An Economic Comparison of Hot Pressing vs. Pressureless Sintering for Transparent Spinel Armor

Hydrolysis-Induced Aqueous Gelcasting of Magnesium Aluminate Spinel

“…These results indicate that an increase in the solids loading did not significantly affect the densification degree of MAS powders. The relatively low values of AP (<0.5%) and WA capacity (<0.1%) of these MAS materials make them suitable for many potential applications 1–10 …”

“…Magnesium aluminate (MgAl 2 O 4 ) spinel (MAS) has attracted much attention from materials scientists and ceramic engineers due to its interesting set of properties such as high melting point (2135°C), high hardness (16.1 GPa), relatively low density (3.58 g/cm 3 ), excellent transmittance in the range of 0.25–5.0 μm wavelength, high strength at room and at elevated temperature (180 MPa), high chemical inertness, relatively low thermal expansion coefficient (9 × 10 −6 /°C between 30°C and 1400°C), high thermal shock resistance, etc 1–14 . Furthermore, MAS does not react with SiO 2 until 1735°C, with MgO or CaO until 2000°C, with Al 2 O 3 until 1925°C and it can be in contact with all metal except alkaline earths 5 .…”

“…Furthermore, MAS does not react with SiO 2 until 1735°C, with MgO or CaO until 2000°C, with Al 2 O 3 until 1925°C and it can be in contact with all metal except alkaline earths 5 . Owing to these properties, MAS has been used as optical windows, pressure vessels, and bullet‐proof vehicles, 6–8 alternative materials to replace the conventional carbon anode in aluminum electrolytic cells, 9 humidity sensors, 10 refractory materials for cement rotary kilns and steel ladles, 11,12 and as a catalyst support for several reactions 13,14 . Despite these advantages, dense MAS bodies are hardly obtainable through a single‐stage reaction sintering process due to a severe volume expansion (∼8%) associated with the formation of MgAl 2 O 4 phase from alumina and magnesia 15 .…”

“…These two consecutive firing cycles significantly increase the production costs of dense MAS ceramics. Moreover, the preparation of MAS components for certain strategic applications such as infrared domes and radomes is also quite expensive due to the involvement of extensive and costly postsintering machining operations 6,7,18 . At present, MAS domes and radomes are being fabricated by hot isostatic pressing (HIPing) (∼1500°C and 200–400 MPa pressure) followed by machining to obtain the desired final shape 6,7 …”

Effect of Room and High Temperature Compaction on Optical and Mechanical Properties of HIPed Transparent Spinel Ceramics

“…[10,11] Transparent spinel has been processed by several routes, such as pressureless sintering (PLS) or hot pressing (HP) followed by HIP. [15] Vacuum sintering and sintering in hydrogen have been employed by earlier studies. [15] Vacuum sintering and sintering in hydrogen have been employed by earlier studies.…”