Function Of Immersion Time Research Articles

In situ spectroscopic ellipsometry studies of trivalent chromium coating on aluminum

In situ spectroscopic ellipsometry in the spectral region of 1.3–4.3 eV has been employed to monitor, in real-time, the formation of trivalent Cr process (TCP) conversion coatings on polished Al substrates. The measured ellipsometry parameters (Ψ and Δ), as a function of immersion time, reveal that the initial stages of film formation include the chemical thinning of the native oxide layer, formation of a very thin initiation layer and the subsequent rapid formation of the TCP film. The film optical constant is modeled using Cauchy dispersion relation and its thickness was determined as a function of immersion time during growth.

Silicate, borosilicate, and borate bioactive glass scaffolds with controllable degradation rate for bone tissue engineering applications. II. In vitro and in vivo biological evaluation

In Part I, the in vitro degradation of bioactivAR52115e glass scaffolds with a microstructure similar to that of human trabecular bone, but with three different compositions, was investigated as a function of immersion time in a simulated body fluid. The glasses consisted of a silicate (13-93) composition, a borosilicate composition (designated 13-93B1), and a borate composition (13-93B3), in which one-third or all of the SiO2 content of 13-93 was replaced by B2O3, respectively. This work is an extension of Part I, to investigate the effect of the glass composition on the in vitro response of osteogenic MLO-A5 cells to these scaffolds, and on the ability of the scaffolds to support tissue infiltration in a rat subcutaneous implantation model. The results of assays for cell viability and alkaline phosphatase activity showed that the slower degrading silicate 13-93 and borosilicate 13-93B1 scaffolds were far better than the borate 13-93B3 scaffolds in supporting cell proliferation and function. However, all three groups of scaffolds showed the ability to support tissue infiltration in vivo after implantation for 6 weeks. The results indicate that the required bioactivity and degradation rate may be achieved by substituting an appropriate amount of SiO2 in 13-93 glass with B2O3, and that these trabecular glass scaffolds could serve as substrates for the repair and regeneration of contained bone defects.

Changes on surface morphology of corn starch blend films

This study aims at evaluating the influence of enzymatic degradation solution on the surface morphology and thermal properties of a poly(ethylene-vinyl alcohol) copolymer-corn starch thermoplastic blend (SEVA-C), as a function of immersion time. To perform this study, three different batches were assessed using SEVA-C samples of different thicknesses and a fixed weight of 1.6 g, immersed in alpha-amylase (50 u/L) up to 90 days at 37 degrees C. TGA, contact angle measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were used. Three degradation mechanisms are considered in these systems: namely, mass loss due to plasticizer leaching (glycerol), starch enzymatic cleavage, and synthetic polymer fractions degradation. Enzymatic hydrolysis of the starch fraction and subsequent leaching from the internal bulk structure led to an increase in surface porosity, pore size, roughness, and to the development of small pits throughout the surface, as observed by SEM and AFM.

Acceleration of Electrocatalytic Activity on Pt–Sn Nanoparticles

A shell on Pt metal core nanoparticle synthesis technique has recently been demonstrated to permit electrostatic layer-by-layer (LbL) assembly of well-ordered electrocatalysts without precipitation onto porous carbon supports. In this paper, the electrocatalytic activity of the LbL-assembled Pt nanoparticles is shown to depend critically upon removal of surface-adsorbed Sn . By subjecting the synthesized Pt nanoparticle electrodes to potential sweeps greater than 1.0 V vs reversible hydrogen electrode, are removed and a nearly threefold enhancement in oxygen reduction reaction (ORR) specific activity over commercial catalysts is obtained. In contrast to this electrochemical acceleration approach, we also investigate electroless, wet-acceleration methods for removal. Energy-dispersive spectroscopy and inductively coupled plasma-mass spectrometry are used to quantify the Pt/Sn ratio in the electrode assemblies as a function of immersion time in solution (both alkaline and acidic) and during electrochemical acceleration, respectively. Charging current for the underpotential deposition of protons on the Pt nanoparticle surface is used to monitor the removal of during electrochemical acceleration, followed by ORR activity measurement in saturated perchloric acid . Wet-chemical acceleration in NaOH solution is found to remove similar amounts of Sn as compared to the electrochemical technique.

Investigation of the inhibition effect of 5-((E)-4-phenylbuta-1,3-dienylideneamino)-1,3,4-thiadiazole-2-thiol Schiff base on mild steel corrosion in hydrochloric acid

The inhibition effect of 5-((E)-4-phenylbuta-1,3-dienylideneamino)-1,3,4-thiadiazole-2-thiol (PDTT) Schiff base on mild steel corrosion in 0.5 M HCl was studied for both short and long immersion time. For this purpose, potentiodynamic polarization, electrochemical impedance spectroscopy, linear polarization resistance, hydrogen gas evolution, the change of open circuit potential as a function of immersion time, SEM and AFM techniques were utilized. The PDTT Schiff base has shown remarkable inhibition on the corrosion of mild steel in 0.5 M HCl solution. The high inhibition efficiency was attributed to the blocking of active sites by adsorption of inhibitor molecules on the steel surface.

Apatite-forming ability and magnetic properties of glass-ceramics containing zinc ferrite and calcium sodium phosphate phases

Fine particles of zinc ferrite (ZnFe 2O 4) and calcium sodium phosphate [NaCaPO 4] were crystallized in bulk x(ZnO, Fe 2O 3)(65− x)SiO 220(CaO, P 2O 5)15Na 2O (6 ≤ x ≤ 21 mol %) glassy matrix by heat treatment. Initial magnetization curves reveal that samples with x = 6 and 9 mol % zinc–iron oxide exhibit both ferrimagnetic and paramagnetic contributions, whereas, samples with x > 9 mol % zinc–iron oxide exhibit only ferrimagnetic contribution. This observation is supported by the disappearance of the electron paramagnetic resonance (EPR) absorption line centered at g ≈ 4.3 in samples with x > 9 mol % zinc–iron oxide. Apatite-forming ability of the glass-ceramic samples was investigated by examining apatite formation on the surface of the samples treated in simulated body fluid (SBF). Increase in apatite-forming ability was observed with an increase in zinc–iron oxide content. The results obtained have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass-ceramic composition. A good correlation has also been observed between the magnetic nature of the samples and their apatite-forming ability. These materials are expected to find application as thermo-seeds in hyperthermia treatment of bone cancer.

Compatibility between cataphoretic electro-coating and silane surface layer for the corrosion protection of galvanized steel

The compatibility between a cataphoretic electro-coating and a silane layer applied on galvanized steel was evaluated by performing electrochemical impedance measurements on coated and uncoated samples. During electro-deposition, the water electrolysis induces hydrogen production. This process can induce degradation or destruction of the silane layer. This process was simulated by reproducing the application conditions of electro-coating in an aqueous solution of same pH (6) and conductivity (1600 μS) than the electro-coating bath, but without any pigments and binder. A current of 2 mA/cm 2 was applied between the sample and the counter-electrode during 10 and 20 s. These conditions are representative of the mean real application conditions just before the coating formation. The loss of the barrier effect offered by the silane layer was evaluated by EIS before and after simulation. This simulation shows whether it is possible to conveniently design the properties of the silane layer to maintain its protection and adhesion promotion properties after polarization. The barrier properties and the water uptake of the electro-coated samples were evaluated by EIS as a function of immersion time in a sodium chloride solution (0.1 M). The coated silane pre-treated samples show a good behaviour compared to the samples coated without pre-treatment. By properly managing the deposition conditions of sol–gel films it is possible to obtain cataphoretic coating with improved corrosion resistance. Silane sol–gel films of different thicknesses and curing temperature were produced. It was demonstrated that a 120 nm thick silane sol gel film cured at 180 °C ensures a very good compatibility with the electro-coat. In fact, this system shows a very high corrosion resistance even after 50 days of immersion in a sodium chloride solution. Also the resistance in the salt spray chamber of the electro-coated thin silane layer cured at 180 °C is remarkable. The results confirm that, if conveniently designed, silane sol–gel film properties, the silane layer is a good adhesion promoter of the cataphoretic coating on galvanized steel and this property is maintained for long exposure times.

Self-assembled octadecyltrichlorosilane monolayer formation on a highly hydrated silica film

A MVD silica layer that consists of a highly hydrated surface favorable for organosilane surface reaction is investigated. The MVD silica layer lacks free surface silanol groups while supporting a more extensive adsorbed water layer as compared to oxidized Si(1 0 0). Octadecyltrichlorosilane monolayers (OTS) deposited on the MVD silica layer are found to follow the same mechanisms of growth and exhibit properties comparable to those formed on oxidized Si(1 0 0) surfaces. The growth process of octadecylsiloxane films is investigated as a function of immersion time and temperature by utilizing ATR-FTIR, ellipsometry, contact angle analysis, and AFM. The MVD silica layer is shown to support an ordered interfacial water structure that is more tightly bound due to a higher degree of hydrogen bonding associated with the hydroxylated surface. The importance of interfacial water on the OTS film formation process is highlighted and the role of free OH groups on the adsorption mechanism is diminished. It is shown that OTS films can be formed on a highly hydrated surface comparable to those formed on oxidized Si(1 0 0) surfaces.

Inhibition effect of cerium in hybrid sol–gel films on aluminium alloy AA2024

AbstractAluminium alloys such as AA2024 are susceptible to severe corrosion attack in aggressive solutions (e.g. chlorides). Conversion coatings, like chromate, or rare earth conversion coatings are usually applied in order to improve corrosion behaviour of aluminium alloys. Methacrylate‐based hybrid films deposited with sol–gel technique might be an alternative to conversion coatings. Barrier properties, paint adhesion and possibly self‐healing ability are important aspects for replacement of chromate‐based pre‐treatments. This work evaluates the behaviour of cerium as corrosion inhibitor in methacrylate silane‐based hybrid films containing SiO2 nano‐particles on AA2024. Hybrid films were deposited on aluminium alloy AA2024 by means of dip‐coating technique. Two different types of coating were applied: a non‐inhibited film consisting of two layers (non‐inhibited system) and a similar film doped with cerium nitrate in an intermediate layer (inhibited system). The film thickness was 5 µm for the non‐inhibited system and 8 µm for the inhibited system. Film morphology and composition were investigated by means of GDOES (glow discharge optical emission spectroscopy). Moreover, GDOES qualitative composition profiles were recorded in order to investigate Ce content in the hybrid films as a function of immersion time in 0.05 M NaCl solution. The electrochemical behaviour of the hybrid films was studied in the same electrolyte by means of EIS technique (electrochemical impedance spectroscopy). Electrochemical measurements provide evidence that the inhibited system containing cerium displays recovery of electrochemical properties. This behaviour is not observed for the non‐inhibited coating. GDOES measurements provide evidence that the behaviour of inhibited system can be related to migration of Ce species to the substrate/coating interface. Copyright © 2010 John Wiley & Sons, Ltd.

Bioactivity and Viscoelastic Characterization in Physiological Simulated Conditions of Chitosan/Bioglass® Composite Membranes

A number of combinations of biodegradable polymers and bioactive ceramics have been used for orthopaedic applications including in hard tissue regeneration. Ideally, composites aimed to be used in orthopaedic applications should combine adequate mechanical properties and bioactivity. Chitosan (CTS) has been widely used for biomedical applications, namely in tissue regeneration or drug delivery. In this sense, membranes of chitosan and chitosan with Bioglass® (BG) were prepared by solvent casting and characterised using Scanning Electron Microscopy. In vitro bioactivity tests were performed in the composite membranes, namely by monitoring their capability to induce the precipitation of apatite upon immersion in simulated body fluid (SBF). The results showed that the addition of BG promoted the deposition of an apatite-like layer. The deposition of apatite could influence the mechanical performance of the material. Therefore, in order to follow this biomineralization, the viscoelastic properties of these composite membranes (immersed in SBF) were evaluated. The change in the storage modulus (E’) and the loss factor (Tan δ) were measured as a function of immersion time using non-conventional dynamic mechanical analysis (DMA) tests, in which the samples were kept in wet conditions and at 37°C during the measurements. The mechanical properties of the chitosan membranes were improved by the addition of BG particles. An increase on the storage modulus was observed by the composite membranes while for the pure chitosan membranes the storage modulus was stable up to 7 days. Clear changes were detected in the composite membranes that contrasted with pure chitosan (CTS) membranes that exhibit stable viscoelastic properties up to 7 days. In addition, this work showed that sample characterization in the hydrated state can be useful to predict the mechanical performance of composites under meaningful physiological conditions.

Elution characteristics of teicoplanin-loaded biodegradable borate glass/chitosan composite

Local antibiotic delivery system has an advantage over systemic antibiotic for osteomyelitis treatment due to the delivery of high local antibiotic concentration while avoiding potential systemic toxicity. Composite biomaterials with multifunctional roles, consisting of a controlled antibiotic release, a mechanical (load-bearing) function, and the ability to promote bone regeneration, gradually become the most active area of investigation and development of local antibiotic delivery vehicles. In the present study, a composite of borate glass and chitosan (designated BG/C) was developed as teicoplanin delivery vehicle. The in vitro elution kinetics and antibacterial activity of teicoplanin released from BG/C composite as a function of immersion time were determined. Moreover, the pH changes of eluents and the bioactivity of the composite were characterized using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction analysis.

Modeling of potassium sorbate diffusion through chitosan films

The mechanism of potassium sorbate (K-sorbate) release from chitosan films was studied as a function of immersion time in aqueous solution. Fick's law was applied to calculate the diffusion coefficient and the power law defining the type of diffusion mechanism. The novelty in this study is the compound diffusion mechanisms comparison through chitosan film (CF) and chitosan emulsion film. Initially, the lipid was selected to obtain the emulsion films. The evaluation was based on the water vapor permeability (WVP). The lower WVP (32.45% less than chitosan film) was found using 0.5 g/100 g of palmitic acid for 2.0 g/100 g of chitosan. Then, active chitosan films (ACF) were obtained incorporating K-sorbate on CF at 0.1 and 0.5 g/100 g of K-sorbate. Also, active palmitic acid-chitosan films (APEF) were obtained, incorporating 0.1 g/100 g of K-sorbate. The mechanisms of K-sorbate diffusion through ACF and APEF were mainly non-Fickian. However, the K-sorbate diffusion coefficient did not reduced in lipid presence.

Natural Stimulus Responsive Scaffolds/Cells for Bone Tissue Engineering: Influence of Lysozyme upon Scaffold Degradation and Osteogenic Differentiation of Cultured Marrow Stromal Cells Induced by CaP Coatings

This work proposes the use of nonporous, smart, and stimulus responsive chitosan-based scaffolds for bone tissue engineering applications. The overall vision is to use biodegradable scaffolds based on chitosan and starch that present properties that will be regulated by bone regeneration, with the capability of gradual in situ pore formation. Biomimetic calcium phosphate (CaP) coatings were used as a strategy to incorporate lysozyme at the surface of chitosan-based materials with the main objective of controlling and tailoring their degradation profile as a function of immersion time. To confirm the concept, degradation tests with a lysozyme concentration similar to that incorporated into CaP chitosan-based scaffolds were used to study the degradation of the scaffolds and the formation of pores as a function of immersion time. Degradation studies with lysozyme (1.5 g/L) showed the formation of pores, indicating an increase of porosity ( approximately 5-55% up to 21 days) resulting in porous three-dimensional structures with interconnected pores. Additional studies investigated the influence of a CaP biomimetic coating on osteogenic differentiation of rat marrow stromal cells (MSCs) and showed enhanced differentiation of rat MSCs seeded on the CaP-coated chitosan-based scaffolds with lysozyme incorporated. At all culture times, CaP-coated chitosan-based scaffolds with incorporated lysozyme demonstrated greater osteogenic differentiation of MSCs, bone matrix production, and mineralization as demonstrated by calcium deposition measurements, compared with controls (uncoated scaffolds). The ability of these CaP-coated chitosan-based scaffolds with incorporated lysozyme to create an interconnected pore network in situ coupled with the demonstrated positive effect of these scaffolds upon osteogenic differentiation of MSCs and mineralized matrix production illustrates the strong potential of these scaffolds for application in bone tissue engineering strategies.

In vitro evaluation of bioactivity of CaO–SiO 2–P 2O 5–Na 2O–Fe 2O 3 glasses

Glasses with compositions 41CaO(52 − x)SiO 24P 2O 5· xFe 2O 33Na 2O (2 ≤ x ≤ 10 mol.%) were prepared by melt quenching method. Bioactivity of the different glass compositions was studied in vitro by treating them with simulated body fluid (SBF). The glasses treated for various time periods in SBF were evaluated by examining apatite formation on their surface using grazing incidence X-ray diffraction, Fourier transform infrared reflection spectroscopy, scanning electron microscopy and energy dispersive spectroscopy techniques. Increase in bioactivity with increasing iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass composition.

A new acceleration factor for the testing of corrosion protective coatings: flow-induced coating degradation

For corrosion protective coatings that are designed to give lifetimes of protection that may extend to 50 years, valid accelerated test methods are necessary to develop improved systems and validate performance. Fluid flow over metals has long been believed to influence the corrosion process. Studies have been focused on the effects of flow rate on the corrosion of bare metals. The influence of fluid flow on the degradation of metal-protective coatings has received less attention. This paper describes a preliminary study on the influence of laminar flow on organic coatings. A Hele-Shaw cell and its associated fluid control apparatuses are incorporated into the electrochemical cell setup. The barrier properties of the coating as a function of immersion time and flow rate have been monitored by electrochemical impedance spectroscopy. We observe that the barrier properties of the coating measured electrochemically decrease exponentially with the increasing flow rate. We propose that the flowing electrolyte solution could be used in acceleration tests for the lifetime prediction of organic coatings as the acceleration of failure we have observed does not appear to change the mechanism of failure. Further analysis is proposed to validate immersion flow rate as a universal accelerating parameter for coating failure.

Diffusion behavior of water and sulfuric acid in epoxy/organoclay nanocomposites

AbstractThe research on polymer‐layered silicate nanocomposites is currently an expanding field of study because they often exhibit a wide range of improved properties over their unmodified starting polymers. Epoxy/organoclay nanocomposites have been prepared by intercalating epoxy into the organoclay montmorillonite. The intercalation and/or exfoliation of the clay within the nanocomposite were monitored using X‐ray diffraction and transmission electron microscopy. Diffusion was studied through epoxy samples containing up to 10 phr of organically treated montmorillonite following the gravity method. The water and sulfuric acid diffusion within the epoxy‐based nanocomposites were evaluated in terms of diffusivity, weight change and penetration depth of the sulfuric acid element S as function of immersion time and immersion temperature. An investigation of the resistance of epoxy nanocomposite to a corrosive environment by immersion into sulfuric acid at elevated temperature was performed. The effect of the degree of exfoliation of the clay on moisture barrier effect and corrosion resistance is specifically studied. The data has been compared to those obtained from the neat epoxy resin to evaluate the diffusion properties of the nanocomposites. It was found that the diffusion of water and that of acid do not obey Fick's law, and that the higher the organoclay content the higher weight change was obtained. The presence of the organoclay enhanced the diffusivity and delayed the penetration of the sulfuric acid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A Novel Isotherm, Modeling Self-Assembled Monolayer Adsorption and Structural Changes

Self-assembled monolayers (SAMs) have numerous applications, for example, engine wear inhibitors, surface profiling signal enhancement, nanostructure production, sensor production, and catalysis. The adsorbed SAM structure has a major impact on the properties of the outer monolayer surface which dictates the performance and viability of the SAM for individual applications. Substrate growth phases of SAMs have been extensively studied, and two structures have been identified. Initially, a lying down SAM structure is formed that evolves into a standing up structure. It is often critical to know how both structures form as a function of substrate immersion time to be able to design the properties of this structure. The formation of mercaptopropionic acid (MPA) SAMs on gold has been studied. Electrochemical impedance spectroscopy (EIS) was used to measure the adsorption isotherms at five temperatures in the range 4-40 degrees C. Infrared reflectance absorption spectroscopy (IRRAS) was also used, and the results show close agreement. A new monolayer adsorption isotherm is proposed which models SAM structure formation as a function of immersion time, representing all phases of SAM adsorption. This model represents a significant improvement on previous models based on Langmuir and Kisliuk adsorption isotherms that only model the fractional coverage of a surface with a SAM. The new model predicts the optimum immersion time taken for an MPA monolayer on gold to attain a surface saturated with MPA. It accounts for temperature effects on the rate of formation and the degree of monolayer disorder. It has potential for use in other SAM systems and may become the method of choice for modeling many instances of sequential substrate adsorption of two different structures, each of which exhibits different properties, as a function of immersion time.

Dissolution of alumina ceramics in HCl aqueous solution

Dissolution of a cold isostatically pressed high purity alumina ceramics in aqueous HCl solutions was studied as a function of immersion time and acid concentration. From the amounts of Al 3+, Mg 2+, Ca 2+, Na +, Si 4+ and Fe 3+ ions released in the corrosive solution, a degree of dissolution χ i for each component was calculated according to the equation χ i = A/ B, where A and B are respectively the amount of the element released in the corrosive solution and the amount of the element in the untreated material. The determination of the amounts of ions released in the corrosive solutions was carried out by means of atomic absorption spectrometry (AAS). The corrosion of alumina ceramics in the HCl aqueous solution is determined by the solubility of alumina and the solubility of grain-boundary impurities. Very low dissolution values of Al 3+, Mg 2+, Ca 2+, Na +, Si 4+ and Fe 3+ ions after the corrosion test of alumina ceramics showed a very good corrosion resistance in the HCl aqueous solution.

Evaluation of a simple microstructural-electrochemical model for corrosion damage accumulation in microstructurally complex aluminum alloys

Stereological and electrochemical data collected in 0.1 M NaCl is presented for the intermetallic particles found in AA7075-T651. These values are used as inputs for a mechanistic-based corrosion model which yields a distribution of pit radii (assuming hemispherical pitting) as function of immersion time. With an optical profilometer (OP), a distribution of damage depths were collected from samples exposed to 0.1 M NaCl solution for times ranging from 10 to 1344 h. Damage depths were compared with the model predictions of pit depth. The model is able to predict observations of corrosion damage depths to within a factor of two, but tends to under-predict damage depth at short times and over-predict at long times. Under-prediction may be associated with early rapid dissolution of active particles. Over-prediction by the model at longer exposure times may be associated with the fact that repassivation is not included as a part of this simple model.

Bioactive glass sol‐gel foam scaffolds: Evolution of nanoporosity during processing and in situ monitoring of apatite layer formation using small‐ and wide‐angle X‐ray scattering

Recent work has highlighted the potential of sol-gel-derived calcium silicate glasses for the regeneration or replacement of damaged bone tissue. The work presented herein provides new insight into the processing of bioactive calcia-silica sol-gel foams, and the reaction mechanisms associated with them when immersed in vitro in a simulated body fluid (SBF). Small-angle X-ray scattering and wide-angle X-ray scattering (diffraction) have been used to study the stabilization of these foams via heat treatment, with analogous in situ time-resolved data being gathered for a foam immersed in SBF. During thermal processing, pore sizes have been identified in the range of 16.5-62.0 nm and are only present once foams have been heated to 400 degrees C and above. Calcium nitrate crystallites were present until foams were heated to 600 degrees C; the crystallite size varied from 75 to 145 nm and increased in size with heat treatment up to 300 degrees C, then decreased in size down to 95 nm at 400 degrees C. The in situ time-resolved data show that the average pore diameter decreases as a function of immersion time in SBF, as calcium phosphates grow on the glass surfaces. Over the same time, Bragg peaks indicative of tricalcium phosphate were evident after only 1-h immersion time, and later, hydroxycarbonate apatite was also seen. The hydroxycarbonate apatite appears to have preferred orientation in the (h,k,0) direction.