Papers by Author: Antonio Licciulli

Abstract: In this work a novel three-dimensional ostechondral substitute is proposed that is made of an inorganic/organic hybrid material, namely collagen/hydroxyapatite. The two components of the substitute have been characterized separately. The inorganic part, a hydroxyapatite scaffold, was fabricated by a polymer sponge templating method using a reactive sub-micron powder synthesized in our laboratory by hydroxide precipitation sol-gel route. The organic part, a collagen scaffold, was fabricated by a freeze-dying technique varying design parameters. Both the parts were analysed by scanning electron microscopy and their mechanical properties assessed by compression tests. The hydroxyapatite scaffold showed a high and highly interconnected porosity and a mechanical strength equal to 0.55 MPa, higher than those reported in literature. The collagen scaffolds were seeded by chondrocytes, processed for histology analysis and tested in compression. The biological tests proved the ability of the scaffolds to be positively populated by chondrocytes and the mechanical analysis showed that the mechanical strength of the scaffolds significantly increased after 3 weeks of culture.

Abstract: A highly porous (~90%) interconnected hydroxyapatite/wollastonite (HA/WS) scaffolds were prepared by polymeric sponge replica method using a slurry containing HA:Calcium silicate in the weight ratio of 50:50 and sintered at 1300 °C. The phase purity of the scaffolds were analyzed by using XRD. The pore size, pore structure, microstructure and elemental analysis of the scaffolds before and after SBF soaking were analyzed using SEM and EDS. In-vitro bioactivity and bioresorbability confirmed the feasibility of the developed scaffolds. The HA/WS scaffold shows two fold increase in the compressive strength compared to pure HA scaffold.

Abstract: In the present work, the melting behaviour of ashes obtained from the combustion of coals from different seams were investigated by a laboratory-scale equipment. The ash melting behaviour was studied by heating the specimens in a tubular furnace under a controlled gas atmosphere, while continuous monitoring the shape transformation by a digital camera. The ash fusibility temperatures (AFT) were determined by using an application which allows the in-line identification of the AFT-related shapes specified in the ASTM D 1857-04. The effect of the furnace gas-atmosphere on the determination of the ash fusion temperatures were studied by performing the measurements under dry-air, SO2-rich-air and humidified air environments. It was found that under dry conditions, AFT determination is significantly affected by slag foaming, leading to an overestimation of the melting temperatures. Low water vapour concentrations does not appreciably change the results obtained under dry air, while SO2-rich atmosphere seems to reduce foaming. As a result, since no volume expansion was observed, samples heated under SO2-air flow, apparently melt at lower temperatures with respect to dry air conditions. The mineral phases transformation of the ashes during the heating process was studied by X-Ray diffraction and it was found that the low temperature transformations are essentially related to Iron and Alkalis reaction with aluminosilicates to form a glassy phase. On the other hand, high temperatures transformations are related to quartz and mullite solubilization which is closely dependent to the amount of Calcium, and therefore of anorthite phase, in the ash sample.

Abstract: Sintered fused silica is often used for making sacrificial cores in investment castings of Ni superalloys. Their usage is fundamental in the manufacture of precise superalloy gas turbine components with complex internal cooling passages. In this study SiO2/ZrSiO4/TiO2 cores were prepared from fused silica powders with different grain size and zircon and TiO2 content by slip casting method. Green samples were sintered at 1230°C at various soaking time: from 0,5 to 10 hours. Thermomechanical and microstructural properties of optimized silica obtained by add of 1,5%wt of TiO2 to SiO2/ZrSiO4 composition have been investigated by three point bending tests, XRD and Hg porosimetric analysis. The influence of cristobalite content on thermal stability at high temperature was studied by an optical dilatometer. At temperature below 1200°C TiO2 appears to act as a phase transformation inhibitor reducing the transformation rate of fused silica to cristobalite at high temperatures. At higher temperature it speeds up the formation of cristobalite. A comparison with commercial silica cores made by injection moulding has been performed. A prototype core was obtained and an investment casting was performed on that.

Abstract: Advanced structural ceramics such as Hot Pressed Silicon Nitride (HPSN) and Reaction Bonded Silicon Carbide (RBSC), thanks to their low density (3.1 ÷ 3.4 gr/cm3) and to their thermostructural properties, are interesting candidates for aerospace applications. This research investigates the feasibility of employing such monolithic advanced ceramics for the production of turbine vanes for aerospace applications, by means of a finite element analysis. A parametric study is performed to analyse the influence of the coefficient of thermal expansion, the specific heat, the thermal conductivity, and the Weibull modulus on structural stability, heat transfer properties and thermomechanical stresses under take-off and flying conditions. A nodal point that is evidenced is the high intensity of thermal stresses on the vane, both on steady state and in transient conditions. In order to reduce such stresses various simulations have been carried out varying geometrical parameters such as the wall thickness. Several open questions are evidenced and guidelines are drawn for the design and production of ceramic vanes for gas turbines.

Abstract: Advanced braking devices can represent a promising application for ceramic matrix composites (CMC) with functional and structural properties. If the actual advanced braking materials could be at least partially replaced by CMCs, it might become the first consumer market for these materials. CMC containing three main phases, silicon carbide, graphite and carbon fibers were prepared. A systematic analysis of the processing-structure-properties relationship of the composite is carried out. In particular, silicon carbide provides the necessary hardness, whereas graphite is used for its lubricating properties, and carbon fibers are used as reinforcement. The samples, prepared using a reactive bonding technique, exhibited adequate mechanical properties, high resistance to thermal shocks and good stability after many thermal cycles. Morphological and structural investigations have been performed to optimize the content of each component. Preliminary tribological investigations are presented.