Joao Alziro Herz da Jornada

Influence of the comonomer content on the thermal and dynamic mechanical properties of metallocene ethylene/1-octene copolymers

Studies of ethylene/1-octene copolymers prepared by a metallocene catalyst were carried out through dynamic-mechanical experiments (DMTA), differential scanning calorimetry (DSC), Raman spectroscopy and gel permeation chromatography (GPC). The influence of comonomer content on the ethylene/1-octene properties, specially those related to the dynamic-mechanical behaviour were studied. It was observed that the intensity of the β-transition increases as the comonomer content increases and decreases crystallinity.

Fluorescence properties of benzoxazole type dyes entrapped in a silica matrix by the sol-gel method

For the first time, the incorporation of 2,5-bis(benzoxazol-2′-yl)-4-methoxyphenol (BM) in a silica matrix by the sol–gel method has been accomplished, producing transparent and translucent monoliths with fluorescence properties. The intensity and wavelength range of the fluorescence bands F1 (primary structures) and F2 (proton-transferred forms) were extremely sensitive to the presence of solvents and to the dye concentration in the silica pores. The F2 band was observed when the silica pores contained solvent; however, after the solvent evaporation, the interactions of the dye with the silica host hindered the proton-transfer reaction, eliminating the F2 band and indicating the polar and acidic character of this host. Nevertheless, it was observed that the proton-transfer could be recovered after insertion of suitable solvents inside the matrix, like water, ethanol or DMF. Changes in the fluorescence spectra due to the use of different dye concentrations were observed when the monoliths were prepared with ethanol as solvent. During the aging process, the F2 band persists at high dye concentrations, but it disappears for low dye concentrations. The high sensitivity of the proton-transfer reaction of this dye in a particular environment, where the solvent and the host play important roles, suggests the possible application of this dye as a photoprobe for this kind of system.

Dynamic-Mechanical Properties of Ethylene/α-Olefin Copolymers Prepared by a Metallocene Catalyst

The influence of comonomer content and type on the dynamic-mechanical behavior of some ethylene/α-olefin (1-hexene, 1-octene, 1-decene, 1-octadecene and 4-methyl-1-pentene) copolymers was studied. It was observed that the comonomer content has great influence on α- and β-transitions, but almost no influence on γ-transition. Thus the α-transition intensity decreases and β-transition intensity increases as the comonomer content increases. Only 1-octadecene shows a different behavior. A higher comonomer content, ethylene/1-octadecene copolymer shows two defined transitions in the α-transition region, suggesting the presence of crystals of different sizes.

High-Pressure Entrapment of Rhodamine 6G into a Silica Matrix

The entrapment of organic dyes with interesting optical properties in silica produced by sol-gel method, has been studied over the last years, aiming to obtain a new class of optical materials. The monoliths produced by this method present cracks, large shrinkage during the silica gelation and drying, and a great porosity, which decreases their optical performance. In a previous work, to overcome these difficulties, a high pressure (4.5 GPa) technique at room temperature was used to produce compacts of silica gel doped with rhodamine 6G (R6G). In this work, we extended this study to pressures up to 7.7 GPa to verify the effect of high pressure in the fluorescence spectra of the R6G and in the density and hardness of the compacts. High density (98% of the silica density), transparent and crack-free compacts were produced, being resistent to polishing. The fluorescence spectra were similar to the ones observed in ethanol solutions. These new class of materials are potentially useful for optical applications.

Evaluation of the adhesion strength of diamond films brazed on K-10 type hard metal

The coating of cutting tools with diamond films considerably increases the tool performance due to the combination of the unique tribological properties of diamond with the bulk properties of the substrate (toughness). The tool performance, however, is strongly related to the adhesion strength between the film and the substrate. In this work our main goal was to propose and to test a procedure, based on a tensile strength test, to evaluate the adhesion strength of a diamond wafer brazed on a hard metal substrate, taking into account the effect of the brazing temperature and time. The temperature range studied was from 800 to 980 °C and the brazing time ranged from 3 to 40 min. The obtained results could be used to optimize the costs and time required to the production of high performance cutting tools with brazed diamond wafers.