Chemical solution method for fabrication of nanocrystalline iron(III) oxide thin films

A chemical solution technique for preparation of nanocrystalline iron(III) oxide thin films is developed. The deposition process is essentially based on the thermal decomposition of urea. The as-deposited and post-deposition heat-treated materials were characterized by X-ray analysis and Fourier transform infrared (FTIR) spectroscopy. Basic optical and electrical investigations were also performed. X-ray analysis confirmed that post-deposition heat-treated material is nontextured -iron(III) oxide, with an average crystal size of 22 nm. The optical investigations show that the absorption of films (as-deposited and post-deposition treated) gradually decreases with an increase of the wavelength in the 390–820 nm region. The optical band gap for the as-deposited and post-deposition heat-treated films was determined to be 3.2 eV and 2.0 eV, respectively. The obtained -Fe₂O₃ thin films exhibit a rather high resistivity at room temperature. However, our preliminary qualitative investigations have shown that the room temperature resistivity of -Fe₂O₃ thin films is highly sensitive to moisture, indicating their potential applicability in moisture sensing systems.     

Formation of oxide phases in the system Fe2O3-NiO

Mixed metal oxides in the system Fe₂O₃-NiO were prepared by coprecipitation of Fe(OH)₃/Ni(OH)₂ and the thermal treatment of hydroxide coprecipitates up to 800 or 1100°C. X-ray diffraction showed the presence of -Fe₂O₃, NiO and NiFe₂O₄ in samples prepared at 800°C. The oxide phases -Fe₂O₃, NiO, NiFe₂O₄ and a phase with structure similar to NiFe₂O₄ were found in samples prepared at 1100°C. Fourier transform-infrared spectra of oxide phases formed in the system Fe₂O₃-NiO are discussed. Two very strong infrared bands at 553 and 475 cm^–1, a weak intensity infrared band at 383 cm^–1 and two shoulders at 626 and 441 cm^–1 were observed for -Fe₂O₃ prepared at 1100°C. NiFe₂O₄, prepared at the same temperature, showed two broad and very strong infrared bands at 602 and 411 cm^–1, while NiO showed a broad infrared band at 466 cm^–1. Fourier transform infrared spectroscopic results were in agreement with X-ray diffraction.     

Microstructure and morphology of α-Si : H solar cells grown on metallized flexible substrates

Results are presented for the microstructure of -Si : H solar cells grown on metallized polymer substrates. The structures studied were Kapton/metal/n-i-p -Si : H/ZnO, where silver and aluminum were used as the metal back contacts. The -Si : was deposited at temperatures ranging from 100–200 °C. A second identical range of cells, except for the insertion of an 80 nm thick ZnO buffer-layer between the metal and n-layer, was also studied. A range of measurements utilising scanning electron microscopy, energy dispersive x-ray spectroscopy, Raman scattering and X-ray diffraction were made on the samples to determine the material properties. It is demonstrated that the surface morphology and microstructure of these cells are strongly dependent on the substrate temperature during deposition of the -Si : H, choice of back contact metal, and the ZnO buffer-layer. It is argued that the material properties of cells grown on flexible metallized substrates differ from those grown on conventional TCO covered glass substrates.     

Structure of nickel-doped α-FeOOH

Colloidal particles of nickel-doped-FeOOH prepared under varied conditions were characterized using transmission electron microscopy, X-ray diffraction thermogravimetry-differential thermal analysis, Fourier transform infrared analysis, inductively coupled plasma spectroscopy and nitrogen adsorption. The unit cell dimensions of the resulting-FeOOH slightly changed on doping with nickel. Both the total and surface hydroxyl ions decreased with increasing amounts of nickel. The nickel content in the surface layer determined by X-ray photoelectron spectroscopy was larger than the total nickel content determined by inductively coupled plasma spectroscopy. The results obtained indicate that the substitution of iron with nickel took place in the surface layer more than in the internal phase.     

Effects of citrate ions on the formation of ferric oxide hydroxide particles

The effects of citrate ions on the formation of - and -FeOOH particles were investigated using various techniques. The formation and crystallization of both particles were inhibited by citrate ions, and their particle sizes decreased with increase in the concentration of these ions. Finally, aggregated amorphous particles were formed. The effects of citrate ions appeared to be more significant for -FeOOH than for -FeOOH. This difference could be explained by the pH dependence of the affinity of citrate ions to Fe³⁺ ions. The amorphous -FeOOH particles prepared in the presence of > 10 mol% citrate ions selectively adsorbed water molecules.     

Isoconversion method for kinetic analysis of solid-state reactions from dynamic thermoanalytical data

The activation energy for a heterogeneous reaction involving a solid may be obtained from a plot of ₀ ln(d/dt) d against ₀(1/T) d, where represents the fractional conversion of the solid reactant, and T(t) is the (time-dependent) reactant temperature. This new approach to the analysis of dynamic thermoanalytical kinetic data has distinct advantages over existing methods, as it needs to make no assumption about the kinetic model, involves no approximation to the temperature integral, and is easy to implement on the computer.     

Structural properties of precipitates formed by hydrolysis of Fe3+ ions in aqueous solutions containing NO 3 − and Cl− ions

The structural properties of precipitates formed by hydrolysis of Fe³⁺ ions in aqueous solutions, containing N0 ₃ ^– and Cl^– ions, were investigated. The reactions of hydrolysis were performed in glass autoclaves at 120 °C. X-ray diffraction showed that -FeOOH and -Fe₂O₃ were present in hydrolytical products formed in solutions containing N0 ₃ ^– ions, while -FeOOH and -Fe₂O₃ were typical hydrolytical products in solutions containing Cl^– ions. In the mixed Fe(N0₃)₃+FeCl₃ solutions, the phase composition of the hydrolytical products was determined by the concentration of the dominant Fe(III)-salt. Fourier transform infrared spectroscopy and Mössbauer spectroscopy were also used for the structural characterizations of the hydrolytical products. Transmission electron microscopy showed a diversity of shapes of the particles, which depended strongly on the experimental conditions. All types of particle, observed by transmission electron microscopy, were interpreted.     

Spectroscopic characterization of passivated titanium in a physiologic solution

Titanium (Ti) has been used for many biomedical applications. Surface characteristics of titanium devices are critical to their success. In this study, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyse Ti surfaces prior to immersion in alpha-modification of Eagle's medium (-MEM). The ionic constituents deposited onto Ti surfaces after in vitro exposure to -MEM were investigated using XPS and Fourier transform infrared spectroscopy (FTIR). Surface studies revealed an amorphous oxide layer on the Ti surface, with a chemistry similar to TiO₂. However, after exposure to the physiologic solution for 12 days, dynamic changes in surface chemistry were observed. Ions such as phosphorus (P) and calcium (Ca) were increasingly deposited as amorphous fine crystalline calcium-phosphate (Ca–P) compounds, having a Ca/P ratio of 1.2 and a chemistry similar to brushite.     

Magneto-optical properties of obliquely evaporated Ni films

Longitudinal magneto-optical Kerr effect (MOKE) configuration and scanning electron microscopy (SEM) were used to investigate the effects of deposition angle, on magnetic properties and morphology of obliquely evaporated Ni films. The results show that the angle of deposition has a critical effect on the magnetic anisotropy of the films. These effects are due to the microstructure of the films, which is controlled by the angle of deposition with respect to the sample normal. The results show the presence of shape anisotropy governing the demagnetization of the magnetic fields. The anisotropy, coercivity and squareness of the hysteresis loops increased with an increase in of the vapour flux. These properties and surface roughness became marked for off-normal deposition angles larger than 50°. At low s, the easy axis of magnetization lay perpendicular to the incidence plane. At large s the easy axis changed parallel to the incidence plane. The results may be quantitatively understood from the presence of an inclined columnar microstructure with shape anisotropy governing the demagnetization of the magnetic fields.     

Mechanisms of the Allotropic Transition of Sn

The mechanisms of -Sn nucleation on foreign seeds, including metastable ones, are considered. Based on earlier and new experimental data for induction times of -Sn nucleation from 10² to 10¹¹ s, it is suggested that spontaneous -Sn nucleation is impossible because of kinetic hindrances in the solid phase.     

Direct and inverse heat-conduction problems for a semiinfinite rod for a partial outflow of heat through the surface

Analytical solutions of the direct and inverse problems of nonstationary heat conduction in a thin semiinfinite rod are given for the case of radiative heat fluxes at the lateral surfaces and a partial outflow of heat by convection and radiation through the end of the rod.Notation thermal diffusivity - x₁ coordinate along the length of the rod - t₁ time - t=t₁/d² dimensionless time (Fourier number) - x=X₁/d relative coordinate - T_o initial temperature - Boltzmann constant - Sk=aT_c ³d/ Stark number - Bi=d/ reduced Biot number - emissivity Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 148–153, July, 1984.     

Morphology of nitrated layers in titanium alloys of different structural classes

This paper generalizes the results of investigations of the effect of nitrogen on titanium alloys at temperatures of isothermal exposure of 800 – 1100°C and gas pressures of 10⁵ – 10^–1 Pa. As a result of nitration, a gas-saturated area appears on the surfaces of the alloys (in addition to the nitride area). Its qualitative and quantitative characteristics depend on the phase composition of the alloys. The gas-saturated area consists of two layers. For all the investigated alloys, the first layer (adjacent to the nitride area) can be described as the -titanium structure stabilized with nitrogen. If the saturation temperature is lower than the temperature of the polymorphic transformation, then the structure of the second layer is identical to the alloy matrix. As a result of nitration in the (+)--region, this structure undergoes the transformation and, for - and pseudo--alloys, turns into an -grain of smaller size but with higher etchability compared to the -structure of the first layer. For (+)-alloys, this is mainly the -phase (-plates) in the -transformed structure. For -alloys, the morphology of the gas-saturated area does not depend on the saturation temperature and is identical to other structural types nitrated in the -region.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 35–41, September–October, 1993.     

Die Herleitung von Schalengleichungen über ein erweitertes Variationsprinzip bei Berücksichtigung der Querschubverzerrungen

Ohne ZusammenfassungBezeichnungen L Bezugsgrößen für dimensionslose Koordinaten - L charakteristische Schalenabmessung - t Schalendicke - Schalenparameter - körperfeste, krummlinige, dimensionslose Koordinaten der Schalenmittelfläche - Dimensionslose Koordinate in Richtung der Schalennormalen - i, j,...=1,2,3 Indizierung des dreidimensionalen Euklidischen Raumes - ,,...=1,2 Indizierung des zweidimensionalen Riemannschen Raumes - (...), Partielle Differentiation nach der Koordinate - (...), Kovariante Differentiation für Tensorkomponenten des zweidimensionalen Raumes nach der Koordinate - (...)| Kovariante Differentiation für Tensorkomponenten des dreidimensionalen Raumes nach der Koordinate - Variationssymbol - a ,a ₃ Basisvektoren der Schalenmittelfläche - V Verschiebungsvektor - U ,U ₃ Verschiebungskomponenten des Schalenraumes - v ,w,w ,W Verschiebungskomponenten der Schalenmittelfläche - Verhältnis der Metriktensoren des Schalenraumes und der Schalenmittelfläche - _ik Verzerrungstensor des Raumes - _{(, )}, Symmetrische Verzerrungstensoren der Schalenmittelfläche - _{[, ]} Antimetrischer Term des Verzerrungsmaßes - ^, Spannungstensor - n ,m ,q Tensorkomponenten der Schnittgrößenvektoren - p ,p,c Tensorielle Lastkomponenten     

Torsional Oscillations of a Rotating Column of 3He-B

No Heading We have analysed the axisymmetric and non-axisymmetric modes of a continuum of vortices in a rotating superfluid. We have investigated how changing the temperature affects the growth rate of the disturbances. We find that, in the long axial wavelength limit the condition q = /(1 – ) = 1, where and are temperature-dependent mutual friction parameters, is the crossover between damped and propagating Kelvin waves. Thus at temperatures for which q > 1, perturbations on the vortices are unlikely to cause vortex reconnections and turbulence. These results are in agreement with the recent discovery of Finne et al¹ of an intrinsic condition for the onset of quantum turbulence in ³He-B.PACS numbers: 67.40. Vs, 67.57.–z     

Microstructural refinement of β-sintered and Ti-6Al-4V porous-coated by temporary alloying with hydrogen

A series of thermochemical treatments, in which hydrogen was used as a temporary alloying element to refine the lamellar microstructure of -sintered and porous-coated Ti-6Al-4V was formulated. Each step of the treatment sequence (hydrogenation, eutectoid decomposition and dehydrogenation) was studied separately, on uncoated specimens and then on porous-coated specimens. The resultant microstructures can have -grain sizes less than 1 m, aspect ratios near unity and discontinuous grain boundary (GB), microstructural attributes which increase the fatigue strength. Microstructural refinement occurs because hydrogen-alloying reduces the (+) transition temperature and enables a eutectoid decomposition reaction to occur. The optimal hydrogenation temperature is 850 °C, because hydrogen concentrations of 0.71 to 0.85 wt% are in-diffused and -transformation is achieved. These weight percentages are in the optimal range for efficient eutectoid decomposition kinetics, -transformation obviates the need for a separate -transformation treatment step. A separate eutectoid decomposition treatment step may be used, or eutectoid decomposition may be combined with dehydrogenation. The finest eutectoid microstructures are obtained if hydrogen concentrations are in the range 0.5 to 0.8 wt%. The criteria for dehydrogenation are efficient removal of hydrogen, with minimal grain growth and absence of GB. These criteria are best met by using dehydrogenation temperatures <700 °C. Altering the sintering temperature or adding a porous coating does not affect the parameters of the hydrogen-alloying treatment steps.     

On dual solutions occurring in mixed convection in a porous medium

Summary The dual solutions to an equation, which arose previously in mixed convection in a porous medium, occuring for the parameter in the range 0 < < ₀ are considered. It is shown that the lower branch of solutions terminates at =0 with an essential singularity. It is also shown that both branches of solutions bifurcate out of the single solution at =₀ with an amplitude proportional to (₀-)^1/2. Then, by considering a simple time-dependent problem, it is shown that the upper branch of solutions is stable and the lower branch unstable, with the change in temporal stability at =₀ being equivalent to the bifurcation at that point.     

Microstructure and mechanical properties of metastable lath martensite wires in the Fe-Ni-Cr-Al-C system produced by melt spinning in rotating water

Metastable lath martensite ( _L ) phase wires with high strengths have been produced in the Fe-Ni-Cr-Al-C alloy system by melt spinning in rotating water. These wires have a circular cross section and a white lustre and the wire diameter is in the range of 100 to 140m. The width and length of each lath in the _L phase are as small as about 0.3 and 2m, respectively. The _y, _f and _p are about 900 and 1650 MPa and 2.0% for the _L wires. The subsequent annealing causes an increase in _p as well as _y and _f and the attained values are about 1000 and 1700 MPa and 3.0% for Fe-10Ni-10Cr-6.5 Al-1.0C wire annealed at 773 K for 1 h owing to the precipitation strengthening of a very fine unidentified carbide and to a high density of dislocations and lath boundaries in the _L phase. Further annealing causes a significant decrease in _p through decomposition of _L to+M₇C₃+M₂₃C₆. Therefore, the high strength combined with relatively good ductility for the _L wires is interpreted as due to the suppression of the phase transformation of _L to a mixed structure of+M₇C₃+M₂₃C₆ by melt quenching.     

Optical properties of SPS-ed Y- and (Dy,Y)-α-sialon ceramics

Y_0.67Si₉Al₃ON₁₅ and Dy_0.4Y_0.3Si_8.85Al_3.15O_1.05N_14.95 ceramics were prepared by Spark Plasma Sintering (SPS) with and without heat treatment at 1700°C for 7 h or 17 h, and their optical transmittance were investigated over the wavenumber range 4000–1500 cm^–1. The results showed that the assemblages of the SPS-ed samples consisted of single crystallized -sialon phase in both compositions. EDS analysis indicated that -sialon was mainly stabilized by Dy³⁺ in the multi-cation (Dy,Y)--sialon composition. The SPS-ed specimens showed relatively high optical transmission properties, and the maximum transmittance reached around 65% at 2800 cm^–1 for 0.5 mm thick specimens of both compositions. The 7 h heat treatment caused the formation of small amount of melilite phase, resulting in non-uniform microstructure and decrease in optical transmittance. Extended heat treatment for 17 h led to more homogenous microstructure and increased the transmittance to some extent. Less melilite was formed in the multi-cation (Dy,Y)--sialon composition than in the single cation Y--sialon after heat treatment, and the transmittance of (Dy,Y)--sialon was also higher than that of Y--sialon.     

On the solution of nonstationary heat-conduction problems with variable heat-transfer coefficient

The article describes an exact method for calculating the temperature field in solids when they are heated in a medium with a variable heat-transfer coefficient and a nonuniform initial temperature distribution.Notation temperature - L thickness of plate - x space coordinate - a thermal diffusivity - thermal conductivity - heat-transfer coefficient - t time - X=x/L dimensionless coordinate - Fo=at/L² Fourier number - Bi(Fo)=(Fo)L/ Biot number Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 921–924, May, 1971.     

Temperature dependence and microwave enhancement of the critical current of superconducting microbridges

The temperature dependence of superconducting tin, thin-film, narrow bridges has been investigated. NearT _c the critical current varies with (1 – T/T_c ), with a distribution of values between 1 and 3/2. It is suggested that the values can be used to characterize the bridges. The microwave enhancement ofI _c andT _c was measured and these data were compared with a recent theory by Christiansenet al. on the microbridges. We found that their theory gives a correct prediction for the Dayem effect in the bulklike bridges (with =3/2) while their theoretical values for the junction-like bridges (with =1) are not in agreement with our data.Work supported in part by the National Science Foundation.