Regina Monteiro

Cathode Ray Tube (CRT) waste glasses produced from dismantling TV sets were used to prepare glass foams by a simple and economic processing route, consisting of a direct sintering process of mixtures of CRT waste as glass powder with different foaming agents (coal fly ash and limestone quarrying residues). The influence of firing temperature, amount and type of foaming agent on the apparent density, pore size distribution and compressive strength have been studied. The aim of the work was to investigate the possibility to obtain glass foams using exclusively wastes as starting materials, and therefore replacing the conventional raw materials. © 2015 Taylor & Francis Group, London.

This study deals with SiO2-P2O5 powders obtained by sol-gel process, starting from tetraethoxysilane (TEOS) as precursor for SiO2 and either triethylphosphate (TEP) or phosphoric acid (H3PO4) as precursors for P2O5. In the case of samples prepared with H3PO4, TG-DTA data showed an accentuated weight loss associated to an endothermic effect up to about 140 °C, specific for the evaporation of water and ethylic alcohol from structural pores, and also due to alkyl-amines evaporation. Sol-gel samples prepared with TEP exhibited different thermal effects, depending on the type of atmosphere used in the experiments, i.e. argon or air. XRD analysis revealed that annealed sol-gel samples prepared with H3PO4 showed specific peaks for silicophosphate compounds such as Si3(PO4)4, Si2P2O9, and SiP2O7. XRD results for annealed sol-gel samples prepared with TEP indicated mainly the presence of a vitreous (amorphous) phase, which could be correlated with SEM images. The presence of SiO2 in the sample might be expected. Thus, we have searched for any SiO2 polymorph possible to crystallize. Only potential peaks of cristobalite were identified but some of them are overlapping with peaks of other crystalline phosphates. SEM analysis indicated a decrease of the amount of crystalline phases with the increase in the annealing temperature. © 2009 Elsevier B.V. All rights reserved.

Cobalt oxide doped silica films were synthesized by a dip-coating technique. Initial compounds were cobalt acetate Co(CH3COO)2-4H 2O and tetraethoxysilane Si(OC2H5)4. The chemical composition was studied by X-ray diffraction and UV-Vis spectroscopy. The morphology analyses were carried out by means of atomic force microscopy. The average diameter of cobalt oxide dispersed particles increases with the molar ratio Co:Si and with the aging time of the initial colloidal solution. © 2009 American Institute of Physics.

The possibility of using fly ash and shale as alternative raw materials for the production of structural ceramics was investigated. Fly ash is a by-product from coal-burning power plants, and shale is a sedimentary rock that if ground finely enough can exhibit a clay-like plasticity. Ceramic samples containing 10-50 wt% fly ash were formed from mechanical mixing of both kinds of powders that were packed and sintered in the temperature range 950-1200°C It was verified that powders with larger fly ash content exhibited lower packing density resulting in compacts with a lower sintered density. Although an increase in fly ash content was associated to a larger presence of porosity in the sintered samples, as confirmed by microstructural analysis, all studied compositions when sintered at the highest temperatures exhibited satisfactory values for water absorption (< 10%), for flexural strength (20-64 MPa) and for hardness (20-30 GPa) indicating that they have potential to be applied in the production of structural ceramics.

This paper is mainly focused on the characterisation of a glass material (GM) obtained from the thermal treatment of a bottom ash (BA) produced at the Municipal Solid Waste (MSW) incineration plant of Valorsul. By melting the BA at 1400°C during 2 hours, and without using any chemical additives, a homogeneous black-coloured glass was obtained. The thermal and mechanical properties of this glass were characterised. The thermal expansion coefficient, measured by dilatometry, was 9-10 × 10-6 per °C and the modulus of rupture, determined by four-point bending test, was 75±6 MPa, which are similar values to those exhibited by commercial soda-lime-silica glasses used in structural applications. The chemical and the ecotoxicological leaching behaviour of the GM were also analysed. The GM was submitted to a leaching procedure composed of 15 sequential extraction cycles. A liquid/solid (L/S) ratio of 2 1/kg was applied in each cycle. The leachates were filtered through a membrane of PTFE (porosity: 0.45 μm). The filtered leachates were characterised for different chemical parameters and for an ecotoxicological indicator (bacterium Vibrio fischeri). The GM was also submitted to a microwave acidic digestion for the assessment of the total metal content. The crude BA was also submitted to the same experimental procedures. The GM showed levels of chemical emission and ecotoxicity for V. fischeri much lower than those determined for the crude BA. Similar characterisation studies will be pursued with the glass-ceramics produced by adequate thermal treatment of the glass, in order to investigate the effect of the crystallization on the final properties.