ASTM_D_6739_-_11_2015.pdf

Designation:D673911(Reapproved 2015)Standard Test Method forSilicapH Value1This standard is issued under the fixed designation D6739;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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.Scope1.1 This test method is used to measure the pH of a 5%silica/water suspension or mechanical dispersion and is indica-tive of the relative acidity or alkalinity of the silica.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 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 regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E70 Test Method for pH of Aqueous Solutions With theGlass ElectrodeE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Significance and Use3.1 The pH level of silica,as measured by this test method,is known to affect the vulcanization of some rubber com-pounds.Refer to Test Method E70 for a fuller understanding ofpH and a more detailed procedure for making pH measure-ments.4.Apparatus4.1 pH Meter,(digital is recommended),having an accuracyof 60.05 pH and equipped with a combination electrode.4.2 Mortar and Pestle.4.3 Beaker,glass,150 cm3with watch glass.4.4 Magnetic Stirring Bar and Stirrer.5.Reagents5.1 Degassed,Neutral Water.Boil a container of eitherdistilled or deionized water for 10 min,cover,and allow to coolto room temperature,or purge the water with nitrogen gas for20 min using a fritted bubbler.5.2 Buffer Solutions,pH of 4.00,7.00,and 10.00.6.Procedure6.1 Pulverize pelleted or granulated silica to a fine powder,using a mortar and pestle.6.2 Weigh 5 g of silica to the nearest 0.1 g into a 150 cm3glass beaker.6.3 Add 100 cm3of degassed,neutral water.6.4 Cover the glass beaker with a watch glass and stir themixture for 5 min at room temperature.6.5 Standardize the pH meter with two buffer solutions thatbracket the expected pH value of the silica.Rinse the electrodewith distilled water and wipe clean after each test.6.6 Place the electrode in the silica/water mixture,continu-ing to stir with the magnetic stirrer.When a constant pH isobtained,record the pH to the nearest 0.05 pH unit.6.7 Rinse the electrode with distilled water.Store electrodein accordance with manufacturers instructions when not inuse.7.Report7.1 Report the following information:7.1.1 Identification of the sample,and7.1.2 Result obtained,reported to the nearest 0.1 unit.8.Precision and Bias38.1 The precision of this test method is based on aninterlaboratory study conducted in 2010.Eleven laboratories1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.20 on Compounding Materialsand Procedures.Current edition approved Nov.1,2015.Published December 2015.Originallyapproved in 2001.Last previous edition approved in 2011 as D6739 11.DOI:10.1520/D6739-11R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D11-1108.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 tested two types of silica samples.Every“test result”repre-sents an individual determination.Each laboratory was in-structed to report four replicate test results for each material.Practice E691 was followed for the design and analysis of thedata.8.1.1 Repeatability Limit(r)Two test results obtainedwithin one laboratory shall be judged not equivalent if theydiffer by more than the“r”value for that material;“r”is theinterval representing the critical difference between two testresults for the same material,obtained by the same operatorusing the same equipment on the same day in the samelaboratory.8.1.1.1 Repeatability limits are listed in Table 1.8.1.2 Reproducibility Limit(R)Two test results shall bejudged not equivalent if they differ by more than the“R”valuefor that material;“R”is the interval representing the criticaldifference between two test results for the same material,obtained by different operators using different equipment indifferent laboratories.8.1.2.1 Reproducibility limits are listed in Table 1.8.1.3 The above terms(repeatability limit and reproducibil-ity limit)are used as specified i