1、Designation: B 923 02Standard Test Method forMetal Powder Skeletal Density by Helium or NitrogenPycnometry1This standard is issued under the fixed designation B 923; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of skeletal den-sity of metal powders. The test method specifies generalprocedures t
3、hat are applicable to many commercial pycnom-etry instruments. The method provides specific sample outgas-sing procedures for listed materials. It includes additionalgeneral outgassing instructions for other metals. The ideal gaslaw forms the basis for all calculations.1.2 This test method does not
4、include all existing proce-dures appropriate for outgassing metal materials. The includedprocedures provided acceptable results for samples analyzedduring an interlaboratory study. The investigator shall deter-mine the appropriateness of listed procedures.1.3 This method uses SI units as standard ac
5、cording toPractice E 380. State all numerical values in terms of SI unitsunless specific instrumentation software reports volume and/ordensity using alternate units. In this case, present both reportedand equivalent SI units in the final written report. Manyinstruments report skeletal density as g/c
6、m3instead of usingcorrect SI units (kg/m3).1.4 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 establish appro-priate safety and health practices and determine the applica-bility of regulato
7、ry limitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 215 Practices for Sampling Finished Lots of Metal Pow-ders2B 243 Definitions of Terms Used in Powder Metallurgy2E 380 Practice for Use of the International System of Units(SI)3E 691 Practice for Conducting an Interlaboratory Stu
8、dy toDetermine the Precision of a Test Method33. Terminology3.1 DefinitionsRefer to Terminology B 243 for additionaldefinitions relating to metal powders.3.2 Definitions: Definitions of Terms Specific to This Stan-dard:3.2.1 density, nthe mass per unit volume of a material.3.2.2 density, skeletal, n
9、the ratio of mass of discretepieces of solid material to the sum of the volumes of the solidmaterial in the pieces and closed (or blind) pores within thepieces.3.2.3 outgassing, nthe evolution of gas from a material ina vacuum or inert gas flow, at or above ambient temperature.3.2.4 skeletal volume,
10、 nthe sum of the volumes: the solidmaterial in the pieces and closed (or blind) pores within thepieces.4. Summary of Test Method4.1 An appropriately sized sample (to provide at least theminimum skeletal volume required for reliable results for theinstrument or apparatus used) is outgassed under appr
11、opriateconditions prior to analysis.4.2 The sample is weighed to nearest 0.1 mg. It is importantto use an analytical balance to determine the sample mass. Thepycnometer measures the total displaced skeletal volume of thesample under analysis. The sample mass is then used tocalculate the skeletal den
12、sity of the metal. Any error in thesample mass will affect the calculated density. Some cleaningof the sample surface may take place inside the pycnometer.Therefore, it is best to reweigh the sample after analysis anduse the final mass when calculating skeletal density.4.3 Sample skeletal volume is
13、determined a minimum offive times. Skeletal volume average and standard deviation arecalculated using standard statistical methods.4.4 Calculations are based on the ideal gas law, as requiredby the instrument being used for the determination. Theassumption of ideal behavior is accepted as valid at a
14、nalyticaltemperatures and pressures. For instruments designed with twopressure chambers, one a sample compartment, and the other agas expansion chamber, the equation for sample volumecalculation takes the form:1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Meta
15、l Powder Product and is the direct responsibility of SubcommitteeB09.03 on Refractory Metal Powders.Current edition approved Oct. 10, 2002. Published December 2002.2Annual Book of ASTM Standards, Vol 02.05.3Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive
16、, PO Box C700, West Conshohocken, PA 19428-2959, United States.Vsample5 Vcell2 VexpSP2P12 P2D(1)where:Vsample= calculated sample volume,Vcell= calibrated sample compartment volume,Vexp= calibrated expansion volume,P1= measured gas pressure when only Vcellis filledwith analysis gas, andP2= measured g
17、as pressure after expansion of theanalysis gas into Vexp.5. Significance and Use5.1 Both suppliers and users of metals can benefit fromknowledge of the skeletal density of these materials. Results ofmany intermediate and final processing steps are controlled byor related to skeletal density of the m
18、etal. In addition, theperformance of many sintered or cast metal structures may bepredicted from the skeletal density of the starting metalpowder, for all or a portion of the finished piece.6. Interferences6.1 This test method can be used to determine the skeletalvolume of a powder or solid only aft
19、er the open pores havebeen emptied of any physically adsorbed molecules. Suchadsorbed species (for example, water or volatile organiccompounds) prevent entry of the gas probe molecules into theopen porosity of the sample. Therefore, it is necessary toremove these adsorbed contaminants prior to pycno
20、metryanalysis. Generally, such outgassing is performed by evacuat-ing or flushing the sample. Outgassing can be accelerated byusing elevated temperatures, provided no irreversible samplechanges occur. Typical minimum vacuum levels attained are10-1Pa. Typical flushing gases are those used for analysi
21、s.Outgassing is complete when duplicate skeletal volume analy-ses produce results within expected instrument repeatabilitylimits. Some commercial instruments include capabilities forautomated evacuation, or flushing of the sample, or both.Elevated temperatures should not be used when outgassingsampl
22、es inside the pycnometer.6.2 This test method can be used to determine the volume ofa sample whose pores have been deliberately filled with asecond phase. In this case, removal of the second phase shouldbe avoided. Vacuum degassing or flushing of the sample is notnecessary in this case.7. Apparatus7
23、.1 Commercial instruments are available from severalmanufacturers for the measurement of skeletal volume by gaspycnometry. Some instruments perform calculations of skeletalvolume, or density, or both, upon completion of the analysis.Others require manual calculation of skeletal volume anddensity.7.2
24、 Analytical Balance, capable of weighing to 0.1 mg.8. Reagents and Materials8.1 Helium, 99.999 mole percent, with the sum of N2,O2,argon, CO2, hydrocarbons (as CH4), and H2O totaling less than10 parts per million; dry and oil-free; cylinder, or other sourceof purified helium.8.2 Nitrogen, 99.999 mol
25、e percent, with the sum of O2,argon, CO2, hydrocarbons (as CH4), and H2O totaling less than10 parts per million; dry and oil-free; cylinder, or other sourceof purified nitrogen.8.3 Other High Purity Gas, dry and oil-free; cylinder, orother source of gas, if other gas is to be used as the analysis or
26、flushing gas. The actual composition of the gas shall be known.9. Hazards9.1 Precautions applying to the use of compressed gasesshould be observed.10. Sampling, Test Specimens, and Test Units10.1 No specific instructions are given. However, it isimportant that the test portion being analyzed represe
27、nt thelarger bulk sample from which it is taken. The bulk sampleshould be homogenized before any sampling takes place. Bestresults are obtained when a flowing bulk material is tempo-rarily diverted into a collector for an appropriate time. It isbetter to sample the entire flow for a short time than
28、to samplea portion of the flow for a longer time. Collecting several smalltest portions and combining them improves the reliability ofthe sampling process. Rotating rifflers are available whichsatisfy these requirements. Refer to Practices B 215 for infor-mation on the use of a chute sample splitter
29、.11. Calibration and Standardization11.1 Follow manufacturers instructions for calibration andoperational verification of the instrument.12. Conditioning12.1 Weigh (to nearest 0.1 mg) a clean, empty sampleholder. Record the empty sample holder mass.12.2 Add sample aliquant to empty sample holder. Sa
30、mplequantity should be sufficient to satisfy minimum skeletalvolume as required by manufacturer. Weigh (to nearest 0.1 mg)and record sample and sample holder mass.12.3 Sample outgassing may be performed inside the pyc-nometer. If so proceed to the Procedure section of this testmethod. Otherwise, fol
31、low the remaining steps in this sectionfor external outgassing.12.3.1 Place prepared sample holder in outgassing device.12.3.2 Program outgassing device for initial outgassingtemperature. Increase temperature as appropriate for thesample. Allow sample to continue to outgas until prescribedvacuum lev
32、el is achieved, or for prescribed outgassing time, orboth.12.3.3 The metal powders analyzed during the interlabora-tory study were prepared inside the instruments by purgingwith analysis gas. Had preliminary outgassing been desired, atemperature of 200C applied for 1 h would have been used.12.3.4 Re
33、duce temperature of outgassing device to ambient.Remove sample holder.12.3.5 Weigh sample holder (to nearest 0.1 mg) to obtainsample and sample holder mass. Record mass. Subtract emptysample holder mass determined in 12.1 to obtain outgassedsample mass. Record calculated mass.B92302213. Procedure13.
34、1 Place filled sample holder in pycnometer. Close samplechamber.13.2 Use helium, nitrogen, or other high purity gas foranalysis and flushing gas.13.3 Automated Instruments onlyselect, or input, desiredanalysis and report parameters. Include outgassing parametersif sample preparation is performed as
35、a part of the sampleanalysis. If necessary, input the outgassed sample mass. (Thefinal mass should be determined and entered after the analysis.)Determine skeletal volume a minimum of five times.13.4 Manually Operated Instruments onlycollect five setsof analysis data according to manufacturers recom
36、mendedprocedure for maximum accuracy and precision.13.5 When the analysis has finished, remove the sampleholder. Weigh holder (to nearest 0.1 mg). Record the finalsample holder and sample mass. Subtract the empty sampleholder mass recorded in 12.1 to obtain the final sample mass.Record final sample
37、mass.13.6 Automated Instruments only, input the final samplemass. Generate final sample report.14. Calculations14.1 Automated Instruments only, software automaticallycalculates results for the chosen reports using the final massinput in 13.5.14.2 Manually Operated Instruments only, calculate skel-et
38、al volume using collected data according to manufacturersinstructions. Use final sample mass from 13.4 to calculateskeletal densities. Calculated average and standard deviationfor skeletal volume and density as described in Practice E 691.15. Report15.1 Report the following information:15.1.1 Comple
39、te sample identification.15.1.2 Measured skeletal volumes and statistics. Note anyunits used other than standard.15.1.3 Skeletal density determined. Note any units usedother than standard.15.1.4 Final sample mass. Note any units used other thanstandard.15.1.5 Analysis gas used.15.1.6 Sample outgassi
40、ng method, including total time andoutgassing temperature(s).16. Precision and Bias16.1 An interlaboratory study is underway, conducted ac-cording to Practice E 691. The study includes iron, tungsten,nickel, cobalt, molybdenum, chromium carbide, and tungstencarbide powders. Expected precision will b
41、e determined forthese materials. No statement is given for other metal powders.16.2 PrecisionThe repeatability standard deviation andreproducibility standard deviation will be determined uponcompletion of the interlaboratory study.16.3 BiasNo information can be presented on the bias ofthe procedure
42、in this test method for measuring skeletal densitybecause no metal powder having an accepted reference value isavailable.17. Keywords17.1 density; metal powders; outgassing; pycnometry; re-fractory metal powders; skeletal density; skeletal volumeASTM International takes no position respecting the va
43、lidity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is su
44、bject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headqu
45、arters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This stand
46、ard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B923023
