Preparation and Properties of ${\hbox {Mg}}({\hbox {B}}_{1-{\rm x}}{\hbox {C}}_{\rm x})_{2}$ Using Carbon Chemical Vapor Coated Boron

Promising initial results on bulk Mg(B_1-xC_x)₂ prepared with carbon doped boron are presented. Carbon doping is achieved by reaction of ethylene gas on boron powder using a stainless steel tube furnace, a technique suitable for industrial scale processing. The nominal amount of doping was controlled by varying the reaction time with a fixed volume of ethylene gas, and the actual carbon uptake was determined by weight change after the reaction. The amount of carbon substitution x in the Mg(B_1-xC_x)₂ was found using the angular shift in the (100) X-ray reflection. Carbon substitution by the full nominal content in the C doped precursor boron was obtained for doping up to 7.2 at%, as shown by a o-axis compression consistent with that of carbon doped single crystals. The critical current density of the 4 at% C doped sample for temperatures at 20-30 K and fields up to 4 T, relevant to high temperature applications, was significantly higher than those in the published literature. The J_C of a 10 wt% nano-SiC doped sample, used as a comparative benchmark, was found to be lower than the C doped sample at field below 2 T, but to reduce slower at higher fields. Structure analysis of the SiC doped sample revealed a coexistence of two C substitution levels of 2.25% at and 5.25% at.