Authors:T. Sopcak, L. Medvecky, T. Zagyva, M. Dzupon, J. Balko, K. Balázsi, and C. Balázsi
The current study was initiated in order to evaluate the adhesion strength of thin and porous hydroxyapatite (Hap) coatings on titanium (Ti) substrates deposited by the low temperature electrospraying method. The nanocrystalline hydroxyapatite powder was synthesized by coprecipitation method using eggshell biowaste as a nontoxic and natural source of the calcium precursor. Five hydroxyapatite coatings were electrosprayed onto Ti substrates by varying the concentration (0.05 and 0.1 wt%) of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) polymers in Hap suspensions. It has been shown that the adhesion strength of composite polymer–Hap coatings increased with increasing polymer concentration and the highest value (8.75 ± 0.75 MPa) was measured for the sample containing 0.1 wt% of PVP. The reason for the change in bonding strength was ascribed owing to microstructural changes caused by polymer addition whereas on one hand lower adhesion strength in Hap–0.1PEG was caused by the presence of separated polymer contained islands, and hence, weaker adhesion to substrate was found in this sample. On the other hand, more uniform, homogeneous, and denser microstructure resulted in an increasing cohesive strength inside the Hap–0.1PVP layer which lead to stronger mechanical bonding at the coating–substrate interface.
Authors:I. Szilágyi, Judit Pfeifer, C. Balázsi, A. Tóth, Katalin Varga-Josepovits, J. Madarász, and G. Pokol
We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM
and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations
were all affected.