1、Designation: D6714 01 (Reapproved 2015)Standard 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, th
2、e 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 chromicoxide in wet blue that has been partly or completely tan
3、nedwith 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 resultan
4、t ash following the execution ofTest Method D6716.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil
5、ity 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 Volatile Matter (Moisture) of WetBlu
6、e by Oven DryingD6659 Practice for Sampling and Preparation of Wet Bluefor 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Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals (Withdrawn 2009)33.
7、 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 Test Method D6716. The resultant ash is diss
8、olvedinto 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 is indirectly (back) titrated volumetrically
9、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. Theperchloric acid method also tends to give low
10、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 the sampling of thewet blue itself, and the
11、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 this purpose.6. Apparatus6.1 Analytical Balance
12、, 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 capacity or equivalent.6.6 Small Glass Filter F
13、unnel.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 Dec. 1, 2015. Published December 2015. Originallyapproved in 2001. Last previous edition approved in 2010 as D6714 - 01(2010)
14、.DOI: 10.1520/D6714-01R15.2For 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.3The last approved version of this
15、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 Vessels, of suitable size and design.6.9 Drying
16、Oven, with accurate variable temperature con-trols.6.10 Hot Plate, with accurate variable temperature controls.7. Reagents7.1 Purity of ReagentsAnalytical Reagent (AR) gradechemicals shall be used in all tests. Unless otherwise indicated,it is intended that all reagents shall conform to specificatio
17、ns 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 its use withoutlessening the accuracy of the determination.7.2 Purity
18、 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 those reagents and solutions have beenprepa
19、red 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 hazardous.7.6 Sulfuric Acid(H2SO4), 96 to 98 % w/w.
20、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, preparedaccording to accepted procedures available in analytical hand-books.7.10 Oxidizing MixtureMix
21、 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 % phosphoric acid with water to 100 mL.7.12 H
22、ydrochloric 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.7.15 Sodium Thiosulfate(Na2S2O35H2O). Use
23、d 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 StandardizationDry potassium dichromate(K2Cr2O7) i
24、n 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 KI solution. Stopperthe flask, and allow
25、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 the titration. Calculate the normality oft
26、he thiosulfate solution as follows:Normality 5 A0.04903 3B!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 Alternatively, a commercially available pre-stand
27、ardized 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 tosituations where concentrated perchloric acid has c
28、ome 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 perchloric acid should never be usedwithout acc
29、ompanying 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 perchloric acid hood, reserved for perchlo-ric acid dig
30、estions, 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 acid must not be permitted to go dry in thepres
31、ence of organics, metals or metal salts.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 Laboratory Chemicals ,DBH Ltd, Poole, Dorset, U.K., a
32、nd the United States Pharmacopeia and NationalFormulary , U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D6714 01 (2015)28.8 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 co
33、mposite wet blue sample prepared in accordancewith Test Method D6659, and weighed and ashed according toTest Methods D6659 and D6716.10. 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 ai
34、r (rendering the sampleincomplete), it is important 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.10.3 Next, carefully and slowly add 25 mL of the oxidizingmixture to the flask.10.4 Add a few glass anti
35、-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 of the flask) until all organic matter isdestroy
36、ed 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, then dilute to 125 mL with water. Rapidcooling can
37、 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.10.9 Once cool, add 30 mL of phosphoric acid and 25
38、 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 solution.10.12 When the solution color has faded to a
39、 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 mL, repeat the entire procedure, after adjusting
40、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 follows:Chromic Oxide Cr2O3!,%5 T 3N 3E 3 100W !where
41、:T = titration volume of sodium thiosulfate solution used,mL,N = Normality of 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 calc
42、ulation 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 D6658,should be run in accordance with the appropriate and acceptedprocedures for wet blue. If
43、D is the percentage moisture foundin the sample, calculate the Cr2O3, dry basis (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.1
44、2.2 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) obtainedby analysts in different laboratories will approximate 0
45、.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 NBSK2Cr2O7. The 99 % confidence limits on this value are 1.50 to2.00 %
46、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 laboratories. The precision statementswere developed using Practi
47、ce E180.14. Keywords14.1 ash; blue stock; chrome content; chromic oxide; per-chloric acid oxidation; wet blueD6714 01 (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 are ex
48、pressly 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 revi
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