Davide Gardini

On the possibility of silicon nitride as a ceramic for structural orthopaedic implants. Part II: chemical stability and wear resistance in body environment

In Part I, the processing, microstructure and mechanical properties of three silicon nitride-based ceramics were examined and their non-toxicity was demonstrated. In this Part II, some features critical to biomedical applications were investigated: (i) the wetting behaviour against aqueous media, including physiological solutions; (ii) the chemical stability in water and in physiological solutions; and (iii) the wear resistance, measured under experimental procedures that simulate the conditions typical of the hip joint prosthesis. The results confirmed that silicon nitride may serve as a biomaterial for bone substitution in load bearing prosthesis.

An analysis of current transients during electrophoretic deposition (EPD) from colloidal TiO2 suspensions

This is a simple quantitative analysis of the electrical current transients recorded during the electrophoretic deposition (EPD) of TiO(2) particles from ethanol-based suspensions in which the linear correlation between the mass deposited and the charge passed was verified experimentally. Using this experimental knowledge as our starting point, we were able to test a simple electrical model of a deposition cell for its consistency with electrical current density data measured during EPD. Assuming that the background electrochemistry was controlled resistively rather than diffusively, we then tentatively exploited the electrochemical data to gain information on the structure of the deposit during its growth.

Silica-coating as protective shell for the risk management of nanoparticles

Nanoparticles (NPs) surface functionalization with silica (SiO2) has attracted high attention due to hydrophilicity, biocompatibility, chemical and thermal stability of silica. The present work is addressed to the production and characterization of SiO2-coatings on titanium dioxide (TiO2) and silver (Ag) NPs dispersed in aqueous solutions (commercial nanosols) with the aim to manage the potential risk that such NPs could generate in occupational exposure scenarios. A colloidal approach, based on principles of heterocoagulation in which opposite charged NPs are forced to coagulate in hierarchical structures, imposed by their relative size and weight ratio, was followed. The results were compared with a chemical approach, based on nucleation of silica phase from silica precursor solutions on the surfaces of TiO2 or Ag NPs seeds. In order to increase the adhesion of silica on TiO2 and Ag surfaces, heterocoagulated sols were spray-dried and subsequently redispersed in water to check the feasibility of such approach at industrial level. Physicochemical properties such as zeta potential, electrical conductivity, particle-size distribution, specific surface area and morphology of the samples produced with different SiO2:TiO2 and SiO2:Ag weight ratios were collected and compared. Indirect evidences of silica coating were obtained.

Industrial Ink-Jet Application of Nano-sized Ceramic Inks

Ink-jet printing is becoming a leading technology for traditional ceramics, due to its capacity of reproducing highly resolved and customized images on tile surfaces. Nano-sized inks, produced by the polyol synthesis route, proved to fulfil the printing requirements, tailoring their chemico-physical properties (e.g. viscosity, surface tension) on industrial ink-jet devices, so representing a major breakthrough in the quadrichromy process.

A Controlled Colloidal Destabilization Approach for the Electrophoretic Deposition (EPD) from Cobalt Ferrite and Magnetite Nanoparticles Suspensions in Diethylene Glycol

Cobalt ferrite (CoFe2O4) and magnetite (Fe3O4) nanoparticles suspensions in diethylene glycol were tested as candidate systems for the EPD of CoFe2O4 and Fe3O4. It was found that despite the high stability and high zeta potential of such suspensions and the occurrence of mass transport at the electrode, they are not viable systems for EPD, due to coagulation failure. However, dilution of both suspensions with ethanol caused film coagulation at electric field between 20 and 60 V cm-1. Combinations of electric field and DEG volume fraction in ethanol/suspension mixtures that allow EPD to take place are detailed, and a description of the outcome of EPD trials is provided. A qualitative discussion of the causes of film consolidation in the presence of ethanol is presented.

Simple Rheological Tests and Protocols for SME Ceramic Producers

The rheological behaviour of ceramic suspensions affects the quality of the products and the yield of the processes. Therefore, rheology control is needed to obtain materials with enhanced properties and to reduce energy consumption. The importance of rheology control in slip casting, spray-drying, screen-printing, ink-jet printing, glazing, and so on, either for Quality Control (QC) aims or for system formulation, has been acknowledged from many years. As in these control procedures the determination of the rheological behavior is a critical issue, this work is focused on the assessment of viscosity (flow behavior) and its dependency on time (usually, thixotropic behavior). Most of ceramic factories still use simple and cheap instruments to investigate rheological behaviors (or something related to it). However, the information provided by such instruments is not completely satisfactory. Therefore, optimization of the procedures is important to improve reproducibility and precision. Suggestions about simple tests and protocols applicable to viscometers ordinarily available in ceramic factories are given. Protocols consider besides a precise description of the tests, all other factors that can affect the results, such as the thermo-mechanical history of the samples before testing.

Processing and characterization of screen printing Ba0.5Sr0.5Co0.8Fe0.2O3−δ inks

Oxygen-selective membranes based on thin layers of barium–strontium–cobalt ferrite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxide were manufactured. Five BSCF inks prepared with different carriers and milling treatments were rheologically characterized, screen printed on three different porous alumina substrates and sintered at 1050 and 1150∘C. The resulting membranes were characterized. The data collected on the rheological properties of inks (flow curves, thixotropic behaviour, linear viscoelasticity), their processability by screen printing, and the quality of the layers obtained after sintering represents an important starting point to set up the next research activities.