Plasma synthesized doped boron nanopowder for magnesium diboride superconductors

描述(由申请人提供)：二硼化镁(MgB2)的受控化学掺杂已被证明可显著提高超导性能，达到高场磁体所需的水平，但通过通常的固态反应和扩散途径很难实现稳定的掺杂浓度和均匀性。此外，需要建立一个高质量的掺硼来源，以提高技术水平，并最终实现MgB2超导体的商业化。将掺杂剂和硼原子混合在等离子体中的气相等离子体合成硼粉将产生纳米级的掺杂硼粉。初步实验证明，采用等离子体合成方法可以制备出适合于制备高性能的MgB_2导体的掺碳硼粉。在20K时，2T时的临界电流密度为10万A/cm~2；在5K时，4~5T时的临界电流密度为10万A/cm~2。获得了高达37特斯拉的高临界磁场(Hc2)。在第一阶段，将进行碳、钛和碳化硅作为添加剂添加到硼粉中的研究，以改善上述性能。将等离子体合成方法应用于粉末生产，考察了掺杂化学成分和掺杂浓度对粉末性能的影响。将掺杂的硼粉转化为硼化镁超导颗粒和管内粉末线材，并对其超导性能进行测试。研究了粉末粒度、纯度、掺杂浓度和化学均匀度对硼化镁超导性能的影响。化学掺杂的二硼化镁(MgB_2)超导磁体在高场强磁场中的性能至少可以达到NbTi和NbSn3的水平，但在工作温度方面仍优于后者。这些特性使掺杂的硼化镁成为一种有效的医用核磁共振器件材料。更便宜、更高效的医用核磁共振设备可以降低检查成本，更早发现潜在的健康问题，从而造福整个社会。

DESCRIPTION (provided by applicant): Controlled chemical doping of magnesium diboride (MgB2) has been shown to substantially improve superconducting properties to the levels required for high field magnets, but consistent dopant concentrations and homogeneity are difficult to accomplish through the usual route of solid state reaction and diffusion. Furthermore, a high quality source of doped boron needs to be established to advance the state of the art and to ultimately commercialize MgB2 superconductors. Gas phase plasma synthesis of boron powder in which dopants and boron are atomically mixed in the plasma will produce nano-sized batches of doped boron powder. Initial experiments using plasma synthesis methods proved satisfactory to prepare carbon-doped boron powders suitable for the fabrication of high performance MgB2 conductors. At 20 K, critical current density (Jc) values of 100,000 A/cm2 were obtained at 2 Tesla and at 5 K, Jc values of 100,000 A/cm2 were obtained at 4-5 Tesla. Upper critical magnetic field (Hc2) values as high as 37 tesla were achieved. In Phase I, an investigation of carbon, titanium, and silicon carbide as dopant additions to boron powder will be carried out to improve on the above properties. The plasma synthesis method will be used for powder production and the effect of dopant chemistry and concentration on the properties of boron powder will be examined. Doped boron powder will be converted to MgB2 superconducting pellets and powder-in-tube wires, and the superconducting properties will be measured. The effect of powder particle size, purity, dopant concentration, and chemical homogeneity on the superconducting properties of MgB2 will be investigated. Chemically doped magnesium diboride (MgB2) superconducting magnets can perform at least as well as NbTi and NbSn3 in high field magnetic fields and still offer an improvement over the latter in terms of operating temperature. These characteristics make doped MgB2 an effective material for medical MRI devices. Cheaper and more efficient medical MRI devices could lower examination costs, find potential health problems earlier, and thus benefit society as a whole.