Abstract: New silicate glass-ceramic compositions have been investigated due to their interesting chemical, mechanical, thermal, and electrical properties. LZSA glass-ceramics based on -spodumene (Li2O•Al2O3•4-10SiO2) and zircon (ZrSiO4) crystalline phases have shown good chemical resistance, high bending strength as well as high abrasion resistance, when compared with traditional ceramic materials, and coefficient of thermal expansion from 4.6 to 9.110-6 °C-1. These features basically depend on the nature, size and distribution of the formed crystals as well as on the residual glassy phase. The nature of the formed crystalline phases and consequently the final properties can be controlled by modifying the chemical composition of the parent glass and also by adequate selection of the heat-treatment parameters. The classical fabrication of glass-ceramic materials consists on the preparation of monolithic glass components followed by heat treatments for crystallisation. However, this technology requires high investments and can be justified only for large production. A viable alternative could be the production of glass-ceramics processed from glass powders and consolidated by sintering using the same equipments of traditional ceramic plants. This work reports the manufacturing and characterization of glass-ceramic materials and composites processed by pressing, injection moulding, extrusion, casting, replication, and rapid prototyping.
Abstract: We illustrate the x-ray Combined Analysis approach capabilities in characterizing silicates and phyllosilicates for samples exhibiting crystallographic textures. Two mullite composite ceramics, one elaborated under uniaxial pressure the other under centrifugation, and one uniaxially pressed montmorillonite aggregate, are studied in terms of texture, cell parameters and phase contents. Several weak texture components are present in the mullite samples, combinations of planar- and fibre-like textures. The methodology is able to take account of the amorphous silica-like matrix of the composite, and cell parameters and structure of mullite correspond to the commonly modelled used for this phase. The montmorillonite turbostratic phase is correctly reproduced with its fibre texture, eventhough minor phases are also present and modelled in the aggregate.
Abstract: The optical measurement of thermo-mechanical properties allows the sample to be completely free from constraints. This enables the possibility to measure the true change in size or volume of a material during a sintering process. Thanks to the fact that the measure is carried out with no contact in becomes possible to carry out other measurements during the test, like the change in mass. Joining a double beam optical dilatometer and an electronic scale we can measure simultaneously the change in size with a resolution of one part over 100.000 and the change in weight of the specimen, with a resolution of 1 part over 10.000.
Moreover, thanks to a innovative temperature controller design, the heat treatment can be designed with complete freedom, even from a mathematical formula (i.e. sinusoidal or exponential) and it can be controlled by the change in size of the specimen during the test. This makes it possible to perform the controlled rate sintering (shrinkage) even if the driving force of the sintering process is the viscous flow of glassy phases, like in traditional ceramics.
Abstract: Silicate ceramics with clays are some of the most complicated ceramic systems
because of the very complex relationship between the behavior of mineral materials during
the ceramic processing and the transformations during heating. A major challenge is to predict
the phase transformations in silicate ceramics, since complex relationship occur between the
microstructural and structural characteristics of fired product and the physical properties.
Clay minerals undergo strong structural transformations during heating, simultaneously to a
complex path of thermal transformations. Individual reactions cannot simply identify since
they are closely related and overlapped. At temperature above 800°C, new phases are
recrystallized and many of the reactions are strongly topotactic.
Mullite is the most important phase, which recrystallizes with a range of morphology and
stoichiometry. Variables affecting the mullite formation include the clay mineral type and
behavior during heating, the possible occurrence of liquid and impurities as Fe. It results in
large variations of the stoichiometry and shape of mullite crystals, which are embedded in a
low ordered phase to form a micro-composite microstructure.
This presentation will review recent research, looking at structural transformations in some
typically used phyllosilicate systems : (i) structural transformation of kaolinite and mica
phases were identified at temperature up to 1100°C. They evidence a residual structural order
of high temperature phases which is favorable to the topotactic recrystallization of mullite; (ii)
from the high temperature form of phyllosilicates, an organized network of mullite can be
obtained; (iii) the composition of a local and transient liquid and the presence of minor
elements as Fe has a significant influence on the mullite morphology; (iv) mechanical
properties are closely related to size and organization degree of the mullite network; (v) the
process itself influence the kinetic of structural transformation and particularly the powder
compact density and the thermal cycle. These research in silicate ceramics evidence multiple
and complex challenges, providing opportunities for future development.
Abstract: Kaolinite (2SiO2.Al2O3.2H¬¬¬¬2O), an aluminosilicate mineral, is the most common constituent mineral in clay used in manufacturing traditional ceramics such as whitewares, some refractories and structural clay products. On firing, kaolin (mainly kaolinite) undergoes several phase transformations. Immediately following firing, kaolin starts to chemically combine with atmospheric moisture. This reaction causes a mass increase that is proportional to the fourth root of time. The consequence of this mass gain is an accompanying expansive strain. Kaolinite transformations following firing at a range of temperatures between 700 and 1200 oC were examined by XRD. Following firing, high accuracy mass gain measurements were carried out using a microbalance under precisely controlled conditions of temperature and relative humidity. It was found that the formation and development of crystalline phases increases with increasing firing temperature. This causes a reduction in the amorphous phase which, in turn, leads to reduced mass gain. Kaolin fired at 1200 oC exhibited the least reactivity with moisture and mullite was found to be the dominant crystalline phase after firing at that temperature. SEM was used to examine microstructural changes in the fired specimens. The reactivity of the ceramic with moisture is shown to be directly related to the crystallinity of the fired clay.
Abstract: This paper is focused on the preparation and characterization of different lamellar silica
prepared by liquid crystal templating and silanisation. The initial template can be removed and
replaced in the interlamellar spaces by different types of silane, being covalently grafted to the solid
by reaction with the surface silanols. The lamellar stacking periodicity remains after this
modification. The surfactant extraction can lead in significant grafting of isopropanol if the solid is
simply refluxed in isopropanol, which have the effect of preserving the periodicity of the lamellar
stacking. The surfactant extraction in an Soxhlet equipment avoid this reaction, with the effect of
platelets organization collapsing. The lamellar silica studied exhibit great specific surface and
combination of meso and microporosity, making them interesting materials for nanocomposite or
Abstract: Many ceramic tiles are used as outer skins of office and residential buildings and they
prevent severe weathers of solar ray, temperature, wetness and wind. The solar irradiance to the outer
walls is a significant factor to influence the heat flow into room and consequently the energy load due
to air conditioning. Particularly in the region where clear seasonal change is experienced, optical and
thermal properties of the wall surfaces are desired to be controlled as a function of season; solar
reflective in hot days in summer; solar absorptive in chilly days in winter. The ceramic walls with
solar-altitude dependent reflectance are expected to be a simple and efficient method for autonomous
control of heat flow into the room and in this study they were investigated from the viewpoints of
optical property and shape of the tiles. The correlation between solar absorption and luminous
reflectance revealed that there are some ceramic tiles whose solar absorption slightly depends on
solar altitude. The triangular-shaped ceramic tiles that have reflective-upward and
absorptive-downward surfaces were investigated in optical and thermal properties, based on one-year
exposure of the tiles to solar radiation and ray-tracing simulation. These measurement and simulation
found that the triangular-shaped tiles are an effective approach to the control of solar absorption and
suggested the effective shape and surface property of the tiles such as optical reflectance, surface
specularity and triangular angle.
Abstract: The crystallisation mechanism of glass-ceramic materials from a CMAS group Al0.37B0.34Fe0.01Mg0.02Zn0.29Ca0.05Si0.78O3 was tested under non-isothermal conditions by the DTA method. Glass-ceramic material of two-phase composition with precipitation of crystallites from islet silicates Zn2SiO4 and a crystalline phase from a spinel group, gahnite ZnAl2O4 was obtained in the system under investigation. Activation energy of a crystallization process Ea was determined and a crystal growth morphology parameter n was computed. It was revealed that in the test material from a CMAS group one could obtain the crystalline phase in the form of ghanite as a result of a controlled process of crystallization. The occurrence of a spinel phase caused the obtained glass-ceramic material had higher fracture toughness (KIC) than material from a CMAS group, containing pyroxene crystalline phases typical for this system.