Thermal stability of phosphorylated cellulose modified with various transition metals

Complexes of cellulose phosphate with transition metals such as chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, silver, cadmium and mercury have been characterized by reflectance UV-visible spectra. The thermal behaviour of cellulose and the metal complexes of cellulose phosphate in air has been studied by differential thermal analysis and thermogravimetry from ambient temperature to 750°C. From the resulting data, various thermodynamic parameters for different stages of thermal degradation can be obtained following the method of Broido. The activation energies for decomposition of cellulose and metal complexes of cellulose phosphatewere found to kJ mol⁻¹.Pyrolysis-mass spectrometric studies of metal complexes of cellulose phosphate using soft ionization modes such as field ionization and field desorption give very low abundances of volatile products in the spectra compared with the yields with untreated cellulose. The IR and reflectance UV-visible spectra of the pyrolysis residues of metal complexes of cellulose phosphate indicate that dehydration takes place and the metal complexes are stable up to 250°C. At higher temperatures, a compound containing carbonyl groups is formed. A mechanism for the thermal degradation of metal complexes of cellulose phosphate is proposed which explains the generation of reduced amounts of smoke.Scanning electron microscopic studies of cellulose phosphate and its transition metal complexes showed that the fibrillar sites have mostly reacted and throw light on the morphological changes of treated cellulose in the thermal degradation range. The observed effects are of interest with respect to the flame-proofing of cellulose.     

Synthesis and properties of magnetic FeNi3 alloyed microchains obtained by hydrothermal reduction

In this paper, stoichiometric FeNi₃ alloyed microchains were successfully synthesized via a simple hydrothermal method without surfactants or external magnetic fields. The effect of synthetic parameters, including citrate concentration, the reactant molar ratio and reaction time, on the formation and morphologies of the FeNi₃ assemblies were investigated. The as-prepared chain-like structures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Furthermore, magnetic measurements by superconducting quantum interference device were also carried out to explore their magnetic properties, which confirmed that the as-prepared samples had the symmetric hysteresis loop behavior of ferromagnetic materials.     

Physicochemical characterizations and semiconducting properties of a manganese tungstate MnWO4 obtained by hydrothermal route

Journal of Solid State Electrochemistry - Manganese tungstate (MnWO4) synthesized by hydrothermal method is characterized by many physicochemical techniques. X-ray diffraction pattern (XRD)...     

Thermal stability and sintering behaviour of hydroxyapatite nanopowders

Hydroxyapatite (HA) nanopowders were synthesised following two different precipitation routes: (a) from calcium nitrate and diammonium hydrogen phosphate solutions and (b) from calcium hydroxide suspension and phosphoric acid solution. The influence of precipitation process, concentration, and synthesis temperature on HA particle size and morphology, phase composition, thermal stability, and sintering behaviour was investigated by means of: thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma–atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron microscopy (TEM, SEM) and dilatometry.     

Thermal stability of solid solutions obtained by mechanical alloying

Summary The heats of ordering for mechanochemically synthesized nano-sized supersaturated solid solutions were demonstrated for Ni-In, Ni-Sn, Ni-Al, Cu-Sn, Cu-Hg systems. It is shown that increasing concentration of doping element leads to decreasing of decomposition temperature and to increasing of decomposition enthalpy. The concentration heterogeneity of doping elements in mechanochemically synthesized supersaturated solid solutions was found. The reactivity of alloys Cu 20 mass % Sn for commercial powder and MA powder was investigated.     

Selective hydrothermal microwave synthesis of various manganese dioxide polymorphs

Hydrothermal microwave treatment of mixed solutions of potassium permanganate and hexamethylenetetramine within the pH range 0.5–6.9, resulted in various polymorphs of nanocrystalline manganese dioxide: α-MnO₂ (cryptomelane), γ-MnO₂ (nsutite), β-MnO₂ (pyrolusite), and δ-MnO₂ (birnessite). The pH values of the medium at which single-phase samples form were determined.     

Influences of Co doping on the structural,optical and magnetic properties of ZnO nanorods synthesized by hydrothermal route

Pure and Co-doped ZnO nanorods have been synthesized by a hydrothermal process. The structure, morphology and properties of as-prepared samples have been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectrometer as well as by superconducting quantum interference device (SQUID). The structure and morphology analyses show that Co doping can slightly impede the ZnO crystallinity, influence the nanorods morphology, but cannot change the preferred growth orientation of ZnO nanorods. The amount of Co doping contents is about 3.0 at% in ZnO nanorods and dopant Co²⁺ ions substitute Zn²⁺ ions sites in ZnO nanocrystal without forming any secondary phase. The optical measurements show that the Co doping can effectively tune energy band structure and enrich surface states in both UV and VL regions, which lead to novel PL properties of ZnO nanorods. In addition, ferromagnetic ordering of the as-synthesized Zn_1?xCo_xO nanorod arrays has been observed at room temperature, which should be ascribed to sp–d and d–d carrier exchange interactions and presence of abundant defects and oxygen vacancies.     

Thermal stability of polymer compositions with modified alumina

Thermal stability and combustibility of polymer compositions: foam plastic (trade mark PEN-I) based on an epoxide novolak block copolymer, and poly(methyl methacrylate, containing modified alumina of various dispersion as a filler, were investigated.     

Thermal stability and degradation of chitosan modified by benzophenone

N-(biphenylmethylidenyl) chitosan polymer was prepared, characterized and thermal stability was compared with chitosan. Thermal degradation products of the modified polymer were identified by GC-MS technique. It seems that the mechanism of degradation of the prepared polymer is characterized by formation of low molecular weight radicals, followed by random scission mechanism along the backbond chain.     

Nickel nanoparticles obtained by a modified polyol process: synthesis, characterization, and magnetic properties

The synthesis of nickel nanoparticles using poly(N-vinilpyrrolidone) (PVP) as protective agent was studied. The nanoparticles were prepared in air according to a modified polyol route, using nickel chloride as precursor and sodium borohydride as reducing agent. Samples with different nickel/PVP ratio were obtained. The X-ray diffraction and transmission electron microscopy (TEM) measurements indicate the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of 3.8 nm and good size dispersion. Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) data show an effective interaction between the nickel nanoparticles surface and the carboxyl oxygen atoms of PVP. Magnetic measurements show single-domain nonideal superparamagnetism behavior due to dipolar magnetic coupling between particles.     

Thermal stability of paracetamol and its pre-formulates obtained by spray drying

Organobentonites were synthesized by treating Na-bentonites (Wyomingand Re?adiye) with cetylpyridinium chloride (CPC) using ion exchangemethod. The difference in the basal spacing by 0.65 Å and a higher massloss by 13.32% of organobentonite (Wyoming) in the temperature range 200–550°Ccomparing with that of organobentonite (Re?adiye) were in conformitywith the CEC values of organobentonites. The HOH stretching and bending peaksof bentonites became sharper following the treatment with the organo-cation.The intensity decrease of the Al–OH band for organobentonite (Re?adiye)and in particular, the significantly higher amount of m-cresolretained by the organobentonite of lower CEC than that by the organobentonite(Wyoming) indicate the influence of the CP cation on the adsorption process.     

Thermal stability and UV-shielding properties of polymethyl methacrylate and polystyrene modified with calcium carbonate nanoparticles

The influences of nanosized CaCO₃ on the thermal and optical properties embedded in poly(methyl methacrylate) (PMMA) and polystyrene (PS) were investigated. Calcium carbonate nanoparticles were synthesized by in situ deposition technique, and its nano size (32–35 nm) was confirmed by scanning electron microscope (SEM) and X-ray studies. Nanocomposites samples of PMMA/CaCO₃ and PS/CaCO₃ were prepared with different filler loading (0–4 wt%) of CaCO₃ nanoparticles by solution mixing technique. The Fourier transform infrared analysis confirmed that CaCO₃ nanoparticles were present in the polymers matrices. The morphology and elemental composition of nanocomposites were evaluated by SEM and energy dispersive X-ray spectroscopy. The thermal properties of nanocomposites were characterized by differential scanning calorimetric, thermogravimetric, and differential thermogravimetry analysis, and the results indicate that the incorporation of CaCO₃ nanoparticles could significantly improve the thermal properties of PMMA/CaCO₃ and PS/CaCO₃ nanocomposites. The glass transition temperature (T _g ) and decomposition temperature (T _d ) of nanocomposites with 4 wt% of CaCO₃ nanoparticles were increased by 30 and 24 K in case of PMMA/CaCO₃ and 32  and 15 K in the case of PS/CaCO₃ nanocomposites, respectively. The obtained transparent nanocomposites films were characterized using UV–Vis spectrophotometer which shows the transparencies of nanocomposites are almost maintained in visible region while the intensity of absorption band in ultraviolet (UV) region is increased with CaCO₃ nanoparticles contents and these composites particles could enhance the UV-shielding properties of polymers.     

Thermal stability of modified telechelic polystyrenes

The thermal stability of telechelic polystyrenes bearing quaternary ammonium iodide or ammonium sulfonate end groups is presented. It appears that the ammonium iodide functions are stable below 200°C. Above that temperature, the polystyrene irreversibly looses its functional end groups. The weight loss then observed leads to the conclusion that a Hofmann-type degradation mechanism is likely to take place. In contrast, the ammonium sulfonate-terminated polystyrene begins to degrade at 180°C and leads to a polymer which is no longer end-capped with sulfonic acid or sulfonate groups. This behavior is of importance, especially for the study of multiblock ionic copolymers which are prepared by blending two telechelic polymers, one of them bearing sulfonic acid end groups and the other one tertiary amine functional groups. © 1993 John Wiley & Sons, Inc.     

Dielectric properties of Ni-doped Ba0.5Sr0.5TiO3 ceramics prepared with hydrothermal synthesized nanopowders

Ba_0.5Sr_0.5Ti_1?xNi_xO₃ (BSTN) ceramics were prepared from BSTN nanopowders synthesized by a hydrothermal method. The phase and microstructure of samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy. XRD results indicate a cubic structure of the pure BST nanopowders. The cubic structure can be converted to the orthorhombic phase with increasing of Ni content to x = 0.01 and returned to the cubic structure with the presence of Ni(OH)₂ impurity phase for x = 0.03 and 0.05. However, the BSTN ceramics sintered at 1,200 °C for 3 h revealed the orthorhombic phase structure with NiO impurity phase for all Ni content. The doping of Ni in Ba_0.5Sr_0.5TiO₃ structure can increase the grain size of samples from 1.47 to 3.26 μm. The dielectric constant, loss tangent (tanδ) and phase transition temperature of BSTN ceramics were reduced with increasing Ni content.     

Influence of the synthesis media in the properties of CuO obtained by microwave-assisted hydrothermal method

Copper monoxide (CuO) was successfully obtained by microwave-assisted hydrothermal method, using different conditions—in a solution without base, in a solution alkalinized with NaOH or with NH₄OH. The powders were analyzed by thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared spectroscopy, UV–Visible spectroscopy, and scanning electronic microscopy. XRD results showed that CuO was obtained with monoclinic structure and without secondary phases. Thermal analysis and infrared spectra indicated the presence of acetate groups on the powder surface. TG curves also showed a mass gain assigned to the Cu(I) oxidation indicating that a reduction possibly occurred during synthesis. The high and broad absorption band in the UV–Vis spectroscopy from 250 to 750 nm indicated the coexistence of Cu(II) and Cu(I), confirming the Cu(II) reduction, inside the CuO lattice. It was also possible to confirm the Cu(II) reduction by a displacement of the Me–O vibration bands observed in the IR spectra at around 500 cm⁻¹.     

Tuning physical surface properties of tin dioxide nanopowders using zinc oxide as template

With a view to energetic and (opto)electronic applications, tin (IV) oxide (SnO₂) nanoparticles have been successfully prepared at the nanoscale by a templating approach based on the use of zinc (II) oxide (ZnO) as template. The procedure consisted in preparing a mixture of tin precursor and template, subsequently calcined at 650 °C under air to lead to the formation of a SnO₂/ZnO composite material. Finally, the material was washed with an alkali solution to remove the template. The template/tin precursor mass ratio was varied in order to tailor the tin (IV) oxide material, especially with a view to main particle size. The resulting SnO₂ nanomaterials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption and electron microscopy. The tin (IV) oxide nanomaterial exhibited enhanced textural and physical surface properties (particle size, surface area, pore size) correlated to an increasing template/tin precursor mass ratio. For instance, from optimized experimental conditions, the specific surface area and pore volume were heightened twofold, reaching values of 49 m²/g and 0.32 cm³/g, respectively.     

Thermal stability of wüstite structure modified with calcium cations

Wüstite modified with calcium cations was prepared by high temperature fusion. M?ssbauer spectroscopy and X-ray diffraction were employed to identify wüstite phases before and after thermal treatment at elevated temperatures in vacuum with a base pressure of 1.33 Pa for 60 h. Experimental results demonstrated that the location of calcium cations inside the wüstite structure could prevent disproportionation into magnetite and α-iron. This revised version was published online in August 2006 with corrections to the Cover Date.