Ceramic item deformation during firing: effects of composition and microstructure (review)

Abstract

The scope is considered for increasing the high-temperature stability to deformation in ceramic items as regards comprehensive improvement in characteristics corresponding to current economic trends.It is becoming increasingly important to examine deformation during firing for molded semifinished products made of materials sintered at high temperatures and subsequently acquiring a vitrocrystalline nature, particularly on account of the tendency to reduce the firing times and temperatures by the use of suitable additives, and also in connection with tightening specifications for the size accuracy. Large ceramic products such as drainage pipes may be reduced in mass by reducing the wall thickness, which reduces the amount of raw material used and the energy consumption, but then there is an increase in the tendency of the semifinished product to pyroplastic deformation.Researches have been done on a large scale on the creep in ceramics at high surface temperatures, but they have not been focused on the deformation in multicomponent systems such as porcelain during firing [1]. The variety of compositions and firing modes must determine the substantial differences in deformation [2]. It is not always possible to extend the phenomenology of deformation for materials whose elementary rheological properties differ substantially to other materials characterized by more complicated behavior. One approach is to examine porous vitrocrystalline material such as porcelain during firing, whose behavior is represented by a very complicated set of properties.The task of giving a proper description of deformation splits up into several very complicated subtasks: determination of key parameters of the structure and composition, the changes in them during firing under load, the effects on the deformation, determination of the effects of firing conditions and shape of a component on processes, and this combines with the choice or creation of rheological models and software for calculating the deformation from the significant parameters.The chemical and mineral compositions had the main effects on the deformation at high temperatures. Although there are many forms of porcelain, one can distinguish in their compositions the quartz component, whose grains are rarely greatly altered during firing, and which only partially dissolve in the liquid, together with the clay-mineral component and the fluxes, which form a liquid at a high temperature. One can control the properties of the porcelain, including the deformation behavior on firing, by adjusting the nature, grain size, and method of preparation for those components.It is simplest to regulate the properties of a porcelain by varying the contents of low-activity crystalline phases: the oxides of silicon, aluminum, zirconium [3], and so on. One needs to consider not only the grain size but also the firing conditions, since the amounts of the crystalline phases may be reduced substantially by prolonged hold. There has been a study [4] of the reactions between porcelain components with m...

Evaluation of dynamic viscosity and rheological properties of ceramic materials during liquid phase sintering by numerical‐experimental procedure

“…It has been proposed that through the measurement of bending deformation test, the system viscosity can be calculated by the steady‐state creep equation. But, by a little change in the mineral, chemical composition, manufacturing and firing process of ceramic sample, the deformation and system viscosity might be alter significantly . An alternative to overcome the experimental problems as well as the inherent unpredictable pyroplastic deformation is finite element method (FEM).…”

“…An alternative to overcome the experimental problems as well as the inherent unpredictable pyroplastic deformation is finite element method (FEM). With this goal, constitutive models have to be developed, taking into account the different deformation factors such as anisotropic shrinkage, gravity, and friction influences …”

“…The uniaxial dynamic viscosity is one of the key parameters in highly vitrified ceramic bodies which is responsible for undesired shape distortion and viscous flow deformation at high temperatures . It has been proposed that the best procedure to determine the strain‐stress relationship and constitutive equations are bending creep test .…”

“…It has been proposed that the best procedure to determine the strain‐stress relationship and constitutive equations are bending creep test . At low stresses (about 1 Mpa), the green ceramic body undergoing densification can be treated as a linear viscous material …”

Structure and rheology of semivitreous porcelain during kilning

“…A review illuminating modern aspects of the phenomenology of kilning porcelain is given in [5]. The most relevant studies concern the possibility of increasing the strength of porcelainware by introducing a low-activity crystalline phase and adjusting the particle-size distribution of the initial components.…”