Processing, properties and arc jet oxidation of hafnium diboride/silicon carbide ultra high temperature ceramics

Field‐Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments

“…The use of additives also improves the mechanical properties and the resistance to oxidation at high temperature that are critical factors for the final applications of UHTC materials. [128,129] Despite the reduction of the sintering temperatures and the better control of the final microstructure provided by FAST/ SPS, the existence of specific mechanisms present in FAST/ SPS in comparison with other techniques has not been cleared out yet. At least one property of UHTC to consider is the high electrical conductivity (%10 7 S m -1 at room temperature, more than 2 orders of magnitude in comparison with the graphite used for pressing tools).…”

Thermochemical and Mechanical Stabilities of the Oxide Scale of ZrB2+SiC and Oxygen Transport Mechanisms

“…SiOðgÞ þ COðgÞ (4) a gas-solid reaction without going through the liquid phase, 22 which will lead to a porous ''SiC-depleted'' substrate layer in the ZrB 2 1SiC. 13 The ZrO 2 (c) ''solid pillars'' will also grow longer at the base by gas-solid reaction, with O 2 (g) reactant and B X O Y (g) product. On the other end of the gas finger, we will have the reverse of reaction (3):…”

“…4 that disfavors the Deal-Grove mechanism: (a) the DFT calculations indicate that the O Ã s not only have entropy advantage, but also mobility advantages over O 2 Ã , (b) intense aerothermal heating environment may introduce a significant level of dissociated oxygen on the outer liquid surface, 14,33 which would favor O Ã diffusion from a nonequilibrium kinetics perspective, (c) as pO 2 drops from B10 4 Pa on the outer liquid surface to o 10 À5 Pa equivalent at the internal gas finger-liquid interface ( Fig. 2(b) The mobility advantage of the peroxyl linkage over O 2 Ã suggests that arc-jet testing, 13,33 which introduces a nonequilibrium distribution of dissociated oxygen atoms on the surface, will likely lead to faster oxidation than ordinary furnace testing at the same temperature. Also, because the network defects are chemically incorporated into the network and thus interact more strongly with solutes than O 2 Ã , small changes in the glass chemistry could lead to large changes in the oxygen diffusivity by defect trapping/gettering, 30 much more than what Eq.…”

“…15 and 16 of Monteverde and Bellosi). 12,13 Thus, oxygen diffusion should be more sluggish in the silica-rich liquid than in pure B 2 O 3 (l), which furthermore will be evaporating rather quickly above 11001C.…”

Thermal Analysis of Tantalum Carbide-Hafnium Carbide Solid Solutions from Room Temperature to 1400 °C

“…As a result, the resultant oxide would melt and lose its structural integrity, and fail catastrophically. To reduce the gaseous products as well as retain the integrity of oxide scales under extremely high temperatures, Hafnium diboride (HfB 2 ) and its composites have been investigated as promising candidate materials for use on next-generation hypersonic vehicles [8,9]. During oxidation, HfB 2 forms a solid scaffold-like structure that mainly consists of HfO 2 and molten B 2 O 3 infiltrated between the HfO 2 .…”