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Ultra-High Temperature Materials (UHTMs) are at the base of entire aerospace industry; these high stable materials at temperatures exceeding 1600 °C are used to manage the heat shielding to protect vehicles and probes during the hypersonic flight through reentry trajectory against aerodynamic heating and reducing plasma surface interaction. Those materials are also recognized as Thermal Protection System Materials (TPSMs). The structural materials used during the high-temperature oxidizing environment are mainly limited to SiC, oxide ceramics, and composites. In addition to that, silicon-based ceramic has a maximum-use at 1700 °C approximately; as it is an active oxidation process over low temperature and water vapor environment condition. However, a great emphasis is required for developing structural materials in oxidation and rapid heating environment where the temperature is greater than 1700 °C. This review covers briefly all main types of Thermal Protection Systems (TPSs) and all the materials are used to fabricate them with the maximum operational temperatures. Also, it covers the promised UHTMs (SiC, ZrB2, HfB2, SiB6 and B4C) which are currently using for several aerospace applications, especially for TPS. Besides, it discusses the oxidation of SiC, B4C, SiB6, ZrB2 and HfB2. Therefore, the carbides and borides of the transition metals, Zr and Hf have a high-melting temperature and good stability in forming high-melting temperature oxides.

The purpose of this research is to investigate the influence of different powder loadings of 316L stainless steel (SS) powders on rheological behavior of feedstocks required for low pressure powder injection molding (L-PIM) process. The main idea consists in development of various formulations by varying 316L SS powder contents in feedstocks and evaluating the temperature sensitivity of feedstock via flow behavior index and activation energy. For this purpose, the irregular shape, spherical shape, and combination of both shapes and sizes (bimodal approach) of 316L SS powders are compounded with wax based composite binder. Moreover, the influence of elemental nanosized boron (nB) addition (up to 1.5 wt.%) on rheological properties of irregular shape 316L SS powders is also evaluated using capillary rheometer method. It is observed that rheological parameters for solid powder loading of powder gas atomized (PGA) and bimodal powder P25/75 316L SS underwent sudden change from PGA-69 vol.% to PGA-72 vol.% and P25/75-67 vol.% to P25/75 316L SS 70 vol.%, respectively. Thus it is concluded that PGA-69 vol.% and P25/75-67 vol.% are optimal powder solid loadings corresponding to the lowest values of activation energies.

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Abstract. Currently, natural cellulose fiber composite is a promising prospect in the composite world. However, achieving uniform strength in natural fiber composite is a challenge due to limited fiber length and its random orientation in the composite. Thus, the focus of this paper was to obtain a continuous cellulose fiber from mengkuang leaves using chemical extraction process. The chemical extraction involved alkaline treatment of the mengkuang leave followed by bleaching. This paper focused on extraction using sodium hydroxide (NaOH) and its process parameters. The process parameters of the extraction were varied in terms of concentration of NaOH solution and also the soaking time. The texture and structure of the chemically purified continuous cellulose fiber were observed by visual inspection. Detailed microstructural analysis was carried out using Field Emission Scanning Electron Microscopy (FESEM) while chemical composition analysis in term of cellulose percentage was conducted using Technical Association of the Pulp and Paper Industry (TAPPI); TAPPI T203. Preliminary results showed that increment in cellulose percentage when the concentration of NaOH and soaking time were increased.