Novel composites of $$\upbeta $$ β -SiAlON and radome manufacturing technology developed at ARCI, Hyderabad, for hypervelocity vehicles
TL;DR: In this paper, 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 SiAlON-based radome structures with all the desired properties.
Abstract: 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.
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TL;DR: In this paper, a review of ceramic materials used as radome materials is presented, including high-purity alumina, pyroceram, slip-cast-fused-silica, porosity and its influence on electromagnetic properties.
29 citations
01 Jan 2020
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References
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TL;DR: Sialons as mentioned in this paper are phases in the Si-Al-O-N and related systems and are comparable in variety and diversity with the mineral silicates, and are built up of one-, two-, and threedimensional arrangements of (Si, Al) (O, N)4 tetrahedra.
Abstract: Although silicon nitride is at present a leading contender for gas turbines and other hightemperature engineering applications, it is only the first of a wide field of nitrogen ceramics, other members of which offer better prospects for technological exploitation. “Sialons” are phases in the Si-Al-O-N and related systems and are comparable in variety and diversity with the mineral silicates. They are built up of one-, two-, and threedimensional arrangements of (Si, Al) (O, N)4 tetrahedra in the same way that the fundamental structural unit in the silicates is the SiO4 tetrahedron. These new oxynitrides include structure types based uponα andΒ silicon nitrides, silicon oxynitride, aluminium nitride and silicon carbide, eucryptite, spinel, melilite and apatite. They are being explored for their thermal, mechanical, chemical and electrical properties.
838 citations
TL;DR: Gelcasting is a novel method for molding ceramic powder based on a synthesis of concepts derived from traditional ceramics and polymer chemistry as discussed by the authors, which is described in this paper.
Abstract: Gelcasting is a novel method for molding ceramic powder based on a synthesis of concepts derived from traditional ceramics and polymer chemistry. Gelcasting of alumina is described in this paper. The process is based on the in situ polymerization of acrylamide monomers as the setting mechanism for forming the green body. It has the following features: slurries with high solids loading and low viscosity (1.8 Pa {center dot} s at 62 vol% solids), dried bodies containing less than 4 wt% binder, and the ability to fabricate complex-shaped bodies.
666 citations
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TL;DR: In this article, the authors showed a variation in dimensions for the α-lithium sialon when lithium aluminate, LiAlO2, was reacted in different proportions with Si3N4.
Abstract: OUR previous report1 on Si–Al–O–N ceramics stated that expanded α-silicon ‘nitride’ structures had been obtained by reaction of lithium–silicon nitride, LiSi2N3, with alumina. The unit-cell dimensions of one example (a, 7.822; c, 5.677A) gave a cell volume about 3% greater than that of α-silicon nitride. Subsequent work2 showed a variation in dimensions for the α′-lithium sialon when lithium aluminate, LiAlO2, was reacted in different proportions with Si3N4. However, other phases, such as β′-sialon and nitrogen–eucryptite, were always present and the product never contained more than ∼30% of the α′ material. αν-Sialons were also found in the Mg–Si–Al–O–N system3 but again never pure, and were observed by Masaki et al.4 during the nitriding of silicon with A1N and A12O3 additions. A recent claim by Mitomo5 of α′ solid solutions of Si3N4–Al2O3 and/or Si3N4–Y2O3 occurring during the sintering of Si3N4 at 1,700–1,800 °C with Al2O3–Y2O3 mixtures prompted this report of the preparation and characterisation of pure α′-phases in M–Si–Al–O–N systems where M is Li, Ca or Y. Such phases also occur, but have not so far been prepared in a pure form, in magnesium and other sialon systems.
449 citations
Journal Article•
TL;DR: In this article, a suspension de poudre ceramique dans une solution de monomeres organiques est coulee dans un moule, and on polymerise in situ le melange de monemeres pour former des pieces gelifiees which seront ensuite sechees and frittees.
Abstract: Dans ce procede, une suspension de poudre ceramique dans une solution de monomeres organiques est coulee dans un moule. On polymerise in situ le melange de monomeres pour former des pieces gelifiees qui seront ensuite sechees et frittees. Le procede peut se pratiquer avec des dispersions aqueuses ou non-aqueuses. On presente les etudes realisees avec des systemes d'acrylamide.
428 citations
TL;DR: Gelcasting as discussed by the authors is a combination of polymer chemistry with slip processing and represents minimal departure from standard ceramic processing and has attracted industrial partners and by collaboration between them and the developers, the process is being advanced from the laboratory toward industrial production.
Abstract: Gelcasting, a ceramic forming process, was developed to overcome some of the limitations of other complex-shape forming techniques such as injection molding and slip casting. In gelcasting, a concentrated slurry of ceramic powder in a solution of organic monomers is poured into a mold and then polymerized in situ to form a green body in the shape of the mold cavity. Thus, it is a combination of polymer chemistry with slip processing and represents minimal departure from standard ceramic processing. The simplicity of the process has attracted industrial partners and by collaboration between them and the developers, the process is being advanced from the laboratory toward industrial production.
326 citations