DTA study of the chlorination of fly ash and bauxite in the presence of carbon

The chlorination processes of fly ash and bauxite in the presence of carbon were studied by means of a gas-flow type DTA, X-ray analysis and SEM observation, and the reactivity of Al-compounds as their constituents was compared. In the case of fly ash, the exothermic peak due to the formation of AlCl₃ (mainly) and FeCl₃ appeared at about 790–920°C. The reactivity of Al estimated from the DTA peak temperature depended on the particle size, carbon content and preparation temperature of fly ash, and was much lower than that of bauxite. Fractional conversion of Al was about 60–70%, when fly ash (?300 mesh) was heated up to 900°C in Cl₂ at 5°C min^?1 of heating rate. In the case of bauxite, two exothermic peaks due to the chlorination of Fe and Al appeared at about 270 and 490°C, respectively. The chlorination of Al was completed at 550°C under the above conditions.     

Urea and CaCl2 as inhibitors of coal low-temperature oxidation

Thermal analysis was used to study the influence of CaCl₂ and urea as possible chemical additives inhibiting coal oxidation process at temperatures 100?C300?°C. Weight increase due to oxygen chemisorption and corresponding amount of evolved heat were evaluated as main indicative parameters. TA experiments with different heating rates enabled determination of effective activation energy E _a as a dependence of conversion. In the studied range of temperatures, the interaction of oxygen with (untreated) coal was confirmed rather as a complex process giving effective activation energies changing continuously from 70?kJ?mol^?1 (at about 100?°C) to ca. 180?kJ?mol^?1 at temperatures about 250?°C. The similar trend in E _a was found when chemical agents were added to the coal. However, while the presence of CaCl₂ leads to higher values of the effective activation energies during the whole temperature range, urea causes increase in E _a only at temperatures below 200?°C. Exceeding the temperature 200?°C, the presence of urea in the coal induces decrease in activation energy of the oxidation process indicating rather catalysing than inhibiting action on coal oxidation. Thus, CaCl₂ can only be recommended as a ??real?? inhibitor affecting interaction of coal with oxygen at temperatures up to 300?°C.     

Effect of heating on speciation of copper in Si/Al/Ca-based environmental matrices

X-ray absorption spectroscopy is used to investigate the speciation of sorbed copper in heated fly ash. CuO and Cu(OH)₂ are determined to be the principal copper species in the Cu-sorbing fly ash heated at 500 °C for 2 h. Heating the Cu-sorbing fly ash to 900 °C or 1100 °C can result in the formation of CuSO₄, representing 41% and 32% of the total copper, respectively. Ash sintering and/or co-melting at 900 and 1100 °C occur, thereby triggering chemical reaction between CuO/Cu(OH)₂ and sulfur compounds.     

Characterization of Bio-Fuel and Bio-Fuel Ash

Three bio-fuels with or without additives and their fly ash samples were characterized using simultaneous Thermogravimetry-Differential Thermal Analysis-Fourier Transform Infrared Spectrometry-Mass Spectrometry (TG-DTA-FTIR-MS), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy-Energy Dispersive Spectrometry (SEM-EDS). The results show that the additives increase the reactivity of the bio-fuel during combustion. The additives also significantly decrease the amount of unburned carbon in the fly ash. The additives affect the compounds formed in the fly ash sample, and consequently the thermal behaviour of the fly ash. The fly ash samples are thermally stable in air up to 100°C. The fly ash samples contain fine particles with irregular shape, small round particles, and large hollow spherical particles with entrapped gases. This revised version was published online in July 2006 with corrections to the Cover Date.     

The difference among the effects of high-temperature curing on the early hydration properties of different cementitious systems

The difference among the effects of high-temperature curing on the early hydration properties of the pure cement, the binder containing fly ash, the binder containing GGBS, and the binder containing steel slag was investigated by determining the compressive strength, non-evaporable water content, hydration heat, and Ca(OH)₂ content. Results show that the order of the influence degrees of high-temperature on the early hydration of different binders is the binder containing GGBS > the binder containing steel slag > the binder containing fly ash > the pure cement. In the case of short period of high-temperature curing (only 1 day), the strength growth rate of the concrete containing GGBS is the greatest. Though the influence of increasing high-temperature curing period on the hydration degree of the binder containing fly ash is not the most significant, the strength growth rate of the concrete containing fly ash is the most significant due to the excessive consumption of Ca(OH)₂ by reaction of fly ash. In the case of high-temperature curing, the Ca(OH)₂ content of the paste containing steel slag is much higher than those of the paste containing GGBS and the paste containing fly ash, so though high-temperature curing promotes the hydration of the binder containing steel slag significantly, its influence on the strength growth rate of the concrete containing steel slag is not so significant.     

Mössbauer study of semiconducting and ferrimagnetic fly ash-recycled glass

Summary Room temperature M?ssbauer spectrum of fly ash-recycled glass (FARG), prepared with more than 86 mass% of fly ash and less than 14 mass% of Fe₂O₃, comprises two types of doublets due to Fe(II) and Fe(III) of magnetite nanoparticles. Isothermal annealing of fly ash-recycled glass at 1100 °C for 60 minutes results in a precipitation of ferrimagnetic magnetite phase having an internal magnetic field of 46.4-48.2 T. When the Fe₂O₃ content is equal to or more than 14%, room temperature M?ssbauer spectrum of FARG shows a magnetic hyperfine structure due to a magnetite phase, in addition to two doublets due to Fe(II) and Fe(III). An increase in the electric conductivity is observed from the order of 10^-8 to 10^-6 S ^. cm^-1 after heat treatment at around the crystallization temperature. This can be ascribed to an improved step-by-step electron hopping from Fe(II) to Fe(III) of distorted FeO₄ tetrahedra in the three-dimensional glass network.     

Thermal behavior of some Estonian clays and their mixtures with oil shale ash additives

Thermal behavior of green clay samples from Kunda and Arumetsa deposits (Estonia) as potential raw materials for production of ceramics and the influence of previously fired clay and hydrated oil shale ash additives on it were the objectives of this research. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1,200–1,400 °C) of Estonian oil shale at Estonian Power Plant. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer OmniStar Mass Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 1,050 °C at the heating rate of 5 °C min^?1 in an oxidizing atmosphere containing 79 % of Ar and 21 % of O₂. Standard 100 µL Pt crucibles were used, the mass of samples was 50 ± 0.5 mg, and the gas flow 60 mL min^?1. The results obtained indicate the complex character of transformations and show certain differences in the thermal behavior of Arumetsa and Kunda clays and their mixtures with oil shale ashes depending on the chemical and mineralogical composition of the clays as well as of the oil shale ashes studied.     

Improvement of surface cementitious properties of coarse fly ash by dehydration and rehydration processes

Owing to poor bonding between coarse fly ash particles and hydration products, gap-graded blended cements with fly ash usually show lower compressive strengths than Portland cement. Surface cementitious properties of coarse fly ash were improved by dehydration and rehydration processes in the present study. The results show that during the calcination at 750?°C, C?CS?CH gel is mainly transformed into a new nesosilicate, which is similar to a less crystalline C₂S. The formation of melilite from hydration products is also noticed at 900?°C, however, this will not contribute to rehydration of calcined fly ash. Rehydration of new generated nesosilicate on the surface of coarse fly ash leads to a better bonding between coarse fly ash particles and hydration products. As a result, both early and late mechanical properties of gap-graded blended cements containing 25% cement clinker and 39% calcined coarse fly ash are higher than those of 100% Portland cements.     

Investigations of cement early hydration in the presence of chemically activated fly ash

The paper describes an attempt of chemical activation of fly ash and claims the usefulness of combination of such investigation methods as calorimetry and infrared absorption for investigations of early periods of cement hydration. The research samples were cement pastes made with an addition of fly ash and admixtures of chemical activators, CaCl₂, Na₂SO₄ and NaOH, whereas a cement paste without fly ash addition and a cement-fly ash paste (both without admixtures) were used as reference samples. In order to investigate early periods of cement pastes hydration, the amount and rate of heat release were registered, and IR spectrums were checked at appointed hydration moments. As a result, it was shown that the combination of calorimetric and IR absorption methods in the investigations of early periods of cement hydration was useful. It was confirmed that the use of chemical activators CaCl₂, Na₂SO₄ and NaOH accelerated the hydration of cement pastes containing fly ash additive in early hours after adding water. The action of activators on hydrating cement system is different for each of investigated compounds.     

Phase diagrams for the binary systems CaCl2-KCl and CaCl2-CaCrO4

Phase diagrams have been determined using differential thermal analysis for the binary systems CaCl₂-KCl and CaCl₂-CaCrO₄. CaCl₂-KCl phase diagrams have been previously reported but results were not consistent. No prior studies have been reported for the CaCl₂-CaCrO₄ system. In the CaCl₂-KCl binary system two eutectics have been located at 24.0 mole % KCl (m.p. 615°C) and 74.3 mole % KCl (m.p. 594°C). A double salt of composition CaKCl3 melting congruently at 741°C has been found. The CaCl₂-CaCrO₄ system is a simple eutectic system with the eutectic occurring at 23.4 mole % CaCrO₄ and melting at 660°C.     

Thermochemische,kristallographische und infrarotuntersuchungen an calciumkupferhydroxychlorid-hydraten

Copper immersed in 1 N CaCl₂ solution containing NH₃ corrodes in the presence of oxygen with the formation of blue crystals of the compound 4 Cu(OH)₂ · CaCl₂ · 3.5 H₂O. The unit cell is tetragonal with a = 9.392 Å, c = 15.077 Å, c/a = 1.605; Z = 4. The calculated density is 2.818 g cm^?3 and the observed density 2.80 g cm^?3 at 22°C. The crystallographic aspect is P4₂**. Heating up to 400°C results in stepwise decomposition without sharp separation of the steps. The first step (165°C) gives 4 Cu(OH)₂ · CaCl₂ · 0.5 H₂O, tetragonal body centered, a = 9.34₂ Å, c = 7.53₃ Å, c/a = 0.806₄. The second step (215°C) gives CuO + 2 Cu(OH)₂ · CuO · CaCl₂ · H₂O, cubic primitive (pseudocubic?) a = 5.74 ± 0.017 Å and the third step (260°C): 4 CuO + CaCl₂.The first and the third step rehydrate in air at ambient temperature, the first step to the original material and the 3rd step to CuO + 3 Cu(OH)₂ · CaCl₂ · H₂O. This compound is hexagonal a = 6.66₃ Å, c = 5.81₅ Å, c/a = 0.872₇.The decomposition process is characterized by pseudomorphosis. At least for the first decomposition step, a topotaxial relationship is assumed.Diffraction and infrared data of the different compounds are given.     

Strength of granules based on calcium sulfate crystal solvates

The effect of urea additives forming calcium sulfate crystalline adduct CaSO₄ · 4CO(NH₂)₂ on the strength of granules prepared from phosphogypsum as industrial waste of phosphoric acid manufacture was studied. The strength of granules based on various crystal hydrates and crystal solvates was compared.     

Neue Verbindungen im System CaO/SiO2/CaCl2/H2O

New Compounds in the System CaO/SiO₂/CaCl₂/H₂O The hydrothermal formation of novel calcium silicate hydrates of compositions 5 CaO · 2 SiO₂ · CaCl₂ · 4 H₂O, 5 CaO · 2 SiO₂ · CaCl₂ · 2 H₂O and 4 CaO · 2 SiO₂ · CaCl₂ · H₂O from Ca₃SiO₅ and mixtures of CaO and SiO₂, respectively, in presence of calciumchloride at 200°–350 °C is described. From molybdate-reaction, ²⁹Si MAS NMR, DTA and TG measurements it is concluded that these compounds are based on disilicate anions and are to be interpreted as calcium hydroxide disilicate chlorides.     

Effect of CaCl2 on the desulphurization by CaO of a carbon-saturated Fe-Si-S alloy

The desulphurization of a carbon-saturated Fe-Si-S alloy by CaO and CaO-7.5% CaCl₂ slags at 1300 °C, and by CaO-10% CaF₂ and CaO-7.5% CaCl₂ slags at 1450 °C were investigated. The results indicated that the addition of 7.5% CaCl₂ to CaO improved the desulphurization of the carbon-saturated Fe-Si-S alloy at 1300 °C by forming a liquid reaction surface. X-ray diffraction studies on the reaction surface of CaO showed that solid CaS formed on the lime surface. This solid reaction product reduces the transfer of sulfur to the CaO surface. At 1450 °C, CaO-10% CaF₂ and CaO-7.5% CaCl₂ slags contain both liquid and solid phases. X-ray diffraction studies showed that a smaller amount of solid CaS formed on the reaction surface of the CaO-7.5% CaCl₂ slag than on the CaO-10% CaF₂ slag. The formation of a smaller amount of solid CaS and the presence of a liquid phase at the metal-slag interface enhanced the desulphurization with CaO-7.5% CaCl₂ at 1450 °C.     

Performance improvement of EPDM and EPDM/Silicone rubber composites using modified fumed silica,titanium dioxide and graphene additives

In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO₂) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO_2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.     

Molecular origin for rheological characteristics of native gellan gum

The ¹H-nuclear magnetic resonance spectrum showed that the l-rhamnosyl residues of native gellan gum were coinvolved in both a small number of ⁴C₁-pyranose conformations and a large number of ¹C₄-pyranose conformations, whereas for deacylated polymer, almost of the residues were involved in ⁴C₁-pyranose conformation. The flow curves of native gellan gum showed plastic behavior above 0.2%. The elastic modulus stayed at a constant value with increase in temperature up to 40 °C, then decreased rapidly. The elastic modulus increased with addition of CaCl₂ (6.8 mM) and stayed constant value with increase in temperature up to 65 °C, then decreased rapidly. The stronger elastic modulus was observed in deacylated gellan gum with addition of CaCl₂. The elastic modulus of native gellan gum showed larger value than that in aqueous solution in the presence of urea (4.0 M). Intra- and intermolecular associations of native gellan gum molecules in the presence of Ca⁺² were proposed.     

Sewage sludge ash as an alternative low-cost oxygen carrier for chemical looping combustion

In this paper, novel low-cost oxygen carriers containing Fe₂O₃ are evaluated for use in chemical looping combustion. Sewage sludge ashes and reference samples were prepared and used in cyclic reduction and oxidation experiments in a thermogravimetric analyzer (TG). A gaseous (3 % H₂) fuel and a solid fuel (hard coal) were tested. Three-cycle CLC tests were carried out in the 600–800 °C temperature range and long-term testing was performed at 950 °C. A reactivity study showed that the natural sewage sludge ash sample was stable during the cycling TG tests when hydrogen was used as a fuel at all of the temperatures investigated. Strong temperature effects on the oxygen transport capacity were observed. An one-cycle test at 900 °C showed also that the sewage sludge ash successfully reacted with coal. The oxygen released was fully used for coal combustion, with appreciable reaction rate at temperature of ~750–800 °C, that is significantly lower than that obtained for pure Fe₂O₃-based oxygen carrier. The oxidation reaction was much faster than the reduction reaction. Moreover, the sewage sludge ash showed a low tendency toward agglomeration in the cyclic test, which was superior to the behavior of synthetic materials. The sewage sludge ash exhibited also high mechanical strength, an attrition index of 1 % and a high-temperature resistance of 1,170 °C in a reducing atmosphere. We conclude that sewage sludge ash can be effectively used as a low-cost, valuable oxygen carrier in practical application in chemical looping combustion technology for power generation.     

Fast physics-chemical characterization of fly ash

This paper analyzes the effect of fly ash chemical character on early Portland cement hydration and the possible adverse effects generated by the addition of gypsum. Behaviour was analyzed for pure Portland cements with varying mineralogical compositions and two types of fly ash, likewise differing in chemical composition, which were previously characterized under sulphate attack as: silicic-ferric-aluminic or aluminic-silicic ash in chemical character, irrespective if they are in nature, siliceous or siliceous and aluminous materials according to the ASTM C 618-94a. The experimental results showed that water demand for paste with a normal consistency increased with the replacement ratio in fly ash with a more aluminic than silicic chemical character, whereas it declined when silicic-ferric-aluminic ash was used. On the other hand, the differences between the total heat of hydration released at the first valley and the second peak also clearly differentiated the two types of ash. While the relative differences increased in the more aluminic than silicic ash, they declined in the more silicic than aluminic. In another vein, the findings indicate that within a comparable Blaine fineness range, the reactive alumina (Al₂O₃^r−) content in pozzolanic additions has a greater effect on mortar strength than the reactive silica (SiO₂^r−) content, at least in early ages up to 28 days. Finally, the adverse effect generated in the presence of excess gypsum is due primarily to the chemical interaction between the gypsum and the C₃A in the Portland cement and the reactive alumina (Al₂O₃^r−) in the fly ash.     

Phase diagram for the ternary system LiClCaCl2CaCrO4

The phase diagram for the system LiClCaCl₂CaCrO₄ has been studied using differential thermal analysis. LiClCaCl₂CaCrO₄ has been shown by X-ray diffraction to be a stable, diagonal section of the Li, Ca//Cl, CrO₄ reciprocal ternary system. The three binary systems are: LiClCaCl₂ which exhibits a double salt (LiCaCl₃), which decomposes without melting at 439°C and a eutectic at 36.3 mole % CaCl₂ (m.p. 487°C); CaCl₂CaCrO₄ which shows a eutectic at 23.4 mole % CaCrO₄ (m.p. 660°C); and LiClCaCrO₄ with a eutectic at 14.3 mole % CaCrO₄ (m.p. 538°C).In the ternary system, a eutectic exists at 63.2 mole % LiCl32.9% CaCl₂3.9% CaCrO₄ (m.p. 479°C). In addition, a four-phase equilibrium, involving all solid phases, exists at nearly all compositions at 435°C.Isotherms are shown for the liquidus surface (primary crystallization) and for the secondary crystallization surface. Isothermal and vertical sections through the ternary phase diagram are shown.     

Hydrothermal solidification of municipal solid waste incineration fly ash

Hydrothermal solidification of municipal solid waste incineration (MSWI) fly ash has been conducted under saturated steam pressure at 200 °C for up to 48 h with quartz addition. To enhance the strength of solidified specimens further, the raw fly ash was pre-treated by water-washing and mixed with NaOH solution (2 M) as reaction solvent. Experimental results showed that curing time and temperature had significant effects on strength development. Strength development was found to be mainly due to tobermorite formation, and addition of quartz and NaOH solution promoted tobermorite formation. The raw fly ash could also be used as an additive to solidify MSWI bottom ash, and with raw fly ash addition (10%) the flexural strength of solidified specimens reached more than 21 MPa, suggesting high potential to recycle 100% MSWI ash (e.g. as 10% fly ash + 90% bottom ash). Leaching tests were conducted to determine amounts of heavy metals dissolved from solidified specimens. The results showed that under the hydrothermal conditions of this study, leaching of heavy metals was very low. As such, the hydrothermal processing method might have high potential for recycling/reusing MSWI fly ash on a large scale.