Materials Science Forum Vols. 498-499

Abstract: The industrial use of wastes in the brick and tile industry has been intensively investigated in the last decade. This work describes a research carried out on the manufacturing of a clay material with granite and marble reject. The reject was obtained direct by from a ceramic industry from rocks which were sawed in blocks or slices. This industrial process produces a very large amount of this reject. The reject is launched in decanting lagoon, landing area or throw in river, resulting environment pollution and degradation. The reject material was investigated in function of chemical and mineralogical compositions using x-ray diffraction and thermal analysis. Granite and marble reject and clay material were mixed and uniaxial pressed. Samples were sintered in an electric furnace at temperature range from 950 to 1150º C. The experimental results (porosity, dilatometric analyses, water absorption, x-ray diffraction) are also presented. The results indicate that it is possible to use granite and marble reject in clay material without to predicate its properties.

Abstract: Engineering ceramics have found use in many applications, such as engine parts, ball bearings, artificial bone and hip replacements and gyroscopes, because of their good chemical inertness, hardness, high temperature stability and excellent wear resistance. Oxide ceramic may meet these demands. Alumina (Al2O3) ceramics offer a high potential for many engineering applications, such as wear- and/or corrosion-resistant components, and as material for substrates or housings in microelectronic devices. Alumina is used among other things for seal ring, draw-cones, guides, water mixing tapes, bearing parts, medical prostheses and cutting tools. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occurs in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in Al2O3 samples using commercial starch. These measurements were carried out in a torsion pendulum operating in frequencies around 40 Hz. The results shown strongly influence of the type of forming in the elastic modulus obtained by anelastic relaxation measurements.

Abstract: In this work, an yttrium and rare-earth oxides mixture, CRE2O3, produced at DEMAR-FAENQUIL, was used as sintering additive for silicon nitride (Si3N4) ceramics. Samples were produced by uniaxial hot-pressing, using mixtures of CRE2O3- Al2O3 or CRE2O3-AlN as additives. Four kind of hot-pressed Si3N4 were used as oxidation samples: Si3N4+ 5vol% or 20vol.% of CRE2O3-Al2O3 (forming only β-Si3N4 as crystalline phase), Si3N4+ 5vol.%CRE2O3-AlN (α-SiAlON+β) and Si3N4+ 20vol.%CRE2O3-AlN (only α-SiAlON). The oxidation behavior was evaluated at 13500C, in air up to 160 hours. The oxidation rate of Si3N4 ceramics increased with increasing CRE2O3/Al2O3 content, and oxidation kinetics obeyed the usual parabolic law. Pure α-SiAlONs (Si3N4 +20 vol.% CRE2O3-AlN) were high oxidation resistant with weight gain, after 160 hours, of 0.1 mg.cm-2, while β-Si3N4+20vol.%CRE2O3- Al2O3 showed a weight gain of 1.4 mg.cm-2 after only 10 hours. The oxidation behavior of these ceramics was comparable with ceramics sintered with Y2O3. This result confirms the possibility of the fabrication of high oxidation resistance Si3N4 ceramics using the low cost sintering additive CRE2O3.

Abstract: a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.

Abstract: Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the "step" in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and O5 of the lattice.

Abstract: Molybdenum silicides were obtained by the self-propagating synthesis (SHS) method. Diamond composites containing 30 mass% of MoSi2 or Mo5Si3 bonding phase had been prepared using HT-HP Bridgman type apparatus. Sintering of the diamond composites were carried out at 2073±50 K and 8±0.2 GPa. The interactions in diamond-silicide composites were studied by means of X-ray diffractometry and transmission electron microscopy (TEM). Results of both mechanical properties and thermal resistance measurements are reported. Hardness HV1 for the composite with the predominantly MoSi2 bonding phase was found to be around 42 GPa. After heat treatment in 1200 °C for 30 min. in vacuum HV1 decreases to 29 GPa. In the second composite containing the Mo5Si3 bonding phase the HV1 of 28.0 GPa after thermal exposure changes to 21.0 GPa.

Abstract: The present work deals with cold plasma organosilicon treatment of glass powder surfaces. The treated material underwent subsequent chemical derivations by storing samples inside an evacuated chamber, allowing chemical penetration at controlled pressures. The radicals’ inductions were characterized by XPS within each stage of modification. The enzyme peroxidase was immobilized using functionalized materials to check the resultant biocompatibility. A sequence of surface tailoring is proposed suggesting the anchoring of enzyme via C = O groups implanted on the glass surface. The experimental results demonstrate that the proposed process is suitable for the functionalization of materials with irregular shapes.

Abstract: In this work, a combination of methods for HAp synthesis is investigated. Fish bones were calcined at 900oC between 4h and 12h, followed by milling in a high-energy ball mill, by 2h and 4h at 300rpm. The obtained material was characterized by using techniques such as laser granulometry, X-ray diffraction, scanning electron microscopy (SEM) and atomic absorption spectroscopy. The performed analysis permitted us to obtain the Ca/P ratio, the morphology and the phase structure of hydroxyapatite particles powder.

Abstract: Prosthetic substructures for dental application are veneered by porcelain comprising a structure with different elastic modulus and thermal expansion coefficients layers. This structure may present residual stresses in different layers leading to crack propagation and delamination. Although veneering porcelain remains basically on same strength than standard feldspathic porcelains, new ceramic cores have been developed with higher mechanical properties overcoming metal substructures, improving esthetics and biocompatibility. The interface between the Procera dense sintered alumina core and the manufacturer recommended veneering porcelain (AllCeram-Degussa) were evaluated using SEM in coping shaped specimen simulating the standard dental preparation. There were neither crack presences at the interface nor porcelain delamination.

Abstract: Nickel oxide – 8 mol% yttria stabilized zirconia (NiO-8YSZ) powders containing 25 to 75 wt% of NiO were prepared by coprecipitation. The entire process includes the reaction of metals aqueous chloride solutions (heated at 95 oC) with ammonium hydroxide, washing steps of the resulting gel, butanol azeotropic distillation treatment to prevent the formation of hard agglomerates, drying, calcination and ball milling. The yield of precipitation of metals was determined by inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES). Powders were characterized by X-ray and laser diffraction, infrared analysis, gas adsorption (BET) and scanning electron microscopy. It was observed that zirconium and yttrium hydroxides are easily precipitated in alkaline medium, while nickel precipitation yield is in the range of 80 to 95% due to the formation of soluble complexes. NiO appears as a second phase in synthesized powders and contributes to decreasing of specific surface area and agglomerate mean size.