M. Gábor

Thermal behavior and decomposition of intercalated kaolinite

Intercalation complexes of a Hungarian kaolinite were prepared with hydrazine and potassium acetate. The thermal behavior and decomposition of the kaolinite-potassium acetate complex was studied by simultaneous TA-EGA, XRD, and FTIR methods. The intercalation complex is stable up to 300°C, and decomposition takes place in two stages after melting of potassium acetate intercalated in the interlayer spaces. Dehydroxylation occurred, in the presence of a molten phase, at a lower temperature than for the pure kaolinite. FTIR studies revealed that there is a sequence of dehydroxylation for the various OH groups of intercalated kaolinite. The reaction mechanism was followed up to 1000°C via identification of the gaseous and solid decomposition products formed: H2O, CO2, CO, C3H6O, intercalated phases with basal spacings of 14.1 Å, 11.5 Å, and 8.5 Å as well as elemental carbon, K4H2(CO3)3 · 1.5H2O, K2CO3 · 1.5H2O, and KAlSiO4.

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.

Study of the structure and thermal behaviour of intercalated kaolinites

Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration — reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 Å halloysite present in the same mineral.

Effect of ambient atmosphere on solid state reaction of kaolin-salt mixtures

The reaction of kaolin with NaCl was followed by dynamic thermal analysis and mass spectrometry under N2, CO2, and air atmospheres and in a 10−5-torr vacuum. The weight loss was a function of the atmosphere used and, according to mass spectrometry, was due to the evolution of H2O, HCl, and very small amounts of H2. HCl was formed only after the release of 85% of the hydroxyl content of the kaolin. When the clay was pretreated with saturated salt solution, H2O and HCl evolved in more or less the same temperature range, indicating that only some of the OH groups reacted with the chloride ion. High-temperature X-ray powder diffraction patterns showed that the sodium ion reacted with the noncrystalline metakaolin to give NaAlSiO4. Chemical analysis showed that the reaction of kaolinite and sodium chloride started below 400°C. The rate of the reaction increased at higher water vapor concentration. From mass spectrometric data, the NaCl-treated kaolin appeared to adsorb CO2. Desorption at several distinct temperatures suggests that CO2 was adsorbed by different parts of the structure, i.e., holes and channels. X-ray powder diffraction and infrared absorption data indicate that the kaolinite structure persisted even after it had been heated with NaCl in a CO2 atmosphere to as high as 800°C.

Interaction of kaolinite with organic and inorganic alkali metal salts at 25–1300 °C

Abstract The reactions of Georgian kaolinite with saturated solutions of alkali metal Chlorides, potassium acetate and with solid salts resp. were followed by XRD, FTIR and TA-MS methods. The results show that in the case of solid MCl and solutions thereof already at room temperature alkali metal ions have been incorporated into kaolinite. The quantity of incorporated cations increased with rising temperature. CH 3 COOK was intercalated into the interlayer spaces. The solid state reactions and the gaseous reaction products up to 1000 °C were followed by different methods. The crystal phases formed in the course of the reactions between kaolinite and the decomposed salts have been investigated up to 1300°C. The reaction mechanisms on the basis of experimental data and literature are discussed.

Synthesis and characterizations of hydroxy-aluminum cross-linked montmorillonite

Cross-linked montmorillonite was prepared by reacting homoionic sodium form of bentonite (Na-M) from Istenmezeje (Hungary) with high molecular weight polyhydroxy-aluminum complex. The complex was prepared by controlled hydrolysis of alumina macrocation. The intercalated clay (Na-Al-M) was thermally treated to convert the hydroxy cations to oxide pillars. The pillared products were characterized by X-ray powder diffraction (XRD), Fourie transform infrared spectroscopy (FTIR), (thermogravimetry (TG), differential thermal analysis (DTA) and thermal analysis-mass spectrometry (TA-MS) methods. The specific surface area as well as pore size and pore structure distribution of samples were measured by nitrogen, water and carbon tetrachloride adsorption, and the heat of immersion was also determined. The pillared products were characterized by d(001) reflections of 19 Å, which is stable even at 500°C. The interaction of polymer alumina caused several changes in the obtained FTIR spectra due to the formation of different new bonds. The rate of dehydroxylation of the pillared product is very moderate, the water release occurred in different temperature ranges according to TA-MS results. Dehydration starts at interfaces and at the wall of pores, occurring nearly with uniform rate at 250-500°C. DTA curve indicates the formation of a new phase at 950°C. The obtained surface area of the pillared product by nitrogen adsorption becomes larger (208 m2 g-1) with respect to the non pillared clay, which decreases less than 10% upto 700°C. The pillared sample has a definite pore structure, the quantity of micropores (0-40 Å) decreased with increasing of macropores (>1000 Å). The obtained domestic pillared montmorillonite possesses a high degree of thermal stability and may be used as adsorbent.

The role of magnesia and alumina in promoting the nitridation of magnesium and aluminium

Abstract The nitridation of magnesium, aluminium and their alloys is promoted by the addition of the oxides MgO or Al2O3. Non-isothermal kinetic measurements (TG and DTA) show that nitride formation proceeds to completion more rapidly in the presence of these oxides than when metal and gas only are present. The mechanisms of these reactions are discussed with reference to electron micrographs obtained for the magnesium/nitrogen reactions in the presence and absence of MgO, the only system where melting was absent. It is concluded that MgO provides an active surface across which there may be transport of reactants and products. MgO also accommodates the product Mg3N2 where it does not represent an adherent layer on the metal constituting the barrier to solid (Mg)/gas (N2) interaction that opposes the uncatalyzed reaction.

Study of the binary CaCO3-SiO2 system by quantatitative DTA

Solid-state reactions in the CaCO3-SiO2 system with different mass ratios (CaCO3:SiO2=from 1∶0.2 to 1∶10) were studied by means of thermogravimetry, quantitative DTA and high-temperature X-ray diffraction up to 1500 °C.It was found that not CaCO3, but CaO reacted with SiO2. The rate of decarboxylation increased and the temperature of formation of silicate phases decreased significantly with increasing silica content. Only mono- and dicalcium silicates could be detected as solid-state reaction products. Above 1400 °C, an intensive melting process took place; the amount of silica had no clear effect on its temperature range.Quantitative DTA and X-ray diffraction data proved that, below 1000 °C, not only the decarboxylation process, but also silicate formation must be taken into consideration.

Steps in Low Temperature Dehydroxylation of Clay

Thermal changes in the kaolinite structure belonging to the group of layer silicates are well known. On heating dehydroxylation of silicates begins, resulting in the Metakaolinite structure. However, the mechanism of the solid phase transformation cannot be taken as understood, not even on the basis of the latest literary data (1,2).

Studies of the silicon dioxide-dolomite system by thermal analysis

Abstract A study of the processes occurring in the SiO2-dolomite system at a temperature in the range 25–1500 °C was carried cut with the use of thermoanalytical and high temperature X-ray diffraction methods. The purpose of this study was to reveal the effect of the composition on the transformation processes applied to similar mixtures which are frequently used in the silicate and glass industries.