High‐Temperature Neutron Diffraction,Raman Spectroscopy,and First‐Principles Calculations of Ti3SnC2 and Ti2SnC

Herein, we report—for the first time—on the additive‐free bulk synthesis of Ti₃SnC₂. A detailed experimental study of the structure of the latter together with a secondary phase, Ti₂SnC, is presented through the use of X‐ray diffraction (XRD), and high‐resolution transmission microscopy (HRTEM). A previous sample of Ti₃SnC₂, made using Fe as an additive and Ti₂SnC as a secondary phase, was studied by high‐temperature neutron diffraction (HTND) and XRD. The room‐temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti₃SnC₂ in the a and c directions were found to be 8.5 (2)·10^?6 K^?1 and 8.9 (1)·10^?6 K^?1, respectively. The respective values for the Ti₂SnC phase are 10.1 (3)·10^?6 K^?1 and 10.8 (6)·10^?6 K^?1. Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti₃SnC₂ are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti₂SnC and Ti₃SnC₂ and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.     

Optimization of osmotic dehydration of yacon slices

Osmotic dehydration assisted by ultrasound (ODAU) at low temperatures reduces water activity (a_w) and maintains nutrients. The influence of solution concentration (SC; 20 to 60° Brix, xylitol and sorbitol) and ultrasound application time (t_us, 0 to 40 min) in ODAU of yacon was studied with the aid of a response surface method. The optimum condition with respect to mass transfer parameters, a_w, and fructan retention was SC of 60° Brix for both solutions and t_us of 2.67 min for xylitol samples and 0 min for sorbitol samples. The application of ultrasound improved dehydration but resulted in depolymerization of fructans.     

Effect of the complexation with copper(II) on the hydrodynamic behaviour of some polyelectrolytes

Summary The complex formation between copper and a number of polyelectrolytes derived from amino-acids was studied by viscosimetry. It was concluded that the complexes involving two side chains of the polymer form between two neighbouring side chains of the same polymeric chain. The effect of copper on the viscosity of the polymer solutions was thus accounted for mainly by changes in the net charge of the polymer and changes in the electrostatic interactions.     

Functionalization of PVC by grafting of plasticizing group in a twin screw extruder

Substitution reactions are an appropriate way to attach chemical functions to polymer chains for improving properties and to diversify the application of polymer materials. The stereoselective substitution of chlorine atoms affords a useful way to plasticize polyvinychloride (PVC) by attaching appropriate plasticizing functions (ester group) such as isooctylthiosalicylate. Thus, the substitution of chlorine atoms of PVC by reactant bearing plasticizing groups was carried out in a continuous mixing apparatus such as a twin screw extruder. This continuous chemical engineering process taking place in the extruder is studied as the function of the residence time distribution (RTD) measured by a UV method. This function combined with the kinetics of the chemical reaction allows to define a new function G as the distribution of the extent of conversion by analogy with the RTD function.     

Control of the growth of the diffusional boundary layer on a rotating axisymmetric electrode of arbitrary shape in an ostwaldian fluid

Using a suitable coordinate transformation, an analysis is first described for the prediction of the velocity distribution in a laminar boundary layer flow near a rotating axisymmetric electrode of arbitrary shape in an Ostwaldian fluid, by expressing the governing conservation equations in a series representation universal with respect to electrode contour parameters, patterned by Blasius procedure.Using the first leading term of the series, we define the profiles of the electrodes which fulfil the diffusional limiting density flux j_x = j₀$\text{x}$^p, in which j₀ is an independent coordinate coefficient, p is a numerical power-factor and $\text{x}$, is measured along the direction of the longitudinal component of the flow. The relation between the permitted values of p with the behaviour coefficient of the fluid is described. The particular case of the uniformly accessible electrode (p = 0) is discussed.     

Multivariate analysis of the correlation between noctuidae subfamilies and the chemical structure of their sex pheromones or male attractants

Female-emitted pheromones and sex attractants of Noctuidae were investigated using a specific computer procedure to analyze data collected from the literature. Correspondence analysis was used to survey the structure-activity relationships of sex pheromones in seven subfamilies. Structural, stereochemical, and functional features of active molecules were related to taxonomy. This multidimensional analysis revealed that the prevalent chemical frame of noctuid moth pheromones was a monounsaturated acetate withZ stereochemistry and a double bond on the fifth carbon closest to the nonfunctional branch of the molecule. Possible phylogenetic relationships within Noctuidae and between Noctuidae and other families are discussed in light of the sex pheromone biochemistry. Female sex pheromones appeared to be an additional character to be considered in the classification of noctuid moths.     

Influence of chloride ions and pH level on the durability of high performance cement pastes

The resistance to chemical attack of low water to binder ratio pastes containing silica fume was studied by soaking small paste disks in three different pH controlled solutions, with or without sodium chloride, for periods of up to three months. The pastes were made using water to binder ratios of 0,25 and 0,38. The three solutions in which the paste disks were soaked were the following: 3% NaCl (by weight) at a pH level of 8,5,0% NaCl at 8,5, and 0% NaCl at 4,5. After three months of exposure, the results show that the pH level of the aggressive solution is the most important factor controlling the durability of cement pastes subjected to chemical attack. The total porosity and the depth of decalcification was found to increase with the decrease of the pH level. It was also found that the3water to binder ratio does not significantly affect the deterioration processes, but only influences the kinetics of these processes. The decrease of the water to binder ratio reduces significantly the rate of deterioration. Chloroaluminate crystals were observed only in the cement pastes having a water to binder ratio of 0,38.     

Nitrogen dioxide effect in the reduction of nitric oxide by propane in oxidizing atmosphere

The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO₂ and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C₃H₈ does not differ significantly from that of NO₂. In the absence of oxygen, the reduction of NO₂ by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO₂ formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process.     

Optical study of zinc blend SnS and cubic In2S3:Al thin films prepared by chemical bath deposition

Multilayers of zinc blend SnS crystalline thin film have been deposited onto glass substrates by a chemical bath deposition (CBD) method. The envelope method, based on the optical transmission spectrum taken at normal incidence, has been successfully applied to determine the layer thickness and to characterize optical properties of thin films having low surface roughness. Optical constants such as refractive index n, extinction coefficient k, as well as the real (??_r) and imaginary (??_i) parts of the dielectric constant were determined from transmittance spectrum using this method. Obtained low value of the extinction coefficient in the transparency domain is a good indication of film surface smoothness and homogeneity. To perform the heterojunction structure based on SnS absorber material, cubic In₂S₃:Al was deposited on SnO₂:F/glass as window layer using CBD with different aluminum content. Optical properties of these films were evaluated.