Oxidation of boron nitride under nonisothermal conditions

Podobeda, L. G.; Tsapuk, A. K.; Buravov, A. D.

doi:10.1007/bf01157838

Cited by 17 publications

(14 citation statements)

References 2 publications

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“…From the SEM‐based analysis, it could be seen that from the shortest exposure times the boundaries between individual particles became less distinct and they tended to increase in size. This is consistent with the findings of Podobeda et al who measured a decrease in specific surface area with oxidation . It is similarly consistent with models that propose that a layer of molten boron trioxide forms around the individual basal plane peripheries, which causes them to agglomerate as it thickens .…”

Section: Discussionsupporting

confidence: 92%

“…The high temperature oxidation of h‐BN powder has been well studied. Oxidation has been said to commence at 800 °C and it does so according to the three stoichiometric relationships in Equations ‐(c)

B N (s) + \frac{3}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + \frac{1}{2} {normalN}_{2} (g)

B N (s) + \frac{5}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + N O (g)

B N (s) + \frac{7}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + {N O}_{2} (g)

…”

Section: Introductionmentioning

confidence: 99%

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Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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In contrast to a mass of powder in air at 900 °C, the oxidation rate of hexagonal boron nitride does not tend to a plateau when present as a coating on austenitic stainless steel type 304 and type 310, and a real‐world hot forming tool alloy. As with a mass of powder, a molten boron trioxide diffusion barrier encapsulates each hexagonal boron nitride grain around the basal plane. These subsequently merge to form a dispersion of remnant grains throughout a molten matrix. Boron trioxide is semipermeable, and as such, the substrate oxidizes concurrently. As it does so, outwardly diffusing chromium (III) ions react with boron trioxide to form chromium borate, which depletes the diffusion barrier. This causes the oxidation of hexagonal boron nitride to be sustained at an enhanced rate and the overlayer ultimately undergoes complete decomposition. During this process, the scale comprises chromium borate and chromia only. While manganese chromium spinel and iron chromium spinel form readily at the oxide‐atmosphere interface of equivalently heat‐treated uncoated substrates, they do not form until after the coating has completely decomposed.

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Section: Discussionsupporting

confidence: 92%

B N (s) + \frac{3}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + \frac{1}{2} {normalN}_{2} (g)

B N (s) + \frac{5}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + N O (g)

B N (s) + \frac{7}{4} {normalO}_{2} (g) \to \frac{1}{2} {normalB}_{2} {normalO}_{3} (1) + {N O}_{2} (g)

…”

Section: Introductionmentioning

confidence: 99%

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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“…In general, highertemperature synthesis routes for BN lead to a more ordered structure. 3 The literature contains numerous studies of BN oxidation, [4][5][6][7][8][9][10][11][12] which indicate the oxidation behavior of BN is complex and dependent on structure. There is general agreement that the primary oxidation reaction is…”

Section: Introductionmentioning

confidence: 99%

“…These varying results suggest that oxidation behavior is dependent on issues such as porosity, impurities, and crystalline form. Podobeda et al 7 have studied the nonisothermal oxidation of BN powders. They observe two stages of chemical reaction in heating these powders.…”

Section: Introductionmentioning

confidence: 99%

High‐Temperature Oxidation of Boron Nitride: I, Monolithic Boron Nitride

Jacobson

Farmer

Moore

et al. 1999

Journal of the American Ceramic Society

172

138

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High‐temperature oxidation of monolithic boron nitride (BN) is examined at 900–1200°C. Hot‐pressed BN and both low‐ and high‐density chemically vapor‐deposited BN are studied. The oxidation product is B2O3(l) and the oxidation kinetics are sensitive to crystallographic orientation, porosity, and impurity levels. The B2O3 product also reacts readily with ambient water vapor in the test furnace (ppm levels) to form the volatile species HBO2(g), leading to overall paralinear kinetics. The linear rate constant extracted from these experiments agreed with that predicted from diffusion of HBO2(g) across a static boundary layer.

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“…Several investigations into the high temperature oxidation of a mass of h‐BN powder have been reported in the literature . Oxidation has been found to commence at 800 °C, and proceeds predominantly around the basal plane peripheries of the roundish plate‐like particles. The primary reaction is accepted to be Equation (1):

italicBN (s) + \frac{3}{4} O_{2} (g) goodbreakinfix\to \frac{1}{2} B_{2} O_{3} (l) goodbreakinfix+ \frac{1}{2} N_{2} (g)

…”

Section: Introductionmentioning

confidence: 99%

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Ti‐6Al‐4V

Fleming

2019

Materials & Corrosion

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Hexagonal boron nitride (h‐BN) coatings on Ti‐6Al‐4V substrates undergo complete decomposition in air at 900 °C. This fate is similar to that of this ceramic material on chromia‐former alloys, and unlike that of a mass of powder treated in isolation. As the ceramic and alloy oxidize concurrently, outwardly diffusing aluminum (III) ions but not the predominant titanium (IV) ions react with the boron trioxide that forms around the h‐BN basal plane peripheries. Resultant aluminum borate is incorporated into the growing scale and the boron trioxide diffusion barrier is depleted. By this mechanism, the oxidation of h‐BN is maintained at an enhanced rate, until both this material and its oxide completely decompose. Liberated nitrogen from the oxidation of h‐BN can enter the underlying scale as a randomly distributed solute in rutile solid solution. The post‐coating oxide‐atmosphere interface comprises elongated aluminum borate crystallites protruding through at the boundaries between 3–5 at% nitrogen‐doped rutile grains. It differs significantly from that of oxidized, uncoated Ti‐6Al‐4V, which is occupied by a thin α‐alumina layer atop rutile. This interface does not change with an additional 72 h of heat‐treatment.

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Oxidation of boron nitride under nonisothermal conditions

Cited by 17 publications

References 2 publications

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

High‐Temperature Oxidation of Boron Nitride: I, Monolithic Boron Nitride

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Ti‐6Al‐4V

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