Shoji Uchimura

Fabrication of Bi2-xSbxTe3 (x=0-1.5) Thick Film by Centrifugal Deposition

A Bi2-xSbxTe3(x=0-1.5) thick film thermoelectric element was fabricated using centrifugal deposition and its Sb content-dependent thermoelectric properties were investigated. When the Sb content was low (x=0.5), two types of fine structure along the direction of the thickness were observed. Pole figure measurements revealed that the vicinity of the film surface was composed of single crystal layers oriented along the c-axis and the vicinity of the interface with the substrate was composed of randomly orientated layers. As the content of Sb increased, the degree of orientation improved, and at x=1.5 the entire film was close to a single crystal. A Bi0.5Sb1.5Te3 thick film showed p-type thermoelectric properties and a thermoelectric power factor of 3.5 ×10-3W/mK2. It was thus demonstrated that centrifugal deposition can be used to fabricate thermoelectric elements with high efficiency.

Centrifugal Sintering - Development of a New Pressure Sintering Process -

Centrifugal sintering is a novel process for the preparation of thick films. In this process, high gravity such as 104g is applied at high temperatures. Because of the distinctive measure of pressing by the centrifugal force, gradient of pressure arises in the specimen, resulting in the graded porous structure during the progress of sintering. After the sintering, highly densified thick films are obtained. Furthermore, crack formation was suppressed by this process.

Centrifugal Sintering of Copper

The ceramic film with thickness of several ten μm to several mm on a substrate and small ceramic piece with a complicated shape have been interested because of highly integrated, small electric devices. In this work, we suggest novel centrifugal sintering method, which can be sintered ceramic film and small ceramic piece by applying high pressure without pressure medium, and its processing merit. Furthermore, outline of installed sintering equipment and experimental result were shown. Introduction Since ceramic thin and thick films are key materials for highly integrated electronic devices, their processing strategy is very significant. As for chemical processing, ceramic film is conventionally obtained by preparing chemical solution, dip-coating on a substrate material, drying, followed by sintering. In this case, formation of crack can not avoid in ceramic film. The crack formation is mainly divided into three categories. During dip-coating, crack forms due to difference between vapor pressure and capillary pressure of slurry solvent. In the drying, mismatch occurs due to shrinkage of ceramic dry structure and restriction of ceramic around substrate, making significant breakage in ceramic. Similar crack formation is also found during sintering [1]. Therefore, plastic materials to relax the mismatch are always added to slurry solvent [1]. Furthermore, low-temperature sintering of ceramic film on substrate is strongly required because of limitation of heat resistance in substrate. In order to solve these problems, we suggest a novel high-pressure firing/sintering technique without pressure media. Concept of Centrifugal Sintering To avoid crack formation and promote densification, we offer centrifugal sintering Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 757-760 doi:10.4028/www.scientific.net/KEM.264-268.757

Ceramics Processing Assisted by Centrifugal Pressure

Constrained sintering, as seen in the sintering of laminated structure or thick film, inherently involves the problem of macroand micro-defect formation such as cracks and/or de-lamination. The origin of these defects lies in mismatches of sintering shrinkage between materials. Sintering under centrifugal acceleration has been found to be a successful strategy for eliminating these mismatches, leading to a crack-free homogeneous microstructure. This distinctive feature of centrifugal sintering arises from anisotropic shrinkage that is caused by chief densification progress along the radius of rotation.

Porosity-grading porous materials by centrifugal sintering

We have demonstrated a new synthesis of ceramics with porosity-grading microstructure, being achieved by applying high acceleration to ceramics during sintering. The acceleration was generated by high-speed rotation of ceramics, which allows pressing materials gradually along the radius of rotation. The origin of microstructure has been explained quantitatively from the basis of sintering kinetics, in which non-uniform shrinkage caused by a centrifugal pressure has been taken in account.