Reactant Material Research Articles

The Mohanad Transforms and Their Applications for Solving Systems of Differential Equations

In recent years, Mohanad transform, a mathematical approach, has drawn a lot of interest from researchers. It is useful for solving many engineering and scientific problems, such as those involving electric circuits, population growth, vibrational beams, and heat conduction. The Mohanad transform is defined and introduced in this study, along with its fundamental qualities,including linearity and convolution. It is also discussed in connection with other integral transforms and how it is used in derivatives. Additionally, we use the Mohanad transform to solve a few systems of ordinary differential equations (ODEs) and review its properties in this paper. Determining the concentration of a chemical reactant (material) in a series is a physical chemistry problem that we use in the application part. We achieve this by developing a model based on ordinary differential equations (ODEs) and then solving them using the Mohanad transform. This research proves that, with little computational effort, we can get the exact solutions of ordinary differential equations (ODEs) via the Mohanad transform. We used graphs and tables to show our answer.

Predicting optimal membrane hydration and ohmic losses in operating fuel cells with machine learning

The absence of proper membrane hydration in membrane electrode assembly (MEA)-based electrochemical energy conversion technologies can lead to disastrous effects, such as reactant crossover, material degradation, and cell failure. In this work, we are the first to apply machine learning to predict if the optimal membrane hydration has been reached in polymer electrolyte membrane (PEM) fuel cells. We evaluate the ability of machine and deep learning algorithms to predict the high frequency resistance (HFR) and whether the optimal hydration current density (OHCD) has been reached via parameters measured from electrochemical impedance spectroscopy (EIS). We accurately predict the HFR using a long short-term memory recurrent neural network model (3.11% mean absolute percentage error and over 0.95 R2). We also accurately predict OHCD with precision and recall values over 98% using deep learning and a k-nearest neighbours model. Furthermore, our models provide a powerful tool for real-time parameter estimation and control systems to monitor and improve the performance of PEM fuel cells and other electrochemical energy devices, such as water and carbon dioxide electrolyzers.

Modelling and analysis of salt-convection effect on oxide reduction process for uranium oxides using smoothed particle hydrodynamics

Oxygen ion transport via molten salt continuum is a key kinetic feature of electrochemical reduction process for uranium oxides in molten salt. During the electrolysis, the evolution of oxygen ion concentration field in molten salt continuum appears from porous metallic layer to open bulk salt. Despite the important role affecting process throughput, its effect coupled with controlled salt movement was not adequately investigated. To capture the reactive oxygen ion transport phenomena, a multidimensional reduction model based on smoothed particle hydrodynamics (SPH) was combined with the advection-diffusion model. A pelletized oxide fuel bed capturing interconnected salt continuum is considered as a reactant material geometry, which allows forced convective delivery of molten salt through the reactant materials with a relatively low pressure head. In this study, reduction time of a pelletized-fuel bed was quantified with respect to key design parameters of the reactant material configuration. The simulation results demonstrated the advantage of salt convection which effectively removes oxygen ion products from the reactant materials and consequently accelerates the reduction process. Moreover, the reduction-time correlation of a single pelletized fuel was developed as a function of relevant dimensionless parameters and was extended to the application for a pelletized-fuel bed. Finally, several insights and implications in the use of a pelletized oxide fuel were presented. The developed SPH-based framework enabled multi-physics analysis of governing dynamics in appreciating and screening candidate reactant material configurations in a cost-effective manner.

A preliminary approach based on numerical simulation modelling and evaluation of permeable reactive barrier for aquifer remediation susceptible to selenium contaminant

In this study, numerical groundwater modelling software (GMS) was applied for a 2D transient state predictive (flow and contaminant fate and transport) conceptual model for heavy metal (Selenium in this research) contaminated groundwater, Imamzadeh-Jafar Aquifer, Kohgiluyeh and Boyer-Ahmad Province, Iran. The performances of permeable reactive barrier (PRB) in pollutant removal in the contaminated aquifers were studied by helping the MODFLOW-MT3DMS model. The spatiotemporal distribution of Selenium (Se) contaminant over the aquifer was illustrated using the calibrated flow and contaminant model. According to the findings, the downward movement of Se has resulted in an unsafe and undesirable water quality status in the Imamzadeh-Jafar aquifer, which is supported by field data. The sensitivity analysis of PRB layouts, geometric features, and reactant material characteristics was conducted in groundwater remediation. The numerical model results illustrated that the PRB thickness, ranging from 10 to 500 m, manifested the drop in Se concentration approximately from 40 to 46%. The results shed light on the hydraulic conductivity variations of reactant materials have effects less than 0.5% in Se removals. Furthermore, the decay rate variations in the ranges from 0.0001 to 0.01 d−1 could result in Se removal from 5 to 100%. According to studies, if the contaminant sources are prevented, in a) installation of PRB and b) not installation of PRB scenarios, the Imamzadeh-Jafar aquifer remediation will take 6 months and 84 months, respectively.

Eco-friendly deicer prepared from waste oyster shells and its deicing properties with metal corrosion

ABSTRACT Calcium acetate eco-friendly deicer was prepared using waste oyster shell as a raw reactant material and its physicochemical properties were investigated. The waste oyster shells were converted to a calcium acetate deicer by reaction with acetic acid at ambient temperature. The physicochemical properties of the prepared calcium acetate deicer were analysed using various analytical method. The ice melting and metal corrosion characteristics of the calcium acetate deicer synthesized from the waste oyster shell were evaluated by comparison with those of the calcium chloride and sodium chloride deicers. The chloride deicers severely corroded the metal, but the calcium acetate deicer prepared from the waste oyster shell did not cause metal corrosion. The ice melting performance of calcium acetate prepared from the waste oyster shell was lower than that of calcium chlorides, however, the addition of sodium hydroxide could significantly improve the ice melting capacity.

Operando Analysis of Reactant Conversion and Material Stability in Next‐Generation Batteries

AbstractLatest advances on operando analysis in the field of next‐generation battery research are highlighted by means of three examples: recording the pressure change and performing X‐ray diffraction analysis of metal‐oxygen batteries allows to gain detailed understanding of the main reactions and side reactions; analyzing a solid electrolyte in a hot‐press setup allows to monitor crystallization and stability during its synthesis. Since batteries are (electro)chemical reactors, the benefit of using the introduced operando techniques for classical reaction engineering is highlighted thereof.

Kinetics Analysis of Synthesis Reaction of Struvite With Air-Flow Continous Vertical Reactors

Kinetics reaction is a knowledge about a rate of chemical reaction. The differential of the reaction rate can be determined from the reactant material or the formed material. The reaction mechanism of a reactor may include a stage of reaction occurring sequentially during the process of converting the reactants into products. In the determination of reaction kinetics, the order of reaction and the rate constant reaction must be recognized. This study was carried out using air as a stirrer as a medium in the vertical reactor for crystallization of struvite. Stirring is one of the important aspects in struvite crystallization process. Struvite crystals or magnesium ammonium phosphate hexahydrates (MgNH4PO4·6H2O) is commonly formed in reversible reactions and can be generated as an orthorhombic crystal. Air is selected as a stirrer on the existing flow pattern in the reactor determining the reaction kinetics of the crystal from the solution. The experimental study was conducted by mixing an equimolar solution of 0.03 M NH4OH, MgCl2 and H3PO4 with a ratio of 1: 1: 1. The crystallization process of the mixed solution was observed in an inside reactor at the flow rate ranges of 16-38 ml/min and the temperature of 30°C was selected in the study. The air inlet rate was kept constant at 0.25 liters/min. The pH solution was adjusted to be 8, 9 and 10 by dropping wisely of 1 N KOH solution. The crystallization kinetics was examined until the steady state of the reaction was reached. The precipitates were filtered and dried at a temperature for subsequent material characterization, including Scanning Electron Microscope (SEM) and XRD (X-Ray diffraction) method. The results show that higher flow rate leads to less mass of struvite.

Predicting synergy in atomic layer etching

Atomic layer etching (ALE) is a multistep process used today in manufacturing for removing ultrathin layers of material. In this article, the authors report on ALE of Si, Ge, C, W, GaN, and SiO2 using a directional (anisotropic) plasma-enhanced approach. The authors analyze these systems by defining an “ALE synergy” parameter which quantifies the degree to which a process approaches the ideal ALE regime. This parameter is inspired by the ion-neutral synergy concept introduced in the 1979 paper by Coburn and Winters [J. Appl. Phys. 50, 5 (1979)]. ALE synergy is related to the energetics of underlying surface interactions and is understood in terms of energy criteria for the energy barriers involved in the reactions. Synergistic behavior is observed for all of the systems studied, with each exhibiting behavior unique to the reactant–material combination. By systematically studying atomic layer etching of a group of materials, the authors show that ALE synergy scales with the surface binding energy of the bulk material. This insight explains why some materials are more or less amenable to the directional ALE approach. They conclude that ALE is both simpler to understand than conventional plasma etch processing and is applicable to metals, semiconductors, and dielectrics.

Integrated Design of Control Actuator Layer and Economic Model Predictive Control for Nonlinear Processes

In the present work, an economic model predictive control (EMPC) system is designed that accounts for the dynamics of the control actuators. A combined process-actuator dynamic model is developed to describe the process and control actuator dynamics and is used within the EMPC system. Integrating the design of the regulatory control layer, which controls the control actuators, and the supervisory control layer consisting of an EMPC system is an important consideration given the fact that EMPC may force an unsteady-state operating policy to optimize the process economics and the dynamics of the control actuator layer may affect the closed-loop process-actuator dynamics. Moreover, integral or average input constraints are often imposed within the EMPC solution. However, if the actuator layer is not accounted for in the EMPC system, the actuator output trajectory may not satisfy the integral input constraints. To address closed-loop stability of the combined process-actuator closed-loop system, stability constraints, designed via Lyapunov-based techniques, are imposed on the EMPC problem to guarantee closed-loop stability of the process system under the EMPC. An EMPC system accounting for the control actuator dynamics is applied to a benchmark chemical process example to study the impact of the actuator dynamics on closed-loop economic performance and reactant material constraint satisfaction.

Closed Batch Initiated Chemical Vapor Deposition of Ultrathin, Functional, and Conformal Polymer Films

A modified fabrication process based on initiated chemical vapor deposition (iCVD) has been developed for producing ultrathin and uniform polymer films. This so-called "closed batch" (CB) iCVD process provides fine-tuning of the thickness and deposition rate of polymeric materials while using significantly less reactant material than the conventional continuous flow (CF) iCVD process. Four different polymers, poly(N-isopropylacrylamide), poly(trivinyltrimethylcyclotrisiloxane), poly(1H,1H,2H,2H-perfluorodecyl acrylate), and poly(ε-caprolactone), were synthesized by both CB and traditional CF iCVD. The resulting CB iCVD polymers are functionally identical to CF iCVD and solution-polymerized materials. Additionally, the new CB process retains the desirable ability to achieve conformal coverage over microstructures. Ultrathin (<30 nm) films can be controllably and reproducibly deposited; no prior optimization process is required to obtain excellent film thickness uniformity. The CB iCVD films are also extremely smooth, exhibiting RMS roughness values between 0.4 and 0.7 nm. Use of the CB process improves reaction yield by factors of 10-200 for the four different film chemistries and decreases material cost per 100 nm of film by 1-2 orders of magnitude.

The use of hydrothermal carbonization to recycle nutrients in algal biofuel production

The high fertilizer demand for biodiesel production from microalgae is a significant challenge facing the commercialization of this promising technology. We investigated a processing strategy called hydrothermal carbonization (HTC) to convert wet algal biomass into a lipid‐rich hydrochar and aqueous phase (AP) co‐product. By reacting biomass at 200°C for 15 min, about 50% of the algae biomass became a solid hydrochar and roughly 40–70% of the C, N, and P in the reactant material dissolved into the AP. For the first time, an AP co‐product of this nature was analyzed by HPLC, GC‐MS and FT‐ICR‐MS to identify and characterize the dissolved organic matter. Using a unique marine bi‐culture suspected to contain a green algae (Nannochloris) and a cyanobacteria (Synechocystis), we demonstrated that this AP co‐product can support biomass growth better than a medium containing only inorganic nutrients. To manage unwanted contamination and optimize AP utilization, we employed a two‐stage growth process and fed‐batch additions of the AP co‐product. The effect of media recycling and nutrient supplementation, as well as a production model for a large‐scale facility, are discussed. Our work suggests that HTC can play a critical role in making algal biorefineries more sustainable by obviating biomass drying for fuel processing and recycling nutrients. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 962–975, 2013

Economic Model Predictive Control of Transport-Reaction Processes

This work focuses on the development of economic model predictive control (EMPC) systems for transport-reaction processes described by nonlinear parabolic partial differential equations (PDEs) and their applications to a non-isothermal tubular reactor where a second-order chemical reaction takes place. The tubular reactor is modeled by two nonlinear parabolic PDEs. Galerkin’s method is used to derive finite-dimensional systems that capture the dominant dynamics of the parabolic PDEs which are subsequently used for the EMPC design. The EMPC formulation uses the integral of the reaction rate along the length of the reactor as an economic cost function subject to constraints on the control action and states over an operation period. Closed-loop simulations are conducted of a low-order EMPC system, formulated with a constraint on the available reactant material over each operation period, applied to a high-order discretization of the PDEs and of a high-order EMPC system formulated with a specific state constraint and with the constraint on the available reactant material. Simulation results demonstrate that the EMPC operates the process in a time-varying fashion and improves the economic cost over steady-state operation using the same amount of reactant material over a fixed period of operation, as well as meeting state constraints.

State-estimation-based economic model predictive control of nonlinear systems

In this work, we focus on a class of nonlinear systems and design an estimator-based economic model predictive control (MPC) system which is capable of optimizing closed-loop performance with respect to general economic considerations taken into account in the construction of the cost function. Working with the class of full-state feedback linearizable nonlinear systems, we use a high-gain observer to estimate the nonlinear system state using output measurements and a Lyapunov-based approach to design an economic MPC system that uses the observer state estimates. We prove, using singular perturbation arguments, that the closed-loop system is practically stable provided the observer gain is sufficiently large. We use a chemical process example to demonstrate the ability of the state-estimation-based economic MPC to achieve process time-varying operation that leads to a superior cost performance metric compared to steady-state operation using the same amount of reactant material.

Combustion synthesis/quasi-isostatic pressing of TiC–NiTi cermets: processing and mechanical response

TiC-NiTi composites were produced by a technique combining self-propagating high-temperature synthesis (SHS) of elemental powders of Ni, Ti, and C with densification by quasi-isostatic pressing (QIP). In order to create a one-step synthesis/densification process, the Ti ? Ni ? C reactant material was surrounded in a bed of graphite and alumina particulate before initiation of the combustion reaction. The sample was ignited within the particulate and subjected to a uniaxial load immediately after passage of the combustion wave. The constitutive response, composition and resulting structures of the composites with varying volume fractions of NiTi are characterized. Powder mixtures prepared anticipating the formation of stoichiometric TiC result in the formation of composites with a eutectic matrix of Ni3Ti and NiTi. This titanium impoverishment of the matrix is consistent with the formation of nonstoichiometric TiCx during the com- bustion reaction. The Ni3Ti phase can be suppressed by anticipating the formation of TiC0.7 and adjusting the chemical content of the reactant mixture to include addi- tional titanium. These cermets combine the high hardness of the ceramic phase with the possible shape memory and superelastic effects of NiTi. Introduction and objectives

Chemical kinetics and mass transport effects in solution-based selective-area growth of ZnO nanorods

We present a combined experimental and modeling study of the dependence of solution-based zinc oxide (ZnO) selective-area growth rates on pattern dimension. Selective growth is achieved by patterning a portion of the substrate with an organic template that inhibits growth. The density of ZnO nanorods and the mass grown per unit area of exposed surface increases as the distance between the exposed growth regions is increased and as the width of the exposed lines is decreased. A 2-D model was developed to calculate selective growth at the exposed surface regions, the loss of reactant material due to a competing reaction in solution, liquid-phase and surface diffusive mass transport to (or on) the growth surface, and the ZnO growth reaction at the surface. To explain the experimental results, we found it necessary to include a reaction by-product in the chemistry model, the desorption of which is the rate limiting step. A relatively simple, three-step reaction mechanism, combined with the species mass transport model, provides a good, semi-quantitative description of the experimental observations in the selective-area growth of ZnO from supersaturated solutions.

Optimal design of thermochemical reactors based on constructal approach

AbstractThis work aims to optimize the design of thermochemical reactors such as solid/gas fixed bed reactors working in dynamic mode. The optimization is based on the constructal approach. A thermodynamic criterion, the ratio of reactor output power to its entropy generation, has to be used to take into account the coupled phenomena and the end purpose of such reactors. Two reactors are considered with same overall volume, but different internal configuration of collectors (constructal scales): a “basic” single‐scale configuration (basic reactor), and a “constructal” two‐scale configuration (constructal 1 reactor). Reaction rates notably vary with reactor shape, and an optimal shape factor is found for each reactor, depending on the reactant material density. For both reactors, an important remark is pointed out: the correspondence between the maximum of power/entropy ratio (PER) and the highest reaction rate. Comparison between the optimal basic and constructal 1 reactors shows that the latter presents higher energy efficiency (based on second law analysis), but lower output power than the first. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Fabrication and characterizations of new nanocomposite WC/Al 2O 3 materials by room temperature ball milling and subsequent consolidation

Reactant material powders of pure WO 3, Al and graphite have been milled at room temperature using a high-energy ball mill. After a few kiloseconds of milling (11 ks), numerous fresh surfaces of the reactant materials are created as a result of the repeated impact and shear forces which are generated by the balls. After 43 ks of milling, a mechanical solid state reduction is successfully achieved between the fresh Al and WO 3 particles to form a product of nanocrystalline mixture of Al 2O 3 and W powders. A typical mechanical solid state reaction takes place between the W particles and graphite powders to obtain fine grains of nanocrystalline WC. Towards the end-stage of ball milling (360 ks), the nanocrystalline WC grains (5 nm) are embedded into the fine matrix of Al 2O 3 to form fine nanocomposite powders (less than 1 μm in diameter) of WC–32 at.% Al 2O 3 material with spherical-like morphology. This composite powder was then consolidated under vacuum at 1963 K, with a pressure ranging from 19.6 to 38.2 MPa for 0.3 ks, using a plasma activated sintering method. The consolidation step does not lead to a dramatic grain growth and the compacted samples that are fully dense still maintain their unique nanocrystalline characteristics. The elastic properties and the hardness of both the consolidated samples have been investigated. A model for fabrication of new refractory nanocomposite WC/Al 2O 3 materials at room temperature is proposed.

Fabrication of nanocrystalline WC and nanocomposite WC–MgO refractory materials at room temperature

Reactant material powders of pure WO3, Mg and graphite have been milled at room temperature using a high-energy ball mill. After a few kiloseconds of milling (11 ks), numerous fresh surfaces of the reactant materials are created as a result of the repeated impact and shear forces generated by the balls. After 86 ks of milling, a mechanical solid state reduction is successfully achieved between the fresh Mg and WO3 particles to form a product of nanocrystalline mixture of MgO and W. A typical mechanical solid state reaction takes place between the W particles and graphite powders to obtain fine grains of nanocrystalline WC. Towards the end-stage of ball-milling (173 ks), the nanocrystalline MgO grains (10 nm) are embedded into the fine matrix of WC to form fine nanocomposite powders (1 μm in diameter) of WC–18% MgO material with spherical-like morphology. This composite powder was then consolidated under vacuum at 1963 K, with a pressure ranging from 19.6 to 38.2 MPa for 0.3 ks, using a plasma activated sintering method. In addition, pure nanocrystalline WC powders (7 nm in diameter) obtained by removing the MgO from the milled powders, using a simple leaching technique have been also consolidated by the same consolidation technique. The consolidation step does not lead to a dramatic grain growth and the compacted samples that are fully dense still maintain their unique nanocrystalline characteristics. The elastic properties and the hardness of both consolidated samples have been investigated. A model for fabrication of refractory nanocrystalline WC and nanocomposite WC–18% MgO materials at room temperature is proposed.

Modeling the solid state reaction CO2·C2H2 → CO2+C2H2

Crystalline CO2·C2H2 is metastable with respect to solid CO2 and solid C2H2. Infrared spectra of the bending regions of the three solids are presented and it is shown that the solid phase decomposition of CO2·C2H2 preserves the integrity of the cryofilm sample. Although the plot of fractional decomposition against time is sigmoidal it is not well described by the Avrami equation. It is shown that the kinetics of the transformation are well described by a growth in three dimensions, unimpeded until reactant material is locally exhausted.

Simulation of morphological instabilities during diamond chemical vapor deposition

Abstract The diamond chemical vapor deposition (CVD) process has been investigated theoretically and the morphological instabilities associated with the growth of diamond films have been examined with a model based on the continuum species conservation equation coupled to surface reaction kinetics. A linear stability analysis and numerical calculations have been carried out to determine critical parameters affecting the diamond deposition layer morphology. A two-dimensional model describes the evolution of the gas-solid interface. The dynamic behavior of the interface depends on the reactants' diffusivity and surface kinetics. These factors depend upon the reactant material properties and film growth conditions such as the reactor temperature and pressure. From the analyses, it has been found that the ratio ( D /k) of gas phase diffusivity ( D ) to the surface reaction rate constant (k) plays the critical role in promoting diamond morphological instabilities because the film morphology stabilizing processes of surface diffusion and re-evaporation are absent or negligible during diamond CVD. It is found that the film nonuniformity increases as the ratio ( D /k) decreases. Increasing growth rates also result in increasing morphological instability, leading to rough surfaces. It is shown that increasing reactor pressure and decreasing gas-phase temperature and/or substrate temperature promote deposition layer nonuniformity. An approach to avoiding these instabilities is proposed.