Papers by Oscar Rubem Klegues Montedo
Materials Science Forum, 2018
In the context of energy economy and thermal comfort, phase change materials (PCMs) have many use... more In the context of energy economy and thermal comfort, phase change materials (PCMs) have many useful applications. In this study, type A zeolite was tested as a matrix for impregnating obtaining a PCM-impregnated zeolite. A sample of type A zeolite was analyzed by X-ray diffraction (XRD) and X-ray fluorescence (XRF). The porosity was evaluated by scanning electron microscopy. Following that, an apparatus was mounted for vacuum impregnation to incorporate calcium chloride hexahydrate (CaCl2.6H2O), which is a PCM, in the pores of the zeolite. The impregnation and the retention of the phase change material in zeolites were assessed using Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS) on the scanning electron microscopy (SEM) and Differential Thermal Analysis (DTA) to simulate thermal cycles testing to determine the thermal behavior of the compound. The results of the XRD and FTIR analyses showed that CaCl2.6H2O remains in the zeolite phase after the impregnation and the thermal cycling performed on the material shows that there is a positive influence on the thermal behavior of the impregnated material. Varying the amount of the studied PCM between 0 and 30 wt%, different grout boards were constructed. The thermal behavior of the PCM-impregnated zeolite compared to the reference material (pure zeolite) showed an effective temperature difference (38.1 to 33.9 °C), which can lead to significant energy savings.
Process Safety and Environmental Protection
Ceramics International, 2021
Abstract Hydroxyapatite is the main mineral component of the bone and the main responsible for th... more Abstract Hydroxyapatite is the main mineral component of the bone and the main responsible for their hardness and mechanical strength. It shows enormous scientific and technological value as it presents a potential for application in medical purposes and pharmaceutical, chemical, and environmental remedy industries. Many authors have demonstrated the possibility of hydroxyapatite synthesis from different sources and synthesis methodologies. However, studies which lead to an effectively controlled crystallite size and crystallinity are still scarce. Our study aims to evaluate the effects of heat treatment temperature and high energy milling time on obtaining nanometric hydroxyapatite from a natural source. The characterization has been performed by employing thermal, chemical, structural, morphological, and surface area analysis. It has been possible to verify only hydroxyapatite formation. In the milled samples, it's been possible to verify a reduction in the crystallite size and crystallinity. The surface area increased from 0.07 to 41.37 m2/g, but excessive milling times caused agglomeration and reduced the surface area. The results showed that it is possible to synthetize nanostructured hydroxyapatite (9,8–95 nm) with crystallinity ranging from 3 to 99% from Tilapia bones. ANOVA has validated the results. The produced materials present an excellent potential for application in the biomedical or adsorption substances area.
Materials Science Forum, 2016
This work presents a study about thermal properties of a ceramic material based on NdBaCu system ... more This work presents a study about thermal properties of a ceramic material based on NdBaCu system sintered with barium carbonate. These specialized ceramics are manufactured under special conditions and due to its unique electrical and thermal properties are frequently used by the electronic industry. Ceramics containing neodymium-barium-copper (NdBaCu) exhibit high conductivity at low temperatures. In this work, the ceramic samples were sintered with different percentage of barium carbonate, cupric and neodymium oxide and were characterized with Termogravimetric Analysis (TGA), Differential Scanning Calorimetric (DSC), Thermal Dilatometric Analysis (TDA) and X-Ray Diffraction Analysis (DRX). The results showed that the electrical conductivity of NdBaCu system is dependent on the calcination temperature. In turn, the complete calcination is dependent on the barium percentage and the thermal treatment conditions.
Cerâmica, Sep 1, 2013
This work reports on the characterization of ZrSiO 4 particulate-reinforced Li 2 O-ZrO 2-SiO 2-Al... more This work reports on the characterization of ZrSiO 4 particulate-reinforced Li 2 O-ZrO 2-SiO 2-Al 2 O 3 (LZSA) glass-ceramic matrix composites. The typical physical/mechanical and chemical properties of the glass batches and the composites were measured. A composition with 60 wt.% ZrSiO 4 was preliminarily selected because it demonstrated the highest values of bending strength (190 MPa) and deep abrasion resistance (51 mm 3). To this same composition was given a 7 wt.% bentonite addition in order to obtain plasticity behavior suitable for extrusion. The sintered samples (1150 °C for 10 min) presented a thermal linear shrinkage of 14% and bending strength values of 220 MPa.
Cerâmica, Sep 1, 2019
Efeito da temperatura de sinterização e da adição de fibras poliméricas em cerâmica porosa obtida... more Efeito da temperatura de sinterização e da adição de fibras poliméricas em cerâmica porosa obtida a partir de resíduos do processo Kraft (Effect of sintering temperature and polymeric fiber addition on porous ceramics obtained from residues of Kraft process)
Resources Policy, Mar 1, 2022
Materials Research Express, 2017
Zeolites are microporous crystalline hydrated aluminosilicates with absorbent and catalytic prope... more Zeolites are microporous crystalline hydrated aluminosilicates with absorbent and catalytic properties. This material can be used in many applications in stored-pest management such as: pesticide and fertilizer carriers, animal feed additives, mycotoxin binders and food packaging materials. Herein, four 4A zeolite forms were prepared by ion-exchange and their antifungal effect against Aspergillus flavus was highlighted. Additionally, the antimycotoxin activity and the aflatoxin B1 (AFB1) adsorption capacity of these zeolites as well as their toxic effects on Artemia sp. were investigated. The ion-exchanged zeolites with Li+ and Cu2+ showed the best antifungal activity against A. flavus, including effects on conidia germination and hyphae morphological alterations. Regarding to antimycotoxin activity, all zeolite samples efficiently inhibited the AFB1 production by A. flavus. However, the ion-exchanged zeolites exhibited better results than the 4A zeolite. On the other hand, the AFB1 adsorption capacity was only observed by the 4A zeolite and zeolite-Li+. Lastly, our data showed that all zeolites samples used at effective concentrations for antifungal and antimycotoxin assays (2 mg ml−1) showed no toxic effects towards Artemia sp. Results suggest that some these ion-exchanged zeolites have great potential as an effective fungicide and antimycotoxin agent for agricultural and food safety applications.
Journal of Cleaner Production, Jun 1, 2023
Materials Science Forum, 2018
In Brazil, ceramic plates are widely used in the construction industry for both small and large c... more In Brazil, ceramic plates are widely used in the construction industry for both small and large constructions in view of their advantages compared with other coating systems [1]. These advantages include ease of maintenance, durability, impermeability, and ease of cleaning. Despite these favorable characteristics, problems occur due to aging of a building. The most common of these problems is the loss of adhesion of ceramic tiles with facades [2]. It is commonly observed that after a few years of use the plates begin to loosen, thereby endangering individuals and properties.
Materials Today Chemistry, Dec 1, 2020
Zirconia-supported tungsten oxide (WO x /ZrO 2) catalysts were successfully synthesized using a s... more Zirconia-supported tungsten oxide (WO x /ZrO 2) catalysts were successfully synthesized using a suspension containing amorphous hydrous zirconia precipitates [ZrO x (OH) 4-2x $yH 2 O] n and tungstate monohydrate (WO 3 $H 2 O) precipitates. The procedure involved the dissolution of the WO 3 $H 2 O precipitate during the aging process with the release of oxyanion [WO 4 ] 2species, interaction of this species with the surface of the [ZrO x (OH) 4-2x $yH 2 O] n precipitate and, formation of active WO x species after thermal treatment. Non-bridging hydroxyl (OH À) groups present in the [ZrO x (OH) 4-2x $yH 2 O] n precipitate act as an active agent for the WO 3 $H 2 O dissolution. N 2 physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction using hydrogen (H 2-TPR), temperature-programmed desorption of ammonia (NH 3-TPD), Fourier-transform infrared (FTIR) spectroscopy of adsorbed pyridine, and Raman spectroscopy were used to elucidate the catalyst structure eperformance relationship. The catalytic activity was evaluated for the oxidative desulfurization (ODS) of a model fuel containing dibenzothiophene (DBT). For a fixed WO 3 $H 2 O content, longer aging times improved the catalyst activity, reaching a maximum when WO 3 $H 2 O was completely dissolved. The increase in surface area and formation of more active Zr-WO x clusters and polytungstates are observed for the highest active catalysts. A synergetic effect between local Lewis and Brønsted acid sites seems to have contributed to the observed superior activity. The proposed strategy provides an efficient approach to produce active WO x /ZrO 2 catalysts and may be applicable for designing other heterogeneous catalytic systems.
Journal of Alloys and Compounds, Nov 1, 2016
Abstract InO 1.5 -stabilized zirconia (InSZ) possess high ionic conductivity at intermediate temp... more Abstract InO 1.5 -stabilized zirconia (InSZ) possess high ionic conductivity at intermediate temperatures and thus it is a potential candidate for use as electrolyte for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). However, the technological application of InSZ is restricted by its low phase stability and poor physical properties. In this study, the effect of codoping with MoO 3 on the microstructure and properties of a series of cubic InSZ samples were investigated. We observe that the lattice parameter was not dependent on the concentrations of InO 1.5 and MoO 3 and in all of the InSZ samples codoped with MoO 3 there was stabilization of the cubic phase with an average lattice parameter of 0.5116 nm. With respect to the physical properties, the addition of MoO 3 to the cubic InSZ resulted in a 13.5% increase in the hardness and 9% increase in the thermal expansion coefficient. In addition to these improvements, the most important result was an increase of about one order of magnitude in the ionic conductivity of InSZ after the addition of MoO 3 . As will be demonstrated herein, all of the improvements are associated with the action of the codopant MoO 3 in relation to changes in the microstructure of the InSZ cubic matrix.
Journal of Thermal Analysis and Calorimetry, Nov 20, 2015
Abstract This work evaluated the effect of a LZSA (Li2O·ZrO2·SiO2·Al2O3) glass-ceramic on the sin... more Abstract This work evaluated the effect of a LZSA (Li2O·ZrO2·SiO2·Al2O3) glass-ceramic on the sintering behavior of alumina obtained via liquid-phase sintering. An experimental plan based on three different contents (7, 15 and 21 vol%) of a particulated (d50 = 1.52 µm) 11.6Li2O·16.8ZrO2·68.2SiO2·3.4Al2O3 glass-ceramic and three different particulate aluminas (d50 = 0.5, 1.7 and 2.8 µm) was defined. Each formulated composition (composite) was wet-mixed, dried and formed by uniaxial pressing (128 MPa). The sintering behavior and microstructural characteristics were studied and observed by optical dilatometry and scanning electron microscopy, respectively. The results showed that the LZSA glass-ceramic increased the densification of the studied aluminas, resulting in a reduction of 25–100 °C in the sintering initiation temperature. The higher the LZSA content was, the lower the maximum linear shrinkage, the higher the maximum LS rate and the higher the relative density, regardless of the alumina used. These effects were more pronounced for coarse alumina (Ac). The composite Ac21 achieved a relative density of 95 % in the samples sintered at 1600 °C/40 min compared to 85 % for the samples sintered at 1600 °C/4 h. Thus, the LZSA glass-ceramic is a potential candidate for improving the densification of alumina in applications where wear resistance is the main requirement.
Ceramics International, Aug 1, 2017
Effect of temperature and holding time on the densification of alumina obtained by two-step sinte... more Effect of temperature and holding time on the densification of alumina obtained by two-step sintering, Ceramics International,
Materials Science Forum, 2018
Pulp and paper mills have a process that generates waste with high levels of CaO and SiO2, which ... more Pulp and paper mills have a process that generates waste with high levels of CaO and SiO2, which can be valued as an alternative mineral source in the cement industry. In this work the lime mud, biomass ashes and WWTP sludge are used in the production of clinker. Analysis of X-ray diffraction (XRD) confirmed the crystalline phases calcite and quartz. Chemical analysis by X-ray fluorescence (XRF) identified Al2O3, CaO and SiO2, providing support for the calculation of theoretical stages by applying the Bogue equations. Five formulations and three processing temperatures (1350, 1400, 1455 °C) were studied. The products obtained and an ordinary Portland cement (OPC) were characterized by XRD with quantification by the Rietveld method. The results showed that the processing conditions used produced belíticos (higher content of C2S) and Portland (C3S content greater) ecoclinker.
Chemical Engineering Research & Design, Jul 1, 2017
Waste streams generated from pulp and paper mills show high potential to be used as alternatives ... more Waste streams generated from pulp and paper mills show high potential to be used as alternatives raw materials for production of clinker. In this context, this work aims to evaluate the use of such materials to obtain hydraulic binders, which are referred to as Ecoclinkers and Ecocements. Lime mud, wastewater treatment process sludge and biomass ashes were characterized, and five formulations (F1 to F5) were developed by applying the Bogue equations. These compositions were processed at three different clinkering temperatures (1350, 1440 and 1455 °C). The formulated Ecoclinkers and a reference hydraulic binder were characterized by X-ray diffractometry to identify the crystalline phases, which were subsequently quantified by the Rietveld method. The results showed that crystalline phase characteristics of clinkers and cements, and compression strengths of ~20 MPa after 28 days curing time were obtained, confirming the potential use of the investigated waste as alternative materials for production of clinker.
Ceramics International, Feb 1, 2022
Ceramics International, Jun 1, 2020
The impact of the microstructural properties of alumina on its mechanical properties is examined ... more The impact of the microstructural properties of alumina on its mechanical properties is examined in this study. Furthermore, a comparison of the mechanical behaviours of alumina samples obtained by two-step and existing sintering techniques is presented. The results are rationalised by evaluating the changes in the densities and grain sizes of alumina samples. Different two-step treatments were used on commercial alumina (99.7 mass %-Al 2 O 3 content, 0.73 μm average particle size) and compared with the existing sintering technique. Alumina powder was formed by uniaxial pressing, and the samples were treated using heat. Microstructural analyses of the samples were performed with a scanning electron microscope. The mean grain size was determined via the intercept method. Porosity was determined by the relationship between the apparent and theoretical densities of the sintered alumina. The bending strength test was performed based on ASTM 1161-13. Fracture toughness was measured based on the notch method. The microhardness test was performed using the Knoop technique. The results showed that mechanical properties of the samples prepared using two-step sintering were improved-the bending strength, fracture toughness, and Knoop microhardness increased from 286 to 303 MPa, 4.09-4.35 MPa m 0.5 , and 17.5-17.6 GPa, respectively-compared with those fabricated using the existing sintering technique, even with a higher porosity of 2.36% in samples obtained by two-step sintering and 1.80% in the existing sintering technique. Factorial analysis demonstrated that the temperature and holding time of the second step individually affect the relative density; however, the impact of temperature is more significant. Despite this, the interaction between temperature and holding time of the second step has the most significant impact on the average grain size.
Revista Internacional De Contaminacion Ambiental, Feb 1, 2019
Waste generation is increasing in many industries. Therefore, effective measures are required to ... more Waste generation is increasing in many industries. Therefore, effective measures are required to secure an environmentally sustainable and economically viable waste destination. Co-processing in clinker kilns at high temperatures and incorporation into cement matrices may stabilize many types of industrial waste. This paper presents the results of a study that characterized pulp and paper mill waste and their recycling in clinker production. Chemical characterization and estimation of the hazardous potential of lime mud, biomass ash, and wastewater treatment plant (WWTP) sludge were performed in accordance with brazilian standard (NBR) 10004:2004. Biomass ash and WWTP sludge were classified as non-hazardous (class II), while lime mud was classified as hazardous (pH > 12.5, class I). These wastes were mixed (69 wt % lime mud, 29 wt % biomass ash, and 2 wt % WWTP sludge), and the resulting mixture was processed at 1455 ºC to generate 'Ecoclinker'. The clinker was characterized, milled, and mixed with calcium sulphate for use as an 'Ecocement'. Mortars were obtained and cured for periods of seven and twenty-eight days. The hardened product exhibited a mechanical strength of ~20 MPa. The leaching and pH tests indicated that these parameters were within the permitted limits, confirming that this waste-based cement was non-hazardous. Palabras clave: reciclaje de residuos, clínker, mortero RESUMEN La generación de residuos sólidos está aumentando en muchos sectores industriales; por lo tanto, se requieren medidas efectivas para garantizar un descarte de residuos que sea ambientalmente adecuado y económicamente viable. El coprocesamiento en hornos de producción de clínker a altas temperaturas, así como la incorporación en
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Papers by Oscar Rubem Klegues Montedo