in the present work, a titanium-based ziegler-natta catalyst was employed to synthesize ultra molecular weight polyethylene in a slurry medium. the effect of different parameters such as ethylene pressure, temperature, catalyst composition, and hydrogen pressure was studied. as the results indicate, increasing either [al]/[ti] ratio or temperature causes polymerization rate to go through a maxi...

A ferroelectric heater under A.C. field was demonstrated by using lead zirconate titanate and barium titanate ceramics. The temperature of the ceramics was increased from room temperature to its curie temperature of phase transition under an A.C. field. The heating characteristics greatly depend on the compositions of ceramics. It is proposed that the heating behavior is related to the domain s...

Emissivity as a function of wavelength, direction, and temperature correlates to material's efficiency in radiating thermal energy. Knowledge emissivity is essential for designing developing radiation-cooled protective systems hypersonic applications. It desirable achieve high (with value close 1) maximize heat radiation from hot surface vehicle's leading edge during atmospheric re-entry. With ...

High temperature ceramics with porosity on multiple length scales offer great promise in high temperature catalytic applications for their high surface area and low flow resistance in combination with thermal and chemical stability. We have developed a bottom-up approach to functional, porous, high-temperature ceramics structured on eight distinct length scales integrating functional Pt nanopar...

The 1 wt % Li-doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O₃ (BCZT-Li) ceramics prepared by the citrate method exhibit improved phase purity, densification and electrical properties, which provide prospective possibility to develop high-performance electrocaloric materials. The electrocaloric effect was evaluated by phenomenological method, and the BCZT-Li ceramics present large electrocaloric temperature ...

Of the principal classes of engineering materials, ceramics are in many ways the most interesting and challenging. Many properties, or combination, of properties, not achievable with other classes of materials give ceramics enormous technical potential. The main obstacles that prevent the wider use of ceramics include insufficient reliability, reproducibility, and high cost. The physical basis ...