1、Designation: B923 10B923 16Standard 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
2、last revision. 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 density of metal powders. The test method specifies general procedu
3、resthat are applicable to many commercial pycnometry instruments. The method provides specific sample outgassing procedures forlisted materials. It includes additional general outgassing instructions for other metals. The ideal gas law forms the basis for allcalculations.1.2 This test method does no
4、t include all existing procedures appropriate for outgassing metal materials. The includedprocedures provided acceptable results for samples analyzed during an interlaboratory study. The investigator shall determine theappropriateness of listed procedures.1.3 The values stated in SI units are to be
5、regarded as standard. No other units of measurement are included in this standard.1.3.1 This test method uses SI units as standard in accordance with IEEE/ASTM SI 10. State all numerical values in terms ofSI units unless specific instrumentation software reports volume and/or density using alternate
6、or density, or both, using alternativeunits. In this case, present both reported and equivalent SI units in the final written report. Many instruments report skeletal densityas g/cm3 instead of using correct SI units (kg/m3).1.4 This standard does not purport to address all of the safety concerns, i
7、f any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B215 Practices for Sampling Metal PowdersB243 Ter
8、minology of Powder MetallurgyE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodIEEE/ASTM SI 10 American National Standard for Metric Practice3. Terminology3.1 Definitions:3.1.1 Refer to Terminology B243 for additional definitions relating to metal powde
9、rs.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 discrete pieces of solid material to the sum of the volumes of the solid materialin the pieces and closed (or blind) pores within the pieces.3.2
10、.3 outgassing, nthe evolution of gas from a material in a vacuum or inert gas flow, at or above ambient temperature.3.2.4 skeletal volume, nthe sum of the volumes: the solid material in the pieces and closed (or blind) pores within the pieces.1 This test method is under the jurisdiction ofASTM Commi
11、ttee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.03on Refractory Metal Powders.Current edition approved May 1, 2010Oct. 1, 2016. Published June 2010October 2016. Originally approved in 2002. Last previous edition approved in 20082010 asB92302(2
12、008).B92310. DOI: 10.1520/B0923-10.10.1520/B0923-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This docu
13、ment is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as
14、appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United
15、 States14. Summary of Test Method4.1 An appropriately sized sample (to provide at least the minimum skeletal volume required for reliable results for theinstrument or apparatus used) is outgassed under appropriate conditions prior to analysis.4.2 The sample is weighed to nearest 0.1 mg. It is import
16、ant to use an analytical balance to determine the sample mass. Thepycnometer measures the total displaced skeletal volume of the sample under analysis. The sample mass is then used to calculatethe skeletal density of the metal. Any error in the sample mass will affect the calculated density. Some cl
17、eaning of the samplesurface may take place inside the pycnometer. Therefore, it is best to reweigh the sample after analysis and use the final mass whencalculating skeletal density.4.3 Sample skeletal volume is determined a minimum of five times. Skeletal volume average and standard deviation arecal
18、culated using standard statistical methods.4.4 Calculations are based on the ideal gas law, as required by the instrument being used for the determination. The assumptionof ideal behavior is accepted as valid at analytical temperatures and pressures. For instruments designed with two pressurechamber
19、s, one a sample compartment, and the other a gas expansion chamber, the equation for sample volume calculation takesthe form:Vsample5Vcell2VexpS P2P12P2D (1)where:Vsample = calculated sample volume,Vcell = calibrated sample compartment volume,Vexp = calibrated expansion volume,P1 = measured gas pres
20、sure when only Vcell is filled with analysis gas, andP2 = measured gas pressure after expansion of the analysis gas into Vexp.5. Significance and Use5.1 Both suppliers and users of metals can benefit from knowledge of the skeletal density of these materials. Results of manyintermediate and final pro
21、cessing steps are controlled by or related to skeletal density of the metal. In addition, the performanceof many sintered or cast metal structures may be predicted from the skeletal density of the starting metal powder, for all or a portionof the finished piece.6. Interferences6.1 This test method c
22、an be used to determine the skeletal volume of a powder or solid only after the open pores have beenemptied of any physically adsorbed molecules. Such adsorbed species (for example, water or volatile organic compounds) prevententry of the gas probe molecules into the open porosity of the sample. The
23、refore, it is necessary to remove these adsorbedcontaminants prior to pycnometry analysis. Generally, such outgassing is performed by evacuating or flushing the sample.Outgassing can be accelerated by using elevated temperatures, provided no irreversible sample changes occur. Typical minimumvacuum l
24、evels attained are 10-1 Pa. Typical flushing gases are those used for analysis. Outgassing is complete when duplicateskeletal volume analyses produce results within expected instrument repeatability limits. Some commercial instruments includecapabilities for automated evacuation, or flushing of the
25、sample, or both. Elevated temperatures should not be used whenoutgassing samples inside the pycnometer.6.2 This test method can be used to determine the volume of a sample whose pores have been deliberately filled with a secondphase. In this case, removal of the second phase should be avoided. Vacuu
26、m degassing or flushing of the sample is not necessaryin this case.7. Apparatus7.1 Commercial instruments are available from several manufacturers for the measurement of skeletal volume by gaspycnometry. Some instruments perform calculations of skeletal volume, or density, or both, upon completion o
27、f the analysis.Others require manual calculation of skeletal volume and density.7.2 Analytical Balance, Balancecapable of weighing to 0.1 A balance readable to 0.1 mg, with a capacity adequate for themass of the test portion, and capable of determining the mass of the test portion to the nearest 1 m
28、g.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 than 10parts per million; dry and oil-free; cylinder, or other source of purified helium.8.2 Nitrogen, 99.999 mole percent, with the sum of O2, argon, CO2, hyd
29、rocarbons (as CH4), and H2O totaling less than 10 partsper million; dry and oil-free; cylinder, or other source of purified nitrogen.B923 1628.3 Other High Purity Gas, dry and oil-free; cylinder, or other source of gas, if other gas is to be used as the analysis or flushinggas. The actual compositio
30、n of the gas shall be known.9. Hazards9.1 Precautions applying to the use of compressed gases should be observed.10. Sampling, Test Specimens, and Test Units10.1 No specific instructions are given. However,Nevertheless, it is important that the test portion being analyzed represent thelarger bulk sa
31、mple from which it is taken. The bulk sample should be homogenized before any sampling takes place. Best resultsare obtained when a flowing bulk material is temporarily diverted into a collector for an appropriate time. It is better to samplethe entire flow for a short time than to sample a portion
32、of the flow for a longer time. Collecting several small test portions andcombining them improves the reliability of the sampling process. Rotating rifflers are available whichthat satisfy theserequirements. Refer to Practices B215 for information on the use of a chute sample splitter.11. Calibration
33、 and Standardization11.1 Follow manufacturers instructions for calibration and operational verification of the instrument.12. Conditioning12.1 Weigh (to nearest 0.1 mg) a clean, empty sample holder. Record the empty sample holder mass.12.2 Add sample aliquant to empty sample holder. Sample quantity
34、should be sufficient to satisfy minimum skeletal volume asrequired by manufacturer. Weigh (to nearest 0.1 mg) and record sample and sample holder mass.12.3 Sample outgassing may be performed inside the pycnometer. If so, proceed to the Procedure section of this test method.Otherwise, follow the rema
35、ining steps in this section for external outgassing.12.3.1 Place prepared sample holder in outgassing device.12.3.2 Program outgassing device for initial outgassing temperature. Increase temperature as appropriate for the sample. Allowsample to continue to outgas until prescribed vacuum level is ach
36、ieved, or for prescribed outgassing time, or both.12.3.3 The metal powders analyzed during the interlaboratory study were prepared inside the instruments by purging withanalysis gas. Had preliminary outgassing been desired, a temperature of 200C200 C applied for 1 h would have been used.12.3.4 Reduc
37、e temperature of outgassing device to ambient. Remove sample holder.12.3.5 Weigh sample holder (to nearest 0.1 mg) to obtain sample and sample holder mass. Record mass. Subtract empty sampleholder mass determined in 12.1 to obtain outgassed sample mass. Record calculated mass.13. Procedure13.1 Place
38、 filled sample holder in pycnometer. Close sample chamber.13.2 Use helium, nitrogen, or other high purity gas for analysis and flushing gas.13.3 Automated Instruments OnlySelect, or input, desired analysis and report parameters. Include outgassing parameters ifsample preparation is performed as a pa
39、rt of the sample analysis. If necessary, input the outgassed sample mass. (The final massshould be determined and entered after the analysis.) Determine skeletal volume a minimum of five times.13.4 Manually Operated Instruments OnlyCollect five sets of analysis data according to manufacturers recomm
40、endedprocedure for maximum accuracy and precision.13.5 When the analysis has finished, remove the sample holder. Weigh holder (to nearest 0.1 mg). Record the final sampleholder and sample mass. Subtract the empty sample holder mass recorded in 12.1 to obtain the final sample mass. Record finalsample
41、 mass.13.6 Automated Instruments OnlyInput the final sample mass. Generate final sample report.14. Calculations14.1 Automated Instruments OnlySoftware automatically calculates results for the chosen reports using the final mass inputin 13.513.6.14.2 Manually Operated Instruments OnlyCalculate skelet
42、al volume using collected data according to manufacturersinstructions. Use final sample mass from 13.413.5 to calculate skeletal densities. Calculated average and standard deviation forskeletal volume and density as described in Practice E691.15. Report15.1 Report the following information:15.1.1 Co
43、mplete sample identification.B923 16315.1.2 Measured skeletal volumes and statistics. Note any units used other than standard.15.1.3 Skeletal density determined. Note any units used other than standard.15.1.4 Final sample mass. Note any units used other than standard.15.1.5 Analysis gas used.15.1.6
44、Sample outgassing method, including total time and outgassing temperature(s).16. Precision and Bias16.1 An interlaboratory study is underway, conducted according to Practice E691. The study includes iron, tungsten, nickel,cobalt, molybdenum, chromium carbide, and tungsten carbide powders. Expected p
45、recision will be determined for these materials.No statement is given for other metal powders.16.2 PrecisionThe repeatability standard deviation of skeletal density for one tungsten carbide sample has been determinedto be 60.06 % relative standard deviation, based upon analyses in one laboratory, an
46、d for one nickel sample to be 60.2 % relativestandard deviation. The reproducibility of this test method is being determined and will be available on or before June 30,2011.2020.16.3 BiasNo information can be presented on the bias of the procedure in this test method for measuring skeletal densitybe
47、cause no metal powder having an accepted reference value is available.17. Keywords17.1 density; metal powders; outgassing; pycnometry; refractory metal powders; skeletal density; skeletal volumeSUMMARY OF CHANGESCommittee B09 has identified the location of selected changes to this standard since the
48、 last issue(B923 - 02B923 - 10(2008) that may impact the use of this standard. (May 1, 2010)(1) The definitions for “skeletal density” and “skeletal volume” in subsections 3.2.2 and 3.2.4 have been changed by deletingreference to “blind pores.”(2) SubsectionThe 16.2 has been updated analytical balan
49、ce requirements have been changed in section 7.2 to include a temporaryprecision statement to be used while the Interlaboratory Study is underway. Rationale: The repeatability of a single laboratory willprovide some guidance to the user of the Test Method as to what to expect from use of the procedures described here until a finalprecision statement can be completed.indicate a balance readable to 0.1 mg with a capacity adequate for the mass of the test portionand capable of determining the mass of the test portion to the nearest 1 mg.ASTM International takes
