Corrosion inhibitors for the rehabilitation of reinforced concrete

Four corrosion inhibitors namely sodium nitrite, sodium monofluorophosphate, ethanolamine and an alkanolamine-based mixture were studied by immersing mild steel bars for 42 days in model electrolytes of varied pH and chloride concentration which were intended to simulate the pore solution phase present within carbonated and/or chloride-contaminated concrete. Site trials were carried out on sodium monofluorophosphate and the alkanolamine-based inhibitor to study their depth of penetration into concrete. The influence of various carbonating atmospheres on the pore solution chemistry and microstructure of hydrated cement paste was investigated. Physical realkalisation of carbonated cement paste and a calcium nitrite-based corrosion rehabilitation system for chloride-contaminated cement paste were investigated by monitoring ionic transport within the pore solution phase of laboratory specimens. The main findings were as follows: 1,Sodium nitrite, sodium monofluorophosphate, ethanolamine and the alkanolamine-based mixture all behaved as passivating anodic inhibitors of steel corrosion in air-saturated aqueous solutions of varied pH and chloride concentration. 2,Sodium monofluorophosphate failed to penetrate significantly into partially carbonated site concrete when applied as recommended by the supplier. Phosphate and fluoride penetrated 5mm into partially carbonated site concrete treated with sodium monofluorophosphate. 3,The ethanolamine component of the alkanolamine-based inhibitor was found to have penetrated significant depths into partially carbonated site concrete. 4,Carbonating hydrated cement paste over saturated solutions of sodium nitrite resulted in significant concentrations of nitrite in the pore solution of the carbonated paste. Saturated solutions of sodium chloride, ammonium nitrate, magnesium nitrate and sodium dichromate were investigated and identified as alternatives for controlling the relative humidity of the carbonating environment. 5,Hardened carbonated cement paste can by physically realkalised to a limited extent due to the diffusion of hydroxyl ions under saturated conditions. A substantial proportion of the hydroxyl ions that diffused into the carbonated cement paste however, became bound into the cement matrix. Hydroxyl ion concentrations remained below 5mmol/l within the pore solution of the realkalised cement paste. 6, Nitrite ions penetrated significant distances by diffusion within the pore solution of saturated uncarbonated hydrated cement paste.

Technology of repair for corroded reinforced concrete

A number of factors relating to various methods of repair for chloride initiated corrosion damage of reinforced concrete have been studied. A novel methodology has been developed to facilitate the measurement of macro and micro-cell corrosion rates for steel electrodes embedded in mortar prisms containing a chloride gradient. The galvanic bar specimen comprised electrically isolatable segmental mild steel electrodes and was constructed such that macro-cell corrosion currents were determinable for a number of electrode combinations. From this, the conditions giving rise to an incipient anode were established. The influence of several reinforcement and substrate primer systems upon macro-cell corrosion, arising from an incipient anode, within a patch repair have been investigated. Measurements of electrochemical noise were made in order to investigate the suitability of the technique as an on-site means of assessing corrosion activity within chloride contaminated reinforced concrete. For this purpose the standard deviation of potential noise was compared to macro-cell galvanic current data and micro-cell corrosion intensity determined by linear polarisation. Hydroxyl ion pore solution analyses were carried out on mortar taken from cathodically protected specimens. These specimens, containing sodium chloride, were cathodically protected over a range of polarisation potentials. Measurement of the hydroxyl ion concentrations were made in order to examine the possibility of alkali-silica reactions initiated by cathodic protection of reinfored concrete. A range of mortars containing a variety of generic type additives were examined in order to establish their resistances to chloride ion diffusion. The effect of surfactant addition rate was investigated within a cement paste containing various dosages of naphthalene sulphonate.

Charge effects on hindrance factors for diffusion and convection of solute in pores I

The transport of a spherical solute through a long circular cylindrical pore filled with an electrolyte solution is studied numerically, in the presence of constant surface charge on the solute and the pore wall. Fluid dynamic analyses were carried out to calculate the flow field around the solute in the pore to evaluate the drag coefficients exerted on the solute. Electrical potentials around the solute in the electrolyte solution were computed based on a mean-field theory to provide the interaction energy between the charged solute and the pore wall. Combining the results of the fluid dynamic and electrostatic analyses, we estimated the rate of the diffusive and convective transport of the solute across the pore. Although the present estimates of the drag coefficients on the solute suggest more than 10% difference from existing studies, depending on the radius ratio of the solute relative to the pore and the radial position of the solute center in the pore, this difference leads to a minor effect on the hindrance factors. It was found that even at rather large ion concentrations, the repulsive electrostatic interaction between the charged solute and the pore wall of like charge could significantly reduce the transport rate of the solute.

Contact lens interactions with the tear film

Biochemical changes brought about by the influence of the contact lens on the tear film are conveniently split into two categories. Firstly, the lens can remove or reduce the levels of specific components in the tear film, and secondly, the lens can augment the tear film, by stimulating the influx of new components or increasing the level of existing components. The most obvious tear film components for study in this context are lipids, proteins, mucins and electrolytes. The interactions are affected by the properties of the lens, the characteristics of the individual wearer and the wear schedule. An additional complicating factor is the fact that the lens is many times thicker than the tear film and any immobilised tear components will be more extensively exposed to oxygen and UV radiation than is the case in the absence of a lens. It is arguably the lipoidal components that are most markedly affected by lens wear, since their immobilisation on the lens surface markedly increases their susceptibility to autoxidative degradation. The limited information that is available highlights the importance of subject specificity and suggests that lipid oxidation phenomena are potentially important in contributing to the 'end of day' discomfort of symptomatic contact lens patients. It is clear that tear lipids, although regarded as relatively inert for many years, are now seen as a reactive and potentially important family of compounds in the search for understanding of contact lens-induced discomfort. The influence of the lens on tear proteins shows the greatest range of complexity. Deposition and denaturation can stimulate immune response, lower molecular weight proteins can be extensively absorbed into the lens matrix and the lens can stimulate cascade or upregulation processes leading either to the generation of additional proteins and peptides or an increase in concentration of existing components. Added to this is the stimulating influence of the lens on vascular leakage leading to the influx of plasma proteins such as albumin. The evidence from studies of mucin expression in tears is not consistent and conclusive. This is in part because sample sources, lens materials and methods of analysis vary considerably, and in some cases the study population numbers are low. Expression levels show mucin and material specificity but clear patterns of behaviour are elusive. The electrolyte composition of tears is significantly different from that of other body fluids. Sodium and potassium dominate but potassium ion concentrations in tears are much higher than in serum levels. Calcium and magnesium concentrations in tears are lower than in serum but closer to interstitial fluids. The contact lens provides the potential for increased osmolarity through enhanced evaporation and differential electrolyte concentrations between the anterior and posterior tear films. Since the changes in ocular biochemistry consequent upon contact lens wear are known to be subject-dependent - as indeed is wearer response to the lens - pre-characterisation of individual participant tear chemistry in clinical studies would enhance understanding of these complex effects. © 2013 Elsevier Ltd.

Characterization of metal ion-induced [3H]inositol hexakisphosphate binding to rat cerebellar membranes

The binding of [3H]inositol hexakisphosphate ([3H] InsP6) to rat cerebellar membranes has been characterized with the objective of establishing the role, if any, of a membrane protein receptor. In the presence of EDTA, we have previously identified an InsP6-binding site with a capacity of approximately 20 pmol/mg protein (Hawkins, P. T., Reynolds, D. J. M., Poyner, D. R., and Hanley, M. R. (1990) Biochem. Biophys. Res. Commun. 167, 819-827). However, in the presence of 1 mM Mg2+, the capacity of [3H]InsP6 binding to membranes was increased approximately 9-fold. This enhancing effect of Mg2+ was reversed by addition of 10 microM of several cation chelators, suggesting that the increased binding required trace quantities of other metal cations. This is supported by experiments where it was possible to saturate binding by addition of excess membranes, despite not significantly depleting radioligand, pointing to removal of some other factor. Removal of endogenous cations from the binding assay by pretreatment with chelex resin also prevents the Mg(2+)-induced potentiation. Consideration of the specificity of the chelators able to abolish this potentiation suggested involvement of Fe3+ or Al3+. Both these ions (but not several others) were able to increase [3H]InsP6 binding to chelex-pretreated membranes at concentrations of 1 microM. It is possible to demonstrate synergy between Fe3+ and Mg2+ under these conditions. We propose that [3H]InsP6 may interact with membranes through non-protein recognition possibly via phospholipids, in a manner dependent upon trace metals. The implications of this for InsP6 biology are considered.

Development and evaluation of an ion induced x-ray emission system for the analysis of light and medium weight elements

The present work describes the development of a proton induced X-ray emission (PIXE) analysis system, especially designed and builtfor routine quantitative multi-elemental analysis of a large number of samples. The historical and general developments of the analytical technique and the physical processes involved are discussed. The philosophy, design, constructional details and evaluation of a versatile vacuum chamber, an automatic multi-sample changer, an on-demand beam pulsing system and ion beam current monitoring facility are described.The system calibration using thin standard foils of Si, P, S,Cl, K, Ca, Ti, V, Fe, Cu, Ga, Ge, Rb, Y and Mo was undertaken at proton beam energies of 1 to 3 MeV in steps of 0.5 MeV energy and compared with theoretical calculations. An independent calibration check using bovine liver Standard Reference Material was performed.  The minimum detectable limits have been experimentally determined at detector positions of 90° and 135° with respect to the incident beam for the above range of proton energies as a function of atomic number Z. The system has detection limits of typically 10- 7 to 10- 9 g for elements 14ions of areal density of thin foils using Rutherford backscattering data.  Amniotic fluid samples supplied by South Sefton Health Authority were successfully analysed for their low base line elemental concentrations. In conclusion the findings of this work are discussed with suggestions for further work .

Size dependent enhancement of helium ion irradiation tolerance in sputtered Cu/V nanolaminates

We have investigated the evolution of radiation damage and changes in hardness of sputter-deposited Cu/V nanolaminates upon room temperature helium ion irradiation. As the individual layer thickness decreases from 200 to 5 nm, helium bubble density and radiation hardening both decrease. The magnitude of radiation hardening becomes negligible for individual layer thickness of 2.5 nm or less. These observations indicate that nearly immiscible Cu/V interface can effectively absorb radiation-induced point defects and reduce their concentrations.

Cracking in hydrogen ion-implanted Si/Si0.8Ge0.2/Si heterostructures

We demonstrate that a controllable cracking can be realized in Si with a buried strain layer when hydrogen is introduced using traditional H-ion implantation techniques. However, H stimulated cracking is dependent on H projected ranges; cracking occurs along a Si0.8Ge0.2 strain layer only if the H projected range is shallower than the depth of the strained layer. The absence of cracking for H ranges deeper than the strain layer is attributed to ion-irradiation induced strain relaxation, which is confirmed by Rutherford-backscattering-spectrometry channeling angular scans. The study reveals the importance of strain in initializing continuous cracking with extremely low H concentrations.

A novel concentration dependent amino acid ion pair strategy to mediate drug permeation using indomethacin as a model insoluble drug

Assessment of oral drug bioavailability is an important parameter for new chemical entities (NCEs) in drug development cycle. After evaluating the pharmacological response of these new molecules, the following critical stage is to investigate their in vitro permeability. Despite the great success achieved by prodrugs, covalent linking the drug molecule with a hydrophobic moiety might result in a new entity that might be toxic or ineffective. Therefore, an alternative that would improve the drug uptake without affecting the efficacy of the drug molecule would be advantageous. The aim of the current study is to investigate the effect of ion-pairing on the permeability profile of a model drug: indomethacin (IND) to understand the mechanism behind the permeability improvement across Caco-2 monolayers. Arginine and lysine formed ion-pairs with IND at various molar ratios 1:1, 1:2, 1:4 and 1:8 as reflected by the double reciprocal graphs. The partitioning capacities of the IND were evaluated using octanol/water partitioning studies and the apparent permeabilities (P app) were measured across Caco-2 monolayers for the different formulations. Partitioning studies reflected the high hydrophobicity of IND (Log P = 3) which dropped upon increasing the concentrations of arginine/lysine in the ion pairs. Nevertheless, the prepared ion pairs improved IND permeability especially after 60 min of the start of the experiment. Coupling partitioning and permeability results suggest a decrease in the passive transcellular uptake due to the drop in IND portioning capacities and a possible involvement of active carriers. Future work will investigate which transport gene might be involved in the absorption of the ion paired formulations using molecular biology technologies. © 2014 Elsevier B.V. All rights reserved.