Wide Range Of Process Conditions Research Articles

First evaluation of a multicomponent flue gas cleaning concept using chlorine dioxide gas – Experiments on chemistry and process performance

This work has investigated a multi-pollutant flue gas cleaning concept based on oxidation using chlorine dioxide (ClO2) gas with subsequent absorption. The chlorine dioxide gas converts the relatively insoluble nitric oxide (NO) to the more soluble nitrogen dioxide (NO2). This makes a downstream wet scrubbing process feasible for simultaneous removal of sulphur oxides (SOx) and nitrogen dioxide (NO2).An experimental evaluation of the proposed process using chlorine dioxide gas has been performed on a laboratory scale. The experimental setup, designed and built by Akzo Nobel, consists of a reactor for oxidation, a flue gas condenser and a wet scrubber. The results show that ClO2 gas oxidises NO with high efficiencies under a wide range of process conditions, also in the presence of sulphur dioxide (SO2). The more ClO2 gas is added, the higher the degree of NO oxidation and the total nitrogen oxides (NOx) removal efficiency becomes. The results also show that the presence of water strongly increases the removal of SO2, which is believed to be an effect of liquid phase nitrogen-sulphur interactions. The absorption solution, sodium carbonate and sodium sulphite, is efficient in removing NOx (especially NO2) from the oxidised flue gas. The total NOx reduction at 0.6 ClO2:NO mole ratio and subsequent wet scrubbing is between 79% and 94%, depending on the process conditions used. The total SO2 reduction in the scrubber is between 97% and 100% independent of ClO2 gas addition. Furthermore, the total NOx balance shows that the major part of the NOx is converted to nitrate in the condensate liquor and as nitrite in the absorption solution. A higher ClO2 gas addition and a higher reactor temperature convert more of the NOx to nitrite in the absorption solution.

A molecular lump based model for simulation of industrial naphtha hydro treators

A detailed, molecule-based kinetic model has been developed to simulate industrial naphtha hydro treators. A feed characterization module has been developed to calculate the composition of pre-defined pure molecules representing the feed quality without any detailed experimental component analysis. Feed naphtha is represented by a pre-defined set of 95 pure molecules, from carbon numbers C5 to C11, and the proportion of these components is calculated using an optimization algorithm so as to match the physico-chemical properties of the mixture with those of naphtha, as measured in the laboratory. The output from this optimization model is used as a direct input to a model of a hydro treating reactor. The main reactions occurring in the hydro treator, such as hydro desulfurization reactions and olefin saturation reactions, are modeled. The kinetic parameters for these reactions have been estimated from a comprehensive set of experimental pilot plant data spanning a wide range of process conditions. The kinetic model quantitatively predicts the exit composition, temperature rise and pressure drop in the catalyst bed for a range of conditions for two industrial refinery units.

Analysis of Effect of Machining Parameters During Electrical Discharge Machining Using Taguchi-Based Multi-Objective PSO

The present contribution describes an application of a hybrid approach using response surface methodology (RSM) and particle swarm optimization (PSO) for optimizing the machining parameters in electric discharge machining (EDM) of compo casted Al6061/ cenosphere AMCs. Compo casting processing route was employed to prepare the AMCs. Each experimentation in EDM was performed under different machining conditions of Peak Current (Amp), Pulse on time ([Formula: see text]s), and Flushing Pressure (bar). Performance characteristics such as material removal rates (MRRs), surface roughness (SR), and electrode wear rates (EWRs) were evaluated. A Taguchi L27 orthogonal array was considered to plan the experimentation and RSM was applied to model the inter relationship between the input process parameters and responses. A mathematic model has been developed to provide a fitness function to PSO by unifying the multiple responses. Finally, PSO was used to predict the optimal settings of the processing condition for the multi-performance optimization of the EDM operation. The experimental observations confirm the feasibility of the strategy and are in good accordance with the predicted value over a wide range of processing conditions employed in the process.

Properties of binderless coal slime briquette via hydrothermal hot pressing dewatering

ABSTRACTDewatering and binderless briquetting of Liulin coal slime by hydrothermal hot pressing (HHP) method were studied under a wide range of process conditions. Fourier transform infrared spectroscopy and XRD were used for characterization. Results indicated that the optimal conditions were a pressure at 4.2 Mpa, a temperature of 150℃, and additive NaOH at 3.0%. The increase of temperature caused the loss of absorbed water in clay minerals and also some organic species having functional groups, such as -CH3 and -CH2. The alkalinity caused the loss of oxygen functional groups and the formation of hydroxysodalite, which reduced the water storage capacity and promoted coal particles agglomeration.

Controlled foam generation using cyclic diphasic flows through a constriction

Numerous industrial and academic applications of liquid foams require a fine control over their bubble size distribution and their liquid content. A particular challenge remains the generation of foams with very small bubbles and low liquid content. A simple technique which fulfils these different criteria, the “double-syringe technique”, has been exploited for decades in hospital applications. In this technique, the foaming liquid and gas are pushed repeatedly back and forth through the constriction that connects two syringes. After having motorised the technique we investigate here the influence of the different processing conditions on the obtained foam properties in a quantitative manner. We show that this technique is unique in producing foams with the same characteristic bubble size distributions over a wide range of processing conditions (tubing, fluid velocities,...), making it an ideal tool for controlled foam generation. In contrast to other techniques, the liquid fraction in the double-syringe technique can be varied without impacting the bubble size distribution. Using high-speed imaging we show that bubbles are dispersed in the aqueous phase at two different places in the device via a hitherto unreported fragmentation mechanism. We put in evidence that the obtained bubble size distributions are largely independent of most processing parameters with the exception of the geometry of the constriction and the foam formulation. We put forward a first analysis of the non-dimensional numbers of the flow and compare our results with bubbles size distributions obtained from fragmentation processes. Future work on simplified model systems is required to explain the observed mechanisms.

Assessment of Corn Quality for Nixtamalization: Development of a Convenient Bench‐Top Cooking Method

A convenient small‐scale laboratory method that can be used to simultaneously analyze multiple samples was developed to rapidly assess suitability of corn for nixtamalization. This new 100 g method was developed based on a previously reported 500 g laboratory process that has been shown to mimic the industrial nixtamalization process. The two methods were compared for nixtamal moisture, dry matter loss, degree of pericarp removal, and gelatinization properties of the cooked corn. The heating and cooling profiles of the 100 g method were developed using the 500 g method, by monitoring temperature every 30 s during cooking and steeping. Nixtamalization was conducted with a 1:4 corn/water ratio, with 1% lime. A response surface central composite design was used to model a wide range of processing conditions for the two methods: cook temperature (80–95°C), cook time (3–40 min), and steep time (2–12 h). Parameter estimates and response surfaces were compared, and predictive models were fitted. The response surface models for the two methods were not significantly different for nixtamal moisture, dry matter loss, and gelatinization enthalpy; there was an overlap of the 90% Bonferroni confidence intervals (P < 0.05, r2 > 0.7). The bench‐top 100 g nixtamalization process can successfully mimic the 500 g method over a wide range of processing conditions.

Development of extrusion technology for magnesium alloy ZE20

Abstract The development of extrusion technology for a new magnesium alloy ZE20 (2.4 %wt. Zn, 0.2 %wt. Ce) requires evaluation of a model for the alloy’s deformation behavior. In this study, compression tests have been carried out for a wide range of temperatures (350-425 °C) and strain rates (0.01-10.0 s -1 ) corresponding to a wide range of extrusion parameters. An inverse analysis was applied to produce accurate true stress-strain data. A Johnson-Cook type flow stress model was selected and flow curves for a wide range of processing conditions have been developed. Friction has a significant influence on thermomechanical process parameters and increases deformation temperature. A comparison with compression test results was performed. This metallurgical knowledge was then applied together with the calibrated ZE20 material model to the design of an industrial direct extrusion process of a customized hollow beam. Both the indirect and direct extrusion processes were designed, numerically simulated, and carried out for development of new numerical DEFORM-3D TM model. It has been demonstrated that the numerical model accurately predicted high-strain plastic flow stress values as compared with experiments for the new alloy as well as strain, strain rate, and temperature values within the formed extrudate.

Modelling and monitoring of out-time and moisture absorption effects on cure kinetics and viscosity for an out-of-autoclave (OoA) prepreg

Out-time and moisture absorption during out-of-autoclave (OoA) prepreg preparation are generally unavoidable. The resulting cross-linking and increase in resin viscosity can prevent sufficient flow into the fiber tows during processing and cause porosity. In this study, efficient modelling and in situ methods to monitor cure kinetics and viscosity were developed to account for the effects of out-time and absorbed moisture. First, a commercial OoA prepreg was conditioned to specific levels of out-time and relative humidity (RH). Property data were obtained from differential scanning calorimetry (DSC) and rheometry and used to develop cure kinetics and viscosity models for a wide range of process conditions, initial out-times, and humidity conditions. The dielectric signals were correlated to the measured data and used to demonstrate real-time monitoring of resin state during cure. The predictive models were then used to understand the influence of out-time and absorbed moisture on resin viscosity during consolidation of OoA prepreg.

Reaction mechanism and kinetic modeling for the hydrodeoxygenation of triglycerides over alumina supported nickel catalyst

The present work provides a systematic study to delineate the reaction mechanism and develop a mechanistic kinetic model for the hydrodeoxygenation (HDO) of triglycerides (TG) over alumina supported nickel catalyst. The HDO of 1:2 molar mixtures of tripalmitin and tristearin was studied in a batch reactor over a wide range of process conditions. The results showed that TG instantaneously converted to respective fatty acids. The fatty acids further converted to the fatty aldehydes. The fatty aldehydes, then, rapidly converted to alkanes by two parallel reaction pathways. The decarbonylation of fatty aldehyde (RP-I) was the dominating route compared to the reduction of the fatty aldehyde to fatty alcohol followed by its dehydration and hydrogenation (RP-II). A mechanistic kinetic model was developed based on the observed reaction pathway to correlate the experimental results. The rate constants for the conversion of palmitic acid and stearic acid to alkanes were matched closely with each other thereby demonstrating that HDO is independent of fatty acid chain length. The developed kinetic model was further validated using experimental data at various hydrogen-to-nitrogen mole ratios in the gas phase. Furthermore, the rate constants obtained for various catalyst loadings were correlated by a linear equation with zero intercept.

Grain size versus microstructural stability in the high strain rate superplastic response of a severely friction stir processed Al-Zn-Mg-Cu alloy

An Al-Zn-Mg-Cu, Al 7075, alloy in an overaged state was subjected to friction stir processing (FSP) using a wide range of processing conditions. The goal was to diminish the heat index, increasing therefore the processing severity. Additionally, two backing anvils were selected that strongly influence the heat extraction rate. Grain sizes obtained by transmission electron microscopy were situated in the range 210–820nm. High temperature tensile tests and the scanning electron micrographs of the topography of the tensile samples after testing revealed that grain boundary sliding (GBS) operated at an initial strain rate of ε̇=10−2s−1 in a wide range of temperatures for the processed alloy. That temperature window was wider and situated at lower temperatures for the finer grain sizes. The high processing severity imposed to create such fine microstructures introduces high values of stored energy in the material, which is the driving force for the increasing grain coarsening at high temperatures. This fact limited the operation of GBS at the highest tested temperatures in some conditions. An optimum balance between grain refinement and microstructural stability was obtained using a low heat index, corresponding to the processing conditions of ω=1000rpm, V =500mm/min, and the use of refrigerated backing anvil.

(Invited) Optimal Target Functions for Epitaxy in New Channel Applications Such As Horizontal Gate-All-Around (h-GAA) Device Architectures Using Nano-Sheets or Nanowires

Continuation of Moore’s law, an observation of the economics and technological progress in semiconductor manufacturing, is becoming increasingly challenging due to many factors, since it is getting harder to advance the 3 technological P’s and the economic P: Performance/Watt, Precision, Perfection and Price/Transistor [JY Chen, Proc. of SPIE Vol. 8522 (2012) 852202]. Epitaxy allows precise control of the critical dimension(s) in new channel applications (h-GAA device architectures and epitaxially defined FinFETs), directly impacting Device Performance and Yield (DPY) and Cost of Ownership (CoO). "Target functions" include: (1) Uniformity and repeatability (perfection & precision) of thickness and composition, (2) abruptness of SL stack (precision & perfection), (3) crystalline perfection (absence of gas phase nucleation potentially causing defects), (4) Cost of Ownership (CoO) including precursor conversion (determining precursor consumption and waste) and throughput (TP) {wph=60min/(toverhead + tprocess)}, and (5) only applicable to self-aligned selective epitaxial growth (SEG) processes on structured topographies: (a) selectivity, (b) macro- and micro loading, (c) doping level & distribution (d) different shapes: faceting vs. conformality (perfection). Tight control of the critical dimension (epitaxial thickness) its distribution WiW (uniformity, perfection) and WtW (repeatability, precision) are essential for high volume manufacturing [WS Yoo, RTP’06, pp. 159-175]. Analyzing growth rate dependence on temperature (T) with an Arrhenius plot, two distinct growth regimes can be identified: (a) In the ‘low-T’, reaction rate (kinetic) limited regime growth rate is limited by the density of ‘free’ surface sites (1-σH/Cl) available for precursor absorption, thus by the rate of H2/HCl desorption from the surface. Precursor is offered in abundance, conversion rate is low, growth is slow and film uniformities are strongly correlated with thermal uniformity, making T-control (WiW & WtW) the single most important item. {Massive and slow hot wall systems operating in thermal equilibrium provide such T conditions, but challenges include (i) deposit build-up on hot quartz tubes, (ii) sub-optimal pre-clean strategy and difficult Q-time control may result in defective films and degraded particle performance.} (b) In the ‘high-T’, mass flow limited regime growth is fast and only limited by precursor supply and is quite in-sensitive to T variations/excursions (WiW & WtW). High precursor conversion accompanied with depletion of reactants, as they flow over hot surfaces, mandates wafer rotation and a ‘favorable’ flow pattern in order to achieve good WiW uniformities. Precision & Perfection (impacting DP&Y): The interface abruptness of the as grown SiGe/Si super-lattice (SL) is mainly controlled by Ge surface segregation, rather than bulk inter-diffusion. Surface segregation, a thermally activated exchange reaction between surface and sub-surface atoms, is governed by (a) phonons (lattice vibrations => growth temperature), (b) ‘burying rate’ (time constant => growth rate) and (c) H/Cl surface coverage (acting as surfactants). Process flows minimizing channel material loss (thinning and tapering) require: (a) SL stacks with sharp ‘as-grown’ alloy transitions and sufficient material contrast [Δ Ge], (b) well controlled thermal budget (T*t) and (c) a wet or dry etch chemistry (process) with high etch rate selectivity for sacrificial layer removal. Conversely, (i) imperfect alloy transitions, (ii) excessive thermal budget causing inter-diffusion (or even strain relaxation in metastable strained SiGe layers) and (iii) poor etch rate selectivity will cause deleterious channel thickness variations ultimately leading to increased device variability. Requirements for crystalline perfection of channel materials are far more stringent compared to S/D SEG. The tolerance for crystalline defects is virtually zero, requiring strict suppression of any gas phase nucleation or excessive reactor wall coating. Cost of Ownership (CoO): Precursor conversion (and related precursor consumption = cost) speaks for itself. Reducing precursor flow and reducing deposition on hot parts, other than the wafer itself, yields cleaner processing (and likely fewer particles) and might allow reducing intensity and/or frequency of chamber cleaning time. Throughput (TP) is impacted by both, overhead and processing time, thus isothermal processing (or within a small T range for low-T chamber clean, wafer load, pre-epi surface treatment, epitaxial growth and unload) minimizes timefor T ramps and T stabilization. Thermal budget is reduced, thanks to low-T pre-epi surface preparation and reduced processing time (faster growth). Strategies to meet all essential value criteria have been developed and experimentally demonstrated for a single wafer tool. Epitaxial process conditions have been studied over a quite wide range of process conditions. Repeatability (precision) of SiGe & Si thickness, [Ge] and its WiW distributions (perfection) as well as crystalline perfection have been demonstrated using Spectroscopic Ellipsometry and Light Scatterometry (SP3, <32nm defect size). Composition & thickness are controlled by HR-XRD. STEM is used to assess abruptness (perfection) of SiGe/Si SL interfaces and layer thicknesses (precision).

The development of a growth regime map for a novel reverse-phase wet granulation process

The feasibility of a novel reverse-phase wet granulation process has been established and potential advantages identified. Granule growth in the reverse-phase process proceeds via a steady state growth mechanism controlled by capillary forces, whereas granule growth in the conventional process proceeds via an induction growth regime controlled by viscous forces. The resultant reverse-phase granules generally have greater mass mean diameter and lower intragranular porosity when compared to conventional granules prepared under the same liquid saturation and impeller speed conditions indicating the two processes may be operating under different growth regimes. Given the observed differences in growth mechanism and consolidation behaviour of the reverse-phase and conventional granules the applicability of the current conventional granulation regime map is unclear. The aim of the present study was therefore to construct and evaluate a growth regime map, which depicts the regime as a function of liquid saturation and Stokes deformation number, for the reverse-phase granulation process. Stokes deformation number was shown to be a good predictor of both granule mass mean diameter and intragranular porosity over a wide range of process conditions. The data presented support the hypothesis that reverse-phase granules have a greater amount of surface liquid present which can dissipate collision energy and resist granule rebound resulting in the greater granule growth observed. As a result the reverse-phase granulation process results in a greater degree of granule consolidation than that produced using the conventional granulation process. Stokes deformation number was capable of differentiating these differences in the granulation process.

The effect of materials, process settings and screw geometry on energy consumption and melt temperature in single screw extrusion

Polymer extrusion is an energy intensive production process and process energy efficiency has become a key concern in the current industry with the pressure of reducing the global carbon footprint. Here, knowledge of the pattern of energy usage and losses of each component in the plant is highly useful in the process energy optimization. Moreover, it is essential to maintain the melt quality while improving the energy efficiency in polymer processing. In this work, an investigation was made on the total energy consumption, drive motor energy consumption, power factor and the melt temperature profile across the die melt flow (as an indication of the melt thermal quality) of an industrial scale extruder with three different screw geometries, three polymer types and wide range of processing conditions (altogether 135 different processing situations were observed). This aims to widen the knowledge on process energy and thermal behaviors while exploring possible correlation/s between energy demand and melt quality (in terms of melt temperature fluctuations across the melt flow). The results showed that the level and fluctuations of the extruder’s power factor is particularly dependent upon the material being processed. Moreover, it seems that there is a relation between the level of energy demand of the heaters and the level of melt temperature fluctuations. While the extruder specific energy consumption decreases with increasing screw speed, specific energy consumption of the drive motor may have either increasing or decreasing behavior. Overall, this study provides new insights in a wide range on process energy demand and melt thermal quality in polymer extrusion. Moreover, further research is recommended to establish strong correlation/s between process energy consumption and melt thermal quality which should help to enhance process control and hence the product quality in single screw polymer extrusion.

Cellulolytic enzyme expression and simultaneous conversion of lignocellulosic sugars into ethanol and xylitol by a new Candida tropicalis strain.

BackgroundLignocellulosic ethanol production involves major steps such as thermochemical pretreatment of biomass, enzymatic hydrolysis of pre-treated biomass and the fermentation of released sugars into ethanol. At least two different organisms are conventionally utilized for producing cellulolytic enzymes and for ethanol production through fermentation, whereas in the present study a single yeast isolate with the capacity to simultaneously produce cellulases and xylanases and ferment the released sugars into ethanol and xylitol has been described.ResultsA yeast strain isolated from soil samples and identified as Candida tropicalis MTCC 25057 expressed cellulases and xylanases over a wide range of temperatures (32 and 42 °C) and in the presence of different cellulosic substrates [carboxymethylcellulose and wheat straw (WS)]. The studies indicated that the cultivation of yeast at 42 °C in pre-treated hydrolysate containing 0.5 % WS resulted in proportional expression of cellulases (exoglucanases and endoglucanases) at concentrations of 114.1 and 97.8 U g−1 ds, respectively. A high xylanase activity (689.3 U g−1 ds) was also exhibited by the yeast under similar growth conditions. Maximum expression of cellulolytic enzymes by the yeast occurred within 24 h of incubation. Of the sugars released from biomass after pretreatment, 49 g L−1 xylose was aerobically converted into 15.8 g L−1 of xylitol. In addition, 25.4 g L−1 glucose released after the enzymatic hydrolysis of biomass was fermented by the same yeast to obtain an ethanol titer of 7.3 g L−1.ConclusionsDuring the present study, a new strain of C. tropicalis was isolated and found to have potential for consolidated bioprocessing (CBP) applications. The strain could grow in a wide range of process conditions (temperature, pH) and in the presence of lignocellulosic inhibitors such as furfural, HMF and acetic acid. The new yeast produced cellulolytic enzymes over a wide temperature range and in the presence of various cellulosic substrates. The cellulolytic enzymes produced by the yeast were effectively used for the hydrolysis of pretreated biomass. The released sugars, xylose and glucose were, respectively, converted into xylitol and ethanol. The potential shown by the new inhibitor tolerant cellulolytic C. tropicalis to produce ethanol or xylitol is of great industrial significance.

Geometrical assembly of ultrastable protein templates for nanomaterials.

The fabrication of nanoscale devices requires architectural templates on which to position functional molecules in complex arrangements. Protein scaffolds are particularly promising templates for nanomaterials due to inherent molecular recognition and self-assembly capabilities combined with genetically encoded functionalities. However, difficulties in engineering protein quaternary structure into stable and well-ordered shapes have hampered progress. Here we report the development of an ultrastable biomolecular construction kit for the assembly of filamentous proteins into geometrically defined templates of controllable size and symmetry. The strategy combines redesign of protein–protein interaction specificity with the creation of tunable connector proteins that govern the assembly and projection angles of the filaments. The functionality of these nanoarchitectures is illustrated by incorporation of nanoparticles at specific locations and orientations to create hybrid materials such as conductive nanowires. These new structural components facilitate the manufacturing of nanomaterials with diverse shapes and functional properties over a wide range of processing conditions.

Evaluation of oscillation-free fluid-porous interface treatments for segregated finite volume flow solvers

The volume-averaged approach to simulate flow in porous media is often used because of its practicality and computational efficiency. Derivation of the volume-averaged porous flow equations introduces additional porous resistance terms to the momentum equation. These porous resistance terms create body force discontinuities at fluid-porous interfaces, which may lead to spurious oscillations if not accounted for properly. A variety of techniques has been proposed to treat this problem, but only recently two approaches were developed by Nordlund et al. [Improved PISO algorithms for modeling density varying flow in conjugate fluid-porous domains. Journal of Computational Physics 2016;306:199–215. http://www.sciencedirect.com/science/article/pii/S0021999115007755. http://dx.doi.org/10.1016/j.jcp.2015.11.035; . Modified Rhie–Chow/PISO algorithm for collocated variable finite porous media flow solvers. No. 40 in ECI Symposium Series; 5th International Conference on Porous Media and Their Applications in Science, Engineering and Industry; 2014], concentrating on the combination of collocated grids and segregated solvers, which are commonly used for industrial applications. In this paper, we compared these two methods for the treatment of fluid-porous interfaces: (i) the Re-Distributed Resistivity (RDR) and (ii) the Face Consistent Pressure (FCP) methods, for a wide range of process conditions and porous media parameters, covering most practical porous media flow applications. The numerical robustness and accuracy of both methods were evaluated by applying a systematic quantitative comparison procedure. Both the RDR and the FCP approaches proved to be suitable for treating discontinuities in the porous resistance terms, yielding smooth solutions around the interface and good convergence with grid refinement. The RDR method was found to be the most robust method, particularly at very low Darcy numbers and on unstructured grids, distinguishing it from the FCP approach.

A novel hyper-viscoelastic model for consolidation of toughened prepregs under processing conditions

The paper presents a new modelling concept for describing the compressibility of toughened uncured prepregs over a wide range of processing conditions (i.e. automatic fibre deposition, hot debulking and pre-curing consolidation). The primary challenge of the work is to simulate the material response due complex flow and deformation mechanisms. This generation of prepreg systems exhibits both percolation (bleeding) flow typical for conventional thermosets, where the pressure gradient causes resin flow relative to the fibres, and shear (squeezing) flow typical for thermoplastics, where the laminate behaves as a highly viscous incompressible fluid. As a result, it holds features of both the systems: e.g. a convergence to a certain compaction limit at high temperatures and pressure levels and size/ply configuration-dependent material response. The modelling starts from micro-structural considerations, which give the foundation for an analytical model that assumes a transition from percolation to shear flow. It is shown that this model can capture the material behaviour very well. A hyper-viscoelastic material model is then constructed and implemented within the finite element package Abaqus/Standard. The model parameters are identified from an experimental programme and validated against compaction experiments over a wide range of load rates, temperatures and laminate configurations.

On the Modeling of Acrylic Acid Copolymerization in an Aqueous Solution: A Modular, Integrated Approach

A complete mathematical model of the free‐radical copolymerization of acrylic acid in an aqueous solution, taking place in a pilot‐scale tubular reactor equipped with static mixers, is presented. The developed kinetic/reactor model is numerically integrated in terms of a coupled deterministic–stochastic numerical approach that combines the advantages of speed, efficiency, and increased predictive capabilities. A series of experimental measurements on the monomer conversion and the molecular weight characteristics of the produced copolymer, under a wide range of process conditions, are used for the identification of the kinetic model parameters while a thorough analysis of the compositional characteristics of the produced copolymers is also carried out in terms of a series of bivariate distributed properties. image

Smart Polishing of Hard-to-Machine Materials with an Innovative Dilatancy Pad under High-Pressure, High-Speed, Immersed Condition

An innovative dilatancy polishing pad of which characteristics are controlled with processing conditions is proposed to establish high-efficiency, high-quality polishing of hard-to-machine materials for next-generation high-power devices. To make the best use of the property of the dilatancy pad, a highly durable polishing machine which enables high-pressure, high-speed, and immersed polishing was developed. Dilatancy properties were evaluated for various viscoelastic materials to select appropriate materials for a pad. The selected viscoelastic material was mixed with a special filler and abrasive particles, and integrated into a conventional polishing pad to form a dilatancy pad. Application of the dilatancy pad to polishing of SiC realized a smart polishing which achieves both high efficiency and high quality in any processing conditions. In addition, it was demonstrated that the processing conditions could be selected for the purpose of each polishing step, i.e. mid- to high-speed conditions for high-efficiency polishing and low-speed condition for high-quality finishing. A newly developed highly durable polishing machine is capable of achieving wide range of processing conditions. To avoid overheating under high load conditions, the machine can polish a work piece in slurry fluid. The material removal rate using the dilatancy pad showed superlinear dependence on the rotation speed, which outperforms the conventional polishing following the Preston's law. This innovative process can significantly reduce the polishing time of hard-to-machine materials for next-generation semiconductor devices.

Solidification Microstructure of Laser Additive Manufactured Ti[sbnd]6Al[sbnd]2Zr[sbnd]2Sn[sbnd]3Mo[sbnd]1.5Cr[sbnd]2Nb Titanium Alloy

Solidification microstructure of powder fed laser additive manufactured Ti 6Al 2Zr 2Sn 3Mo 1.5Cr 2Nb titanium alloy was investigated. The results showed that by deliberately increasing the powder feed rate, partially melted powders were retained at the top of the molten pool, which can promote heterogeneous nucleus. Thus, each cladding layer is composed of two regions: (i) randomly orientated cellular structure region caused by partially melted powders at the top of each cladding layer; and (ii) epitaxial cellular structure region adjacent to the fusion line. Usually, randomly orientated cellular structure region was totally remelted for a wide range of process conditions. The remelting effect ensures the continuity of epitaxial growth of cellular structure and leads to the formation of columnar β grains. In order to obtain equiaxed grains the scanning velocity and powder feed rate should be carefully selected to enlarge the randomly orientated cellular structure region.