This paper presents the effect of post-heating temperature and atmosphere on the electrical and optical properties of ZnO:Al thin films prepared by the sol–gel method. The electrical properties of the n-type semiconductor thin films showed that for the final films, the values of carrier concentration ranged between 2.76 and 9.96×1019 cm−3, the Hall mobility values between 7 and 34.1 cm2/V s and the resistivity values between 2.9×10−3 and 5.0×10−2 Ω cm, depending on the processing conditions. For the thin film doped with 2 wt.% Al, preheated at 400 °C and post-heated for 1 h in air at 600 °C, a resistivity of 2.9×10−3 Ω cm has been reached after annealing under a reducing atmosphere of forming gas. The optical transmittance spectra of the only post-heated films and of the post-heated and annealed films showed a good transmittance (75–90%) within the visible wavelength region and some small effects of Al-doping concentration and annealing treatment in forming gas.

The kinetics of crystallization of transparent and conductive high preferential c-axis oriented Al-doped ZnO thin films on Coming 1737 glass substrate from amorphous sol-gel precursor prepared using zinc acetate and aluminum chloride as cations source, 2-methoxiethanol as solvent and monoethanolamine as sol stabilizer has been investigated. The effect of preheating temperature on the values of the kinetic parameters and crystallization mechanism is discussed. Some data concerning the microstructure, the electrical and optical properties of the thin films are presented.

Mixtures of fly ash, calcite and soda ash were prepared by keeping the amount of fly ash at 80 wt% and adding the other raw materials in order to obtain Na2O/CaO ratios of 1/3, one and three. On melting all mixtures led to black glassy materials. Several heat treatments were performed on these glasses at temperatures suggested by DTA. The crystalline phases precipitated during the heat treatments were identified by XRD on powdered samples and the microstructures of the obtained glass ceramics were observed by SEM. The formulations tended to precipitate pyroxene solid solutions and aluminium silicates of calcium and/or sodium, during the heat treatments. The glass ceramics mainly contained fine crystals. However some of the materials obtained from glasses with Na2O/CaO ratios of 1/3 and three had non-uniform microstructures. It is generally concluded that the microstructure of these crystallised glasses is critically dependent on both composition and heat treatment.

A uniform shiny black-coloured glass was obtained using bottom ash produced by a Portuguese municipal solid waste incinerator (MSWI). The bottom ash was the single batch material used in the formation of the glass, which was obtained by vitrification of the solid waste at 1400°C for 2h. Under these conditions, a homogeneous melt with an appropriate viscosity to be shaped was obtained, indicating the suitability of this waste material to be employed in the development of vitreous products. The characterization of the resulting glass was performed in order to assess its structural, physical, mechanical, thermal and chemical features. The glass had a density of 2.69gcm−3, a hardness of 5.5GPa, a fracture strength of 75MPa, a thermal expansion coefficient of 9.5×10−6°C−1 and it exhibited a very good chemical stability. In summary, the MSWI bottom ash glass has good mechanical and chemical properties and may, therefore, be used in several applications, particularly as a construction material.

A batch of coal fly-ash, soda and lime was melted, quenched to a glass and then devitrified, by one-step heating cycles, forming coarse fibrous microstructures with pores and cracks, resulting in low strength materials. The crystallization behaviour of the based glass was further studied by adding a nucleating agent, TiO(2). The resulting structural and microstrutural changes were investigated by differential thermal analysis, scanning electron microscopy, x-ray diffraction, dilatometry and density measurements. The results indicated that the addition of TiO(2) could provide a finer grained microstructure, suitable for the production of structural materials.

Transparent and conductive high preferential c-axis oriented ZnO thin films doped with Al have been prepared by sol–gel method using zinc acetate and aluminium chloride as cations source, 2-methoxiethanol as solvent and monoethanolamine as sol stabilizer. Film deposition was performed by dip-coating technique at a withdrawal rate of 1.5 cm min−1 on Corning 1737 glass substrate. The effect of dopant concentration, heating treatment and annealing in reducing atmosphere on the microstructure as well as on the electrical and optical properties of the thin films is discussed. The optical transmittance spectra of the films showed a very good transmittance, between 85 and 95%, within the visible wavelength region. The minimum resistivity of 1.3×10−3 Ω cm was obtained for the film doped with 2 wt.% Al, preheated at 400 °C and post-heated at 600 °C, after annealing under a reduced atmosphere of forming gas.

The crystallization of a borosilicate glass, when compacts of powdered glass were sintered under various conditions, was investigated by dilatometric and XRD analysis. The dilatometry results from non-isothermal sintering experiments until 800oC, performed at different heating rates (1, 2, 5, 8 and 10oC/min), revealed that the compacts started to shrink above ~ 600oC and that the shrinkage decreased with the increase of the heating rate for temperatures up to ~750oC. Above this temperature, and specifically when the samples were heated at heating rates < 5oC /min, the shrinkage was hindered, while samples heated at heating rates 5oC/min showed continuous shrinkage. XRD results showed that the formation of cristobalite had occurred during the sintering at the lowest heating rates and therefore, the presence of this crystalline phase was affecting the shrinkage of the compacts, inhibiting further sintering of the glass. The crystallization of the glass when sintered at a temperature in the range 700-850oC and hold at the selected temperature during various times was also analysed. XRD results showed that both cristobalite and quartz were present in glass compacts sintered under particular conditions (for example, after heating during 24h at 725oC and 765oC). Quartz dissolution took place when the glass samples were sintered at 850oC. At this temperature and whatever the sintering time, cristobalite was the only crystalline phase present in the sintered compacts. Introduction In many glass systems devitrification occurs frequently. The rate and mechanism of devitrification are dependent upon the chemical composition of the glass, the temperature, the furnace atmosphere and the impurities in the glass network [1, 2]. Usually, devitrification takes place during the sintering of glass powders [3]. Viscous flow is the main densification mechanism during sintering of glass powders [2, 3]. The precipitation of a crystalline phase during the sintering of a glass will originate a matrix of higher viscosity than the initial single glass phase hindering the densification and thus, it is desirable that the glass remains in the amorphous state during and after firing [3]. Some borosilicate glasses in powdered form have considerable interest, either for use in the production of sintered glass with controlled porosity [4] or for application in the manufacturing of composite materials [5-9], with particular relevance as borosilicate glass matrix composites for microelectronic substrates [9]. Borosilicate glasses have a low thermal expansion coefficient (3-6 x10 -6 C -1 ) [10], a low dielectric constant and a high resistance to chemical attack [5, 9]. The precipitation of cristobalite takes place frequently during the sintering of borosilicate glass powders [3, 10]. Cristobalite is an unfavourable transformation product in view of its large thermal expansion coefficient (50x10 -6 C -1 ) [2]. The large volume change associated with cristobalite martensitic transformation from the tetragonal ( -cristobalite) to the cubic phase ( -cristobalite) above 272oC reduces dramatically both the thermal shock resistance and the mechanical strength of the glass composite [11]. Materials Science Forum Online: 2004-05-15 ISSN: 1662-9752, Vols. 455-456, pp 212-215 doi:10.4028/www.scientific.net/MSF.455-456.212 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:41:17) Title of Publication (to be inserted by the publisher) 213 In the present work, the crystallization of a borosilicate glass during sintering of glass powder compacts and the effect of the crystalline phase formation on the thermal behaviour of the sintered glass have been investigated by XRD, dilatometric analysis and SEM. Experimental A commercial borosilicate glass powder of the Pyrex type (code 658909 from Corning, France) was used in this work. The as-received powder had a particle size in the range 80-160μm, which was reduced by agate ball milling. The mean particle size of the ground glass powder was ~10μm, as determined in a Coulter Multisizer, and its chemical composition (wt %) was as follows: 79.8 SiO2, 12.3 B2O3, 2.3 Al2O3, 4.8 Na2O and 0.8 K2O. Green cylindrical compacts of 5mm in diameter and ~20mm thickness were obtained by isostatic pressing at 200 MPa. To study the effect of the devitrification of the borosilicate glass on the thermal shrinkage behaviour, glass powder compacts were heated in air at various heating rates (1, 2, 5 8 and 10oC min -1 ) up to a selected temperature using an Adamel Lhomargy dilatometer, model DI24. Also the compacts were heated from room temperature up to a temperature in the range 725850oC and maintained at the selected temperature from 1 to 24 hours. After the heating stage, the dilatometer was switched off and the samples were cooled to room temperature inside the furnace. XRD analyses, at room temperature, were performed in a Rigaku Dmax III-C 3kW diffractometer in order to determine the crystallinity of the starting glass powder (which was totally amorphous) and of the sintered compacts. The XRD patterns were recorded using Cu K radiation, at 40 kV and 20 mA, in the 2 range from 20 to 60o at a scanning speed of 2omin -1 . The microstructure of the sintered glass samples, in polished surfaces, was observed using a scanning electron microscope (Zeiss, DSM 962). Results and Discussion Fig. 1 presents the results obtained by dilatometric analysis when the samples were heated nonisothermally at various heating rates (1, 2, 5, 8 and 10oC/min). The samples started to shrink at temperatures above ~ 600oC and the shrinkage decreased with the increase of the heating rate for temperatures up to ~ 750oC. Above this temperature, the shrinkage was hindered for samples heated at heating rates < 5oC /min, while continuous shrinkage occurred for samples heated at heating rates 5oC/min. XRD patterns (Fig. 2) showed the presence of a crystalline phase, identified as cristobalite, in samples heated at heating rates <5oC/min, while on the contrary, in samples heated at heating rates 5oC/min no diffraction peaks were observed. 550 600 650 700 750 -16 -12 -8 -4 0 8oC/min 10oC/min 5oC/min 2oC/min

This paper presents preliminary results on Al doped ZnO thin films prepared by the sol-gel method. The thin films were produced by a dip-coater technique on glass substrate, using zinc acetate dihydrate, aluminium chloride hexahydrate, 2-methoxyethanol and monoethanolamine as raw materials. The ZnO thin films were analysed by XRD, Hall effect and SEM measurements. In order to determine the influence of the thermal treatments on the film properties, a set of four different heat treatments (atmosphere and temperature) were studied. All the films are polycrystalline presenting a crystallographic c-axis orientation (002) perpendicular to the substrate. The best results were obtained for films pre-heated at 400degreesC and post-heated for 1 hour in air at 600degreesC, after annealing under a reduced atmosphere of forming gas, where a resistivity of 3.9 x 10(-3) Omegacm, a Hall mobility of 34.1 cm(2)/Vs, a carrier concentration of 4.7 x 10(19) cm(-3) and an optical transmittance of 90% were achieved.

A glass was made using bottom ash produced by a Portuguese municipal solid waste (MSW) incinerator. The bottom ash was the single batch material used in the formation of the glass, which was obtained through a conventional melt-quenching method. The glass was then converted to glass-ceramic for further recycling to construction materials. After submitting the glass samples to several heat treatments, between 820 and 1050degreesC and during different times, it was verified that the optimum heat treatment schedule for the ceramization of the glass was at 1000degreesC for 10h, as confirmed by microstructural observation and by X-ray diffraction. The major crystalline phases precipitated in the glass-ceramic were wollastonite (CaSiO3) and diopside (Ca(Mg,Al)(Si,Al)(2)O-6). Microstructural analysis of the glass-ceramic revealed that the crystalline phases were present as dendrites and fiber-like structures that were homogeneously distributed in the material. The glass-ceramic showed good mechanical properties with a hardness of 5.6 MPa and a bending strength of 101 MPa. This material had a density of 2.8 gcm(-3) and a thermal expansion coefficient of 9.10(-6) degreesC(-1). The glass and the glass-ceramic showed an excellent chemical stability against leaching in acidic solution and in alkaline solution. In summary, both the glass and the glass-ceramic have good chemical and mechanical properties and can, therefore, be applied as construction materials.

The effect of initial compaction on the sintering of borosilicate glass matrix composites reinforced with 25 vol.% alumina (Al2O3) particles has been Studied using powder compacts that were uniaxially pressed at 74, 200 and 370 MPa. The sintering behaviour of the samples heated in the temperature range 850-1150 degreesC was investigated by density measurement, axial and radial shrinkage measurement and microstructural observation. The density of the sintered composites increased continuously with temperature for compacts pressed at 74 MPa. while for compacts pressed at 200 and 370 MPa it reached the maximum value at 1050 degreesC and at higher temperatures it decreased slightly due to swelling. The results showed anisotropic shrinkage behaviour for all the samples, which exhibited an axial shrinkage higher than the radial shrinkage, and the anisotropic character increased with the initial compaction pressure. (C) 2003 Elsevier Science Ltd. All rights reserved.

The crystallization of a commercial borosilicate glass powder has been studied in the temperature range 750-900degreesC. Crystal growth was investigated by high temperature XRD and cristobalite precipitation was identified. Glass devitrification exhibited a characteristic incubation period that decreased with increasing temperature: 25-30 min at 750degreesC, 9-12 min at 775degreesC, 5-10 min at 810degreesC, and 0-5 min at 840degreesC. Cristobalite is an unfavorable transformation product in terms of thermal expansion behavior. The precipitation of cristobalite in sintered glass compacts was confirmed by dilatometric analysis, where the increase in thermal expansion coefficient due to the presence of cristobalite and its transition from the tetragonal to the cubic phase were verified. Correlation between the XRD results and the dilatometric data from sintered glass compacts showed the partial dissolution of cristobalite when the glass was heated at the highest temperatures.

Coal fly ashes have been vitrified by melting with Na2O and CaO as fluxing additives. Adequate heat treatments on the fly ash derived glass produced attractive dark green glass-ceramics. These glass-ceramics exhibited fine-grained microstructures consisting of esseneite and nepheline crystals, with average size below 200 nm, homogeneously dispersed in a residual glassy matrix. Several properties, such as density, thermal expansion coefficient, bending strength, hardness and brittleness index were determined and the correlation microstructure-properties is discussed. The results suggest that these coal ash-based glass-ceramics have potential applications as structural materials or as cladding materials.

Coal fly ashes produced by an extinguished power plant in the north of Portugal have been melted with addition of CaCO3 and Na2CO3 to obtain glasses. One of the formulated compositions was selected for further studies and it was possible to manufacture glass-ceramics by crystallising the parent glass through adequate time–temperature schedules. The macroscopic appearance, microstructure, mechanical, thermal and chemical properties indicated that these materials are quite attractive for cladding applications, exhibiting in some cases better performances than the conventional ceramic tiles.