Lightweight porous silica-alumina ceramics with ultra-low thermal conductivity

Thermal protection has always been an important issue in the energy, environment and aerospace fields. Porous ceramics produced by the particle-stabilized foaming method have become a competitive material for thermal protection because of their low density and low thermal conductivity. However, the study of porous ceramics for composite systems using particle-stabilized foaming method was relatively rare. Here, silica-alumina composite porous ceramics were prepared by particle-stabilized foaming method, which was achieved by tailoring the surface charges of silica and alumina through adjustment of the pH. Porous ceramics exhibited porosity as high as 97.49% and thermal conductivity (25 °C) as low as 0.063 W m^?1 K^?1. The compressive strength of porous ceramics sintered at 1500 °C with a solid content of 30 wt% could reach 0.765 MPa. Based on the light weight and excellent thermal insulation properties, the composite porous ceramic could be used as a potential thermal insulation material in the spacecraft industry.     

A fractal analysis of crack branching in borosilicate glass

Many fractography techniques involve precise measurements of features on the fracture surface and can be difficult to perform in the field, or rapidly. Macroscopic crack branching observations offer a more robust and forgiving method of analysis, but often are not strongly correlated with standard fractography techniques. In this study, the crack branching patterns of annealed borosilicate glass disks previously fractured in biaxial tension were analyzed using fractal methods and compared with more typical fracture surface measurement techniques. The results confirm that the fractal dimension of macroscopic crack branching (called the Crack Branching Coefficient) increases with increasing failure stress, as has been shown with other brittle materials. In addition, the existence of a threshold stress previously reported was confirmed using new techniques. The findings herein can be used to further increase the fidelity of fractography-based failure analysis of brittle materials.     

Biocompatible glass ceramics

Glass ceramic biomaterials in the Mg₃[PO₄]₂ - Ca₅[PO₄]₃F system are synthesized. The physicotechnical properties, phase composition, and microstructure of glass ceramics are investigated. The obtained glass ceramic biomaterials can be used for medical purposes.     

分形理论在高技术陶瓷材料研究中的应用

分形方法是研究材料科学的一种数学工具。本文以Mo／β＇－Sialon系梯度功能材料为例，探讨了分形在材料科学研究中的应用。     

Bioactive fluorapatite-containing glass ceramics

Fluorapatite-containing glass ceramics were synthesized on the basis of the glass-forming system SiO₂–Al₂O₃–P₂O₅–CaO–CaF₂. The introduction of phosphorus and fluorine containing materials, as well as the specific regime of heat treatment of the glasses gave glass ceramic materials with crystalline phases of the apatite group—fluorapatite (Ca₁₀(PO₄)₆F₂), apatite (Ca₃(PO₄)₂), vitlokite (Ca₉P₆O₂₄), etc. The X-ray phase analysis showed that the main phase in all the glass ceramic samples was fluorapatite. The phase composition, structure and some of the basic properties of the glass ceramic samples were determined.     

Pressureless joining of SiC ceramics with magnesia-alumina-silica glass ceramics

Liquid phase sintered SiC ceramics were joined using magnesia-alumina-silica (MAS) glass-ceramic fillers without applied pressure. Four different filler compositions with 9.3–25.2 wt.% MgO, 20.7–33.6 wt.% Al₂O₃, and 49.2–68.1 wt.% SiO₂ were studied. The effects of filler composition and joining temperature (1450–1600°C) on the joint strength were investigated. All compositions exhibited an optimum joining temperature at which the maximum joint strength was obtained. A low joining temperature resulted in poor wetting of the SiC substrate due to the high viscosity of the filler. Whereas a high joining temperature caused dewetting and large unfilled sections in the interlayer due to the deleterious interfacial reactions. The joint strength was inversely proportional to the interlayer thickness, which was a function of filler composition and joining temperature. The SiC ceramic joined at 1525°C with MgO-25 wt.% Al₂O₃-60 wt.% SiO₂ filler exhibited a four-point bending strength of 286 ± 40 MPa.     

Phase composition and microstructure of cinder-based glass ceramics

The paper sums up a study of the crystallization of cinder-based glasses in the system CaO−Al₂O₃−SiO₂. The manner in which heat treatment affects the phase composition, microstructure, and properties of the glass ceramics is described. The principal crystalline phases are identified and the dependence of the properties on the microstructure is determined. Translated from Steklo i Keramika, No. 7, pp. 21–23, July, 1997.     

Construction ceramics based on glass waste

Different technological methods for using waste from the glass industry (glass scrap) for the production of decorative building materials, i.e., facing and roof tile, are presented.Translated from Steklo i Keramika, No. 10, p. 6, October, 1995.     

Optimal design on the mechanical and thermal properties of porous alumina ceramics based on fractal dimension analysis

In order to investigate the relationship between pore structure and thermal conductivity as well as mechanical strength, porous alumina ceramics (PAC) with various pore structures were fabricated, using starch as the pore‐forming agent. Fractal theory was employed to characterize the pore size distribution more accurately than ever used parameters. The results show that the increase in starch content in PAC leads to an enhanced porosity, a higher mean pore size, and reduced fracture dimension, thermal conductivity and strength. The fractal analysis indicated that the fractal dimension decreases gradually and reaches its minimum value with increasing the starch content up to 25 wt%, but the further incorporation results in an opposite trend. It is suggested from micro‐pore fractographic analysis that the optimization of both thermal insulation performance and mechanical strength are positively correlated with the increase in the mean pore size and proportion of 2‐14 μm pores but negatively corrected with the porosity. These results provide a new perspective and a deeper understanding for fabrication of PAC with both excellent thermal insulation and mechanical performance.