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Understanding Rheology
Linear Viscoelastic Behavior of Bentonite-Water Suspensions
Bentonite are extensively used materials in a wide range of applications. Creep and oscillatory shear experiments in the linear viscoelastic domain were carried out on bentonite-water suspensions at different solid fractions. It was found that bentonite dispersions exhibit important viscoelastic behavior which could b…
Synthesis of Titania-Silica Materials by Sol-Gel
In this work TiO2-SiO2 glasses containing as much as 20 mol % of TiO2 were prepared via sol-gel process using titanium and silicon alkoxides, in the presence of chlorine, in the form of titanium tetrachloride or HCl. The gels were heat-treated until 800 °C. X-ray diffraction and Fourier transform infrared spectroscopy…
Effect of the Addition of Potassium or Lithium on the Columbite Precursor Microstructure
Pechini method has been used to synthesize MN powders with stoichiometric control. By this method, K and Li-doped MN in the range from 0.1 to 5.0 mol% of dopants have been obtained at relatively lower temperatures than it is possible with the conventional mixture of oxides. The results from BET analysis indicated that…
Synthesis of Group IVB Metals Oxicarbides by Carboreduction Reactions
The metals of the group IV B (Ti, Zr, Hf) present a series of carbides and oxicarbides with scientific and technological interest. Many of these compounds belong to the subsystem "MO - MC" of the pseudoternary "MO - MN - MC" system (where M = Ti, Zr or Hf). In this work carboreduction reactions of TiO2 and ZrO2 were p…
TABLE OF CONTENTS
Repair of Concrete Elements Using CFRP: Parametrical Study and Evaluation of Dynamic Properties
On the Nature of Sandwiched Chromium Complexes in Exchanged alpha-Zirconium Phosphate
Layered alpha-zirconium hydrogenphosphate monohydrate was prepared by direct precipitation, exchanged with n-propylamine and then by chromium aquacomplexes. The solids were characterized by X-ray diffraction, mass spectrometry, infrared and UV-Visible spectroscopy. The results suggest that monomer complexes form exten…
Effect of Fluoride-containing Mouthrinses on the Translucence of Resin Modified Glass Ionomer Cements
The aim of this in vitro study was to assess the effect of different fluoride-containing mouthrinses on the translucence of resin-modified glass ionomer cements, as a function of the restorative material used, the fluoride-containing solution employed and the time of immersion. Disks were prepared (10 mm × 2 mm) with…
Silica Derived from Burned Rice Hulls
Three new processes to obtain silica having high specific surface area from burned pre-treated rice hulls are presented and discussed. These procedures allow for the simultaneous recovery of biomass energy and the production of high quality silica at thermoelectric plants, without the risk of using corrosive substance…
Editorial
4th International Conference on Polymer – Solvent Complexes and Intercalates
Evaluation of the Influence of Microwaves in the Structure of Silica Gels
In this work we studied the influence of microwaves in the pore structure of silica gels obtained via sol-gel polymerization process. We analised the feasibility of replacing conventional heating by microwave heating during drying. Structural parameters such as specific volume of pores (Vp), specific surface area (Sp)…
How are colloidal suspensions that age rejuvenated by strain application?
We present here a microscopic study of the effect of shear on a dense purely repulsive colloidal suspension. We use multispeckle diffusing wave spectroscopy to monitor the transient motions of colloidal particles after being submitted to an oscillatory strain. This technique proves efficient to record the time evoluti…
Raman Spectroscopy and Field Emission Measurements on Catalytically Grown Carbon Nanotubes
We used microcontact printing to pattern a silicon surface with an iron-containing catalytic solution. Multiwall carbon nanotubes were subsequently grown on the patterned areas by chemical vapor deposition at temperatures between 650 and 1000 °C. We demonstrate that the diameter of the catalytically grown multiwall na…
Aging of polymeric and composite insulating materials. Aspects of interfacial performance in aging
Aging of polymeric and composite materials is reviewed mainly from the standpoint of their interfacial performance. Insulating materials can be divided into simple polymers and composites. Polymers for power cables, transformers, insulators and rotating machines consist of thermoplastics such as PE, PET and PPS, elast…
The metal‐insulator transitions of VO 2 : A band theoretical approach
Abstract The results of first principles electronic structure calculations for the metallic rutile and the insulating monoclinic phase of vanadium dioxide are presented. In addition, the insulating phase is investigated for the first time. The density functional calculations allow for a consistent understanding of all…
Vibrational Analysis of Palygorskite and Sepiolite
Abstract Lattice dynamic calculations for the sepiolite and palygorskite structures using polarized Raman and FTIR spectra provide a fundamental basis for interpreting spectral features by assigning vibrational modes. The Si-O stretch and O-Si-O bond bending force constants determined for palygorskite are similar to e…
On the quantum and classical scattering times due to charged dislocations in an impure electron gas
We derive the ratio of transport and single particle relaxation times in three and two - dimensional electron gases due to scattering from charged dislocations in semiconductors. The results are compared to the respective relaxation times due to randomly placed charged impurities. We find that the ratio is larger than…