Papers by Author: Ana P. Carvalho

Abstract: Portuguese ceramic tiles of different origins from XVIth century to XXth century were studied. In this work we describe microstructural, mechanical and mineralogical characterisation and water absorption studies. Microstructural features (pore size) were determined using Scanning Electron Microscope (SEM) photographs. Mechanical tests (four point bending) were performed and the bending strength was determined from the fracture loads. From water absorption essays the absorption coefficient and the total amount of water retained were obtained and the open porosity was estimated. The maximum water absorbed tends to decrease from XVIth century until XXth century, showing a more pronounced drop for the tiles of the XIXth and XXth centuries. This evolution is also observed in the open porosity values. From image analysis data we also observed that porosity decreases progressively with time and an important drop is observed for XXth century tiles. The bending resistance of tiles from XVIIth to XXth century is almost constant and higher than that of XVIth century samples. This evolution does not correlate with porosity. Advances in ceramic processing, such as higher firing temperatures may lead to the appearance of quartz as almost the only crystalline phase. We consider that an increase in the bending strength is due to a more effective vitrification and a lower porosity.

Abstract: A hydride tungsten complex, [WH2(η2-OOCCH3)(Ph2PCH2CH2PPh2)2][BPh4], was entrapped in the interlayer of a pillared layered clay (PILC) and in NaY zeolite. The adsorption of the complex in the liquid phase was the immobilization process used. The free complex and the new materials were characterized by several techniques: structural analysis by DRX, nitrogen adsorption isotherms and spectroscopic methods (ICP-AES, FTIR and UV/Vis). Analysis of the data indicates that the tungsten(IV) complex is immobilized in the host microporous structures, and exhibit structural properties that are different from those of the free complex. These differences could arise either from distortions caused by steric effects imposed by the structures or from interactions with the host matrix.

Abstract: A flexible foam was developed based on polymeric diphenylmethane diisocyanate (MDI) to be used as support for pre-synthesized adsorbent additives (activated carbon) for air-conditioning filters that provide air purification and improve indoor air quality. Foam for air purification filters must be an open cell foam with low density, air permeability and the adsorbents must retain indoor air pollutants, such as volatile organic compounds (VOCs). To achieve the right structural characteristics different polyether polyols, catalysts and surfactants were used and several tests of pressure drop, apparent volume, real volume and densities were performed. Another aspect that was studied in this work was the adsorption capacity of several activated carbons and the foam matrix influence in the adsorption. For that purpose room temperature adsorption isotherms of toluene, which is a probe of noxious aromatic VOCs, were determined and compared. For scale up purpose, rise time curves of the foams were measured. This study was made at different starting temperatures and with different types and quantities of catalyst. The relationships rise time/starting temperature and rise time/quantity of catalyst were obtained and expressed in equations.

Abstract: A new porous benzene-silica hybrid clay heterostructure has been prepared by a template-assisted method. The synthesis of Hybrid Porous Clay Heterostructures (HPCH) has been performed via the intercalation of a quaternary ammonium cation surfactant (cetyltrimethylammonium bromide) and a neutral amine (octylamine) as cosurfactant, in a Portuguese clay, to direct the interlamellar hydrolysis and condensation polymerisation of neutral inorganic etraethylorthosilicate (TEOS) together with an organic precursor, the 1,4- bis(triethoxysilyl)benzene (BTEB). The material has been characterised by elemental analysis, powder X-ray diffraction, nitrogen adsorption, 13C CP MAS, 29Si MAS and CP MAS NMR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermal analyses. The hydrophobicity of the material was tested by water adsorption. Its potential application as adsorbent of volatile organic compounds was studied by the adsorption of methanol, methyl ethyl ketone, toluene and trichloroethylene.