Thermophysical and thermochemical properties of new thermal barrier materials based on Dy2O3–Y2O3 co-doped zirconia

Dy2O3-Y2O3 co-doped ZrO2 would potentially give lower thermal conductivity and higher coefficient of thermal expansion, which is a promising ceramic thermal barrier coating material for aero gas turbines and high temperature applications in metallurgical and chemical industry. In this study, Dy2O3-Y2O3 co-doped ZrO2 ceramics were prepared using solid state reaction methods. Dy0.5Zr0.5O1.75 and Dy0.25Y0.25Zr0.5O1.75 consist of pure cubic fluorite phase, whereas both Dy0.06Y0.072Zr0.868O1.934 and Dy0.02Y0.075Zr0.905O1.953 have tetragonal and cubic composite phases. The influence of the chemical composition on coefficient of thermal expansion (CTE) and the thermal conductivity was investigated by varying the content of rare earth dopant. Dy0.06Y0.072Zr0.868O1.934 exhibited a lower thermal conductivity and higher coefficient of thermal expansion as compared with standard 8 wt.% Y2O3 stabilized ZrO2 which is used in conventional thermal barrier coatings. The compatibility between the thermally grown oxide that consists of Al2O3 and the new compositions is critical to ensure the durability of thermal barrier coatings. Hence, the compatibility between Al2O3 and Dy2O3-Y2O3 codoped YSZ was investigated by mixing two types of powders and eventually sintered at 1300˚C. Dy0.06Y0.072Zr0.868O1.934 is compatible with Al2O3, whereas YAlO3 and Dy3Al2(AlO4)3 were formed when Dy0.25Y0.25Zr0.5O1.75 and Al2O3 were mixed and sintered

Dynamic analysis of flexible rotor-bearing systems using a modal approach

The generalized dynamic equations of motion were obtained by the direct stiffness method for multimass flexible rotor-bearing systems. The direct solution of the equations of motion is illustrated on a simple 3-mass system. For complex rotor-bearing systems, the direct solution of the equations becomes very difficult. The transformation of the equations of motion into modal coordinates can greatly simplify the computation for the solution. The use of undamped and damped system mode shapes in the transformation are discussed. A set of undamped critical speed modes is used to transform the equations of motion into a set of coupled modal equations of motion. A rapid procedure for computing stability, steady state unbalance response, and transient response of the rotor-bearing system is presented. Examples of the application of this modal approach are presented. The dynamics of the system is further investigated with frequency spectrum analysis of the transient response

Novel Nanostructured SiO2/ZrO2 Based Electrodes with Enhanced Electrochemical Performance for Lithium-ion Batteries

In this article, a novel anode material with high electrochemical performance, made of elements abundant on the Earth, is reported for use in lithium ion batteries. A chemically synthesised material (SiO2/ZrO2) containing Si-O-Zr bonds, exhibits as much as 2.1 times better electrochemical performance at the 10th cycle than a physically mixed material (SiO2 + ZrO2) of the same elements. When compared to synthesized SiO2 or conventional graphite-based electrodes, the SiO2/ZrO2 anode shows superior capability and cycling performance. This superior performance is ascribed to the effect of ternary compounds, which contributes not only to increasing the packing density, but also to creating the Si-O-Zr bond that makes additional reactions between SiO2/ZrO2 and lithium ions possible. The Si-O-Zr bond also contributes to improved conductivity for SSZ and provides facile paths for charge transfer at the electrode/electrolyte interface. Therefore, the overall internal resistance in a battery would be decreased and better performance could thus be obtained, with this type of anode. In every result, the positive influence of the Si-O-Zr bonds in the anode of a lithium ion battery was confirmed

The synthesis of thermochemically stable single phase lanthanum titanium aluminium oxide

Lanthanum titanium aluminium oxide (LaTi2Al9O19, LTA) synthesized by solid state reaction has been proven to be a promising thermal barrier material. However, LTA synthesized via solid state reaction requires a high processing temperature of at least 1500 °C for 24 h. In this paper, single phase LTA was synthesized by sol–gel at a lower temperature (1350 °C) and the process parameters, phase composition, and relative thermal properties were investigated. Two-step calcination was used to obtain fine LTA powders. According to X-ray diffraction, the best calcination temperature of sol–gel synthesized LTA is 1350 °C. XRD results also showed the thermochemical stability of sol–gel synthesized LTA, which does not react with Al2O3 up to 1500 °C, to be excellent. Compared to LTA synthesized by solid state reaction, sol–gel synthesized LTA has higher coefficients of thermal expansion (CTEs) which are circa 10.2×10−6 °C−1 at 950 °C, related to the size dependent characteristic of CTEs. Therefore, sol–gel synthesized LTA can be a promising candidate as a thermal barrier material on Ni-based superalloys

Theoretical and experimental studies of doping effects on thermodynamic properties of (Dy, Y)-ZrO2

Ionic oxide materials play a vital role in technical applications owing to their high-temperature capability and when used as thermal barrier coating (TBC) materials, for example, they have environmentally friendly effects such as improved fuel efficiency and reduced emissions. Doped ZrO2 based solid solution is attracting attention, whereas doping effects on thermodynamic properties are not well understood. This work reports the synthesis and characterization of doped ZrO2 with Dy3+ and Y3+ via a sol-gel route. The relationship between chemical composition and thermodynamic properties is investigated via experiment and molecular dynamics (MD) simulation. MD simulation has been employed to theoretically explore the crystal structure and to calculate the intrinsic thermal conductivity, which agrees well with the experiment measurement. The thermal conductivity of dense samples is lower than that of conventional 6–8 wt.% Y2O3 stabilized ZrO2 (equivalent to 4 mol% Y2O3 stabilized ZrO2, 4YSZ) at room temperature. The coefficient of thermal expansion is higher due to the doping Dy3+ ion compared with that of 4YSZ. The thermochemical compatibility of Dy0.06Y0.072Zr0.868O1.934 with Al2O3 which is critical for the durability of the TBC system has been studied and can be maintained up to 1500 °C

Improving efficiency of electrostatic spray-assisted vapor deposited Cu2ZnSn(S,Se)4 solar cells by modification of Mo/absorber interface

Electrostatic spray-assisted vapor deposition (ESAVD) is a non-vacuum, low cost and eco-friendly method to produce Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 (CZTSSe) absorbers for thin film solar cells, and it is a very promising method for industrialization due to it is high deposition speed and close to unity deposition efficiency. In this work, in order to improve the efficiency of ESAVD deposited CZTSSe solar cells, an ultrathin ZnO (circa 10 nm) layer was employed as an intermediate layer between CZTSSe and Mo back contact to avoid the direct contact between Mo and CZTSSe and reduce the decomposition of CZTSSe during annealing process. XRF and EDX were used to characterize the chemical composition of CZTSSe before and after selenization respectively. SEM and Raman results showed the improved absorber morphology and the reduced direct interfacial reaction between CZTSSe and Mo. The improvement of the CZTSSe/Mo interface due to the intermediate layer was also reflected in the quality of the derived photovoltaic devices, leading to an improved efficiency of ESAVDdeposited kesterite solar cells from 3.25% to 4.03%

The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO2, but quantitative analysis of the role of facile TiCl4 treatment and thickness control of the compact TiO2 layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO2 layer to produce highly efficient planar PSCs. TiCl4 treatment of TiO2 layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl4 aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl4 treatment, PCE of 16.42% was achieved for PSCs with TiCl4 aqueous solution-treated TiO2 and 19.24% for PSCs with TiCl4 aqueous/ethanol solution-treated TiO2, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer

Rapid detection of free and bound toxins using molecularly imprinted silica/graphene oxide hybrids dagger

Rapid, selective detection of biological analytes is necessary for early diagnosis, but is often complicated by the analytes being bound to proteins and the lack of fast and reliable systems available for their direct assessment. Here, a cheap, easily-assembled molecularly imprinted silica/graphene oxide hybrid is developed, which can selectively detect toxins linked to early-stage chronic kidney disease, down to femtomolar concentrations within 5 minutes. The hybrid material is capable of simultaneously and separately measuring free and bound analytes using with an ultra-low limit of detection in the femtomolar range, and uses processes intrinsically adaptable to any charged molecular analy

Machine Learning Approach for Predicting the Discharging Capacities of Doped lithium Nickel- Cobalt-Manganese Cathode Materials in Li-ion Batteries

Understanding the governing dopant feature for cyclic discharge capacity is vital for the design and discovery of new doped lithium nickel–cobalt–manganese (NCM) oxide cathodes for lithium-ion battery applications. We herein apply six machine-learning regression algorithms to study the correlations of the structural, elemental features of 168 distinct doped NCM systems with their respective initial discharge capacity (IC) and 50th cycle discharge capacity (EC). First, a Pearson correlation coefficient study suggests that the lithium content ratio is highly correlated to both discharge capacity variables. Among all six regression algorithms, gradient boosting models have demonstrated the best prediction power for both IC and EC, with the root-mean-square errors calculated to be 16.66 mAhg–1 and 18.59 mAhg–1, respectively, against a hold-out test set. Furthermore, a game-theory-based variable-importance analysis reveals that doped NCM materials with higher lithium content, smaller dopant content, and lower-electronegativity atoms as the dopant are more likely to possess higher IC and EC. This study has demonstrated the exciting potentials of applying cutting-edge machine-learning techniques to accurately capture the complex structure–property relationship of doped NCM systems, and the models can be used as fast screening tools for new doped NCM structures with more superior electrochemical discharging properties