Papers by Keyword: ß-SiAlON

Abstract: β-Sialon/Ti(C,N) composites were prepared using low and middle grade bauxite and ilmenite as raw material,while coke as reducing agent in high purity nitrogen atmosphere through carbothermal reducrion-nitridation(CRN).The main phases of low and middle grade bauxite are kaolinire(Al2O3•2SiO2•2H2O) and (Al2O3•H2O)2 and ilmenite mainly contain ilmenite(FeTiO3) and rutile(TiO2).The reaction products of bauxite are the β-Sialon(Z=3,Si3Al3O3N5) while those of ilmenite are TiC and Fe.The results showed that the main phases are β-Sialon,Ti(C,N),Al2O3 and Fe when the reaction temperature is at 1400°C holding for 4 hours(10wt% ilmenite and 90wt% bauxite as raw material).However,β-Sialon decomposes into 21R at 1450°C and into 15R and AlN at 1500°C.So 1400°C is selected as the proper temperature to synthesize β-Sialon/Ti(C,N) composites.At 1400°C,the β-Sialon crystals with the largest quantity grow well and show long column in shape.With the increase of the reacrion temperature β-Sialon begin to decompose,the β-Sialon crystals change to short columnar,with the number decreasing quickly.

Abstract: β-Sialon/ZrO2 composites were prepared using 10 wt. % β-Sialon powder (where the z =1, 2, 3, respectively) and 90 wt. % ZrO2 powder as the starting materials. The effects of the Z value of β-Sialon on the bulk density, apparent porosity, water absorption rate, room temperature modulus of rupture, thermal shock resistance, microstructure and composition of the composites were investigated. The microstructure of sintered specimens was analyzed by scanning electron microscope (SEM), and X-Ray diffraction (XRD). The results revealed that with increase of the Z value of β–Sialon, bulk density gradually increased, apparent porosity and water absorption rate gradually decreased. The specimen possessed a maximum MOR (71.46MPa) when the z=2. In carbon embedded condition, the residual strength ratio of the specimen reached 60% and the lowest thermal expansion rate was obtained (0.55%) when the z=1. The phase compositions were cubic ZrO2 (c-ZrO2) and monoclinic ZrO2 (m-ZrO2). β-Sialon/ZrO2 composites exhibited overall optimum performance when the z equals 2

Abstract: β-Sialon bonded ZrO₂ composites were prepared by reaction sintering process using β-Sialon and CaO stabilized ZrO₂ powders as raw materials.The effect of β-Sialon powder additions on the properties of the composites was investigated. The results show that the samples with 10 wt% of β-Sialon addition had the lowest apparent porosity (29.80%) and the highest of flexural strength (68.70MPa). The thermal shock resistance in carbon addition of the composites could be improved by addtion of 5wt% β-Sialon. It may be relative with that the sample had the lowest thermal expansion coefficient in vacuum.

Abstract: Rutile and fly ash powders were nitridized at different temperatures for 4 h. The influence of temperature on phase composition of nitridation products from rutile and fly ash was studied. XRD, SEM and EDS analyses show that: the phase compositions of the products was quite dependent on the reaction temperature. Mullite, O'-Sialon and X-Sialon were formed from 1400 °C to 1450 °C. Rising temperature would get Mullite nitrided. Meanwhile, O'-Sialon and X-Sialon would be nitrided and transformed into β-Sialon. At temperatures above 1550 °C, the main phases of the products were hexagonal columnar β-Sialon and irregular TiC_0.3N_0.7 grains.

Abstract: Eu²⁺ doped b-SiAlON (z = 1, 3, 4) phosphor were synthesized by carbothermal reduction- nitridation (CRN) using precursors powder as materials. The precursors powder prepared by sol-gel method using the SiO₂, AlCl₃×6H₂O, Eu(NO₃)₃, ammonia water, carbon powders as starting materials. The CRN reaction proceeded at 1380°C for 6 h in an N₂ atmosphere. Eu²⁺ doped b-SiAlON (z = 1, 3, 4) had high adsorption in the UV-visible spectral region. While z = 1, one bands were observed in the emission spectrum centered at about 425 nm monitored at 282 nm. The excitation bands centered at about 282 nm. While z = 3, one bands were observed in the emission spectrum centered at about 425 nm monitored at 282 nm. The excitation bands centered at about 282 nm. While z = 3, the emission spectra exhibit one bands with maxima at about 419 nm under 280 nm excitation. The excitation bands centered at about 280 nm. While z = 4, the emission spectrum centered at about 419 nm monitored at 280 nm. The excitation bands centered at about 280 nm. In this work, luminescence properties of Eu²⁺ doped b-SiAlON (z = 1, 3, 4) are independent of z value. It is possible related to the low synthesis temperature.

Abstract: The composite specimens have been prepared using fused corundum, silicon and bauxite-based β-SiAlON powder as starting materials. The physical properties, high temperature modulus of rupture (HMOR), thermal shock resistance (TSR), phase composition and microstructure of the specimens after firing at 1500°C have been studied. The results show: (1) Al₂O₃-SiC-SiAlON composites are sintered well at 1500°C. (2) HMOR and TSR of the specimens increase with increase of Si content, high temperature properties are further increased with appropriate β-SiAlON addition. (3) The in-situ formed SiC and O’-SiAlON fill in the interstices of corundum skeleton structure, forming interlocking network structure, thus creating strengthening and toughening effects.

Abstract: Using corundum particles and fine powder, α-Al₂O3 powder, silicon powder, aluminum powder and some additives as raw materials, β-Sialon bonded corundum composite was synthesized in-situ at the nitrogen atmosphere. The influence of Z value in sialon phase and sintering temperature on physical properties, mechanical properties, thermal shock resistance and anti-oxidation performance of β-Sialon bonded corundum composite was investigated. The results indicate that the comprehensive properties of β-Sialon bonded corundum composite is excellent on condition that Z=2.75, sintering temperature is 1500°C at nitrogen atmosphere.

Abstract: Diffusion bonding of sialon and 7.5%-Cr Ferritic Steel (FS) in as-received and nitrided condition was studied. Decomposition of sialon and interdiffusion of elements between the sialon and the steel were observed. The interdiffusion of elements produced reaction layers at the joint. The steel moved into the decomposition part of the sialon and replaced the decomposed sialon in this part. Diffusion of silicon into the steel resulted in the silicon-diffusion layer. FeSi2 was formed in the reaction layer when Si in the decomposition part of the sialon reacted with Fe. The use of nitrided steel in the diffusion bonding had suppressed the formation of the FeSi2 in the layer.

Abstract: β-Sialon powder was synthesized by in-situ carbothermal reduction-nitridation process, with fly ash and carbon black as raw materials. The influence of raw materials composition on synthesis process was investigated, and the phase composition and microstructure of the synthesized products were characterized by X-ray diffraction and scanning electronic microscope. The carbothermal reduction-nitridation reaction process was also discussed. It was found that increasing carbon content in a sample could promote the decomposition of mullite in fly ash and the formation of β-Sialon. The β-Sialon could be synthesized at 1550°C for 6h by heating the sample with the mass ratio of fly ash to carbon black of 100:56. The β-Sialon as-received in this study existed as granular with an average particle size of about 2μm. The carbothermal reduction-nitridation reaction process consisted of the nitridation processes of mullite, SiO₂ and Al₂O₃ in fly ash as well as the conversion process of X-Sialon to β-Sialon.

Abstract: The joining of high temperature structural ceramics to other materials is an important process commercially and technologically. Due to the existence of physical and economic limitations for the manufacture of large parts, joining is essential. Functional gradient materials (FGMs) are designed to exhibit a desirable gradient in a property, due ether to a gradient in composition, or microstructure, or both. In this paper, Si3N4-Al2O3 functional gradient joining material was prepared by hot press sintering of multilayered FGMs with 20 layers of thickness 400um each using β-Sialon as transient interlayer. The structure and properties of the materials were analyzed by the means of scan electron microscopy(SEM), X-ray diffraction(XRD) and micro-sclerometer. The components of the materials have gradient distribution and successional. The microhardness is gradient changing with the change of micro-structure. The interface between layers is tightly coupling and has no stress convergence. The test of thermal shock and fatigue cracks of FGM between 1300 °C and 900 °C show good properties of thermal stress relaxing and resistance for high temperature.