Argon boron carbides

MacKinnon and Wickens (37) have prepared boron carbide in the form of submicron particles by injecting BCI3, Hg, and CH into the tail of a 20-kW argon RF plasma. A 3 factorial experiment to study the effect of operating variables was carried out a preliminary analysis of which gave the following indications ... 

Figure 7—92. Thermal ICP reactor for boron carbide produetion by BCI3 eonversion in hydrocarbon plasma (1) RF generator, (2) discharge chamber, (3) argon injection system, (4) RF inductor, (5) water-cooling system, (6) distributor of reagents.

Which of the following materials could be classified as a ceramic. Justify your answer, (a) Solid argon (Ar) (b) molybdenum disilicide (MoSi2) (c) NaCl (d) crystalline sulfur (S) (e) ice (f) boron carbide (B4C). 

Figure 11.3 Results of pressureless sintering of boron carbide of different stoichiometric compositions (green density 60%, 1 h soaking time at final temperature, 1 bar argon atmosphere). The numbers in italics refer to percentage theoretical density.

Ma and Bando reported a systemic investigation of the growth of boron carbide nanowires via a vapor-liquid-solid mechanism. A template- and catalyst-free carbothennal route of nanowire production has been employed with boron powder, boron oxide, and carbon black, mixed in a 2 1 1 ratio, as the precursor. The component mixture was subjected to 1650°C temperature for 2 h under an argon flow inside a high-frequency induction furnace and resulted in boron carbide nanowires of diameters ranging from 50 to 200 nm (Figure 20.17b). 

In a method described by Wei et al., boron carbide nanorods were prepared from carbon nanotubes. Carbon nanotubes, mixed with boron powder in 1 4 atomic ratio, was heated up to 1150°C under argon gas. The as-grown structure varied from that of the parent nanotubes. They were found to be straight with occasional bents (Figure 20.18a), contrary to the tubular structure of the CNTs. The length of the nanorods corresponded to that of the nanotubes, while the diameters of than were slightly larger. 

For the adsorption of argon on boron carbide, Knowles and Moffat [182] found that the application of the BET theory gave more consistent results using liquid aigon pressure rather than the solid-vapor pressure. 

The process is effectively stimnlated by argon heated up inside of the RF-ICP discharge and takes place downstream from the thermal discharge, where reactive gases are injected into argon (Tumanov, 1981 see Fig. 7-92). The yield achieved by the process is 93-95%, the composition of the boron chloride is close to a stoichiometric value Bs gC, the size of the produced particles is 200-300 nm, and the particles color varies from gray to black depending on the fraction of carbon in the carbide. 

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