Microstructure and Ablation Behavior of C/C-SiC-(ZrxHf1−x)C Composites Prepared by Reactive Melt Infiltration Method

Abstract

C/C-SiC-(ZrxHf1−x)C composites were prepared by the reactive melt infiltration method. The microstructure of the porous C/C skeleton and the C/C-SiC-(ZrxHf1−x)C composites, as well as the structural evolution and ablation behavior of the C/C-SiC-(ZrxHf1−x)C composites, were systematically investigated. The results show that the C/C-SiC-(ZrxHf1−x)C composites were mainly composed of carbon fiber, carbon matrix, SiC ceramic, (ZrxHf1−x)C and (ZrxHf1−x)Si2 solid solutions. The refinement of the pore structure is beneficial to promote the formation of (ZrxHf1−x)C ceramic. The C/C-SiC-(ZrxHf1−x)C composites exhibited outstanding ablation resistance under an air–plasma environment at around 2000 °C. After ablation for 60 s, CMC-1 appeared to possess the minimum mass and linear ablation rates of only 2.696 mg/s and −0.814 µm/s, respectively, which are lower than those of CMC-2 and CMC-3. During the ablation process, a Bi-liquid phase and a liquid–solid two-phase structure were formed on the ablation surface which could act as an oxygen diffusion barrier to retard further ablation, which is responsible for the excellent ablation resistance of the C/C-SiC-(ZrxHf1−x)C composites.

Oxygen Plasma Treatment of Thermally Evaporated MoO3-x Films: An Approach to Tune the Work Function

“…It is possible that the oxygen atom reaction with MoO 3-x during plasma treatment is changing the surface dipole by filling the oxygen anion vacancies present inside the material and thus changing the cation oxidation state. 12 Also, OPT helps in the removal of surface contaminations, which can also be one of the reasons for the observed increment in work function. Work function is increased from 4.47 ± 0.01 eV (no OPT) to 4.99 ± 0.01 eV (OPT) for 23 nm films and from 4.58 ± 0.02 eV (no OPT) to 4.95 ± 0.01 eV (OPT) for 14 nm films.…”

“…About 1 eV of decrease in work function value is reported when thin films of MoO 3-x are air exposed for long times. 12,15 It is mainly due to surface contaminations and the adsorption of oxygen present in the atmosphere on the surface. Work function reduction degrades the hole selectivity and deteriorates the overall performance of a photovoltaic device.…”

“…3,10 MoO 3-x is a thermally stable metal oxide, but its properties are sensitive toward film preparation methods and air exposure. 11,12 Lots of literature are available stating the importance of stoichiometry, cation oxidation state, and position of oxygen vacant sites in MoO 3-x. 9,13,14 These parameters affect the optical properties, conductivity, and work function of MoO 3-x .…”

“…15 Liu et al have used oxygen plasma treatment under ultra-high vacuum conditions (6.66 × 10 −8 mbar) to regain the work function of MoO 3-x films. 12 This group has carried out all the measurements in a vacuum state and claimed this method as an option that can help in the recovery of lost work function by up to 64%. In this article, oxygen plasma treatment (OPT) is chosen as an approach to tune the work function of MoO 3-x deposited by thermal evaporation.…”

Facile preparation and dielectric properties of BaTiO3 with different particle sizes and morphologies

“…16,17 At present, BaTiO 3 particles obtained by hydrothermal preparation with Ba(OH) 2 $8H 2 O and TiO 2 as raw materials are is generally >100 nm in size and require high-temperature calcination to obtain smaller particles. 17,18 Therefore, how to reduce the average size of nano-BaTiO 3 particles by hydrothermal synthesis under mild conditions is an active area of research.…”