Translucent Sintered MgAl<sub>2</sub>O<sub>4</sub>

Bratton, R. J.

doi:10.1111/j.1151-2916.1974.tb10901.x

Cited by 105 publications

(46 citation statements)

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“…13), 14) The transmission level attained after the AS stage, while demonstrating the high sinterability of the FSP powder, is not high enough for the intended application. In order to further reduce the residual porosity, under the 0.01 vol% required for good transmission, 6) the use of HIPing proved necessary.…”

Section: Jcs-japanmentioning

confidence: 99%

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Goldstein¹,

Gol'denberg²,

Hefetz³

2009

J. Ceram. Soc. Japan

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Transparent, polycrystalline MgAl2O4 ceramics have been fabricated by sintering optimized-configuration, powder compacts formed from a material prepared by flame spray pyrolysis. Transparent parts (80% light transmission at 2 mm thickness) could be obtained after pressureless sintering in air at 1280°C/3 h, followed by hot isostatic pressing at 1320°C/3 h/200 MPa.The average grain size was 0.45 μ m. Such materials exhibit property combinations suitable for transparent armor applications.©2009 The Ceramic Society of Japan. All rights reserved.Key-words : Transparent spinel, Ceramics, Sintering, Optical materials [Received June 12, 2009; Accepted August 20, 2009] Polycrystalline MgAl2O4 spinel is one of the most suitable materials for transparent armor panels strike-face fabrication. 1)-4)For such an application, besides a high optical real in-line transmission (RIT), a submicron grain size (GS) is desired. This is so because a fine microstructure facilitates projectile erosion by causing an optimal ceramic fragmentation pattern and increasing hardness (compared to that of large grains spinel)Most of the fabrication technologies previously developed, allow the obtainment of spinel parts exhibiting excellent optical transmission but associated with coarse microstructure.3),4),7),8)Only a few workers focused on the obtainment of low grains size. For instance, remarkably fine microstructure (GS in the 1-5 μ m range) was reported by Gazza and, respectively, Tsukuma. 9),10) Krell et al. were able to further refine, to the submicron region, the microstructure, and obtain, as a result, transparent spinel plates (TSP) showing improved performance in ballistic tests. 1),5),6) Their technology, though, is presented in the literature only in general terms, which do not allow reproduction of the results. For instance, 6) it requires the use of sintering additives, the nature and amount of which were not disclosed.It was recently determined by us 11) that spinel powders prepared by flame spray pyrolysis exhibit an unusually high sinterability. Transparent parts could be derived from such powders by sintering at relatively low temperature (1400°C/80 h, in air) followed by hot isostatic pressing (HIP) at 1500°C. The microstructure of the specimens was quite fine (average grains size ~ 8 μ m), but not at the level optimal for ballistic applications.The objective of this work was to examine whether it is possible to further reduce the sintering temperature of FSP spinel powder compacts, by improvement of the green-body configuration, to a level at which submicron grains size can be obtained while the optical transmission is kept at ≥ 78% in the visible (VIS) range.A stoichiometric MgAl2O4 spinel powder (Nanocerox, Ann Arbor, MI, USA), prepared by flame spray pyrolysis, having a specific surface area A = 30 m 2 /g and including as main impurities 25 ppm of Cl + 20 ppm Si + 10 ppm Ca was used. The powder is made of spheroidal basic particles (individual crystallites or non-porous clusters of them) 20 to 50 nm in size, assembled i...

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Section: Jcs-japanmentioning

confidence: 99%

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Goldstein¹,

Gol'denberg²,

Hefetz³

2009

J. Ceram. Soc. Japan

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“…After being shown to be transparent in early 1960's, spinel has received considerable attention and has been the subject of numerous studies. 1,2,6,8,[10][11][12] It has been considered to be well suited especially for armor applications because of its ideal combination of optical transparency, hardness, impact resistance, strength, modulus, ease of fabrication and crystal size capability. [3][4][5] In various studies, it has been shown to be superior to other available armor materials such as sapphire, AlON, soda-lime silicate glass and MgF 2 in terms of its excellent balance of performance and affordability.…”

Section: Introductionmentioning

confidence: 99%

Effect of Chemical Composition on the Optical Properties and Fracture Toughness of Transparent Magnesium Aluminate Spinel Ceramics

et al. 2005

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Polycrystalline transparent magnesium aluminate ''spinel'' ceramics were fabricated by hot-pressing and hot isostatic pressing (HIPing) using commercially available MgO and Al 2 O 3 powders. Al 2 O 3 content of spinel was systematically changed that can be expressed as MgOÁnAl 2 O 3 with n ¼ 1:0, 1.5 and 2.0. UV/visible and near-IR wavelength region light reflection and transmission behaviors of the spinel ceramics were quantitatively correlated to their microstructure to account for the optical quality of the fabricated materials. The stoichiometric spinel ceramic with n ¼ 1:0 revealed a relatively poor optical transparency due to pronounced light scattering at the microcracked grain boundaries with a specular light transmission of $20{40% in the visible wavelength range. On the other hand, Al 2 O 3 rich compositions revealed a specular transmission of $40{60% in the same wavelength range with a high degree of transparency. Additionally, effect of chemical composition on the fracture toughness of spinel ceramics was investigated applying indentation and chevron notched specimen fracture toughness measurement techniques. The spinel ceramic with n ¼ 2:0 revealed the highest fracture toughness with a mean value of $2:02 MPaÁm 1=2 . Based on their optical and mechanical properties, potential of Al 2 O 3 rich non-stoichiometric polycrystalline spinel ceramics for engineering applications requiring high optical transparency and improved fracture toughness was addressed.

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“…There are extensive research efforts all over the world to improve the process for producing well-known transparent Lucalox and Yttralox (90 mol.% Y 2 O 3 -10 mol.% ThO 2 solid solution) materials and to obtain new types of transparent functional ceramics with complex physical composition and specific characteristics [3][4][5][6][7][8][9][10][11]. These include x-ray scintillators, ceramics resistant in vapors of alkaline and rare-earth elements, indium, and zinc, ceramics for instrumented optics (lenses, laser materials (Y 2 O 3 -ThO 2 -Nd 2 O 3 ), and materials with electrooptic effect (lanthanum-doped lead titanate-zirconate Pb, La(ZrTi)O 3 ).…”

Section: Introductionmentioning

confidence: 99%

Transparent ceramics based on yttrium subgroup lanthanide, yttrium, and scandium oxides

Shevchenko

Dubok

Dudnik

et al. 2011

Powder Metall Met Ceram

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Transparent C-Y 2 O 3 -based ceramics characterized by optical transmission in visible and nearinfrared regions and translucent ceramics based on oxides of yttrium subgroup lanthanides are produced. Initial nanocrystalline powders are produced with heterophase mechanochemical treatment in an acid medium with doping cations. The effect from oxides of subgroup IVb (SiO 2 , PbO) elements, which promote liquid-phase sintering in the production of transparent ceramics, is established.

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Translucent Sintered MgAl₂O₄

Cited by 105 publications

References 1 publication

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Effect of Chemical Composition on the Optical Properties and Fracture Toughness of Transparent Magnesium Aluminate Spinel Ceramics

Transparent ceramics based on yttrium subgroup lanthanide, yttrium, and scandium oxides

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Translucent Sintered MgAl2O4

Cited by 105 publications

References 1 publication

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Transparent polycrystalline MgAl2O4 spinel with submicron grains, by low temperature sintering

Effect of Chemical Composition on the Optical Properties and Fracture Toughness of Transparent Magnesium Aluminate Spinel Ceramics

Transparent ceramics based on yttrium subgroup lanthanide, yttrium, and scandium oxides

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Translucent Sintered MgAl₂O₄