摘要:

AbstractThe author has summarized the results of thirty years’research on the properties of powdered materials. These studies have been concerned with powders of all types, but most of the conclusions are applicable to metallic powders. The complex properties of powders can be resolved only by first defining those fundamental properties that can be measured individually; the first section of the paper defines these and shows how they may be combined to assess the more complex properties, according to the nature of the problem and the circumstances of usage. The second section describes the essential features of methods for the sizing analysis of powders, with brief consideration of their characteristics and some indication of recent tendencies in the application of electronic devices and automatic recording.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.001

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractCurrent methods of sampling and determination of flow, apparent and tap density, particle size,“fillability”, and“hydrogen loss”are reviewed. The general conclusion is that present tests are adequate, but that new tests more suited to powder usage should be devised.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.002

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractA large number of tests based on observations made on compacts have been devised to evaluate the pressing and sintering characteristics of metal powders. These are summarized under four headings: behaviour during pressing, properties of the green compact, behaviour during sintering, and the properties of the sintered compact. The specifications which set down standard testing techniques are described and reviewed. The principles involved in the various proposed tests are given, together with any limitations or precautions that need special consideration. In a number of cases there is obvious scope for further study and research, and these are pointed out.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.003

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractSome experimental aspects of the construction and use of a conventional BET apparatus are discussed. Certain improvements in the method of measuring adsorption and in the size of the equipment resulted in the development of the“micro BET”apparatus described here. A considerable simplification in the technique of measurement has been attained. The application of the apparatus is demonstrated by examples.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.004

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractEleven powders of widely different properties (various grades of WC, WO3, tungsten, iron, cobalt, SiO2, Al2O3), considered typical of the raw materials encountered in powder metallurgy, have been studied by“single value methods”(apparent and tap density, air permeametry, gas adsorption (BET)) and by“size-distribution methods”(electron- and light microscope sizing, turbidimetry, sedimentation balance (with gaseous and with liquid medium), centrifugal air classification, and sieve analysis). In addition, a series of WC powders having varying degrees of fineness has been studied by air permeametry, gas adsorption, optical reflectivity, turbidimetry, and sedimentation in air, to assess the reliable working ranges of these methods.The following topics are treated in detail: air-permeability measurements and their relation to the results of BET and other tests; electron and light-microscope sizing techniques; turbidimetry; and optical reflectivity. A microscopic study of the breakdown of agglomerates in a tungsten carbide powder is reported. The importance of large agglomerates in all work concerned with particle-size distributions is stressed. For highly agglomerated powders the size distribution of the ultimate units (individual particles within agglomerates) is difficult or impossible to determine, but it is pointed out that this“true”distribution has much less technical significance than that of the agglomerated powder, provided that the degree of agglomeration in which the powder is analysed corresponds to, or can be correlated with, that prevailing in the process for which it is intended.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.005

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe paper surveys the existing routes available for the preparation of beryllium powders, and comments on the effect of certain properties, such as particle-size distribution, on the compaction of powders by different techniques. It is emphasized that particle size, degree of oxidation, and overall purity are interdependent variables, and that little attempt has so far been made to study their effects separately.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.006

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractAn investigation of the powder metallurgy of ruthenium is described, from the reduction of ammonium ruthenium chloride to the working of sintered compacts. The powder properties measured were specific surface area, by a simplified BET method, and tap density. The dependence of these properties on the conditions of reduction has been determined. The surface area of powders varies from 1 to 10 m2/g in the temperature-of-reduction range 700-350°C. The tap density is also variable (1–3 g/c.c.) and is generally related to the surface area. The effects of compacting pressure and temperature on sintering are described, the progress of sintering being observed by measurements of the“open”and“closed”porosity present in samples. Compact densities up to 95% of theoretical can be obtained by sintering at 1500°C. The selection of powder properties and compacting pressures to be used in the production, by vacuum sintering at 1500°C, of high-density compacts for working, is governed by the necessity to maintain open porosity during the heating cycle up to at least 1200°C, as considerable gas evolution occurs at this temperature; at the same time it is essential that good densification shall have occurred even at this stage. These conditions can be met by using powder with a surface area of 2–5 m2/g and compacting pressures in the range 0·5–25 tons/in2.Observations on the hot working of sintered compacts indicate that ease of working is related to the surface area of the powder.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.007

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractExperiments have been carried out to determine the relationship between the properties of tantalum powder and its compressibility, and to examine the effect of carbon and niobium on the hardness and tensile and electrical properties of semi-manufactured products of tantalum. The influence of the particle-size distribution of niobium powder upon the properties of sintered bars has also been studied, with particular reference to the problem of swelling of the bars during sintering.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.008

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractStudies of the sintering of uncompacted uranium powders in vacuum have shown that sintering behaviour is markedly affected by the nature of the surface films on the powder. Of the variables in the powder production route that might affect the nature of the surface films, the leaching stage is the most important.The deleterious effect of surface contaminants on the vacuum-sintering behaviour of beryllium is demonstrated. During the development of a technique for the production of a stable powder from electrolytic flake, the nature of the leaching treatment again proved to have a marked influence on the sintering behaviour of the resultant powder.Both sets of investigations were hampered by lack of methods for identification of surface films on powders.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.009

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractBy the application of several modern techniques, a fairly thorough characterization of even the finest oxide powders with respect to particle and crystallite size and shape may be obtained. The application of these techniques is discussed with particular reference to the characterization of a sample of Mg(OH2) and the oxides prepared from it by calcinationin vacuo. The techniques described are, however, exacting and time consuming and whilst invaluable for any basic study cannot, in general, be considered practicable in routine work. For this reason a final section is devoted to a discussion of attempts to“calibrate”the results from conventional techniques in terms of the more fundamental parameters of powder characterization.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.7.010

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor