[en] The aim of the present work is to realise ceramic tiles with superior surface mechanical characteristics and chemical resistance, by the addition of nano-oxides, such as zirconia and alumina, since such advanced ceramics oxides are well known for their excellent mechanical properties and good resistance to chemical etching. In order to avoid any dangerousness, the nanoparticles were used in form of aqueous suspension and they were sprayed, by airbrush, directly onto the dried ceramic support, before firing. To observe the distribution of the nanoparticles and to optimise the surface treatment, SEM-EDS analyses were carried out on the fired samples. XRD analysis was conducted to assess the phases evolution of the different materials during the firing step. The surface mechanical characteristics of the samples have been evaluated by Vickers hardness and scratch test. In addition, also chemical resistance tests were performed. Microstructural observations allowed to understand how alumina and zirconia nanoparticles acted to improve the surface performances of the modified ceramic tiles. (Author) 20 refs.

[en] To investigate the complex interrelationships between the characteristics of powders and the corresponding densified samples, submicronic alumina and partially stabilized zirconia powders were used as starting materials. The powders were previously treated in order to eliminate hard agglomerates to which were ascribed defects and flaws in green and sintered bodies. Further possible agglomerations were avoided using the forming techniques like slip casting in gypsum molds and pressure slip casting at 10 MPa; an improved microstructure was noticed if pressure slip casting was used. Extended investigation of powder treatments and slip processing allowed to obtain the green and sintered bodies with extremely fine and homogeneous microstructure and superior physical and mechanical properties. In this way the practical contribution to reach a high quality and reliability potential of structural ceramics was given

[en] In order to obtain dense, fine grained ceramic materials the efforts should be devoted to the synthesis of highly reactive starting powder and/or to the application of appropriate consolidation technique. The advantages of the investigated submicronic and agglomerate free alumina and zirconia powders, treated by milling and ultrasonication, were exploited avoiding the drying step. So, the comparative investigation of characteristic parameters of slip casting and pressure slip casting of previously treated water suspensions of the powders was done. The interrelationships between slip properties, e.g., concentration of solids, deflocculation agent content, viscosity, pH, etc., and consolidation parameters, like casting rate and density were studied. The investigation of mechanical and microstructural properties of sintered bodies allowed a better understanding of the consolidation processes

[en] Short communication

[en] Nuclear magnetic resonance (NMR) relaxation and imaging are shown to give information on the changes of the pore space structure in ceramics during the sintering process. On a set of ceramic samples held at fixed maximum firing temperature of 1280 deg. C for different lengths of time, called 'soaking times' in the ceramics industry, NMR methods were applied to quantify pore space properties such as connected porosity and pore size distributions. The longer the soaking time the lower the connected porosity, but no corresponding general statement can be made with regard to the pore size distribution. The homogeneous distribution of pores where the porosity is 17% for minimal soaking times becomes heterogeneous and with bigger pores but with porosity only about 5% after 10 min of soaking time. The results obtained are combined with those from traditional techniques such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The measured connected porosities and SEM analysis are in agreement with the NMR results. The 'pore size' distributions obtained by magnetic resonance relaxation and MIP differ substantially and give complementary information, because in relaxation measurements 'size' tends to correspond to pore dimensions, while in MIP 'size' corresponds to the dimensions of the pore 'throats', the channels connecting the pores. The discrepancy between pore and pore-channel size increases with the soaking time and makes it clear that a higher level of sintering allows the formation of larger pores connected by smaller channels. For the longest soaking time sample, the SEM photos and the lack of a NMR signal make it clear that there is substantial isolated porosity and essentially no connected porosity

[en] Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al₂O₃-ZrO₂ laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al₂O₃ external layers and an intermediate thick one, consisting of a mixture of Al₂O₃ and monoclinic ZrO₂ in the range 0-30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO₂-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia content. A correlation between the PAS parameters and the microstructural changes caused by the presence of residual stresses was found. Nanoindentation measurements were used to trace the sign and magnitude of the residual stress gradient across the interface between the layers.

[en] We report on the development and implementation of analytical methodology for investigating elemental accumulation in different layers within plant leaves, with in-situ spatial resolution mapping, exploiting the technique of LIBS. The spectrochemical analysis of lead-doped leaf samples is demonstrated to develop a real time identification procedure in order to complement other analytical techniques not lending themselves for spatial resolution analysis. Our findings suggest that with elevated levels of Pb within the plants transportation and storage of some nutrition elements is changed