Determination of Scattering and Absorption Coefficients for Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings

Prediction of radiative transport through translucent thermal barrier coatings (TBCs) can only be performed if the scattering and absorption coefficients and index of refraction of the TBC are known. To date, very limited information on these coefficients, which depend on both the coating composition and the microstructure, has been available for the very commonly utilized plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) TBCs. In this work, the scattering and absorption coefficients of freestanding plasma-sprayed 8YSZ coatings were determined from room-temperature normal-incidence directional-hemispherical reflectance and transmittance spectra over the wavelength range from 0.8 to 7.5 μm. Spectra were collected over a wide range of coating thickness from 60 to almost 900 μm. From the reflectance and transmittance spectra, the scattering and absorption coefficients as a function of wavelength were obtained by fitting the reflectance and transmittance values predicted by a four flux model to the experimentally measured values at all measured 8YSZ thicknesses. While the combined effects of absorption and scattering were shown in general to exhibit a nonexponential dependence of transmittance on specimen thickness, it was shown that for sufficiently high absorption and optical thickness, an exponential dependence becomes a good approximation. In addition, the implications of the wavelength dependence of the plasma-sprayed 8YSZ scattering and absorption coefficients on (1) obtaining accurate surface-temperature pyrometer measurements and on (2) applying mid-infrared reflectance to monitor TBC delamination are discussed.     

Kinetics modeling of a modified epoxy–amine formulation cured by thermal and microwave energy

The reaction kinetics of a rubber-modified epoxy formulation cured by microwave or thermal energy were investigated. Two phenomenological models were developed to predict the time and temperature dependence of the conversion for the neat and the modified systems. Good agreement was observed between the kinetic models and experimental results generated by chromatographic and calorimetric techniques. The same kinetic behavior was observed whatever the curing process (conventional or microwave heating). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 543–552, 1998     

Process-resolved morphology of bismaleimide matrix composites

A series of silicone-modified bismaleimide resins have been examined as matrices for high performance continuous fiber-reinforced composite materials. Detailed studies of the interrelation between processing, structure, and properties of both the neat resin and corresponding carbon-fiber-reinforced composite have identified that the silicone additive provides important morphological modification to the bismaleimide matrix for toughness improvements while, at the same time, retaining the elevated temperature performance. Micrographs of fracture surfaces of cured samples demonstrate remarkable similarities to fracture surfaces of rubber-modified epoxy matrices. Specifically, a fracture surface covered with noncommunicating microcavities of 1.5 μm in diameter was observed. However, unlike rubber-modified epoxies where the observed features are assumed to be created during fracture of the specimen, this study demonstrates that the microcavities are created during the cure process and, thus, exist in the bulk of the material before fracture. In simulated cures of the material either while obsered directly in a polarizing microscope or indirectly inside thermal analysis cells (DSC, TGA) and with examination of fractured surfaces of samples cured according to different temperature profiles, it is established that the silicone modifier, in conjunction with the processing conditions, is responsible for the morphological developments. Accordingly, a mechanism describing the observed morphology was proposed based on physical changes that the silicone additive experiences in relation to specific volatile products emitted during the cure process.     

三种有机成核剂成核聚丙烯的非等温结晶动力学研究

采用DSC研究了聚丙烯（PP）和三种有机成核剂成核的PP在不同的降温速率下的非等温结晶动力学。用Avrami对DSC的测试结果进行了分析。结果表明,三种有机透明成核剂能显著提高PP的结晶温度和结晶速率。可以用修正Avrami方程的Jeziorny法来处理三种有机成核剂成核PP的非结晶等温结晶行为,处理结果表明：三种有机成核透明成核剂成核PP的半结晶时间减少,结晶动力学常数(Zc)增加,结晶速率增加;松香型成核剂能最快提高PP的结晶速率;同一降温速率下,三种有机成核透明剂成核PP的n值较纯PP减少,结晶成核方式发生了改变。     

Diffuse reflectance‐factor measurements of rose petals

The diffuse reflectance factor for different colored rose petals is measured as a function of wavelength using a high resolution optical spectrometer. The tristimulus values, the CIE chromaticity coordinates, the dominant wavelength and purity, the CIE whiteness index, the tint index, the CIE 1976 LAB coordinates, as well as CIELAB hue‐angle and chroma are reported. The data on diffuse reflectance factor are presented in the 390?800 nm range at intervals of 10 nm. Using the data, one can generate the perceived color of the roses and the color coordinates in different illuminating light sources and environments. The present data will be useful for the color characterization of flowers, realistic rendering of flowers in computer graphics, color photography, and in the development of filters for color photography. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Effect of matrix ductility on the fracture behavior of rubber toughened epoxy resins

This paper investigates the effect of matrix ductility on toughness in a carboxyl-terminated butadiene-acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol-A (DGEBA)-piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′-diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix T_g was significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber-modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery-phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during crack initiation.     

Deformation and fracture behaviour of a rubber-toughened epoxy: 1. Microstructure and fracture studies

The microstructure and fracture behaviour of an unmodified and a rubber-modified epoxy have been studied. Values of the stress intensity factor, K_Ic, at the onset of crack growth, the type of crack growth, and the detailed nature of the associated fracture surfaces have been ascertained. Both materials exhibit essentially the same types of crack growth but the values of K_Ic for the rubber-modified material were usually significantly higher than those for the nmodified epoxy. The mechanisms for this increased toughness have been considered and a mechanism that accounts for all the observed characteristics has been proposed.     

Water absorption and disc cracking in urethane–methacrylate resins

Water absorption at 23 and 100°C has been studied in three materials based on a single type of urethane–methacrylate resin: the neat resin, a rubber-toughened blend containing 15 wt % of core-shell modifier, and a filled rubber-toughened resin containing 46 wt % silica plus 8 wt % core-shell modifier. In all six absorption experiments, water diffusion followed Fick's law. However, in neat resin at 100°C, the period of Fickian diffusion, during which the material appeared to reach saturation, was followed by an additional period of water uptake, which was accompanied by formation of internal disc cracks up to 1 mm in diameter. At both 23 and 100°C, fracture of water-saturated neat resin was defect dominated: cracks were initiated at inorganic impurities between 40 and 80 μm in diameter. The adverse effects of water are attributed to hydration and consequent swelling of these insoluble impurities. No internal cracking was detected in either the rubber-modified or hybrid resin, which have higher a K_ICs than the neat resin. © 1994 John Wiley & Sons, Inc.     

Use of solution crystallization analysis by laser light scattering for studying the solution crystallization of various Ziegler–Natta‐catalysed polypropylenes

Solution crystallization analysis by laser light scattering (SCALLS) involves the observation of the scattering of diode mercury laser lamp light after it passes through a polymer solution. An increase in turbidity occurs when the hot polymer solution is cooled and the polymer starts to crystallize out of solution. This causes a decrease in the amount of laser light that can pass through the solution and an increase in the amount of scattered light. The reverse of this process leads to the turbidity decreasing with an increase in temperature. According to this concept, it is possible to follow the solution crystallization of various polypropylenes under controlled cooling. In this study, SCALLS was able to differentiate between different isotactic and syndiotactic polypropylenes with similar chemical structures, but different tacticity and molecular weights. Furthermore, SCALLS provided good crystallization information that is similar to that from crystallization analysis fractionation and temperature rising elution fractionation. In addition, SCALLS can be used as a quantitative tool for the measurement of weight fractions during dissolution. © 2014 Society of Chemical Industry     

Ethylene–methacrylic acid copolymers as stress whitening suppressants in polypropylenes

Impact-modified polypropylenes were prepared by incorporating copolymers of ethylenemethacrylic acid (E-MAA) with different cations (zinc or sodium) and varying degrees of neutralization. These blends gave low stress whitening on impact. This phenomenon was due to the unique morphology of the blend. It was found that unneutralized acid copolymer and the zinc ionomer formed chainlike structures in the polypropylene matrix. These uniform chains crisscrossed the polypropylene matrix providing impact strength to the matrix. The matrix deformed on impact by the shear yielding mechanism, thus suppressing stress whitening. The impact modifier in the matrix did not form micro crazes in the matrix but formed several layers of crisscrossing chains. On the other hand, the sodium ionomer did not form chainlike structures. The impact modifier was dispersed evenly in the matrix. This type of morphology resulted in a higher degree of stress whitening. The failure on impact was due to crazing and not by shear yielding. This size of the impact modifier in the polypropylene matrix varied significantly depending on the melt processing equipment used. The dependence of polymer alloy mechanical properties on the composition has been studied to help in ionomer comparison.     

Direct correlation between aromatization of carbon-rich organic matter and its visible electronic absorption edge

The evolution of the electronic absorption edge of type I, II and III kerogen is studied by diffuse reflectance UV–Visible absorption spectroscopy. The functional form of the electronic absorption edge for all kerogens measured is in excellent agreement with the “Urbach tail” phenomenology. The Urbach decay width extracted from the exponential fit within the visible range is strongly correlated with the aliphatic/aromatic ratio in isolated kerogen, regardless of the kerogen type. No correlation is found between the decay width and the average size of aromatic clusters, which is explained in terms of a non-linear increase in optical absorption with increasing size of the aromatic clusters determined by ¹³C NMR. Further, absorption spectra calculated with density functional theory calculations on proxy ensemble models of kerogen are in excellent agreement with the experimental results. The correlation of the decay width with conventional maturity indicators such as vitrinite reflectance is found to be good within a particular kerogen type, but not consistent across different kerogen types, reflecting systematic variations in bulk composition for different type kerogen types with the same vitrinite reflectance. Thus, diffuse reflectance visible absorption spectroscopy is presented as a rapid, calibrated and non-destructive method to monitor both the maturity and the chemical composition of kerogen. The chemical insight of kerogen in relation to its optical absorption provided by this methodology may serve for rapid screening of kerogen for electronics and optical devices in place of functionalized produced carbon.     

Influence of β nucleation on the mechanical properties of isotactic polypropylene and rubber modified isotactic polypropylene

The tensile and fracture behaviour of neat α and β nucleated isotactic polypropylene and rubber-modified α and β nucleated isotactic polypropylene has been investigated at test speeds of 0.0001-10 ms⁻¹ in the temperature range −30 to +60 °C. The presence of the β phase had little effect at low temperature. However, at +25 and +60 °C, it increased the speeds corresponding to the ductile-brittle transition in the neat polymer by more than three decades. This behaviour has been linked to changes in microdeformation mechanisms observed at the lamellar and spherulitic level, an increase in cavitational deformation in tensile tests and an increase in the strength of the β relaxation in dynamic mechanical spectra. In the blends, the presence of the β phase led to somewhat higher energy dissipation in regimes of ductile fracture. However, the ductile-brittle transitions were not significantly affected. The modifier phase was therefore inferred to control the initiation and propagation of the plastic zone ahead of the crack tip during fracture.     

Deformations- und Bruchmechanismen in mehrphasigen Polymersystemen

Firstly a short survey is given on the deformation and fracture mechanisms which are essential with respect to the mechanical behaviour of thermoplastics, i.e. on the quasi-brittle fracture, the fracture after shear yielding, and the fracture after yielding owing to crazes. Then the general fracture and flow criteria are treated that are applicable to polymer materials under multiaxial stress. In rubber-modified polymer systems the initiation and the growth of crazes work as the most important deformation mechanisms. Therefore the problems relating to them are discussed more detailed. Since the mechanical properties of rubber-modified systems are strongly dependent on the type and the morphology of the rubber phase, the next chapter deals with the problems in this field. In this connection also the interactions between the two deformation mechanisms—shear yielding and deformation by crazes—are important Finally a historical survey on the observations and theories of rubber toughening is given in an annex.     

Determination of the fracture toughness of thermoformed polypropylene cups by the essential work method

In this work the anisotropic fracture behavior of neat and rubber-modified polypropylene cups induced by a vacuum thermoforming process is studied. The effect of different draw-ratios is also examined. An elasto-plastic fracture mechanics approach, based on the method of the essential work of fracture, is applied to samples cut from the thermoformed cups both longitudinally and transversally to the drawing direction. For all the products examined a strong anisotropy in the fracture behavior is observed. The fracture resistance for cracks propagating along the drawing direction is lower than in the transverse direction, this fracture anisotropy being enhanced at higher draw-ratio. The presence of the rubber particles results in an increase in the fracture toughness for cracks running transversally to the drawing direction, but, at the same time, it seriously reduces the fracture resistance for cracks propagating along the drawing direction. In order to better understand the dependence of the fracture behavior upon the processing conditions and material structure, dynamic mechanical thermal analysis, transmission electron microscopy, and X-ray diffraction measurements are also carried out.     

Monitoring Delamination Progression in Thermal Barrier Coatings by Mid-Infrared Reflectance Imaging

Mid-infrared (MIR) reflectance imaging is shown to be a reliable diagnostic tool for monitoring delamination progression in thermal barrier coatings (TBCs). MIR reflectance imaging utilizes the maximum transparency of TBCs in the 3–6 μm wavelength region to probe below-surface delamination crack propagation that is typically hidden from visible wavelength inspection. The image contrast that identifies delamination progression arises from the increased reflectance produced by a large component of total internal reflection at the TBC/buried-crack interface. Imaging was performed at a wavelength of 4 μm to take advantage of the relatively high transmittance of plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) TBCs along with a desirable relative insensitivity to potentially interfering absorptions by atmospheric constituents at that wavelength. A key advantage of MIR reflectance imaging over competing techniques is that it is sensitive to delamination progression even at very early stages before delamination cracks start linking together; therefore, TBC health assessment can be achieved throughout the life of the TBC well before TBC failure is imminent. Examples are presented to demonstrate monitoring delamination progression by MIR reflectance imaging in 8YSZ TBC-coated specimens subjected to furnace cycling to 1163°C. The experimental results were in good agreement with reflectance values predicted by a four-flux Kulbelka–Munk approximation applied to the extreme cases of a completely adherent and a completely detached TBC. Practical considerations, including potential interfering effects from surface contamination, sintering, and erosion are discussed.     

Interfacial studies in CTBN-modified epoxies

Rubber particle cavitation and concomitant shear deformation of the matrix is known to be a major source of toughening in rubber-modified epoxies. The role of the rubber-matrix interface in this toughening mechanism, however, is not well studied. It has been claimed by Chen and Jan [Polym. Eng. Sci., 31,577 (1991)] that introduction of a ductile interphase around the rubbery phase enhances plastic dilation of particles and thus contributes to fracture energy of modified blend. In spite of this promising development in rubber toughening, very few studies on the use of ductile interfaces to improve the fracture resistance of rubber-modified polymers have been initiated. The objective of this investigation is to examine the role of ductility of interface on the fracture toughness of rubber-modified epoxies. Both ductile and rigid interphases are incorporated around CTBN particles in a DGEBA epoxy matrix via end-capping of rubber with epoxy monomers different from that of the matrix. The results of this investigation suggest that introduction of a ductile interphase may indeed further improve the crack growth resistance of material under certain test conditions. In contrast, introduction of the rigid interphase, in the system studied, promoted interfacial debonding and plastic dilation but did not alter the mechanical performance of the rubber-modified blend. © 1995 John Wiley & Sons, Inc.     

Rapid absolute diffuse spectral reflectance factor measurements using a silicon-photodiode array

The absolute diffuse reflectance factors of white standard reference materials have been measured in d/0 geometry (Sharp–Little method) over the visible spectral range using a silicon-photodiode array. This method reduces the measuring time to a few seconds to obtain complete spectral reflectance factor data from 380–780 nm in the visible range. The effects of the openings and the wall thickness at the sample port onto the spectral reflectance factors were considered to get more accurate results. The precision of the diffuse reflectance factors in our system was 0.1% in the wavelength region longer than 550 nm and 0.4% in that shorter than 400 nm. We have obtained the absolute diffuse reflectance factors in the visible range of two kinds of barium sulfate, and of pressed polytetrafluoroethylene (PTFE) at three different densities. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 275–279, 1997     

Reflection of light from semi‐infinite absorbing turbid media. Part 1: Spherical albedo

The purpose of this article is to study the accuracy of a number of simple approximate equations for the spherical albedo r (or the hemispherical reflectance under diffuse illumination conditions) of semi‐infinite light scattering absorbing media, using numerical solutions of the nonlinear integral equation for the reflection function of a semi‐infinite turbid medium, as formulated by V. A. Ambartsumian. We find that the van de Hulst approximation provides the most accurate approximation for the diffuse reflectance r under diffuse illumination conditions. The value of r depends almost exclusively on the value of the similarity parameter , where ω₀ is the single scattering albedo and g is the asymmetry parameter. A simple approach to derive the normalized absorption spectra of particulate matter from reflectance measurements is proposed. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 491–497, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20262     

Temperature dependence of rheological properties of poly(methyl methacrylate) filled with silica nanoparticles

Creep-recovery experiments up to the steady state were performed on neat poly (methyl methacrylate) and on composites filled with 2.1 vol.% silica nanoparticles in order to get information on the long retardation times that occur due to polymer-particle interactions. The temperature dependence of the elasticity was investigated, varying the temperatures between 170 °C and 200 °C. For the neat polymer it was found that it behaves thermorheologically simple, whereas the composite exhibits a thermorheological complexity. An interpretation of these findings can be given, if the corresponding retardation spectra are regarded. The interactions between the polymer molecules and the particle surface is reflected by a particular maximum at longer retardation times, which exhibits a different temperature dependence compared to the spectra of the unfilled polymer matrix. This thermorheological complex behaviour is not seen in the usual dynamic-mechanical measurements down to angular frequencies of ω = 10⁻² s⁻¹. If the frequency range of the dynamic moduli is extended, however, by making use of the retardation spectra, a thermorheological complexity can be found, too. These results demonstrate that appropriate experimental time windows have to be applied to obtain a comprehensive picture of the rheological behaviour of nano particle-filled polymer melts.     

Characterization of Poly(Aminosiloxane) Surface Chemistry on Aluminum Oxide

N-2-aminoethyl-3-aminopropyltrimethoxysilane (AAPS) was shown to react with aluminum oxide powder to form an amine/carbonate salt, as observed by diffuse reflectance infrared spectroscopy (DRIFT) and thermogravimetric analysis with mass spectroscopy (TGA-MS). TGA-MS, together with electron spectroscopy for chemical analysis (ESCA), reveal that the stoichiometric ratio of amine salt to free amine is higher on the surface of aluminum oxide powder than in a comparable neat film. In addition, TGA-MS shows that a nonstoichiometric ratio of CO₂H₂O is evolved upon heating the surface-treated powder (4.5/1), whereas the neat film evolves CO₂/H₂O at a ratio near unity. The high fraction of protonated amines, together with the higher ratio of CO₂/H₂O in the presence of alumina, is consistent with a proposed bonding mechanism which involves carbonate bridging between protonated amines and hydroxyl sites on the aluminum oxide surface.