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This paper presents a study on graphene platelet (GPL)-reinforced alumina (Al2O3) ceramic composites and the relationships between the loading of GPL and both mechanical properties and in vitro biocompatibility. Al2O3 powders with different GPL contents were prepared and sintered using a gas protected pressure-less furnace. The examination of the results shows the density of the composites varying from 99.2% to 95.6% with the loading of GPL from 0.75 to 1.48 vol %. Raman studies show that moderate agglomerations of GPLs occur during the ball milling process and graphitic defects were produced during the high temperature processing. Mechanical properties of the Al2O3 matrix are significantly improved by adding GPLs. A maximum increase of approximately 60% in flexural strength and 70% in fracture toughness are achieved by introducing 0.75 vol % GPLs. In the biocompatibility tests, it was found that cells directly seeding on top of GPL/Al2O3 samples showed better initial attachment (3 h after seeding) and viability (3 days after incubation) than the monolithic Al2O3, indicating that the GPL/Al2O3 composites have comparable or more favorable biocompatibility. The excellent mechanical and biomedical properties of the GPL/Al2O3 composites may enable them to be applied to a wide range of engineering and biomedical applications.

Additive manufacturing (AM), also known as 3D printing, is a revolutionary manufacturing technology that has attracted many industries in the past two decades. This is because AM enables the manufacturing of complex-shaped geometries without the limitations of other manufacturing techniques. In this paper, the design, development and testing of additively manufactured, monolithic catalyst beds are described. A novel design methodology was employed and achieved catalyst bed designs with complex geometry and high geometrical surface area whilst achieving an acceptable pressure drop. Catalyst bed samples incorporating alumina ceramic lattices with strut diameters ranging from 0.15 to 0.30 mm were fabricated via AM and a subsequent heat treatment. The surface areas of the samples were improved using different wash coats, including the use of gamma alumina and a mixture of gamma alumina and carbon nanotubes (CNT). Manganese oxides were used to coat the catalyst bed and decompose hydrogen peroxide. Four full-scale catalyst beds with the most promising candidate geometries and wash coats were then manufactured and subsequently tested in a 20 N-class HTP (High Test Peroxide) monopropellant thruster. The firing results show that the additively manufactured catalyst beds generally outperformed the baseline catalyst bed containing ceria pellets that were also coated with manganese oxides. [ABSTRACT FROM AUTHOR]

Presented in this paper is a novel net shape manufacturing technology for making three-dimensional micro parts with functionally graded layers. Alumina/zirconia micro parts with either core–shell or top–bottom functionally graded material (FGM) profiles have been successfully fabricated by altering both the surface characteristics of polydimethylsiloxane (PDMS) micro moulds and ceramic suspensions composition. PDMS surface modifications were performed to achieve moulds with hydrophilic surfaces, which were used to form core/shell FGM green layers. On the other hand, moulds with hydrophobic surfaces were used to form top–bottom green layers. Cracks have been found between consecutive layers in both the green and sintered micro parts. It was found that, at dispersant concentration of about 9.0 mg g−1, the differences in the drying shrinkage between layers is less than 0.5%. In addition, layers of composition of 100% Al2O3–0% YSZ, 20% Al2O3–80% YSZ and 40% Al2O3–60% YSZ were found to produce less shrinkage difference during sintering. After optimization of both green and sintering layers, crack free core/shell and top–bottom alumina/zirconia FGM micro parts were successfully obtained. The proposed process enables the production of micro patterns tailored with functionally graded microstructures to locally enhance properties and performance. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports a preparation process of alumina suspension for microfabrication of nanoparticle-alumina composites. A preceramic coating resin (PCR) was used both as binder instead of traditionally organic binders and as an additive of SiC or Si3N4 or both. The gravity-settling behaviour of the Al2O3/acetonitrile suspensions has been characterized with varying poly vinyl pyrrolidone (PVP) concentration. Appropriate PCR amount and optimized curing conditions have been found and proven to be successful in achieving dense and uniform green and sintered microcomponents. The optimal parameters of alumina composite suspension for mould filling are achieved as PVP concentration in acetonitrile=0.1g/ml, minimum amount of PCR=18%, and solid loading=60wt.%. [Copyright &y& Elsevier]