Search

Stimulated by the growing demand for more sustainable polymer systems, experiments were performed to develop completely recyclable epoxy‐based thermoset composite materials involving the separation, recovery, and complete reuse of both components of the composite, the resin and the fibers. In this study, a possibility to design such composites by incorporation of reversible chemistry for dedicated repair and recycling is demonstrated. Relying on Diels–Alder (DA) adducts located on the cross‐links between the polymeric chains, uncross‐linking the thermoset via the reverse DA reactions becomes possible. The network breaks up at elevated temperatures in shorter segments, which can be solubilized in solvents like acetic acid, butan‐1‐ol, or toluene. Specific processes for each of these solvents were developed to recover the resin and fibers with virtually unchanged properties. Both components were used in a second manufacturing step to produce recycled composites which display properties comparable with the original composites.

The solid-state hydration of salts has gained particular interest within the frame of thermochemical energy storage. In this work, the water vapor pressure-temperature (p-T) phase diagram of the following thermochemical salts was constructed by combining equilibrium and nonequilibrium hydration experiments: CuCl 2 , K 2 CO 3 , MgCl 2 ·4H 2 O, and LiCl. The hydration of CuCl 2 and K 2 CO 3 involves a metastable zone of ca. 10 K, and the induction times preceding hydration are well-described by classical homogeneous nucleation theory. It is further shown for K 2 CO 3 (metastable) and MgCl 2 ·4H 2 O (not metastable) through solubility calculations that the phase transition is not mediated by bulk dissolution. We conclude that the hydration proceeds as a solid-solid phase transition, mobilized by a wetting layer, where the mobility of the wetting layer increases with increasing vapor pressure. In view of heat storage application, the finding of metastability in thermochemical salts reveals the impact of nucleation and growth processes on the thermochemical performance and demonstrates that practical aspects like the output temperature of a thermochemical salt are defined by its metastable zone width (MZW) rather than its equilibrium phase diagram. Manipulation of the MZW by e.g. prenucleation or heterogeneous nucleation is a potential way to raise the output temperature and power on material level in thermochemical applications. © Copyright 2019 American Chemical Society.

Six different bitumina of comparable PEN grade were investigated to gain a relation between the composition

The curing kinetics of UV-curable powder coatings based on commercial unsaturated polyesters were monitored using photo-DSC, Real-Time FTIRATR and a modified rheometer equipped with a UV source. The effect of physical and chemical factors on curing such as type of photoinitiator, photoinitiator concentration, temperature and atmosphere of curing were evaluated. Coatings containing amounts of photoinitiator from 0.5 to 10 wt% were cured at different temperatures in less than 10 s reaching conversions approximately of 60%. The increase of the temperature of curing reduces the final conversion and also the rate of polymerization due to the chain transfer process and depolymerization that dominates the photopolymerization at high temperatures. The reactivity of the photoinitiators was similar for all the studied photoinitiators apart from benzophenone that was found to be the slowest initiator.ring kinetics of UV-curable powder coatings based on commercial unsaturated polyesters were monitored using photo-DSC, Real-Time FTIRATR and a modified rheometer equipped with a UV source. The effect of physical and chemical factors on curing such as type of photoinitiator, photoinitiator concentration, temperature and atmosphere of curing were evaluated. Coatings containing amounts of photoinitiator from 0.5 to 10 wt% were cured at different temperatures in less than 10 s reaching conversions approximately of 60%. The increase of the temperature of curing reduces the final conversion and also the rate of polymerization due to the chain transfer process and depolymerization that dominates the photopolymerization at high temperatures. The reactivity of the photoinitiators was similar for all the studied photoinitiators apart from benzophenone that was found to be the slowest initiator.

Bitumen and bituminous binders are a mixture of a wide variety of molecules with different size and nature; a-polar as well as polar, aromatic as well as aliphatic, chain-like as well as two-dimensional in nature. However, most of the bitumina display at ambient temperatures a spontaneous formation of micro-phases displaying different mechanical properties such as stiffness or adhesive behaviour. The actual chemical composition of the individual phases is still a matter/subject of discussion. The application of different scanning probe microscopy modes such as FFM, SThM and SNOM enabled the investigation of the relationships between asphalt microstructure and material characteristics such as friction coefficient, thermal conductivity and chemical composition and polarity. It was possible to collect data providing more and detailed information's on a nano-scale and in detail with respect to the different micro-phases present in bituminous binders. All data collected fit into the present picture of structuring of bitumen and the characteristics of the present phases.

Realising self-healing composites in a commercial environment remains a challenge for the transport sector. Herein, this research considers the design envelope and the implications of embedding self-healing agents into commercially relevant fibre reinforced polymer (FRP) composite applications. A novel epoxy resin containing reversible bondable Diels-Alder structures was developed and implemented into bulk polymer tapered double cantilever beam (TDCB) and FRP double cantilever beam (DCB) test specimens to evaluate the recovery of mechanical performance. Fractured test specimens were exposed to 150 °C for a short duration (5 minutes) to facilitate the polymer reconfiguration process. Mode I testing highlighted a combined adhesive and cohesive fracture mechanisms depending on the self-healing material integration method. Healing efficiency values of >50% resulted for the recovery of fracture toughness (KIc), after the first and subsequent second and third healing cycles.

Secondary resources containing (catcium) atuminium-silicate phases, e.g., fly ash, slag or bottom ash are used as precursor for binders such as geopolymers. Because secondary resources can be highly variable in terms of their potential to dissolve and form reaction products, analytical methods are needed to evaluate their potential as a precursor and to optimize the geopolymer mix design. The most commonly used methods (e.g., XRF, XRD) for measuring the characteristics of source materials which influence binder performance, do not capture heterogeneity of the particles and do not necessarily reveal the key parameter that is most dominant for the binder performance. This presentation therefore discusses the applicability of several techniques we have investigated to capture inter- and intra-particle variations of aluminium-silicates and to evaluate the potential influence of these variations on geopolymer performance. The evaluated techniques are: automated phase mapping based on EDS spectral imaging and processing using principal component analysis; feature sizing and chemical typing (fS&CT); semi-quantitative fTIR 29 and solid state Si NMR.

Molding compounds are key materials to deliver well packaged reliable IC’s for demanding applications, such as automotive electronics. With shrinking sizes of IC’s and the increased requirements with respect to loading conditions, application environment and lifetime, the reliability of the packaging becomes increasingly important. The performance of the package is closely connected to the morphology and the microstructure of the molding compound as well as to the processing conditions during molding. The first issue is a factor which is often overlooked and not always well understood. In our paper we will elaborate on the micro-mechanical mechanisms that play a role in cracking and delamination of the composite molding compound. We will introduce a multi-scale modelling approach as tool for understanding of the conditions and constraints during molding and use of packaged IC’s. Consequently, such an approach can serve as a design tool for next generation molding compounds.

Geopolymers are systems of inorganic binders that can be used for sustainable, cementless concrete and are formed by alkali activation of an aluminium–silicate precursor (often secondary resources like fly ash or slag). The type of aluminium– silicate precursor and its potential variations within one batch may influence geopolymer performance. Therefore, if geopolymers are to be applied for sustainable concrete with reproducible quality, a characterization tool for quality control of precursors and optimizing mix design is needed, which links the (variable) secondary resource characteristics to the performance of geopolymers. This paper shows the potential of using FT-IR and solid state 29Si-NMR for a (semi-)quantitative evaluation of secondary resources suitable for geopolymers. More specifically, the aim is to investigate whether the presence of particular aluminium–silicate phases may have a dominant influence on the strength of a simple geopolymer system. Based on deconvolution of FT-IR and NMR spectra of 9 source materials (fly ash and slag) and their geopolymers, relative amounts of different (aluminium– silicate) phases were estimated and trends with strength were evaluated. A clear trend is observed for bothNMRand FT-IR results: the precursors containing a higher amount of ‘active bonds’, predominantly from silicates with a medium amount of aluminium and alkalis incorporated in their framework, result in higher paste strengths. As such, due to its relatively quick and easy measurements, FT-IR for estimating relative amounts of these aluminium–silicate phases, can be a useful tool for evaluating geopolymer precursors

After millions of years of evolution, nature has developed materials and systems based on the concept of damage management (healing) in order to extend survival possibilities. In the last 20 years, the dream of implementing this concept to engineering systems to extend service lifetime has become a reality. The field of self-healing engineering materials is growing exponentially both in numbers of research groups involved and concepts explored, although finding applications for many of these new concepts is not straightforward. In this chapter we focus on the latest developments in the field of self-healing polymeric systems, analysing the main mechanisms and concepts as well as possible applications. © 2014 Woodhead Publishing Limited. All rights reserved.

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T g temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T g's obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called "Bee" structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content. cop. 2013 RILEM.

The occurrence of discrete cracking of bitumen and asphalt is difficult to observe/analyse mainly because of the viscous nature of the bitumen binder. Many techniques simply do not have the required resolution or analysis techniques do not get a good response from the highly dissipative bitumen. In this study, an attempt is made to visualise failure development under straining conditions in bitumen with the use of an in situ tensile tester combined with atomic force microscopy. From the experiments, it was observed that cracks or strain localisations occur in the perpetua phase though only significantly for aged binder (i.e. more than six months at room temperature). Furthermore, the locations of these cracks or strain localisations occur on the edges of the more rigid peri phase and were oriented in the direction of tension. This is a clear indication that the bitumen's microstructure does affect homogeneity of the internal stress and strain fields and effectively causes non-homogeneous straining and even localisation in regions where stress concentrations are present. Furthermore, the recovery of the strain localised zones was studied. The strain localised zones completely recovered in the course of several hours.

Bituminous binders are known to have microstructures at typical length scales of micrometers. This microstructure can be probed with Atomic Force Microscopy (AFM). Now that worldwide several research groups are reporting AFM results on bitumen, it is becoming important to improve the understanding of the reproducibility and objectivity of the technique for studying bituminous samples. When reproducibility and stability are proven, AFM can be a tool for asphalt professionals to rapidly screen bituminous binders. In this context two independent laboratories have developed a standard method for preparing and conditioning bitumen for AFM imaging. By means of an inter-laboratory comparison of independently imaged specimen, the reproducibility of microstructure measurements was investigated. A quantitative comparison on different microstructures was developed, and the consistency of independently obtained results was confirmed. The results from both labs were comparable: the microstructural properties were found to be randomly distributed within a 5% interval. Also the influence of temperature on the microstructure was demonstrated to be reproducible and consistent. With the increase of temperature, the microstructure gradually disappeared, however traces of the microstructure remained visible up to the highest measurement temperature of 60°C. It is concluded that given well defined sample preparation and measurement procedures, the microstructure of bitumen can be reproducibly imaged by AFM from room temperature up to temperatures where bitumen has become soft and too sticky to be probed by the same setup as used for lower temperatures.

Hermetic wafer-level encapsulation of atmosphere sensitive Micro-Electric-Mechanical Systems (MEMS) devices is vital to achieve a high yield, a high performance and a long operating lifetime. An interesting and gradually more employed packaging technique is flux-less wafer-level copper-tin (Cu-Sn) solid-liquid interdiffusion (SLID) bonding. The process is being employed for several next generation high performance infrared bolometers. The hermeticity and the reliability of the bond are studied through the key parameters: probability for void percolation, conversion into intermetallic compounds and residual stress using both characterization and modelling. Characterization using Scanning Acoustic Microscopy (SAM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and optical microscopy showed different defects in the Cu-Sn bond in case of non-optimized process settings. Defects observed are incomplete conversion into the targeted intermetallic Cu3Sn and voiding. Incomplete conversion influences the thermo-mechanical and environmental robustness of the bond negatively due to less favourable material properties of the intermediately formed Cu 6Sn5 in comparison to the targeted Cu3Sn. Voiding may result in lower thermo-mechanical robustness of the bond and loss of hermeticity. The probability for percolation through voiding is calculated. The reliability of the Cu-Sn bond is also studied using a Finite Element Model (FEM). The calculated residual stress in the Cu-Sn bond caused by volumetric shrinkage during formation of the IMCs is significant and should be taken into account during design to avoid a negative influence on the reliability of the bond. © 2013 IMAPS.

Accelerated testing of white thermal control coatings was performed using the high intensity UV radiation generated by a synchrotron and resulting in a substantial shortening of test times. The origin of coloration of metal oxides upon UV irradiation has been identified to be most likely a generation of oxygen vacancies connected with the appearance of colour centers in the crystal lattice.

Due to their low atomic oxygen erosion yields PI-b-PDMS block copolymer films have considerable potential for application onto space exposed surfaces of satellites in low earth orbit. On solar arrays these materials might be used as electrical electrical insulation film, flexprint outer layer, electrical wire wrapping, adhesive tape and/or metallised thermal control film. In this study PI-b-PDMS block copolymers with 8 and 15% PDMS were synthesized and films were cast and successfully used for the production of front side skin, solar panel and flexprint sheet samples using standard production methods. Surface analysis studies showed the presence of a siloxane-enriched surface layer. After a 1000esh UV exposure test most samples showed only minor changes of properties. Copyright © 2013 European Space Agency.

The meso-scale surface roughness of piezoelectric fiber composites can be manipulated by applying an electric field to a piezocomposite with a polished surface. In the absence of an applied voltage, the tips of the embedded piezoelectric ceramic fibers are below the surface of the piezocomposite and a silicon wafer counter surface rests solely on the matrix region of the piezocomposite surface. When actuated, the piezoelectric ceramic fibers protrude from the surface and the wafer rests solely on these protrusions. A threefold decrease in engineering static friction coefficient upon actuation of the piezocomposite was observed: from μ 1.65 to μ 0.50. These experimental results could be linked to the change in contact surface area and roughness using capillary adhesion theory, which relates the adhesive force to the number and size of the contacting asperities for the different surface states. © 2013 AIP Publishing LLC.

The mechanical properties of bitumen, such as elasticity/Young's modulus, stickiness/adhesion, hardness and energy loss, and sample deformation were acquired quantitatively and simultaneously with the topology at the microscale, discriminating clearly two separate phases within the bitumen. Temperature-dependent measurements revealed detailed and specific data about the changes of these properties with temperature, enabling the development of predictive models for the performance and durability of asphalt. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

A carbonate form of MgAl hydrotalcite, Mg(2)Al-CO3 and its p-aminobenzoate (pAB) modified derivative, Mg(2)Al-pAB, were synthesized and characterized by means of XRD, FT-IR and TG/DSC. The anticorrosion behavior of Mg(2)Al-pAB was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and on chloride-exchange experiments. The results reported in this paper demonstrate that ion-exchange indeed occurred between chlorides and intercalated pAB anions, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released pAB anions were found to exhibit the envisioned inhibiting effect and caused corrosion initiation of the steel to shift to higher chloride concentrations than without the modified hydrotalcites. © 2013 Elsevier Ltd. All rights reserved.

Modified hydrotalcites (MTHs) represent a group of technologically promising materials for addition to concrete to improve its durability in aggressive environment, owing to their low cost, relative simplicity of preparation, and plenty of unique composition variables that may be adopted. Up to date, a lot of academic work and commercial interest on MHTs have been invested, but relatively few studies focus on cementitious materials, particularly in exploiting their potential applications in corrosion protection of reinforced concrete structures. In this article, the mechanism of corrosion in reinforced concrete and concrete properties that affect corrosion of reinforcement are briefly introduced. In addition, the existing knowledge with regard to synthesis and characterisation methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in the cementitious materials were reviewed accordingly. As a new emerging class of smart additive of reinforced concrete, MHTs are expected to contribute to the effort of searching for effective measures to improve the durability of reinforced concrete.

A carbonate form of Mg-Al-hydrotalcite with Mg/Al =2 and its p-aminobenzoate (pAB) modified derivative were synthesized and characterized by means of XRD, IR and TG/DSC. Mg(2)Al-CO3 was prepared by a coprecipitation method and was subsequently modified by pAB through the calcination-rehydration technique. The results from the relevant characterizations combined with total organic carbon (TOC) analysis further confirmed that pAB anions were successfully intercalated into the interlayer space of the hydrotalcite. The anticorrosion behavior of Mg(2)Al-pAB was evaluated on the basis of open circuit potential (OCP) monitoring of carbon steel in simulated concrete pore solution at pH 13 contaminated with chloride. The preliminary results from this study demonstrated that ion-exchange indeed occurred between free chloride ions in simulated concrete pore solution and the intercalated pAB anions in Mg(2)Al-pAB structure. The simultaneously released pAB anions were found to exhibit the envisaged inhibiting effect and cause a shift of corrosion initiation of the steel to higher chloride concentrations than without the modified hydrotalcite.

Modified Hydrotalcites (MHTs) represent a group of technologically promising materials for improving corrosion protection in concrete owing to their low cost, relative simplicity of preparation, and plenty of composition variables. Numerous academic and commercial studies on MHTs have been carried out, but few of them on cementious materials particularly in exploiting their potential application in corrosion protection of reinforced concrete. In this paper, the corrosion mechanism in reinforced concrete and concrete properties that affect it are briefly inroduced. In addition, the existing knowledge with regard to synthesis and characterization methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in cementitious materials were reviewed. © RILEM 2012.

We describe a water dispersed nano sensor cocktail based on InP/ZnS quantum dots (QDs) and atomic silver clusters with a bright and visible luminescence combined with optimized sensor functionalities for the water flooding process. The QDs and Ag nano sensors were tested in simulated reservoir conditions (high salinity, Ca2+, pH, high temperature, oil and solids). The nano sensors showed enhanced sensor functionalities towards pH, temperature, sub-terrain chemistry and reservoir solids like clay or calcium carbonate. Copyright 2012, Society of Petroleum Engineers.

The work addressed involves the preparation and application of a compartmented polymer fibre, containing multiple separated domains with liquid agent for controlled release. The created fibre is a design for improvement to the existing liquid encapsulated self-healing systems such as fibre reinforced composites, i.e. increasing the released volume per intersection and maintaining self-repairing functionality. Additionally, we have focused on optimization of the fibre mechanical properties and control over liquid vacuole morphology.