Thermal transformations of floor tile pastes containing petroleum waste

This study focuses on the thermal and mineralogical transformations of floor tile pastes containing petroleum waste. The tile pastes prepared by the dry process contain up to 10 wt% of petroleum waste in replacement of kaolin. Thermal and mineralogical changes occurring during firing were characterized by differential thermal analysis, thermogravimetry analysis, derivative thermogravimetry, dilatometric analysis, open photoacoustic cell technique, X-ray diffraction, and scanning electron microscopy. During heating an endothermic transformation within the 511.4–577.5 °C range and an exothermic transformation within the 997.8–1001.6 °C range were identified. The endothermic transformation can be mainly attributed to the dehydroxylation of kaolinite. The exothermic transformation is mainly associated with the crystallization of primary mullite. TG measurements indicate that the total mass loss of the floor tile pastes is dependent on the amount of petroleum waste addition. It was found that the replacement of kaolin with petroleum waste, in the range up to 10 wt%, influenced the thermal expansion–shrinkage curve. In addition, the floor tile pastes containing petroleum waste have low values of thermal diffusivity.     

Thermal study of clay ceramic pastes containing sugarcane bagasse ash waste

This study focuses on the thermal and mineralogical transformations of clay ceramic pastes. The pastes contain different amounts of sugarcane bagasse ash waste. Thermal and mineralogical changes occurring during firing were characterized by differential thermal analysis, thermogravimetry analysis (TG), X-ray diffraction (XRD), and scanning electron microscopy. On heating three endothermic events within the 73.5–75.7, 276.9–283.5, and 567.1–573.5 °C temperature ranges were identified. The endothermic valleys could be mainly interpreted as the release of physically adsorbed water, dehydration of hydroxides, and dehydroxylation of kaolinite, respectively. Two exothermic events within the 618.9–690.1 and 948 °C temperature ranges were identified. The exothermic peaks are associated with the decomposition of organic compounds and crystallization of mullite from metakaolinite, respectively. TG results indicate that the clay ceramic pastes had a total mass loss in the 13.1–13.6 % range, and are dependent on the sugarcane bagasse ash waste amount added. It was found that the replacement of natural clay with sugarcane bagasse ash waste, in the range up to 20 wt%, influenced the thermal behavior and technological properties of the clay ceramic pastes. In addition, the thermal analysis results agree well with the XRD.     

Thermal transformations of red wall tile pastes

This work focuses on the thermal and mineralogical transformations of red wall tile pastes. The pastes contain different amounts of calcareous and are prepared with Brazilian raw materials. Thermal transformations are evaluated by TG, DTG and DTA, dilatometric analysis, and X-ray diffraction. Four endothermic transformations were identified and interpreted as the release of physically adsorbed water, dehydration of hydroxides, dehydroxylation of kaolinite, and decomposition of carbonate. An exothermic transformation within the 925–950°C range is associated to crystallization of new phases such as calcium aluminosilicates and mullite. TG measurements indicate that the total mass loss of the pastes is dependent on the amount of calcareous addition. Dilatometric analysis indicates the onset of sintering at around 900°C, leading to shrinkage of the pellets. The thermal analysis results agree well with the X-ray diffraction.     

A comparative study of the dehydroxylation process in untreated and hydrazine-deintercalated dickite

A dickite from Tarifa (Spain) was used to study the influence of the intercalation and the later deintercalation of hydrazine on the dehydroxylation process. The dehydroxylation of the untreated dickite occurs through three overlapping endothermic stages whose DTA peaks are centred at 586, 657 and 676°C. These endothermic effects correspond, respectively, to the loss of the inner-surface, the inner hydroxyl groups, and the loss of the water molecules, product of dehydroxylation process, which has been trapped in the framework of the dehydroxylated dickite. The intercalation of hydrazine in the interlayer space of dickite and the later deintercalation affect the dehydroxylation process. It occurs through only two endothermic stages which DTA peaks are centred at 575 and 650°C. The first corresponds to the simultaneous loss of both the inner and the inner-surface hydroxyl groups, whereas the second one is analogous to that at 676°C observed in the DTA curve of untreated dickite. These effects appear shifted to lower temperatures compared to those observed in the untreated dickite.     

Differential thermal study of Mg-bearing clays from saline lakes of Southern Tunisia

Clays high in Mg content occur frequently in the high saline environment of salt lakes in southern Tunisia. The DTA curves of these clays show a striking endothermic-exothermic reaction in the temperature range of 800–820°C. A strong correlation is observed between the intensity of these coupled reactions and the Mg content of the initial clay sample. The initial endothermic reaction is interpreted as the melting/dehydroxylation of the Mg-bearing smectites. The subsequent exothermic peak is interpreted as caused by the crystallisation of the new Mg-silicate phase enstatite. Therefore, the DTA is considered as a suitable method for the identification and relative quantification of high Mg clay minerals (e.g. trioctahedral smectites). Variations of the Mg content of the studied samples were well detectable by means of DTA, disclosing a distinct distribution pattern of the salt lake clays. Clues to bulk chemical composition of the initial clay assemblage can also be found in the results of the X-ray analysis of the firing products.     

Thermal behavior and immersion heats of selected clays from Turkey

Four clays (two bentonites and two kaolinites) from Turkey were investigated by X-ray diffraction (XRD), thermal analysis (DTA/TG-DSC) and surface area measurement techniques. Mineralogically bentonite samples were characterized low concentration of montmorillonite and high level of impurities. Both kaolinite samples mainly contained kaolinite and quartz as major mineral. TG-DTA curves of all clay samples were measured in the temperature range 30–1200 °C. The total % weight losses for the bentonite samples (B1 and B2) and the kaolinite samples (K1 and K2) were determined as 14.50, 13.42, 5.55 and 11.85%, respectively. Differential Scanning Calorimeter (DSC) analyses of samples were carried out by heating the samples from 30 to 550 °C. The immersion heats of clay samples were measured using with a Calvet-type C-80 calorimeter. The higher exothermic Q_imm values were determined for bentonite samples compared to kaolinite samples.     

New Data on Thermal Effects of Kaolinite in the High temperature Region

DTA study of an Indian Kaolinite has been performed by varying packing density and rate of heating. Both these two parameters influence the intensities of both endothermic and exothermic peaks related to the dehydration, dehydroxylation and then crystallizations of Al-Si spinel, mullite and cristobalite phases. Significantly, the study reveals that mullitization takes place by two separate reactions as indicated by two exotherms in the 1200-1400°C range of DTA trace. This revised version was published online in July 2006 with corrections to the Cover Date.     

The non-isothermal kinetics of mullite formation in mechanically activated kaolinite–alumina ceramic system

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite?+?alumina ceramic system have been studied by differential thermal analysis (DTA). The mixture of kaolinite and alumina was activated mechanically in a planetary mill, while amorphization in the kaolinite and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20?°C?min^?1. The mechanical activation of the kaolinite and alumina mixture resulted in the decrease in activation energy values for mullite formation.     

Effect of degradation of montmorillonite by vibration grinding on the dTA curves in the range 20–1500°C

The effect of vibration grinding on the DTA curves of montmorillonite isolated from the most important locality of bentonite in the Slovak Republic (Jel?ovy potok, Middle Slovakia) was studied in the temperature range 20–1500°C. Interpretation is offered for 6 endothermic and 3 exothermic peaks. vibration grinding modified the course of dehydration of the mineral, suppresses the “dehydroxylation’ peak at 700°C, enables the crystallization of high-temperature quartz, cristobalite and cordierite at lower temperatures in comparison with unground natural montmorillonite. Vibration griding slows down the crystallization of mullite which—unlike quartz, cristobalite and cordierite—does not belong to high-temperature phases of Cheto-montmorillonite. The order in which these high-temperature phases occur is not influenced by vibration grinding.     

Thermal analysis to assess pozzolanic activity of calcined kaolinitic clays

The use of calcined clays as partial replacement of cement is encouraged since it promotes the reduction of the green-house gas emission and the energy requirement of cement-based material, maintaining or enhancing the mechanical properties and the durable performance of these materials. In this paper, the use of thermal methods—DTA/TG and calorimetry—to select and to evaluate two kaolinitic clays for their use as pozzolanic materials was explored. The content and crystallinity of kaolinite in clays can be determined by DTA/TG analysis, and this technique is also suitable to select the calcination temperature for complete kaolinite dehydroxylation. Calorimetric analysis on blended cements (30 % by mass of replacement) can differentiate the reactivity of calcined kaolinitic clays. Results show that more reactive calcined kaolinitic clay develops the second and third peaks earlier than those of PC with great intensity and high acceleration. The reactivity of calcined clays is associated to raw materials containing kaolinite with high structural disorder that determines calcined clays with large specific surface area, high grindability, and small mean particles size (d ₅₀) for the same grinding objective. Finally, the DTA/TG analysis can determine the type and the amount of hydrated phases obtained at different ages to evaluate the pozzolanic reaction of calcined clay in accordance with the standardized pozzolanic activity index.     

Thermal decomposition and kinetics studies on poly(BDFAO/THF), poly(DFAMO/THF), and poly(BDFAO/DFAMO/THF)

The thermal behavior of kaolinite–urea intercalation complex was investigated by thermogravimetry–differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). In addition, the interaction mode of urea molecules intercalated into the kaolinite gallery was studied by means of molecular dynamics simulation. Three main mass losses were observed at 136 °C, in the range of 210–270 °C, and at 500 °C in the TG–DSC curves, which were, respectively, attributed to (1) melting of the surface-adsorbed urea, (2) removal of the intercalated urea, and (3) dehydroxylation of the deintercalated kaolinite. The three DSC endothermic peaks at 218, 250, and 261 °C were related to the successive removals of intercalated urea with three different distribution structures. Based on the angle between the dipole moment vector of urea and the basal surface of kaolinite, the three urea models could be described as follows: (1) Type A, the dipole moment vector is nearly parallel to the basal surface of kaolinite; (2) Type B, the dipole moment vector points to the silica tetrahedron with the angle between it and the basal surface of kaolinite ranging from 20°to 40°; and (3) Type C, the dipole moment vector is nearly perpendicular to the basal surface of kaolinite. The three distribution structures of urea molecules were validated by the results of the molecular dynamics simulation. Furthermore, the thermal behavior of the kaolinite–urea intercalation complex investigated by TG–DSC was also supported by FTIR and XRD analyses.     

Effect of grinding on thermal reactivity of ceramic clay minerals

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.     

Effects of mechanical activation on the non-isothermal kinetics of mullite formation from kaolinite

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite have been studied by differential thermal analysis (DTA). Kaolinite was mechanically activated in a planetary mill, while amorphization in the structure was studied by X-ray diffraction analysis. It was established that the mechanical activation especially affected the loss of structural water. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20 °C min⁻¹. The mechanical activation and amorphization of the kaolinite brings to the formation of mullite at a lower heating temperature.     

Formation of mullite,topaz and corundum

The influence of aluminium fluoride on the thermal behavior of quartz and the formation of topaz, mullite and corundum have been examined in the present work using the derivatograph. The products of sintering were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curves indicate the formation of topaz at 760°C and the formation of mullite at 1000°C using the theoretical amount of aluminium fluoride. The reaction between quartz and aluminium fluoride takes place in two distinct steps using 50% excess of aluminium fluoride. The first is marked by a large endothermic peak at 780°C, representing the formation of topaz and the second by a sharp endothermic peak at 960°C, representing its subsequent dissociation with the formation of corundum or alpha-aluminium oxide.     

Thermal evolution of a slate

The thermal evolution of a slate rock sample (Berja, Almería, Spain) has been studied. The phase minerals identified in this sample were mica (illite), chlorite (clinochlore) and quartz as major components, with minor microcline, iron oxide and a mixed-layer or interstratified phase (montmorillonite-chlorite). This slate is highly silico-aluminous (48.33 mass% silica, 22.04 mass% alumina), and ca. 20 mass% of other elements, mainly Fe₂O₃ (8.35 mass%), alkaline-earths and alkaline oxides. Two main endothermic DTA effects, centered at 640 and 730°C, were observed. The more important contribution of total mass loss (7.15 mass%) was found between 500–900°C, with two DTG peaks detected at 630 and 725°C. All these effects were associated to the dehydroxylation of structural OH groups of 2:1 layered silicates mixed in the slate. The dehydroxylation of the layered silicates evidenced by dilatometry, produced a rapid increase of expansion between 600–800°C. The thermal evolution of the slate upper 800°C indicated the first sintering effects associated to shrinkage, which is also favoured by its low particle size (average 23 μm) and the presence of a liquid or vitreous phase as increasing the heating temperature. The application of thermal diffractometry to the slate sample allowed to study the formation of dehydroxylated crystalline phases from the layered silicates after heating. At 1000°C, β-quartz, dehydroxylated illite, iron oxide, relicts of microcline and the vitreous phase were present in the sample. All these results are interesting to know the thermal behaviour of a complex mineral mixture as identified in the slate.     

The non-isothermal kinetics of mullite formation in boehmite–zircon mixtures

In this work, we studied the kinetics of mullite formation in different composites under non-isothermal conditions using DTA. Different composites based of mullite, alumina, zircon and zirconia were prepared by reaction sintering of boehmite (as alumina source) and zircon. Several mixtures were used while varying the percentage of the boehmite from 30 to 70 mass% with a step of 10. Five compositions marked as B30, B40, B50, B60 and B70 corresponding to boehmite–zircon ratios (mass%) of 30/70, 40/60, 50/50, 60/40 and 70/30 were fabricated and studied. The DTA conducted at heating rates of 10, 20 and 30 K min^?1 showed an endothermic peak in all composites at about 1,603 K associated with mullite formation. The activation energies measured from non-isothermal treatments for five compositions (30, 40, 50, 60 and 70 mass% of boehmite) were 1,029, 1,085, 1,262, 1,508 and 1,321 kJ mol^?1, respectively. The n values (Avrami parameter) for all compositions are larger than 2.5, the mullite crystallization of these composites is followed by three-dimensional growth.     

Research on historical bricks from a Baroque Church

Baroque bricks were investigated by DTA, TG, EGA, TDA, and XRD. The analyses showed that the brick consisted of dehydroxylated illite, quartz, and calcite. Dehydroxylation as a consequence of the former rehydroxylation was not found probably because of protection of the bricks by plaster. Between the temperatures 600 and 800 °C, (a) intensive mass loss in TG, (b) endothermic minimum in DTA, (c) intensive escape of CO₂ in EGA, and (d) contraction of the sample in TDA were observed. All these events belong to decomposition of calcite. As follows from these results, the maximum firing temperature was about 700 °C. The bricks have relatively high porosity ~43 % and specific surface area ~18.6 m² g^?1.     

A study of a New Zealand oil shale by differential thermal analysis

The heats of combustion of 95 samples of oil shale from the Nevis Valley have been determined from DTA peak areas obtained by combustion in 1.5 atm oxygen. The heats of combustion of the oil shale ranged from 0.2 to 8.5 MJ kg⁻¹, with an average of 2.6 MJ kg⁻¹, while that of the kerogen was calculated to be 34.2 MJ kg⁻¹. Up to four peaks were obtained in the DTA combustion curve, suggesting that different parts of the kerogen molecule were being oxidised at different temperatures.

In nitrogen, DTA endotherms were observed due to decarbonation of siderite (ca. 455°C), and dehydroxylation of kaolinite (ca. 570°C) and chlorite (ca. 760°C), and an exotherm due to formation of mullite (ca. 980°C).     

Some thermal characteristics of a mineral mixture of palygorskite,metahalloysite, magnesite and dolomite

An industrial raw material taken from Sivrihisar (Eskişehir, Turkey) region was heat-treated at different temperatures in the range of 100–1000°C for 2 h. The volumetric percentage of the particles having a diameter below 2 μm after staying in an aqueous suspension of the material was determined as 67% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 32% palygorskite, 10% metahalloysite, 35% magnesite, 20% dolomite and 3% interparticle water by using the acid treatment, X-ray diffraction and thermal analysis (TG, DTA) data. The temperature ranges were determined for the endothermic dehydrations for the interparticle water as 25–140°C, for the zeolitic water as 140–320°C, and for the bound water as 320–480°C, in the palygorskite. The temperature range for the endothermic dehydroxylation and exothermic recrystalization of the palygorskite is 780–840°C. The temperature range for the endothermic dehydroxylation of the metahalloysite and calcinations of magnesite are coincided at 480–600°C. Dolomite calcined in the temperature range of 600–1000°C by two steps. The zig-zag changes in the specific surface area (S/m² g⁻¹) and specific micro and mesopore volume (V/cm³ g⁻¹) as the temperature increases were discussed according to the dehydrations in the palygorkskite, dehydroxylation of palygorskite and metahalloysite, and calcinations in magnesite and dolomite.     

Thermal decomposition of Bayer precipitates formed at varying temperatures

Bayer hydrotalcites prepared using the seawater neutralisation (SWN) process of Bayer liquors are characterised using X-ray diffraction and thermal analysis techniques. The Bayer hydrotalcites are synthesised at four different temperatures (0, 25, 55, and 75 °C) to determine the effect of synthesis temperature on the thermal stability of the Bayer hydrotalcite structures and the mineralogical phases that form. The interlayer distance increased with increasing synthesis temperature, up to 55 °C, and then decreased by 0.14 Å for Bayer hydrotalcites prepared at 75 °C. The three mineralogical phases identified in this investigation are; (1) Bayer hydrotalcite, (2), calcium carbonate species, and (3) hydromagnesite. The DTG curve can be separated into four decomposition steps; (1) the removal of adsorbed water and free interlayer water in hydrotalcite (30–230 °C), (2) the dehydroxylation of hydrotalcite and the decarbonation of hydrotalcite (250–400 °C), (3) the decarbonation of hydromagnesite (400–550 °C), and (4) the decarbonation of aragonite (550–650 °C).