1、Designation: D 6714 01 (Reapproved 2006)Standard Test Method forChromic Oxide in Ashed Wet Blue (Perchloric AcidOxidation)1This standard is issued under the fixed designation D 6714; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of chromicoxide in wet blue that has been partly or completely
3、tannedwith chromium compounds. In general the samples will con-tain chromium content between 1 and 5 %, calculated aschromic oxide expressed upon a dry basis otherwise referred toas moisture-free basis (mfb).1.2 This test method is specific in that it applies to a sampleor samples that are the resul
4、tant ash following the execution ofTest Method D 6716.1.3 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
5、of regulatory limitations prior to use. Specific hazards aregiven in Section 8.2. Referenced Documents2.1 ASTM Standards:2D 6658 Test Method for Volatile Matter (Moisture) of WetBlue by Oven DryingD 6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsD 6716 Test Meth
6、od for Total Ash in Wet BlueE 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals3. Terminology3.1 DefinitionsThe terms and definitions employed withinthis test method are commonly used in normal laboratorypractice and require no
7、special comment.4. Summary of Test Method4.1 The perchloric acid method may be applied to the ashobtained in Test Method D 6716. The resultant ash is dissolvedinto acidic solution in a blend of nitric acid and a preparedoxidation mixture consisting of sulfuric and perchloric acids.Once completed, ox
8、idation of all trivalent to hexavalentchromium is executed by controlled heating. Upon dilution, thechromium is indirectly (back) titrated volumetrically withstandardized thiosulfate using released iodine as the titrate. Theperchloric acid method requires less manipulation than proce-dures based on
9、fusion of the ash. However care must be takenbecause of potential hazards in the use of perchloric acid. Theperchloric acid method also tends to give low results.5. Significance and Use5.1 The procedure described is specific for chromium in wetblue. Vanadium is the only common interfering element an
10、dthis is rarely present in quantity. The precision and accuracy ofthe methods are usually at least as good as the sampling of thewet blue itself, and the accuracy of previously performed testmethods.5.2 The chromium content of wet blue is related to thedegree of tannage obtained, and hence may be a
11、matter forspecification in the purchase of wet blue. The proceduredescribed provides adequate accuracy for this purpose.6. Apparatus6.1 Analytical Balance, accurate and calibrated to 0.001 g.6.2 Erlenmeyer Flasks, 250 mL capacity or equivalent.6.3 Burette, 50 mL capacity of suitable calibration grad
12、e,minimum calibration of 0.1 mL.6.4 Glass Anti-bumping Beads, or equivalent.6.5 Measuring Cylinders, 50 mL capacity or equivalent.6.6 Small Glass Filter Funnel.6.7 Dessicator, of suitable size and design and charged withfresh dessicant.6.8 Weighing Vessels, of suitable size and design.6.9 Drying Ove
13、n, with accurate variable temperature con-trols.6.10 Hot Plate, with accurate variable temperature controls.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on Blue Stock.Current edition approved Oct. 1, 2006. Publish
14、ed November 2006. Originallyapproved in 2001. Last previous edition approved in 2001 as D 6714 - 01.2For 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 Do
15、cument Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Reagents7.1 Purity of ReagentsAnalytical Reagent (AR) gradechemicals shall be used in all tests. Unless otherwise indicated,it is intended that
16、 all reagents shall conform to specifications ofthe Committee onAnalytical Reagents of theAmerican Chemi-cal Society,3where such specifications are available. Othergrades may be used, provided it is first ascertained that thereagent is of sufficiently high purity to permit its use withoutlessening t
17、he accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled water or water ofequal purity.7.3 Commercial ReagentsThe use of commercially avail-able pre-standardized analytical reagents and solutions isappropriate, providing
18、those reagents and solutions have beenprepared in accordance with and conforming to the previouslymentioned specifications (see 7.1).7.4 Nitric Acid(HNO3), 70 % w/w.7.5 Perchloric Acid(HClO4), 60 to 62 % w/w. 70 or 72 %w/w perchloric acid may be substituted, however, storage issomewhat more hazardou
19、s.7.6 Sulfuric Acid(H2SO4), 96 to 98 % w/w.7.7 Potassium Iodide(KI), 99 to 100 % purity.7.8 Potassium Iodide Solution(KI) 10 % w/w. Dissolve10g(60.1 g) of potassium iodide into 100 mL of water.7.9 Starch Indicator Solution2 % or equivalent, preparedaccording to accepted procedures available in analy
20、tical hand-books.7.10 Oxidizing MixtureMix 1666 mL of concentratedsulfuric acid into an appropriate glass container that contains2500 mL of perchloric acid, using extreme caution whileadding. Cool the mixture to room temperature before use.7.11 Phosphoric Acid(H3PO4), 40 % v/v. Dilute 45 mL of85 % p
21、hosphoric acid with water to 100 mL.7.12 Hydrochloric Acid(HCl), 1:1 dilution of 37 % HClw/w. Used in standardization of thiosulfate solution.7.13 Potassium Dichromate(K2Cr2O7). Used in standard-ization of thiosulfate solution.7.14 Sodium Carbonate(Na2CO3). Used in preparation ofthiosulfate solution
22、.7.15 Sodium Thiosulfate(Na2S2O35H2O). Used to pre-pare thiosulfate solution.7.16 Sodium Thiosulfate Standard Solution(Na2S2O3),0.1N (60.0002). Dissolve 24.85 g of sodium thiosulfate(Na2S2O35H2O) in previously boiled water, add 1.00 g ofsodium carbonate (Na2CO3) and dilute to 1000 mL.7.16.1 Standard
23、izationDry potassium dichromate(K2Cr2O7) in an oven at 130C for 2 h and cool in a dessicator.Once cool, weigh about 0.2 g (60.0001 g) of this drypotassium dichromate into a clean 250 mL, glass-stopperedErlenmeyer flask. Dissolve in 50 mL of water; add 4 mL ofhydrochloric acid (HCl, 1:1) and 20 mL of
24、 KI solution. Stopperthe flask, and allow to stand 5 min in the dark. Titrate with thethiosulfate solution to be standardized. When the color of thesolution has faded to a brownish-green, add 2 mL of 2 % starchsolution and continue titrating until the deep blue color changesto a clear green. Record
25、the titration. Calculate the normality ofthe thiosulfate solution as follows:Normality 5 A 4 0.04903 3 B!where:A =K2Cr2O7used, g, andB = amount required for titration, mL.7.16.2 Shelf LifeThe thiosulfate solution is relativelystable. However, it should be restandardized at least once amonth.7.17 Alt
26、ernatively, a commercially available pre-standardized sodium thiosulfate analytical solution may besubstituted.8. Hazards8.1 Chemicals used can be harmful, or explosive, or both.8.2 The improper use of perchloric acid can lead to violentand serious explosions. In general, these can be traced tositua
27、tions where concentrated perchloric acid has come incontact with organic or easily oxidized materials.8.3 The exact procedures given must be followed and thedigestion, once started, should be kept from possible contactwith other organic matter. The digestion should never beallowed to boil dry. The p
28、erchloric acid should never be usedwithout accompanying use of nitric and sulfuric acids.8.4 All spills involving perchloric acid should be flushedwith water and a liquid acid neutralizer. Rags, sawdust, andother organic materials should never be used to mop up spilledacid.8.5 The use of a perchlori
29、c acid hood, reserved for perchlo-ric acid digestions, equipped with wash-down facilities andconstructed entirely of nonporous inorganic material, is re-quired.8.6 Perchloric acid bottles should be stored on a ceramic ornon-porous tray or shelf and never on a wooden or perviousshelf.8.7 Perchloric a
30、cid must not be permitted to go dry in thepresence of organics, metals or metal salts.8.8 It is advisable to keep only one 1-lb (0.45-kg) bottle ofacid in the working area.9. Test Specimens9.1 The specimen shall be the ash of wet blue producedfrom the composite wet blue sample prepared in accordance
31、with Test Method D 6659, and weighed and ashed according toTest Methods D 6659 and D 6716.10. Procedure10.1 Transfer the ash obtained from the determination oftotal ash into a 250-mL Erlenmeyer flask. Since the ash is verylight and easily blown by moving air (rendering the sampleincomplete), it is i
32、mportant to take extreme care to ensure thatall the ash is successfully transferred.10.2 Using extreme care, add 20 mL of nitric acid (HNO3)to the flask.3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, D.C. For suggestions on the reagents not liste
33、d bythe American Chemical Society, see Analar Standards for Laboratory Chemicals,DBH Ltd, Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary , U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D 6714 01 (2006)210.3 Next, carefully and slowly add 25 mL of the oxidiz
34、ingmixture to the flask.10.4 Add a few glass anti-bumping beads (these will allowthe solution to boil evenly), then place the filter funnel into theneck of the flask.10.5 Under the perchloric acid hood, heat the solutiongently under reflux conditions (using the small funnel as acondenser in the neck
35、 of the flask) until all organic matter isdestroyed and the color changes to a clear red-orange, indicat-ing oxidation of chromium. Do not allow the sample to boildry.10.6 Heat the solution for an additional 2 min to ensurecomplete oxidation; then rapidly cool the solution, rinse andremove funnel, t
36、hen dilute to 125 mL with water. Rapidcooling can be achieved with the use of a cold water bath.10.7 Reheat the solution to boiling and continue boiling for7 to 10 min to expel any chlorine or oxides of nitrogen.10.8 Remove the flask from the heat and allow the solutionto cool to room temperature.10
37、.9 Once cool, add 30 mL of phosphoric acid and 25 mL ofthe 10 % potassium iodide solution, then stopper the flask.10.10 Place the flask in the dark and allow to stand for 5 minto allow complete release of iodine (dark brown color).10.11 Titrate volumetrically with 0.1N standardized thiosul-fate solu
38、tion.10.12 When the solution color has faded to a pale yellow-brown, add approximately 2 mL of the starch indicatorsolution. Continue the titration until the deep blue colorchanges to a clear blue-green.10.13 Record the titration volume.10.14 If the titration volume is less than 5 mL or more than50
39、mL, repeat the entire procedure, after adjusting the sampleweight so that the titration volume is toward the middle of theburette.10.15 Calculate the results in accordance with Section 11.11. Calculation11.1 Calculate the chromium content as percentage ofchromic oxide (Cr2O3) in the wet blue as foll
40、ows:Chromic Oxide Cr2O3!,%5 T 3 N 3 E 3 100 4 W !where:T = titration volume of sodium thiosulfate solution used,mL,N = Normality of the sodium thiosulfate solution,E = 0.025332 = chromic oxide (Cr2O3) equivalentweight, g,W = weight of wet blue originally weighed (for ashingduring Test Method D 6716)
41、, g, and100 = conversion to percent.11.2 The above calculation gives the Cr2O3content of theleather on an “as weighed” basis. Since the chromium contentof wet blue is expressed upon a dry (moisture-free) basis, amoisture determination, as found in Test Method D 6658,should be run in accordance with
42、the appropriate and acceptedprocedures for wet blue. If D is the percentage moisture foundin the sample, calculate the Cr2O3, dry basis (mfb) as follows:Chromic Oxide Cr2O3!,%5 T 3 N 3 E 3 100 4 W! 3 1 4 1 D4 100!#!where T, N, E, and W have the same significance as in 11.1.12. Report12.1 Report the
43、percentage of Cr2O3to the nearest 0.01 %for each and all values.12.2 Duplicate runs that agree within 0.09 % absolute areacceptable for averaging (95 % confidence level).13. Precision and Bias13.1 ReproducibilityThe average difference between tworesults (each the average of duplicate determinations)
44、 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.13.2 BiasThe test method yields results that average1.75 % lower in relation to the standard sample of NBSK2C
45、r2O7. The 99 % confidence limits on this value are 1.50 to2.00 % as determined by triplicate analyses in five laboratories.NOTE 1The estimates of checks for duplicates and reproducibility in13.1 and 13.2 are based on an interlaboratory study of four leather samplesrun in triplicate in each of eight
46、laboratories. The precision statementswere developed using Practice E 180.14. Keywords14.1 ash; blue stock; chrome content; chromic oxide; per-chloric acid oxidation; wet blueASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentio
47、nedin this standard. Users of this standard are 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 an
48、d must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting o
49、f theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United 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 t
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