Real Processing Conditions Research Articles

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

Cobalt nanoparticles play an important role as catalysts for the Fischer–Tropsch synthesis, which is an attractive route for production of synthetic fuels. It is of particular interest to understand the varying conversion rate during the first hours after introducing synthesis gas (H2 and CO) to the system. To this end, several in situ characterization studies have previously been done on both idealized model systems and commercially relevant catalyst nanoparticles, using bulk techniques, such as X-ray powder diffraction and X-ray absorption spectroscopy. Since catalysis takes place at the surface of the cobalt particles, it is important to develop methods to gain surface-specific structural information under realistic processing conditions. We addressed this challenge using small-angle X-ray scattering (SAXS), a technique exploiting the penetrating nature of X-rays to provide information about particle morphology during in situ experiments. Simultaneous wide-angle X-ray scattering was used for monitoring the reduction from oxide to catalytically active metal cobalt, and anomalous SAXS was used for distinguishing the cobalt particles from the other phases present. After introducing the synthesis gas, we found that the slope of the scattered intensity in the Porod region increased significantly, while the scattering invariant remained essentially constant, indicating a change in the shape or surface structure of the particles. Shape- and surface change models are discussed in light of the experimental results, leading to an improved understanding of catalytic nanoparticles.

Large amplitude oscillatory shear of xanthan gum solutions. Effect of sodium chloride (NaCl) concentration

Large amplitude oscillatory shear (LAOS) results are shown to be useful to describe the mechanical behaviour of materials at large deformations, well beyond the linear viscoelastic region, which are closer to real processing conditions. We illustrate the applications of LAOS with xanthan gum aqueous dispersions at different NaCl concentrations, on account of the great technological interest in this bacterial polysaccharide. LAOS is shown to be much more sensitive than small amplitude oscillatory shear (SAOS) to the influence of NaCl concentration. This is illustrated by a complete rheological characterisation of the system by means of both full-cycle (average elastic modulus and dynamic viscosity) and local methods (strain-hardening and shear-thickening ratios). The different rheological behaviours observed were related to the microstructures of the xanthan gum molecules as a function of the NaCl content.

Age-dependent face detection and face categorization performance.

Empirical studies on the development of face processing skills with age show inconsistent patterns concerning qualitative vs. quantitative changes over time or the age range for peak cognitive performance. In the present study, we tested the proficiency in face detection and face categorization with a large sample of participants (N = 312; age range: 2-88 yrs). As test objects, we used so-called Mooney faces, two-tone (black and white) images of faces lacking critical information of a local, featural and relational nature, reflecting difficult real world face processing conditions. We found that performance in the assessment of gender and age from Mooney faces increases up to about age 15, and decreases from 65 years on. The implications of these findings are discussed in the light of classic and recent findings from face development literature.

Flow‐enhanced Crystallization Kinetics of iPP during Cooling at Elevated Pressure: Characterization, Validation, and Development

Using dilatometry combined with shear flow at conditions comparable to realistic processing conditions, the flow‐induced crystallization of polymers is modelled. The model describes the kinetics of quiescent nucleation, flow‐enhanced point nucleation, fibrillar growth, and the time evolution of the dimensions of the resulting crystalline structures. The growth rate of nuclei is coupled to the backbone stretch of a mode with a relaxation time representative of the average of the molecular weight distribution. The eXtended Pom‐Pom (XPP) model is used to calculate the backbone stretches from flow conditions. Three important model parameters are determined over a broad range of temperatures, pressures, and shear rates for a fixed shear time; a prefactor to the creation rate of flow‐induced nucleation, a prefactor to the shish growth rate, and the critical molecular stretch defining the transition between flow‐enhanced nucleation and flow‐induced crystallization of oriented fibrilar structures. Excellent agreement is obtained between calculated and experimentally determined crystallization kinetics of iPP. Moreover, the extended experimental dataset leads to an important adaption of the model, i.e., a new criterion for the initiation of shish growth.

Defect chemical modeling of Pd/ZnO Schottky junctions

We describe a comprehensive calculation procedure for modeling metal/semiconducting oxide Schottky junctions and present detailed model calculations of the electrostatic potential, defect distribution profiles, and energy band diagrams across Pd/ZnO Schottky junctions simulated for realistic processing conditions. The underlying approach involves self consistent numerical solution of Poisson's equation coupled with the defect equilibria of ZnO. According to our calculations the built-in voltage is predicted to be 0.63 or 0.57V and the space charge region width is predicted to be 0.61 or 2.46μm for undoped ZnO films grown at 800 or 700°C, respectively, and subsequently annealed at 450°C following the metallization step. Our calculation procedure can be readily extended to simulate other processing conditions and other material systems.

Flow Visualisation in Co-rotating Twin Screw Extruders: Positron Emission Particle Tracking and Numerical Particle Trajectories

Abstract Co-rotating twin-screw extruders are widely used compounding machines. They are mainly configured based on extensive experience and iterative approaches to optimise output and composite quality. The visualisation technology developed in the EU-project PEPTFlow allows visualisation of composite flow in twin-screw extruders under realistic processing conditions by tracking radioactive tracer particles in the polymer melt, using a specially developed camera system. This new approach allows polymer flow to be studied in different screw elements and screw configurations under realistic compounding conditions at normal temperatures and melt pressures. The paper presents the latest developments in the camera systems as well as the different ways to use and interpret the results. Detailed analysis of residence times and residence time distributions for standard compound screw elements, like kneading discs, conveying elements and reverse elements are presented. In addition for a better understanding of the flow field inside twin-screw extruders, numerical particle tracking is done. The Stokes equation, using XFEM method, are solved and the numerical RTD's (residence time distribution) are compared for various screw designs.

Numerical investigation of powder heating in coaxial laser metal deposition

The laser metal deposition process is characterised by the occurrence of mutually influencing phenomena. Particularly important for understanding particle deposition are the phenomena originated by the three-way interaction of the laser beam, the powder stream and the substrate, which in previous models have been consistently oversimplified or neglected. This work presents a numerical model useful for studying powder stream formation, powder heating and mass addition into the melt pool, as well as various interactions that occur during processing. Experimental work is performed to validate powder stream formation and heating, and particle addition to melt pool. Good agreement is found with the modelled results. It is revealed from this work that the role of the substrate is more significant than previously thought and that considering the beam–stream–substrate interrelations allows simulations closer to real processing conditions to be performed.

HEAT RESISTANCE OF G. STEAROTHERMOPHILUS AND C. SPOROGENES IN CARROT AND MEAT ALGINATE PUREES

The main objective of this study was to investigate the heat resistance of nonpathogenic, heat-resistant Geobacillus stearothermophilus and Clostridium sporogenes spores in meat and carrot alginate purees. Alginate is used as a viscosity modifier in liquid foods and has been used to fabricate thermally stable and firm simulated particles for biological validation studies of thermal processing, when conventional temperature gathering is not possible. Pureed carrot and meat were mixed with sodium alginate and inoculated with high concentrations of spores of G. stearothermophilus or C. sporogenes and filled into capillary tubes, flame sealed and heat treated in an oil bath for different times at selected temperatures. D values were computed from the slopes of log(N/N0) versus time, and z values from log(D) versus temperature curves. For meat alginates, D values for G. stearothermophilus ranged between 1.9 min and 40.8 min with a z value of 11.7C and D values for C. sporogenes ranged between 0.9 min and 28.7 min with a z value of 10.1C. For carrot alginates, D values for G. stearothermophilus ranged between 1.9 min and 42.6 min with a z value of 11.5C and D values for C. sporogenes ranged from 1.1 min and 31.0 min with a z value of 10.2C. The results were also fitted to Weibull model, but the model did not result in any better fit than the conventional first-order model. PRACTICAL APPLICATIONS Thermal process establishment is generally based on gathered time temperature data from test cans under real processing conditions. There are many situation like aseptic processing, continuous flow biaxial rotary processing, etc. in which such temperature measurements are often difficult. Biological validation is generally considered useful in such processes to validate the processes as well as computer simulations. Such concepts have been tried to some limited extent in the past. With new thermal processing equipment and processes surfacing time and again, such concepts need to be redesigned. In order to successfully use such applications, thermal destruction kinetics data under controlled conditions are needed. This study provides thermal destruction kinetics baseline data for one such study making use of alginate-impregnated meat and carrot-simulated particles. Further, the study compare two modeling procedures: the conventional first-order log-linear model versus the log-nonlinear Weibull models.

Calculation of the total lethality of conductive heat in cylindrical cans sterilization using linear and non linear survival kinetic models

There is growing evidence suggesting that inactivation of bacterial spores may follow the Weibullian model, of which the log linear relationship between survival ratio and time is just a special case. Where true, the time and not only the temperature dependence of the rate must be taken into account. Also, it is of interest to estimate spores survival not only at the coldest point but also throughout the whole container's volume. Numerical calculation on changing survival ratios was performed by combining the conductive heat transfer model with that of the nonlinear inactivation kinetics. Results are based on published linear and non linear inactivation parameters of Clostridium botulinum spores, typical thermal properties of solid foods and realistic thermal processing conditions. Results could be used to quantify the efficacy of thermal processes of solid products in terms of spores' residual survival ratio at the coldest point and in the container as a whole.

Modeling processing of silicone rubber: Liquid versus hard silicone rubbers

AbstractThe processing of hard and liquid silicone rubbers (LSR) are compared by means of modeling and simulation. The curing process for both, hard and liquid silicone, are modeled using the auto‐catalytic Kamal‐Sourour model and a nonlinear regression method is used to find the kinetic parameters. The fitted kinetic model is then combined with the heat balance equations to simulate real processing conditions. Both resins are compared in terms of process performance and consistency of the final part. The results show that even though hard silicone rubbers are less expensive resins, its processing conditions present several issues of consistency and quality control when compared with LSR. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119:1864–1871, 2011

Morphology of poly(ethylene terephthalate) blends: An analysis under real processing conditions by rheology and microscopy

AbstractThe present work describes the formation of co‐continuous phase morphologies in uncompatibilized and compatibilized poly(ethylene terephthalate) (PET)–poly(m‐xylene adipamide) (MXD6) and PET– poly(ethylene‐co‐vinyl alcohol) (EVOH) melt‐extruded blends. Phase continuity has been determined by using the Jordhamo relationship. Viscosity values, which are essential for the calculation of the phase continuity, have been obtained by capillary rheometry. Thermal behavior of the blends has been analyzed by employing differential scanning calorimetry and phase continuity has been investigated for the noncompatibilized and the compatibilized blends by scanning electron microscopy. PET–MXD6 blends [92.35:7.65 (v/v) and 84.5:15.5 (v/v)] and PET–EVOH blends [73.63:26.37 (v/v)] exhibit droplet‐in‐matrix phase morphology, whereas uncompatibilized PET–MXD6 [75.8:24.2 (v/v)] blend has a combination of rod‐like, droplet–matrix structure, and quasi‐interpenetrating network structure. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:173–184, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20156

Modelling the browning of bread during baking

In this work, we study the development of browning at bread surface during baking. Computer vision is applied to follow the progress of browning at surface, while the variations of temperature and water activity are obtained by numerical simulation of a mathematical model previously validated. The formation of the bread crust is a complex process where temperature and water content change continuously during baking, making browning a non-isothermal process occurring in a non-ideal system. Minimum requirements for initiation of colour formation are temperature greater than 120 °C and water activity less than 0.6. We apply a non-isothermal kinetics approach to model the browning development at bread surface during baking, where the variation of local temperature and water activity is taken into account. The methodology presented here is suitable for modelling and predicting browning during baking; model parameters can be estimated by using a non-ideal system closer to real processing conditions.

The effect of processing conditions on the durability of polymer products

The work discusses new possibilities of modifying the functionality of polymer products by changing their material structure during processing and consequently the time-dependent properties which define the durability of the final product. The research addresses two questions: 1) does current industrial-scale polymer processing equipment allow processing in conditions which enhance the nonlinear processes during structure formation; 2) what is the magnitude of the structural changes and what, consequently, are the time-dependent mechanical and other physical properties of the final polymer product which can be achieved by changing processing conditions in the industrial environment? By analysing the low density polyethylene (LDPE) extrudates produced with a laboratory extruder PolyLab OS, which simulates real industrial processing conditions, we observed that changing the processing conditions in the industrial environment improves the durability (time-dependency) of extrudates by several orders of magnitude. This opens new possibilities in the field of modifying the functionality of polymer products, and hence, better competitiveness on the world market.

Photodegradation of lauric acid at an anatase single crystal surface studied by atomic force microscopy

The photodegradation of lauric acid at an anatase single crystal surface was visualized using atomic force microscopy (AFM). Photooxidation was performed for lauric acid thin films with thickness about 80–90nm to simulate more realistic processing conditions rather than using submonolayer films. It was noticed that lauric acid deposited by spin coating technique formed domain structure at the TiO2 surface. The phenomenon of domain surface decrease without change in the film thickness was observed. This suggests that only molecules at the crystal–air–lauric acid contact line and extended therefrom were degraded.

Prediction of an organism's inactivation patterns from three single survival ratios determined at the end of three non-isothermal heat treatments

Traditionally, an organism's heat resistance parameters have been determined from a set of experimental isothermal survival data. Sometimes, however, even approximating an isothermal profile, and/or obtaining counts at sufficiently short time intervals, is extremely difficult for technical and logistic reasons. The problem would be avoided if the survival parameters could be calculated from the final survival ratios determined at the end of non-isothermal heat treatments with known temperature profiles. Theoretically, if the heat resistance were characterized by three unknown survival parameters, they could be extracted by solving three simultaneous dynamic survival curves' equations. In practice, because of the three equation's complexity – they are themselves the numerical solutions of three differential rate equations – and because the experimental final survival ratios might have a scatter, realistic estimates of the survival parameters require short cut and averaging methods for their calculation. Such a method has been tried with published dynamic inactivation data on Salmonella enteritidis and Escherichia coli. The concept was validated by the ability of the Weibullian–Log logistic model, whose three survival parameters had been obtained directly from final experimental survival ratios only, to predict entire non-isothermal survival curves that had not been used in the model's formulation. The methodology need not be restricted to Weibullian and simpler survival patterns but its practicality might be lost if there are more than three survival parameters. In principle, the same procedure can be extended to biochemical processes that occur during heat preservation, especially at very high temperatures. Estimating inactivation kinetic parameters without isothermal data could also facilitate the quantification of microbial survival under realistic processing conditions and in the actual food rather than in a surrogate medium.

New epoxy resins for printed wiring board applications

PurposeThis paper seeks to give an overview of problems arising with the change to lead‐free soldering and to give guidance on possible counter actions in the context of the chemical structure of the base material.Design/methodology/approachThe paper contains a number of correlations between different physical measurements and their impacts on real life processing conditions. The problem areas are highlighted and the corrective actions that need to be taken on the base materials are described. The impact of the choice of flame retardant on material properties is demonstrated.FindingsResults suggest that conventional resin systems seem to be still suitable for standard FR‐4 applications with only a few reflow cycles. Higher thermally resistant products are necessary for more complex structures that require multiple reflow cycles. There are basically two ways to increase the thermal resistance. Replace dicyandiamide by a phenolic hardener or change to a bromine‐free flame retardant. Both approaches are successful in raising the decomposition temperature, with the latter having the additional advantage of achieving better electrical performance and lower density.Originality/valueThe value of the paper lies in its ability to provide guidance on the critical base material properties. It describes the change in physical properties that laminates will see when moving up in temperature to facilitate lead‐free soldering. Selection criteria for base materials are given in order to neutralize the impact of the higher temperature.

Development of an in situ neutron-scattering facility for research and education in the mechanical behavior of materials

The present work is to establish a suite of instruments for studying the mechanical behavior of advanced materials using in situ neutron-scattering at the impending Spallation Neutron Source (SNS, The Oak Ridge National Laboratory), which will provide the most intense pulsed-neutron source in the world. The state-of-the-art in situ and real-time characterization instrumentation will be developed for VULCAN at SNS. The VULCAN diffractometer is designed to conduct fundamental studies in materials science and engineering with a focus on the mechanical behavior. The instrumentation described here will enable VULCAN to fulfill its full potential. The characterization capabilities to be developed will far surpass anything else available in the world. The simultaneous neutron diffraction and small-angle neutron-scattering (SANS) during mechanical testing will have a tremendous impact on the fundamental understanding of the mechanical behavior of materials. The successful development of the present instrumentation will give materials scientists many new and valuable capabilities for the fundamental study of advanced materials with complex multi-phase/-scale microstructures and various sizes/types (1) under large static/dynamic mechanical loads (including tension, compression, and torsion, i.e., real-world conditions), (2) at high temperatures, and/or (3) under chemical environments. Moreover, such capabilities will allow engineers to probe the behavior of materials and components under realistic operating and processing conditions.

Polymorphic transformation of l-glutamic acid monitored using combined on-line video microscopy and X-ray diffraction

Enhancement of process monitoring for detecting transformations of the organic solid state is an important, strategic area currently of substantial interest particularly to the pharmaceutical sector and, more generally, manufacturers of speciality chemical products. A feasibility study is reported in which a solution-mediated polymorphic transformation of l-glutamic acid (LGA) was monitored using, concurrently, both video microscopy accompanied by advanced image processing and, on-line X-ray diffraction. The applicability of these monitoring approaches, applied individually, has been demonstrated previously; however, it was useful to assess the relative sensitivity of the two techniques by their direct comparison, via simultaneous use, during application on-line to monitor a polymorphic transformation process. It was found that the onset of the polymorphic transformation, manifested as the point in time when crystals of the β phase of LGA were first detected, was elucidated as being significantly sooner via video microscopy. This reflects the fact that the concentration regimes of maximum sensitivity for the individual approaches are complementary, hence video microscopy provides considerable added-value allowing detection of the early stages of the transformation process. Currently, the upper bound on solids concentration that is compatible with extracting useful information about the phase composition using video microscopy, based on particle shape, is restricted. However, it is anticipated that improvements to both the experimental design and the image processing algorithms applied will substantially increase this upper bound allowing practical application under realistic processing conditions.

Ocena poprawki Bagleya na podstawie pomiarow w linii wytlaczarskiej

Bagley correction (eg) measurements usually are done using capillary rheometers. In this article a method of eg value determination on the basis of the measurements done in real processing conditions is presented. Extrusion head with exchangeable dies (Fig. 3, Table 2) installed to the single-screw extruder was used as a measuring device. Two commercial grades of low-density polyethylene (PE-LD) (Table 1) were used. The peculiarity of the action of plastifying system of an extruder, far different from plastifying system of capillary rheometer, forced us to elaborate the special measuring - computational procedure allowing to evaluate eg during the process of extrusion (Fig. 4-6). Bagley correction was determined for shear rate range from 27 s - 1 up to 629 s - 1 (Table 3). Ability of dies to be exchanged allowed estimating the effect of geometric elements of the channel on e B value (Fig. 7-9). On the basis of velocity profiles courses (Fig. 10 and 11) the interpretation of differences in Bagley correction value, dependently on PE-LD grades and measuring dies' dimensions, has been done.

Characterization and Modelling of Moisture Driven Interface Failures

Since moisture sensitivity level (MSL) tests are part of the international reliability qualification standards, all the microelectronics components/products have to pass these specifications. Therefore, it is important to be able to efficiently and accurately characterize and predict the moisture related material and interface behaviour in the real manufacturing, processing, testing and application conditions. This paper focuses on our research efforts in and results of developing and verifying efficient and accurate characterization and modelling methods for moisture driven interface failures. The methodology incorporates the characterization of the strength of critical interfaces as function of temperature and humidity using the four-point bending test. Using multi-physics-based Finite Element (FE) models, which take into account both the moisture and thermo-mechanical related failure mechanisms, enables the prediction of interface failures. The developed methodology is used for understanding the observed interface failures of an industry carrier.