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Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Glass products may be annealed to reduce internal stresses that have been set up due to uneven cooling. Glass, such as plate glass for windows, may also be toughened by heat treatment. If glass is held at its annealing temperature and very slowly cooled, it can be made to crystallise. The process is called ‘devitrification’ and produces a structure with crystals that are smaller and more uniform than in other bonded ceramics. Depending on their composition, glass ceramics can be made with better thermal and mechanical properties than glass itself. The ‘pyroceramics’ used for cooker hobs are materials of this type and they are also used for aerospace applications.
Materials
Published in Ansel C. Ugural, Youngjin Chung, Errol A. Ugural, Mechanical Engineering Design, 2020
Ansel C. Ugural, Youngjin Chung, Errol A. Ugural
Ceramics are basically compounds of nonmetallic as well as metallic elements, mostly oxides, nitrides, and carbides. Generally, silica and graphite ceramics dominate the industry. However, newer ceramics, often called technical ceramics, play a major role in many applications. Glasses also consist of metallic and nonmetallic elements; however, they have a crystal structure. Glass ceramics are in widespread usage as electrical, electronic, and laboratory ware.
Glasses
Published in William Bolton, R.A. Higgins, Materials for Engineers and Technicians, 2020
Glass ceramics are designed so that crystallisation occurs to give a fine-grained polycrystalline material. Such a material has considerably higher strength than most glasses and retains its strength to much higher temperatures, and has a very low coefficient of expansion and excellent resistance to thermal shock. Glass ceramics are produced by using a raw material containing a large number of nuclei on which crystal growth can start, e.g. small amounts of oxides such as those of titanium, phosphorus or zirconium. Most forms of glass ceramic are based on Li2O-Al2O3-SiO2 and MgO-Al2O3-SiO2. The material is heated to form a glass, e.g. to 1650°C, in the required product shape and then cooled and cut to size. The product might be in the form of sheets, e.g. for cooker hobs (Figure 22.3). After finishing the edges and applying the surface decoration, they are heated to a high enough temperature, e.g. 900°C, to give controlled grain growth until the required grain size is obtained. Glass ceramics are used for cooker tops, cooking ware and telescope mirrors.
Comprehensive performance evaluation of plasma vitrification for detoxification and valorization of residual wastes
Published in Critical Reviews in Environmental Science and Technology, 2023
Yao-Jian Li, Si-Lu Pei, Zhong-Hua Sun, Lei Zhong, Cheng-Chun He, Shu-Yuan Pan
Although the vitreous slag has considerable improvements in chemical stability and mechanical performance, additional thermal treatment can be further considered to obtain glass-ceramic with a higher quality. Table 1 presents the changes of physico-chemical properties of MSWI fly ash after various thermal treatment. The results indicate that considerable valorization potential of the MSWI fly ash as construction materials can be realized due to their improved mechanical strength. Generally speaking, the microstructure of glass-ceramic after thermal treatment is thoroughly compact and homogeneous with a density ranging in 2.7–3.0 g/cm3 and a porosity lower than 4.7%. As a result, the Knoop hardness can reach 1.3–5.6 GPa, depending on the compositions and the cooling method.
An energy-efficient two-stage hybrid flow shop scheduling problem in a glass production
Published in International Journal of Production Research, 2019
Shijin Wang, Xiaodong Wang, Feng Chu, Jianbo Yu
Glass-ceramics is a kind of composite materials combined by crystal phase and glass, they are made through the process of high temperature melting, forming and heating. The schematic manufacturing process of this kind of glass is shown in Figure 1. Once production orders are placed by customers, raw glass already fabricated are cut into the customers' desired sizes. Then, the edges of each glass are smoothed and bevelled. Next, small and large holes are drilled for future controlling knobs installation. After cleaning, customised logos and graphs are printed on the glass immediately followed by drying process. In the last step, each piece of glass is heated to a certain high degree, which makes the glass change at the molecular level and the glass is partially crystallising and the glass-ceramic is formed finally (Wang, Liu, et al. 2016).
Surface and volume crystallization in fluorrichterite based glasses
Published in Journal of Asian Ceramic Societies, 2020
R. Casasola, J. M. Pérez, M. Romero
Glass-ceramics are ceramic materials developed through the controlled crystallization (nucleation and crystal growth) of a glass. Given that the main glass-forming systems are based on silicates compositions, the major crystalline phases in glass-ceramics are also silicates [1]. Among crystalline silicates of interest in glass-ceramics, inosilicates or chain silicates are a silicate group whose structure is characterized by the arrangement of silicate tetrahedra in chains. Single chains ([SinO3n]2n−), double chains ([Si4nO11n]6n−) and even complex chains are feasible. Minerals belonging to the inosilicate group include the pyroxenes (single chain) and the amphiboles (double chain) [2].