Zuotai Zhang

Coexistence of superconductivity and magnetism in KxFe2-ySe2-zSz (z=0,0.4)

High-quality single crystals of K0.8Fe2Se1.4S0.4 are successfully synthesized by self-flux method with the superconducting transition temperatures Tconset = 32.8 K and Tczero = 31.2 K. In contrast to external pressure effect on superconductivity, the substitution of S for Se does not suppress Tc, which suggests that chemical doping may mainly modulate the anion height from Fe-layer rather than compressing interlayer distance. The investigation of the micromagnetism by electron spin resonance shows clear evidence for strong spin fluctuation at temperatures above Tc. Accompanied by the superconducting feature spectra, a novel resonance signal develops gradually upon cooling below Tc, indicating the coexistence of superconductivity and magnetism in K0.8Fe2Se1.4S0.4 crystal.

Magnetism and superconductivity in MxFe1+yTe1–zSez (M = Cr, Mn, Co, Ni, Cu, and Zn) single crystals

High-quality single crystals with nominal composition M0.05Fe0.95Te0.8Se0.2 (Mu2009=u2009Cr, Mn, Co, Ni, Cu, and Zn) have been grown, through which the doping effect on magnetism and superconductivity is studied. Elementary analysis reveals that Cu, Co, and Ni, with smaller ionic radii for valence state 2+, can substitute effectively for Fe with doping levels near 5%. In contrast, the solid solution of Cr, Mn, and Zn in the host system is low. Magnetic and electronic investigations show that the substitution of Co, Ni, or Cu for Fe leads to the formation of spin-glass state and suppression of superconductivity. The superconductivity is partly suppressed by Co doping, while completely destroyed by Ni and Cu doping. Compared with Cu- and Ni-doped samples, the Co-doped sample has the smallest lattice constant, indicating that the superconductivity might be also modulated by the changes of microstructure.

Inconsistent pressure effect on superconducting transition temperature and volume in Fe1+yTe1−xSex single crystals

The role of Se in determining the superconductivity of Fe1+yTe1−xSex is still unclear. In this paper, we examine the chemical effect generated by Se substitution by applying external pressure on Fe1+yTe1−xSex single crystals. With increasing pressure, the superconducting volume increases; however, the onset temperature of the superconducting diamagnetic signal, Tcmag, does not change monotonically. The inconsistent pressure effect on superconducting volume and Tcmag is in agreement with Se substitution, which suggests that the chemical pressure effect dominates the superconductivity. Our results also imply that the superconducting and magnetic phases coexist in the form of phase separation.

Effect of water-washing on the co-removal of chlorine and heavy metals in air pollution control residue from MSW incineration

The present study systemically investigated the effect of a water-washing process on the removal of harmful chlorides, sulfates, and heavy metals in the air pollution control (APC) residue from municipal solid wastes incineration (MSWI), for sake of a better reuse and disposal of this kind of waste. In addition, the kinetic study was conducted to reveal the releasing mechanism of relevant element in the residue. The results show that, over 70wt.% of chlorides and nearly 25wt.% of sulfates in the residue could be removed by water washing. Based on an economical consideration, the optimal operation conditions for water washing of APC residue was at liquid/solid (L/S) ratio of 3mL:1g and extracting time of 5min. As expected, the concentrations of Co, Cr, Fe, Ni, V and Cu in the washing effluent increased with time during the washing process. However, the extracting regime differs among different heavy metals. The concentrations of Ba and Mn increased firstly but declined afterwards, and concentrations of Pb and Zn gradually declined while Cd and As kept constant with the increase of extracting time. It is worth mentioning that the bubbling of CO2 into the washing effluent is promisingly effective for a further removal of Pb, Cu and Zn. Furthermore, kinetic study of the water washing process reveals that the extracting of heavy metals during water washing follows a second-order model.

Pressure effects on superconductivity of Fe1+yTe1-xSx single crystals

We have investigated the pressure effect on superconductivity of Fe1+yTe1−xSx single crystals. We show that the applied pressure leads to opposite variation in the superconductivity between homogeneous and inhomogeneous samples. With increasing pressure to 10 kbar, the superconductivity of homogenous sample S1 is suppressed gradually, however Tcmag of inhomogeneous S4 can be raised up to 21 K. The increase in Tcmag in S4 is believed as stabilizing the structure by strain effect in inhomogeneous sample, thereby avoiding structural transition under pressure. Our results imply that higher Tc could be expected in iron chalcogenides if this structural instability could be suppressed.

Effect of inherent minerals on sewage sludge pyrolysis: Product characteristics, kinetics and thermodynamics

Inherent minerals in sludge influence sludge pyrolysis behaviors and the final products. In this study, the effects of inherent minerals on sewage sludge pyrolysis were systematically investigated by studying the pyrolysis behaviors of raw sewage sludge (RS) and HCl-washed sludge (WS), and in combination with thermodynamic equilibrium simulations for the hypothetical mineral-free sludge (AS) assumed. The pyrolysis of RS and WS was performed with a novel online thermogravimetric analyzer equipped with an infrared spectrometer and a gas chromatograph coupled with a mass spectrometer (TG-IR-GC/MS). It was found that inherent minerals influenced both the release of volatile products as a function of pyrolysis temperature, and the development of the physicochemical properties of the derived char. In the temperature range of 300-500u202f°C, hydrocarbons with more than 4 carbon atoms as well as aromatic compounds showed an increased release during WS pyrolysis, with respect to RS, while hydrocarbons with less than 3 carbon atoms such as CH4 and C3H6 exhibited a decreased release. In addition, the inherent minerals enhanced the release of HCN and NH3, both leading to increased NO2 release, and the release of H2S and COS was also promoted while the release of CH3SH, SO2 and CS2 was mitigated. Kinetic analysis confirmed that a catalytic effect induced by the inherent minerals decreased the activation energy at 300-500u202f°C. Thermodynamic simulations suggested that inherent minerals influenced sludge pyrolysis and the derived products formation by increasing the total Gibbs energy of the sludge pyrolysis system. Therefore, considerations of sludge inherent minerals should be taken into account during pyrolysis for the purpose of value-added commodity production and pollutant mitigation.

Application of washed MSWI fly ash in cement composites: long-term environmental impacts

In the present study, long-term environmental impacts of compact and ground cement composites, in which 30xa0wt.% of cement was replaced by washed municipal solid wastes incineration (MSWI) fly ash, were investigated for use in building industry. Consecutive leaching tests over a time span of 180xa0days were performed in acid water, deionized water, and saline water, respectively, with the accumulative concentration of different elements determined in the leachate. Different leaching behaviors are observed among different potential toxic elements (PTEs). For instance, higher concentrations of V in the leachate were observed from the compact cement composites than those from the ground ones. The concentration of Ba in the leachate increased with the decrease of particle size of the cement composites, and an initial increase in the leaching efficiency of Sn was followed by a clear decline with the leaching time. In addition, kinetic study revealed that the leaching behaviors of potential toxic elements follow a second-order model. The results demonstrated that the addition of washed MSWI fly ash into cement can contribute to the attrition resistance, indicating that the washed MSWI fly ash could be a promising alternative for cement as supplementary building materials.