912 resultados para Ceramic tubes


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This study was conducted to observe the rat subcutaneous connective tissue reaction to the implanted dentin tubes filled with calcium hydroxide or mineral trioxide aggregate. The animals were sacrificed after 7 and 30 days, and the specimens were prepared for morphological study. Some undecalcified specimens were prepared for histological analysis with polarized light and Von Kossa technique for calcium. The results were similar for both studied materials. At the tube openings, there were Von Kossa-positive granules that were birefringent to polarized light. Next to these granulations, there was an irregular tissue like a bridge that was Von Kossa-positive. The dentin walls of the tubes exhibited in the tubules a structure highly birefringent to polarized light, usually like a layer and at different depths. It is possible that the mechanism of action of both materials has some similarity. Copyright © 1999 by The American Association of Endodontists.

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For retarding carbon oxidation in refractories during the preheating of metallurgical furnaces, a ceramic coating, made mainly of sodium phosphosilicate and clay was developed. The coating presents high adherence to the substrate with no swelling. The coating was characterized by thermal analysis, X-ray diffraction at room temperature (XRD) and at high temperature (HTXRD), X-ray fluorescence and scanning electronic microscopy (SEM). The glass transition temperature is reached at 800 °C and only glassy phase is observed above this temperature. Thus the mechanism of protection seems to be the formation of a glassy phase on the surface of the refractory, and the coating tends to be more efficient at temperatures higher than 800 °C.

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The present paper describes the morphological alterations of the epithelial layer of the uterine tubes of rats submitted to experimental chronic alcoholism using anatomical, histological, ultrastructural and morphometric methods. Sixty adult rats (Rattus norvegicus albinus) at the same age (3 months) and with a mean body weight of 228 g were divided into two groups. The control group received solid diet (Purina rat chow) and tap water ad libitum. The alcoholic group received the same solid diet and was allowed to drink only sugar cane brandy dissolved in 30° Gay Lussac (v/v). After periods of 90, 180 and 270 days of treatment animals at normal estrus were anaesthetised with ethyl ether, weighed and sacrificed. Subsequently, the uterine tubes were dissected, weighed and prepared for TEM and SEM methods. The final mean body weights were similar in the control and alcoholic groups. The morphometric analysis showed no difference between control and alcoholic epithelial height. The alcoholic animals showed ultrastructural alterations: intense lipid droplet and lysosomes accumulation, dilated rough endoplasmic reticulum cisternae and vacuolization in both periods of treatment. It was concluded that alcohol acts as a toxin on the epithelial layer of the uterine tubes of rats.

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The preparation and characterization of transparent glass-ceramics in the composition of 30Li2O:5ZrO2:xBaO:(100-x) SiO2 with x = 0, 5, 10, 15, and 20 mol% are described. Glasses were melted in a platinum crucible at 1100°C for 2 h and then heat-treated at 900°C for 3 h. The characterizations were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, and scanning electron microscopy (SEM). The experimental results indicate that there was a structural change in the glass-ceramics as the BaO concentration in the mixture increased. In the XRD patterns of samples without heat treatment, only the halo was observed. After heat treatment, the appearance of the materials was verified by X-ray diffraction peaks. The reorganization of the amorphous solid was confirmed by Raman and IR spectroscopy along with XPS and SEM, with a more homogeneous phase formation being observed.

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Tin dioxide is an n-type semiconductor that when doped with other metallic oxides exhibits non-linear electric behavior with high non-linear coefficient values typical of a varistor. In this work, electrical properties of the SnO2.CoO.Ta2O5 and SnO2.CoO.MnO2.Ta2O5 ceramics systems were studied with the objective of analyzing the influence of MnO2 on sintering behavior and electrical properties of these systems. The compacts were prepared by powder mixture process and sintered at 1300°C for 1 hour, in air, using a constant heating rate of 10°C/min. The morphological and structural properties were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The densities of the sintered ceramics were measured using the Archimedes method. The SnO2.CoO.Ta2O5 and SnO2.CoO.MnO2.Ta2O5 systems presented breakdown fields (Eb) about 3100 V.cm-1 and 3800 V.cm-1, respectively, and non-linear coefficient (α) about 10 and 20, respectively.

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A novel fractal model for grain boundary regions of ceramic materials was developed. The model considers laterally inhomogeneous distribution of charge carriers in the vicinity of grain boundaries as the main cause of the non-Debye behaviour and distribution of relaxation times in ceramic materials. Considering the equivalent circuit the impedance of the grain boundary region was expressed. It was shown that the impedance of the grain boundary region has the form of the Davidson-Cole equation. The fractal dimension of the inhomogeneous distribution of charge carriers in the region close to the grain boundaries could be calculated based on the relation ds = 1 + β, where β is the constant from the Davidson-Cole equation.

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The pulsed electric acoustic technique, PEA, has been usually applied to probe space charge profiles in polymers. Preliminary PEA results using a ferroelectric ceramic are presented. If the reverse applied electric field i of the order of the coercive field the switching polarization process occurs in a period larger than hundreds of seconds. Such a slow process allows one to use the PEA setup to follow the polarization switching dynamics and determine the electric field profile. The PEA signal obtained in the lead zirconate-titanate doped with niobium ceramic, PZTN, indicates that the polarization distribution and field are not uniform during the switching period. We were also able to observe that the acoustic wave velocity and attenuation depends on the stage of the polarization switching, which agrees with results obtained using the ultrasonic method.

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This work presents an investigation into the use of the finite element method and artificial neural networks in the identification of defects in industrial plants metallic tubes, due to the aggressive actions of the fluids contained by them, and/or atmospheric agents. The methodology used in this study consists of simulating a very large number of defects in a metallic tube, using the finite element method. Both variations in width and height of the defects are considered. Then, the obtained results are used to generate a set of vectors for the training of a perceptron multilayer artificial neural network. Finally, the obtained neural network is used to classify a group of new defects, simulated by the finite element method, but that do not belong to the original dataset. The reached results demonstrate the efficiency of the proposed approach, and encourage future works on this subject.

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The purpose of this paper was to study the reaction of rat subcutaneous connective tissue to the implantation of dentin tubes filled with white mineral trioxide aggregate (MTA), a material that will be marketed. The tubes were implanted into rat subcutaneous tissue and the animals were sacrificed after 7 and 30 days. The undecalcified pieces were prepared for histological analysis with polarized light and von Kossa technique for mineralized tissues. Granulations birefringent to polarized light and an irregular structure like a bridge were observed next to the material; both were von Kossa positive. Also, in the dentin wall tubules a layer of birefringent granulations was observed. The results were similar to those reported for gray MTA, indicating that the mechanisms of action of the white and gray MTA are similar.

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The pulsed electric acoustic technique, PEA, have been usually applied to probe space charge profiles in polymers. In this work we show preliminary results obtained with lead zirconate-titanate and niobium, PZTN, ferroelectric ceramic samples. Experiments showed that induced charge densities on sample electrodes are mainly due to the ferroelectric polarization of the sample. We present results of the typical PEA response and the procedure to deconvolute the signal in order to obtain the charge densities and the electric field profiles. The PEA setup allows us to show a non-uniform polarization during ferroelectric switching.

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A very simple and robust method for ceramics grains quantitative image analysis is presented. Based on the use of optimal imaging conditions for reflective light microscopy of bulk samples, a digital image processing routine was developed for shading correction, noise suppressing and contours enhancement. Image analysis was done for grains selected according to their concavities, evaluated by perimeter ratio shape factor, to avoid consider the effects of breakouts and ghost boundaries due to ceramographic preparation limitations. As an example, the method was applied for two ceramics, to compare grain size and morphology distributions. In this case, most of artefacts introduced by ceramographic preparation could be discarded due to the use of perimeter ratio exclusion range.

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Heavy metal oxide (HMO) glasses have received special attention due to their optical, electrical and magnetic properties. The problem with these glasses is their corrosive nature. In this work, three ceramic crucibles (Al 2O 3, SnO 2 and ZrO 2) were tested in the melting of the system 40 PbO-35 BiO 1.5-25 GaO 1.5 (cation-%). After glass melting, crucibles were transversally cut and analyzed by scanning electronic microscopy (SEM), coupled to microanalysis by energy dispersive spectroscopy (EDS). Results indicated that zirconia crucibles presented the highest corrosion, probably due to its smallest grain size. Tin oxide crucibles presented a low corrosion with small penetration of the glass into the crucible. This way, these crucibles are an interesting alternative to melt corrosive glasses in instead of gold or platinum crucibles. It is important to emphasize the lower cost of tin oxide crucibles, compared to gold or platinum ones.

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Due to their low cost and high resistance to corrosion, ceramic crucibles can be used for the melting of PBG glasses (PbO-BiO 1.5GaO 1.5). These glasses present good window transmission from ultra-violet to infrared, making their use as optical fibres promising. However, their disadvantage is the high reactivity, leading to the corrosion of different crucibles, including gold and platinum ones. In this work, the corrosion of Al 2O 3, SnO 2 and ZrO 2 crucibles after melting at temperatures varying from 850 to 1000°C, was evaluated by Scanning Electronic Microscopy (SEM) in conjunction with microanalysis by EDS. The lead diffusion profile in the crucible material was obtained. Diffusion coefficients were calculated according to the Fick and Fisher theories. Results indicated that the different crucibles presented similar behaviour: in the region near the interface, diffusion occurs in the volumetric way and in regions away from the interface, diffusion occurs through grain boundary.

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Purpose: The objective of this study was to test the following hypothesis: the silica coating on ceramic surface increases the bond strength of resin cement to a ceramic. Materials and Methods: In-Ceram Alumina blocks were made and the ceramic surface was treated: G1 - sandblasting with 110-μm aluminum oxide particles; G2 - Rocatec System: tribochemicai silica coating (Rocatec-Pre powder + Rocatec-Plus powder + Rocatec-Sil); G3 - CoJet System: silica coating (CoJet-Sand) + ESPE-Sil. The ceramic blocks were cemented to composite blocks with Panavia F resin cement (under a load of 750 g/1 min). The cemented blocks were stored in distilled water at 37°C for 7 days and sectioned along the x and y axes with a diamond disk. Samples with an adhesive area of ca 0.8 mm 2 (n = 45) were obtained. The samples were attached to an adapted device for the microtensile test, which was performed in a universal testing machine (EMIC) at a crosshead speed of 1 mm/min. Results: The obtained results were submitted to ANOVA and Tukey's test. Mean values of tensile strength (MPa) and standard deviation values were: (G1) 16.8 ± 3.2; (G2) 30.6 ± 4.5; (G3) 33.0 ± 5.0. G2 and 63 presented greater tensile strength than G1. There was no significant difference between G2 and G3. All the failures took place at the ceramic/resin cement interface. Conclusion: The silica coating (Rocatec or CoJet systems) of the ceramic surface increased the bond strength between the Panavia F resin cement and alumina-based ceramic.

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Purpose: This study tested the hypothesis that the tribochemical silica coating on ceramic surfaces increases the bond strength of resin cement to a glass-infiltrated zirconium-based ceramic. Materials and Methods: Fifteen blocks of In-Ceram Zirconia from CEREC InLab (5 per group) and 15 composite blocks (Z-250) 5 mm x 5 mm x 4 mm were made. The ceramic surfaces were polished, and the blocks were divided into three groups: (1) airborne abrasion with 110-μm aluminum oxide particles; (2) Rocatec system, tribochemical silica coating; and (3) CoJet system, tribochemical silica coating. The ceramic blocks were cemented to the composite blocks using Panavia F according to the manufacturer's specifications. All samples were stored in 37°C distilled water for 7 days and later sectioned in two axes using a diamond disk under cooling to obtain specimens with a cross-sectional area of approximately 1 mm2 (n = 45). Each specimen was then attached with cyanoacrylate glue to an adapted device for the microtensile test, which was carried out on a universal testing machine. Results: The results were subjected to ANOVA and Tukey's test. Group 2 (23.0 ± 6.7 MPa) and group 3 (26.8 ± 7.4 MPa) showed greater bond strength than group 1 (15.1 ± 5.3 MPa). There was no significant difference between groups 2 and 3. All failures were in the adhesive zone. Conclusion: The hypothesis was confirmed - the tribochemical systems increased the bond strength between Panavia F and In-Ceram Zirconia.