AlF3 Research Articles

Novel Synergistic Process of Impurities Extraction and Phophogypsum Crystallization Control in Wet-Process Phosphoric Acid.

Phosphogypsum, as a byproduct of wet-process phosphoric acid reaction, has caused many environmental pollution problems. To improve the property and purity of phosphogypsum in the wet-process phosphoric acid process, a liquid-solid-liquid three-phase acid hydrolysis synergistic extraction reaction system was established by adding a certain amount of extractant in the actual production process. In order to study the extraction effect and residue of impurities in the reaction system, the phase, morphology, and impurity occurrences of phosphogypsum were systematically analyzed. The results showed that when the reaction time was 7 h, the reaction temperature was 80 °C, the reaction speed was 200 r/min, the volume ratio of the extractant to diluent (dilution ratio) was 1:4 and the volume ratio of the oil phase/aqueous phase (O/A ratio) was 1:1, P2O5 conversion was the highest in phosphate rock, and the residual P2O5 content in phosphogypsum was as low as 0.36%. The morphology of the phosphogypsum crystal was uniform and coarse long strip. The main forms of residual impurities were silicate, aluminum fluoride with crystal water, aluminate, phosphate, and fluoride. Meanwhile, the residual amount of main impurities in phosphogypsum was significantly reduced. Through this novel method, the property of phosphogypsum can be improved through the generation process and is greatly beneficial for its utilization and the recycling development of the wet-process phosphoric acid industry.

Hydride‐Enhanced Plating and Stripping of Aluminum from Triflate‐based Organic Electrolytes**

AbstractIn the quest for developing rechargeable aluminum (Al) batteries, reversible Al plating in the absence of active‐halide components is considered an immense challenge. For this reason, the choice of electrolyte has been primarily limited to the highly corrosive chloroaluminate systems based on aluminum trichloride (AlCl3). In this work, we demonstrate reversible room‐temperature Al plating from an active‐halide‐free (AHF) organic electrolyte based on aluminum trifluoromethanesulfonate (Al(OTF)3) and lithium aluminum hydride (LiAlH4) in tetrahydrofuran (THF), as well as its AlCl3 counterpart. From insights obtained by Density Functional Theory (DFT) and Fourier‐Transform Infrared (FTIR) spectroscopy, ionic speciation in the electrolyte is explored, and mechanisms for the underlying electrochemical processes in the trifluoromethanesulfonate (OTF−)‐based electrolytes are proposed. Al plating and stripping were confirmed by optical microscopy, scanning electron microscopy (SEM) and X‐ray diffraction (XRD). Characterizing the Al deposits from either the OTF−‐ or the chloride (Cl−)‐based electrolytes via depth‐profile X‐ray Photoelectron Spectroscopy (XPS) analyses, we find that these deposits consist of metallic Al, aluminum oxide (Al2O3), and either aluminum trifluoride (AlF3) or aluminum chloride (AlxCly) contaminants arising from a reaction with the electrolyte components which occurs during the plating process.

Post-Synthesis of HZSM-5 by Aluminum Fluoride in an Acidic Fluoride Solution for Enhanced Reforming of Lignite Pyrolytic Volatiles into Light Aromatics

Post-Synthesis of HZSM-5 by Aluminum Fluoride in an Acidic Fluoride Solution for Enhanced Reforming of Lignite Pyrolytic Volatiles into Light Aromatics

Lewis acid fluorine-donating additive enables an excellent semi-solid-state electrolyte for ultra-stable lithium metal batteries

Solid-state lithium metal battery via in-situ polymerization is considered one of the most promising candidates for commercial applications with flexibility, favorable energy density and reliable safety. However, the undesirable side reactions and lithium dendrite growth are frequently observed due to the unstable electrode/electrolyte interface and the poor ion diffusion interfacial kinetics, giving rise to the low Coulombic efficiency and unsatisfactory lifespan of the lithium metal batteries. In this work, aluminum fluoride (AlF3) Lewis acid additive was introduced into a three-dimensional crosslinked in-situ semi-solid-state polymer electrolyte via in-situ polymerization process. The results demonstrate that AlF3 additive can not only immobilize anions to improve electrochemical properties, but also construct a robust and highly adhesive solid electrolyte interphase (SEI) layer with fast Li+ diffusion kinetics to effectively protect Li metal anode from side reactions and lithium dendrite growth, which is attributed to attractive components of enriched LiF, lithiophilic Li-Al alloy and AlF3 species. It is notable that the Li/Li symmetrical batteries deliver a stable Li stripping/plating cycling over 1700 h at 0.1 mA cm−2, and the Li/LFP batteries achieve a favorable long-term cycling with a capacity retention of 93.5% over 340 cycles at 3 C rate. This strategy provides a distinctive insight to facilitate the commercial applications of lithium metal battery utilizing in-situ polymerized solid-state electrolyte.

Controlling the Surface of Aluminum Nanocrystals: From Aluminum Oxide to Aluminum Fluoride.

Aluminum nanocrystals are emerging as a promising alternative to silver and gold for various applications ranging from plasmonic functionalities to photocatalysis and as energetic materials. Such nanocrystals often exhibit an inherent surface oxidation layer, as aluminum is highly reactive. Its controlled removal is challenging but required, as it can hinder the properties of the encaged metal. Herein, two wet-chemical colloidal approaches toward the surface coating of Al nanocrystals, which afford control over the surface chemistry of the nanocrystals and the oxide thickness, are presented. The first approach utilizes oleic acid as a surface ligand by its addition toward the end of the Al nanocrystals synthesis, and the second approach is the post-synthesis treatment of Al nanocrystals with NOBF4 , in a "wet" colloidal-based approach, which is found to etch and fluorinate the surface oxides. As surface chemistry is an important handle for controlling materials' properties, this research paves a path for manipulating Al nanocrystals while promoting their utilization in diverse applications.

Fibrous ceramic membrane constructed by mullite whiskers for the treatment of oil‐in‐water emulsions

AbstractCeramic membranes with high porosity and excellent separation efficiency are necessary for the efficient treatment of large‐scale wastewaters. However, the conventional ceramic membranes are usually prepared by particles‐packing, which inhibits the advances of separation efficiency because of the low porosity and connectivity. Here, a fibrous ceramic membrane with mullite whiskers‐interlocked structure was prepared by gas‐solid reaction. The effects of aluminum fluoride (AlF3) on the formation and growth of mullite whiskers, and then the permeability and selectivity of the ceramic membranes were investigated. With the increase of AlF3 contents, the mullite phase evolved from needle‐like, rod‐like to flake‐like structure, thus the catalyst accelerated the growth of mullite whiskers in the diameter direction. For the ceramic membrane sintered at 1400°C, the porosity increased from 58% to 76% while the average pore sizes increased from 0.65 to 3.93 μm because of the whisker‐constructed structures. For the ceramic membrane sintered at 1450°C, the emulsion flux increased stably from 295 L/(m2·h) to 992 L/(m2·h) with the increase of trans‐membrane pressure, and the oil rejection exceeded 98%. Thus, this study provides a feasible strategy for the preparation of ceramic membranes with high porosity and excellent separation performances.

Visualization of Activated Fibroblasts in Heart Failure with Preserved Ejection Fraction with [18F]AlF-NOTA-FAPI-04 PET/CT Imaging.

During the pathogenesis of heart failure with preserved ejection fraction (HFpEF), fibroblasts are activated and express the fibroblast activation protein (FAP). Targeted imaging of FAP can qualitatively and quantitatively assess the fibroblast activity. This study aimed to use [18F]AlF-NOTA-FAPI-04 (AlF = aluminum fluoride; NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid; FAPI = FAP inhibitor) positron emission tomography/computed tomography (PET/CT) imaging to detect activated fibroblasts in a rat HFpEF model. The rat HfpEF model was established by feeding a high-fat diet plus l-NAME (Nω-nitro-l-arginine methyl ester) for 10 weeks. Blood pressure, echocardiography, and [18F]AlF-NOTA-FAPI-04 PET/CT were used to assess the progression of HfpEF. The biodistribution of [18F]AlF-NOTA-FAPI-04 in healthy rats was obtained. Cardiac tissue sections were also analyzed using Masson's, hematoxylin and eosin (H&E), and FAP immunohistochemistry (IHC) staining. The echocardiography and blood pressure data indicated that the rat HfpEF model was successfully established. [18F]AlF-NOTA-FAPI-04 PET/CT imaging showed obvious radiotracer accumulation in the left ventricular wall of the HfpEF rats from the seventh week. A biodistribution test showed that the tracer was cleared mainly via renal and intestinal excretion. Percentage of injected dose per gram tissue (% ID) of the heart and its surrounding organs was lower in normal rats, which was conducive to image analysis. Masson's and H&E stainings showed large areas of vascular and interstitial fibrosis in the HfpEF rat hearts. IHC staining also confirmed the presence of FAP-positive cardiac fibroblasts of the HfpEF rat hearts, with a good correlation with FAPI PET. Thus, [18F]AlF-NOTA-FAPI-04 PET/CT is a promising and non-invasive method to assess the progression of fibrosis in HfpEF to facilitate the clinical management.

Thermoluminescence investigations and kinetic analysis of highly sensitive LiCaAlF6: Eu,Y phosphor for dosimetric applications

The paper presents detailed thermoluminescence characterization and kinetic analysis of highly sensitive and dosimetric grade lithium calcium aluminum fluoride doped with europium and co-doped with yttrium (LiCaAlF6:Eu,Y). It is synthesized by melt processing technique. The thermoluminescence (TL) and optically stimulated luminescence (OSL) correlation was systematically studied. The study reveals that the OSL signal is attributed to the observed TL peaks in this material. Thus, same defects are responsible for TL and OSL in LiCaAlF6:Eu,Y. Further characterization involved measurement of TL emission spectrum, OSL emission spectrum, steady state photoluminescence (PL) spectra, phosphorescence, sensitivity, fading, dose response etc. The TL sensitivity of this phosphor was observed to be ∼5 times and ∼3 times to that of CaSO4:Dy and commercially available Al2O3:C respectively. PL, TL and OSL emission spectra suggest that Eu2+ ion acts as a luminescence center in this material. Minimum measureable dose for the phosphor in TL mode was found to be 0.3 μGy with negligible fading post 10 days of irradiation. The fading of TL signal in this material is similar to the one observed for OSL signal. The thermal stability and hygroscopic nature of LiCaAlF6:Eu, Y were studied using thermogravimetric and differential scanning calorimetry techniques. Owing to the attributes like high sensitivity, wide dynamic dose range it stands as a viable and excellent phosphor material for various radiological and dosimetric applications.

Analysis of Influencing Factors in the Preparation of Mullite Whiskers from Recovering Silicon-Rich Waste under Low-Temperature Conditions.

A large amount of catalyst waste containing silicon is deposited or buried every year, resulting in serious environmental pollution and a waste of resources. In this paper, a method to prepare mullite whiskers by recycling silica-rich waste under low-temperature conditions was investigated. The effects of raw materials, sintering temperature, catalyst addition, holding time and co-solvent addition on the structure, morphology and phase transition of the synthesized whiskers were investigated and characterized with SEM, XRD, TEM, TG and DTA. The results show that the addition of 10% Na2SO4 as the liquid-phase mass transfer medium could effectively improve the crystallization efficiency of mullite whiskers, while providing an ideal living environment for the growth of whiskers. The crystallinity and uniformity of mullite were positively correlated with the addition of aluminum fluoride trihydrate and the holding time, respectively. The growth law and conditions of mullite whiskers are discussed, and the optimal growth process conditions of mullite whiskers were optimized. The optimal conditions for mullite whiskers were determined as follows: the addition of aluminum fluoride is 5 wt%, the sintering temperature is 825 °C, and the holding time is 5 h at the time of sintering. This work offers new prospects for the industrial production of mullite whiskers from recycled silica-rich waste.

Regeneration of raw materials for aluminum electrolysis from spent carbon anodes via a closed-loop environmentally-friendly process based on aluminum–fluorine complexation

Spent carbon anode (SCA) discharged from the aluminum electrolysis industry is an unavoidable solid waste with an estimated production of 700 kilotons in 2021, which has been widely identified as the hazardous solid waste. A new two-stage leaching scheme comprising an aluminum salt leaching and an alkali leaching has been investigated in this study, by which valuable elements have been extracted from SCA. Effect of reaction conditions on the first-stage aluminum salt leaching process was investigated in detail. Under the optimal leaching conditions, the leaching rates of F, Na, and Al reached 98.00%, 94.94%, and 93.94%, respectively, and the recovered carbon purity was 85.84%. The fluorine recovery route was followed by the preparation of aluminum hydroxyfluoride precursor, namely Al2F3.24(OH)2.76 1.65H2O, through the mixing of two filtrates. Then thermogravimetry-differential scanning calorimetry (TG-DSC) curves were used to explore its calcination temperature point in detail. The final product was obtained as a mixture of AlF3 and Al2O3 with 95.94% purity. The characterization results showed that the calcined product was very similar to the commercial aluminum fluoride. Finally, the neutralized filtrate will be prepared by freezing and crystallizing Na2SO4, and the crystallized solution will be returned to the aluminum salt leaching process for recycling, which is the promise of green, recyclable, and high-value technology for realizing the detoxification of SCA and its subsequent utilization.

Sodium Nitroprusside Inhibits Detrusor Muscle Contraction through G-protein Mediated Inhibition of Intracellular Ca2+ Release

Background: Nitric oxide (NO) physiology is very complex in detrusor smooth muscle (DSM). While NO relaxes detrusor in some species, in contrary, it produces contraction in other. NO donor sodium nitroprusside (SNP) was found to inhibit CCh-induced contraction in goat DSM in earlier studies, but it is not known how SNP produces inhibitory action on goat DSM. Therefore, the aim of this in vitro study was to investigate the mechanism of inhibitory action of SNP pertaining to involvement of G- protein and other second messenger on goat DSM. Methods: Goat detrusor muscle strips collected from local abattoir were mounted in a thermostatically controlled (37o±0.5oC) organ bath (20 ml capacity) containing physiological solution. Following 1 hr of equilibration, carbachol (CCh) (10-5 M) induced sub-maximal contraction was elicited both in the absence and presence of SNP (10-5 M). Involvement of NO and guanylyl cyclase was assessed using nitric oxide synthase inhibitor L-NAME (10-5 M) and guanylyl cyclase inhibitor ODQ (10-5 M). Experiments were also carried out in the presence of G-protein activator aluminium fluoride (AlF) (10-5 M), protein kinase C (PKC) activator phorbol-12-myristate (PMA) (10-5 M), nifedipine, low Ca2+ PSS, theophylline and Zero Ca2+ PSS. Result: Inhibitory effect of SNP (10-5 M) on CCh-induced contraction on goat DSM was reversed by nitric oxide synthase inhibitor L-name (10-5 M) and guanylyl cyclase inhibitor ODQ (10-5 M). Prior incubation of the tissues with AlF and PMA also reversed the SNP mediated inhibition. On the other hand, nifedipine and low Ca2+ PSS; and theophylline and zero Ca2+ PSS potentiated the SNP-mediated inhibition. Thus, the present study shows that SNP elicited inhibitory effect on goat DSM is both NO-dependent and cGMP-dependent. In addition, the result shows that SNP inhibits G-protein coupled PKC leading to inhibition of both Ca2+ entry and intracellular Ca2+ release with a resultant decrease in intracellular Ca2+.

Reactive ion beam smoothing of rapidly solidified aluminum (RSA) 501 surfaces for potential visible and ultraviolet light applications

Optical elements made of aluminum with surface roughness in the sub-nanometer range are required for applications in the visible (VIS) and ultraviolet (UV) spectral range. Rapidly solidified aluminum (RSA) 501 is an interesting candidate to produce sufficiently smooth surfaces for these applications in an ultra-precision (UP) fly-cutting process. However, the polycrystalline grain structure and precipitates contained in the material limit the achievable surface roughness. In this research, a reactive ion beam finishing process of RSA 501 is investigated employing an electron cyclotron resonance (ECR)-driven ion source using CF4 and N2 gasses. Emphasis is placed on understanding the etching mechanisms that influence the topographic evolution to provide the basis for future production processes using the material for UV optics. Material composition characterization is applied to analyze the interaction between the reactive ion species and the RSA material. Surface modification transferring the native oxide top layer to an in situ forming and developing aluminum fluoride or -nitride etch front layer is found to prevent grain orientation-dependent etching. The effect of the ion incidence angle on the etch rates of precipitates and bulk material can be used to reduce the height of precipitates protruding from the surface after the UP-machining process. A surface roughness value of Sq = 0.9 nm ± 0.1 nm (areal root mean square height) is achieved in the micro-roughness range when etching at 40° and 80° angle of incidence using collimated ion beams with CF4 process gas.

Sintering inhibition and oil-absorption properties of calcined coal-series kaolin

AbstractIn this study, aluminium fluoride trihydrate (AlF3⋅3H2O) was used to inhibit the sintering of calcined coal-series kaolin (CCSK). In addition, the oil absorption properties of CCSK were studied. The particle-size distribution, specific surface area and porosity of the samples were investigated as a function of calcination temperature and the addition of AlF3⋅3H2O. Moreover, the ability of AlF3⋅3H2O to improve the oil absorption of CCSK was explored. The morphology, structure and phase composition of the specimens were investigated using scanning electron microscopy and X-ray diffraction. The phase transition during heating of the samples was studied using thermogravimetric analysis. The preparation with 10 wt.% AlF3⋅3H2O had the optimal sintering inhibition effect on CCSK at 1000°C. The release of SiF4 gas during heating and the formation of mullite whiskers on the particle surface caused by AlF3⋅3H2O moderated the formation of molten-phase liquid bridges between particles and inhibited sintering of the raw material powder. Furthermore, the formation of submicron mullite whiskers on the surface of the CCSK particles enhanced the oil-absorption properties of the sample significantly.

Effects of Using Aluminum Sulfate as an Accelerator and Acrylic Acid, Aluminum Fluoride, or Alkanolamine as a Regulator in Early Cement Setting.

Aluminum sulfate was employed as the main accelerator in order to explore new non-chloride and alkali-free cement accelerators. Acrylic acid, aluminum fluoride, or alkanolamine were used as regulators to further accelerate cement setting. The setting time, compressive, and flexural strengths in cement early strength progress were detected, and both the cement (raw material) and hydrated mortar were fully characterized. The cement setting experiments revealed that only loading acrylic acid as the regulator would decrease the setting time of cement and increase the compressive and flexural strengths of mortar, but further introduction of aluminum fluoride or alkanolamine improved this process drastically. In the meantime, structural characterizations indicated that the raw material (cement) used in this work was composed of C3S (alite), while hydrated mortar consisted of quartz and C3A (tricalcium aluminate). During this transformation, the coordination polyhedron of Al3+ was changed from a tetrahedron to octahedron. This work puts forward a significant strategy for promoting the activity of aluminum sulfate in cement setting and would contribute to the future design of new non-chloride and alkali-free cement accelerators.

Low sintering shrinkage porous mullite ceramics with high strength and low thermal conductivity via foam‐gelcasting

AbstractExcessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near‐net‐size forming is one of the effective ways to prepare high‐performance porous ceramics. Herein, low‐shrinkage porous mullite ceramics were prepared by foam‐gelcasting using kyanite as raw material and aluminum fluoride (AlF3) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF3 content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite‐based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF3 content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high‐performance porous ceramics.

Accelerator based epithermal neutron source for clinical boron neutron capture therapy

The world’s first accelerator based epithermal neutron source for clinical boron neutron capture therapy (BNCT) was designed, developed, and commissioned between 2008 and 2010 by Sumitomo Heavy Industries in collaboration with Kyoto University at the Kyoto University Institute for Integrated Radiation and Nuclear Science. The accelerator system is cyclotron-based and accelerates a proton up to an energy of approximately 30 MeV. The proton strikes a beryllium target, which produces fast neutrons that traverse a beam shaping assembly composed of a combination of lead, iron, aluminum, and calcium fluoride to reduce the neutron energy down to the epithermal range (∼10 keV) suitable for BNCT. The system is designed to produce an epithermal neutron flux of up to 1.4 × 10 9 n · cm − 2 · s − 1 (exiting from the moderator of a 12 cm diameter collimator) with a proton current of 1 mA. In 2017, the same type of accelerator was installed at the Kansai BNCT Medical Center and in March 2020 the system received medical device approval in Japan (Sumitomo Heavy Industries, NeuCure® BNCT system). Soon after, BNCT for unresectable, locally advanced, and recurrent carcinoma of the head and neck region was approved by the Japanese government for reimbursement covered by the national health insurance system.

Preparation of metakaolin-based geopolymer microspheres (MK@GMs) and efficient adsorption of F- from acidic wastewater

Herein, metakaolin-based geopolymer microspheres (MK@GMs: mean size 65.44 μm) are prepared by dispersion-suspension-solidification method. The fabricated MK@GMs is applied for the adsorption of F- from wastewater achieving the optimal adsorption condition of F-: pH = 1, dosage of 0.2 g/100 mL and F- concentration is 30 mg/L. Under the above conditions, the removal rate of F- in water by MK@GMs reach 89.18 % in 1 min, and the drinking water standard (less than1.5 mg/L) set by World Health Organization (WHO) is reached in 20 min. The adsorption kinetics fits the pseudo-second order kinetic model with a faster adsorption rate (k2 = 0.8 g·mg−1·min−1), and adsorption isotherm follows Langmuir model with the maximum adsorption capacity of 202.27 mg/g. According to the competitive adsorption experiment, MK@GMs have high selectivity and follow an order of: PO43- > SO42- > NO3– > Cl-. Meanwhile, MK@GMs still provide excellent removal of F- in real water bodies such as surface water, seawater and tap water. MK@GMs pro and post F- adsorption are analyzed by SEM-EDS, HRTEM, XRD, FT-IR and XPS, which show that aluminum fluoride (AlF3) is formed after adsorption, indicating the adsorption mechanism is mainly chemisorption and ion exchange. In addition, MK@GMs have an excellent immobilization effect on the adsorbed F-. This study is attributed to the facile and environmental-friendly preparation process of MK@GMs, could be deemed as promising application in acidic wastewater on large-scale.

Protective Effects of Aloe Vera on Aluminium Fluoride Toxicity on Haematological Parameters in Male Albino Rats

High concentration of AlF3 is known to cause serious effects on several body functions. Fluoride while low level of fluoride help strengthen and protect tooth enamel, too much F can cause dental fluorosis. Aloe vera plant is a medicinal plant its belonging to the family Liliaceae. The quality of Aloe vera is wound healing, burns, diabetes, to relieve the intestinal, arthritis swelling and cure ulcers. Extract of Aloe vera managed to male albino rats with high blood glucose levels resulted in a significant decrease in the plasma glucose levels of the male rats. Healthy and adult male albino rats weighted between 150-200g were administrated orally Aluminium fluoride (AlF3) 200mg/kg body weight and Aloe vera 300mg/kg body weight for a period of 60 days. Male albino rats divided in two groups. Group l–Control group, rats were maintained on normal diet and tap water. Group ll-Treated group, Aluminium fluoride treated group and Aluminium fluoride + Aloe vera treated group. After 60 days the rats were fasted overnight and sacrificed under mild ether anesthesia. In this study observed that aluminium fluoride administration toxic effects on haematological parameters in male albino rats. The value of TEC (Total Erythrocyte Counts) and Hb.con. (Haemoglobin Concentration) are decreased and TLC (Total Leucocyte Count) is increased. This study revealed that Aloe vera alleviated the toxic effect of aluminium fluoride. Aloe vera has protective influences on the haematological parameters in male albino rats

Preparation of anhydrous aluminum fluoride

Because direct roasting of aluminum fluoride hydrate will hydrolysis, resulting in higher alumina content in aluminum fluoride products. To solve this problem, a two-step process for the preparation of anhydrous AlF3 from AlF3·3H2O and NH4HF is described in this paper. First, AlF3·3H2O was dried at 220 ℃ for 9–12 h, and then NH4HF (the mass ratio of AlF3·3H2O to NH4HF was 1:20) was added, and the mixture was roasted from room temperature to 650 ℃. The results showed that the hydrolysis of aluminum fluoride can be avoided effectively by the two-step roasting method with NH4HF, the purity of the anhydrous AlF3 was 99.8 wt%, and the concentration of alumina, the main impurity, was less than 0.1 wt%.

A study of the growth mechanism of large-diameter double-wall TiO2 nanotube arrays fabricated by high voltage anodization.

Research on the growth mechanism of titanium dioxide (TiO2) nanotube arrays fabricated by anodic oxidation is essential to achieve artificial control of the microstructure and to expand their applications. In our previous work, we reported the preparation of highly ordered large-diameter double-wall TiO2 nanotube arrays prepared by high voltage anodization. In this paper, we observed and analyzed the initial growth process of large-diameter double-wall TiO2 nanotube arrays anodized at 120 V in ethylene glycol electrolyte containing aluminum fluoride (NH4F) and water (H2O), such as the evolution of surface and cross-sectional morphologies, the influence of current density on growth rate, the transition process from nanoholes to nanotubes, and the evolution of dimples on the remaining substrate. On the basis of our observations and inspirations from the existing viewpoints, we established growth models of large-diameter double-wall TiO2 nanotube arrays corresponding to different growth stages to explain the growth process. The growth rate of anodic oxide film changes accordingly with the current density. The compact anodic oxide film formed initially actually contains outer layer and inner layer, with no obvious interface between them. Then, the bottom even levels of the inner layer and outer layer bulge towards the substrate and become individual hemisphere-like structures. The inner layer becomes the outer wall, and the outer layer becomes inner wall. Eventually, V-shaped large-diameter and double-wall TiO2 nanotube arrays form. The results presented in this work are significant and provide a better understanding of the growth mechanism of large-diameter double-wall TiO2 nanotube arrays anodized by high voltage.