Aluminum Passivation Research Articles

Material effects on V-nanoantenna performance

There is great interest in aluminum based plasmonic devices due to the relatively high plasma frequency of this material as well as its low cost and self-passivating oxide layer. The passivation layer provides aluminum plasmonics with the long-term stability required for practical applications. While several studies have investigated the impact of this oxide layer on the plasmon resonances of aluminum nanostructures on glass substrates, little is known about the effect of high-refractive index substrates on these resonances. Here we present an investigation of aluminum V-shaped antennas resonant in the visible on a silicon substrate. Through comparison between numerical and experimental results, we show that the aluminium passivation layer has little effect on the antenna resonances by comparing numerical simulations both with and without. We show, however, that inclusion of the native oxide layer of the silicon substrate in numerical models is critical for achieving good agreement with experimental data. Furthermore, we computationally explore the influence of the 1.5 eV interband transition of aluminum on plasmon resonances, and find that its effect on the material properties of the resonant structures results in narrower resonances in the blue part of the spectrum than if it was not present.

PECVD-AlOx/SiNx passivation stacks on wet chemically oxidized silicon: Constant voltage stress investigations of charge dynamics and interface defect states

The negative charge formation, the charge-trapping mechanisms and the interface defect passivation of aluminum oxide/silicon nitride (AlOx/SiNx) stacks deposited by plasma-enhanced chemical vapor deposition on p-type crystalline silicon (c-Si) are investigated. Constant voltage stress (CVS) investigations combined with capacitance–voltage (C–V) hysteresis analysis indicate the influence of different thermal treatments on the negative charge formation and allow discerning between fixed and trapped charges in the AlOx/SiNx system. The thermal budget during SiNx deposition activates negatively charged traps. An annealing step leads to the formation of a stable, fixed negative charge and reduces the defect state density (Dit) at the c-Si/AlOx interface. A wet-chemical silicon oxidation (SiOx) of the c-Si surface reduces Dit even further, but introduces additional traps at the wet-chemical SiOx/AlOx interface. These traps lead to instabilities of the negative charge density and have a detrimental effect on the passivation quality. However, a firing step leads to the formation of a higher negative charge density due to charged traps. Combined with the enhanced chemical passivation, this results in a higher passivation quality than upon annealing. The trap-related negative charge upon firing is unstable due to electron detrapping. However, a positive CVS can recharge traps in the wet-chemical SiOx/AlOx/SiNx system negatively through electron injection from the c-Si.

Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates

The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx) stacks on both p-type and n-type crystalline silicon (c-Si) substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD) at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD) to form anti-reflection coating (ARC) stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300–1200 nm) without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (Seff,max) was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450–1000 nm.

Passivation of aluminium–n+ silicon contacts for solar cells by ultrathin Al2O3 and SiO2 dielectric layers

AbstractUltra‐thin thermally grown SiO2 and atomic‐layer‐deposited (ALD) Al2O3 films are trialled as passivating dielectrics for metal–insulator–semiconductor (MIS) type contacts on top of phosphorus diffused regions applicable to high efficiency silicon solar cells. An investigation of the optimum insulator thickness in terms of contact recombination factor J0_cont and contact resistivity ρc is undertaken on 85 Ω/□ and 103 Ω/□ diffusions. An optimum ALD Al2O3 thickness of ∼22 Å produces a J0_cont of ∼300 fAcm–2 whilst maintaining a ρc lower than 1 mΩ cm2 for the 103 Ω/□ diffusion. This has the potential to improve the open‐circuit voltage by a maximum 15 mV. The thermally grown SiO2 fails to achieve equivalently low J0_cont values but exhibits greater thermal stability, resulting in slight improvements in ρc when annealed for 10 minutes at 300 °C without significant changes in J0_cont. The after‐anneal J0_cont reaches ∼600 fAcm–2 with a ρc of ∼2.5 mΩ cm2 for the 85 Ω/□ diffusion amounting to a maximum gain in open‐circuit voltage of 6 mV. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of oxide shell growth on nano-aluminum thermite propagation rates

Flame propagation rates for nanometric particle composites of aluminum (Al) and molybdenum trioxide (MoO3) were examined. The Al particles were prepared by thermally treating the particles at 480°C for time increments up to 180min in oxygen and 90min in argon. This treatment caused the aluminum passivation shell to grow and there is also evidence of shell damage due to treatment. Results reveal several interesting behaviors: flame speeds initially on the order of several hundred meters per second were reduced with damage to the oxide shell, and there is a weak dependence of the flame speed on the ratio of particle radius to shell thickness (M) in the range 6.1<M<13.4. The sharp drop in flame rate at further reduction in M down to 5.0 is consistent with a similar drop observed for adding alumina to the reactive mixture. All observations are consistent with the melt dispersion mechanism associated with Al nanoparticle oxidation.

Passivity and Local Activation of Aluminum in Borate Buffer Solution under Action of Bromide-Ions Additives

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Activation Energy for the Corrosion of Aluminum Powders in Water

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the potential for corroding aluminum to produce quantities of hydrogen at a lower total system mass compared to compressed storage tanks is spurring research into accelerating aluminum corrosion by ball milling and mixing with other powders. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. To further study the mechanism behind the increased rate the activation energies were calculated for hydrogen evolution from pure aluminum, aluminum that had been ball milled, and aluminum mixed with alumina powder. Overall, aluminum that is in contact with higher amounts of aluminum hydroxide, either grown or added, showed a drop in activation energy from approximately 80 kJ/mole down to 24 kJ/mole.

Polypyrrole coating doped with dihydrogenophosphate ion to protect aluminium against corrosion in sodium chloride medium

The electrodeposition of polypyrrole (PPy) on aluminium electrodes has been achieved in phosphoric acid medium by using potentiodynamic, potentiostatic and galvanostatic techniques. The corrosion behavior of polypyrrole on aluminium in sodium chloride medium has been investigated by open circuit potential and electrochemical impedance spectroscopy. A mechanism to explain the beneficial effect of PPy-doping dihydrogenophosphate ion in the passivation of aluminium is proposed.

Passivation Rates for Small Particulate Aluminum in Contact with Oxide and Nitride Powders

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the corrosion rate of aluminum powders is seen to greatly increase when in contact with alumina powder. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. Scratch tests were run on aluminum disks covered with oxide and nitride powders to look at repassivation rates after the surface film was disturbed and a decrease in the repassivation time observed. Small pellets of aluminum powder mixed with oxide or nitride powders were also studied with scratch events showing far lower current perturbation than seen for pure aluminum.

Hydroxide Precipitation in Aluminum Passivation in the Presence of other Inert Surfaces

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Hydrogen production by aluminum corrosion in hydrochloric acid and using inhibitors to control hydrogen evolution

This study reports on the systematic assessment of hydrogen (H 2) production by corrosion of aluminum alloy (AA) in hydrochloric acid (HCl) at different temperature. Rare earth inhibitors, lanthanum (La) and cerium (Ce) have been applied to control the H 2 production process. The production process is based on electrochemical reaction of aluminum (anodic reaction) in the HCl solution, which has a high concentration of hydrogen ions (H +), the H + ions are reduced and H 2 is evolved. Preliminary results showed that an increase in temperature of working solution produced an increase of the H 2 production rate. The H 2 production rate increases because acid can prevent aluminum passivation during H 2 evolution. The rare earth inhibitors La and Ce control the H 2 evolution, especially, when using mixture of both inhibitors. This result demonstrates a synergistic effect between the La and the Ce inhibitors. X-ray diffraction studies were performed on the surface structure before and after immersion, and a scanning electron microscope (SEM) was used to study the morphology of the AA.

Paint pretreatments for aluminum

Chemical conversion coatings are the most widely used prepaint treatment processes for metal substrates. Processes specifically designed for aluminum are of recent origin. These include accelerated chromate phosphates, chromate oxides, anodizing and, very recently, nonchromate formulations. Historically, however, phosphoric acid cleaners, wash primers, and iron and zinc phosphates have all been utilized as paint pretreatments with satisfactory results. Among these, the chromate types provide the most reliable underfilm corrosion protection and paint adhesion. Anodized coatings, especially unsealed sulfuric and chromic acid types, are also comparable in performance, but fall far short of the productivity and cost effectiveness of the chromate processes. A careful evaluation of critical product requirements is essential in selecting the right conversion coating for anticipated field performance. Paint pretreatments must assure these corrosion protection functions passivation of base aluminum, action as a barrier against moisture, oxygen, and other corrosive agents, electrochemical insulation, and protection against mechanical erosion. In addition, conversion coatings must provide other essential interfacial properties complementary to the paint top coat, including an effective and continuous bonding site; chemical stability during the service life of painted products; remaining insoluble, impervious, and flexible; providing a wettable subsurface for paint application; and maintaining adhesive integrity between the base metal and painted film. See Table 1 for typical performance data.

The Role of Alumina in Aluminum Corrosion and Passivation

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the corrosion rate of aluminum powders and thin foils is seen to greatly increase when in contact with alumina powder. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. Data is presented to support the claim that proton availability from the alumina surface is responsible for the increased hydrogen evolution rates, and hydrogen capture tests show passivation no longer stops the corrosion reaction.

ChemInform Abstract: The Influence of Tungsten Alloying Additions on the Passivity of Aluminum.

Transition metals such as Mo, W, Ta, Cr, and W can be used to significantly enhance the localized corrosion resistance of Al. Since these elements exhibit very low solubilities in aluminum, a nonequilibrium alloying method, such as sputter deposition, must be used to produce single-phase alloys. The addition of approximately 9 atom percent W to Al can shift its pitting potential in the positive direction as much as 2600 mV. Heat-treatment of these nonequilibrium alloys results in the precipitation of a second phase that is detrimental, but not catastrophic, to corrosion performance. Surface analysis of the Al-W passive film formed as a function of applied anodic potential reveals that it remains thin throughout the polarization sequence and contains very little oxidized solute, regardless of the applied potential. The oxidized W present in the film is in the form of WO{sub 2} and WO{sub 3} (or WO{sup {minus}2}{sub 4}). The results of this paper reveal that the electrostatic-repulsion or oxidized-solute barrier-layer mechanisms are not responsible for the dramatic enhancement in the passivity of Al with the addition of W. Instead, the small amount of oxidized W in the passive film may interact synergistically with the hydrated aluminum oxide structure to formmore » a more protective film.« less

Revisiting LiClO4 as an Electrolyte for Rechargeable Lithium-Ion Batteries

In this work, was revisited and explored as a possible electrolyte in Li-ion batteries. and solutions in alkyl carbonate solvent mixtures were compared in several aspects: electrochemical windows with noble metal and aluminum electrodes, anodic stability, surface chemistry developed on negative electrodes (Li, Li–graphite, Li–Si), the electrochemical behavior of graphite anodes and cathodes, and thermal behavior (solutions alone and mixtures of solutions and electrode materials). The anodic stability and the aluminum passivation are much better in solutions than in solutions. However, HF contamination in the former solutions worsens the passivation of negative electrodes due to reactions with surface and ROLi species. Thermal reactions of produce more specific heat than solutions. However, in terms of onset temperatures for thermal runaway, the two electrolytes are equivalent. In conclusion, is still an electrolyte that may be considered for use in lithium-ion batteries.

Passivation of aluminum with alkyl phosphonic acids for biochip applications

Self-assembly of decylphosphonic acid (DPA) and octadecylphosphonic acid (ODPA) was studied on aluminum films using XPS, ToF-SIMS and surface wettability. Modified aluminum films were tested for passivation against silanization and subsequent oligonucleotide attachment. Passivation ratios of at least 450:1 compared to unprotected aluminum were obtained, as quantified by attachment of radio-labeled oligos.

Hydrogen generation through massive corrosion of deformed aluminum in water

Aluminum, one of most reactive metals, rapidly corrodes in strong acidic or alkaline solutions but passivates at pH of about 5–9. We have determined that the passivation of aluminum in this range of pH, and in particular in regular tap water, can be substantially prevented after milling of aluminum with water-soluble inorganic salts (referred to as “WIS”), such as KCl or NaCl. Ensuing corrosion of Al in tap water, with accompanying release of hydrogen and precipitation of aluminum hydroxide, at normal pressure and moderate temperatures (∼55 °C) is rapid and substantial. For example, ∼92% of the Al in the Al–WIS system when milled for 1 h and ∼81% when milled for 15 min, corrodes in 1 h, with the release of 1.5 mol of hydrogen per each mole of Al consumed in the reaction. Besides gaseous hydrogen, only solid aluminum hydroxides were formed as the reaction byproducts, opening up the possibility of straightforward recycling of the system. The effects of WIS concentration, chemistry of other additives, powder particle size, temperature, and milling conditions on the reaction kinetics are reported.

LOCA이후 환경에서 원자로건물집수조 여과기의 수두손실에 대한 화학적 영향

냉각재상실사고이후 원전의 원자로건물집수조 여과기에서 화학적 영향을 고려한 수두손실을 종합적으로 평가하기 위한 시험장치를 개발하였다. 시험장치에서 원자로건물집수조와 시험장치에서 물 부피에 대한 여과기 면적의 비가 일치하도록 시험조건을 설정하고 시험을 수행하였다. TSP pH 조절제 조건에서 칼슘실리케이트는 시험 초기에 수두손실을 급격히 상승시켰기 때문에 원자로건물에서 모든 칼슘실리케이트를 제거하여야 함을 확인하였다. 비상노심냉각계통 살수지속시간의 차이에 따른 시험결과는 장기살수조건이 단기살수조건에 비해 12배 정도 높은 수두손실을 보였다. 살수조건 시험결과를 화학적 영향이 없는 수두손실과 비교하면 단기살수와 장기살수의 각 조건에서 5.6배 및 60.8배 수두손실이 증가하는 결과를 보였다. 화학적 영향은 재순환수에 노출된 물질의 양에 따라 초기의 일정기간 동안 알루미늄 및 아연도금 판의 부식에 의해 급격히 증가하고 이들이 부동피막을 형성한 이후에는 NUKONTM 및 콘크리트 등에서 침출된 화학종의 침전에 기인하여 증가율이 감소하는 경향을 보였다. 실험결과는 TSP에 의한 알루미늄의 부동피막 형성이 살수시간이 길어지고 알루미늄의 양이 많을 경우 효과적이지 않다는 것을 보였다. A test apparatus has been fabricated to simulate chemical effect on head loss through a strainer in a pressurized water reactor (PWR) containment water pool after a loss of coolant accident (LOCA). Tests were conducted under condition of same ratio of strainer surface area to water volume between the test appratus and the containment sump. A series of tests have been performed to investigate the effects of spray, existence of calcium-silicate with tri-sodium phosphate (TSP), and composition of materials. The results showed that head loss across the chemical bed with even a small amount of calcium-silicate insulation instantaneously increased as soon as TSP was added to the test solution. Also, the head loss across the test screen is strongly affected by spray duration and is increased rapidly at the early stage, because of high dissolution and precipitation of aluminum and zinc. After passivation of aluminum and zinc by corrosion, the head loss increase is much slowed down and is mainly induced by materials such as calcium, silicon, and magnesium leached from NUKONTM and concrete. Furthermore, it is newly found that the spay buffer agent, tri-sodium phosphate, to form protective coating on the aluminum surface and reduce aluminum leaching is not effective for a large amount of aluminum and a long spray.

Passivation of Aluminum–Molybdenum Alloys in Hydrochloric Acid

The electrochemical properties of the system Al–Mo alloy∣anodic oxide film∣1.0 M HCl solution were investigated as a function of alloy composition and applied potential in 1.0 M HCl. Voltammetry measurements have revealed that the alloy systems with behave almost like pure Mo. The alloy systems with showed the potential regions of primary and secondary passivities in which the structural and protective properties of the anodic oxide films were studied using electrochemical impedance spectroscopy. Orazem’s graphical methods and Mott–Schottky analysis were used to extract the values of parameters of the constant-phase element, interfacial capacitance, ohmic resistance, type of conductivity, and concentration of charge carriers in the semiconducting oxide film, which are all from the high frequency impedance data. The pseudoinductive behavior observed at low frequencies in the potential range of the secondary passivity was discussed in terms of the surface-charge approach based on the chemistry of the point defect model.

Experimental investigation of material chemical effects on emergency core cooling pump suction filter performance after loss of coolant accident

Integral tests of head loss through an emergency core cooling filter screen are conducted, simulating reactor building environmental conditions for 30 days after a loss of coolant accident. A test rig with five individual loops each of whose chamber is established to test chemical product formation and measure the head loss through a sample filter. The screen area at each chamber and the amounts of reactor building materials are scaled down according to specific plant condition. A series of tests have been performed to investigate the effects of calcium-silicate, reactor building spray, existence of calcium-silicate with tri-sodium phosphate (TSP), and composition of materials. The results showed that head loss across the chemical bed with even a small amount of calcium-silicate insulation instantaneously increased as soon as TSP was added to the test solution. Also, the head loss across the filter screen is strongly affected by spray duration and the head loss increase is rapid at the early stage, because of high dissolution and precipitation of aluminum and zinc. After passivation of aluminum and zinc by corrosion, the head loss increase is much slowed down and is mainly induced by materials such as calcium, silicon, and magnesium leached from NUKON™ and concrete. Furthermore, it is newly found that the spay buffer agent, tri-sodium phosphate, to form protective coating on the aluminum surface and reduce aluminum leaching is not effective for a large amount of aluminum and a long spray.