Fabrication of Transparent Spinel Honeycomb Structures by Methyl Cellulose–Based Thermal Gelation Processing

Abstract

Transparent MgAl 2 O 4 spinel of flat as well as honeycomb structure was fabricated by employing thermally induced gel casting of the slurry with 56 wt% solid loading containing 0.2 wt% of methylcellulose. The green specimens were pressureless sintered to 98%-99% of theoretical density with no open porosity at an optimum temperature of 1700°C. Final densification by hot isostatic pressing of both the specimens at the optimum temperature of 1800°C and 195 MPa pressure enabled further elimination of residual porosities and full densification resulting in theoretical density of 3.58 g/cc. The design of the honeycomb was such that it exhibited a surface area to volume ratio of 0.65 cm 2 /cm 3 and a relative density of 0.69. The hardness of the honeycomb specimens has been found to be 13 GPa, which is at par with the solid specimens processed under identical conditions. Solid specimens of around 4 mm thickness exhibited a transmission of >80% in the visible (0.4-0.8 lm) region. Specimens were also tested according to ASTM procedures and have shown a flexural strength (r f ) of 195 MPa and plane-strain fracture toughness (K Ic ) of 1.87 MPaÁm 1/2 as reported in this study.

Guar gum: A novel binder for ceramic extrusion

“…A further trial at a heating rate of 1 °C/min resulted in a defect-free densified extrudate. This is a common rate in thermal debinding [47][48][49]. On the other hand, GG is water soluble and thus be of interest where the two-step debinding approach comprising water-debinding is incorporated [50,51].…”

Flash‐sintering of magnesium aluminate spinel (MgAl2O4) ceramics

“…[1][2][3][4][5][6][7] However, dense spinel is difficult to fabricate. 7 In earlier works, dense polycrystalline spinel has been obtained through high-temperature conventional sintering (typically >1500°C), 8,9 hot-pressing, [10][11][12] hot isostatic pressing (HIP), [13][14][15][16] spark plasma sintering, 17,18 and microwave sintering. [19][20][21] Electric fieldassisted sintering (FAST) is gaining interest in recent years due to the accelerated consolidation compared to conventional, pressureless sintering.…”

3D printing of cordierite honeycomb structures and evaluation of compressive strength under quasi‐static condition

“…Thermal gelation results in dehydration of hydrated methoxyl groups, which then undergo hydrophobic association giving rise to the formation of the gel network providing high green strength values as reported in our earlier studies. 23,24 Figures 2A-C shows the honeycombs with hexagonal, square, and triangular channels, respectively (virtual model and printed) along with the 3D printer ( Figure 2D) used in the current study. A printing speed of 4 mm/s for initial layer formation followed by 5 mm/s to print rest of the layers is found to be optimum for printing all honeycomb samples with different configurations.…”