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Tricalcium phosphate (b-TCP) can be used as bone graft, exhibiting suitable bioabsorption and osteoconduction properties. The presence of silica may induce the formation of a hydroxyapatite layer, enhancing the integration between implant... more
Tricalcium phosphate (b-TCP) can be used as bone graft, exhibiting suitable bioabsorption and osteoconduction properties. The presence of silica may induce the formation of a hydroxyapatite layer, enhancing the integration between implant and bone tissue. Preceramic polymers present silicon in their composition, being a source of SiO2 after thermal treatment. Using the versatility of 3D printing, b-TCP and a polysiloxane were combined to manufacture a bulkb-TCP with a silica coating. For the additive manufacturing process, PMMA powder was used as passive binder for the b-TCP particles, and polymethylsilsesquioxane (MK), dissolved in an organic solvent, was used both as a printing binder (ink) and as the source of SiO2 for the coating. Five distinct coating compositions were printed with increasing amounts of MK. The structures were then submitted to heat treatment at 1180 °C for 4 h. XRD and FTIR showed no chemical reaction between the calcium phosphate and silica. SEM allowed obser...
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Zirconia-toughened alumina (ZTA) laminates with 5 vol% (95A) and 30 vol% (70A) of yttria-partially stabilized zirconia (Y-PSZ), as well as laminated composites with thick ZTA layers and thin Y-PSZ layers were developed and processed by... more
Zirconia-toughened alumina (ZTA) laminates with 5 vol% (95A) and 30 vol% (70A) of yttria-partially stabilized zirconia (Y-PSZ), as well as laminated composites with thick ZTA layers and thin Y-PSZ layers were developed and processed by means of tape casting followed by co-firing. The addition of 5 vol% Y-PSZ led to grain refinement, higher densification and an increase in mechanical properties compared to those of pure alumina. In contrast, the addition of 30 vol% Y-PSZ refined the alumina grains and formed clusters of zirconia. However, it promoted lower densification when compared to pure alumina and 95A. Nevertheless, mechanical strength increased in the 70A composites owing to the zirconia toughening mechanism. Laminated composites with intermediate Y-PSZ layers have shown thermal residual stresses after sintering as a result of the different coefficients of thermal expansion (CTE) of the components and higher performance in mechanical behaviour owing to compressive stresses in ...
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Abstract The mechanical behavior of bundles of ceramic fibers exhibits a characteristic rupture process when subjected to tensile known as avalanche failure. This process is related to the load sharing among fiber bundles once some of the... more
Abstract The mechanical behavior of bundles of ceramic fibers exhibits a characteristic rupture process when subjected to tensile known as avalanche failure. This process is related to the load sharing among fiber bundles once some of the elements begin to fail. Mechanical tests were performed with bundles and Weibull statistics was used to interpret the results of the maximum stress supported by the bundles before the avalanche failure. A computational simulation was originally adapted introducing load sharing models. The simulations were compared with experimental results. Finally, the newly proposed load model was considered to be a better approach for the understanding of the rupture avalanche effect.
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Experimental tests which match the application conditions might be used to properly evaluate materials for specific applications. High velocity impacts can be simulated using light-gas gun facilities, which come in different types and... more
Experimental tests which match the application conditions might be used to properly evaluate materials for specific applications. High velocity impacts can be simulated using light-gas gun facilities, which come in different types and complexities. In this work different setups for a one-stage light-gas gun facility have been numerically analyzed in order to evaluate their suitability for testing materials and composites used as armor protection. A maximal barrel length of 6 m and a maximal reservoir pressure of a standard industrial gas bottle (20 MPa) were chosen as limitations. The numerical predictions show that it is not possible to accelerate the projectile directly to the desired velocity with nitrogen, helium, or hydrogen as propellant gas. When using a sabot corresponding to a higher bore diameter, the necessary velocity is achievable with helium and hydrogen gases.
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Coatings of polysilazane-based ceramics are a promising technology for the protection of steels for applications at high temperatures and chemically harsh environments where, currently, special and expensive grades of steel are used for.... more
Coatings of polysilazane-based ceramics are a promising technology for the protection of steels for applications at high temperatures and chemically harsh environments where, currently, special and expensive grades of steel are used for. To this work, the polymer-ceramic transformation behavior of VL-20 polysilazane precursor and 8%YSZ and glassceramic powders as fillers, and their variables were evaluated, and the coatings on stainless steel AISI 304 substrates were characterized. The first obtained coatings showed good adherence, but also high porosity.
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A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repetido a solda a frio e a fratura de partículas de pó em um moinho de alta energia. A técnica foi originalmente desenvolvida para produzir... more
A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repetido a solda a frio e a fratura de partículas de pó em um moinho de alta energia. A técnica foi originalmente desenvolvida para produzir superligas reforçadas por óxidos dispersos para aplicações na indústria aeroespacial. Atualmente pode-se sintetizar uma grande variedade de ligas. Variáveis de processo e materiais de partida envolvidos na mecanossíntese são revisadas e discutidas neste artigo.
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In this work aqueous ceramic suspensions were prepared from a parent glass-ceramic powder (3.8 μm) belonging to the LZSA (Li2O-ZrO2-SiO2-Al2O3) system without or with additions of different volume fractions (1.0-7.5%) of TiO2... more
In this work aqueous ceramic suspensions were prepared from a parent glass-ceramic powder (3.8 μm) belonging to the LZSA (Li2O-ZrO2-SiO2-Al2O3) system without or with additions of different volume fractions (1.0-7.5%) of TiO2 nanoparticles (25 nm). The obtained suspensions were rheologically characterized so that stable suspensions were defined e formed by slip casting. The obtained compacts were sintered (850-950°C/60 min) and their green and sintered densities were determined and related to linear shrinkage measurements. The results showed that samples sintered at 950oC for 60 min with 1.0% TiO2 addicted presented linear shrinkage of 12% and relative densities of 97%.
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ABSTRACT journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses,... more
ABSTRACT journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: Abstract In this work, TiO 2 (0–50 vol%) nanoparticles (25 nm) were added to a 11.7Li 2 O Á 12.6ZrO 2 Á 68.6SiO 2 Á 7.1Al 2 O 3 , LZSA (4 μm) glass-ceramic matrix to prepare composites in order to investigate the influence of TiO 2 on the sinterability, crystallinity and some properties to obtain information to design materials for low temperature co-fired ceramics (LTCCs) applications. The sintered composites (700–1000 1C/30 min) with relative densities between 95% and 98%, showed β-podumene,TiO 2 and L i2 TiSiO 5 as main crystalline phases. The maximum bending strength (235 7 84 MPa) was achieved for composites with 40% TiO 2 sintered at 1000 1C/30 min. The coefficient of thermal expansion increased linearly with the concentration of TiO 2 , i.e., 3.5 Â 10 À 6 1C À 1 for 0% TiO 2 and 9.5 Â 10 À 6 1C À 1 to 100% TiO 2 . The values of thermal conductivity were low and increased with the increase of the volumetric fraction of TiO 2 , reaching a maximum (3.30 W/mK) for samples (40% TiO 2) sintered at 1000 1C/30 min. The measurements of electrical conductivity indicate that the obtained materials are electrical insulators ($10 À 10 S cm À 1).
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The goal of this study was the biosynthesis of silver nanoparticles (SNPs) mediated by the fungus Fusarium oxysporum, as well as the characterization of these nanoparticles including evaluation of the particles size and stability under... more
The goal of this study was the biosynthesis of silver nanoparticles (SNPs) mediated by the fungus Fusarium oxysporum, as well as the characterization of these nanoparticles including evaluation of the particles size and stability under different processing conditions. The results showed that the biosynthesis produced silver nanoparticles having a mean size of 34 nm and zeta potential values below -30 mV at the conditions used, characterizing the nanoparticles as being stable in suspension. Ultraviolet-visible spectroscopy and flame atomic absorption spectroscopy confirmed the formation of silver nanoparticles and Fourier transform infrared spectroscopy detected the bands corresponding to the binding vibration of amide I and II bands of proteins in addition to the presence of cyclic alkanes, cyclohexane, ethers, and aromatic hydrocarbons. Finally, field emission scanning electron microscopy and transmission electron microscopy revealed the formation of spherical and well-dispersed SNPs.
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Preliminary results of the use of electroomosis technique for removal of organic contaminants in ceramic filtration porous structure are presented. The method employed provokes the migration of chemical residue and waste retained or... more
Preliminary results of the use of electroomosis technique for removal of organic contaminants in ceramic filtration porous structure are presented. The method employed provokes the migration of chemical residue and waste retained or adsorbed on the pore surfaces by applying a controlled tension within an electrochemical system. Porous ceramics have been the most common filtration medium employed within a broad range of applications. Conventional cleaning of a ceramic medium is not entirely effective for organic contaminants since they cannot be excluded by size, but retained through chemical affinity to the oxide surface. Under the influence of an electrical current, adsorbed molecules underwent shear stress due to the diffuse moving layer. In their ionic state the specimens are dragged and thus move towards the opposite charged electrode. Phenol was chosen as a standard contaminant and tests carried out using commercial ceramic filtration candles. Relative contaminant concentration was assessed by optical densities (UV-Vis spectroscopy). The results show that removal is proportional for up to 58% of the contaminant in diluted condition.
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The industrial use of wastes in the brick and tile industry has been intensively investigated in the last decade. This work describes a research carried out on the manufacturing of a clay material with granite and marble reject. The... more
The industrial use of wastes in the brick and tile industry has been intensively investigated in the last decade. This work describes a research carried out on the manufacturing of a clay material with granite and marble reject. The reject was obtained direct by from a ceramic industry from rocks which were sawed in blocks or slices. This industrial process produces a very large amount of this reject. The reject is launched in decanting lagoon, landing area or throw in river, resulting environment pollution and degradation. The reject material was investigated in function of chemical and mineralogical compositions using x-ray diffraction and thermal analysis. Granite and marble reject and clay material were mixed and uniaxial pressed. Samples were sintered in an electric furnace at temperature range from 950 to 1150º C. The experimental results (porosity, dilatometric analyses, water absorption, x-ray diffraction) are also presented. The results indicate that it is possible to use g...
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A mixture experiment approach has been found suitable to verify the influence of individual components and their interactions on the properties of a lead-free transparent frit.
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ABSTRACT
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In the development and manufacture stages of floor and wall ceramic tiles, firing shrinkage is basically determined by the combination of raw materials and frequently used as quality control parameters. This configures the ideal scenario... more
In the development and manufacture stages of floor and wall ceramic tiles, firing shrinkage is basically determined by the combination of raw materials and frequently used as quality control parameters. This configures the ideal scenario to apply the techniques of experiments design, often used in various other areas, to model those properties of such ceramics bodies. In this work, ten formulations of three different raw materials, namely a clay mixture, potash feldspar and quartz (triaxial compositions) were selected and processed under conditions similar to those used in the ceramics industry. With the experimental results, a regression model was calculated, relating linear shrinkage with composition. After statistical analysis and verification experiments, the significance and validity of the model was confirmed. The regression model can then be used to select the best combination of those three raw materials to produce a ceramic body with specified properties.
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A new concept for the production of porous oxide ceramic matrix composites (OCMCs) was developed and used to produce alumina fiber reinforced samples. This new route is based on the lamination of thermoplastic prepregs produced with... more
A new concept for the production of porous oxide ceramic matrix composites (OCMCs) was developed and used to produce alumina fiber reinforced samples. This new route is based on the lamination of thermoplastic prepregs produced with paraffin‐based suspensions of the matrix powder (in this work a mixture of 80 vol% Al 2 O 3 and 20 vol% ZrO 2). For a better infiltration of fiber bundles, fiber textiles were infiltrated with a liquid slurry of the matrix prior to lamination. The advantage of using prepregs laminated with paraffin‐based suspensions is the possibility of joining different OCMC parts in the green state to form complex‐shaped composites. Additionally, the shelf life of these prepregs is much longer than those produced with conventional liquid slurry infiltration. 3M TM Nextel TM 610 woven fabrics were used as reinforcement and the prepregs were laid up in a cross‐ply configuration, followed by warm‐pressing, debinding and sintering. Microstructural analysis of the sintered...
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