Aluminum Oxynitride Spinel Research Articles

New Method of Synthesizing Aluminum Oxynitride Spinel Powders

Aluminum oxynitride spinel (AlON) powders were synthesized by aluminothermic reaction in a reducing N2‐CO atmosphere. Low cost and easily available aluminum and γ‐Al2O3 alumina micrometer‐sized powders were employed as starting materials. Mixed powders consisting of 75 wt% Al and 25 wt% Al2O3 were milled together and pressed into billets with diameter of 20 mm and height of 15 mm. Green‐body billets were then calcined in charcoal‐protected condition (namely in a N2‐CO atmosphere) at 1600°C. Phase composition and microstructure of final sintered products were analyzed. The results showed that AlON phase with AlN as a minor phase was formed at 1600°C for 3 h. At the same time, grains of AlON were tabular in shape and whiskers can be found in samples after being sintered at 1600°C.

Preparation of Aluminum Oxynitride Spinel γ-ALON Powders and Transparent Ceramics

With AlN, Al2O3 and Al powders as starting materials, ALON powders were prepared by high temperature solid state reaction at 1650°C, 1750°C and 1850°C respectively. Nitrogen gas at 1atm was selected as reaction atmosphere. X-ray diffraction analysis and scanning electron microscope analysis were carried out for the as-prepared ALON powders. In this paper, single-component γ-ALON porous materials were obtained at temperatures below 1800 degree with void ratio more than 75%, which is prone to be grinded to powders less than 1μm and applicable for the preparation of transparent ceramics. Aluminum oxynitride spinel γ-ALON transparent ceramics were successfully obtained with the as-prepared ALON powders. The volume density of the transparent ceramics was 3.67g/cm2, which is 99.3 percent of the theoretical density of γ-ALON materials. The bending strength of the transparent ceramics was 296MPa and the transmittance was about 75% in the wavelength range of 1.2 to 5.3μm.

AlON: A brief history of its emergence and evolution

In the early 1970s in Japan, the United States and France it was found that additions of nitrogen into aluminum oxide resulted in new spinel-like phases. At about the same time there was much increased interest in oxynitrides, stimulated by Professor K. Jack in the UK and Y. Oyama in Japan. Following these activities a major research program in this area was initiated at the Army Materials and Mechanics Research Center in Watertown, Massachusetts in 1974. These efforts resulted in the first complete Al 2O 3–AlN phase equilibrium diagram and a process to reactively sinter to nearly full density, translucent aluminum oxynitride spinel ceramic, which was named AlON. Subsequently, the Raytheon Company further developed AlON into a highly transparent material (ALON™) with many applications including transparent armor and EM domes and windows, among others—the technology was recently transferred to the Surmet Corporation. This paper will review the early history, phase equilibrium, crystal chemistry, and properties of this material, along with more recent work in our laboratory on transient liquid phase sintering and new data on lattice parameter measurements. In addition, recent results of collaborative work on AlON's dynamic mechanical properties using plate impact, Kolsky bar and edge-on impact (EoI) experimental techniques, including preliminary modeling at the microstructural scale of AlON in the EoI test, will be presented.

Phase Relations and Transformations in Advanced Ceramic Materials

This article reviews the phase diagrams contributing to the understanding of compound formations, phase transformations, phase separation and microstructural development in advanced ceramic systems. Phase equilibrium relations in the Al 2 O 3 -AlN and AlN-B 2 O 3 systems are presented for the fabrication of translucent aluminum oxynitride spinel ceramics and in-situ hexagonal boron nitride composites. In oxide systems, especially in glass-forming systems, crystallized phases vary with not only composition and temperature but also time of heat-treatment. Considering this aspect, time-temperature-transformation (TTT) diagrams in the solidification processes of cordierite, high-T c superconducting oxide and fluorphlogopite melts and the phase transformations of ammonium aluminum carbonate hydroxide to α-alumina are introduced and specific phase transformations in these systems are also discussed. The effect of treatment atmosphere on microstructure in phase transformations is described in the surface-treatment of AlN ceramics and the sintering of transparent silica glass.

アルミナと窒化アルミニウムからの酸窒化アルミニウムスピネルの生成

The mixture of Al2O3 and AlN at a mole ratio of 7 to 3 was heated at various temperatures from 1973 to 2048 K in N2 atmosphere, to investigate the effects of crystal type of Al2O3 and of additives on the formation rate of aluminum oxynitride spinel (ALON). ALON was formed more rapidly for γAl2O3 than for αAl2O3. The addition of CaB4O7 to the mixture accelerated the formation of ALON, whereas the additives such as NaF, CaF2 and CaCl2 retarded its formation. It was found by the analysis of EPMA that the formation of ALON proceeded topochemically from the surface of Al2O3 particles to the inside. On the basis of the XPS analysis of AlN/Al2O3 interface, the diffusion of the O2− and N3− through the ALON layer was presumed to be a rate-determining step of the formation reaction. According to kinetic analysis of a solid-diffusion controlled equation, the apparent activation energy in the formation reaction using αAl2O3 was estimated to be 1143 kJ/mol for no additive and to be 1085 kJ/mol for the addition of 1 mass%CaB4O7. Whereas the apparent activation energy in the formation reaction using γAl2O3 was estimated to be 515 kJ/mol for the addition of 1 mass%CaB4O7.

Reaction and Phase Relations in the AlN–B<SUB>2</SUB>O<SUB>3</SUB> System

The reaction and phase changes of the AIN-B 2 O 3 mixtures with 5-33.3 mol% B 2 O 3 was studied at high temperatures up to 1800 o C. Boron nitride (BN), Al 2 O 3 , 2Al 2 O 3 -B 2 O 3 , 9Al 2 O 3 -2B 2 O 3 , and aluminum oxynitride spinel (AlON) are formed during the reactions. Phases of product formed at 1800 o C are BN, AlON, Al 2 O 3 , and AlN. The effect of the formation mechanism of AlON on the growth of BN grains is discussed. The phase relation diagram is proposed based on the reaction results

Aluminum oxynitride spinel: A review

Aluminum oxynitride spinel (ALON) is a relatively new ceramic which can be processed into fully dense transparent material. This material could replace alumina in a variety of applications, especially where optical transparency is important. This report reviews the current status of ALON, including phase equilibria, processing and properties. Aluminiumoxinitridspinell (ALON) ist eine relativ neue Keramik, die zu einem völlig dichten und transparenten Material gesintert werden kann. Dieser Werkstoff könnte Aluminiumoxid in einer Vielfalt von Anwendungen ersetzen, speziell wenn es auf die optische Durchsichtigkeit ankommt. Dieser Artikel gibt einen Überblick über den derzeitigen Wissensstand der ALON-Keramik, einschließlich der Phasengleichgewichte, des Processing und der Eigenschaften. L'oxynitrure d'aluminium spinelle (ALON) est une céramique relativement nouvelle pouvant conduire à un matériau transparent entièrement dense. Il pourrait remplacer l'alumine dans diverses applications, surtout celles où la transparence optique est recherchée. Cet article analyse l'état actuel des connaissances sur l'ALON en ce qui concerne les équilibres de phases, l'élaboration et les propriétés.

ChemInform Abstract: Elastic Properties of Polycrystalline Aluminum Oxynitride Spinel and Their Dependence on Pressure, Temperature, and Composition.

AbstractThe isotropic elastic moduli of nitrogen‐stabilized cubic aluminum oxides (ALON) containing 30.0 or 35.7 mol% AlN are measured between 0 and 25 °C at pressures ranging from ambient pressure to 1 GPa.

Elastic Properties of Polycrystalline Aluminum Oxynitride Spinel and Their Dependence on Pressure, Temperature, and Composition

The isotropic elastic moduli of four specimens of nitrogen‐stabilized cubic aluminum oxide (ALON) were measured using pulse superposition interferometry. Experiments were carried out as a function of both pressure (ambient to 1 GPa) and temperature (0° to 25°C) for specimens of 30.0 and 35.7 mol% AlN. The second‐order moduli results were corrected for porosity using the “self‐consistent‐scheme” approach. Pertinent ambient results for isotropic pore‐free ALON are K= 226.3 GPa and G= 132.0 GPa for the 30.0 mol% AlN material, and K= 229.8 GPa and G= 135.5 GPa for 35.7 mol% ALON (K and G denote the bulk and shear moduli, respectively). The estimated uncertainties in these values are about 2%. The second‐order elastic properties of ALON, as well as their pressure and temperature derivatives, fall midway between spinel (MgAl2O4) and corundum (Al2O3), indicating the excellent potential of this material for structural engineering purposes.

Damage structures in fast neutron irradiated magnesium aluminate and electron irradiated aluminum oxynitride spinels

Single crystals of magnesium aluminate spinel, MgO(Al 2O 3) n , n = 1, 1.1. and 2. were neutron irradiated in EBR-II to a fluence of 2 × 10 26 n/m 2 (E > 0.111 MeV) at 680 and 815 K. Control specimens were aged 1 year at 815 K for comparison. TEM analysis of the irradiated specimens showed that they contained faulted prismatic dislocation loops with fault vectors R = a/4 〈110〉 on {110} planes in the n = 1 and 1.1 spinels, and with R = a/6 〈111〉 on {111} in the n = 1.1 and 2 spinels. Alumina-rich control specimens precipitated a new ordered phase. Polycrystalline aluminum oxynitride spinel, AlN(Al 2O 3) 1.8, was electron irradiated with 0.8 and 1 MeV electrons in the HVEM over the temperature range 300–1100 K. No defect aggregation was observed at any temperature, through thick or thin sections. Coherent twins developed on the facets of sintering pores open to the surface.

High‐Temperature Electrical Conductivity of Aluminum Oxynitride Spinel

The electrical conductivity of pure aluminum oxynitride spinel was measured at 1300° to 1500°C under flowing nitrogen gas. The re sults for two nonstoichiometric spinel compositions can be fitted by exponential expressions with an activation energy of 116± I Wlmol. The mobilities calculated from aluminum vacancy concentrations and conductivities, 8.07x cm'/V‐s, are reasonable for ionic conduction. The complex impedance plot suggests electrode double‐layer effects being damped out at higher frequencies in the range 10’to lo4 Hz.

Phase Relations and Reaction Sintering of Transparent Cubic Aluminum Oxynitride Spinel (ALON)

A new isobaric, condensed phase diagram in the region of stability of cubic aluminum oxynitride spinel (ALON) along the pseudobinary AI2O3‐AIN composition join is presented, deduced primarily from various analytical measurements and microstructural observations. It is shown that cubic aluminum oxynitride spinel melts incongruently at ≊2050°C and is compositionally centered at ≊35.7 mol% AIN, which is equivalent to the following stoichiometric composition: AI23O27N5 or 5AIN·9AI2O3. Single‐phase ALON material sintered to nearly full density exhibits transparency in visible light.

Structure à antiphases périodiques de l'oxynitrure d'aluminium δ1non-stoechiométrique de composition 9Al2O3–AlN

The ordered non-stoichiometric aluminum oxynitride spinel 9Al2O3–AlN has been investigated by X-ray diffraction and electron microscopy. This phase has a one-dimensional periodic antiphase-domain structure. The antiphase boundaries are parallel to the (001) plane and the displacement vector is R = ½〈100〉 when referred to the spinel structure. Periodically spaced clusters of tetrahedral vacancies are grouped in the neighbourhood of each antiphase boundary. These clusters occur in order to avoid an increase in the antiphase-boundary energy, which otherwise would arise, mainly as a result of the Coulomb repulsion between Al3+ ions displaced from their normal sites in the spinel lattice adjacent to the boundary.