Pressure Effect on Superconductivity and Magnetism in α-FeSe x

In this paper, the pressure effect on superconductivity and magnetism has been investigated in FeSe _x (x=0.80,0.88). The magnetization curves display anomaly at T _s1∼106 K and T _s2∼78 K except for the superconducting diamagnetic transition around T _c ∼8 K. The magnetic anomaly at T _s1 and T _s2 can be related to a ferromagnetic and an antiferromagnetic phase transition, respectively, as revealed by specific heat measurements. The application of pressure not only raises T _c , but also increases both T _s1 and T _s2.      

Superconductivity and magnetism in 11-structure iron chalcogenides in relation to the iron pnictides

Abstract

This is a review of the magnetism and superconductivity in ‘11’-type Fe chalcogenides, as compared to the Fe-pnictide materials. The chalcogenides show many differences from the pnictides, as might be anticipated from their very varied chemistries. These differences include stronger renormalizations that might imply stronger correlation effects as well as different magnetic ordering patterns. Nevertheless the superconducting state and mechanism for superconductivity are apparently similar for the two classes of materials. Unanswered questions and challenges to theory are emphasized.     

Superconductivity and magnetism in 11-structure iron chalcogenides in relation to the iron pnictides

This is a review of the magnetism and superconductivity in ‘11’-type Fe chalcogenides, as compared to the Fe-pnictide materials. The chalcogenides show many differences from the pnictides, as might be anticipated from their very varied chemistries. These differences include stronger renormalizations that might imply stronger correlation effects as well as different magnetic ordering patterns. Nevertheless the superconducting state and mechanism for superconductivity are apparently similar for the two classes of materials. Unanswered questions and challenges to theory are emphasized.     

Transformation mismatch plasticity in Pd induced by cyclic hydrogen charging

Transformation mismatch plasticity is achieved in swaged palladium wires by cyclical hydriding–dehydriding. Upon multiple cycles at ambient temperature, a total strain of 40% is accumulated under a constant tensile stress. This value is much higher than the tensile ductility for swaged Pd subjected to monotonic deformation without transformation (<2% for this wire). Strain increments after a single cycle are proportional to the applied stress, in agreement with the Greenwood–Johnson equation for transformation mismatch plasticity. The yield stress of hydrogen-cycled Pd calculated from this equation is 760 MPa, which is much higher than the value of the original wire and about 50% higher than previous values reported for Pd that was hydrogen cycled at 100 °C without an applied stress.     

Visualization of hydrogen diffusion in steels by high sensitivity hydrogen microprint technique

Hydrogen diffusion in steels was examined by both a high sensitivity hydrogen microprint technique (HMT) and an electrochemical hydrogen permeation method. The main diffusion path in an extremely low carbon steel was lattice within grains; grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, hydrogen diffused through proeutectoid ferrite and ferrite in pearlite under steady-state of hydrogen diffusion. The diffusion paths, however, were carbide/ferrite interfaces when hydrogen charging was interrupted before achievement of the steady state. This is probably ascribable to the reversible trapping effect of the interface. The detection efficiency of the high sensitivity HMT was 75% for the low carbon steel and 40% for the hypo-eutectoid steel.     

Spontaneous Stoichiometry Change in Single Crystals of Superconducting (Ba1−x K x )Fe2As2 Grown by a Rapid-Heating Sn-Flux Method

To prevent the loss of K in growing single crystals of Ba_1−x K _x Fe₂As₂ we developed a rapid-heating Sn-flux method. Large single crystals with the optimal superconducting transition temperature T _C≈38 K were obtained and their structural, chemical and superconducting properties were investigated. Additionally, the effect of post-growth annealing on these crystals at different temperatures was examined. Scanning electron microscopy microprobe studies on a crystal with the composition goal of Ba_0.25K_0.75Fe₂As₂ revealed a well defined separation of two phases with compositions that are suggestive of rational ratios of the K and Ba content.     

Critical Assessment 17: Mechanisms of hydrogen induced cracking in pipeline steels

Hydrogen induced cracking (HIC) remains a prominent issue for oil and gas exploration in challenging environments. This assessment discusses HIC in light of hydrogen transport through pipeline steel microstructures and crack initiation and propagation processes. While there has been significant research in hydrogen permeation through steel alloys, additional understanding is necessary in microstructures specific to pipeline steels. Furthermore, a standard model for crack initiation and propagation processes needs to be established; a fracture mechanics based model, which has been used by some researchers, is presented in the present paper to predict crack propagation. Advanced characterisation techniques can help elucidate mechanisms of hydrogen induced crack growth. Ultimately, linking hydrogen transport and cracking processes during HIC will enable optimised alloy and microstructure design.     

Visualization of hydrogen diffusion in steels by high sensitivity hydrogen microprint technique

Hydrogen diffusion in steels was examined by both a high sensitivity hydrogen microprint technique (HMT) and an electrochemical hydrogen permeation method. The main diffusion path in an extremely low carbon steel was lattice within grains; grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, hydrogen diffused through proeutectoid ferrite and ferrite in pearlite under steady-state of hydrogen diffusion. The diffusion paths, however, were carbide/ferrite interfaces when hydrogen charging was interrupted before achievement of the steady state. This is probably ascribable to the reversible trapping effect of the interface. The detection efficiency of the high sensitivity HMT was 75% for the low carbon steel and 40% for the hypo-eutectoid steel.     

Effect of grain size and second phase particles on the hydrogen occlusivity of iron and steels

The trapping of hydrogen by various interfaces in iron and steels has been studied. The hydrogen content of pure iron specimens was found to depend more on hydrogen than those of low angle, and thus specimens with low angle grain boundaries were less susceptible to hydrogen damage. Inclusions and thermo-mechanical treatments were also significant in determining the hydrogen pick-up in iron. A critical volume fraction of inclusions was detected, below which no hydrogen- induced cracking occurred. Ferrite/pearlite and pearlite/pearlite colony interfaces in steel were found to trap hydrogen, whereas the ferrite/comentite interface within the pearlitic colonies had little effect on the hydrogen occlusivity. Received: 26 May 1999 / Reviewed and accepted: 28 October 1999     

The effect of lattice defects induced by cathodic hydrogen charging on the apparent diffusivity of hydrogen in pure iron

The variation of apparent hydrogen diffuoivity with the applied current density and the types and amounts of hydrogen -induced damage caused by hydrogen during the cathodic charging of hydrogen in pure iron are investigated by thermal analysis techniques, and analysed in the light of theoretical models. Internal microcracks and microvoids are generated predominantly below 1 mA cm^–2 and are the major trapping sites of hydrogen in pure iron when charging hydrogen cathodically. Blisters on the surface of iron specimens are found tD be interconnected to the surface of the specimen through microcracks remaining in the vicinity of blisters. The peak temperature of hydrogen released from an internal microcrack or microvoid decreased as the applied current density is increased. The apparent diffusivity of hydrogen at 458 K decreases linearly with the reciprocal value of the square root of applied current density during cathodic charging. This implies that the amounts of internal microcracks or microvoids are linearly proportional to the lattice hydrogen solubility or the square root of the applied current density.     

Thermally induced changes in the magnetic properties of iron oxide nanoparticles under reducing and oxidizing conditions

Application of iron oxide nanoparticles in the fields of water purification, biomedicine or chemistry often requires controlled magnetic properties that can be modified by changing temperature and redox conditions. Therefore, this work investigates the changes in the magnetic properties of iron oxide nanoparticles in the FeOOH − Fe₂O₃ − Fe₃O₄ system (i.e. hematite, goethite, lepidocrocite, maghemite and magnetite) at heating under reducing and oxidizing conditions. The results show that heat treatment of hematite and goethite in the presence of a reducing agent (5% starch) leads to their conversion into high magnetic magnetite. The starting temperature of transformation is approximately 350 °C for both samples. The magnetization increases to 86 Am²/kg for hematite reduced at 700 °C and to 88 Am²/kg for goethite reduced at 900 °C. An intense reaction occurs within the first 10 min and then the conversion process decelerates. Thermal treatment of lepidocrocite under both oxidizing and reducing conditions leads to an increase in magnetization due to the formation of maghemite and magnetite, respectively. Regardless of the redox conditions, the formation of magnetic phase begins at a temperature of 250 °C and is associated with the formation of maghemite from lepidocrocite. Under oxidizing conditions, the magnetization begins to decrease at 350 °C, which is associated with the conversion of maghemite to hematite. On the contrary, under reducing conditions, the magnetization of lepidocrocite increases up to 900 °C, which is associated with the formation of magnetite. Maximum values of magnetization are 36 Am²/kg for maghemite obtained at 350 °C, and 88 Am²/kg for magnetite obtained at 900 °C from lepidocrocite. With the help of conventional heating, the magnetic properties of IONs can be altered by phase transformations in the FeOOH − Fe₂O₃ − Fe₃O₄ system. Temperature and redox conditions are the two most important factors controlling the transformation pathways and the magnetic properties of the resulting IONs.     

Melting of iron nanoparticles embedded in silica prepared by mechanical milling

For decades, experimental studies on the size-dependent melting of metals are regretfully limited to some eight archetypal examples. In this work, to expand this slim range of materials, the melting behavior of Fe nanoparticles embedded in SiO₂ prepared by using mechanical milling are investigated. Effects of factors in sample preparation on the size, isolation and thermal stability of Fe nanoparticles are systematically studied. On this basis, the size-dependent melting of Fe is successfully traced: for Fe nanoparticles with a diameter of about 15 nm, the melting point depression is 30 °C in comparison with bulk Fe, in accordance with our recent theoretical prediction.     

Use of an amorphous iron oxide hydrated as catalyst for hydrogen peroxide oxidation of ferulic acid in water

The abatement of ferulic acid (FA), a polyphenolic constituent of olive mill wastewater, is studied in the pH range 5.0-7.0 by using hydrogen peroxide and an amorphous iron oxide as catalyst. The effect of pH, catalyst load, hydrogen peroxide and substrate starting concentrations is assessed during the investigation. A suitable reaction scheme is developed and used to build a mathematical model which satisfactorily describes the system's behavior. Kinetic constants for the proposed scheme as well as the total active site concentration of the catalyst in the studied pH range are estimated. The occurrence of internal mass-transfer limitation for the adopted granulometric fraction of the catalyst is demonstrated.     

Two-dimensional hole localization induced by Zn, Ni, and Mg dopings in Cu sites in La1.85Sr0.15Cu1-x M x O y

Samples of La_1.85Sr_0.15Cu_1-xM_xO_y(M = Ni, Zn, and Mg) with a wide range of dopant concentration (0≤x≤0.30) were synthesized. X-ray diffraction analysis shows that the Zn doping results in a tetragonal-orthorhombic transition asx- >0.15. while both Ni- and Mg-doped samples still remain tetragonal up tox = 0.3. Furthermore, the Ni, Zn, and Mg dopings all reduce the local Jahn -Teller distortion of the CuO₆ octahedron in a similar way. The metalinsulator transition at the region of higher doping levei (x> 0.1) is observed in all three doped systems. The observed metal-insulator transition can be well interpreted in the context of Anderson’s theory of disorder-induced localization. For most of the semiconducting-like samples with higher doping level (x> 0.1), the conductive behavior is dominated by two-dimensional variable-range-hopping (2D-VRH) with {ie-13-01} This suggests that all the dopings of Ni, Zn, and Mg in Cu sites cause the localization of the holes. In addition, a remarkable difference in the room-temperature resistivity for the heavily doped samples with the same dopant (Zn, Ni, Mg) concentrations is also observed. A possible explanation is provided for this phenomenon.     

Effect of hydrogen dilution in preparation of carbon nanowall by hot-wire CVD

Carbon nanowall films prepared on the stainless steel substrates by hot-wire chemical vapor deposition using CH₄ with different hydrogen dilution ratios and structure variation in the CNWs against hydrogen dilution have been studied. In the scanning electron microscope images, the wall height and width in the samples prepared with the hydrogen dilution ratio, H₂/(CH₄ + H₂), between 10% and 25% were larger than that prepared without hydrogen dilution. In the Raman spectra for the samples prepared with the H₂/(CH₄ + H₂) below 25%, the intensity ratio of the G peak to the D peak, I_G/I_D, increased with increasing the H₂/(CH₄ + H₂). In the samples prepared with the H₂/(CH₄ + H₂) over 25%, the wall size and the I_G/I_D decreased.     

地下水中Fe的ICP-MS检测和修正方法

提出了使用电感耦合等离子体质谱法检测地下水中Fe的过程中,标准系列溶液与样品溶液由于基体不同,随雾化气流量变化时所受到的影响程度不一致,对样品中Fe的分析结果的准确性和可靠性产生不利影响。同时提出在线内标溶液含有一定浓度的Fe,并把相应的检测值带入分析结果,对低含量样品中Fe的分析结果的准确性和可靠性产生不利影响。通过实验研究,说明了使用监控样技术对这两个问题进行修正能够获得良好效果,并且相应说明了监控样的制备方法、保存条件和使用期限及对在线内标溶液的处理方法。在这个基础上,建立了新的电感耦合等离子体质谱法检测地下水中Fe的方法,重新确定了方法参数。方法的检出限(DL)达到18.9ng/mL。方法精密度(RSD)为6.11%～8.56%(n=12)。加标回收率为97.55%。     

Mechanism of the enhanced degradation of pentachlorophenol by ultrasound in the presence of elemental iron

Ultrasound combined with elemental iron (US/Fe(0)) is effective in oxidizing organic contaminants in water. The sonolysis degradation of pentachlorophenol (PCP) was significantly enhanced by a factor of 4.2 with the addition of elemental iron, mainly via reaction with hydroxyl radicals (OH radicals), and the synergistic mechanism of the enhancement in the combined system was investigated. Experiments were performed with (1) sole ultrasonic treatment; (2) ultrasound in presence of iron; (3) ultrasound combined with copper powder as the same particle size as iron powder; (4) ultrasound in presence of Fe(II). It was observed that PCP degradation and OH radicals production were both enhanced in these combined methods, and the pitting on the sonicated iron surface was apparent. These results indicated that the rate enhancements in US/Fe(0) system were attributed to (1) the iron solid effect and the catalysis of Fe(II) produced from corroded-iron with promoting the production of OH radicals; (2) the increased surface area of iron particles by acoustic cavitation with promoting the adsorption process.     

Inhibition of sulfate reduction by iron, cadmium and sulfide in granular sludge

This study investigated the inhibition effect of iron, cadmium and sulfide on the substrate utilization rate of sulfate reducing granular sludge. A series of batch experiments in a UASB reactor were conducted with different concentrations of iron (Fe²⁺, 4.0–8.5 mM), cadmium (Cd²⁺, 0.53–3.0 mM) and sulfide (4.2–10.6 mM), the reactor was fed with ethanol at 1 g chemical oxygen demand (COD)/L and sulfate to yield a COD/SO₄²⁻ (g/g) ratio of 0.5. The addition of iron, up to a concentration of 8.1 mM, had a positive effect on the substrate utilization rate which increased 40% compared to the rate obtained without metal addition (0.25 g COD/g VSS-d). Nonetheless, iron concentration of 8.5 mM inhibited the specific substrate utilization rate by 57% compared to the substrate utilization rate obtained in the batch amended with 4.0 mM Fe²⁺ (0.44 g COD/g VSS-d). Cadmium had a negative effect on the specific substrate utilization rate at the concentrations tested; at 3.0 mM Cd²⁺ the substrate utilization rate was inhibited by 44% compared with the substrate utilization rate without metal addition. Cadmium precipitation with sulfide did not decrease the inhibition of cadmium on sulfate reduction. These results could have important practical implications mainly when considering the application of the sulfate reducing process to treat effluents with high concentrations of sulfate and dissolved metals such as iron and cadmium.