Kinetic study of high-temperature oxidation of hafnium

Kofstad, Per; Espevik, Svein

doi:10.1016/0022-5088(67)90006-9

Cited by 32 publications

(15 citation statements)

References 16 publications

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“…HfO 2 is an undesired product because it is an insulator that impedes the machinability of Hf 3 AlN by the electrical‐discharge method. Furthermore, HfO 2 phase appears only above 1200°C, indicating that oxides was not introduced during the mixing process but formed during the sintering process at high temperature, probably as a result of the high affinity of Hf to oxygen at high temperature 17–19 …”

Section: Resultsmentioning

confidence: 99%

Hf₃AlN: A Novel Layered Ternary Ceramic with Excellent Damage Tolerance

Liu

Wang

et al. 2009

Journal of the American Ceramic Society

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In this work, bulk Hf3AlN ceramic was synthesized by an in situ reaction/hot pressing method using Hf and AlN as initial materials. The reaction path during the synthesis process was investigated. Hf3AlN was found to form via the reaction of Hf and AlN above 1000°C. Furthermore, physical and mechanical properties of Hf3AlN, such as electrical conductivity, flexural strength, and elastic moduli were also characterized. Similar to typical layered ternary ceramics Ti3SiC2 and Ti3AlC2, Hf3AlN possesses metallic conductivity and excellent damage tolerance, which is also the first one of this type that has ever been reported to crystallize in an orthorhombic structure. It is believed that a typical layered crystal structure and weak interlayer bondings contribute to the damage tolerance of Hf3AlN. Moreover, the stiffness of Hf3AlN can sustain a temperature as high as 1450°C, being 250°C higher than that of Ti3AlC2, which renders it a promising high‐temperature structural material.

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Section: Resultsmentioning

confidence: 99%

Hf₃AlN: A Novel Layered Ternary Ceramic with Excellent Damage Tolerance

Liu

Wang

et al. 2009

Journal of the American Ceramic Society

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“…This is consistent with the much higher formation rate of oxide for tungsten (17.57 mg/cm 2 at 900 C for 120 min) 66 as compared to hafnium (<5 mg/cm 2 at 900 C for 120 min). 67,68 Consequently, the oxide coverage is maintained even when substantial etching occurs during long pulses, so that stoichiometric films are deposited under all conditions tested. In the sputtering process, the thickness of the oxide layer formed on the tungsten target has been reported to be significantly greater than that formed on other metallic targets.…”

Section: Discussionmentioning

confidence: 99%

Evolution of target condition in reactive HiPIMS as a function of duty cycle: An opportunity for refractive index grading

Ganesan

Akhavan

Partridge

et al. 2017

Journal of Applied Physics

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Competition between target erosion and compound layer formation during pulse cycles in reactive HiPIMS opens up the possibility of tuning discharge conditions and the properties of deposited films by varying the duty cycle in situ without altering the reactive gas mixture. Three different reactive systems, hafnium in oxygen, tungsten in oxygen, and tungsten in oxygen/nitrogen, are studied in which amorphous films of hafnium oxide (HfO 2), tungsten oxide (WO 3), and tungsten oxynitride (WO x N y) are deposited. We show that the cyclic evolution of the target surface composition depends on the properties of the target including its affinity for the reactive gas mix and the compound layer melting point and volatility. We find that pulse length variations modulate the target compound layer and hence the discharge chemistry and properties of the films deposited. The refractive indices of HfO 2 and WO 3 were progressively reduced with the duty cycle, whereas that of WO x N y increased. These variations were found to be due to changes in the chemical composition and/or densification. We present and validate a phenomenological model that explains these findings in terms of a compound layer on the target surface that undergoes evolution during each pulse resulting in a cyclic equilibrium. The end points of the composition of the target surface depend on the duty cycle. Tuning the pulse characteristics holds great promise for the fabrication of multilayer films with through thickness graded properties. Published by AIP Publishing.

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“…This phase was originally named b in [24] but to avoid confusion in the ternary Al-Ta-Ti system, where b usually denotes the (b-Ti,Ta) solution phase (see [34]) it is designated here as 4. The s-phase was unambiguously identified in the Ta-rich side for a wide concentration range including the ideal composition Ta 2 Al [6,7,14,19,20,24,29,31,32,44,47]. Lately, the homogeneity range of the s-phase was investigated by Boulineau et al [24].…”

Section: Literature Data On Crystal Structure and Phase Equilibriamentioning

confidence: 98%

“…The Al-Ta system is of interest for technologies related with films [1][2][3][4][5], coatings [6] (oxidation), barrier layers [5], amorphization by rapid solidification [7,8], and mechanical alloying [9] (high-energy rod-milling), as well as for reinforcing and refining of Al alloys [10,11].…”

Section: Introductionmentioning

confidence: 99%