A New Modification of Elemental Boron

Talley, Claude P.; Post, B.; LaPlaca, S. J.

doi:10.1007/978-1-4899-6572-1_11

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…The first stage, the low temperature stage where a solid boron particle is coated with a liquid oxide layer, involved modeling of the regression rate of the boron oxide layer due to diffusion controlled 3 reaction at the solid particle surface and vaporization of the oxide to the atmosphere. The steady state condition of this model successfully predicted the ignition temperature that both Talley [ 19] and Macek and Semple [14] had found experimentally. The second stage of combustion was the high temperature combustion process, where the boron has liquefied and the oxide layer has evaporated.…”

Section: Physical Modeling Researchsupporting

confidence: 55%

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Shock initiation of crystalline boron in oxygen and fluorine compounds

Krier

Burton

Pirman

et al. 1996

Journal of Propulsion and Power

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Section: Physical Modeling Researchsupporting

confidence: 55%

“…Talley [19]. The method of his experiments was to heat cylindrical boron rods 1 mm in diameter in a stream of pure oxygen using electrical resistance within the rod.…”

Section: Resultsmentioning

confidence: 99%

Shock initiation of crystalline boron in oxygen and fluorine compounds

Krier

Burton

Pirman

et al. 1996

Journal of Propulsion and Power

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“…6 suggest that at temperatures above 300' C sheath diffusion may indeed become the limiting process during oxidation processing. Possible reasons for this include an oxide diffusion rate which increases more rapidly with temperature than sheath diffusion and/or a continuous removal of the oxide layer itself due to gravity-induced flow and higher volitility (14). Thus the empirical guidelines of Fig. 14 may just be a reflection of the fact that formation of the near-core flaw during oxidation processing can best be avoided by using thermal conditions which allow boron atom removal at the surface to be more rapid than boron atom removal from the coresheath interface.…”

Section: Fiber Strengthmentioning

confidence: 99%

Oxidation-Induced Contraction and Strengthening of Boron Fibers

DiCarlo¹,

Wagner²

Ceramic Engineering and Science Proceedings

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In terms of impact resistance, the practical advantage of the combined use of the impure argon and etch treatments becomes evident when one realizes that by raising fiber tensile strengths to 5.5 GN/m 2 (800 ksi), the tensile work of fracture is improved to more than twice that of the as produced fiber. The fact that the CVD sheath has shown strength potential over 6.9 GN/m2 (1000 ksi) indicates the possibility for still further improvement if the formation mechanisms for the new sheath flaws could be understood and possibly avoided. Thus the objectives of this study were to 3 measure and understand the physical and mechanical effects of heat treating boron fibers in impure argon gas so that this treatment method might be optimized as a secondary processing technique for boron fiber strength improvement. Although no definite identification of the impurity gas responsible for contraction was obtained in previous work, the recent results from ti the boron fiber contraction study of Wawner, et al. (7) pointed to oxygen as the most likely impurity. For this reason the approach taken here was to broaden the impure argon studies by also measuring the effects of heat treating fibers in oxygen-argon gaseous mixtures containing much higher and better controlled oxygen contents. It will be shown that although the high oxygen approach did not achieve any additional strengthening for temperatures below 900° C, it did aid in clarifying the physical processes that occurred during treatment and by so doing also indicated possible processing conditions for further strength improvement. EXPERIMENTAL PROCEDUREThe specimens used in this study were 203 um (8 mil) diameter fibers commercially supplied by Avco Specialty Materials Division. These fibers were produced in a single stage CVD reactor by the iiydregen reduction of boron trichloride on a 13 um (0.5 mil) diameter tungsten wire substrate.Deposition temperatures were maintained near 1300' C by do resistance heating augmented by very high frequency heating (8). During deposition the substrate became completely borided to form a 17 um diameter tungsten boride core. From previous studies (4,5) it was determined that the 203 um boron fiber produced in the above manner is excellent material for achieving strengthening by core compression because in the as-received condition the probability for observing core-initiated fracture after a slight surface etch is essentially 100 percent. 4The apparatus employed for the oxidation-contraction studies is shown schematically in Fig. 1. It is a glass column, similar to a commercial CVD reactor, in which a static fiber is resistance heated within a controlled gaseous environment. Water-cooled stainless steel caps at each end of a 2.5 cm diameter pyrex tube contained inlet and outlet gas ports and mercury seals for electrical contact to the boron sheath. Prior to insertion in the reactor, each fiber was wiped with methanol to remove any existing boron oxide layers. Within the reactor the fiber was clamped above the top end cap and subjected to ...

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Crystal Chemistry of Boron and of Some Boron-Rich Phases; Preparation of Boron Modifications

Naslain¹

1977

Boron and Refractory Borides

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A New Modification of Elemental Boron

Cited by 3 publications

References 6 publications

Shock initiation of crystalline boron in oxygen and fluorine compounds

Shock initiation of crystalline boron in oxygen and fluorine compounds

Oxidation-Induced Contraction and Strengthening of Boron Fibers

Crystal Chemistry of Boron and of Some Boron-Rich Phases; Preparation of Boron Modifications

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