Study on the thermal decomposition of chrysotile asbestos

This article reports the possibility of detoxification of chrysotile asbestos through a low temperature heating and grinding treatment. The effect of thermal treatment at different temperatures in the range from 500 to 725 °C for 3 h on raw natural asbestos was characterized by thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that an isothermal treatment at 650 °C caused the complete dehydroxylation of chrysotile Mg₃Si₂O₅(OH)₄. Transformation of the dehydroxylated phase to forsterite Mg₂SiO₄ was obtained by heat treatment in the range 650–725 °C. The study of microstructure changes of heated asbestos show the destruction of characteristic fibers of chrysotile and formation of strips of forsterite. It is easily milled to pulverulent-shape material by mechanical milling in vibratory mill.     

Photoluminescence of new Tb3+-intercalated octosilicates depending on phase transition caused by annealing

A new Tb³⁺-intercalated layered octosilicate (Tb-Oct) was prepared through protonation, exfoliation and intercalation processing. Photoluminescence of the Tb-Oct silicates dependant of phase transition has been investigated in detail. The emissions attributed to ⁵D₄-⁷F_J (J = 3, 4, 5, 6) transition of Tb³⁺were observed from the emission spectra of the as-prepared Tb-Oct silicates. After the as-prepared Tb-Oct silicates thermal treatment at 200 °C, all diffraction peaks disappeared, suggesting the collapse of layered structure. With the increase in the annealing temperature from 200 to 1000 °C, no diffraction peaks appeared in all the annealed samples. Photoluminescence spectra show that the green emission ascribed to ⁵D₄-⁷F₅ transition of Tb³⁺ markedly increased as the sample was annealed at 800 °C. However, this green emission disappeared while the sample was annealed at 400, 600, and 1000 °C, which may relate to actual surroundings of Tb³⁺ ions. That is, the amorphous phase formed at 800 °C is more favorable for the green emission of Tb³⁺.     

Thermal behavior of a bentonite

The mineralogical composition of the Kütahya calcium bentonite (CaB) from Turkey was obtained as mass% of 60% calcium rich smectite (CaS), 30% opal-CT (OCT), trace amount illite (I), and some non-clay impurities by using chemical analysis (CA), X-ray diffraction (XRD), and thermal analysis (TG-DTA) data. The crystallinity, porosity, and surface area of the samples heated between 25–1300°C for 2 h were examined by using XRD, TG, DTA and N₂-adsorption-desorption data. The position of the 001 reflection which is the most characteristic for CaS does not affect from heating between 25–600°C and then disappeared. The decrease in relative intensity (I/I ₀) from 1.0 to zero and the increase in full width at half-maximum peak height (FWHM) from 0.25 to 1.0° of the 001 reflection show that the crystallinity of the CaS decreased continuously by rising the heating temperature from 25 to 900°C and then collapsed. The most characteristic 101 reflection for opals intensifies greatly between 900 and 1100°C with the opal becoming more crystalline. The total water content of the natural bentonite after dried at 25, 105 and 150°C for 48 h were determined as 8.8, 5.0 and 2.5%, respectively. The mass loss occurs between 25 and 400°C over two steps with the maximum rate at 80 and 150°C, respectively. The exact distinction of the dehydration temperatures for the adsorbed water and interlayer water is seen almost impossible. The temperature interval, maximum rate temperature, and mass loss during dehydroxylation are 400–800°C, 670°C and 4.6–5.0%, respectively. The maximum rate temperatures for decrystallization and recrystallization are 980 and 1030°C, respectively. The changes in specific micropore volume (V _mi), specific mesopore volume (V _me), specific surface area (S) were discussed according to the dehydration and dehydroxylation of the CaS. The V _mi, V _me and S reach to their maxima at around 400°C with the values of 0.045, 0.115 cm³ g⁻¹ and 90 m² g⁻¹, respectively. The radii of mesopores for the bentonite heated at 400°C are distributed between 1–10 nm and intensified approximately at 1.5 nm.     

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 behavior of a mineral mixture of sepiolite and dolomite

An industrial raw material taken from Beypazarı (Ankara, Turkey) region was heated at different temperatures in the 100–1100°C interval for 2 h. The volumetric percentage of particles having diameter below 2 μm in an aqueous suspension of the material held 24 h were determined as 85% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 81% sepiolite, 15% dolomite, and 4% interparticle water by using the X-ray diffraction (XRD) and thermal analysis (TG, DTA) data. The temperature ranges were determined for the dehydrations of the interparticle water and the zeolitic water as 25–340°C, for the dehydration of the bound water as 340–580°C, and for the dehydroxylation of the hydroxyls as 800–833°C in the sepiolite. The zig-zag changes in the specific surface area (S/m² g⁻¹) and specific micro-and mesopore volume (V/cm³ g⁻¹) with the temperature increases were discussed according to the dehydrations and dehydroxylation of the sepiolite.     

Thermal behaviour of sericite clays as precursors of mullite materials

Thermal analysis of some sericite clays, from several deposits in Spain, which are not exploited at this time, has been studied. The samples have been previously characterized by mineralogical and chemical analysis. Sericite clays have interesting properties, with implications in ceramics and advanced materials, in particular concerning the formation of mullite by heating. According to this investigation by differential thermal and thermogravimetric analysis (DTA-TG), the sericite clay samples can be classified as: Group (I), sericite–kaolinite clays, with high or medium sericite content, characterized by an endothermic DTA peak of dehydroxylation of kaolinite with mass loss, which overlapped with dehydroxylation of sericite, and Group (II), sericite–kaolinite–pyrophyllite clays, with broader endothermic DTA peaks, in which kaolinite is dehydroxylated first and later sericite and pyrophyllite with the main mass loss, appearing the peaks overlapped. X-ray diffraction analysis of the heated sericite clay samples evidenced the decomposition of dehydroxylated sericite and its disappearance at 1050 °C, with formation of mullite, the progressive disappearance of quartz and the formation of amorphous glassy phase. The vitrification temperature is ~ 1250 °C in all these samples, with slight variations in the temperatures of maximum apparent density (2.41–2.52 g mL^?1) in the range 1200–1300 °C. The fine-grained sericite content and the presence of some mineralogical components contribute to the formation of mullite and the increase in the glassy phase by heating. Mullite is the only crystalline phase detected at 1400 °C with good crystallinity. SEM revealed the dense network of rod-shaped and elongated needle-like mullite crystals in the thermally treated samples. These characteristics are advantageous when sericite clays are applied as ceramic raw materials.     

Kombinierte thermische analyse an dreischichttonmineralen

Three-layer silicates were studied by thermal investigations with the derivatograph (DTA/TG and DTA/dilatometry). Differential dilatometry is a sensitive method for studying the dehydratation properties of a montmorillonite with Li saturation. This method is also useful for the determination of the natural cation saturation of montmorillonites. The range of dehydroxylation of a montmorillonite with various cation saturation is studied by DTG and differential dilatometric methods. The investigation shows that the dehydroxylation range is influenced by the type and the valency of the cations. The differential dilatometry is a valuable method for the distinction of various Smectite-types, nontronite, illite and muscovite in the temperature range above 700°C. The amount of octahedral iron can be calculated from the dilatometric curves. Finally, some problems of the thermal investigation of illitemontmorillonite mixed-layer minerals are discussed.     

Thermal analysis of beaverite in comparisonwith plumbojarosite

The thermal decomposition of beaverite and plumbojarosite was studied using a combination of thermogravimetric analysis coupled to a mass spectrometer. The mineral beaverite Pb(Fe,Cu)₃(SO₄)₂(OH)₆ decomposes in three stages attributed to dehydroxylation, loss of sulphate and loss of oxygen, which take place at 376 and 420, 539 and 844°C. In comparison three thermal decomposition steps are observed for plumbojarosite PbFe₆(SO₄)₄(OH)₁₂ at 376, 420 and 502°C attributed to dehydroxylation; loss of sulphate occurs at 599°C; and loss of oxygen and formation of lead occurs at 844 and 953°C. The temperatures of the thermal decomposition of the natural plumbojarosite were found to be less than that for the synthetic jarosite. A comparison of the thermal decomposition of plumbojarosite with argentojarosite is made. The understanding of the chemistry of the thermal decomposition of minerals such as beaverite, argentojarosite and plumbojarosite and related minerals is of vital importance in the study known as ‘archeochemistry’.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Thermal stability of crandallite CaAl<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>5</Subscript>·(H<Subscript>2</Subscript>O)

Thermogravimetry combined with evolved gas mass spectrometry has been used to characterise the mineral crandallite CaAl₃(PO₄)₂(OH)₅·(H₂O) and to ascertain the thermal stability of this ‘cave’ mineral. X-ray diffraction proves the presence of the mineral and identifies the products of the thermal decomposition. The mineral crandallite is formed through the reaction of calcite with bat guano. Thermal analysis shows that the mineral starts to decompose through dehydration at low temperatures at around 139 °C and the dehydroxylation occurs over the temperature range 200–700 °C with loss of the OH units. The critical temperature for OH loss is around 416 °C and above this temperature the mineral structure is altered. Some minor loss of carbonate impurity occurs at 788 °C. This study shows the mineral is unstable above 139 °C. This temperature is well above the temperature in the caves of 15 °C maximum. A chemical reaction for the synthesis of crandallite is offered and the mechanism for the thermal decomposition is given.     

Gelled Na<Subscript>2</Subscript>HPO<Subscript>4</Subscript> · 12H<Subscript>2</Subscript>O with amylose-g-sodium acrylate: heat storage performance,heat capacity and heat of fusion

A novel gelling method was studied to stabilize phase change material Na₂HPO₄ · 12H₂O with amylose grafted sodium acrylate. Gelled Na₂HPO₄ · 12H₂O shows stable heat storage performance prepared at optimized conditions: 2.7mass/mass% sodium acrylate, 0.4 mass/mass% amylose, 0.05–0.09 mass/mass% N, N′-methylenebisacrylamide, 0.05–0.09 mass/mass% K₂S₂O₈ and Na₂SO₃ (mass ratio 1:1), at 50 °C. Na₂HPO₄ · 12H₂O was dispersed in gel network as tiny crystals less than 0.1 mm. Melting points were in the range 35.4 ± 2 °C. Short-term thermal cycling proves the effectiveness of the novel method for eliminating phase separation in the gelled salt. Adiabatic calorimetric measurement of heat capacities shows two phase transitions, which correspond to melting of Na₂HPO₄ · 12H₂O and freezable bond water in gel, respectively. Heat of fusion of pure Na₂HPO₄ · 12H₂O was determined as 260.9 J g⁻¹. Distribution of extra water is: free water:freezable water:nonfreezing water = 0:0.85:0.15.     

Free and bound water influence on Spirulina platensis survival

The heat effects arising at heating of Spirulina platensis cell culture containing different quantity of water (from 98.2 to 10.5 mass% H₂O) have been studied. The hydration of Sp. pl. cells determined by the method of microcalorimetry at 25°C (Δn) was equal to 0.32±0.02 g H₂O/g of dry biomass. The heat (–Q) evolved by cells in the temperature range 5–52°C decreased exponentially at decrease of mass% H₂O and reached zero value at 30.5±3.0 mass% H₂O. The total heat of cell denaturation did not change in the range 98.2–40.5 mass% H₂O and it sharply dropped at lower values of water.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

The process of hydrolysis of aqueous aluminium sulfate was carried on in ammonia medium at 100°C and for different time intervals (0, 20, 39 or 59 h). The products thus obtained were calcined at 550, 900 or 1200°C for 2 h with the aim to obtain aluminium oxides. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption–desorption of benzene vapours and scanning electron microscopy. Freshly precipitated material was an amorphous basic aluminium sulfate which after prolonged refluxing at elevated temperature in a mother liquor underwent a phase transformation into highly crystalline NH₄Al₁₃(SO₄)₂(OH)₆ containing tridecameric unit Al₁₃. It was accompanied by a decrease of specific surface area and the formation of a porous structure less accessible for benzene molecules. Regardless of the duration of the hydrolysis process, all products were characterised with poorly developed porous structure and hydrophilic character. Their calcination at the temperature up to 1200°C resulted in the formation of α-Al₂O₃ via transition forms of γ/η- and δ-Al₂O₃. The samples of aluminium oxides obtained after calcination at 550 and 900°C had higher values of specific surface area than starting materials due to processes of dehydroxylation and desulfurization. The process of calcination up to 900°C was reflected in developing of not only porous structure but also hydrophobic character of prepared materials. The S _BET values calculated for the oxide samples obtained from aged products of hydrolysis at 1200°C were lower than for the analogous sample prepared without the ageing step. It was concluded that prolonged refluxing at elevated temperature of the products of hydrolysis of aluminium sulfate decreased thermal stability of final aluminium oxides.     

Controlled rate thermal analysis of sepiolite

Controlled rate thermal analysis (CRTA) technology offers better resolution and a more detailed interpretation of the decomposition processes of a clay mineral such as sepiolite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal changes in the sepiolite as the sepiolite is converted to an anhydride. In the dynamic experiment two dehydration steps are observed over the ~20–170 and 170–350 °C temperature range. In the dynamic experiment three dehydroxylation steps are observed over the temperature ranges 201–337, 337–638 and 638–982 °C. The CRTA technology enables the separation of the thermal decomposition steps.     

Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses

The degree of dehydroxylation of kaolinite, D_TG and D_IR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm⁻¹ is established. Three regions can clearly be distinguished: the dehydroxylation region (D_TG<0.9), the metakaolinite region (0.9<D_TG<1) and the ‘spinel’ region(D_TG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is retrieved as an additive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of natural iowaite

The thermal decomposition of natural iowaite of formula Mg₆Fe₂(Cl,(CO₃)_0.5)(OH)₁₆·4H₂O was studied by using a combination of thermogravimetry and evolved gas mass spectrometry. Thermal decomposition occurs over a number of mass loss steps at 60°C attributed to dehydration, 266 and 308°C assigned to dehydroxylation of ferric ions, at 551°C attributed to decarbonation and dehydroxylation, and 644, 703 and 761°C attributed to further dehydroxylation. The mass spectrum of carbon dioxide exhibits a maximum at 523°C. The use of TG coupled to MS shows the complexity of the thermal decomposition of iowaite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal transformations of lead oxides

Differential scanning calorimetry, differential thermogravimetry, X-ray analysis and electronic microscopic studies of thermal transformations of PbO₂ were carried out. Formation of fine dispersed (less than 100 nm) particles of α-PbO was observed at PbO₂ thermal decomposition at heating to 580°C. Reverse reaction of Pb₃O₄ formation from PbO was found at cooling and annealing at 400°C in air. At heating of α-PbO to 650°C the particle growth to 1 μm with formation of β-PbO took place. Thermal decomposition with formation of β-PbO particles with size from 0.3 to 1 μm at PbO₂ heating to 650°C was observed. Transition from PbO to Pb₃O₄ at cooling of sample heated to 650°C was not detected. Interpretation of observed phenomena from the point of view of particle size influences on the shift of α-PbO↔β-PbO phase transition temperature and on the chemical activity of phases are presented.     

Dynamic and controlled rate thermal analysis of hydrozincite and smithsonite

The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO₂. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO₂-H₂O system at ambient temperature and atmospheric CO₂ is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere. The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA) pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO₂ at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc carbonate minerals via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. The CRTA technology offers a mechanism for the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite.     

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.     

Study of thermal properties of flame retardant epoxy resin treated with hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene (HHPCP) is prepared and characterized by FTIR, ¹H-NMR, and ³¹P-NMR spectroscopy. Then an investigation of the flame retardancy, thermal decomposition behavior of epoxy resin (EP) containing HHPCP is carried out using limiting oxygen (LOI) test, horizontal flame test, smoke density rate (SDR) test, thermogravimetric analysis (TG), and thermal gravimetric analyzer-mass spectrometry (TG-MS). The decomposition process of HHPCP is studied by TG-MS and FTIR. The result shows that the LOI value of EP increase from 20.5 to 26.5 %, when 7.5 mass% HHPCP is added into EP. The addition of 1 mass% nano-montmorillonite (nMMT) into EP–7.5 mass% HHPCP sample as synergist can increase the LOI value of EP–7.5 mass% HHPCP–1 mass% nMMT sample from 26.5 to 27.5 %. The SDR test indicates that smoke suppression of HHPCP on EP is not significant. TG analysis reflects that the EP–7.5 mass% HHPCP sample and EP–7.5 mass% HHPCP–1 mass% nMMT show higher thermal stability properties with an increasing T _onset and T _max comparing with neat-EP. TG-MS result indicates that the main pyrolysis product of EP is H₂O, CO, CO₂, C₆H₆, C₆H₅OH, HOC₆H₄CH₃, and flammable hydrocarbon fragments C_xH_y. Compared with neat-EP sample, nonflammable water vapor of EP–7.5 mass% HHPCP sample increased, whereas CO₂ and the flammable hydrocarbon fragments C_xH_y and flammable gas CO decreased. TG-MS and FTIR result suggests that HHPCP decomposed first by inter-molecular dehydration, then P–N hexatomic ring of HHPCP decomposed during 470 and 560 °C, and a little no-flame gas containing nitrogen element volatilized into the gaseous phase.