Single and Polycrystalline Transparent Ceramic Armor with Different Crystal Structure

Abstract

Contrary to the moderate ballistic advantage of Al2O3 ceramics over MgAl2O4 polycrystals, the present study shows a reverse ratio of the ballistic strength of alumina and spinel single crystals: Spinel single crystals outperform sapphire and exhibit a similarly high stability as submicrometer Al2O3 ceramics. The results correlate with different cleavage of single crystalline spinel and sapphire, changing the fragmentation on ballistic impact.

High-pressure spark plasma sintering of MgO-doped transparent alumina

“…An in-line transmission of 69% is the highest value for alumina obtained by SPS, and is slightly lower than the maximum value (72%) attained by HIP. 9), 10) For highly transparent alumina, extremely low porosities and fine grain sizes are necessary and hence densification at low temperatures is indispensable. In the present study, such microstructure for high transmission was achieved by applying high pressures.…”

Field‐Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments

“…Possible applications of transparent ceramics include solid state lasers, lenses, wavelength converters for LED lighting, scintillators, arc discharge tubes, windows for infrared detection and thermography, transparent armors, or protective windows for watches, jewels, etc. [131] The development of such advanced materials has recently raised a large interest in the research community. Fine microstructure including the removal of possible sources of light scattering (inclusions, second phases, and porosity) is challenging.…”

“…Nevertheless, initial powder quality and homogeneous packing are crucial to obtain transparency. [131] By first manufacturing agglomerate-free green compacts by slip casting or pressure filtration, larger pores detrimental to light transmission can be removed. [149] Doping, mixing with additive forming a transient liquid phase such as LiF are further means to improve densification and transparency.…”

Nanopore Characterization and Optical Modeling of Transparent Polycrystalline Alumina

“…Research activity in the fabrication of transparent ceramic materials has seen remarkable growth over the last decades, [1][2][3][4][5][6][7][8][9] with applications in an impressively broad and ever-expanding range of industries including optoelectronics and lighting, [ 10 ] medical and dental implants, [ 11 , 12 ] ceramic armors, [ 8 ] and solar energy. [13][14][15] One key feature and driving force of such activity is the possibility of sintering transparent ceramics to a near net shape, which has a potentially large economic and design impact, [ 16 ] particularly in comparison to machining the single-crystal bulk material.…”

“…Despite the general inferiority of the mechanical properties (depending on the grain size) of the isotropic materials, this strategy limits the challenge for improved optical properties to the residual porosity reduction. [ 8 ] Specifi cally for transparent polycrystalline alumina (PCA), the birefringence is small ( n o = 1.760, n e = 1.768) but by no means non-negligible. Experimentally, relatively high real in-line transmittance (RIT) values have been achieved (50-70% at 640 nm, cf.…”