Equilibration kinetics of (La,Sr)MnO3

The present work reports isothermal changes of oxygen non-stoichiometry for the perovskite-type electrode material (La_0.8Sr_0.2)MnO₃ in the temperature range 945–1255 K. A thermogravimetric method was used to monitor the rate of the gas/solid equilibration. For equilibration degrees larger than 0.5, the equilibration kinetic data can be described by a diffusion equation. The determined chemical diffusion coefficient depends essentially on the oxygen partial pressure. Its temperature dependence can be expressed by the following expressions at low and high p(O₂), respectively:

Determination of standard Gibbs energies of formation of ternary oxides in the system Co-Sb-O by solid electrolyte emf method

An isothermal section of the phase diagram of the system Co-Sb-O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. The following galvanic cells were designed to measure the Gibbs energies of formation of the three ternary oxides namely CoSb₂O₄, Co₇Sb₂O₁₂ and CoSb₂O₆ present in the system.

The thermal behaviour of copper diphosphates made by wet process

Copper diphosphates (Cu₂P₂O₇ · 5H₂O, Cu_1.6K_0.8P₂O₇ · 1.7H₂O, and Cu_1.5K_1.0P₂O₇ · 2.8H₂O) were made by mixing aqueous solutions of tetrapotassium diphosphate and copper dichloride. When the diphosphates were heated, the decomposition of the diphosphates to orthophosphate was observed at a temperature lower than 150° C. The orthophosphate was polymerized by condensation to polyphosphates in the temperature range of about 150 to 450° C. The polyphosphates reorganized to diphosphate at 450 to 550° C according to the following reaction:

Surface and grain-boundary energies of cubic zirconia

Using the multiphase equilibration technique for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline cubic ZrO₂ in the temperature range of 1173 to 1523 K were determined. The temperature coefficients of the linear temperature function obtained, are expressed as $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.431{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.004{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ and $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} - {\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.392{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.126{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ respectively. The surface fracture energy obtained with a Vickers microhardness indenter at room temperature is found to be γ _F=3.1 J m^?2.     

Study on the behavior of elastic-plastic fracture under mixed I+II mode loading in aluminum alloy Ly12-J-integral analysis

The elastic-plastic fracture behavior of aluminum alloy Ly12 under mixed I+II mode loading was studied by finite element method and fracture test. A mixed mode elastic-plastic fracture criterion of J-integral was proposed by using the J-resistance curve, and the maximum fracture effective plastic strain _p max of different mixed ratios at crack tip were also calculated. The results show that(1) the initiation J-integral values of different mixed ratios have the equation

Electrical, magnetic and Mössbauer properties of cadmium - cobalt ferrites prepared by the tartarate precursor method

Six samples of the system Cd_1–x Co _x Fe₂O₄ were prepared by the tartarate precursor method with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. The formation of ferrispinels were studied by X-ray powder diffraction, infrared spectroscopy, electrical conductivity, thermoelectric power, magnetic hysteresis, initial magnetic susceptibility and Mössbauer spectroscopy. The data of the temperature variation of the direct current electrical conductivity showed a definite kink (390°C) except x = 0.0 and 0.2, which corresponds to the ferrimagnetic to paramagnetic transitions. Magnetic properties of the samples with x 0.6 showed definite hysteresis loops. The observed low magnetic moment can be explained in terms of the non collinear spin arrangement. A well defined hyperfine Zeeman spectra are observed for samples with x 0.6 at room temperature and resolved into two sextets corresponding to octahedral and tetrahedral sites. The electrical, magnetic and Mössbauer properties suggest that, a canted spin arrangement upto x = 0.8 and Néel's configuration above this composition. The probable ionic configuration for the system is suggested as

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

The interface microstructure in alumina (FP) fibre/magnesium alloy composite

The objective of this work was to characterize the interfacial reaction zone in the metal matrix composite system-Al₂O₃(FP)/Mg (ZE41A). The composite was fabricated by liquid infiltration method. The reaction zone, a result of the reaction between magnesium in the alloy and the alumina fibres, was analysed for its morphology, chemistry, and crystallographic orientation using transmission electron microscopy. The results of this study showed the reaction zone to be, on average, 100nm wide and composed of MgO. The grains of the reaction zone ranged from less than 10 nm at the fibre/reaction zone interface to greater than 100nm at the matrix/reaction zone interface. It is proposed that the growth of the reaction zone was controlled by a seepage mechanism involving infiltration of liquid magnesium between MgO crystalS. Finally, it was observed that the MgO grains have the following crystallographic orientation relationship with the alumina grains from which they grew:

The Distribution of N-Grams

N-grams are generalized words consisting of N consecutive symbols, as they are used in a text. This paper determines the rank-frequency distribution for redundant N-grams. For entire texts this is known to be Zipf's law (i.e., an inverse power law). For N-grams, however, we show that the rank (r)-frequency distribution is

Phase relations in the system Cu-La-O and thermodynamic properties of CuLaO2 and CuLa2O4

Phase relations in the system Cu-La-O at 1200 K have been determined by equilibrating samples of different average composition at 1200 K, and phase analysis of quenched samples using optical microscopy, XRD, SEM and EDX. The equilibration experiments were conducted in evacuated ampoules, and under flowing inert gas and pure oxygen. There is only one stable binary oxide La₂O₃ along the binary La-O, and two oxides Cu₂O and CuO along the binary Cu-O. The Cu-La alloys were found to be in equilibrium with La₂O₃. Two ternary oxides CuLaO₂ and CuLa₂O₄₊ were found to be stable. The value of varies from close to zero at the dissociation partial pressure of oxygen to 0.12 at 0.1 MPa. The ternary oxide CuLaO₂, with copper in monovalent state, coexisted with Cu, Cu₂O, La₂O₃, and/or CuLa₂O₄₊ in different phase fields. The compound CuLa₂O₄₊, with copper in divalent state, equilibrated with Cu₂O, CuO, CuLaO₂, La₂O₃, and/or O₂ gas under different conditions at 1200 K. Thermodynamic properties of the ternary oxides were determined using three solid-state cells based on yttria-stabilized zirconia as the electrolyte in the temperature range from 875 K to 1250 K. The cells essentially measure the oxygen chemical potential in the three-phase fields, Cu + La₂O₃ + CuLaO₂, Cu₂O + CuLaO₂ + CuLa₂O₄ and La₂O₃ + CuLaO₂ + CuLa₂O₄. Although measurements on two cells were sufficient for deriving thermodynamic properties of the two ternary oxides, the third cell was used for independent verification of the derived data. The Gibbs energy of formation of the ternary oxides from their component binary oxides can be represented as a function of temperature by the equations:

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn_0.71Zn_0.22Fe_2.07O₄ ferrite was prepared by calcination with small amounts of CaCO₃, SiO₂, Nb₂O₅ and SnO₂. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and amount of Fe₂O₃ and Mn₃O₄ and sintering the mixture of the calcined powders and the remaining of Fe₂O₃ and Mn₃O₄. Initially, from the 40 min secondary milling and the partial calcination, lower temperature (1300°C) sintered samples showed a power loss of 340 mW cm^–3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm^–3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.     

Sputter deposition of bismuth and aluminum substituted dysprosium iron garnet films using sol-gel derived targets

Bismuth and aluminum substituted dysprosium iron garnet (Bi, Al:DylG) films were prepared by r.f. sputtering using sol-gel derived targets. The sol-gel derived target was coating on a rigid wafer. The coating was derived from the paste formed by a mixture of powders and viscous sol, which were prepared by the sol-gel process using nitrates as precursors, in appropriate stoichiometric ratios of . X-ray diffraction (XRD) patterns show that the crystallized films sputtered from the sol-gel derived targets are single phase garnet in nature, indicating that the sol-gel derived target is indeed a feasible alternative to a ceramic target. Magneto-optical measurements show that the prepared garnet film exhibits a strongest Faraday rotation of about 4.5°/m at a wavelength of 550 nm. It is believed that this sol-gel method for preparing the sputtering targets comprised of multi-component oxides provides a low cost target preparation process.     

The effect of temperature on the electric conductivity property of Bi3Zn2Sb3O14 pyrochlore type phase

The electric conductivity characteristic of ceramics was investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz. Electric measurements were performed at temperatures in the range from 25 to 700 °C. The phase type pyrochlore was synthesized by the polimeric precursors method. Ceramic presenting a relative density of 98% of the theoretical density was prepared. The data were presented in Nyquist diagrams form, from which the electric resistivity was determined. The electric conductivity followed the Arrhenius law with an apparent activation energy of the conduction process equal to 1.37 eV. The electric conductivity at room temperature was determined by extrapolation being equal to . Between 400 and 700 °C, the conductivity values were and , respectively.     

Structural properties of nickel manganite Ni x Mn3−x O4 with 0.5 ⩽x ⩽ 1

Single-phase nickel manganite spinels, Ni _x Mn_3–x O₄, with 0.5 x 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni²⁺ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni²⁺ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni²⁺ in A sites =P = – 82.1x ²+192.4x–81.5 and thus the general formula for cation distribution is

High-field ESR on Light-Induced Transition of Spin Multiplicity in FeCo Complex

Cyanide-bridged Fe-Co complex [Fe(Tp)(CN)₃]₂Co(bpe)?5H₂O (1?5H₂O; Tp = hydro-tris(pyrazolyl)borate; bpe = 1,2-bis(4-pyridyl)ethane) shows temperature- and light- induced metal-to-metal charge transfer (MMCT) involving spin state changes between magnetic $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ (HS = high spin, LS = low spin) state and nonmagnetic $\mathrm{Fe}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}$ state, while the dehydrated material 1 does not show any MMCT and holds $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ state. We have investigated the magnetic properties of each spin state in 1 and 1?5H₂O by means of magnetization and ESR measurement under pulsed high magnetic field. At low temperature below T _N, in both 1 and 1?5H₂O, the saturation magnetization in the induced ferromagnetic phase is well explained by S and g values derived from the magnetic susceptibility study. In the ESR of 1, we observed characteristic modes corresponding to a spin excitation in the induced ferromagnetic phase where its temperature dependence shows an evolution of spin correlation in the $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ state at low temperature. We further found that the similar ESR modes grow in the light-induced state of 1?5H₂O. The results strongly suggest that the light-induced magnetization in 1?5H₂O is driven by a light-induced MMCT, which involves transition of spin multiplicity from the nonmagnetic $\mathrm{Fe}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}$ to the magnetic $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{\mathrm{II}}}\mathrm{HS}}$ pair.     

Determination of diffusivity of sodium in liquid tin using Na-ß″ alumina

Diffusivity of sodium in molten tin was determined using an electrochemical cell of the type Na/Na-β″-Al₂O₃/(Na)Sn where Na-β″-Al₂O₃, which is a sodium-ion conductor, was the solid electrolyte. Using the above cell in which a small amount of sodium dissolved in tin was transported through β″-Al₂O₃ upon application of an external voltage, and using a known solution to Fick's second law for appropriate boundary conditions, the diffusivity was determined to be $$D{\text{ = 4}}{\text{.4 }}\left( {\begin{array}{*{20}c} {{\text{ + 1}}{\text{.0}}} \\ {{\text{ - 0}}{\text{.5}}} \\ \end{array} } \right){\text{ x 10}}^{{\text{ - 4}}} {\text{ exp }}\left( {{\text{ - }}\frac{Q}{{RT}}} \right){\text{ cm}}^{\text{2}} {\text{ sec}}^{{\text{ - 1}}} $$ withQ = 16320 J mol^?1 over a range of temperatures from 240 to 440° C. From the solution to Fick's second law, it was shown that first term approximations, which have often been used in the past, lead to an estimate of diffusivity which is about a factor of 2 too high indicating that more terms should be considered. The diffusivity was also determined using a transient technique in which the decay in voltage upon removal of externally applied voltage was recorded as a function of time. The diffusivity so determined, in which it was assumed that the only polarization was the concentration polarization, was higher than the previous method. The difference between the two diffusivities became smaller with increasing temperature. These experiments thus suggested that interfacial or activation polarization must also be present.     

Thermal expansion of molybdenum in the range 1500–2800 K by a transient interferometric technique

The linear thermal expansion of molybdenum has been measured in the temperature range 1500–2800 K by means of a transient (subsecond) interferometric technique. The molybdenum selected for these measurements was the Standard Reference Material SRM 781 (a high-temperature enthalpy and heat capacity standard). The results are expressed by the relation where T is in K and l ₀ is the specimen length at 20°C. The maximum error in the reported values of thermal expansion is estimated to be about 1% at 2000 K and not more than 2% at 2800 K.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Defect structure of acceptor-doped calcium titanate at elevated temperatures

The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to for the oxygen pressure range < 10^–10 atm and proportional to for the oxygen pressure range ( 10^–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO₃. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO₃. The defect chemistry of CaTiO₃ is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation.     

Conservation of the elastic and flexural moduli of osteopenic femoral cortical bone in experimental inflammatory arthritis in the rabbit*

Experimental inflammatory arthritis (EIA) produced by carrageenan injection provokes a rapid bone remodeling state with cortical and cancellous bone loss. The objective of this study was to determine whether changes in cortical mechanical properties and/or geometry occur in long bones, either near or remote to the site of inflammation. EIA was induced in the right tibio-femoral joint of rabbits over 56 days. The right humerus and right femur from 15 normal and 25 arthritis group animals were excized. Semi-cylindrical specimens of the medial cortical shaft were subjected to non-destructive four-point bending tests. Transverse sections at the four contact sites of the loading jig were photographed and digitized to obtain average cross-sectional area (A) and moment of inertia (I). Moment of inertia and slope of the load/deflection curve permitted calculation of modulus of elasticity (E) for each specimen. Load/time curves were also used to calculate per cent stress remaining in relaxation experiments. Per cent stress remaining, E, A, I and \sqrt {{\text{I/A}}} (radius of gyration) were examined for differences by bone (humerus, femur) and by treatment (N,A) using two way ANOVA. The induction of inflammatory arthritis did not significantly alter the modulus of elasticity in either the femur or humerus; however, arthritis reduced the moment of inertia from . This was observed in the femur (near the arthritic joint), but not in the humerus (remote from arthritic joint). Analysis of area and ratio I/A demonstrated that this geometric effect of treatment was due to reduced area without gross cross-sectional shape changes. Per cent stress remaining in the femur (but not in the humerus) was higher in the arthritis specimens than in the normal specimens . Thus, in this arthritis model, the principal mechanical or geometric effect on cortical bone was reduction of the cross-sectional area and moment of inertia. The viscoelastic relaxation response of bone was also altered, perhaps due to loss of water or collagen degradation.     

Diffusion of platinum, vanadium and manganese in Ni3Al phase under high pressure

Diffusion of platinum, vanadium, and manganese in the Ni₃Al phase is investigated under high pressure. Platinum atoms occupy cubic face centred sites (α) in the L1₂ ordering structure. Vanadium atoms occupy cubic corner sites (β). Manganese atoms occupy both sites. Activation volumes ΔV for diffusion of these diffusing atoms to the molar volume of the Ni₃Al phase V₀ are as follows: