Aluminum Oxynitride Powders Research Articles

The role of magnesium oxide addition in densification of AlON transparent ceramics by pressureless sintering

AbstractPressureless sintering processing was adopted to fabricate transparent aluminum oxynitride (AlON) ceramics by using magnesium oxide (MgO) as a sintering additive into synthetic single phased aluminum oxynitride powder. Under the condition of adding 0.6 wt% magnesium oxide, the relative density of aluminum oxynitride ceramics increased from 98.67% with no addition to 99.9% after being held at 1800°C for 24 h, coupled by a reducing of average grain size from 190 µm to 130 µm. The optical linear transmittance of the AlON ceramic sample (thickness 1.2 mm) reached 84.2% at the wavelength of 1100 nm. The microstructural characterizations by energy dispersive spectroscopy and atom probe tomography indicated that the doping Mg element was uniformly dispersed inside aluminum oxynitride grains of as‐sintered ceramics. It was demonstrated that magnesium oxide played a key role in inhibiting the movement of grain boundaries, eliminating pores, leading to the fully densification of aluminum oxynitride ceramics.

Zircoborate glass-ceramic composite reinforced with aluminum oxynitride: Microstructural evolution, physical properties, and charged radiation attenuation analysis

This study used the powder metallurgy method to create aluminum oxynitride (AlON)-reinforced zircoborate glass-ceramic composites. The solid-phase reaction method was used to synthesize AlON powder, which was then added to Zr-based glass-ceramic in different amounts (0, 4, and 8 % by weight) to make it stronger and harder. The prepared materials were characterized for their structural, physical, and radiation shielding properties. The density of GZr8 (AlON-free) had a value of 2.9 g/cm3, and the sintered glass-ceramic density with 4 % wt. AlON reinforcement (GZr8Al4) reached 3.05 g/cm3. The highest density of 3.11 g/cm3 was obtained for the GZr8Al8 sample with 8 % AlON wt. The Vickers hardness for GZr8, GZr8Al4, and GZr8Al8 was measured to be 4.89, 5.94, and 6.33 GPa, respectively. The AlON-reinforced GZr8 samples had fast neutron (FN) removal cross-sections of 0.0796 cm−1 and 0.0824 cm−1 for AlON content of 4 and 8 wt%, respectively. Generally, the coherent scattering cross-section (σcoh), incoherent scattering cross-section (σinc), and absorption cross-section (σabs) of thermal neutrons (TNs) increase from 0.047856 cm−1, 0.02072 cm−1, and 0.01498 cm−1, respectively for GZr8 to 0.53124 cm−1, 0.02074 cm−1, and 0.01795 cm−1, for GZr8Al8. AlON was proven to improve the ability of the Zr-based glass-ceramics to attenuate FNs and TNs. Stopping powers of electrons, protons, alpha particles and carbon ions increase with the AlON content of the materials. Comparatively, the range of charged radiation in AlON-rich samples is lower. The inclusion of AlON in the matrix of the Zr-based glass-ceramics makes it more efficient at absorbing charged radiation and can be used in ion beam or hadron therapy, ion beam analysis, or other charged radiation environments as an absorber.

Preparation of transparent AlON ceramics with controlled shapes by a novel spontaneous coagulation casting and pressureless sintering method

Aluminum oxynitride (AlON) exhibits excellent mechanical properties and good optical transparency in the ultraviolet to near-infrared range and can be used in military and civilian fields. However, the troublesome molding of AlON, especially for complex shapes, limits its promotion and application. Therefore, transparent AlON ceramics with complex morphologies were prepared for the first time by a novel spontaneous coagulation casting (SCC) and pressureless sintering method. In this study, we report a simple carbothermal reduction and nitridation (CRN) method for synthesizing high-purity AlON powder, which is especially suitable for wet casting without anti-hydration treatment. The dispersion and gelation behavior of AlON slurries by isobutene maleic anhydride copolymer (Isobam104) and tetramethylammonium hydroxide (TMAH) were extensively investigated. With the addition of 0.9 wt% Isobam104 and 15 mL/L TMAH, the AlON slurries can achieve a solids loading of up to 45 vol% with the lowest viscosity (460.4 mPa·s-10 r/min) and the AlON green body is free of cracks and deformation during drying and demolding processes. Finally, the AlON green bodies with square and polygonal irregular morphologies were fabricated via a simple SCC method. High transparent AlON ceramics of a maximum transmittance up to 77.3% at 2000 nm and 72.2% at 632 nm were obtained by pressureless sintered at 2000 °C for 6 h. The SCC method has great potential in preparing ceramics with controllable shapes.

AlON transparent ceramics from powders synthesized by improved direct nitridation

Single-phase aluminum oxynitride (AlON) powders were synthesized by improved direct nitridation (DN). The improved DN method is to obtain high quality powder by adding high nitrogen pressure on the basis of ordinary DN method. Compared with the ordinary DN method, the average particle size of the synthesized powder is reduced by about 20 μm, the morphology tends to be spherical and the sintering activity is higher. Using different particle size α-Al2O3 precursor, a modified DN method was adopted to synthesize spherical, good dispersibility and fine AlON powders. The influence of particle size of raw material α-Al2O3 on sintering properties was investigated. Transparent AlON ceramics with dimensions of φ 103mm × 3 mm with in-line transmittance greater than 80%were fabricated by pressureless sintering from above AlON powders. In addition, the effects of different nitrogen pressure on the morphology, particle size distribution and average particle size of synthetic powder were investigated. On this basis, the differences between DN method and improved DN method on synthetic powder and the possible synthesis mechanism were proposed.

Study on Preparation of Homogenized Highly Dispersible AlON Powder

The quality of Aluminum oxynitride (AlON) powder is the main factor affecting the properties of ceramics. To accurately control the nitrogen AlON content and improve the dispersion degree of powder, AlON powder was prepared from γ-Al2O3 and activated carbon powder by carbothermic reduction and nitridation. The uniformity of distribution of raw materials and the dimension and microstructure of AlON powder was controlled by changing the time and rotation rate of the ball milling process. The influences of ball milling process parameters on the microstructure and distribution uniformity of Al2O3/C mixed powder, microstructure, and particle size of AlON powder were studied. The results show that powder agglomeration was effectively reduced, and the uniformity of raw material distribution was increased by controlling the time and rotation rate of the ball milling process. The Al2O3/C mixed powder has good particle size and uniform distribution with roller ball milling for 24 h. After holding the powder at 1700 °C for 60 min, the homogenized AlON powder was obtained, and the residual carbon content was about 0.04 wt%. When the time of planetary ball milling at 250 rpm was 16 h, highly dispersible AlON powder was obtained.

Preparation of AlON Powder by Carbothermal Reduction and Nitridation with Assisting by Silane Coupling Agent

In the preparation processes of aluminum oxynitride (AlON) powders by carbothermal reduction and nitridation, the homogeneity of mixed raw powders between Al2O3 and C is a critical factor by which the final composition and related properties of AlON transparent ceramic will be decided. In this paper, a silane coupling agent was used as a dispersant to optimize the distribution uniformity of raw material of Al2O3 and C, and the preparation of AlON powder with controllable composition and its distribution is investigated. The results show that the silane dispersant could effectively improve the distribution uniformity of raw material. The silane coupling agent contains functional groups of -SiH3 and -CnH2n+1O. XPS showed that the silane could react with C and Al2O3 to form the Si-C bond and C-Al2O3 bond, respectively. The silane coupling agent provides a connected bridge for raw material powders. When the amount of the silane was 5 wt%, the mixed powder had a great distribution uniformity. The addition of silane coupling agent improved the reactivity of raw materials and decreased the synthesis temperature of AlON. The single-phase AlON powder was obtained after the Al2O3/C mixed powder was kept at 1670 °C for 30 min. Furthermore, the grain size of AlON powder was 100-200 nm with an AlN content of 27.5 mol%. With the increase of holding time to 4 h, the grain size increased to 15 μm, indicating that sintering between particles occurred, which may reduce the sintering activity of the powder.

Preparation of transparent AlON from powders synthesized by novel CRN method

Aluminum oxynitride (AlON) powders were synthesized by a novel carbothermal reduction and nitridation (CRN) method. Homogenous and fluffy AlOOH/C core-shell nanoparticle precursor was hydrothermally synthesized with aluminum nitrate hydrate, sucrose and urea as starting materials. Then single-phase AlON powders were synthesized by CRN method at 1700 °C for 2 h. The phase transition and growth of Al2O3 particles was effectively retarded by the amorphous carbon nano-layers on the surface of precursor, resulting in significantly lower reaction temperature and further smaller particle size. Based on above fine AlON raw material, transparent AlON ceramic was prepared by pressureless sintering at 1880 ℃ with the in-line transmittance above 80 %.

Rapid synthesis of AlON powders by nitriding combustion synthesis precursor

Polycrystalline aluminum oxynitride (AlON) powders have been prepared by the carbothermal reduction nitridation of amorphous precursor obtained by solution combustion synthesis (SCS). Firstly, a mixed precursor of amorphous transition alumina and incompletely combusted organic matter has been combustion synthesized of a mixed solution of aluminum nitrate, urea and glucose. Then the pure phase AlON powders with D50 = 0.846 μm can be prepared by calcining the SCS precursor at 1700 °C for only 10 min. The influences of different urea/aluminum nitrate nonahydrate ratio, calcining temperature and holding time on the properties of products have been discussed in detail. The research can provide a valuable reference for the efficient synthesis of AlON powders.

Structure of Aluminum Oxynitride Powders Produced by Plasma-Chemical Synthesis

Structure of Aluminum Oxynitride Powders Produced by Plasma-Chemical Synthesis

Oxidation behavior and mechanism of aluminum oxynitride (AlON) at elevated temperatures

AbstractThe oxidation behavior and mechanism of aluminum oxynitride (AlON) powder exposed to air at elevated temperatures between 800°C and 1300°C was investigated by X‐ray diffractometry (XRD), scanning electron microscope (SEM), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and simultaneous thermogravimetry, differential thermal analysis, and mass spectrometry techniques (TG‐DTA‐MS). The weight of AlON gradually increases to a maximum value at 1150°C and then decreases with further heating. Meanwhile, AlON powder undergoes chemical changes, as evidenced by lattice expansion, and turns eventually into alumina. ESR spectra reveal the occurrence of lone pair electrons in the oxidized products and the intensity of corresponding resonance signal increases before disappearing with the increase in temperature. Combined with the results of NMR and TG‐DTA‐MS, the measured data suggest that Al‐N in [AlO3N] tetrahedron and [AlO5N] octahedron are gradually oxidized into Al‐O‐N group with lone pair electrons, which causes continuous weight gain and lattice expansion. Further oxidation at higher temperatures results in alumina and N2.

Структура порошков оксинитрида алюминия, полученных плазмохимическим синтезом

Структура порошков оксинитрида алюминия, полученных плазмохимическим синтезом

Development of a new sol-gel route for the preparation of aluminum oxynitride nano-powders

In the present research, a novel low-temperature sol-gel process was developed for the synthesis of the aluminum oxynitride (AlON) phase using aluminum tri-sec-butoxide, acetonitrile, chloroform, and hydrazinium hydroxide. This straightforward process involves the nitridation of the as-synthesized sols under ultra-high purity nitrogen to form the AlON nano-powders. The effect of various parameters such as pH in the range of 8–11, the solvent to alkoxide molar ratio (30–100), and acetonitrile to chloroform molar ratio (20–100%), and heat treatment temperature (900–1500 °C) and time (4–12 h) on the composition of the prepared powders were studied. The characterization of the powders by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) demonstrated that the pure phase of AlON (nano powder) was obtained in the sample having the pH value of 10, the molar ratio of solvent to alkoxide of 100, the molar ratio of acetonitrile to chloroform of 80%, which annealed at 1500 °C for 8 h at nitrogen atmosphere with the heating rate of 3 °C/min. Finally, transparent AlON ceramic was fabricated by the spark plasma sintering of as-synthesized AlON powder at 1600 °C for 30 min with a density of 3.64 gr/cm3 and about 54% IR in-line transmission.

The stability of aluminum oxynitride (AlON) powder in aqueous system and feasible gel-casting for highly-transparent ceramic

The stability of AlON powder in the aqueous system was studied during the gel-casting procedure of AlON ceramic. The pH value of AlON slurry, the phase assemblage and the morphology of AlON powder all suggested the excellent stability of untreated AlON powder even in hot water. Finally, highly-transparent AlON ceramic pellets (D = 110 mm and D = 22 mm) were fabricated by a feasible and easy aqueous gel-casting method. The polished AlON ceramics with 3.5 mm thickness possesses the highest inline transmittance above 86% at the wavelength of 2000 nm.

Effect of Sintering Parameters on the Phase Composition of Ceramic Based on Aluminum Oxynitride

In this paper, we analyzed the methods of synthesis and sintering of aluminum oxynitride powders. Samples of a ceramic material based on aluminum oxynitride were produced. The effectiveness of two sintering methods in induction and resistance furnaces was evaluated in the temperature range of 1750–1950°C and for the exposure time from 2 to 10 h. Structures of the obtained samples were studied by scanning electron microscopy, while the phase composition was studied using X-ray phase analysis. The effect of the heating parameters, sintering atmosphere, and quality of the initial powders on the formation of the aluminum oxynitride phase was considered. A sample sintered in a vacuum furnace without a nitrogen atmosphere did not have the aluminum oxynitride phase because of the release of nitrogen from the sample volume and had a strong shrinkage. Induction sintering in a nitrogen atmosphere made it possible to achieve ~85% concentration of the target phase, aluminum oxynitride, with density of 85% of theoretical (3.69 g/cm3). These results were obtained in the mode of exposure for 10 h at 1750°C.

Effect of heating rate on properties of transparent aluminum oxynitride sintered by spark plasma sintering

AbstractHigh heating rates ranging from 50 to 250°C/min are selected to rapidly sinter transparent aluminum oxynitride (AlON) ceramics by spark plasma sintering (SPS) at 1600°C under 60 MPa using a bimodal AlON powder synthesized by the carbothermal reduction and nitridation method. With 1 minute holding time before cooling, all the specimens show high density and high transparence. The maximum transmittance is up to 74.5%‐80.6%, where the maximum transmittance is positively correlated with the heating rate. Further analysis reveals that faster heating rates enable the decrease in the amount of the AlON phase decomposed into the α‐Al2O3 and AlN phases during heating. These α‐Al2O3 and AlN phases have to be converted back to AlON at the final stage of sintering, which indicates that a decrease in the amount of the α‐Al2O3 and AlN phases via the boosted heating leads to the higher transmittance of the AlON ceramics. The high heating rates and short holding duration of the SPS utilized in this study result in the fine grain size of the obtained ceramics (1‐6 μm) compared to that of the AlON ceramics fabricated by the conventional sintering method. This effect of high heating rates is confirmed by the coupled densification‐grain growth modeling. In turn, the obtained AlON specimens exhibit a Vickers hardness of 15.87‐16.62 GPa.

Pressureless sintering of highly transparent AlON ceramics with CaCO3 doping

Employing CaCO3 as sintering additive, highly transparent aluminum oxynitride (AlON) ceramics were pressurelessly fabricated from AlON powder at 1870 °C during150 min. The transmittance of the AlON doped with 0.3–0.4 wt% CaCO3 is up to 83–85% at ~3700 nm for 2 mm thickness samples, and their transmittances are consistently higher than that of the AlON doped with the ideal amount of Y2O3 at wavelength ranging from 200 nm to 6000 nm. The AlON doped with CaCO3 exhibits the transmittance of 71% at 4800 nm (typical band for infrared targeting), which is higher by 6% than that of the doped Y2O3.

Highly photocatalytic activity of porous skeleton structure AlON powder synthesized by CRN under ultraviolet-light irradiation

A large-sized (∼20 μm) pure aluminum oxynitride (AlON) powder characterized by its porous skeleton structure was synthesized by carbothermal reduction and nitridation (CRN) method using α-Al2O3. The photocatalytic performance of the obtained AlON powder was studied under ultraviolet-light in methylene blue (MB) solution. In 40 ml MB solution doped with 30 mg as-synthesized AlON powder, a photogradation efficiency as high as 97% was measured after irradiating 120 min, and 80% MB was mineralized by determining the total organic carbon (TOC) in the solution, i.e., mineralization is the main degradation mode of MB in the solution due to the added AlON powder. Further radical scavenger’s experiments reveal that both h+ and OH were the dominant reactive species in the photogradation process of MB by the AlON powder. It should be pointed out that the specific surface area of the obtained AlON powder is smaller than that of solid small-sized powder (∼800 nm) due to its porous skeleton structure. However, the measured photogradation efficiency of the obtained AlON powder is slightly higher than the reported value, which is mainly attributed to light reflection and scattering within its skeleton. The as-synthesized AlON powder has excellent dispersibility for its large particle size. Moreover, the obtained AlON powder also exhibits high reusability. Therefore, the obtained large-sized porous skeleton structure pure AlON powder is an efficient and promising photocatalyst.

Sintering of Aluminum-Oxynitride Powder Prepared by Self-Propagating High-Temperature Synthesis

Sintering of aluminum-oxynitride powders prepared by self-propagating high-temperature synthesis in a nitrogen-containing gel was researched. Use of the powders without extensive mechanical grinding was problematical because of their low specific surface areas. Equipment fitted with grinding containers lined with high-density plates and grinding balls made of the same material, 9Al2O3·5AlN, were required to solve this problem.

THE SINTERING OF THE ALUMINUM-OXYNITRIDE POWDER PREPARED BY MEANS OF SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS (SHS) METHOD

The investigating results are given in the article on the sintering of the aluminum-oxynitride powder prepared by means of SHS-method in the nitrogen-containing gel. It was established that without the intensive mechanical grinding it presents itself as problematic to use the aluminumoxynitride powder prepared by means of the SHS-method in the aluminum-containing alumogel because of their low level specific surface. To solve this problem one has to have the equipment fitted with the grinding containers lined with the high-dense plates, as well as with the grinding balls made out of the same material ― 9Al 2 O 3 ·5AlN.

Preparation and properties of AlON powders

Aluminum oxynitride (AlON) powders were synthesized using the raw materials of γ-Al2O3 and carbon black through the carbothermal reduction and nitridation process. The carbon content in the γ-Al2O3/C mixture and heating temperature were investigated. The AlON powders were synthesized by calcination for 2h at 1750°C when the carbon content in the γ-Al2O3/C mixture was 5.8wt%. The particle size of powder is important to the transparency of ceramics, but the size of the synthesized powder was large. Therefore, a few methods, such as freeze-drying, ultrasonic dispersion, and liquid nitrogen ball milling, were used to reduce the particle size of powders. Among the three methods, liquid nitrogen milling had the best results.