1、Designation: C721 14Standard Test Methods forEstimating Average Particle Size of Alumina and SilicaPowders by Air Permeability1This standard is issued under the fixed designation C721; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, the year of 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 These test methods cover the estimation of the averageparticle size in micrometres of alumina and silic
3、a powdersusing an air permeability method. The test methods areintended to apply to the testing of alumina and silica powdersin the particle size range from 0.2 to 75 m.1.2 UnitsWith the exception of the values for density andthe mass used to determine density, for which the use of thegram per cubic
4、 centimetre (g/cm3) and gram (g) units is thelong-standing industry practice; and the units for pressure, cmH2Oalso long-standing practice; the values in SI units are tobe regarded as standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I
5、t 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:2B330 Test Methods for Estimating Average Particle Size ofMetal Powders and Rela
6、ted Compounds Using Air Per-meabilityE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE456 Terminology Relating to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1
7、Definitions of Terms Specific to This Standard:3.1.1 air permeability, nmeasurement of air pressure dropacross a packed bed of powder.3.1.2 agglomerate, nseveral particles adhering together.3.1.3 average particle size, n(for the purposes of thesetest methods only)an estimate of the equivalent averag
8、espherical particle diameter, calculated from the measuredenvelope-specific surface area, assuming that all the powderparticles are spherical and that all are exactly the same size.The average particle size obtained by this procedure is acalculated average based on air permeability. It will have ava
9、lue that is numerically equal to six times the total volume ofthe sample under test divided by the total envelope-specificsurface area of all the particles contained in the sample, or:davg5 6s (1)davg= the estimated average particle size obtained by thisprocedure, m, = absolute density of the partic
10、les, g/cm3, ands = total envelope-specific surface area of the sample,m2/g.NOTE 1The value of davgwill probably not be numerically equal tothe average particle size as obtained by particle size distribution analysismethods since it is independent of particle shape or size distribution. Thetest metho
11、ds actually measure sample surface area by air permeability andconverts that to an average particle diameter.3.1.4 de-agglomeration, nprocess used to break up ag-glomerates of particles.3.1.5 envelope-specific surface area, nspecific surfacearea of a powder as determined by gas permeametry.3.1.6 Fis
12、her calibrator tube, njewel with a precisionorifice mounted in a tube similar to a sample tube; thecalibrator tube value is directly traceable to the master tubemaintained by ASTM International Subcommittee B09.03 onRefractory Metal Powders.3.1.7 Fisher Number, ncalculated value equated to anaverage
13、 particle diameter, assuming all the particles are spheri-cal and of uniform size.1These test methods are under the jurisdiction of ASTM Committee C21 onCeramic Whitewares and Related Products and is the direct responsibility ofSubcommittee C21.04 on Raw Materials.Current edition approved July 1, 20
14、14. Published September 2014. Originallyapproved in 1972. Last previous edition approved in 1997 as C721 81 (1997)1,which was withdrawn in 2002 and reinstated in July 2014. DOI: 10.1520/C0721-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
15、serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*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. U
16、nited States13.1.8 Fisher Sub-Sieve Sizer (FSSS), na permeabilityinstrument for measuring envelope-specific surface area andestimating average particle size (Fisher Number) from 0.5 to50 m.3.1.9 HEL Sub-sieve AutoSizer (HEL SAS), nacommercially-available permeability instrument for measuringenvelope
17、-specific surface area and estimating average particlesize from 0.2 to 75 m.3.1.10 porosity of a bed of powder, nratio of the volume ofthe void space in the powder bed to that of the overall volumeof the powder bed.4. Significance and Use4.1 The estimation of average particle size has two chieffunct
18、ions: first, as a guide to the degree of fineness orcoarseness of a powder as this, in turn, is related to the flow andpacking properties; and, second, as a control test on theuniformity of a product.4.2 These test methods provide procedures for determiningthe envelope-specific surface area of powde
19、rs, from which iscalculated an “average” particle diameter, assuming the par-ticles are monosize, smooth surface, nonporous, sphericalparticles. For this reason, values obtained by these test methodswill be reported as an average particle size or Fisher Number.The degree of correlation between the r
20、esults of these testmethods and the quality of powders in use will vary with eachparticular application and has not been fully determined.4.3 These test methods are generally applicable to aluminaand silica powders, for particles having diameters between 0.2and 75 m (HEL SAS) or between 0.5 and 50 m
21、 (FSSS). Theymay be used for other similar ceramic powders, with caution asto their applicability. They should not be used for powderscomposed of particles whose shape is too far from equiaxedthat is, flakes or fibers. In these cases, it is permissible to usethe test methods described only by agreem
22、ent between theparties concerned. These test methods shall not be used formixtures of different powders, nor for powders containingbinders or lubricants. When the powder contains agglomerates,the measured surface area may be affected by the degree ofagglomeration. Methods of de-agglomeration may be
23、used ifagreed upon between the parties concerned.4.4 When an “average” particle size of powders is deter-mined using either the HEL SAS or the FSSS, it should beclearly kept in mind that this average size is derived from thedetermination of the specific surface area of the powder usinga relationship
24、 that is true only for powders of uniform size andspherical shape. Thus, the results of these methods are onlyestimates of average particle size.5. Apparatus5.1 HEL Sub-sieve AutoSizer (HEL SAS)3Method1consisting of an air pump, a calibrated gas mass flowcontroller, a precision-bore sample tube, a s
25、ample tube retain-ing collar, a spacer tool, a gas flow metering valve, twoprecision pressure transducers (inlet and outlet), a steppermotor controlled ballscrew-mounted piston, and computerhardware and software for instrument control and calculationand reporting of results. Included is accessory eq
26、uipmentconsisting of a plug manipulator (extraction rod), two porousplugs, and a supply of paper disks.NOTE 2When homing the piston, adjust the sample packing assembly(1) as described in the manufacturers directions, with the plugs and paperdisks stacked together and placed on the fixed anvil spigot
27、, or (2) using aspecially designed baseline (homing) gauge instead of the plugs and paperdisks. This baseline gauge shall have a height of 20.30 6 0.10 mm. Checkall plug heights when new plugs are purchased and periodically thereafterto make sure all are equal in height.5.1.1 Powder funnelstainless
28、steel, with spout outsidediameter slightly smaller than the sample tube inside diameter.5.1.2 The manufacturer provides instructions which shouldbe followed, using the “Inorganics Test” procedure whentesting ceramic powders. Particular attention should be givento proper maintenance of the instrument
29、 with special referenceto the instructions on (1) “homing” the piston when turning onfrom an unpowered state, (2) setting the pressure and periodicchecking of the pressure, (3) condition of O-rings on the pistonand sample spigot, and (4) the sample packing assembly (plugsand paper disks).5.2 Fisher
30、Sub-Sieve Sizer (FSSS)4Method2consisting of an air pump, an air-pressure regulatingdevice, a precision-bore sample tube, a standardized double-range air flowmeter, and a calculator chart. Included is acces-sory equipment consisting of a plug manipulator, powderfunnel, two porous plugs, a supply of p
31、aper disks, and a rubbertube support stand.5.2.1 The manufacturer has also furnished instructionswhich should be followed except as amended as follows.Particular attention should be given to proper maintenance of3The sole source of supply of the HEL Sub-sieve AutoSizer (HEL SAS) knownto the committe
32、e is Hazard Evaluation Laboratory Limited, 9-10 Capital BusinessPark, Manor Way, Borehamwood, Hertfordshire, WD6 1GW. UK. The instrument isexclusively distributed globally by Micromeritics Instrument Corporation, Particu-late Systems, 4356 Communications Drive, Norcross, GA 30093-2901, USA. If youar
33、e aware of alternative suppliers, please provide this information to ASTMInternational Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend.4The Fisher Sub-Sieve Sizer (FSSS) is no longer commercially available, nor i
34、sit supported with parts and service. It is included here as apparatus for Method 2because of several instruments still operating in the field. In-house repair or partsreplacement is discouraged, as these are likely to detrimentally affect results andprecision.C721 142the instrument with special ref
35、erence to the instructions on (1)periodic checking of the water level in the pressure regulatorstandpipe, (2) manometer level before the sample tube isinserted, and (3) the sample packing assembly.5.2.2 Jewel Calibrator Tube5a tube to be used as astandard for average particle size measurement. It al
36、lowsoperators to relate their data to that of other analysts. Eachcalibrator has been factory tested three times with the resultingreadings and associated porosity recorded on the tube.NOTE 3Adjust the sample packing assembly (1) as described in themanufacturers instructions with the exception that
37、the plugs and paperdisks are not inserted in the sample tube, but are merely stacked togetherand placed between the brass support and the “flat” of the bottom of therack, and (2) as previously described except that a specially made baselinegauge is used instead of the plugs and paper disks. This bas
38、eline gaugeshall have a height of 19.30 6 0.10 mm. Check all plug heights when newplugs are purchased and periodically thereafter to make sure all are equalin height.5.3 Balancehaving a capacity of at least 50 g and asensitivity of 0.01 g.6. Standardization of Apparatus6.1 Method 1HEL Sub-sieve Auto
39、Sizer (HEL SAS):6.1.1 Before proceeding with standardization of the HELSAS, the following items shall be checked:6.1.1.1 The sample tube and plugs shall not be worn to thepoint where results are affected.6.1.1.2 Inspect the O-ring seals for tears and abrasionmarks. The O-ring seals shall not be worn
40、 to the point wherethe sample tube moves easily by hand or the pressure readingvaries as the sample tube is moved.6.1.1.3 The drying agent shall be in proper condition6.1.2 Whenever the instrument is turned on from an unpow-ered state, the piston shall be “homed” according to themanufacturers instru
41、ctions. See Note 2.6.1.3 Before running the initial sample, the pressure shall beset to 50.0 (+0.1, -0.5) cm H2O, using the metering valve; thenchecked and reset if necessary every few hours, or if theambient temperature changes more than 62C.NOTE 4The metering valve position should not be adjusted
42、for repeatruns of the same sample as this will likely lead to a loss of precision evenif the inlet pressure reading has drifted a little outside the 50.0 (+0.1, -0.5)cm H2O range. Further adjustment is not necessary as the pressure iscontrolled precisely during the particle size measurement.6.1.4 St
43、andardization is recommended before and after anyseries of determinations or at least every four hours ofcontinued operation. Warm-up of the instrument is required ifit has been off for more than 30 min.6.1.5 Calibration of the pressure transducers is recom-mended every 3 to 6 months, using a tracea
44、ble externalpressure gauge per the manufacturers instructions.6.2 Method 2Fisher Sub-Sieve Sizer (FSSS):6.2.1 Before proceeding with standardization of the FSSS,the following items shall be checked:6.2.1.1 The chart shall be properly aligned horizontally withthe indicator pointer.6.2.1.2 The rack an
45、d pinion shall be properly alignedvertically with the chart.6.2.1.3 The sample tube or plugs shall not be worn to thepoint where results are affected.6.2.1.4 The manometer and air resistors shall be free ofvisible contamination.6.2.1.5 The rubber sample tube seals shall not be worn tothe point where
46、 leakage occurs.6.2.1.6 The sample packing post shall be properly adjusted.6.2.1.7 The drying agent shall be in proper condition.6.2.1.8 The manometer and standpipe levels shall bechecked.6.2.1.9 Adjust the manometer only when the machine is notoperating and with the pressure released for a minimum
47、of5 min to allow the manometer tube to drain completely.6.2.2 The standardization of the Fisher Sub-Sieve Sizershall be made using the Fisher jewel calibrator tube (jewelorifice tube) as the primary standard. Specification shall bemade at both ranges of the machine. The Fisher jewel calibratortube u
48、sed for standardization shall be checked under a micro-scope at least once a month to determine the condition andcleanliness of the orifice. If the orifice is not clean, clean asdescribed in the Fisher Sub-Sieve Sizer instruction manual.6.2.3 With the sub-sieve sizer properly adjusted and set tothe
49、proper range, proceed as follows:6.2.3.1 Mount the Fisher jewel calibrator tube between therubber seal supports just to the right of the brass post. Clampthe upper cap down onto the tube so that an airtight seal isobtained at both ends.6.2.3.2 Adjust the calculator chart so that the porosityreading corresponds to the value indicated on the jewelcalibrator tube.6.2.3.3 Switch on the instrument and allow it to warm up fora minimum of 20 min. Adjust the pressure-control knob,located near the bubble observation window at the lower left ofthe p
