Step Chemical Reaction Research Articles

Crystal-scale modelling of pore collapse in cyclotetramethylene tetranitramine (HMX) under different shock strengths

A physically-based anisotropic thermal-mechanical-chemical crystal model is developed for cyclotetramethylene tetranitramine (HMX), which includes nonlinear thermoelasticity, inelasticity due to both dislocation-based plasticity and shear cracking damage, melting, and single step chemical reaction. Based on the proposed model, thermal-mechanical-chemical responses and related physics of shock induced pore collapse in HMX single crystal under low to high strengths were investigated. Under low shock strength (3.4 GPa), obvious orientation dependency of pore collapse is shown for (011) and (110) orientations, where dislocation slip and shear cracking are the dominant mechanisms. The collapsing pore morphologies of the two orientations are distinctly different. Under medium shock strength (8.8 GPa), adiabatic shear bands around the pore area become prominent and they develop along ∼45° relative to the shock direction. Under strong shock strength (23.8 GPa), significant adiabatic shear bands are formed, and the hydrodynamic jetting and impingement afterwards directly lead to the formation of hot spot and eventually the ignition. For the first time, this work clarifies the pore collapse behaviors under various loading strengths with the crystal-scale mechanisms in a unifying framework, which automatically transits from a strength-dominated regime to a hydrodynamic regime. Moreover, in this work, all of potential deformation mechanisms are decoupled and evaluated, which could provide insights into the understanding of ignition mechanism and the development of microstructure-aware predictive models at the macroscale.

Solution Combustion Synthesis, Characterization, Photocatalytic Activity and Electrochemical Studies of Yttrium Stabilised Zirconia (Zr0.72 Y0.28 O1.862) Nanopowder

Background: Yttria stabilized zirconia (YSZ) is an attractive material which exhibits a characteristic combination of physical and chemical properties of YSZ in terms of inertness, resistant to corrosion, high mechanical strength, thermal stability, chemical stability and photostability. Because of these properties and applications, it is very important to synthesize yttrium stabilized zirconia (YSZ) powder. Till date, various preparative techniques have been reported for the synthesis of high porous YSZ nano powders. However, special equipment, long time with multistep processing, high calcination temperature, small surface area and low product yield are the usual drawbacks of most of the methods. Therefore. Solution combustion method (SCS) method has been established for the synthesis of YSZ nanopowder with high surface area. Objective: The main objective of our present research work is to effectively synthesized the Yttrium stabilized zirconia (YSZ) Zr0.72 Y0.28 O1.862 nanopowder by solution combustion method using yttrium nitrate (Y(NO3)3.6H2O), zirconyl nitrate (ZrO(NO3)2.XH3O) as oxidizers and ethylenediamine tetra acetic acid (EDTA) as a fuel and the synthesized powder was used in the application of photodegradation of dyes. Methods: YSZ nanopowder was synthesized by using Solution combustion synthesis. Solution combustion synthesis (SCS) is a simple exothermic self-sustaining one step chemical reaction, which will produce a large number of pores in the oxide material and inhibit their agglomeration leading to a large specific surface area and small crystallite size of the resulting material. Results and Discussion: Powder X-ray diffraction (PXRD) revealed the formation of pure cubic phase of YSZ (Zr0.72 Y0.28 O1.862) nanopowder and the crystallite size of 15.4 nm was calculated by using Scherrer’s formula. The porous morphology of the product was observed by SEM images. BET surface area reveals that the relatively larger surface area of 87.17 m2g-1. TEM analysis revealed uniform particle size distribution with average particle sizes varying in the range of 20-100 nm. The UV-Vis DRS spectrum was used to calculate the absorption wavelength (339 nm) and the corresponding band gap (3.72 eV) using Tauc plot. The photoluminescence spectrum of YSZ nanopowder showed an emission peak at 339 nm. The photodegradation (decolourisation) of methylene blue (MB) dye was increased from 75-90% with increase in the concentration of YSZ photocatalyst from 100 mg to 400 mg due to availability of OH radicals in the presence of UV radiation. The electrochemical studies using cyclic voltammetry reveal a substantial increase in current density of YSZ electrode from 0.0001A to 0.0005A when compared with bare carbon electrode and the instantaneous rise in redox current for the YSZ electrodes from 0.0001A to 0.0005A with increasing scan rate from 10 mVs-1 to 90 mVs-1. Conclusion: In our reported work, we start a simple and rapid solution combustion synthetic approach to produce highly effective YSZ nanopowder using EDTA as organic fuel. Because of large surface area and small particle size of the YSZ nanopowder shows 85% of degradation of MB takes place in presence of UV light. In order to understand the electrochemical property of YSZ, the redox current measurement was carried out using cyclic voltametry and resulted that increase in redox current for the YSZ electrodes with increasing scan rate from 10 mVs-1 to 90 mVs-1.

Effect of pH and ammonia concentration on the shape and size of fluorapatite nanoparticles obtained by chemical reaction

Nanoparticles of fluorapatite (FAp Nps) were prepared by one step chemical reaction in aqueous solutions. The pH of the system was kept constant at 6 and 8. The FAp Nps were characterized with Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDAX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The Ca/P calculated from EDAX analysis was 1.69. The results of XRD analysis and FTIR showed the presence of FAp phases. The DRX results confirm the formation of FAp with a hexagonal structure. TEM images show semispherical and elongated nanoparticles with mean diameter of 3.78 nm, 8.63 nm and 10.46 nm, when the pH and ammonia concentrations is varied. Ammonia concentration and pH influence the morphology and size of the FAp Nps.

Numerical Simulation of Solid Combustion in Microporous Particles.

In the present study, direct numerical simulations for smoldering in simplified geometries are performed for multicomponent and dilatable flows. The reactant gas is passing inside an array of permeable and microporous cylinders. The chemical reaction takes place within the grains. For the sake of simplicity, the smoldering is treated as a single step chemical reaction. We define a Darcy-Brinkman model to deal with the multi-scale nature of this problem. Varying the flow rate, and carbon content, we can investigate the response of our model, and try to compare with existing solutions or available experimental investigations. Thus, the ability of the Darcy Brinkman approach to capture such situations of porous particles combustion will be checked. The numerical model sensitivity to the inner grain permeability is also investigated.

Synthesis and characterization of NiO colloidal ink solution for printing components of solid oxide fuel cells anodes

A synthesis of NiO colloidal ink solution for printing of the main anode component of solid oxide fuel cells (SOFCs) by commercial printer was shown in the work. The ink was synthesized by a single step chemical reaction of the dissolved nickel nitrate hexahydrate and ammonium carbonate solution with the addition of Triton X-100 surfactant. Results revealed that the obtained ink was stable for at least 4 months contained almost the same NiO nanoparticles with the size at the range of 7–9 nm. These nanoparticles structural and morphology investigation was conducted by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy and selected area electron diffraction (SAED) analytical methods. Detected rheological properties of the ink revealed that materials for anode in SOFC can be deposited using a commercial printer followed by calcination at 900 °C. Processes occurred during calcination were investigated by TGA and DSC analytical techniques. Finally, the printed coating was subjected to the investigation using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM).

A review of phenformin, metformin, and imeglimin

Diabetes mellitus is a serious metabolic disorder affecting millions of people worldwide. Phenformin and metformin are biguanide antidiabetic agents that are conveniently synthesized in a single-step chemical reaction. Phenformin was once used to lower blood glucose levels, but later withdrawn from the market in several countries because it was frequently associated with lactic acidosis. Metformin is still a widely prescribed medication for the treatment of type 2 diabetes despite the introduction of several newer antidiabetic agents. Metformin is administered orally and has desirable pharmacokinetics. Incidence of metformin-induced lactic acidosis is serious but very rare. Imeglimin, a novel molecule being investigated by Poxel and Sumitomo Dainippon Pharma in Japan, is currently in clinical trials for the treatment of type 2 diabetes. Unlike metformin, imeglimin is a cyclic molecule containing a triazine ring. However, like metformin, imeglimin is also a basic small molecule. Imeglimin is synthesized from metformin as a precursor via a single step chemical reaction. Recent mechanism of action studies suggests that imeglimin improves mitochondria function, when given in combination with metformin it helps achieve better glycemic control in patients with type 2 diabetes. We herein describe and compare the current status, synthesis, physicochemical properties, pharmacokinetic parameters, mechanism of action, and preclinical/clinical studies of metformin and imeglimin.

Tip-to-tail numerical simulation of a hypersonic air-breathing engine with ethylene fuel

End to end CFD simulations of external and internal flow paths of an ethylene fueled hypersonic airbreathing vehicle with including forebody, horizontal fins, vertical fins, intake, combustor, single expansion ramp nozzle are carried out. The performance of the scramjet combustor and vehicle net thrust-drag is calculated for hypersonic cruise condition. Three-dimensional Navier–Stokes equations are solved along with SST-k–ω turbulence model using the commercial CFD software CFX-14. Single step chemical reaction based on fast chemistry assumption is used for combustion of gaseous ethylene fuel. Simulations captured complex shock structures including the shocks generated from the vehicle nose and compression ramps, impingement of cowl-shock on vehicle undersurface and its reflection in the intake and combustor etc. Various thermochemical parameters are analyzed and performance parameters are evaluated for nonreacting and reacting cases. Very good mixing (~98%) of fuel with incoming air stream is observed. Positive thrust–drag margins are obtained for fuel equivalence ratio of 0.6 and computed combustion efficiency is observed to be 94 %. Effect of equivalence ratio on the vehicle performance is studied parametrically. Though the combustion efficiency has come down by 8% for fuel equivalence ratio of 0.8, net vehicle thrust is increased by 44%. Heat flux distribution on the various walls of the whole vehicle including combustor is estimated for the isothermal wall condition of 1000K in reacting flow. Higher local heat flux values are observed at all the leading edges of the vehicle (i.e., nose, wing, fin and cowl leading edges) and strut regions of the combustor.

Impacts of inner/outer reactor heat recirculation on the characteristic of micro-scale combustion system

Flame stability and thermal performance of two different heat recirculation micro-combustors (inner reactor heat recirculation (IHR) and outer reactor heat recirculation (OHR)) are investigated using computational fluid dynamics (CFD) and compared together. A two-dimensional steady state CFD model including temperature dependent properties, laminar flow and transport, one step chemical reaction, surface-to-surface radiation, and heat conduction within solid walls has been carried out to assess flame propagation velocity, flame thickness, excess enthalpy, heat loss, and emitter efficiency. It is observed that both cases significantly extend flammability and blow-off limits due to preheating of the reactive mixture. The maximum flame propagation velocities of IHR and OHR in stoichiometric mixture are predicted 160.2cm/s and 126.1cm/s, respectively. It is found that super-adiabatic flame temperature takes place when dimensionless excess enthalpy is positive and it is maximum in the stoichiometric equivalence ratio. Heat loss can be varied from 245.8 to 248.6W for IHR and from 249.6 to 254W for OHR configuration. Therefore, there is a relative improvement in the Thermal quenching limit of IHR. It is concluded that IHR micro-combustor profoundly affects flame characteristic and stability, but OHR presents a higher range of emitter efficiency.

Evolution of structural and thermal properties of carbon-coated TaC nanopowder synthesized by single step reduction of Ta-ethoxide

Carbon-coated nano-TaC has been synthesized at 800 °C using tantalum-ethoxide by single step chemical reaction route and no external carbon source

Numerical Simulations for Smoldering in a Horizontal Channel: Comparisons Between Variable Density-Based Formulation and Incompressible One

In the present study, numerical simulations for smoldering in a horizontal channel are performed for both compressible and incompressible flows. The reactant gas is passing through the char surface, where the chemical reaction is going to take place. For the sake of simplicity, the smoldering is treated to be a single step chemical reaction. In the incompressible flow, a set of governing parameters are discussed to elucidate their influences on the process of smoldering. Furthermore, the variations of density and dynamic viscosity of gaseous mixture are taken into account in the compressible flow. The comparison between the compressible and incompressible flows reveals that the effects of local compressibility and gaseous mixture on the propagation of smoldering wave are striking.

Numerical study of radiative heat transfer effects on a complex configuration of rack storage fire

This work describes the application and the performance of a new radiation model in CFD calculations for the simulation of thermal radiation transfer effects on a fire scenario. A 3D Cartesian coordinates radiative heat transfer procedure based on coupling of the FTn finite volume method (FTnFVM) with the bounded high-order resolution CLAM scheme is developed. The narrow-band based weighted-sum-of-gray-gases (NB-WSGG) model is applied to take account of nongray effects by CO 2, H 2O and soot. To treat irregular boundaries, the present model used the blocked-off-region procedure. This radiation code is implemented in the Fire Dynamics Simulator (FDS), a Computational-Fluid-Dynamics-based fire model, where a the combustion is represented by means of the mixture fraction with a single step chemical reaction model and the Large Eddy Simulation (LES) is used to model the dissipative processes. Computational results with and without radiation effects are compared against available experimental data and quasi-steady state law correlations of in-rack storage fire, which consists a complex configuration of double tri-wall corrugated paper cartons placed onto a wood pallet. Sensibility analyses of spatial and angular grids demonstrate the improvements due to the FTnFVM and to the CLAM scheme in the configuration studied. Results show that the simulations of the flame height, the gas temperature and the gas velocity are strongly influenced by thermal radiation. Overall, simulations predicted closer profiles to the experimental results only when the nongray-sooting radiation model was incorporated and an over-prediction of the gas temperature and the flame height is found when radiation is neglected. A sensibility analysis has shown that the flame characteristics are strongly affected by the soot yield.

Rectification of a Modified Nanofluidic Diode Dependent on the pH

We study the affect of varying pH on the rectification of a nanofluidic diode. The diode is a conically shaped nanopore in PET or Kapton that has a distribution of charge along the surface. The distribution is such that there is a boundary where one side is positively charged and the other side is negatively charged. We also measure nanopores that have neutral and negative charges on either side of the boundary. The charges are modified by a 2 step chemical reaction using EDC/PFP for the 1st step and ethylenediamine or propylamine for the second step. Characterization of the nanopore was done by taking I-V curves from −5V to 5V with buffered solutions of KCl.

NUMERICAL INSPECTION OF TURBULENT/LAMINAR NONREACTIVE AND LAMINAR COMBUSTIVE REACTIVE FLOWS IN POROUS MEDIA

In this study, the two-dimensional (2D) axisymmetric models of the turbulent/laminar nonreactive and the laminar combustive reactive flows in porous media are simulated numerically by the finite volume method along with the SIMPLE algorithm. The turbulence is simulated by a k − ε model adapted to the porous structure due to the additional source terms. The premixed combustion of methane-air is simulated by applying the single step chemical reaction mechanism. The obtained results for the flow simulation in porous media show that the turbulent kinetic energy is amplified within the foam and separated flow regions do not form or penetrate inside the porous material in the turbulent flow model. The simulation of the premixed laminar submerged flames indicates the super adiabatic combustion in the lean mixtures and implies the flame acceleration which results in higher thermal loads in these flames. Furthermore, the stabilization process and the position of flame within the foam are examined through using different methods for convergence of the numerical code and the acquired predictions are compared to the previous results of the similar research.

Synthesis and characterization of nanosize cobalt sulfide for rechargeable lithium batteries

Nanosize cobalt sulfides were synthesized through a one step chemical reaction method at room temperature. The cobalt sulfide nanopowders were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy and electrochemical testing. The results revealed that the cobalt sulfide is a semiconductor; the reversible capacity is increased with increasing content of electronic conductors in the active material of electrodes. The as prepared sample with 10 wt.% carbon black and 10 wt.% polypyrrole (PPy) powder as electronic conductors shows the best electrochemical properties, with a reversible capacity of over 300 mAh g −1 based on the total mass of the electrode. Cobalt sulfide nanopowders show promise as cathode active materials for lithium-rechargeable batteries.

Synthesis of NiO nanotubes for use as negative electrodes in lithium ion batteries

Nickel oxide (NiO) nanotubes have been produced for the first time via a template processing method. The synthesis involved a two step chemical reaction in which nickel hydroxide (Ni(OH) 2) nanotubes were firstly formed within the walls of an anodic aluminium oxide (AAO) template. The template was then dissolved away using concentrated NaOH, and the freed nanotubes were converted to NiO by heat treatment in air at 350 °C. Individual nanotubes measured 60 μm in length with a 200 nm outer diameter and a wall thickness of 20–30 nm. The NiO nanotube powder was used in Li-ion cells for assessment of the lithium storage ability. Preliminary testing indicates that the cells demonstrate controlled and sustainable lithium diffusion after the formation of an SEI. Reversible capacities in the 300 mAh g −1 range were typical.

High order effects in one step reaction sheet jump conditions for premixed flames

The differences need to be understood between the leading order jump conditions, often assumed at a flame sheet in combustion theory, and the actual effect of a one step chemical reaction governed by Arrhenius kinetics. These differences are higher order in terms of a large activation temperature analysis and can be estimated using an asymptotic approach. This paper derives one order of asymptotic correction to the leading order jump conditions that are normally used for describing premixed laminar combustion, providing additional contributions that are due to curvature, flow through the flame sheet and the temperature gradient into the burnt gas. As well as offering more accurate asymptotic results, these can be used to estimate the errors that are inherent in adopting only the leading order version and they can point towards major qualitative changes that can occur at finite activation temperatures in some cases. Applied to steady non-adiabatic flame balls it is found that the effect of a non-zero temperature gradient in the burnt gas provokes the most serious deficiency in the asymptotic approach.

Chapman-Jouguet detonation profile for a qualitative model

In this article, the existence of traveling wave fronts for a one step chemical reaction with a natural discontinuous reaction rate function is studied. This discontinuity occurs because of the cold boundary difficulty and implies a discontinuous system of ordinary differential equations. By some general topological arguments in ordinary differential equations, the Chapman-Jouguet detonation for exothermic reactions is shown to exist. In addition, the uniqueness of this wave is considered.

Attractor Dimension for a Simple Premixed Flame Propagation Model

—A premixed two-dimensional flame propagating from below in the vertical plane generates a convective motion,which is treated here in the Boussinescq approximation. A simple one–step chemical reaction model is assumed. Recently developed methods of functional analysis arc used to estimate the dimension of the attractor (essentially the number of degrees of freedom) characterizing the time asymptotic behavior of the flame propagation and the accompanying fluid motion. The attractor dimension is to found to depend on four characteristic lengths intrinsic to the model of the combustion process and to the fluid motion. In particular. for a laminar flame the estimate of the attractor dimension is dominated by the flame diffusion length and the thickness of the reaction zone.

Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos

AbstractA now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.

An analysis of lewis number and flow effects on the ignition of premixed gases

We have analysed numerically the ignition of a combustible gas to which heat is added over a specified period at a spherical boundary of small diameter. We solve conservation equations for reactant and sensible enthalpy and allow the gas to undergo a one step chemical reaction. The numerical technique involves a finite difference scheme with an adaptive grid. We find that, until the flame has grown beyond a critical radius, it relies upon the heat source to prevent its extinction. A minimum energy is required for successful ignition. This minimum increases as the Lewis number of the mixture increases. The minimum ignition energy also increases if the flame front is stretched. This behaviour is in very close agreement with experimental observations of the spark ignition of turbulent mixtures.