Combustion Synthesis of Aluminum Oxynitride in Loose Powder Beds.

Alan Wilmański,Zbigniew Pędzich,Magdalena Zarzecka-Napierała

doi:10.3390/ma14154182

Abstract

This paper describes combusting loose powder beds of mixtures of aluminum metal powders and aluminum oxide powders with various grain sizes under various nitrogen pressure. The synthesis conditions required at least 20/80 weight ratio of aluminum metal powder to alumina powder in the mix to reach approximately 80 wt% of γ-AlON in the products. Finely ground fused white alumina with a mean grain size of 5 μm was sufficient to achieve results similar to very fine alumina with 0.3 μm grains. A lower nitrogen pressure of 1 MPa provided good results, allowing a less robust apparatus to be used. The salt-assisted combustion synthesis upon addition of 10 wt% of ammonium nitrite resulted in a slight increase in product yield and allowed lower aluminum metal powder content in mixes to be ignited. Increasing the charge mass five times resulted in a very similar γ-AlON yield, providing a promising technology for scaling up. Synthesis in loose powder beds could be utilized for effective production of relatively cheap and uniform AlON powder, which could be easily prepared for forming and sintering without intensive grounding and milling, which usually introduce serious contamination.

Highlights

Materials 2021, 14, 4182. https://The binary Al2 O3 –AlN system contains a solid solution known as aluminum oxynitride with a cubic structure usually abbreviated as γ-AlON [1]
Manufacturing of aluminum oxynitride ceramics usually starts with the synthesis of γ-AlON powder with one of the well-known methods, i.e., carbothermal reduction and nitridation (CRN) [7,8,9,10,11] or solid-state synthesis (SS) [12,13,14,15], or one less frequently used, such as aluminothermic reduction and nitridation (ARN) [16,17] or self-propagating high temperature synthesis (SHS) [18,19,20,21,22]
We present a broad approach to investigate the influence of the grain size of aluminum metal and oxide powders, nitrogen pressure in the reaction chamber, proportion of Al/Al2 O3, and the use of ammonium nitrite in loose powder beds on phase composition and γ-AlON phase yield of SHS-derived powders

Summary

Introduction

Materials 2021, 14, 4182. https://The binary Al2 O3 –AlN system contains a solid solution known as aluminum oxynitride with a cubic structure usually abbreviated as γ-AlON [1]. The material can achieve excellent transmittance from ultraviolet to mid-infrared wavelengths [3] These ceramics have various favorable properties, such as good mechanical strength, temperature stability, and chemical resistance, that allow them to be applied as transparent armor, missile domes, refractory materials, optoelectronics, and high temperature windows [4,5,6]. The main drawbacks of the most popular processes are high temperatures of over 1650 ◦ C and prolonged soaking times Dealing with these problems by employing the sol-gel method results in other disadvantages, such as high cost of chemical reactants and long gel preparation times, producing, in return, extremely fine γ-AlON powders after synthesis [23,24]. Another concern of the CRN method relates to oxidizing the remaining carbon, present in the powder batch post reaction, in open air furnaces at 600–700 ◦ C for a few hours that can lead to a change in the aluminum oxynitride stoichiometry, which has not been addressed in any of the publications on CRN

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Discussion

Conclusion