Stability of the δ-TeO2 phase in the binary and ternary TeO2 glasses

The stability of δ-TeO₂ phase was studied in binary TeO₂–WO₃, TeO₂–CdO and ternary TeO₂–WO₃–CdO glasses. The samples were prepared by heating high purity powder mixtures of TeO₂, WO₃ and/or CdO to 800 °C in a platinum crucible with a closed lid, holding for 30 min and quenching in water bath. Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the thermal, phase and microstructural properties of the δ-TeO₂ phase. The addition of CdO into the tellurite glasses increased the stability range of the δ-TeO₂ phase up to higher temperature values and expanded the compositional δ-TeO₂ formation range. The formation of δ-TeO₂ phase in the binary systems was observed for samples containing 5–10 mol% WO₃ and 5–15 mol% CdO. However, for the ternary TeO₂–WO₃–CdO system the formation of δ-TeO₂ phase was determined in a wider compositional range.     

Carbon nanotube/boehmite-derived alumina ceramics obtained by hydrothermal synthesis and spark plasma sintering (SPS)

Preparation, structure and properties of hydrothermally treated carbon nanotube/boehmite (CNT/γ-AlOOH) and densification with spark plasma sintering of Al₂O₃ and CNT/Al₂O₃ nanocomposites were investigated. Hydrothermal synthesis was employed to produce CNT/boehmite from an aluminum acetate (Al(OH)(C₂H₃O₂)₂) and multiwall-CNTs mixture (200 °C/2 h.). TEM observations revealed that the size of the cubic shape boehmite particles lies around 40 nm and the presence of the interaction between surface functionalized CNTs and boehmite particles acts to form ‘nanocomposite particles’. Al₂O₃ and CNT/Al₂O₃ compact bodies were formed by means of spark plasma sintering (SPS) at 1600 °C for 5 min using an applied pressure of 50MPa resulting in the formation of stable α-Al₂O₃ phase and CNT–alumina compacts with nearly full density. It was also found that CNTs tend to locate along the alumina grain boundaries and therefore inhibit the grain coarsening and cause inter-granular fracture mode. The DC conductivity measurements reveal that the DC conductivity of CNT/Al₂O₃ is 10^?4 S/m which indicate that there is a 4 orders of magnitude increase in conductivity compared to monolithic Al₂O₃. The results of the microhardness tests indicate a slight increase in hardness for CNT/Al₂O₃ (28.35 GPa for Al₂O₃ and 28.57 GPa for CNT/Al₂O₃).     

Separation of gas and organic/water mixtures by MFI type zeolite membranes synthesized in a flow system

MFI type zeolite membranes were synthesized in a recirculating flow system at 95 °C where the synthesis solution was flown over the tubular α-alumina supports. The performance of the membranes for the separation of binary gas mixtures and alcohol/water liquid mixtures was investigated. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 15 and 11 for equimolar mixtures of n-C₄H₁₀/CH₄ and n-C₄H₁₀/N₂ at 200 °C, respectively. The membrane selectively permeated large n-C₄H₁₀ over small CH₄ and N₂, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores. The selectivities in the pervaporation separation of 5% ethanol/95% water mixture were 43 and 23 with permeate fluxes of 0.2 and 1.9 kg/m² h at 25 and 85 °C, respectively. The separation performance of membranes showed that MFI type membranes prepared in a recirculating flow system can be used both in the separation of gas and liquid mixtures.     

New quality criteria in wastewater reuse : The case of Gran Canaria

Wastewater reuse plays a key role in this vital cycle of water because it is able to reduce the wastewater spilled. Simultaneously, the supply of water for specific uses is increased. A new regulation (Royal Decree 1620/2007) came into force in Spain in December 2007 and regulates the basic conditions for the wastewater reuse and establishes the required criteria of quality to waters according to use.In the present paper, different kinds of tertiary treatments in reuse of wastewater are described. We focused on the applied tertiary treatments in most wastewater treatment plants of Gran Canaria Island. Particularly, we analysed Hoya del Pozo wastewater treatment plant due to its wide number of technologies and processes.Finally, we reviewed the quality criteria used in the regenerated waters, in agreement with the new regulations.     

Effect of Nitric Acid “Washing” Procedure on Electrochemical Behavior of Carbon Nanotubes and Glassy Carbon μ-Particles

The electroanalytic performances of glassy carbon paste electrode (GCPE), multi-walled carbon nanotube (MWCNT)-GCPE and double-walled carbon nanotube (DWCNT)-GCPE, which include HNO₃ washed/unwashed materials, were compared by monitoring cyclic voltammograms of potassium ferricyanide and catechol. Electrodes were prepared by introducing proper amount of DWCNT and MWCNT into GCPE. First untreated materials (DWCNT, MWCNT, GC μ-particles) were used in the electrodes and then HNO₃-treated materials were utilized for comparing difference in electrochemical performances. The effect of treatment procedure was also examined by applying Raman spectroscopy to treated and untreated materials. Moreover, TEM images were obtained for further investigation of MWCNT and DWCNT.