Effect of Pressure on Electronic and Optical Properties of SrAl2O4

The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.

Effect of pressure on the phase transformations and mechanical properties of 10 mol% Mg-PSZ sintered by HPHT

MgO (10 mol%)-stabilized zirconia ceramics were obtained using high-pressure high-temperature (HPHT) sintering. The effects of the sintering pressure (2.5, 3.7, and 5.0 GPa) on the phase transformations and hardness were...

The interplay between ternary molten carbonate and biomaterials during pressurized slow pyrolysis

The effect of pressure on the thermochemical conversion of woody biomass and lignin in the presence of carbonate additives has been investigated at moderate temperatures (600 and 800°C). A ternary...

Cerium d-Block Element (Co, Ni) Bimetallic Oxides as Catalysts for the Methanation of CO2: Effect of Pressure

Nickel– and cobalt–cerium bimetallic oxides were used as catalysts for the methanation of CO2 under pressure. The catalysts’ activity increases with pressure and an increase of just 10 bar is enough to double the yield of methane and to significantly improve the selectivity. The best results were those obtained over nickel–cerium bimetallic oxides, but the effect of pressure was particularly relevant over cobalt–cerium bimetallic oxides, which yield to methane increases from almost zero at atmospheric pressure to 50–60% at 30 bar. Both catalyst types are remarkably competitive, especially those containing nickel, which were always more active than a commercial rhodium catalyst used as a reference (5wt.% Rh/Al2O3) and tested under the same conditions. For the cobalt–cerium bimetallic oxides, the existence of a synergetic interaction between Co and CoO and the formation of cobalt carbides seems to play an important role in their catalytic behavior. Correlation between experimental reaction rates and simulated data confirms that the catalysts’ behavior follows the Langmuir–Hinshelwood–Hougen–Watson kinetic model, but Le Chatelier’s principle is also important to understand the catalysts’ behavior under pressure. A catalyst recycle study was also performed. The results obtained after five cycles using a nickel–cerium catalyst show insignificant variations in activity and selectivity, which are important for any type of practical application.

EXPERIMENTAL STUDIES OF THE INTERACTION OF TRACTOR DRIVE WHEELS WITH THE SOIL IN THE PLOWED FIELD

The article defines the influence of structural and operational parameters of a machine-tractor unit on changes in the hardness of freshly plowed soil due to deformation and compaction of the soil by wheeled running systems. An experimental model of the effect of pressure in the pneumatic chamber of the wheel, working width and speed of the unit on changes in soil hardness in the area of operation of running systems is obtained. The obtained mathematical models make it possible to predict changes in soil hardness, which makes it possible to reduce the negative impact on the soil of running systems by optimally completing, configuring and selecting the MTU operating mode.