Sol-gel derived porous ultra-high temperature ceramics

Abstract

Ultra-high temperature ceramics (UHTCs) are considered as a family of nonmetallic and inorganic materials that have melting point over 3000 ℃. Chemically, nearly all UHTCs are borides, carbides, and nitrides of early transition metals (e.g., Zr, Hf, Nb, Ta). Within the last two decades, except for the great achievements in the densification, microstructure tailoring, and mechanical property improvements of UHTCs, many methods have been established for the preparation of porous UHTCs, aiming to develop high-temperature resistant, sintering resistant, and lightweight materials that will withstand temperatures as high as 2000 ℃ for long periods of time. Amongst the synthesis methods for porous UHTCs, sol-gel methods enable the preparation of porous UHTCs with pore sizes from 1 to 500 μm and porosity within the range of 60%-95% at relatively low temperature. In this article, we review the currently available sol-gel methods for the preparation of porous UHTCs. Templating, foaming, and solvent evaporation methods are described and compared in terms of processing-microstructure relations. The properties and high temperature resistance of sol-gel derived porous UHTCs are discussed. Finally, directions to future investigations on the processing and applications of porous UHTCs are proposed.

Effects of Sintering Behaviors on Dimensional Accuracy, Surface Quality, and Mechanical Properties of Stereolithography-printed 3Y-ZrO2 Ceramics

“…4 (b-d), the surfaces of the SLA-printed 3Y-ZrO2 ceramic bodies presented a clearly anisotropic feature, and the surface roughness of XOY, YOZ, and XOZ surfaces were Ra=0.51 μm, Ra=1.79 μm, and Ra=2.10 μm, respectively. The low surface roughness values proved that the quality fabricated by SLA showed a better potential than that of other 3D printing technologies [34,35]. Meanwhile, there was an obvious layer-and-layer process in the YOZ and XOZ surfaces, which demonstrated that the surface roughness on the YOZ and XOZ were quite severe than the XOY surface.…”

Microstructure and mechanical properties of Zr3Al3C5-based ceramics synthesized by Al-Si melt infiltration

“…Ultra-high-temperature ceramics (UHTCs), a group of advanced structural ceramics, exhibit indispensable advantages in ultra-high-temperature service environment for the thermal protection system of hypersonic vehicles [1,2]. The strong covalent bonding makes them have high hardness, high melting point, high strength and stiffness, and chemical inertness, simultaneously.…”

Strength Analysis of Porous YSZ Ceramics With the Same Porosity and Different Pore Structure

“…To get lighter ceramics with larger speci c surface area and lower thermal conductivity, it is hoped that the porosity of porous ceramics can be further reduced. Many practicable processes have been studied and developed, such as pore forming agents, controlled sintering, sacri cial template, gelcasting, direct foaming [6][7][8][9][10][11][12][13][14][15]. However, the porosity and strength of porous ceramics are contradictory.…”