Thermoelectric Power Measurements Research Articles

Structural ordering in bulk amorphous Ge x Se 1-x samples

From temperature dependence of thermoelectric power and dc conductivity measurements [1] on bulk amorphous GexSe1-x samples (x = 10, 20, 30, 40) a dimensionless structural parameter ‘A-r/k’ was computed from intercept of thermoelectric power versus reciprocal temperature (1/T) plots. Based on ‘A-r/k’ and the slope ‘M’ of thermoelectric power versus logarithm of resistivity (ln ρ) plots, it was found that as Se content decreases, the bulk amorphous samples exhibit a transition from chalcogenides to tetrahedrally bonded amorphous semiconductors. There is a widespread agreement that tetrahedrally coordinated amorphous semiconductors crystallise at much higher temperature then the lone pair chalcogenide glasses. Therefore a decrease in Se content is considered as increase in the hardness of the samples.

Quantum oscillations and physical properties of LaCu2Si2

High quality single crystals of LaCu2Si2 are successfully grown from a high temperature ternary melt. The physical properties are investigated by measurements of specific heat, electrical resistivity, thermoelectric power, and magnetization. The electrical resistivity follows an ordinary metallic behavior with a residual resistivity ρ0 = 0.87 μΩ cm and residual resistivity ratio (RRR) ρ(300 K)/ρ0 ∼ 13. Quantum oscillations for H || ab are clearly observed from electrical resistivity, magnetization, and thermoelectric power measurements in magnetic fields as low as 30 kOe and at temperatures as high as 20 K. In the earlier studies no quantum oscillations have been observed from both single crystal and polycrystalline samples. The small value of ρ0 and quantum oscillations indicate a high quality of LaCu2Si2 samples used in the present study. The cyclotron effective mass obtained from the analysis of the de Haas – van Alphen (dHvA) oscillations is small m0 ∼ 0.14me, which is consistent with the small electronic specific heat coefficient γ ∼ 3.4 mJ/mol K2. The detected dHvA frequencies of LaCu2Si2 are compared with those of the RCu2Si2 (R = Y, Th, and Ce) family.

Experimental verification of semimetallic band structure in PtSe2 via thermoelectric power measurements

This study presents an investigation of the band structure in a semimetallic two-dimensional (2D) PtSe2 nanosheet based on thermoelectric transport phenomena. Mechanically exfoliated PtSe2 nanosheets, including naturally doped nonneutral samples, were studied. The gate-tuned electrical conductivity and thermoelectric power were measured by varying the temperature. Based on the combined effects of gate-tuning and shifting of zero-gate energy level, the semimetallic band structure of 2D PtSe2 was confirmed in the band over a wide energy range. Furthermore, the temperature dependence of transport properties was investigated to determine the band structure and intrinsic properties.

FeWO4 Single Crystals: Structure, Oxidation States, and Magnetic and Transport Properties

Synthetic crystals of the ferberite FeWO4 have been grown by the chemical transport reaction starting from a polycrystalline sample of this phase. Magnetic susceptibility measurements showed an antiferromagnetic Néel temperature of TN = 75 K. The anisotropy in the magnetic susceptibility can be ascribed to the magnetocrystalline anisotropy of the Fe2+ ion, the oxidation state of which was confirmed by X-ray absorption spectroscopy. While X-ray photoemission analysis indicated that all W ions are in the expected 6+ charge state, the dielectric permittivity of the FeWO4 crystals was found to be leaky, hindering changes at TN to be detected. Subsequent thermoelectric power measurements suggested the presence of about 1.5% Fe3+. X-ray diffraction experiments confirmed the basic crystal structure of the wolframite type and revealed some structural disorder in the 1% range. Transmission electron microscopy allowed us to unveil the occurrence of stacking faults attributed to the similarity of the atomic environment of the Fe and W species.

Screen-printed film deposited using quasi 2-dimensional Bi2Se3 nanostructures for desalination membrane filler application

Chalcogenides and 2D graphene are the emerging materials being investigated rigorously as efficient membrane filler materials for recovering minerals from seawater and for desalination through recrystallization. In this work quasi-2-dimensional bismuth selenide (Bi2Se3) nanostructure synthesized by microwave-assisted solvothermal method - mixed in ethylene glycol is used as the ink for depositing screen-printed film (SPF). A laboratory-scale experiment univocally demonstrates the possibility of application of SPF as an efficient membrane filler material for desalination processes such as in direct contact membrane distillation (DCMD). Morphology and topography studies confirm the growth of homogeneous hexagonal micro structures with an edge-to-edge length of 20–40 µm with a thickness of ~ 2–3 µm respectively and elemental mapping studies confirm the growth of sodium chloride (NaCl) crystals over the Bi2Se3 SPF. Growth of different morphology of NaCl (20–40 µm) including the metastable (111) oriented NaCl depicts that Bi2Se3 film assists the efficient crystallization process and helps in retaining the morphology of NaCl crystals with an enhanced crystal growth rate of the order of 10−8–10−9 m/s. Interestingly, thermoelectric power measurement in these Bi2Se3 nanostructures with n-type carriers and with Seebeck coefficient value of − 98 μV/K around the room temperature open up a new possibility for a combined desalination membrane filler application along with thermoelectric (TEP) application where the waste heat used for desalination/membrane crystallization can also be harvested in the form of useful electrical energy.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Ferromagnetic CeSi1.2Ga0.8 alloy: Study on magnetocaloric and thermoelectric properties

We present the magnetic, specific heat, electrical resistivity, and thermoelectric power measurements for the intermetallic compound CeSi1.2Ga0.8. This composition belongs to the series CeSi2-xGax, which exhibits diverse magnetic orderings and different crystallographic structures depending on the substitution level x. It has been previously suggested that for 0.0 < x < 1.3 the compounds crystallize in the α-ThSi2 type structure and for 0.7 < x < 1.3 they order ferromagnetically below 14 K. Our complementary studies for x = 0.8 reveal that it is a complex system due to the Kondo scattering competing with the RKKY interactions. The transition from the paramagnetic to the ferromagnetic state takes place at TC = 12.5(1) K. Moreover, the Seebeck coefficient and electrical resistivity show not only an anomaly related to the magnetic transition, but also a broad maximum at ∼90 K related to the crystal field effect. The case of x = 0.8 is of special interest as it is at the crossing of the characteristic temperatures, i.e. Tord (magnetic ordering temperature) ∼ TK (Kondo temperature) ∼10 K. Additionally, ab initio electronic structure calculations were performed allowing us to determine phase stability, (revealing two stable phases - α-GdSi2-type and α-ThSi2-type structures) as well as spin and orbital moment decomposition on Ce-states for both considered structures.

Structural, morphological and electrical properties of ternary CdxZn1-xSe thin films

Pure Zinc Selenide thin films were produced onto the glass micro-slides and stainless-steel substrates as well employing chemical bath deposition method by optimising the preparation and deposition parameters. The concentration of Cadmium (x) in Zinc selenide lattice was changed from 0 to 1. The structural and surface morphological properties of these as deposited thin films were investigated and studied utilising XRD and SEM techniques respectively. These as deposited thin films were poly-crystalline in character and exhibit cubic phase for 0 ≤ x ≤ 0.3 and distinct/mixed phases of cubic and hexagonal wurtzite structures were observed for the 0.4 ≤ x ≤ 0.8 region. Thereafter, again cubic phase seems to be prevailing.The electrical conductivity increased with increase in composition × at the ambient temperature and at higher temperature as well. The thermoelectric power measurements revealed that these semiconducting thin films exhibit ‘n’ type conductivity.

Chiral Radical Cation Salts of Me-EDT-TTF and DM-EDT-TTF with Octahedral, Linear and Tetrahedral Monoanions

Methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF (1) and dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF (2) are valuable precursors for chiral molecular conductors, which are generally obtained by electrocrystallization in the presence of various counter-ions. The number of the stereogenic centers, their relative location on the molecule, the nature of the counter-ion and the electrocrystallization conditions play a paramount role in the crystal structures and conducting properties of the resulting materials. Here, we report the preparation and detailed structural characterization of the following series of radical cation salts: (i) mixed valence (1)2AsF6 as racemic, and (S) and (R) enantiomers; (ii) [(S)-1]AsF6·C4H8O and [(R)-1]AsF6·C4H8O where a strong dimerization of the donors is observed; (iii) (1)I3 and (2)I3 as racemic and enantiopure forms and (iv) [(meso)-2]PF6 and [(meso)-2]XO4 (X = Cl, Re), based on the new donor (meso)-2. In the latter, the two methyl substituents necessarily adopt axial and equatorial conformations, thus leading to a completely different packing of the donors when compared to the chiral form (S,S)/(R,R) of 2 in its radical cation salts. Single crystal resistivity measurements, complemented by thermoelectric power measurements in the case of (1)2AsF6, suggest quasi-metallic conductivity for the latter in the high temperature regime, with σRT ≈ 1–10 S cm–1, while semiconducting behavior is observed for the (meso)-2 based salts.

Structural, electrical and magnetic properties of substituted pyrochlore oxide nanoparticles synthesized by the co-precipitation method

Five substituted pyrochlore nanooxides such as Nd1.9Ho0.1Zr1.8Ce0.2O7, La1.95Ce0.05Zr0.29Ce1.71O7, Y1.79Pr0.21Ru1.99Pr0.01O7, Dy1.9Yb0.1Mn1.93Cu0.07O7 and Dy1.99Sr0.01Sn2O7 were synthesized by coprecipitation method. These precursors were monitored by thermal studies (TGA-DTA). The prepared nanosized substituted pyrochlore oxides were characterized by EDS, XRD, SEM, TEM, d. c. electrical conductivity, Thermoelectric power, Hall effect measurement, dielectric properties and magnetization measurements. XRD confirmed the formation of a single phase crystalline substituted pyrochlores with a cubic nature of nanoparticles. All substituted compounds were adopted a stable pyrochlore structure with rA3+/rB4+ = 1.395 except La1.95Ce0.05Zr0.29Ce1.71O7 compound, which has rA3+/rB4+ = 1.175 indicate disorder pyrochlore structure (i.e. fluorite structure). The temperature dependence of d. c. electrical conductivity for all substituted pyrochlores exhibits two distinct slopes with a break. This discontinuity can be attributed to extrinsic to intrinsic semiconducting properties. The thermoelectric power and Hall effect measurements for all compounds were confirmed the p-type semiconductivity except Y1.79Pr0.21Ru1.99Pr0.01O7 compound and which showed n-type semiconductivity. The dielectric constant (ε’) and dielectric loss (tan δ) i. e dissipation factor decreases with an increase in frequencies and reaching constant at particular frequencies. The applied field dependence of magnetization curve at room temperature (300 K) for Nd1.9Ho0.1Zr1.8Ce0.2O7, Y1.79Pr0.21Ru1.99Pr0.01O7 and Dy1.9Yb0.1Mn1.93Cu0.07O7, showed hysteresis loop with a small kink around the origin and which can be attributed to small but definite ferromagnetic ordering along with significant paramagnetic and superparamagnetic components. The magnetization at 2K showed a clear hysteresis loop for Dy1.9Yb0.1Mn1.93Cu0.07O7 and Dy1.99Sr0.01Sn2O7 pyrochlores are soft (weak) ferromagnets.

Effect of the reaction of ammonia gas on the swelling of metallic iron and its oxides during nitriding processes

In order to study the relationship and effect of nitrogen gas in the reducing gases used in the reducibility tests of iron oxides, under isothermal conditions, a test scheme was executed using ammonia gas, such that its decomposition of the gas in the reactor produced a mixture of H2 and N2 gases. Furthermore, the addition of 6% NH3 in a 28% H2 and 68% N2 gas stream was planned to obtain a gas composition of 70% N2 and 30% H2. This would allow comparing the reducibility curves between both conditions, assuming that the possible difference between both conditions to compare the volume changes of the reduced samples. The difference to be studied will be based on the estimation and comparison of the rate of formation of metallic iron in the stages of reduction of Hematite / Magnetite / Wustite (FeO), as well as the effects of nitrogen absorbed by the fresh metallic iron produced, or present. in iron catalysts to produce ammonia, from the reducing gas mixture, on the volume change of the samples. Likewise, the catastrophic volume changes caused by nitrogen are compared by comparing sources of this gas in solid carbonaceous reducers.&#x0D; Keywords: Gaseous Reduction, Direct Reduced Iron, isothermal tests.&#x0D; References&#x0D; [1]O. Dam G. “The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction”. Univ. of London. PhD Thesis 1983.&#x0D; [2]J. Bogde. “Thermoelectric Power Measurements in Wustite. Univ. of Michigan”. 1976.&#x0D; [3]O. Dam G. y J. Jeffes. “Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking”. Vol. 14, N`5. 1987.&#x0D; [4]M. Yang. “Nitriding-Fundamentals, modelling and process optimization”. Tesis PhD. Worcester Polytech Institute. 2012.&#x0D; [5]EL Kasabgy. T and W-K. LU. “The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation”. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, pp. 410-414. 1980.&#x0D; [6]“Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets”. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012.&#x0D; [7]R. Agarwal, S. Hembram. “To Study the Reduction and Swelling Behavior Iron Ore Pellets”. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013.&#x0D; [8]C. Seaton., J. Foster. and J. Velasco. “Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char”. Transactions ISIJ, Vol. 23, 1983, pp.&#x0D; [10]C. Bozco. “Interaction of Nitrogen with Iron Surfaces”. Journal of Catalysis 49. pp16-41. 1977.&#x0D; [11]L. Darken y R. Gurry. “Physical Chemistry of Metals”. Mc Graw hIll . 1953.&#x0D; [12]H. Weirdt and Z. Zwell, Trans. AIME. 229. 142. 1969.&#x0D; [13]J. Schulten. Trans. Soc. Faraday. 53, 1363, 1957.&#x0D; [14]E. Barret y C. Wood. Bureau of Mines R-I 3229. 1934

Structural, optical and electrical properties of spray-deposited Fe-doped nanocrystalline ZnS0.2Se0.8 thin films

ABSTRACT In this work, ZnS0.2Se0.8 thin films doped with Fe of various concentrations were spray deposited to investigate the influence of Fe doping concentration on the most significative structural, morphological, optical and electrical properties. An X-ray diffraction study showed that all films were polycrystalline and had a cubic zinc blende crystal structure. SEM showed that the Fe-doped ZnS0.2Se0.8 thin films had a spherical-like structure with agglomeration of grains and that their particle size was slightly increased. EDAX confirmed that the ZnS0.2Se0.8 lattice was doped with Fe. An optical study indicated that there was a direct allowed type transition. The band gap of ZnS0.2Se0.8 thin films sharply increased to 3.25 eV with Fe doping upto 0.2 mol% and then gradually decreased with increasing Fe doping concentration. DC electrical resistivity measurements confirmed that the films were semiconducting; with a minimum resistivity of 0.617 × 105 Ω-cm. Hall Effect and thermoelectric power measurements confirmed n-type conductivity.

SYNTHESIS AND CHARACTERIZATION STUDY OF HGXCR2-X S4 COMPOSITE THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION TECHNIQUE

The ternary thin films of composite HgxCr2-xS4 (x = 0.6) have been deposited by simple chemical bath deposition (CBD) technique on glass substrate. The thin films have been deposited at optimized conditions pH at 10 0.1, bath temperature 650C, deposition time 120 minutes. The films were uniform and adherent to glass substrates. They were characterized by structural, optical, and electrical measurement techniques. According to their X-ray diffraction patterns HgxCr2-xS4(x = 0.6) films are crystalline with band gap of 2.4 eV. Scanning electron micrographs showed that the substrates were well covered with films no cracks or pinholes were observed. The electrical resistivity of the films is found to be 1.3703 x 103 Ω-cm to 2.1243 x 103 Ω-cm at temperature range 3030k to 4230K. According to thermoelectric power measurements HgxCr2-xS4(x = 0.6) thin films are of n-type nature.

Synthesis of multifunctional CdSe and Pd quantum dot decorated CdSe thin films for photocatalytic,electrocatalytic and thermoelectric applications

The present paper describes the galvanic (electrochemical) synthesis of CdSe thin films on FTO (Fluorine doped tin oxide) coated glass substrates. The phase and surface microstructure of the coatings were characterized using X-Ray Diffraction(XRD), Field Emission Scanning Electron Microscopy(FESEM), Transmission electron microscopy(TEM). Elemental state composition of annealed CdSe films containing Pd was analysed using X-ray photoelectron spectroscopy(XPS). Spectroscopic analyses were carried out with UV-Vis spectroscopy. Photocatalytic degradation study of toxic dyes and photoreduction of metal ions in solution were carried out with these films to ascertain their utility as an efficient material for wastewater treatment. Electrocatalytic behaviour was established by carrying out Oxygen Evolution Reaction (OER) with these CdSe films as electrodes. Thermoelectric power (S) and thermal conductivity (Ƙ) measurements were performed to identify their potential as thermoelectric material.

ESR Investigations of (BaSnO3)x/(Cu, Tl) 1223 composite in the normal and superconducting state

ABSTRACT (BaSnO3)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconducting composites (0.00 ≤ x ≤ 1.50 wt.%) were prepared by the solid-state reaction technique. The crystalline structure and superconducting transition temperature were investigated by X-ray powder diffraction (XRD) and dc-electrical resistivity measurements, respectively. X-Band electron spin resonance (ESR) measurements were carried out at different temperatures 103 ≤ T ≤ 298 K. ESR spectra are dominated by a single asymmetric line corresponding to Cu2+ ions at the rhombic site. The temperature dependence of the g factors allowed the determination of the pseudo-gap onset temperature T*. The results of T* are compatible with those obtained from resistivity and thermoelectric power measurements. The contribution of delocalized electrons from Cu2+ ions in the disordered part of the impurity phases BaCuO2 and Ba2CuO3 is significant for the high addition of nanoparticles. Moreover, the number of spins N participating in ESR and the activation energy Ea were enhanced with the addition of BaSnO3.

Understanding the effect of thickness on the thermoelectric properties of Ca3Co4O9 thin films

We are reporting the effect of thickness on the Seebeck coefficient, electrical conductivity and power factor of Ca3Co4O9 thin films grown on single-crystal Sapphire (0001) substrate. Pulsed laser deposition (PLD) technique was employed to deposit Ca3Co4O9 films with precisely controlled thickness values ranging from 15 to 75 nm. Structural characterization performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the growth of Ca3Co4O9 on Sapphire (0001) follows the island growth-mode. It was observed that in-plane grain sizes decrease from 126 to 31 nm as the thickness of the films decreases from 75 to 15 nm. The thermoelectric power measurements showed an overall increase in the value of the Seebeck coefficient as the films’ thickness decreased. The above increase in the Seebeck coefficient was accompanied with a simultaneous decrease in the electrical conductivity of the thinner films due to enhanced scattering of the charge carriers at the grain boundaries. Because of the competing mechanisms of the thickness dependence of Seebeck coefficient and electrical conductivity, the power factor of the films showed a non-monotonous functional dependence on thickness. The films with the intermediate thickness (60 nm) showed the highest power factor (~ 0.27 mW/m-K2 at 720 K).

Synthesis, structural and electrical conduction of some dual doped semiconductor oxides nanoparticles for photocatalytic degradation of Victoria blue-B and Brilliant yellow under solar light irradiation

In this study, the nanoparticles of undoped and dual (codoped) doped semiconductor oxides such as Bi2O3, Bi1.9Sm0.038Cu0.062O3; Co3O4, Co2.902Mn0.049Dy0.049O4; V2O5, V1.91Ni0.043Gd0.047O5; Cu2O, Cu1.927Mn0.036Yb0.037O; CeO2, and Ce0.938Ni0.028Zn0.034O2 were synthesized by tartarate and hydroxide coprecipitation method. The composition, structure, morphology, surface and optical properties of undoped and dual doped semiconductor oxides have been investigated by X-ray fluorescence spectroscopy (XRF), Energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analyzer and UV–Vis diffuse reflectance absorption spectra (UV–vis DRS). The XRD and SEM studies showcase monodispersion of undoped and dual (co-doped) doped semiconductor oxides in the average grain size range of 36–65 nm with a monoclinic structure for Bi2O3 and its doped oxide, cubic structure for Co3O4, Cu2O, CeO2 and their respective doped oxides and orthorhombic structure for V2O5 and its doped oxide. Rietveld refinements of XRD pattern and XPS results confirmed that the dual dopants exist in + 2 or + 3 states and successfully incorporated into the semiconductor oxide matrix. BET surface areas for these oxides were found in the range of 25.3–65.4 m2g−1. The band gap energy (Eg) of undoped and doped semiconductor had a direct transition to fall between 2.10 and 3.12 eV as estimated from the optical absorption data (UV–vis DRS) and found absorption band edge (λg) in the visible-light range. The d.c. electrical conductivity and thermo-electric power measurements for all compounds showed n-type semiconductor except undoped and doped Cu2O and Co3O4 compounds showed p-type semiconductivity. The photo catalytic activity of undoped and dual doped semiconductor oxides in the Victoria blue-B (VB) and Brilliant yellow (BY) solutions were studied in sunlight irradiation. A set of optimized conditions such as the amount of these oxides, initial dye concentration, pH, contact time and dopants on the photodegradation of these dyes were investigated in detail. The dual doped semiconductor oxides showed a noteworthy enhancement in the degradation of VB and BY dyes under exposure to sunlight. The enhanced photocatalytic activity can be attributed to the incorporation of multivalent dopants in semiconductor oxide matrix promoted the separation of photogenerated charges, inhibited the recombination of photogenerated carriers, and thus prolonged the charges lifetime to participate in the photocatalytic reaction. The kinetic measurements indicate the dominance of pseudo-first order rate constant for Victoria blue-B (VB) were higher than that of Brilliant yellow (BY) in all cases, indicating that the photocatalytic degradation of VB was easier and more rapid than BY dye during the adsorption and also ascribed to different molecular structure to these dyes. A tentative reaction mechanism has also been proposed for this photocatalytic reaction.

Efecto de la descomposición de gas de amoniaco (NH3) sobre el hinchamiento de óxidos de hierro durante reducción

Con el objeto de estudiar la relación y efecto del gas nitrógeno en los gases reductores utilizados en los ensayos de reducibilidad de óxidos de hierro, en condiciones isotérmicas, se ejecutó un esquema de ensayos utilizando gas amoniaco, tal que la descomposición del gas en el reactor produjera un gas de H2 y N2. Además, se planifico la adición de 6% de NH3 en una corriente de gas 28% H2 y 68% N2 para obtener una composición de gas de 70% N2 y 30% H2. Esto permitiría la reinterpretación de los datos de laboratorio para comparar las curvas d reducibilidad entre ambas condiciones, asumiendo que la posible diferencia entre ambas condiciones a comparar los cambios de volumen de las muestras reducidas. La diferencia a estudiar se basará en la estimación y comparación de la velocidad de formación de hierro metálico en las etapas de reducción de hematita/magnetita/wustita (FeO), así como los efectos del nitrógeno absorbido por el hierro metálico fresco producido, partir de la mezcla de gas reductor, sobre el cambio de volumen de las muestras. Así mismo se comparan empíricamente los cambios catastróficos de volumen causados por el nitrógeno comparando fuentes de este gas en reductores carbonosos sólidos.&#x0D; Palabras clave: reducción gaseosa, hierro de reducción directa (HRD), catálisis, catalizador de hierro, amoniaco, hinchamiento, absorción, nitruración. ensayos isotérmicos, nitrógeno en carbón.&#x0D; Referencias&#x0D; [1]O.G. Dam . The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction. Univ. of London. PhD Thesis 1983.&#x0D; [2]J.D Bogde.- Thermoelectric Power Measurements in Wustite. Univ. of Michigan. 1976.&#x0D; [3]O.G. Dam y J. Jeffes. Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking. 1987. Vol. 14, N`5.&#x0D; [4]M. Yang. Nitriding-Fundamentals, modelling and process optimization. Tesis PhD. Worcester PolytechInstitute. 2012.&#x0D; [5]T. EL Kasabgy y W-K. LU. (1980). The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, September 1980, pp. 410-414.&#x0D; [6]Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012.&#x0D; [7]R.S Agarwal y S.S. Hembram. To Study the Reduction and Swelling Behavior Iron Ore Pellets. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013.&#x0D; [8]C.E. Seaton y J.S. Foster. and Velasco. Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char. Transactions ISIJ, Vol. 23, 1983, pp.&#x0D; [10]C. Bozco. et.al. Interaction of Nitrogen with Iron Surfaces. Journal of Catalysis 49. 1977.&#x0D; [11]L.S. Darken y R.W. Gurry, Physical Chemistry of Metals. Mc Graw hIll . 1953.&#x0D; [12]H. A. Weirdt, y Z .Zwell. Trans. AIME. 229. 142. 1969.&#x0D; [13]J.J.S.Schulten. et al. Trans. Soc. Faraday. 53, 1363, 1957.&#x0D; [14]E.G.Barret y C.F. Wood. Bureau of Mines R-I 3229. 1934.

Kinetics of the α-α′ phase separation in a 14%Cr oxide dispersion steel at intermediate temperatures

Current paper presents a study of the α–α′ phase separation during prolonged heat treatments at 400 and 450 °C of 14%Cr oxide dispersion strengthened steel. Vickers hardness, thermo-electric power and differential scanning calorimetry measurements enabled to conclude that α′ precipitates already after 5,000 hr at 400 °C, while at 450 °C precipitation is detected only after 10,000 hr. Yet, the amount of α′ after 10,000 hr at 450 °C was larger. The results, combined with thermodynamic and diffusion length calculations, affirm that in 14%Cr ODS steel the separation occurs by the nucleation and growth mechanism rather than spinodal decomposition.

Effect of cold rolling on phase separation in 2202 lean duplex stainless steel

The effect of plastic deformation (cold rolling) on the thermal aging of a lean 2202 duplex stainless steel at intermediate temperatures (280 °C–450 °C) was studied using a combination of atom probe tomography and thermoelectric power measurements. In the undeformed condition, spinodal decomposition of ferrite was shown to be the prime aging process with an activation energy of 206 kJ/mol. Plastic deformation enhanced the aging and the austenite partly transformed into martensite. When no precipitation or phase transformation was observed in austenite, both ferrite and martensite decomposed. The spinodal decomposition kinetics of ferrite increased with increasing deformation rate. The FeCr-rich martensite also decomposed at 450 °C, via a nucleation and growth process, owing to a decrease of the Cr content in the matrix. Chromium nitrides, G-Phase, and Cu-rich precipitates were observed in the decomposed martensite.