ASTM E372-13

Designation: E372 − 13Standard Test Method forDetermination of Calcium and Magnesium in MagnesiumFerrosilicon by EDTA Titration1This standard is issued under the fixed designation E372; the number immediately following the designation indicates the year oforiginal adoption or, in the case 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 chemical analysis of mag-nesium ferrosilicon having chemical compositions within thefollowing limits:Element Composition Range, %Aluminum 2.0 maxCalcium 0.25 to 3.00Carbon 0.50 maxCerium 1.0 maxChromium 0.50 maxMagnesium 2.00 to 12.00Manganese 1.0 maxSilicon 40.00 to 55.00Sulfur 0.025 maxTitanium 0.2 max1.2 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 of regulatory limitations prior to use. For generalprecautions to be observed in this test method, refer toPractices E50.2. Referenced Documents2.1 ASTM Standards:2E29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE32 Practices for Sampling Ferroalloys and Steel Additivesfor Determination of Chemical CompositionE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE173 Practice for Conducting Interlaboratory Studies ofMethods for Chemical Analysis of Metals (Withdrawn1998)33. Terminology3.1 For definitions of terms used in this test method refer toTerminology E135.4. Significance and Use4.1 This test method for the chemical analysis of metals andalloys is primarily intended to test such materials for compli-ance with compositional specifications. It is assumed that allwho use this test method will be trained analysts capable ofperforming common laboratory procedures skillfully andsafely. It is expected that work will be performed in a properlyequipped laboratory.5. Hazards5.1 For precautions to be observed in the use of certainreagents and equipment in this test method, refer to PracticesE50.5.2 Specific hazard statements are given in 13.7.1 and 14.1.6. Sampling6.1 For procedures for sampling the material, refer toPractices E32.7. Rounding Calculated Values7.1 Calculated values shall be rounded to the desired num-ber of places as directed in Practice E29.8. Interlaboratory Studies8.1 This test method has been evaluated in accordance withPractice E173, unless otherwise noted in the precision and biassection.1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and are the directresponsibility of Subcommittee E01.01 on Iron, Steel, and Ferroalloys.Current edition approved Nov. 15, 2013. Published January 2014. Originallyapproved in 1976. Redesignated E372 in 1980. Last previous edition approved in2006 as E372 – 01 (2006). DOI: 10.1520/E0372-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.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 States1CALCIUM AND MAGNESIUM BY THE(ETHYLENEDINITRILO)TETRAACETIC ACID(EDTA) TITRIMETRIC METHOD9. Scope9.1 This test method covers the determination of magne-sium in compositions from2%to12%andcalcium incompositions from 0.25 % to 3.0 %.10. Summary of Test Method10.1 After dissolution of the sample in nitric and hydroflu-oric acids, an ammonium hydroxide precipitation is made toseparate other elements from calcium and magnesium.Calcium, and magnesium plus calcium are titrated in separatealiquot portions after adding triethanolamine and potassiumcyanide to mask residual traces of iron, copper, nickel,manganese, and aluminum that may be present. Calcium istitrated with disodium (ethylenedinitrilo)tetraacetate (EDTA)at pH 12. Magnesium plus calcium is titrated with EDTA at pH10.0 and the magnesium content is calculated by correcting forthe volume of EDTA required to titrate the calcium.11. Interferences11.1 Provision is made for the removal or masking ofinterfering elements ordinarily present in magnesium ferrosili-con.12. Apparatus12.1 Beakers, TFE-fluorocarbon 500-mL.12.2 pH Meter.13. Reagents13.1 Ammonium Chloride Buffer Solution (pH 10.0)—Dissolve 60 g of ammonium chloride (NH4Cl) in 200 mL ofwater, add 570 mL of NH4OH, and dilute to 1 L.13.2 Calcium, Standard Solution (1 mL = 0.2002 mg Ca)—Dissolve 0.5000 g of calcium carbonate (CaCO3) (purity:99.9 % min) in 100 mL of HCl (5 + 95). Boil 1 min, cool,transfer to a 1-L volumetric flask, dilute to volume, and mix.13.3 Disodium Ethylenedinitrilo-Tetraacetate Dihydrate(EDTA), Standard Solution: (0.005 M)13.3.1 Dissolve 1.8613 g of EDTA in water; transfer to a1-L volumetric flask; dilute to volume; and mix. The solutionwill remain stable for several months when stored in plastic orborosilicate glass bottles.13.3.2 Standardize the solution as follows: Using a pipet,tranfer 25 mL of the calcium solution (1 mL = 0.2002 mg Ca)to a 250-mL beaker, add 1 mL of MgCl2(13.6) solution and100 mL of water, and proceed as directed in 14.4.NOTE 1—Containers used for the storage of dilute solutions of EDTAshould be pretreated with a hot alkaline EDTA solution (10 g/L), andrinsed with water.13.3.3 Calculate the calcium equivalent of the EDTA solu-tion as follows:Calcium equivalent, mg/mL 5 A/B (1)where:A = calcium, mg, andB = EDTA solution required to titrate the calcium solution,mL.13.3.4 Calculate the magnesium equivalent of the solutionas follows:Magnesium equivalent, mg/mL 5 C 30.6068 (2)where C = calcium equivalent (13.3.3).13.4 Eriochrome Black-T Indicator Solution (6 g/L ofmethanol)—Dissolve 0.3 g of Eriochrome Black-T and1gofsodium borate decahydrate (Na2B4O7·10H2O) in 50 mL ofmethanol. Do not use a solution that has stood for more than 8h.13.5 Hydroxy Naphthol Blue Mixture—Add 1.0 g of hy-droxy napthol blue indicator to 100 g NaCl and mix thor-oughly.13.6 Magnesium Chloride (2.5 g/L) —Dissolve 0.25 g ofmagnesium chloride hexahydrate (MgCl2·6H2O) in 50 mL ofwater, and dilute to 100 mL.13.7 Potassium Cyanide Solution (50 g/L)—Dissolve2gofpotassium hydroxide (KOH) in water, add5gofpotassiumcyanide (KCN) (Warning; see 13.7.1 ), dilute to 100 mL, andtransfer to a plastic bottle.13.7.1 Warning: The preparation, storage, and use of KCNrequire care and attention. Avoid inhalation of fumes andexposure of the skin to the chemical and its solutions. Work ina well-ventilated hood. Refer to Section 8 of Practices E50.13.8 Potassium Hydroxide Buffer Solution (pH 12.5)—Dissolve 531 g of KOH in water, add 50 g of KCN (Warning;see 13.7.1 ), and dilute to 1 L. Store the solution in a plasticcontainer.13.9 Triethanolamine Solution (200 mL/L)—Dilute 20 mLof triethanolamine to 100 mL with water.14. Procedure14.1 Transfer a 1.0-g sample, weighed to the nearest 0.1 mg,to a dry 500-mL TFE-fluorocarbon beaker. Add 10 mL ofHNO3. Cautiously add 10 mL of HF, and heat gently until thesample is dissolved. Wash the sides of the beaker with a finestream of water.Add 20 mLof HClO4, place on a hot plate witha surface temperature not exceeding 300 °C, and evaporate todense fumes of HClO4. Cool, add 10 mL of HCl (1 + 1), andheat to dissolve salts. Transfer to a 600-mL glass beaker andevaporate to moderate dryness on a hot plate. Place on a hotplate and evaporate to complete dryness (indicated by theabsence of fumes). Add 20 mL of HCl (1 + 1), wash the sidesof the beaker with a fine stream of water, and heat to dissolvesalts.(Warning: HF produces very serious burns which may ormay not be painful on first contact. Such burns often damagebone and other tissue within the body. Standard procedure is touse gloves and protective clothing when handling this reagent.After the material is added, the closed container, gloves, and allsurfaces that may later be touched are rinsed with largequantities of water. Even one drop of HF on the skin orE372 − 132fingernail must receive immediate first aid and medical atten-tion should be promptly sought.)14.2 Add 200 mL of water and5gofNH4Cl. Heat toboiling. Remove from the hot plate and cool.Add NH4OH untilthe iron begins to precipitate. Using a pH meter, adjust the pHto 4.25 6 0.25 by adding NH4OH dropwise. Cool to roomtemperature, transfer to a 500-mL volumetric flask, dilute tovolume, and mix. Let stand1htoallow the precipitate to settle.14.3 Dry-filter approximately 200 mL of the solutionthrough a 12.5-cm medium filter paper into a dry beaker. Usinga pipet, transfer 50 mL of the solution to a 250-mL beaker.14.4 Titration of Calcium—Add 5 mL of triethanolaminesolution, stir, and immediately add 5 mL of the KOH buffersolution (Warning; see 13.7.1 ). Add 100 mg of hydroxynaphthol blue indicator mixture. Titrate with EDTA solution(0.005 M) to the disappearance of the last trace of the red color.14.5 Titration of Calcium and Magnesium—Using a pipet,transfer a second aliquot portion of the filtered solution from14.3 to a 250-mL beaker in accordance with the following:Magnesium, %SampleWeight, gAliquot forMagnesiumDetermination, mL2.0to5.0 1.0 505.0 to 12.0 1.0 2514.6 Add 5 mL of triethanolamine solution, stir, and imme-diately add 10 mL of the NH4Cl buffer solution. Add 5 mL ofthe KCN solution (Warning; see 13.7.1 ), and 3 drops to 5drops of Eriochrome Black-T solution. Titrate with the EDTAsolution (0.005 M) to the disappearance of the last trace of thered color.NOTE 2—In going through the end point, the color changes from red toblue to blue-green. The appearance of a blue-green color indicatesover-titration.15. Calculation15.1 Calculate the percentage of calcium as follows:Calcium, % 5 @~A 3B!/C# 3100 (3)where:A = EDTA solution required to titrate the calcium (14.4),mLB = calcium equivalent of the EDTA solution, mg/mL(13.3.3), andC = sample represented in the final aliquot, mg.15.2 Calculate the percentage of magnesium as follows:Magnesium, % 5@D 2 ~A/E!# 3FG3100 (4)where:A = EDTA solution required to titrate the calcium (14.4),mL,D = EDTA solution required to titrate the magnesium andcalcium (14.6), mL,E = 50 divided by millilitres of aliquot taken for titration ofmagnesium and calcium (14.5),F = magnesium equivalent of the EDTA solution, mg/mL(13.3.4), andG = sample represented in the final aliquot, mg.16. Precision and Bias416.1 Precision—Eight laboratories cooperated in testing thismethod and obtained the data summarized in Table 1 and Table2. Samples with calcium and magnesium compositions near theupper limit of the scope were not available for testing.16.2 Bias—The bias of this method could not be evaluatedbecause adequate certified reference materials were unavail-able at the time of testing. The user is cautioned to verify by theuse of certified reference materials, if available, that theaccuracy of this method is adequate for the intended use.17. Keywords17.1 calcium ; chemical analysis; ferrosilicon; magnesium;magnesium ferrosilicon; titrimetric methodASTM 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 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 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 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 service@astm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:E01-1005. ContactASTM CustomerService at service@astm.org.TABLE 1 Statistical Information—CalciumTest SpecimenCalciumFound, %Repeatability(R1, E173)Reproducibility(R2, E173)1. 48Si-45Fe 0.496 0.035 0.0442. 46Si-43Fe 1.06 0.04 0.08TABLE 2 Statistical Information—MagnesiumTest SpecimenMagnesiumFound, %Repeatability(R1, E173)Reproducibility(R2, E173)1. 48Si-45Fe 5.16 0.13 0.152. 46Si-43Fe 8.98 0.18 0.30E372 − 133