Dissolution rate determination of alumina in molten cryolite-based aluminum electrolyte

Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which can measure the dissolution rate of alumina was presented. Effect of factors on dissolution rate of alumina was studied intuitively and roundly using transparent quartz electrobath and image analysis techniques. Images about dissolution process of alumina were taken at an interval of fixed time from transparent quartz electrobath of double rooms. Gabor wavelet transforms were used for extracting and describing the texture features of each image. After subsampling several times, the dissolution rate of alumina was computed using these texture features in local neighborhood of samples. Regression equation of the dissolution rate of alumina was obtained using these dissolution rates. Experiments show that the regression equation of the dissolution rate of alumina is y=-0.000 5x^3＋0.024 0x^2-0.287 3x＋ 1.276 7 for Na3AIF6-AIF3-Al2O3-CaF2-LiF- MgF2 system at 920 ℃.

Determining the Boundary of Molten Electrolyte and Aluminum in Electrolytic Cells by Detecting Their Vertical Distribution of Potential

Aluminum production is a high energy consumption process so that maintaining fundamental compositions in balance and optimal conditions are essential.The molten electrolyte and melted aluminum are primary materials and their boundary needs to be monitored from time to time.An automatic measurement technic is presented in the paper to substitute for the traditional manual measurement work that is dull,poor efficiency and dangerous for operators.The boundary forming mechanism is analyzed,the vertical profile of electric potential is simulated,an automatic instrument is developed to sense the potential distribution,and a strategy is provided to identify the boundary according to the potential curves.Finally,some practical results are compared with manual measurements,which shows good consistency.

Reliability of DC-link capacitor in pulsed power supply for accelerator magnet

Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage,store energy,and decrease power variation.In this study,DC-link capacitors in pulsed power supplies were investigated.By deriving an analytical method for the capacitor current on the H-bridge topology side,the root-mean-square value of the capacitor current was calculated,which helps in selecting the DC-link capacitors.The proposed method solves this problem quickly and with high accuracy.The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement,and the capacitor’s hotspot temperature and temperature rise are calculated using the FFT transform.The test results showed that the error between the calculated and measured temperature increases was within 1.5℃.Finally,the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis.The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.

Numerical modeling of effect of slot on bubble motion in aluminum electrolytic process

A transient three-dimensional（3 D） model was established to understand the bubble motion in an industrial electrolytic process. An anode with a new design was tested. It incorporates two slots that allow an efficient removal of gas bubbles. The electromagnetic fields were described by solving Maxwell＇s equations. The bubble movement was studied with two-way coupling Euler-Lagrange approach. The interplay of current density and bubble nucleation rate was included. The collision and coalescence of bubbles were considered. Random walk module was invoked for involving the chaotic effect of the turbulence. The numerical results were validated by experimental measurements. The results indicate that the current distribution and the bubble nucleation periodically change. Due to the slot, the bubble elimination heavily increases. The contribution of the slot to the bubble removal exceeds 50% in the case of three currents, and the promotion of the slot decays with increasing the current.

Growth and passivation of aluminum etch tunnels at on-off controlling direct current in 6 wt.% HCI solution

Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunnel length was only a function of the turn-on interval of DC. The potential of Al foil broke at on-off controlling DC by the result from anode polarization curves and potential-time （E-t） responding curves. When DC was switched on, the potential increased abruptly over pitting potential, leading to nucleation of pits at the surface and the growth of tunnels at special length. When DC was switched off, the potential decreased rapidly to a passive value, leading to stoppage of nucleation and death of tunnels. By this way, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Hence, etching of Al foil at this current is beneficial for maintaining a good mechanical strength.

Grain refining action of Ti existing in electrolytic low-titanium aluminum with Al-4B addition for superheated Al melt

The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum(ELTA)without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower,but the efficiency decreases rapidly when the superheating temperature is higher.The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature,but it also decreases obviously with the increase of the superheating temperature.One important reason is that the TiB2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased,thus decrease the number of the potent heterogeneous nuclei retained in the Al melt.If the Al-4B master alloy is added to the ELTA melt,the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature.This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..

Kalman-Filtering-Based Frequency Control Strategy Considering Electrolytic Aluminum Load

Traditional thermal power units are continuously replaced by renewable energies,of which fluctuations and intermittence impose pressure on the frequency stability of the power system.Electrolytic aluminum load(EAL)accounts for large amount of the local electric loads in some areas.The participation of EAL in local frequency control has huge application prospects.However,the controller design of EAL is difficult due to the measurement noise of the system frequency and the nonlinear dynamics of the EAL’s electric power consumption.Focusing on this problem,this paper proposes a control strategy for EAL to participate in the frequency control.For the controller design of the EAL system,the system frequency response model is established and the EAL transfer function model is developed based on the equivalent circuit of EAL.For the problem of load-side frequency measurement error,the frequency estimation method based on Kalman-filtering is designed.To improve the performance of EAL in the frequency control,a fuzzy EAL controller is designed.The testing examples show that the designed Kalman-filter has good performance in de-noising the measured frequency,and the designed fuzzy controller has better performance in stabilizing system frequency than traditional methods.

Influence of titanium content on wear resistance of electrolytic low-titanium eutectic Al-Si piston alloys

The wear resistance of six kinds of the electrolytic low-titanium eutectic AI-Si piston alloys with various Ti content ranging from 0.00wt.% to 0.21wt.% has been studied. A new method of adding Ti is adopted in the electrolytic low-titanium aluminum alloy ingots. The electrolytic low-titanium eutectic AI-Si piston alloys are produced by remelting the electrolytic low-titanium aluminum alloy, crystal silicon, pure magnesium, AI-50%Cu and AI-10%Mn master alloy. The wear experiments are conducted using MM200 wear testing machine under lubricating condition. The results indicate that the better wear resistance and the less weight loss are achieved in the study for the eutectic AI-Si piston alloys with 0.08wt.%-0.12wt.% Ti content. The highest ultimate tensile strength of 135.94 MPa at 300℃ and HV141.70 hardness of the alloys are obtained at 0.12wt.% and 0.08wt.% Ti content, respectively. The wear mechanism of the eutectic AI-Si piston alloys under lubricating condition is abrasive wear.

Al_2O_3-TiO_2 composite oxide films on etched aluminum foil fabricated by electrodeposition and anodization

Ti species have been deposited on low-voltage etched aluminum foils by a simple electrochemical method using a Ti anode as Ti source in a Ti-free I2-dissolved acetone solution. After annealing at 500-600℃ in air, an Al2O3-TiO2 composite oxide film was formed on the surface of the etched aluminum foil by anodizing galvanostatically in an ammonium adipate solution. The effects of I2 concentration in the acetone solution, applied anode voltage, electrolysis time, and annealing temperature on the specific capacitance of the aluminum anode foils were investigated. The TiO2-deposited specimens prepared by applying a po-tential of 50V for 3 min in 2.5m MI2-added acetone solution followed by annealing at 550℃ after anodization exhibited the highest specific capacitance, with an enhancement of 22% compared with pure etched aluminum foil specimens. The electro-deposition process and the change of the anode voltage during the anodization were analyzed.

Effect of Shot Peening and Plasma Electrolytic Oxidation on the Intergranular Corrosion Behavior of 7A85 Aluminum Alloy

The effects of shot peening（SP） and plasma electrolytic oxidation（PEO） on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85（AA 7A85） were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.

A demand side controller of electrolytic aluminum industrial microgrids considering wind power fluctuations

Direct wind power purchase for large industrial users is a meaningful way to improve wind power consumption and decrease industrial production costs.Short-term wind power fluctuations may lead to large-scale wind power curtailment problems.To promote use of wind energy,a demand side control method is proposed based on output regulator theory for a grid-connected industrial microgrid with electrolytic aluminum loads to continuously track and respond to wind power fluctuations.The control model of the EALs and the dominant frequencies of the wind power fluctuation signals are analyzed and incorporated into the demand side control plant.The feedback control signals with active power deviations on the tie-line are used to design the demand side controller.Simulations are conducted for an actual industrial microgrid to validate the feasibility and effectiveness of the proposed method.The results demonstrate that the proposed controller based on output regulator theory is able to effectively track wind power fluctuations.