Influence of the conformation method on flash sintering of ZnO ceramics

Flash Sintering has been shown to be a promising alternative in obtaining high-density ceramics with grain growth control. However, some conditions are still under development. Regarding the dimension of the ceramic, there is a limitation related to obtaining a homogeneous material in large specimens, in order to avoid the formation of preferential current flow paths. Depending on the temperature required for the flash event to occur, some electrode materials have a high cost, or controlled atmosphere operations are required. Typically, the electrodes used in flash sintering consist of platinum, however, in some cases, other materials may be a cheaper suitable alternative, such as stainless steel[1] or nickel-chromium alloys. Also, the use of different compositions in the electrode influences the conductivity of the material, which affects the onset of thermal runaway[2]. In this regard, different conformation techniques were studied in order to improve the homogeneity of the sintered ZnO ceramic body. Additionally, the feasibility of the use of Inconel (nickel-chromium) electrodes in the replacement of platinum electrodes was evaluated. Then, ZnO specimens were conformed (cylindrical shape - 6 mm diameter and 5 mm thickness) by uniaxial pressing under 140MPa and 300 MPa, isostatic pressing under 200 MPa, and slip casting. All experiments were conducted isothermally at 800 °C in an adapted tube furnace[3], with an applied field of 60 V/cm and 200mA/mm2 as maximum current density, using either platinum or Inconel electrode. Figure 1 shows the variating in time incubation with respect to the conformation method used. The distinct incubation times are justified by the difference in the pore distribution, which affects the electrical resistivity of the samples. Also, according to Figure 1, it can be seen that in addition to presenting a higher electrical resistivity, which increased the incubation time, the samples conformed by slip casting are also characterized by the high formation of hotspots, which can be observed by the appearance of several spikes during the occurrence of the flash event. Figure 2 shows, for the samples conformed by uniaxial pressing (140 MPa), the difference between incubation times in relation to the material used for the electrode. It can be seen that, in this case, the use of Inconel increased the incubation time. Microstructural and further analyzes are being conducted. Please click Additional Files below to see the full abstract

Properties of concrete manufactured with use of ceramic sanitary ware waste as aggregate

In concrete manufacture, cement (Portland type is the most used), water and aggregates (classified intocoarse and fine) are used. With the use of several raw materials the generation of waste is inevitable, both inconstruction and in other sectors, such as the industries producing ceramic materials. Among the types ofwaste from such industries, can be mentioned the ceramic scrap (from the sanitary ware industry). Accordingto the above, the aim of this research was to study the addition of ceramic scrap as a coarse aggregate in differentproportions in the concrete formulation. In order to do this, was select wastes from an industry in thesouth of Minas Gerais (Brazil), and prepare specimens to determine the fresh (slump test, adhesiveness andporosity) and hardened (compression strength) of concrete. Were fabricated five concrete formulations, onereference (RC) and four with ceramic scrap substituted for coarse aggregate in the proportions of 25% (CSCI),50% (CSC-II), 75% (CSC-III) and 100% (CSC -IV). Fresh concretes, two formulations did not show adhesiveness(CSC-III and CSC-IV) and two a small water runoff (CSC-I and CSC-II), however, without compromisingthe concrete’s workability. Regarding the compression strength, the average values presented werevery good, including the formulation with 100% ceramic scrap (fc = 47.78 MPa). Another important aspectobserved in the rupture modes was the small adhesion between the ceramic scrap and the mortar due to theglazing in the contour of the waste. As for the porosity of the concretes, those with 25%, 75% and 100% ofceramic scrap in their composition presented lower values than the reference concrete.Keywords: Ceramic scrap; Concrete; Waste; Mechanical properties

Interdisciplinary project applied to engineering education: construction of a miniature ceramic industry

The greatest challenge of undergraduate engineering courses is to encourage creativity, cooperation with other students, teamwork, and motivation in the first years of their courses. While students have little or no contact with advanced disciplines, it is very difficult to attract their interests and encourage them to develop the skills in their undergraduate courses. This work aims to achieve these objectives through a mini-factory project involving the construction of a production line of ceramic tiles on a laboratory scale, from the ceramic processing using raw materials to the shipping of the final product. Having been given an established monthly demand for ceramic tiles, the students determined the construction requirements of the mini-factory, as they have created the layout, including the processing equipment, the dimensioning of equipment, and its operational structure. This article intends to describe the successful creation of the ceramic tile mini-factory, including the objectives, benefits, and inherent difficulties of the process and the receptivity of the exercise by the students involved

Evaluation of the Photocatalytic Potential of TiO2 and ZnO Obtained by Different Wet Chemical Methods

<div><p>This paper describes the development of TiO2 and ZnO particles by a chemical route, using two different wet synthesis methods: polymeric precursor (PP) and sol-gel (SG). This study aimed to shed a light on how the synthesis method affects the photocatalytic activity of these oxides. Rhodamine B (RhB) degradation was used as a probe reaction to test the as-synthesized TiO2 and ZnO photoactivity. It was observed that surface availability, which is related to the presence of synthesis residue, is the key parameter to determine photoactivity. ZnO PP and ZnO SG presented degradation of 88% to RhB. Both samples presented synthesis residue on the surface. On the other hand, TiO2 PP presented a better performance than TiO2 SG, once 90% of RhB was degraded, while TiO2 SG degraded 80% of the dye. In this case, TiO2 PP was free of synthesis residue on the surface, while TiO2 SG presented residues.</p></div

Tempering Temperature Influence on 13Cr4Ni0.02C Steel Corrosion Resistance

<div><p>The thermal treatments employed in alloys are essential to obtaining desired microstructures and corrosion resistance properties. In this paper the low carbon martensitic steel 13Cr4Ni0.2C with different tempering temperatures was studied using potentiodynamic polarization technique in synthetic marine environment, in order to evaluate the effect of the tempering temperature on the steel corrosion resistance in an environment that simulates the conditions of use in oil and gas production. Microscopy results showed differences in the microstructure of tempered steel at low (620°C) and high (770°C) temperatures, indicating the appearance and extending of martensite laths with increasing temperature. Polarization tests showed that tempering temperature located between 620°C and 710°C indicated passive film formation and tempering temperatures of around 620 °C showed better resistance values to pitting corrosion.</p></div

Obtention and characterization of collagen and chitosan based cements for bone regerneration. Part 1: extraction and characterization of collagen

Several cements are used as biomaterials. Biopolymers such as chitosan and collagen exhibit excellent biocompatibility and can be used in the remodeling of bone tissue. The cement must have high mechanical strength and compatibility with original tissue. In this context, the objective of this study was to extract, characterize and cross-link collagen from bovine tendon, forlater associate it with chitosan and calcium phosphate to obtain cements for bone regeneration. Glutaraldehyde was used as cross-linker in 0.1, 0.5, 1.0 and 10% concentration. Infrared analysis confirmed the presence of functional groups characteristic of collagen, whereas the capacity of water absorption decreased with the increasing of cross-linking degree. Denaturation temperatures of collagen samples were obtained by Differential Scanning Calorimetry and Scanning Electron Microscopy showed the fiber structure characteristics of collagen, which were more organized for high degree of cross-linking samples