Protective Organic Coatings Research Articles

High-Throughput Adhesion Evaluation and Scale-up of Combinatorial Leads of Organic Protective Coatings

ABSTRACTCoupling of combinatorial chemistry methods with high-throughput (HT) performance testing and measurements of resulting properties has provided a powerful set of tools for the 10-fold accelerated discovery of new high-performance coating materials for automotive applications. This approach replaces labor-intensive steps with automated systems for evaluation of adhesion of 8 × 6 arrays of coating elements that are discretely deposited on a single 9 × 12 cm plastic substrate. Performance of coatings is evaluated with respect to their resistance to adhesion loss. This parameter is one primary consideration in end-use automotive applications. Coating leads identified from the HT screening have been validated on the traditional scale. Details of these validation studies are discussed.

Biogenic silica dissolution in the oceans: Reconciling experimental and field‐based dissolution rates

On average, 50–60% of diatomaceous opal produced in the euphotic zone redissolves within the upper 100 m of the water column. High specific silica dissolution rates in the surface ocean contrast with order‐of‐magnitude lower values in deep‐sea sediments. The lack of a mechanistic understanding of these large variations in dissolution kinetics is a major source of uncertainty in models of nutrient silicon cycling in the oceans. Here we show that the observed variability in biogenic silica reactivity is consistent with results of experimental dissolution studies. Differences in aluminum content and specific surface area of the diatom skeletons, plus differences in temperature and degree of undersaturation, all contribute to lowering silica dissolution rates in deep‐sea sediments relative to the euphotic zone. When variations in these material and environmental properties are accounted for, the predicted specific opal dissolution rate in average surface ocean water is over 2 orders of magnitude faster than the rate measured in recently deposited biosiliceous oozes of the Southern Ocean. The predicted specific dissolution rate, however, is approximately 5 times higher than the value obtained from global estimates of the depth‐integrated dissolution rate and biogenic silica concentration in the upper water column. This discrepancy likely reflects the inhibitory effect of protective organic coatings on fresh diatom shells in surface waters. The experimental data further imply that aluminum incorporation in the silica matrix, during biomineralization or after death of the organisms, enhances the preservation efficiency of biogenic opal in marine sediments.

Measure of the driving forces of underfilm differential contamination cells and differential aeration cells

Specially designed multilaminar electrochemical sensors (MS) are used to determine the difference in potential between the local anodes and cathodes of corrosion cells that form under protective organic coatings. These MS not only allow quantification of the effect of underfilm contamination and differential aeration on corrosion kinetics but also supply valuable information for a better understanding of the corrosion process mechanism. The use of MS with alternately clean and contaminated laminae clearly shows that differential contamination cells are capable of generating potential differences (driving forces) of hundreds of millivolt, as also occurred with underfilm differential aeration cells.

Development of combinatorial chemistry methods for coatings: high-throughput optimization of curing parameters of coatings libraries.

An automated analytical system has been implemented for the high-throughput optimization of processing conditions such as curing parameters in fabrication of UV-cured automotive organic protective coatings. Selection of optimum process conditions of combinatorial arrays of coatings is essential to correlate the high-throughput screening and conventional processes and to achieve the desired physical properties of coatings. For monitoring of curing conditions of each coating in the array, a viscosity-sensitive fluorophore 4,4'-bis(2-benzoxazolyl)stilbene was incorporated into coating formulations. This fluorescence tagging approach permitted us to combine a gradient temperature heater and a UV curing system with the full capabilities of our high-throughput screening system, including generation of spectroscopic data and its analysis. This investigation demonstrated the possibility of rapid decoupling of temperature and radiation effects in curing of UV-curable coating formulations by using multiple coatings and process conditions at once. While the system described here was implemented for high-throughput optimization of temperature conditions of radiation curing of arrays of organic protective coatings for automotive applications, this system can be further applied for a variety of other applications where optimization of process parameters can be studied in situ or off-line using optical spectroscopic tools.

Studies on the thermal ageing of organic coatings

The ageing of organic protective coatings depends on environmental impacts and is associated with a variety of chemical and physical processes. The results of former thermal ageing studies indicate that evaporation and polymer degradation are the decisive processes for changes in coating properties. For the verification of these assumptions the impact of the thermal exposure temperature T L and the length of the exposure time t L on properties of clear lacquer coatings was determined by further studies. The gradation of T L was aimed at creating conditions where on the one hand only evaporation processes occur, while on the other hand evaporation and polymer degradation reactions occur in parallel. The objective was to find the time t L and the temperature T L at which degradation starts to prevail.

Development of combinatorial chemistry methods for coatings: high-throughput screening of abrasion resistance of coatings libraries.

Design, validation, and implementation of an optical spectroscopic system for high-throughput analysis of combinatorially developed protective organic coatings are reported. Our approach replaces labor-intensive coating evaluation steps with an automated system that rapidly analyzes 8 x 6 arrays of coating elements that are discretely deposited on a single plastic substrate. Each coating element of the library is 10 mm in diameter and 2-5 microm thick. Performance of coatings is evaluated with respect to their resistance to wear abrasion because this parameter is one of the primary considerations in end-use applications. Upon testing, the coating materials undergo changes that are impossible to quantitatively predict using existing knowledge. Coatings are abraded using industry-accepted abrasion test methods at a single or multiple abrasion conditions followed by the high-throughput analysis of abrasion-induced light scatter. The developed automated system is optimized for the analysis of diffusively scattered light that corresponds to 0-30% haze. System precision of 0.1-2.5% relative standard deviation provides capability for the reliable ranking of coatings performance. Although the system was implemented for high-throughput screening of combinatorially developed organic protective coatings for automotive applications, it can be applied for a variety of other applications for which materials ranking can be achieved using optical spectroscopic tools.

The environmental degradation mechanism and protective organic thin film coatings on a high-temperature bismuth–cuprate superconductor

The degradation mechanism for Bi 2Sr 2CaCu 2O x (Bi-2212) in a highly humid air has been investigated. Using diffuse reflectance infrared Fourier transform spectroscopy, different reaction steps for carbonate formation with aging time were found to occur on the surface of the superconductors. During the initial stage, the calcium carbonate species mainly formed due to the preferred hydration of calcium ions because of their lower ionic–dipole interaction energy. At a later stage, the strontium carbonate species became the more dominant species because of the kinetics of this step along with the higher molar ratio of Sr 2+ to Ca 2+. In addition to the carbonates, larger amounts of Sr(OH) 2 · nH 2O ( n=1 or 8) and CuBi 2O 4, along with relatively small amounts of Ca(OH) 2 were also found on the surface along with Sr(OH) 2. The formation of larger amounts of strontium-related degradation products also led to larger amounts of Bi 2CuO 4 being formed. The effect of stearic acid coating on the degradation of the superconductor was also investigated with respect to long term durability in a very humid atmosphere. These coatings strongly prevented the formation of carbonates on the surface of (Bi,Pb) 2Sr 2Ca 2Cu 3O y (Bi,Pb-2223). Strong complex bonds between the carboxylate groups of the organic acids and the metal ions on the surface of the superconductor were formed, which helped to retard the degradation process for the superconducting phase.

防食塗装の現状と展望

防食塗装の現状と展望

Degradation of Protective Organic Coatings after Cupping Test

Abstract Coil coating products generally are shaped by deforming and bending after coating. These deformations can produce defects inducing a significant deterioration of the protective properties ...

Chemical conditions inside occluded regions on corroding aircraft aluminum alloys

Corrosion of aluminum alloy structures costs the US Air Force in the order of US$1×10 9 annually. Corrosion develops in areas of overlap such as aircraft lap-splice joints and under protective organic coatings. Capillary electrophoresis (CE) has been used to determine the local chemistries at these corrosion sites of solutions that were extracted using a microsampling system. Analysis of the local solution within lap-splice joints from aircraft has been performed in two ways: rehydration of corrosion products and direct microsampling. The solutions collected were analyzed with CE to quantitatively determine the species present during corrosion. The most common ions detected were Cl −, NO 2 −, NO 3 −, HCO 3 −, K +, Al 3+, Ca 2+, Na + and Mg 2+. Studies of the solution chemistry under local coating defects are required to understand coating failure and develop more durable coatings. A microsampling system and micro pH sensor were developed to extract solution from and measure pH in defects with diameters as small as 170 μm. Actively corroding defects contained high concentrations of Cl −, Al 3+, Mg 2+, Mn 2+ and Cu 2+ whereas only trace levels of Mg 2+ were found in repassivated defects. The effects of these species on initiation and propagation of corrosion are discussed.

Adhesion characterization of protective organic coatings by electrochemical impedance spectroscopy

Adhesion is considered in many situations to be a very important property of organic coatings for corrosion protection and much scientific work is devoted both to the study of the mechanism involved in polymer-metal adhesion and to the ways of measuring this property. The large number of experimental methods in existence to obtain information on coating adhesion is an indication of both the scientific and the technological interests in this material science and engineering area, but it is also a consequence of the difficulty in measuring adhesion in a general sense. As a partial alternative to the traditional adhesion measurement approaches for organic coatings, the evaluation of adhesion by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) is discussed for different examples. The influences on adhesion of different pretreatments or organic coatings are discussed, considering aluminium, galvanized steel, and stainless steel substrates, and we have shown that the information obtained by using an electrochemical approach can be used for adhesion evaluation, with particular attention to the monitoring of adhesion in an aqueous environment, which is the most detrimental for protective organic coatings.

Thermal Transition Effects and Electrochemical Properties in Organic Coatings: Part 1 — Initial Studies on Corrosion Protective Organic Coatings

Abstract Thermal effects in a high-performance fusion-bonded epoxy (FBE) powder coating on steel were measured by electrochemical means. Experimental performance of the coating in immersion indicated the coating resistance as acquired by electrochemical noise methods (ENM), electrochemical impedance spectroscopy (EIS), and direct current resistance (RDC) measurements decreased in an Arrhenius manner with increasing temperature up to the glass transition temperature (Tg) of the immersed coating film. Coating resistance then abruptly decreased more rapidly. The abrupt change in film resistance (a coating transport property) at Tg was seen in all three film resistance measures. Using independent differential scanning calorimetry (DSC) experiments, Tg was shown to be that of the water-plasticized film and not of the dry film. Calculation of film capacitance values from EIS indicated increased water uptake with temperature consistent with water-plasticization as seen in Tg measurements. Data implied that use o...

Electrochemical Impedance Spectroscopy and Fourier Transform Infrared Spectroscopy of Natural and Accelerated Weathering of Organic Coatings

Effects of the natural degradation of protective organic coatings after exposure for some years in an industrial atmosphere (Turin, Italy) and the consequences of artificial weathering in an ultraviolet (UV) chamber (ASTM G 53) and salt spray test chamber (ASTM B 117) were compared using electrochemical, infrared, and calorimetric techniques. The comparison showed some differences between natural and accelerated weathering in the degradation mechanisms and provided information regarding future developments for new testing procedures.

The sorption characteristics of epoxy coatings electrodeposited on steel during exposure to different corrosive agents

Organic protective coatings on steel were formed by cathodic electrodeposition of an epoxy resin modified by an amine and isocyanate using a constant voltage method (resin concentration 10%wt, temperature 26 °C, applied voltage 250 V). The corrosion behaviour of these coatings was investigated during exposure to different corrosive agents (H 2O, 3% NaCl, 3% Na 2SO 4, 3% sodium salt of 2-naphthol-3,6 disulphonic acid) using a.c. impedance measurements, gravimetric liquid sorption experiments and differential scanning calorimetry (DSC), with the aim of explaining the mechanism of coating degradation. The time required to saturate the coating with pure water, obtained from the sorption data, coincides with the initial increase in coating capacitance and initial decrease in pore resistance, obtained from a.c. impedance measurements, denoting the entry of electrolyte into the coating. The first step of electrolyte penetration through the coating is related to water uptake, when molecules of pure water diffuse in the micropores of polymer net according to Fick's law and it is independent of type and dimensions of ions in the electrolyte. Similar values of enthalpy of vaporization of different volatile electrolytes and the quantity of water inside the coating, obtained from DSC measurements were in agreement with the proposed mechanism. From the calculated diffusion coefficient for coatings where external layers were mechanically removed, it can be concluded that the micropores of the polymer net are homogeneously distributed throughout the coating.

Effect of PCB finish on the reliability and wettability of ball grid array packages

Organic protective coatings (OPC) and metallic plating chemistries have emerged as alternatives to traditional hot air solder leveling (HASL) to ensure the solderability of printed circuit boards (PCB). This study examined a number of commercially-available printed circuit board finishes to determine their intrinsic solderability and their effect on the solder joint reliability of ball grid array (BGA) packages. The PCB finishes included OPC (Entek Plus CU-106A and MEC-seal), immersion Au over electroless Ni (LeaRonal, MacDermid, Shipley, and Technique), electroless Pd over Ni, electroless Sn over Cu, immersion Bi over Cu, and HASL. Solderability tests were performed by reflowing 20-mil diameter solder spheres on variously aged test coupons and then quantitatively measuring the area and shape of the solder after cooling. The immersion Au finishes generally exhibited excellent wettability as a function of N/sub 2/ reflow aging as compared with the OPCs and HASL. The Pd-Ni, Sn, and one of the Ni-Au finishes exhibited poor wetting when exposed to an 85/spl deg/C/85% RH environment. Solder joint reliability was measured for a 41 I/O ceramic BGA using cyclic thermal shock (nominally -55-125/spl deg/C) and three point bending. All finishes tested behaved similarly in thermal shock. The Au finishes generally performed worse in three-point bending as compared to OPC and HASL. The wetting and reliability results are correlated with the structure and composition of the finishes and the solder joints.

Hybrid Substrates for Real-Time SERS-Based Chemical Sensors

Since the discovery of the surface-enhanced Raman scattering (SERS) effect, numerous substrate designs have been proposed for a variety of analytical applications. Although many of these have offered exceptional electromagnetic enhancement, the durability and reusability of substrates have not always been acceptable for routine analytical use. This paper discusses the design and testing of a new class of hybrid SERS substrates specifically designed to optimize electromagnetic enhancement while also affording exceptional ruggedness and reversibility of response under challenging conditions. Substrate templates are fabricated lithographically into a quartz surface, then a thin metal film is deposited, and finally the entire surface is coated with a protective layer. Examples of inorganic and organic protective coatings are provided. Analytes are measured in flowing streams of airborne vapor and aqueous liquid. Properly designed surface coatings serve a dual role as both a protective layer and as a rapidly reversible selective adsorbent for specific analytes.

Atomic Oxygen Treatment for Non-Contact Removal of Organic Protective Coatings from Painting Surfaces

Current techniques for removal of varnish (lacquer) and other organic protective coatingsfrom paintings involve contact with the surface. This contact can remove pigment, or alter the shape and location of paint on the canvas surface. A thermal energy atomic oxygen plasma, developed to simulate the space environment in low Earth orbit, easily removes these organic materials. Uniform removal of organic protective coatings from the surfaces ofpaintings is accomplished through chemical reaction. Atomic oxygen will not react with oxides so that most paint pigments will not be affected by the reaction. For paintings containing organic pigments, the exposure can be carefully timed so that the removal stops just short of the pigment. Color samples of Alizarin Crimson, Sap Green, and Zinc White coated with Damar lacquer were exposed to atomic oxygen. The lacquer was easily removed fromall of the samples. Additionally, no noticeable change in appearance was observed after the lacquer was reapplied. The same observations were made on a painted canvas test sampleobtained from the Cleveland Museum of Art. Scanning electron microscope photographs showed a slight microscopic texturing of the vehicle after exposure. However, there was no removal or disturbance of the paint pigment on the surface. It appears that noncontact cleaning using atomic oxygen may provide a viable alternative to other cleaning techniques. Itis especially attractive in cases where the organic protective surface cannot be acceptably or safely removed by conventional techniques.

Film coating technologies and adhesion

Solid Polymer Electrolyte (SPE) films must be formed in a reproducible, controlled manner in order to construct devices which take advantage of their unique properties. Film coating processes that yield reproducible thin films will be reviewed vis-à-vis the device requirements ( eg thin film lithium batteries) of SPE films. Solution characteristics important for film coating processes will be presented and process control parameters outlined. Film defects and their control in processing are major problems which must be addressed in the choice of materials and coating process for thin film applications. Proper processing of SPE films will be a key to their utilization, and the criteria for correct choice of a coating process for this type of film will be examined. A further key to the proper utilization of SPE film will be their wetting and adhesion to device substrates, ie lithium, in the case of thin film batteries. Poly(ethylene oxide) SPE films may have advantages in this respect if their adhesion behavior is analogous to that of PEO-based polymers used in the protective organic coatings.

Influence of barrier pigments on the performance of protective organic coatings

Article de synthese sur l'utilisation de pigments et de charges lamellaires: mica, oxyde de fer micace, copeaux de verre, aluminium, zinc et autres pigments metalliques

Lifetime Prediction of Organic Coatings on Steel

ABSTRACTA review of methods for predicting the lifetime of protective organic coatings on steel is presented in terms of a model which includes the steps of defect formation, transport of corrodents, loss of adhesion, and corrosion. Electrochemical impedance methods and acoustic techniques have played important roles in characterizing how the four processes interact and depend on coating processes and environmental effects. A major result of this work has been the observation that both the anodic and cathodic partial processes of the corrosion reaction limit adhesion of organic coatings on steel by generating tensile stresses and polymer degradation, thereby limiting the life of the protective system.