Study of purification process of single-walled carbon nanotubes by thermoanalytical techniques

The thermal behaviour of commercial Carbolex single-walled carbon nanotubes (SWCNTs) both as-received and after purification by a novel method has been studied by thermogravimetric/derivative thermogravimetric/difference thermal analysis (TG/DTG/DTA). Purification from metal catalysts (Ni and Y) has been successfully obtained using 0.1 M I₂ in iso-propanol instead of the usual concentrated HNO₃. The final residues of thermal analysis have been characterised by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The gathered results showed that the as-received SWCNTs burns out in a one-step between 573 and 923 K, whereas the SWCNTs treated with HNO₃ become highly hygroscopic. The I₂-iso-propanol-treated SWCNTs showed three overlapped exothermic peaks between 500 and 973 K in the DTA curve, which allowed separating amorphous carbon from SWCNTs by air-thermal treatment at 573 K. The graphite-like compounds, which are present in both untreated and treated SWCNTs, does not burn up to 1173 K.     

Zum Chemischen Transport im System Mg/Mo/O ‐ Experimente und Modellrechnungen

On the Chemical Vapour Transport in the Mg/Mo/O System ‐ Experiments and Model Calculations Single crystals of MgMoO₄ and Mg₂Mo₃O₈ have been obtained via chemical vapour transport in a temperature gradient 1273 to 1173 K using Cl₂ and Br₂ as transport agents. Pure powders of the ternary compounds have been used as starting materials as well as mixtures of three coexisting phases. The observed transport behaviour is compared with results of thermodynamical model calculations. The influence of source composition, transport agent and the moisture contents is described in detail.     

Chemischer Transport ternärer Indiummolybdate

Chemical Vapor Transport of Ternary Indium Molybdates An isothermal section of the phase diagram of the system In/Mo/O at 1273 K was established by isothermal equilibration and XRD analyses of quenched samples. The chemical vapor transport of In₂Mo₃O₁₂ was investigated in dependence on mean transport temperature (823 K to 1123 K) and amount of transport agent (Cl₂ or Br₂). The observed transport behaviour is compared with results of thermodynamical calculations and the influence of mean temperature, transport agent and moisture contents is described in detail. Single crystals of the metal rich compound InMo₄O₆ were grown by chemical vapor transport in a temperature gradient 1273 K to 1173 K using H₂O as transport agent. The gaseous compound In₂MoO₄(g) accounts for the chemical vapor transport of molybdenium compounds in the metal rich part of the ternary phase diagram In/Mo/O.     

Thermogravimetric analysis on gasification reactivity of Hailar lignite

Comparative studies on the Hailar lignite pyrolysis/gasification characteristics at N₂/CO₂ atmosphere and the influence of inherent mineral matters, external ash and pyrolysis temperature on its reactivity during gasification at CO₂ atmosphere were conducted by non-isothermal thermogravimetric analysis, FTIR, and X-ray diffraction (XRD) analysis. Thermogravimetric test results show that the atmosphere of N₂ or CO₂ almost has no effects on the pyrolysis behavior, and the gasification reaction under CO₂ atmosphere occurs over 943?K at the heating rate of 40?K?min^?1. The external ash prepared at 1173 and 1223?K shows a certain catalytic effect on promoting the gasification reaction, although the inherent mineral matters of Hailar lignite are found in stronger catalytic effects on gasification than the external ash. The lignite gasification reactivity decreases with increasing pyrolytic temperature between 1073 and 1273?K.     

Zum Chemischer Transport ternärer Übergangsmetall‐ und Erdalkaliwolframate MWO4 mit Chlor

On the Chemical Vapor Transport of Ternary Transition Metal‐ and Earth Alkaline Tungstates MWO₄ with Chlorine The chemical vapor transport of transition metal tungstates MWO₄ (M=Mn, Co, Ni, Cu, Zn, Cd) was investigated in dependence on mean transport temperature (923 K to 1223 K) and amount of transport agent Cl₂. All tungstates migrate in a temperature gradient ΔT = 100 K from the region of higher temperature to the lower temperature with migration rates of 0.5 to 8 mg/h depending on experimental conditions. The transport behaviour was determined by continuous measurement of mass change during the transport experiments. The results were compared to thermo chemical calculations and the influence of moisture content discussed in detail. MgWO₄ migrates under the influence of Cl₂ in a temperature gradient 1273 K to 1173 K (migration rate 0.7 mg/h), CaWO₄ and SrWO₄ in a temperature gradient 1423 K to 1323 K (migration rate <0.1 mg/h).     

Thermodynamic studies on the ferroelectric phase transition in neutron irradiated (LixK1−x)2SO4 crystals at high temperature

Thermodynamic studies of (Li_xK_1?x)₂SO₄, LKS, mixed crystals have been made in the concentration range (x=0.1, 0.2, ...,x=0.5). The thermal behaviour has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the thermal neutron irradiations on the thermal properties of mixed crystals was studied. The results showed a change in the transition temperatureT _c, as well as the value of specific heatC _p at transition temperature, due to the change of stoichiometric ratio and radiation doses. The change of enthalpy and entropy of mixed crystals have been estimated numerically.     

Studies on Thermal Stability of Titanium Substituted Iron Molybdenum Spinel Oxide

The thermal stability of the solid solutions of Fe₂Mo_1–xTi_xO₄ for x=0.0 to 1.0 in air, had been investigated in the temperature range 303–1173 K using differential thermal analysis and thermogravimetry (DTA and TG). The products obtained by heating the sample in air, at different temperatures, have been characterized by X-ray diffraction and IR-studies. The results show that all the ferrite samples undergo surface oxidation during initial heating. On heating to 823 K, the samples undergo oxidation of the octahedral site cations only and forma cation deficient spinel phase. On further heating in air, the ferrites undergo complete oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and textural evolution of alumina particles with mesoporous structures

Alumina particles with mesostructures were synthesized through a chemical precipitation method by using different inorganic aluminum salts followed by a heterogeneous azeotropic distillation and calcination process. The obtained mesoporous γ-alumina particles were systematically characterized by the X-ray diffraction, transmission electron microscopy and nitrogen adsorption-desorption measurement. Effects of the aluminum salt counter anion, pH value and the azeotropic distillation process on the structural or textural evolution of alumina particles were investigated. It is found that Cl⁻ in the reaction solution can restrain the textural evolution of the resultant precipitates into two-dimensional crystallized pseudoboehmite lamellae during the heterogeneous azeotropic distillation, and then transformed into γ-Al₂O₃ particles with mesostructures after further calcination at 1173 K, whereas coexisting SO₄²⁻ can promote above morphology evolution and then transformed into γ-Al₂O₃ nanofibers after calcination at 1173 K. Moreover nearly all materials retain relatively high specific surface areas larger than 100 m² g⁻¹ even after calcinations at 1173 K.     

Electrical conduction nature and phase transition in CaTi1−x FexO3−δ (x = 0.1–0.5)

Transport numbers for oxygen ions and protons are measured by an emf method in the system CaTi_1?x Fe_xO_3?δ (x = 0.1–0.5) in the oxidizing and reducing atmospheres in the temperature interval 973–1173 K. It is shown that the compounds under study are mixed ion-electron conductors at small iron concentrations and electron conductors, at large iron contents. The proton conductivity in the compounds is very poor and does not exceed 0.5% in air. On the basis of the temperature dependences of transport numbers for ions and linear expansion, it is established that the CaTi_0.9Fe_0.1O_3?δ system has a phase transition of a second order in a reducing environment at 1020–1050 K. The total and partial electron conductivities of CaTi_0.9Fe_0.1O_3?δ are studied as a function of the partial pressure of oxygen at 1173 K. The nature of electroconduction in CaTi_1?x Fe_xO_3?δ is discussed.     

Solvent Dependent Spin‐Crossover and Photomagnetic Properties in an Imidazolylimine FeII Complex

The synthesis and physico‐chemical characterization of an Fe^II complex [Fe( L1 )₃](ClO₄)₂?CH₃CN?0.5H₂O, 1 , incorporating a bidentate imidazolylimine‐based ligand are reported. Complex 1 crystallises as the mer‐isomer and the crystal lattice is replete with hydrogen bonding interactions between ClO₄^? anions, solvent molecules and imidazole N‐H groups. Variable‐temperature structural, magnetic, photomagnetic and optical reflectivity techniques have been deployed to fully characterise the spin‐crossover (SCO) behaviour in 1 along with its desolvated phase, 1?desolv . Variable‐temperature (1.8–300 K) magnetic‐susceptibility measurements reveal a broad two‐step full SCO for 1 (T_1/2=158 and 184 K) and photomagnetic experiments at 10 K under white‐light irradiation revealed complete photo‐induced SCO. 1?desolv displays considerably different magnetic behaviour with sharp single‐step SCO accompanied by a thermal hysteresis (T_1/2↑=105 K, T_1/2↓=95 K) in addition to full photo‐induced SCO at lower temperatures.     

Combining thermal analysis with other techniques to monitor the decomposition of poly(m-phenylene isophthalamide)

The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acid-Base properties of MgCuAl mixed oxides

MgCuAl layered double hydroxides (LDHs) with a hydrotalcite like structure containing different proportions of Mg²⁺ and Cu²⁺ cations have been prepared. Thermogravimetry and X-ray diffraction data indicated that the transformation of LDH into mixed oxides is effective after calcination at 723 K, irrespective of the composition. The acid-base properties of these mixed oxides have been investigated using adsorption microcalorimetry and X-ray photoelectron spectroscopy with NH₃ (for acidity) and SO₂ (for basicity) as probe molecules. Their catalytic behaviour for the conversion of cyclohexanol has been tested. The acid-base properties and the selectivity of catalysts has been related to their composition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural investigations of silicon-rich CVD-SiC

Silicon Carbide (SiC) and Silicon Carbide with free Silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using an CH₃SiCl₃-H₂-Ar gas mixture at temperatures of 1173 to 1323 K. The structure of these films were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The effects of crystallinity, morphology and Si-concentration of the deposits were examinated in some detail.     

Crystallochemical causes of the different thermal properties of [Cu(py)2(NCS)2] and [Cu(4-Mepy)2(NCS)2] complexes

The crystal structures and thermal behaviour of [Cu(py)₂(NCS)₂] (at 293) and [Cu(4-Mepy)₂(NCS)₂] and 180 K) complexes have been compared with their different temperature behaviour. It was found that the thermal stability of coordinated thiocyanate ligands in the course of thermal decomposition depends not only on the properties of the ligand L, but it is related to the arrangement of the thiocyanatocopper chains in the crystal structures.     

Thermal runaway analyses for two organic peroxides with H2O and dry fire-extinguishing chemicals by DSC and VSP2

In recent years, organic peroxides, including methyl ethyl ketone peroxide (MEKPO) and cumene hydroperoxide (CHP), have often caused thermal runaway reactions, fires, and thermal explosions worldwide. Under normal circumstances, H₂O and dry fire-extinguishing chemicals are often employed to eliminate fire situations. We evaluated the thermal runaway reaction for MEKPO and CHP mixed with H₂O and dry fire-extinguishing chemicals by differential scanning calorimetry, and thermal runaway reaction for CHP mixed with dry fire-extinguishing chemicals by vent sizing package 2. The results showed that ABC dry chemical, BC dry chemical, and XBC dry chemical all caused the decomposition of MEKPO to occur at lower onset temperature and H₂O caused the ΔH _d of MEKPO to become higher. On the other hand, H₂O and XBC dry chemical induced the decomposition of CHP to occur at lower onset temperature as well as lower thermal explosion temperature. The maximum of self-heating rate ((dT/dt)_max) and the maximum pressure-rise rate ((dP/dt)_max) of CHP mixed with dry fire-extinguishing chemicals were measured lower than CHP alone. The results indicated that MEKPO and CHP are highly hazardous when mixed with H₂O and some dry fire-extinguishing chemicals. In view of loss prevention, the results can be useful references for fire fighters dealing with thermal upsets in chemical plants.     

Properties of NiO–ThO2 Mixed Oxides From Hydroxides and Their Hydrogen Reducibility Behaviour

Some physico-chemical properties of NiO–ThO₂ mixed oxides of various compositions have been investigated. The presence of strongly bound constitutional water in the hydrogel of reactive forms of thorium dioxide, determined by their origin (thermal decomposition of mixed hydroxides) caused the different reduction behaviour as compared with other mixed oxide systems containing the only, thermodynamically less stabile reducible component. The significant effects of the thermal treatment in oxygen atmosphere, pre-irradiation by the gamma rays or accelerated electrons under various conditions (in air or in water suspension) as well as of surface chemical activation with a platinum complex on the reactivity of mixed oxides or reoxidized samples during their hydrogen reduction have been also proved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pr<Subscript>5</Subscript>Mo<Subscript>3</Subscript>O<Subscript>16 + δ</Subscript>: A New Anode Material for Solid Oxide Fuel Cells

The thermomechanical and electrical conductivity properties of praseodymium molybdate Pr₅Mo₃O_{16 + δ} prepared by a solid-phase method were studied. The electrical conductivity of praseodymium molybdate samples measured at temperatures in the range 373–1173 K with the oxygen partial pressure in the gas of 10^–3 to 0.21 atm was found to increase from ~10^–7 to ~10^–2 S/cm and to be almost independent of oxygen pressure. It is for the first time that electrical conductivity a reductive atmosphere (Ar/H₂ 5%) was found to increase from 0.1 to 1.2 S/cm in the same temperature range. Studies of the chemical stability of Pr₅Mo₃O_{16 + δ} with respect to solid electrolytes showed the absence of chemical reactions with GDC at 1273 K and with YSZ at 1223 K. The combination of these properties evidences for the potential of praseodymium molybdate for use as an anode material for solid oxide fuel cells (SOFCs).     

Thermal stability of crandallite CaAl<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>5</Subscript>·(H<Subscript>2</Subscript>O)

Thermogravimetry combined with evolved gas mass spectrometry has been used to characterise the mineral crandallite CaAl₃(PO₄)₂(OH)₅·(H₂O) and to ascertain the thermal stability of this ‘cave’ mineral. X-ray diffraction proves the presence of the mineral and identifies the products of the thermal decomposition. The mineral crandallite is formed through the reaction of calcite with bat guano. Thermal analysis shows that the mineral starts to decompose through dehydration at low temperatures at around 139 °C and the dehydroxylation occurs over the temperature range 200–700 °C with loss of the OH units. The critical temperature for OH loss is around 416 °C and above this temperature the mineral structure is altered. Some minor loss of carbonate impurity occurs at 788 °C. This study shows the mineral is unstable above 139 °C. This temperature is well above the temperature in the caves of 15 °C maximum. A chemical reaction for the synthesis of crandallite is offered and the mechanism for the thermal decomposition is given.     

Pentastrontium Tris[tetraoxovanadate(V)] catena‐Monoxocuprate(I), Sr5(VO4)3(CuO) – An Apatite Derivative with Inserted Linear 1Ë[CuO]1– Chains

Sr₅(VO₄)₃(CuO) was prepared via solid state reactions from mixed powders of the metal oxides or carbonates in corundum crucibles in air (1173–1740 K). The compound is transparent and stable in air. The color changes with the preparation temperature from light gray (1173 K) to gray (1740 K). The crystal structure (space group P6₃/m, No. 176; Z = 2; a = 10.126 Å, c = 7.415 Å) is a derivative of the apatite Ca₅(PO₄)₃OH, and is characterized by isolated [VO₄]^3– anions (d(V–O) = 1.710 Å) and infinite linear ^1∞[CuO]^1– chains (d(Cu–O) = 1.854 Å) inserted in the channels parallel to the hexagonal axis. The compound prepared at 1740 K contains vacancies at the copper and oxygen positions of the linear chains (about 10% and 5%, respectively).     

Thermal Stability of 4-Chloro-3-Nitro- and 5-Chloro-2-Nitrobenzoates of Rare Earth Elements

The physico-chemical properties and thermal stabilities in air of rare earth element 4-chloro-3-nitrobenzoates and 5-chloro-2-nitrobenzoates were compared and the influence of the positions of the Cl and NO₂ substituents on their thermal stabilities was investigated. The complexes of both series are crystalline, hydrated or anhydrous salts with colours typical of Ln³⁺. The carboxylate group in these complexes is a bidentate, chelating ligand. The NO₂ group in the chloronitro complexes does not undergo isomerization. The thermal stabilities of the 4-chloro-3-nitrobenzoates of Y and the lanthanides were studied in the temperature range 273-1173 K, but those of the 5-chloro-2-nitrobenzoates of these elements were studied only at 273-523 K, because they decompose explosively above 523 K. The positions of the Cl and NO₂ substituents on the benzene ring influence the thermal properties of the complexes and their decomposition mechanisms. The different thermal stabilities of the complexes are connected with various inductive and mesomeric effects of the Cl and NO₂ substituents on the electron density in the benzene ring. This revised version was published online in July 2006 with corrections to the Cover Date.