Interpore Distance Research Articles

The enhanced properties of anodic films on AZ91D magnesium alloy by addition of oxide nanoparticles

Anodic films are prepared on AZ91D magnesium alloy in the electrolytes with Al2O3、SiC、TiO2、ZrO2 and CeO2 nanoparticles respectively. The oxide nanoparticles are partly embedded in the anodic films during the oxidation process. The film porosity decreases with the addition of oxide nanoparticles. As the film porosity increases, the film microhardness decreases while the bonding strength increases, and the microhardness of the anodic film prepared with SiC nanoparticles is as high as 900.7 HV. The increased interpore distance and the decreased film porosity could decrease the thermal cracking tendency of the anodic films. Particularly, the anodic film prepared with CeO2 nanoparticles does not crack after heating. The crack density increases more quickly than the crack width with the changed pore parameters. After 1200 h immersion in NaCl solution the resistance values of the anodic films prepared in the electrolytes with SiC、TiO2、ZrO2 and CeO2 nanoparticles are still higher than 105 Ω cm2, two orders of magnitude higher than the values of the films prepared with Al2O3 and without oxide nanoparticles, and the film capacity increases very slowly. The anodic film prepared with ZrO2 nanoparticles shows the best corrosion resistance. The better corrosion resistance of the anodic films is attributed to the oxide nanoparticles filling the defect position, changing the film composition and improving the film defect structure.

Hexagonal diameter in cadmium sulfide/anodic alumina nanoporous bi-layer membrane by a sol–gel spin coating and their sensing application

Cadmium sulfide/anodic alumina nanoporous bi-layer film was designed for the first time by two-step anodization followed by a sol–gel spin coating method. The chemical composition, morphological, electrical and structural properties of the AA and Cd/AA nanoporous membranes have been examined. The morphological investigation of AA layer demonstrates the development of an exceptionally ordered hexagonal exhibit of nanoporous anodic alumina of pore diameter ~ 55 nm and inter-pore distance ~ 125 nm. Though, CdS/AA demonstrated the deposition of nanoporous CdS layer from agglomerated CdS nanoparticles on the surface of the membrane of AA. The energy-dispersive X-ray spectrum of CdS/AA outlined signs of O, Al, Cd, and S, which shows its high purity. The X-ray diffraction affirmed the development of cubic-phase CdS in the favored (220) orientation with normal ~ 86.2 nm crystallite size. The present voltage and resistance–concentration attributes of the CdS/AA layer as a glucose biosensor are fitted well with second-order polynomial behavior (correlation coefficient = 0.981). The glucose concentration changed from 0 to 400 mg/dl. In light of the upsides of the fabrication approach, this new age of minimal effort biosensors can be utilized as a guarantee building block for nanophotonic and nanoelectronic gadgets.

Anodic alumina oxide surfaces prepared by dual hard and mild anodization at subzero temperature: Surface microscopic characterization and influence on wettability

Multistage anodizations allow the preparation of new generations of ordered anodic alumina oxide porous structures with large interpore distances, yet the influence of second anodization and pore widening times on pore dimensions and wettability of the obtained structures has not yet been fully studied. The main objective of this study was to characterize the obtained pores (dimensions and morphology), for different anodizations and pore widening times, and to investigate their respective influence on surface wettability. Anodic alumina oxide ordered porous surfaces were prepared using a dual hard and mild anodization process with oxalic and phosphoric acids at subzero temperature, with or without pore widening. Statistical analyses were realized on pore measurements from samples produced with a large range of anodization durations (7 different tested times). The obtained surfaces possessed regular ordered pores of 99 nm and 307 nm for respectively median pore diameter and inter-pore distance, before pore widening, and did not conform to expected theoretical values for either usual lone mild or hard anodization conditions. The slow growth of pore depth (median of 11 nm/min) observed during second anodization could be explained by the subzero electrolyte temperature used. Pore widening effectively increased pore diameter, but had statistically a bigger impact on diameters for shorter second anodization time than for longer ones. Also, pore widening significantly decreased pore depth as well as the oxide barrier thickness. Additionally, porosity increased from 9.57% to 14.8% after 3 hours of pore widening, but did not significantly affect surface wettability, which was however increased when compared to flat control surfaces. The obtained results showed that a dual anodization with different electrolytes at a subzero temperature had a significant impact on pores dimensions. A discussion on the respective effects of surface chemistry and surface roughness in the wetting evolution was proposed.

Evaluation of the influence of synthesis conditions on the morphology of nanostructured anodic aluminum oxide coatings on Al 1050

Currently, the use of nanostructured films of anodic aluminum oxide (AAO) arouses great interest for a variety of nanotechnological applications. Previous studies have shown that the most important parameters in the anodic synthesis of nanoporous AAO films are the pretreatment of the substrate, the anodization voltage, and the nature, concentration and temperature of the electrolyte. To advance the development of nanomaterials, which are increasingly specific according to their functionality, in a simple and inexpensive way, it is essential to study the combined effect of the synthesis variables on the morphological properties of the coatings. The objective of this work was to study and predict the combined effect of the concentration and temperature of oxalic acid and the anodization voltage in the ordering, the pore diameter, the interpore distance, the pore density and the thickness of nanostructured films of AAO synthesized at 20, 30, 40 and 60 V and 20, 30 and 40 °C in 0.3 and 0.9 M oxalic acid, from the Al 1050 alloy. For this, surface images were obtained by optical microscopy and scanning electron microscopy, the latter being processed through the Fast Fourier Transform, and non-linear regressions were performed with the data obtained.The results proved which anodic synthesis conditions have the greatest influence on the ordering and each of the morphological parameters of the AAO films. The optimum voltage and temperature of the self-ordering regime for both oxalic acid concentrations tested were 40 V and 20 °C. The combined effect of the synthesis variables allowed obtaining coatings with a pore diameter of 27–150 nm, an interpore distance of 51–160 nm, a pore density of 35 × 108–390 × 108 and a thickness of 10–130 μm.

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.

Optimization of Initiation Sites of Tunnel Pits on Aluminum Foil Using Self-Ordered Concave Structures

The self-ordered concave structures fabricated on aluminum surface by aluminum anodic oxidation and oxide removal procedures were applied to control the pit initiation sites for tunnel etching of aluminum foil, where the tunnel pits would be correspondingly generated under the sites of self-ordered concave structures. The obtained sizes of the tunnel pits were 100–600 nm in width and 1.6 μm in length, which were mainly determined by the interpore distances of the concave structures and the tunnel etching conditions. Based on this process, the distribution of the tunnel pits on aluminum surface was improved observably, so that a high aspect ratio was successfully achieved.

In-vitro Analysis of Titanium Cellular Structures Fabricated by Direct Metal Laser Sintering

Abstract In vitro analysis of implants helps in determining biocompatibility, growth of cell and reaction of material to fluids of body. Mandibular implant is considered for the application of cellular structures in this work and Titanium alloy (Ti64) being a biomaterial, is selected for the study. The Ti64 cellular structures were designed with 10mm x 10mm x 3mm size, with pore size 1 mm and inter-pore distance 1.6 mm and were fabricated using Direct Metal Laser Sintering (DMLS) process. MG-63 Osteosarcoma cells were utilized for the analysis to mimic the bone cells associated with the mandibular implant. The cellular structure’s biocompatibility analysis was performed after a particular time interval of 12th hour, 24th hour and 36th hour (through measurement of the growing cells). On an average, the control samples showed 100 % viability whereas treatment samples showed nearly 139.83 % viability i.e there is an improvement in cell growth with respect to Ti64 cellular structures. Thus the direct metal laser sintered Ti64 cellular structure is suitable for mandibular implant application

The effects of pore widening and calcination on anodized aluminum oxide prepared from Al6082

In this study, semi-organized anodized aluminum oxide (AAO) is prepared by two-step anodization in oxalic acid using a low-purity aluminum (Al) alloy (Al6082) as the source material. Obtaining ideally ordered AAO layers from Al alloys is confounded by the presence of impurities and requires specialized post-anodization treatment. Here, a process is proposed for obtaining an AAO layer with a semi-ordered pore arrangement by means of calcination and pore-widening procedures. Calcination temperatures of 400–600 °C and pore–widening times of 15–120 min were explored. It was found that calcination improved the pore order of AAO layers from disordered to semi-ordered (defined as being near ideally ordered—one pore surrounded by six neighboring pores). In addition, it was found that calcination at 600 °C resulted in suitable pore widening of the AAO layer. The morphology of the AAO layers was characterized using scanning electron microscopy, which was applied to determine pore diameter, inter-pore distance, pore density, and AAO layer thickness. We found that calcinated and pore-widened AAO layers with pore diameters of 48.7 nm, inter-pore distances of 80.6 nm, and pore densities of 178 pores/μm2 could be prepared. The AAO preparation method proposed here is an economically attractive process suitable for the preparation of AAO layers due to the utilization of an inexpensive Al source.

Optimized nanoporous alumina coating on AA3003-H14 aluminum alloy with enhanced tribo-corrosion performance in palm oil

This study aimed to prepare nanoporous anodic alumina on AA3003-H14 aluminum alloy using a mild anodization process with minimal working voltage and treatment time. The microstructural features, mechanical properties, and tribocorrosion behavior of the coatings were assessed to determine the optimum conditions for the fabrication of nanoporous anodic alumina on AA3003-H14 alloy. The microstructural analysis showed both uniform and nonuniform pore nucleations during anodization in H2SO4/C2H2O4, H2SO4/H2CrO4, and EG/H2O/NH4F electrolytes, where the optimal nanoporous structure with an average thickness, porosity, pore diameter, and interpore distance of 382 nm, 19%, 16 nm, and 35 nm, respectively, was developed after a short-time mild anodization for 30 min at constant potential of 12 V using 15 wt% H2SO4 electrolyte. The XRD profiles indicated formation of a highly-disordered and amorphous nanoporous anodic alumina. Due to the loss of mechanical properties after heat treatment at 450 °C for 90 min, Vickers microhardness of the samples decreased drastically from 124 to 90.5 HV, respectively. The wear analysis indicated an improved tribological behavior by mild electrochemical anodization owing to the development of nanoporous anodic alumina, which acted as the liquid lubricant reservoir and increased the tribological performance of the workpiece. In addition, the heat treated specimen showed the lowest corrosion rate of 0.079 mm.y-1 and utmost corrosion protection efficiency of 95.24% following exposure in palm oil methyl ester (B100). This novel nanoporous configuration not only endows excellent tribological performance in the biofuel combustion environment, but also particularly decreases consumption of liquid lubricants through a facilitated multiphase lubrication mechanism.

Thermal rectification optimization in nanoporous Si using Monte Carlo simulations

We investigate thermal rectification in nanoporous silicon using a semiclassical Monte Carlo simulation method. We consider geometrically asymmetric nanoporous structures and investigate the combined effects of porosity, interpore distance, and pore position relative to the device boundaries. Two basis geometries are considered, one in which the pores are arranged in rectangular arrays and ones in which they form triangular arrangements. We show that systems (i) with denser, compressed pore arrangements (i.e., with smaller interpore distances), (ii) with the pores positioned closer to the device edge/contact, and (iii) with the pores in a triangular arrangement can achieve rectification of over 55%. Introducing smaller pores into existing porous geometries in a hierarchical fashion increases rectification even further to over 60%. Importantly, for the structures we simulate, we show that sharp rectifying junctions, separating regions of long from short phonon mean-free-paths, are more beneficial for rectification than spreading the asymmetry throughout the material along the heat direction in a graded fashion.

Formation and tribological properties of MoS2 self-lubricating porous anodic alumina thin flims

MoS2 self-lubricating films were prepared on long-range ordered porous anodic alumina (PAA) by an electrophoretic deposition (EPD) method. The PAA was prepared by two-step anodization of aluminum plates. Oxalic-acid-based electrolytes were used in the first step and phosphoric-acid-based electrolytes were used in the second step. This process offers a new approach to preparing PAA with wide adjustable boundary distances (43.5–21 nm) by increasing the voltage from 80 V to 100 V. The boundary distances were decreased from 78 nm to 42.2 nm by increasing the solution concentration, which increased the interpore distance. The coefficient of friction and hard-wearing of the MoS2 lubrication film on the PAA were studied by a ball-on-disk friction and wear tester. The results showed that the nanotubes stored MoS2 particles, which provided continuous lubrication.

Ultra-slow growth rate: Accurate control of the thickness of porous anodic aluminum oxide films

Porous anodic aluminum oxide (PAAO) films have attracted widespread attention because they can be used as porous templates for the preparation of various nanomaterials. However, there are still some challenges. For example, although fine control of the thickness of AAO films is generally quite easy to achieve, it is difficult to control the thickness of extremely thin films (e.g. <1 µm). This is important for practical applications where accurate control of film thickness is necessary. In the present work, PAAO films have been prepared in an electrolyte composed of a mixture of ethanol and oxalic acid under 40–50 V (at −20 to 0 °C), attaining a minimum growth rate (νa) of ~1.4 nm min−1 (at −20 °C). The influence of anodization conditions on νa, the regularity of structural cells, and the interpore distance has been studied in detail. The results show that νa can be reduced effectively by using an extremely low anodization temperature. Ultra-thin PAAO films with precisely controlled thicknesses have been fabricated using this approach.

Total effective surface area principle for enhancement of capacitive humidity sensor of thick-film nanoporous alumina

Total effective surface area is an important factor for environmentally sensing performance. The porous anodic aluminum oxide (AAO) film with a high density of nanopores leads to atremendous surface area for absorbing water molecules. But such an AAO humidity sensor formed in oxalic acid exhibits a low response of capacitance, especially under the low relative humidity (RH). Here, we demonstrate total effective surface area principle to greatly enhance the performance of AAO capacitive humidity sensor using small anodizing potential in oxalic acid. For pore-dependent surface area, the AAO pore wall would directly affect the absorbance of water molecules and the response of capacitive sensor. Decreasing the anodizing potential reduces both of the pore diameter and interpore distance proportionally but increases the surface area inversely. Therefore, the AAO sensor formed at small 20 V can greatly increase the amount of water molecules absorbed on the wall for enhancing 2–3 times response under low-to-high RH compared to those at 40 and 50 V. The good stability and reliable response/recovery time are also obtained for the AAO sensor synthesized at 20 V in oxalic acid.

Combined mild and hard novel fabrication approach for nanoporous membrane

Anodization of aluminum by a hard anodizing or mild anodizing process is usually done to obtain metal top surface finishing. Recently, this process has been becoming famous for the formation of through-hole porous oxide membranes (TH-POM) which act as a template for fabrication of nanowires/tubes. Membranes with different pore diameters, interpore distance, depth of pore and porosity can be obtained by selecting different parameters such as type and concentration of electrolyte, pH, temperature, time and applied voltage. In this research paper, exclusive experiments were studied and conducted to obtain TH-POM which will be template for generation of ordered nanowires by an electrochemical process. This research is carried out using a combination of mild anodization (MA) and hard anodization (HA) with novel heterogeneous control parameters by using DC power supply, magnetic stirrer and data acquisition system (DAQ) and at high temperature in order to minimize the refrigeration cost required for cooling the electrolyte. Excellent ordered membranes of 24–29 nm and 40–50 nm pore diameter were obtained in short time, characterized by SEM and EDS and analyzed by I–V curves obtained using an Arduino-based current/voltage data logger. A thermal stress test is also performed on the TH-POM formed using MA and HA.

Preparation of anodized aluminium oxide at high temperatures using low purity aluminium (Al6082)

A rapid two-step anodization process was developed to prepare semi-ordered nanoporous anodized aluminium oxide (AAO) layers using an inexpensive aluminium (Al) alloy, Al6082 (97.53% Al) as the Al source material. Al anodizing was performed at various anodization voltages (30, 45, 60 V) and temperatures (20, 30, 40 °C) using 0.4 M oxalic acid as the electrolyte. The effects of temperature and voltage on the morphological characteristics of the obtained AAO formed by one- and two-step anodization were investigated. The obtained AAO surfaces were characterized by scanning electron microscopy. Morphological characteristics of importance here were the pore diameter, inter-pore distance, porosity and pore density. An AAO layer with a semi-ordered pore arrangement was prepared using a two-step anodization process, which included an AAO etching step before the second anodization. The obtained AAO had a pore diameter of 43.8 ± 6.0 nm, inter-pore distance of 82.6 ± 19 nm, 25% porosity, pore density of 169 pores/μm2 and layer thickness of 53 μm. Energy-dispersive X-ray spectroscopy results suggested that non-Al elements present in Al6082 were present on the surface of AAO. From an economic perspective, the AAO preparation process proposed in this study makes the fabrication of AAO more attractive.

Anodization of Al in Neutral Oxalate Solution to Form Unusually Fine Nanoporous Film

Al was anodized in a 0.20 M potassium oxalate solution at 40 V vs Hg/Hg2SO4 at 25 °C. The oxide film was composed of three layers. The interpore distance in the lower fine porous layer was ∼25 nm, ...

Structural Characterization of Anodic Porous Alumina Formed By Galvanostatic Anodizing in Etidronic Acid

Anodizing aluminum in etidronic acid (1-hydroxyethane-1,1-diphosphonic acid) causes the formation of porous alumina at higher voltage more than 200 V. Highly ordered porous alumina with a large-scale cell can be easily fabricated via two-step constant voltage anodizing in etidronic acid. However, extremely little has been reported on the growth behavior during galvanostatic anodizing in etidronic acid and its structural characterization. In the present investigation, we demonstrate the details of the anodizing behaviors and nanostructures of the porous alumina formed via galvanostatic anodizing in etidronic acid under various operating conditions. High-purity aluminum plates were electrochemically polished, and then were anodized at a constant current density of 0.005-500 Am-2 in 0.03-3 M etidronic acid solutions (273-333 K). After anodizing, the specimens were immersed in a 0.20 M CrO3/0.51 M H3PO4 solution (353 K) to dissolve the porous alumina, and the aluminum dimple array was exposed to the surface. The surface and cross-section of the anodized specimens were examined by field-emission scanning electron microscopy (FE-SEM). The cell size (interpore distance) of the porous alumina was calculated using image analysis software. As the electropolished aluminum specimens were anodized galvanostatically under various conditions, the voltage linearly increased, gradually decreased, and then reached plateau value (U p). However, excess current density led to a burning phenomenon and the formation of non-uniform porous alumina. Figure 1 shows the changes in the plateau voltage, U p, and the current density, i a, during anodizing in a 0.3 M etidronic acid solution. The plateau voltage greatly increased with the current density at each temperature, and various porous alumina films were successfully fabricated by anodizing at a wide voltage range measuring 7-218 V. Figure 2 shows the relationship between the cell size, D c and the anodizing voltage, U a. The cell size linearly increased with the anodizing voltage at each solution temperature and current density. A linear proportional constant of 2.5 nmV-1 was obtained, which is similar to the self-ordering condition via constant voltage anodizing. Figure 1

Alkaline Corrosion-Resistant Anodic Aluminum Oxide Formed By Etidronic Acid Anodizing

A newly discovered electrolyte for anodizing aluminum, etidronic acid (CH3C(OH)[PO(OH)2]2), operates at high voltages of more than 200 V, and ordered porous alumina measuring 400-670 nm in cell diameter (interpore distance) can be fabricated via constant voltage anodizing. Because such porous alumina film formed at high voltages possesses a thick barrier layer, etidronic acid anodizing may be useful for corrosion protection of aluminum. Here, we describe the alkaline corrosion-resistant porous alumina formed by high voltage anodizing in an etidronic acid solution, and its hydration behavior in boiling water was investigated. Highly pure aluminum plates (99.999 wt%) were anodized in 0.3 M sulfuric acid, 0.3 M oxalic acid, 0.3 M citric acid, and 0.3 M etidronic acid solutions (293 K) at a constant current density of 30 Am-2 or a constant voltage of 250 V. The anodized specimens were immersed in a 2.5 M NaOH solution (293 K). The nanostructural changes were examined by electrochemical impedance spectroscopy (EIS). The anodized specimens were immersed in boiling water to seal the pores in the porous alumina film. The surface and cross-section of the specimens were characterized by field-emission scanning electron microscopy (FE-SEM) The plateau voltages during anodizing aluminum at a constant current density of 30 Am-2 in sulfuric and etidronic acid solutions exhibited approximately 16 V and 197 V, respectively. As the specimen anodized in sulfuric acid was immersed in a 2.5 M sodium hydroxide solution, H2 gas evolution was observed from the surface at the beginning of immersion, and the amount increased with the immersion time. In contrast, the specimen anodized in etidronic acid did not result in hydrogen gas evolution during immersion until 8 min. Here, the capacitance (Cb ) is inversely proportional to the thickness of the barrier layer. Figure 1 shows the changes in the reciprocal Cb with the immersion time, ti . Complete dissolution of porous alumina formed in etidronic acid takes 15 times longer than dissolution of the alumina formed by sulfuric acid anodizing due to the formation of a thick barrier layer. As the porous alumina formed by etidronic acid anodizing is immersed in boiling water, plate-like hydroxides were formed at the bottom of the pores in the initial immersion stage. The thickness of the hydroxide layer increased with the immersion time, and the nanopores are completely sealed by long-term immersion. Figure 1

Plasma electrolytic oxidation ceramic coatings proceed by porous anodic film

Ceramic coatings were performed on aluminum through plasma electrolytic oxidation (PEO) in a Na5P3O10 solution with various concentrations of NaOH. It was revealed that the concentration of NaOH affected the types of anodic films and the activity of plasma discharges. Emphatic investigation was performed on the coatings fabricated in the electrolyte with addition of 1 g L−1 NaOH, focusing on the coating microstructure evolution and coating corrosion resistance. Some coatings were detached from the substrate, showing that the oxide particles on the anodic film C/S interface underwent profile variations from hemisphere to polygon, and its interpore distance decreased over time. The formations of pores of anodic films and plasma discharge of the PEO coatings were both easy to occur around the existing pores and the existing discharge channels. Fractured cross-section showed that a pancake-like structure corresponded to a discharge channel, a cavity, and a barrier layer protrusion whose area was similar to that of the corresponding pancake-like structure. The data of potentiodynamic polarization measurements showed that the sample treated with PEO for 10 min possessed the lowest icorr value of 4.97E-8 A cm−2, the most positive Epit value of −0.63 V, and the highest Rp value of 2.66E5 Ω cm2. EIS data of 10 min sample exhibited the highest R2 value of 1.61E6 Ω cm2, demonstrating the best corrosion resistance among these samples.

Fabrication of alumina with ordered tapered-nanopore nested in micro-bowl hierarchical structure by a combined anodization

We report that porous anodic alumina (PAA) with ordered tapered-nanopore nested in micro-bowl hierarchical structure can be facilely and controllably fabricated by a combined anodization process. It includes three main steps: I, stable anodization in citric acid to fabricate micro-bowl; II, mild anodization and chemically dissolving PAA to fabricate nanopit pattern; III, multi-step mild anodization and etching pore-widening to fabricate tapered-nanopore. Although the used anodization technology in each step is well established, the smart combination for realizing hierarchical structure is unreported but very effective. It is found that the original interpore distance of the micro-bowl obtained by stable anodization in citric acid can be enlarged by the followed mild anodization, which can be tuned from 0.88 μm to 1.3 μm. The structural parameters of tapered-nanopore can be tailored by changing the mild anodization conditions. Because of the curvature of the micro-bowl, the average number of the tapered-nanopore can be as high as 1.68 × 1015/cm2, which is about 1.5 times more than that (1.16 × 1015/cm2) on the flat surface. This method is simple and effective, which opens a door for boosting investigations into the physical and chemical properties of micro- and nanostructure made of metal or polymer materials as combining with nanoimprinting or electrochemical deposition.