Adsorption of N2 and N2O on Ni(7 5 5) surface: ab initio periodic density functional study

Adsorption of N₂ and N₂O at various sites on Ni(7 5 5) has been investigated by density functional theory (DFT) method (periodic DMol³). Several possible adsorption structures (attaching the nitrogen atom to the surface, or lying parallel) are found for both molecules. There is a clear binding energy preference of N₂ and N₂O for step sites in contrast to the case of CO. It is revealed that the decomposition of N₂O occurs exclusively near the step, but not on the terrace. Two decomposition channels can be considered; dissociative adsorption and spontaneous decomposition during TPD ramp. Three possible candidates for the precursor of the spontaneous decomposition of N₂O during TPD ramp are discussed.     

Surface Nucleation Kinetics on Active Centers from Supersaturated Vapor

The formation of nuclei from a supersaturated vapor on a surface with active centers is treated within standard self-consistent classical model with exhaustion of active centers. Basic characteristics of nucleation process (total number of nuclei, nucleation rate, time lag and size distribution of nuclei) are determined by numerical solution of kinetic equations. It is shown that standard approach to nucleation on active centers based on Avrami model coincides with our approach in the values of time lag of nucleation process, but it differs in the total number of nuclei.     

二甲苯在TFJF型催化剂上深度氧化动力学的研究

在193-225 iC温度范围内，在轴向取样的管式积分反应器中研究了二甲苯在TFJF型催化剂上深度氧化的宏观动力学，在试验条件下，该反应的速度方程为:     

氨酯丙烯酸酯树脂的合成及其固化反应动力学研究

用不同分子量的聚氧化丙烯二元醇合成了一系列氨酯丙烯酸酯齐聚物（ＵＡＯ）以及含硬段／软段结构的ＵＡＯ，并用ＦＴ－ＩＲ跟踪了这类ＵＡＯ的合成过程。通过ＵＡＯ的链端双键测定，以及ＧＰＣ、ＶＰＯ测定的分子量，表征了ＵＡＯ的数均官能团度。进一步通过ＦＴ－ＩＲ研究了由ＵＡＯ与甲基丙烯酸甲酯形成的氨酯丙烯酸酯树脂（ＵＡＲ）固化时的共聚反应动力学，发现其共聚反应速率与体系中的扩散效应密切相关。在这类ＵＡＯ中引入硬段后，共聚合体系呈现出反常的动力学行为，与网络结构形成过程中材料的形态发展有关。     

Submonolayer Au on Si(111) phase diagram

Based on a review of the current literature, a surface phase diagram is proposed for the submonolayer Au on Si(111) system. Kinetic considerations are reviewed and key surface phase diagram features such as the Θ < 0.4 ML metastable structure and the high temperature to Si(111)-(1 × 1)Au second order phase transition are discussed. Experiments to verify certain portions of the phase diagram are proposed.     

Kinetics of the thermal decomposition of cadmium carbonate (CdCO3)

Cadmium carbonate used in the study was prepared from cadmium chloride, ammonium carbonate and ammonia. The X-ray powder diffraction, infrared spectral and chemical analysis conducted on the product show that the sample is of analytically acceptable purity. The thermal decomposition kinetics of cadmium carbonate was then studied by using the isothermal thermogravimetric method under a flow of dry nitrogen gas. The decomposition kinetics is best described by a two-dimensional phase boundary reaction mechanism (R ₂). An activation energy (E _a) of 135.006 kJ·mol^?1 and natural logarithm of the frequency factor (lnZ) of 16.754 were obtained in the range of 9 temperatures (400, 390, 380, 370, 360, 350, 340, 330 and 320°C).     

Thermal dehydration of some food products and kinetic parameters of this process

Metal poly(vinyl acetates) polymers were obtained by radical polymerization with azodiisobutyronitrile. The thermal stabilities of the metal polymers (M-PVAC) have been studied by thermogravimetry (TG) between 25 and 550°C under nitrogen flow. The decomposition temperature was obtained from the maximum of the first derivative from TG curve. The kinetic parameters of the thermal decomposition were determined by the Arrhenius equation. All these polymers degrade mainly in a single step with a very small second step, probably via a complex reaction. The kinetic data thus obtained show that the thermostabilities decrease in the order: Sb-PVA_c～Ge-PVA_c>Bi-PVA_c～Cd-PCA_c>Ag-PVA_c～PVA_c>Zn-PVA_c> Au-PVA_c>In-PVA_c>Sn-PVA_c>Ga-PVA_c>Pd-PVA_c. Again, the thermal stability is dependent upon the metal incorporated in the backbone polymer. They loose weight after 320°C. The order of reaction from the thermal decomposition of these metal polymers was found to be ?0.5 for the first step and 0 for the second. The pre-exponential factor, the reaction order and the activation energy of the decomposition for metal (PVA_c) have been determined in most of them.     

Discrete dihedral-angle modulation in porphyrin wheels adsorbed on Cu(1 0 0) observed by scanning tunneling microscopy

Conformations of two dodecameric porphyrin wheels adsorbed on a Cu(1 0 0) were probed by using scanning tunneling microscopy (STM). Whereas a wheel consisting of six meso-meso linked diporphyrins was detected as uniform ring structure, several different images with three discrete molecular heights were detected for a wheel consisting of six meso-meso, β-β,β-β triply-linked planar diporphyrins. These results indicate that the former has a conformation similar to that in a free space, while the latter has various conformations with respect to orientation of planar diporphyrin units toward the metal surface. Several discrete STM images of the latter have been interpreted in terms of possible eight conformations, which vary as to relative orientation of neighboring diporphyrin units.     

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

Isothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007     

TA on Mo(W)/Cu(Ag)/S clusters derived with [Cp*MS3]- Kinetics of [PPh4]2[Cp*WS3(CuBr)3]2 and [PPh4]2[Cp*MoS3(CuBr)3]2

Thermal analysis on two new heterometallic sulfide clusters, [PPh4]2[WS3(CuBr)3]2 and [PPh4]2[MoS3(CuBr)3]2 (where PPh4=tetraphenyl phosphonium, =pentamethylcyclopenta- dienyl), was carried out using a simultaneous TG-DTA unit in an atmosphere of flowing nitrogen and at various heating rates. Supplemented using EDS method, their thermal behavior and properties, together with the composition of their intermediate product, were examined and discussed in connection with their distinctive molecular structure as a dianion, which provided some theoretically and practically significant information. Both clusters decomposed in a two-step mode, but without a stable new phase composed of Mo/W-Cu-S formed during their decomposition process as we expected. Based on TG-DTG data, four methods, i.e. Achar-Brindley-Sharp, Coats-Redfern, Kissinger and Flynn- Wall-Ozawa equation, were used to calculate the non-isothermal kinetic parameters and to determine the most probable mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.