Electrochemical metallization of abrasive materials and their physical-mechanical properties

In this work, the kinetics of molybdenum carbide electroplating from ionic melts on abrasive grains (diamond, silicon and boron carbides) as a function of electrolysis parameters has been studied, and the physical, mechanical and service properties of metallized materials have been evaluated. Vernadskiy Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 6, pp. 27–30, November–December, 1997.     

Automotive applications of stampable reinforced thermoplastics development prospects

Reinforced thermoplastics sheet that can be used to produce components by stamping is of particular interest to the automotive industry since it offers a process akin to the conventional methods of forming metal sheet. These materials, presently based on polyolefins and nylons, are now being used to produce under-the-bonnet components such as rocker and timing-chain covers, battery trays and oil pans, and for truly structural assemblies including seat shells, spare wheel compartments, front panels and bumper inserts, at realistic production levels.     

Oxidation, microstructure and metallization of aluminum nitride substrates

Oxidation kinetics and the effect of oxide scale on interfacial microstructure of polycrystalline aluminum nitride substrate metallized with conductor and resistor thick-film pastes have been investigated over an oxidation temperature range of 1150–1450 °C at 50 °C intervals in ambient air. At temperatures below 1150 °C, weight gain increased linearly with the isothermal time. The grown oxide layer was porous and was not protective at the temperature, revealing an interface-controlled mechanism. By contrast, the oxidation kinetics exhibited a parabolic behavior as the temperature was raised further above 1250 °C, which is indicative of a diffusion-controlled mechanism. The oxide scale effectively reduced the population of gas bubbles located at the film-substrate interface when coated with the resistor film on the AlN substrate, while the conductor paste provided a hermetic interface even when the AlN was not pre-oxidized. Elemental analyses showed that glass composition of the pastes, e.g., lead, was crucial in determining the interface defects. The differences in interface microstructure of the resistor and conductor metallization, as well as the implication of the thick-film structures to the formation of blisters at the interface, are discussed.     

Nanodiamonds of static and detonation syntheses and prospects for their applications

Basic physical, physicomechanical and physicochemical characteristics of diamond nanopowders of detonation and static syntheses and carbon composites on their base have been discussed. It has been shown that the above properties depend on the composition of the initial raw material, thermobaric conditions of the synthesis of nanopowders, and the methods of their recovery from the synthesis products. The applications, for which nanodiamonds hold the greatest promise, have been listed.     

Progress and prospects in chitosan derivatives:Modification strategies and medical applications

Chitosan (CS) is the only natural alkaline polysaccharide originated from deacetylation of chitin that is the main component of shell from marine organisms.It h...     

Neural networks for computing in structural analysis: Methods and prospects of applications

A neural network model is proposed and studied for the treatment of structural analysis problems. Both the cases of bilateral and unilateral constraints are considered and Hopfield-like neural models are proposed. Moreover, new results, generalizing the results of Hopfield and Tank,¹⁰ are obtained. Numerical applications illustrate the theory and show clearly the advantages of the neural network approach. Finally, the parameter identification problem is formulated and solved as a ‘learning’ problem for a neural network.     

Catalysis: principles, progress, prospects

In this introductory paper, we endeavour to bridge the gaps that currently exist between the three main subdivisions of catalysis: enzymatic, homogeneous and heterogeneous. Hitherto, there has been a tendency for each of these three divisions to grow separately using their own concepts, phrases and techniques. However, there is much that unites them, not least the notion of the catalytically active site and, in particular, its often unusual (constrained) state of electronic or atomic environmental disposition. We identify many points of similarity between, for example, the mode of action of, metalloenzymes on the one hand and the recent generation of transition metal ions embedded within nanoporous (usually siliceous) solids on the other. Useful unifying principles emerge from considerations of free-energy/reaction-coordinate plots.We present a number of tabulations and comparisons designed to facilitate the understanding of the mode of operation of existing, and the performance of new, catalysts. In doing so, we have drawn on our own work as well as that of others, including contributions that are to be found in this volume, with the intention of covering the great variety of catalytic phenomena.     

Advanced composites for aerospace applications: A review of current status and future prospects

In less than 20 years advanced composites have become established as highly efficient, high performance structural materials and their use is increasing rapidly. This paper presents a brief review of the current status of composite materials technology, in terms of materials available and properties, and an outline of some of the trends, obvious and speculative, with particular emphasis on aerospace applications.     

Contact resistance characteristics with AlSi alloy metallization

Contact resistance characteristics of n⁺ Si shallow junctions metallized by sputtering an AlSi 2% alloy were investigated for different contact window sizes varying from 2 to 8 μm. The increase in the contact resistance with reducing contact area is measured employing Kelvin test structure. The effect of AlSi microstructure, silicon precipitation and annealing cycle on the contact resistance is discussed.     

Strength characteristics of coatings in electric-arc metallization

The adhesive and cohesive strengths of powder-wire metal coatings as functions of the technological parameters in electric-arc metallization are investigated experimentally.     

Design of metallization equipment for web coating

As a result of the increasing demands created by the wide range of such applications as decorative, packaging, energy conservation and electronic materials, the continuous web metallizing process has become sophisticated and exacting. High system reliability and precise quality control are required to achieve the continuous deposition of thin metallic coatings onto polyester films, paper and cloth in roll form. An in-depth discussion of the critical areas in the design and operation of equipment, together with the various deposition processes, is presented, with emphasis on the significance of vacuum level, uniformity of coating thickness and web transport properties, such as tension and temperature control.     

Investigation of Cu coatings deposited by kinetic metallization

Interfacial characterisation of Kinetic Metallization (KM) sprayed Cu coatings applied on metal substrates was performed using optical and electron microscopy, as well as microindentation hardness testing and microchemical analysis. The interfacial characterisation of KM coatings remains scarce to date. Cross sectional observations of KM coatings on light metal substrates revealed an undulating, patelliform profile with thin-lipped cusps at the interface. Pure Al and Mg substrates exhibited a mechanically impinged zone <~5 μm on the substrate material, approximately the size of deformed Cu powder particles. Examination of the Cu side of the interface indicated there was no long range interaction in the coating. On the substrate side of the interface, the KM process induced phase transformations (i.e. recrystallisation and an alloyed zone) in thin layers contiguous to the interface on pure Al and Mg substrates. Zones of elemental interdiffusion were identified at the interface upon Al and Mg substrates using scanning TEM. The width of intermixing zones was in the vicinity of < 1 μm. This metallurgical interaction at the interface occurred on the length scales involving the initial single layer of Cu particles bonded on the substrate.     

A review of LPCVD metallization for semiconductor devices

The paper reviews chemical vapour deposition (CVD) processes suitable for applying metal interconnection layers to semiconductor integrated circuits. The conditions under which uniform, smooth films can be grown are discussed. The principal metals reviewed and its alloys; refractory metals and silicides; and platinum and PtSi. The review concentrates on the period 1966–1983.