Water vapour in the coatings of alkyd and polyurethane varnish

Absorption and desorption of water vapour in alkyd and polyurethane varnish were studied by quartz crystal microbalance (QCM). The absorption and desorption kinetics curves were Fickian in nature when the relative humidity is higher than 30%, while the solubility followed Henry’s law. The average diffusion coefficient D was calculated. A residual amount of water was found to remain in the coatings after extended exposure to dry air. FTIR analysis showed that the molecular structure of the coatings changed after the absorption and desorption of water vapour. The results showed that the residual water reacted with the coatings molecule.     

Influence of temperature on crack-bridging ability of coatings for concrete

The crack-bridging properties of different organic coatings have been studied over a range of thicknesses and applied temperatures. In each case the data allowed to determine linear relationships between crack-bridging ability (CBA) and coating thickness. In addition, a direct correlation between crack bridging ability and elongation at break of the unsupported films has been found, once verified that adhesion properties do not change over temperature.     

Gas and water vapour transport in a polyketone terpolymer

Gas and water vapour transport properties of a polyketone terpolymer (0.93/0.07/1 ethylene/propylene/carbon monoxide) have been investigated and related to the polymer structure. Permeability tests have been performed at several temperatures (from 25 to about 65°C) with five different gases (oxygen, nitrogen, methane, ethane and carbon dioxide), evaluating permeabilities, diffusivities and solubilities. Their dependence on temperature was interpreted on the basis of apparent activation energies of permeation and diffusion (E_P and E_D) and of heats of solution (ΔH_S). The investigated polymer was found to be rubbery at the test temperatures (glass transition temperature is about 17°C), but the detected permeabilities are comparable to those of the glassy polymers widely used for packaging applications. Data obtained in this investigation on samples exposed to moulding temperatures (240°C) for 3 min were compared to gas permeation data (presented in a previous paper) obtained for samples exposed at that temperature for 33 min in order to assess possible effects on gas transport properties. Water vapour transport was analysed by performing both sorption (35, 34, 55 and 65°C) and permeation (35°C) experiments at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering, which was confirmed by a reduction of water diffusivity as a function of water concentration in the polymer.     

Crack-bridging ability of organic coatings for concrete: influence of the method of concrete cracking, thickness and nature of the coating

Some concern about the determination of a standardised test for crack-bridging ability (CBA) measurements exists. The present work focuses on the analysis of the results of experimental tests performed to simulate the mechanical behaviour of a coating when a crack in the beneath concrete opens and grows. The influence of the method of concrete cracking, thickness and nature of the coating on the CBA are studied. Experimental results suggest that: (i) the same coating has higher CBA when the crack in the beneath concrete is produced through slight bending rather than through tensile loading; (ii) the CBA clearly depends on the nature (then mechanical properties) of the applied coating; (iii) power law relationships between CBA and thickness of the coating exist.     

Natural versus accelerated weathering: Understanding water kinetics in bilayer coatings

Exposure to water is a key issue in the performance of multilayer coatings. It may take place in different forms, i.e. as rainfall, dew and humidity variation. Consequently, coatings will experience time-dependent water activity fluctuations. In industrial practice, coatings are subjected to artificial water activity fluctuations in weathering tests. Little is known about the connection between these tests and the reality experience by a coating.     

Calculation of sand-aggregate ratio and water dosage of ordinary concrete

In the calculation of concrete mix proportion, sand-aggregate ratio and water dosage are determined by referring table, which is fairly arbitrary. In this paper, according to the concept of coordination number and Bingham model rheology, we deduced the formulas of sand-aggregate ratio and water dosage, respectively, and then utilized the experimental data to test and verify the formulas. Thereby, the calculation of sand-aggregate ratio and water dosage is more exact.     

Studies on the evaluation of the performance of organic coatings used for the prevention of corrosion of steel rebars in concrete structures

Corrosion of steel rebars in reinforced concrete constructions, particularly those located in marine environments and industrially polluted areas is one of the major problems baffling the construction industry all over the world including India. A suitable protective coating to rebar is found to improve the durability of such structures under aggressive exposures. The performance of a few polymeric coatings based on different resins such as acrylic polyol-aromatic isocyanate, polyester polyol-aromatic isocyanate, acrylic resin and epoxy–silicone–polyamide containing ordinary Portland cement or flyash as extenders and titanium dioxide and zinc phosphate as main pigments on rebar in concrete has been evaluated using mechanical strength tests and accelerated corrosion tests. It is observed that, of the 16 coating formulations, four have been found to perform well as effective and durable coatings.     

Temperature sensitive water vapour permeability and shape memory effect of polyurethane with crystalline reversible phase and hydrophilic segments

Polyurethanes based on poly(caprolactone) (PCL) diol, hexamethylene diisocyanate, 4,4′‐diphenylmethane diisocyanate and hexamethylene diamine were modified by hydrophilic segments, diol‐terminated poly(ethylene oxide) or dimethylol propionic acid (DMPA). Differential scanning calorimetry, dynamic mechanical tests, tensile tests, and measurement of water vapour permeability were carried out to characterize these polyurethanes. Temperature sensitive water vapour permeability, that is, the abrupt increase of water vapour permeability at the melting temperature of the PCL phase, was enhanced by modification with hydrophilic segments. Fatigue in shape memory effects was minimized by introducing some amount of DMPA units into the polyurethane chain. © 2000 Society of Chemical Industry     

Organic coatings for pre-treated galvanized steel technology

Fluorinated coatings are at the moment one of the best solutions to protect steel and aluminium substrate against corrosion. New VF2-based fluopolymer coatings, by the addition of OH groups in the polymeric chain and with lower curing temperature, have been formulated by ELF-ATOCHEM. Electrochemical characterization of this material has been performed by means of impedance spectroscopy. The results obtained and the comparison with the traditional PVDF system show an interesting improvement of the protective properties.     

BSL-based coatings for bamboo protection

Bhilawanut shell liquid is a natural product, and because of its phenolic nature it undergoes reactions similar to those of phenol. Surface coatings based on BSL were prepared from formaldehyde, styrene, hexamine, and epichlorohydrin for the protection of bamboo surfaces. BSL-based coatings were applied on bamboo and the performance of these coatings was evaluated by accelerated and chemical resistance tests. It was observed that these coatings can be used for the protection of bamboo from corrosive environments. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 487–493, 1998     

Nanostructured coatings approach for corrosion protection

Nanostructured surface treatment coatings based on the Self-assembled Nanophase Particle (SNAP) approach were investigated as potential replacement for chromate-based surface treatments on aircraft aluminum alloys. In the traditional sol–gel method, hydrolysis-condensation processes are followed by condensation polymerization upon film application. This process sequence provides a low temperature route to the preparation if thin coatings which are readily applied to most metallic substrates. The recent discovery of a method of forming functionalized silica nanoparticles in situ in an aqueous sol–gel process, and then cross-linking the nanoparticles to form a thin film, is an excellent example of a nanoscience approach to coatings. This Self-assembled Nanophase Particle (SNAP) process can be used to form thin, dense protective organic surface treatment coatings on Al aerospace alloys. The ability to design coating components from the molecular level upward offers tremendous potential for creating multifunctional coatings.

The important components of Al alloy corrosion inhibition by chromate are storage and release of Cr^VI species, inhibition of cathodic reactions (primarily oxygen reduction), and inhibition of attack at active sites in the alloy. Unlike chromate-based treatments, current SNAP coatings provide barrier-type corrosion resistance but do not have the ability to leach corrosion inhibitors upon coating damage and minimize corrosion of the unprotected area. In this study, organic inhibitors were tested for corrosion protection of aluminum alloys in combination with the (SNAP). Scanning Vibrating Electrode Technique, anodic polarization, electrochemical impedance spectroscopy, and salt spray test were used to study this new approach for chromate replacement.     

Ingress of water into organic coatings: Real-time monitoring of the capacitance and increase in mass

Water ingress into a cataphoretic coating employed in the car industry was studied using real-time mass and capacitance measurements. The results showed the presence of three well-differentiated time constants associated with the process. The corresponding time scales were 2–3 min, 1 and 10 h. The first time constant (fastest process) was assumed to be associated with the filling of surface pores by water. This process involved about 50% of the total water uptake. The second time constant was assumed to be due to the water occupancy of pores in the bulk of the coating. Finally, the slowest process was assumed to be due to water diffusion through the bulk coating. This process presented capacitive effects only if fillers were present in the coating.     

Water permeability and chloride penetrability of high-strength lightweight aggregate concrete

This paper presents an experimental study on the water permeability and chloride penetrability of high-strength lightweight concrete (LWC) in comparison to that of high-strength normal-weight concrete (NWC) with or without silica fume. The results were also compared with those of the concrete at a normal-strength level of about 30-40 MPa. In order to compare the water permeability and chloride-ion penetrability, LWC and NWC had the same proportion by volume. The only difference between them was the coarse aggregate used. The results indicated that at the strength level of about 30-40 MPa, the water permeability of the LWC was lower than that of the corresponding NWC. However, the water permeability of the high-strength LWC and NWC was of the same order. The resistance of the LWC to the chloride penetration was similar to that of the corresponding NWC both in the normal-strength and high-strength levels. As the compressive strength of the LWC was lower than that of the corresponding NWC, the results indicated that for a given 28-day strength, the LWC would probably have high resistance to water and chloride-ion penetration than the NWC. The results indicated that the resistance to the chloride penetration does not seem to be correlated to the water permeability of the concrete. There appears to be, however, a direct relationship between the rapid chloride penetrability determined by ASTM C1202 and the observed chloride penetration depth determined by the immersion and salt ponding tests.     

Mechanism of water vapour gasification of carbon—A new model

The mechanism of water vapour gasification of carbon was studied by temperature-programmed desorption measurements of carbon monoxide from polyvinyl chloride cokes of different heat treatment temperatures, which were pregasified in water vapour atmospheres, and quenched before desorption in an inert atmosphere. A new mechanism of water vapour gasification of coal, coke or carbon is proposed, which assumes condention of hydroxyl groups formed by dissociation of water at active sites. The resulting ether groups which are already formed at the ‘carbon’ surface by 500°C are extremely stable (desorption of carbon monoxide in inert atmosphere above 900°C). The onset of gasification by 700°C is explained by an equilibrium shift from the ether groups prevailing at the lower temperatures to desorbable hydroxyl groups by interaction with water vapour. The subsequent steps are identical to those proposed in the generally discussed mechanism of water vapour gasification.     

Polymeric coatings for protection of historic monuments: Opportunities and challenges

The conservation and protection of historic monuments or culturally significant structures have recently attracted much attention from material scientists. This review is given of the various aspects of the monuments protection such as the main reasons of damaging and spoiling of the historical monuments, the factor of contact angle as one of the essential parameters in the selection of polymeric coatings, and some of usual types of polymeric materials used for monument protection. There has been growing interest in developing novel materials for using in protective fields. Nowadays, the polymeric coatings, especially those with high hydrophobicity, are widely used to decrease or even stop further deterioration of historical monument. This review presents some of the most well‐known polymers used as protective materials such as acrylics, alkoxysilanes, fluorinated polymers, and hybrid organic–inorganic coatings. Furthermore, hybrid organic–inorganic coatings as a new class of materials are increasingly interesting materials because of their extraordinary properties deriving from the combination of the different building blocks and it is attempted to focus on this materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

新型混凝土结构防火涂料的研制

采用隔热矿物、耐火纤维、无机粘结材料和复合添加剂制成无机单组分混凝土结构防火涂料。该涂料具有耐火极限高、粘结强度大及耐潮湿、干燥快等特性,适用于公路、铁路、城市地铁和隧道等各种混凝土结构表面的防火保护。     

Accelerated formation of barium titanate by solid-state reaction in water vapour atmosphere

Barium titanate (BaTiO₃) powders were synthesized from commercially available raw materials (BaCO₃ and rutile) without particular mechanochemical processing by solid-state reactions in water vapour atmosphere. The formation rate of BaTiO₃ was accelerated by water vapour and single phase of BaTiO₃ was obtained by calcination at 700 °C for 4 h in water vapour atmosphere, though high temperature (850 °C for 2.5 h) was required by calcinations in air to complete the reaction. The formation kinetics followed the Valensi–Carter equation, which suggested that the reaction proceeded by a diffusion controlled process. The apparent activation energy for the formation of BaTiO₃ in air and water vapour atmosphere was estimated to be 361 ± 20 kJ/mol and 142 ± 17 kJ/mol, respectively. Water vapour is considered to enhance thermal decomposition of BaCO₃ and formation of BaTiO₃ by attacking surface Ti–O–Ti bonds in TiO₂, increasing partial pressure of Ba(OH)₂, and producing vacancies in the BaTiO₃ structure.     

Ionic liquid enhanced electrochemical characterization of organic coatings

Our laboratory recently began work on the use of room temperature ionic liquids ((RTIL's) to enhance our capabilities for the electrochemical characterization of organic coatings [A.M. Simões, D. Tallman, G.P. Bierwagen, The use of ionic liquids for the electrochemical characterization of water transport in organic coatings, Electrochem. Solid-State Lett. 8 (2005) 60]. The RTIL's are electrically conductive liquids consisting of large molecules that can be used to investigate the electrochemical properties of coatings in a non-aqueous medium. The enhancement of coating characterization comes from the fact that RTIL's have sufficient conductivity to be an immersion medium for electrochemical measurements, but they do not directly penetrate and effect organic coatings as do aqueous electrolyte solutions. This allows the separate examination of the effects of water on coatings in immersion or cyclic exposure. Indeed, our initial studies showed that a hydrophilic RTIL could be used to electrochemically characterize the drying of a coating after immersion, a process which heretofore had not been followed electrochemically. Thus, electrochemical measurements of coatings based on aqueous electrolyte immersion can be enhanced by the use of RTIL's and the effects of water on the coatings under study isolated and analyzed separately, especially the diffusion of water out of coatings during drying processes. Recent papers from our group have introduced the methodology whereby RTIL's in conjunction with capacitance monitoring via electrochemical impedance spectroscopy (EIS) can be used to determine the diffusion coefficient of water out of a non-pigmented, additive free coating [A.M. Simões, D. Tallman, G.P. Bierwagen, The use of ionic liquids for the electrochemical characterization of water transport in organic coatings, Electrochem. Solid-State Lett. 8 (2005) 60; K. Allahar, B. Hinderliter, A. Simoes, D. Tallman, G. Bierwagen, S. Croll, Simulation of wet–dry cycling of organic coatings using ionic liquids, J. Electrochem. Soc. 154 (2007) 177–185; B. Hinderliter, K. Allahar, O. Stafford, S. Croll, Using Ionic Liquids to Measure Coating Properties via Electrochemical Impedance Spectroscopy, Presented the 2006 International Coatings Exposition, Federation of Societies for Coatings Technology, New Orleans, LA, 2006 Oct.; B.R. Hinderliter, K.N. Allahar, G.P. Bierwagen, D.E. Tallman, S.G. Croll, Thermal cycling of epoxy coatings using room temperature ionic liquids, J. Electrochem. Soc. 155 (3) (2008) 1]. The technique has been extended to several types of coatings as well as the study of the cyclic wetting and drying of coatings [K. Allahar, B. Hinderliter, A. Simoes, D. Tallman, G. Bierwagen, S. Croll, Simulation of wet–dry cycling of organic coatings using ionic liquids, J. Electrochem. Soc. 154 (2007) 177–185]. This latter set of processes is one of the key set of events in exterior exposure that causes the failure of exterior protective coatings. Recently, RTIL's have been used to simulate the alternate wetting and drying of a Zn-rich epoxy coating system. EIS experiments were conducted on the Zn-rich epoxy under constant immersion in 0.05 M NaCl and RTIL. The experimental results were analyzed to determine the dielectric response and changes due to Zn oxidation within the Zn-rich system.     

Water vapour corrosion of rare earth monosilicates for environmental barrier coating application

Water vapour corrosion resistance of five rare earth monosilicates Y₂SiO₅, Gd₂SiO₅, Er₂SiO₅, Yb₂SiO₅, and Lu₂SiO₅ was investigated during testing at 1350 °C for up to 166 h in static air with 90% water vapour. Four of the RE-silicates showed little weight gain (0.859 mg cm⁻²) after 166 h of exposure. Prior to testing the microstructure consists of equiaxed grains of 4- 7±0.4 µm. XRD analysis showed that after 50 h exposure to water vapour corrosion Y, Er, Yb and Lu-silicates had both mono and disilicates present on their surfaces as a result of the reaction between monosilicate and water vapour to form disilicate, while Gd-silicate has converted completely to G_4.67Si₃O₁₃ making it less stable for environmental barrier coating application. The microstructures of corroded Y, Er, Yb and Lu-silicates contain ridges and cracks, while that of Gd-silicate contains rounded grains suggesting melting along with striped contract grains.     

Assessment of the unsaturated water transport properties of an old concrete: Determination of the pore-interaction factor

In this study all the data needed to describe water transport (drying) within an existing concrete structure were characterized using a simple drying experiment. The properties (desorption isotherm, porosity and the unsaturated water transport properties namely, diffusivity and permeability) were evaluated by post-processing the weight loss data. Once obtained, the permeability evolution was used to check the validity of the Mualem–van Genuchten equations. It appeared that the default pore-interaction factor value proposed by Mualem (p = + 0.5) is just a rough estimate: the values obtained in this study were all negative. Comparing these values to the literature, the pore-interaction factor seems to be correlated to the van Genuchten's exponent m.