Synthesis of lithium ferrite by precursor and combustion methods: A comparative study

The thermal decomposition of lithium hexa(carboxylato)ferrate(III) precursors, (Li₃[Fe(L)₆]·xH₂O, L = formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature upto 500 °C. Various physico-chemical techniques, i.e., TG, DTG, DTA, XRD, SEM, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo decomposition to yield various intermediates, i.e., lithium oxalate/acetate/propionate/butyrate, ferrous oxalate/acetate and α-Fe₂O₃ in the temperature range of 185–240 °C. A subsequent decomposition of these intermediates leads to the formation of nanosized lithium ferrite (LiFeO₂). Ferrites have been obtained at much lower temperature (255–310 °C) as compared to conventional ceramic method. The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature (400 °C) and in less time than that of conventional ceramic method.     

Synthesis of potassium ferrite by precursor and combustion methods

The thermolysis of potassium hexa(carboxylato)ferrate(III) precursors, K₃[Fe(L)₆]·xH₂O (L=formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature to 900°C. Various physico-chemical techniques i.e. TG, DTG, DTA, XRD, IR, Mössbauer spectroscopy etc. have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo exothermic decomposition to yield various intermediates i.e. potassium carbonate/acetate/propionate/butyrate and α-Fe₂O₃. A subsequent decomposition of these intermediates leads to the formation of potassium ferrite (KFeO₂) above 700°C. The same ferrite has also been prepared by the combustion method at a comparatively lower temperature (600°C) and in less time than that of conventional ceramic method.     

Ni–Al hydrotalcite-like material as the catalyst precursors for the dry reforming of methane at low temperature

Nickel–aluminium and magnesium–aluminium hydrotalcites were prepared by co-precipitation and subsequently submitted to calcination. The mixed oxides obtained from the thermal decomposition of the synthesized materials were characterized by XRD, H₂-TPR, N₂ sorption and elemental analysis and subsequently tested in the reaction of methane dry reforming (DRM) in the presence of excess of methane (CH₄/CO₂/Ar = 2/1/7). DMR in the presence of the nickel-containing hydrotalcite-derived material showed CH₄ and CO₂ conversions of ca. 50% at 550 °C. The high values of the H₂/CO molar ratio indicate that at 550 °C methane decomposition was strongly influencing the DRM process. The sample reduced at 900 °C showed better catalytic performance than the sample activated at 550 °C. The catalytic performance in isothermal conditions from 550 °C to 750 °C was also determined.     

Thermal decomposition of lutetium propionate

The thermal decomposition of lutetium(III) propionate monohydrate (Lu(C₂H₅CO₂)₃·H₂O) in argon was studied by means of thermogravimetry, differential thermal analysis, IR-spectroscopy and X-ray diffraction. Dehydration takes place around 90 °C. It is followed by the decomposition of the anhydrous propionate to Lu₂O₂CO₃ with evolution of CO₂ and 3-pentanone (C₂H₅COC₂H₅) between 300 °C and 400 °C. The further decomposition of Lu₂O₂CO₃ to Lu₂O₃ is characterized by an intermediate constant mass plateau corresponding to a Lu₂O_2.5(CO₃)_0.5 overall composition and extending from approximately 550 °C to 720 °C. Full conversion to Lu₂O₃ is achieved at about 1000 °C. Whereas the temperatures and solid reaction products of the first two decomposition steps are similar to those previously reported for the thermal decomposition of lanthanum(III) propionate monohydrate, the final decomposition of the oxycarbonate to the rare-earth oxide proceeds in a different way, which is here reminiscent of the thermal decomposition path of Lu(C₃H₅O₂)·2CO(NH₂)₂·2H₂O.     

Chiral separation of trans-stilbene oxide through cellulose acetate butyrate membrane

An enantioselective membrane was prepared using cellulose acetate butyrate as a membrane material. The flux and permselective properties of membrane using 50% ethanol solution of (R,S)-trans-stilbene oxide as feed solution were studied. The top surface and cross-section morphology of the resulting membrane were examined by scanning electron microscopy. The resolution of over 92% enantiomeric excess was achieved when the enantioselective membrane was prepared with 15 wt % cellulose acetate butyrate and 30 wt % N,N-dimethylformamide in the casting solution of acetone, 10 °C temperature of water bath for the gelation of the membrane, and the operating pressure and the feed concentration of the trans-stilbene oxide were 3 kgf/cm² and 5.2 mmol/L, respectively. Since the cellulose acetate butyrate contained a large amount of asymmetric carbons on the backbone structure, it was possible to form helical structure, this was considered to be the reason for the enantioselectivity of the membrane.     

Tio2@Sn core–shell nanotubes for fast and high density Li-ion storage material

TiO₂@Sn core–shell nanotube material prepared by thermal decomposition of SnCl₄ on TiO₂ nanotubes at 300 °C has been demonstrated superior Li-ion storage capability of 176 mA h/g even at high current rate of 4000 mA/g (charge and discharge of all TiO₂ within 5 min) in spite of using low carbon content (5 wt%). This value corresponds to volumetric energy densities of 317 mA h/cm³, and its value was 3.5-fold larger than that of the bare TiO₂ nanotubes.     

Influence of iron on the synthesis and stability of yttrium silicate apatite

The stability of yttrium silicate apatite has been investigated by studying the influence of iron as a “stabilising cation” and also by using different synthesis routes. The formation of apatite in samples has been followed by X-ray diffraction and by ²⁹Si MAS NMR spectroscopy. The apatite phase appears to be stable at high temperatures (≈1700 °C) especially when heated in a nitrogen atmosphere; it can also occur in a metastable state when heated in air at lower temperatures; ≈1600 °C if prepared from a Y₂O₃SiO₂ mixture or in the range 950 °C <T< 1150 °C if synthesised by the sol–gel process. Longer heat-treatments result in its decomposition into Y₂Si₂O₇ and Y₂SiO₅. Iron appears to have two roles depending on the temperature; it stabilises the apatite phase at high temperatures when produced by the sol–gel route and catalyses the decomposition of sol–gel derived apatite at low temperatures.     

Comprehensive evolved gas analysis (EGA) of amorphous precursors for S-doped titania by in situ TG–FTIR and TG/DTA–MS in air: Part 2. Precursor from thiourea and titanium(IV)-n-butoxide

Thermal decomposition of an amorphous precursor for sulfur-doped titania (S:TiO₂) nanopowders, prepared by controlled sol–gel hydrolysis-condensation of titanium(IV) tetrabutoxide and thiourea in aqueous butanol, has been studied in situ up to 850 °C in flowing air by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA–MS) and FTIR spectrometric gas cell (TG–FTIR) for analysis of gases and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication techniques aimed S:TiO₂ photocatalysts with photocatalytic activities under visible light.The studied S-doped precursor's decomposition course remembers to that of non-doped xerogel from Ti(IV)-n-butoxide, which seems to retard a considerable amount of organics in the solid phase even at high temperature, probably in polymeric forms, proven by evolution of CO₂ in several temperature regions of decomposition stages. The incorporation form of thiourea in the original xerogel seems to be chemically bounded, resulting lower decomposition temperature than that of pure thiourea, and producing evolution of carbonyl sulfide (COS) already between 120 and 190 °C. Nevertheless, evolution of SO₂, and that of CO₂ is also observed above 500 °C by both EGA detection methods. The latter observation implies that the blackish grey samples obtained even at 750 °C might be simultaneously S- and C-doped ones.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.     

An investigation on the solid state pyrolytic decomposition of bimetallic oxalate precursors of Ca,Sr and Ba with cobalt: A mechanistic approach

The mixed metal oxalate precursors, calcium(II)bis(oxalato)cobaltate(II)hydrate (COC), strontium(II)bis(oxalato)cobaltate(II)pentahydrate (SOC) and barium(II)bis(oxalato)cobaltate(II)octahydrate (BOC) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR spectral and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound COC decomposed mainly to CaC₂O₄ and Co₃O₄ at 340 °C, and a mixture of CaCO₃ and Co₃O₄ identified at 510 °C. A mixture of CaCO₃ and Ca₃Co₂O₆ along with the oxides and carbides of both the cobalt and calcium were attributed at 1000 °C as end products. DSC study in nitrogen ascertained the formation of a mixture of CaO and CoO along with a trace of carbon at 550 °C. The mixture species, SrC₂O₄, CoC₂O₄ and Co₃O₄ were generated at 255 °C in case of SOC in air, which ultimately changed to CoSrO₃, SrCO₃ and oxides of strontium and cobalt at 1000 °C. The several mixture species also generated as intermediate at 332 and 532 °C. The DSC study in nitrogen indicated the formation of CoSrO_x (0.5 < x < 1) as end product. In case of BOC in air, a mixture of BaCoO₂, BaO, CoO and carbides are identified as end product at 1000 °C through the generation of several intermediate species at 350 and 530 °C. A mixture of BaO and CoO is identified as end product in DSC study in nitrogen. The kinetic parameters have been evaluated for all the dehydration and decomposition steps of all the three compounds using four non-mechanistic equations. Using seven mechanistic equations, the kind of dominance of kinetic control mechanism of the dehydration and decomposition steps are also inferred. The kinetic parameters, ΔH and ΔS of all the steps are explored from the DSC studies. Some of the decomposition products are identified by IR and X-ray powder diffraction studies.     

A practical synthesis of optically active arylglycines via catalytic asymmetric Strecker reaction

A practical procedure for catalytic asymmetric synthesis of optically active arylglycine derivatives via optically active α-aminonitriles has been developed. The N-benzhydryl α-arylaminonitrile intermediates were prepared in excellent yield (89–99%) and enantiomeric purity (96 to >98% ee) by enantioselective cyanation of aldimines with TMSCN/ⁱPrOH in the presence of 2.5 mol % of an easily prepared Ti/chiral amino alcohol complex at 0 °C, without requiring slow addition of the cyanating agent. The easily racemized α-aminonitrile intermediates were efficiently hydrolyzed by an aqueous HCl/TFA mixture to give the arylglycine derivatives in good yield (60–92%) and moderate to excellent enantiomeric purity (85–98% ee).     

Studies of dielectric characteristics of BaBi2Nb2O9 ferroelectrics prepared by chemical precursor decomposition method

BaBiNb₂O₉ (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG–DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size (D) and the effective strain (η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ∼1.67 μm. A relative density of ∼93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.     

Characterization of the different fractions obtained from the pyrolysis of rope industry waste

A study of the possibilities of pyrolysis for recovering wastes of the rope's industry has been carried out. The pyrolysis of this lignocellulosic residue started at 250 °C, with the main region of decomposition occurring at temperatures between 300 and 350 °C. As the reaction temperature increased, the yields of pyrolyzed gas and oil increased, yielding 22 wt.% of a carbonaceous residue, 50 wt.% tars and a gas fraction at 800 °C. The chemical composition and textural characterization of the chars obtained at various temperatures confirmed that even if most decomposition occurs at 400 °C, there are some pyrolytic reactions still going on above 550 °C. The different pyrolysis fractions were analyzed by GC–MS; the produced oil was rich in hydrocarbons and alcohols. On the other hand, the gas fraction is mainly composed of CO₂, CO and CH₄. Finally, the carbonaceous solid residue (char) displayed porous features, with a more developed porous structure as the pyrolysis temperature increased.     

Tunability of the optical properties in the Y6(W,Mo)(O,N)12 system

New fluorite-type solid solution domains have been evidenced in the system Y₆(W,Mo)(O,N)₁₂ using precursors prepared by the amorphous citrate route. The oxynitrides as well as the low temperature oxides (600 °C) crystallize in a cubic-type symmetry while the oxides annealed above 1200 °C exhibit a rhombohedral symmetry. Either cationic (W/Mo) or anionic (O/N) substitutions bring the possibility to tune the optical absorption of the yttrium tungstate Y₆WO₁₂, which potential as inorganic UV absorbers is discussed.     

Thermal degradation and evolved gas analysis: A polymeric blend of urea formaldehyde (UF) and epoxy (DGEBA) resin

A polymeric blend has been prepared using urea formaldehyde (UF) and epoxy (DGEBA) resin in 1:1 mass ratio. The thermal degradation of UF/epoxy resin blend (UFE) was investigated by using thermogravimetric analyses (TGA), coupled with FTIR and MS. The results of TGA revealed that the pyrolysis process can be divided into three stages: drying process, fast thermal decomposition and cracking of the sample. There were no solid products except ash content for UFE during combustion at high temperature. The total mass loss during pyrolysis at 775 °C is found to be 97.32%, while 54.14% of the original mass was lost in the second stage between 225 °C and 400 °C. It is observed that the activation energy of the second stage degradation during combustion (6.23 × 10⁻⁴ J mol⁻¹) is more than that of pyrolysis (5.89 × 10⁻⁴ J mol⁻¹). The emissions of CO₂, CO, H₂O, HCN, HNCO, and NH₃ are identified during thermal degradation of UFE.     

Surface structures and electrochemical characteristics of surface-modified carbon anodes for lithium ion battery

Petroleum coke and those heat-treated at 1860 °C, 2100 °C, 2300 °C 2600 °C and 2800 °C (abbreviated as PC, PC1860, PC2100, PC2300, PC2600 and PC2800) were fluorinated by elemental fluorine of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Natural graphite powder samples with average particle sizes of 5 μm, 10 μm and 15 μm (abbreviated as NG5μm, NG10μm and NG15μm) were also fluorinated by ClF₃ of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Transmission electron microscopic (TEM) observation revealed that closed edge of PC2800 was destroyed and opened by surface fluorination, which increased the first coulombic efficiencies of PC2300, PC2600 and PC2800 by 12.1–18.2% at 60 mA/g and by 13.3–25.8% at 150 mA/g in 1 mol/dm³ LiClO₄–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 in volume). Light fluorination of NG10μm and NG15μm increased the first coulombic efficiencies by 22.1–28.4% at 150 mA/g in 1 mol/dm³ LiClO₄–EC/DEC/PC (PC: propylene carbonate, 1:1:1 in volume).     

Phase transitions of CaTiO3 ceramics sintered with the aid of NaF and MgF2

New phases with initial composition (1 ? x)CaTiO₃ ? xNaF ? xMgF₂ (0 ≤ x ≤ 0.20) have been prepared at low temperature (950 °C) from mixtures of CaTiO₃ and fluorides NaF and MgF₂. The oxyfluorides obtained have been characterized by X-ray diffraction at room temperature and indexed by isotypy with orthorhombic CaTiO₃. The microstructures of these phases are observed by scanning electron microscopy. Dielectric measurements have been carried out during cooling cycle from 500 °C to room temperature at two frequencies (100 Hz, 1 kHz). Differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG) analyses have been performed, respectively, from room temperature up to 550 °C (DSC) and 920 °C (TG–DTG). The dielectric measurements revealed two anomalies which have been confirmed by DSC analyses. These phenomena are ascribed to second order phase transitions. The variation of the real permittivity with temperature is in agreement with the class I capacitor specifications. However, the dielectric losses have to be improved.     

Low-temperature performance of LiFePO4/C cathode in a quaternary carbonate-based electrolyte

The low-temperature performance of LiFePO₄/C cathode in a quaternary carbonate-based electrolyte (1.0 M LiPF₆/EC+DMC+DEC+EMC (1:1:1:3, v/v)) was studied. The discharge capacities of the LiFePO₄/C cathode were about 134.5 mAh/g (20 °C), 114 mAh/g (0 °C), 90 mAh/g (−20 °C) and 69 mAh/g (−40 °C) using a 1C charge–discharge rate. Cyclic voltammetry measurements show obviously sluggish of the lithium insertion–extraction process of the LiFePO₄/C cathode as the operation temperature falls below −20 °C. Electrochemical impedance analyses demonstrate that the sluggish of charge-transfer reaction on the electrolyte/LiFePO₄/C interface and the decrease of lithium diffusion capability in the bulk LiFePO₄ was the main performance limiting factors at low-temperature.     

Novel core–shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs

Novel core–shell SDC (Ce_0.8Sm_0.2O_1.9)/amorphous Na₂CO₃ nanocomposite was prepared for the first time. The core–shell nanocomposite particles are smaller than 100 nm with amorphous Na₂CO₃ shell of 4–6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm⁻¹. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm⁻² at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as ‘superionic highway’ in two-phase materials based on coated SDC.     

Structural characterization and activation energy of NiTiO3 nanopowders prepared by the co-precipitation and impregnation with calcinations

In this paper, we report on the formation of novel hexagonal NiTiO₃ nanopowders synthesized by the impregnation or co-precipitation methods through the thermal decomposition reaction of the precursors. The decomposition course was followed using differential thermal analysis (DTA) and thermogravimetric analysis (TGA) techniques. The intermediate decomposition products as well as the formed titanate were characterized using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. XRD patterns of the precursors calcined at 1000 °C showed the formation of the single ilmenite-type rhombohedral structure only with the impregnated precursor, while with the precipitated NiTiO₃ powders one it indicates the presence of some NiO and TiO₂ impurities. Transmission electron microscopy (TEM) exhibited loosely agglomerated hexagonal particles with uniform morphology having a size around 61 nm. The Brunauer-Emmett-Teller (BET) surface area measurements showed a type III isotherm with calculated surface area of 152 m²/g. The plot of ln σ_ac vs. temperature as a function of frequency indicates a semiconducting behavior with ferroelectric phase transition at 605 K. The calculated activation in the ferroelectric region is 0.93 eV suggests the predominance of hopping conduction mechanism. Kinetic analysis of TG data according to different integral methods showed that in the NiC₂O₄·2H₂O–TiO₂ precursor, the water molecules are coordinately bounded and the presence of TiO₂ reduces the activation energy needed to the oxalate decomposition reaction.