Regarding the higher demand of the total joint replacement (TJR) and revision surgeries in recent years, an implant material should provide much longer lifetime without failure. Nickel titanium (NiTi) is the most popular shape memory alloy in the industry, especially in medical devices due to its unique mechanical properties such as pseudo-elasticity, damping capacity, shape memory and good biocompatibility. However, concerns of nickel ion release of this alloy still exist if it is implanted for a prolonged period of time. Nickel is well known for the possibility of causing allergic response and degeneration of muscle tissue as well as being carcinogenic for the human body beyond a certain threshold. Therefore, drastically improving the surface properties (e.g. wear resistance) of NiTi is a vital step for its adoption as orthopaedic implants. To overcome the above-mentioned risks, different surface treatment techniques have been proposed and investigated, such as Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD), ion implantation, plasma spraying, etc. Yet all of these techniques have similar limitations such as high treatment temperature, poor metallurgical bonding between coated film and substrate, and lower flexibility and efficiency. As a result, laser gas nitriding would be an ideal treatment method as it could overcome these drawbacks. Moreover, the shape memory effect and pseudo-elasticity of NiTi from a reversible phase transformation between the martensitic phase and the austenitic phase are very sensitive to heat. Hence, NiTi implant is subjected to the following provisions of the thermo-mechanical treatment process, and this implant provides desired characteristics. It is important to suggest a surface treatment, which would not disturb the original build-in properties. As a result, the low-temperature methods for substrate have to be employed on the surface of NiTi. This present study aims to investigate the feasibility of applying diffusion laser gas nitriding technique to improve the wettability and wear resistance of NiTi as well as establish the optimization technique. The current report summaries the result of laser nitrided NiTi by continuous-wave (CW) fibre laser in nitrogen environment. The microstructure, surface morphology, wettability, wear resistance of the coating layer has been analysed using scanning electron microscopy (SEM), X-ray diffractometry (XRD), sessile drop technique, 3-D profile measurement and reciprocating wear test. The resulting surface layer is free of cracks, and the wetting behaviour is better than the bare NiTi. The wear resistance of the optimised nitride sample with different hatch patterns is also evaluated using reciprocating wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in Hanks’ solution. The results indicate that the wear rates of the nitride samples and the UHMWPE counter-part were both significantly reduced. It is concluded that the diffusion laser gas nitriding is a potential low-temperature treatment technique to improve the surface properties of NiTi. This technique can be applied to a femoral head or a bone fixation plates with relatively large surface area and movable components.

Liquid menisci in small pores exhibit a curved surface across which there is a significant pressure difference. The capillary properties of such surfaces are important in many areas of science and technology. Pores of uniform section can be broadly classified according to whether the perimeter is smooth (as in cylindrical tubes) or angular (as in triangular tubes). A meniscus that is entirely bounded by the pore walls has a curvature that is inversely proportional to the tubes' hydraulic radius. A meniscus in an angular tube, however, has liquid wedges in the corners and this reduces the effective area of the pore. In the past it has been difficult to calculate the curvatures, of this class of menisci. Some recent studies have shown that a relatively straightforward, but hitherto neglected, method originated by Mayer & Stowe (1965) and Princen (1969a) can be applied to analyse wedging menisci. However, the method has lacked a comprehensive experimental verification. This investigation follows on from the previously limited studies. A standardised method for the application of the analysis is described, the results from which are compared to observations made using modified experimental procedures. The behaviour of the capillary surfaces formed in several model pores are analysed with the method. The model systems studied are rectangular ducts, the pores formed by a rod in an angled corner, by two contacting rods and a plate and the space between a rod and a plate. For the latter two shapes the analysis is extended to include systems of mixed wettability which have a particular bearing on enhanced oil recovery operations. Experiments in which curvatures are inferred from observations of capillary rise, are performed using two comparative techniques. An involved procedure confurns predictions of meniscus curvature to within 0.3%. Use of a more straightforward, though less accurate, technique enables variations of curvature with tube shape or contact angle(s) to be conveniently studied. Results obtained are excellent and confmn the theory within the determined experimental errors. In addition the analysis has been extended to predict more complex meniscus behaviour. The tubular space formed by three rods and a plate gives rise to a whole family of meniscus shapes. With certain geometries a capillary surface regards the tube as a pore doublet where the behaviour in one neighbouring pore depends on that in the other. The capillary properties of this model system shed light on the behaviour of adjacent pores in a porous medium undergoing drainage (ordesorption). Experiments show excellent agreement with predictions of meniscus shapes, curvatures and, most interestingly, points of spontaneous transition from one meniscus shape to another. The system also has a potential future application because one panicular arrangement of rods produces a meniscus with a curvature virtually independent of the geometry. This makes it suitable for producing a standard meniscus of known curvature.

The adsorption of iodine on a platinum(111) single-crystal surface has been investigated using LEED, Auger spectroscopy, and work function measurements. The phase transformations and work function changes have also been measured during desorption. Mass spectroscopy shows that above 300 K the main desorption product is atomic iodine with a small amount of molecular iodine detected as well. The desorption kinetics at these temperatures were studied by different techniques to extract the kinetic parameters and the orders of the desorption reactions. There are two main desorption features, one displaying zero-order desorption kinetics typical of a phase transition and the other displaying first-order kinetics with a coverage-dependent activation energy. The work function changes during adsorption and desorption were shown to be a function of coverage rather than having a site dependence. The adsorption of iodine at temperatures below 200 K was also studied. Multilayers of molecular iodine are formed that desorb with essentially zeroth order kinetics. Two multilayer desorptions were observed with thermal desorption spectroscopy. One of the multilayer desorptions had a significant work function change associated with it. The work function changes were modelled by calculating the hybridization dipole moment using extended-Hückel theory with Bloch wavefunctions. The calculations are sensitive to the atomic position of the adsorbate and require further refinement. Due to the protective nature of the iodine layer and its high polarizability, the iodine layers were used to study the ambient pressure adsorption of fluorinated carbosilane dendrimers. These dendrimers are stable in vacuum but do not form an ordered structure at ambient temperature. Heating the adsorbed dendrimer in vacuum to 1100 K produced a new ordered structure on the platinum surface. This structure was shown not to be an intact dendrimer molecule as two different dendrimers with similar structural moieties produced the same (√19x√19)R23.4° LEED pattern. The ordered structure was studied by Auger spectroscopy to determine the carbon coverage. This structure is proposed to be islands of a coincidental lattice of graphite. / Graduate

Ph.D. (Chemistry) / This work describes the activation by steam, carbon dioxide, or air of specially prepared cane sugar and commercial carbon granules. The following determinations were done on these carbons. Densities in various fluids, crushing strengths (utilising an arbitrary developed method), chemical composition, surface appearance (from electron micrographs), and low temperature isotherms (utilising three volumetric methods)...

The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.

No description available.

The mechanical properties of ion implanted ceramics are primarily a function of the radiation damage produced by the implantation process. For crystalline ceramics this damage is chiefly nuclear displacements, though for glasses electronic effects have also been observed. In this study a number of single crystal and polycrystalline ceramics and a soda-lime-silica glass have been implanted with a range of ions in the energy range 90keV to 400keV and the changes in mechanical properties produced have been followed using hardness, indentation fracture and scratch testing. The damage structures which remain after implantation will control both the indentation hardness and surface fracture properties of cetamics. Changing the temperature of the substrate during implantation (in the range. 150K to 760K) has been found to alter this damage state and hence produce changes in the measured mechanical properties. In this temperature range, the effects of damage annealing at low doses were found to be minor for sapphire although for MgO damage annealing was found to result in a eduction of the radiation-induced hardening above 473K. The surface softening and stress relief accompanying amorphisation at higher doses was found to be strongly temperature dependent. Thus, the recrystallisation of amorphous material is important in determining the final mechanical properties of the implanted specimens. The tribological properties of the implanted ceramics were investigated using single pass scratch tests. Friction coefficients were found to increase with dose up to the onset of amorphisation, even when visible scratch tracks were produced. This increse is due to changes in adhesion between the slider and the flat induced by ion implantation. The reasons for these changes are as of yet unclear, though a possible explanation could be the removal of surface adsorbates which has been observed for MgO. Similar mechanical and tribological property changes observed for the polycrystalline ceramics as for the single crystal systems, but some extra effects were observed.

No description available.

This thesis deals with both mathematical and analogue models for studying electromagnetic variations at the earth's surface. The field components are studied for frequencies in the range 10ˉ⁴ to 10³ cycles/sec and for earth conductivities in the range 10ˉ¹⁶ to 10ˉ¹º emu. Expressions are developed for the electric and magnetic field components at the surface and within the upper layer of a horizontally stratified flat conducting earth in the field of incident plane waves. Extensive results of amplitudes and phase angles are obtained for various frequencies, angles of incidence, layer thicknesses, depths, and conductivities. As an extension of this problem, expressions for a multilayer earth (n layers) are developed and evaluated. Each of several thick layers is divided into a sufficient number of sublayers, with changing conductivity, to represent to a good approximation a continuous change in conductivity. The conductivity distributions used are of interest in geophysics. The results for the plane wave model indicate that the amplitudes and phase angles are strongly affected by the conductivity structure. The electric and magnetic fields at the surface of a flat homogeneous conducting earth in the near field of an oscillating line current are studied. The equations for the amplitudes and phase angles developed by Law and Fannin (1961) are used for the calculations. Extensive results of amplitudes and phase angles are obtained for various frequencies, conductivities, source heights, and locations with respect to the overhead current. The results indicate that the vertical to horizontal magnetic field ratios are in the range of experimentally observed values. An analogue model suitable for studying the behavior of the natural geomagnetic and telluric field variations for various geological structures was constructed. The two types of field sources used were an oscillating sheet current and an oscillating line current. Extensive measurements of amplitudes and phase angles for the horizontal electric, the horizontal magnetic, and the vertical magnetic field components are obtained and discussed for various geological structures including a flat layered earth, cylindrical bodies embedded in the surface layer, vertical faults and dykes, sea mounts and conducting domes, coastline structures (sea-land interface and an upwelling in a high-conductivity zone within the mantle), and islands in an ocean channel. The results obtained for the coastline structures and islands in an ocean channel tend to support the proposed structures suggested by various workers (Schmucker 1964, Lambert and Caner 1965, Lokken and Maclure 1966) in describing the experimentally observed coastal magnetic field anomalies. The analogue model constructed and used for this work readily lends itself to studying a wide range of geological structures for a variety of source fields in addition to the ones used here. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The surface tension of solid commercially pure nickel was determined by the force measurement technique using fine wires as proposed by Udin, Shaler, and Wulff. Grain boundary measurements were also made on the same metal. After finding experimentally that tests in a vacuum of approximately 5 x 10⁻⁵ mm Hg were unsuccessful because of the high power vapour pressure of nickel at high temperatures, similar tests were made in helium and argon atmospheres, the pressure being kept constant at 760 mm Hg during the experiments. The average surface tension of nickel in argon was found to be 2220 ± 300 dynes per centimeter for a temperature range from 1370°C to 1390°C. The relative grain boundary energy of solid nickel was determined by measuring the dihedral grain boundary groove angles of thermally etched nickel. The interferometric method developed by Hilliard and Harrold was used for this purpose. An average value of 161 degrees was found for the dihedral angle. The grain boundary energy was calculated to be 740± 300 dynes per centimeter. Examination of thermally etched nickel surfaces was inconclusive with respect to physical evidence for dislocation. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate