Thermal characteristics of bitumen pyrolysis

The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated at 79 kJ mol⁻¹. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds, such as H₂, H₂S, COS, and SO₂, released at about 380 °C while the CO₂ had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis.     

Investigation of early hydration of high aluminate cement-based binder at different ambient temperatures

The effect of spent FCC catalyst on early hydration (up to 48?h) of high aluminate cement (Al₂O₃ >70%) at different ambient temperatures (10, 20, and 30?°C) was investigated. Cement pastes with constant ratio of water/binder?=?0.35 (binder?=?cement?+?addition) and containing 0, 5, 10, and 15% mass of addition as replacement of cement were studied. The hydration kinetics was determined by calorimetric measurements and the structure of hardened binders after 2?days of curing at an appropriate temperature was also investigated using X-ray, SEM, and thermal analysis methods. Due to the fact that hydration of aluminate cements is highly sensitive to temperature conditions as well as certain changes of temperature are inevitable in practice, the evaluation of the impact of the waste catalyst addition in such conditions is justified. On the basis of obtained results, it was stated that the temperature determines the early hydration of high aluminate cement and decides about the influence of waste aluminosilicate. The introduction of the discussed addition has a big impact on the kinetics of cement hydration closely related to the curing temperature. The presence of spent catalyst accelerates the hydration at the temperatures of 20 and 30?°C, but at the temperature of 10?°C this waste aluminosilicate acts as a retarding agent. The effect of the addition on the microstructure of hardened binders after 48?h of hydration is rather insignificant, especially at 20?°C, compared to the influence of the temperature on hydration. At the temperature of 10?°C, a formation of low amount of C₂AH₈ can be observed because of the presence of spent catalyst, while at the temperature of 30?°C the introduction of the mineral addition prevents the hydrogarnet formation.     

Investigation of ageing of alumina cement-based mixtures using thermal analysis and calorimetry

The shelf life of cement and cement-based dry mixtures is often determined by ageing of such materials. The ageing is the result of interactions between cement and other components of cementitious mixtures with moisture as well as with CO₂ from the atmosphere. In this work, the ageing behaviour of calcium aluminate cement and its mixtures with additives of microsilica, fluidized catalytic cracking catalyst waste and ground quartz sand were investigated. The ageing was achieved by storing cement and its mixtures in a climatic chamber for 7 and 14 days at 95% relative humidity and 20 ± 1 °C temperature. Applying thermal analysis, XRD analysis as well as scanning electronic microscopy, it was established that hydration of the cement minerals takes place along with carbonation during the ageing process of cement and its mixtures. The quantities of the products formed during ageing and their crystallinity depend on the nature of additives and the duration of ageing. When applying the method of calorimetric analysis, the influence of ageing on the kinetics of hydration of cement and as well as of its mixtures with the additives used in the work has been established.     

Reactivity of lithium and barium carbonates with ZrO2:Y2O3 and Nasicon in solid state electrochemical gas sensors

The mutual reactivity in mixtures containing Nasicon (Na₃Zr₂Si₂PO₁₂) or YSZ (ZrO₂:Y₂O₃) solid electrolytes with Li₂CO₃ or Li₂CO₃:BaCO₃ sensing electrode materials was investigated using simultaneous DTA and TG and ex situ XRD techniques. The uncontrolled chemical reaction is suspected to be responsible for the instability of electrochemical gas sensors constructed from these materials. DTA and TG results obtained for Nasicon-carbonate mixtures indicate the possibility of reaction in the temperature range from about 470 to 650°C, which overlaps the sensor operating temperature range (300–525°C). The results obtained for YSZ-carbonate mixtures indicate that reaction between carbonate and the ZrO₂ takes place at higher temperatures and cannot explain the instability drift of investigated sensors. The mechanism of observed reactions in systems studied is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sample pretreatment for the determination of gamma emitting nuclides in dry radioactive waste using a dry ashing and high-performance microwave digestion system

A sample pretreatment procedure for the dry radioactive waste such as paper, cotton, vinyl, and plastic generated from nuclear power plants (NPPs) was established to determine the activity concentrations of ⁶⁰Co and ¹³⁷Cs. Because the volatility of cesium is temperature-dependent, the heating temperature was examined from 300 to 650 °C. Although the cesium was not volatile until 500, 450 °C was selected to save time. Cesium with a paper towel and a planchet of stainless steel were quantitatively recovered at 450 °C. The produced ash was completely dissolved with 10 mL of HNO₃, 4 mL of HCl, and 0.25 mL of HF in a high-performance microwave digestion system using a nova high temperature rotor at 250 °C for 90 min until 0.2 g was reached. This procedure was applied to low and intermediate level radioactive wastes generated from NPPs.     

Preparation and reactivity of metal-containing monomers

The thermal decomposition of iron (III) acrylate, [Fe₃O(CH₂=CHCOO)₆ · 3H₂O]OH (FeAcr), a monomer with a complex cluster cation, has been studied at 200–370 °C. Thermal transformations of FeAcr occur in two temperature regions. The rates of gas evolution in the low temperature region (200–300 °C) and the high temperature region (300–370 °C) are described by first-order equations withk=4.2 · 10²¹exp[−59000/(RT)] s⁻¹ andk=1.3 · 10⁶exp[−30500/(RT)] s⁻¹, respectively. A study of the qualitative and quantitative composition of the products of FeAcr thermolysis was carried out. The thermal transformation of FeAcr is a complex process of dehydration, degradation, and polymerization in the solid phase followed by decarboxylation of the metal-carboxyl groups of the polymer. for part 33 see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1743–1750, October, 1993.     

Thermal study of naphthylammonium- and naphthylazonaphthylammonium-montmorillonite

The blue organo-clay color pigment (OCCP) naphthylazonaphthylammonium-montmorillonite was synthesized from the white naphthylammonium-montmorillonite by treating with NaNO₂, the azo colorant being located in the interlayer space. The following effects on the basal spacing of naphthylazonaphthylammonium-and naphthylammonium-clay were investigated: (1) the amount of naphthylammonium loading the clay, (2) the amount of NaNO₂ used for the staining, (3) aging of the preparation suspension and (4) thermal treatment. Samples were heated at 120, 180, 240, 300 and 360°C and diffracted by X-ray. During aging, some of the dye decomposed. Samples, after one day aging, were investigated by DTA. During the dehydration stage both organo-clays gradually decomposed, the naphthylammonium-clay at 120°C and the OCCP at 180°C. That fraction of organic matter, which did not escape, was air-oxidized at above 200°C and charcoal was obtained. The appearance and size of the DTA exothermic peaks depended on the amount of organic matter, which did not escape and this depended on the total amount of organic matter in the DTA cell. DTA proved that naphthylammonium reacted with NaNO₂ to form OCCP.     

Thermogravimetric investigation of the effect of annealing conditions on the soft ferrite phase homogeneity

In the present work, the conventional method of increasing the efficiency of solid-phase synthesis of lithium–zinc ferrites that involves multiple intermediate grinding of briquetted reaction mixtures annealed at high temperatures is compared with a new radiation-thermal (RT) method using a high-power pulsed beam of accelerated electrons for heating of reaction mixtures. An analysis of the TG(M)/DTG(M) curves recorded in a magnetic field demonstrates that the efficiency of Li_0.3Zn_0.4Fe_2.3O₄ synthesis from Li₂CO₃–Fe₂O₃–ZnO mechanical mixture at a temperature of 700 °C during 120 min is equivalent to thermal annealing at 800 °C, but with the triple annealing duration.     

On the theoretical basis of the hancock and sharp “ln.ln method” of kinetic analysis of isothermal data

A high-temperature calorimeter of the twin type designed for the enthalpy measurement of latent-heat storage materials is described. The measured enthalpy change of the N.B.S. calorimetric standard sapphire was in agreement with N.B.S. data within ±1.5% from room temperature up to 400°C. The enthalpy changes of LiNO₃ and NaNO₂ were determined through the fusion up to 300°C. Their enthalpies of fusion and heat capacities are presented.     

Improving safety performance of lactose-fueled binary pyrotechnic systems of smoke dyes

The lactose/KClO₃ is a widely used pyrotechnic mixture to vaporize organic materials, such as smoke dyes. However, because of low ignition temperature of this mixture, serious precaution should be taken into account to prevent its accidental self-ignition. In order to find a safe and efficient alternative of this conventional mixture, KClO₃ has been replaced by common oxidizing agents including KMnO₄, KNO₃, KClO₄, Ba(NO₃)₂, PbO₂ and NH₄ClO₄. TG and DTA analysis have been used to obtain thermal characteristic of the mixtures. Based on ignition temperature of the pyrotechnic mixtures we can divide them into four categories as follows: (1) the mixture igniting at low temperature, i.e., at about 200 °C. (2) Moderate temperature igniting mixture, in which ignition occurs at 300–400 °C. (3) High temperature igniting mixture with ignition temperature higher than 400 °C .(4) Not igniting mixtures. Also, the apparent activation energy (E), ΔG ^#, ΔH ^#, ΔS ^# and critical ignition temperature (T _b ) of the ignition processes of low and moderate temperature igniting mixtures were obtained from the DSC experiments. Finally, among the investigated mixtures, lactose/KNO₃ can be considered as a safe and efficient pyrotechnic composition for vaporization of organic materials, such as smoke dyes, due to its moderate safe ignition temperature.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.     

Thermal Decompositions of Pure and Mixed Manganese Carbonate and Ammonium Molybdate Tetrahydrate

The thermal decompositions of pure and mixed manganese carbonate and ammonium molybdate tetrahydrate in molar ratios of 3:1, 1:1 and1:3 were studied by DTA and TG techniques. The prepared mixed solid samples were calcined in air at 500, 750 or 1000°C and then investigated by means of an XRD technique. The results revealed that manganese carbonate decomposed in the range 300–1000°C, within termediate formation of MnO₂, Mn₂O₃ andMn₃O₄. Ammonium molybdate tetrahydrate first lost its water of crystallization on heating, and then decomposed, yielding water and ammonia. At 340°C,MoO₃ was the final product, which melts at 790°C. The thermal treatment of the mixed solids at 500, 750 or 1000°C led to solid-solid interactions between the produced oxides, with the formation of manganese molybdate. At 1000°C, Mn₂O₃ and MoO₃ were detected, due to the mutual stabilization effect of these oxides at this temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of the aluminum/potassium chlorate mixtures by simultaneous TG-DTA

Thermogravimetry (TG) and differential thermal analysis (DTA) in the non-isothermal mode have been used to examine the thermal behaviour of the micron sized aluminum (Al) powder/potassium chlorate pyrotechnic systems in air, in relation to the behaviour of the individual constituents. The effects of different parameters of Al powder, such as particle size and its content in the mixtures, on their thermal property were investigated. The results showed that, the reactivity of Al powder in air increases as the particle size decreases. Also, it was found that neat Al with 5 μm particle sizes (Al₅) has a fusion temperature of about 647°C, that for 18 μm powder (Al₁₈) is 660°C. Pure potassium chlorate has a fusion temperature around 356°C and decomposes at 472°C. DTA curves for Al₅/KClO₃ (30:70) mixture showed a maximum peak temperature for the ignition of mixture at 485°C. Also, by increasing the particle size of Al powder, the ignition temperature of the mixture increased. On the other hand, the oxidation temperature increased by enhancing the Al content of the mixtures. In this particular study, we observed that the width of reaction peak for the mixtures corresponds to their Al contents of samples.     

THERMAL REACTIONS IN SYNTHETIC APATITE–AMMONIUM SULFATE MIXTURE

The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH₄)₂SO₄up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH₄)₂SO₄and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO₄with CaNH₄P₃O₉at 320–500°C. Higher concentrations of NH₃in the gas phase promote the formation of CaNH₄P₃O₉and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH₄P₃O₉with a decrease in the content of water-soluble phosphorus and evolvement of SO₂.     

Thermal degradation of fire retardant chloroparaffin-metal compound mixtures: Part II—Bismuth compounds

The mechanisms of reactions which occur on heating mixtures of Bi compounds and a chloroparaffin, which are suitable fire retardant additives for polymers, have been studied.BiCl₃, which is evolved at a high initial rate by reaction of Bi compounds with HCl eliminated by the chloroparaffin, has a strong catalytic effect on the dehydrochlorination process of the chloroparaffin itself. BiCl₃ evolution occurs in a two-stage process: a fast step characterised by a maximum rate at 300°C followed by a slower step which occurs between 300 and 500°C.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

Interactions between the iron and the aluminum minerals during the heating of Venezuelan lateritic bauxites. II. X-ray diffraction study

Four samples of Venezuelan lateritic bauxites were heated to 300, 600 and 1000°C and the thermal reactions were studied by X-ray diffraction (XED) and by chemical extractability of silica and alumina. Gibbsite was converted to boehmite at 300°C, to an amorphous phase at 600°C and partly to corundum at 1000°C, with isomorphic substitution of Fe for some of the Al in the corundum structure. Goethite was converted to protohematite at 600°C and the hematite at 1000°C, with isomorphic substitution for Al for some of the Fe in both α-Fe₂O₃ varieties. Ti contributed by ilmenite is also occluded by the hematites. The occlusion of Ti takes place at 1000°C during the decomposition of the ilmenite and concomitant recrystallization of α-Fe₂O₃.     

Physico-chemical characterization of thermal decomposition course in zinc nitrate-copper nitrate hexahydrates

This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O and their mixtures of known compositions in the temperature range 30–1200°C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0–60°C. The mixture with composition 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O showed single melting peak at 29°C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu₂O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl₂·2H₂O into the mixture 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.     

The differential thermal analysis behavior of lead zirconate titanate materials

Differential thermal analysis has been used to examine the reactions involved in the formation of lead zirconate titanate and related materials. The reaction of PbO and TiO₂ produced an exothermic peak near 600°C, while mixtures of PbO and ZrO₂ gave endothermic peak at 760°C. Lead titanate and lead zirconate mixtures showed no evidence of reaction below 900°C. Evidence is presented which suggests that PbO and PbTiO₃ react in the vicinity of 750°C. For ternary mixtures of PbO, titanate, the thermograms indicate a complicated behavior between 600–800°C, depending on the ratios of the reactant materials. The results suggest that the calcination reaction to form lead zirconate titanate is a more complex process than has been recognized. Data on the various phase transitions for the lead zirconate titanate materials are also presented.     

Thermal reactions of kaolinite with potassium carbonate

It was previously established that kaolinite reacts with K₂CO₃ on heating to form products of KSiAlO4 composition. In the present study we investigated the solid state reactions with K₂CO₃ of four kaolinites of different thermal stability. The mixtures were calcined at temperatures ranging from 400-700°C and washed before or after boiling with the remaining K₂CO₃. FTIR spectra indicated that the X-ray amorphous material formed after calcining the mixtures at 500-590°C had a SiAlO₄ tetrahedral framework. Attempts to convert the products to zeolites gave promising results. After calcining at 700°C under atmospheric pressure synthetic kaliophilite (KSiAlO₄) was obtained. These conditions are appreciably milder than previously reported for kaliophilite syntheses. Conversion to kalsilite increased with decreasing thermal stability of the original kaolinite. In similar reactions with KCl much less K was incorporated into the amorphous phase and kaliophilite was not obtained. The reactions of the four kaolinites with K₂CO₃ or with KCl were similar in trend, but differed in detail. This revised version was published online in July 2006 with corrections to the Cover Date.