γ-AlON Powders Research Articles

The hydrolysis process of γ-AlON powder and preparation of highly transparent ceramics with aqueous gel-casting

The untreated γ-AlON powders were proposed to prepare highly transparent γ-AlON ceramics by aqueous gel-casting technique and two-step sintering process. The related mechanism of hydrolysis of γ-AlON powders was discussed. The surface of the synthesized γ-AlON powders is covered with a layer of aluminum hydroxides compound. As the period of hydrolysis extends, the surface layer dissolved, and the boehmite and bayerite gradually formed, which is characterized by various techniques including XRD, FT-IR, XPS and TEM. The low viscosity slurry with high solids loading (53 vol%) was obtained by γ-AlON powders without any surface modification treatments as a result of the slow hydrolysis process. In addition, compared with the dry pressed sample, the sample (4.12 mm in thickness) prepared by aqueous gel-casting exhibits superior in-line transmittance of 81–83% in the visible region, which could be ascribed to the more homogenous and denser microstructure of the green body. Finally, the Weibull modulus and characteristic strength of γ-AlON transparent ceramic were determined to be 4.85 and 295 MPa, respectively.

Preparation and fluorescence properties of a Cr3+:γ-AlON powder by high temperature solid state reaction

Abstract γ-AlON and Cr3+: γ-AlON powders were successfully synthesized by high temperature solid state reaction in nitrogen atmosphere with γ-Al2O3, Cr3+: γ-Al2O3 and AlN as raw materials. The γ-AlON and Cr3+: γ-AlON powders possess uniform morphology with spinel structure and the size distribution of 50 ~ 100 nm. Cr3+ ions exist in the main lattice of γ-AlON, which is verified by XPS and PL spectra. The excitation of the d-d energy level transition of Cr3+ ions can be attributed to the transition of 4A2(2F) → 4 T1 (4F) (located at 430 nm) and 4A2(4F) → 4 T2 (4F) (located at 588 nm), respectively. The luminescence peaks can be due to the defects of the matrix by the characteristic luminescence peaks of Cr3+. The Cr3+: γ-AlON powders with luminescent performance will be a candidate for new laser materials.

Formation of twins in AlON material and its effects on the Vickers hardness and fracture toughness

Aluminum oxynitride (γ-AlON) powders were synchronously synthesized by carbothermal reduction-nitridation (CRN) and high-temperature solid state reaction (SSR) methods. Twin structures existing in γ-AlON powders and transparent AlON ceramics were investigated by systematically employing electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the twin structures in synthetic powder and transparent ceramics exhibit quite different microstructural features; binary twin structures were widely observed in powders and ceramics, whereas the sandwich-like twin structure was produced only in transparent ceramics. High-resolution electron backscattered diffraction (HREBSD) was used to determine the residual elastic stress distributions in AlON powders and ceramics. Discrepancies in the magnitude and distribution of the residual stress between binary twins and sandwich-like twins were fully clarified. The formation of two kinds of twins in powders and ceramics was discussed in detail. The Vickers hardness and its corresponding indentation size effect (ISE) were studied in CRN-AlON and SSR-AlON ceramics. The effects of the twin structure on the Vickers hardness and fracture toughness were investigated simultaneously.

Structure and phase formation of combustion products during the synthesis of γ-AlON in self-propagating high-temperature synthesis

Synthesis of aluminum oxynitride (γ-AlON) in conditions of self-propagating high-temperature synthesis (SHS) gas-statting under high pressures (10–100 MPa) of gaseous nitrogen, including the mode of so-called coupled combustion reactions (chemical furnaces) is investigated. It is shown that chemical and phase compositions of combustion products, as well as their structure and morphology of powder particles, depend on the reagent ratio in Al–Al2O3 initial mixture, as well as on nitrogen pressure, combustion temperature of highly exothermic components of chemical furnaces, and grade of initial reagents. The structure of γ-AlON powder particles are determind and its relation with operation conditions of SHS. Optimal SHS parameters for Al5O6N (γ-AlON) formation are established.

Highly infrared transparent spark plasma sintered AlON ceramics

Abstract

Aluminum oxynitride by SHS under high pressure of nitrogen gas

Aluminum oxynitride (γ-AlON) powders were prepared from low-caloric Al–Al2O3 mixtures by SHS under high pressure of nitrogen gas in the presence of heat-generating agent, Mg(ClO4)2, as a booster. The preparation procedure was characterized and optimized with respect to Al/Al2O3 ratio, amount of heatgenerating additive, and nitrogen gas pressure. The morphology of synthesized γ-AlON powders was found to depend on Al powder brand. Compared to γ-AlON powders obtained in chemical furnace, we managed to prepare less sintered arenaceous cakes that could be easily disintegrated into target γ-AlON powder. SHSproduced powders may find their application in production of optical ceramics.

STRUCTURE AND PHASE FORMATION OF COMBUSTION PRODUCTS DURING Γ-ALON SYNTHESIS IN SHS GAS-STATTING MODE

The paper studies synthesis of aluminum oxynitride (γ-AlON) under the conditions of SHS gas-statting at high pressures (10–100 MPa) of gaseous nitrogen including the mode of so-called conjoint combustion reactions (chemical furnaces). It was shown that chemical and phase compositions of combustion products, their structure and morphology of powder particles depend on the reagent ratio in the initial Al–Al 2 O 3 mixture, as well as nitrogen pressure, combustion temperature of high-exothermic components of chemical furnaces, and type of initial reagents. The structure of γ-AlON powder particles was studied and its relation to self-propagating high-temperature synthesis conditions was found. It determines the optimum SHS parameters for Al 5 O 6 N (γ-AlON) synthesis.

Consolidation of Aluminium Oxynitride Powders Using Hydrolysis of Aluminium Nitride

One of the materials with high potential for application as a refractory material is aluminum oxynitride with spinel-type structure, γ-alon. Alon materials, single-phase or composites, are characterized by good mechanical properties, high thermal shock resistance and a high corrosion and erosion resistance. Another advantage is possibility of usage of SHS method for producing of relatively good sinterable powders of γ-alon, however, are characterized by poor compressibility. This paper describes a method of compaction of SHS-derived γ-alon powder using the hydrolysis reaction of aluminum nitride, which is one of the products of SHS synthesis. The green bodies made from the powder with addition of 10 mas.% of water after two weeks of storage reach a strength level up to 30 MPa and an open porosity of less than 30%. Pressureless sintering of the such compacts allows to achieve 95% of theoretical density at 1700°C in less than one minute.

Synthesis of polycrystalline γ-AlON powders by novel wet chemical processing

The synthesis of polycrystalline aluminum oxynitride (AlON) powders was investigated by the carbothermal reduction and nitridation (CRN) of amorphous precursor obtained by wet chemical processing. Co-precipitation processing was employed to achieve amorphous precursor from Al(NO3)3 solution dispersed by nanosized carbon particles, which was composed of Al(OH)3 and C particles homogeneously. The effects of the content of carbon black, pH value, and calcination temperature on formation of AlON phase were investigated by means of XRD, SEM and TEM, respectively. It was found that single phase AlON powder could be synthesized when the resultant precursors were calcined at 1750°C for 2 hours under flowing N2. Under optimal additional content of C (5.6wt%), the resultant AlON powders exhibited the primary particle size of about 1–3 μm with a specific surface area of 3.2 m2/g, which were superior to that of carbothermal reduction of immediate mixture of γ-Al2O3/C powders.

Carbothermal Reduction and Nitridation Synthesis of γ-AlON Powder under High Heating Rate

In this paper, a carbothermal reduction and nitridation (CRN) synthesis for cubic aluminum oxynitride (γ-AlON) powders is reported. The CRN reaction was conducted via a two-step synthesis procedure at a heating rate of 100 °C/min. In the first step, the mixture of fine γ-Al2O3 and soluble starch was annealed at 1550~1580 °C for different duration. It is found that the mixture of α-Al2O3 and AlN with an appropriate ratio can be obtained by CRN reaction. The content of AlN in mixture is closely related with the reaction condition. In the second step, the as-received mixture of α-Al2O3 and AlN was heat-treated at 1700 °C for 10 min. The single phase γ-AlON powders with particle size less than 3 µm were obtained.