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Since the introduction of suspension thermal spray (STS) in 1997, the rapid evolution of this technology has resulted in a critical number of inventions justifying a comprehensive review. Today STS is one of the most important research and development topics in thermal spray. Due to the efforts of different industries, universities, and governmental institutions, STS has reached a certain maturity for implementation in different applications. STS includes any thermal spray process that is based on injection of a suspension of solid particles in a liquid carrier into the gas jet, such as suspension plasma spray, suspension high-velocity oxy-fuel, and high-velocity suspension flame spray. This review is on the state of the art of the STS technology and includes an overview of the current patent situation including the number of patents published in English language, patenting institutions and invention domains. Apparatus and methods, feedstock, and new material systems and applications were identified as the three main domains of focus for the STS inventions. The presented patents show a general perspective of the current situation and present the technology advancements in each domain. It also shows the potential of implementing this technology in new applications based on the needs of thermal spray market through further technology development. [ABSTRACT FROM AUTHOR]

Abstract: In the present work on pseudo-eutectic alumina–yttria stabilized zirconia (YSZ) composite, the influence of spray parameters on amorphous phase formation during suspension plasma spray deposition is investigated. Several variables were evaluated as the most probable key factors influencing the amorphous phase formation. These variables include powder feed size, in-flight particle characteristics (temperature and velocity), spraying robot travel speed, preheating the substrate, number of deposition passes and the presence of bond coat. It was found that larger particle size, higher robot speed and substrate preheating lead to larger amounts of amorphous phase. Moreover, it is shown that particle velocity and temperature need to be reasonably low to get greater amorphous content while the presence of a bond coat has no significant influence on the amorphous phase formation. In contrast, increasing the number of deposition passes is detrimental to this phase. This work also discusses some correlations observed between the amorphous phase content and the in-flight particle characteristics and coating grain sizes. [Copyright &y& Elsevier]

Stable water-based suspension of titanium dioxide has been used to fabricate ceramic micro filtration membranes with the suspension plasma spraying (SPS) process. The results of this study confirmed the potential of SPS as an emerging process in ceramic membrane manufacturing. A hybrid filtration/photocatalysis titanium dioxide membrane with 14% of open porosity and water permeability of 430 L/m2.h.bar was produced. The SPS TiO 2 membrane was characterized using scanning electron microscopy and X-ray diffraction methods. The microstructural analysis of the membrane revealed the generation of a unique porous microstructure due to the considerable amount of un-melted particles present in the membrane. Porosity measurements were performed using two analytical methods: image analyzing and mercury intrusion porosimetry. Clean water permeability of the SPS TiO 2 membrane was measured in a dead end stirred cell. The photocatalytic activity of the membrane was evaluated by measuring the degradation rate constant of the organic dye, methylene blue, in an aqueous solution. • Ceramic filtration membranes can be fabricated with suspension plasma spray process. • A unique porous microstructure was generated. • Porous structure is based on presence of un-melted and re-solidified particles. • Hybrid filtration/photolysis membranes were produced. [ABSTRACT FROM AUTHOR]

The demand for suspensions that are used in thermal spray processes is expanding from research labs using the lab-prepared suspensions toward actual coating production in different industrial sectors. Industrial applications dictate the reduced production time and effort, which may in turn justify the development of the market for ready-to-use commercial suspensions. To this end, some of the powder suppliers have already taken steps forward by introducing, to the market, suspensions of some of the most used materials, such as yttria-stabilized zirconia (YSZ), alumina, and titania. However, there is a need to compare the suspension characteristics over time and the resultant coatings when using these suspensions when compared with the freshly prepared homemade suspensions. In this work, such a comparison is done using YSZ suspensions of the sub-micron to a few micron powders. In addition, some changes in the suspensions' formula were performed as a tool to vary the coatings' microstructures in a more predictable way, without any variation of the spray parameters. The coatings were generated while using both radial and axial injection of the suspensions into Oerlikon-Metco 3MB and Mettech Axial III plasma spray torches, respectively. A clear effect of suspension viscosity on the coating microstructure was observed using the 3MB torch with a radial injection of suspension (i.e., cross flow atomization). However, the viscosity role was not dominant when using the Axial III torch with an axial feed injection system (i.e., coaxial flow atomization). [ABSTRACT FROM AUTHOR]