No abstract

No abstract

No abstract

Adsorption properties determined by physical adsorption of nitrogen for a series of ZSM-5 zeolite samples with various Si/Al ratios and different crystal size were compared. In addition to the BET method, the t-plot method was used to determine the microporosity of samples. Very small crystals of ZSM-5 zeolites, generally below 1 μm, with Si/Al ratio between 14 and 21 exhibit adsorption isotherms typical for purely microporous solids. Samples with Si/Al ratios larger than (about) 95 show low-pressure steps and hysteresis loops and, depending on crystal morphology, also high-pressure hysteresis loops. The low-pressure steps were associated with steps on t-plots which showed two linear parts. Small increase of adsorption up to relative pressure 0.2 is characteristic for samples with Si/Al ratios between 25 and 50.

Glass samples in Li 2 O-SiO 2 -CaO-P 2 O 5 -CaF 2 system with different contents of P 2 O 5 , CaO and CaF 2 in relative ratios responded to fluoroapatite (FA) composition (referred to P 2 O 5 addition) have been prepared and heat treated at 550 and 750uC to obtain glass ceramics. Bioactivity of all samples has been proved in vitro by the presence of new layer of apatite-like phases formed after soaking in simulated body fluid (SBF). The development and the apatitic character of created layers have been demonstrated by Fourier transform infrared analysis. Scanning electron microscopy and electron probe microanalysis have demonstrated that the density and the thickness of new layer depend on P 2 O 5 content, crystallisation temperature and immersion time. The bioactivity has been enhanced by P 2 O 5 addition as well in the case of the base glasses as in the case of glass ceramics. The additional heat treatment appeared to inhibit the bioactive behaviour, though the longer SBF acting leads to the additional formation of apatite-like layer. The mechanical properties, expressed as Vicker hardness, have been found higher and increasing with P 2 O 5 in glass ceramics treated at 750uC comparatively with base glass samples and the highest value of 7?37 GPa has been achieved by 14 wt-%P 2 O 5 addition. The same content of P 2 O 5 in glass ceramics heat treated at 550uC resulted in a decrease in hardness to a minimum value from all samples. The increase and decrease in hardness responded to development and suppression of crystallisation respectively. The inhibition of crystallisation has been affected by the presence of 'amorphous' FA according to X-ray diffraction and differential thermal analysis results.