碳纳米管掺杂MgB2的磁通钉扎特性

利用固相反应法制备了按不同质量比掺杂CNTs的MgB2超导材料.10 K时,1%掺杂量的样品在零场下Jc=1.89× Acm-2,不可逆场为6.9 T,退火以后样品的不可逆场提高到7.5 T.20 K时,0.5%掺杂量的样品在零场下Jc=1.15× Acm-2,不可逆场为4 T.样品的钉扎作用主要来自晶粒间的晶面钉扎作用.     

简便的双环化反应合成3,7-二甲基-4a,16-二羟基-1H-苯并[5,6]茚并[2,1-l]氧杂蒽-1,9-二酮化合物及其结构表征

标题化合物C26H26O5以2,3-萘二甲醛和5-甲基-1,3-环己二酮为原料,在醋酸溶剂中,室温下经搅拌多组分一锅法合成得到.其结构通过单晶X-射线衍射法确定,晶体属单斜晶系,空间群P21,相对分子质量Mr=418.47,晶胞参数a=0.990 04(8)nm,b=1.090 98(9)nm,c=1.042 46(11)nm,V=1.087 53(17)nm3,Z=2,晶胞密度Dc=1.278g/cm3,吸收系数μ=0.088mm-1,单胞中电子的数目F(000)=444.晶体结构用直接法解出,经全矩阵最小二乘法对原子参数进行修正,最终的偏离因子为R1=0.053 3,wR2=0.129 3.在晶体结构中新形成的吡喃环为半椅式构象,而茚中五元环则为信封式构象.     

柠檬酸用量对碳纳米管制备的影响

Carbon nanotubes (CNTs) were prepared by chemical vapor catalytic deposition using the catalyst prepared by citric acid complexometry. The effect of the dosage of citric acid on the CNTs yield and morphologywas studied. The transmission electron microscopy and X-ray diffraction were used to characterize CNTs morphology and crystal structures of the catalysts, respectively. The results show that the dosage of citric acid can greatly affect the CNTs yield and morphology: the CNTs have a high yield about 1 345.8% (1 h) at a 2∶1 molar ratio of citric acid and metal ion, and the obtained CNTs diameter is relatively narrow distributed (25～30 nm); when themolar ratio of citric acidto metal ion is 3∶1, the CNTs yield is about 407.2% (1 h), and the obtained CNTs diameter is relatively wide distributed (25～50 nm), moreover, the CNTs is more rough than that obtained with 2∶1 molar ratio of citric acid to metal ion.