Abstract
The choice of the right material is essential in microwave processing. The carbon materials are good microwave absorbers, which allows them to be transformed by microwave heating into new carbon materials with adapted properties, capable of heating other materials indirectly. In this paper, the microwave heating of graphene as reinforcement of the lithium aluminosilicate (LAS) ceramics has been explored. LAS ceramics have a near-zero coefficient of thermal expansion and exhibit an effective and efficient heating by microwave. Nevertheless, we have found that the graphene did not show any significant response to the microwave radiation and, hence, the interaction as mechanical reinforcement with the LAS material is harmful. The possible benefits of graphene materials to microwave technology are widely known; however, the mechanism involved in the interaction of microwave radiation with ceramic-graphene composites with high dielectric loss factors has not been addressed earlier.
Highlights
The lithium aluminosilicate (LAS) system has been extensively studied in the last decades, due to its very low or even negative coefficient of thermal expansion (CTE) [1,2,3,4,5]
Raman spectroscopy is a very useful technique in order to evaluate the thermal reduction of the graphene oxide along the composite
The study of the behavior of graphene as a second phase in LAS matrix composites obtained by a non-conventional microwave sintering technique has been carried out for the first time, to the best of our knowledge, in the current investigation
Summary
The lithium aluminosilicate (LAS) system has been extensively studied in the last decades, due to its very low or even negative coefficient of thermal expansion (CTE) [1,2,3,4,5]. LAS materials have found a wide application field including cookware, bakeware, electronic devices, telescope mirror blanks, ring-laser gyroscopes, optically stable platforms and new materials for space missions. These applications have been focused on the glass-ceramic materials. To obtain LAS in the solid state with high mechanical properties and a near-zero CTE values has been a great challenge [6,7,8]. The high temperatures required to fully densify LAS powders result in vitreous phase transformation, large grain sizes and decreased mechanical and thermal properties. There are two ways to overcome these problems; to employ non-conventional sintering alternative methods such as spark plasma sintering (SPS) and microwave sintering or to reinforce the LAS matrix with a second phase (i.e., Al2 O3 , SiC, carbon nanofibers . . . ) [9,10,11,12]
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