1、Designation: B923 10Standard Test Method forMetal Powder Skeletal Density by Helium or NitrogenPycnometry1This standard is issued under the fixed designation B923; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers determination of skeletal den-sity of metal powders. The test method specifies generalprocedures tha
3、t 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 in
4、clude 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 The values stated in SI units are to be re
5、garded asstandard. No other units of measurement are included in thisstandard.1.3.1 This test method uses SI units as standard in accor-dance with IEEE/ASTM SI-10. State all numerical values interms of SI units unless specific instrumentation softwarereports volume and/or density using alternate uni
6、ts. In thiscase, present both reported and equivalent SI units in the finalwritten report. Many instruments report skeletal density asg/cm3instead of using correct 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 theresp
7、onsibility 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:2B215 Practices for Sampling Metal PowdersB243 Terminology of Powder MetallurgyE691 Practice
8、 for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodIEEE/ASTM SI-10 American National Standard for Use ofthe International System of Units (SI): The Modern MetricSystem3. Terminology3.1 Definitions:3.1.1 Refer to Terminology B243 for additional definitionsrelating to m
9、etal powders.3.2 Definitions of Terms Specific to This Standard:3.2.1 density, nthe mass per unit volume of a material.3.2.2 density, skeletal, nthe 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 thepi
10、eces.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, 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
11、sample (to provide at least theminimum skeletal volume required for reliable results for theinstrument or apparatus used) is outgassed under appropriateconditions 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.
12、Thepycnometer measures the total displaced skeletal volume of thesample under analysis. The sample mass is then used tocalculate the skeletal density of the metal. Any error in thesample mass will affect the calculated density. Some cleaningof the sample surface may take place inside the pycnometer.
13、Therefore, it is best to reweigh the sample after analysis anduse the final mass when calculating skeletal density.4.3 Sample skeletal volume is determined a minimum offive times. Skeletal volume average and standard deviation arecalculated using standard statistical methods.4.4 Calculations are bas
14、ed on the ideal gas law, as requiredby the instrument being used for the determination. Theassumption of ideal behavior is accepted as valid at analytical1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Su
15、bcom-mittee B09.03 on Refractory Metal Powders.Current edition approved May 1, 2010. Published June 2010. Originallyapproved in 2002. Last previous edition approved in 2008 as B92302(2008). DOI:10.1520/B0923-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cust
16、omer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
17、, PA 19428-2959, United States.temperatures 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:Vsample5 Vcell2 VexpSP2P12 P2D(1)where:Vsample= calculated sample vo
18、lume,Vcell= calibrated sample compartment volume,Vexp= calibrated expansion volume,P1= measured gas pressure when only Vcellis filledwith analysis gas, andP2= measured gas pressure after expansion of theanalysis gas into Vexp.5. Significance and Use5.1 Both suppliers and users of metals can benefit
19、fromknowledge of the skeletal density of these materials. Results ofmany intermediate and final processing steps are controlled byor related to skeletal density of the metal. In addition, theperformance of many sintered or cast metal structures may bepredicted from the skeletal density of the starti
20、ng 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 after the open pores havebeen emptied of any physically adsorbed molecules. Suchadsorbed species (for example, water or volatile organ
21、iccompounds) prevent entry of the gas probe molecules into theopen porosity of the sample. Therefore, it is necessary toremove these adsorbed contaminants prior to pycnometryanalysis. Generally, such outgassing is performed by evacuat-ing or flushing the sample. Outgassing can be accelerated byusing
22、 elevated temperatures, provided no irreversible samplechanges occur. Typical minimum vacuum levels attained are10-1Pa. Typical flushing gases are those used for analysis.Outgassing is complete when duplicate skeletal volume analy-ses produce results within expected instrument repeatabilitylimits. S
23、ome commercial instruments include capabilities forautomated evacuation, or flushing of the sample, or both.Elevated temperatures should not be used when outgassingsamples inside the pycnometer.6.2 This test method can be used to determine the volume ofa sample whose pores have been deliberately fil
24、led 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. Apparatus7.1 Commercial instruments are available from severalmanufacturers for the measurement of skeletal volume by gaspycnometry. Some ins
25、truments perform calculations of skeletalvolume, or density, or both, upon completion of the analysis.Others require manual calculation of skeletal volume anddensity.7.2 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,
26、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 mole percent, with the sum of O2,argon, CO2, hydrocarbons (as CH4), and H2O totaling less than10 parts per million; dry and oil-free;
27、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 orflushing gas. The actual composition of the gas shall be known.9. Hazards9.1 Precautions applying to the use of compressed gasessho
28、uld be observed.10. Sampling, Test Specimens, and Test Units10.1 No specific instructions are given. However, it isimportant that the test portion being analyzed represent thelarger bulk sample from which it is taken. The bulk sampleshould be homogenized before any sampling takes place. Bestresults
29、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 to samplea portion of the flow for a longer time. Collecting several smalltest portions and combining them improves the reliability
30、 ofthe sampling process. Rotating rifflers are available whichsatisfy these requirements. Refer to Practices B215 for infor-mation on the use of a chute sample splitter.11. Calibration and Standardization11.1 Follow manufacturers instructions for calibration andoperational verification of the instru
31、ment.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. Samplequantity should be sufficient to satisfy minimum skeletalvolume as required by manufacturer. Weigh (to nearest 0.1 mg)and record
32、 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, follow the remaining steps in this sectionfor external outgassing.12.3.1 Place prepared sample holder in outgassing device.12.3.2 Progr
33、am outgassing device for initial outgassingtemperature. Increase temperature as appropriate for thesample. Allow sample to continue to outgas until prescribedvacuum level is achieved, or for prescribed outgassing time, orboth.12.3.3 The metal powders analyzed during the interlabora-tory study were p
34、repared 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 Reduce temperature of outgassing device to ambient.Remove sample holder.B923 10212.3.5 Weigh sample holder (to nearest 0.1 mg) to obta
35、insample and sample holder mass. Record mass. Subtract emptysample holder mass determined in 12.1 to obtain outgassedsample mass. Record calculated mass.13. Procedure13.1 Place filled sample holder in pycnometer. Close samplechamber.13.2 Use helium, nitrogen, or other high purity gas foranalysis and
36、 flushing gas.13.3 Automated Instruments OnlySelect, or input, desiredanalysis and report parameters. Include outgassing parametersif sample preparation is performed as a part of the sampleanalysis. If necessary, input the outgassed sample mass. (Thefinal mass should be determined and entered after
37、the analysis.)Determine skeletal volume a minimum of five times.13.4 Manually Operated Instruments OnlyCollect fivesets of analysis data according to manufacturers recommendedprocedure for maximum accuracy and precision.13.5 When the analysis has finished, remove the sampleholder. Weigh holder (to n
38、earest 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 mass.13.6 Automated Instruments OnlyInput the final samplemass. Generate final sample report.14. Calculations14.1 Automated Instrum
39、ents OnlySoftware automaticallycalculates results for the chosen reports using the final massinput in 13.5.14.2 Manually Operated Instruments OnlyCalculate skel-etal volume using collected data according to manufacturersinstructions. Use final sample mass from 13.4 to calculateskeletal densities. Ca
40、lculated average and standard deviationfor skeletal volume and density as described in Practice E691.15. Report15.1 Report the following information:15.1.1 Complete sample identification.15.1.2 Measured skeletal volumes and statistics. Note anyunits used other than standard.15.1.3 Skeletal density d
41、etermined. 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 outgassing method, including total time andoutgassing temperature(s).16. Precision and Bias16.1 An interlaboratory study is underway, conducted ac
42、-cording to Practice E691. The study includes iron, tungsten,nickel, cobalt, molybdenum, chromium carbide, and tungstencarbide powders. Expected precision will be determined forthese materials. No statement is given for other metal powders.16.2 PrecisionThe repeatability standard deviation ofskeleta
43、l density for one tungsten carbide sample has beendetermined to be 60.06 % relative standard deviation, basedupon analyses in one laboratory, and for one nickel sample tobe 60.2 % relative standard deviation. The reproducibility ofthis test method is being determined and will be available on orbefor
44、e June 30, 2011.16.3 BiasNo information can be presented on the bias ofthe procedure 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; sk
45、eletal density; skeletal volumeSUMMARY OF CHANGESCommittee B09 has identified the location of selected changes to this standard since the last issue(B923 - 02(2008) that may impact the use of this standard. (May 1, 2010)(1) Subsection 16.2 has been updated to include a temporaryprecision statement t
46、o be used while the Interlaboratory Studyis underway. Rationale: The repeatability of a single laboratorywill provide some guidance to the user of the Test Method asto what to expect from use of the procedures described hereuntil a final precision statement can be completed.B923 103ASTM Internationa
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48、wn responsibility.This standard is subject 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 a
49、ddressed to ASTM International Headquarters. 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 standard 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 a
