1、CEN EN*F24491-1 93 3404589 004?7052 400 EUROPEAN STANDARD EN 24491-1 NORME EUROPENNE EUROPISCHE NORM 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 powd
2、ers - Determination of oxygen content by reduction methods - Part 1 : General guidelines (IS0 4491-1 : 1989) Poudres mtalliques - Dosage de l?oxygne par les mthodes de rduction - Partie 1: Directive gnrales (IS0 4491-1 : 1989) Metallpulver - Bestimmung des Sauerstoffgehaltes durch Reduktionsverfahre
3、n - Ri1 1: Allgemeine Hinweise (IS0 4491-1 : 1989) This European Standard was approved by CEN on 1993-04-02. CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterat
4、ion. 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 translat
5、ion 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,
6、Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels O 1993 Copyright reserved to CEN members Ref. No. EN 24491-1
7、 : 1993 E CEN EN+2449L-L 93 - 3404589 0047053 347 Page 2 EN 24491-1 : 1993 Foreword In 1992, IS0 24491-1: 1993 Metallic powders - Deterrnimtion of oxygen content bp reduction methods - Part 1: Geneml guidelines was submitted to the CEN Primary Questionnaire procedure. Following the positive result o
8、f the CEN/CS Proposal IS0 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 conflict
9、ing national standards shall be withdrawn at the latest by October 1993. According to the Internal Regulations of CENKENELEC, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Nethe
10、rlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. NOTE. The European references to international publications are given in annex ZA (normative). CEN EN+24491-1 93 = 3404589 O047054 283 W Page 3 EN 24491-1 : 1993 Introduction In powder metallurgy, the purity of the powders is a
11、n 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
12、 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 loca
13、lly 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
14、 the range 0,l % (rn/m) to 1 % (m/rn). 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
15、 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/CO, produced by the reaction; c) separation methods, in which - either the oxide phase is selectively dissolved
16、 and determined chemically (for exaniple 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
17、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. Page 4 EN 24491-1 1993 Metallic powders - Determination of oxygen content by reduction methods - Part I :
18、 General guidelines 1 Scope This part of IS0 4491 is the first part of a series dealing with the determination of oxygen content in metallic powders by reduc- tion methods. It gives general guidance to these methods, and gives some recommendations for the correct interpretation of the results obtain
19、ed. 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 de
20、pend 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 IS0 4491. At the time of publication, the editions indicated were va
21、lid. All standards are subject to revision, and parties to agreements based on this part of IS0 4491 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standar
22、ds. IS0 4491-2 : 1989, Metallic powders - Determination of oxygen content by reduction methods - Part2: Loss of mass on hydrogen reduction (hydrogen lossl. IS0 4491-3 : 1989, Metaliic powders - Determination. of oxygen content by reduction methods - Part 3: Hydrogen- reducible oxygen. IS0 44914 : 19
23、89, Metaliic 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 IS0 3954 : 1977, Powders for powder metallurgical purposes - Sam- pling, are recommended. The powder shall be test
24、ed 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.
25、 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 determi- nation, 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 reduci
26、ble, in particular Alzo3, Sioz, ZrOz 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) Wate
27、r vapour and/or hydrocarbons present in the sam- ple, and also gases, which possibly by adsorption or occlu- sion 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 com- pletely or partially remo
28、ved, 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. di Carbon present
29、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. CEN EN+24491-1 93 = 3404589 004705b 05b e) Alloy powders containing metallic el
30、ements 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 (IS0 449
31、1-21, 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
32、 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 rou
33、tine control of powders of certain defined metals as stated in IS0 4491-2. 4.1.4 In the method determination of oxygen emanating from hydrogen-reducible oxides (IS0 4491-31, the quantity of water formed by hydrogen reduction of these oxides is measured by titration. In comparison with the loss in hy
34、drogen 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 deter- mine the water content of the sample. - avoided. The interf
35、erence of metalloids and of volatile metals is 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 measure
36、d 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 car- bon interference. This method is applicable in practice when the sampled powde
37、r is known to be almost free of carbon for example C 0.02 % (rn/rn)l or the carbon present is in an unreactive form. Then the result represents the oxygen content from hydrogen-reducible oxides. - Method 2: Oxygen content corresponding to hydrogen-reducible oxides, taking into account carbon in- ter
38、ference. In this method the CO + CO;! gases released by carbon reduction of some of the oxides and contained in the H, carrier gas, are quantitatively converted to methane and water on a nickel catalyst at 380 OC. The total water deter- mined represents the oxygen content emanating from hydrogen-red
39、ucible oxides, irrespective of whether the actual reduction has taken place by means of hydrogen or carbon. NOTE - With reference to 4.1.2 di, certain oxides may be partially reduced by carbon. .e. oxides which otherwise would not be reduced by hydrogen. In such a case, the test conditions shall be
40、subject to a special agreement and interpretation of the result should be made with great care. Page 5 EN 24491-1 : 1993 4.2 Carbon as a reducing agent: reduction- extraction method This method (IS0 4491-41 is based on the reduction of the sam- ple by graphite at very high temperature (2 O00 to 3 O0
41、0 OC), either under vacuum, or in a flow of pure inert gas (for example argon). Depending on the metal analysed, the operating condi- tions are chosen so that all the oxides, even the most refractory ones, are reduced totally. Any interference is completely ex- cluded and the result represents accur
42、ately the total oxygen content of the sample. 5 Practical application of the standard methods The following table gives a summary of the applicable methods, depending on the type of powder analysed and on the nature of the oxygen which shall be determined. It should be emphasized that a combination
43、of several methods can bring precise information, for example: - on the “hydrogen-reducible“ and “hydrogen- irreducible“ oxygen, .e. the presence of refractory oxides in “hydrogen-reducible“ metals; - on the internal effect of carbon, when present, on the reduction of oxides. An interesting alternat
44、ive is to carry out the total oxygen deter- mination on a test portion already reduced by hydrogen (by means of a loss in hydrogen test or a hydrogen-reducible oxygen test). In this way the content of oxygen not reduced by hydrogen (and by internal carbon) under the conditions of hydrogen reduction
45、can be determined. 6 Summary of the implementation of methods for oxygen determination by reduction Two cases are considered : a) Metals of oxides which are reducible by hydrogen I“H reducible“) and which may possibly contain carbon, for example: Fe, Ni, Co, Cu, Ag, Sn, Pb, W, Mo, Re When such a met
46、al is reduced by hydrogen, the behaviour of the oxygen and carbon content is represented by the following analytical results contained in hydrogen reduced oxides O, contained in carbon reduced oxides from remaining (unreduced) oxides O, O, content of carbon having reacted CO b) Any metal (containing
47、 carbon or not) When reduced totally by graphite (reduction-extraction method), the total oxygen content (O,) is measured. EN EN*2447L-L 93 3404587 0047057 T92 Powder Metals with hydrogen-reducible oxides: not containing carbon containing Any other metal carbon Page 6 EN 24491-1 : 1993 Hydrogen-redu
48、cible oxygen Reduction-extraction Hydrogen loss With correction On initial sample On sample reduced Direct method for carbon by hydrogen OH OH OH 0, = OH + 0, Or Or 0, = OH + oc + 0 OH + OC + CO OH OH OC I 0, Table 1 - Content determined depending on method used Annex ZA (normative) Normative refere
49、nces to international publications with their relevant European publications This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment br revision. For undated references the latest edition of the publication referred to applies (including amendments). Pub
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