Thickness Of Reactive Layer Research Articles

Microstructure and Mechanical Properties of Laser Welded Magnesium Alloy/Steel Joint Using Cu-Si Composite Interlayer

In this study, Cu-Si composite powder was used as the interlayer to carry out laser lap deep penetration welding of AZ31B magnesium alloy and DP590 dual-phase steel. The effects of Cu-Si composite powder on the weld formation, microstructure, and mechanical properties of magnesium alloy and steel joint were studied. The results show that the addition of Si can improve the laser absorption rate of the interlayer and increase the melting depth at the magnesium side. In addition, the Cu-Si composite interlayer hindered the diffusion of Al, and reduced the thickness of reactive layer at the magnesium alloy and the steel interface. After adding Si into the interlayer, the reactive layer changed from Fe3Al+α-Mg to Fe-(Al, Si) +α-Mg and the content of intermetallic compounds in the reactive layer decreased, which improved the plastic deformation capacity and the ductility of the reactive layer. As a result, the tensile shear force firstly increased and then decreased with the Si increase. The maximum tensile shear force of 86.2 N/mm was achieved when the Si content was 5%, which was 20.4% higher than that of the Cu interlayer. Plus, the fracture location changed from near the steel side to near the magnesium side weld.

Microstructures and mechanical properties of Cf/LAS composite and Ti60 alloy joints brazed with TiZrNiCu + Cf mixed powders

AbstractIn this paper, carbon fiber reinforced lithium aluminosilicate (LAS) glass‐ceramics matrix composites (Cf/LAS composites) are joined to Ti60 alloy using TiZrNiCu + Cf mixed powders by proper process parameters. The carbon fibers distribute uniformly in the brazing interlayer and react with Ti, Zr elements in the brazing alloy to form (Ti, Zr)C thin reactive layers, which are between the carbon fibers and the Ti, Zr elements. The effect of Cf content on the mechanical properties and microstructure of brazed joints are investigated. The microstructure of brazed joints varied obviously with the increasing of Cf content. The thickness of reactive layer between interlayer and Cf/LAS composites and Ti solid solution (Ti (s.s)) decrease gradually, and the volume of eutectic structure (Ti(s,s) + (Ti,Zr)2(Ni,Cu)) decrease gradually. The obtained brazed joints exhibit a maximum shear strength of 73.5 MPa at room temperature using TiZrNiCu + 0.3 wt% Cf mixed powders. The enhanced shear strength can be attributed to the reduction in thermal stress and the reinforcing effect originated from the carbon fiber addition.

Oxygen transfer in co‐extruded multilayer active films for food packaging

Oxygen scavenger applications in flexible food packaging are still limited due to the difficulty to ensure scavenging activity during storage and throughout the product shelf life. To avoid fast inactivation of the scavenger, multilayer active structures can be realized by inserting the active layer between two or more inert layers. In this work, an unsteady‐state 1D reaction‐diffusion mass transfer model was developed for predicting and optimizing the barrier‐to‐oxygen performance and the physical configurations of the co‐extruded multilayer active films. The film configuration was a three‐layers structure composed of polyethylene terephthalate (PET) as external inert layers, and PET with a polymeric oxygen scavenger as the core reactive layer. Scavenging activity of the multilayer film increased with the reactive layer thickness. Oxygen absorption reaction at short times decreased proportionally with the thickness of the external layers. The most appropriate combinations of inert‐to‐active film thickness were studied and analyzed. © 2017 American Institute of Chemical Engineers AIChE J, 2017

An improved parameterisation of ozone dry deposition to the ocean and its impact in a global climate–chemistry model

Abstract. Schemes used to parameterise ozone dry deposition velocity at the oceanic surface mainly differ in terms of how the dominant term of surface resistance is parameterised. We examine three such schemes and test them in a global climate–chemistry model that incorporates meteorological nudging and monthly-varying reactive-gas emissions. The default scheme invokes the commonly used assumption that the water surface resistance is constant. The other two schemes, named the one-layer and two-layer reactivity schemes, include the simultaneous influence on the water surface resistance of ozone solubility in water, waterside molecular diffusion and turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. Unlike the one-layer scheme, the two-layer scheme can indirectly control the degree of interaction between chemical reaction and turbulent transfer through the specification of a surface reactive layer thickness. A comparison is made of the modelled deposition velocity dependencies on sea surface temperature (SST) and wind speed with recently reported cruise-based observations. The default scheme overestimates the observed deposition velocities by a factor of 2–4 when the chemical reaction is slow (e.g. under colder SSTs in the Southern Ocean). The default scheme has almost no temperature, wind speed, or latitudinal variations in contrast with the observations. The one-layer scheme provides noticeably better variations, but it overestimates deposition velocity by a factor of 2–3 due to an enhancement of the interaction between chemical reaction and turbulent transfer. The two-layer scheme with a surface reactive layer thickness specification of 2.5 µm, which is approximately equal to the reaction-diffusive length scale of the ozone–iodide reaction, is able to simulate the field measurements most closely with respect to absolute values as well as SST and wind-speed dependence. The annual global oceanic deposition of ozone determined using this scheme is approximately half of the original oceanic deposition obtained using the default scheme, and it corresponds to a 10 % decrease in the original estimate of the total global ozone deposition. The previously reported modelled estimate of oceanic deposition is roughly one-third of total deposition and with this new parameterisation it is reduced to 12 % of the modelled total global ozone deposition. Deposition parameterisation influences the predicted atmospheric ozone mixing ratios, especially in the Southern Hemisphere. For the latitudes 45–70° S, the two-layer scheme improves the prediction of ozone observed at an altitude of 1 km by 7 % and that within the altitude range 1–6 km by 5 % compared to the default scheme.

Numerical Model for Interfacial Reaction between Titanium and Zirconia in Electromagnetic Field

Based on the interfacial reaction model between Ti and ZrO2 in gravity field, taking account of the effect of electromagnetic field, a comprehensive numerical model for simulation of heat and mass transfer is established to study the interfacial reaction between liquid Ti and ZrO2 in electromagnetic field. With the proposed model, numerical simulations are preformed to investigate the influences of pouring temperature, holding time on the oxygen concentration and reactive layer thickness in metal. The results show that both the oxygen concentration and the thickness of reactive layer in metal increase with increasing the holding time and the pouring temperature. The thickness of reactive layer in electromagnetic field is greater than that in gravity field.

A mathematical model describing voltammograms and transport numbers under intensive electrodialysis modes

A three-layer mathematical model of overlimiting state is developed. A reactive layer with a thickness depending on the current density is introduced into the model. A decrease in the thickness of diffusion layer, which donates the counterions, with increasing current density as a result of electroconvection is also taken into account. A boundary-value problem is formulated within the Nernst-Planck and Poisson’s model in the three-layer region with the boundary conditions of constant concentrations in the bulk solution. It is shown that an increase in the reactive layer thickness with increasing current density determines the behavior of effective transport numbers in the overlimiting state of ion-exchange electromembrane system. In the current range under consideration (from 1 to 20 limiting currents), the reactive layer thickness is several tens nanometers and reaches 70 nm at a 100-fold excess over the limiting current. To calculate the voltammograms, the dependence of effective thickness δN of diffusion layer on the current density is required. This dependence can be obtained by solving an inverse problem, from the laser interferometry experiments, or calculated by the Navier-Stokes hydrodynamic model. The model enables one to calculate the distribution of electric field strength, potential, concentrations in the diffusion layers and membrane.

Electron-beam initiated polymerization of acrylate compositions, 2. Simulation of thermal effects in thin films

The thermal effects taking place during the electron beam-induced polymerization of acrylate type formulations were numerically simulated on the basis of the general heat equation applied to a one-dimensional system, The nature, the dimensions and the environment of the polymerizing medium were defined for representing the actual conditions of kinetic experiments performed with a 175 kV laboratory accelerator and FTIR monitoring. The modeled system was constituted of a polymerizable composition coated onto a NaCl plate, initially at 20°C in gaseous nitrogen at the same constant temperature, with or without a PET film covering the reactive layer, Polymerization profiles describing the progress of the reaction as a function of dose were modeled on a phenomenological basis from actual data obtained by discontinuous FTIR monitoring of typical epoxy acrylate or polyurethane acrylate compositions. The influence of the reactive layer thickness (10/100 μm), dose rate (10-110 kGy.s -1 ), maximum polymerization heat (200-400 J.g -1 ) on the temperature-time variations was examined for continuous irradiation. In spite of the relatively small thickness of the reactive layer, significant temperature rise is simulated when heat production is large and fast compared to energy dissipation at the reactive layer boundaries. The obtained data substantiate the fact that upon fractionated EB-treatment with small dose increments (down to 0.6 kGy per pass) at low dose rate (down to 10 kGy.s -1 ) the heat release can be considered weak and without noticeable influence on the conversion data processed for a detailed kinetic analysis. For example, a maximal temperature rise of 6°C was calculated for a fractionated irradiation of 2 kGy increments at 19 kGy.s -1 applied to a polymerizable formulation releasing a maximum enthalpy of 300 J.g -1 .

Temperature mapping of reactive gas layer in thermal plasma chemical vapor deposition

Two-dimensional temperature maps of reactive gas layers were produced using pulsed laser Rayleigh scattering thermometry. The measurements were made in conditions of diamond film chemical vapor deposition (CVD) using a thermal inductively coupled plasma. In these conditions, the reactive gas layer is typically a few millimeters thick and the temperature drops across the layer from 4000 K at the free stream boundary to about 1200 K at the substrate. The reactive layer exhibits strong chemical nonequilibrium. Rayleigh scattering was induced using a pulsed laser sheet at 532 nm wavelength. The scattered radiation was detected and calibrated with an intensified charge coupled device camera. Temperature maps and axial profiles obtained under parametric variation of the gas flow conditions demonstrate how the technique can be employed to measure the reactive layer thickness and its radial distribution across the substrate. The results demonstrate that imaging Rayleigh scattering thermometry can be employed as a nonintrusive diagnostic tool to obtain useful experimental information pertinent to the gas phase chemistry in diamond CVD under conditions of extremely large temperature gradients.