Adhesion of bituminous and cementitious materials using Particle-Probe Scanning Force Microscopy

As the most important materials in civil engineering, bituminous and cementitious materials have been used widely in pavements and constructions for many years. Accurate determination of adhesion is important to the bonding properties of bituminous and cementitious materials. In this work, we presented a novel approach to measure the adhesion between binders and aggregate mineral particles at microscopic scale. Particle probe scanning force microscopes (SFM) were used to study the adhesion between mineral microspheres representing the primary aggregate constituents (Al2O3, SiO2 and CaCO3) and various control (PG 64-22 and PG 58-22) and modified binders. Results showed that these modified SFM probes could effectively measure the adhesion between binders and aggregate minerals. Consistent adhesion measurements were obtained between different asphalt binders and aggregate mineral particles. Statistical analyses were performed to evaluate effects of different factors on the aggregate-modified binder adhesion, including aggregate constituents, binder types, modifier types and cantilever properties. Due to the stronger polarity of alumina particles, stronger interactions occur within alumina-binder pairs than within silica- and calcium carbonate-binder pairs. Meanwhile, morphologies of different modified binders clearly demonstrated microstructural variations in these binders. The adhesion between steel and different cement hydrated products was measured using particle probe SFM. Adhesive forces are collected between steel microspheres and new (four-week old) and old (six-month old) cement in air and saturated lime water. Mixed Gaussian models were applied to predict phase distributions in the cement paste, i.e., low density C-S-H, high density C-S-H, CH, other hydrated products and the unreacted components. For new cement in saturated lime water, adhesive forces between steel and low density C-S-H, high density C-S-H and other hydrated products are intermediate among all groups selected. The adhesive forces between steel and calcium hydroxide are smallest, whereas the adhesive forces between steel and the unreacted phases are largest. For the six-month old cement, the interweaving of calcium carbonate crystals and C-S-H during the carbonation produces greater adhesive forces to steel, consistent with the adhesive forces between steel and the control calcium carbonate specimen. CH turned into calcium carbonate by reacting with carbon dioxide in air. An increase in adhesive forces was found between steel and calcium carbonate in the old cement than those between steel and CH in the new cement. Particle probe SFM is able to measure the adhesion in bimaterials. For bituminous materials, this methodology provides opportunities to evaluate the effects of different processing methods and to generate quantitative information for the development of multi- scale asphalt mixture cracking models. For cementitious materials, these studies opened new avenues to study the interactions between steel and cement at microscale under a variety of environmental conditions and can be formulated as crack initiation and propagation criteria incorporated in multiscale models for reinforced concrete structures

Using inclined plane test to compare tracking on silicon rubber under HVAC and HVDC.

Masters Degree. University of KwaZulu-Natal, Durban.This dissertation presents research work conducted on high-temperature vulcanised (HTV) silicon rubber electrical tracking and erosion performances under HVDC and HVAC. The aim was to evaluate the performance under outdoor environmental conditions. Failure of polymer insulators is an area that has not been researched thoroughly in the past decade. The aging mechanism of insulators is of paramount importance in manufacturing and design. Outdoor conditions like humidity, moisture, pollution affect the durability of most insulators. Silicon rubber is widely used in power distribution and transmission insulation networks. It is also being used in power devices such as metal oxide surge arresters as the electrical insulation. Its advantages are that it is lightweight, low cost, easily processed, has good dielectric and hydrophobicity properties and has better pollution performance in outdoor insulation systems. The first part of this research looks at the procedure for testing following the normative recommendations as per IEC 60587: 2007 standard. Constant tracking voltage method was implemented in the inclined plane test for electrical tracking and erosion. A voltage of 4.5 kV was applied for all +DC, -DC and AC testing. The failure criteria as per IEC-60587 were followed. The most monitored criteria were that the leakage current magnitude should be below 60 mA. An increase in leakage current magnitude and duration of discharges were observed under +DC test conditions. The tracking time was recorded to be less under –DC than in +DC. The average current under +DC increases with the voltage application duration, however under AC the current does not increase. Under –DC voltage the current flow was observed to be less intermittent. Sample surface degradation mechanism was seen to be different in +DC, -DC and AC. A data logger monitored the leakage current measurements. An average leakage current of 9.40 mA was found under +DC. An average leakage current under –DC was measured to be 8.92 mA. Under AC voltage an average current of 11.90 mA was recorded. The second part of the study looked at the quantitative analysis techniques of silicon rubber. Silicon rubber test samples were carried out using scanning electron microscope (SEM) with Energy Dispersive Spectroscope (EDS), Fourier transform infrared microscope (FTIR) and transmission electron microscope (TEM). These physiochemical tests results were comparable for both DC and AC, it was concluded that the insulator deterioration was due to surface tracking and dry-band arcing discharges which resulted in the erosion of the test samples. The work reveals that +DC is more aggressive for the test samples tested. It was concluded that under +DC conditions tracking is more severe as compared to –DC and AC

PROPERTY ANALYSIS OF THE ASPHALT MATERIALS USING MOLECULAR DYNAMICS (MD) METHOD

The main objectives of this dissertation are to build the Molecular Dynamics (MD) model for the asphalt binders with three components, asphaltenes, aromatics and saturates, and analyze the properties of the asphalt models to discover the interactions and mechanisms of asphalt-aggregate and asphalt-modifier. The contributions of this dissertation are summarized as follows: (1) the Amber Cornell Extension Force Field (ACEFF) was assigned to each component, and most of the parameters of the force field were obtained from the General Amber Force Field (GAFF). Electrostatic Potential (ESP) charges were assigned to each atom with the NWChem calculation; (2) the modified asphalt model with the multi-layer graphite nanoplatelets (xGNP) was generated by the MD method to analyze the effect of the modifier on the asphalt binder model; (3) the aged components of the asphalt model were proposed, and the analysis of moisture susceptibility of asphalt-aggregate by the MD method; (4) the interaction or diffusion of the asphalt binder on aggregates was also realized by the MD method. The MD simulations and laboratory test evaluations show that (1) the MD asphalt model with ACEFF and ESP charges has a better prediction for the different properties than the reference model; (2) The primary aging products in the asphalt binder contain ketones, carboxylic acids and anhydrides. The difference in adhesion was observed between aggregate-asphalt and aggregate-water interfaces; (3) the addition of xGNP nanoplatelets in the asphalt model increased the density, viscosity and thermal conductivity. The same trend was observed in the experimental data. A better observation of these properties was found in the xGNP modified asphalt model compared to the base asphalt model; (4) Different moduli of the asphalt binder models had a trend similar to that of the laboratory test results; (5) The asphalt started to diffuse when the activation energy was reached, and the contact angle and area of the asphalt-aggregate interface changed. Therefore, the findings or conclusions in this dissertation have a good guidance for improving the performance of asphalt binders. Most importantly, this dissertation provides a promising way to analyze and develop the material and its properties

Polymer Electrolyte Membrane (PEM) fuel cell seals durability

Polymer electrolyte membrane fuel cell (PEMFC) stacks require sealing around the perimeter of the cells to prevent the gases inside the cell from leaking. Elastomeric materials are commonly used for this purpose. The overall performance and durability of the fuel cell is heavily dependent on the long-term stability of the gasket. In this study, the degradation of three elastomeric gasket materials (silicone rubber, commercial EPDM and a developed EPDM 2 compound) in an accelerated ageing environment was investigated. The change in properties and structure of a silicone rubber gasket caused by use in a real fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140°C) and greater acidity. Three accelerated ageing media were used. The first one was dilute sulphuric acid solution with the pH values of 1, 2 and 4. Secondly, Nafion ® membrane suspended in water was used for accelerated ageing at a pH 3 to 4. Finally, diluted trifluoroacetic acid (TFA) solution of pH 3.3 was chosen. Weight change and the tensile properties of the aged gasket samples were measured. In addition, compression set behaviour of the elastomeric seal materials was investigated in order to evaluate their potential sealing performance in PEM fuel cells. The results showed that acid hydrolysis was the most likely mechanism of silicone rubber degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. The effect of TFA solution on silicone rubber was more aggressive than sulphuric acid and Nafion® solutions with the same acidity (pH value) suggesting that TFA accelerated the acid hydrolysis of silicone rubber. In addition, acid ageing in all three acidic solutions caused visible surface damage and a significant decrease in tensile strength of the silicone rubber material, but did not significantly affect the EPDM materials. EPDM 2 compound had a desirable (low) compression set value which was similar to silicone rubber and much better than the commercial EPDM. It also showed a very good performance in the fuel cell test rig conforming that it a potential replacement for silicone rubber in PEMFCs

Polymer Composites for Electrical and Electronic Engineering Application

Polymer composite materials have attracted great interest for the development of electrical and electronic engineering and technology, and have been widely applied in electrical power systems, electrical insulation equipment, electrical and electronic devices, etc. Due to the significant expansion in the use of newly developed polymer composite materials, it is necessary to understand and accurately describe the relationship between composite structure and material properties, as only based on thorough laboratory characterization is it possible to estimate the properties for their future commercial applications. This book focuses on polymer composites applied in the field of electrical and electronic equipment, including but not limited to synthesis and preparation of new polymeric materials, structure–properties relationship of polymer composites, evaluation of materials application, simulation and modelling of material performance

Investigation of Oxidation Profile in PMR-15 Polyimide using Atomic Microscope (AFM)

Nanoindentation measurements are made on thermosetting materials using cantiever deflection vs. piezoelectric scanner position behavior determined by AFM. The spring model is used to determine mechanical properties of materials. The generalized Sneddon's equation is utilized to calculate Young's moduli for thermosetting materials at ambient conditions. Our investigations show that the force-penetration depth curves during unloading in these materials can be described accurately by a power law relationship. The results show that the accuracy of the measurements can be controlled within 7%. The above method is used to study oxidation profiles in Pl\1R-15 polyimide. The thermo-mechanical profiles ofPNIR-15 indicate that the elastic modulus at the surface portion of the specimen is different from that at the interior of the material. It is also shown that there are two zones within the oxidized portion of the samples. Results confirm that the surface layer and the core material have substantially different properties

Development of self-cleaning polymeric surfaces using polymer processing systems for application to high-voltage insulators

Herein, polymer processing systems are used to fabricate superhydrophobic high-temperature vulcanized (HTV) silicone rubber surfaces by direct replication. HTV silicone rubber is one of the main polymeric housing materials used in high-voltage insulators. The selected polymer processing techniques are compression molding and injection molding.The direct replication approach requires that a template or insert having the desired surface patterns be replicated onto a target polymer surface via a polymer processing. The appropriate micro-nanostructures, required for achieving ultra-water-repellency, were created on the insert materials (an aluminum alloy) using a wet-chemical etching method. As a flawless demolding is essential to acquire desirable replication quality, an antistiction coating was applied to the insert surfaces prior to the molding process to ensure the thorough removal of the silicone rubber during the demolding. The resulting silicone rubber surfaces possessed micro-nanostructures producing a water contact angle (WCA) of >160° and a contact angle hysteresis (CAH) of <3°. The surface roughness of the aluminum inserts was optimized at HCl concentrations of 15 wt.%. The self-cleaning properties of the produced ultra-water-repellent silicone rubber surfaces were rigorously investigated to ensure a self-cleaning surface at real outdoor imitated conditions. The presence of air pockets in between the surface asperities produced the Cassie-Baxter regime. The consistency of these air pockets is crucial for attaining the self-cleaning properties. A series of tests, including droplet impact, water-jet impact, trapped air layer, and severe droplet contact tests were conducted to confirm the stability of the Cassie-Baxter regime. A comprehensive series of self-cleaning experiments involving both suspended and non-suspended contaminants, e.g., kaolin, carbon black, and silica as well as contaminant-applying methods, e.g., dropwise, spraying, wet or dry contamination were performed. Self-cleaning tests were organized from less severe, i.e., non-suspended contamination tests, to severe, i.e., the wet suspended contamination test, to most severe, i.e., the dry suspended contamination test. Due to their ultra-low CAH, the produced surfaces demonstrated favorable self-cleaning properties against the various types of contaminants and the different means of contaminant application. The produced surfaces retained their water repellency following the application of the contaminants and successful cleaning of the surfaces, thereby verifying the self-cleaning performance and resistance of the fabricated superhydrophobic silicone rubber surfaces. The anti-icing properties (delayed ice formation) and de-icing properties (reduced ice adhesion strength) of the produced surfaces were evaluated. Two types of icing (atmospheric glaze and bulk ice) were considered to accumulate ice on the surfaces. The well-known ice adhesion measurement techniques, i.e., the centrifuge adhesion and push-off tests were employed to provide quantitative comparisons of the ice adhesion strength of the produced surfaces. The produced surfaces significantly delayed ice formation and reduced the ice adhesion strength. To rigorously assess the durability of the produced surfaces, a comprehensive series of experiments that covered a wide range of real-life conditions were carried out. In some cases, where the water repellency was lost, the silicone rubber surfaces demonstrated a satisfactory recovery of their anti-wetting properties. Given the importance of replication quality in the direct replication of micro-nanostructures and the role of micro-nanostructures in the formation of superhydrophobic and icephobic surfaces, the effect of processing parameters on the superhydrophobicity, icephobicity, and replication quality in the compression molding of silicone rubber surfaces were evaluated. Curing time, mold temperature, molding pressure, and part thickness were assessed via response surface methodology to determine the optimal processing parameters. Molding pressure and part thickness were revealed as two main influencing parameters in the superhydrophobic properties. The crosslink density of the fabricated silicone rubber samples, however, was found to be significantly affected by curing time and mold temperature. Replication quality was determined for various molding pressures and part thicknesses. There was an optimal molding pressure value at each part thickness level to obtain the best replication quality. Surfaces having the highest replication quality showed the longest freezing delay reflecting their potential use as anti-icing surfaces. Although all superhydrophobic surfaces offered potential icephobic properties, identifying the influential parameters controlling ice adhesion was more complicated. As this PhD project is part of an industrial-academic collaboration, the results obtained in the laboratory experiments were used for implementation in the industry (K-Line Insulators Limited). This step includes the use of aluminum and stainless-steel inserts. Using the injection molding system available at K-Line Insulators Ltd., silicone rubber insulators having superhydrophobic properties were produced successfully. The industrial partner provided facilities to modify its mold to produce superhydrophobic insulators in an industrial scale. Dans cette thèse, les systèmes de transformation des polymères sont utilisés pour fabriquer des surfaces superhydrophobes de caoutchouc de silicone vulcanisé à haute température (HTV) à partir d’une réplication directe. Le HTV est l’un des principaux matériaux polymères utilisés dans la fabrication des isolateurs à haute tension. Les systèmes considérés sont des procédés de moulage par compression et de moulage par injection. L'approche de réplication directe nécessite un modèle ou un insert ayant les structures de surface souhaitée à répliquer sur la surface du polymère. Les micronanostructures appropriées pour obtenir la non-mouillabilité de la surface ont été créées sur les matériaux d'insert (alliage d'aluminium) en utilisant un procédé de gravure chimique. Comme un démoulage sans défaut est essentiel pour obtenir la qualité de réplication souhaitable, un revêtement antiadhésif est appliqué sur les surfaces de l'insert avant le processus de moulage afin d’assurer l'élimination complète du caoutchouc de silicone lors du démoulage. Les surfaces de caoutchouc de silicone développées possédaient des micronanostructures produisant un angle de contact eau (WCA) de > 160 ° et une hystérésis angle de contact (CAH) de < 3 °. La rugosité optimale de surface des inserts en aluminium est obtenue à une concentration massique de HCl de 15%. Les propriétés autonettoyantes des surfaces produites ont été rigoureusement étudiées pour assurer que ces propriétés autonettoyantes demeuraient efficaces dans des conditions extérieures réelles. La présence de poches d'air entre les aspérités de surface est responsable de la formation du régime de Cassie-Baxter. La consistance de ces poches d’air est cruciale pour obtenir des propriétés autonettoyantes. Par conséquent, une série d’essais ont été effectués pour confirmer la stabilité du régime Cassie-Baxter. Ensuite, une série complète d'expériences de propriétés autonettoyantes a été réalisée en impliquant des contaminants en suspension et non suspendus (non dispersés) utilisant divers matériaux (par exemple, le kaolin, le noir de carbone, la silice, etc.) et des méthodes d'application de contaminants (par exemple, goutte à goutte, pulvérisation, contaminants humides ou secs) ont été effectuées. Les tests d’autonettoyage ont été organisés, du test le moins sévère, c’est-à-dire de la contamination non suspendue (non dispersée), au test plus sévère, c’est-à-dire de la contamination en suspension humide, et se terminant par le test le plus sévère, à savoir la contamination en suspension sèche. En raison du CAH ultra-bas, les surfaces produites ont montré des propriétés autonettoyantes favorables contre les différents types de contaminants et de différents moyens d'application de contaminants. Les surfaces produites ont conservé leurs propriétés répulsives après l'application des contaminants et après le nettoyage des surfaces, permettant ainsi de vérifier les performances d'autonettoyage et la résistance des surfaces en silicone superhydrophobe fabriquées. Les propriétés anti-givrantes (la formation retardée de la glace) et les propriétés glaciophobes (la force d'adhérence réduite de la glace) des surfaces produites ont été évaluées. Les surfaces produites sont exposées à la formation de deux types de givrage. Les techniques bien connues de mesure de l'adhésion sur la glace, à savoir le test d'adhérence par centrifugation et le test de poussée, ont été utilisées pour obtenir une comparaison précise des résultats. Les surfaces superhydrophobes produites ont considérablement retardé la formation de glace et réduit la force d'adhérence de la glace. Afin d’évaluer de manière rigoureuse les propriétés de durabilité, une série complète d’expériences a été réalisée sur les surfaces. Les expériences de durabilité ont été menées pour couvrir un large éventail d'applications réelles. En ce qui concerne la capacité attractive du caoutchouc de silicone dans la récupération des propriétés anti-mouillantes, la perte de la propriété de répulsion de l’eau a été régénérée jusqu’à un niveau satisfaisant dans certains cas. Compte tenu de l’importance de la qualité de la réplication dans la réplication directe des micronanostructures d’une part, et d’autre part du rôle des micronanostructures dans la formation de surfaces superhydrophobes et glaciophobes, les effets des paramètres de moulage par compression des surfaces en caoutchouc de silicone sur la superhydrophobicité, la glaciophobicité et la qualité de la réplication ont été évaluées. Le temps de durcissement, la température de moulage, la pression de moulage et l'épaisseur de la pièce ont été choisis comme paramètres de traitement à évaluer. La méthodologie de surface de réponse a été utilisée pour déterminer les paramètres de traitement optimaux. Bénéficiant des résultats, la pression et l'épaisseur ont été révélées comme les deux paramètres d'influence principaux des propriétés superhydrophobes. La densité de réticulation des échantillons de caoutchouc de silicone fabriqués s'est toutefois révélée être significativement affectée par le temps et la température. Les valeurs de qualité de réplication ont été déterminées en fonction de diverses pressions et épaisseurs. Il y avait une valeur de pression optimale à chaque niveau d'épaisseur pour obtenir la meilleure qualité de réplication. Il a également été observé que les surfaces présentant la meilleure qualité de réplication affichaient le plus long retard de gel de la gouttelette d’eau, ce qui représentait leur potentiel élevé d'utilisation en tant que surfaces antigivrantes. Bien que toutes les surfaces superhydrophobes aient présenté des propriétés potentiellement glaciophobes, il a été constaté que le scénario d’adhérence sur la glace était plus compliqué en termes de paramètres influents. Ce projet de doctorat fait partie d'une collaboration industrielle-académique. Les résultats obtenus en laboratoire ont été utilisés pour la mise en œuvre dans l'industrie (K-Line Insulators Limited). À cette étape, des inserts en aluminium et en acier inoxydable ont été utilisés. En utilisant le système de moulage par injection disponible chez K-Line Insulators Ltd., des isolateurs en caoutchouc de silicone ayant des propriétés superhydrophobes ont été produits avec succès. Par conséquent, le partenaire industriel fournit des installations pour modifier son moule afin de produire des isolateurs superhydrophobes à l'échelle industrielle

Investigation of electrical properties of field grading materials based ZnO microvaristors

Field grading material based microvaristors are widely used to minimise the localised field enhancement which could trigger corona and partial discharges in high voltage equipment. In this research, two different microvaristor powders, A and B are composed of silicone rubber matrix at certain filler concentration. The fabrication process of this composite is done by mixing the insulating matrix with filler using high shear mixer, follow by degassing and curing. The additional procedure, heat treatment, is introduced to avoid the agglomeration risk. Such challenges during running this process are well discussed. The composites are subjected to three high voltage tests, alternating current (AC), direct current (DC) and impulse. The non-linearity behaviour of these composite is characterised as dependent on the microvaristor loading, material properties and voltage application. The microscopic evaluations are conducted to examine the effect of material properties toward the electrical properties of composites. An 11 kV polymeric insulator has been modelled and simulated in COMSOL® platform. The performance of this insulator is assessed under a number of simulation scenarios. The potential voltage and field profile of this insulator are identified. Such improvement of field distribution along the insulator is required, therefore the electrical properties of field grading material is adopted into numerical simulation. The introduction of microvaristor material with an appropriate switching characteristic has led to a substantial improvement in the electric field and heat distributions along the insulator profile