Synthesis of composite AlN-AlON-Al2O3 powders and ceramics prepared by high-pressure sintering

Abstract

The process of carbothermal reduction of Al2O3 in a nitrogen flow at temperatures of 1450 and 1600ºC has been studied. It was established that the powder synthesized at 1450ºC is a mixture of Al2O3 and AlN particles and that the powders synthesized at 1600ºC are mixtures of AlN, AlON, and Al2O3. Amorphous and crystalline AlON films form on the surface of Al2O3 and AlN particles. Both synthesized powders contain unreacted residual carbon. In the stage of high-pressure sintering of specimens at a temperature of 1750ºC under a pressure of 7 GPa for 110 s, AlON decomposes into AlN and Al2O3. Residual graphite transforms into a crystalline graphite phase, which decreases the strength and increases the fracture toughness. The highest hardness of 19.5 GPa was achieved in the ceramics obtained from the powder synthesized at 1600ºC for 4 h, and the largest fracture toughness of ~7.2 MPa•m1/2 was achieved in the ceramics obtained from the powder synthesized at 1450ºC for 4h

Gas‐Phase and Solid‐State Simultaneous Mechanism for Two‐Step Carbothermal AlON Formation

“…Meanwhile, the vapor phase growth (VPG) of AlON under low supersaturation leads to inevitable formation of step‐shape surface morphology . The construction of such AlON thin layer single crystals on the bulk AlON polycrystalline particles determines the final morphology of products, which is in good accordance with previous investigations . In contrast, the intermediate with little or no residual carbon results in much less significant agglomeration and better dispersity of AlON powder [Fig.…”

“…In such multistep process, it is crucial to make sure the AlON powder is narrowly sized, fine and high‐purity . Nowadays, the most widely used method for AlON powder synthesis is carbothermal reduction nitridation (CRN) of Al 2 O 3 , as it starts with low‐cost starting materials and results in high‐quality final products . Furthermore, CRN was optimized by Hartnett et al .…”

Poly(methyl methacrylate) as an Environmentally Responsive Capping Material for Aluminum Nanoparticles

“…51−54 Meanwhile, the same lattice planes can be assigned to those of oxygen-depleted alumina with the exception of that at 71.5°, which corresponds to diffraction from the (200) plane. 50,55 The formation of aluminum nitride is not surprising given that the DSC/TGA protocol flows nitrogen over the sample during heating. The formation of alumina can be accounted for by recalling that PMMA contains 13 mol % oxygen, and this presumably is the oxygen source.…”

“…To have a deeper understanding of this phenomenon, the samples produced by DSC/TGA analysis were studied using PXRD analysis (Figure ). It indicates that the final product comprises both oxygen-depleted aluminum oxide (PDF# 01-078-5519) and aluminum nitride (PDF# 01-080-6097). , Thus, the peaks at 33.3, 36.3, 38.1, 50.0, 59.4, 66.7, and 71.5° correspond with diffraction from the lattice planes (100), (002), (101), (102), (110), (103), and (112) of aluminum nitride, respectively. − Meanwhile, the same lattice planes can be assigned to those of oxygen-depleted alumina with the exception of that at 71.5°, which corresponds to diffraction from the (200) plane. , The formation of aluminum nitride is not surprising given that the DSC/TGA protocol flows nitrogen over the sample during heating. The formation of alumina can be accounted for by recalling that PMMA contains 13 mol % oxygen, and this presumably is the oxygen source.…”

Highly transparent AlON fabricated via SPS synthesized by Al2O3/C core–shell starting powder and CRN method

“…The absorption bands at 1622 cm −1 indicate the remaining carbon in the powder, which has bonded to the carbon dioxide or nitrogen in the form of a double bond. The broad absorption band in the 400‐1000 cm −1 region is related to the Al‐O‐N vibration existed in the AlON structure 14,20 …”