Oxidation kinetics of LaB 6 in oxygen rich conditions

Wen, Chung-Han; Wei, Wen‐Cheng J.

doi:10.1016/j.jeurceramsoc.2003.11.016

Cited by 28 publications

(8 citation statements)

References 10 publications

(8 reference statements)

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“…A few previous studies have shown that the oxidation of LaB 6 starts at ~700 °C and forms a few intermediate oxides, which may be converted to La 2 O 3 at temperatures ‡ 1200 °C. [40,41] On the other hand, it has been shown in another study that the oxidation of ZrB 2 and SiC starts at ‡ 800 °C and ‡ 1100 °C, respectively. [21] It has been also mentioned that the oxidation of SiC is much slower than ZrB 2 at temperatures £ 1200 °C; and therefore, it is intuitive that the overall mass gain of the composite at lower temperatures (£ 1200 °C) during heating should depend on the oxidation kinetics of ZrB 2 and LaB 6 , which might be responsible for a lower rate of mass change as indicated in Figure 2.…”

Section: Mechanism Of Oxidation In Non-isothermal Conditionmentioning

confidence: 99%

Oxidation Resistance and Evolution of Multi-layered Oxide Scale During Isothermal and Cyclic Exposure of ZrB2–SiC–LaB6 Composites at 1300 °C to 1500 °C

Kashyap

Sala

Mitra

2021

Metall Mater Trans A

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The effect of LaB 6 (7, 10, and 14 vol pct) addition on oxidation behavior of spark plasma-sintered ZrB 2 -20 vol pct SiC composites involving heating under non-isothermal condition till 1400 °C, and isothermal and cyclic exposures at 1300 °C to 1500 °C have been examined. The mass gain of the composite with 14 vol pct LaB 6 is found as the highest during non-isothermal oxidation, whereas it appears as the least on isothermal exposure for 24 hours at 1400 °C or 1500 °C. The mass gain after 24 cycles of 1-hour exposure at 1300 °C to 1500 °C is found to be lower than that recorded under isothermal condition for all the composites, with the difference decreasing with LaB 6 content. The oxidation exponent (n) is found to decrease to near parabolic rate law with the increase in cyclic exposure temperature. The parabolic rate constant (k p ) is found to decrease with the increase in LaB 6 content after a few cycles of exposure at all the investigated temperatures. The oxide scales formed on isothermal exposure at 1400 °C or 1500 °C have shown a thin La 2 Si 2 O 7 layer with borosilicate glass (BSG) as the outer layer, followed by layers containing BSG along with coarse and fine ZrO 2 , and a SiC-depleted ZrB 2 layer. The oxide scales formed during cyclic exposure contain an outer compact layer comprising BSG, La 2 Si 2 O 7 , and ZrSiO 4 , followed by ZrO 2 + BSG. Additionally, a SiC-depleted layer is found at the oxide-composite interface on cyclic exposure at 1500 °C for 24 hours, and at 1400 °C for 100 hours. The outer compact layer appears to have a critical role in protection against oxidation, with k p decreasing with the increase in its thickness.

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Section: Mechanism Of Oxidation In Non-isothermal Conditionmentioning

confidence: 99%

Oxidation Resistance and Evolution of Multi-layered Oxide Scale During Isothermal and Cyclic Exposure of ZrB2–SiC–LaB6 Composites at 1300 °C to 1500 °C

Kashyap

Sala

Mitra

2021

Metall Mater Trans A

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“…9 shows the thickness of the glassy layer and the extended SiC-depleted layer as a function of oxidation time for the ZB10S and ZB30S specimens at 1500 • C. Combining the mass gain data with the glassy layer thicknesses and the extended SiC-depleted layer thicknesses from Figs. 3 and 9, the oxidation kinetics were analyzed for ZB10S and ZB30S using a generalized power rate equation 17,18 :…”

Section: Oxidation Behavior and Kinetics Of Zrb 2 -Sic Ceramicsmentioning

confidence: 99%

Oxidation resistance and strength retention of ZrB2–SiC ceramics

Guo

Zhang

2010

Journal of the European Ceramic Society

106

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“…80–85 When the crystal is heated in an oxygen atmosphere to around 500–700 °C, the surface starts to be oxidized to yield LaO, La 2 O 3 , B 2 O 3 , LaBO 3 , LaB 3 O 6 , and La 3 BO 6 on the macroscopic scale. 69,86 However, in our experimental conditions, 25 the LaB 6 tip was heated for cleaning in an ultrahigh vacuum, where the desorption processes are as significant as the oxidation processes. The oxide layers would then be limited to several atomic layers.…”

Section: Resultsmentioning

confidence: 99%

“…Regarding La borates and metaborates (LaBO 3 , LaB 3 O 6 , and La 3 BO 6 ) that have been synthesized in an oxygen atmosphere, 69,86 it is uncertain whether they can be synthesized under oxygen-depleted conditions. Considering the fact that these materials are synthesized at temperatures (∼900 °C) slightly higher than the temperature at which boron oxides BO and B 2 O 2 are desorbed in a vacuum (727 °C), 81,82 it seems unlikely that La borates and metaborates are preferably synthesized on the LaB 6 surface in an ultrahigh vacuum.…”

Section: Resultsmentioning

confidence: 99%