1、Designation: D6714 16Standard Test Method forChromic Oxide in Ashed Wet Blue (Perchloric AcidOxidation)1This standard is issued under the fixed designation D6714; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. 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 chromicoxide in Wet Blue that has been partly or completely tannedwith chromium c
3、ompounds. 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 resultant ash following th
4、e execution ofTest Method D6716.1.3 This test method does not apply to Wet White.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated wit
5、h 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. Specific hazards aregiven in Section 8.2. Referenced Documents2.1 ASTM Standards:2D6658 Test Method for Volat
6、ile Matter (Moisture) of WetBlue by Oven DryingD6659 Practice for Sampling and Preparation of Wet Blueand Wet White for Physical and Chemical TestsD6716 Test Method for Total Ash in Wet Blue or Wet WhiteE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial
7、 and Spe-cialty Chemicals (Withdrawn 2009)33. Terminology3.1 DefinitionsThe terms and definitions employed withinthis test method are commonly used in normal laboratorypractice and require no special comment.4. Summary of Test Method4.1 The perchloric acid method may be applied to the ashobtained in
8、 Test Method D6716. 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, oxidation of all trivalent to hexavalentchromium is executed by controlled heating. Upon dilution, thechromium
9、is indirectly (back) titrated volumetrically withstandardized thiosulfate using released iodine as the titrate. Theperchloric acid method requires less manipulation than proce-dures based on fusion of the ash. However care must be takenbecause of potential hazards in the use of perchloric acid. Thep
10、erchloric 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 andthis is rarely present in quantity. The precision and accuracy ofthe methods are usually at least as good as
11、 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 matter forspecification in the purchase of Wet Blue. The proceduredescribed provides adequate accuracy for th
12、is 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 grade,minimum calibration of 0.1 mL.6.4 Glass Anti-bumping Beads, or equivalent.6.5 Measuring Cylinders, 50 mL ca
13、pacity or equivalent.6.6 Small Glass Filter Funnel.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on Wet Blue.Current edition approved Sept. 1, 2016. Published October 2016. Originallyapproved in 2001. Last previous
14、 edition approved in 2015 as D6714 - 01(2015).DOI: 10.1520/D6714-16.2For 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.7 Dessicator, of suitable size and design and charged withfresh dessicant.6.8 Weighing Vessel
16、s, of suitable size and design.6.9 Drying Oven, with accurate variable temperature con-trols.6.10 Hot Plate, with accurate variable temperature controls.6.11 Perchloric Acid Hood .7. Reagents7.1 Purity of ReagentsAnalytical Reagent (AR) gradechemicals shall be used in all tests. Unless otherwise ind
17、icated,it is intended that all reagents shall conform to specifications ofthe Committee onAnalytical Reagents of theAmerican Chemi-cal Society,4where such specifications are available. Othergrades may be used, provided it is first ascertained that thereagent is of sufficiently high purity to permit
18、its use withoutlessening the accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled water, deionizedwater, or water of equal purity.7.3 Commercial ReagentsThe use of commercially avail-able pre-standardized analytical reag
19、ents and solutions isappropriate, providing 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 substitute
20、d, however, storage issomewhat more hazardous.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. Dissolve 10g(60.1 g) of potassium iodide into 100 mL of water.7.9 Starch Indicator Solution2 % or equivalent, preparedaccord
21、ing to accepted procedures available in analytical 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.NOTE 1The reage
22、nts may be added individually according to 10.3.1.7.11 Phosphoric Acid(H3PO4), 40 % v/v. Dilute 45 mL of85 % phosphoric 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 stan
23、dard-ization of thiosulfate solution.7.14 Sodium Carbonate(Na2CO3). Used in preparation ofthiosulfate solution.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(Na2S2O3
24、5H2O) in previously boiled water, add 1.00 g ofsodium carbonate (Na2CO3) and dilute to 1000 mL.7.16.1 StandardizationDry 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, gla
25、ss-stopperedErlenmeyer flask. Dissolve in 50 mL of water; add 4 mL ofhydrochloric acid (HCl, 1:1) and 20 mL of 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, ad
26、d 2 mL of 2 % starchsolution and continue titrating until the deep blue color changesto a clear green. Record the titration. Calculate the normality ofthe thiosulfate solution as follows:Normality 5 A0.04903 3B!where:A =K2Cr2O7used, g, andB = amount required for titration, mL.7.16.2 Shelf LifeThe th
27、iosulfate solution is relativelystable. However, it should be restandardized at least once amonth.7.17 Alternatively, 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
28、 use of perchloric acid can lead to violentand serious explosions. In general, these can be traced tosituations 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 ke
29、pt from possible contactwith other organic matter. The digestion should never beallowed to boil dry. The perchloric 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,
30、 sawdust, andother organic materials should never be used to mop up spilledacid.8.5 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-quired.8.6 Perchloric acid bottles should
31、 be stored on a ceramic ornon-porous tray or shelf and never on a wooden or perviousshelf.4Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, D.C. For suggestions on the reagents not listed bythe American Chemical Society, see Analar Standards for Lab
32、oratory Chemicals ,DBH Ltd, Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary , U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D6714 1628.7 Perchloric acid must not be permitted to go dry in thepresence of organics, metals or metal salts.8.8 It is advisable to
33、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 accordancewith Test Method D6659, and weighed and ashed according toTest Methods D6659 and D6716.10. Procedure10.1 Tran
34、sfer 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 important to take extreme care to ensure thatall the ash is successfully transferred.10.2 Using extreme care, add
35、 20 mL of nitric acid (HNO3)to the flask.10.3 Next, carefully and slowly add 25 mL of the oxidizingmixture to the flask.10.3.1 Alternatively, add in this order: 20 mL HNO3,15mLHC1O4, and 10 mL H2SO4.10.4 Add a few glass anti-bumping beads (these will allowthe solution to boil evenly), then place the
36、 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 of the flask) until all organic matter isdestroyed and the color changes to a clear red-orange, indicat-ing oxidation of chr
37、omium. 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, then dilute to 125 mL with water. Rapidcooling can be achieved with the use of a cold water bath.10.7 Reheat the solution to b
38、oiling 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.10.9 Once cool, add 30 mL of phosphoric acid and 25 mL ofthe 10 % potassium iodide solution, then stopper the flask.10.10 Place
39、 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 solution.10.12 When the solution color has faded to a pale yellow-brown, add approximately 2 mL of the starch indicatorsolution.
40、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 mL, repeat the entire procedure, after adjusting the sampleweight so that the titration volume is toward the middle of thebur
41、ette.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 follows:Chromic Oxide Cr2O3!,%5 T 3N 3E 3 100W !where:T = titration volume of sodium thiosulfate solution used,mL,N = Normality o
42、f the sodium thiosulfate solution,E = 0.025332 = chromic oxide (Cr2O3) equivalent weight,g,W = weight of Wet Blue originally weighed (for ashingduring Test Method D6716), g, and100 = conversion to percent.11.2 The above calculation gives the Cr2O3content of theleather on an “as weighed” basis. Since
43、 the chromium contentof Wet Blue is expressed upon a dry (moisture-free) basis, amoisture determination, as found in Test Method D6658,should be run in accordance with the appropriate and acceptedprocedures for Wet Blue. If D is the percentage moisture foundin the sample, calculate the Cr2O3, dry ba
44、sis (mfb) as follows:Chromic Oxide Cr2O3!,%5 T 3N 3E 3 100W! 3 112 D100!#!where T, N, E, and W have the same significance as in 11.1.12. Report12.1 Report the percentage of Cr2O3to the nearest 0.01 %for each and all values.12.2 Duplicate runs that agree within 0.09 % absolute areacceptable for avera
45、ging (95 % confidence level).13. Precision and Bias13.1 ReproducibilityThe average difference between tworesults (each the average of duplicate determinations) obtainedby analysts in different laboratories will approximate 0.06 %absolute. Two such values should be considered suspect (95 %confidence
46、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 NBSK2Cr2O7. The 99 % confidence limits on this value are 1.50 to2.00 % as determined by triplicate analyses in five laboratories.NOTE 2The estimate
47、s 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 laboratories. The precision statementswere developed using Practice E180.14. Keywords14.1 ash; blue stock; chrome content; chromic oxide; per
48、-chloric acid oxidation; Wet BlueD6714 163ASTM 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 such patent rights, and t
49、he 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 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 of theresponsible technical committee, which you may attend. If you feel that your c
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