Silicon coatings have been developed for environmental barrier coatings by thermal spraying. Until now, these coatings have been produced almost exclusively by Atmospheric Plasma Spraying (APS). High Velocity Oxy-Fuel (HVOF) spraying is commonly used to produce dense metallic and carbide-based coatings due to high particle velocities. However, there have been no scientific reports on HVOF-sprayed silicon coatings in the literature. This study was conducted to investigate the feasibility of fabricating silicon coatings by HVOF using a DJ2600 spray system. Both the spray powders and the parameters were varied. The coatings were investigated on their surfaces and cross-sections using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The hardness and indentation modulus of the silicon coatings were also determined. The results show that the particle size distribution and the stand-off distance are important influencing factors. Dense coatings could be produced by HVOF spraying, confirming the feasibility.

Thermal plasma spray of silicon has large potential for economic impact in the semiconductor and solar power industries. By post processing a thermally sprayed silicon deposition using directional re-solidification, impurities in the substrate can be controlled. We used a Thermach gun and powder feeder (SG100 and AT-1200, respectively, Appleton, WI), to deposit silicon onto steel samples. These samples were optically heat treated up to their melting point in order to increase crystal grain sizes. The depth and microstructure of the melted region was analyzed through imaging of the cross-sectioned samples. Directional re-solidification also had an effect on the impurity concentration along the depth sample. Control of impurities is demonstrated through this heat treatment and analyzed using SIMS and Laser Ablated ICP-MS. Understanding and controlling the impurity concentration has important implications in producing coatings in the solar industry as well as wafer processing equipment in the semiconductor industry.

Silicon based coatings are showing great promise for power applications in the semiconductor, target, and solar industries. In order for thermal plasma spraying of silicon to continue to have an industrial impact in these industries, careful investigations into the deposition properties must be undertaken. We used a Thermach gun and powder feeder, to deposit silicon onto 100 mm x 50 mm x 1.6 mm steel samples. Coating cross-sectioning and image analysis was performed in order to evaluate the coating’s microstructure and porosity. Mechanical property measurements consisted of hardness testing on the coating cross sections. In addition, scanning electron microscopy and optical microscopy were conducted. These results combined for an analysis into the deposition properties of silicon coatings using various particle sizings, plasma power, and spray distances. Correlations between these input parameters and their effect on the microstructure are critical to semiconductor depositions of silicon.

Currently, graphite is used for anodes of the lithium ion battery. The higher capacity of a battery with the lithium alloy anode requires the development of a larger theoretical electrochemical capacity than graphite. Silicon is a promising anode material, having a theoretical capacity more than 10 times that of the graphite used in these lithium alloy batteries. There are two common methods of fabricating silicon anodes: direct deposition techniques such as electron beam deposition and sputtering; and slurry coating of silicon particles with a binder. Alternative methods are being investigated. One of such methods is cold spray. In this study, numerical simulation of, and experiments investigating, cold spray conditions and the performances of cold-sprayed silicon anodes are presented. Silicon was cold-sprayed on copper foil substrates using three different starting materials (with particle sizes of 4.65 µm, 6.74 µm and 9.63 µm). First cycle efficiency was about 90%. Charge capacity initially improves with cycling (up to the 10th cycle). This is probably due to better electrolyte soaking during the first several cycles. A decrease in charge capacity is observed upon further cycling.

In the present work, silicon coating was deposited using air plasma spraying technology. The temperature and velocity of particles in the plasma spraying were measured. The phase composition and microstructure of the coating was studied. And some mechanical and thermal properties of the coating were evaluated.

In thermal barrier coating (TBC) system, thermally grown oxide (TGO) forms at the interface between the top-coat and bond-coat during service. Delamination or spallation at the interface can be occurred by the TGO formation and growth. Therefore, Modifications of the bond-coat materials are one means to inhibit the TGO formation and to improve the bonding strength of TBCs. In this study, morphologies of TGO were controlled by using Ce and Si addition to conventional CoNiCrAlY bond-coat material. As a result, when the TBCs with Ce added bond-coat materials were aged at 1373K for 100 hours, morphologies of TGO were changed drastically. It is expected that the morphologies can improve bonding strength of TBCs. We carried out to evaluate the bonding strength by using four-point bending tests. As a result, TBC coated with Ce added bond-coat materials indicated excellent bonding strength.

RF Ar-H2 plasma spraying of metallurgical grade silicon particles (80-125 µm) was used in order to combine the purification and the deposition process of silicon particles with a high deposition rate (300 - 600 µm). The hydrogen and oxygen content of the plasma gas turned out to be of a great importance to purify metallurgical silicon powders. The whole process was investigated through ex-situ characterisation of the deposits and on-line diagnostics of the plasma which results matched quite well with the mathematical modelling. The deposits were characterised using SEM, EDX analysis, SIMS, XPS in order to explain the composition and overall properties of the layers in view of their use in photovoltaic applications. Characterisation of silicon deposits was completed by the hydrogen rate analysis using exodiffusion method. Hydrogen trapping in plasma sprayed deposits was found in order of 1019 at/cm 3 . The oxygen contained in the original powders (30%) was decreased down to 3 - 5% in the deposits. Finally, the on-line diagnostics of the plasma used was : Laser Doppler Anemometry (LDA), Laser Doppler Granulometry (LDG) and Optical Emission Spectroscopy (OES). The mean velocity and surface temperature of particles was found to be in agreement with modelling results.

The silicon coating was sprayed on titanium substrate by low pressure plasma spraying and the subsequent coating was heat-treated in vacuum. It is found that a titanium silicide coating with the composition changed gradually can be formed through thermal diffusion treatment of silicon coating sprayed by low pressure plasma on titanium substrate. The formed silicide coatings are characterized by optical microscopy, scanning electron microscopy, EPMA analysis and X-ray diffraction (XRD). The forming process of the silicide coating is investigated by examining the relationship between silicide coating thickness and thermal diffusion parameters. The results show that the composition of silicide coating changes gradually from TiSi, at the silicon coating side through TiSi and Ti5Si4, to Ti5Si4, near substrate side. The thickness of such graded silicide coating is determined by temperature and holding time during heat-treatment. The diffusion of silicon into titanium substrate is mainly responsible for the formation of silicide. Moreover, the investigation of oxidation behavior of silicide coating shows that the formation of silicide coating on the titanium substrate can improve the oxidation resistance of titanium.

A novel plasma spray process for producing nanostructured coatings, hypersonic plasma particle deposition (HPPD), has been experimentally investigated. In HPPD, vapor phase precursors are injected into a plasma stream generated by a DC arc. The plasma is quenched by supersonic expansion through a nozzle into a vacuum (~ 2 torr) deposition chamber. Ultrafine particles nucleated in the nozzle are accelerated in the hypersonic free jet downstream of the nozzle and inertially deposited onto a substrate. The short transit times between the nozzle and the substrate (< 50 μs) prevent inflight agglomeration, while the high particle deposition velocities result in the formation of a consolidated coating. We have investigated the production of silicon and silicon carbide coatings using SiCl 4 and CH 4 precursors. Silicon deposits analyzed by transmission electron microscopy were found to have nanostructured regions with grain sizes varying from 5-20 nm. Corresponding particle size distributions measured before deposition using an extractive aerosol probe peaked around 15 nm, suggesting negligible grain growth occurred in the samples studied. Silicon carbide particle size distributions measured at various deposition chamber pressures verify that the low residence time characteristic of the HPPD process minimizes in-flight agglomeration.

MoSi 2 provides good high temperature oxidation and corrosion resistance. However, the lower silicides such as MosSis do not provide such resistance. In this study, atmosphereic plasma sprayed (APS) MoSi 2 particle temperatures and velocities were measured under various torch conditions chosen to span the majority of typically utilized spray parameters. Empirical models of particle temperature and velocity were computed from the data. Three spray conditions were chosen to produce high, medium and low particle temperatures and velocities. Coatings produced under these spray conditions were characterized by profile tracing, quantitative x-ray diffraction, and SEM analysis. The Mo 5 Si 3 level in the coatings ranged from 5% to 8% while the Mo 5 Si 3 level in the starting powder was 0.6%. Particle size, particle trajectory, and torch parameters were found to be important factors in the Si loss process when APS depositing MoSi 2 .