Precision abrasive processes are commonly employed to machine glasses, single crystals and ceramic materials for various industrial applications. Until now, precision machining of hard and brittle solids are poorly investigated in Brazil from the fundamental and applied point of views. Taking into account the major technological importance of this subject to the production of functional and structural components used in high performance systems, the present study investigated the ultrasonic abrasion of different workpiece materials - alumina, zirconia, quartz, glass, ferrite and LiF - by using a stationary ultrasonic machine. Experiments were conducted using a rectangular shaped cutting toll and SiC particles with mean grain size of 15mm. The machined surfaces were characterized by surface profilometry and scanning electron microscopy. In the case of alumina, zirconia and quartz, the rates of material removal decrease with the depth of machining. The rate of material removal remained constant for the others materials. The micrographs showed that brittle microcracking was the primary mechanism involved with material removal. The rates of material removal and the machined surface topographies were discussed as a function of intrinsic stiffness, hardness and fracture toughness of workpiece materials

This article reports the sensitization of the glow peak at 300 °C in crystalline quartz by using high doses of gamma radiation. Five lots of samples were prepared from single crystals extracted from different geological occurrences in Brazil. The specimens were submitted to high doses of ⁶⁰Co radiation starting at 25 kGy and going up to a cumulative dose of 350 kGy. After each high dose application, the samples were submitted to a thermal treatment and then irradiated with gamma radiation doses ranging from 2 to 20 mGy. The thermoluminescence (TL) response for each quartz lot was then determined. The results showed a remarkable increase in the TL peak at 300 °C for samples from three of the lots after the administration of a dose of 25 kGy. The pre-dose necessary to obtain the maximum in sensitization was dependent on the origin of the quartz samples and on their Al, Li and OH impurity contents.

This work investigates the effect of particle size in the thermoluminescence (TL) response of a quartz crystal that was initially crushed and classified into ten size fractions between 38 μm and 5 mm. Aliquots of each size fraction were sensitized with a dose of 25 kGy of γ rays and heat-treatments at 400 °C. TL glow curves of sensitized and non-sensitized samples were recorded as a function of different test-doses of γ rays. For the non-sensitized samples, the TL peak near 325 °C increases with the decrease in particle size. In the case of sensitized samples, a strong TL peak near 300 °C increases with the increase in particle size up to mean grain size equal to 304 μm. Above 304 μm, an abrupt reduction in the TL intensity is noticed for the sensitized peak. These effects are discussed in relation to the specific surface area of quartz particles and the intensity of the electron paramagnetic resonance signal of the E'1 center induced by the sensitization process