Thesis (Ph.D.)--Worcester Polytechnic Institute. / Keywords: composite Pd and Pd/Ag membranes, alloying, Pd/Ag barrier, intermetallic diffusion, bi-metal multi-layer BMML deposition, electroless plating kinetics, high temperature x-ray diffraction, aluminum hydroxide surface grading, porous sintered metal supports, hydrogen separation. Includes bibliographical references (leaves 279-296 ).

Near-net-shape manufacturing of titanium metal components through powder metallurgy confers various cost-saving benefits, from improved material utilisation to reduced energy consumption. Further savings can be realised by reducing the cost of the titanium metal powder that is used as feed material in powder metallurgy. Titanium metal-powder production costs can be reduced by removing the steps currently needed (i.e. milling, vacuum arc re-melting and atomisation) to convert titanium Kroll sponge into a powder product that is suitable for use in powder metallurgy. This can be potentially achieved through a controlled metallothermic reduction of titanium tetrachloride to produce a titanium metal powder product that can be used directly in powder metallurgy. Consequently, this thesis divides titanium metal-powder into two main categories, namely primary and secondary metal powder products. Titanium metal-powder is classified as a primary product when it can be used directly as feed material in powder metallurgy. In contrast, a secondary metal-powder product requires extra processing steps after chemical reduction before it can be used in powder metallurgy. To illustrate, titanium metal powder produced through plasma spheroidization is an example of a secondary metal powder product. The metallothermic reduction reaction is known to have two dominant reaction mechanisms. These mechanisms have a characteristic product morphology that forms under specific reaction conditions. The first mechanism is responsible for the sponge-like morphology obtained from the Kroll process, while the second mechanism results in an ultrafine precipitate that has a surface area to volume ratio large enough to oxidise in air to the extent that it cannot be regarded as commercially pure. Consequently, a primary titanium metal-powder product has to date not been realised as efforts to achieve particle growth on this ultrafine precipitate have been unsuccessful. This thesis's main objective was to demonstrate that metal particle growth on suspended metal particles is indeed possible through a controlled metallothermic reduction in a molten salt reaction medium. Subsequent efforts resulted in the postulation of a third reaction mechanism that would enable titanium metal particle growth. The postulated growth mechanism is electrochemical and referred to as “autocatalytic electroless deposition on suspended titanium metal particles”. Theory development and modelling efforts indicated that the postulated growth mechanism is possible, but only in a particular and low concentration range where both reagents are present in a meta-stable equilibrium with each other in the molten chloride reaction medium. The concentration range is estimated to be in the range of parts per million for each reagent. It was further shown that more than one product morphology is inherent in the conditions where the postulated mechanism is possible as there is no dominant reaction mechanism at such low reagent concentrations. Therefore, the metallothermic reduction reaction should be regarded as a system of reaction mechanisms at these conditions. Experimental results substantiated the postulated growth mechanism's existence to the extent where β-titanium metal was deposited on the surface of metallised ilmenite particles. The deposited layer was distinguishable from the substrate particle as ilmenite contains α-titanium (i.e. a hexagonally closed packed crystal system). Therefore, controlled titanium metal particle growth is hypothetically possible through a mechanism known as “autocatalytic electroless deposition”. However, further effort is still needed to demonstrate whether a viable primary titanium metal powder product can be produced. / Thesis (PhD (Engineering))--University of Pretoria, 2021. / Department of Science and Innovation / Chemical Engineering / PhD (Engineering) / Unrestricted

Phase transformation behavior, micro structural development, mechanical and tribological properties of electroless Ni-B coating was characterized using different characterization techniques. As deposited electroless Ni-B coating containing 94 wt. % of NI and 6 wt. % of B is amorphous. It crystallizes via two exothermic reactions one at 3000C and another at 430˚C. It has been observed that there is also slow evolution of the heat in between this two exothermic reactions. XRD studies display that as deposited coating undergoes multi-stage crystallization events. At the first exothermic peak NI3B phases crystallizes, in between two a phase mixture of Ni and Ni3B and at the second exothermic peak NI2B + Ni3B crystallizes. Evolution of the free Ni in the complete crystalline coating is not predicted by the equilibrium phase diagram of the Ni-B system. Microscopic observation of the as deposited coating displays a novel compositionally modulated microstructure comprises of different length scales ranging from micrometer to nanometer level. In situ TEM study along with composition analysis were carried out in order to track the crystallization pathway and microstructural development. This kind of composition fluctuation of the coating is intrinsic to the deposition process. In best of our knowledge this kind of microstructure is the first time reported example of phase separation in a binary metal-metalloid system without spinoidal decomposition. Effect of this kind of microstructure and phase evolution on the mechanical and tribological properties of the coating is very profound. Increase in the nanocrystalline borides content of the coating increases the hardness value of the coating as well as improved tribological properties of the coating. In the low load regime (5 N and less) wear resistance of the coating is provided by the oxide layer formed on the wear track by preventing the direct contact between the coating and counterface. Local temperature rise due to friction and nancrystalline nature of the coating enhances the tendency of oxide layer formation. Characterization of the oxide layer was carried out using SEM, EPMA, Nanoindenation and Raman Spectroscopy. Whereas in case high load regime (above 5 N) this oxide layer breaks off and direct contact between the coating and counterface is established. This increases the wear rate of the coating. Material is removed from the coating through subsurface crack formation and propagation by low cycle fatigue mechanism. Effect of amorphous phase and free Ni on the tribological properties of the coating is detrimental by promoting a strong adhesion between the coating and steel counter face, whereas nanocrystalline borides shows opposite effect. A nano tribological studies using lateral force microscopy shows that nanocrystalline borides decreases the coefficient of friction of the coating. Phase evolution and microstructural characterization also shows that above 450˚C there is a significant diffusion of the boron from the coating to the steel substrate. This restrict the high temperature tribological studies of the coating up to a temperature range of 450˚C. Wear data along with worn track characterization demonstrate the fact that above 100˚C even in low load regime wear rate is very high. Wear of the coating is mainly governed by the plastic deformation of the coating and breakage of the protective oxide layer. Analytical calculation as well experimental observation shows that during the time of wear the temperature at the local contact region reaches a very high value even up to 1100˚C. This may soften the coating and causes the wear though plastic deformation of the coating.

One of the key elements to the success of Pd-Ag membrane based reactor for the H2 production is the synthesis of thin and highly selective membranes using the electroless plating method. This work describes the effect of electroless plating conditions on the obtained Pd and Ag deposits properties (morphology, compactness, phase structure, compositional homogeneity and adhesion) important from synthesis of thin and H2 selective membrane viewpoint. Both sequential and co-deposition deposition methods were investigated. The conventional Pd and Ag plating conditions (NH3+EDTA based bath) produced dendritic and non-uniform sequential (multi layer) deposits, not suitable for synthesizing the thin and H2 selective Pd-Ag membranes. Ag under the conventional plating conditions deposited at high overpotential resulting in the dendritic and non-uniform sequential deposits. The modified Ag plating conditions eliminated Ag deposition at high overpotential and the sequential deposits obtained were non-dendritic and uniform. Thin (< 10 µm thick) and H2 selective Pd-Ag membranes were successfully synthesized using the modified Ag plating conditions. The membranes were then successfully annealed at 550 oC. After the annealing step, the membranes showed activation energy for the H2 permeation (4.3-11.5 kJ/mole) lower than that of the pure Pd membrane (12-16.4 kJ/mole) meaning that the Pd-Ag membranes were more effective for the H2 separation at lower temperatures than the pure Pd membrane. A Pd-Ag (20 wt%) membrane showed H2 permeance higher by a factor of 2.47 at 250 oC than the pure Pd foil. The Pd-Ag membranes also showed decline in the H2/He selectivity on exposure to the annealing and H2 permeation (300-500 oC) study conditions. The Pd-Ag co-deposits obtained (using NH3+EDTA bath) were dendritic, inhomogeneous with poor substrate adhesion, therefore not suitable for the membrane synthesis. The co-deposits were bi-metallic and required the annealing step to form the Pd-Ag alloy. There existed a large difference in the deposition potentials (600 to 650 mV) of Pd and Ag. The Ag deposition was severely controlled by its mass transfer in the solution resulting in the dendritic and inhomogeneous deposits. Among the different complexing agents investigated, KCl showed the least difference between the Pd and Ag deposition potentials. The co-deposits obtained using the KCl bath were non-dendritic, homogeneous and were Pd-Ag alloy therefore required no annealing step. Finally, the multi step plating, annealing and polishing approach was used to avoid the decline in the selectivity of the sequentially prepared Pd-Ag membranes. The membranes prepared by the plating, annealing and polishing approach showed very high selectivity (H2/He) and no decline in the selectivity was observed between 300-450 oC for the total exposure time > 550 h (> 200 h at 450 oC).

Tese de mestrado integrado. Bioengenharia (Área de Especialização de Engenharia Biomédica). Faculdade de Engenharia. Universidade do Porto. 2012

This study presents thin film transistor (TFT) electrode structures in flat panel displays by imprint and electroless silver plating techniques. Imprint technique is not limited to the physical properties of optical lithography. In the imprinting process, the glass mold designed for imprinting process is fabricated by semiconductor manufacturing technology to imprint photoresist (AZ-650). The material is evaluated for imprint process. In addition, at present, electrode materials used in TFT process are aluminum (Al), chromium (Cr) and so on. In other research, the thin film plating technique adopts sputtering process to manufacture TFT electrode structures. This study uses electroless silver plating process to fabricate TFT electrode structures. The experimental result shows that the silver film can be deposited on the glass wafer by electroless plating, The mechanical properties of the silver films such as hardness, coefficient of elasticity and Young¡¦s module are measured by nanoindentation system,compared with the bulk materials.

Improvements for Chip-Chip Interconnects and MEMS Packaging Through Materials and Processing Research Erdal Uzunlar 129 Pages Directed by Dr. Paul A. Kohl The work presented in this dissertation focuses on improvements for ever-evolving modern microelectronic technology. Specifically, three topics were investigated in this work: electroless copper deposition on printed wiring boards (PWBs), polymer-based air-gap microelectromechanical systems (MEMS) packaging technology, and thermal stability enhancement in sacrificial polymers, such as poly(propylene carbonate) (PPC). In the electroless copper deposition study, Ag-based catalysts were identified as a low-cost and equally active alternative to expensive Pd-based catalysts. Hot H2SO4 treatment of PWBs was found as a non-roughening surface treatment method to minimize electrical losses. In MEMS packaging study, a sacrificial polymer-based air-gap packaging technique was improved in terms of identification and simplification of air-gap formation process options, optimization of thermal treatment steps, assessing air-gap formation performance, and analyzing the chemical composition of residue. It was found that non-photosensitive PPC leaves less residue, and creates more reliable air-gaps. The mechanical strength of air-gaps was found to come from residual stress in benzocyclobutene (BCB) caps. In thermal stability of PPC study, the mechanism of thermal stability increase on copper (Cu) surfaces was found as the complex formation between Cu(I) and iodonium of the photoacid generator (PAG), leading to hindrance of acid formation by PAG and restriction of acid-catalyzed decomposition of PPC.

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