Beryllium Extraction and Utilisation— Prospects and Constraints

Beryllium and beryllium compounds find wide variety of applications in diverse industries. Low density, high strength, and attractive nuclear properties like low neutron absorption cross section and high scattering cross section have created great interest in the metal for space, aeronautical, and nuclear applications. The extraction technology of beryllium is now fairly well established and significant progress has also been made in the powder metallurgy fabrication of the metal. Conventional fabrication methods like rolling, wire drawing, extrusion etc. have not been found quite suitable for beryllium because of its low ductility.

This paper presents an overview of the extraction processes and the fabrication methods presently employed for beryllium metal and alloys. The various applications are described and the prospects and constraints in the large scale utilization of beryllium in industry are analysed.     

THE INFLUENCE OF SILICON AND OTHER ELEMENTS IN CONTROLLING INTERPARTICLE FRICTION AND SINTERING OF BERYLLIUM POWDER

Abstract

The effect of small additions of activating elements such as silicon on the consolidation behaviour of beryllium powder has been investigated. Evidence is given that compacts of activated powder have more uniform high density than those produced from non-activated material. Studies carried out on prepared beryllium discs show that silicon modifies the micro-structure of the surface layer of beryllium oxide and, in consequence, affects its sliding behaviour and bonding characteristics.

From these results a model is proposed to account for the observations made on both sintered and hot-pressed beryllium which leads to the conclusion that, in addition to interparticle bonding, some measure of metal particle rearrangement is necessary for maximum densification. Activating elements may, in modifying the surface characteristics of the individual powder particles, assist in achieving an improved balance between particle sliding on the one hand and interparticle bonding on the other. In taking into account the bulk consolidation characteristics as well as the micromechanics of the process, the model also explains the observed influence of particle-size distribution on porosity in the compact.

The extent to which friction and sliding can influence compaction has been demonstrated by using a system of coloured Plasticine balls to simulate individual powder particles. Analysis of the behaviour of the Plasticine compacts substantiates the proposed model of the hot pressing of beryllium powder.     

Extractive Metallurgy of Beryllium

A comprehensive review of the extractive metallurgy of beryllium is presented. Due to the strategic importance and element of secrecy surrounding the metal, any open literature on beryllium is rather limited. However, this review has been made to cover all important aspects of beryllium extraction technology namely, resources of the metal; processing of ores; reduction of fluoride and oxide to get metal and alloy; refining of the metal; post preparation processes to shape metal through powder metallurgical route and preparation of foils and ceramics. Special attention has been given to the topic of toxicology and pollution control. Recycling of beryllium will form the concluding section. Information on the removal of impurities during the preparation of intermediate products as well as during reduction to metal and its alloys are described with process principles. Thus this review, with the help of discussion on each unit process and at the same time emphasising on the problems faced in large scale handling of this toxic metal and its compounds, shall provide substantial information presently available on the extractive metallurgy of beryllium.     

Extractive Metallurgy of Beryllium

Abstract

A comprehensive review of the extractive metallurgy of beryllium is presented. Due to the strategic importance and element of secrecy surrounding the metal, any open literature on beryllium is rather limited. However, this review has been made to cover all important aspects of beryllium extraction technology namely, resources of the metal; processing of ores; reduction of fluoride and oxide to get metal and alloy; refining of the metal; post preparation processes to shape metal through powder metallurgical route and preparation of foils and ceramics. Special attention has been given to the topic of toxicology and pollution control. Recyclfng of beryllium will form the concluding section. Information on the removal of impurities during the preparation of intermediate products as well as during reduction to metal and its alloys are described with process principles. Thus this review, with the help of discussion on each unit process and at the same time emphasising on the problems faced in large scale handling of this toxic metal and its compounds, shall provide substantial information presently available on the extractive metallurgy of beryllium.     

Hydrometallurgy of Beryllium in the Indian Perspective

Hydrometallurgy is the major part in the extraction flow sheet of beryllium from beryl ore. The overall process aims at converting the beryllium values of the ore into ammonium beryllium fluoride which, on thermal decomposition, yields anhydrous beryllium fluoride—a common intermediate for the production of beryllium metal and its master alloys.

This paper gives the details of the individual steps and discusses the processes developed to standardize the production of ammonium beryllium fluoride from Indian beryl. It also highlights the safety measures adopted and the waste management practice followed during the production of this double fluoride.     

Glass formation and nanocrystallization in Zr based alloys

In the present paper bulk glass forming behaviour of some of Zr based Ni, Cu, Al and Ti bearing alloys has been investigated. Examination of the as solidified microstructure of these alloys in the partially crystalline state has shown that the predominance presence of the Zr₂Ni or its derivatives phases as the phases competing with glass formation whereas in the fully amorphous microstructure, quenched-in nuclei and the atomic short range order existing in the amorphous phase were observed. The aim of the microstructural examinations of the fully amorphous phase was to ascertain the nature and morphology of the quench-in nuclei. In the partially crystalline microstructures, study of the crystalline phases competing with glass formation has helped in better understanding of the solidification process during BMG formation. The kinetics of crystallization of the as solidified Zr based bulk metallic glasses were studied by differential scanning calorimetry (DSC) and crystallized microstructures were examined by conventional and high-resolution electron microscopy. The activation energies of crystallization and the Avrami exponent have been evaluated. The Avrami exponent values have been rationalized in terms of the observed nucleation and growth behaviour of the phases forming on crystallisation. Conditions of crystallization leading to the formation of nanocrystals have been identified.     

Beryllium Extraction—A Review

This paper reviews the current status of beryllium process metallurgy. Emphasis is laid on the extraction of beryllium metal from beryl ore. The resource position, demand and application of the metal and its alloys are also summarised.     

Electrolytic Extraction of Beryllium

Beryllium possesses certain unique mechanical and physical properties which make it a special engineering material and an important alloy addition. However, its low density, high reactivity and high melting point along with its occurrence in the form of a very stable beryl ore—containing only about five percent beryllium—make its extraction difficult. The electrowinning of beryllium from molten beryllium and sodium chloride salt-mix is a low temperature commercial process. Conversion of beryl ore into beryllia precedes the fused salt electrolysis and several purification techniques are followed to produce high purity beryllium metal. This paper reviews the existing major industrial processes for beryllium production. A modified beryllium chloride-beryllium fluoride fused salt electrolysis is suggested on similar principles but with added advantage of a semi-continuous high efficiency process. The electrode reactions for this salt system have been analysed on the basis of reaction rate theory and the influence of operating parameters, such as the temperature, electrode areas, current density, etc., on the cell potential has been identified. A possible basic cell design has also been proposed.     

Powder metallurgy of beryllium: The developments of the national scientific center “Khar’kov physicotechnical institute”

For the first time in the production of construction beryllium an integrated technology for the production of a new generation of high-purity isotropic materials has been developed and mastered. The technology combines processes of vacuum distillation of the metal, gas flow atomization of a melt, specialized processing of the powder prior to densification and hot isostatic pressing. A technology for the production of spherical powders of beryllium and beryllium-based alloys by atomization of a melt is also developed and employed for the first time. A technology is developed and optimal conditions of isostatic pressing of spherical powders are determined. Isotropic beryllium with high physico-mechanical characteristics is obtained. The properties of the materials thus obtained are studied. The strength of the new materials is 20%, and their plasticity two to three times greater, than commercial beryllium. It is shown that the high purity of the initial powder, the cellular structure, uniform distribution, and dispersity of the particles of beryllium oxide and segregations of secondary phases are the principal factors that govern the level of the properties of compact beryllium materials. __________ Translated from Poroshkaya Metallurgiya,Nos. 3–4(448), pp. 118–125, March—April, 2006.     

Role of Nanostructure in Electrochemical Corrosion and High Temperature Oxidation: A Review

The extremely fine grain size of nanocrystalline (nc) metallic alloys results in significantly different mechanical, electrochemical and oxidation properties as compared to the coarse-grained alloys of the same composition. Although the synthesis and attractive mechanical properties of nanocrystalline materials have been investigated and reviewed in great depth, the high temperature oxidation and electrochemical corrosion of these materials has received limited attention. The difference in the active dissolution and passivation behavior of nc alloys as compared to their microcrystalline counterparts varies for each alloy system. However, a unified theory explaining these phenomena still eludes us. In this context, this article reviews the progress in the electrochemical corrosion behavior of different nanocrystalline alloys, and hence, develops a better understanding of the effect of grain size, composition, interfacial phenomena and selective dissolution on corrosion of nanocrystalline alloys. This review also presents the role of nanometric grain size and the associated increase in grain boundary diffusion on the high temperature oxidation of nc alloys. The attractive possibility of enhanced oxidation resistance at lower alloying additions as compared to the coarse-grained alloys has been discussed. Although the primary focus of the article is on ferrous alloy systems, however, the lead studies on the role of ultrafine grain size in oxidation/corrosion behavior of other alloys systems have also been reviewed.     

Slip Transfer Across Hetero-Interfaces in Two-Phase Titanium Aluminum Intermetallics

The role of slip transfer processes across the heterophase interfaces in two-phase TiAl intermetallics has been studied. Polysynthetically twinned (PST) crystals of TiAl (PST-TiAl) have been used as model systems for individual grains in technologically relevant polycrystalline lamellar TiAl alloys. Compressive plastic loads have been applied for orientations of the lamellar interfaces parallel and perpendicular to the loading directions to produce hard mode slip activity in both the γ and the α ₂ phases. Transmission electron microscopy has been used to determine the active deformation modes in the constituent phases and to study details of the hard mode of the slip transfer across heterophase interfaces. The results are discussed with respect to the mechanical behavior of PST-TiAl.     

Applications of Beryllium and Its Alloys

Whereas the beryllium metal is an ideal choice for many applications in nuclear and space technology, its alloys with copper, aluminium, nickel, titanium, oxide and beryllides are equally important and find numerous applications not only in hightech areas, but also in various other fields. This paper presents an appraisal of these uses of beryllium.     

The welding metallurgy of HASTELLOY alloys C-4, C-22, and C-276

The welding metallurgy (solidification and solid state transformations) of HASTELLOY* Alloys C-4, C-22, and C-276 has been determined. Varestraint hot-cracking tests performed on commercial alloys revealed a weldability ranking as follows: C-4 > C-22 > C-276. All alloys would be expected to have good weldability, with Alloy C-4 having a very low hot-cracking tendency, comparable to 304L stainless steel. Microstructures of gas-tungsten-arc welds of these alloys have been characterized by scanning electron microscopy and analytical electron microscopy. Intermetallic secondary solidification constituents have been found associated with weld metal hot cracks in Alloys C-276 and C-22. In Alloy C-276, this constituent is a combination ofP and ώ phases, and in Alloy C-22, this constituent is composed of σ,P, and ώ phases. With phase composition data obtained by AEM techniques and available ternary (Ni-Cr-Mo) phase diagrams, an equivalent chemistry model is proposed to account for the microstructures observed in each alloy's weld metal.     

Nucleation-controlled microstructures and anomalous eutectic formation in undercooled Co-Sn and Ni-Si eutectic melts

Co-20.5 at. pct Sn and Ni-21.4 at. pct Si eutectic alloys have been levitated and undercooled in an electromagnetic levitator (EML) and then solidified spontaneously at different undercoolings. The original surface and cross-sectional morphologies of these solidified samples consist of separate eutectic colonies regardless of melt undercooling, indicating that microstructures in the free solidification of the eutectic systems are nucleation controlled. Regular lamellae always grow from the periphery of an independent anomalous eutectic grain in each eutectic colony. This typical morphology shows that the basic unit should be a single eutectic colony, when discussing the solidification behavior. Special emphasis is focused on the anomalous eutectic formation after a significant difference in linear kinetic coefficients is recognized for terminal eutectic phases, in particular when a eutectic reaction contains a nonfaceted disordered solid solution and a faceted ordered intermetallic compound as the terminal eutectic phases. It is this remarkable difference in the linear kinetic coefficients that leads to a pronounced difference in kinetic undercoolings. The sluggish kinetics in the interface atomic attachment of the intermetallic compound originates the occurrence of the decoupled growth of two eutectic phases. Hence, the current eutectic models are modified to incorporate kinetic undercooling, in order to account for the competitive growth behavior of eutectic phases in a single eutectic colony. The critical condition for generating the decoupled growth of eutectic phases is proposed. Further analysis reveals that a dimensionless critical undercooling may be appropriate to show the tendency for the anomalous eutectic-forming ability when considering the difference in linear kinetic coefficients of terminal eutectic phases. This qualitative criterion, albeit crude with several approximations and assumptions, can elucidate most of the published experimental results with the correct order of magnitude. Solidification modes in some eutectic alloys are predicted on the basis of the present criterion. Future work that may result in some probable errors is briefly directed to improve the model.     

The mechanisms of grain refinement in dilute aluminum alloys

The contribution of the peritectic reaction in producing grain refinement in aluminum alloys has been studied in three binary aluminum systems. It appears that titanium has a unique effect compared with zirconium or chromium; there is evidence of a refinement mechanism associated with the peritectic reaction in Al?Ti alloys which was not observed in the other two systems. Additions of boron to Al?Ti and Al?Zr alloys emphasizes the difference in effect of these two transition elements as grain refiners. The significance of the present work is discussed with reference to conflicts apparent in earlier experimental data.     

铍铝合金室温拉伸及原位疲劳失效分析

通过室温拉伸试验和SEM原位疲劳测试,研究了金属型复合材料铍铝合金的拉伸性能及拉伸和原位疲劳的断裂机制.结果表明,合金在室温下具有较好的拉伸性能,且对应变速率有明显的敏感性.拉伸断裂是由脆性铍相的解理断裂和韧性铝相的延性断裂构成的混合型断裂.在拉拉疲劳载荷下,疲劳裂纹萌生于铍相颗粒,断裂模式仍由铍相的解理断裂和铝相的韧性断裂组成.     

Grain Refinement of Magnesium Alloys: A Review of Recent Research, Theoretical Developments, and Their Application

This paper builds on the “Grain Refinement of Mg Alloys” published in 2005 and reviews the grain refinement research on Mg alloys that has been undertaken since then with an emphasis on the theoretical and analytical methods that have been developed. Consideration of recent research results and current theoretical knowledge has highlighted two important factors that affect an alloy’s as-cast grain size. The first factor applies to commercial Mg-Al alloys where it is concluded that impurity and minor elements such as Fe and Mn have a substantially negative impact on grain size because, in combination with Al, intermetallic phases can be formed that tend to poison the more potent native or deliberately added nucleant particles present in the melt. This factor appears to explain the contradictory experimental outcomes reported in the literature and suggests that the search for a more potent and reliable grain refining technology may need to take a different approach. The second factor applies to all alloys and is related to the role of constitutional supercooling which, on the one hand, promotes grain nucleation and, on the other hand, forms a nucleation-free zone preventing further nucleation within this zone, consequently limiting the grain refinement achievable, particularly in low solute-containing alloys. Strategies to reduce the negative impact of these two factors are discussed. Further, the Interdependence model has been shown to apply to a broad range of casting methods from slow cooling gravity die casting to fast cooling high pressure die casting and dynamic methods such as ultrasonic treatment.     

惯性器件用铍材微屈服强度的研究

介绍了惯性器件用铍材微屈服强度（ＭＹＳ）的研究概况、测试方法,讨论了晶粒尺寸、杂质（主要是ＢｅＯ）、热处理与微合金化等对铍材ＭＹＳ的影响。结果表明,采用粒径细小低氧化铍的冲击研磨粉末和等静压固结工艺是获得高ＭＹＳ铍材的重要途径。     

美国铍工业概况

本文介绍了美国铍工业矿藏资源和储量的分布以及主要厂家的生产现状。详细叙述了金属铍、铍铜合金、铍合金以及氧化铍在各方面的用途。最后分析和预测了２０００年美国铍工业的市场供需情况。     

RECENT DEVELOPMENTS IN THE FIELD OF SILICIDES AND BORIDES OF THE HIGH-MELTING-POINT TRANSITION METALS

Abstract

The binary systems of silicides of the high-melting-point transition metals are now well understood, except for the hafnium-silicon system. Research since 1954 is reviewed, with particular reference to the compound Me₅Si₃ and its position in the silicide systems. Reference is also made to the pseudo-binary and pseudo-ternary silicide systems.

The structures of many of the intermetallic phases in the binary boride systems have now been determined, but complete equilibrium diagrams still remain to be established in some cases. New tentative diagrams are given for the systems vanadium–boron, niobium–boron, and tantalum–boron, and structures are suggested for the borides V₃B₂, Nb₃B₂, and Ta₃B₂ with the T2 structure (isostructural with U₃Si₂).

Ternary alloys of the systems Me–Si–B are of great interest, not only structurally but also for practical reasons. The complete systems Me–Si–B of Group VI (Mo–Si–B and W–Si–B) have accordingly been studied by X-ray, thermal-analysis, and micrographic methods. The system Cr–Si–B has been determined and attention is directed to the possible commercial applications of certain alloys containing additions of metals of the iron group, in particular nickel, for sprayed coatings resistant to liquid aluminium.

The question of cementing silicides and borides with metals and alloys is discussed theoretically. The character of the silicide or boride system in question and the behaviour of the intermediate phase in relation to the bonding material are of decisive importance for the selection of the latter. Only very limited data are to be found in the literature on the behaviour of silicides and borides in relation to metals and alloys. Alloys based on TiB₂, ZrB₂, MoSi₂, and WSi₂, impregnated with numerous metals and alloys, have been prepared. Their structures have been studied and the technical suitability of various combinations is discussed on the basis of their technological properties.