Mechanical Behavior of Lightweight Ceramics Based on Sintered Hollow Spheres

Abstract

Mechanical Behavior of Lightweight Ceramics Based on Sintered Hollow Spheres 395rattling in a cage, which has been suggested as the mechanism for the high microwave susceptibility of pure sodium nepheline.8 The role of the size and shape of the sample in relation to the wavelength at 2.45 GHz has yet to be studied. Also, the role of the microstructure of each gel which is dependent upon various process parameters" also needs to be investigated. Such detailed studies are under way. V. ConclusionsIt has been demonstrated that alumina, silica, and mullite gels could be heated rapidly to very high temperatures in a 600-W kitchen oven with proper insulation. In fact, silica gel was melted under the present experimental conditions. Studies are presently under way to unravel the mechanism for the high susceptibility of the gels to microwave radiation. With the emergence of sol-gel technology in the ceramic industry, the high susceptibility of gels to microwave radiation gives an excellent processing option. A simple micromechanical model, describing the Young's modulus, fracture toughness, and density of a lightweight ceramic structure produced by the sintering of hollow spheres and based on shell theory, was developed. The approach combined an analysis of the elastic deformation using shell theory and a simple analysis of the densification in terms of the microstructural parameters. The results were compared with experimental data for materials produced by the sintering of hollow glass spheres and gave reasonable to good agreement, especially in the prediction of the nonlinear variation of Young's modulus and fracture toughness with density. The model should provide a useful basis for rationalizing the relation between mechanical properties and fabrication procedure for such materials.

Thermal Conductivity of Zinc Oxide: From Green to Sintered State

“…To understand the microstructural dependence of physical properties of ceramics, especially during sintering, many models have been derived using idealized structures. 7,8 Property-porosity models based on a minimum solid area (MSA) of idealized stacking of partially sintered spherical particles were shown to agree with appropriate physical property data for bodies whose porosity is represented by such stacking. 9 -11 This paper, which builds on what is available in the literature, examines the microstructure-thermal conductivity relationship in ceramic materials, starting with the earliest stages of sintering before densification is measurable.…”

Fracture toughness of re-entrant foam materials with a negative Poisson's ratio: experiment and analysis

“…It is therefore important to assess the strength and toughness of the material and to understand the physical causes which govern these properties. Recent studies [1][2][3][4][5] have led to a better understanding of these issues.…”

Microstructure Optimization of Sintered Fly Ash/Acid Composition for Use as Structural Thermal Insulation in Buildings

“…It is the case that closed cells have less heat loss due to conduction through gas, the dominant mode of heat loss [2]. Studies by these and other researchers [2,3,5] have verified that improved thermal and lightweight performance and less water absorption as well as improved compressive strength per unit weight were to be expected as a result of the substitution of closed cell spheres in place of the open cell foamed structure. The sintering of fly ash spheres to produce a closed cell microstructure for thermal insulation material has been successfully done by Briggs and also Green [3,4].…”

“…In their work on sintered hollow ceramic spheres, Green and Hoagland [3] found that with close packing of spheres at higher densities, the mechanical behavior could be understood in terms of shell theory, i.e., the fracture of cell edges and the associated forces predominated and therefore imparted higher Young's modulus and compressive strength. They also found that before close packing or densification occurs, the size of the contact area or intersections of the spheres is small (see Figure 7) [3]. For these lower densities, the fracture involved failure in the immediate vicinity of a sintered contact area between two spheres.…”

“…For these lower densities, the fracture involved failure in the immediate vicinity of a sintered contact area between two spheres. At greater densities and more close parking, there is a rapid increase in Young's modulus and fracture toughness (with density) [3]. Green found that fly ash spheres packed 52% of the total volume in the green bodies.…”