1、Designation: D6714 01 (Reapproved 2010)1Standard 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, t
2、he 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.1NOTEThe SI statement was added and the Subcommittee name in footnote 1 was corrected editorially in November 2010.1. S
3、cope1.1 This test method covers the determination of chromicoxide in wet blue that has been partly or completely 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 moist
4、ure-free basis (mfb).1.2 This test method is specific in that it applies to a sampleor samples that are the resultant 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 s
5、tandard 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 prior to use. Specific hazards aregive
6、n in Section 8.2. Referenced Documents2.1 ASTM Standards:2D6658 Test Method for Volatile Matter (Moisture) of WetBlue by Oven DryingD6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsD6716 Test Method for TotalAsh in Wet Blue or Wet WhiteE180 Practice for Determini
7、ng the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals33. 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 perchl
8、oric acid method may be applied to the ashobtained in 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 execut
9、ed 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 fusion of the ash. However care must be takenbecause of
10、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 andthis is rarely present in quantity. The precision and a
11、ccuracy 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 matter forspecification in the purchase of wet blue. The
12、 proceduredescribed provides adequate accuracy for this purpose.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 Oct. 1, 2010. Published November 2010. Originallyapproved in 2001.
13、Last previous edition approved in 2006 as D6714 - 01 (2006).DOI: 10.1520/D6714-01R10E01.2For 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 Summa
14、ry page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Apparatus6.1 Analytical Balance, accurate and calibrated to
15、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 Funnel.6.7 Dessicator, of suit
16、able size and design and charged withfresh dessicant.6.8 Weighing Vessels, of suitable size and design.6.9 Drying 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 sha
17、ll be used in all tests. Unless otherwise indicated,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 thereag
18、ent is of sufficiently high purity to permit its use withoutlessening the 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-s
19、tandardized analytical reagents 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 perchl
20、oric acid may be substituted, 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. Dissolve10g(60.1 g) of potassium iodide into 100 mL of water.7.9 Starch Indicator Solution2 % or
21、equivalent, preparedaccording 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
22、before use.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 standard-ization of thiosulfate solution.7.
23、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(Na2S2O35H2O) in previously boiled water, add 1
24、.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, glass-stopperedErlenmeyer flask. Dissolve
25、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, add 2 mL of 2 % starchsolution and contin
26、ue titrating until the deep blue color changesto a clear green. Record 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 relativelysta
27、ble. 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 use of perchloric acid can lead to
28、 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 kept from possible contactwith other
29、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, sawdust, andother organic material
30、s 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 be stored on a ceramic ornon-porou
31、s tray or shelf and never on a wooden or perviousshelf.8.7 Perchloric acid 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.4Reagent Chemicals, American Chemical Society Specificati
32、ons , 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., and the United States Pharmacopeia and NationalFormulary , U.S. Pharmacopeial Convention, Inc. (US
33、PC), Rockville, MD.D6714 01 (2010)129. 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 Transfer the ash obtained from
34、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 20 mL of nitric acid (HNO3
35、)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-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 unde
36、r 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 chromium. Do not allow the sample to boildry.10.6 Heat the solution for an additional 2 min to ensurecomplete
37、 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 boiling and continue boiling for7 to 10 min to expel any chlorine or oxides of nitrogen.10.8 Remove the fla
38、sk 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 the flask in the dark and allow to stand for 5 minto allow complete release of iodine (dark brown color).
39、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. Continue the titration until the deep blue colorchanges to a clear blue-green.10.13 Record the titration v
40、olume.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 theburette.10.15 Calculate the results in accordance with Section 11.11. Calculation11.1 Calculate the chromium
41、content as percentage ofchromic oxide (Cr2O3) in the wet blue as follows: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
42、 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 the chromium contentof wet blue is expressed upon a dry (moisture-free) basis, amoisture determinati
43、on, 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 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
44、 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 averaging (95 % confidence level).13. Precision and Bias13.1 ReproducibilityThe average differenc
45、e 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 level) if they differ by more than 0.2 % absolute.13.2 BiasThe test method yields results th
46、at 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 1The estimates of checks for duplicates and reproducibility in13.1 and 13.2 are based on an interlaborato
47、ry 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-chloric acid oxidation; wet blueD6714 01 (2010)13ASTM International takes no position respe
48、cting 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 the riskof infringement of such rights, are entirely their own responsibility.This st
49、andard 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 comments have not received a fair hearing you shouldmake your views known to the AST
