M.J. Ribeiro

Development of glass-ceramics by sintering and crystallization of fine powders of calcium-magnesium-aluminosilicate glass

Abstract Natural raw materials normally used in the ceramic and glass industry were studied for the production of calcium–magnesium–aluminosilicate glass or glass-ceramic materials. Sintering and crystallization processes of fine powders of parent glass with chemical composition (wt.%) 46.00 SiO 2 , 15.90 Al 2 O 3 , 1.20 Fe 2 O 3 , 0.42 TiO 2 , 23.50 CaO, 9.37 MgO, 0.04 Na 2 O, 0.98 K 2 O, 1.95 P 2 O 5 and 0.35 CaF 2 were studied. Crystallization kinetics of glass-ceramics was carefully examined by DTA, XRD, and SEM techniques and by dilatometric studies. The desired sequence of events, i.e. nucleation, sintering and devitrification occurred by heat-treating the glassy powder. However, crystallization of the parent glass did not follow phase diagram predictions, since anomalous appearance of akermanite phase was detected along with expected anorthite and diopside precipitation. A reasonable explanation for this unexpected observation is given.

Removal of nickel from aqueous solutions by clay-based beds

The use of spray-dried natural clays for the removal of nickel ions in aqueous solution is discussed in this paper. Two different clays were tested and their mineralogical composition and physical characteristics related to efficiency of nickel removal. In particular, relevant parameters including flow rate and overall removal efficiency were evaluated for 4.8 cm depth filters. The removal efficiency of the tested clays was generally similar or greater than that of granular activated carbon (GAC). The mineralogical composition of the clays, particularly the presence of montmorilonite, might explain this behaviour. Higher cation exchange capacity and development of surface negative charge on clay particles in contact with water also contribute to this promising performance, despite the lower available specific surface area of the spray-dried grains in comparison with granular activated carbon. The calcination of pressed pellets made of contaminated filter grains gives consolidated ceramic bodies that can be used in the fabrication of common products like wall or floor tiles, where nickel ions remain firmly attached and inertized.

Processing of cordierite based ceramics from alkaline-earth-aluminosilicate glass, kaolin, alumina and magnesite

Abstract Microstructural changes, porosity evolution and properties of cordierite based composites have been studied as a function of cordierite–anorthite ratio in modelled ceramic systems. The model systems were composed of alkaline-earth-aluminosilicate glass powder, kaolin, alumina and magnesite. Suitable densification levels of investigated compositions are attained in a narrow temperature range and relatively high residual porosity levels are observed. These features were attributed to the role of the liquid phase during high temperature sintering. Cordierite, anorthite or mixtures of each with mullite are the formed crystalline phases when maximum densification levels are achieved. Their properties are correlated to the processing route and to the composition of sintered materials. Control of the porous structure through manipulation of heating rate was found feasible and easy to implement.

Mullite-Alumina Refractory Ceramics Obtained from Mixtures of Natural Common Materials and Recycled Al-Rich Anodizing Sludge

This work describes attempts to reuse Al-rich sludge produced from industrial anodizing and surface treatment processes in the fabrication of mullite-based refractory materials. The complete characterization of the residue is reported, including physical and compositional parameters. Mixtures with common natural silica-containing materials, like ball clay, kaolin, and/or diatomite were prepared in order to achieve interesting final fired compositions. Rheological characterization of the suspensions, their slip casting performance, the thermal behavior of the consolidated bodies, and crystalline phase evolution are also detailed. From the knowledge acquired, pretreatment operations have been suggested to facilitate the recycling of the Al-rich sludge and to improve the characteristics of mullite-based materials.

Influence of NiO on the crystallization kinetics of near stoichiometric cordierite glasses nucleated with TiO2

This work presents the effect of NiO on the thermal behavior and the crystallization kinetics of glasses lying near the stoichiometric cordierite composition nucleated with TiO2. Three glasses with NiO content varying between 1 and 5 mol% have been synthesized in Pt crucibles. Activation energies for structural relaxation and viscous flow have been calculated using the data obtained from differential thermal analysis (DTA). Kinetic fragility of the glasses along with other thermal parameters has been calculated. Non-isothermal crystallization kinetic studies have been employed to study the mechanism of crystallization in all three glasses. The crystallization sequence in the glasses has been followed by x-ray diffraction analysis of the heat treated glass samples in the temperature range of 800–1200 °C. μ-cordierite has been observed to be the first crystalline phase in all the glass samples after heat treatment at 850 °C, while NiO plays an important role in determining the crystallization sequence at higher temperatures, leading to the formation of α-cordierite.

Vitrification of low silica fly ash: suitability of resulting glass ceramics for architectural or electrical insulator applications

Abstract The study concerns the recycling of the fly ash (FA) derived from the thermal power stations of Ptolemaida (Greece) and its potential use of this FA as precursor in production of bulk nucleated GCs. The first attempt was addressed to produce a glass from the fine powder of as received FA without any additives. To overcome some drawbacks such as spontaneous crystallisation upon cooling of FA based glass and to improve its working properties, production of pyroxene based glasses from FA was undertaken. The parent glass approached the composition of CaMg0⋅75Al0⋅4Fe0⋅1Si1⋅75O6, derived from CaMg0⋅75Al0⋅5Si1⋅75O6, which belongs to diopside–Ca-Tschermak solid solutions. Cr2O3 nucleated fine grained mono mineral glass ceramics of augite were produced from the glasses comprising FA and additives of SiO2, Al2O3 and MgCO3. The influence of Cr2O3 content on the development of crystalline phases, the properties and the microstructure of the resultant glass ceramics crystallised at different temperatures was investigated.

Removal of Pb2+ and Ni2 ions from aqueous media by filtration through clay-based beds

Abstract This work examines possible new applications for common, clay-based formulations. We processed spray-dried grains of a common clay (ZA-4) and collected fines/rejects from the production of lightweight aggregates (LWA), which were used as filtration beds for removal of Pb2+ and Ni2+ from aqueous solutions. Experiments were performed at different contaminant concentrations and by testing several operational conditions. The removal performance of both tested materials is strongly dependent on the particle-size distribution of the batch, being better for beds made of smaller grain size, since packing density and specific contact area for removal are greater. In general, the efficiency for removal of Pb2+ was greater than for Ni2+. When compared with granular activated carbon, clay-based beds performed well. In particular, finer fractions of LWA show stable behaviour, without saturation after consecutive runs. Saturated beds can potentially be reused, in appropriate amounts, for production of new lightweight aggregates or common ceramic items (e.g. bricks), since retained contaminants will be fixed by firing in the clay matrix. Calcination of pressed pellets made of contaminated filter grains created consolidated ceramic components and sorbed metallic species became inert.

Sintering and crystallization behavior of CaMgSi2O6–NaFeSi2O6 based glass-ceramics

We report on the synthesis, sintering, and crystallization behaviors of a glass with a composition corresponding to 90 mol % CaMgSi2O6−10 mol % NaFeSi2O6. The investigated glass composition crystallized superficially immediately after casting of the melt and needs a high cooling rate (rapid quenching) in order to produce an amorphous glass. Differential thermal analysis and hot-stage microscopy were employed to investigate the glass forming ability, sintering behavior, relative nucleation rate, and crystallization behavior of the glass composition. The crystalline phase assemblage in the glass-ceramics was studied under nonisothermal heating conditions in the temperature range of 850–950 °C in both air and N2 atmosphere. X-ray diffraction studies adjoined with the Rietveld–reference intensity ratio method were employed to quantify the amount of crystalline phases, while electron microscopy was used to shed some light on the microstructure of the resultant glass-ceramics. Well sintered glass-ceramics with ...

Development of Waste-Containing Malayaite Ceramic Pigments

The preparation of ceramic pigments using industrial waste, a galvanizing sludge from the Cr/Ni plating process, as primary source is here reported. The ceramic pigments were prepared using the common solid state reaction process, investigating the optimal formulation, milling and firing conditions. The main focus will be given on the synthesis of chrome-tin red malayaite Ca(Cr,Sn)SiO5 pigment that was fully characterised and then tested in a standard ceramic glaze. Typical working conditions and colour development will be also reported.

Extrusion of Recycled Pastes Based on Al-Rich Anodising Sludge

Al-rich anodising sludge has been tested as main component of alumina, mullite or cordierite based refractory materials and bodies have been processed by using different techniques, such as slip casting, dry pressing and extrusion. The success of the last technique is strongly dependent on the materials composition and proper additives, such as plasticizers and lubricants. Operation conditions might be also adjusted within certain limits and includes the design and size of the die, the flowing speed, and as consequence the applied pressure. In the current work, cordierite hole-tubes of different diameters had been processed by extrusion. The effect of mentioned parameters was evaluated based on the Benbow’s equation and ultimate extrusion quality of samples was estimated.