Studies on Photocatalytic Performance of MgO Nanoparticles Prepared by Wet Chemical Method

In the present article, we explore a cost-effective and an environmentally benign route to prepare magnesium oxide (MgO) nanoparticles through thermal decomposition of magnesium hydroxide (Mg(OH)₂) nanoparticles. Mg(OH)₂ nanoparticles were prepared using different solvents namely ethylenediamine (EDA) and triethanolamine (TEA) by wet chemical method, and subsequently the as-synthesized Mg(OH)₂ nanoparticles were calcinated at 400°C for 2 h in air to obtain MgO nanoparticles. XRD pattern revealed that as-synthesized Mg(OH)₂ nanoparticles are polycrystalline in nature with hexagonal structure, and after annealing it transforms to MgO nanoparticles with cubic structure. FTIR spectrum of as-synthesized Mg(OH)₂ nanoparticles indicated the OH⁻ antisymmetric stretching vibration of the Mg(OH)₂ and after annealing the sharp peak at 3686 cm⁻¹ disappears, which confirms the complete transformation of hexagonal Mg(OH)₂ to cubic MgO. SEM analysis showed the formation of interfused Mg(OH)₂ nanoflakes and coral-like hierarchical MgO nanostructure made up of stacked nanoflakes. Optical band gap energy of Mg(OH)₂ and MgO nanoparticles prepared using different solvent were estimated using UV–Vis DRS. Degradation of methyl orange was performed to investigate the photocatalytic activity of coral-like hierarchical MgO nanostructure. Results demonstrate that coral-like hierarchical MgO nanostructure possessing large surface area and porous morphology exhibited good photocatalytic degradation of methyl orange.     

EDTA滴定法直接测定水氯镁石脱水产品中氧化镁

研究了用EDTA滴定法测定水氯镁石脱水产品中主体成分后用差减法求得杂质含量而间接测定水氯镁石脱水产品中Mg（OH）Cl、MgO含量（间接法）时产生很大误差的原因, 提出了通过用EDTA滴定法直接测定水氯镁石脱水产品样品的水溶渣中镁含量而得到产品中总MgO含量（直接法A）以及同时直接测定脱水产品样品的醇溶渣和水溶渣中镁含量而得到产品中Mg（OH）Cl、MgO含量(直接法B)的两种直接测定方法。醇或水溶渣中镁的测定是将渣用煮沸的5%（V/V）H₂SO₄溶解后用EDTA滴定。实验证明, 直接法测定脱水产品中氧化镁或碱式氯化镁的绝对误差很小（质量分数小于0.1%）。其中直接法A测得的脱水产品中总氧化镁含量更稳定、可靠, 具有更高的精密度和准确度（加标回收率在94%-117%）, 因此, 更适合于用盐酸苯胺(C₆H₅NH₂·HCl)作脱水剂的复盐法得到水氯镁石脱水产品中总MgO含量的准确测定。     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Synthesis of Ceramic Materials Based on Titanium Carbide with a Cobalt Binder for the Pulsed Electrospark Deposition of Bioactive Coatings with an Antibacterial Effect

The goal of this study was to produce biocompatible ceramic materials in the Ti–C–Co–Ca₃(PO₄)₂–Ag–Mg system by combustion mode synthesis. The influence of cobalt on combustion parameters of the mixture, structure, and properties of the products was investigated. Compact ceramics consist of a combined grain frame of nonstoichiometric titanium carbide (TiC_0.5–TiC_0.6) with the titanium phosphate (Ti₃PO_x) phase homogeneously distributed along grain boundaries and local isolations of calcium oxide (CaO). The introduction of cobalt promotes the formation of a complex phosphide CoTiP and TiCo intermetallic compound. Alloying with silver and magnesium leads to the formation of a silver-based solid solution.     

烟气脱硫石膏粉化学物相分析

介绍了燃煤发电厂产出的烟气脱硫石膏粉中的化学组分分析方法。根据烟气脱硫石膏粉的特性,采用X射线能谱(EDS)仪对样品进行半定量分析,样品经过水洗去除50%的主成分后,不溶于水的物质用X射线衍射（XRD）仪进行定性分析,根据定性和半定量的分析结果,采用电感耦合等离子体原子发射光谱(ICP-AES)法、离子色谱(IC)法和重量法进行元素和组分的定量分析,综合分析结果,确定了烟气脱硫石膏粉是由82.2% CaSO₄·0.5H₂O,3.0% CaCO₃,1.0% CaMg(CO₃)₂,11.1% SiO₂,1.4% Al₂SiO₅和1.3% Fe₂O₃组成。     

Preparation of an As(V) solution for scorodite synthesis and a proposal for an integrated As fixation process in a Zn refinery

A method for producing an As(V) solution from an As-bearing material obtained from a nonferrous hydrometallurgical process was investigated. Preparation of the As(V) solution included oxidative leaching of As with a NaOH solution, elimination of As as a calcium arsenate precipitate (johnbaumite: Ca₅(AsO₄)₃(OH)) with a Ca(OH)₂ secondary salt, washing the Ca–As compounds, and reaction of the Ca–As precipitate with H₂SO₄. This process was shown to be industrially applicable. The As ions and Cu ions were effectively separated by oxidative leaching with O₂ gas injection under strongly basic conditions. In this system, As dissolved in the NaOH solution and Cu precipitated with the residue. The dissolved As in this highly concentrated NaOH solution was then effectively precipitated from the solution by addition of a surplus amount of CaO, which allowed recycling of the NaOH solution. The addition of surplus Ca precipitated Ca₅(AsO₄)₃(OH) and Ca(OH)₂, which inhibited the leaching of As but did leach Ca and Na. When the Ca–As compounds were dissolved with H₂SO₄, Ca ions precipitated in the form of gypsum from the As-bearing solution. The gypsum produced by this process is likely to give rise to a number of As-related issues and the As level, therefore, needs to be reduced. This process is advantageous for the treatment of As since it is stabilized as scorodite. The production of an As(V) solution could be applied to hydrometallurgical operations as it necessary for the removal of As. This process is shown to be practically useful to As removal in Zn refining and a closed flow circuit is proposed for integration of this process into a Zn hydrometallurgical operation.     

Dynamics of phase formation during the synthesis of magnesium diboride from elements in thermal explosion mode

The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB₂ phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB₂. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB₂ reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB₂ and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB₂ by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB₂ and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.     

A novel oxidant for nickel hydrometallurgy

Nickelic hydroxide is an important metallurgical reagent used for precipitating cobalt from nickel sulfate solutions. Existing methods of preparation of nickelic hydroxide involve electrolytic oxidation of Ni(OH)₂ or the use of strong oxidizing agents such as chlorine, ozone and persulfate. The present paper describes a new method for chemical preparation of nickelic hydroxide, developed in INCO laboratories, by a technique consisting of reacting nickelous hydroxide suspensions with a slurry of calcium sulfite in the presence of air or oxygen. The main advantage of the process is the cost of reagents and an absence of soluble by-products (e.g. Cl^?). The chemistry of this process is unusual since the redox potential obtained during the reaction exceeds the theoretical potential of the oxygen electrode. The effect of CaSO₃, therefore, is not just a catalytic acceleration of the reaction Ni(OH)₂ + O₂, for the SO₃^2? must be involved in the stoichiometry of the overall reaction by producing, in the initial phase, some strongly oxidizing intermediate species, most likely the peroxomonosulfate ion SO₅^$\text{2}$?.     

Sintering and aging behaviours of Al4CuXMg PM alloy

Sintering and aging behaviours of Al–Cu–Mg powder metallurgy (PM) alloy produced from elemental powders were examined. After evaluating results from thermal analysis, tests were carried out on Al–4Cu alloys with magnesium contents of 0.5, 1 and 2?wt-% and it was found that additions of 1?wt-% Mg was most effective for enhancing the transverse rupture strength (TRS) of the Al–Cu PM alloys for both as sintered and after a heat-treatment conditions. Grain size reduction in the range of 14–45% was achieved by adding magnesium into Al–Cu system. Analyses showed that produced alloys were composed of Al, Al₂Cu, Al₂CuMg and Al₇Cu₂Fe phases. Differential scanning calorimeter and dilatometer analyses revealed that alloys show swelling behaviour after the eutectic melting reaction at 548°C and swelling rates increasing as a function of magnesium content. Both high hardness value (120 HB) and TRS (650?MPa) were achieved via aging of Al4Cu1Mg alloy for 24 hours.     

Electrochemical Properties of Intermetallic Compounds Mg2Ni,MgNi2, and the Hydride Mg2NiH4 in 30% KOH Solution

Using the potentiodynamic polarization curve method, x-ray phase analysis, and Auger electron spectroscopy, we have studied the mechanisms for cathodic and anodic processes occurring in a 30% KOH solution on the surface of the intermetallic compounds Mg₂Ni, MgNi₂ and the hydride Mg₂NiH₄. In contrast to MgNi₂, we observed hysteresis of the cathodic polarization curve for Mg₂Ni due to formation of a surface layer (a mixture of the hydride phases β‐Mg₂NiH₄ and Mg₂NiH_3.85) on the sample, as a result of reaction between Mg₂Ni and atomic hydrogen. We have shown that the surface of the samples is considerably enriched in magnesium and depleted of nickel, and their corrosion resistance in the indicated electrolyte is determined by active dissolution of nickel and formation of a surface layer (～25 nm) on the electrodes consisting of MgO and Mg(OH)₂ in the case of Mg₂Ni and Mg₂NiH₄, and also of MgO, Mg(OH)₂, and NiO in the case of MgNi₂. The intermetallic compound MgNi₂ was the most corrosion-resistant, probably because of the presence of a monolayer of the oxides MgO and NiO on the original surface.     

Selective Precipitation of Phosphate from Semiconductor Wastewater

Selective precipitation of phosphate from fluoride-containing wastewater was studied using magnesium salts. Wastewater sampled from a semiconductor manufacture was found to contain 936 mg/L of fluoride (F?), 640 mg/L of sulfate (SO42?), 118 mg/L of phosphate (PO43?), and 26.72 mg/L ammonium (NH4+). Magnesium chloride (MgCl2) was more effective than magnesium oxide (MgO) in inducing precipitation reactions between magnesium and phosphate. Effects of both molar ratio ([Mg2+]:[PO43?]) and pH were examined and experimental results were compared with those from equilibrium modeling by PHREEQC. A total of 41.72% of phosphate was removed and recovered when at molar ratio of 3:2 and pH of 10. Precipitation of phosphate increased with increasing molar ratio and 66.19% of phosphate was recovered when molar ratio was 3:1. Precipitation of phosphate increased as pH changed from 8 to 10. However, it decreased as pH increased from 10 to 12, probably because of competition between phosphate and hydroxyl (OH?) ions. Solid precipitates were characterized by field emission scanning electron microscope with energy dispersive spectrometer and X-ray diffraction. In accordance with theoretical modeling, it was found that the precipitate in pH range of 8–10 was predominantly bobierrite [Mg3(PO4)2.8H2O] and some amorphous precipitates. However, brucite [Mg(OH)2] precipitate would start to form when pH became higher than 10. Results showed that MgCl2 can be a selective precipitation reagent for phosphate removal from semiconductor wastewater since it does not form precipitate with fluoride, sulfate, and ammonium.     

Pentlandite: Preparation, hydrogen reduction in the presence of lime to yield an iron-nickel alloy

The present paper describes the hydrogen reduction of synthetic pentlandite and pentlandite concentrate in the presence and the absence of added calcium hydroxide. Synthetic pentlandite was prepared by heating a stoichiometric mixture of an iron-nickel alloy and sulfur for about 10 days at 473 to 723 K. Differential thermal analysis (DTA) apparatus was used to study the thermal decomposition of the synthetic pentlandite. Hydrogen reduction of synthetic pentlandite in the presence and the absence of added Ca(OH)₂ was studied at 673 to 1023 K in a thermogravimetric apparatus. Additions of Ca(OH)₂ to penlandite accelerated the reduction rates. An acetic acid leach of a product obtained by H₂ reduction of a mixture of pentlandite and Ca(OH)₂ yielded a leach residue containing mainly an iron-nickel alloy. The iron and nickel content in the leach residue averaged about 44 pct iron and 52 pct nickel with recoveries of about 82 pct iron and 94 pct nickel.     

Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO_3)_2 precipitation method

The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_4~(2-)1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_4~(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_3)_2 as a precipitant.The results indicate that the contents of SO_4~(2+) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La2(CO_3)_(2.15)(-SO_4)_(0.85)·4 H_2 O and Ce2(CO_3)_(2.15)(SO_4)_(0.85)·3 H_2 O,while those of the Pr and Nd precipitates are 4 wt%-5 wt%since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_4~(2-) enclosed in the precipitation.The content of SO_4~(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_4~(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_4~(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO_3)_2 precipitation method.     

Gadolinium solubility and precipitate identification in Mg-Gd binary alloy

Gadolinium (Gd) solubility in magnesium (Mg) matrix and precipitate composition in Mg-Gd binary alloys were investigated. The alloys containing different Gd contents (10wt.%-35wt.%) were employed to identify Gd solubility after annealing at different temperatures. It was confirmed that the maximum Gd solubility was 22.8wt.% at 550℃ based on the regression analysis method. Mg5+xGd (0相似文献   

Sulfide and sulfate solid solubility in lime,magnesia, and calcined dolomite: Part II. free energy of formation of magnesium sulfate

The free energy of formation of magnesium sulfate and its solubility in magnesia have been determined. The salient feature of the results is that trace amounts of calcium impurity in magnesia noticeably lower the dissociation temperature and pressure of magnesium sulfate. A high-purity magnesia, which was prepared by oxidation of a high-purity magnesium, was used to determine the equilibrium constant for the formation of MgSO₄. The sulfate solubil-ity In magnesia saturated with MgSO₄ was found to be higher than that in lime saturated with CaSO₄. At 1100°C, CaSO₄ and CaS form in calcined dolomite at SO₂ partial pressures higher than those in pure CaO. From these findings it is estimated that at MgO saturation the ac-tivity coefficient relative to CaO is about 0.8.     

Solvent extraction of gallium(III) from sodium hydroxide solution by alkylated hydroxyquinoline

The distribution equilibria and kinetics of the extraction of gallium(III) from sodium hydroxide solutions by 7-(5,5,7,7-tetramethyl-locten-3-yl)-8-hydroxyquinoline (Kelex 100, designated HQ in the following) in kerosene have been examined under various conditions. From the dependence of the distribution coefficient on the concentrations of aqueous hydroxide and Kelex 100 it is deduced that the extraction can be expressed as Ga(OH)⁻₄(a) + 3 HQ(o) ⇄ GaQ₃(a) + OH⁻(a) + 3 H₂ O(a). Furthermore, the kinetic results suggest that gallium(III) is taken up through the formation of either of two different activated species, Na⁺[Ga(OH)₃ ], OH⁻ and Na⁺ · Na⁺[Ga(OH)₃], depending on the concentration of sodium hydroxide in the aqueous phase.     

Dissolution of iron oxide using oxalic acid

Iron oxide is the main contaminant of clay and silicate minerals used during the production of high quality ceramics. Its content has to be removed to generally less than 0.1% for achieving the required whiteness of 90% ISO or higher for clay and silicate materials. Oxalate has been used to dissolve iron oxide from various sources. The dissolution is affected by oxalate concentration, solution pH and temperature. The mineral phase is also critical in determining the reaction rate. Hematite is slow to dissolve whereas iron hydroxide and hydroxyoxides such as goethite and lepidocrosite can be easily dissolved. As the dissolution requires a pH controlled in the region 2.5–3.0 for maximum reaction rate, it is essential to create a hydroxide-oxalate mixture for use in the leaching process. The characteristics of NaOH-, KOH- and NH₄OH-oxalic acid mixtures were also determined in this study. Due to the precipitation of salts such as Na₂C₂O_4(s) and NaHC₂O_4(s) the NaOH-oxalic acid could act as pH buffer for the leaching. Such precipitation also reduces the concentration of the free bioxalate, HC₂O₄⁻ required for the dissolution of iron oxide. KOH behaves the same as NaOH whereas NH₄OH precipitates the less stable salt NH₄HC₂O_4(s) which easily re-dissolves forming soluble oxalate species. Ammonium hydroxide is therefore the most suitable reagent that can be used for pH control during the leaching of iron oxide using oxalate. Using STABCAL, several Eh–pH and stability diagrams were developed to explain the dissolution process.     

Analysis of the Fe–Ce–O–C–<Emphasis Type="Italic">M</Emphasis> phase diagrams (<Emphasis Type="Italic">M</Emphasis> = Ca,Mg, Al,Si) by constructing a component-solubility surface

Analysis of the ternary phase diagrams of Ce₂O₃- and CeO₂-containing oxide systems allowed us to find the oxide compounds that form during steel deoxidizing with cerium and with cerium together with aluminum, calcium, magnesium, or silicon. The temperature dependences of the equilibrium constants of formation of Ce₂O₃ oxides and Ce₂O₃ · Al₂O₃, Ce₂O₃ · 11Al₂O₃, Ce₂O₃ · 2SiO₂, 7Ce₂O₃ · 9SiO₂ and Ce₂O₃ · SiO₂ compounds are found. Surfaces for the component solubility in metallic melts Fe–Al–Ce–O–C, Fe- Ca–Ce–O–C, Fe–Mg–Ce–O–C, and Fe–Si–Ce–O–C are constructed. Nonmetallic inclusions that form in the course of experimental melts of St20 steel after its deoxidizing with silicocalcium and rare-earth metal (REM)-containing master alloys in a ladle furnace after degassing are studied. Phase inhomogeneity of the inclusions is found. As a rule, they consist of phases classified into the following three groups: oxide–sulfide, sulfide–oxide, and multiphase oxide–sulfide melt. Calcium aluminates are found to be components of complex sulfide-oxide noncorrosive inclusions.     

Influence of small additives of calcium on the structure and properties of ML5 alloy (AZ91)

The influence of the calcium additive (from 0.1 to 1.0 wt %) on the phase composition and solidus temperature of ML5 magnesium alloy is investigated. Calcium transfers into the intermetallic compound of the variable composition during alloy crystallization. This compound contains Al (53.4–57.4%), Ca (42.6–42.8%), and Mg (0.002–3.8%) and is transformed with a decrease in temperature into the Al₂Ca compound. The influence of calcium on the amount of phases Mg₁₇Al₁₂ and Al₂Ca and its distribution in the casting and thermally treated ML5 alloy structures are investigated. It is revealed with the help of the electron probe microanalysis that calcium and aluminum are concentrated along the boundaries of the magnesium solid solution. It is shown that, in order to acquire satisfactory mechanical properties and pouring of calcium-containing magnesium alloys should be performed according to the production process preventing the contamination of metal of the coarse inclusions. It is established that small additives of calcium (up to 1 wt %) increase the ignition temperature and lower the alloy oxidability at elevated temperatures (up to 715°C). The influence of the sulfur hexafluoride (SF6) for the calcium loss during flux-free melting was established.