Indirect Dissolution Research Articles

Improved slag corrosion resistance of MgO–C refractories with calcium magnesium aluminate aggregate and silicon carbide: Corrosion behavior and thermodynamic simulation

The influence of calcium magnesium aluminate (CMA) aggregate and silicon carbide on the slag corrosion resistance of MgO–C refractories was investigated by the induction furnace tests. The corrosion behavior and the formation of protective slag layer were also comprehensively discussed in present work. The results showed that CaAl2O4 in CMA converted into Al-containing liquid phase when facing the slag, while spinel with better slag corrosion resistance diffused into the refractory-slag interface. The Al-containing liquid phase melted from CaAl2O4 mixed with slag and increased the Al content, increasing the proportion of indirect dissolution, forming more spinel and decreasing the corrosion rate. Furthermore, the spinel and liquid slag formed solid-liquid mixture at the interface, increasing the viscosity and promoting the formation of protective slag layer, which avoided direct contact between slag and refractory. The combined use of CMA aggregate and silicon carbide showed better slag corrosion resistance because silicon carbide increased the oxidation resistance and inhibited the decarburized layer, while the FeSi alloy and higher viscosity also enhanced the slag corrosion resistance of such refractories.

Effect of MgO on wetting and corrosion behaviour of corundum substrate by CaO–SiO2–MgO (–Al2O3) slags

ABSTRACT Effect of MgO content on wetting and corrosion behaviour of corundum substrate by CaO–SiO2–MgO (−15%Al2O3) molten slags was investigated at 1450°C via joint application of a sessile drop technique, SEM–EDS detection and FactSage thermodynamic software. All slags exhibit good wettability on the substrate, and the contact angle values are small. Increasing MgO content from 7% to 9% in CaO-SiO2-MgO slags can increase the contact angle between the droplet and the substrate, while the substrate dissolution thickness and the slag penetration depth tend to decrease. Increasing MgO content from 8% to 15% in CaO-SiO2-MgO-15% Al2O3 slags can also increase the contact angle, but significantly decrease the slag penetration depth. The indirect dissolution thickness increases instead due to the formation of a large amount of MgAl2O4 by the interface reaction. The wettability can give an indication of the slag penetration depth in the substrate but not the dissolution thickness of the substrate.

Simultaneous recycling of Si and Ti from diamond wire saw silicon powder and Ti–bearing blast furnace slag via reduction smelting: An investigation of the effects of refractories on recycling

The industrial wastes diamond wire saw silicon powder (DWSSP) and Ti–bearing blast furnace slag (TBFS) are important Si and Ti secondary resources, respectively. During the industrial application of recycling DWSSP and TBFS via reduction smelting, the refractories can dissolve into the molten slag, which can change the composition of the slag and influence the extraction of Si and Ti. Unfortunately, few studies on the reduction smelting of DWSSP and TBFS related to refractories have been reported, making such studies urgently needed. Therefore, the main purpose of this work was to reveal the dissolution mechanism of refractories (alumina and magnesia bricks) and the effect of refractory dissolution on Si-Ti alloy preparation. The results show that during the reduction smelting, the dissolution of alumina and magnesia bricks changed from direct dissolution into the molten slag to indirect dissolution, and the amount of magnesia bricks dissolved was less than that of aluminum bricks. Al3+ (aluminum brick) entering the slag could replace Si4+ in [SinO2n] to form [AlxSin–xO2n]x-, increasing the viscosity of the slag. The O2– (magnesia brick) entering the slag could dissociate [AlxSin–xO2n]x-, decreasing the viscosity of the slag. Therefore, compared with alumina bricks, magnesia bricks can promote slag-alloy separation and improve the extraction ratios of Ti and Si. In the case of magnesia bricks, the maximum reduction ratio of TiO2 was 98.4 %, and the maximum extraction ratio of Si was 95.8 %. This work provides essential experimental data for the Si-Ti alloys prepared via recycling DWSSP and TBFS.

Formulation, Characterization and Permeability Studies of Fenugreek (Trigonella foenum-graecum) Containing Self-Emulsifying Drug Delivery System (SEDDS).

Fenugreek is used as a spice and a traditional herbal medicine for a variety of purposes, given its antidiabetic and antioxidant effects. Self-emulsifying drug delivery systems (SEDDS) of herbal drugs are targets of extensive research aiming to increase bioavailability and stability. The study’s objective was to formulate SEDDS containing Trigonella foenum-graecum extract to improve the stability of herbal extract and to increase their permeability through a Caco-2 monolayer. A characterized fenugreek dry extract was used for the formulations, while the SEDDS properties were examined by particle size analysis and zeta potential measurements. Permeability assays were carried out on Caco-2 cell monolayers, the integrity of which was monitored by follow-up trans-epithelial electric resistance measurements (TEER). Cytocompatibility was tested by the MTT method, and an indirect dissolution test was performed, using DPPH antioxidant reagent. Two different SEDDS compositions were formulated from a standardized fenugreek dry extract at either the micro- or the nanoemulsion scale with sufficient stability, enhanced bioavailability of the compounds, and sustained release from HPMC capsules. Based on our results, a modern, non-toxic, cytocompatible fenugreek SEDDS formulation with high antioxidant capacity was developed in order to improve the permeability and bioavailability of all components.

Influence of Al2O3 Level in CaO-SiO2-MgO-Al2O3 Refining Slags on Slag/Magnesia-Doloma Refractory Interactions

The influence of the Al2O3 level in CaO-SiO2-MgO-Al2O3 (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was investigated through static refractory finger corrosion tests. The tests were performed at 1620 °C under Ar atmosphere, using slags with Al2O3 contents of 5, 10, and 20 wt pct, respectively. The results indicate that the formation of 2CaO·SiO2 at the slag/refractory interface was suppressed by increasing the Al2O3 content to 20 wt pct, thereby changing the corrosion mechanism from an indirect dissolution to a direct dissolution of CaO and MgO from the refractories. The increased solubility limit of MgO by the Al2O3-rich CSMA slags results in an overall higher corrosion rate of the MgO-doloma refractory.

Macroporous silicon formation by electrochemical anodization of n-type silicon without illumination

This work reports the electrochemical anodization of low-doped n-type silicon in aqueous hydrofluoride (HF) solution without the use of external illumination to generate macroporous silicon with a thin mesoporous transition layer. We have shown that pore formation during the electrochemical anodization of low-doped n-Si in the dark is due to the avalanche breakdown mechanism. Studies of dissolution valence revealed a competition between divalent direct and tetravalent indirect dissolution processes. The effect of pore morphology on anodization parameters such as applied potential, HF concentration, and anodization time was systematically investigated. The fabricated porous silicon has well-separated and straight macropores of pore diameters ranging from 89 ± 9 to 285 ± 28 nm and with limited branching or interconnectivity. Pore diameter uniformity is maintained throughout the porous layer. XRD and Raman spectroscopy have shown that the porous Si fabricated here is highly crystalline, retaining its original crystallinity. The fabricated porous Si presented in this work with tunable pore sizes, depths, and surface features can have potential applications in various fields of microelectronics, photonics, and sensors.

Time-resolved high-temperature X-ray diffraction for studying the kinetics of corrosion of high-alumina refractory by molten oxides

The aim of this work is to quantify the corrosion kinetics of high-alumina refractories by a binary slag (Al2O3 50 wt.% CaO 50 wt.%) and a ternary slag (Al2O3 45 wt.% CaO 45 wt.% SiO2 10 wt.%). The main objectives are i) to determine corrosion kinetics based on time-resolved X-ray diffraction at high temperature (1600 °C) combined with Rietveld quantification and (ii) to propose a reaction model based on the dissolution/precipitation/diffusion mechanisms. The results show that the corrosion process is very fast and involves an indirect dissolution mechanism with the formation of Al2O3/CA6/CA2/slag interfaces.

Self-Nanoemulsifying Drug Delivery Systems Containing Plantago lanceolata-An Assessment of Their Antioxidant and Antiinflammatory Effects.

The most important components of Plantago lanceolata L. leaves are catalpol, aucubin, and acteoside (=verbascoside). These bioactive compounds possess different pharmacological effects: anti-inflammatory, antioxidant, antineoplastic, and hepatoprotective. The aim of this study was to protect Plantago lanceolata extract from hydrolysis and to improve its antioxidant effect using self-nano-emulsifying drug delivery systems (SNEDDS). Eight SNEDDS compositions were prepared, and their physical properties, in vitro cytotoxicity, and in vivo AST/ALT values were investigated. MTT cell viability assay was performed on Caco-2 cells. The well-diluted samples (200 to 1000-fold dilutions) proved to be non-cytotoxic. The acute administration of PL-SNEDDS compositions resulted in minor changes in hepatic markers (AST, ALT), except for compositions 4 and 8 due to their high Transcutol contents (80%). The non-toxic compositions showed a significant increase in free radical scavenger activity measured by the DPPH test compared to the blank SNEDDS. An indirect dissolution test was performed, based on the result of the DPPH antioxidant assay; the dissolution profiles of Plantago lancolata extract were statistically different from each SNEDDS. The anti-inflammatory effect of PL-SNEDDS compositions was confirmed by the ear inflammation test. For the complete examination period, all compositions decreased ear edema as compared to the positive (untreated) control. It can be concluded that PL-SNEDDS compositions could be used to deliver active natural compounds in a stable, efficient, and safe manner.

Metal removal and associated binding fraction transformation in contaminated river sediment washed by different types of agents.

In ex-situ washing, HCl, EDTA and H2O2 solutions can effectively extract heavy metals in river sediment. Nevertheless they often target different sediment components, possibly transforming metal species into more bioavailable and hence toxic ones. This study, in batch settings, investigated the influences of different types of washing agents (i.e. HCl, EDTA and H2O2) on metal (i.e. Cu and Zn) removal from contaminated river sediment, destroy or dissolution of sediment components, and transformation of metal fractions during chemical washing treatment. Additionally, bioavailability of these metals left in the washed sediment was assessed. Results showed that HCl obtained the highest Cu and Zn removal through destroying the reducible, oxidizable and residual sediment components. Meanwhile, it transformed metal fractions to acid extractable one, resulting in an increase in metal bioavailability. Thus, the feasibility of washing with HCl for sediment remediation shall be reconsidered due to the caused high metal bioavailability. EDTA was capable of removing metals via direct complexation of labile metal species and indirect dissolution of reducible and oxidizable sediment components, where the transformation of corresponding metal binding fraction may occur. H2O2 obtained the lowest total Cu and Zn removal, but it preferentially removed the oxidizable metal species by oxidizing sulfides in the sediment. The bioavailable levels of Cu and Zn in the sediment washed by EDTA or H2O2 seemed not increase. To maintain a good balance between labile metal species removal and avoiding increase of metal bioavailability, EDTA and H2O2 are promising additives for metal removal by sediment washing.

Anodic dissolution of vanadium in molten LiCl–KCl–TiCl2

The mechanism of anodic dissolution of pure vanadium in a titanium-enriched alkali chloride molten salt was investigated to determine whether it can be used as an ion source for a continuous Ti–V alloy deposition process. This study represents the first step towards the preparation of ternary Ti–Al–V alloys. Cyclic voltammetry as well electrochemical impedance spectroscopy (EIS) was performed and potentials for dissolution experiments were determined. Additionally, the influence of anode morphologies on the dissolution process, as a consequence of pre-treatment, was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicate that anodic vanadium dissolution is possible, but hindered by the electroless formation of a thin titanium layer. Additionally, a secondary reaction, namely the oxidation of Ti2+ ions, takes place, lowering the current efficiency of the process. Morphology investigations revealed the risk of grain detachment (material loss) from the vanadium electrode, which is critical in direct dissolution, whereas under indirect dissolution conditions, passivation impedes the controlled process. Thus, electrolysis is best carried out with coarse-grained vanadium electrodes in the direct dissolution range.

Melt corrosion of refractories in the nonferrous industry and the electric arc furnace: A thermochemical approach

A thermochemical approach was implemented to study the dissolution mechanisms of a wide range of refractory oxides and silicates in slags of the nonferrous metals industry and electric arc furnaces. First of all, the slags have been characterized regarding their working range, phase assemblage, and melting behavior. Subsequently, the interactions of different combinations of refractory and slag have been examined, and emphasis has been placed on the determination of possible reaction products formed during dissolution and the solubilities of the refractory oxides and silicates in various slags. Direct dissolution, decisive in the case of high corrosion rates, as well as indirect dissolution have been described. Varying operation conditions (e.g., temperature, atmosphere) have been incorporated into the investigations. In addition to the thermochemical calculations, the solubility of magnesia in fayalite slags has been determined experimentally with the quenching method and the calculated results have been compared to published corrosion studies of other authors. These studies revealed that thermochemical calculations are a suitable tool to examine melt corrosion. The thermochemical approach provides information that can be incorporated into product development and in the operation mode, giving a proper choice of process conditions.

Lattice Boltzmann model for diffusion-controlled indirect dissolution

Indirect dissolution is modelled using a two-component lattice Boltzmann model. A boundary condition is developed to impose equilibrium concentrations on the interfaces. The interfaces are captured using a volume-tracking scheme. The model is applied to a one-dimensional diffusion couple and the expected behaviour is observed. A two-dimensional situation with and without convection is also simulated, and the behaviour under grid refinement is studied.

Morphology of Poly(ethylene oxide)‐block‐Polycaprolatone Block Copolymer Micelles Controlled via the Preparation Method

AbstractBiocompatible poly(ethylene oxide)‐b‐polycaprolatone (PEO‐b‐PCL) micelles have been successfully tested in many fields as nano‐carries, especially in drug delivery. We demonstrate herein that using indirect dissolution methods to prepare PEO‐b‐PCL nano‐objects in water, copolymers with volume fractions of PCL (ϕPCL) ranging from 0.35 to 0.58 self‐assemble into spherical micelles when either DMF or THF is used as organic solvent to dissolve the diblocks before the micellization. Striking different, regular wormlike morphologies are however obtained using acetone as solvent for copolymers with ϕPCL = 0.50–0.58. These results emphasize, therefore, that control over the shape of PEO‐b‐PCL micelles can be achieved not only by precise macromolecular engineering but also through clever processing strategies.

In situ observation of the direct and indirect dissolution of MgO particles in CaO–Al 2O 3–SiO 2-based slags

The dissolution of magnesia particles in synthetic CaO–Al 2O 3–SiO 2 (CAS)-based slags with and without MgO addition was investigated in situ with a confocal scanning laser microscope (CSLM) at 1500 and 1600 °C. The dissolution process was recorded. The effects of slag composition and temperature on the dissolution process and the time dependency of the MgO particle size during dissolution were obtained. Increasing the temperature increases the dissolution rate. However, MgO addition to the slag retards the dissolution rate significantly. The rate limiting steps are discussed. It is shown that boundary layer diffusion is responsible for the dissolution. By combining in situ observations with post mortem analyses, thermodynamic calculations of local and global equilibrium, and kinetic considerations, the conditions under which MgAl 2O 4 spinel can be formed at the particle–slag interface are clarified.

Degradation of MgO refractory in CaO-SiO2-MgO-FeO x and CaO-SiO2-Al2O3-MgO-FeO x slags under forced convection

Experiments based on exposure of MgO to slags under forced convection flow conditions allowed the identification of different degradation mechanisms and the assessment of the role of Al2O3 in the degradation process. Slag with no alumina present resulted in direct dissolution. Samples immersed in alumina containing slag underwent indirect dissolution, with a spinel forming at the MgO-slag interface. At 1530 °C, the spinel was not effective in reducing the corrosion rate, as the scattered spinel grains were easily removed from the MgO surface. At 1500 °C, the loss of MgO was reduced due to the formation of a more cohesive spinel layer. Mechanical erosion then appears to play a greater role. Strength of the bond between the spinel and underlying MgO needs to be considered in strategies to reduce degradation of MgO refractories.

SLAG LINE DISSOLUTION OF MgO REFRACTORY

Abstract The high temperature dip technique has been used to investigate the corrosion of MgO refractory in SiO2-CaO-FeOx-MgO slag and Al2O3-SiO2-CaO-FeOx-MgO slag at 1530 °C. In both systems, significant slag line corrosion was observed and this corresponded to increasing MgO in the slag. There was significant evidence that a solid spinel phase had attached to the surface of the sample in the case of slag containing 20 wt% alumina. This type of corrosion is due to surface tension induced flow patterns at the refractory slag interface and a semi-empirical model of that phenomenon described the observed progression of corrosion with time for direct dissolution well. However, the model did not work well when indirect dissolution occurred.On a utilise la technique de trempe a haute temperature pour etudier la corrosion du refractaire MgO dans un laitier de SiO2-CaO-FeOx-MgO et dans un laitier de Al2O3-SiO2-CaO-FeOx- MgO a 1530 °C. Dans les deux systemes, on a observe une corrosion importante a la ligne de ni...

Alumina Dissolution into Silicate Slag

Dissolution of commercial white fused and tabular Al2O3 grains into a model silicate slag was investigated after 1 h at 1450° and 1600°C. Formation of CA6 and hercynitic spinel layers was observed at all Al2O3/slag interfaces. The spinel layer was not always continuous, and so, compared with the CA6 layer, it had a less‐significant effect on the dissolution process. The CA6 layer that formed adjacent to the tabular Al2O3 was incomplete at both temperatures, so that its dissolution was not a totally indirect process. These incomplete CA6 and spinel layers meant that slag penetrated into the tabular Al2O3 grains, which, thus, were corroded and disintegrated by the penetrating slag. There was evidence of liquid in the CA6 layer adjacent to the fused Al2O3 after 1 h at 1450°C, which also enabled direct dissolution. After 1 h at 1600°C, fused Al2O3 revealed a thick (∼60 μm), continuous and unpene‐trated CA6 layer, indicating fully indirect dissolution at this temperature.

Aragonite preservation in late Quaternary sediment cores on the Brazilian Continental Slope: implications for intermediate water circulation

We present late Quaternary records of aragonite preservation determined for sediment cores recovered on the Brazilian Continental Slope (1790–2585 m water depth) where North Atlantic Deep Water (NADW) dominates at present. We have used various indirect dissolution proxies (carbonate content, aragonite/calcite contents, and sand percentages) as well as gastropodal abundances and fragmentation of Limacina inflata to determine the state of aragonite preservation. In addition, microscopic investigations of the dissolution susceptibility of three Limacina species yielded the Limacina Dissolution Index which correlates well with most of the other proxies. Excellent preservation of aragonite was found in the Holocene section, whereas aragonite dissolution gradually increases downcore. This general pattern is attributed to an overall increase in aragonite corrosiveness of pore waters. Overprinted on this early diagenetic trend are high-frequency fluctuations of aragonite preservation, which may be related to climatically induced variations of intermediate water masses.

Use of phase diagrams in studies of refractories corrosion

Typical applications of phase diagrams to specific problems of refractories corrosion are highlighted. Saturation solubilities of refractories components in molten slags can be estimated using existing phase diagrams. These can then be used to predict the corrosion behaviour, and qualitatively compare the corrosion resistance, of a refractory in different slags or different refractories in the same slag. If the slag is not saturated with refractories components, using relevant phase diagrams, the conditions under which solid reaction product phases form at refractories/slag interfaces can be predicted, which assists understanding of direct and indirect dissolution. By checking the compatibility between impurities or additives and refractories components at high temperatures, their influence on corrosion resistance can be predicted, aiding their selection. Phase diagrams also reveal that atmosphere affects refractories corrosion resistance by altering the valence of some components (in particular, iron oxide) in the refractories and/or slags. The compatibility between refractories and slags indicates the corrosion resistance of different refractories, assisting refractories selection for specific applications. Finally, phase diagrams can be used to assist design of refractories composition. Repeated experimental corrosion test results show good agreement with phase diagram predictions. Therefore, use of the information which is available in existing phase diagrams can reduce the need for expensive and time consuming experiments to evaluate high temperature corrosion of refractories (and other ceramics).

Bio-dissolution of spent nickel–cadmium batteries using Thiobacillus ferrooxidans

In this study, the production of sulphuric acid in bioreactors with Thiobacillus ferrooxidans attached on elemental sulphur was investigated. These bioreactors reached a maximum H + productivity of 80 mmol kg −1 d −1 of support. This medium was used for the indirect dissolution of spent nickel–cadmium batteries recovering after 93 days 100% of cadmium, 96.5% of nickel and 95.0% of iron. Moreover, recoveries higher than 90.0% were reached when anodic and cathodic materials were directly added to Thiobacillus ferrooxidans cultures with sulphur as the sole energy source. The results presented show an economic and effective method which could be considered the first step to recycle spent and discarded batteries preventing one of the many problems of environmental pollution.