排序方式: 共有36条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
A new polyoxometalate dimer based on lacunary Wells-Dawson anion and lanthanide cation, Na14[{Nd(H2O)3 (α2-PeWt7O61)2]·17H2O, was isolated as a sodium salt under ambient conditions and characterized by IR, TG, and X-ray single crystal structure analysis and electrochemistry. It belonged to the triclinic, space group Pi with a=1.26738 (15) nm, b=1.41464 (17) nm, c=2.3254 (4) nm, α=103.142 (2)°, β = 95.122 (2)°, γ=113.9690 (10)°, V=3.6317 (8)nm^3, Z=2, Dc=4.274 mg/m^3, and μ=27.695 mm^-1. The Nd^3+ ion was substituted for a [W=O]^4+ unit in the "cap" site of the tungsten-oxygen framework of the parent Wells-Dawson ion. The cyclic voltammograms of the title compound exhibited nearly chemically reversible one-step one-electron transfer process and two-step irreversible reduction processes. Thermogravimetric showed a one-step slow weight loss stage in the range of 25-850 ℃. 相似文献
36.
采用原位热压烧结工艺, 以Cr3C2 、Cr和Al粉为原料制备Cr2AlC块体材料. 采用X射线和扫描电镜(SEM)对制备的样品进行表征. 利用差热法对反应过程进行了研究, 以失重法研究Cr2AlC在酸和碱溶液中的腐蚀性能. 结果表明, 以n(Cr3C2)∶n(Cr)∶n(Al)=0.5∶0.5∶1.2配比, 1350℃, 30MPa压力热压2h得到高纯Cr2AlC块体, 其合成过程首先为Al的溶化, 在700℃时Cr与Al生成Cr5Al8, 最后Cr5Al8与Cr3C2反应生成Cr2AlC. 样品断面的扫描照片显示, 烧结试样呈板状和片状结晶形貌特征, 平均粒径为6.4μm. 除在浓H2SO4和浓HCl中失重较大外, Cr2AlC在其它溶液中均表现较低的失重. 样品浸泡在浓和稀的NaOH溶液150d几乎没有质量损失, 腐蚀率仅为0.4和0.7μm/a. 相似文献