The effect of incorporation of a Brazilian water treatment plant sludge on the properties of ceramic materials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Reuse of sugarcane bagasse ash (SCBA) to produce ceramic materials

Sugarcane bagasse ash (SCBA) is a residue resulting from the burning of bagasse in boilers in the sugarcane/alcohol industry. SCBA has a very high silica concentration and contains aluminum, iron, alkalis and alkaline earth oxides in smaller amounts. In this work, the properties of sintered ceramic bodies were evaluated based on the concentration of SCBA, which replaced non-plastic material. The ash was mixed (up to 60 wt%) with a clayed raw material that is used to produce roof tiles. Prismatic probes were pressed and sintered at different temperatures (up to 1200 degrees C). Technological tests of ceramic probes showed that the addition of ash has little influence on the ceramic properties up to 1000 C. X-ray diffraction and thermal analysis data showed that, above this temperature the ash participates in the sintering process and in the formation of new important phases. The results reported show that the reuse of SCBA in the ceramic industry is feasible. (C) 2011 Elsevier Ltd. All rights reserved.

Detection of cracks in scratching tests in ceramic materials through acoustic emission

The mechanisms of material removal and the interactions among scratches performed in ceramic materials were investigated using acoustic emission signals, and scanning electron microscopy, in scratching experiments. Several testing conditions were used to produce different types of removing mechanism on a glass as well as on a polycrystalline alumina sample composed by heterogeneous grain size. It is known that the material removing process on a polycrystalline ceramic involves intergranular microfracture and grain dislodgement, unlike the chipping produced by the extension of lateral cracks in non-granular materials, such as glass. Distinct settings for velocities, loads, and two types of diamond indenter were tested. The material removal was carried out by three different methods of scratching: single passes, repeated overlapping passes, and parallel scratches. As a general result, there was a clear relationship between the acoustic emission signals and the damage intensity occurred in the material removal. More specifically, there were differences in the acoustic emission signal levels in the scratches made on the alumina and on the glass owing to the material removal mechanisms associated with the structure of these materials. A gradual increase in the acoustic emission levels was observed when the number of repeated passes was increased as a result of the damage accumulation process followed by severe material removal. It was also noticed that the acoustic emission signals were capable of reflecting the interactions between two parallel scratches.

Vertical marginal discrepancy of ceramic copings with different ceramic materials finish lines and luting agents: An in vitro evaluation

Statement of problem. Prosthetic restorations that fit poorly may affect periodontal health and occlusion. Studies that have evaluated the accuracy of fit of ceramic restorations before and after cementation assessed primarily intracoronal restorations.Purpose. This in vitro study evaluated the effect of different finish lines, ceramic manufacturing techniques, and luting agents on the vertical discrepancy of ceramic copings.Material and methods. Two stainless steel molars were prepared for complete crowns with 2 different finish lines (heavy chamfer and rounded shoulder); each molar was duplicated to fabricate 90 copings. A total of 180 copings generated 18 groups (n=10 for each finish line-coping material-luting agent combination). Luting agents tested included zinc phosphate, resin-modified glass ionomer (Fuji Plus), and resin composite cements (Panavia F). A metal frame was developed on which to screw the stainless steel model and a ceramic coping; the distance (mum) between 2 predetermined points was measured before and after cementation by a profile projector under a torquing force. A 4-way ANOVA with repeated measurements was performed to assess the influence of each factor in the vertical marginal discrepancy: 3 between-coping factors (finish line-coping material-luting agent) and 1 within-coping factor (before and after cementation) (alpha=.05).Results. Procera copings presented the lowest mean values (P<.05) of vertical marginal discrepancy before and after cementation (25/44 mum) when compared to Empress 2 (68/110 mum) and InCeram Alumina copings (57/117 mum), regardless of any combinations among all finish lines and luting agents tested.Conclusion. Considering each factor separately, the ceramic manufacturing technique appeared to be the most important factor tested for the definitive vertical discrepancy of all-ceramic copings, with lower mean values for Procera copings.

Ceramic materials in dentistry: historical evolution and current practice

Dental ceramics are presented within a simplifying framework allowing for facile understanding of their development, composition and indications. Engineering assessments of clinical function are dealt with and literature is reviewed on the clinical behaviour of all-ceramic systems. Practical aspects are presented regarding the choice and use of dental ceramics to maximize aesthetics and durability, emphasizing what we know and how we know it.

Preparation and characterization of glass-ceramic materials in the BaO-Li2O-ZrO2-SiO2 system and their dependence on treatment temperatures

The preparation and characterization of transparent glass-ceramics in the composition of 30Li2O:5ZrO2:xBaO:(100-x) SiO2 with x = 0, 5, 10, 15, and 20 mol% are described. Glasses were melted in a platinum crucible at 1100°C for 2 h and then heat-treated at 900°C for 3 h. The characterizations were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, and scanning electron microscopy (SEM). The experimental results indicate that there was a structural change in the glass-ceramics as the BaO concentration in the mixture increased. In the XRD patterns of samples without heat treatment, only the halo was observed. After heat treatment, the appearance of the materials was verified by X-ray diffraction peaks. The reorganization of the amorphous solid was confirmed by Raman and IR spectroscopy along with XPS and SEM, with a more homogeneous phase formation being observed.

Fractal approach to ac impedance spectroscopy studies of ceramic materials

A novel fractal model for grain boundary regions of ceramic materials was developed. The model considers laterally inhomogeneous distribution of charge carriers in the vicinity of grain boundaries as the main cause of the non-Debye behaviour and distribution of relaxation times in ceramic materials. Considering the equivalent circuit the impedance of the grain boundary region was expressed. It was shown that the impedance of the grain boundary region has the form of the Davidson-Cole equation. The fractal dimension of the inhomogeneous distribution of charge carriers in the region close to the grain boundaries could be calculated based on the relation ds = 1 + β, where β is the constant from the Davidson-Cole equation.

Characteristics of the double-torsion test to determine the R-curve of ceramic materials

Double-torsion tests were carried out on a commercial ceramic floor tile to verify whether this test is suitable for determining the R-curve of ceramics. The instantaneous crack length was obtained by means of compliance calibration, and it was found that the experimental compliance underestimates the real crack length. The load vs. displacement curves were also found to drop after maximum loading, causing the stress intensity factor to decline. The R-curves were calculated by two methods: linear elastic fracture mechanics and the energetic method. It was obtained that the average values of crack resistance, R, and the double of the work of fracture, 2 · γwof, did not depend on notch length, a0, which is a highly relevant finding, indicating that these parameters were less dependent on the test specimen's geometry. The proposal was to use small notches, which produce long stable crack propagation paths that in turn are particularly important in the case of coarse microstructures.

Sintering of porous alumina obtained by biotemplate fibers for low thermal conductivity applications

In this research report, a sintering process of porous ceramic materials based on Al2O3 was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100-1600°C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14m2/g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al2O3 in the sintered samples. Thermal properties of the sintered Al2O3 fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al2O3 and therefore improved its potential use as an insulating material. © 2012 Elsevier Ltd.

Local order of Pb1-xLaxZr0.40Ti 0.60O3 ferroelectric ceramic materials probed by X-ray absorption and Raman spectroscopies

This paper reports on the structural characterization of Pb 1-xLaxZr0.40Ti0.60O3 (PLZT) ferroelectric ceramic compositions prepared by the conventional solid state reaction method. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used to probe the local structure of PLZT samples that exhibits a normal and relaxor ferroelectric behavior. From the Zr K-edge and Pb LIII-edge EXAFS spectra, a considerable dissymmetry of Zr and Pb sites was observed in all samples, including those showing a long-range order cubic symmetry and a relaxor behavior. The Raman spectroscopy results confirmed the existence of a local disorder in all PLZT samples through the observation of Raman active vibrational modes. The variation in the intensity of the E(TO 3) mode in the PLZT relaxor samples indicates that the process of correlation between nanodomains stabilizes at temperatures lower than T m. © 2013 Elsevier B.V. All rights reserved.

Valorization of sugarcane bagasse ash: Producing glass-ceramic materials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of Ba-substitution on the structural and ferroelectric properties of Pb1-xBaxZr0.40Ti0.60O3 ceramic materials

This work presents a comprehensive study about the influence of Ba-substitution on the structural and ferroelectric properties of Pb1-xBaxZr0.40Ti0.60O3 (PBZT) ceramic system. Pb1-xBaxZr0.40Ti0.60O3 ceramic samples were then prepared by solid state reaction method and characterized as a function of composition and temperature by X-ray diffraction (XRD) and impedance spectroscopy techniques. The dielectric measurements show that the substitution of Pb2+ for Ba2+ ions leads to a diffuse behavior of the dielectric permittivity curves for all samples and that only the x = 0.50 sample presents a typical relaxor behavior. In good agreement with dielectric measurements, the structural phase transition study showed a phase transition from a tetragonal structure with P4mm space group to a cubic structure with Pm-3m space group for all samples, except for the x = 0.50 sample were a cubic structure was observed in the complete temperature interval measured.

Influence of Surface Roughness on Mechanical Properties of Two Computer-aided Design/Computer-aided Manufacturing (CAD/CAM) Ceramic Materials

SUMMARY The aim of this study was to evaluate the influence of surface roughness on surface hardness (Vickers; VHN), elastic modulus (EM), and flexural strength (FLS) of two computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic materials. One hundred sixty-two samples of VITABLOCS Mark II (VMII) and 162 samples of IPS Empress CAD (IPS) were ground according to six standardized protocols producing decreasing surface roughnesses (n=27/group): grinding with 1) silicon carbide (SiC) paper #80, 2) SiC paper #120, 3) SiC paper #220, 4) SiC paper #320, 5) SiC paper #500, and 6) SiC paper #1000. Surface roughness (Ra/Rz) was measured with a surface roughness meter, VHN and EM with a hardness indentation device, and FLS with a three-point bending test. To test for a correlation between surface roughness (Ra/Rz) and VHN, EM, or FLS, Spearman rank correlation coefficients were calculated. The decrease in surface roughness led to an increase in VHN from (VMII/IPS; medians) 263.7/256.5 VHN to 646.8/601.5 VHN, an increase in EM from 45.4/41.0 GPa to 66.8/58.4 GPa, and an increase in FLS from 49.5/44.3 MPa to 73.0/97.2 MPa. For both ceramic materials, Spearman rank correlation coefficients showed a strong negative correlation between surface roughness (Ra/Rz) and VHN or EM and a moderate negative correlation between Ra/Rz and FLS. In conclusion, a decrease in surface roughness generally improved the mechanical properties of the CAD/CAM ceramic materials tested. However, FLS was less influenced by surface roughness than expected.

Crack mechanical failure in ceramic materials under ion irradiation: case of lithium niobate crystal

Swift heavy ion irradiation (ions with mass heavier than 15 and energy exceeding MeV/amu) transfer their energy mainly to the electronic system with small momentum transfer per collision. Therefore, they produce linear regions (columnar nano-tracks) around the straight ion trajectory, with marked modifications with respect to the virgin material, e.g., phase transition, amorphization, compaction, changes in physical or chemical properties. In the case of crystalline materials the most distinctive feature of swift heavy ion irradiation is the production of amorphous tracks embedded in the crystal. Lithium niobate is a relevant optical material that presents birefringence due to its anysotropic trigonal structure. The amorphous phase is certainly isotropic. In addition, its refractive index exhibits high contrast with those of the crystalline phase. This allows one to fabricate waveguides by swift ion irradiation with important technological relevance. From the mechanical point of view, the inclusion of an amorphous nano-track (with a density 15% lower than that of the crystal) leads to the generation of important stress/strain fields around the track. Eventually these fields are the origin of crack formation with fatal consequences for the integrity of the samples and the viability of the method for nano-track formation. For certain crystal cuts (X and Y), these fields are clearly anisotropic due to the crystal anisotropy. We have used finite element methods to calculate the stress/strain fields that appear around the ion- generated amorphous nano-tracks for a variety of ion energies and doses. A very remarkable feature for X cut-samples is that the maximum shear stress appears on preferential planes that form +/-45º with respect to the crystallographic planes. This leads to the generation of oriented surface cracks when the dose increases. The growth of the cracks along the anisotropic crystal has been studied by means of novel extended finite element methods, which include cracks as discontinuities. In this way we can study how the length and depth of a crack evolves as function of the ion dose. In this work we will show how the simulations compare with experiments and their application in materials modification by ion irradiation.

Electrochemical Performance of Hierarchical Porous Carbon Materials Obtained from the Infiltration of Lignin into Zeolite Templates

Hierarchical porous carbon materials prepared by the direct carbonization of lignin/zeolite mixtures and the subsequent basic etching of the inorganic template have been electrochemically characterized in acidic media. These lignin-based templated carbons have interesting surface chemistry features, such as a variety of surface oxygen groups and also pyridone and pyridinic groups, which results in a high capacitance enhancement compared to petroleum-pitch-based carbons obtained by the same procedure. Furthermore, they are easily electro-oxidized in a sulfuric acid electrolyte under positive polarization to produce a large amount of surface oxygen groups that boosts the pseudocapacitance. The lignin-based templated carbons showed a specific capacitance as high as 250 F g−1 at 50 mA g−1, with a capacitance retention of 50 % and volumetric capacitance of 75 F cm−3 at current densities higher than 20 A g−1 thanks to their suitable porous texture. These results indicate the potential use of inexpensive biomass byproducts, such as lignin, as carbon precursors in the production of hierarchical carbon materials for electrodes in electrochemical capacitors.