J. Kristóf

Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.

Modification of kaolinite surfaces through mechanochemical treatment--a mid-IR and near-IR spectroscopic study.

The modification of kaolinite surfaces through mechanochemical treatment has been studied using a combination of mid-IR and near-IR spectroscopy. Kaolinite hydroxyls were lost after 10 h of grinding as evidenced by the decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm(-1) and the deformation modes at 937 and 915 cm(-1). Concomitantly an increase in the hydroxyl-stretching vibrations of water is observed. The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the O-H, Al-OH, Al-O-Si and Si-O bonds. Evidence of this destruction may be followed using near-IR spectroscopy. Two intense bands are observed in the spectral region of the first overtone of the hydroxyl-stretching vibration at 7065 and 7163 cm(-1). These two bands decrease in intensity with mechanochemical treatment and two new bands are observed at 6842 and 6978 cm(-1) assigned to the first overtone of the hydroxyl-stretching band of water. Concomitantly the water combination bands observed at 5238 and 5161 cm(-1) increase in intensity with mechanochemical treatment. The destruction of the kaolinite surface may be also followed by the loss of intensity of the two hydroxyl combination bands at 4526 and 4623 cm(-1). Infrared spectroscopy shows that the kaolinite surface has been modified by the removal of the kaolinite hydroxyls and their replacement with water adsorbed on the kaolinite surface. NIR spectroscopy enables the determination of the optimum time for grinding of the kaolinite. Further NIR allows the possibility of continual on-line analysis of the mechanochemical treatment of kaolinite.

Thermal Behaviour of Kaolinite Intercalated with Formamide, Dimethyl Sulphoxide and Hydrazine

The thermal behaviour of kaolinites intercalated with formamide, dimethyl sulphoxide and hydrazine has been studied by simultaneous TG-DTG-DTA-EGA and TG-MS techniques. The complexes can be decomposed completely without dehydroxylating the mineral. It was found that the amount of intercalated guest molecules per inner surface OH-group is close to unity for the formamide and dimethyl sulphoxide intercalates. For the intercalation of hydrazine it was found that hydrazine is locked in the expanded mineral as hydrazine hydrate and its amount is somewhat higher than that obtained for the other two reagents. The thermal evolution patterns of the guest molecules revealed that all the three reagents are bonded at least in two different ways in the interlayer space.

Investigation on the formation of RuO2-based mixed oxide coatings by spectroscopic methods

Abstract Surface species formed as a function of the temperature during the preparation of RuO 2 /TiO 2 mixed oxide films were identified by emission FT-IR and FT-Raman spectroscopy. The formation of surface carbonyls from precursor mixtures of hydrated RuCl 3 and titanium diisopropoxide bis-2,4-pentanedionate was confirmed. The intensity of the CO stretching band increases with decreasing ruthenium content due to the increasing dispersity of the noble metal. The negative emission bands of the coating 20%Ru+ 80%Ti proves the occurrence of a segregation phenomenon resulting in a TiO 2 -enriched surface layer. The results obtained are in agreement with those of former measurements by simultaneous thermogravimetry-differential thermal analysis (TGA-DTA), thermogravimetry combined with mass spectrometry (TGA-MS) and secondary ion mass spectrometry (SIMS).

Emission FTIR studies on the formation mechanism of IrO2/TiO2 based coatings

Abstract The formation reactions of IrO 2 /TiO 2 mixed oxide films supported on metal titanium plate were followed by emission FTIR method. Coatings of the composition 50% Ir + 50% Ti obtained by thermal decomposition from the precursor mixture of IrCl 3 x 3H 2 O/titanium(di-isopropoxide) bis-2,4-pentanedionate were preheated to 210, 392 and 500°C. At 210°C—in addition to 2,4-pentanedionate—the presence of surface carbonyls as a result of decomposition of solvent (isopropanol) chemisorbed to iridium was confirmed. At 500°C the negative emission bands of rutile prove the occurrence of a surface segregation phenomenon resulting in a TiO 2 (or a TiO 2 -enriched) surface layer. The conversion of IrCl 3 to IrO 2 was also followed.

Thermoanalytical Investigation of Formamide Intercalated Kaolinites Under Quasi-isothermal Conditions

The thermal behaviour of fully and partially expanded kaolinites intercalated with formamide has been investigated in nitrogen atmosphere under quasi-isothermal heating conditions at a constant, pre-set decomposition rate of 0.20 mg min−1 . With this technique it is possible to distinguish between loosely bonded (surface bonded) and strongly bonded (intercalated) formamide. Loosely bonded formamide is liberated in an equilibrium reaction under quasi-isothermal conditions at 118°C, while the strongly bonded (intercalated) portion is lost in an equilibrium, but non-isothermal process between 130 and 200°C. The presence of water in the intercalation solution can influence the amount of adsorbed formamide, but has no effect on the amount of the intercalated reagent. When the kaolinite is fully expanded, the amount of formamide hydrogen bonded to the inner surface of the mineral is 0.25 mol formamide/mol inner surface OH group. While the amount of surface bonded formamide is decreasing with time, no change can be observed in the amount of the intercalated reagent. With this technique the mass loss stages belonging to adsorbed and intercalated formamide can be resolved thereby providing a complex containing only one type of bonded (intercalated) formamide.

SECONDARY ION MASS SPECTROMETRIC STUDIES ON THE FORMATION MECHANISM OF IRO2/ZRO2 BASED ELECTROCATALYTIC THIN FILMS

Secondary ion mass spectrometry (SIMS) was used to analyse the formation mechanism of IrO2/ZrO2 film electrodes. The coating mixtures with compositions 20% Ir+80% Zr and 50% Ir+50% Zr prepared on titanium supports from alcoholic solutions of IrCl3.3H2O and ZrOCl2.8H2O precursors were heated to specified temperatures and analysed by SIMS. The process of the electrode film evolution was followed via concentration depth profiles of O−, Cl−, IrO

Study of ZrO2 Coatings by Thermoanalytical and Fourier Spectroscopic Methods

The formation mechanism of ZrO2 — used for the stabilization of electrocatalytic thin films — from ZrOCl2·8H2O precursor was followed as the function of the firing temperature for the powder form as well as for the form of a thin film deposited on a titanium support. It was found that an intramolecular hydrolysis takes place upon heating, resulting in the liberation of hydrogen chloride. XRD, FT-IR and FT-Raman investigations revealed that polymorphism occurs in the oxide film. The upper surface of the film is of tetragonal structure, while the bulk is of cubic form stabilized by TiO2 formed by oxidation of the support.