Transparent MgAl₂O₄Spinel from a Powder Prepared by Flame Spray Pyrolysis

Abstract

The densification of an MgAl2O4 spinel powder prepared by flame spray pyrolysis was examined in order to determine whether it is suitable for fabricating transparent parts using a sinter/HIP approach. It was found that the powder exhibits excellent sinterability. Firing pressed powder compacts to 1650°C/2 h in air increases the bulk density to 99.9% TD. Similar densification, within the precision range of He picnometry, but a higher level of light transmission, is obtained by firing for 80 h at 1400°C. By HIPing, both specimens, sintered at 1650° and 1400°C, are made transparent but the level of transparency attained is higher in the case of specimens presintered according to the latter conditions. Such specimens (2 mm thick) exhibit, after HIPing at 1500°C/3 h (Ar, 200 MPa), a real in‐line transmission (RIT) of 63% (635 nm), an average grain size of 2.2 μm, and a hardness of 13.2 GPa. After HIPing at 1700°C, the RIT attains a value of 77%, while the average grain increases to 17 μm and the Vickers hardness slightly decreases to 12.8 GPa.

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

“…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 RIT was measured by the aid of a spectrometer (model JASCO V-570, Nihon Burko Co., Tokyo, Japan). In order to eliminate the scattered component of the light beam, a 4 × 4 mm slit was located between the specimen and detector, as recommended by Dericioglu et al 12) In our previous work, 11) an FSP powder sintering material having A = 60 m 2 /g was used. It was deagglomerated by dispersing in water, and parts were formed by rapid CIPing.…”

“…As the figure shows, the BDf of the sintered specimens gets very close to TD (3.578 g/cm 3 ) at temperatures as low as 1370-1400°C. To attain a similar level of densification required firing at 1400°C/80 h when green parts, derived from powder dispersed in water 11) were subjected to AS. At a thickness t ≤ 2 mm the disks sintered here at 1400°C/3 h, in air, exhibit considerable optical transmission, even before HIPing (RIT ≈ 50% at λ = 750 nm), as curve "c" of Fig.…”

Enhanced infrared transmittance properties in ultrafine MgAl 2 O 4 nanoparticles synthesised by a single step combustion method, followed by hybrid microwave sintering

“…Hence various fabrication techniques such as sol-gel citrate technique [5],ureaformaldehyde polymer gel combustion [6], mixed fuel combustion [7], microwave assisted combustion [8], coprecipitation [9][10][11], flame spray pyrolysis [12], molten salt method [13], pechini method [14], organic precursor method [15] have been employed for the synthesis of nanoparticles of MgAl 2 O 4 .However in all these processes either complex and cumbersome steps or prolonged multiple calcinations are essentially required to obtain phase pure nano powder.…”

Sustainable production of acetaldehyde from lactic acid over the magnesium aluminate spinel

“…Several preparation methods such as hydrothermal techniques [11,12], sol-gel [13,14], flame spray pyrolysis [15], cool drying [16,17], controlled hydrolysis [18], co-precipitation [5,19] and aerosol method [20,21] have been developed to synthesize magnesium aluminate spinels. Among these methods, co-precipitation is viewed as a simple method to synthesize spinel.…”