Biodiesel Preparation from Jatropha curcas Oil Catalyzed by Hydrotalcite Loaded With K2CO3

This paper discusses the synthesis of biodiesel catalyzed by solid base of K₂CO₃/HT using Jatropha curcas oil as feedstock. Mg–Al hydrotalcite was prepared using co-precipitation methods, in which the molar ratio of Mg to Al was 3:1. After calcined at 600 °C for 3 h, the Mg–Al hydrotalcite and K₂CO₃ were grinded and mixed according to certain mass ratios, in which some water was added. The mixture was dried at 65 °C, and after that it was calcined at 600 °C for 3 h. Then, this Mg–Al hydrotalcite loaded with potassium carbonate was obtained and used as catalyst in the experiments. Analyses of XRD and SEM characterizations for catalyst showed the metal oxides formed in the process of calcination brought about excellent catalysis effect. In order to achieve the optimal technical reaction condition, five impact factors were also investigated in the experiments, which were mass ratio, molar ratio, reaction temperature, catalyst amount and reaction time. Under the best condition, the biodiesel yield could reach up to 96%.     

TG–DSC–FTIR–MS study of gaseous compounds evolved during thermal decomposition of styrene-butadiene rubber

The thermal decomposition behavior of styrene-butadiene rubber was studied using a system equipped with thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and mass spectroscopy. Two different experiments were conducted. From these experiments, thermogravimetric analysis results indicated a mass loss of 58 % in the temperature range of ~290–480 °C and a mass loss of 39 % in the temperature range beyond 600 °C. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed the presence of oxides, even at 1,000 °C, accounting for the Zn, Mg, Al, Si, and Ca in the original sample.     

Formation of Al‐enriched surface layers through reaction at the Mg‐substrate/Al‐powder interface

Al‐enriched surface layers containing a Mg₁₇Al₁₂ intermetallic phase and a solid solution of Al in Mg were fabricated by heating Mg specimens in contact with Al powder in a vacuum furnace. The layer formation process proceeded through partial melting at the Mg‐substrate/Al‐powder interface. The test results suggest that a good contact between the Al powder and the Mg substrate is required during heat treatment. In this study, a pressure of 1 MPa was applied to improve the contact of the Al powder with the Mg specimen. When the powder was pressed down during heating, it was possible to reduce the process temperature from 450 °C to 440 °C. The layers produced at 440 °C in a short heating time (40 min) were thick, continuous and uniform. The microhardness of the Al‐enriched layers was much higher than that of the Mg substrate. The results of the electrochemical corrosion tests indicated that the Mg specimens with an Al‐enriched surface layer had better corrosion resistance than the bare Mg. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

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.     

Simulation approach to decomposition kinetics and thermal hazards of hexamethylenetetramine

The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (T_peak) with the heating rates 1, 2, 4 and 8 °C min⁻¹. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg⁻¹. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as T_D24, T_D8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters.

     

Interfacial mutations in the Al‐polyimide system

Understanding the thermal stability of metal‐polymer interfaces is essential for the reliability of innovative high‐tech devices, including flexible electronics or satellite insulation. In this study, the interfacial stability of aluminum‐polyimide (Al‐PI) is investigated as a function of thermal cycling (±150°C) and thermal annealing treatments (150°C‐300°C) with X‐ray photoelectron spectroscopy measurements performed after peeling and cross‐sectional transmission electron microscopy analysis. Small mutations in the interface chemistry and structure were detected and identified after annealing at 225°C for 140 hours, including the thickness increase of an amorphous interlayer between Al and PI of about 2 nm and a change in the failure mechanism during the peeling. Being able to trace subcritical mutations before they become fatal is essential to predict the reliability and lifetime of metal‐polymer composites.     

Thermal transformations up to 1200 °C of Al-pillared montmorillonite precursors prepared by different OH–Al polymers

Aluminum-pillared montmorillonites are useful materials for their application as catalysts, adsorbents and ceramic composites. The precursor is a pillared montmorillonite that is not thermally stabilized. The precursor preparation methods, textural properties and catalytic activity have been extensively investigated, but comparatively, studies concerning their thermal transformations at high temperature are limited. In this work, precursors were prepared using two types of montmorillonites, Cheto (Ch) and Wyoming (W), and using two different OH–Al polymer sources: hydrolyzed (H) and commercial (C) solutions. Structural and thermal transformations of the precursors with heating up to 1200 °C were determined by X-ray diffraction and thermogravimetric analysis. Thermal analysis of these precursors below 600 °C revealed the influence of OH–Al polymers from the two solutions. The major phases developed at 1200 °C from the original montmorillonites were mullite for W and cordierite for Ch. The content of these phases depended on the aluminum in the octahedral sheet of the pristine montmorillonites. Amorphous phase, cristobalite, spinel, sapphirine and others phases were also found. The intercalation of OH–Al polymers in montmorillonites caused an increase in amorphous content after treatment at 1030 °C; however, it favored mullite development above 1100 °C. Although total aluminum content of both W and Ch precursors was similar, the transformation to mullite was directly related to the octahedral aluminum/magnesium ratio. The phase composition of the products at 1200 °C was not dependent on the type of intercalated OH–Al polymers. The increase in mullite content of the thermally treated precursors contributes to its possible application as advanced ceramic products.     

Effect of multivalent cations,temperature, and aging on SOM thermal properties

Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (>40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

Preparation of acid–base bi-functional hydrotalcite based catalyst for converting Vietnamese coconut oil to green hydrocarbons

Acid–base bi-functional hydrotalcite like compounds based on partial incorporation of Al³⁺ into brucite structure of Mg(OH)₂ with various molar ratios were prepared through co-precipitation method. The co-precipitation of the precursors produced precipitations followed by drying at 120 °C for 12 h and calcination in air flow at 500 °C for 6 h to obtain the catalysts (Mg–Al HLCs). Many techniques including XRD, TG–DTA, EDX, NH₃-TPD, CO₂-TPD, GC–MS and XANES were used to characterize and optimize Mg/Al molar ratio based on the thermal stability of the Mg–Al HLCs and their activities in decarboxylation process of coconut oil. The results showed that the best molar ratio of Mg/Al was 3/1 providing a stable hydrotalcite like structure, and the catalyst possessed both acid and base sites on its surface enhancing its activity and selectivity in the decarboxylation process. The catalysts revealed high performance in the decarboxylation process of coconut oil established at 400 °C for 4 h for green hydrocarbons belonging to kerosene fractions.     

Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.     

Study of martensite transformation and microstructural evolution of Cu–Al–Ni–Fe shape memory alloys

In this study, variations in the transformation temperature, crystal structure, and microstructure of the arc melted alloy having nominal composition of Cu–13%Al–4%Ni–4%Fe (in mass%) were investigated for two different treatment conditions, homogenized and heat treated at 950 °C for 1 h. For both conditions, transformation temperature of the alloy was examined by DSC and it was determined as ~200 °C, similar to the value for Cu–Al–Ni alloys given in the literature. The crystal structure of the martensite Cu–13%Al–4%Ni–4%Fe (in mass%) alloy was identified as 18R using XRD. By heat treatment performed at 950 °C, diffraction peaks become more distinct. The microstructure of the alloy was studied with the help of optical microscope as a result of which parallel martensite plates and precipitates were detected. Microhardness value of the alloy was found as 361 and 375 Hv for homogenized and heat-treated conditions, respectively.     

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.     

Enhancement of electron-induced X-ray intensity for single particles under grazing-exit conditions

Grazing-exit electron probe microanalysis (GE-EPMA) was performed for single Al₂O₃ and atmospheric particles, deposited on a flat Si substrate coated by gold, by using an aperture (1 mm in diameter) in front of an energy-dispersive X-ray detector. Silicon Kα X-rays from the Si substrate were strongly observed at an exit angle of ∼45°. However, they disappeared at grazing-exit angles about 0° and only the X-rays from particles were detected. Furthermore, Al Kα and O Kα intensities from single Al₂O₃ particle were enhanced approximately three- and sixfold at the grazing-exit angles (∼1°), respectively, in comparison with those at large angle (∼7°). The background intensities at the energy of Al Kα and O Kα almost monotonously decreased with decreasing exit angle. As a result, the intensity ratios of Al Kα and O Kα X-rays to the background intensities were enhanced five- and sixfold, respectively. This enhancement is considered to be caused by the interference effect of both directly detected X-rays and reflected X-rays on the flat substrate. The similar results are also obtained for Al Kα, Si Kα, K Kα and Ca Kα emitted from single atmospheric particle. The significance of the matrix effect in the particle is also pointed out.     

ZnO:Al thin films used in ZnO: Al/p-Si heterojunctions

Al-doped n-ZnO/p-Si heterojunctions were fabricated using a sol–gel dip coating technique at 700 °C, in a nitrogen ambient. The structural, optical, and electrical properties of ZnO:Al thin films, and the heterojunction properties of ZnO:Al/p-Si were investigated with respect to the effects of Al doping concentration. Hexagonal nano-structured ZnO: Al thin films with a 1.2% and a 1.6 at.% Al concentration exhibited high optical transmittance in visible ranges. Electrical resistivity changed with respect to Al doping concentration, and minimum resistivity was detected at a 1.2 at.% Al concentration. The ZnO:Al/p-Si heterojunction properties were analysed using current–voltage (I–V) measurements at four different Al concentrations, ranging from 0.8 to 1.6 (at.%). The ZnO:Al/p-Si heterojunctions exhibited diode-like rectifying behaviour. Under UV illumination, the photoelectric behaviour observed for the ZnO:Al/p-Si heterojunctions was diode.     

Study on mineral surface reacted with water at temperatures above 300��C and 23?MPa

In this work, we carried out experiments on silicate mineral dissolution using a flow-through reactor from 20 to 400°C at 23 MPa. The dissolution of silicate minerals such as actinolite, diopside, and albite in water may require the breaking of more than one metal?Coxygen bond type. Different metal elements in silicate minerals have different release rates and the dissolution product is often non-stoichiometric. Na, Mg, Fe, and Ca dissolve faster than Si at T < 300°C. At T ?? 300°C, the release rate of Si is higher than that of the other metals. The molar concentration ratios of the dissolving metal Mi versus Si such as Mg/Si, Ca/Si and Al/Si, which are the release ratios in the effluent solutions, are often different from the molar ratios of these elements in the minerals. The results show that the incongruent dissolution of minerals is related to surface chemical modifications. Non-stoichiometric dissolution is caused by the formation of a non-stoichiometric leaching layer at the surface or by the presence of a secondary mineral at the surface. Our experiments indicate that the dissolution of most silicate minerals is close to stoichiometric at 200 and 300°C, e.g., for actinolite and albite at 300°C. The surfaces after reaction with aqueous solutions were investigated using SEM and TEM. At T < 300°C, the mineral surfaces (e.g., for actinolite) after the reaction with water are slightly Si-rich and slightly Fe (and/or Mg, Ca) deficient. In contrast, at T ?? 300°C, the surfaces after reaction with water are slightly Fe-rich and somewhat Si deficient.     

Redox behavior of high Si/Al ratio Cu-ZSM5 in NO decomposition

Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged using copper acetate aqueous solutions with different concentrations. Copper saturation is reached at the 130 and 230% level of Cu exchange for Si/Al equal to 25 and 75, respectively, although FTIR spectra showed that a fraction of Al-OH exchange positions is still available. Catalytic activity experiments of NO decomposition have been carried out at 450°C in a fixed bed reactor. Catalysts have been characterized with H₂ TPR and NO adsorption experiments at 120°C. All samples are partially reduced upon thermal treatment under inert flow (He) leading to the formation of Cu⁺-containing sites in addition to a fraction of differently reduced copper species. The Cu⁺-containing sites, also responsible for NO adsorption and subsequent production of N₂O at 120°C, have been proposed to be the active centers. A quantitative estimation of these species, likely having multi-ionic structure, has been provided.     

Chain-backbone motion in glassy polycarbonate studied by polarized infrared spectroscopy

Chain-backbone motion in glassy polycarbonate has been investigated both under isothermal stress, and also under zero stress during isothermal annealing of freely contracting film specimens. In both types of experiment, backbone motion was detected by measuring the change in infrared dichroism. The dichroism of absorption bands at 1364 and 2971 cm^?1, which have transition moment vectors directly related to the chain-backbone orientation, was studied. Under tensile stress in the homogeneous region of deformation, changes of up to 2.2° in the mean chain-backbone orientation angle were measured at 23°C. With the onset of cold drawing a total orientation change of some 8° was observed. For the isothermal annealing experiments, a film specimen holder employing conductive heating with radiative losses was employed. It enables infrared measurements to be made while the temperature of the contracting specimen is maintained constant to ± 0.5°C. Oriented specimens were prepared by isothermal stretching of polycarbonate films to strains of the order of 100%. Changes in the mean chain-backbone orientation angle were observed during annealing of these oriented films at temperatures between 80°C and the glass transition (149°C). Chain motion proceeded during annealing, and chain segments were observed to move cooperatively. The temperature at which the polymer is prestretched has a pronounced effect on its subsequent relaxation during annealing: when the sample was stretched at 23°C. motions were detected during annealing at temperatures as low as 81°C, while, if it was stretched at 154°C, no motion was detected at annealing temperatures below 127°C. The data are discussed in comparison with theories of the glassy state that predict the absence of chain-backbone motion at temperatures significantly below the glass transition. A shift in frequency of the ν_a (CH₃) absorption peak in stretched polycarbonate was measured by using polarized radiation. The effect was interpreted in terms of changes in the intermolecular bonding structure of the oriented polymer.     

Sensitive spectrofluorimetric determination of aluminium(III) with Eriochrome Red B

A spectrofluorimetric method is reported for the determination of Al(III), based on the formation of a fluorescent Al(III)-Eriochrome Red B complex in the presence of hexamethylenetetramine at 60°C. Fluorescence measurements were made at 2°C and all variables that affect the development of the complex are reported. The method is very selective and the detection limit is 0.1 ng ml^?1. It was applied to the determination of Al(III) in tap water.