Comparative Lattice-Dynamical Study of the Raman Spectra of Monoclinic and Tetragonal Phases of Zirconia and Hafnia

An interpretation of the Raman spectra of monoclinic ZrO₂ and monoclinic HfO₂ is made by analyzing the results of the zirconia–hafnia substitution jointly with a lattice dynamical treatment of both structures. The Raman spectra of tetragonal ZrO₂ and tetragonal HfO₂ are also interpreted. Emphasis is put on their relations to the spectrum of the parent cubic structure and on the position of the soft mode. The band assignment proposed earlier by other researchers is critically reconsidered.     

Simulation of polymer flow through a coat-hanger die: A comparison of two numerical approaches

Coat-hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat-hanger die, a two-dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat-hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical treatments.     

Use of a dispersed iron catalyst for upgrading extra-heavy crude oil using methane as source of hydrogen

The use of an iron dispersed catalyst, derived from Fe₃(CO)₁₂, for extra-heavy crude oil upgrading using methane as source of hydrogen was studied. The upgrading reactions were carried out batchwise in a stainless-steel 300 ml Parr reactor with 250 ppm of Fe at a temperature of 410-420 °C, a pressure of 11 MPa of CH₄, and a residence time of 1 h. In the presence of Fe₃(CO)₁₂, the reaction of Hamaca extra-heavy crude oil led to a reduction of two orders of magnitude in the viscosity (from 500 to 1.3 Pa s), 14% reduction in sulfur content, and 41% conversion of the >500 °C fraction in the upgraded product with respect to the original crude. The iron catalyst was isolated from the coke produced from the upgrading reaction and was analyzed by XPS, EDAX, and Mössbauer spectroscopy. The results indicated the presence of a Fe-V mixed sulfide species with a composition ca. (Fe_0.6V_0.4)_zS, where z is in the range 0.8-0.9.     

Behavior of silica aerogel networks as highly porous solid solvent media for lipases in a model transesterification reaction

Highly porous silica aerogels with differing balances of hydrophobic and hydrophilic functionalities were studied as a new immobilization medium for enzymes. Two types of lipases from Candida rugosa and Burkholderia cepacia were homogeneously dispersed in wet gel precursors before gelation. The materials obtained were compared in a simple model reaction: transesterification of vinyl laurate by 1-octanol. To allow a better comparison of the hydrophobic/hydrophilic action of the solid, very open aerogel networks with traditional organic hydrophobic/hydrophilic liquid solvents, this reaction was studied in mixtures containing different proportions of 2-methyl-2-butanol, isooctane, and water. The results are discussed in relation to the porous and hydrophobic nature of aerogels, characterized by nitrogen adsorption. It was found that silica aerogels can be considered as "solid" solvents for the enzymes, able to provide hydrophobic/hydrophilic characteristics different from those prevailing in the liquid surrounding the aerogels. A simple mechanism of action for these aerogel networks is proposed.     

A 3D EFFECT IN THE WEDGE ADHESION TEST: APPLICATION OF SPECKLE INTERFEROMETRY

The wedge test is of considerable use for evaluating adhesion between two bonded rigid substrates. In its (usual) static form, release of elastic strain energy is equated to effective adhesion energy during crack growth. However, the test is usually treated as two-dimensional. In fact, it is really three-dimensional due to anticlastic bending effects of the bent beam(s) during crack propagation.

We studied a composite material/epoxy/aluminium alloy system and observed a curved crack front during propagation. This leads to doubt as to the value of crack length to be inserted in the adhesion energy formula. In addition, by using the highly sensitive technique of speckle interferometry, it was possible to study anticlastic bending effects in a quantitative manner. Far from the crack front, agreement between theory and experimental is good, yet work remains to be done to understand the zone near the fracture zone.     

Structure-function studies of an IGF-I analogue that can be chemically cleaved to a two-chain mini-IGF-I

The structure and biological activities of two disulphide isomersof a C-region deletion mutant of insulin-like growth factor-I(IGF-I) which has an Asn–Gly link engineered at the junctionof the A- and B-regions were studied before and after chemicalcleavage. Circular dichroism (CD) spectra and binding affinityto IGF binding protein 3 (IGFBP3) indicated that the treatmentwith hydroxylamine did not disrupt the overall tertiary foldof the hormones. Cleavage restored some binding affinity forthe IGF-I receptor in both isomers and weakly restored the abilityto stimulate incorporation of tritiated thymidine into DNA inNIH 3T3 fibroblasts transfected with the human IGF-I receptor.Cleavage also restored metabolic capacity, as measured by theability of the isomers to promote lipogenesis in isolated ratadipocytes through the insulin receptor. These results are consistentwith the theory that binding of IGF-I to the IGF-I receptorrequires a conformational change similar to that involved ininsulin binding the insulin receptor. The weak affinity forthe IGF-I receptor after cleavage is consistent with the beliefthat residues in the C-region interact with the IGF-I receptor.This structural difference between insulin and IGF-I gives eacha higher binding affinity for its own receptor.     

Two ways of synthesis of polymer networks based on diglycidyl ether of bisphenol A,bisphenol A,and sulfanilamide: Kinetics study

The kinetics of reactions of ternary systems based on bisphenol A diglycidyl ether, bisphenol A, and a sulfanilamide curing agent were investigated using HPLC, during two different synthesis paths. The influence of tetrabutylphosphonium tetrafluoroborate as a catalyst for the epoxy–phenol reaction was studied. For the same initial composition, polymers differing by the crosslink point distribution and the chain length between crosslinks were synthesized. Different solid‐state behavior is expected in these two categories of networks. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 580–591, 2001     

Effect of high shear stress on microbial viability

Escherichia coli and Saccharomyces cerevisiae suspensions were submitted to controlled shear stress. Above a threshold value shear stress induced a decrease in micro‐organism viability. The threshold of shear stress efficiency depended on the micro‐organisms, being between 1292 Pa and 2770 Pa for S cerevisiae, and about 1250 Pa for E coli. Above 1810 Pa, E coli cells were disrupted whereas the S cerevisiae cells remained intact. The higher the cellular concentration, the greater the rate of decrease in viability. Viability loss was influenced by the number of passages through the experimental shear stress device and by exposure time. © 2001 Society of Chemical Industry     

Structure and properties of clay ceramics for thermal energy storage

In this paper, the structure‐property relationships of a clay ceramic with organic additives (biomass and biochar) are investigated to develop an alternative material for thermal energy storage. The firing transformations were elucidated using X‐ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the biomass increased the porosity, which resulted in a decrease of the specific heat capacity. On the other hand, the biochar remained in the clay ceramic without any interaction with the clay matrix up to 950°C. The specific heat capacity of the clay ceramic increased from 1.20 to 1.49 kJ/kg·K for a 30 wt% addition of biochar. The clay ceramic with a 30 wt% addition of biochar also conserved a high flexural strength of 11.1 MPa compared to that of the clay ceramic without organic additives (i.e., 18.9 MPa). Furthermore, the flexural strength only decreased by 23% after 100 thermal cycles. The crack growth associated with the thermal fatigue was limited by crack bridging and crack trapping. Hence, the current results suggest that clay/biochar ceramics can be as efficient as molten salts in thermal energy storage with the added benefit of an ease of use in the physical form of bricks.     

A 3D EFFECT IN THE WEDGE ADHESION TEST: APPLICATION OF SPECKLE INTERFEROMETRY

The wedge test is of considerable use for evaluating adhesion between two bonded rigid substrates. In its (usual) static form, release of elastic strain energy is equated to effective adhesion energy during crack growth. However, the test is usually treated as two-dimensional. In fact, it is really three-dimensional due to anticlastic bending effects of the bent beam(s) during crack propagation.

We studied a composite material/epoxy/aluminium alloy system and observed a curved crack front during propagation. This leads to doubt as to the value of crack length to be inserted in the adhesion energy formula. In addition, by using the highly sensitive technique of speckle interferometry, it was possible to study anticlastic bending effects in a quantitative manner. Far from the crack front, agreement between theory and experimental is good, yet work remains to be done to understand the zone near the fracture zone.