Papers by Author: Tiziano Manfredini

Abstract: One of the most common materials-measures to counteract Urban Heat Island Effect can be identified in cool roof: white surface characterized by high solar reflectance and high thermal emissivity. One of the problems for the realization of cool roof is the difficult matching of white color with urban planning needs. In order to better integrate cool roofs into skylines cool colors were developed integrating pigments into cool roof surfaces. Cool roof market is actually dominated by organic based products with optimal solar performances but low durability against ageing. The use of ceramic-based products is crucial in the design of a new durable cool roof thanks to their naturally high thermal emissivity (ε=0.90) and their high chemical durability. The development of a new ceramic-based product made by a traditional porcelain stoneware tile as support, an inorganic engobe was started in the last years. In order to complete the product with a suitable glaze, eight different inorganic pigments were added to three different glazes, each one characterized by different surfaces features. Even if the addition of glazes, and pigments decrease the reflectance values of the solar reflective engobe, some promising results were achieved in this study especially regarding warm colored glazes.

Abstract: The present work was focused on glass-alumina functionally graded materials. The samples, produced by plasma spraying, were built as multi-layered systems by depositing several layers of slightly different composition, since their alumina and glass content was progressively changed. After fabricating the graded materials, several, proper characterization techniques were set up to investigate the gradient in composition, microstructure and related performances. A particular attention was paid to the observation of the graded cross sections by scanning electron microscopy, which allowed to visualize directly the graded microstructural changes. The scanning electron microscopy (SEM) inspection was integrated with accurate mechanical measurements, such as systematic depth-sensing Vickers microindentation tests performed on the graded cross sections.

Abstract: Hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is a well-known and a valuable implant material with biocompatibility and bioactive properties. Full utilisation of the unique properties of hydroxyapatite bulk ceramics is, however, enhanced by a proper reinforcement, i.e. by preparation of composites. The goal of this study was to synthesize a HAP-coated zirconia composite powder by the precipitation of HAP in presence of zirconia. The idea was to avoid uncontrolled agglomeration of the zirconia nanostructured reinforcement during the sintering step. ZrO2 nanopowders, previously synthesized by hydrothermal crystallisation, were added in an appropriate amount to an intensively stirred aqueous suspension of Ca(OH)2. HAP was precipitated by addition of H2PO4 at controlled pH in order to obtain a 50:50 composite powders. The obtained powders, fully characterized by TEM, XRD, TG-DTA and BET, were used for the preparation of the nanostructured composite speciments. The sintered materials were characterized in order to evaluate their structural and morphological properties.

Abstract: Four samples of Ba-exchanged zeolite A, bearing 0.27, 0.43, 0.58 and 0.74 meq/g Na residual amounts, were thermally treated in the temperature range 200-1500 °C for times up to 28 hours. The same samples were pressed at 30 and 60 MPa to manufacture cylindrical pellets, which were thermally treated at 1300 °C for 5 hours. Thermally treated materials were characterized by room temperature XRD. The sequence of thermal transformations that Ba-exchanged zeolite A undergoes (zeolite ® amorphous phase ® hexacelsian ® monoclinic celsian) and the strong mineralizing action developed by Na are confirmed. Pressing the Ba-exchanged zeolite A powder-like samples to obtain cylindrical pellets is found to expedite the sluggish final phase transition hexacelsian ® monoclinic celsian. The optimum residual Na content of Ba-exchanged zeolite A to be transformed into monoclinic celsian is assessed to range between 0.27 and 0.43 meq/g.

Abstract: Functionally graded materials are a new and attractive class of materials incorporating an engineered spatial variation in composition and/or microstructure: this idea has immediately revealed successful since it allows to reach peculiar mechanical properties such as resistance to wear and contact damage. As a matter of fact, the final behaviour of a Functionally Graded Material is mainly influenced by its graded composition and/or microstructure. Therefore a good fabrication technique should provide a high control and reproducibility of the spatial variation in composition and/or microstructure; on the other hand, a reliable model should take into account the gradient in order to accurately predict the final behaviour of a Functionally Graded Material. The present study is focused on glass-alumina FGMs: the compositional variation, which occurs along only one direction, has been realized through percolation of a molten glass into a bulk polycrystalline alumina. The resulting Functionally Graded Coatings have been carefully characterized through Scanning Electron Microscopy, X-ray diffraction, classical mechanical tests and analysis. Moreover, their behaviour has been modeled by means of a microstructure-based FEM method. A great attention has been paid to the validation of the computational model on the basis of the experimental data. Furthermore, the experimental and the computational approaches have been combined in order to define the correlation between fabrication parameters, such as time and temperature, and resulting gradients in composition and microstructure as well as related performances. Since changes in material properties can be easily evaluated, the resulting model may be useful to simulate the material response to a given thermo-mechanical loading and to tailor the gradient as a function of the specific application.