High thermal conductivity SiC/SiC composites for fusion applications
SiC/SiC composites offer excellent potential for fusion energy as well as numerous commercial applications. High manufacturing cost and very low through-the-thickness (transverse) thermal conductivity (below 15 W/m K) hinders wider applications of SiC/SiC composites. To overcome these obstacles, a low cost chemical vapor reaction (CVR) process was developed to fabricate crystalline, high-purity SiC fibers. Several variations of the CVR process were used to fabricate SiC/SiC composites. An unirradiated, 4-mm thick SiC/SiC composite was completely CVR-converted from a converted SiC fiber preform with a pitch graphite matrix, and exhibited a bulk density of 2.65 g/cc, 10% open porosity, room temperature (RT) and 1000°C thermal conductivity values of 70 and 35 W/m K, respectively, and an RT bend strength of 200 MPa.
Microstructure, Mechanical and Thermal Properties of Plasma- Sprayed W/SiC Metal Matrix Composite Coating
** Abstract A functionally graded SiC/W metal matrix composite (MMC) has been successfully produced by gas tunnel type plasma spraying. The starting powder was a mixture of 12% W and 88 wt% SiC. The effect of plasma gun current on the microstructure, mechanical and thermal conductivity properties was investigated. The results revealed that the reaction phases, namely tungsten silicides (WSi2, W5Si3) and tungsten carbides (WC, W2C), were not formed in various processing conditions. The presence of WO3 was detected in the composite deposits, which indicated that the tungsten partially oxidized during plasma spraying. Also, the composite deposited was dense and nearly free of pores due to the small mismatch between the coefficients of thermal expansion (CTE) for W and SiC. Microhardness values gradually decreased as a function of input current due to the formation of WO3 and the decomposition of SiC particles in the high temperature flame region. A thermal conductivity as high as ~ 59 W/m.K was obtained. It was found that both tungsten oxide and structure imperfections have a significant influence on the thermal conductivity and mechanical properties.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.