BS-EN-24491-1-1993 ISO-4491-1-1989.pdf

BRITISH STANDARD BS EN 24491-1:1993 ISO 4491-1: 1989 Metallic powders Determination of oxygen content by reduction methods Part 1: General guidelines The European Standard EN 24491-1:1993 has the status of a British Standard UDC 621.762:669-492.2:543.73:546.21 Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 24491-1:1993 This British Standard, having been prepared under the direction of the Iron and Steel Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 June 1993 © BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference ISM/65 Special announcement in BSI News January 1993 ISBN 0 580 21916 X Cooperating organizations The European Committee for Standardization (CEN), under whose supervision this European Standard was prepared, comprises the national standards organizations of the following countries: AustriaOesterreichisches Normungsinstitut BelgiumInstitut belge de normalisation DenmarkDansk Standardiseringsraad FinlandSuomen Standardisoimisliito, r.y. FranceAssociation française de normalisation GermanyDeutsches Institut für Normung e.V. GreeceHellenic Organization for Standardization IcelandTechnological Institute of Iceland IrelandNational Standards Authority of Ireland ItalyEnte Nazionale Italiano di Unificazione LuxembourgInspection du Travail et des Mines NetherlandsNederlands Normalisatie-instituut NorwayNorges Standardiseringsforbund PortugalInstituto Portuguès da Qualidade SpainAsociación Española de Normalización y Certificación SwedenStandardiseringskommissionen i Sverige SwitzerlandAssociation suisse de normalisation United KingdomBritish Standards Institution Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 24491-1:1993 © BSI 11-1999i Contents Page Cooperating organizationsInside front cover National forewordii Foreword2 Introduction3 1Scope3 2Normative references3 3Sampling3 4Meaning of the results according to the method used4 5Practical application of the standard methods5 6Summary of the implementation of methods for oxygen determination by reduction5 Annex ZA (normative) Normative references to international publications with their relevant European publications6 National annex NA (informative) Committees responsibleInside back cover National annex NB (informative) Cross-referencesInside back cover Table 1 Content determined depending on method used5 Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 24491-1:1993 ii © BSI 11-1999 National foreword This British Standard has been prepared under the direction of the Iron and Steel Standards Policy Committee and is the English language version of EN 24491-1:1993 Metallic powders Determination of oxygen content by reduction methods Part 1: General guidelines, published by the European Committee for Standardization (CEN). It is identical with ISO 4491-1:1989, prepared by Technical Committee 119, Powder metallurgy, of the International Organization for Standardization (ISO) with the active participation of the UK. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages 2 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM EN 24491-1 April 1993 UDC 621.762:669-492.2:543.73:546.21 Descriptors: Powder metallurgy, metallic powder, chemical analysis, determination of content, oxygen, reduction method English version Metallic powders Determination of oxygen content by reduction methods Part 1: General guidelines (ISO 4491-1:1989) Poudres métalliques Dosage de loxygène par les méthodes de réduction Partie 1: Directive générales (ISO 4491-1:1989) Metallpulver Bestimmung des Sauerstoffgehaltes durch Reduktionsverfahren Teil 1: Allgemeine Hinweise (ISO 4491-1:1989) This European Standard was approved by CEN on 1993-04-02. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard, without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comité Européen de Normalisation Europäisches Komitee für Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels © 1993 Copyright reserved to CEN members Ref. No. EN 24491-1:1993 E Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 24491-1:1993 © BSI 11-1999 2 Foreword In 1992, ISO 24491-1:1993 Metallic powders Determination of oxygen content by reduction methods Part 1: General guidelines was submitted to the CEN Primary Questionnaire procedure. Following the positive result of the CEN/CS Proposal ISO 4491-1:1989 was submitted to the CEN Formal Vote. The result of the Formal Vote was positive. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by October 1993, and conflicting national standards shall be withdrawn at the latest by October 1993. According to the Internal Regulations of CEN/CENELEC, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. NOTEThe European references to international publications are given in Annex ZA (normative). Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 24491-1:1993 © BSI 11-19993 Introduction In powder metallurgy, the purity of the powders is an important parameter for the manufacture of sintered metals. Among the various impurities which may be present in a powder, oxygen plays a particular role as it is always present in any metal or alloy powder, and in amounts greater than those encountered in compact metals. Oxygen is mostly combined in the form of oxides which appear in the following ways: Oxide film coatings on particle surfaces, spontaneously formed by oxidation of the metal by air or moisture during powder preparation and during handling and storage. Oxide inclusions, being either oxides of the main metal remaining locally unreduced during the production process (in the case of reduced powders), or other oxide impurities originating from the raw material and/or from the equipment (e.g. refractory ceramics from melting furnace in atomization processes). In practice, oxygen contents in metallic powders lie mostly in the range 0,1 % (m/m) to 1 % (m/m). The determination of oxygen content can be made by means of many physical or chemical methods, for example a) specific methods, such as activation analysis or mass spectrometry, in which the element O is directly determined; b) reduction methods, in which oxides present are, totally or partially, reduced by hydrogen or by carbon. Oxygen content is related, either to the loss of mass of the sample through reduction, or to the amount of water or CO/CO2 produced by the reaction; c) separation methods, in which either the oxide phase is selectively dissolved and determined chemically (for example in copper powder, where copper oxide is dissolved by hydrochloric acid); or the metal phase is selectively dissolved, and the insoluble residue (assumed to be oxide) is evaluated (for example in aluminium powder, aluminium is dissolved in bromine-methanol reagent, leaving aluminium oxide). The present International Standard considers only reduction methods, as these are commonly used in laboratories for analysing a great variety of metal powders. 1 Scope This part of ISO 4491 is the first part of a series dealing with the determination of oxygen content in metallic powders by reduction methods. It gives general guidance to these methods, and gives some recommendations for the correct interpretation of the results obtained. The test methods are applicable generally to all powders of metals, alloys, carbides and mixtures thereof. The constituents of the powder shall be non-volatile under the conditions of test. The powder shall be free of lubricant or organic binder. However, there exist certain limitations which depend upon the nature of the analysed metal. These limitations are discussed in clause 4. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 4491. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 4491 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 4491-2:1989, Metallic powders Determination of oxygen content by reduction methods Part 2: Loss of mass on hydrogen reduction (hydrogen loss). ISO 4491-3:1989, Metallic powders Determination of oxygen content by reduction methods Part 3: Hydrogen-reducible oxygen. ISO 4491-4:1989, Metallic powders Determination of oxygen content by reduction methods Part 4: Total oxygen by reduction-extraction. 3 Sampling For sampling of the powder the procedures given in ISO 3954:1977, Powders for powder metallurgical purposes Sampling, are recommended. The powder shall be tested in the as-received condition. Metallic powders are frequently reactive substances with respect to air and moisture. Therefore, particular attention shall be given to adequate conditions for handling and storage of the test sample. The test portion shall be taken immediately prior to the analysis. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 03 09:15:37 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 24491-1:1993 4 © BSI 11-1999 4 Meaning of the results according to the method used 4.1 Hydrogen as a reducing agent 4.1.1 At the test temperatures prescribed in the determination, only the following metals have oxides totally reducible by hydrogen: Fe, Ni, Co, Cu, Ag, Sn, Pb, W, Mo, Re All other common oxides are not reducible, in particular Al2O3, SiO2, ZrO2 and other oxides of alkali, alkali-earth and most rare-earth metals. Oxides of chromium, manganese, titanium, and vanadium may be partially reducible. 4.1.2 However, other reactions with constituents of the powder take place during the reduction process: a) Water vapour and/or hydrocarbons present in the sample, and also gases, which possibly by adsorption or occlusion are contained in the powder, are released during heating. b) Elements, such as carbon, nitrogen, sulfur, phosphorus, free or combined in the powder, may be completely or partially removed, either because they are volatile or because they react with hydrogen or with oxides in the powder, forming volatile compounds. c) Some metals present in the powder, such as lead, tin, cadmium, zinc, may be partially or completely volatilized, depending on the test conditions. d) Carbon present in the powder can also reduce oxides under the specified test conditions, and possibly also oxides that normally are not reduced or are only partially reduced by hydrogen, such as chromium, manganese and vanadium oxides. e) Alloy powders containing metallic elements with high affinity for oxygen, such as chromium, manganese, silicon, aluminium and titanium, may be oxidized during the test by reaction with the atmosphere or with less refractory oxides, entailing an apparent decrease of measured oxygen content. 4.1.3 In the loss in hydrogen method (ISO 4491-2), the loss of mass of the test portion, when submitted to a specified heat treatment in hydrogen, is measured. Originally this test was considered to give an estimate of the oxygen content of a metal powder, the oxide of which is reducible by hydrogen. However, with the advent of more complex or alloyed powders, all the reactions considered above (4.1.2) may contribute, positively or negatively, to the measured loss of mass. Therefore this test method is purely conventional and its reproducibility requires a scrupulous respect of the operating procedure. This method is commonly used in routine control of powders of certain defined metals as stated in ISO 4491-2. 4.1.4 In the method determination of oxygen emanating from hydrogen-reducible oxides (ISO 4491-3), the quantity of water formed by hydrogen reduction of these oxides is measured by titration. In comparison with the loss in hydrogen method, this method is more specific for the following reasons: The interference of moisture and adsorbed gases is prevented by pre-treatment at low temperature. With a slight modification of the procedure, it is possible to determine the water content of the sample. The interference of metalloids and of volatile metals is avoided. However, interference of carbon present in the sample may have to be taken into account. Some part of the metal oxides, which otherwise may have been reduced by hydrogen, are reduced by carbon, producing carbon monoxide or dioxide, which are not measured by water titration. Consequently a lower result will be obtained. Therefore two alternative methods are specified: Method 1: Oxygen content corresponding to hydrogen-reducible oxides, without taking into account carbon interference. This method is applicable in practice when the sampled powder is known to be almost free of carbon for example C 0,02 % (m/m) or the carbon present is in an unreactive form. Then the result represents the oxygen content