Showing papers on "Sialon published in 1991"

α'-Sialon ceramics : a review

Abstract: a' -Sialon ceramics promise the possibility of a reduction of the amount of glassy grain boundary phases by incorporating the oxides, present in the starting mixture as either sintering additives or impurities, into its rmallattice. It has been shown that techniques such as gas pressure sintering can be used successfully to obtain fully reacted and dense a'- or (a' + s')-sialons. By combination of suitable modifier cations and heat treatment the amount of grain boundary phases can be kept very low. This may lead to improved mechanical properties, especially at elevated temperatures. The equiaxed microstructure of a' -sialons, compared with the needlelike structure of s'sialons, leads to specific differences in mechanical behavior. However, at this moment the complicated interrelationships between the formation sequence, fabrication conditions, properties, and microstructures are still insufficiently understood. Yet, even with the resent-day materials, wear resistance, high-temperature mechanical strength, thermal shock resistance, and oxidation resistance are such that further studies are worth-while.

Sintering, properties and applications of silicon nitride and sialon ceramics

Abstract: Vue d'ensemble des mecanismes du frittage et des facteurs influant sur le frittage pour des systemes a base de nitrures contenant des additifs solubles ou insolubles. Discussion des relations microstructure-proprietes. Presentation de quelques applications (composants de moteurs, paliers et billes de roulement, outils de coupe).

Silicon nitride sintered body and process for producing the same

Abstract: Disclosed is a silicon nitride sintered body produced by subjecting a green compact of a mixed powder composed of 1) a silicon nitride powder having a percentage a crystallization of 93% or more and a mean grain diameter of 0.7 µm or less and 2) 5 to 15% by weight in total of a first sintering aid selected from among rare earth element, yttrium oxide and lanthanide oxides and a second sintering aid consisting of aluminum oxide or nitride and at least one selected from among oxides and nitrides of Mg, Ca and Li, to primary sintering in a nitrogen gas atmosphere under a pressure of 1.1 atm or less at 1500 to 1700 °C; and subjecting the sintered body to secondary sintering in a nitrogen gas atmosphere under a pressure of 10 atm or more at the primary sintering temperature or below, thereby giving a sintered body wherein the relative density of the sintered body is 99% or more and the precipitation ratio of an .alpha.-Si3N4 (including .alpha.'-sialon) crystal phase to a .beta.-Si3N4 (including .beta.'-sialon) crystal phase ranges from 1 : 3 to 1 : 8 in terms of the peak intensity ratio in X-ray diffraction.

Deformational behaviour of ceramics

Abstract: The application of modern ceramics, such as cordierite or partially stabilized zircona (PSZ), calls for more detailed data than those provided by conventional investigation of strength or crack-resistance characteristics. To provide data on deformational behaviour (including possible inelasticity), a parameter is proposed in the form of a ‘brittleness measure’, χ. At χ = 1, a ceramic obeys Hooke's law and in its mechanical behaviour is similar to glass. At the same time, its behaviour under loading is like that of concrete and it does not correspond to the elastic-solid model. It has been found that aluminium oxide toughened by zirconium dioxide and zirconium dioxide stabilized by yttrium oxide are characterized by the χ = 1 parameter, while cordierite, silicon nitride with boron nitride, corundum refractory material with zirconium dioxide, and zirconium dioxide stabilized by magnesium oxide are characterized by χ < 1. It is shown that, unlike ceramics with χ = 1, ceramics with χ < 1 retain residual stresses. Being inelastic, they have an ascending R-curve and show insignificant differences in the values of the critical-stress-intensity factor obtained for specimens with a notch and sharp crack. The analytical evaluation of such ceramic materials should be based on the proportionality limits rather than on the ultimate-strength values. Thermal-shock-resistance criteria should take into account the actual values of ultimate strains. The data presented reveal that, in the evaluation of serviceability, specific features of mechanical behaviour are as important as absolute values of properties. The values of the parameter χ and ultimate strains may be regarded as important physicomechanical characteristics of this type of material.

Formation of an Y/Ce-doped α-sialon phase

Abstract: α-β-Sialon materials were prepared with a constant molar addition of Y2O3 + CeO2 sintering aid with varied composition: 0, 25, 50, 75 and 100 mol% Y2O3. The α-sialon grains formed in the microstructure were carefully investigated by analytical and high-resolution electron microscopy. It was found that the α-sialon structure can accept a small amount of cerium to enter the large interstitial cages, if it is stabilized by simultaneous additions of yttrium. Extended crystal defects were found to occur in the α-phase framework; this has not been observed with only yttrium added.

Sialon-based sintered body and process for producing same

Abstract: A SiAlON-based sintered body having a high mechanical strength and fracture toughness, as well as an excellent oxidation resistance, is provided. The SiAlON-based sintered body comprises 5 to 50% by weight of a first crystal phase of REα-SiAlON represented by RE x (Si, Al) 12 (O, N) 16 , where RE stands for at least one modifying rare earth element selected from the group consisting of Ho, Er, Tm, Yb and Lu and x has a value of 0

Synthesis and Characterization of β’-SiAlON Ceramics from Organosilicon Polymers

Abstract: A polycarbosilane has been modified with aluminum alkoxide to obtain a new preceramic compound. The pyrolysis in NH3 flow of this polyaluminocarbosilane leads to the formation of an amorphous Si-Al-O-N phase. The nitridation process has been followed by IR and 29Si MAS-NMR spectroscopies. A fine-grained β-SiAION ceramic is obtained by firing the amorphous phase at 1500°C. The crystallization process has been studied by XRD, 29Si MAS-NMR, and TEM techniques.

Tribochemical Lubrication of Ceramics by Carbonaceous Vapors

Abstract: Friction coefficients of less than 0.02 and negligible wear have been attained and continuously maintained in a pin-on-disc apparatus between a sapphire pin and discs of Sialon, silicon carbide, zirconia or zirconialalumina as long as a carbonaceous gas or vapor, such as ethylene, propane, benzene, or 1-propanol, was supplied to the conjunction region. Mean contact pressures were around 300 MPa and bulk temperatures were varied between ambient and 700°C. For every ceramic and vapor combination some temperature ranges exhibited high friction and wear, others very low friction and wear. Raman and Auger spectroscopies of the carbonaceous deposits formed in the wear tracks show significant differences depending on the temperature range and the feed gases or vapors supplied. In general, friction and wear reduction occurred in two steps at different rates. The tribochemistry involved is likely to comprise hydrocarbon acid-catalytic cracking at low temperatures and pyrolysis at high temperatures. Presented as a ...

Synthesis of nitrogen ceramic povvders by carbothermal reduction and nitridation Part 2 Silicon aluminium oxynitride (sialon)

Abstract: Silicon aluminium oxynitride (β′ sialon) powders have been prepared by reacting kaolin–carbon mixtures at 1400–1500°C in flowing nitrogen. The kaolin/carbon ratio in the starting mixtures must be accurately controlled to obtain single phase β′ powders. The overall reaction rate increased with increasing nitrogen flowrate. However, if the nitrogen flowrate was too high, the amount of 15Rand AlN phases in the reaction products increased. A change of carbon source in the starting mixtures affected the phase composition as well as the morphology of the product powders. It was found that the evaporation of SiO is a most important factor in the reaction, strongly affecting the phase composition of the reaction products.MST/1346b

The SiAlON system at temperatures of 1700–1775°C

Abstract: Mixtures of Si3N4, SiO2, Al2O3 and AlN have been used to prepare series of specimens heat treated at 1700, 1730, 1750 and 1775°C. The phase relations of the liquid-rich area of the SiAlON system were studied in detail by X-ray diffraction and scanning electron microscope analysis. Each specimen was chemically analysed after the heat treatment to determine any changes in the overall composition. Finally, the observations have been used to obtain a slightly revised phase diagram at a temperature range of 1700–1730°C for the system Si3N4-SiO2-Al2O3-AlN.

The formation of β′-sialon from a montmorillonite-polyacrylonitrile composite by carbothermal reduction: an NMR, TGA, XRD and EM study

Abstract: The products of carbothermal reduction in N2 of a nanocomposite between dodecylammonium-exchanged montmorillonite and polyacrylonitrile (PAN) have been studied by solid-state 27Al and 29SiNMR spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetry. Comparison with analogous reactions involving sodium-exchanged montmorillonite and dodecylammonium-exchanged montmorillonite (without PAN) shows that in the presence of PAN, the formation of silica, cordierite or mullite is almost completely suppressed. The only crystalline phase detected between 1000 and 1300 °C was a β′-sialon, having a much higher Si∶Al ratio (7.05∶1) than that of the precursor clay (2.44∶1). Reduction of the octahedral AlO6 begins near 1200 °C, forming increasing amounts of Al(N,O)4 tetrahedra with temperature, so that by 1600 °C, complete reduction to AlN4 (i.e. bulk AlN) has occurred. In contrast, reduction of the tetrahedral SiO4 is appreciable at 1100 °C, and is almost complete (SiN4 tetrahedra only) by 1200 °C. No intermediate Si(N,0)4 environments are found. By 1600 °C, only the SiC4 environment (i.e. bulk SiC) remains. A mechanism is suggested, involving the formation of alternating slabs of an amorphous aluminosilicate and carbon at 1000 °C, followed by diffusion of silicon from the outer regions of the aluminosilicate band towards the centre, and sequential reduction of Si(OSi)4 and Si(OSi)3 (OAl) groups.

Refractory materials formed from refractory grains bonded by a sialon matrix containing dispersed graphite and/or boron nitride particles and a process for the preparation of these materials

Abstract: The invention relates to refractory materials having high resistance to corrosion, high mechanical strength at elevated temperature and high resistance to thermal shock, comprising: (A) grains of at least one refractory material whose melting point or, where appropriate, thermal decomposition temperature is higher than 1700° C., these particles being dispersed in (B) a binding matrix consisting predominantly of a sialon of formula Si 6-z Al z O z N 8-z , where z ranges from 0.5 to 4, as determined from an X-ray diffraction pattern, wherein said refractory materials also comprise: (C) particles of hexagonal boron nitride and/or crystalline graphite dispersed in the binding matrix. Use in iron and steel metallurgy, in particular as slide closing plates, immersed nozzles, etc.

Dense β- and α/β-SiAlON materials by pressureless sintering of combustion-synthesized powders

Abstract: On montre la possibilite de synthese in situ de divers sialons β et α/β par une technique de combustion sous pression d'azote elevee. On etudie en detail l'effet de la composition des reactifs, de la morphologie des particules et de la dilution de la phase solide initiale sur la conversion finale et l'homogeneite de phase du produit. Les conditions optimales de reaction sont proposees. Des details sur la microstructure, la microdurete et la tenacite des sialons β et α/β frittes sont aussi presentes.

Drying of gelcast ceramics

Abstract: Plates (8.9 {times} 90.2 {times} 228.6 mm) of silicon nitride, sialon, and alumina made by gelcasting, a generic near-net-shape forming process, have been dried in a controlled humidity chamber. No constant-rate period was found in drying the gelcast plates. A linear shrinkage of 3--4% was observed, the shrinkage stopping after only about 20% of the total moisture had been lost. Dried parts, free of warpage and cracking, were obtained in reasonable times by controlling the humidity and temperature. 12 refs., 4 figs.

Microstructure and mechanical properties of β′-Si3Al3O3N5 ceramics

Abstract: The properties of 21 different ceramics of β′-Si3Al3O3N5 were measured. The sialons were prepared by three methods: reaction sintering in a gas pressure sintering furnace, reaction hot-pressing and sintering of sialon powder produced by carbothermal reaction from kaolin. Furthermore, the series differed in kind (CeO2 or CaO) and concentration of additive and process conditions. The quantities measured were composition (X-ray diffraction), density, microstructure, Vickers hardness (2 N), Young's modulus, Poisson's ratio, fracture toughness (SEN B) and biaxial strength. Generally the room temperature properties were hardly influenced by the production route, composition or process conditions. Fracture toughness and bi-axial strength were most sensitive to the process conditions. The mechanical properties of kaolin-derived sialon appeared to be as good as those of the other sialons.

The formation of phases in the AlN-rich corner of the Si-Al-O-N system

Abstract: The reaction of AlN with Al2O3, SiO2 or Si3N4 and Al2O3 at temperatures of 1820°C and 1950°C and for compositions rich in AlN have been investigated using powder X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. At 1820°C, Al2O3 reacted with AlN to form the non-stoichiometric oxynitride spinel phase (≈Al23O27N5), whereas samples on the AlN-SiO2 and AlN-‘X-phase’ tie-lines did not react. At 1950°C, AlN-Al2O3 mixtures reacted to form the 27R aluminium oxynitride polytypoid, AlNSiO2 mixtures reacted to form 21R and 27R sialon polytypoids and AlN-‘X-phase’ mixtures reacted to form the 12H, 21R and 27R sialon polytypoids, all of which possessed a needle-like morphology. Ordered and disordered intergrowths were also observed in the polytypoid crystals but the disordered 2Hδ sialon phase was not found.

Reaction chemistry at joined interfaces between silicon nitride and aluminium

Abstract: Joined interfaces of HIPed additive-free silicon nitride ceramics/aluminium braze bonded at a low temperature of 1073 K for 18 ks or at a high temperature of 1473 K for 1.8 ks in vacuum of 1.3 mPa and of β silicon nitride powders/aluminium powders bonded at the low temperature for 1.8 ks or 18 ks in the same vacuum are identified by analytical transmission electron microscopy and X-ray diffraction method. Mullite, some small crystals and β′-sialon are detected at the interface of the ceramics/aluminium braze bonded at the low temperature and 15R AIN-polytype sialon, β′-sialon, aluminium nitride, mullite and silica-alumina noncrystalline are detected at that bonded at the high temperature. At the interface of the two kinds of powders, aluminium nitride and silicon are also detected besides β′-sialon and silica-alumina noncrystalline even though the bonding was conducted at the low temperature. The interfacial reactions of the joints are influenced not only by bonding temperature but also by the oxide formed at the interface before bonded.

Plasma Etching of α‐Sialon Ceramics

Abstract: Plasma etching of β-Si 3 N 4 , α-sialon/β-Si 3 N 4 and α-sialon ceramics were performed with hydrogen glow plasma at 600°C for 10 h. The preferential etching of β-Si 3 N 4 grains was observed. The etching rate of α-sialon grains and of the grain-boundary glassy phase was distinctly lower than that of β-Si 3 N 4 grains. The size, shape, and distribution of β-Si 3 N 4 grains in the α-sialon/β-Si 3 N 4 composite ceramics were revealed by the present method

Mechanical properties of SiC-particle/sialon composites

Abstract: On a utilise des particules de carbure de silicium pour renforcer des sialons. On examine la microstructure et les proprietes mecaniques des composites obtenus

Wetting of tin-based active solder on sialon ceramic

Abstract: xian, ap (reprint author), acad sinica,inst met res,72 wen hua rd,shenyang 110015,peoples r china

Preparation and crystal structure of U-phase Ln3(Si3 –xAl3 +x)O12 +xN2 –x(x≈ 0.5, Ln = La, Nd)

Abstract: U-phase Ln3(Si3 –xAl3 +x)O12 +xN2 –x(Ln = La, Nd) occurs as a crystalline phase in rare-earth sialon ceramics formed by devitrification of grain-boundary glasses at 1000–1400 °C. The crystal structure of Nd U-phase has been determined from Cu-Kα X-ray powder diffractometer data and refined by the Rietveld full-profile technique to RF= 0.028. The space group is P321 and the cell dimensions are a= 7.974(1)A, c= 4.873(1)A and V= 268.29 A3. The structure is isomorphic with the La3Ga5GeO14 structure, and exhibits corner-shared layers of (Si,Al)(O,N)4 tetrahedra interconnected by AlO6 octahedra. The rare-earth cations occupy sites between the tetrahedral layers. Transmission electron microscopy and lattice imaging studies support the X-ray structural findings. The structural relationship of the U-phase to other nitrogen-containing ceramic phases is discussed.

Sialon precursor composition

Abstract: A precursor material is disclosed. This precursor material is comprised of at least about 16 weight percent of beta-sialon, from about 54 to about 28 weight percent of alumina, from about 0 to about 8 weight percent of aluminum nitride, from about 0 to about 25 weight percent of silicon nitride, and from about 30 to about 24 weight percent of free silicon.

Production of high-strength sialon-based sintered compact

Abstract: PURPOSE:To provide a method for producing a sialon-based sintered compact remarkably improved in homogeneity of structure as compared with that of conventional sialon-based sintered compacts, capable of solving color shading, remarkably improved in not only corrosion resistance and mechanical characteristics such as high-temperature strength and fracture toughness, as a matter of course but also especially oxidation resistance by homogenization of the grain boundary glass phase. CONSTITUTION:A sialon-based sintered compact containing REalpha-sialon crystals and beta-sialon crystals is produced by a method characterized as follows: Fine powder having 5-50nm crystallite diameter, 0.01-0.1mum primary particle diameter, 20-100m /g specific surface area and <=5mum secondary particle diameter is used as the RE-containing powder which is a starting raw material.

Improved Processing Methods for Silicon Nitride Ceramics

Abstract: This paper reviews the status of a program1 to develop silicon nitride ceramics of high strength and reliability, with the material performance goals being a tensile strength of 900 MPa at room temperature and 500 MPa at 1370°C, both with a Weibull modulus of 20. The selected process consists of injection molding and hot isostatic pressing of a silicon nitride formulation containing 6 w/o yttria as sintering aid. A comprehensive experimental approach has been adopted which consists of: a. complete characterization and subsequent modification of the starting silicon nitride powder in an attempt to correlate powder characteristics to ceramic properties; b. the design and fabrication of appropriate specimens for tensile strength testing; c. the implementation of alternate powder processing and shaping techniques, including the design of new compounding/molding equipment; and d. the expansion of non-destructive evaluation capabilities.Copyright © 1991 by ASME

Sialon type sintered bodies and method of producing the same

Abstract: Sintered bodies with the primary phase of β and/or α prime sialon. In the sialon phase which is the primary phase, hafnium oxide and silicon carbide are dispersedly contained as dispersion phases. 1 to 60 parts by weight of hafnium oxide are contained in 100 parts by weight of the primary phase. 5 to 30 parts by weight of silicon carbide are contained in 100 parts by weight of the primary phase. Hafnium oxide suppresses decrease of sintering characteristic which is caused by silicon carbide. Thus, a large amount of silicon carbide can be added, thereby improving the fracture toughness value.