Combustion synthesis of compounds in the Y2O3-Al2O3 system

In the Y₂O₃-Al₂O₃ system, compounds Y₃Al₅O₁₂ (yttrium aluminum garnet, YAG), YAlO₃ (yttrium aluminum perovskite, YAP), and Y₄Al₂O₉ (yttrium aluminate monoclinic, YAM) are well known. YAG and YAP are of considerable technological importance. Conventional solid-state reaction techniques require high sintering temperatures (above 1800°C) to prepare phase-pure compounds. Though several soft chemical routes have been explored for synthesis of YAG, YAP and YAM, most of these methods are complex. Moreover, phase-pure materials are not obtained in one step and prolonged annealing at temperatures around 1000°C is necessary. In this paper, one-step combustion synthesis of these compounds is reported using a modified procedure and employing mixed (glycine + urea) fuel. Phosphors based on Ce³⁺ activation were also prepared and exhibited characteristic photoluminescence.     

The effect of platinum on the performance of WO3 nanocrystal photocatalysts for the oxidation of Methyl Orange and iso‐propanol

BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO₃) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO₃) photocatalysts were synthesised by a sol‐gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO₃ materials were also studied for the same reaction. These materials were fully characterised using X‐ray diffraction (XRD), UV‐visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso‐propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co‐catalyst for the multi‐electron reduction of oxygen. The platinised WO₃ catalysts were stable for multiple oxidation–reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO₃ is a superior oxidation photocatalyst when compared with bulk WO₃. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt‐WO₃ is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co‐catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO₂, which requires UV light. Copyright © 2011 Society of Chemical Industry     

The Classroom of the Future: An Internet‐Delivered National Course on Thermal Management of Electronics

Teaching inter‐disciplinary material poses special challenges due to the diversity of student backgrounds. This problem is compounded if the material being taught is intended for both undergraduate and graduate students. Mechanical Engineering faculty members from three universities have come together to address this problem using a layered, multimedia delivery mechanism via the Internet. This has resulted in the first‐ever, live, full‐duplex, Internet course taught at any of the three partner universities: Auburn University, the University of Maryland, and the University of Minnesota. With the addition of colleagues from industrial sites such as Philips in the Netherlands and three other universities in Japan, Singapore, and Australia, the next offering will expand to become an international course. The authors hope to illustrate that a course delivered over the Internet adds significantly to the learning process in a cost‐effective manner .     

Enhanced dielectric properties of modified Ta2O5 thin films

 Tantalum oxide (Ta₂O₅) is a promising high dielectric constant material for the DRAM applications because of its ease of integration compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta₂O₅ samples were reported to enhance significantly through small substitutions of Al₂O₃. However, this improvement in the dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ is not clearly understood. The present research attempts to explain the higher dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta₂O₅–0.1Al₂O₃ thin films compared to that reported for pure Ta₂O₅ (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta₂O₅ thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. The leakage current properties and the reliability characteristics were also found to be improved with Al₂O₃ addition. Received: 24 November 1998 / Reviewed and accepted: 7 December 1998     

Long-lasting luminescence in garnet-based phosphors prepared by combustion synthesis

Recently long-lasting luminescence (LL) has been reported in YAG doped with Pr³⁺ or Ce³⁺ processed in reducing atmosphere. However, YAG:Ce emission is yellow which is not attractive for long lasting applications. On the other hand, Ga substituted garnets give green emission at shorter wavelengths. We explored Ga substituted garnets prepared by combustion synthesis for LL. These phosphors do exhibit green LL, although the intensities are lower compared to that of YAG:Ce.     

Quick and reliable estimation of BOD load of beverage industrial wastewater by developing BOD biosensor

An amperometric biosensor for determination of biochemical oxygen demand in wastewater has been developed to overcome the time consuming monitoring procedures. The performance and stability of the immobilized membrane have been investigated at 37 °C and pH 6.8. Immobilized microbial membranes maintain their stability and activity after intermittent use for 400 cycles when stored at 4 °C in sodium phosphate buffer pH 6.8. The response time of the BOD sensor was only 90 min, being independent of the concentration, and the lower detection limit was 1 mg/l. The obtained BOD values showed correlation with that of the conventional method for BOD determination (BOD5) with a deviation of ±10%. Moreover, the sensor exhibits good repeatability (3.39–4.45%) and reproducibility (1.85–2.25%). Software was added to upgrade this sensor and to make it a promising candidate for online monitoring.