Modification of interface chemistry and slag structure by transition element Cr

A comparative study on CaO–MgO–Al₂O₃–SiO₂ slag and CaO–MgO–Al₂O₃–SiO₂–Cr₂O₃ slag was conducted to investigate the distribution of the elements at the gas-slag interface. The effect of redox states of chromium on the distribution of sulfur and oxygen at the interface was revealed by gas-slag equilibrium method using X-ray photoelectron spectroscopy at 1873K. From the analysis of the S2p core-level spectra, the negative divalent sulfur(S^2?) was detected at the interface in the Cr-bearing slag, which directly proved that sulfur exists in the form of S^2? in the slag for the first time. However, the S^2? peak is very weak at the interface of Cr-free slag. The reason for the difference between the two slags may be due to chromium changing the interface structure. According to the O1s and Cr2p core-level spectra, non-bridged oxygen(O^?) increased, while bridged oxygen(O⁰) decreased with the etching depth deepened. The increase of NBO/BO and Cr²⁺/Cr³⁺ elucidates that Cr³⁺ can modify the structure of the slag as basicity substance, but its effect is weaker than that of Cr²⁺. Meanwhile, due to the affinity of sulfur and chromium, the addition of chromium may also lead to the enhancement of the S^2? peak at the gas-slag interface. Gradient change of elements at the interface proved the existence of the boundary layer.     

Fe-C熔体与熔渣反应的电化学机理

研究了含碳金属熔体与CSO—SiO2—Al2O3—FeOx熔渣体系反应的电化学机理．实验表明,在敞开体系中,无论金属熔体与熔渣之间是否存在电子导体,随着气相氧分压的降低,金属熔体的最终碳含量均逐渐增大,反应速率逐渐减小．但有电子导体贯穿反应体系时,熔体的最终碳含量远低于无电子导体的情况,其反应速率是后者的2～3倍．可以推断：氧离子在渣中的传递受控于电子的传递,电子导体的存在为电子的传递提供了一条捷径,因而加快了氧离子的传递．     

THE USE OF THE PENETRATION MODEL FOR THE DISSOLUTION OF LIMESTONE IN THE CO2-WATER SYSTEM

The penetration model was implemented for the dissolution of limestone in the CO₂-water system. The model includes the acid-base reactions of the carbonate species as well as the autoprotolysis of water. It was also assumed that there is no surface resistance to the dissolution of the solid. This assumption restricts the use of the model to those conditions where the dissolution rate is limited by the rate of mass transfer. When using the model, only the hydrodynamics of the water solution need to be experimentally determined and put in terms of the model's hydrodynamic parameter. All other model inputs are either physical constants or known bulk concentrations. Dissolution experiments, performed on a rotating cylinder system, were used to test the ability of the model to predict the dissolution rate of limestone in an aqueous solution. Of special significance was the ability of the model to predict the dissolution rate at different pH-values, CO₂ partial pressures, temperatures and hydrodynamic conditions. An explicit finite differences method was used to deal with the system of non-linear partial differential and algebraic equations, which arose from the implementation of the penetration model. This investigation has shown that the limestone dissolution process in the mass transfer controlled region, can be modelled and described by the penetration model. The penetration model accurately describes the effects of all parameters investigated, including the enhancement effect from CO₂ (up to a factor of 10 compared with dissolution in a CO₂-free atmosphere) and temperature. The penetration model has also been compared with the film theory model. The comparison of the two models shows that the penetration model yields a better correlation to the experimental data in a CO, atmosphere. In a CO₂-free atmosphere the models are almost identical. However, the penetration model is computationally more difficult. A numerical procedure for solving the penetration model has been designed. This procedure includes a method of dealing with the unusual boundary conditions at the surface.     

The capacitance of the diffuse layer of electric double layer of electrodes in molten salts

Similarly to aqueous electrolytes, the electric double layer of electrodes in molten salts is assumed to be composed of compact and diffuse layers. The charge density of the compact layer, formed as a monolayer of specifically adsorbed anions (primary ionic shell), is calculated as the difference between the charge of the primary ionic shell and the charge removed by the exchange current density. The centre of the specifically adsorbed anions create the inner Helmholtz plane (iHp). The counterions to the specifically adsorbed anions in the primary ionic shell, take place in the numerous neighbouring holes, introduced into the molten salt structure by the melting process, and being subjected to thermal motion, create the diffuse layer. The electrostatically adsorbed metal cations form the outer Helmholtz plane (oHp) with the value of the inner potential equal φ₂. Using the Boltzman and Poissone equations, the equation for the capacitance of the diffuse layer of the metallic electrode in molten salt is derived and tested on some literature experimental results.     

利用熔渣规则溶液模型计算渣铁间S、P分配比

利用Lumsden熔渣规则溶液模型能够计算渣中各组份的活度系数，从而能够用于计算渣铁间S、P分配比．     

Dissolution and diffusion kinetics of yttria-stabilized zirconia into molten silicates

The degradation of thermal barrier coatings (TBCs) by molten silicates (CMAS) represents a fundamental barrier to progress in gas turbine technology, requiring a mechanistic understanding of the problem to guide the development of improved coatings. This article investigates the dissolution of yttria-stabilized zirconia (7YSZ and 20YSZ) into two model silicate melts at 1300–1400 °C. The approach involves the 1D dissolution of YSZ into a semi-infinite melt, characterizing the dissolution rates of YSZ and the diffusion rates of Zr⁴⁺ and Y³⁺ therein. The assessed kinetics of YSZ dissolution and diffusion were then applied to modeling the same phenomena on TBC-relevant length scales. These findings provide fundamental insight into (i) the dissolution mechanism of YSZ, (ii) the subsequent reprecipitation upon saturation, (iii) the quantitative effects of temperature and melt composition on the dissolution and diffusion kinetics, and (iv) how the measured kinetics manifests on the scale of flow channels present in TBCs.     

In situ investigation on deformation and dissolution behavior of porous nickel during its oxidation/lithiation in Li/K2CO3 eutectic

On the basis of previous work, the home-made deformation-testing system was further applied to detect the thickness change of porous nickel materials in the various experimental condition of molten carbonate. The deformation and dissolution behavior of porous nickel and the loading effect on the behavior were in situ studied in the process of oxidation and lithiation. The results indicated that both an obvious deformation and a severe nickel dissolution occurred during the oxidation/lithiation of porous nickel in molten carbonate under loading conditions. Furthermore, the dissolution of nickel from porous nickel was still significant even if without loading. It was found that the deformation of porous nickel closely corresponded to its dissolution during the oxidation/lithiation of porous nickel in molten carbonate.     

Dissolution behavior of spent MgO–C refractory in the CaO–SiO2–FeO slag system as a steelmaking flux

A large amount of spent MgO–C refractory is generated in steel plant every year. Because of the similarities in chemical and mineralogical composition of slag formers and MgO–C refractory, it is possible to reuse the spent MgO–C refractory as a steelmaking flux. To achieve this goal, it should promote the dissolution of MgO–C refractory during slag forming. In this study, the effect of slag composition on the dissolution behavior of spent MgO–C refractory in the CaO–SiO₂–FeO slag system and the dissolution kinetics were investigated. It showed that the dissolution rate of MgO–C refractory was controlled by surface chemical reaction. The dissolution of MgO–C refractory led to an increase in the MgO content in slag while the FeO content decreased because the graphite in refractory was oxidized by FeO. Increasing temperature significantly promoted the dissolution of MgO–C refractory. The MgO–C refractory was readily dissolved in the low-basicity slag. A higher FeO content in slag was beneficial for the oxidation of graphite in refractory, resulting in better dissolution. The dissolution thickness of MgO–C refractory could exceed 4.0 mm under these conditions and its dissolution supplied some MgO to slag.     

利用固体激发剂生产^#525碱矿渣水泥

本文阐述了碱矿渣水泥的应用前景及国内碱矿渣水泥研究中存在的问题，介绍了利用固体激发剂生产碱矿渣水泥的研究结果，找出了在试验条件下利用固体激发剂生产碱矿渣水泥的最佳参数，测试了所得碱矿渣水泥性能，初步探索了碱矿渣水泥性能优异的原因。碱矿渣水泥生产能耗低、生产成本低、性能优良，有可能成为一种有发展前途的新型水泥。     

The effect of solid concentration on the secondary air-jetting penetration in a bubbling fluidized bed

The introduction of secondary air (SA) in fluidized bed boilers is of important engineering significance. In the present work, an experimental study on the characteristics of SA penetration is carried out by operating a bubbling fluidized bed model. Floater, the ash formed from coal combustion, is used as experimental bed material. It has an average size of 0.83 mm and a low density of 620 kg/m³. Results indicate that the floater is more suitable to be operated in a spouted or a bubbling bed. Comparing with the conventional sand and FCC, the fluidizing characteristics of the floater are similar to those of Geldart Group D particles. From measurements of the solid concentration in the bed cross section at SA injection level by use of a solid concentration measuring thief probe of own design, the relation between SA jetting distance and SA velocity under different solid concentrations is obtained when the properties of bed material and SA ports are fixed. Furthermore, a dimensionless correlation is proposed for general cases. The results may provide a basis for further study.     

Wetting,spreading and corrosion behavior of molten slag on dense MgO and MgO-C refractory

The wetting and spreading phenomena of molten slag were observed in situ on dense MgO and MgO-C refractory substrates. Parameters associated with wetting and spreading of molten slag, such as the contact angle, droplet height, diameter, and volume, were measured and calculated. The microstructure and chemical composition of the corroded dense MgO and MgO-C refractory were studied using SEM and EDS analysis. The droplet volume of molten slag on dense MgO declined faster than that on MgO-C refractory during the first 90?s of the testing period, whereas the droplet volume exhibited little difference across the two cases after 150?s. Molten slag penetrated the dense MgO and MgO-C refractory through grain boundaries and the channels which were formed by the dissolution of MgO. Besides, the slag also penetrated into the MgO-C refractory through the pores and channels formed by the redox reaction between slag and carbon, and a reaction product (Fe) was found at the interface. The dissolution of MgO and redox reactions changed the wetting process and increased corrosion of the MgO-C refractory.     

Influence of ash composition on heavy metal emissions in ash melting process

Two kinds of fly ash, discharged in the combustion of either refused derived fuel (RDF) or car shredder dust (SD), were examined for the emission of heavy metals in melting process under oxidizing and reducing conditions. The residual fractions of heavy metal in slag were experimentally estimated. As a result, it was confirmed that several volatile heavy metals were readily emitted during melting process. The type of atmosphere provided for the melting process was found to affect the emission of some volatile metals in RDF ash, but not in SD ash. The emission of volatile heavy metals in RDF ash under oxidizing conditions was lower than under any other conditions in this study. The emission behavior of iron and heavy metals in RDF ash under reducing conditions was similar to that in SD ash. These facts indicated that phosphorous in RDF ash had the property of fixing the volatile metals in the slag only under oxidizing conditions. Then the mixture of SD ash with phosphorous oxide powder was also tested in a melting process, and the result was consistent with the above inference of the effect of phosphorous.     

水煤浆气化操作条件对高铬耐火材料的影响

水煤浆气化是在高温、高压、强还原气氛下操作的 ,其气体成分及煤熔渣成分对耐火材料产生严重的侵蚀和损毁。通过分析气氛、熔渣及操作条件对耐火材料的影响 ,将有助于延长气化炉用耐火材料的寿命     

Mechanism of MgO dissolution in MgF2–CaF2–MF (M=Li or Na) melts: Kinetic analysis via in-situ high temperature confocal scanning laser microscopy (HT-CSLM)

The solid oxide membrane (SOM) process is a direct electrolysis method for refining magnesium and has become a popular and promising technology. In the electrolysis process of SOM, the metal oxide is dissociated into the metal cation and oxygen anion. Thus, it is important to investigate the dissolution reaction of metal oxides in molten fluoride flux, which contributes to the overall reaction mechanism and reaction rate. However, there are few fundamental studies on the reaction between oxide particles and fluoride flux. Notably, the dissolution behavior of magnesium oxide (MgO), which is a major source of magnesium production, into fluoride flux has not been reported. In addition, the dissolution behavior is mediated by the chemical and physical properties of the flux. Therefore, we investigated the dissolution reaction of MgO in fluoride flux using high temperature confocal scanning laser microscopy (HT-CSLM) measurements to demonstrate the reaction mechanism governing the dissolution rate of MgO particles. Consequently, the rate-limiting mechanism is a diffusion of O²⁻ ion, dissociated from MgO, through the boundary layer.     

Structural and magnetic properties of steel slag based glass–ceramics

Crystallisation of magnetite in multicomponent glass melts was investigated. Structural features and magnetic properties were tested using X-ray diffraction, scanning electron microscope techniques, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. The results show that the magnetite phase was detected in the glass–ceramic samples after heat treatment at higher crystallisation temperature (over 900°C). Fe²⁺ and Fe³⁺ ions contribute to the formation of magnetite crystal. Various crystal morphologies were observed. Isomer shift values suggest that Fe³⁺ and Fe²⁺ are in tetrahedral and octahedral coordination respectively. The saturation magnetisation tends to increase with the crystallisation temperature.     

Effect of diffusion on residence time distribution in chaotic channel flow

We consider the residence time distribution (RTD) of a liquid flowing through a spatially periodic channel. It is shown that chaotic advection significantly reduces deviation of the RTD which then consist of two parts: the main pulse which does not depend on the Péclet number and a long tail which is formed in the near-boundary layer, where the advection is weak. Boundary layer approximation provides the dependence of the statistical moments of the RTD on Péclet number. It is shown that the length of the tail increases with Pe, while its mass decreases. The numerical results support the theoretical findings.     

高强石膏的研究现状

简要介绍了石膏的种类,高强石膏的制备方法及晶体结构,根据目前国内外石膏的研究进展情况,重点叙述了由二水石膏转变成α型半水石膏的结晶理论以及晶型控制机理。并阐明双掺金属和羧酸盐作为调晶剂制备的石膏强度更高。针对α型高强石膏的特点介绍了应用范围并对今后的应用领域提出了期望。