Longer Immersion Research Articles

SiO 2 based hybrid inorganic–organic films doped with TiO 2–CeO 2 nanoparticles for corrosion protection of AA2024 and Mg-AZ31B alloys

Hybrid sol–gel coatings provide an approach as protective layers on metals. In this work, corrosion protection of aluminium and magnesium alloys by SiO 2-methacrylate coatings doped with TiO 2–CeO 2 nanoparticles was studied. The films show an improvement of the barrier properties at initial immersion. The reactivity of both alloys produces a deterioration of the protection with longer immersion, although TiO 2–CeO 2 nanoparticles let to observe signals of self-healing effect. Aluminium oxide/sol–gel interface was found to be stable. In combination with excellent paint adhesion on sol–gel films, these coatings can be a promising alternative pre-treatment for high strength aluminium alloys prior to painting.

Enhanced Efficiency Dye Sensitized Solar Cells Through Acid Pre-treatment

AbstractA nitric acid (2M) pre-treatment is shown to increase the efficiency of a standard dye sensitized solar cell mounted on a FTO glass substrate from 4.15% to 5.12%. The pre-treatment involves immersing an FTO glass electrode coated with commercial ethyl cellulose based TiO2 paste for 1-60 minutes prior to sintering at 450°C. The pre-treatment leads to agglomeration of the TiO2 creating a scattering layer which covers the acid treated surface on short term immersion (<30 mins) and penetrates the bulk layer upon long immersion. The scattering layer itself takes up less of the sensitizing (N719) dye but scatters photons in the rest of the film. The optimum immersion time under room temperature conditions was found to be ca 20 minutes since at much longer immersion times the bulk film particle agglomeration reduced efficiency. The choice of anion in the acid is critical with certain species, notably phosphate, resulting in blockage of dye absorption sites in the entire film resulting in reduced cell efficiency.

Corrosion resistance of Zn–Co–Fe alloy coatings on high strength steel

The corrosion properties of electrodeposited zinc–cobalt–iron (Zn–Co–Fe) alloys (up to 40 wt.% Co and 1 wt.% Fe) on steel were studied by using various electrochemical techniques and compared with zinc (Zn) and cadmium (Cd) coatings in 3.5% NaCl solution. It was found that with an increase in Co content in the coating the open circuit potential (OCP) became more positive than that of the zinc coating. For Co contents higher than 30 wt.% the OCP shifted close to that of Cd, but still remained electronegative to the steel substrate. Zn–Co–Fe coatings with ≥ 30 wt.% Co + 1 wt.% Fe are nano-crystalline in nature and show superior corrosion resistance as compared to the Zn, low Co content Zn–Co–Fe and Cd coatings. During longer immersion, Zn–Co–Fe alloys with 34–40 wt.% Co became more noble to steel due to dezincification of the surface but the corresponding corrosion current density decreased. The corrosion resistance determined by the electrochemical techniques are confirmed by salt spray testing showing the superior corrosion resistance for Cd and high Co content Zn–Co–Fe alloys and poor performance of alloys with lower Co contents and pure Zn.

Hydrogen induced cracking and pitting of brass heat exchanger tube

Tin brass heat exchanger tube specimens were precharged with hydrogen at different cathodic charging conditions. Cathodic hydrogen charging was found to induce severe cracking and blistering on the surface of brass heat exchanger tube without externally applied stress. Microscopic observations revealed that the hydrogen cracks were intergranular (IG) or transgranular (TG) or mixed mode of cracking, i.e. IG and TG, while the blisters were observed to be spherically shaped. The severity of hydrogen induced cracking and blistering increased with the cathodic current density. Free corrosion immersion experiments were conducted on the hydrogen precharged tin brass heat exchanger tube specimens in 0·5M NaCl solution to investigate the role of hydrogen in pitting corrosion. It was found that hydrogen significantly promoted pit initiation and pit growth. Moreover, the pit formation and growth increased with charging time. The corrosion potential measurements revealed that the hydrogen precharged tin brass heat exchanger tube specimens exhibited lower corrosion resistance as compared with the non-precharged specimen. The corrosion potential of hydrogen precharged specimens reached a steady state after a longer immersion time. Furthermore, with increasing precharging time, the immersion time required to reach a steady state potential increased.

Influence of Ni-electrodeposited pretreatment on galvanized coatings of reactive steels

Four types of steel sheets containing 0.04%, 0.09%, 0.14% and 0.36% Si, respectively, were electrodeposited with a nickel layer of 3 μm in thickness and then galvanized in molten Zn at 450°C for various periods of time. The formation and growth of intermetallic compound layers on the surface of the samples were investigated by SEM and EDS. The experimental results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with a proper thickness, bright appearance and strong adherence. EDS results indicate that a series of Ni-Zn intermetallic compounds γ′, γ and δ2 are first formed on the surface of the samples. With a prolonged immersion time, the Γ2-Fe-Zn-Ni and δ-Fe-Zn are formed accompanied by the gradual disappearance of γ′, γ and δ2 layer. After a longer immersion time, the lumpy ζ-Fe-Zn occurs between δ and liquid Zn and the Γ-Fe-Zn does between steel substrate and δ. Subsequently, ζ is in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changes the formation of Fe-Zn intermetallic compounds, which delay the growth of lumpy ζ and promote the growth of compact δ. Consequently, the abnormal growth of reactive steels is eliminated.

Use of electrochemical impedance spectroscopy to Study corrosion of galvanised steel in 0·6M NaCl solution

The corrosion mechanism of commercially galvanised steel (containing Pb) in sodium chloride solution was evaluated using electrochemical impedance spectroscopy and polarisation curves. The behaviour of the system was simulated by an equivalent circuit with two time constants, including a Warburg element to consider the diffusion process at longer immersion times. To begin with, the impedance measurements indicated a non-stationary system with two time constants which could be related to the charge transfer resistance and the adsorption of the intermediate species. With increasing immersion time, the impedance spectra showed a corrosion mechanism that is under activation control. With immersion times of up to one month, the influence of diffusion processes on the overall corrosion mechanism increases significantly.

Effects of Duration of Immersion in a Virtual Reality Environment on Postural Stability

Few studies have been carried out to examine the relation between postural stability and subjective reports or feelings of motion sickness. Two views seem to exist on the relation between immersion in a virtual reality (VR) environment and subjective feelings of motion sickness. One predicts that the immersion induces both postural instability and motion sickness. Another view is that preimmersion postural instability predisposes people to motion sickness. However, these views are not supported by empirical research. Longer immersions in a VR environment may induce higher levels of postural instability and symptoms of motion sickness. In this study, effects of long-hours immersion in a VR environment on postural stability were examined to approach the underlying mechanism of postural instability and motion sickness using force platform measurement and self-reported questionnaire on motion sickness. As a result, it was suggested that longer immersion in a VR environment induced postural instability and symptoms of motion sickness.

Preparation and characterization of a novel bioactive bone cement: Glass based nanoscale hydroxyapatite bone cement

A novel type of glass-based nanoscale hydorxypatite (HAP) bioactive bone cement (designed as GBNHAPC) was synthesized by adding nanoscale hydroxyapatite (HAP) crystalline (20-40 nm), into the self-setting glass-based bone cement (GBC). The inhibition rate of nanoscale HAP and micron HAP on osteosarcoma U2-OS cells was examined. The effects of nanoscale HAP on the crystal phase, microstructure and compressive strength of GBNHAPC were studied respectively. It was concluded that nanoscale HAP could inhibit the cell proliferation, while micron HAP could not, and that nanoscale HAP could be dispersed in the cement evenly and the morphology did not change significantly after a longer immersion time. XRD and FTIR results show nanoscale HAP did not affect the setting reaction of the cement. Furthermore, GBNHAPC had a higher compressive strength (92 MPa) than GBC. It was believed that GBNHAPC might be a desirable biomaterial that could not only fill bone defects but also inhibit cancer cell growth.

Effect of ageing on the bond strength of a permanent denture soft lining material.

Molloplast-B is a widely used, long-term, heat-cured silicone denture soft lining material. Adhesion failure of this material to poly (methyl methacrylate) denture base material is a problem that is encountered clinically. The purpose of this study was to investigate the effects of long-term immersion in water at 37 +/- 1 degrees C and of accelerated ageing in water at 50 +/- 1 degrees C on the tensile and shear bond strength values of this denture resilient lining material bonded to a heat-cured denture base material. Immersion in water for 1 week at 37 +/- 1 degrees C had no significant effect on the measured bond strength values. Longer immersion of specimens in water at 37 +/- 1 degrees C led to a significant reduction in the measured tensile and shear bond strengths. The present study has demonstrated that the reduction in Molloplast-B bond strength that occurs as a result of long-term ageing in water at 37 +/- 1 degrees C can be achieved in a shorter period of time by ageing the specimens in water at a higher temperature.

Sulfonation of UHMW-PE fibers for adhesion promotion in epoxy polymers

This paper reports the effects of a controlled sulfonation process using sulfur trioxide in Freon® to treat UHMW-PE fibers in order to improve their adhesion to a thermosetting polymer. Following sulfonation treatment, PE fibers were evaluated by both chemical and physical methods to determine the effectiveness of treatment. Infrared spectroscopy, X-ray photoelectron spectroscopy, titration, and contact angle measurements were used to investigate the chemical pathway of sulfonation on UHMW-PE fibers. The physical effects of sulfonation on fiber topography and strength were investigated using scanning electron microscopy and conducting tensile strength measurements on treated and virgin samples. The effect of sulfonation on adhesion was measured using micromechanical test methods to quantify the level of bonding between sulfonated UHMW-PE fibers and a thermosetting matrix. For comparative purposes, the sulfonated UHMW-PE fibers were compared to plasma and corona treatments. The interfacial shear strength demonstrated an increase in adhesion with longer immersion times in the sulfonating solution which may be an effect of higher levels of mechanical interlocking caused by fiber pitting and etching.

Chemically Treated InP(100) Surfaces in Aqueous HCl Solutions

Chemically treated InP(100) surfaces in aqueous HCl (0.009 ≤ x ≤ 36 wt %) solutions at 20°C have been studied using X‐ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), and contact‐angle measurements. The XPS data indicate that the solutions cause the removal of the native oxide and leave behind an InP surface terminated by atomic chlorine. The SE data also suggest the immediate removal of the native oxide upon immersing the sample in the solutions. Longer immersion in the concentrated HCl solutions results in surface roughening; the roughened layer thickness obtained in the x = 12 wt % solution for t = 6000 s, for example, is ∼6 nm. Such SE‐estimated surface roughness values are considerably larger than the AFM rms values; the difference is considered to be due to the SE technique being sensitive to both the surface microroughness and the adsorbed chemical species. The HCl‐cleaned InP surface is hydrophobic. The adsorbed Cl species may be the cause for the hydrophobicity. © 2000 The Electrochemical Society. All rights reserved.

Impedance measurements on lacquered tinplate: fitting with equivalent circuits

Experimental impedance data previously obtained for various kinds of lacquered tinplate are fitted using two different equivalent electrical circuits, with the aim of assessing the advantages/disadvantages of this procedure for quality control of the material as compared to direct evaluation of the impedance diagrams. It is shown that for screening purposes the same conclusions can be obtained either by fitting or by qualitative analysis of the diagrams. The physical meaning of parameters obtained from the impedance measurements is also discussed. The results are interpreted on the basis that the lacquer is characterized by intact and porous areas which are associated with a capacitance in parallel with the pore resistance in the high frequency range. At lower frequencies other processes occur in series with the resistance of the pores. For short immersion times, the passivation film present on tinplate is detected, whereas for longer immersion times, faradaic processes are detected.

Friction and wear properties of film formed in the immersion test of oil containing the complex of lanthanide diethyldithiocarbamate and phenanthroline

Oil immersion tests of steel blocks in liquid paraffin containing a complex of lanthanide diethyldithiocarbamate and phenanthroline were carried out at various temperatures for two test durations. The friction and wear properties of protective films formed during such oil immersion tests were evaluated using a one-way reciprocating friction tester. The chemical composition and chemical state of the protective films formed during this immersion were investigated using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The results of the friction and wear tests indicated that the protective films exhibited good antiwear and reduction friction properties. It was also found that the higher immersion temperature and longer immersion duration correspond to the longer the antiwear lifetime of the protective film. The results of the XPS and AES analyses indicate that the film formed during the oil immersion tests might contain lanthanum oxide, sulfide and organic nitrogen compounds.

表面処理の異なるガラスクロス／エポキシ積層材の力学的特性に及ぼす水浸漬の影響

This study deals with the effects of water immersion on the mechanical properties of glass fabric/epoxy laminates with different silane treatments. Both γ-aminopropyltrimethoxysilane (amino silane) and γ-methacryloxypropyltrimethoxysilane (methacryl silane) were used as silane coupling agents. The laminates were immersed in distilled water at 80°C, and the weight change and the tensile and impact properties were measured. The weight loss occurred for the methacryl silane treated laminate, and as a result, the debonding at the interface with water penetration occurred. On the other hand, the amino silane treated laminate kept good bonding at the fiber/matrix interface even after longer immersion. The mechanical properties were affected by only the degradation of the matrix in the amino silane treated laminate, while they were affected by the degradation of both the matrix and the interface in the methacryl silane treated laminate. The degradation of the interface induced the change of fracture behavior due to water immersion, and as a result, the strength reduction process changed due to the degradation of the interface.

A two‐stream, four‐sector, recurrence pattern: Implications from WIND for the 22‐year geomagnetic activity cycle

Continuous solar wind data from WIND reveals a new recurrence pattern which implies that speed variations contribute to the 22‐year cycle of geomagnetic activity. Near December 1994 solstice, in keeping with expectation, a four‐sector interplanetary magnetic field pattern was accompanied by four streams. As the season advanced toward March equinox, however, the streams in the two sectors with away polarity diminished, leaving a strikingly unusual two‐stream, four‐sector pattern until late April. Since the magnetic field pointed toward the sun in both streams, the polarity effect of Russell and McPherron [1973] combined with the high‐speed flow resulted in a recurrent pattern of sustained geomagnetic activity during these sector passages. The solar wind pattern is consistent with Earth's excursion to southern heliographic latitudes at March equinox enabling WIND to sample high‐speed flow from only the southern coronal hole. The WIND data imply that the 22‐year variation in geomagnetic activity results not only from longer immersion in toward sectors in March and away sectors in September during even solar cycles, as proposed by Russell and McPherron [1973], but also from higher flow speeds in those sectors.

Investigation of Pre-Tungsten Silicide Deposition Wet Chemical Processing

ABSTRACTRemoving the native oxide from the poly-Si surface prior to WSix deposition is essential for achieving high quality silicides as well as sufficient film adhesion, particularly after high temperature anneal or oxidation. Contact angle studies have been used to determine initial and time-dependent surface characteristics of several types of silicon surfaces following immersions in HF-based etchants for varying amounts of time. The morphological characteristics of the surfaces before and after exposure to etchants, as well as the relative etch rates and wetting capabilities of the etchants have been used to explain the following results: With respect to initial contact angle studies, the implanted & annealed polycrystalline silicon surface has the lowest contact angle followed by polycrystalline and monocrystalline surfaces. Longer immersion times yield lower initial contact angles. The 0.1% lightly-buffered HF solution results in the highest contact angle followed by the 1% buffered HF solution with surfactant, and the 1% HF solution. With respect to contact angle changes during ambient air exposure time, the asdeposited polycrystalline silicon surface is most stable followed by monocrystalline, and implanted & annealed polycrystalline silicon surfaces. Longer immersion times improve surface stability while the 0.1% lightly-buffered HF solution results in the most stable surface followed by the 1% buffered HF solution with surfactant, and the 1% HF solution.

Progression and Surface Ultrastructure of in vitro Caused Erosive Lesions in Human and Bovine Enamel

Surface prismatic and aprismatic human enamel and unpolished or diamond-polished specimens of bovine enamel, with test and control surfaces on each studied block, were immersed in phosphoric acid containing cola beverage (pH 2.6) and citric or malic acid containing sports drinks (pH 2.8 and 3.4, respectively) for 15-180 min. The specimens were then prepared and studied in a JEOL 35C scanning electron microscope. In human aprismatic surface enamel an irregular type of dissolution was observed, with severely affected areas adjacent to less affected ones. Prismatic human and bovine specimens showed a characteristic dissolution where initial erosion after 15 min immersion was seen to affect specifically the prism sheath areas. Longer immersion caused dissolution of enamel prism cores followed by interprismatic areas. In bovine enamel malic acid affected least the surface ultrastructure when compared with citric and phosphoric acids after 15-30 min of immersion, but thereafter no difference was observed between the acids in causing erosion. Diamond-polished enamel was found more liable to erosion than non-polished enamel. Thus, the structure of enamel greatly modified the progression of in vitro caused erosion, in particular in human tooth specimens.

Durability of bonding between 4-META/MMA-TBB resin to dentin pretreated with 10-3. The effect of 10-3 pretreating period and subsequent glutaraldehyde treatment

Adhesion durability between dentin pretreated with 10-3 and 4-META/MMA-TBB resin was studied. Reduction of etching periods with 10-3 was not so effective as expected. The weakening of bond strength during immersion in water at 37 degrees C to the dentin pretreated for 1 sec occurred faster than those for either 5 sec or 10 sec. The strength decreased from 12 MPa at 1 day to 9 MPa at 3 months, 3 MPa at 6 months and finally 2 MPa at 1 year in the case of 1 sec pretreated dentin. On the other hand, the strength became half after the storage in water for 1 year in the cases of 5 and 10 sec pretreated dentins. Combination of 10-3 pretreatment and subsequent glutaraldehyde treatment could stabilize the decrease but not completely. SEM and TEM examinations suggested that dentinal collagen exposed by the etching but not entangled and impregnated by poly (4-META-co-MMA) easily deteriorated by water during the longer immersion. Collagen modified with 10-3 and then with glutaraldehyde was also changed by the longer immersion.

Environmental effects on the interlaminar shear strength of aramid-epoxy composites

Resin-reinforced composites have quite good mechanical properties but are very susceptible to environmental degradation [1]. Although considerable work has been carried out on the effect of water on these composites [2-5], much less attention has been paid to other potentially aggressive substances such as gasoline and oil. In addition, the extant work mainly deals with carbon-epoxy composites [6, 7] and few data are available on the behaviour of a ramid-epoxy composites. This letter deals with the effect of immersion in gasoline and motor oil on the interlaminar shear strength (ILSS) of unidirectional (0 °) aramid-epoxy composites. The ILSS was chosen because it gives a qualitative measure of the matrix-fibre interface integrity [8]. The composites were fabricated by the pre-preg route using standard lay-up and vacuum bagging procedures. They were made with a standard epoxy resin (DER 383), cured with an aromatic polyamine (DEH 50), reinforced with Kevlar-49 aramid fibres. The cure cycle and resin-to-hardener ratio were chosen according to the manufacturer 's specifications. The final fibre volume fraction was 65% with no more than 0.5% of voids. The specimens (thickness 3.3 ram, width 10mm and length 18.5 ram) were cut from the 300ram x 300ram panels, dried at 50 °C, for 24h and subsequently cooled in a desiccator. They were then immersed in commercial gasoline or motor oil SAE 30 (Havoline HD) for 0, 500, 1000 and 2000h. The mechanical tests were performed, according to ASTM-D 2344 standard, in a hydraulic Instron machine using a span-to-thickness ratio of 5. Ten specimens were tested for each conditioning time. A plot of residual ILSS against immersion time is shown in Fig. 1. The aramid-epoxy composite shows no reduction of ILSS value up to 2000 h when immersed in motor oil. In the first 1000h gasoline reduces the ILSS by approximately 20%. Beyond 1000 h up to 2000 h no further reduction was observed. This trend agrees well with the results of Kanellopoulos et al. [6]. In their work it was shown that large organic molecules have less ability than water to enter into polymer. Therefore, it is reasonable to say that the ability of a molecule to go into the polymer and consequently to degrade its mechanical properties is inversely proportional to its size and/or atomic weight. This is in good agreement with the present results, and suggests good performance of a ramidepoxy composites when exposed to gasoline or motor oil. The behaviour for longer immersion times is now under investigation.

Protection of mild steel in sulphuric acid by Magnetic fields

AbstractDissolution of mild steel in sulphuric acid was studied in the presence and absence of a magnetic field, with and without inhibitor, under various conditions. The magnetic field reduced the dissolution of the steel, the effect being greater at lower concentrations of acid and in the absence of inhibitor. The steel was protected to a greater extent at longer immersion times.