Hydrophobic coagulation of alumina slurries

Abstract

Wet forming 1,2 is an important ceramic forming technology, characterized by the transformation of slurry (suspension) to wet body. Based on the coagulation mode, wet forming can be divided into two types: (a) obtaining wet body through solidliquid separation, including slip casting, 3 pressure filtration, 4 tape casting, 5 and centrifugal molding 6 and (b) obtaining wet body through in-situ coagulation of slurry, including polymer additive transformation (agarose 7 and gelatin 8), gel casting, 9,10 and direct coagulation casting (DCC). 11 Wet bodies formed by in-situ coagulation do not have the gradient problem caused by solid-liquid separation but usually require kinds of additives to achieve coagulation. In addition, an inducer (temperature, pH value, or initiator, etc) is needed to trigger the slurry state change, which increases the technical difficulty in practical operations. Recently, Yang et al 12 reported the spontaneous coagulation casting (SCC) method in which PIBM (a copolymer of isobutylene and maleic anhydride; commercial name,

Re-fluidising the aged gel for high-density alumina green body

“…The same phenomenon was observed between the samples 56.5 vol%-0 and 56.5 vol%-1. The bulk density increased from 2.539 to 2.580 g/cm 3 , and the relative density increased from 63.7% to 64.7%. The reason for the density improvement of green body was ascribed to the increase in the solid loading.…”

“…The mechanism of SCC is hydrophobic interaction and hydrogen bonding. Based on this, a series of agents were synthesised for the forming of both dense and porous ceramics by grafting a surfactant with a short or long chain on a dispersant [3]. Many dense ceramics such as Al 2 O 3 , YAG, MgAl 2 O 4 , Y 2 O 3 , and AlON, as well as porous ceramics such as Al 2 O 3 and mullite, have been formed by the SCC system [4][5][6][7][8][9][10].…”

Transparent Alumina Nanoceramics Prepared under High Pressure and Low Temperature

“…[1] Bulks of alumina with a high transparency can be fabricated using numerous approaches. 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.…”

“…The abovementioned results mainly used nanosized or submicrometer alumina powder as starting materials. By doping with MgO, [2,5,7,14] ZrO 2 , [6,9] or La, [15] orienting the grain using a magnetic field, [10,18] using a templated grain growth method, [4] or using an applied pressure of 600 MPa in SPS sintering, the grain sizes of the samples could be minimized, and birefringence at the grain boundaries could be effectively suppressed. The transmittance of alumina bulks with a thickness of approximately 0.8 mm reaches 47-78% at a wavelength of approximately 640 nm, which is close to the reported value of 84.5% for sapphire.…”