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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

The Characteristics of Green Calcium Oxide Derived from Aquatic Materials

Thermogravimetric Analysis of three aquatic materials, i.e. cuttlebone, mussel shell and oyster shell, and other physicochemical characteristics were investigated. The highest decomposition rates of aquatic materials under two surrounding gases, i.e. oxygen and nitrogen, exhibited no significant difference for cuttlebone (3.6×10^-5-4.8×10^-5 mg s^-1 mg_initial^-1 at heating rate 5 °C/min and 11.8 ×10^-5 -12.5×10^-5 mg s^-1 mg_initial^-1 at heating rate 15 °C/min) and mussel shell (3.4×10^-5- 5.2×10^-5 mg s^-1 mg_initial^-1 at heating rate 5 °C/min and 11.9×10^-5 – 12.4×10^-5 mg s^-1 mg_initial^-1 at heating rate 15 °C/min), while oyster shell provided the higher decomposition rate under nitrogen surrounding gas (7.6×10^-4 mg s^-1 mg_initial^-1 at heat rate 5 °C/min and 21.53×10^-4 mg s^-1 mg_initial^-1 at heating rate 15 °C/min). This is probably because of the difference in their starting crystalline structures, i.e. aragonite (cuttlebone and mussel shell) and calcite (oyster shell). The cubic calcium oxides were prepared by calcination of three aquatic materials under oxygen and nitrogen surrounding gases at 5 °C/min ramping to 850 °C for 2 hours. All resulting calcium oxides obtained from oxygen atmosphere provided only cubic crystalline phases and the adsorption-desorption isotherms (IUPAC Type III), whereas the calcinations under nitrogen surrounding gas gave a presence of calcium hydroxide crystalline or hydroxyl- contaminate existing with cubic calcium oxide that influences on the strength and the number of carbon dioxide adsorption sites. The specific surface area of all resulting calcium oxides ranged from 0.1 – 1.5 m²/g and the average pore diameter was found in the range of 40-60 nm. The the number of basic sites belonging to CaO derived from Oyster shell or Cuttlebone were improved while firing under oxygen atmosphere. The suitable firing condition is at the low heating rate to develop porous materials.     

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).     

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.     

Utilization of Low-grade Iron Ore in Ammonia Decomposition

Due to its cleanliness, fast energy cycle, and convenience of energy conversion, hydrogen has been regarded as the new energy source. Conventional process to produce hydrogen yield large amount of CO as byproduct. Moreover, the hydrogen storage and transportation have become the drawbacks in hydrogen economy. Thus, there has been increased interest in the hydrogen transportation medium as alternatives from the conventional process to produce and transport hydrogen. Ammonia has drawn worldwide attention as the most reliable hydrogen transportation medium. Through the decomposition of ammonia, hydrogen and nitrogen gas were produces as the byproduct without any CO or CO₂ emission. In this experiment, the ore were introduced as the medium for ammonia decomposition. The ore were put into quartz tube reactor and were dehydrated at 400 °C for 1 hour, then hydrogen reduced for 2 hours before and undergone ammonia decomposition at 500-700 °C for 3 hours. The effects of temperature to the % conversion of ammonia decomposition were also studied. Ammonia decomposition at higher temperature gives higher conversion. As seen in the results, the NH₃ conversion decreased with increasing time and the value after 3 hours of reaction increased in the sequence of 500 °C<600 °C< 700 °C. During ammonia decomposition, nitriding of iron occurred. The relation between temperature and the nitriding potential, K_N is also investigated. The purpose of this study is to investigate the utilization of low-grade ore as medium for ammonia decomposition to produce hydrogen.     

Nonstoichiometry,point defects and magnetic properties in Sr2FeMoO6−δ double perovskites

The phase stability, nonstoichiometry and point defect chemistry of polycrystalline Sr₂FeMoO_6?δ (SFMO) was studied by thermogravimety at 1000, 1100, and 1200 °C. Single-phase SFMO exists between ?10.2≤log pO₂≤?13.7 at 1200 °C. At lower oxygen partial pressure a mass loss signals reductive decomposition. At higher pO₂ a mass gain indicates oxidative decomposition into SrMoO₄ and SrFeO_3?x. The nonstoichiometry δ at 1000, 1100, and 1200 °C was determined as function of pO₂. SFMO is almost stoichiometric at the upper phase boundary (e.g. δ=0.006 at 1200 °C and log pO₂=?10.2) and becomes more defective with decreasing oxygen partial pressure (e.g. δ=0.085 at 1200 °C and log pO₂=?13.5). Oxygen vacancies are shown to represent majority defects. From the temperature dependence of the oxygen vacancy concentration the defect formation enthalpy was estimated (ΔH_OV=253±8 kJ/mol). Samples of different nonstoichiometry δ were prepared by quenching from 1200 °C at various pO₂. An increase of the unit cell volume with increasing defect concentration δ was found. The saturation magnetization is reduced with increasing nonstoichiometry δ. This demonstrates that in addition to Fe/Mo site disorder, oxygen nonstoichiometry is another source of reduced magnetization values.     

Coupling of terminal alkynes by RuHXL2 (X = Cl or N(SiMe3)2, L = PiPr3)

The compounds RuL₂HX, where L = PⁱPr₃ and X = Cl or N(SiMe₃)₂, are catalyst precursors for dimerization of terminal alkynes to enynes and also to cumulenes at 23 °C; selectivity among these products is X-dependent, but not high. Conversion of Ru species onto the catalytic cycle was undetectably small, so alternative approaches to understanding the catalytic mechanism were employed: stoichiometric reactions, independent synthesis of candidate intermediates, and trapping with CO. These show the intermediacy of vinylidenes and vinyl compounds, and reveal conversion of cumulenes to the thermodynamically more stable enynes.     

Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn, Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid at a temperature of 90 °C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M_s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid with current density of 0.5 mA/cm² was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods.     

Thermal behaviour of malonic acid,sodium malonate and its compounds with some bivalent transition metal ions

Characterization, thermal stability and thermal decomposition of transition metal malonates, MCH₂C₂O₄·nH₂O (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)), as well as, the thermal behaviour of malonic acid (C₃H₄O₄) and its sodium salt (Na₂CH₂C₂O₄·H₂O) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), infrared spectroscopy, TG-FTIR system, elemental analysis and complexometry. The dehydration, as well as, the thermal decomposition of the anhydrous compounds occurs in a single step. For the sodium malonate the final residue up to 700 °C is sodium carbonate, while the transition metal malonates the final residue up to 335 °C (Mn), 400 °C (Fe), 340 °C (Co), 350 °C (Ni), 520 °C (Cu) and 450 °C (Zn) is Mn₃O₄, Fe₂O₃, Co₃O₄, NiO, CuO and ZnO, respectively. The results also provided information concerning the ligand's denticity, thermal behaviour and identification of some gaseous products evolved during the thermal decomposition of these compounds.