Transparent alumina ceramics: Effect of standard and plasma generated stabilizing approaches in colloidal processing

Abstract

The study is focused on an optimization of the slip‐casting process used for the fabrication of the transparent/translucent alumina ceramics; more precisely, on specifying the most appropriate way to stabilize the cast alumina suspensions. An innovative method of the particles’ stabilization by plasma treatment was compared with the classical electrostatic and the most frequently used electrosteric approach. Properties of green bodies (pore size distribution, density) and sintered samples (density, mean grain size, real in‐line transmittance) were measured in term to evaluate the impact of the individual stabilization mechanism on the final properties of the transparent/translucent ceramics. The results showed that all tested approaches enable the preparation of the transparent/translucent alumina ceramics by Hot Isostatic Pressing. Ceramics prepared from the plasma treated as well as the electrostatically stabilized powders exhibited narrower pore size distribution, higher density, and lower mean grain size in comparison to ceramics fabricated from only electrosterically stabilized powders. Despite these promising properties the plasma‐treated samples resulted in an unexpectedly low RIT of 36% caused by the presence of thin cracks. However, the electrostatically stabilized samples achieved the highest RIT value of 57%.

Highly permeable Al2O3 microfiltration membranes with holey interior structure achieved through sacrificial C particles

“…The thicknesses of the holey intermediate layer and the active layer were measured based on the SEM images of the cross‐sections, and the reported thickness values were the average of 30 points from 10 images. The porosity of the holey layer was calculated using the following Equation ():where ε is the porosity, m is the total mass of the membrane with only holey layer, m 0 is the mass of the single support, s is the area of the coated surface, h is the thickness of the holey layer, and ρ is the theoretical density of the Al 2 O 3 (3.99 g/cm 3 ) . The reported values of porosity were the average of 10 specimens.…”

“…where ε is the porosity, m is the total mass of the membrane with only holey layer, m 0 is the mass of the single support, s is the area of the coated surface, h is the thickness of the holey layer, and ρ is the theoretical density of the Al 2 O 3 (3.99 g/ cm 3 ). 25 The reported values of porosity were the average of 10 specimens. The bonding characteristics among the support, the holey layer, and the top layer were evaluated by measuring the loss of mass and the change in surface color of the membranes before and after ultrasonic vibration (40 kHz, 20 minutes).…”

Role of Surface-Chemistry in Colloidal Processing of Ceramics: A Review

“…Slip casting was used to produce transparent alumina ceramics using three stabilization methods: (a) plasma treatment (b) electrostatic stabilization and (c) electrosteric stabilization [68]. Electrostatic stabilisation performed best in terms of all examined metrics (green body porosity and density, sintering temperatures, densities, and real in-line transmittance (RIT)).…”

Transparent Alumina Nanoceramics Prepared under High Pressure and Low Temperature

“…Vacuum sintering [2][3][4] and microwave sintering [5] require a melting point near the sintering temperature, which produces transparent alumina samples with micrometer-sized grains. Hot isostatic pressing (HIP) sintering [6][7][8][9][10][11] under hundreds of megapascals obviously decreases the preparation temperature of transparent alumina ceramics to approximately 2/3 of their melting point and suppresses the sample grain size to 300-400 nm. Furthermore, spark plasma sintering (SPS) assisted with hundreds of megapascal of pressure [12][13][14][15][16][17][18][19][20] further decreases the sintering temperature to approximately 1000 °C because of its rapid heating rate and short holding time, which effectively suppresses grain growth and results in samples with approximately 200 nm grains.…”