ISO INTERNATIONAL 4491-3 STANDARD Second edition 1997-04-01 Metallic powders - Determination of oxygen content by reduction methods Part 3: Hydrogen-reducible oxygen Poudres metalliques - Dosage de I'oxygene par les meéthodes de reduction Partie 3: Oxygene réductible par I'hydrogene ISO Reference number ISO 4491-3:1997(E) ISO 4491-3:1997(E) Foreword iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through IsO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non- governmental, in liaison with Iso, also take part in the work. IsO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 4491-3 was prepared by Technical Committee ISO/TC 119, Powder metallurgy, Subcommittee SC 2, Sampling and testing methods for powders (including powders for hardmetals). This second edition cancels and replaces the first edition (ISO 4491-3:1989), clauses 7 and 8 of which have been technically revised. IsO 4491 consists of the following parts, under the general title Metallic powders -- Determination of oxygen content by reduction methods: Part 1: General guidelines Part 2: Loss of mass on hydrogen reduction (hydrogen loss) Part 3: Hydrogen-reducible oxygen Part 4: Total oxygen by reduction-extraction ISO1997 All rights reserved.Unless otherwise specified, nopart ofthispublication may be reproduced or utilized in any form orbyany means, electronic or mechanical, includingphotocopying and microfilm, without permission in writing from the publisher. InternationalOrganizationforStandardization Casepostale56.CH-1211Genove20.Switzerland Internet central@iso.ch X.400 c=ch; a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii @ ISO ISO 4491-3:1997(E) Introduction The International Standard which the first edition of this part of ISO 4491 (ISO 4491-3:1989) replaced (ISO 4993:1981) described one particular reducible oxygen. However, it has since been established that other schemes will give equally valid results and these are therefore described in this part of ISO 4491. in addition, the scope of the method has been extended to include powders containing carbon. If carbon is present in the powder, some metal oxides which may otherwise have been reduced by hydrogen are instead reduced by carbon, producing the titration with Karl Fischer reagent which is used to determine the amount of water produced. Consequently a lower result will be obtained for the hydrogen-reducible oxygen content. reduction furnace over a catalyst which converts the CO and CO2 formed into methane and water, in accordance with the following equations: CO + 3H2 → CH4 + H2O CO2 + 4H2 → CH4 + 2H20O The conversion reaction is carried out at 380 °C over a nickel catalyst. NOTE— Certain oxides may be partially reduced by carbon which otherwise would not be reduced by hydrogen. In such cases the interpretation of results should be made with great care [see ISO 4491-1:1989, subclause 4.1.2 d)]. ili