Anton Tonejc

Mechanochemistry of zeolites: Part 1. Amorphization of zeolites A and X and synthetic mordenite by ball milling

Abstract X-ray diffractometry, FT i.r. analysis, cation-exchange capacity, and solubility were used to characterize the effect of ball milling on zeolite A, zeolite X, and synthetic mordenite. Changes of i.r. spectra during the ball milling show that a loss of crystallinity, a decrease of cation-exchange capacity, and an increase of solubility were caused by breaking of SiOSi and SiOAl bonds in the zeolite structure. Based on such a conclusion, the kinetic equation of the amorphization process was derived and evaluated.

Mechanochemistry of zeolites: Part 3. Amorphization of zeolite ZSM-5 by ball milling

Abstract The samples obtained during ball milling of zeolite ZSM-5 were characterized by different methods such as X-ray diffractometry, scanning-electron microscopy, FT i.r. spectrometry, and simultaneous thermal analysis. The milling caused considerable change of morphological and particulate properties followed by loss of crystallinity of the treated zeolite. The loss of crystallinity is caused by breaking of external TOT bonds of zeolite framework. Very slow rate of amorphization of “as-synthesized” zeolite as compared with the rate of amorphization of its “activated” form is explained by the stabilizing effect of TPA + ions present in the structure of the as-synthesized zeolite.

The influence of gel properties on the kinetics of crystallization and particulate properties of MFI-type zeolities. I. The influence of time and temperature of gel ageing on the particulate properties of silicalite-1 microcrystals

Abstract The influence of time and temperature of ageing of the amorphous gel precursor (2.5Na 2 O-8TPABr-60SiO 2 -800H 2 O) on the particulate properties (particle size distribution, particle shape, number of particles) of silicalite-1 synthesized at 170°C were studied by different experimental methods such as X-ray diffractometry (XRD), differential thermogravimetric analysis (TGA), particle size analysis, FT infra-red spectroscopy and scanning-electron microscopy (SEM). In spite of negligible changes in the crystal morphology, ageing of the gel considerably affects the number and size of silicalite-1 crystals in the crystalline end products. The observed effects were discussed in terms of the formation of specific ordered subunits between silicate species and TPA + ions (germ nuclei) and their role in the nucleation and crystal growth of silicalite-1 crystals.

Mechanochemistry of zeolites: Part 2. Change in particulate properties of zeolites during ball milling

Abstract Change of particulate and morphological properties of the samples obtained during the high-energy ball milling of zeolites A and X were studied by scanning-electron microscopy, X-ray diffraction, and determination of particle size distribution. It was found that decrease of crystallinity is followed by considerable change of particulate properties during the milling, but that the change of particulate properties and amorphization are two independent processes. Type of amorphization induced by ball milling was defined on the basis of the analysis of the change of effective crystallite size during the milling.

Mechanochemistry of zeolites. Part 4: Influence of cations on the rate of amorphization of zeolite A by ball milling

Abstract Based on previous mechanochemical studies of zeolites it was assumed that different cations may influence their mechanical stability. To prove this assumption, the influence of the partial exchange of sodium ions from zeolite A by other cations (Li + , Na + , K + , Cs + , and NH 4 + ) on the kinetics of amorphization was investigated. X-ray diffractometry and FT i.r. analysis were used to characterize the effect of the exchange on the rate of amorphization of zeolite A during its ball milling. Analysis of the experimental results has shown that a partial exchange of sodium with Li + , K + , Cs + , and NH 4 + does not affect the basic mechanism of the amorphization process, but only the rate of amorphization, R . The decrease of R in the sequence R (Na + ) > R (Li + ,Na + ) > R (Na + ,K + ) > R (Na + ,Cs + ) > R (Na + ,NH 4 + ) was explained by the increase of the volume, V oc , occupied in a unit cell of zeolite A by the cations (Na + + R + ) in the sequence V oc (Na + ) V oc (Na + ,K + ) V oc (Na + ,Cs + ) V oc (Na + ,NH 4 + ).

Crystal Growth of Lead Fluoride Phases Using the Constant Composition Method. III. Effect of pH and Ionic Strength

Abstract The kinetics of crystal growth of the lead fluoride phases was studied at 25°C using the so-called constant composition method (pF-stat method). A linear growth law was obeyed for αPbF 2 growth from equivalent lead nitrate and potassium fluoride solutions with low supersaturation and pH between 5.2 and 5.6 in pure water and in 0.1 mol dm −3 KNO 3 solution. The rate is about 5 times greater at high ionic strength. It decreases linearly with changing pH of the supersaturated solution both to higher and to lower values than mentioned (addition of KOH and HNO 3 , respectively), i.e. reaching the pHs at which two other lead fluoride phases grow: (a) with large excess of Pb(NO 3 ) 2 over KF and KOH to pH = 5.2 phase(s) of so far unresolved structure, which undergoes the recrystallization in water to pure αPbF 2 , and after annealing to 450°C decomposes into β-PbF 2 , and an unidentified phase (probably α(K N Pb N−1 )F 2−N phase with N varied); (b) with large excess of KF over Pb(NO 3 ) 2 and HNO 3 to pH = 4.3, the βPbF 2 phase was identified. The characterization of the grown phases was done on the basis of polarizing microscopy, Fourier transform infrared (FTIR) spectra and X-ray powder diffraction analysis.

Electron diffraction and infrared spectroscopy of amorphous aluminosilicate gels

Electron diffraction, thermal analysis and FTIR spectroscopy were used in the study of structural properties of x-ray amorphous sodium(G1) and potassium(G5) aluminosilicate gels. Results of the analysis showed that the x-ray amorphous gels contain structurally ordered regions, or particles of partly-crystalline phase which can be destroyed by heating at appropriate temperature. The partly-crystalline phase exhibit structural properties of zeolites, and thus can act as potential nuclei in zeolite crystallization. The influence of the observed structural properties of gels on the results of their hydrothermal treatment(type(s) of zeolite(s) formed, rate of crystallization, particulate properties of crystalline end product(s)) is discussed.

CdS nanocrystals formed in SiO2 substrates by ion implantation

Abstract In this work, CdS nanocrystals were formed in SiO 2 substrates by implantation of Cd and S atoms (up to 10 17 /cm 2 ) and subsequent annealing (up to 900°C). The implanted and annealed layer was studied by X-ray diffraction (XRD), UV transmittance and reflectance measurements (energy range 1.4–6.5 eV), and Raman spectroscopy. Upon annealing, all methods proved the synthesis of CdS crystallites from the starting components, and the features characteristic of the CdS-phase were strongly and consistently dependent on ion dose and annealing temperature. The analysis of the results shows that by implantation and post-implantation treatment, the average size of CdS crystallites can be controlled, and that smaller CdS nanocrystals are obtained for lower doses and lower annealing temperatures.