Aluminum Nitride Oxidation by Simultaneous TG and DTA

This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods. In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies for oxidation of the water resistant AlN, obtained by the Kissinger method, are 357±10 kJ mol^–1, 392±12 kJ mol^–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 243±7 and 257±8 kJ mol^–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively, 323±10 and 224±7 kJ mol^–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance to oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phenoxy-benzothiadiazole dyes: Synthesis,photophysical properties and preliminary application in OLEDs

The synthesis of a phenoxy-benzothiadiazole (BTD) derivative is reported for the first time. This derivative was employed as an intermediate in the obtention of two novel highly fluorescent aryl-phenoxy-BTD dyes. Their photophysical properties were evaluated in solution and the results indicate a strong intramolecular charge transfer (ICT) character in the excited state. The luminophore 3a, possessing a donor-BTD-phenoxide architecture, exhibits superior fluorescence quantum yield (0.67) than the designed acceptor-BTD-phenoxide dye (0.06). After electrochemical and photoluminescence characterization of thin films of 3a, an OLED with the configuration ITO/PEDOT:PSS/3a/TPBi/LiF/Al was constructed. This device displayed a green emission centered at 547?nm, with CIE coordinates of (0.40, 0.55). For comparison, an OLED using a previously reported luminescent BTD-pyridyl derivative was also constructed. The OLED made with the phenoxy-BTD derivative operated using less current density and led to higher irradiance and electrical stability, indicating the high potential of ArO-BTD dyes for future application in electroluminescent devices.     

Evaluating cement hydration by non-conventional DTA; An Application to Waste Solidification

This paper presents a method to study cement hydration at ambient temperatures by using a micro processed non-conventional differential thermal analysis (DTA) system, which was used to evaluate the solidification/stabilization process of tannery wastes produced in the leather industry. The DTA curves of pastes composed by slag cement, Wyoming bentonite and waste are obtained in real time and used to analyze the heat effects of the reactions during the first 24 h of hydration. By applying a deconvolution method to separate the overlapped DTA peaks, the energy released in the several hydration stages may be estimated and consequently, the effects of each component on the solidification process. The highest separated DTA peak occurs during the several early stages of cement hydration and is due mainly to tricalcium silicate hydration. Very good correlation shows that the greater is the waste content in the paste composition, the higher is its effect on the rates of reactions occurring during the induction (dormant) period of cement hydration. The presence of bentonite used as a solidification additive in the stabilization process has a similar but less dramatic effect on the dormant period. This revised version was published online in July 2006 with corrections to the Cover Date.