Study of solid state reactions in Nb/Al multilayer thin films

Solid state reactions of sputter-deposited Nb/Al multilayer thin films, with periodicities in the range 10–333 nm, have been studied by differential scanning calorimetry. The first phase to form upon annealing the films in NbAl₃. Constant-heating-rate calorimetric measurements show the presence of two peaks for the formation of this phase, while isothermal scans reveal that the first peak is associated with a nucleation and growth type transformation. The formation of NbAl₃ is thus interpreted as a two-stage process of nucleation and growth to coalescence (first peak) followed by growth until the consumption of one or both reactants (second peak).We thank NSF for support through DMR-9308651, K. Coffey, S. Vivekanand and B. Gadicharla for assistance and TA Instruments for the donation of a 1600°C furnace.     

Solid state reactions in the platinum–mercury system

Thermogravimetry, Differential Scanning Calorimetry and other analytical techniques (Energy Dispersive X-ray Analysis; Scanning Electron Microscopy; Mapping Surface; X-ray Diffraction; Inductively Coupled Plasma Atomic Emission Spectroscopy and Cold Vapor Generation Atomic Absorption Spectroscopy) have been used to study the reaction of mercury with platinum foils. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt to form intermetallic compounds each having a different stability, indicated by at least three mass loss steps. Intermetallic compounds such as PtHg₄, PtHg and PtHg₂ were characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of bulk mercury via thermal desorption. The Pt(Hg) solid solution formation caused great surface instability, attributed to the atomic size factor between Hg and Pt, facilitating the acid solution’s attack to the surface.     

Solid state electrochemical reactions in systems with miscibility gaps

Cyclic voltammograms of electroactive solid compounds with partial immiscibility between the oxidized and reduced phases can exhibit a splitting of the peaks. If the free energy of transformation between the oxidized and reduced phases is small, the formal potentials of the redox pair will be almost the same in both solid phases. This results in an inert potential range in which no appreciable electrochemical activity is possible. The kinetic implications of this situation have been analysed in relation to the width of the miscibility gap. The diffusion of ions in the particle, which is hindered by the immiscibility, can proceed when a transition zone between the two phases exists in which the crystal structure is changed. If there is no such transition zone the voltammogram will display several spikes, which are caused by the collapse of concentration barriers at the sharp interfaces between the two phases in the mixed crystals. Received: 14 October 1999 / Accepted: 4 November 1999     

Solid state reactions of nitrogenous heterocyclic compounds (I) —Solid state reactions of 3-methyl-1-phenyl-5-pyrazolone with carbonyl compounds

The solid state reaction of 3-methyl-1-phenyl-5-pyrazolon(eM PP) with aromatic aldehydes and ketones, benzil derivatives and imides, and the solid state Michael addition reaction of MPP with 4-arylidene-3-methyl-lphenyl-5-pyrazolone2 were investigated. Some new solid state reactions between the reactants were found, from which a series of new compounds were obtained. The structures of the products were identified by IR,¹H NMR, MS, elemental analyses and also by X-ray crystal analysis, and the reaction mechanism of MPP with aromatic aldehydes and ketones was proposed. Project supported by the National Natural Science Foundation of China.     

过渡金属促进的固相偶联反应

固相有机合成作为组合化学的基石近几年发展很快,本文就1994～1999年被过渡金属促进的固相偶联反应进行了综述。     

Development of master curves for discriminating the mechanism of solid state reactions from experimental data obtained by using the cyclic and controlled rate thermal analysis

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of?E/R(1/T-1/T _0.5),T _0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO₃.     

芳香醛与硫代巴比妥酸固相缩合反应的研究

研究了芳香醛与硫代巴比妥酸固态加热及室温下的缩合反应，两种反应条件得 到同一产物——5—亚烃基硫代巴比妥酸．由^1H NMR，^13C NMR，IR，UV等手段确 定了产物的结构．     

A unified theory for the kinetic analysis of solid state reactions under any thermal pathway

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pseudo‐Fivefold Diffraction Symmetries in Tetrahedral Packing

We review the way in which atomic tetrahedra composed of metallic elements pack naturally into fused icosahedra. Orthorhombic, hexagonal, and cubic intermetallic crystals based on this packing are all shown to be united in having pseudo‐fivefold rotational diffraction symmetry. A unified geometric model involving the 600‐cell is presented: the model accounts for the observed pseudo‐fivefold symmetries among the different Bravais lattice types. The model accounts for vertex‐, edge‐, polygon‐, and cell‐centered fused‐icosahedral clusters. Vertex‐centered and edge‐centered types correspond to the well‐known pseudo‐fivefold symmetries in I_h and D_5h quasicrystalline approximants. The concept of a tetrahedrally‐packed reciprocal space cluster is introduced, the vectors between sites in this cluster corresponding to the principal diffraction peaks of fused‐icosahedrally‐packed crystals. This reciprocal‐space cluster is a direct result of the pseudosymmetry and, just as the real‐space clusters, can be rationalized by the 600‐cell. The reciprocal space cluster provides insights for the Jones model of metal stability. For tetrahedrally‐packed crystals, Jones zone faces prove to be pseudosymmetric with one another. Lower and upper electron per atom bounds calculated for this pseudosymmetry‐based Jones model are shown to accord with the observed electron counts for a variety of Group 10–12 tetrahedrally‐packed structures, among which are the four known Cu/Cd intermetallic compounds: CdCu₂, Cd₃Cu₄, Cu₅Cd₈, and Cu₃Cd₁₀. The rationale behind the Jones lower and upper bounds is reviewed. The crystal structure of Zn₁₁Au₁₅Cd₂₃, an example of a 1:1 MacKay cubic quasicrystalline approximant based solely on Groups 10–12 elements is presented. This compound crystallizes in Im$\bar 3$ (space group no. 204) with a=13.842(2) Å. The structure was solved with R₁=3.53 %, I>2σ;=5.33 %, all data with 1282/0/38 data/restraints/parameters.     

微环境影响下的乙酰基香豆素与吲哚的固相光反应

本文研究了乙酰基香豆素及其衍生物与吲哚的混晶在微环境影响下的固相光反应，并用固体紫外光谱、固体荧光光谱和X-射线粉末衍射技术考察了混晶的特征。实验结果表明，3-乙酰基香豆素及其7-乙酰氧基、7-苯甲酰氧基、5,6-苯并和6-溴衍生物与吲哚的固相光反应分别得到1:2缩合产物1～5，而6-硝基衍生物与吲哚的固相光反应却得到开环脱羰加成产物6。通过IR、MS、^1H NMR和元素分析结果确定了这六个新产物的结构。固体光谱的测试结果表明，取代乙酰基香豆素与吲哚间混晶的形成，分子间存在相互作用，使分子所处的微环境条件发生了变化。     

固态有机反应新进展

总结了一些典型的固态有机反应。由于固态反应的特性，多数固态有机反应表现出较溶液中更高的反应效率和更好的选择性，在某些情况下，利用光活性主体与反应物形成包结物，可实现对映选择性的不对称固态合成。     

The Antimony‐Based Type I Clathrate Compounds Cs8Cd18Sb28 and Cs8Zn18Sb28

In phase : The title compounds lie in a new region of phase space for such a structure, and have stoichiometries in accord with a classical Zintl phase formulation. The small semiconductor gaps indicated by DFT calculations are also supported by their diamagnetic susceptibilities.

     

Molten state and solvent-free systems studied by NMR spectroscopy: addition reactions catalyzed by transition metal complexes

In the present review we address scarcely studied application area of NMR spectroscopy — investigation of molten state and solvent-free systems. In such a case NMR spectra are recorded without a solvent and without magnetic field stabilization on any nucleus. Taking our recent studies of catalytic addition of sulfur- and selenium-containing compounds to alkynes as examples, we describe most important practical aspects of NMR studies and their application for solving important chemical problems. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 740–746, April, 2008.     

Solid state reactions of nitrogenous heterocyclic compounds (II)

Solid state Michael addition reaction of indole with α, β-unsaturated carbonyl compounds was carried out, by which a series of compounds containing three different heterocyclic groups binding to one carbon atom were ob-tained. In the presence of Lewis acid, indole could undergo the solid state condensation reaction with aromatic ketones and aldehydes or quinones. The solid state reaction showed higher selectivity and yield than solution reaction. The structures of products were identified by IR,¹H NMR, MS. elemental analysis and X-ray crystal analysis. The reac-tion mechanism was also proposed. Project supported by the National Natural Science Foundation of China