1、Designation: D2807 93 (Reapproved 2015)Standard Test Method forChromic Oxide in Leather (Perchloric Acid Oxidation)1This standard is issued under the fixed designation D2807; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers the
3、determination of chromicoxide in leathers that have been partly or completely tannedwith chromium compounds. In general the samples will con-tain between 1 and 5 % chromium, calculated as chromicoxide.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are
4、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 pri
5、or to use. See Section 7 forspecific safety hazards.2. Referenced Documents2.1 ASTM Standards:2D2617 Test Method for Total Ash in LeatherD2813 Practice for Sampling Leather for Physical andChemical TestsE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial
6、 and Spe-cialty Chemicals (Withdrawn 2009)33. Summary of Test Method3.1 The perchloric acid method is applied to the ashobtained in Test Method D2617. In the acid digestion, anyremaining organic matter is destroyed and the chromiumoxidized to the hexavalent state. On dilution, the chromium istitrate
7、d volumetrically with thiosulfate or ferrous salt. Theperchloric acid method requires less manipulation than proce-dures based on fusion of the ash, but care must be takenbecause of potential hazards in the use of this reagent. Theperchloric acid method also tends to give low results.4. Significance
8、 and Use4.1 The procedure described is specific for chromium inleather. Vanadium is the only common interfering element andthis is rarely present in quantity. The precision and accuracy ofthe methods are usually at least as good as the sampling of theleather itself.4.2 The chromium content of leathe
9、r relates to the degree oftannage obtained, and hence may be a matter for specificationin the purchase of leather. The procedure described providesadequate accuracy for this purpose.5. Apparatus5.1 Potentiometric Titration EquipmentThis is required inan alternative method for titrating chromium (Cr6
10、+) withferrous ammonium sulfate solution. The equipment consists of:5.1.1 Stirrer.5.1.2 Calomel and Platinum Electrodes.5.1.3 PotentiometerA variety of instruments is satisfac-tory.4The most convenient common feature of these instru-ments is a null-point device (either a cathode-ray electron tubeor
11、galvanometer) that will signal the abrupt change occurringin the potential when the end point is reached.5.2 In carrying out the titration, the electrodes are immersedin the sample, the solution agitated by the stirrer, and thepotential balanced with the galvanometer or cathode-ray tube.Titrant is a
12、dded dropwise until a sharp permanent change inpotential occurs.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to specifications of the Committee1This test method is under the jurisdiction
13、ofASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis Thistest method was developed in cooperation with the American Leather ChemistsAssn.Current edition approved Sept. 1, 2015. Published October 2015. Originallyapproved in 1969. Last previous ed
14、ition approved in 2009 as D2807 93 (2009)1.DOI: 10.1520/D2807-93R15.2For 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 w
15、ebsite.3The last approved version of this historical standard is referenced onwww.astm.org.4Satisfactory equipment include, among others the following: the Kelley,Serfass, and Fisher tritrimeters, Leeds add 4 mL of hydrochloric acid (HCl, 1+1) 20 mLof KI solution, stopper the flask, and allow to sta
16、nd 5 min in thedark. Titrate with the thiosulfate solution to be standardized.When the color of the solution has faded to a brownish-green,add 2 mL of 2 % starch solution and continue titrating until thedeep blue color changes to a clear green. Record the titration.Calculate the normality of the thi
17、osulfate solution as follows:Normality 5 A/0.04903 3 B! (2)where:A = grams of K2Cr2O7used, andB = millilitres required for titration.6.9.2 The thiosulfate solution is quite stable but should berestandardized at least once a month.6.10 Starch Indicator Solution, prepared according to ac-cepted proced
18、ures available in analytical handbooks.6.11 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).7. Hazards7.1 The improper use of HClO4can lead to violent andserious explosions. In general, these can be traced to situationswhere concentrated HClO4has come in contact with organic oreasily oxi
19、dized materials.7.2 The exact procedures given must be followed and thedigestions, once started, should be kept from possible contactwith other organic matter. The digestions should never beallowed to boil dry. HClO4should never be used withoutaccompanying use of HNO3and H2SO4.7.3 All spills involvi
20、ng HClO4should be flushed with water.Rags, sawdust, and other organic materials should never beused to mop up spilled acid.7.4 The use of a perchloric acid hood, reserved for perchlo-ric acid digestions, equipped with wash-down facilities andconstructed entirely of nonporous inorganic material is re
21、-quired.7.5 Perchloric acid bottles should be stored on a ceramictray or shelf and never on a wooden or pervious shelf. It isadvisable to keep only one 1-lb (0.45-kg) bottle of acid in theworking area.8. Test Specimen8.1 The specimen shall be 2 g leather from the compositesample prepared in accordan
22、ce with an accepted procedure,weighed and ashed according to Test Method D2617.5Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for Labo
23、ratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.6A satisfactory reagent, Ferroin, is manufactured by the G. Frederick SmithChemical Co., Columbus, Ohio.D2807 93 (2015)29. Procedure9.1 T
24、ransfer the ash obtained from the determination of ash,Test Method D2617, to a 250-mLErlenmeyer flask.Add, in theorder named,20mLofHNO3, 15 mL of HClO4, and 10 mL ofH2SO4. Add a few glass beads. In the perchloric acid hood,heat gently under reflux conditions, using a small funnel as acondenser in th
25、e neck of the flask, until all organic matter isdestroyed and the color changes to a clear red-orange, indicat-ing oxidation of chromium. Heat an additional 2 min, coolquickly, rinse and remove funnel, and dilute to 125 mL withwater. Heat to boiling and continue boiling for 7 min. Cool andtitrate by
26、 the procedure given in 9.2or9.3.NOTE 1If the titration volume is less than 5 mL or more than 50 mL,adjust the size of the sample to give a titration volume between theselimits and repeat the determination.9.2 Titration with Na2S2O3SolutionAdd 30 mL of H3PO4and 20 mL of KI solution to the solution o
27、btained in 9.1 andstopper the flask.Allow to stand 5 min in the dark. Titrate with0.1 N sodium thiosulfate solution standardized as described in6.9.1. When the color of the solution hasfaded to a brownish-green, add 2 mL of 2 % starch solution and continue thetitration until the deep blue color chan
28、ges to a clear green.Record the titration. Calculate the results in accordance withSection 9.9.3 Titration with Ferrous Ammonium Sulfate SolutionAdd2mLofH3PO4and titrate with 0.1 N ferrous ammoniumsulfate solution standardized as described in 6.3.1. When thecolor of the solution has changed from yel
29、low through yel-lowgreen to blue-green, add 5 drops of indicator6and continuetitrating until the blue-green solution changes to a red-brown.Record titration. Calculate results as described in Section 10.9.4 Alternatively, the titration may be done potentiometri-cally. After adding the H3PO4, transfe
30、r the solution to a 250-mL beaker and titrate with 0.1 N ferrous ammonium sulfatesolution, using the potentiometric apparatus described in 5.1.The end point is signalled by a sudden large change inpotential. Record the titration. Calculate results as described inSection 10.9.5 It is preferable to us
31、e the same method of determiningthe end point in both the standardization of the ferrousammonium sulfate solution and in the analysis of the sample.10. Calculation10.1 Calculate the chromium content as percentage ofchromic oxide (Cr2O3) in the leather as follows:Cr2O3,%5 A 3 B 30.02533 3 100/C! (3)w
32、here:A = millilitres of titrating solution used (either thiosulfateor ferrous ammonium sulfate),B = normality of titrating solution, andC = mass of leather. Use the mass of leather recorded asC B in Section 7 of Test Method D2617.10.2 The above calculation gives the Cr2O3content of theleather on an
33、“as weighed” basis. If it is desired to express thison a dry basis, a moisture determination should be run on asample weighed from the same leather at the same timeaccording to accepted procedures.7If D is the percentagemoisture found in the sample, calculate the Cr2O3, dry basis, %as follows:Cr2O3,
34、%5 A 3 B 30.02533 3 100/C! 3 1/1 2 D/100!#! (4)where A, B, and C have the same significance as above.10.3 If the determination of Cr2O3is performed on a leatherthat has been conditioned and weighed at constant temperatureand humidity, the fact should be indicated in reporting theresults.11. Report11
35、.1 Report the following information.11.1.1 Report the percentage of Cr2O3to the nearest 0.1 %.Duplicate runs that agree within 0.09 % absolute are acceptablefor averaging (95 % confidence level).12. Precision and Bias812.1 ReproducibilityThe average difference between tworesults (each the average of
36、 duplicate determination) obtainedby analysts in different laboratories will approximate 0.06 %absolute. Two such values should be considered suspect (95 %confidence level) if they differ by more than 0.2 % absolute.12.2 BiasThe test method yields results that average1.75 % relative low when compare
37、d to a standard sample ofNBS K2Cr2O7. The 99 % confidence limits on this value are1.50 to 2.00 % as determined by triplicate analyses in fivelaboratories.NOTE 2The estimates of checks for duplicates and reproducibility in12.1 and 12.2 are based on an interlaboratory study of four leathers run intrip
38、licate in each of eight laboratories. The precision statements weredeveloped9using Practice E180.13. Keywords13.1 ash; chromic oxide; perchloric acid oxidation7Acceptable procedures are published in Journal of the American LeatherChemists Association, JALCA,Vol 51, 1956, p. 497; or Offcial Methods o
39、f Analysis,Am. Leather Chemists Assn., available through the Office of Secretary-Treasurer,TexasTech University, P.O. Box 45300, Lubbock,TX 79409; or see Practice D2813.8Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting RR:D31-10069The actual data up
40、on which the results are based are reported in Journal,American Leather Chemists Assn. JALCA, Vol 54, 1959, p. 2.D2807 93 (2015)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard ar
41、e 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 subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not
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44、 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 93 (2015)4
