Low-temperature high-pressure preparation of transparent nanocrystalline MgAl2O4 ceramics

Abstract

Transparent MgAl2O4 spinel nanoceramics have been sintered at relatively low-temperature (500–700°C) under high pressure (2–5GPa) using a hydrostatic press with high-temperature-calcined nanopowders. The morphology, nanostructure, optical property, and density of ceramics were analyzed by scanning electron microscopy, transmission electron microscopy, UV-VIS-IR transmission spectrum, and Archimedes draining method. The average grain size (<100nm for all samples sintered) depends on the sintering pressure and temperature. The nanoceramics are highly transparent even though their relative densities are all less than 99%, due to the low or negligible light scattering from the nanosized grains and pores.

Sintering to Transparency of Polycrystalline Ceramic Materials

“…These authors have synthesized spinel powders which subsequently formed by cold isostatic pressing and sintered in a hot pressing machine by applying a mechanical pressure of 4 MPa obtaining a transparent material. Lu et al, (2006) have obtained a transparent spinel material after sintering at low temperature and high pressure (2-5 GPa). Morita et al, (2008) have obtained a transparent spinel material after sintering at 1300ºC in plasma sintering equipment (Spark Plasma Sintering, SPS), reaching 47% of transmittance at 550nm.…”

Electronic and optical properties of the spinel oxides MgxZn1-xAl2O4 by first-principles calculations

“…13 Simultaneously, much work has been done on the structural, electronic and optical properties of MgAl 2 O 4 and ZnAl 2 O 4 over the past few years. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] The effect of point vacancies on the spectral properties of MgAl 2 O 4 has been studied by S. L. Jiang et al 14 They revealed that the absorption peak at 5.3 eV is attributed to the neutral oxygen vacancy V o 0 , while two peaks at 3.2 eV and 4.75 eV are attributed to the 1+ charged oxygen vacancy V o 1 + . A related mechanism of transparency in MgAl 2 O 4 nanoceramics prepared by sintering under high pressure and low temperature has been studied by J. Zhang et al 15 , who suggested that the decrease in the transparency with increasing temperature (>700°C) is therefore a result of the light scattering at large pores.…”

“…A related mechanism of transparency in MgAl 2 O 4 nanoceramics prepared by sintering under high pressure and low temperature has been studied by J. Zhang et al 15 , who suggested that the decrease in the transparency with increasing temperature (>700°C) is therefore a result of the light scattering at large pores. The low-temperature, high-pressure preparation of transparent nanocrystalline MgAl 2 O 4 ceramics has been investigated by T. C. Lu et al, 16 indicating that the nanoceramics are highly transparent even though their relative densities are all less than 99 %, owing to the low or negligible light scattering from the nanosized grains and pores. The optical properties of ZnAl 2 O 4 nanomaterials obtained by the hydrothermal method have been investigated by Miron and co-workers, 17 demonstrating that the band gap is determined from the absorbance spectra, and it depends strongly on the temperature used for further heating the samples.…”

Nanocrystalline BaTi2O5 dielectric ceramic prepared by full crystallization from containerless solidified glass

“…Two-step sintering has a short high temperature sintering followed by a long low temperature treatment to frozen the grain boundary migration, which can obtain nanocrystalline ceramics [10]. Microwave and ultra-high pressure sintering are recognized as two effective routes to fabricate ceramics by sintering the nanopowder [11,12]. Despite these achievements, obstacles remain on the path forward to widespread deployment of dense nanocrystalline ceramics.…”

“…[1][2][3][4][5][6]. A number of nanocrystalline ceramics have been fabricated by using spark plasma sintering (SPS) [7,8], two-step sintering [9,10], microwave sintering [11], ultra-high pressure sintering [12], and so on [13,14]. SPS is used as a good method of preparing ceramics with pure phase because of short duration within sintering process [15].…”