Olga García-Moreno

Lithium aluminosilicate reinforced with carbon nanofiber and alumina for controlled-thermal-expansion materials

Abstract Materials with a very low or tailored thermal expansion have many applications ranging from cookware to the aerospace industry. Among others, lithium aluminosilicates (LAS) are the most studied family with low and negative thermal expansion coefficients. However, LAS materials are electrical insulators and have poor mechanical properties. Nanocomposites using LAS as a matrix are promising in many applications where special properties are achieved by the addition of one or two more phases. The main scope of this work is to study the sinterability of carbon nanofiber (CNFs)/LAS and CNFs/alumina/LAS nanocomposites, and to adjust the ratio among components for obtaining a near-zero or tailored thermal expansion. Spark plasma sintering of nanocomposites, consisting of commercial CNFs and alumina powders and an ad hoc synthesized β-eucryptite phase, is proposed as a solution to improving mechanical and electrical properties compared with the LAS ceramics obtained under the same conditions. X-ray diffraction results on phase compositions and microstructure are discussed together with dilatometry data obtained in a wide temperature range (−150 to 450 °C). The use of a ceramic LAS phase makes it possible to design a nanocomposite with a very low or tailored thermal expansion coefficient and exceptional electrical and mechanical properties.

Sintering of mullite-b-eucryptite ceramics with very low thermal expansion

Abstract Sintering of composite ceramic materials with an appropriate proportion of mullite and β-eucryptite to obtain a very low thermal expansion material has been tested by conventional and spark plasma sintering methods. The adjustment of the thermal expansion coefficient of the composites was performed by means of dilatometries and modifying the mullite–β-eucryptite proportions in the starting materials. Control of the reactivity between both phases at high temperature is the key to controlling not only the sinterability of the composites in the solid state, but also to controlling the final expansion properties of the material. X-ray diffraction with Rietveld refinement and field emission scanning microscopy have been used to characterize the sintered materials, together with some mechanical characterization.