W. H. Song

Emissions of SO2, NO and N2O in a circulating fluidized bed combustor during co-firing coal and biomass

This paper presents the experimental investigations of the emissions of SO2, NO and N20 in a bench scale circulating fluidized bed combustor for coal combustion and co-firing coal and biomass. The thermal capacity of the combustor is 30 kW. The setup is electrically heated during startup. The influence of the excess air, the degree of the air staging, the biomass share and the feeding position of the fuels on the emissions of SO2, NO and N2O were studied. The results showed that an increase in the biomass shares resulted in an increase of the CO concentration in the flue gas, probably due to the high volatile content of the biomass. In co-firing, the emission of SO2 increased with increasing biomass share slightly, however, non-linear increase relationship between SO2 emission and fuel sulfur content was observed. Air staging significantly decreased the NO emission without raising the SO2 level. Although the change of the fuel feeding position from riser to downer resulted in a decrease in the NO emission level, no obvious change was observed for the SO2 level. Taking the coal feeding position R as a reference, the relative NO emission could significantly decrease during co-firing coal and biomass when feeding fuel at position D and keeping the first stage stoichiometry greater than 0.95. The possible mechanisms of the sulfur and nitrogen chemistry at these conditions were discussed and the ways of simultaneous reduction of SO2, NO and N20 were proposed.

Large magnetic entropy change near room temperature in antiperovskite SnCMn3

We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.

Magnetic and dielectric properties of Aurivillius phase Bi6Fe2Ti3O18 and the doped compounds

The magnetic and dielectric properties of Bi6Fe2Ti3O18, Bi6FeCoTi3O18, and Bi5LaFeCoTi3O18 are investigated. The room-temperature ferromagnetism is observed in the samples Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 compared with the paramagnetic behavior in Bi6Fe2Ti3O18 at room temperature. The ferromagnetism in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 can be ascribed to spin canting of the Fe-based and Co-based sublattices via the antisymmetric Dzyaloshinskii-Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 manifests itself a thermally activated relaxation process. The rather large activation energy (2.62 ± 0.11 eV for Bi6FeCoTi3O18 and 1.97 ± 0.07 eV for Bi5LaFeCoTi3O18) implies that the relaxation process is not due to the thermal motion of oxygen vacancies inside ceramics.

Enhanced giant magnetoresistance in Ni-doped antipervoskite compounds GaCMn3−xNix(x=0.05,0.10)

We report an enhanced negative giant magnetoresistance (GMR) with larger temperature span in Ni-doped antipervoskite compounds GaCMn3−xNix. The observed GMR can peak at ∼75% (at 85 kOe) and exceed 60% (at 50 kOe) over a temperature span of approximate 110 and 50K for x=0.05 and 0.10, respectively. Compared with the parent GaCMn3, the well-enhanced GMR in Ni-doped samples is suggested to be associated with the partially suppressed antiferromagnetic (AFM) ground state, which favors the transition from the high-resistivity AFM state to the low-resistivity canted ferromagnetic state under an external magnetic field.

Crystal growth and superconductivity of FeSex

In this work, crystals of FeSex have been grown by a flux approach. The crystallization process is divided into two stages. First, stoichiometric polycrystal FeSe0.82 was sintered in a solid state reaction. Then, FeSex crystals with a size about 500 µm were successfully grown in an evacuated sealed quartz tube using a NaCl/KCl flux. The products include two crystal structures: tetragonal and hexagonal. The electronic transport and magnetic property measurements show that FeSex crystals exhibit a superconducting transition at about 10 K.

Magnetic and transport properties in the Ti doped cobaltite Ca3Co4−xTixO9(0⩽x⩽0.8) single crystals

Single crystals of Ca3Co4−xTixO9 (x=0, 0.2, 0.4, 0.6, and 0.8) are grown by flux growth technique. The effect of Ti doping at Co site on magnetic and transport properties is studied. All samples show Curie-Weiss behavior at temperatures above 50K except for the x=0.8 sample, and the effective magnetic moment μeff increases with increasing Ti content. The free-doped sample Ca3Co4O9 shows a ferrimagnetic transition at 19K. However, a spin-glass transition at Tf(∼20K) appears for the Ti doped samples and the transition temperature Tf shifts to higher temperature as the Ti content increases. The magnetic moment values M at Tf and 5K under the applied field of 4.5T increase with increasing Ti doping content. The variation of the magnetic properties may be related to the induced extra Co2+ ions in the CoO2 layer by substituting Ti4+ for Co3+. The resistivity ρ of the x=0, 0.2, 0.4, and 0.6 samples shows metalliclike behavior at high temperatures and a broad metal-insulator (M-I) transition appears as the temper...

Observation of spin-glass behavior in antiperovskite compound SnCFe3

We investigated the physical properties of antiperovskite compound SnCFe3 by comprehensive magnetic measurements. The strong irreversibility is clearly observed from zero-field-cooled and field-cooled magnetizations. The peaks of ac susceptibility display strong dependences on the frequency and magnetic field. Both the magnetic relaxation effects and related analysis indicate a typical spin-glass (SG) behavior in SnCFe3. The corresponding characteristic parameters are obtained: the freezing temperature T0=20.3 K, the dynamical exponent zν=9.441, and the flipping time τ0=2.42×10−11 s. Furthermore, the Sn deficiency affects significantly the SG behavior and results in a sharp decrease in T0.

Structural, magnetic, and transport properties of the Cu-doped manganite La0.85Te0.15Mn1-xCuxO3 (0≤x≤0.20)

The effect of Cu-doping at Mn-site on structural, magnetic and transport properties in electron-doped manganites La0.85Te0.15Mn1-xCuxO3 has been investigated. Based on the analysis of structural parameter variations, the valence state of the Cu ion in Cu-doped manganites is suggested to be +2. All samples undergo the paramagnetic-ferromagnetic (PM-FM) phase transition. The Curie temperature decreases and the transition becomes broader with increasing Cu-doping level, in contrast, the magnetization magnitude of Cu-doping samples at low temperatures increase as x \leq 0.15. The insulator-metal (I-M) transition moves to lower temperatures with increasing Cu-doping content and disappears as x > 0.1. In addition, the higher temperature resistivity r peak in double-peak-like r(T) curves observed in no Cu-doping sample is completely suppressed as Cu-doping level x = 0.1 and r(T) curve only shows single I-M transition at the low temperature well below . The results are discussed according to the change of magnetic exchange interaction caused by Cu-doping.

Multiferroicity and magnetoelectric coupling enhanced large magnetocaloric effect in DyFe0.5Cr0.5O3

DyFe0.5Cr0.5O3 has been synthesized using a sol-gel method. It exhibits ferroelectricity at the antiferromagnetic ordering temperature TN1∼261 K. Large magnetocaloric effect (MCE) (11.3 J/kg K at 4.5 T) enhanced by magnetoelectric coupling due to magnetic field and temperature induced magnetic transition was observed. Temperature-dependent Raman study shows an anomalous behavior near TN1 in the phonon modes related to the vibration of Dy atoms and stretching of CrO6/FeO6 octahedra, suggesting the ferroelectricity in DyFe0.5Cr0.5O3 is associated with the spin-phonon coupling with respect to both Dy and Cr/Fe ions. These results suggest routes to obtain high-temperature multiferroicity and large MCE for practical applications.

Diamagnetism, transport, magnetothermoelectric power, and magnetothermal conductivity in electron-doped CaMn1−xVxO3 manganites

The effects of V doping on field-cooled magnetization MFC(T), zero-field-cooled magnetization MZFC(T), resistivity ρ, thermoelectric power S, and thermal conductivity κ in manganites CaMn1−xVxO3 (0.02⩽x⩽0.08) have been investigated systematically. As the V doping level exceeds 0.02, an anomalous “diamagnetism” has been observed. It is suggested that the force generated by the orbit rotation of eg electron in Mn3+O6 octahedron makes the spin tilt, as a result, the vector sum of individual spins may be along or opposite to the direction of the applied magnetic field, and macroscopically, the average magnetization exhibits positive or negative values. In addition, the transport mechanism in the high and low temperature ranges is dominated by the small polaron conduction and the variable-range-hopping conduction, respectively, according to the fitting analysis of the temperature dependence of Seebeck coefficient S(T) and resistivity ρ(T). Both S and κ peaks appearing at low temperature is gradually suppressed...