Crystallization study of SrSnO3:Fe

Alkaline earth stannates have recently become important materials in ceramic technology due to its application as humidity sensor. In this work, alkaline earth stannates doped with Fe³⁺ were synthesized by the polymeric precursor method, with calcination at 300 °C/7 h and between 400 and 1100 °C/4 h. The powder precursors were characterized by TG/DTA after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, infrared spectroscopy, and UV?Cvis spectroscopy. Results confirmed the formation of the SrSnO₃:Fe with orthorhombic perovskite structure, besides SrCO₃ as secondary phase. Crystallization occurred at 600 °C, being much lower than the crystallization temperature of perovskites synthesized by solid state reaction. The analysis of TG curves indicated that the phase crystallization was preceded by two thermal decomposition steps. Carbonate elimination occurred at two different temperatures, around 800 °C and above 1000 °C.     

Effect of the thermal treatment conditions on the formation of zinc ferrite nanocomposite, ZnFe2O4, by sol–gel method

Zinc ferrite nanocomposite was synthesized via thermal decomposition of zinc acetate and iron nitrate at three different temperatures (350, 450, and 550 °C). The influence of the thermal decomposition of precursors on the formation zinc ferrites was studied by differential thermal gravimetry and thermogravimetry (TG). The TG curve shows two steps for the thermal decomposition with mass loss of 17.3 % at 78 °C and 63.3 % at 315 °C. The prepared zinc ferrites nanocomposite was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffractograms of ZnFe₂O₄ shows that a crystalline phase, spinel system is formed. SEM micrograph of the zinc ferrite nanocomposite indicates the formation of uniformly spherical 48-nm nanograins. The properties of the zinc ferrite phase were strongly dependent on their calcinations temperature and molar ratio of precursors.     

Combustion study of HTPB–sugar hybrid fuel with gaseous oxygen

In the present investigation, some combustion studies have been carried out with 50 % HTPB + 50 % sugar fuel grain, burning in the gaseous oxygen stream using swirl and showerhead injectors, and the regression rate has been compared. The combustion of fuel grain has been carried out for burning duration of 10 ± 1 s at four different oxidizer injection pressures, viz 1.52, 2.21, 2.76 and 3.24 MPa. The regression rates were found to increase with increasing injection pressure. Use of swirl injector exhibited higher regression rate compared to the showerhead injector. The average regression rate and fuel mass consumption rate in case of swirl injector were found to be higher than that of showerhead injector. The average regression rate for the fuel with swirl injector has been found to be 18.81, 15.11, 17.73 and 20.23 % more than that of shower head injector. The exhaust plume was also found out to be brighter and longer for a swirl injector compared to that of the showerhead injector. The thermal decomposition characteristic of fuel has been determined using differential thermal analysis and thermo gravimetric analysis techniques. The decomposition study was carried out at heating rate of 10 °C min^?1 in an oxygen atmosphere. The exothermic peak indicating that major decomposition takes place at a higher temperature of 483.3 °C. Mass loss have been found using TG analysis. Residual mass of 1.262 % has been obtained in the heating range of 30–500 °C. Heat of combustion of fuel is found to be 6972.41 Cal g^?1.     

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.     

Low temperature synthesis of Li5La3Nb2O12 with cubic garnet-type structure by sol–gel process

A cubic Li₅La₃Nb₂O₁₂ phase with a garnet framework was synthesized by the sol–gel process, in which lithium hydroxide, niobium oxide and acetic lanthanum were used as starting materials, while water was used as solvent. Pure garnet-like Li₅La₃Nb₂O₁₂ powders were obtained after heating the gel precursor at 700 °C for 6 h with 10 % excess lithium salt. The calcination temperature is nearly 250 °C lower than that by the solid state reaction. The phase transforms from cubic to tetragonal symmetry with loss of lithium at 717 °C, but the garnet framework remains stable to above 900 °C. A pellet annealed at 900 °C for 6 h had a room-temperature Li⁺-ion conductivity σ_Li (22 °C) = 1.0 × 10^?5 S cm^?1, a little higher than that attained by solid-state synthesis. The Li₅La₃Nb₂O₁₂ compound was chemically stable against two commonly used cathode materials, LiMn₂O₄ and LiCoO₂, up to 900 °C and against metallic lithium.     

Charcoal produced from cellulosic raw materials by microwave-assisted hydrothermal carbonization

In this work, cellulose-based renewable raw materials were hydrothermally carbonized in a microwave oven at 200 °C during 60, 120, and 240 min. The charcoals obtained were characterized by proximate analysis, gross calorific value, and thermogravimetric analysis on inert and oxidizing atmosphere. The values of fixed carbon were between 38 and 52 %. The mass loss between 300 and 470 °C was assigned to the thermal decomposition of cellulose, followed by the second stage between 470 and 740 °C, attributed to the thermal decomposition of lignin. The gross calorific values were between 22.60 and 27.12 MJ kg^?1, which are comparable to those of charcoals and coals.     

Effect of solvent on phase composition and particle morphology of lanthanum niobates prepared by polymeric complex sol–gel method

Lanthanum niobates were prepared by a new polymeric complex sol–gel method using Nb-citrate or -tartrate complexes in different solvent (ethanol or methanol) and calcination at 750–1,050 °C. The perovskite La_1/3NbO₃ and pyrochlore LaNb₅O₁₄ phases were formed after calcination at 900 and 1,050 °C from gels synthesized from ethanol and methanol solvents respectively. The very similar xerogel thermal decomposition processes were observed independently on applied solvents, where the pyrochlore monoclinic LaNbO₄ and Nb₂O₅ phases were intermediate products at lower calcination temperatures during transformation. The particle morphologies changed from spherical 20–50 nm particles at 750 °C to granular LN particles (ethanol) or rectangular (methanol) at 1,050 °C. HRTEM images and SAED verified the coexistence of minority monoclinic LaNbO₄ phase with majority phases in individual LN particles after annealing. The strong effect of alcohol solvent on phase formation was shown, while the effect of chelating agent was insignificant.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion Batteries

Li₄Ti₅O₁₂ (LTO) nanoparticles were prepared by gel‐hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid‐state reaction or by sol‐gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X‐ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge‐discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li₄Ti₅O₁₂ anode material prepared through gel‐hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g^?1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g^?1. The gel‐hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells.     

Environmentally benign sol–gel derived nanocrystalline rod shaped calcium doped cerium phosphate yellow-green pigment

Nanocrystalline rod shaped calcium doped cerium phosphate yellow-green pigment particles having an average length of ~100 nm and aspect ratio 10 even after calcination at 600 °C have been realized through an aqueous sol–gel process. The morphology, particle size and identification of the phase are determined by using different analytical tools such as transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), Fourier-transform IR (FTIR) and X-ray diffraction (XRD). Brunauer–Emmett–Teller (BET) nitrogen adsorption analysis showed the pigment particles are mesoporous texture having specific surface area 42 m² g^?1 and average pore size 153 Å. Thermogravimetric (TG) analysis is used to explain the thermal phase stability of the pigment. UV–Visible spectroscopy and colorimetric analysis are also done. The typical yellow-green color has been obtained even after heating to as low as 600 °C, which is 300 °C lesser than reported. Systematic study on synthesis and effect of temperature on color are presented.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

Investigation of clinoptilolite rich natural zeolites from Turkey: a combined XRF,TG/DTG,DTA and DSC study

Turkey clinoptilolite-rich tuffs from Gördes and Bigadiç regions of western of Anatolia and their exchanged forms (K⁺, Na⁺, Mg²⁺ and Ca²⁺) were characterized by TG/DTG-DTA, DSC and XRF methods and the surface areas were also determined for both tuffs. TG-DTG and DTA curves of all clinoptilolite samples were measured in the temperature range 30–1000 °C. All clinoptilolite samples had major, rapid mass losses between 30 and 200 °C, with slower and less significant mass losses at higher temperatures. The mass loss of the Natural-G is 9.54% while that of the Natural-B sample is 10.50%. Water content increases in the order of K < Na < Ca < Mg for Bigadiç clinoptilolite samples and in the following sequence K < Na < Mg < Ca for Gördes clinoptilolite samples. One mass loss step for all clinoptilolite samples was observed using differential scanning calorimeter (DSC) in the range of 30–550 °C.     

Regulatory Aspects in Development of Stability-Indicating Methods: A Review

Poly(N-vinylcaprolactam) (PVCL) connected to aminopropyl silica is a new stationary phase for temperature responsive liquid chromatography (TR-LC). PVCL shows a transition from hydrophilic to hydrophobic interaction between 30 and 40 °C. The synthesis is described in detail. The temperature responsive characteristic of the phase is illustrated with a mixture of steroids using pure water as mobile phase. An increase in retention is observed when raising the temperature. H–u plots at different temperatures were constructed. Below the lower critical solution temperature (LCST), no optimal velocity could be measured because of substantial resistance to mass transfer. Above the LCST, u _opt was ca. 0.3 mm s^?1 with reduced plate heights from 4 at 45 °C to 3 at 65 °C. The temperature responsive nature of the polymer is lost in green chromatography with ethanol as modifier in concentrations above 5%.     

Fibers and fiber cocktails to improve fire resistance of concrete

Hybrid organic–inorganic resin matrix, i.e., hexa[3,4-dicyano]-phenyl phosphonitrile trimer (HPPT) has been prepared by the reaction of hexachlorophosphonitrile and 4-hydroxyphthalonitrile in the presence of sodium hydride which on heating at 300 °C yielded a high-temperature-stable highly crosslinked hybrid resin (C-HPPT). The elemental analysis (C, H, and N), FTIR, and ¹H and ¹³C-NMR studies were used to characterize the synthesized hybrid resin. The thermal analysis studies viz. TG and DSC were also carried out to determine the thermal stability and glass transition temperature of the cured resin. The isothermal study of the cured resin after 300 h at 300 °C showed only a mass loss of 4.36%.     

Decomposition of perfluoropolyether lubricants

Decomposition has been studied in the chemistry of perfluoropolyethers (PFPE), thus far no molecular structure information is reported. TG-MS is a tool to follow the off gassing of decomposition for clues. We selected two PFPEs that have different properties: Krytox® XHT-1000 and Fomblin Z60 heating to normal decomposition and catalytic decomposition in the presence of alumina powder. Comparing the decomposition fragment intensities, the molecular structure of the branched Krytox® XHT-1000 oil is more stable than the blocky Fomblin Z60. We see aluminum-containing fluorine fragments in the rapid decomposition of oils in contact with alumina powder. It has been suggested the formation of Al(O_6?n F _n ), where n = 1, 2, and 3, in which the fluorine atoms are selectively associated with aluminum atom. The major decomposition products are small and large fragments of fluorocarbons and perfluoroalkoxy. In the absence of alumina powder, Krytox XHT-1000 shows only a loss of 13 mass/% after several hours at 330 °C, whereas in the presence of 1 mass/% alumina powder the oil has rapidly decomposed to 67 mass/% of its original mass within 15 min. Fomblin Z60, a product might not be designed for high temperature, exposing to the same conditions at 330 °C for several hours and shows a loss of 98 mass/% alone, but in the presence of 1 mass/% alumina powder shows a loss of 98 mass/% in 3.6 min. When 3 mass/% of two new developmental additives were added to the both oils, the catalytic decomposition in the presence of 1 mass/% alumina powder was significantly reduced in Krytox® XHT-1000, showing only a loss of 23 mass/% in 4 h, but nearly all weight for Z60 in 60 min. In the oil grades that contain the new additives, we see the fragments of Al–O–S, and F–Al–O–S. The sulfur-containing compound has been reported ionically bonded to oxide in a tripod configuration of alumina surface, which shields the formation of Al–F.     

Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO₄ and ZnWO₄ were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO₄ was crystalline after calcination at 350 °C/12 h while ZnWO₄ only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO₄ heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO₄ presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO₄ has indicating that nickel made carbon elimination easier.     

Research on historical bricks from a Baroque Church

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

Comprehensive reinvestigation on the initial coulombic efficiency and capacity fading mechanism of LiNi0.5Mn1.5O4 at low rate and elevated temperature

The effect of different membranes and aluminum current collectors on the initial coulombic efficiency of LiNi_0.5Mn_1.5O₄/Li was investigated, and the cycling performance at different rates and temperatures and the storage performance at 60 °C for a week are discussed for LiNi_0.5Mn_1.5O₄/Li. The results show that the lower initial coulombic efficiency is associated with the lower decomposition voltage of the commercial membrane and electrolyte, and the instability of aluminum current collector under the higher voltage. In addition, both versions of LiNi_0.5Mn_1.5O₄ can deliver about 115 mA?h g^?1 of initial discharge capacity at 1 C at 25 °C and 60 °C; however, it retains only 61.57 % of its initial capacity after the 130th cycles at 60 °C, which is much lower than the 94.46 % rate observed for LiNi_0.5Mn_1.5O₄ at 25 °C, and the cycling performance of the material at 1 C is better than that at 0.5 C. Meanwhile, the initial discharge capacity at 0.1 C after storing at 60 °C is 119.3 mA?h g^?1, which is only a little lower than 121.5 mA?h g^?1 recorded before storing; moreover, the spinel structure and surface state of LiNi_0.5Mn_1.5O₄ after storing at 60 °C has not been changed basically. These results indicate that the electrochemical stability of electrolyte is also related to the temperature. The serious capacity fading of LiNi_0.5Mn_1.5O₄ at 60 °C is attributed to the severe oxidation decomposition and the thermal decomposition in the range of cut-off voltage of the materials, and then the decomposition products interact with active materials to form a solid interface phase, leading to the larger electrode polarization and irreversible capacity loss. Meanwhile, the worse cycling performance at 0.5 C than that at 1 C is attributed to the longer interaction time between the electrolyte and the active materials. However, the storage performance of LiNi_0.5Mn_1.5O₄ corresponds to the thermal stability of electrolyte to a certain extent.     

Enhanced electrochemical performance of LiFePO<Subscript>4</Subscript>/C nanocomposites due to in situ formation of Fe<Subscript>2</Subscript>P impurities

We have studied LiFePO₄/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO₄ phase, all the samples show a varying amount of in situ Fe₂P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe₂P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO₄/C sample calcined at 700 °C which contains ～15 wt% Fe₂P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g^?1 at a rate of 1 C, 121 mA h g^?1 at 10 C (～70 % of the theoretical capacity of LiFePO₄), and excellent cycleability. Although further increase in the amount of Fe₂P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li⁺ diffusion coefficient (～1.3?×?10^?13 cm² s^?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe₂P for obtaining the best capacity for the high power batteries.     

Porous microsphere of magnesium oxide as an effective sorbent for removal of volatile iodine from off-gas stream

Porous microspheres of magnesium oxide were synthesized by calcination of precursor obtained via hydrothermal method. A sample of microsphere was characterized by transmission electron microscopy, scanning electron microscopy–energy dispersion spectroscopy, X-ray diffraction, thermogravimetric analysis, N₂ adsorption–desorption isotherms, and BET surface area. The average pore size and surface area of the microsphere were found to be 9.0 nm and 83.1 m² g^?1, respectively. The performance of sorbent was investigated in a continuous adsorption system. Iodine adsorption on sorbent was studied by varying temperature of adsorption column, sorbent calcination temperature and initial concentration of iodine. The capacity of sorbent increased by ~25 % when calcination temperature was raised from 350 to 500 °C. The maximum iodine adsorption capacity of sorbent was found to be 196 mg g^?1 using Langmuir isotherm. These results indicate the microspherical form of MgO to be effective sorbent to capture iodine vapor from off-gas stream.