Search

The characterization of ceramic foams via X-ray microtomography imaging method is often restricted to a general overview of samples, either to perform qualitative or quantitative analyses. To assess the foam with a focus on some specific components of its structure, such as hollow struts’ cavities and open cells, the generalized characterizations must be overcome. This work presents image analysis methodologies, based on open-source software, tools, and plugins, to achieve the aforementioned characterizations. SiC and ZrO2 foams samples were analyzed and some of the results were compared with those accomplished with pieces of commercial software. The results show good agreement between open-source and commercial software applications, indicating that the presented methodologies can be freely applied by any researcher to analyze their foams.

Resumo Este trabalho estuda o incremento da resistência mecânica à flexão e força de ruptura de porcelanatos através da têmpera química. A troca catiônica resulta em tensões residuais de compressão na superfície do material. Foram selecionados porcelanatos técnicos (60×60 cm) com 100%, 90% e 77% da espessura padrão. Os porcelanatos foram prensados, secos e sinterizados em forno industrial. O processo de têmpera química foi realizado com uma mistura de sais de composição correspondente a 27% de nitrato de potássio (KNO3 > 99%) e 73% de fertilizante (K2O ~ 43%). O tratamento químico foi realizado a 480 ºC durante 25 min. Os resultados mostraram que as propriedades mecânicas do material atenderam à norma vigente (ABNT 10545-4 2018). Mesmo o material com 77% da espessura padrão, obteve-se um aumento de 15% na tensão de ruptura e 16% na força de ruptura. A análise de Weibull comprovou que as propriedades mecânicas foram incrementadas após a têmpera química.

The Mg(OH)2 and MgO nanomaterials were synthesized by precipitation followed by calcination from the industrial waste MgCl2·6H2O originated from the magnesiothermic reaction of solar-grade silicon (P-waste). A similar synthesis process was carried out in parallel with the commercial precursor MgCl2·6H2O (P-com) to compare the products obtained with precursors. For the synthesis of Mg(OH)2 (1st step), aqueous solutions were prepared (low pH for P-waste and natural pH for P-com). NaOH was used as a precipitating agent, and different synthesis temperatures were evaluated (25, 50, 75, and 90 °C). MgO (2nd step) was obtained through calcination at 500 °C for 30 min of previously synthesized Mg(OH)2. The P-waste and the two synthesis products (Mg(OH)2 and MgO) were chemically, thermally, structurally, and morphologically characterized. The results showed that the P-waste is more soluble in an acidic environment, and both precursors present similar thermal behavior and structural profiles. The Mg(OH)2 obtained in the 1st step of synthesis by both precursors presented the crystalline phases Brucite with lamellar morphology and Halite (NaCl) remained of the precursors. The powders obtained from both precursors in the 2nd step presented the same crystalline phase Periclase (MgO), but different morphologies such as fragmented lamellar for the P-com and cubic for the P-waste. However, the particle size distribution narrows, and the D50 of MgO decreases as a function of increasing the synthesis temperature employed in the 1st step for the P-com. In contrast, the D50 of MgO decreases in the P-waste as a function of low pH. Furthermore, surprisingly, it was observed that the morphology of MgO nanocubes can be obtained from residues and commercial precursors at low calcination temperature and short time (500 °C/30 min) when the Halite remaining from the purification washes is above 4.0% by weight.

Feldspathic porcelains are the most used ceramics for esthetic dental restorations due to their superior optical properties and their adhesive behavior, standing out among all the others. However, their mechanical performance is usually not appropriate enough for the oral environment, being chipping and fracture the most commonly reported failures. Different approaches have been suggested to improve their mechanical behavior, including chemical tempering by ion exchange. However, the highlighting of other materials drew attention to this promising process, missing the opportunity to take advantage of the esthetic and adhesive characteristics of feldspathic porcelains in more demanding situations. Chemical tempering by ion exchange has evolved with remarkable improvements, offering new possibilities for feldspathic porcelains. Thus, a contemporary critical perspective is presented.

Scaffolds of PDLLA were produced to be implemented in maxilofacial surgeries inducing bone repair and regeneration. To prepare these scaffolds, bioglass (BG58S) was synthesized by sol-gel method, in order to be applied as osteoconductive dispersed particles in PDLLA matrix. Once presenting greater facility on parts fabrication, this polymeric matrix enables complex geometries production besides presenting compatible degradation rate for scaffold absorption and bone regeneration. Scaffolds production was performed by selective laser sintering in order to obtain tailored-made parts. FTIR and XRD analyses were carried out to observe the composition and evaluate the presence of crystalized phases in bioglass, obtaining Wollastonite. SEM was used to observe the BG particle distribution in PDLLA matrix and flexural test was performed to evaluate the composite mechanical properties. Results showed that was possible to obtain pieces using SLS method and with addition of 10%wt BG to polymeric matrix, flexural modulus and strength increased regarding to pure polymer.

The importance of self-reinforced bioabsorbable polymers has been growing due to their use in orthopedic and dental implants. Bioabsorbable polymeric implants manufactured only by the processes of injection or extrusion without the post processing of self-reinforcing leave a great deal on presenting an appealing alternative in terms of the mechanical strength suitable for use in the fixation of bone fractures. One of the most promising ways to promote the increase of mechanical properties of bioresorbable polymers is through the self-reinforcing technique. Self-reinforcing occurs when the internal structure of the polymer is strongly oriented in the direction of the deformation. Knowing the levels of mechanical strength obtained is essential to determine the sites of application of the component. The objective of this work was to study the method and the influence of self-reinforcing conditions, such as reduction ratio, temperature and deformation speed, on the quality and mechanical properties of small cylindrical bars obtained from the bioresorbable polymer P (L/DL) LA 70:30. The different processing conditions led to distinct levels of mechanical strength. Resistance values obtained in this work are the highest ever recorded for this material. It is important to stress that the values of mechanical strength achieved are within the limits accepted as safe for utilization in the fixation of craniofacial fractures, a fact that significantly enhances the prospects in this area.

Sintered nickel powder is proposed to be used as porous wicks in heat pipes and capillary pumps. In this work the manufacturing procedure for tubular wicks for capillary pump application is discussed. The porosity, mechanical resistance and roundness of tubular wicks made of carbonila powder, atomized powder and a powder mixture of both are analyzed. A powder mixture was selected as the best raw material. In this case, pore size in the range of 2 to 24 mm and porosity about 50% were measured. First tests carried out in the laboratory, using acetone as the working fluid, show capillary pumping pressures up to 4 kPa and heat fluxes of about 1 W/cm2 in a two-phase heat transfer loop.

The rheological behavior of alumina molding feedstocks containing polyethylene glycol (PEG), polyvinylbutyral (PVB) and stearic acid (SA) and having different powder loads were analyzed using a capillary rheometer. Some of the feedstocks showed a pseudoplastic behavior of n < 0, which can lead to the appearance of weld lines on molded parts. Their viscosity also displayed a strong dependence on the shear rate. The slip phenomenon, which can cause an unsteady front flow, was also observed. The results indicate that the feedstock containing a lower powder load displayed the best rheological behavior. The 55 vol. % powder loaded feedstock presented the best rheological behavior, thus appearing to be more suitable than the formulation containing a vol. 59% powder load, which attained viscosities exceeding 10³ Pa.s at low shear rates, indicating its unsuitability for injection molding.

Las fundiciones blancas al alto cromo utilizadas en componentes demolinos de carbón son materiales que presentan diferentes resistencias al desgaste,dependiendo del tratamiento térmico usado en su fabricación. Las propiedades mecánicas,microestructurales y tribológicas de la aleación con 22% de cromo y 3% de carbono (II DASTM A532-10) y su infl uencia en la resistencia al desgaste fueron investigadas. Para lacaracterización de la aleación fueron realizados diversos ensayos, utilizando los siguientesequipos de laboratorio: durómetro, microdurómetro, microscopio óptico, microscopioelectrónico de barrido, difracción de rayos X, espectrofotómetro de emisión óptica, yequipo para ensayo de desgaste abrasivo de acuerdo con la norma ASTM G65-04 (2010).Los resultados encontrados mostraron que la resistencia al desgaste incrementa cuandola matriz tiene una baja fracción volumétrica de austenita retenida y una alta fracción decarburos secundarios. También indican que no es necesario usar largos tiempos durante ladesestabilización en la aleación II D para obtener una óptima resistencia al desgaste, cuandola aleación fue previamente recocida. Estos resultados indican que la industria puede usartiempos cortos durante la desestabilización de los rodillos de molinos de carbón.