PRELIMINARY STUDIES OF THE FABRICATION OF UAl4–Al TEST-PLATES BY POWDER-METALLURGICAL TECHNIQUES

Abstract

The preparation of UAl₄ by induction melting and annealing (720°C, 993 K) yielded a product of restricted UAl₄ content (81 wt.-%). The UAl₄ phase has a variable stoichiometry (UAl_4.0–UAl_4.8), which leads to a slightly modified U–Al phase diagram. UAl₄–Al dispersions can be prepared by powder-metallurgical techniques, resulting in structures with higher UAl₄ content, improved phase-distribution rates, and specific particle sizes, compared with melting techniques. The thermal conductivity and thermal expansion of UAl₄–Al dispersions have been measured over the whole concentration range. No technological difficulties, by comparison with UAl₃-Al plate fabrication, were encountered. The production of UAl₄-Al test plates (33 vol.-% UA1₄ ? 35 wt.-% U) is thus feasible on a laboratory scale. The work reported is the final stage in a series of studies of uranium aluminide-aluminium dispersion fuels obtained by powder routes.     

STUDIES ON THE SINTERING OF MoSi2–Al2O3 CERMETS

Abstract

The porosity of hydrogen-sintered bodies composed of molybdenum disilicide and alumina has been studied as a function of alumina content and grain size. It is found that oxidation-resistant bodies can be made if the grain size of the constituents is ～ 10 μ or less, although the bodies are fairly weak.

In addition, samples were sintered in dissociated ammonia and compared with those sintered in hydrogen. It became apparent that samples sintered in dissociated ammonia underwent a particularly severe form of attack when exposed to air at high temperatures. This is attributed to the formation, during sintering, of Si₃N₄, a phase which decomposes at high temperature in air when enclosed in the cermet bodies.     

THE SUCCESSFUL CONCLUSION OF THE 76 SESSION OF THE CANTON FAIR

The 76 session of the Canton Fair wassuccessfully concluded on the morn-ing of October 30. 1994 in Guangzhou,the provincial capital of GuangdongChina.The Fair lasted 15 days with the atten-dants of 50, 000 man-time, the totalturnover over USD 10 billion.     

THE COMPACTION OF METAL POWDERS BY ROLLING. II.–AN EXAMINATION OF THE COMPACTION PROCESS

Abstract

The compaction process is examined in detail. It is shown that, where particle deformation is concerned, compaction by rolling is similar to compaction by static pressing, with the addition of elongation of the particles in the rolling direction when the rolling pressure is sufficiently high. A method for determining the average roll pressure is described. A comparison of the rolling of a metal powder with the rolling of a solid bar, and the determination of the effect of particle shape and mean size, indicates that not only roll/powder friction but also the slip between particles plays an important role in the compaction process. This leads to an examination of the flow properties of powders, which are measured in terms of a “powder-viscosity factor” that indicates whether and at what order of rolling speed a powder can be coherently compacted. Finally, a mechanism of compaction is proposed on the basis of the present findings and on the authors’ earlier work.     

THE SECOND HALF OF THE YEAR

Production growth in the second half of theyear will continue because of the stimula-tion of prices.Tight supply of concentrateshas appeared domestically due to sharp in-crease of exports.     

THE FABRICATION AND PROPERTIES OF URANIUM OXIDE–IRON CERMETS

Abstract

Cermets of iron–uranium dioxide, containing up to 30 vol.-% UO₂ have been rolled to rod. Although the cores rolled centrally along the length, the core was distorted in section owing to stiffening of the core relative to the sheath as the temperature dropped during rolling. The UO₂ particles were fragmented during rolling and formed as “stringers” along the direction of rolling, seriously weakening the structure transversely.

By extrusion at 1200° C., cermets containing up to 50 vol.-% UO₂ were satisfactorily fabricated. The extrusion pressure increased sharply above 35 vol.-% of ceramic and when large reductions in area were taken. The extrusion characteristics do not conform to isotropic plastic extrusion nor to a pure viscosity effect; the influence of the dispersed particles on metal flow is explained by a strong interference effect between particles and the metal during flow. The properties of the extruded rods were good; the core density was 90–95% of theoretical, decreasing slightly with increasing ceramic content; there were no obvious directional properties in the core, nor was the ceramic fragmented as in rolling. The characteristic “tail-end defect” of the extrusions was partly corrected by using shaped sealing plugs.     

THE PRESENT SITUATION OF THE DEVELOPMENT OF RARE EARTHS IN CHINA

1.Rare Earth Resources in China1.1.Reserves and distributionChina is the country which is the richest in the world in rare earth(RE)resources of allavailable varieties of minerals and their deposits are located in vast areas in China.Reserveshave been estimated at a grand total of 36 million ton,which is 80% of the world(RE)de-posits.The majority of these deposits are concentratedly located in Baiyunebo mine of the     

THE ABSTRACTS OF PAPERS IN THE CHINESE EDITION OF THIS JOURNAL

Synthesis and Crystal Structure of PraseodymiumComplex with Dimethyl Phophaye Ma Aizeng,Li Laiming, Lin Yonghua, Zeng Guangfu, Li Han(Changchun Institute of Applied Chemistry,Academia Sinica,Changchun 130022),1990, 8(3),201. The title complex has been synthesized,which was characterized by elemental analyses.FT-IR spectra of the complex have been studied.The crystal and molecular structure of the complex     

THE FABRICATION AND PROPERTIES OF CHROMIUM–ALUMINA AND MOLYBDENUM–CHROMIUM–ALUMINA CERMETS

Abstract

After a brief review of the literature, various methods for preparing chromium–alumina and molybdenum–chromium–alumina cermets are described. The properties of such materials are discussed and an indication is given of their possible applications.     

THE FOURTEENTH SESSION OF THE CONFERENCE OF MINISTERS OF ATPC (ASSOCIATION OF TIN PRODUCING COUNTRIES)

The Fourteenth Session of the ATPCConference of Ministers was held in Sin-gapore on 23 and 24 September,1996.The Conference considered an overallreview of the ATPC Agreement to reflectthe changing circumstances in the tin in-dustry,agreed that a Sub-Committee be     

THE FIRST EIGHT MONTHS OF THE YEAR

Chinese zinc production growth this year hasbeen the focus of the industry.To the end ofAugust,its production is exceeding 857,000     

Density of Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 molten salt melt for Al–Sm alloy

Samarium (Sm) has been widely used in making aluminum (Al)–Sm magnet alloy materials. The research team for this study developed a molten salt electrolyte system which directly produces Al–Sm alloy to replace the energy intensive conventional distillation technology. In this study, molten melt density was measured and operation conditions were optimized to separate Al–Sm alloy product from the fluoride molten melt electrolysis media based on density differences. Archimedes' principle was applied to measure density for the basic molten fluoride system (BMFS: Na₃AlF₆–AlF₃–LiF–MgF₂) electrolysis media in the temperature range from 905 to 1055 °C. The impact of temperature (t) and the Al₂O₃ and Sm₂O₃ addition ratio (w_(Al2O3), w_(Sm2O3)) in the basic fluoride system on molten melt density was examined. The fluoride molten melt density relationship was determined to be: ρ = 3.11701 ? 0.00802w_(Al2O3) + 0.027825w_(Sm2O3) ? 0.00117t. The test results showed that molten density decreases with increase in temperature and Al₂O₃ addition ratio, and increases with the addition of Sm₂O₃, and/or Al₂O₃ + Sm₂O_3. The separation of Al–Sm (density 2.3 g/cm³) product melt from the BMFS melt is achieved by controlling the BMFS density to less than 2.0 g/cm³. It is concluded that the optimal operation conditions to control the BMFS molten salt density to less than 2.0 g/cm³ are: maintain addition of Al₂O₃ + Sm₂O₃ (w_(Al2O3) + w_(Sm2O3)) < 9% of Na₃AlF₆, Al₂O₃/Sm₂O₃ ratio (w_(Al2O3):w_(Sm2O3)) > 7:3, and temperature between 965 and 995 °C.     

THE EFFECT OF RARE EARTH ELEMENTS ON THE SOLIDIFICATION BEHAVIOR OF Al-Mg ALLOYS

The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in adirectional solidification apparatus.It was found that during the solidification process.the rare earth elementsegregated in the liquid at sold-liquid interface,changed the solidification morphology and reduced thesecondary arm spacing markedly.     

BIBLIOGRAPHY OF SCIENCE AND TECHNOLOGY OF RARE EARTHS PUBLISHED IN CHINA (1988)

Solid State Physics,Solid State Chem-istry and New Materials269 Spectroscopic properties of the Mn~(2 ) dopedCeMgAl_(11)O_(19)-SrAl_(12)O_(19) solid solution,Huang Jinggenet al.,Chinese Journal of Luminescence,1988,9(3),213.270 The energy level splitting of the excited Tb~(3 )4f~75d~1     

BIBLIOGRAPHY OF SCIENCE AND TECHNOLOGY OF RARE EARTHS PUBLISHED IN CHINA(1989)

Geology and Ore Dressing001 A geochemical study of diagnetic andminerogenetic rare earth elements in the LianhuahanW-deposit,Guangdong,Lei Xingong et al.,Geologyand Prospecting,1989,25(3),15.002 The Bayan obo Fe-Nb-REE-deposit:Its basic     

Dissolution rate of Al2O3 into molten CaO–Al2O3–CaF2 flux

Abstract

Dissolution of Al₂O₃ into molten CaO–Al₂O₃–CaF₂, a base system of mould flux for continuous casting of high Al steel, has been investigated by employing a rotating cylinder method. The dissolution rate of an alumina rod into molten CaO–Al₂O₃–CaF₂ flux increased with increase in rotating speed and temperature. The apparent activation energy for mass transport of flux C was calculated to be 255·6 kJ mol^?1. The rate controlling step during the dissolution process of the alumina rod into molten CaO–Al₂O₃–CaF₂ flux was found to be the diffusion of the solute in the flux boundary layer. The dissolution rate of alumina into molten CaO–Al₂O₃–CaF₂ flux increased with increasing CaO/Al₂O₃, and it may be caused by the increase in thermodynamic driving force and the decrease in the viscosity of the flux. When the Al₂O₃ rod was immersed into molten flux, an intermediate compound of CaO.2Al₂O₃ formed firstly and then dissolved into molten flux.     

ANNIVERSARY OF THE JOINT VENTURE

December 18,1994 was the anniversaryof the joint venture company ofNORTH CHINA ALUMINIUM FAB-RICATING PLANT.The production value of 1994 was RMB430.18 million yuan,profit after tax31.25 million yuan,tax 17.65 million     

BIBLIOGRAPHY OF SCIENCE AND TECHNOLOGY OF RARE EARTHS PUBLISHED IN CHINA(1989)

Chemistry and Hydrometallurgy084 SPeetroseopie ProPerties of CeMn、Mg一xAll一O一9,Yu Xinghai er al Journal of Fudan Universiry(NaturalSeienee),1989,28(3),310.085 Investigation of oxidation of phenanthrene(111)toPrePare diphenie aeid by PTC一Ru04一NaCIO nl     

SOME RELATIONS BETWEEN THE STRUCTURE AND MECHANICAL PROPERTIES OF WC–TiC–Co ALLOYS

Abstract

The relationship between the mechanical properties and the structure of the sintered carbide WC–TiC–Co has been studied. Specimens containing 7 and 15% cobalt were sintered at temperatures between 1350 and 1550°C (1625 and 1825 K), for times varying from to 32 h. The structure was examined by electron. microscopy. Density, coercive force, hardnesss, transverse rupture strength, and energy of crack initiation were determined.

The rate of grain growth is governed by the rate at which the carbide dissolves in the cobalt phase. The activation energy for growth was found to be 120 ± 15 kcal/mol (500 ± 63 kJ/mol).

The coercive force is a linear function of the specific grain surface rather than of the specific cobalt surface. The hardness of alloys with different cobalt contents is a function of a single structure parameter [(1– f_β)/f_β]S_γγ, where f_β is the volume fraction of β phase and S_γγ is the specific grain-boundary surface.

It has been suggested that transverse rupture strength should vary as the square root of the specific grain surface. The present results tend to confirm this suggestion. The energy of crack initiation is highly dependent on the contiguity of the carbide phase.