Novel route to β‐SiAlON–SiO2 ceramic composites
01 Feb 2011-Advances in Applied Ceramics (Maney Publishing Suite 1C, Joseph's Well, Hanover Walk, Leeds LS3 1AB, UK)-Vol. 110, Iss: 2, pp 87-94
TL;DR: In this paper, a novel synthetic route to prepare dense β•SiAlON−SiO2 ceramic composites was reported, which were fine ground and mixed with different amounts of commercial fused silica powder, dry pressed and sintered for 3-4h at 1500-1750°C.
Abstract: 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.
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TL;DR: In this paper, a review article covering various methods reported on synthesis of β-SiAlON based ceramic materials and on their net-shape consolidation into radome structures is presented.
Abstract: 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.
36 citations
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.
Abstract: An electromagnetically transparent, structurally robust and environmentally resistant enclosure of radar antenna for ground based systems to modern avionics in military aircraft and missiles is called as radome. Radome materials are classified based on: (i) type of function - surface-based or flight-mode and (ii) speed of operation - subsonic, supersonic to hypersonic. The desired properties of these materials are low dielectric constant and low loss factor in addition to its capacity to withstand the high temperature of operation. Composite laminates of glass or aramid fibre reinforced polymeric resins are radome material candidates for applications in subsonic range. However, ceramics are the only viable option for military aerospace applications such as a fighter jet travelling at Mach 3 or an advanced hypersonic missile speeding up to Mach 5. This review outlines the hand-full of ceramic materials already in application as radome materials like high-purity-alumina, pyroceram, slip-cast-fused-silica, their processing technology, electromagnetic and mechanical properties, advantages and disadvantages with respect to advanced military vehicles. Use of silicon nitride based radome materials, that has exceptional mechanical strength and thermal stability up to 1400 °C is illustrated with respect to reaction bonded silicon nitride, hot pressed silicon nitride, silicon oxynitride, sialon and their composites. Design of new generation radome materials was conceptualized and discussed as applicable to silicon nitride and related ceramics, wherein incorporation of varied degree of porosity improves electromagnetic properties, simultaneously, maintaining the required mechanical strength. Multilayer and graded porosity and its influence on electromagnetic properties were briefly discussed. Si3N4 ceramics having controlled porosity leading to optimum electromagnetic and mechanical properties produced through systematic processing is proposed as the futuristic high temperature radome material for supersonic applications.
29 citations
TL;DR: In this paper, a modified non-aqueous gelcasting technique was used to obtain low-viscosity and high solid-loading AlN slurps with a relative density of 65.5% and flexural strength of 42.3% using 1-methyl-2-pyrrolidinone as solvent and Solsperse® 24,000 as dispersant.
Abstract: Aluminum nitride (AlN) ceramics has been prepared by a modified non-aqueous gelcasting technique, and the ceramic slurries with low viscosity and high solid loading were obtained by using 1-methyl-2-pyrrolidinone as solvent and Solsperse® 24,000 as dispersant. The rheological behaviors of the AlN ceramic slurry and the densities of AlN ceramics were studied. Typically, the AlN ceramic slurry (Solsperse® 24,000 of 0.5 wt% and solid loading of 50 vol%) showed a viscosity of 0.09 Pa·s at shear rate of 100 s −1 . And more interestingly, when increasing solid loading to 55 vol%, the AlN slurry still kept a low viscosity of about 0.28 Pa·s, which was reduced by 30% compared to the reported values. As a result, the resultant green body exhibited a relative density of 65.5%, and a flexural strength of 42.3 MPa. After sintering at 1900 °C for 5 h, the AlN ceramics with an improved relative density of 99.4% was produced. Thus, this research would provide a new way to prepare low-viscosity and high solid-loading AlN slurry.
23 citations
01 Jan 2020
9 citations
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.
3 citations
References
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01 Jan 2012
139,059 citations
"Novel route to β‐SiAlON–SiO2 cerami..." refers background or methods or result in this paper
...In order to reduce the dielectric constant of high strength and high temperature withstanding b-SiAlON composition, several studies have been conducted to introduce SiO2 into the matrix of b-SiAlON.(7,8,20) However, b-Si4Al2O2N6–SiO2 ceramic composites with ....
[...]
...Thus, the absence of any sintering aid during densification of pure fused silica (SS-100) upon sintering at 1675uC for 4 h could be responsible for the noted high porosity in the micrograph as well as in its apparent porosity of 10?72% (Table 1).(1,8,21) Thus, the information obtained from this SEM study is supporting the information obtained through XRD and other characterisation techniques for these b-Si4Al2O2N6–SiO2 based ceramic composites....
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...These values are comparable with the literature values.(1,8,21) It can be seen from this table that all these ceramic composites exhibited considerable amounts of mass losses upon sintering what is common for Si3N4 based ceramics....
[...]
...2–7,15,23 A SiON nanocomposite exhibited a dielectric constant of 4?78 at 25uC and 5?0 at 1000uC and a loss tangent of 0?0014 at 25uC.(8) A dielectric constant value of 6?3 was measured for b-Si4Al2O2N6–9 wt-%SiO2 composite sintered for 4 h at 1750uC for 3 h....
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...On average, three density measurements were performed on each sample (¡0?01 standard deviation).(7,8,23) The XRD patterns were recorded on a Bruker (Karlsruhe, Germany) D8 advanced system using a diffracted beam monochromated Cu Ka (0?15418 nm) radiation source....
[...]
Book•
IBM1
TL;DR: In this paper, the authors present a model for the development of the MICROSTRUCTURE in CERAMICS based on phase transformation, glass formation and glass-Ceramics.
Abstract: INTRODUCTION. Ceramic Processes and Products. CHARACTERISTICS OF CERAMIC SOLIDS. Structure of Crystals. Structure of Glasses. Structural Imperfections. Surfaces, Interfaces, and Grain Boundaries. Atom Mobility. DEVELOPMENT OF MICROSTRUCTURE IN CERAMICS. Ceramic Phase Equilibrium Diagrams. Phase Transformation, Glass Formation and Glass--Ceramics. Reactions with and between Solids. Grain Growth. Sintering and Vitrification. Microstructure of Ceramics. PROPERTIES OF CERAMICS. Thermal Properties. Optical Properties. Plastic Deformation, Viscous Flow and Creep. Elasticity, Anelasticity and Strength. Thermal and Compositional Stresses. Electrical Conductivity. Dielectric Properties. Magnetic Properties.
6,650 citations
TL;DR: In this paper, a method is presented for determining the complex permittivity and permeability of linear materials in the frequency domain by a single time-domain measurement; typically, the frequency band extends from VHF through X band.
Abstract: In this paper a method is presented for determining the complex permittivity and permeability of linear materials in the frequency domain by a single time-domain measurement; typically, the frequency band extends from VHF through X band. The technique described involves placing an unknown sample in a microwave TEM-mode fixture and exciting the sample with a subnanosecond baseband pulse. The fixture is used to facilitate the measurement of the forward- and back-scattered energy, s21(t) and s11(t), respectively. It is shown in this paper that the forward- and back-scattered time-domain "signatures" are uniquely related to the intrinsic properties of the materials, namely, e* and ?*. By appropriately interpreting s21(t) and s11(t), one is able to determine the real and imaginary parts of ? and ? as a function of frequency. Experimental results are presented describing several familiar materials.
2,557 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