This paper is a review article covering various methods reported on synthesis of β-SiAlON based ceramic materials and on their net-shape consolidation into radome structures. It also identifies a composition out of a wide-range β-Si 6-z Al z O z N 8-z (where z = 0–4.1) solid solution suitable for radome applications and discusses about various efficient methods reported on fabrication of radome structures out of these compositions. This article also covers the literature pertaining to β-SiAlON-SiO 2 ceramic composites, which are considered to be materials of choice for certain high speed radome applications. Further, successful techniques employed for passivation of AlN powder against hydrolysis are also covered as this powder is one of the starting materials for both β-SiAlON and β-SiAlON-SiO 2 ceramic composites. Surface passivation of AlN is necessary as it decomposes into alumina and ammonia, when it comes into contact with water during aqueous processing of SiAlON based ceramics, thereby not permitting formation of desired SiAlON phase. Finally, the important properties of various commercial radome materials together with those of β-SiAlON and β-SiAlON-SiO 2 ceramic composites are also reviewed and presented in this article.

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Development of β-SiAlON based ceramics for radome applications

High temperature ceramic radomes (HTCR) – A review

Aluminum nitride shaping by non-aqueous gelcasting of low-viscosity and high solid-loading slurry

Slip-Cast Fused Silica Radomes for Hypervelocity Vehicles: Advantages, Challenges, and Fabrication Techniques

Keeping the importance of developing suitable radome (a word derived from radar 
 $$+$$
  dome) materials and near-net shape consolidation technique for manufacturing radomes suitable for hypersonic (>mach 5) radar-guided missiles in India, the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, has initiated an in-house R&D programme and successfully developed a complete process know-how for manufacturing defect-free prototype $$\upbeta $$
 -SiAlON-based radome structures with all the desired properties. As a part of this R&D programme, total six separate sub-projects mentioned below were undertaken and executed: (i) identification of the best composition out of $$\upbeta $$
 -
 $$\hbox {Si}_{6-z}\hbox {Al}_{z}\hbox {O}_{z}\hbox {N}_{8-z}$$
 (0 $$\le z \le $$
 4.1) solid solution, which possesses a right combination of properties required for radome applications, (ii) designing of an AlN-free precursor mixture for consolidating $$\upbeta $$
 -
 $$\hbox {Si}_{4}\hbox {Al}_{2}\hbox {O}_{2}\hbox {N}_{6}$$
 ceramics by following aqueous colloidal processing routes, (iii) development of a process for passivating water-sensitive AlN powder against hydrolysis, (iv) development of aqueous gelcasting (GC) and hydrolysis-assisted solidification (HAS) powder processing routes for consolidating dense $$\upbeta $$
 -SiAlON ceramics using highly solids loaded (>50 vol%) aqueous slurries, (v) development of an hydrolysis-induced aqueous gelcasting (GCHAS) process, a novel near-net-shape consolidation technique, to produce radomes with very high-production yields and (vi) development of an economic route for synthesizing the low-dielectric constant and high strength novel $$\upbeta $$
 -SiAlON-
 $$\hbox {SiO}_{2}$$
 ceramic composites. In this paper, (i) the basis for choosing $$\upbeta $$
 -SiAlON-based ceramics for hypervelocity radome applications, and (ii) the various bottle-neck problems faced, while executing this entire R&D work and the way they were overcome have been critically analysed and discussed systematically, while citing all the relevant and important references.

/pdf/novel-composites-of-upbeta-b-sialon-and-radome-manufacturing-2bptpdvklt.pdf

Novel composites of $$\upbeta $$ β -SiAlON and radome manufacturing technology developed at ARCI, Hyderabad, for hypervelocity vehicles

This paper reports a novel synthetic route to prepare dense β‐SiAlON–SiO2 ceramic composites. The stoichiometric β‐Si4Al2O2N6 extrudates prepared by the reaction sintering of α‐Si3N4, α‐Al2O3, AlN and Y2O3 precursor mixture at 1675°C for 4 h were fine ground and mixed with different amounts of commercial fused silica (20, 40, 50, 60 and 80 wt‐%) powder, dry pressed and sintered for 3–4 h at 1500–1750°C. These sintered materials were thoroughly characterised for bulk density, apparent porosity, water absorption capacity, phase composition, microstructure, hardness, dielectric constant and coefficient of thermal expansion. These characterisation results are presented and discussed in this paper.

G Sundararajan

Papers

Novel route to β‐SiAlON–SiO2 ceramic composites