Fabrication and characterization of ‘self-binding’ nanocrystalline SnO2 powder based thick film ethanol sensor

Sensing response of ‘self-binding’ nanoparticles of tin dioxide powder deposited on alumina substrate has been investigated. The nanocrystalline SnO₂ powder has been derived from stannic chloride. It has been prepared through fine crystallization in liquid phase. SnO₂ powder has been characterized using SEM, TEM and XRD techniques, which reveal that the average crystallite size is of 12 nm. The slurry blobs deposited on alumina substrate of the powder-thus-prepared have been studied for sensing response to ethanol at various temperatures and concentrations. The observations reveal that the material prepared is ‘self-binding’ and is very sensitive even without catalyst.     

Fluorescence of copper, manganese and antimony ions in phosphate glass host

The paper presents a study based on luminescence characteristics of phosphate glasses containing Cu²⁺, Mn⁴⁺ and Sb³⁺. The glass samples obtained by a wet chemical route belong to Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ oxide system. The oxide composition of the glass samples is calculated to obtain a vitreous network composed of metaphosphate chains bonded by modifier ions (Li⁺, Ba²⁺ and La³⁺) and fluorescent ions. The absorption spectra of the samples were acquired in the UV domain in order to establish the excitation wavelength for each fluorescent ion. The absorption peaks of Sb³⁺ ion are ranged at 285 nm and 250 nm, Mn²⁺ ion at 280 nm and 365 nm, Cu²⁺ ion at 295 nm and 313 nm. The luminescence peaks of Cu²⁺, Mn⁴⁺ and Sb³⁺ ions are found in the visible domain at different wavelengths, depending on the oxidation state and coordination symmetry of each fluorescent ion. The fluorescence of Sb³⁺ ion has a strong signal at 450 nm and a weak one at 465 nm, Mn²⁺ ion shows a fluorescence peak at 600 nm and the pair Cu²⁺/Cu⁺ ions reveals a fluorescence emission at 460 nm.     

Electronic relaxation in zinc iron phosphate glasses

The electrical and dielectric properties of 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glasses, melted at different temperatures were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown that the dc conductivity strongly depends on the Fe(II)/[Fe(II) + Fe(III)] ratio. With increasing Fe(II) ion content from 17% to 37% in these glasses, the dc conductivity increases. Procedure of scaling conductivity data measured at various temperatures into a single master curve is given. The conductivity of the present glasses is made of conduction and conduction-related polarization of the polaron hopping between Fe(II) and Fe(III), both governed by the same relaxation time, τ. The high frequency dispersion in electrical conductivity arises from the distribution in τ caused by the disordered glass structure. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency the dispersion was investigated in terms of dielectric loss. The thermal activated relaxation mechanism dominates the observed relaxation behavior. The relationship between relaxation parameters and electrical conductivity indicates the electronic conductivity controlled by polaron hopping between iron ions.     

Effect of calcination temperature on the textural properties of 3 mol% yttria-stabilized zirconia powders

Zirconia-based ceramics have been commonly used in many different technological fields. This kind of materials have consequently received a great deal of attention. The main goal of this study was to investigate the effect of the calcination temperature on the morphological and textural properties of 3 mol% yttria-stabilized zirconia powders (3YSZ). Scanning electronic microscopy (SEM), nitrogen adsorption isotherms, thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy have been used with such an aim. Once the 3YSZ powders were dried at 100 °C they were subjected to calcination at 300, 500 or 700 °C. The calcination temperature noticeably influences the surface and textural properties of the 3YSZ powders. Textural parameters appear to be closely related to the removal of the alcohol used in the sol-gel synthesis procedure. The largest values of specific surface area and pore volumes correspond to samples prepared at 100 and 500 °C (i.e., 161 and 62 m²/g). In the first case, this fact is attributable to the removal of residual water and alcohol occluded within the powder particles whereas in the second case it may be due to the elimination of gases produced during the calcination stage.     

Influence of the polymer architecture on the high temperature behavior of SiCO glasses: A comparison between linear- and cyclic-derived precursors

Two series of cross-linked polysiloxanes, precursors for silicon oxycarbide glasses, have been synthesized from a linear and a cyclic Si-H-containing siloxane having the same chemical formula (SiCOH₄). The crosslinking has been achieved by hydrosilylation reaction with various amounts of divinylbenzene (DVB). A detailed structural characterization has been performed by ²⁹Si and ¹³C MAS NMR, FT-IR and chemical analysis. As a result, two different structural models have been proposed for the two series of resins. The two resins have been pyrolyzed at 1400 °C and the resulting SiCO ceramics characterized by X-ray diffraction. It has been shown that the stability of the amorphous silica phase present in the SiCO ceramics is strongly influenced by the molecular organization of the starting precursors. The presence of siloxane rings in the cyclic-derived polysiloxane decreases the stability of the amorphous SiO₂ and promotes the crystallization of cristobalite.     

Energy transfer studies of Ce:Eu system in phosphate glasses

The preparation of sodium phosphate glasses singly and doubly doped with rare earth ions Ce³⁺ and Eu³⁺ by melt quench method is described. The spectroscopic characterizations of the samples are done using absorption, excitation and emission spectra. The nonradiative energy transfer between trivalent cerium and europium is achieved through the phosphate lattice and the results are incorporated. The main reason of quenching of Ce³⁺ ions and the mechanism of energy transfer is mainly electric dipole-dipole in nature for Ce³⁺:Eu³⁺ system.     

Spectral properties of PbO-P2O5 glasses

The optical absorption spectra of xPbO-(100 − x) P₂O₅ glasses where x = 5, 10, 15, 20, 25, and 30 is reported. The spectral absorption of these glasses was measured in the spectral range 300-900 nm at room temperature. Optical absorption spectra show that the absorption edge has a tail extending towards lower energies. The edge shifts nearly linearly towards higher energies with increasing PbO content. The degree of the edge shift was found to depend on the PbO content and is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. The optical energy gap increases, from 2.55 to 3.05 eV by increasing PbO content from 5 to 30 mol%. The width of the localized states is decreased by increasing PbO content.     

Selective-controlled synthesis of one-dimensional strontium phosphates

Anorthic SrHPO₄ nanobelts and hexagonal Sr₁₀O(PO₄)₆ nanorods were obtained by a simple hydrothermal method without adding any surfactant as template. The as-synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM and HRTEM observations of the products revealed that the as-prepared SrHPO₄ nanobelts and Sr₁₀O(PO₄)₆ hexagonal nanorods are single crystals with their preferential growth direction along the normal of (1 0 0) and (0 0 1) planes, respectively.     

Thermal stability of amorphous Mg50Ni50 alloy produced by mechanical alloying

Amorphous Mg₅₀Ni₅₀ alloy was produced by mechanical alloying (MA) of the elemental powders Mg and Ni using a SPEX 8000D mill. The alloyed powders were microstructurally characterized by X-ray diffraction (XRD). The thermal transformation of amorphous Mg₅₀Ni₅₀ into stable intermetallics (Mg₅₀Ni₅₀ → remaining amorphous + Mg₂Ni → Mg₂Ni + MgNi₂) was analyzed using the Kissinger and isoconversional methods based on the non-isothermal differential scanning calorimetry (DSC) experiments. The apparent activation energies (E_a) and the transformation diagrams, temperature-time-transformation (T-T-T) and temperature-heating rate-transformation (T-HR-T), were obtained for both processes. A good agreement was observed between the calculated transformation curves and the experimental data, which verifies the reliability of the method utilized.     

AFM investigation of step kinetics and hillock morphology of the {1 0 0} face of KDP

Step velocities and hillock slopes on the {1 0 0} face of KDP were measured over a supersaturation range of 0<σ<0.15, where σ is the supersaturation. The formation of macrosteps and their evolution with distance from the hillock top were also observed. Hillock slope depended linearly on supersaturation and hillock geometry. The two non-equivalent sectors exhibited different slopes and step velocities. AFM shows an elementary step height of 3.7 Å, or half the unit cell height, whereas previous interferometric experiments assumed the elementary step was a unit cell. Values of the step edge energy (), the kinetic coefficients for the slow and fast directions (β_S and β_F), and the activation energies for slow and fast step motion (E_a,S and E_a,F) were calculated to be 24.0 erg/cm², 0.071 cm/s, 0.206 cm/s, 0.26 eV/molecule, and 0.21 eV/molecule, respectively. Analysis of macrostep evolution including the dependence of step height on time and terrace width on distance were performed and compared to predictions of published models. The results do not allow us to distinguish between a shock wave model and a continuous step-doubling model. Analysis within the latter model leads to a characteristic adsorption time for impurities (λ⁻¹) of 0.0716 s.     

Synthesis and structural characterization of amorphous nano-sized SiBONC ceramic powders via polymer pyrolysis

SiBONC ceramic powders have been prepared via a polymer pyrolysis route using silicon tetrachloride (SiCl₄), benzaldehyde (PhCHO), boron trichloride (BCl₃) and aniline (PhNH₂) as starting materials. Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were performed to investigate the structural characteristics of the polymer precursor and the ceramic powders. The SiBONC ceramic powders in spherical shape with a mean diameter of 50 nm are amorphous and composed of B-N, Si-O, Si-C, and SiON_x groups. The SiBONC ceramic powders were sintered at 1700 °C to a dense material which still remained amorphous.     

Influence of some foreign metal ions on crystal growth kinetics of brushite (CaHPO4·2H2O)

Brushite, CaHPO₄·2H₂O, has been precipitated at 25 °C in the presence of Mg²⁺, Ba²⁺ or Cu²⁺ at concentrations up to 0.5 mM. When initial pH is sufficiently low to exclude nanocrystalline apatite as the initial solid phase, overall crystal growth rate may be determined from simple mass crystallization by recording pH as function of time. A combination of surface nucleation (birth-and-spread) and spiral (BCF) growth was found. Edge free energy was determined from the former contribution and was found to be a linear function of chemical potential of the additive, indicating constant adsorption over a wide range of additive concentrations. Average distances between adsorbed additive ions as calculated from slopes of plots are compatible with lattice parameters of brushite: 0.54 nm for Mg²⁺, 0.43 nm for Ba²⁺ and 0.86 nm for Cu²⁺. With the latter a sharp decrease in growth rate occurred early in the crystallization process, followed by an equally sharp increase to the previous level. When interpreted in terms of the Cabrera–Vermilyea theory of crystal growth inhibition, the results are consistent with an average distance between Cu ions of 0.88 nm, in perfect agreement with the above value.     

Synthesis of Nb2O5·nH2O nanoparticles by water-in-oil microemulsion

Hydrous niobium oxide (Nb₂O₅·nH₂O) nanoparticles had been successfully prepared by water-in-oil microemulsion. They were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTG), Fourier transform infrared spectroscopy (FTIR), BET surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the nanoparticle was exactly Nb₂O₅·nH₂O with spherical shape. Their BET surface area was 60 m² g⁻¹. XRD results showed that Nb₂O₅·nH₂O nanoparticles with crystallite size in nanometer scale were formed. The crystallinity and crystallity size increased with increasing annealing temperature. TT-phase of Nb₂O₅ was obtained when the sample is annealed at 550 °C.     

Effect of different fuels on the alumina–zirconia nanopowder synthesized by sol–gel autocombustion method

In this research, a sol–gel autocombustion route has been proposed to synthesize alumina–zirconia nanopowder, using aluminium nitrate, zirconium oxychloride and various fuels such as citric acid, acetylacetone, oxalic acid and urea. The phase analysis and particle size in the presence of different fuel were compared. The results showed 100% tetragonal phase as well as particle size of 60 nm in the presence of citric acid. FTIR confirms the formation of -Al₂O₃ in corroboration with X-ray studies.     

Hydrogen embrittlement assisted by ball-milling to obtain AlCuFe nanoparticles

In this work, we show that the synthesis of AlCuFe nanoparticles can be achieved by a wet ball-milling process. The AlCuFe intermetallic system is highly sensitive to the environmental embrittlement mechanism. Taking advantage of this, the wet ball-milling was used to increase the rate of grinding and accelerate the characteristic cleavage fracture of these phases. This research was carried out by subjecting Al₆₄Cu₂₄Fe₁₂ pre-alloyed ribbons to high-energy ball-milling under different powder–humidity relationships. The pre-alloyed and milled powders were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM). High resolution electron microscopy (HREM) measurements and energy-dispersive X-ray spectroscopy (EDXS) elemental chemical mapping confirm that the nanoparticles have a BCC structure with Al–Cu–Fe chemical composition. During the wet ball-milling, the aluminum content in the ψ-phase diminishes due to embrittlement mechanism which provokes its aperiodic disarrangement. This aluminum loss could be related with a ψ–β transformation.     

Growth and properties of KTP crystals from a new flux

High-quality KTiOPO₄ (KTP) crystals were grown by a top seeded solution growth (TSSG) method using K₈P₆O₁₉–BaF₂ as a flux. The volatility of different solvents, such as K₈P₆O₁₉ (K₈), K₈–NaF, K₈–KF, and K₈–BaF₂, was measured. These fluoride additives in K₈ fluxes and their compositional effects on the growth of KTP crystals were studied and discussed. The transmissivity and optical homogeneity of KTP crystals were also measured.     

Growth and shape control of orthorhombic Fe5(PO4)4(OH)3·2H2O single crystalline dendrites

Orthorhombic Fe₅(PO₄)₄(OH)₃·2H₂O single crystalline dendritic nanostructures have been synthesized by a facile and reproducible hydrothermal method without the aid of any surfactants. The influences of synthetic parameters, such as reaction time, temperature, the amount of H₂O₂ solution, pH values, and types of iron precursors, on the crystal structures and morphologies of the resulting products have been investigated. The formation process of Fe₅(PO₄)₄(OH)₃·2H₂O dendritic nanostructures is time dependent: amorphous FePO₄·nH₂O nanoparticles are formed firstly, and then Fe₅(PO₄)₄(OH)₃·2H₂O dendrites are assembled via a crystallization-orientation attachment process, accompanying a color change from yellow to green. The shapes and sizes of Fe₅(PO₄)₄(OH)₃·2H₂O products can be controlled by adjusting the amount of H₂O₂ solution, pH values, and types of iron precursors in the reaction system.     

Characterization of chemosynthetic Al2O3-2SiO2 geopolymers

Pure chemosynthetic Al₂O₃-2SiO₂ geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin.