Thermodynamic studies on LaFeO3(s)

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO₃(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:

H°(T)−H°(298.15 K)(J mol⁻¹)(±1.2%)=−36887.27+103.53 T(K)+25.997×10⁻³T²(K)+11.055×10⁵/T(K).

The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:

C_p,m°(T)(JK⁻¹mol⁻¹)=103.53+51.994×10⁻³T(K)−11.055×10⁵/T²(K).

From the measured e.m.f. of the cell, (−)Pt/(LaFeO₃(s)+La₂O₃(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant Δ_fG_m°(T) values from the literature, the Δ_fG_m°(LaFeO₃, s, T) was calculated, and is given as:

Δ_fG_m°(LaFeO₃, s, T)(kJmol⁻¹)(±0.72)=−1319.2+0.2317T(K).

The calculated Δ_fH_m°(LaFeO₃, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJ mol⁻¹ and 128.9 J K⁻¹ mol⁻¹, respectively.     

Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 × 10² exp(−39500/RT)% for the former alloy and c_s = 4.19 × 10² exp(−40200/RT)% for the latter, where R is in J mol⁻¹ K⁻¹ (8.314 J mol⁻¹ K⁻¹) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. Appropriate diffusion coefficients vary from 0.16 × 10⁻⁹ to 2.02 × 10⁻⁹ m² s⁻¹. With both alloys, the Ni₃Sn₄ intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni₃Sn₄ layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.     

Crystal structure of single phase and low sintering temperature of α-cordierite synthesized from talc and kaolin

Cordierite body with the formulation of 2.8MgO·1.5Al₂O₃·5SiO₂ was prepared from talc and kaolin as the basic raw materials. Following glass crystallization technique the glass powder was successfully heat treated at 900 °C for 2 h to form a single-phase α-cordierite. The crystal structure of α-cordierite was analysed using X-ray diffraction technique and the Rietveld structural refinement method. Differential thermal analysis (DTA), Fourier-transform infrared (FTIR), field emission scanning electron microscopy (FESEM), coefficient of thermal expansion (CTE) and dielectric properties were also performed. Results show that the materials crystallized as a hexagonal structure with space group of P6/mcc and the room temperature lattice parameters are a = 9.743742 (Å) and c = 9.389365 (Å). FTIR analysis on the glass revealed that only silicate species is the only unit that exists in the glass network. DTA also confirmed that α-cordierite completely formed after 13.5 min of isothermal heating at 900 °C. Coefficient of thermal expansion of synthesized α-cordierite is 2.5 × 10⁻⁶ °C⁻¹. The dielectric constant is between 5.0 and 5.5 for 1 MHz and 1.8 GHz, respectively, and the dielectric loss is in the range 10⁻². FESEM micrographs revealed that the material is fully densified.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Magnetite stability in aqueous solutions as a function of temperature

Magnetite solubility, as a function of temperature and partial hydrogen pressure, with reference to the typical conditions of the operating fluid of a steam generator of a thermal power plant, has been studied by rigorously solving the problem of equilibria and adopting the scheme proposed by Sweeton and Baes [J. Chem. Thermodynamics2, 479 (1970)]. Stoichiometric calculations have proved that magnetite solubility attains its maximum value, which depends on the characteristics of the electrolytic solution, when the temperature is about 100°C, independently of the type of environment. A rigorous pH calculation was carried out using the method of the characteristic function, which can be applied also to complex systems, and assuming that the effect of the ionic strength may be neglected. The main aim of this study, besides helping power plant chemists to select a proper feedwater conditioning, was to calculate the pH, on a molal basis, of a solution through the best-fit of its exact values, as a function of ammonia concentration inside the inverval 1.0 × 10⁻⁸ to 9.0 × 10⁻³ m with a third-degree logarithmic polynomial. The results, which were obtained in the case of a solution containing NH₄OH and H₂CO₃, demonstrate the validity of this technique which allows the pH of a fairly complex system to be computed accurately. It also allows the correct amount of magnetite dissolution products to be evaluated without considering in detail its chemical equilibria when the solution temperature is above 200°C. This remark was derived from the pH calculations of an ammonia containing solution, which showed its independence of partial hydrogen pressure in the high temperature region, at least as far as the interval 0–1 atm was concerned. The determination of the pH, on a molar basis, of a solution at temperatures of 200, 250, 300 and 350°C, contaminated with sea water so that its acid conductivity was 300μΩ⁻¹cm⁻¹, has been performed. These results have shown that the buffering effectiveness of ammonia is negligible when its concentration falls within the interval 1.0 × 10⁻⁶ to 2.0 × 10⁻⁵ M, whereas in the range 6.0 × 10⁻⁵ to 3.0 × 10⁻⁴ M, its effect is quite pronounced.     

Role of thermal stability and vapor pressure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium(II) and its triamine adduct in producing magnesium oxide thin film using a plasma-assisted LICVD process

Thin films of magnesia were deposited on various substrates using plasma-assisted liquid injection chemical vapor deposition with volatile Mg(tmhd)₂·2H₂O (1) (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione). The precursor complexes, Mg₂(tmhd)₄·(2), and Mg(tmhd)₂·pmdien (3) (pmdien; N,N,N′,N″,N″-pentamethyldiethylenetriamine) were prepared from Mg(tmhd)₂·2H₂O (1). The temperature dependence equilibrium vapor pressure (p_e)_T data yielded a straight line when log p_e was plotted against reciprocal temperature in the range of 360–475 K, leading to standard enthalpy of vaporization (Δ_vapH°) values of 59 ± 1 and 67 ± 2 kJ mol^− 1 for (2) and (3) respectively. Thin films of magnesium oxide were grown at 773 K using complex (1) on various substrate materials. These films were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray for their composition and morphology.     

Thermo-physical and thermal cycling properties of plasma-sprayed BaLa2Ti3O10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa₂Ti₃O₁₀ (BLT) was produced by solid-state reaction of BaCO₃, TiO₂ and La₂O₃ at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10^− 5–12.5 × 10^− 6 K^− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.     

The magnetic ordering in the Ho5Si3 and Ho5Ge3 compounds

A neutron diffraction investigation has been performed on the Ho₅Si₃ and Ho₅Ge₃ compounds (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic orderings (T_N1 and T_N2).Between T_N1 = 24(2) and T_N2 = 16(4) K Ho₅Si₃ shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K₁ = [0, 0, ±0.284(1)]; then, below T_N2 the sine-modulated type ordering is conserved, but by the two propagation vectors K₁ = [0, 0, ±0.2773(7)] and K₂ = [±1/5, ±1/5, 0].For Ho₅Ge₃, between T_N1 = 27(2) and T_N2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K₁ = [0, 0, ±3/10] and K₂ = [0, 1/2, 0], whilst below T_N2 the ordering takes place with propagation vectors K₁ = [0, 0, ±3/10], K₂ = [0, 1/2, 0], K₃ = [0, 0, ±2/5] and K₄ = [±1/5, ±1/5, 0]. For both the Ho₅Si₃ and Ho₅Ge₃ compounds, the dimensions of the magnetic unit cell are 5a × 5a × 10c times the crystal unit cell of Mn₅Si₃-type.     

Low-temperature thermoelectric properties of α- and β-Zn4Sb3 bulk crystals prepared by a gradient freeze method and a spark plasma sintering method

The low temperature thermoelectric properties of Zn₄Sb₃ samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from β- to α-phase; Δl/l=2.8×10⁻⁴ at T_s^GF=257.4 K for GF and Δl/l=1.6×10⁻⁴ at T_s^S=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at T_s^GF and T_s^S, while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the α-phase in the GF sample is twice as large as that of the β-phase; it exceeds 20 μW/cm·K² between 120 and 240 K, indicating that the α-phase Zn₄Sb₃ is one of the prime candidates for thermoelectric materials for cryogenic use.     

High temperature oxidation of Nb-10 at. % W alloy

By means of the “interruption kinetic technique”, as applied to oxidation of tungsten under 0.048 bar O₂, the oxygen diffusion coefficient in growing WO_8−x has been determined for the temperature range of 568–908°C and may be expressed as: D = 6.83 × 10⁻² exp (−29,890/RT), with the activation energy given in cal/mole. Calculations are made to show the influence of temperature on the concentration of oxygen vacancies in WO_3−x, on their free energy of formation and on the ionic conductivity in WO_3−x. From the kinetic data of W oxidation at 800°C, prior to interruption-annealing, values of oxygen diffusion coefficients due to oxygen transport via lattice and short-circuit paths have been calculated as functions of time for growing WO_3−x. A simplified oxidation model is used for evaluation of the oxidation rate constant of W at 800°C.     

Structural and piezoelectric properties of LiNbO3-modified BiScO3–PbTiO3 ceramics

Piezoelectric perovskite materials based on the solid solution (1 − x)BiScO₃–xPbTiO₃ (BSPT) have been attracting attention for their high Curie temperature (T_c = 450 °C) and excellent piezoelectric properties. The LiNbO₃ (LN), which has a T_c as high as 1150 °C, has been recently reported forming a phase pure perovskite solid solution with some perovskite structure compounds. In the current work, the effects of LN substitution on the structural and electrical properties of BSPT ceramics were investigated in the 0.36BiScO₃–0.64{(1 − x)PbTiO₃–xLiNbO₃} (BSPTLNx) system. The results of LN addition in the BSPT ceramics show significant enhancement of the piezoelectric properties. The piezoelectric constant d₃₃, planar electromechanical coupling coefficient and remnant polarization P_r values reached 465 pC/N, 0.57 and 48 μC/cm², respectively, for x = 0.04. The T_c gradually decreases with increasing LN content in the BSPTLNx system, due to the structure transform from the tetragonal to the rhombohedral. A typical relaxor behavior is also produced with the LN substitution in the BSPTLNx system.     

Thermal properties of cerium and thorium tellurates

Enthalpy increment measurements on CeTe₂O₆ (s) and ThTe₂O₆ (s) were carried out using a Calvet micro-calorimeter. The enthalpy increment values were least squares analyzed, with the constraint that H⁰(T)−H⁰ (298.15 K) at 298.15 equals 0 and C_p⁰ (298.15 K) is equal to the value estimated by Kellog’s method.The dependence of the enthalpy increment with temperature can be given as:

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=189.95 T (K)+15.226×10⁻³ T² (K) +15.414×10⁵/T (K)−63157 (CeTe₂O₆ (s), 391.5–848.0 K)

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=191.34 T (K)+14.993×10⁻³ T² (K) +14.668×10⁵/T (K)−63300 (ThTe₂O₆ (s), 391.5–909.3 K)

Molar heat capacity C_p⁰(T), S(T) and Gibb’s free energy functions were evaluated.     

The anodic behaviour of copper in static and flowing hydrochloric acid solutions

The dissolution of copper in 0·36 to 3·6 HCl was studied both in static and in flowing solutions using flow rates between 0·098 and 1·14 ms⁻¹, all in the region of laminar flow.Steady state anode potential current curves, potentiodynamic sweep and potentiostatic pulse techniques and impedance measurements, in the range of 0·02–7 kHz, were used. In both static and flowing solutions dissolution of copper occurs to a monovalent state, as chloro-complexes CuCl⁻₂ and CuCl²⁻ with exchange currents for the two reactions of 1·9 × 10⁻⁵ A mm⁻² and 8 × 10⁻⁷ Amm⁻² respectively in 1·44 MHCl. The cuprous chloride layer first forms a monolayer and subsequently grows to considerable thicknesses. The double layer capacity is constant at 0·17 ± 0·03 μFmm⁻² at potentials below multilayer formation and this is interpreted as implying that there is no specific adsorption of chloride ions prior to formation of the cuprous chloride layer. As the flow rate increases the film becomes thinner so delaying the formation of the film of critical thickness required for passivation.     

Fabrication and study on Ni1−xFexO-YSZ anodes for intermediate temperature anode-supported solid oxide fuel cells

Bimetal oxides Ni_1−xFe_xO (x = 0.01, 0.04, 0.08, 0.1, 0.15, 0.2, 0.4, 0.5) were synthesized and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) based on yttria-stabilized zirconia (YSZ) film electrolyte. A single cell consisted of Ni_1−xFe_xO-YSZ anode, YSZ electrolyte film, LSM–YSZ composite cathode was prepared and tested at the temperature from 600 °C to 850 °C with humidified hydrogen (75 ml min⁻¹) as fuel and ambient air as oxidant. It was found that the cell with Ni_0.9Fe_0.1O-YSZ anode showed the highest power density, 1.238 W cm⁻² at 850 °C, among the cells with different anode composition. The promising performance of Ni_1−xFe_xO as anode suggests that bimetal anodes are worth studied for SOFCs in future.     

New dielectric material system of La(Mg1/2Ti1/2)O3–Ca0.6La0.8/3TiO3 for microwave applications

The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. 0.6La(Mg_1/2Ti_1/2)O₃–0.4Ca_0.6La_0.8/3TiO₃ ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (_r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Crystal structure, thermal expansion and electrical properties of the new Al0.32ErGe2 compound

A new ternary compound Al_0.32ErGe₂ has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al_0.32ErGe₂ crystallizes in the orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and D_calc = 8.326 g/cm³). The average thermal expansion coefficients , and of Al_0.32ErGe₂ are 1.72 × 10⁻⁵ K⁻¹, 1.11 × 10⁻⁵ K⁻¹ and 1.52 × 10⁻⁵ K⁻¹, respectively. The bulk thermal expansion coefficient is 4.35 × 10⁻⁵ K⁻¹. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 K and 300 K.     

Thermophysical properties of lanthanum zirconate coating prepared by plasma spraying and the influence of post-annealing

Nano-scaled lanthanum zirconate powder prepared by co-precipitation–calcination method was plasma-sprayed into a thick coating on an alloy substrate. We investigated the thermophysical properties of the free-standing coating, including thermal conductivity and thermal expansion coefficients (TECs). Minimum value of the thermal conductivity (at 900 °C) of the coating was about 0.73 W m⁻¹ K⁻¹, and the average TEC in the measurement range was about 9.45 × 10⁻⁶ K⁻¹. Although the TEC value was similar to that of the bulk material, the change tendency versus temperature was different. After annealing at 1300 or 1400 °C for 50 h, we found that the heat insulation performance of the coating decreased with the heat treatment temperature, while the hardness and fracture toughness increased. A peak of sudden decrease in TEC value can be observed in the curve, and with increasing temperature, the peak shifted to high-temperature direction.     

Oliogothiophenes end-capped with arylacetylenes for organic thin film transistors

Phenylethynyl, butylphenylethynyl and pentafluorophenylethynyl end-capped terthiophene oligomers (PATTP, BPATTP and FPATTP) have been synthesized and characterized. Their physical, optical and electrochemical properties varied with the end substituents were investigated. DSC results revealed that three compounds were crystalline in the film state and thermally stable by 200 °C under nitrogen atmosphere. The oligothiophenes have exhibited H-aggregation, which was verified by significant blue-shift in UV–vis absorption spectra in the films, indicating a close side-to-side molecular packing. X-ray diffraction measurement on the films has revealed molecular edge-on substrate growth orientation. Top-contact field-effect transistors were demonstrated by spin-coating or ink-jetting the solution of the oligomers. The preliminary results showed that PATTP and BPATTP can serve as p-type carriers with hole-motility as 3 × 10^?4 and 1 × 10^?2 cm²/(V s), respectively, while pentafluorophenylacetylene afforded FPATTP as n-type carriers with electron-motility around 10^?5 cm²/(V s).     

Polymer-induced generation and characterization of electrophoretic properties of hollow TiOX nanospheres for electronic paper

Hollow TiO_X nanospheres have been successfully prepared using hollow core–double shell latex particles (poly(styrene-co-methyl methacrylate-co-butyl acrylate-co-methacrylic acid) (abbreviated in poly(St-co-MMA-co-BA-co-MAA)) as template, which involves the deposition of inorganic coating on the surface of hollow core–shell latex particles and subsequent removal of the latex by calcinations in air or ammonia gas. Ti(OBu)₄ was used as precursor for the preparation of hollow TiO_X nanospheres. TEM of white hollow core–double shell polymers particles with an aperture of approximately 225 nm displays the perfect characteristic hollow nanospheres structure of primary core–double shell particles. The formation of TiO_X was confirmed by XRD analysis and hollow structure of the particles was revealed by transmission electron microscopy (TEM). When the calcined temperature was at 800 °C, hollow TiO₂ nanospheres were arranged regularly with the diameter range of 130–170 nm. The electrophoretic properties were characterized by JS94J micro-electrophoresis apparatus. The electrophoretic mobility of white TiO₂ and black TiO hollow spheres in tetrachloroethylene were 1.09 × 10⁻⁵ and 3.12 × 10⁻⁵ cm²/V s, and the zeta potentials were 7.10 and 20.24 mV, respectively. The results show that white TiO₂ particles and black TiO hollow nanoparticles are suitable as electrophoretic particles and possess the application potential in the future electrophoretic display.     

Structure and optical properties of nanocrystalline NiO thin film synthesized by sol–gel spin-coating method

NiO thin film was prepared by sol–gel spin-coating method. This thin film annealed at T = 600 °C. The structure of NiO thin film was investigated by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The optical properties of the deposited film were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300–800 nm. The values of some important parameters of the studied films are determined, such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α) and band energy gap (E_g). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (_∞), the third-order optical nonlinear susceptibility χ⁽³⁾, volume energy loss function (VELF) and surface energy loss function (SELF) were determined.