Shahabuddin Mohammed, Madhar Niyaz Ahamad, Alzayed Nasser S, Asif Mohammad
Department of Physics and Astronomy, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia.
Department of Chemical Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia.
Materials (Basel). 2019 Sep 19;12(18):3044. doi: 10.3390/ma12183044.
We developed a novel yet commercially viable strategy of synthesizing superior high-T superconducting composites by dispersing fully exfoliated carbon nanotubes (CNTs) uniformly throughout the grain of CNT-MgB composites. First, we optimized the amount of the surfactant required to produce a highly stable and homogeneous colloidal suspension of CNTs. This amount was found to be 1/8th of the amount of CNTs. Second, we prepared a homogeneous CNT-B mixture by adding amorphous nano-boron (B) to the colloidal CNT suspension. Next, two different MgB synthesis routes were explored. In one case, we mixed an appropriate amount of Mg in the CNT-B mixture and carried out sintering. In the second case, the CNT-B mixture was heat treated at 500 °C, prior to mixing with Mg and sintering to form CNT-MgB. Both kinds of samples were rigorously characterized to obtain an insight into their properties. The direct synthesis route shows a clear exfoliation and uniform dispersion of CNTs with a critical current density (J) of 10 A/cm at 3.5 T and 20 K, which is useful for the application in magnetic resonance imaging MRI magnet operating with a cryogen free cooler. Our J(H) result is 10 times higher than that of the pure sample. By contrast, the performance of the sample subjected to heat processing before sintering was severely compromised given the formation of MgO. Despite its simplicity, the direct synthesis route can be used for the cost-effective fabrication of CNT-MgB superconducting composites.
我们开发了一种新颖且具有商业可行性的策略，通过将完全剥离的碳纳米管（CNT）均匀分散在CNT-MgB复合材料的晶粒中来合成优质的高温超导复合材料。首先，我们优化了制备高度稳定且均匀的CNT胶体悬浮液所需的表面活性剂用量。发现该用量为CNT用量的1/8。其次，我们通过向CNT胶体悬浮液中添加非晶态纳米硼（B）制备了均匀的CNT-B混合物。接下来，探索了两种不同的MgB合成路线。在一种情况下，我们在CNT-B混合物中混合适量的Mg并进行烧结。在第二种情况下，在与Mg混合并烧结以形成CNT-MgB之前，将CNT-B混合物在500°C下进行热处理。对这两种样品都进行了严格表征，以深入了解它们的性能。直接合成路线显示出CNT的明显剥离和均匀分散，在3.5 T和20 K时的临界电流密度（J）为10 A/cm²，这对于在使用无低温冷却器运行的磁共振成像（MRI）磁体中的应用很有用。我们的J(H)结果比纯样品高10倍。相比之下，由于形成了MgO，烧结前经过热处理的样品性能严重受损。尽管直接合成路线很简单，但可用于经济高效地制造CNT-MgB超导复合材料。
