Materials Science Forum Vols. 798-799

Abstract: The gadolinia doped ceria was developed in Ce_0,8Gd_0,2O_1,9 composition, with the objective to study the influence of calcination temperature on the ionic conductivity of sintered samples (pellets) used as solid electrolyte for the fuel cells applications. The powder was synthesized by the polymeric precursor method (Pechini) from cerium and gadolinium nitrates hexahydrates, obtaining a polymeric resin characterized by infrared spectroscopy. The heat treatments at 600 and 800°C resulted on oxides formation which have been characterized by infrared spectroscopy and X-ray diffraction for each sample. In each case, the fluorite type structure was identified. The pellets were formed by uniaxial pressure and sintered at 1500°C with relative densities of 93.1 and 89.4% for the samples calcined at 600 and 800°C, respectively. The microstructure evaluation was performed by scanning electron microscopy, and the electrical characterization was carried out by impedance spectroscopy, reaching a conductivity of 1.49x10^-4 S/cm at 400°C in this work.

Abstract: Nanocomposites were prepared from mixture of different concentrations of ferroelectric nanoparticles in an elastomeric matrix based on the vulcanized natural rubber. The morphological characterization of nanocomposites was carried out using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The nanocrystalline ferroelectric oxide is potassium strontium niobate (KSN) with stoichiometry KSr₂Nb₅O₁₅, and was synthesized by the chemical route using a modified polyol method, obtaining particle size and microstrain equal to 20 nm and 0.32, respectively. These ferroelectric nanoparticles were added into the natural rubber in concentrations equal to 1, 3, 5, 10, 20 and 50 phr (parts per hundred of rubber) forming ferroelectric nanocomposites (NR/KSN). Using morphological characterization, we identified the maximum value of surface roughness at low concentrations, in particular, sample with 3 phr of nanoparticles and factors such as encapsulation and uniformity in the distribution of nanoparticles into the natural rubber matrix are investigated and discussed.

Abstract: This paper presents the application of Design of Experiments (DOE) to an alkaline treatment in mordenite zeolite, in order to identify the optimum settings of the variables (temperature and concentration of NaOH) that promote greater desilication. Samples of commercial mordenite with Si / Al ratio = 9 have been treated with aqueuos NaOH solution of various concentration (0,1;0,5;1,0) and temperature (30,50,70°C). Statistical analysis was carried out based on a 2² factorial design with center point replicates. Seven experiments were executed and the data of Si/Al ratio obtained. The resulting samples were characterized by x-ray difraction (XRD) and energy dispersive x-ray (EDX), to identify the structures and crystalline phases, and to determine the percentages of silicon and aluminum, respectively. In all samples, a decrease in the Si / Al ratio was observed, keeping the crystalline structure. The treatment was most effective, especially, at high temperature and NaOH concentration (experiment 4). DOE was shown to be a powerful techinique for the study of the variables, allowing determining which variables and value ranges have more influence on response, enabling optimization.

Abstract: Calcium phosphates biocements are biomaterials that present crystallographic and mineralogical characteristics similar to human skeletal structure. This has led to the development of new calcium phosphates biomaterials for biomedical applications, especially biomaterials for repairing defects and bone reconstruction. Calcium phosphates biocements are a promising alternative in biomedical applications, for they are easy to mold, they have good wettability, hydration and hardening capacity during its application in biological means. This work aimed at the synthesis of hydrated calcium phosphates powder, through a simple reactive method, which will be the basis for the production of calcium phosphate biocimentos with self-setting reaction. Three calcium phosphates compositions were produced via CaCO₃/phosphoric acid reactive method in the ratios Ca/P = 1,5; 1,6 e 1,67 molar. The presented results are associated to hydrated powder morphology and synthesis process control. Scanning Electron Microscopy (SEM) helped with the morphological characterization of the powders, the laser analysis method was used for determining particle size and the Fourier Transformed Infrared Spectroscopy (FTIR) gave support to the identification of H₂O e PO₄^3- grouping vibrational bands. The work showed that for the different powder compositions the hydrated calcium phosphate phase is formed by clustered fine particles. This demonstrated that the chosen synthesis method permits the obtention of hydrated calcium phosphates, precursors for later biocement production.

Abstract: Calcium phosphate nanostructured biomaterials are a new class of biomaterials, they are clinically promising for bone tissue reconstitution. That is because this new class of biomaterials provides new microstructural features, nanostructural, surface area and micropore grains of different conventional biomaterials capable of offering new expectations in the bone tissue reconstitution and formation process [1, 2, 3, 4, 5]. Studies performed in vivo by different authors indicate these bioceramics as innovative biomaterials and may, in the near future, present themselves as biomaterials which can replace conventional biomaterials autogenous, alogenous and exogenous treatments on bone structure of the human skeleton. The calcium phosphate compositions produced from natural raw materials also have being promising for biomedical applications for these new biomaterials that have physical morphology and biological characteristics very similar to the bone tissue [4, 5, 6].

Abstract: In this work, the mechanical properties of magnesium doped tricalcium phosphate ceramics, considered a bioceramic for bone repair applications, were studied. Pure β-TCP and β-TCP doped with 2.25 mol% of Mg powders were synthesized through neutralization, freeze dried, uniaxially pressed and sintered at 1200°C/1h. The mechanical properties were evaluated through four points flexural and compression strength tests, fracture toughness and Young's Modulus. After the flexural strength test, the fracture's surface and their homogeneity were characterized by scanning electron microscopy. It was verified that Mg addition into β-TCP structure lead higher linear shrinkage, followed by higher residual stress, decreasing the mechanical properties compared to pure β-TCP ceramics. However, this behavior does not hinder the use of such bioceramics as bone substitutive materials, mainly in the sites that do not require high mechanical solicitations.

Abstract: This work aims to obtain hybrid from nanoparticles of Fe₃O₄ modified surface with 3-aminopropyltriethoxysilane (APTES) for their use in the immobilization of glucose oxidase (GOX). The obtained material was characterized by XRD, FTIR, SEM, sedimentation test and magnetic separation. Based on the obtained results it showed that the surface modification with APTES was successfully achieved and that the APTES did not changed the magnetic characteristic neither the structure of Fe₃O₄, indicating that the hybrid material obtained is promising for immobilization of GOX.

Abstract: β-Tricalcium phosphate (β-TCP) ceramics are of interest for bone requirements implants due to resoption behavior. The mechanical properties of β-TCP, however, are not yet sufficient to allow load bearing application of implants. The aim of this work was to investigate the effect of Mg²⁺ substitution on the strength sintered TCP. Due to promotion of a liquid phase at 1200°C, Calcium pyrophosphate (CPP-C₂P₂O₇) was used to improve the sintering of the samples. The introduction of CPP was promoted by use of a Ca/P molar ratio of 1.45. The powders were synthesized using a mixture of Ca (OH)₂ suspension and diluted H₃PO₄ with addition of MgO and calcined at 750 °C, 900 °C and 1050 °C. The cold isostatic pressing compacts were sintered at 1200 °C and 1300 °C, respectively.It was shown that a small Mg content (1.5 mol%) increased both compressive strength and fractional density of the TCP material sintered at 1200 °C from 132 ± 39 MPa at 92.1 % of fractional density to 193 ± 29 MPa at 94.5 % of theoretical density. Higher amounts of Mg inhibited the grain growth provoking a increase of the boundary mobility activation energy. Abnormal grain growth (AGG) was observed after sintering at 1300°C, as result CPP - liquid phase formation. Increase of Mg content promoted AGG, due to inhibition of grain growth during normal grain growth resulting in a increase of the residual elastic energy of the system.

Abstract: The deposition of hydroxyapatite coatings on titanium via sputtering techniques has been quite studied on commercial dense substrates, for use as a biomaterial. In this work, porous titanium samples produced by powder metallurgy and commercially dense titanium sheet, used as control, were used as substrates. The coatings were deposited by radio frequency magnetron sputtering using a hydroxyapatite target in argon atmosphere with different deposition times. Samples characterization was performed by Optical Microscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy and low-angle X-ray Diffraction. Hydroxyapatite coating depositions were obtained on both titanium substrates. The results indicated the potential of this methodology for titanium substrates with homogeneous hydroxyapatite coatings.

Abstract: The municipal area of Cachoeiro de Itapemirim, state of Espirito Santo, Brazil, is a major producer of ornamental stones. The sawing process of these stones generates a considerable amount of residues, which is disposed in open air piles, contributing to pollution and landscape degradation. A current solution being investigated for these residues is their incorporation into civil construction products such as clayey ceramics, lining mortars and concrete blocks. However, this incorporation is still subjected to doubt not only by the producers in the industry but also the intermediate seller as well as the final consumer. In order to verify the degree of personal acceptance of concrete structural blocks incorporated with ornamental stone residue, a field poll was conducted by means of questionnaires for inquiring the three directly related segments. The results showed distinct degrees of acceptance, especially by the sellers who fear rejection by the consumer. The acceptance of the residue incorporated block was, in some cases, positive as long as supported by a research work conducted in R&D centers and Universities.