Research and Development of Refractory Oxidation-Resistant Diborides. Part 2, Volume 5: Thermal, Physical, Electrical and Optical Properties

Clougherty, Edward V.; Wilkes, K.E.; Tye, R. P.

doi:10.21236/ad0865321

Cited by 21 publications

(25 citation statements)

References 2 publications

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“…Research in the late 1960s on metal (Zr, Hf, Cr, Y, and Al) and ceramic (SiC, MoSi 2 , and TaB 2 ) additions to ZrB 2 and HfB 2 revealed the superior densification, and more importantly the improved oxidation and thermal stress resistance (TSR), of diborides containing SiC, C, or SiC plus C 107,108 . Fenter 100 reviewed many compositions, the most important of which were ZrB 2 and HfB 2 with 20 vol% SiC or 18 vol% SiC and 10 vol% C. Subsequent to these key studies, recent research using commercial ZrB 2 and HfB 2 powders has typically included non‐reactive additives (e.g., SiC) or liquid phase forming additions (e.g., Ni, Si 3 N 4 , or MoSi 2 ) to improve densification.…”

Section: Densificationmentioning

confidence: 99%

Refractory Diborides of Zirconium and Hafnium

Fahrenholtz

Talmy

Zaykoski

2007

Journal of the American Ceramic Society

1,821

1,134

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This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre‐ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine‐grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re‐entry, and rocket propulsion.

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Section: Densificationmentioning

confidence: 99%

Refractory Diborides of Zirconium and Hafnium

Fahrenholtz

Talmy

Zaykoski

2007

Journal of the American Ceramic Society

1,821

1,134

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“…The change in slope of electrical resistivity as a function of temperature was not unexpected based on previous reports. Measurements from several researchers indicated that the electrical resistivity of ZrB 2 was linear to temperatures as high as ~1573 K (Figure ) . The reason for this discontinuity in linear behavior with temperature is not clear.…”

Section: Resultsmentioning

confidence: 99%

Elevated temperature electrical resistivity measurements of zirconium diboride using the van der Pauw Method

2019

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A novel electrical testing assembly was designed, fabricated, and validated to allow elevated temperature electrical resistivity measurements using the van der Pauw method up to 2173 K. The assembly consisted of h‐BN insulators, ZrB2‐based fixture components, and W signal wires. The assembly was installed in a refractory metal element furnace for temperature control and an oxygen gettering system was utilized to control the oxygen activity of the process gas. The system was validated using high‐purity Mo as a reference standard, demonstrating good agreement with accepted electrical resistivity values for Mo. The system was utilized to measure the electrical resistivity of a ZrB2 ceramic that was produced from commercially available ZrB2 powder using C and ZrH2 as sintering aids and densified by hot‐pressing at 2423 K. The resulting ZrB2 ceramic was ~96% dense with ~0.2 wt.% ZrO2 secondary phase and a grain size of ~40 µm. Electrical resistivity of ZrB2 was measured from room temperature to 2133 K. The electrical resistivity of the ZrB2 exhibited distinct linear behavior with respect to temperature, increasing from 7.3 µΩ‐cm at 298 K to 35.7 µΩ‐cm at 1223 K (~0.031 µΩ‐cm/K), and then further increasing to 76.0 µΩ‐cm at 2133 K (~0.044 µΩ‐cm/K). To the knowledge of the authors, these measurements were performed at the highest temperatures ever reported using this method.

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“…One of the early reports examined densification behavior and characterization [54]. Up to this point, all of the borides examined by ManLabs were densified by hot pressing, but plasma spraying, pressureless sintering, and hot forging were examined as alternative densification methods.…”

Section: Processing Properties Oxidation and Testingmentioning

confidence: 99%

“…The last report in this series focused on the thermal, physical, electrical, and optical properties of diborides [57]. In this study, the use of additives was presented as a method for controlling properties, and extensive tables of data for heat capacity, thermal expansion, electrical resistivity, and other properties were presented (Fig.…”

Section: Processing Properties Oxidation and Testingmentioning

confidence: 99%

“…thermal conductivity of composition i (nominally pure Zrb 2 ) as a function of temperature using two methods, cut bar for temperatures below 1000°C and thermal flash for temperature above 1000°C. the materials were nominally fully dense with a grain size of ~20 µm [57]. oxidation (cold gas/hot wall/low velocity) along with more specialized tests including high-velocity furnace testing (cold gas/hot wall/high velocity) and simulated reentry conditions (hot gas/cold wall/high velocity).…”

Section: Processing Properties Oxidation and Testingmentioning

confidence: 99%

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