A more general structural model which includes the induction time for gas-solid reactions-II. The kinetics of alpha-boron nitride oxidation

Shieh, M.D.; Lee, C.

doi:10.1016/0009-2509(93)80355-t

Cited by 10 publications

(1 citation statement)

References 15 publications

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“…This increase in oxygen content in the BNNTs is accompanied by a change in the B/N atomic ratio from 1.32:1 for MWCNT@BNNTs to 1.67:1 for BNNTs, which is an inflated bias toward B. This is in keeping with the preferential substitution of O at N vacancy sites instead of B sites because of a more similar electronegativity of O with N. , Further, N oxidation product, N 2 , is more easily volatilized than B oxidation product, B 2 O 3 . ,− …”

Section: Resultsmentioning

confidence: 94%

Thermal Conductivity of Carbon/Boron Nitride Heteronanotube and Boron Nitride Nanotube Buckypapers: Implications for Thermal Management Composites

Jones

Gonzalez‐Munoz

Griffiths

et al. 2023

ACS Appl. Nano Mater.

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To date, there has been limited reporting on the fabrication and properties of macroscopic sheet assemblies (specifically buckypapers) composed of carbon/boron nitride core–shell heteronanotubes (MWCNT@BNNT) or boron nitride nanotubes (BNNTs). Herein we report the synthesis of MWCNT@BNNTs via a facile method involving Atmospheric Pressure Chemical Vapor Deposition (APCVD) and the safe h-BN precursor ammonia borane. These MWCNT@BNNTs were used as sacrificial templates for BNNT synthesis by thermal oxidation of the core carbon. Buckypaper fabrication was facilitated by facile sonication and filtration steps. To test the thermal conductivity properties of these new buckypapers, in the interest of thermal management applications, we have developed a novel technique of advanced scanning thermal microscopy (SThM) that we call piercing SThM (pSThM). Our measurements show a 14% increase in thermal conductivity of the MWCNT@BNNT buckypaper relative to a control multiwalled carbon nanotube (MWCNT) buckypaper. Meanwhile, our BNNT buckypaper exhibited approximately half the thermal conductivity of the MWCNT control, which we attribute to the turbostratic quality of our BNNTs. To the best of our knowledge, this work achieves the first thermal conductivity measurement of a MWCNT@BNNT buckypaper and of a BNNT buckypaper composed of BNNTs not synthesized by high energy techniques.

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Section: Resultsmentioning

confidence: 94%

Thermal Conductivity of Carbon/Boron Nitride Heteronanotube and Boron Nitride Nanotube Buckypapers: Implications for Thermal Management Composites

Jones

Gonzalez‐Munoz

Griffiths

et al. 2023

ACS Appl. Nano Mater.

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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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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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A more general structural model which includes the induction time for gas-solid reactions-II. The kinetics of alpha-boron nitride oxidation

Cited by 10 publications

References 15 publications

Thermal Conductivity of Carbon/Boron Nitride Heteronanotube and Boron Nitride Nanotube Buckypapers: Implications for Thermal Management Composites

Thermal Conductivity of Carbon/Boron Nitride Heteronanotube and Boron Nitride Nanotube Buckypapers: Implications for Thermal Management Composites

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: Ti‐6Al‐4V

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