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Precipitation in iron-tungsten alloys containing nitrogen as the predominant interstitial constituent is studied by a variety of techniques including X-ray methods, optical metallography and electron microscopy. Investigations into the tungsten-nitrogen system show the marked effect of oxygen on the formation of tungsten nitrides. "Constant activity nitriding" of iron-tungsten alloys containing up to 9.3 wt.% produces as many as six different equilibrium tungsten or iron-tungsten nitrides and oxynitrides. The phase produced depends upon the tungsten, nitrogen and oxygen potential as well the the temperature. Alloys containing more than about 4.0 wt.% tungsten nitrided at 590-640 C in appropriate nitrogen potentials exhibit a precipitation sequence GP zones -intermediate ---- equilibrium precipitat precipitate The transition from zones to intermediate precipitate occurs by a continuous ordering process in which tungsten atoms replace those of iron in certain sites. The final stage occurs continuously.Tungsten concentrations or nitrogen potentials lower than the critical values prevent rapid homogeneous precipitation and the intermediate phase is precipitated heterogeneously. Metallographic studies of quenoh-aged tungsten nitrogen-ferrites demonstrate that tungsten has a negligible effect on the Para-preoipitation of iron nitrides.

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This research is based on a study of the parameters affecting the adhesion of styrene–butadiene rubber (Solprene 1204) and polyisoprene (Natsyn 2200) to monofilament brass-plated steel wire. Investigations are concentrated on the influence of compounding ingredients and coupling agents on the adhesion between the rubber and wire using H-shape specimens. X-Ray Photo Electron Spectroscopy (ESCA) and Scanning Electron Microscopy (SEM) techniques have been used to identify residues on the wire surface and to interpret the chemical and physical roles of carbon black and silica on the mechanism of bonding rubber to brass-plated wire.

Medium Energy Ion Scattering studies of the thin metallic film systems created by the deposition of Ag on AI(100), non AI(100) and Au on Fe(100) were conducted. Work was specifically focussed on expanding the arsenal of data analysis methods available to the researcher of such structures by the interpretation of the data obtainable from this, the most versatile, of the Rutherford backscattering based techniques. For the Ag on Al(100) system it has been shown that significant surface reconstruction occurs for a coverage of 1.05 ML. An investigation, by means of an original atom-by-atom simulation fitting approach was conducted, with the aim of examining the validity of a documented model of this reconstruction. The results suggested that the documented model is inadequate, but a more suitable model was not found. The 3.57 ML Ag coverage was studied extensively by means of quantitative comparison with simulations, including the use of a novel layer-by-Iayer compositional analysis technique. This study culminated in the production of a highly credible model based on the depth profiling of the first six atomic layers of a prospective, epitaxial, fcc structure. It was qualitatively argued that the 6.12 ML Ag film was fcc in nature with extremely limited intermixing between the substrate and the overlayer.

The kinetics of the high temperature oxidation (250 - 600 C), in purified oxygen, of the intermetallic compounds UAl2, UAl3 and UAl4 have been studied using a microbalance and a thermal balance. The compound UAl42 was prepared by an arc melting process, whilst samples of UAl3 were supplied by the Metallurgy Division, Harwell. UAl4 could not be obtained in a pure form and its behaviour was indirectly assessed by 'extrapolating' the behaviour of uranium-aluminium alloys containing various proportions of UAl4 to that of the pure compound. Alloys containing large amounts of UAl4 oxidised linearly over the range 350-550 C, except for the initial stages of film formation. At 600 C a cubic rate of oxidation was observed which gave much smaller weight gains than at lower temperatures. It is suggested that this phenomenon is due to sintering of the oxide film. Alloys containing small proportions of UAl4 oxidised in a logarithmic manner over short periods and in a slow linear manner thereafter. Sintering and preoxidation experiments were also conducted with the oxide films on UAl4 alloys. UAl2 and UAl3 oxidised linearly after a short initial period of either increasing or decreasing oxidation rate. The oxide films produced have been examined chiefly by X-ray powder microscopy and electron microscopy. The only oxide identified was U3O8. The films have few surface features until after prolonged oxidation, when in the case of UAl4 and UAl3, cracking occurs. A unique system of concentric crack formation occurs in the oxide films formed on UAl4 alloys at 500 C, whilst only random cracking occurs at 600 C. All the linear rates of oxidation are attributed to either the formation of a porous film and a thin coherent barrier film, or to a porous film and a rate determining reaction. These possibilities are fully discussed.

A detailed study of the non-isothermal and the isothermal sinterability of aluminium hydroxide gel powders has been made. It has been confirmed that the gel powders consist of boehmite phase and on dehydroxylation transform to gamma alumina. The formation of other intermediate transition aluminas like delta and theta is morphology dependent. A fibrillar gel (Baymal) studied transformed from gamma to theta to alpha, whereas other two gel powders studied, which consisted of spherical crystallites, transformed to both the delta and the theta phase before converting to the alpha phase. All the gel powders yield alpha alumina in the temperature range 1150--1300°C. The gel powders exhibit poor non-isothermal and isothermal sinterability in spite of extremely fine crystallite size of the as received gel powders and the gamma alumina powders produced from them. It has been shown that poor sinterability of the gel compacts is associated with the simultaneous polymorphic phase transformation to the stable alpha, phase during sintering. The polymorphic phase transformation occurs by a nucleation and growth process which is diffusional in character. The electron diffraction studies have revealed that the metastable delta + theta or theta phases directly transform to the alpha phase, without the formation of any intermediate amorphous phase. The transmission electron microscopy has revealed that considerable redistribution of the fine porosity within the metastable phase matrix occurs into the form of elongated interconnected pores which are left behind within the growing alpha grains, and are effectively trapped. It is concluded that the poor sinterability of the gel compacts is due to considerable grain growth and effective trapping of the pores which occurs during the phase transformation. A geometrical model has been proposed to account for the observed redistribution of the porosity. It is concluded on the basis of model and interface migration kinetics considerations , that the interface remains pinned by the pores allowing pores to redistribute by vacancy diffusion along the interface from smaller to larger pores. The effect of rate of heating, calcination, impurity addition and atmosphere on the non-isothermal sinterability of the gel compacts has also been studied. It has been demonstrated that considerable improvement in the densification of the gel compacts can be achieved by the addition of phase stabilizing impurities like thoria.

It is well known that cold working of a crystalline solid leads to high concentrations of dislocations in the lattice. In this state, the solid contains residual microstrains and is usually observed to have enhanced chemical reactivity when compared with the annealed condition. The residual strain energy, due to the strain fields around the dislocations, increases the free energy of the solid; this has two effects on the reactivity of the solid:- (1) The increased chemical free energy results in an increased thermodynamic tendency for chemical reaction to occur. (2) The increase in free energy results in a decrease in the activation energy for chemical reactions involving the solid. As a consequence, reactions may occur at faster rates. The work presented in this thesis is a quantitative study of the effects of crystal defects on the chemical reactivities of both cold worked and chemically prepared copper and nickel. It has been shown that residual microstrains affect the electrode potential of cold worked copper in the form of wire or powder. The relationship between the strain energy and the change in electrode potential, relative to the annealed state, is linear. Changes of electrode potential have been thermodynamically related to changes of surface chemical free energy, which result from the residual microstrain energy. A polarographic technique has been developed to measure the rates of electrode processes of cold worked copper and nickel wires. It has been shown that residual microstrains affect the rates of anodic dissolution. An extension to standard electrochemical theory has been proposed, which relates the anodic exchange current density with the change in activation energy for dissolution which results from residual microstrains. Experiments have been carried out on cold worked aluminium oxide powder to compare chemisorption and BET adsorption particle sizes with crystallite size. It has been demonstrated that ball-milling caused a change of surface free energy in aluminium oxide powder. This was found to give rise to a change of electrode potential of the milled powder relative to that of the annealed powder. X-ray line broadening has been used to measure crystallite sizes, microstrains and stacking fault probabilities in Raney copper and Raney nickel catalysts, and also in platinum catalysts. The defect concentrations in technically useful Raney nickel catalysts, of high catalytic activities, are considerably higher than those found in the relatively inactive catalysts which had been studied by previous workers Measurements have been made of defect concentrations in catalysts of various activities, prepared by different methods. A relationship has been established between the catalyst structure and the temperature and time period used for digestion of Raney alloy. A similar relationship has been shown for platinum catalyst, prepared by ignition of a platinum salt at various temperatures. In addition, the aging processes occurring in a highly active Raney nickel have been followed by X-ray line broadening. These experiments show that catalysts with high defect concentrations are of high catalytic activity but of low stability, since they are subject to crystallite growth and strain relief at room temperature.

It is often said that whisker/fibre reinforcement would work if perfect unidirectional alignment could be achieved. But this is not always true for most structural materials, perfect unidirectional orientation is neither necessary nor desirable. In most cases, materials with isotropic properties are preferred and therefore reinforcement of composites in three-dimensional random orientation will be necessary. With this aim in mind an exploratory investigation was carried out to study some aspects of whisker distribution, whisker-matrix bond and the composite tensile strength with the system SiC–Al–4.5% Cu alloy.

The effects of porosity and composition on the isothermal transformation characteristics of a plain 0.8% carbon steel, made from a reduced iron powder, and a low-alloy steel containing nominally 0.5% carbon, 1.5% copper, 1.75% nickel and 0.5% molybdenum, made from a diffusion-bonded iron powder, have been investigated using optical and electron microscopy and electron probe microanalysis techniques.