specimens of variable rate according to 11.2, thereport shall consist of the evaporation rate per unit area foreach temperature at intervals of 5 % (based on the sampleweight in 7.3) from the first obtainable one
43、 as far as the data gobut not to exceed a running time of 3 h unless this isspecifically required. Any deviations (see 12.1) are to bereported.12.3 For specimens of variable rate, and such limited supplyas to require reuse at another temperature, the report willcontain the data which could be obtain
44、ed. For example, such areport might indicate:5 %, 10 % measured at 473 K,15 %, 20 % measured at 498 K,25 %, 30 %, 35 % measured at 523 K,40 %, 45 %, 50 % remeasured at 498 K.13. Precision and Bias13.1 The data shown in Figure 3 of the Buckley, Johnsonpaper5were used to prepare the following statemen
45、t onProcedure A. Cooperative testing to prepare a statement onProcedure B is being planned.13.1.1 RepeatabilityDuplicate results by the same opera-tor should be considered suspect if they differ by more than45 % of their mean value (95 % confidence level).13.1.2 ReproducibilityThere is no immediate
46、plan to de-termine the data necessary to develop the reproducibilitystatement.13.2 BiasNo general statement is made on bias for thisstandard since the data used to determine the correlation cannotbe compared with accepted reference material.14. Keywords14.1 lubricants; volatilization; volatilization
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