Boron carbides: Evidence for molecular level disorder

Tallant, D. R.; Aselage, T. L.; Campbell, A. N.; Emin, David

doi:10.1016/0022-3093(88)90290-6

Cited by 23 publications

(20 citation statements)

References 1 publication

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“…[16][17][18][19][20] Consistent with this assignment, changing the boron isotope produces a large shift in the frequencies of peaks above 600 cm Ϫ1 . This assignment is further supported by the lack of a detectable shift in the high-frequency modes of B 12 O 2 upon changing the isotope of the chains' oxygen atoms, Fig.…”

Section: Resultsmentioning

confidence: 56%

“…The features observed in each of these spectra are similar in appearance to those of previous specimens. [16][17][18]35,36 The sample-dependent Fig. 4, is believed to be due to small amounts of an incompletely reacted boron oxide ͑e.g.,…”

Section: Resultsmentioning

confidence: 99%

“…The Raman spectra of boron carbides have been compared with those of other icosahedral borides. [16][17][18] High-frequency (Ϸ1000 cm Ϫ1 ) features that appear to be common to all icosahedral borides are ascribed [16][17][18][19][20] to vibrations of covalently linked icosahedra, the ubiquitous structural element of icosahedral borides. In particular, the highest-frequency modes are attributed to atoms within the polar sites of one icosahedron vibrating against polar atoms within neighboring icosahedra.…”

Section: Introductionmentioning

confidence: 99%

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Isotope dependencies of Raman spectra ofB12As2,

1997

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The structures of B 12 As 2 , B 12 P 2 , B 12 O 2 , and B 12ϩx C 3Ϫx (0.15ϽxϽ1.65) may each be viewed as composed of B 12 or B 11 C icosahedra and As-As, P-P, O-O, or (C 1Ϫy B y )-B-(C 1Ϫz B z ) intericosahedral chains. The relative stiffnesses of the chain atoms' intrachain and extrachain bonding are probed with Raman spectroscopy by measuring the boron-isotope dependence of the chains' symmetric stretching frequencies. The dependencies of chains' symmetric stretching frequencies on boron mass measures the degree to which icosahedral boron atoms are carried along in the chain atoms' motions. The absence of a measurable boron involvement in these modes for B 12 As 2 and B 12 P 2 indicates that the bonding between the two atoms of their chains is much stiffer than these atoms' bonding to icosahedral boron atoms. By contrast, substantial boron involvement in the symmetricstretch mode of B 12 O 2 indicates much softer bonding of the chain oxygen atoms to one another than to icosahedral boron atoms. The strong boron participation in the boron carbide Raman mode assigned to the symmetric stretch of CBC chains suggests relatively soft bonding between the chain's atoms. The declining intensity of this CBC-chain-stretching mode as x increases from 0.15 toward 1.0 in B 12ϩx C 3Ϫx is consistent with the carbon atoms being removed primarily from chains rather than from icosahedra. Other features of our Raman spectra provide complementary evidence that carbon atoms are preferentially retained in boron carbides' icosahedra rather than in its chains. In particular, strong carbon participation in Raman modes associated with vibrations of icosahedral atoms is observed at all carbon concentrations, 0.15ϽxϽ1.65.

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Section: Resultsmentioning

confidence: 56%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Isotope dependencies of Raman spectra ofB12As2,

1997

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“…13 Within the range of inlet gas compositions studied, the formation of technical grade boron carbide (B 4 C) was observed with carbon content around 17 at%, meaning that the product is within the homogeneity range of single stable phase boron carbide. 14 The formation of carbon, boron and any species (WB, WC) formed by an interaction of boron and carbon species with tungsten was not observed at 11508C, at which the kinetic studies were carried out. In addition to this, the FTIR analysis of the reactor effluent stream showed that BHCl 2 and HCl were formed in the gas phase during the CVD of boron carbide from the BCl 3 , CH 4 , H 2 gas mixture.…”

Section: Resultsmentioning

confidence: 96%

Mechanism studies on CVD of boron carbide from a gas mixture of BCL₃, CH₄, and H₂ in a dual impinging‐jet reactor

et al. 2009

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in Wiley InterScience (www.interscience.wiley.com).Nearly pure boron carbide free from impurities was produced on a tungsten substrate in a dual impinging-jet chemical vapor deposition reactor from a BCl 3 , CH 4 , and H 2 mixture. The Fourier Transform Infrared (FTIR) analysis proved the formation of reaction intermediate BHCl 2 , which is proposed to occur mainly in the gaseous boundary layer next to the substrate surface. Among a large number of reaction mechanisms proposed only the ones considering the molecular adsorption of boron carbide on the substrate surface gave reasonable fits. In the proposed mechanism dichloroborane is formed in the gas phase only as a by-product. Boron carbide, on the other hand, is formed through a series of surface reactions involving adsorbed boron trichloride, adsorbed methane and gas phase hydrogen. The simultaneous fit of the experimental rate data to the model expressions gave correlation coefficient values of 0.977 and 0.948, in predicting the B 4 C and BHCl 2 formation rates, respectively. 2009 American Institute of Chemical Engineers AIChE J, 55: 701-709, 2009

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“…As noted in Section 3.4.2, Raman spectra can provide useful qualitative indications of sample stoichiometry [19]. Near carbon-free B 4 C calcined from PV6-1-550 PVAcB powder shows a consistent intensity of the peaks at 270 cm -1 and 320 cm -1 over all…”

Section: Residual Carbonmentioning

confidence: 99%

In-Situ Carbon Control in the Preparation of Precursors to Boron Carbide by a Non-Aqueous Solution Technique

Watts¹,

C.Talbot²,

Alarco³

2015

JMSE-A

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Synthesis of high quality boron carbide (B 4 C) powders is achieved by carbothermal reduction of boron oxide (B 2 O 3 ) from a condensed boric acid (H 3 BO 3 )/polyvinyl acetate (PVAc) product. Precursor solutions are prepared via free radical polymerisation of vinyl acetate (VA) monomer in methanol in the presence of dissolved H 3 BO 3 . A condensed product is then formed by flash evaporation under vacuum. As excess VA monomer is removed at the evaporation step, the polymerisation time is used to manage availability of carbon for reaction. This control of carbon facilitates dispersion of H 3 BO 3 in solution due to the presence of residual VA monomer. B 4 C powders with very low residual carbon are formed at temperatures as low as 1,250 °C with a 4 hour residence time.

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Boron carbides: Evidence for molecular level disorder

Cited by 23 publications

References 1 publication

Isotope dependencies of Raman spectra ofB12As2,

Isotope dependencies of Raman spectra ofB12As2,

Mechanism studies on CVD of boron carbide from a gas mixture of BCL₃, CH₄, and H₂ in a dual impinging‐jet reactor

In-Situ Carbon Control in the Preparation of Precursors to Boron Carbide by a Non-Aqueous Solution Technique

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Boron carbides: Evidence for molecular level disorder

Cited by 23 publications

References 1 publication

Isotope dependencies of Raman spectra ofB12As2,

Isotope dependencies of Raman spectra ofB12As2,

Mechanism studies on CVD of boron carbide from a gas mixture of BCL3, CH4, and H2 in a dual impinging‐jet reactor

In-Situ Carbon Control in the Preparation of Precursors to Boron Carbide by a Non-Aqueous Solution Technique

Contact Info

Product

Resources

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Mechanism studies on CVD of boron carbide from a gas mixture of BCL₃, CH₄, and H₂ in a dual impinging‐jet reactor