No abstract

Proton exchange membranes consisting of Nafion V R and crystallized titania nanoparticles have been developed to improve water-retention and proton conductivity at elevated temperature and low relative humidity. The anatase-type titania nanoparticles were synthesized in situ in Nafion solution through sol-gel process and the size of the formed titiania nanoparticles is in the range of 3-6 nm. The formed nanoparticles are well-dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion-titania composite membrane is about 20 o C higher than that of plain Nafion membrane. At elevated temperature (above 100 C), the Nafion-titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane.

No abstract

An exothermic reaction between MgB₂ and water was observed in our laboratory at high temperature, although no obvious reaction occurred at room temperature. The reaction process of MgB₂ and water was therefore studied by using microcalorimetry. The results showed that the reaction enthalpies of MgB₂ with water and the formation enthalpies of MgB₂ at <i>T</i> = (323.15, 328.15, 333.15 and 338.15) K are (–313.15, –317.85, –322.09, –329.27) kJ?mol^–1, and (–238.96, –237.73, –236.50, –234.30) kJ●mol^–1, respectively. The standard enthalpy of formation and standard molar heat capacity of MgB2 obtained by extrapolation method are –245.11 kJ●mol^–1 and 246 J●mol^–1●K^–1, respectively. The values of activation energy <i>E</i>, pre-exponential factor A and the reaction order for the reaction of MgB₂ and water over the temperature range from 323.15 K to 338.15 K are 50.80 kJ●mol^–1, 10^4.78 s^–1 and about 1.346, respectively. The positive values of Δ<i>G</i>^≠ and Δ<i>H</i>^≠ and negative value of Δ<i>S</i>^≠ indicate that the reaction can take place easily above 314.45 K

In this work, based on physical vapor deposition and high-temperature annealing (HTA), the 4-inch crack-free high-quality AlN template is initialized. Benefiting from the crystal recrystallization during the HTA process, the FWHMs of X-ray rocking curves for (002) and (102) planes are encouragingly decreased to 62 and 282 arcsec, respectively. On such an AlN template, an ultra-thin AlN with a thickness of ~700 nm grown by MOCVD shows good quality, thus avoiding the epitaxial lateral overgrowth (ELOG) process in which 3–4 μm AlN is essential to obtain the flat surface and high crystalline quality. The 4-inch scaled wafer provides an avenue to match UVC-LED with the fabrication process of traditional GaN-based blue LED, therefore significantly improving yields and decreasing cost.