1、Designation: D6019 10D6019 15Test Method forDetermination of Chromic Oxide in Basic ChromiumTanning Liquors (Ammonium Persulfate Oxidation)1This standard is issued under the fixed designation D6019; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se 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 covers the determination of chromic oxide in chrome tanning liquors, eith
3、er simple, with added aluminumor zirconium, or with the usual masking complexing agents.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, asso
4、ciated 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. Summary of Test Method2.1 The solution is oxidized with ammonium persulfate until the chromium is co
5、mpletely converted to the chromate ion. Thesolution is boiled to complete oxidation of organic materials and to destroy excess ammonium persulfate; it is then cooled andacidified. Potassium iodide is added, and the liberated iodine is titrated with standardized sodium thiosulfate.3. Significance and
6、 Use3.1 The procedure described is for the quality control for manufacturing liquors and specifications for the purchase of suchliquors.3.2 The chromium content of the liquors determines the amount to be used to obtain the desired degree of tannage, and hencemay be a matter for specification in the
7、purchase of leather.4. Reagents and Materials4.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of The American Chemical Society, wheresuch s
8、pecifications are available.2 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently highpurity to permit its use without lessening the accuracy of the determination.4.2 Purity of WaterUnless otherwise indicated, reference to water shall be understood to mean
9、distilled water, deionized wateror water of equal purity.4.3 Ammonium Persulfate20 % solution 100 gmg of persulfate into 500 mL water.4.3.1 Alternatively, ammonium persulfate may be added in 5.5 as solid form using plastic scoopula.4.4 Starch Indicator, 1 %2 %Make a paste of 12 g of soluble starch i
10、n about 10 mL of water, add 90 mL water, and boil for1 min with stirring. Cool and add one drop of chloroform. Cool. Refrigerate after use. The solution is subject to decompositionand should be renewed if a deep blue color is not obtained on addition of one drop of indicator to a solution of 1 drop
11、tinctureof iodine in 100 mL of water.4.5 Sodium Thiosulfate Solution, 0.1 NDissolve 24.85 g of Na2S2O35H2O in water, add 1 g Na2CO3, and dilute to 1 L.1 This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the direct responsibility of Subcommittee D31.06 on Chemical Ana
12、lysis.Current edition approved Oct. 1, 2010Dec. 1, 2015. Published October 2010January 2016. Originally approved in 1996. Last previous edition approved in 20062010 asD6019 - 96D6019 10.(2006). DOI: 10.1520/D6019-10.10.1520/D6019-15.2 Reagent Chemicals, American Chemical Society Specifications , Ame
13、rican Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (
14、USPC), Rockville, MD.This document 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 us
15、ers consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.5.1 StandardizationDry po
16、tassium dichromate (K2Cr2O7) in an oven at 130C for 2 h and cool in a desiccator. Weigh intoa glass stoppered Erlenmeyer flask (500 mL) about 0.2 g of potassium dichromate to an accuracy of 0.1 mg. Dissolve in 250 mLwater, add 15 mL 1:4 hydrochloric acid, 20 mL of 10 % potassium iodide solution, sto
17、pper the flask, and allow to stand 5 min inthe dark. Titrate with the sodium thiosulfate to be standardized. When the color of the solution has faded to a brownish-green, add2 mL of 1 %2 % starch solution, and continue titrating until the deep blue color changes to a clear green. Record the titratio
18、n.normality of sodium thiosulfate5weight potassium dichromate0.049033mL titration (1)The thiosulfate solution is quite stable but should be restandardized at least once a month.4.6 Potassium Dichromate, K2Cr2O7, primary standard grade.4.7 Potassium Iodide, 6 %10 %Dissolve 610 g KI in 100 mL water.4.
19、8 Hydrochloric Acid, 1:1Dilute 250 mL concentrated hydrochloric acid (sp gr 1.19) in 250 mL water.4.9 Silver Nitrate, 1 %Dissolve 1 gmg of AgNoAgNO3 in 100 mL water.4.10 Potassium Permanganate, 1 %Dissolve 51 g of KMnO3 in 500100 mL water.5. Procedure5.1 Weigh 11 to 12 g, to the nearest 0.1 mg, of t
20、he chrome tanning material to be analyzed.5.2 Quantitatively transfer to a 500 mL volumetric flask. Dilute to the mark and mix thoroughly.5.3 Pipet 25 mL aliquots into each of 500 mL Erlenmeyer flasks. Run in triplicate.5.4 Dilute to the 200 mL mark of the flask with water.5.5 Add 10 mL concentrated
21、 sulfuric acid. the following chemicals in this order (WarningThis should be done in a hood.Heat and fumes will be generated.)generated):10 mL concentrated sulfuric acid50 mL of 20 % ammonium persulfate solution or 10 g of ammonium persulfate8 mL of 1 % silver nitrate solution1 mL of 1 % potassium p
22、ermanganate solution5.5 Carefully add 200 mL deionized water. Add 8 mL of 1 % silver nitrate and ten drops of approximately 1 % potassiumpermangante. Add 50 mL of 20 % solution of ammonium persulfate.5.6 Add boiling chips or glass beads and bring to a medium boil. At this stage a permanganate color
23、should develop (pink toa purple color). If the permanganate the solution changes to an orange to red-brown color. If the orange to red-brown color failsto develop, remove fromor fades on boiling, remove the heat and carefully add small amounts of additional 5-10 mL of additional20 % ammonium persulf
24、ate solution or 1-2 g of ammonium persulfate. If necessary, continue addition of persulfate until thepermanganate ammonium persulfate (5-10 mL of 20 % ammonium persulfate solution or 1-2 g of ammonium persulfate, at a time)until the orange to red-brown color is permanent. This color will not develop
25、 be permanent until all of the chromium is oxidized.Continue boiling for 20 min.5.6.1 Continue the medium boil for 1-1.5 h.NOTE 1Additional water may be added to keep final volume at least 200 mL.5.7 Add 1025 mL of 1:1 hydrochloric acid. acid and continue boiling for 5 min. This is to destroy the pe
26、rmanganate. If the pinkcolor does not fade after 5 min, add an additional amount of 1:1 HCl. The color is yellow at this stage. Precipitated After additionof the 1:1 HCl the color will change from orange to opaque yellow and precipitated silver chloride will also be present. Boil for10 min. Total bo
27、iling time should be between 30 to 40 min.Continue boiling for an additional 15-30 min. The color will becomemore translucent (less turbid).5.8 Remove from heat and cool in water bath (65 to 70F).to room temperature (60 to 80F). A warm sample will result in lowrecovery.5.9 Add 25 mL of 10 % potassiu
28、m iodide solution.NOTE 2This will produce a purple color.5.9.1 Stopper the flask and place it in a dark location. Let the stoppered flask stand in the dark location for 5 min to allow forcomplete release of iodine.5.10 Titrate with sodium thiosulfate using potassium iodide and starch indicator in th
29、e usual manner.0.1 N sodium thiosulfatesolution.5.10.1 Continue titrating until the yellow/brownish-orange color of the liberated iodine is almost discharged (the solution turnspale yellow/green to yellowish-orange).D6019 1525.10.2 Add 2 mL of 2 % starch indicator solution. The color will turn dark
30、blue to gray-black at this stage. Continue titrating,drop-wise, until the dark blue to gray-black color changes to a green endpoint. Record the titration volume.6. Calculation6.1 Calculate the chromic oxide in the liquor as follows:Cr2O3 %5A3N30.02533W 3V253100 (2)where:A = the number of millilitres
31、 of standard thiosulfate (or ferrous sulfate) required to titrate the 25 mL aliquot of the specimen,N = the normality of the thiosulfate (or ferrous sulfate) solution,W = the weight of the specimen before dilution, g, andV = the volume to which W was diluted, mL.6.2 The chromic oxide in the sample f
32、or the test shall be the average of the test results obtained from the three aliquots tested.6.3 Record the chromic oxide in the sample to the nearest 0.1 %.7. Precision and Bias7.1 PrecisionThe precision of test results obtained within a laboratory (repeatability conditions) was obtained under thed
33、efined conditions of the test method. Based on three daily repetitions on each of three days a maximum range of 0.12 % absoluteand a standard deviation of 0.052 was obtained. The precision of test results obtained in different laboratories (reproducibilityconditions) is a range of the average of det
34、erminations for fourteen laboratories of 0.27 % absolute and the standard deviation was0.071.7.2 BiasPotassium dichromate, a primary standard, was used to determine bias. The chemical was treated with the oxidationprocedure to determine any extraneous oxidation/reduction that may be occurring. Addit
35、ionally, by applying the recovery factorto the results of the test results, errors in standardization might be nullified. The average recovery for ten laboratories was 99.89 %with a standard deviation of 0.54. The average standard deviation for an individual laboratory was 0.26.8. Keywords8.1 basic
36、chromium tanning liquors; chrome oxideoxide; ammonium persulfateASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any suc
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