Improvement strategy on thermophysical properties of A_(2)B_(2)O_(7)-type rare earth zirconates for thermal barrier coatings applications:A review

The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments.This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines.Based on the first principles,molecular dynamics,and new data-driven calculation approaches,doping and high-entropy strategies have now been adopted in advanced TBC materials design.In this paper,the solid-state heat transfer mechanism of TBCs is explained from two aspects,including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature.This paper also provides new insights into design considerations of adaptive TBC materials,and the challenges and potential breakthroughs are further highlighted for extreme environmental applications.Strategies for improving thermophysical performance are proposed in two approaches:defect engineering and material compositing.

Synthesis and Electrical Properties of La_ 0.8Sr_(0.2)-x Ca_xCo_(0.9)Fe_ 0.1O_3-δ

Effects of small amount of Ca doping in La site in LaCoO 3-based oxide on th e synthesis and electrical conductivity were investigated by using X-ray diffra ction (XRD), differential scanning calorimetry and thermogravimetry (DSC/TG), or dinary four-probe dc measurement methods. La 0.8Sr 0.2-xCa x Co 0.9Fe 0.1O 3-δ (LSCCF, 0≤x≤0.1) prepared by solid r eact ion synthesis is all of a single phase and the calcined process may be divided i nt o three stages: (1) decomposition of reactants; (2) formation of LaCoO 3-based oxides; and (3) formation of LSCCF solid solution. The maximum of electrical co nductivity of the LSCCF composites is above 100 S·cm -1 and the co nduction me chanism is attributed to the adiabatic-hopping of p-type small polarons.

Photocatalytic properties of P25-doped TiO_2 composite film synthesized via sol–gel method on cement substrate

TiO2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface water, we herein examined the preparation of a P25-TiO2 composite film on a cement substrate via a sol–gel method. In this case, Rhodamine B（Rh B）was employed as the target organic pollutant. The self-generated TiO2 film and the P25-TiO2 composite film were characterized by X-ray diffraction（XRD）, N2 adsorption/desorption measurements, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and diffuse reflectance spectroscopy（DRS）. The photodegradation efficiencies of the two films were studied by Rh B removal in water under UV（ultraviolet） irradiation. Over 4 day exposure, the P25-TiO2 composite film exhibited higher photocatalytic performance than the self-generated TiO2 film. The photodegradation rate indicated that the efficiency of the P25-TiO2 composite film was enhanced by the addition of the rutile phase Degussa P25 powder. As such, cooperation between the anatase TiO2 and rutile P25 nanoparticles was beneficial for separation of the photo-induced electrons and holes. In addition, the influence of P25 doping on the P25-TiO2 composite films was evaluated. We found that up to a certain saturation point, increased doping enhanced the photodegradation ability of the composite film. Thus, we herein demonstrated that the doping of P25 powders is a simple but effective strategy to prepare a P25-TiO2 composite film on a cement substrate, and the resulting film exhibits excellent removal efficiency in the degradation of organic pollutants.