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Recycling of thermal spray waste in sintered products (LIFE ReTSW-SINT)
Start date: Jul 1, 2013, End date: Jun 30, 2016 PROJECT  FINISHED 

Background Thermal spraying refers to a group of versatile coating technologies that are used to deposit thick (50 μm - >1 mm) layers of ceramic, metallic, cermet or composite materials for a variety of applications in a number of fields, including: the mechanical industry (wear and corrosion protection of mechanical parts, such as shafts, joints, plungers and impellers), aeronautics and energy production (thermal insulation of gas turbine components, protection against high temperature oxidation and hot corrosion), and the biomedical industry (osteoconductive coatings on metallic prosthetic implants for dentistry and orthopaedics). During conventional spraying processes, as much as 80% of the powder is not used and this ‘overspray’ has to be recovered for treatment as waste. Previously, waste treatments have involved negative environmental impact risks because the metallic powders used in thermal spray coatings are often based on nickel, which as metal, is considered to be a human carcinogen. In addition, ceramic powders such as Yttria-stabilised zirconia (YSZ) are also considered to be potentially hazardous. Both YSZ and Ni-alloys are valuable materials, and their waste disposal equates to a loss of primary resources. Objectives The main aim of the LIFE ReTSW-SINT project is to demonstrate the feasibility of valorising and recycling different types of thermal spray waste into high value products for industrial and residential use. The project will select particles with the same base chemical composition in two streams: spherical or with size below 60 micrometres and splat-like or with larger dimensions. The spherical particles will be reused for manufacturing of simple-shaped parts by spark plasma sintering (SPS). The remaining particles will be immobilised in a glass matrix to avoid leaching of heavy metals, used in both reactive and non-reactive silica-based systems to convert the powders into frits (rapidly water-cooled glass powders) and also used to manufacture glazed ceramic tiles that have abrasion resistance, conductivity, electro-magnetic field absorption and aesthetic properties. Specific project actions involve: Characterisation of spent thermal spray powders and definition of usable separation techniques; Implementation of waste powders stream separation according to composition, particle size and morphology; Development of innovative frits modified with the recovered particles and using recycled glass; and Development of innovative glazes modified with direct addition of recovered thermal spray powders or by the new frits. Expected results: Project outcomes will lead to the following main environmental benefits: A zero-waste approach at thermal spraying plants to the reuse and valorisation of the powders in SPS or in ceramic firing, absorbing 100% of waste produced by the thermal spraying plants, with no solid waste production; Immobilisation of harmful contaminants of spent thermal spray powders (mainly heavy metals) in matrixes (glass matrix, ODS composites) that do not leach such elements; Absorption of other waste, such as recycled glass cullet, for preparation of the glass matrix and to lower its softening point; Application of low energy consumption techniques for recycling of thermal spray spent powders; and Realisation of antistatic and electro-magnetic field shielding tiles. The main technical and economical benefits of the project will be: Cost savings for thermal spray powders disposal (approx. €1.2 per kg); Cost savings for supplying refractory ceramic powders by recycling the alumina and zirconia ones; and Recovery of NiCoCrAlY powders as raw material for ceramic tile industry.
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