Georges J. Kipouros

A thermochemical analysis of the production of anhydrous MgCl2

Abstract The electrolytic production of magnesium requires high-purity, anhydrous magnesium chloride which has a high affinity for water and is found in nature as a plurality of hydrates (MgCl2·nH2O, n=1, 2, 4, 6, 8, 12). Their dehydration is nontrivial and can be accompanied by hydrolysis leading to the production of undesirable oxycompounds of magnesium. Through an analysis of the relevant thermochemistry this paper indicates how to prevent hydrolysis and make electrolytic-grade, anhydrous MgCl2.

Electrorefining of Zirconium Metal in Alkali Chloride and Alkali Fluoride Fused Electrolytes

The electrorefining of zirconium metal in alkali halide melts has been investigated. Variables affecting the electrodeposition process such as the composition of the electrolyte, the current density, and the configuration of the electrodes were studied. Two types of electrolytes were used: the alkali chloride-rich and the alkali fluoride-rich electrolytes. The various electrolytes are considered in terms of their ability to complex the soluble zirconium ions, a property which is important for the electrodeposition of coherent metal deposits from these melts. Crystalline zirconium metal of good quality has been obtained from fluoride melts containing NaF, LiF, and either ZrF/sub 4/ or K/sub 2/ZrCl/sub 6/ at about 750/sup 0/C.

On enhancing the mechanical properties of aluminum P/M alloys

Abstract Sintered aluminum alloys are an attractive material for the automobile industry, both because of the low specific gravity and high strength-to-weight ratio of aluminum itself, and the fabrication advantages associated with a powder metallurgy process. However, properties such as impact, stiffness, corrosion and wear resistance are often poor, thereby restricting the widespread use of these materials. Recent work by the authors has shown that hardness, wear resistance and tensile properties of a P/M Al–Cu–Mg ternary master alloy can be improved using a novel diffusion/supersolidus liquid phase sintering process. Improvements were due to in-situ microalloying during sintering, in particular, the influence of Ag and Sn. To complement this work, the present investigation addresses the response of a commercial alloy, AA2014, to the microalloying process. Results show that sintered densities for the commercial alloy were relatively unaffected by the presence of either Ag or Sn, and were superior to the ternary master alloy. Hardness and tensile properties were also improved relative to those obtained for the ternary, and were comparable to wrought 2014. Examination of final microstructure of Ag modified AA2014 using TEM showed the presence of Ω as the principal precipitate, but only after extended sintering times. This particular precipitate is believed to contribute to enhanced hardness. The apparent absence of Ω for short sintering times was due to the presence of silicon in the commercial product. However, the corrosion behavior of the P/M AA2014 was superior to the wrought product and thus the process is presented as a potential P/M alternative to using ingot metallurgy techniques for microalloying.

Electrolytic Regeneration of the Neodymium Oxide Reduction‐Spent Salt

On etudie la regeneration de sels residuaires par decomposition electrolytique de CaO dissous dans du sel fondu CaCl 2 -CaF 2 entre une anode de graphite et une cathode sous forme de bain fondu de Ca-Zn

Development of a thermal barrier material using combustion synthesis

Abstract The present investigation employs combustion synthesis as a method to produce a functionally graded Ni 3 Al/Al 2 O 3 +TiB 2 composite material for use as a thermal barrier system for nickel-based alloys at elevated temperatures. Starting materials were Ni, Al, TiO 2 and B 2 O 3 in powder form. Adiabatic thermodynamic calculations used to determine the maximum theoretical temperature reached during combustion suggest that up to 1600 K may be reached in the Ni+Al metallic layer, easily sufficient to initiate the ceramic-based reaction. The latter reaction is predicted to reach 3000 K. Experiments were first conducted in an induction furnace to establish conditions necessary for combustion to occur. Subsequent experimentation, with applied pressure during combustion, was conducted in a Gleeble 1500 thermomechanical test unit modified to accept the samples of interest. Characterisation of the combustion products by means of hardness measurements, X-ray diffraction, scanning electron microscopy and electron probe microanalysis confirmed that the products were Ni 3 Al and Al 2 O 3 +TiB 2 . Also, the mechanical integrity was unchanged after 10 thermal cycles in the modified Gleeble unit. Finally, the coating thickness required to keep a Ni-based substrate below 850°C in a 1100°C environment is estimated to be 1.8 mm, based on thermal conductivity calculations using a finite element method.

Characterization of neodymium trichloride hydrates and neodymium hydroxychloride

Abstract Neodymium trichloride hexahydrate (NdCl3 · 6H2O) was dehydrated by heating it in either air, argon, HCl or argon-HCl mixtures to germinate the intermediate species. The hexahydrate (NdCl3 · 6H2O) was found to decompose to pentahydrate (NdCl3 · 5H2O) which in turn decomposed to tetrahydrate (NdCl3 · 4H2O). The latter decomposed to monohydrate (NdCl3 · H2O) as the dehydration proceeded towards anhydrous NdCl3. Simultaneously to dehydration, formation of neodymium oxychloride (NdOCl) and neodymium hydroxychloride (Nd(OH)2Cl) took place. Nd(OH)2Cl was isolated and characterized by X-ray diffraction. Its decomposition temperature was determined to be 376°C by differential thermal analysis. Its heat of decomposition to NdOCl and H2O was determined by differential scanning calorimetry to be 23479 cal mol−1 (98283 J mol−1). Its density was found to be 4.596 g cm−3 at 25 °C.

The electrodeposition of improved molybdenum coatings from molten salts by the use of electrolyte additives

The electrodeposition of molybdenum from molten chlorides has been investigated in two electrolyte systems: KCl−K3MoCl6 at a temperature of 800°C and LiCl−KCl−K3MoCl6 at a temperature of 400°C. With the goal of improving the surface quality of the deposits, a search was conducted for electrolyte additives that would act as leveling agents. Activated alumina proved beneficial for deposits produced in the high temperature melt but had little or no effect on deposits generated at low temperatures. Molybdenum disulfide adversely affected the deposits by promoting the growth of surface irregularities.

On enhancing the interfacial chemistry of a simulated AA2014-SiCp composite material

The use of aluminum alloys in automotive applications has increased significantly in recent years due to the need for more fuel-efficient vehicles. These alloys alone do not enjoy the strength offered by traditional ferrous products. However, the development of new alloys through micro/macroalloying and the incorporation of load-bearing materials such as SiC into the matrix have enhanced their popularity. Unfortunately metal matrix composites such as AA2014-SiC often fail catastrophically due to fibre or particulate pullout in service. Such failures are difficult to predict and are often a result of poor wetting at the metal/reinforcement interface. In the present work Sn and Ni were examined as potential sintering/wetting aids. In particular, Sn or Ni (0.5–2 w%) were added to a simulated AA2014 alloy (Al-4Cu-0.5Mg) with and without 14.5 w% SiC following standard powder metallurgy techniques. Because the distribution of blend constituents is of critical importance various dispersants were evaluated. Best particle dispersion was obtained using oleic acid while mixing for 8 h. Sintering temperatures ranged from 605–620°C and both green and final densities were determined using mercury densitometry. Resulting microstructures were examined using scanning electron microscopy and electron probe microanalysis with particular attention directed to the SiC-alloy interface. Nickel was found to enhance the wetting of SiC by AA2014 and the interfacial region was found to be chemically superior to a commercial copper-coated SiC product. Tin contributed to an increase in intermetallic formation. It is believed that the improved interfacial region was due to the presence of a small amount of liquid phase at the AA2014-SiC interface giving a chemical rather than the usual mechanical bond between reinforcement and alloy.

Electroless nickel boron plating on AA6061

Abstract One of the major drawbacks to using aluminum parts in automotive applications is poor wear resistance. Various techniques have been used to address this concern and the purpose of this work was to produce a hard and wear resistant nickel boron coating on AA6061. This was accomplished by using an electroless nickel boron (EN-B) plating preceded by the application of a protective zincating/electroless nickel phosphorus coating. The experimental parameters for nickel phosphorus and nickel boron baths were optimized and the effect of various experimental parameters on the plating rate were examined. The phosphorus and boron contents of each deposit were measured using electron probe microanalysis (EPMA) and atomic absorption spectroscopy (AAS), respectively; the surface morphology of each coating was examined using scanning electron microscopy (SEM). Results showed that the surface morphology of the nickel boron coating varied with that of the intermediate electroless nickel phosphorus (EN-P) coating. In turn, the surface morphology of the intermediate nickel phosphorus coating depended on the thickness of the coating and the EN-P plating bath conditions. These findings are discussed with a view to using the process to enhance the wear resistance of AA6061. L’un des principaux désavantages de l’utilisation de pièces d’aluminium dans les applications pour l’automobile est sa faible résistance à l’usure. Des techniques variées ont été utilisées pour aborder ce sujet et le but de ce travail était de produire un revêtement de nickel–bore sur l’AA6061 qui soit dur et résistant à l’usure. On a accompli cela en utilisant un dépôt chimique de nickel–bore (EN–B) précédé par l’application d’un revêtement protecteur de zingage/nickel–phosphore chimique. On a optimisé les paramètres expérimentaux des bains de nickel–phosphore et de nickel–bore et l’on a examiné l’effet des divers paramètres expérimentaux sur le taux de plaquage. On a mesuré le contenu en phosphore et en bore de chaque dépôt en utilisant la microanalyse par sonde électronique (EPMA) et la spectroscopie d’absorption atomique (AAS), respectivement; on a examiné la morphologie de la surface de chaque revêtement en utilisant la microscopie électronique à balayage (SEM). Les résultats ont montré que la morphologie de la surface du revêtement de nickel–bore variait avec celle du revêtement intermédiaire de nickel–phosphore chimique (EN–P). À son tour, la morphologie de la surface du revêtement intermédiaire nickel–phosphore dépendait de l’épaisseur du revêtement et des conditions du bain de plaquage de EN–P. On discute de ces trouvailles avec, en vue, l’utilisation du procédé pour l’amélioration de la résistance à l’usure de l’AA

Diffusion-based microalloying via reaction sintering.

As a possible means of reducing the costs associated with the production of metal matrix composites, the use of inexpensive, naturally occurring minerals as a reinforcing agent is one alternative currently being considered. In such efforts, the occurrence of extensive chemical reaction between the minerals and matrix alloy has been noted. In an effort to utilize the reaction products from such reactions, a novel technique known as core/shell processing was developed. Core/shell and bulk alloy samples were prepared through powder metallurgy techniques (blending, cold isostatic pressing, and sintering) followed by hot swaging and finally machining as required. Sintered samples were examined by means of mercury densitometry, optical/scanning electron microscopy, electron microprobe analysis, and mechanical testing (tensile and impact). Microprobe analysis of sintered core/shell samples indicated the occurrence of extensive chemical reactions between the alloy and mineral particles in the shell region, resulting in a rejection of calcium from the mineral into the surrounding matrix followed by eventual migration into the intergranular regions of the core. Mechanical testing revealed core/shell processed samples had significantly improved impact properties while maintaining tensile properties similar to bulk alloy samples.