Muhammad Rizwan,
Volume 22, Issue 1 (3-2025)
Abstract
Powder-based Physical Vapor Deposition (PPVD) was utilized to deposit doped TiO2 thin layers, to modify electronic and optical properties. The modification was performed using different dopants (MnO2, Ta2O5, Nb2O5) at different concentrations (0.05 and 0.1 mol%) respectively. The structural characterization by FESEM reveals that the size of the grain varied with respect to the dopants. The sample doped at lower concentration demonstrates a larger crystallite size than the sample doped at higher concentration. This trend is consistent with the measured grain size of the doped thin layer samples. The nonlinearity coefficient (α) and breakdown voltage at lower ranges are enhanced as the dopant concentration in the TiO2 lattice increases due to the reduction of grain size. While, the optical properties of doped TiO2 thin layers with respect to energy bandgap demonstrated enhancement trend with the addition of the dopant as revealed by UV-Vis’s reflectance analysis. The enhancement of electrical and optical properties is contributed by the formation of barrier layer surrounding the grains, which in return increases the conductivity of the doped TiO2 thin layers sample. Conclusively, this study demonstrates the feasibility of the PPVD method in producing a dense thin layer structure for further optical and electrical based applications.
Amin Rezaei Chekani, Malek Naderi, Reza Aliasgarian, Yousef Safaei-Naeini,
Volume 22, Issue 2 (6-2025)
Abstract
This paper presents the novel fabrication method of a three-dimensional orthogonally woven (3DW) C/C-SiC-ZrB2 composite and the effects of ZrB2 and SiC particles on microstructure and the ablation behavior of the C/C–SiC–ZrB2 composite are studied. C/C–SiC–ZrB2 composite was prepared by isothermal-chemical vapor infiltration (I-CVI), slurry infiltration (SI), and liquid silicon infiltration (LSI) combined process. Pyrolytic carbon (PyC) was first infused into the 3DW preform by I-CVI at 1050°C using CH4 as a precursor in order to form a C/C preform with porous media. The next step was graphitization at 2400°C for 1hr. Then ZrB2 was introduced into 3DW C/C preform with a void percentage of 48 by impregnating the mixture of ZrB2 and phenolic resin, followed by a pyrolysis step at 1050°C. A liquid Si alloy was infiltrated, at 1650 °C, into the 3DW C/C composites porous media containing the ZrB2 particles to form a SiC–ZrB2 matrix. An oxyacetylene torch flame was utilized to investigate The ablation behavior. ZrB2 particles, along with the SiC matrix situated between carbon fiber bundles, form a compact ZrO2-SiO2 layer. This layer acts as a barrier, restricting oxygen infiltration into the composite and reducing the erosion of carbon fibers. The findings were supported by FESEM imaging and further confirmed through x-ray diffraction and EDS analysis. The addition of ZrB2 to the C/C-SiC composite resulted in a lower mass and linear ablation rate; 2.20 mg/s and 1.4 µm/s respectively while those for C/C-SiC composite were 4.8 mg/s and 6.75 µm/s after ablation under an oxyacetylene flame (2500°C) for 120 s.
