National Key Laboratory of Advanced Functional Composite Materials

Beijing, China

National Key Laboratory of Advanced Functional Composite Materials

Beijing, China

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Zhang J.,National Key Laboratory of Advanced Functional Composite Materials | Chen J.,Xi'an Jiaotong University | Wang H.,Xi'an Jiaotong University
Key Engineering Materials | Year: 2012

Porous wave transmitting Si 3N 4 ceramics have been of great interest and technological importance in aerospace area. In this paper, the high performance wave transmitting porous Si3N4 ceramics was prepared by gel-casting method, without any pore-former. The porosity was controlled by the solid content of the slurry. The flexural strength and dielectric properties of the material were determined by three bending method and a resonant cavity method. The effect of porosity on dielectric properties was investigated. As a result, the flexural strength of the porous Si 3N 4 is 40-200MPa with porosity of 67-45%, dielectric constant of 2.2-3.4 in the frequency of 8GHz at room temperature. With the increase of porosity, both the dielectric constant and dielectric loss decreased. © (2012) Trans Tech Publications.


Yu J.,Xi'an Jiaotong University | Wang H.,Xi'an Jiaotong University | Zhang J.,National Key Laboratory of Advanced Functional Composite Materials | Zhang D.,National Key Laboratory of Advanced Functional Composite Materials | Yan Y.,Xi'an Jiaotong University
Journal of Sol-Gel Science and Technology | Year: 2010

The gelcasting preparation of high-performance porous Si3N 4 ceramics by merely increasing monomer content in the slurry without other organic additives was presented, and the influences of monomer content and the ratio of monomers on gelcasting preparation of porous Si 3N4 ceramics were investigated. The results suggest that monomer content and the ratio of monomers have great influences on the performances of green body and sintered body of porous Si3N 4 ceramics, and the warpage and shrinkage of green body can be effectively improved by selecting reasonable the ratio of monomers. High-performance sintered body was achieved by high-performance green body. The pore size of porous Si3N4 ceramics is less than 1 μm, and the flexural strength and porosity are above 130 MPa and above 50%, respectively. © 2009 Springer Science+Business Media, LLC.


Wang C.,Xi'an Jiaotong University | Wang H.,Xi'an Jiaotong University | Fan X.,Xi'an Jiaotong University | Zhou J.,National Key Laboratory of Advanced Functional Composite Materials | And 2 more authors.
Journal of the European Ceramic Society | Year: 2015

β-Si3N4-based coating was prepared on the porous Si3N4 ceramic using the liquid infiltration and filling method. The effect of sintering temperature on microstructures, water absorption, mechanical properties and erosion resistance of the coatings were investigated. The results show that phase components of all the coatings consisted of β-Si3N4, Y10Al2Si3O18N4 and Y-Si-Al-O glass. The coatings prepared at 1700 and 1800°C had a good water resistance, which can be attributed to the high density of the coatings. The defects, including large pores and micropores, were produced within the coating when the sintering temperature was up to 1900°C, thus leading to the reduction of the water resistance. Hardness and elastic modulus of the coating increased gradually as the sintering temperature increased from 1700 to 1800°C, but it began to decrease when the sintering temperature was 1900°C. The coating prepared at 1800°C displayed a good erosion resistance. © 2014 Elsevier Ltd.


Gao D.,Beihang University | Zhang Y.,Beihang University | Xu C.-L.,National key Laboratory of Advanced Functional Composite Materials | Song Y.,Beihang University | Shi X.-B.,National key Laboratory of Advanced Functional Composite Materials
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2011

Oxidation of ZrB2-20vol% ceramic composites in air was investigated, and the effects of oxygen partial pressure, oxidation temperature and holding time on the formation of zircon phase ZrSiO4 were analyzed. The formation mechanism of zircon during oxidation in air of zirconium diboride-silicon carbide ceramic composites is proposed. Active oxidation of SiC is the major reason to explain the appearance of zircon according to thermal dynamic calculation results. The experimental results indicate that the formation of zircon can be divided into two steps: (I) Nucleation, which is related to the active oxidation of SiC; (II) Crystal growth, which is fulfilled by the reactions between silicate glass and zirconia crystalline at the interface of the zircon nuclei/melt. Zircon particles with mean size of 100 μm can be observed after oxidation in air for 90 min.


Wang C.,Xi'an Jiaotong University | Fan L.,Xi'an Jiaotong University | Fan J.,National Key Laboratory of Advanced Functional Composite Materials | Zhang D.,National Key Laboratory of Advanced Functional Composite Materials | Wang H.,Xi'an Jiaotong University
Journal of Alloys and Compounds | Year: 2013

Al2O3 coatings were prepared using supersonic plasma spraying on the porous Si3N4 substrate at the spraying power of 52, 54, 58 and 60 kW, respectively. The effect of spraying power on the microstructures and properties of Al2O3 coating was investigated. The feedstock particles were sufficiently melted and Al 2O3 coatings become more and more compact with the increasing spraying power. However, the defects, including the surface cracks, interlamellar cracks and needle-like particles, were produced within the coating when the spraying power was 60 kW due to the excessive power. As-received Al2O3 coatings sealed the surface pores of porous Si 3N4, and decreased the water absorption obviously, but only with a slight decrease of the total porosity. Vickers hardness and flexural strength of porous Si3N4 with Al2O3 coating increased gradually as the spraying power increased from 52 to 58 kW, but it began to decrease when the spraying power was up to 60 kW due to the appearance of defects within the coating. © 2013 Elsevier B.V. All rights reserved.


Yu J.,Xi'an Jiaotong University | Wang H.,Xi'an Jiaotong University | Zhang J.,National Key Laboratory of Advanced Functional Composite Materials | Yan Y.,Xi'an Jiaotong University | And 2 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2010

Based on orthogonal experimental results of porous Si3N4 ceramics by gel casting preparation, a three-layer back propagation (BP) artificial neural network (BP ANN) was developed for prediction of the flexural strength and porosity. The BP ANN is composed of three neurons in the input layer, two neurons in the output layer and six neurons the hidden layer. This study demonstrates that the proposed neural network approach can predict the performances of porous Si3N4 ceramics by gel casting preparation to a high degree of accuracy, and the neural network is a very useful and accurate tool for performances analysis of porous Si3N4 ceramics. By the proposed neural network prediction and analysis, the results suggest that the porosity monotonically decreases with the increase of solid loading, flexural strength is low when solid loading was too low or too high and flexural strength has an optimum value.


Gao D.,Beihang University | Zhang F.,Beihang University | Zhang Y.,Beihang University | Song Y.,National Key Laboratory of Advanced Functional Composite Materials | Shi X.,National Key Laboratory of Advanced Functional Composite Materials
International Journal of Modern Physics B | Year: 2010

Amorphous materials of the Si-(B)-C-N system have recently attracted considerable interest because of its hardness, low density, durability at extremely high temperature and easy to be prepared from precursor compounds by polymer route. The materials show a great potential to be used in the field of the Thermal Protective System (TPS) for the aircrafts, while the microstructure and chemical configuration are still not clearly revealed due to its complicated covalent character for this multi-component amorphous material. This paper focused on the characterization of polymer derived Si-(B)-C-N amorphous ceramic, various method were employed in order to obtain accurate information about the microstructure, chemical composition, bonding mode of components, such as TEM, EPMA, NMR and FT-IR. SiC crystalline was found existing in the amorphous glass, which indicates the preparation process was achieved accompanied by crystallization of SiC from polymer precursor. The microstructure of the researched material was analyzed and relative accurate chemical composition was obtained on the basis of characterization result, furthermore the covalent character of the amorphous material was deduced according to the characterization results obtained. © 2010 World Scientific Publishing Company.


Zhang F.,Beihang University | Zhang Y.,Beihang University | Li A.,Beihang University | Zhang D.,National Key Laboratory of Advanced Functional Composite Materials | Li Z.,National Key Laboratory of Advanced Functional Composite Materials
International Journal of Modern Physics B | Year: 2010

In the present work, a series of samples were prepared by pressureless sintering from the starting materials of Si3N4 (α and/or β phases), SiO2 and Li2CO3. The phase transformation was studied with emphasis on the influence of sintering temperature and Li2CO3 content. Related phase transformation was observed and analyzed by SEM and XRD and probable mechanisms were given, which will be helpful for the further explanation to the oxidation mechanism of Si3N4 based ceramics at elevated temperature. © 2010 World Scientific Publishing Company.


Lu X.,Xi'an Jiaotong University | Wei Y.,Xi'an Jiaotong University | Wang H.,Xi'an Jiaotong University | Wen J.,Xi'an Jiaotong University | And 2 more authors.
Journal of Materials Science and Technology | Year: 2014

A water-quenching technique has been adopted to evaluate thermal shock fracture and fatigue behaviors of porous Si3N4 ceramics in an air atmosphere. The high-porosity Si3N4 ceramics exhibit a higher strength retention and a better resistance to thermal shock fatigue because of its role of the pores as crack arresters. A dense and coherent surface oxide layer leads to a significant benefit in residual strength during thermal fatigue, however, an increased fatigue number to 30th cycle cannot cause a further influence although a thicker oxide layer presents, which is attributed to holes defect and disappearance of part intergranular phase. © 2014.


Wang H.,Xi'an Jiaotong University | Yu J.,Xi'an Jiaotong University | Zhang J.,National Key Laboratory of Advanced Functional Composite Materials | Zhang D.,National Key Laboratory of Advanced Functional Composite Materials
Journal of Materials Science | Year: 2010

Wave-transparent materials used at high temperature environment generated by high supersonic and hypersonic speeds must possess excellent mechanical property. In this paper, porous Si3N4 ceramics with high strength were fabricated by low molding pressure (10 MPa) and pressureless sintering process, without any other pore forming agents. The sintering behavior and the effect of porosity on the mechanical strength and dielectric properties were investigated. The flexural strength of porous Si3N4 ceramics was up to 57-176 MPa with porosity of 45-60%, dielectric constant of 2.35-3.39, and dielectric loss of 1.6-3.5 × 10-3 in the frequency range of 8-18 GHz, at room temperature. With the increase of porosity, the flexural strength, dielectric constant, and dielectric loss all decreased. © 2010 Springer Science+Business Media, LLC.

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