| High temperature transparent material is a kind of multifunctional dielectric material which is specialized in protecting that systems of aircrafts could work normally such as communications, remote control and GPS etc. in a bad environment and is widely used in radio systems such as spacecrafts, carrier rockets, missiles and satellites etc.. It is divided into two types that are window and cover among which cover is in one side of the aircraft usually taking the form of plate object with arc lines or flat structure while window is at the top of the aircraft usually taking the form of paniculate or hemispheric structure sometimes. It is a multifunctional/structural part which combines with heat transfer, insulation, transparent, load bearing and impact resistance. With the development of scientific technology and the need of modern wars, the requirements of such transparent materials are growing more serious. Taken into full consideration of the above conditions, ceramic materials stand out from the crowed materials esp. ceramic composites materials with many characteristics such as high-strength, high-melting-point, corrosion-resistance and transparent etc.. In this essay, BN is the basic ceramic composites material mixed with a little Si3N4to improve mechanical performance of ceramic composites and the low dielectric performance peculiar to BN ceramic materials is also saved in this paper.Different testing instruments are adopted such as XRD, computer control of electronic universal test machine and SEM etc. to study on the Si3N4/BN ceramic composites and to reflect the dielectric and mechanical performance by testing in this paper. Besides, it analyzes the production of BN powder and the influence to the dielectric and mechanical performance of BN ceramic composites mixed with varying amounts of Si3N4In this paper, the BN powders produced by reaction sintering method is introduced which adopts the reaction of H3BO4and (NH2)2CO to produce BN, adding sintering aids Al2O3/Y2O3and addictives of Si3N4with hot-pressing in advance in the synthesis. It analyzes the influence on the dielectric and mechanical performance of BN ceramic composites by Si3N4addictive amounts and temperature.The experiment proves that system produced by adding Al2O3/Y2O3/Si3N4during the production of BN powders produces Sialon-ceramic which can not only decrease the sintering temperature effectively but also can increase the mechanical performance without noticeable loss in dielectric performance of BN ceramic composites.The test result of dielectric performance shows that the dielectric performance can not change with the variation of sintering temperature but has the direct relations with the Si3N4addictive amounts. When the Si3N4addictive amount is10%, the dielectric constant reaches to5.84, about1.5times compared with pure BN2.31.The result of mechanical performance shows that the bending strength of ceramic composites can peak at139.9MPa when the sintering temperature reaches1750℃, increasing by25%compared with1550℃of the homologous component; the fracture toughness can peak at1.75MPa·m1/2, increasing by16%from1550℃; the bending strength and fracture toughness are positive correlated with Si3N4increasing at the same temperature; when Si3N4addictive amount is10%, the bending strength reaches at the highest level, increasing by62%from pure BN and the fracture toughness is increasing by58%from pure BN; when Si3N4addictive amount is8%, the variation of mechanical performance is not noticeable compared with the addictive amount of10%that the bending strength and the fracture toughness are increasing by2.1%and1.7% respectively.This work was supported by the National Natural Science Foundation of China (Nos.50872072and51042005), Science and Technology Development Project of Shandong Province (Nos.2011GGX10205and2009GG10003003), and Independent Innovation Foundation of Shandong University (2009TS001and2012TS213). |
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