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This wok shows the results of a valorisation study to use rice husk ash as raw material to develop glass-ceramic materials. An original glass has been formulated in the base system MgO-Al2O3-SiO2 with addition of B2O3 and Na2O to facilitate the melting and poring processes. Glass characterization was carried out by determining its chemical composition. Sintering behaviour has been examined by Hot Stage Microscopy (HSM). Thermal stability and crystallization mechanism have been studied by Differential Thermal Analysis (DTA). Mineralogy analyses of the glass-ceramic materials were carried out using X-ray Diffraction (XRD). Results show that it is possible to use ash rice husk to produce glass-ceramic materials by a sintercrystallization process, with nepheline (Na2O·Al2O3 · SiO2) as major crystalline phase in the temperature interval 700-950ºC and forsterite (2MgO·SiO2) at temperatures above 950ºC.En este trabajo se muestran los resultados de un estudio de valorización de la ceniza de cáscara de arroz como materia prima en la obtención de materiales vitrocerámicos. Se ha formulado un vidrio en el sistema base MgO-Al2O3-SiO2 incorporando B2O3 y Na2O para facilitar los procesos de fusión y colado del vidrio. El vidrio se ha caracterizado mediante la determinación de su composición química. Su comportamiento frente a la sinterización se ha llevado a cabo mediante Microscopía de Calefacción (MC). La estabilidad térmica de las muestras y el mecanismo de cristalización preferente se ha estudiado mediante Análisis Térmico Diferencial (ATD). La mineralogía de los materiales vitrocerámicos se ha llevado a cabo por Difracción de rayos-X (DRX). Los resultados obtenidos muestran que es posible utilizar ceniza de cáscara de arroz para producir materiales vitrocerámicos mediante un proceso de sinterización seguido de cristalización, con nefelina (Na2O·Al2O3·2SiO2) como fase cristalina mayoritaria en el intervalo de temperatura 700º-950ºC y forsterita (2MgO·SiO2) a temperaturas superiores a 950ºC.

There are here reported the result of the second phase of the investigation on the melting behavior of the slag and the process followed to synthesize glass-ceramic materials using this slag as raw component. Starting from a vitrifying mixture based on slag, glass cullet and precipitated calcium carbonate coming from sugar refining, we have obtained the parent glass named ECSCP, which exhibit a surface tendency of crystallization. Pressed specimens of 40 mm diameter and 7 mm height were conformed with the powdered ECSCP glass. The specimens were heat treated for crystalline phases development at temperatures between 800 and 1100ºC during time intervals from 5 to 60 minutes. A series of wollastonite-anorthite-gehlenite glass-ceramics has been synthesized of different characteristics depending on the time and temperature of devitrification.Se expone en este trabajo la segunda parte de los resultados de la investigación sobre el comportamiento en fusión de las escorias y el proceso seguido para la obtención de materiales vitrocerámicos utilizando estas escorias como materia prima. A partir de una mezcla vitrificable basada en escorias, casco de vidrio y carbonato cálcico precipitado de azucarera, se ha obtenido por fusión a 1450ºC un vidrio (ECSCP) que presenta un mecanismo de cristalización superficial. Con el vidrio pulverizado se conformaron probetas cilíndricas de 40 mm de diámetro y 7 mm de altura aproximada, que fueron posteriormente sometidas a los tratamientos térmicos de desvitrificación a temperaturas entre 800 y 1100ºC, y tiempos de tratamiento entre 5 y 60 minutos, obteniéndose una serie de materiales vitrocerámicos de wollastonita-anortitagehlenita. Estos materiales han sido caracterizados y analizadas sus propiedades en función del tiempo y las temperaturas de desvitrificación.

The waste vitrification of abandoned open sky vermiculite deposits has been considered by combining with a natural phosphate mineral residue. Several batches haven been designed from the composition system: Li 2 O-MgO-Al 2 O 3 -P 2 O 5 -SiO 2 including some Fe 2 O 3 and Fluoride. The resulting glasses are transparent and smooth green coloured, giving rise after TTT treatments to several opal, opaque glass-ceramics with iridescent surface. Full characterization has been carried out by XRD and electron microscopy with EDS, as well as by XPS spectroscopies, concluding that the main crystalline phases formed were α-cordierite and β-spodumene. The surface of these glass-ceramics from vermiculite-amblygonite is enriched in Fe 2 O 3 . Compared to the parent glasses, the final glass-ceramics exhibited and improvement in fracture toughness. [ABSTRACT FROM AUTHOR]

In order to encapsulate nuclear wastes (NW) enriched in Uranium, they have been designed and obtained vitrified matrices of iron aluminum phosphates including substitution of U by Bi. These glasses have been designed and obtained formulating all from the starting binary composition: 60P 2 O 5 ·40Fe 2 O 3 where the Fe/P ratio was 0.67. The thermal behavior has been investigated by DTA/TG analysis and thermal expansion, as well as identification of some phases by TEM/EDS. The vitrified structures are difficult to crystallize as is the case of the (Fe + U) contents in the range of 0.50 per P atom. Glasses with Bi-oxide are less resistant to crystallization than those containing U. The glasses here investigated depict a reasonable water chemical stability due to the high percentage of P O Fe O bonds and the presence of U (4+ to 6+). Lately, it has been also investigated the calcination of simulated miniplates of Si 2 U 3 /Al having additions of these glasses and U 3 O 8 to dilute this Uranium enriched in MTR combustible (Material Testing Reactor). [ABSTRACT FROM AUTHOR]

The thermal behaviour (viscosity variation, dilatometric and crystallization trends) of several iron aluminium magnesium phosphate glasses that contain significant amounts (6--19 wt%) of uranium oxide (UO2·67) is presented as well as new data related to the densification of powder compacts prepared from such compositions. The sintering study of such vitreous powders can help to assess the relative capability for the immobilization and stability of the uranium oxide in these glassy or glass-ceramic matrices. [ABSTRACT FROM AUTHOR]

The arc plasma vitrification of hospital wastes containing metals and inorganic oxides yields to a leach resistant glassy or vitreous slag, which can be environmentally safe for landfill disposal or could be transformed in glass-ceramic tiles with physical and mechanical properties similar to those showed by marketable products for building applications. Standard methods have been used for testing the leachability of elements from this new type of tiles. The water resistance was evaluated by the DIN 38414 S4 standard and the chemical durability of glass and glass ceramics by the weight losses per surface unit, employing NaOH and HCl (5%) aqueous solutions, at boiling temperature. Results show that although glass-ceramic tiles are most water leachable than original plasma vitreous glass, the concentration of toxic minor elements in their leaching solutions are lower than those allowed by the Normative. [ABSTRACT FROM AUTHOR]

The effect of iron oxide content on the crystallisation of a zirconium-based glass-ceramic glaze was investigated using a glass-ceramic “white of zirconium” frit and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that Fe2O3 gives rise to the crystallisation of an iron-zinc ferrite, which is acting as nucleating agent of feather-like crystals of pyroxene while granite frit enhances the partial dissolution of zircon into the glassy phase, which is sharply increased for granite frit additions greater than 50%. [Copyright &y& Elsevier]

The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K2O–ZnO–MgO–CaO–Al2O3–SiO2 system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe3+ ions among different crystalline phases such as franklinite (ZnFe2O4) and hematite Fe2O3 depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively. [Copyright &y& Elsevier]

• The thermal plasma treatment for the hospital incineration fly ash utilization. • Chemical stabilization studies by leachability tests in raw materials and ceramics. • The physical features comparison of vitrificates in the hardness tests. The thermal plasma treatment is an effective method which can be used to convert hazardous waste into less toxic or inert glassy products. The aim of this paper is to show the experimental use of a thermal plasma treatment process to transform the hospital incineration fly ash into glassy products (vitrificates) that can be stored on the land without harmful environmental effects or sintered for producing with some additives coloured tiles useful as construction materials. The aims were achieved by: (i) optimization of temperature and energy used adjusting the process to minimum cost and (ii) stabilization of vitrificates with different compositions of waste mixtures. The chemical stabilization of final products was examined by heavy metals leachability tests. Hardness measurements were done to verify the physical stabilization of vitrificates. Also, it has been tested if the reinforcement and coloration of raw material by various pigments as well as the chemical compounds affect the stability of the final products. It was seen that chemical composition of raw materials influenced the chemical and physical properties of the vitrificates and decided about their internal structures. [ABSTRACT FROM AUTHOR]

The effect of chromium oxide additions (0.05–1.00 mol% interval) on the crystallization of an original 26Li 2 O·74SiO 2 glass (mol%) formulated in the liquid metastable immiscibility dome of the binary system has been investigated by XRD and TEM-replica electron microscopy. Results were discussed by considering the phases that can be formed in the Li 2 O-Cr 2 O 3 -SiO 2 partial equilibrium ternary diagram. From these glasses, lithium disilicate is the main crystalline phase after thermal treatments at 550–650 °C. Maximum crystallization is obtained with the lowest content addition of Cr 2 O 3 (0.05 mol%). Glass-in-glass phase separation was observed in these glasses coexisting with the crystallization areas. [ABSTRACT FROM AUTHOR]

Mullite precursors were prepared using kaolin waste, sericite clay containing kaolinite and industrial kaolin with addition of alumina in a wet medium to synthesize mullite (72 wt% Al 2 O 3 and 28 wt% SiO 2 ). Uniaxial pressed bars of the powdered mullite precursors were fired in the range 1400–1600 °C with soaking times 30–120 min. The resultant materials were studied by XRD and SEM-EDX. Bulk densities, apparent porosities and flexural strengths in four points were determined in the fired bars at 1500, 1550 and 1600 °C. It was concluded that the thermal behaviour of these mullite precursors was influenced by the presence of impurities in the raw materials. These impurities originate a liquid phase forming a glassy phase which produces a progressive and enhanced densification of the mullite materials by reaction sintering at 1500–1600 °C. The technical properties were also influenced by the relative proportion of vitreous phase. The microstructure of characteristic mullite crystals was revealed by SEM. It was emphasized the use of kaolin waste by-products of mining and sericite clays as valuable raw materials for mullite preparation. [ABSTRACT FROM AUTHOR]

Abstract: It is presented the Nd doping of the glassy ZnO–CdO–TeO2 ternary system. The Nd-doped oxide glasses were prepared by conventional melt-quenching method using three different compositions from this system. X-rays diffraction (XRD) diagrams in these materials reveal that they are basically vitreous structure. Infrared (IR) spectra of the glasses showed the characteristic bands at 665, 670, and 675cm−1, which correspond to the trigonal structure of TeO3. The presence of Nd3+ was detected in the visible and infrared region of the spectra by optical absorption (OA) measurements of the band gap and by photoluminescence (PL) experiments. Glasses showed light emission due to the transition: 4F3/2 → 4I9/2. Differential thermal analysis (DTA) of these glasses have shown that T g temperatures are in the 465–485°C and T c in the 800–1000°C ranges. [Copyright &y& Elsevier]

The subject of this study is the application to the construction of soft mud bricks (also known as pressed bricks), both green and heat-treated bodies, built from raw materials from Santa Cruz de Mudela, Ciudad Real, and IGCC slag from the power central of Puertollano (Ciudad Real, Spain). For this purpose, industrial level tests have been performed: the production of these kind of bricks from mixes of waste from ores of construction clays and to significant fraction of different ratios and clay granulometries mixed with IGCC slag. The results of this experimentation suggests that not only can IGCC slag be applied to a ceramic process, but also its use gives several advantages, as water and energy savings, as well as improvements on the final properties of products. [Copyright &y& Elsevier]