Advances in ultra-high temperature ceramics, composites, and coatings

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, highentropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.

SIGHT-GLASS DEGRADATION IN UREA CARBAMATE SOLUTION

In the industrial environment, a sight glass acts as a gauge for the fluid level in a pressure vessel. Sight glass must have the following physical properties: clarity (clear enough to view the fluid in the vessel), hardness (not easily broken), thermal shock resistance, and corrosion resistance. A historical investigation of the equipment placed in the High-Pressure Decomposer (HPD) unit of the Urea Plant-X and Plant-Y has a pressure of 17 Bar and a temperature of 124-155oC, yielded an analysis of sight glass degradation in carbamate solution. The sight glass that was installed is soda-lime fused glass. The average is based on the equipment's history.