Morphology of magnesium lithium aluminum silicate matrix reinforced by silicon carbide fibers during high temperature tests

Ceramics with zero thermal expansion coefficients at room temperature (293K) were investigated. We found the thermal expansion coefficient was controlled by a compounding ratio of lithium aluminum silicate (LAS) and silicon carbide (SiC), which have negative and positive thermal expansion coefficients respectively. Although it was difficult to densify the composite of the LAS and SiC (LAS/SiC) in the sintering process, an addition of nitride improved the sinterability of the LAS/SiC. In order to examine the effect of the nitride additive, at first, the melting point of the LAS with silicon nitride (Si3N4) or aluminum nitride was measured by TG-DTA. The melting point of the LAS decreased with existence of nitride. It is believed that the densification of the LAS/SiC was promoted by the nitride, because the nitride causes the LAS/SiC to form a liquid phase, thereby decreasing the melting point. Next, the lattice constant of the LAS with Si3N4 was measured by XRD and it was verified that the a-axis was longer and the c-axis was shorter than those of the LAS without additive. It is supposed that this phenomenon is due to the substitution of nitrogen for oxygen in the LAS lattice, and the decrease of the melting point of the LAS with nitride seems to be influenced by this substitution of nitrogen.

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High-temperature microwave bilayer absorber based on lithium aluminum silicate/lithium aluminum silicate-SiC composite

Ceramics International ◽

10.1016/j.ceramint.2013.05.101 ◽

2014 ◽

Vol 40 (1) ◽

pp. 47-55 ◽

Cited By ~ 34

Author(s):

Cheng-Hsiung Peng ◽

Pang Shiu Chen ◽

Ching-Chih Chang

Keyword(s):

High Temperature ◽

Aluminum Silicate ◽

Lithium Aluminum

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CVD Coating of Ceramic Monofilaments

MRS Proceedings ◽

10.1557/proc-250-263 ◽

1991 ◽

Vol 250 ◽

Author(s):

Jason R. Guth

Keyword(s):

Silicon Carbide ◽

High Temperature ◽

Hydrogen Reduction ◽

Low Pressure ◽

Refractory Metals ◽

High Toughness ◽

Composite Systems ◽

Silicon Carbide Fibers ◽

Sapphire Fibers

AbstractIn many composite systems it has become apparent that coatings on the reinforcements are necessary to achieve high toughness materials. In order to examine materials which may be used as coatings on ceramic monofilaments and remain stable in high temperature, oxidizing environments, the deposition of a number of refractory metals has been attempted. The results of coating experiments using silicon carbide fibers as substrates as well as general observations concerning the prospects of continuously coating long lengths of fibers will be discussed. The materials studied include carbon, cobalt, zirconium, molybdenum, tantalum, tungsten, and iridium. Carbon has been deposited from methane and propylene onto both SiC and sapphire fibers. Deposition of the metals has been achieved by direct chlorination of the metals followed by hydrogen reduction at the fiber. Iridium(III)2,4-pentanedionate has been used to deposit iridium metal. All metals were deposited at low pressure in a hot wall reactor with fibers continuously spooled through the reactor.

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