Photonic crystal structures can be used to control the spectral distribution of thermal emission. Here, Arpin et al. demonstrate three-dimensional tungsten and hafnium diboride photonic crystals to control high-temperature thermal emission for solar thermophotovoltaic energy devices.

/pdf/three-dimensional-self-assembled-photonic-crystals-with-high-42y84cqzd1.pdf

Three-dimensional self-assembled photonic crystals with high temperature stability for thermal emission modification

Review on ultra-high temperature boride ceramics

The fate and role of in situ formed carbon in polymer-derived ceramics

The oxidation behaviour of transition metal diboride ceramics is reviewed with emphasis on the performance of zirconium diboride and hafnium diboride. First, the oxidation behaviour of nominally pure diborides is discussed, focusing on the transition to linear mass gain kinetics at temperatures above ∼1100°C. Next, the use of SiC and other additives that produce silica based scales when oxidised is reviewed. These additives improve oxidation protection due to the formation/stability of the outer layer of borosilicate glass that acts as a barrier to diffusion of oxygen to the substrate. However, elevated temperatures (>1650°C) and/or the combination of aerodynamic flow, high heat flux and reactive atmosphere associated with hypersonic flight destabilises the outer oxide and decreases oxidation protection. Other additives that affect the composition and structure of the crystalline oxide scale without forming an outer glassy layer are a promising approach to improving oxidation behaviour of diboride...

Oxidation of ultra-high temperature transition metal diboride ceramics

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/pdf/uhtc-composites-for-hypersonic-applications-59v44wakt9.pdf

UHTC composites for hypersonic applications

Dense samples of ZrB2–20 vol% SiC were successfully fabricated by spark plasma sintering without the use of sintering aids. Oxidation behavior of these samples was characterized by exposing them to 1400°, 1500°, and 1600°C in an ambient atmosphere for 150 min, and by measuring the weight gains of the sample and crucible, as well as the thickness of the oxide scale and the glassy outer layer. The effects of gravity on the viscous outer layer are shown to result in significant heterogeneity within a sample. The oxidation scales were characterized by scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy analysis. The oxide scale was found to be composed of three layers: (1) a SiO2-rich glassy outer layer, (2) an intermediate layer of a ZrO2 matrix with interpenetrating SiO2, and (3) a layer containing a ZrO2 matrix enclosing partially oxidized ZrB2 with Si–C–B–O glass inclusions.

Oxidation Behavior of Zirconium Diboride Silicon Carbide Produced by the Spark Plasma Sintering Method

Dense samples of HfB2–SiC, HfB2–SiC–WC, and HfB2–SiC–WB were prepared by field-assisted sintering. The WB and WC additives were incorporated by solid solution into the HfB2 and the HfC that formed during sintering. Oxidation of the samples was studied using isothermal furnace oxidation between 1600° and 2000°C. Sample microstructure and chemistry before and after oxidation were analyzed by scanning electron microscopy and X-ray diffraction. The addition of WC and WB did not alter oxidation kinetics of the baseline HfB2–SiC composition below 1800°C; however, at 2000°C, HfB2–SiC–WC and HfB2–SiC–WB had oxide scales that were 30% thinner than the oxide scale of HfB2–SiC. It is believed that WC and WB promoted liquid-phase densification of the HfO2 scale, thereby reducing the path of oxygen ingress, during oxidation.

Oxidation Resistance of Hafnium Diboride Ceramics with Additions of Silicon Carbide and Tungsten Boride or Tungsten Carbide

Oxidation resistance tests were carried out on HfB2-20 vol.% SiC prepared by spark plasma sintering. The dense samples were exposed from 1400 to 2000 °C in an ambient atmosphere for 1 h. For comparison, the same material was tested using an arc jet to simulate an atmospheric reentry environment. The oxidation properties of the samples were determined by measuring the weight gain per unit surface area and the thicknesses of the oxide scale. The oxide scale consists of a SiO2 outer layer, porous HfO2 layers, and an HfB2 layer depleted in SiC. A transition in HfO2 morphology from equixed to columnar and a decrease in SiO2 viscosity between 1800 and 1900 °C accompanied a rapid increase in weight gain and scale thickness.

Oxidation resistance of hafnium diboride—silicon carbide from 1400 to 2000 °C

https://ceramics.onlinelibrary.wiley.com/doi/epdf/10.1002/ces2.10033

Processing of fiber‐reinforced ultra‐high temperature ceramic composites: A review

Oxidation tests were carried out on HfB2–SiC, HfB2–HfC, HfB2–WC–SiC, and HfB2–WSi2 ceramics using an oxyacetylene torch. The samples were oxidized between 2100 and 2300 °C. From cross-sectional images, scale non-adherence was noted as a limiting factor in oxidation resistance. The sample with the best scale adherence was HfB2–WSi2. Factors involving scale non-adherence such as vapor pressure, coefficient of thermal expansion mismatch and phase transformations were considered. In comparing the scale adherence of the samples it was hypothesized that vapor pressure buildup is the principal contributing factor in the scale adherence differences observed among the tested samples. However, the coefficient of thermal expansion mismatch and HfO2 phase transformation cannot be neglected as contributing factors to scale non-adherence in all samples.

https://research.birmingham.ac.uk/portal/files/26733557/Torch_Paper_07_24_13.pdf

Carmen M. Carney

Papers

Oxidation Behavior of Zirconium Diboride Silicon Carbide Produced by the Spark Plasma Sintering Method

Oxidation Resistance of Hafnium Diboride Ceramics with Additions of Silicon Carbide and Tungsten Boride or Tungsten Carbide

Oxidation resistance of hafnium diboride—silicon carbide from 1400 to 2000 °C

Processing of fiber‐reinforced ultra‐high temperature ceramic composites: A review

Qualitative analysis of hafnium diboride based ultra high temperature ceramics under oxyacetylene torch testing at temperatures above 2100 °C