Mechanosynthesis of YIG and GdIG: A Structural and Mössbauer Study

We have investigated the mechanosynthesis of gadolinium and yttrium iron garnets by high-energy ball-milling of α-Fe₂O₃ and Gd₂O₃ or α-Fe₂O₃ and Y₂O₃, respectively, followed by short thermal annealings conducted at moderate temperatures. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, in order to determine the influence of the milling time and annealing conditions on the final products. For as-milled samples of each rare-earth system, the results revealed the formation of perovskite phases, in relative amounts that depend on the milling time. The formation of garnet phases was observed in as-annealed samples treated at 1000°C for 2 h or 1100°C for 3 h, i.e., at very modest annealing requirements when compared with ordinary solid-state-reaction processes performed without previous high-energy milling. Also, the occurrence was verified of a milling time for which the relative amount of garnet phases formed by annealing was maximized. This time depends on the rare-earth composing the garnet phase and on the annealing temperature.     

Gravitational collapse of a charged and radiating fluid ball in the diffusion limit

The collapse of a charged and radiating ball in the diffusion limit is studied using a method reported by Herrera and collaborators. The interior solution is matched with the exterior Reissner-Nordström-Vaidya metric to obtain a system of differential equations at the surface of the distribution, which can be integrated numerically for some set of initial data. For one model, the profiles of the physical variables are obtained at any piece of the material in terms of Schwarzschild-like coordinates.     

Chemical synthesis of p-type nanocrystalline copper selenide thin films for heterojunction solar cells

Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu_2−xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm² light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.     

KMnO4引发魔芋粉-丙烯腈的接枝共聚反应

以KMnO4为引发剂进行魔芋粉与丙烯腈的接枝共聚反应。研究了魔芋粉预氧化时间、引发剂浓度、单体浓度、酸度、反应时间、反应温度和反应物加料方式等聚合条件对接枝效率的影响，并对接枝机理作了探讨。     

双邻苯二酚锑二甲基羟乙铵的晶体结构

含锑配合物是治疗血吸虫病、肿瘤等的常用药物,我们曾对双邻苯二酚锑二乙基羟乙胺进行了晶体结构测定,本文简要报导双邻苯二酚锑二甲基羟乙胺的结构.锑化合物的制法与其二乙基羟乙铵衍生物类似.产物为淡黄色晶体,它在水溶液中长时间放置会变成紫黑色,因此,制得的晶体须立即用丙酮溶解进行重结晶.晶体的密度为1.667g/cm~3.按C_(16)H_(20)O_5NSb的元素分析结果(％)如下:Sb 28.3(28.5),C 43.9(44.9),N 3.3(3.3),H 4.7(4.7).括号内为理论值.     

N—BOC—8—氨甲基—2—萘甲酸的改进合成法

以２－萘甲酸为原料，经硝化，酯化，重氮化，选择性催化氢化，ＢＯＣ酸酐保护等六步反应，完成了Ｎ－ＢＯＣ－８氨甲基－２－萘甲酸（１ａ）的合成，为化合物１的合成提供了新的合成途径。     

甲烷在二元碱土金属复合体系催化剂上的氧化偶联

碱土金属氧化物或碳酸盐为多种类型甲烷氧化偶联制取C_2烃催化剂的重要组分之一.有关纯碱土金属氧化物及含氧酸盐的研究表明,这类化合物具有较强的表面碱性及高温P型半导性而对活化甲烷生成C_2烃有较高活性,关于不同碱土金属化合物之间混合形成的二元碱土金属复合体系催化剂的报导仍不多见,Aika等人曾报导用BaO与CaO或MgO混合的催化剂上在1073K时可以获得61.1%C_2烃选择性和14.2%的C_2烃收率,但BaO易在反应条件下与水反应生成Ba(OH)_2而腐蚀器壁,不利于长期操作.本文报导了一系列不同碱土金属化合物之间形成的二元碱土复合体系催化剂上甲烷氧化偶联的反应结果.结果表明,这类催化剂由于其结构稳定、活性好而值得进一步研究.     

Crystal Structure and Characterization of a Large Polyoxotungstate (NH4)21{La(H2O)5[Ni(H2O)]2As4W40O140}·53H2O

The heteropolytungstate (NH4)₂₁{La(H₂O)₅[Ni(H₂O)]₂As₄W₄₀O₁₄₀}·53H₂O is obtained by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀]· 60H₂O with NiCl₂·6H₂O, La(NO₃)₃·6H₂O and NH₄Cl at pH‐4.5. The structure and chemical composition are determined by X‐ray diffraction analysis and elemental analysis. The crystal data and main structure refinement are a = 1.9551(3) nm, b = 2.4156(4) nm, c= 3.7068(6) nm, β = 91.505(3)°, V = 17.500 (5) nm³, monoclinic crystal system with space group P2₁/n, Z = 4, R₁ = 0.0573, wR₂ = 0.0717 [I >2<s?(I)], R₁, = 0.2463 and wR₂ = 0.1199 (all data). [La(H₂O)₅] {Ni(H₂O)}₂AS₄W₄₀O₁₄₀ has C₂, symmetry. IR spectra of the ligand [NaAs₄W₄₀O₁₄₀]^27‐ and its three complexes were discussed.