Scielo RSS <![CDATA[Cerâmica]]> vol. 65 num. lang. pt <![CDATA[SciELO Logo]]> <![CDATA[Utilization of gypsum from construction and demolition waste in Portland cement mortar]]> Abstract Civil construction generates the largest amount of construction and demolition waste (CDW), most of which is not reused and is discarded as inert waste in landfills. The purpose of this study was to evaluate the feasibility of reusing gypsum recovered from CDW in the preparation of mortar. This material was examined to determine its specific mass, morphology, elemental composition and particle size distribution. Test specimens were prepared with a mix design of 1:3 (cement:sand), with the gypsum waste substituting part of sand in proportions of 0, 10, 20 and 30% (in volume). The consistency of the fresh mortar was evaluated: the specimens were tested to determine their flexural and compressive strength, apparent density, water absorption, voids index, and specific mass. After 28 days, the mechanical strength of the specimens exceeded the limits specified by NBR 13281 standard, indicating that up to 30% of ground gypsum waste can be included in a mortar. <![CDATA[Development of a microwave absorbing material based on molybdenum-doped niobium pentoxide]]> Abstract This work aimed to perform the characterization of electrical properties of niobium pentoxide, Nb2O5, pure and doped with molybdenum, prepared by powder metallurgy route and to do a comparative analysis of the influence of this material when sintered in a muffle or in a microwave oven. The results showed that the doping of the niobium pentoxide with 0.5% or 1% of molybdenum along with the process of sintering in a microwave oven make the material more applicable as a microwave absorber material for electromagnetic radiation in the UHF (ultra-high frequency) range between 0.3 to 3 GHz. The motivation of this work was associated with the fact that in Brazil are located two of the largest niobium reserves in the world. Under this view, the study of the processing of the ceramic materials is important considering possible technological applications. <![CDATA[Objective criterion for evaluation of the quality decoration in ceramic floor tile production prior to the sintering process]]> Abstract In the ceramic tile decoration process, the set of variables that can cause hue variation is quite wide and independent of the methodology used in the production. The understanding of the effects of these variables over the final expected result is of great importance to the producers, especially if it could be done before the ceramic tile’s sintering stage. The quality of the decoration is linked to the deposited dot shape and its filling with ink. It is proposed in this paper the determination of a ‘quality index’, comparing the theoretical deposition pattern and a real deposition obtained with samples. Measuring the values of the areas with and without ink, using the statistical tool of the ROC curve, it was obtained the values for sensibility=0.791, specificity=0.830, precision=0.802 and quality index=0.768. The method is intended to be used prior to the sintering step for hue variation control. <![CDATA[Effect of sol-gel processing parameters on structure of zirconia]]> Abstract The present study reports the experimental results regarding the effect of molar ratio of hydrolysis water used in the sol-gel synthesis upon the structure of zirconia. The ZrO2 materials were synthesized via simple metal-chelate route using zirconium n-propoxide [Zr(OCH2CH2CH3)4], n-propanol, acetic acid, and deionized water. Thermogravimetric analysis and infrared spectroscopy were performed to evaluate the structural evolution upon samples heating; the complete removal of organic compounds at 330 °C was verified. The results of X-ray diffraction showed that the calcination temperature of 400 °C was enough to the crystallization of the metastable tetragonal zirconia phase. Nitrogen adsorption-desorption measurements indicated that the textural properties of zirconia were affected by the water content used in the synthesis, and the highest surface area was achieved when the water molar ratio of 4 was used. <![CDATA[Construction and demolition waste in concrete: property of pre-molded parts for paving]]> Abstract Construction and demolition waste (CDW) production is a growing factor on a global scale and its incorrect disposal becomes an increasingly common problem in cities. It is estimated to represent, on average, 50% of the urban solid waste mass in the world. In this sense, an alternative to the destination is their reuse. In this work, the properties of interlocking concrete pieces for paving with the CDW in substitution to large aggregates were analyzed. The substitution occurred in fractions from 20 to 100 wt% of CDW in cylindrical test specimens to find the ideal substitution content, so that to prepare pre-molded concrete blocks. The piece properties obtained were analyzed according to Brazilian standards for compressive strength and water absorption. Therefore, the influence of the residue incorporation in the pieces, from the technical viewpoint, was verified. The sample that presented the best performance had a substitution of 20% of the natural aggregate by crushed CDW. <![CDATA[Passive vibration control using a metaconcrete thin plate]]> Abstract We investigated the band structure of flexural waves propagating in a metaconcrete thin plate, consisting of a concrete matrix reinforced by steel inclusions coated by rubber in square and triangular lattices. We considered the classical Kirchhoff-Love thin plate theory. We also studied the influence of inclusion geometry - circular, square and rotated square with a 45° angle of rotation with respect to the x, y axes. Improved plane wave expansion method was used to solve the wave equation considering flexural wave propagation in the xy plane. Flat bands and locally resonant band gaps were observed for all types of inclusion studied regarding square and triangular lattices. The locally resonant band gaps for square and rotated square inclusions in a triangular lattice were slightly shifted to higher frequencies than that given by circular inclusion. We suggest that the metaconcrete thin plate studied should be feasible for flexural vibration control in low frequencies. <![CDATA[Ceramic characterization of raw material with a high content of organic matter reduced by composting]]> Abstract The process of beneficiation of a peaty ceramic raw material extracted from the Poços de Caldas region, MG, through the composting method to reduce organic matter (OM) was analyzed. The raw materials used in separate piles were divided, keeping one of the samples pure (TP) and adding bovine wastes in the second (TB). The process lasted 6 months and, at the end of each month, the amount of MO was analyzed by the Walkley-Black method. Results of maximum degradation of 56%±6% of OM in the TB and 47%±5% of OM in the TP were obtained. The ceramic characterization of the processed raw material was then carried out. It has been proved that the proposed method is efficient for the decrease of OM in the ceramic raw material. Regarding the composting product, the results were positive, showing that this material can be used in ceramic applications. <![CDATA[Brazilian refractory grade bauxite: a new alternative to refractories makers and users]]> Abstract After two centuries of the discovery, we now know that there are several types of bauxites, in which mineralogy points to the most appropriate application. In the non-metallurgical industry, bauxites with refractory grades have been applied as raw materials in the production of high-alumina refractories for both shaped and unshaped. The increase in the cost of other sources of high-alumina raw materials has encouraged the refractory producers to find a more cost-effective substitute, such as refractory-grade calcined bauxites (RGB). Nowadays, concerns rise regarding the availability of RGB due to the continuous restrictions taking place in China, which has a 95% market share. This work presents a new RGB of high-alumina content (~85%) from a Brazilian source in which process enabled a technology with high refractoriness. <![CDATA[Photodegradation of Rhodamine B catalyzed by ZnO pellets]]> Abstract This paper describes the development of ZnO semiconductors applied as photocatalysts for the degradation of water contaminants, with the shape of ceramic pellets thick enough to maintain their structures, prepared by slip casting and sintering. The samples presented porosities around 40% and densities around 3.4 g/cm3, which represented about 61% of the theoretical density of ZnO. After obtaining the ceramic samples, the degradation of Rhodamine B dye by photocatalysis was evaluated in six cycles of degradation. After the cycles, changes in the surface of the samples were verified, possibly due to leaching during photocatalysis since they presented mean grain sizes of 0.61 μm before and 0.36 μm after the photocatalysis. The ceramic ZnO samples were able to satisfactorily degrade Rhodamine B for several cycles, resulting in successful reuse of photocatalysts and increased facility of removing the photocatalysts from the medium after degradation compared to powders in suspensions. <![CDATA[New mathematical modelling for grain size distribution adjustment in concrete]]> Abstract Concrete used in civil engineering is a composite obtained from the combination of coarse and fine aggregates, cement and water, and its cost and quality are normally associated to the proportion of its constituents (ceramic formulation), as well as the reduction of water consumption. The aggregates used in concrete may have diverse origins, and the syenite extracted at Pedra Branca Alkaline Massif is one of the materials that can be used for this substitution. In order to do so, a reference formulation of concrete was calculated and optimized using the mathematical models of Andreasen, and syenite was added substituting 25, 50, 75 and 100% of the fine aggregate. In order to maintain the original granulometric distribution, an algorithm was developed to compensate the different particle size distributions. The grain size correction guaranteed the maintenance of the original properties of the concrete, reaching values of mechanical strength above 35 MPa. <![CDATA[Tribological behavior of hydrogenated W-C/a-C:H coatings deposited by three different sputtering techniques]]> Abstract The evolution of structure, mechanical properties and friction behavior of DC magnetron sputtered (DCMS), high power impulse magnetron sputtered (HiPIMS) and high target utilization sputtered (HiTUS) W-C:H coatings was investigated as a function of the addition of acetylene and hydrogen into Ar atmosphere. The gradual addition of reactive gases caused a transition from PVD toward hybrid PVD-PECVD and even PECVD dominant processes. The coating structure evolved from nanocrystalline toward nanocomposite and amorphous structure with the increase of acetylene addition. Deposition rates in all techniques increased linearly with the increase of acetylene flow until certain saturation limit due to the limited energy available for acetylene fragmentation during hybrid PVD-PECVD deposition. Hardness and coefficient of friction in DCMS and HiTUS W-C:H coatings deposited in this regime followed standard congruent tendencies whereas PECVD dominated deposition process produced coatings with different dependencies. In contrary, HiPIMS W-C:H coatings showed low sensitivity to the influence of acetylene and hydrogen additions. Lower coefficients of friction (&lt;0.1) and moderate hardness (around 20 GPa) of HiPIMS W-C:H coatings over a wide range of acetylene additions seem to be a principal advantage of HiPIMS compared to DCMS and HiTUS techniques in this class of coatings. <![CDATA[Evaluation of mechanical properties of porous alumina ceramics obtained using rice husk as a porogenic agent]]> Abstract The objective of this work was to evaluate the mechanical properties of porous alumina ceramics, using the rice husk as a porogenic element. The rice husk was milled and graded in two granulometry, &lt;65 μm and 65-150 μm, and added in a high purity calcined alumina in the proportion of 5, 15 and 30 wt%. The samples were pressed by uniaxial pressing and sintered at 1450 ºC for 1 h. Sintered density, total porosity, Young’s modulus, modulus of rupture, and compressive strength were evaluated. Samples were also prepared without the addition of rice husk (RH) in order to compare the properties. Porous ceramics with total porosity ranging from 24% to 54% were produced, and with the composition of 5% RH 65-150 μm, a high porosity value was obtained for a lower loss in mechanical properties. <![CDATA[Evaluation of Portland pozzolan blended cements containing diatomaceous earth]]> Abstract Clinker replacement by supplementary cementitious materials (SCMs) is one strategy to reduce CO2 emissions of cement industry. Diatomaceous earth, a natural pozzolan, has been used as SCM. So, this study aimed to evaluate two Portland pozzolan blended cements with distinct content of diatomaceous earth (16DE and 49DE) and compare then with a high clinker content cement (REF). Cements were physically and chemically characterized; pastes and mortars were analyzed in terms of reactivity, water demand, and mechanical strength; finally, environmental indicators were estimated. Cements with diatomaceous earth demanded a similar volume of mix water for mortars without superplasticizer and less water than REF for mortars with superplasticizer. The chemical bound water at 91 days reduced 21% and 27% for 16DE and 49DE, respectively, in relation with REF. For binder intensity indicator, both cements had worst results compared to REF, but for carbon intensity indicator 49DE obtained better results comparing to REF. <![CDATA[Densification and microstructure of Si<sub>3</sub>N<sub>4</sub>-TiN ceramic composites]]> Abstract Silicon nitride is a ceramic material widely used in various structural applications at high temperatures owing to its excellent combination of mechanical and thermal properties. To increase the application of Si3N4, many researches have been developed to improve its fracture toughness and processing conditions. In this study, the sintering and microstructure of Si3N4-TiN composites, containing Al2O3 and Y2O3 as sintering aids, were studied. Samples were obtained by the conventional method of mixing powders and sintered at 1750 ºC/1 h and 1815 ºC/1 h under nitrogen atmosphere. Density values of the samples were determined by the Archimedes method, reaching values between 96.9% and 98.0% of theoretical density, with a porosity of less than 0.5%. The sintered samples were analyzed by X-ray powder diffraction and scanning electron microscopy. The results showed the materials reached high fracture toughness, low hardness and a microstructure with TiN grains dispersed in a β-Si3N4 matrix containing an amorphous intergranular phase. <![CDATA[Development of metakaolin and geopolymer proppants with nanocarbon materials]]> Abstract From the first hydraulic fracturing in the 40’s until nowadays, the techniques of each process step have evolved significantly. This study presents a new approach on the development of metakaolin (MK) and geopolymer based proppant with and without nanocarbon materials such as multi-walled carbon nanotubes and graphene oxide. For manufacturing the microspheres, the chosen method was intensive mixing of raw material with dispersed nanocarbons followed by sintering metakaolin and curing the geopolymer using an alkaline medium (NaOH). Compression mechanical tests, bulk density, turbidity, and K&amp;S method analysis were made following API RP 19C standard. The sample containing 4.3 M NaOH to produce alkali-activated metakaolin sintered at 1300 ºC for 2 h presented higher mechanical resistance generating 2.4% of fines at 3 K (3000 psi). The geopolymer samples showed higher crushing strength and lower bulk density when compared to the MK samples without heat treatment. Furthermore, reduced graphene was produced and incorporated into activated MK. Morphology and presence of carbon nanostructures on the proppants were evaluated by scanning electron microscopy. Crushing test reached 3 K enabling it to be used as a ceramic synthetic proppant containing carbon nanomaterials. <![CDATA[Influence of sintering temperature on the development of alumina membrane shaped by centrifugal casting for gas separation]]> Abstract The development of ceramic membranes for the most diverse separation processes has gained high visibility, mainly due to their better performance in harsh environments in comparison to polymeric materials. Among the different techniques used to prepare tubular ceramic membranes, the centrifugal casting (CC) is interesting for obtaining highly homogeneous structures, essential for gas separations. This study assessed the influence of two sintering temperatures (1450 and 1500 °C) of alumina membranes prepared by CC on the membrane morphology and on the permeation of helium, nitrogen and oxygen gases. The membranes were characterized by their morphology, apparent porosity, and gas permeation. The results indicated that the sintering temperature is a fundamental parameter for controlling membrane properties, an increase of only 50 °C led to a tenfold decrease in the gas permeate flux, indicating densification of membrane porous structure. This was in accordance with the results observed in the membrane micrographs and the apparent porosity. <![CDATA[Effect of sawdust as porosity agent on final properties of geopolymers]]> Abstract The geopolymers synthesis are based on geopolymerization, a sequence of reactions processed in an alkaline medium through oligomers providing a three-dimensional molecular structure. In this work, the polycondensation of metakaolin was performed with alkaline activators (NaOH and sodium silicate), wood sawdust and other additives. Two different compositions were evaluated after and before sintering at a high temperature (850 °C). The effect of sawdust addition and the thermal treatment of geopolymers were evaluated by scanning electronic microscopy, X-ray diffraction, mechanical properties, apparent density and porosity by different characterization techniques to guide of development of high porous and low-density materials for thermal and noise control application on building/home construction engineering applications. <![CDATA[The use of tire rubber in the production of high-performance concrete]]> Abstract The advances in concrete technology lead to the search for alternative materials that provide improvements in concrete properties while at the same time collaborating with sustainable practices in construction. In this study, the influence of the incorporation of waste tire rubber on the mechanical properties of high-performance concrete was discussed. The waste rubber from the tire retreading process was used in partial substitution of the fine aggregate (sand) in the percentages of 7.5%, 15% and 30% with respect to the mass of the sand. For the characterization of the concrete, the following tests were carried out: water absorption, void index, specific density, compressive strength, flexural tensile strength, modulus of elasticity and microscopy analysis. The incorporation of rubber as aggregate in high-performance concrete proved to be promising for the production of a structural concrete with special characteristics, besides collaborating with the proper disposal of waste tires.