Materials Science Forum Vol. 820

Abstract: In the oil production, many types of sensors are used in order to monitor some important parameters such as temperature, pressure and flow. These sensors are subjected to harsh operating conditions. Therefore they must present an inert and stable behavior in these conditions. The temperature sensors that are more suited to the oil industry are the Temperature Detectors by Resistance (TDR), because they have high accuracy and wide temperature range. Usually these devices are built with metals as detectors of temperature by encapsulated resistance in inert ceramics. The main objective of this research is to produce new ceramics of a Ca₂AlZrO_5,5 cubic complex perovskite structure for the encapsulation of temperature sensors. The stoichiometric amounts of the constituent chemicals, with a high degree of purity, are homogenized, through a solid state reaction in a high energy ball mill. They are then compacted by uniaxial pressing and calcined at 1200°C for 24 hours. Soon after, the tablet is crushed giving place to a ceramic powder and the analysis of X-ray diffraction is performed. According to the sintering behavior of the ceramic powder, the microstructure and the homogeneity are studied by the Scanning Electron Microscopy. The results are presented in terms of the potential of this ceramic for applications as components of temperature sensors.

Abstract: Y₃Al₅O₁₂ (YAG - Yttrium Aluminum Garnet) ceramic oxides has been widely used as a reinforcing phase to Al₂O₃ in order to achieve a composite with good mechanical properties. These factors are possible because the Al₂O₃ and YAG oxides possess thermal compatibility and high resistance to oxidation and corrosion, which makes your job quite attractive relative to other ceramics. This research was performed in two compositions, one in the eutectic composition with 63.65% Al₂O₃ and Y₂O₃ 36.35wt.% and one with 80.00% of Al₂O₃ and 20.00wt.% of Y₂O₃. After milling for 2h, the powder mixtures were dried for 48h at 120°C. Mixtures were then comminuted by mortar and pestle and sieved using a 100 mesh sieve. The compositions were compacted uniaxially at 70MPa for 30s. The two mixtures were sintered at 1500°C or 1600°C for 3h. The samples were evaluated for hardness by Vickers indentation, fracture toughness by the indentation method (K_IC) and Scanning Electron Microscopy (SEM). It was verified that the eutectic composition sintered at 1600°C-3h showed the highest hardness among the others, 10GPa, and a fracture toughness of 3.8MPa.m^1/2, both consistent with the literature results. The SEM images showed a reduction in porosity with increasing of sintering temperature.

Abstract: Doped lanthanum chromite has been the most common material used as interconnectors in solid oxide (SOFC) fuel cell, allowing for the stacking of the SOFC. Reducing the operating temperature, to around 800°C, the cells of solid oxide fuel have made the use of metal interconnectors possible as an alternative to ceramic LaCrO₃. From the practical point of view for the material to be a strong candidate as an interconnector, it must have good physical and mechanical properties, such as resistance to oxidizing environments and reducers, facility to manufacture, and adequate thermomechanical properties. In this work, a study was conducted on the thermomechanical properties of metallic interconnectors (AISI 444) covered with La_0,8Ca_0,2CrO₃ by way of deposition technique for pyrolysis spray for the intermediate temperature (IT-SOFC) fuel cell. The material was characterized by X-ray diffraction (XRD), oxidative test, flexural strength at room temperature and at 900°C, and scanning electron microscopy (SEM). The evaluation of the phases formed on metallic interconnectors coated with La_0,8Ca_0,2CrO₃ on both the deposition and after oxidative assay was performed by XRD. The oxidative behavior showed increased resistance to oxidation of the metal substrate covered by La_0,8Ca_0,2CrO₃. In the flexural strength of the coated metal substrate, it was noted only in the increasing temperature. With the aid of SEM, the formation of layers of Cr₂O₃ and (Cr, Mn)₃O₄ on the metallic substrate was seen, and confirmed stability of La_0,8Ca_0,2CrO₃ ceramic film after oxidative test.

Abstract: Zirconium diboride (ZrB₂) is a covalent compound that leads the category of ultra high temperature ceramics materials owing to its unique properties. In this work, the effect of addition of beta-silicon carbide (β-SiC) in pressureless sintering of ZrB₂ was investigated. Four compositions were prepared with 0, 10, 20 e 30 vol% of SiC. ZrB₂ powder and mixtures were prepared in by planetary milling with SiC spheres at 4 h. Two sintering temperatures were used, one at 2050 oC/1h and other at 2150 °C/1h. The addition of SiC has promoted an increasing in densification with the increasing of SiC content. The total densification of sample sintered at 2050 oC was 90% of theoretical density for sample with 30 vol% of SiC, while the maximum densification for temperature of 2150 oC was 91,0 %TD.

Abstract: In this work, we have s produced Al₂O₃-TiO₂ ceramic composites reinforced with rare earth oxide, lantânia (La₂O₃) ranging from 0 to 2 wt%, for the study of their phase stability, structureand microstructural chacteristics. The ceramic composites were produced by thermo-mechanical process. It was observed from the results of XRD after sintering no new phase is formed in addition to the characteristics of the precursor oxides. DTA shows the stability of the composites studied from 460oC temperature, meaning it does not present more phase changes. It was observed through the analysis of the results of X-ray diffraction after sintering the samples that no new phase is formed in addition to the characteristics of the precursor oxides indicating formation of the composite. However, there was variation in the peak concentration and intensities due to variations in the Al₂O₃ and La₂O₃ contents. The results obtained by scanning electron microscopy proved satisfactory with regard to good surface morphology, homogeneity and particle size distribution of the composite sintered at 1390oC for 40 hours. The samples with 1.0% and 1.5% La₂O₃ addition presented best results regarding these aspects

Abstract: Zirconium diboride (ZrB₂) is a material of particular interest because of the excellent and unique property combination of high melting point, high electrical and thermal conductivity. In this work, the effect of addition of beta-silicon carbide (β-SiC) on hot pressing sintering of ZrB₂ was investigated. Four compositions were studied with 0, 10, 20 e 30 vol% of SiC. ZrB₂ powder and mixtures were prepared by planetary milling with SiC spheres during 4 h. Samples were sintered at 1850 °C/1h with a pressure of 20 MPa in argon atmosphere. β-SiC has undergone phase transformation to α-SiC during sintering. The addition of SiC increased densification with increasing of SiC content. The total densification of sample was 96.8 % of theoretical density for sample with 30 vol% of SiC and Vickers hardness was 19.9 ± 0.3 GPa.

Abstract: The improvement on the development of porous ceramic materials has leaded to new technologies in thermal insulation, for example, composite materials for better performance of pressure vessels in rocket engines. Within this context, the present work aims to evaluate the ability of a refractory ceramic base alumina/zirconia through the processes of co-precipitation and replica method in an organic fiber template. The green body was burnt-out and sintered at 1200-1600°C to obtain the continuous porous ceramic fibers. In the FEG-SEM analysis, an interconnected porous structure with small grains was observed. The crystalline phases were determined by X-ray diffraction and compared to micro-Raman results regarding the crystalline structure confirms that there present in the material zirconia is composed of more than one phase. Porosity was calculated through a mercury porosimeter as 77.9%, and the Laser Flash method gave a thermal conductivity value of 1.61 K W.m⁻¹.K⁻¹ for the Al₂O₃-ZrO₂ fibers.

Abstract: The catalytic cracking of sunflower oil over vermiculite clay was studied in a thermal analysis system, the process being accompanied by thermogravimetry. The vermiculite was chemically modified by acid leaching and characterized by techniques of XRD, FTIR, SEM and TG. The catalytic test was performed in a thermal analysis system with heating up to 900 °C, with proportion oil/clay = 100. The results of thermogravimetry showed that in the presence of the catalyst, the thermograms present a single mass loss. The test was also performed with the molecular sieve Al-MCM-41 with proportion Si/Al = 25 and 75, with similar results to those presented by vermiculite.

Abstract: Ceramic materials present interesting properties and generate products that meet engineering requirements referring to this class for several applications. Aluminum oxide is a very good example of this class of materials, being applied widely in high technology areas especially where the abrasive and erosive wear are strongly demanded. Many factors interfere on the wear of alumina: material composition, characteristics of the used oxides, and the manufacturing process that defines the final microstructure. It is know that the grain size of the alumina has a strong influence on the wear rate and is the focus of several studies. The grain growth during sintering as well as the diffusion process can be controlled by using dopants in the alumina composition. Thus the aim of this paper is to present a review about the dopants interference on the grain size of alumina, which in turn influences the wear behavior of the alumina. The results described allow broad understanding on the subject

Abstract: Hydroxyapatite (HA) is the main mineral component of bones and teeth, and for this reason its synthetic analogous has been used with excellent clinical results as bone substitute. The biological apatite is typified as a poorly crystalline carbonate apatite (CHA) formed by nanosized particles with a great superficial area. This work aimed to study the influence of ultrasound technique on the morphology and crystallinity of nanoHA synthesized by chemical precipitation method. The nanoHA particles were obtained from CaCl₂·2H₂O and Na₃PO₄·12H₂O raw solutions and a powerful ultrasonic sound (UP400S) was used at different conditions during the synthesis. X-ray Diffraction, Infrared spectroscopy, Chemical Analysis and Scanning Electron Microscopy were used to characterize the synthesized nanoHA particles. The results indicated that HA nanoparticles with nanorods morphology were obtained in all conditions. By Scherrer`s formula, the crystallite size was determined and it was found that the increasing in ultrasound amplitude enhances the nanoparticles crystallinity.