树脂芯助焊剂性能的基础研究

焊锡丝主要应用于仪器、仪表、各种家用电器等的焊接、补焊以及维修,而其焊接质量的好坏不仅取决于焊锡丝的合金材料,更取决于其树脂芯助焊剂的性能,通过大量的实验对影响其性能的因素进行了分析,并对可焊性进行测试,从而制备出诸如卤素含量低,扩展率好等综合性能优良的树脂芯助焊剂.     

Syntheses and molecular structures of four inorganic–organic hybrid compounds from N-containing aromatic bases and perchlorometallates of Zn,Cu, Sn,and Fe

Four organic–inorganic crystals, [(HL1)₂(ZnCl₄)]·H₂O (1) (L1?=?2-methylquinoline), [(HL1)₂(CuCl₄)] (2), [(HL2)₂SnCl₆] (3) (L2?=?6-bromobenzo[d]thiazol-2-amine), and [(HL3)FeCl₄] (4) (L3?=?5,7-dimethyl-1,8-naphthyridine-2-amine), derived from N-containing aromatic Brønsted bases and metal(II) chlorides (zinc(II) chloride, copper(II) chloride dihydrate, tin(II) chloride dihydrate, and iron(III) chloride hexahydrate) were prepared at room temperature and characterized by IR, X-ray structure analysis, elemental analysis, and TG analysis. The crystals are built up by perchlorometallates (Zn, Cu, Sn, and Fe) associated with organic cations through multiple non-covalent associations. X-ray diffraction analysis reveals that 1 and 2 have 3-D network structures built from hydrogen bonds between the cations and chlorometallates. Water molecules play an important role in structure extension in 1. Anhydrous 3 and 4 produced from 2-aminoheterocyclic derivatives display 2-D sheet structures. Arrangements of anions and cations are dominated by shape and size of cations, and also by the different structures of the chlorometallates as well as non-bonding interactions in the crystal structures. Except for 1, the other compounds are thermally stable below 240°C.     

Cerium oxide stoichiometry alteration via Sn deposition: Influence of temperature

Cerium oxide layers grown on Cu(1 1 1) were studied by conventional X-ray and resonant photoelectron spectroscopy with synchrotron radiation. A quantitative method of determining the cerium chemical state from the Ce 3d photoelectron spectra is described in detail. After the preparation of the ceria layer, Sn films of different thickness were evaporated onto the surface at temperatures of 120, 300 and 520 K. In all three cases, the deposited Sn was oxidized, CeO₂ was partially reduced, and a mixed Sn–Ce–O oxide was formed. The quantitative extent of these reactions was found to be determined by limited diffusion of the deposited Sn atoms into the ceria layer at low temperature. The excess of tin formed a metallic overlayer on the sample surface.     

Complexes of Tin(IV) Tetrachloride with 3-Formylpyridine Semicarbazone and Thiosemicarbazones

The reaction of tin(IV) tetrachloride with 3-formylpyridine semicarbazone and different 3-formylpyridine thiosemicarbazones produces [Sn(HL)CL 3 ][SnCl 5 ] where HL stands for the neutral ligand. The tin(IV) complexes were characterized using a variety of spectroscopic techniques. Coordination through the pyridine nitrogen occurs in all cases. Solvation studies in DMSO indicated that dissociation of the ligands and their complete replacement by solvent molecules occurs.     

Studies on Biologically Potent Tetraazamacrocyclic Complexes of Bivalent Tin

Fourteen- to eighteen-membered tetraamide macrocyclic ligands N 4 L 1 -N 4 L 4 have been prepared by the condensation of 1,2-diaminoethane or 1,3-diaminopropane with malonic or succinic acid in the presence of condensing reagents dicyclohexylcarbodiimide and 4-dimethylaminopyridine. On reduction, these macrocyclic ligands give a new series of tetraazamacrocycles MacL 1 -MacL 4 which form complexes with tin(II) chloride. The ligands and their complexes were characterized by elemental analyses, molecular weight determinations, infrared and 1 H NMR spectral studies. The hexacoordinated state for tin has been confirmed by spectral studies. An octahedral geometry for these complexes has been proposed as the binding sites are the nitrogen atoms of the macrocycles. On the basis of the chemical composition the representation of the complexes as [Sn(MacL n )Cl 2 ] (n = 1-4) has been established. The ligands and their complexes also have been screened for their antifungal and antibacterial activities and the findings have been reported and explained.     

Tin-rich Phases RE2Au3Sn6 with RE = La,Ce, Pr,Nd, Sm – Synthesis,Structure, Magnetic Properties,and 119Sn Mössbauer Spectra

The stannides RE₂Au₃Sn₆ (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements by arc-melting. Small single crystals were grown by annealing samples in sealed tantalum tubes in an induction furnace with a special annealing sequence. The polycrystalline phases were characterized through their X-ray powder diffraction pattern. The structures of Ce₂Au₃Sn₆, Pr₂Au₃Sn₆, and Nd₂Au₃Sn₆ were refined from single-crystal X-ray diffractometer data. The RE₂Au₃Sn₆ stannides crystallize with the orthorhombic La₂Zn₃Ge₆ type, space group Cmcm. The basic structural building units are Au1@Sn₄ tetrahedra and Au2@Sn₅ square pyramids. These units are condensed to layers and the structure can be described by a simple stacking of tetrahedral and pyramidal layers with the rare earth cations in between. Temperature dependent susceptibility studies indicate that all rare earth atoms are in the trivalent oxidation state, as their effective magnetic moments match the expected values of the free RE³⁺ ions. Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ exhibit antiferromagnetic ordering at T_N = 6.3(1) and 6.7(1) K. Investigations of the electrical resistivity of La₂Au₃Sn₆ and Ce₂Au₃Sn₆ confirmed that these compounds are metallic, for La₂Au₃Sn₆ a lower resistivity was observed, in line with the absence of screening unpaired electrons. ¹¹⁹Sn Mössbauer spectra for La₂Au₃Sn₆, Ce₂Au₃Sn₆, Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ show a complex superposition of three sub-spectra which can be differentiated through their distinctly different quadrupole splitting parameters. The isomer shifts (1.87 to 2.22 mm · s^–1) indicate significant s electron density at the tin nuclei.     

元器件纯锡镀层表面晶须风险评估与对策

讨论了各种锡晶须的形态以及其长度的具体测量方法,并在试验研究的基础上进一步分析抑制非光滑(哑光)纯锡镀层上锡晶须生长的对策.研究结果表明,增加锡镀层厚度(＞7 μm),或通过使用添加剂来产生更加粗糙的表面以适当增大晶粒尺寸,电镀完成后及时进行退火程序是进一步减轻雾锡镀层上锡晶须困扰的有效手段.如果引入Ni作为中间镀层,则需要达到一定的厚度(估计＞0.7 μm),方可达到预期的效果.     

Fast algorithms for placing large entries along the diagonal of a sparse matrix

Solving a sparse system of linear equations Ax=b is one of the most fundamental operations inside any circuit simulator. The equations/rows in the matrix A are often rearranged/permuted before factorization and applying direct or iterative methods to obtain the solution. Permuting the rows of the matrix A so that the entries with large absolute values lie on the diagonal has several advantages like better numerical stability for direct methods (e.g., Gaussian elimination) and faster convergence for indirect methods (such as the Jacobi method). Duff (2009) [3] has formulated this as a weighted bipartite matching problem (the MC64 algorithm). In this paper we improve the performance of the MC64 algorithm with a new labeling technique which improves the asymptotic complexity of updating dual variables from O(|V|+|E|) to O(|V|), where |V| is the order of the matrix A and |E| is the number of non-zeros. Experimental results from using the new algorithm, when benchmarked with both industry benchmarks and UFL sparse matrix collection, are very promising. Our algorithm is more than 60 times faster (than Duff’s algorithm) for sparse matrices with at least a million non-zeros.     

Electronic properties of nanocrystalline tin oxide dispersed in monolithic mesoporous silica

This paper is devoted to the study of the electrical properties of nanocrystalline tin oxide dispersed in the mesoporous silica. By immersing the silica in precursor solutions with different concentrations and heat-treatment, different samples were obtained. With precursor concentrations increasing from 0.1 to 4.0 M, the resistivities of the samples decrease from 3.15×10⁶ to 2.43×10³ Ω cm. The resistivity changes with the measurement time, and the deviations from Ohm's law in the voltage–current (V–I) measurements illustrate the capacitance property of these nanocomposites. For this new kind of nanocomposites, the obtained results provide experimental evidence of the conducting mechanism for tin oxide nanoparticles.     

On the pre‐metric foundations of wave mechanics I: massless waves

The mechanics of wave motion in a medium are founded in conservation laws for the physical quantities that the waves carry, combined with the constitutive laws of the medium, and define Lorentzian structures only in degenerate cases of the dispersion laws that follow from the field equations. It is suggested that the transition from wave motion to point motion is best factored into an intermediate step of extended matter motion, which then makes the dimension‐codimension duality of waves and trajectories a natural consequence of the bicharacteristic (geodesic) foliation associated with the dispersion law. This process is illustrated in the conventional case of quadratic dispersion laws, as well as quartic ones, which include the Heisenberg–Euler dispersion law. It is suggested that the contributions to geodesic motion from the non‐quadratic nature of a dispersion law might represent another source of quantum fluctuations about classical extremals, in addition to the diffraction effects that are left out by the geometrical optics approximation.