Aluminum Electrolysis Research Articles

Study on Liquidus Temperature of NaF-KF-LiF-AlF3 System with Low Cryolite Ratio

Development of an energy-efficient method for aluminum manufacturing is the current research trend in the aluminum electrolysis industry. A low-temperature electrolysis process is an appropriate choice for aluminum electrolysis. The NaF-KF-LiF-AlF3 system with its low cryolite ratio may be a suitable candidate electrolyte system because of its reduced liquidus temperature. In this paper, the liquidus temperature of NaF-KF-LiF-AlF3 system with cryolite ratios of 1.3 and 1.4 is investigated via the cooling curve method and the differential thermal analysis method. The effects of both potassium fluoride and lithium fluoride on the NaF-KF-LiF-AlF3 system are studied. The liquidus curves of systems containing potassium fluoride and lithium fluoride are different and depend on the KF/(NaF+KF+LiF) and LiF/(NaF+KF+LiF) ratios. Part of the (NaF-LiF-AlF3)-KF pseudo-binary phase diagram with fixed LiF concentration is plotted according to the data of liquidus temperature and the compositions of the phase diagram containing potassium fluoride and lithium fluoride with a cryolite ratio of 1.3 are analyzed. The change trend of the compositions is similar to the NaF-KF-AlF3 system with a low cryolite ratio. LiF hardly participate in the formation of the compounds at equilibrium state except for the fact that chiolite is the main composition of molten salt.

Effects of Al3+ on the microstructure and bioflocculation of anoxic sludge

The aluminum ions generated from mining aluminum, electrolytic aluminum and the industrial production of aluminum-based coagulants (such as AlCl3 and Al2(SO4)3) enter sewage treatment plants and interact with activated sludges. An anaerobic/anoxic/oxic (A2O) process was used to reveal the effects of Al3+ on the pollutant removal efficiencies, bioflocculation and the microstructure of sludge. The results showed that a low concentration of Al3+ improved the pollutant removal efficiencies and increased the sludge particle size. However, a high concentration of Al3+ hindered microbial flocculation and reduced the pollutant removal efficiencies. With a 10 mg/L Al3+ addition, the chemical oxygen demand (COD), total nitrogen (TN) and NH4+-N increased by 3%, 16% and 27%, and reached as high as 68%, 60% and 87%, respectively. At the same time, the dehydrogenase activity, flocculation ability (FA) and contact angle of the sludge reached their maximum levels at 41.3 mg/L/hr, 45% and 79.63°, respectively. The specific surface area of the sludge decreased to 7.084 m2/g and the sludge pore size distribution shifted to concentrate in the mesoporous range. Most of Al3+ was adsorbed on the surface of sludge, changing the physicochemical properties and physical structure of the sludge.

Dynamic uncertain causality graph based on cloud model theory for knowledge representation and reasoning

The dynamic uncertain causality graph (DUCG), which has been widely applied in many fields, is an important modelling technique for knowledge representation and reasoning. However, the extant DUCG models have been criticized because they cannot precisely represent experts’ knowledge owing to the ignorance of the fuzziness and randomness of uncertain knowledge. In response, we propose a new type of DUCG model called the cloud reasoning dynamic uncertain causality graph (CDUCG). The CDUCG model, which is based on cloud model theory, can handle with the fuzziness and randomness of uncertain information simultaneously. Moreover, an inference algorithm based on the combination of CDUCG and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) is proposed to implement fuzzy knowledge inference effectively and thus make the expert systems more dependable and intelligent. Finally, illustrative examples and an industrial application concerning root cause analysis of aluminum electrolysis are provided to demonstrate the proposed CDUCG model. And experimental results show that the new CDUCG model is flexible and reliable for knowledge representation and reasoning.

Experimental Studies of the Dynamic Formation of the Side Ledge in an Aluminum Electrolysis Cell

An experimental setup is created to study the dynamic behavior of the side ledge under the electrolysis in a cryolite-alumina electrolyte. The installation has a built-in window on the side panel, which allows the lining material and, hence, the heat flow to be varied. The dynamic formation of a side ledge is experimentally studied as a function of temperature, the electrolyte velocity, and the heat flow during the electrolysis of aluminum. The rate of the ledge formation and the ledge thickness are determined by the heat flow caused by the electrolyte temperature, the cell side temperature, and the liquidus temperature. As in an industrial electrolysis cell, the side ledge profile formed in the experimental cell can be conventionally divided into the following three zones: the ledge at the bottom in contact with liquid aluminum, the ledge at metal/electrolyte interface, and the ledge at the electrolyte level. If the temperature of the inner wall is higher than the liquidus temperature, the side ledge does not form; if it is lower, the side ledge forms until these temperatures become the same. Therefore, the stability of the side ledge depends on the heat flow from the center to the walls; however, the dynamic behavior (solidification/melting) of the ledge in the metal zone occurs slowly and differs from the behavior of the side ledge.

THERMAL CAPACITY OF ENRICHED FUEL BRIQUETS PRODUCED FROM THE FINE OF EKIBASTUS COAL

The object of research or development: The object of the research work was coal fines and processes of enrichment of Ekibastuz coal to produce fuel briquettes with increased calorific value and less ash content. Objective: Research, scientific substantiation of technology for obtaining high-calorific coal briquettes from fines of Ekibastuz coal using various binders and the possibility of further coking, designing and manufacturing equipment for the implementation of technology. Method or methodology of the work: The standard methods of theoretical and experimental research widely used in metallurgy, machine building, computer systems, etc. were used in the work. The results of the work and their novelty: The characteristics of briquettes on bio-binding and on petroleum pitch with enrichers in the form of rubber-technical soot and anode dust of electrolysers for aluminum production have been established. It is revealed that the calorific value of briquettes is higher than that of Ekibastuz coal(Pavlodar region) by 20-40%, and the heating value is the highest for briquettes with an enrichment agent in the form of anode dust and a binder in the form of petroleum pitch (-NH combustion = 6840.8 kcal / kg). The structures of the soot separator, sorting and sifting equipment, mixing laboratory equipment, the mouthend briquetting press, the briquetting press and the screw mixer with the heater have been designed. Based on the results of the research, the project manager and co-authors published 15 scientific publications, patents and theses of international conferences. Application area: Briquettes for bio-binding can be used as fuel for combustion in centralized village boiler houses, private houses and farms. Briquettes on petroleum pitch with an enrichment agent in the form of anodic dust of aluminum electrolysis can be used as industrial briquettes for further use in metallurgy. Forecasting assumptions about the development of the object of research: Further studies are required to assess the feasibility of using industrial briquettes for coking and use in metallurgy, the manufacture of laboratory and research equipment to further commercialize the project.

Design of the portable fiber-optic current transformer for electrolytic aluminum industry

A portable fiber-optic current transformer (P-FOCT) based on the Faraday effect utilizing the fiber jumper and the flexible sensing coil is proposed to enhance the portability and improve the design for disassembly of FOCT in the electrolytic aluminum industry. To ensure the accuracy of P-FOCT, the polarization crosstalk of fiber jumper and the conductor eccentric error are studied. According to the theoretical analysis and experimental results, the relative error of P-FOCT would decrease as the distance between the current conductor and the non-closed node of the sensing coil increases. A new sensing head is designed and experiments show that the error is 0.31 % at variable temperature from 233K to 343K, which meets the requirement for accuracy in the electrolytic aluminum industry.

High-temperature oxidation behaviors of plasma electrolytic oxidation coating on hot-dip aluminized HP40Nb alloy

In the current investigation, HP40Nb heat-resistant alloy was successfully aluminized. The procedure of aluminizing consisted of pack aluminizing and subsequent hot-dip aluminizing (HDA) process. Plasma electrolytic oxidation (PEO) ceramic coatings were also synthesized on the surface of hot-dip aluminized HP40Nb alloys. PEO coatings were made using aluminate (mixture of 2 g/L KOH, 5 g/L NaAlO2, and deionized water) and silicate (mixture of 2 g/L KOH, 5 g/L Na2SiO3, and deionized water) electrolytes at 440 V for 10 min. To evaluate the high-temperature oxidation behavior of PEO coatings, interrupted isothermal oxidation at 1100 °C for 100 h was employed. The surface and cross-sectional morphologies before and after high-temperature oxidation test, chemical composition, and phase identification of the coatings were characterized by field emission scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results revealed that the PEO coating using aluminate electrolyte could increase the oxidation resistance of HP40Nb alloy, more than pack aluminized, hot-dip aluminized samples, and also the PEO coating using silicate electrolyte. The PEO coating using silicate electrolyte contains relatively big surface cracks, which can be responsible for oxide spallation during high-temperature oxidation. The weight gain of samples shows that oxidation resistance of hot-dip aluminized specimen, improved 1.2 times by PEO treatment in aluminate electrolyte. The Kirkendall voids may have a deteriorated effect on the anti-oxidation performance of hot-dip aluminized and PEO coated samples.

A Study of the Alumina Distribution in the Lab-Scale Cell during Aluminum Electrolysis

A Study of the Alumina Distribution in the Lab-Scale Cell during Aluminum Electrolysis

Effect of Aluminum Anode Temperature on Growth Rate and Structure of Nanoporous Anodic Alumina

In the present study, we investigated the effect of an anode temperature on current transient process during porous anodic alumina growth and morphology of the anodic layers. Alumina films were formed in a 0.4 M oxalic acid at a constant voltage mode and electrolyte temperature. The temperature of the Al anode was controlled by thermoelectric Peltier element and varied in the range of 5 °C–60 °C. Surface morphology of both sides of anodic films and their cross-sections were analyzed by scanning electron microscopy (SEM) with subsequent statistical analysis of the SEM images by ImageJ software. It was found that when anode temperature was increased from 5 °С to 50 °С the pores diameter and interpore distance has not changed, but the porous structure became more ordered. According to these results, the rate of chemical dissolution of the barrier layer and pore walls did not depend on the anode temperature. At the anode temperature of 60 °С, pores diameter has increased 1.7 times and there was a distortion of the ordering of porous cells. It was concluded that the temperature difference between the aluminum substrate and electrolyte is an important parameter affecting the formation of ordered structure of nanoporous anodic alumina.

Mechanism of aluminum carbide formation in aluminum electrolysis cells

The formation and dissolution of aluminum carbide is considered the primary factor affecting the life of aluminum electrolysis cells. Herein, the characteristics of sodium-graphite intercalation compounds (Na-GICs) were measured and the formation mechanism of Al4C3 during the aluminum electrolysis process was experimentally studied. The Na-GIC characteristics and the products of aluminum and Na-GIC reactions were investigated by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results showed that graphite can react with the sodium metal to form Na-GICs, which were detectable by Raman spectroscopy. Sodium inserted into the graphite layered structure acted as an intercalation agent to change the original graphite layered structure and increase the volume and specific surface area of graphite. Further, Al4C3 was produced by using sodium-graphite intercalation compounds and aluminum as materials. Thus, the presence of sodium plays an important role in the formation process of Al4C3 in aluminum electrolysis cells.

铝电解质高温熔盐输运特性与微观结构研究动态

铝电解质高温熔盐输运特性与微观结构研究动态

Optimal Control for Aluminum Electrolysis Process Using Adaptive Dynamic Programming

Optimal control of aluminum electrolysis production process (AEPP) has long been a challenging industrial issue due to its inherent difficulty in establishing an accurate dynamic model. In this paper, a novel robust optimal control algorithm based on adaptive dynamic programming (ADP) is proposed for the AEPP, where the system subjects to input constraints. First, to establish an accurate dynamic model for the AEPP system, recursive neural network (RNN) is employed to reconstruct the system dynamic using the input-output production data. To ensure input constraints are not to exceed the bound of the actuator, the optimal control problem of the AEPP is formulated under a new nonquadratic form performance index function. Then, considering the perturbation of the AEPP, the robust control problem is effectively converted to the constrained optimal control problem via system transformation. Furthermore, a single critic network framework is developed to obtain the approximate solution of the Hamilton-Jacobi-Bellman (HJB) equation. Finally, the proposed ADP controller is applied to the AEPP system to validate the effectiveness and performance.

Mathematical Model of Magnetic Hydrodynamics and Heat Transfer in an Aluminum Reduction Cell

A new nonstationary three-dimensional mathematical model of an aluminum reduction cell which makes it possible to perform coupled thermoelectric and magneto-hydrodynamic calculation while taking into account sideledge formation is presented. The model takes into account the nonlinear dependence of the coefficients of electrical conductivity and thermal conductivity of materials on temperature, as well as, for ferromagnetic materials, the nonlinear dependence of magnetization on the magnetic field strength. The heat-transfer coefficients on the outer surfaces include radiant and convective components of heat transfer and are functions of the ambient temperature and the local surface temperature. In the energy equation, internal sources of heat are taken into account due to the flow of electric current, exothermic reactions, and additional thermal effects associated with the raw material loading and phase transitions. To obtain a numerical solution, the control volume method is applied. Experimental testing of the developed mathematical model is performed on the S8BME aluminum reduction cell. This paper presents the calculated and experimental data of magnetic, electric, thermal, and hydrodynamic fields. A comparison of the calculation results with the results of industrial experiments shows that the model reflects the physical processes taking place in the aluminum reduction cell with accuracy sufficient for engineering calculations. The calculated values of electrical voltage, magnetic induction, and temperature practically coincide with the measured ones. Values obtained from calculating the direction of velocity in the metal pad and the shape of the sideledge profile differ insignificantly from the experimental values. This model can be used to estimate the performance and design parameters of the operation of new and modernized aluminum electrolysis cells. Further studies will be aimed at clarifying the calculated results by improving the mathematical model.

Method of protection of cathode blocks of aluminium electrolysis cells

Cathode wear is one of the main lifetime limiting factors of an aluminium electrolysis cell. In the present work the composition of the wettable TiB2-based coating and the cost-effective method of its application to protect the most defenseless areas of the cell bottom are proposed in relation with the cathode blocks wear profile and failure mechanisms. The protective coating composition comprises a mixture of TiB2 powders with bimodal or multimodal grain size distribution (65-40 wt. %) and a water-soluble environmentally friendly binder (35-60 wt. %). The proposed TiB2-C protective coating is characterised by high adhesion to the cathode block material, as well as wear resistance, resistance to cracks initiation and their propagation, wettability by liquid aluminium. That leads to a contact electrical resistance decrease and an increase of a chemical resistance at the Al-TiB2-C interface. The developed method of the cathode blocks protection was tested in operating conditions on an industrial electrolysis cell. The expected lifetime of cathode blocks was increased at least for 4 mounts. The results are promising and show the efficiency of the proposed method for cathode blocks protection.

A Novel Kernel-based Extreme Learning Machine with Incremental Hidden Layer Nodes

Extreme learning machine (ELM) is widely used in various fields because of its advantages such as short training time and good generalization performance. The input weights and bias of hidden layer of traditional ELM are generated randomly, and the number of hidden layer nodes is determined by artificial experience. Only by adjusting parameters manually can an appropriate network structure be found. This training method is complex and time-consuming, which increases the workload of workers. To solve this problem, the incremental extreme learning machine (I-ELM) is used to determine the appropriate number of hidden layer nodes and construct a compact network structure in this paper. At the same time, a new hidden layer activation function STR is proposed, which avoids the disadvantages of incomplete output information of hidden layer due to uneven distribution of sample data. The proposed algorithm is evaluated by public data sets and applied to the classification of superheat degree (SD) in aluminum electrolysis industry. The experimental results show that STR activation function has a good learning speed, and the proposed algorithm is superior to the existing SD identification algorithm in terms of accuracy and robustness.

ÜSTÜN ÖZELLİKLERE SAHİP İLERİ TEKNOLOJİ SERAMİĞİ: TİTANYUM DİBORÜR

Humanity has been communed with nature since the beginning of its existence and has invented various instruments by imitating the nature. The most effective factor in the development of these inventions was material science. The importance of the material science has increased with the developing technologies in recent years, and it has become mandatory to find new materials. Ceramic materials have always been of great importance for human. Advanced technology ceramics are used in many commercial applications due to their long life, high performance, superior properties and cost-effectiveness. Titanium diboride (TiB 2 ) with its hardness, high melting point, excellent abrasion and corrosion resistance has a very important place among advanced technology ceramics. There are a wide range of applications such as the production of wear-resistant parts, aluminum electrolysis, protective film layers, military applications (armor), etc. In this article, the physical and chemical properties, production methods, usage areas and the studies carried out in recent years of titanium diboride (TiB 2 ), which has a very important place among the advanced technology ceramics, are briefly presented.

INFLUENCE OF ANODIC ALUMINA USED AS SEPARATING DIELECTRIC OF SILICON AVALANCHE LEDs ON DIODE CHARACTERISTICS

A study of the influence of the formation regimes of avalanche LEDs based on nanostructured silicon on the parameters of the formed devices, such as the light emission voltage and the stability of operation has been performed. These parameters are an important factor for the practical use of avalanche LEDs in the development of silicon photonics products, the progress of which is associated with the future of integrated electronics. For the first time, the technological operation of local through electrochemical anodizing of aluminum in various electrolytes for the formation of a separating dielectric of Schottky contacts is presented. The influence of the built-in electric charge in the separation dielectric of silicon avalanche LEDs on their current-voltage characteristics is studied. It was found that the built-in negative electric charge increases the breakdown voltage of the Schottky contact, which results in an increase of the light emission efficiency of the diode structures. An explanation of this effect is presented on the basis that the built-in negative electric charge inside the anode oxide also creates a space charge region in silicon, which helps to reduce the effect of the concentration of field lines at the edges of diode structures, performing the function of protecting the Schottky contact from edge effects as well as protective areas do. It has been established that the highest avalanche breakdown voltage is observed in diode structures with anodic oxide formed in an electrolyte based on an aqueous solution of phosphoric acid. An analysis of the characteristics of LEDs at different temperatures of silicon substrates showed an increase of breakdown voltage with increasing temperature, which is typical for avalanche breakdown during impact ionization. Stable light emission of the formed LEDs was demonstrated in a wide range of operating voltages (8–16 V). The use of silicon avalanche LEDs both as discrete devices and in integrated electronics in general has been discussed.

Measurement of the molecular ratio of Aluminum electrolytes using laser-induced breakdown spectroscopy

Electrolytes cause the electrolytic reaction of alumina, producing aluminum. Their main component is cryolite. The molecular ratio of electrolytes is an important index to judge the acidity and alkalinity of industrial electrolytes, which are also critical for aluminum electrolysis. The molecular ratio is numerically equal to the molar ratio of NaF to AlF3. The goal of this study was to measure the molecular ratio of electrolytes via laser-induced breakdown spectroscopy (LIBS). First, the micro-morphology, element distribution, and phase structure of industrial electrolytes were analyzed. Second, an artificial neural network (ANN), a support vector machine (SVM), random forest regression (RFR), and gradient-boosting regression (GBR) algorithms were used to establish calibration models for original spectral data and normalized spectral data respectively, and the performances of different models were compared. Calibration models were used to predict independent samples. Finally, partial least squares (PLS) and principal component analysis (PCA) were used to reduce the dimension of the spectral data and screen the variables. Multiple linear regression (MLR), PLS, ANN, and SVM were used to build prediction models based on the new variables screened out, and the generalization abilities of different models were investigated using the leave-one-out cross-validation (LOOCV) method. For the PLS-ANN and PCA-SVM models, the root mean square errors (RMSEs) were 0.100 and 0.136, while the mean relative error (MRE) was 1.204% and 3.142%, respectively. The calibration models were used to test the independent samples, and the measurement results were compared and analyzed. In conclusion, this work provides a temporary new method of testing the electrolyte molecular ratio.

On the PEO treatment of cold sprayed 7075 aluminum alloy and its effects on mechanical, corrosion and dry sliding wear performances thereof

The plasma electrolytic oxidation (PEO) process was used to deposit an alumina coating on a cold sprayed 7075 aluminum alloy to improve the surface properties. The phase compositions, microstructures, basic mechanical properties, as well as the corrosion and the dry sliding wear resistance of cold sprayed 7075 aluminum alloy before and after PEO treatment, were investigated. The results show that a single-layered dense alumina coating with a thickness of ~15–20 μm and hardness of 1353 HV0.01 is realizable on the cold sprayed 7075 aluminum alloy by PEO treatment aided by an aluminate electrolyte. The corrosion current density and wear rate of the alumina PEO coating were 6.27 × 10−7 A/cm2 and 1.22 × 10−6 mm3/N·m respectively, which were three and two orders of magnitude lower compared to the uncoated rolled 7075 aluminum alloy (T6) substrate, thus highlighting the excellent wear and corrosion resistance of the PEO treated cold sprayed Al alloy surface.

The effects of anodic amplitude and waveform of applied voltage on characterization and corrosion performance of the coatings grown by plasma electrolytic oxidation on AZ91 Mg alloy from an aluminate bath

In this study, plasma electrolytic oxidation (PEO) was used to treat AZ91 magnesium alloy in an aluminate electrolyte to increase its corrosion resistance. The PEO process was performed at 350 and 400 V using unipolar and bipolar waveforms. Using unipolar waveform, current density reached zero after a while, but for bipolar waveforms, the current density responded during the PEO process indicating on nonstop coating growth. X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy were applied to characterize the coatings. The coatings produced using unipolar waveform revealed a net-like surface morphology, while a crater-like morphology was observed for bipolar coatings. The presence of MgF2 in all coatings was confirmed whereas the bipolar waveform with higher cathodic duty cycle produced an increased coating thickness with higher content of MgF2. The results of corrosion tests in 3.5 wt% sodium chloride solution were in agreement with the changes observed in morphology and structure, where the samples coated at 400 V using the bipolar waveforms were able to exhibit high corrosion performance. In this way, the coating produced by the bipolar waveform with the higher cathodic duty cycle at the higher voltage (400 V) revealed the highest corrosion performance up to 28 days of immersion, where there was no sign of underlying corrosion in this case.