DETERMINATION OF THE PHASE BOUNDARY OF AI-Mg-Y ALLOY EQUILIBRIUM DIAGRAM IN THE Al-RICH CORNER BY X-RAY METHOD

The alloys based on Al一Mg are very useful in industry.Reeently,suitable rar十earthelements are usually added into them to imProve the Proeessibility and strength.In.Particu-lar,a small amount of Y addition can improve the alloy,5 strength at elevated temPeraturenotably.Determination of the Phase diagram of AI一Mg一Y alloy system 15 imPortant.Inthis work,the Phase boundary of AI一Mg alloys eontaining 0.1 and 0.2wt%of Y in theAI一rich eorner has been determined by the lattiee Parameter…     

THERMODYNAMIC OPTIMIZATION AND CALCULATION OF THE Fe-Pr SYSTEM

Based on the phase diagram of the Fe-Pr system available,the thermodynamic optimization and calcula-tion of the system have been carried out by the least square method.The lattice stabilities of Fe and Pr aredescribed by the expression recommended by SGTE organization.The liquid phase is described by thesubregular solution model.The intermetallic compounds,Fe_(17)Pr_2 and Fe_2Pr,are treated as stoichiometriccompounds.The optimized parameters describing phases in the system are presented.The comparision be-tween the calculated and experimentally determined phase diagram shows that the agreement is generally verygood except for the liquid δ-Fe equilibrium.It is suggested to measure this part of phase diagram again.     

ASSESSMENT AND OPTIMIZATION OF THE PHASE DIAGRAMS AND THERMODYNAMIC DATA OF SOME BINARY SYSTEMS CONTAINING PRASEODYMIUM CHLORIDES

In this paper a critical assessment and optimization of the phase diagrams and thermodynamic propertiesof the PrCl_3-MCl(M=Li,Na)and PrCl_3-MCl_2(M=Mg,Ca,Sr,Ba) binary systems have been per-formed.The assessed and optimized binary phase diagrams and thermodynamic data with self consistency area better basis for constructing multicomponent phase diagrams.     

STUDIES OF THE BINDER PHASE IN WC-Co CEMENTED CARBIDES HEAT-TREATED AT 650°C

Abstract

The binder phase of WC-Co cemented carbide is a Co-rich alloy in which tungsten and carbon are in solid solution. The binder phase is supersaturated with respect to tungsten even after slow cooling from the sintering temperature. In this study the binder phase contained 6% W in solid solution before heat-treatment at 650°C (923 K). Transmission electron microscopy on thin foils of binder phase showed that a finely dispersed. phase, α′, precipitated in the cubic binder phase. After long ageing times Co₃W could be identified by X-ray diffraction methods. As no discontinuous , ‘cells’ of Co₃W and ?-Co could be observed, the following reaction is suggested.

α-Co(W, C)→α-Co+α′→α-Co (C)+Co₃W (needles)

The precipitation of α′ was accompanied by an increase in hardness and a decrease in transverse rupture strength. The effects observed are consistent with those found during annealing of Co-rich cobalt-tungsten-carbon alloys (> 85% Co).     

THE EXTRACTION EQUILIBRIUM MODEL AND SIMULATION OF COUNTERCURRENT SOLVENT EXTRACTION OF Gd-Tb-Dy-HCl-HEH(EHP)-KEROSENE SYSTEM

The extraction equilibrium mathematic models for gadolinium,terbium and dysprosium in HCl-1.5mol/L HEH(EHP)system covering a relatively wide range of lanthanide concentration and acidity,havebeen developed.There are four independent variables and nine parameters.The average relative error is4.56%.A computer program for the simulation of the counter current solvent extraetion process has also beenwritten.Thus,the Gd,Tb and Dy concentrations in both aqueous and organic phase in eaeh stage as well asthe aqueous acidity may be calculated.Product purities,distribution ratio and extraction factors may also beobtained thereby.The simulation results so obtained may serve as the referenee data for designing solvent ex-traction processes including those processes providing apart from the conventional outgoing organic stream,outgoing raffinate and an extra outgoing third exit stream either organic or aqueous.     

THE OXIDATION OF HOT-PRESSED TITANIUM CARBIDE AND TITANIUM BORIDE IN THE TEMPERATURE RANGE 300°–1000° C.

Abstract

The oxidation characteristics of pure hot-pressed titanium carbide and titanium boride (TiB₂) have been studied in the range 300°–1000° C.

Titanium carbide shows a very marked peak in the rate of oxidation at ～450° C., the oxidation product at this temperature being anatase (TiO₂) which is powdery and non-adherent; the oxidation thus follows a linear law. Above ～700° C. the rate increases rapidly again and is approximately parabolic. The scale in this case consists of a dense crystalline film of rutile.

The oxidation of the boride is less rapid than that of the carbide over the whole temperature range but it, too, shows a slight peak at 450° C. The oxidation tends to be parabolic at higher temperatures. The nature of the oxidation products has not been determined.     

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.     

AN INTEGRATED PROCESS FOR THE RECOVERY OF TUNGSTEN AND TIN FROM A COMBINED WOLFRAMITE–SCHEELITE–CASSITERITE CONCENTRATE

This article presents results of the studies on development of viable process route for quantitative recovery of tungsten and tin values occurring together in the form of a multimineral concentrate of wolframite, scheelite, and cassiterite. The investigations were carried out using a tin–tungsten multimineral ore from Kyrgyzstan (Central Asia). Tungsten minerals in this ore occur both as distinct liberated mineral phases and as composites, viz. ultrafine dissemination of wolframite in scheelite and vice versa. Cassiterite also has similar characteristics, albeit to a lesser extent, with few grains containing ex-solution intergrowth of columbite/tantalite and very fine dissemination of tungsten minerals in its lattice. The complex nature of occurrence of both tungsten and tin minerals necessitated an integrated process comprising physical beneficiation and chemical extraction. The process route that was developed gave a tungsten and tin recovery of about 80 and 90%, respectively, on treating a primary gravity preconcentrate analyzing 16.5% WO₃ and 25.7% Sn.     

INFLUENCE OF LANTHANUM ON THE STRUCTURE AND MECHANICAL PROPERTIES OF ALUMINUMSILICON EUTECTIC ALLOY

This paper deals with the characteristics of silicon modification with lanthanum of Al-Si eutectic alloy insand mold and metal mold with optical microscopy,scanning electron microscopy,electron microprobe andX-ray diffractometer.It is found that the amount of lanthanum,liquid alloy condition,holding time and stir-ring liquid influence the modification of silicon.The modification of silicon with lanthanum is of longeffectiveness and has a“incubation time”.The modification can improve the ductility(δ_s)and tensile strength(σ_b)of the alloy,but their maximum values are not corresponding to the same amount of lanthanum.     

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.     

CONSIDERATION AND SUGGESTIONS TO GUARANTEE THE STABLE DEVELOPMENT OF CHINA'S LEAD AND ZINC INDUSTRY

The above mentioned problems can onlybe solved by changing the way in thedevelopment of lead and zinc,i.e.totransform the developing of the industryby expanding capacities into integratingdevelopment:     

THE PRESENT STATE AND DEVELOPMENT TREND OF CHINA'S COPPER INDUSTRY

China spent RMB 11,880 million yuan inaccumulated investment in its copper in-dustry in the period of 1949 to 1995,accounting for 22.3 per cent of her totalinvestments to its nonferrous metals in-dustry in the same period.As a result,China now has 99 copper mines exclusiveof collective-owned,6 complexes,17smelters,67 refineries,and more than500 fabricating plants.     

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.     

TECHNIQUES FOR THE EVALUATION OF POWDERS. I.—FUNDAMENTAL PROPERTIES OF PARTICLES AND METHODS OF SIZING ANALYSIS

Abstract

The 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.     

EFFECTS OF RARE EARTH ELEMENTS ON THE CHARACTERISTICS OF AUTO-TEMPERING AND DECOMPOSITION OF MARTENSITE FOR A LOW CARBON Si-Mn-V STEELS

The effect of rare earth metals(REM)on the characteristics of auto-tempering and decomposition ofmartensite for low-carbon and low-alloy steels(20SiMn2V and 20SiMn2VRE)was investigated usingTEM,dilatometer and microhardness test.Results show that both ε.and θ carbides,during auto-tempering,may precipitate from the low-carbon martensite matrix at the same time in the 20SiMn2V steel,however,theprecipitation of the ε-carbides can be inhibited by the REM contained in the 20SiMn2 VRE steel,resulting inchange of the type of precipitated carbides and decrease of the extent of auto-tempering.The“in-situ”ob-servations show that the decomposition of martensite is also inhibited by the REM contained in the20SiMn2 VRE steel during low temperature tempering.     

STUDY ON THE SEPARATION AND EXTRACTION MECHANISM OF RARE EARTH ELEMENTS BY MEANS OF REVERSED-PHASE PAPER CHROMATOGRAPHY

Reversed-phase paper chromatography technique is used for study on the extraction mechanism and sep-aration of rare earth elements.As the stationary phase,chromatographic paper strips are impregnated with asolution of monomyristyl phosphoric acid (MPA) in chloroform.Mineral acids are used as developers.The effect of concentration of acids and/or salts upon R_f has been investigated.According to the re-sults of R_f values for a given rare earth element in various acids,the order of extraction ability isHCl>HNO_3>H_2SO_4.A tetrad effect is clearly observed.for the R_f value of rare earth elements.Theeffects of other parameters on the R_f value,such as the quantities of extractant retained by the paper and thetemperature are also examined.Based on the determination of the molar ratio of MPA to rare earth elementsand the number of H~ ions released in extraction reaction,a reasonable mechanism is proposed.The mutualseparation of heavy rare earth elements will be better than that of the light rare earth group because of thelarger separation coefficient of the former.A mixture of Ho-Er-Tm-Lu is successfully separated by thepresent method.     

RESEARCH ON THE APPLICATION OF RARE EARTHS IN IRON AND STEEL IN RECENT YEARS

China has the biggest rare earths resource in the world,no wonder she pays much at-tention to the application of rare earth metals (REM).The application of REM in iron andsteel in China began at the end of 1950's.The production of REM-treated iron and steelhad been made steady progress in the period of 1980's.The production of REM-treatediron and steel in 1989 was 1.4 million tons and 250,000 tons respectively.The interest oftreating steel with REM in China keeps growing even in these years,It comes from the nat-     

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.     

SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

In this paper,the influence of crystal-field on the Luminescence properties of Eu~(2 ) in complex oxidesare studied theoretically by using purely electrostatic model,the dependence of the 4f~65d levels on Eu-Obond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f~65d energy band incubic or in octahedral fields will be inversely proportional to R~5,where R is the distance of Eu~(2 ) to oxygenligand.The value of R affects slightly the location of the centre of 4f~65d energy band.According to the exper-imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites ofEu~(2 ) and degree of covalency of Eu-O bond on luminescence properties of Eu~(2 ).Some regularity offluorescence spectrum was observed.In alkali-alkaline earth-phosphates,the splitting extent of 4f~65d band (△E) becomes smaller as theEu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emissionpeak of Eu~(2 ) will shift to shorter wavelength with the increase of x's value.The crystal structure data show that Eu~(2 ) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-fieldand covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu~(2 ) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu~(2 )produces ultraviolet fluorescence.