SANS 11426-2008 Determination of gold in gold jewellery alloys - Cupellation method (fire assay)《金合金首饰中的黄金测定 灰吹法(烤钵试金法)》.pdf

1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-21497-5 SANS 11426:2008Edition 2ISO 11426:1997Edition 2SOUTH AFRICAN NATIONAL STANDARD Determination of gold in gold jewellery alloys Cupe

4、llation method (fire assay) This national standard is the identical implementation of ISO 11426:1997 and is adopted with the permission of the International Organization for Standardization. Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001Tel: +27 12 4

5、28 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS SANS 11426:2008 Edition 2 ISO 11426:1997 Edition 2 Table of changes Change No. Date Scope National foreword This South African standard was approved by National Committee SABS TC 1078, Engineering materials Non-ferrous metals, in accordance with proce

6、dures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This SANS document was published in September 2008. This SANS document supersedes SABS ISO 11426:1993 (first edition). AReference numberISO 11426:1997(E)INTERNATIONALSTANDARDISO11426Second edition1997-12-01Det

7、ermination of gold in gold jewelleryalloys Cupellation method (fire assay)Dosage de lor dans les alliages dor pour la bijouterie-joaillerie Mthodede coupellation (essai au feu)SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO

8、 11426:1997(E) ISO 1997All rights reserved. Unless otherwise specified, no part of this publication may be reproducedor utilized in any form or by any means, electronic or mechanical, including photocopying andmicrofilm, without permission in writing from the publisher.International Organization for

9、 StandardizationCase postale 56 CH-1211 Genve 20 SwitzerlandInternet centraliso.chX.400 c=ch; a=400net; p=iso; o=isocs; s=centralPrinted in SwitzerlandiiForewordISO (the International Organization for Standardization) is a worldwidefederation of national standards bodies (ISO member bodies). The wor

10、k ofpreparing International Standards is normally carried out through ISOtechnical committees. Each member body interested in a subject for whicha technical committee has been established has the right to be representedon that committee. International organizations, governmental and non-governmental

11、, in liaison with ISO, also take part in the work. ISOcollaborates closely with the International Electrotechnical Commission(IEC) on all matters of electrotechnical standardization.Draft International Standards adopted by the technical committees arecirculated to the member bodies for voting. Publi

12、cation as an InternationalStandard requires approval by at least 75 % of the member bodies castinga vote.International Standard ISO 11426 was prepared by Technical CommitteeISO/TC 174, Jewellery.This second edition cancels and replaces the first edition ISO 11426:1993,which has been technically revi

13、sed.SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .INTERNATIONAL STANDARD ISO ISO 11426:1997(E)1Determination of gold in gold jewellery alloys Cupellation method (fire assay)1 ScopeThis International Standard specifies a cupel

14、lation method (fire assay) for thedetermination of gold in gold jewellery alloys. The gold content of the alloys shouldpreferably lie between 333 and 999 parts per thousand ( ).The procedure is applicable specifically to gold alloys incorporating silver, copper andzinc. Some modifications are indica

15、ted where nickel and/or palladium are present in theso-called white gold alloys, as well as for alloys containing 990 or more parts perthousand ( ) of gold.This method is intended to be used as the reference method for the determination offineness in alloys covered by ISO 9202.2 Normative referenceT

16、he following standard contains provisions which, through reference in this text,constitute provisions of this International Standard. At the time of publication, the editionindicated was valid. All standards are subject to revision, and parties to agreementsbased on this International Standard are e

17、ncouraged to investigate the possibility ofapplying the most recent edition of the standard indicated below. Members of IEC andISO maintain registers of currently valid International Standards.ISO 9202:1991, Jewellery Fineness of precious metal alloys3 PrincipleThe gold alloys are inquarted with sil

18、ver, compounded with lead and cupelled in acupellation furnace until a precious metal button is obtained. After flattening and rolling,the silver is extracted (parted) in nitric acid and the gold weighed. Possible systematicerrors in the procedure are eliminated by assaying standard proof samples in

19、 parallel.NOTE White gold alloys containing palladium and/or nickel as well as alloys with 990 or moreparts per thousand ( ) of gold require some procedural changes.4 ReagentsDuring the analysis, unless otherwise stated, use only reagents of recognized analyticalgrade and only distilled water or wat

20、er of equivalent purity.SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO 11426:1997(E) ISO24.1 Nitric acid, 33 % (m/m) (20= 1,2 g/ml), free of halides.4.2 Nitric acid, 49 % (m/m) (20= 1,3 g/ml), free of halides.4.3 Lead, ass

21、ay grade, free of precious metals and bismuth, as foil, beads or tablets.4.4 Silver, for inquartation, minimum purity 999,9 parts per thousand ( ) by mass,free of gold and platinum group metals.4.5 Pure gold, for proof samples for determination of gold between 333 and 990 parts per thousand ( ) byma

22、ss, minimum purity 999,9 parts per thousand ( ) by mass; for determination of gold more than 990 parts per thousand ( ) by mass,minimum purity 999,99 parts per thousand ( ) by mass.4.6 Palladium, for proof samples, minimum purity 999,9 parts per thousand ( ) bymass, free of gold and other platinum g

23、roup metals.4.7 Nickel, for proof samples, minimum purity 999 parts per thousand ( ) by mass,free of gold and platinum group metals.4.8 Copper foil or wire, minimum purity 999 parts per thousand ( ) by mass, free ofgold, and platinum group metals.4.9 Borax (Na2B4O7), anhydrous.5 ApparatusOrdinary la

24、boratory apparatus and the following.5.1 Cupellation furnace, in which an oxidizing atmosphere can be maintained.CAUTION A standard muffle furnace is not satisfactory for this purpose.5.2 Magnesium oxide cupels, usually of diameter 22 mm to absorb 6 g lead, or ofdiameter 26 mm to absorb 10 g lead, o

25、r blocks of cupels of similar absorption.5.3 Parting flasks or platinum basket.5.4 Parting cups, comprising unglazed porcelain crucibles.5.5 Cuppellation tongs.5.6 Assay pliers.5.7 Polished anvil, which may be replaced by a press, polished and reserved for thispurpose.5.8 Polished hammer, of minimum

26、 mass 400 g, which may be replaced by a press,polished and reserved for this purpose.5.9 Scorification dishes, usually of diameter 50 mm.SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS . ISOISO 11426:1997(E)35.10 Jewellers rolls

27、.5.11 Platinum-tipped crucible tongs.5.12 Assay cleaning brush, of stiff bristle or nylon but not brass.6 SamplingThe sampling procedure for jewellery gold alloys shall be agreed upon until acorresponding standard method has been published.For coated articles, appropriate precautions that have been

28、agreed shall be taken toexclude the coating from the determination.7 ProcedureNOTE When the composition of the samples is unknown, use a preliminary assay for theestimation of the fineness of gold. For the distinction between palladium and nickel white golds,the touch stone test can also be used. If

29、 the cornet breaks up during the parting process, this isoften an indication of excess silver.7.1 Yellow gold alloys7.1.1 Analysis samplesTransfer at least two samples of the alloy, preferably between 125 mg and 250 mg,weighed to the nearest 0,01 mg, into assay-grade lead foil (4.3). The mass of the

30、 foil (orfoil + beads) should be at least 4 g for yellow gold samples up to 200 mg, and 6 g forsamples from 201 mg to 300 mg (250 mg). Add pure silver (4.4) equivalent to 2,3 to 3times the mass of fine gold present. Roll and compress the lead foil into a tight ball.7.1.2 Proof assay samplesWeigh, as

31、 in 7.1.1, at least two proof assay samples of proof gold (4.5) and pure silver(4.4) in masses which correspond to the expected gold and silver contents (including theinquartation addition) of the assay sample. The total content of base metals in the assaysamples is taken into consideration by the a

32、ddition of a corresponding quantity ofcopper.Treat the proof assay samples and the assay samples in 7.1.3 and 7.1.4 in the samemanner.7.1.3 Cupellation and treatment of precious metal buttonsPlace the assay and the proof assay samples (7.1.2), tightly wrapped in lead foil, onmagnesium oxide cupels (

33、5.2) which have been preheated to at least 1000 C in thecupellation furnace (5.1).Place the cupels with the proof assay samples as close as possible to the correspondingassay samples in the cupellation furnace maintained at 1050 C to 1150 C. Continueheating until this stage is completed (about 25 mi

34、n) under oxidizing conditions. Removethe cupels from the furnace. Allow the precious metal buttons to cool down before liftingthem from the cupels with the assay pliers (5.6). Squeeze the buttons and brush theirundersides carefully with a brush (5.12) to remove any adhering cupel material. Flattenth

35、e beads on the polished anvil (5.7) with a polished hammer (5.8) and anneal by heatingjust to red heat.SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS .ISO 11426:1997(E) ISO4Roll them into 0,12 mm to 0,15 mm thick strips and ann

36、eal again. Roll the strips intocornets without contamination or loss of gold.NOTE The cupel should be examined carefully to ensure that the precious metal bead containsall the sample gold. Small droplet residues indicate the need for a repeat determination in asmaller cupel.7.1.4 Parting of the silv

37、er/gold samplesCAUTION For the parting operations with nitric acid, a fume hood should be kept cleanand used exclusively for this determination.Place the precious metal cornets in parting flasks (5.3). First immerse the cornet in 20 mlof nitric acid (4.1) at a temperature about at least 5 C below th

38、e boiling point and bringto the boil.Continue heating for 15 min or until the evolution of nitrous fumes has ceased,whichever is longer. Decant, wash with warm water and immerse in 20 ml of nitric acid(4.2). Boil gently for 15 min and decant. Wash, immerse in 20 ml of nitric acid (4.2) andboil for 1

39、0 min. Decant and wash the undissolved remaining gold with warm (60 C to70 C) water until it is free of silver nitrate. Transfer the gold cornets to small porousparting cups (gold crucibles) (5.4). Dry them and anneal at 700 C to 750 C for about 5min. Cool then weigh the gold cornet.When assaying a

40、series of samples of similar composition, instead of using a number ofparting flasks the precious metal cornets can be parted with the aid of a dissolutionbasket consisting of Pt/Ir or Pt/Rh which is equipped with a number of quartz thimbleswith perforated bottoms. The cornets are placed in the thim

41、bles and the basket islowered slowly into nitric acid (4.1) at about 90 C. The acid is brought to the boil andallowed to boil gently for 15 min or until the evolution of nitrous fumes has ceased,whichever is the longer.Remove the basket from the acid, rinse in water, and repeat the treatment in a se

42、condbath of nitric acid (4.2), boiling again for 15 min.Remove the basket from the acid, rinse it with water until it is completely free of silvernitrate and allow to dry. Finally, place the basket with the gold samples for about 5 minin a muffle furnace, heated to approximately 700 C to 750 C. Afte

43、r cooling, the goldsamples can be weighed.7.2 White gold alloys containing nickelIf nickel is present, two equivalent variations on the method specified in this InternationalStandard are acceptable. These involve either the use of additional lead or scorification.7.2.1 Cupellation with additional le

44、adIt is difficult to extract all the nickel in the alloy into the cupel by using the standardquantity of lead. Effective cupellation requires an additional 4 g of lead (4.3) and the useof larger cupels. This extra lead may be incorporated at the start of the test, if the cupel islarge enough to cont

45、ain the increased volume of melt. Alternatively (preferably) a buttonof lead is added to the hot precious metal bead in the cupel after the lead oxide fumesfrom the initial operation have ceased. Care is needed if the cupellation furnace (5.1) isnot adapted for this addition.The proof assays should

46、contain approximately the same proportion of nickel as thesample.SANS 11426:2008This s tandard may only be used and printed by approved subscription and freemailing clients of the SABS . ISOISO 11426:1997(E)57.2.2 ScorificationFor white gold alloys containing nickel, pretreatment of the sample by sc

47、orificationinvolves wrapping it in 2 g of lead foil (4.3). The sample consists of 125 mg to 250 mg ofgold, and is inquarted with silver equivalent to 2,3 to 3 times the mass of fine goldpresent. Place this capsule in a scorification dish (5.9), together with 15 g of lead and 1,5g to 2 g of anhydrous

48、 borax (4.9) and heat to 1000 C in the furnace. An increased airsupply may be needed to oxidise the large quantity of lead. After 20 min to 30 min, whena liquid slag covers the surface of the dish, raise the temperature briefly to 1100 C (forabout 2 min). Remove the dish with the tongs, cool, and se

49、parate the lead button fromthe slag. This button, which contains the original gold and silver, is cupelled as describedin 7.1.3.Proof gold samples made with the appropriate amount of added nickel are treated in asimilar way.7.3 White gold alloys containing palladium (nickel absent)For white gold alloys containing palladium, traces of this metal may remain in the cornetafter a single cupellation and parting. With these alloys, the cornets from the sample andthe proof assays should be recupelled with 4 g of lead, silver equal to 2,5 t