Comparison of the interface reaction behaviors of CaO–V_(2)O_(5) and MnO_(2)–V_(2)O_(5) solid-state systems based on the diffusion couple method

The formation mechanism of calcium vanadate and manganese vanadate and the difference between calcium and manganese in the reaction with vanadium are basic issues in the calcification roasting and manganese roasting process with vanadium slag.In this work,CaO–V_(2)O_(5) and MnO_(2)–V_(2)O_(5) diffusion couples were prepared and roasted for different time periods to illustrate and compare the diffusion reaction mechanisms.Then,the changes in the diffusion product and diffusion coefficient were investigated and calculated based on scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) analysis.Results show that with the extension of the roasting time,the diffusion reaction gradually proceeds among the CaO–V_(2)O_(5) and MnO_(2)–V_(2)O_(5) diffusion couples.The regional boundaries of calcium and vanadium are easily identifiable for the CaO–V_(2)O_(5) diffusion couple.Meanwhile,for the MnO_(2)–V_(2)O_(5) diffusion couple,MnO_(2) gradually decomposes to form Mn_(2)O_(3),and vanadium diffuses into the interior of Mn_(2)O_(3).Only a part of vanadium combines with manganese to form the diffusion production layer.CaV_(2)O_(6) and MnV_(2)O_(6) are the interfacial reaction products of the CaO–V_(2)O_(5) and MnO_(2)–V_(2)O_(5) diffusion couples,respectively,whose thicknesses are 39.85 and 32.13μm when roasted for 16 h.After 16 h,both diffusion couples reach the reaction equilibrium due to the limitation of diffusion.The diffusion coefficient of the CaO–V_(2)O_(5) diffusion couple is higher than that of the MnO_(2)–V_(2)O_(5) diffusion couple for the same roasting time,and the diffusion reaction between vanadium and calcium is easier than that between vanadium and manganese.

Formation and Growth Kinetics of Intermediate Phases in Ni-Al Diffusion Couples

Formation and growth of the intermediate phases in the Ni-Al diffusion couples prepared by pouring technique were investigated. Electron probe microanalysis, scanning electron microscopy and X-ray diffraction were used to characterize the product phases in the joints. The results show that two intermediate phases form in the sequence of NiAl3 and Ni2Al3 during solidification. After annealed, Ni2Al3 and NiAl3 still exist in the joints of the couples. The reasons for the formation of Ni2Al3 and NiAl3, as well as the absence of NiAl, Ni5Al3 and Ni3Al were discussed, respectively. The growth kinetics of both product phase layers indicates that their growth obeys the parabolic rate law. The activation energies and frequency factors for NiAl3 and Ni2Al3 phases were also calculated according to the Arrhenius equation.

Diffusion coefficient of Ti^4+ in calcium ferrite/calcium titanate diffusion couple

This study investigated the interdiffusion of calcium ferrite/calcium titanate system in the time range of 0-120 min by the diffusion couple method in a CO/N2 reducing atmosphere at 700℃.The results show that after the diffusion reaction occurred,no longitudinal agglomerations were present on the substrate surface on the calcium titanate side.When the diffusion time was increased to 105 min,a net vacancy flow from calcium titanate to calcium ferrite might have occurred,causing the surface of the calcium ferrite substrate to collapse.The thickness of the diffusion layer of the calcium ferrite/calcium titanate system was about 17-48μm,which conforms to the parabolic law of diffusion.The diffusion coefficient and the Ti^4+concentration in the calcium ferrite/calcium titanate system are related.This shows an increase in the diffusion coefficient with the increase of Ti^4+concentration,and the diffusion coefficient value was in the range of 10^−12-10^−11 cm^2·s^−1.

Determination of phase diagrams using the diffusion couple technique

It has been demonstrated that the diffusion couple technique is a powerful and efficient approach in establishing phase relationships of ternary systems. Accurate data on the phase equilibria can be obtained if the appropriate alloys are employed as end members of the diffusion couple. It is desirable to combine the diffusion couple technique with an investigation of the afterwards selected equilibrated alloys so that the precision and reliability of the obtained information about a ternary isotherm could be guaranteed.

Preparation of Y-Zr-Hf,Y-Zr-Nb Ternary Diffusion Couples and Phase Diagrams Determination

Work has been done in preparing ternary diffusion couple containing one rare earth element.Though rare earth is highly reactive,we have successfully prepared two ternary diffusion couples containing yttrium by means of special technique.By using electron microprobe analysis(EMPA),the two isothermal sections of Y-Zr-Hf and Y-Zr-Nb ternary systems at 1273K have been determined.The section of Y-Zr-Hf system consists of three one-phase regions,three two-phase regions and one three-phase region.And that of Y-Zr-Nb system consists of two one-phase regions and one two-phase region.The effeet of some factors on EMP measuring ac- curacy was also discussed.

Two-way coupled analysis of lithium diffusion and diffusion induced finite elastoplastic bending of bilayer electrodes in lithium-ion batteries

A fully coupling model for the diffusion induced finite elastoplastic bending of bilayer electrodes in lithium-ion batteries is proposed. The effect of the mechanical stress on the lithium diffusion is accounted for by the mechanical part of the chemical potential derived from the Gibbs free energy along with the logarithmic stress and strain. Eight dimensionless parameters, governing the stress-assisted diffusion and the diffusion induced elastoplastic bending, are identified. It is found that the finite plasticity starting from the interface of the bilayer increases the chemical potential gradient and thereby facilitates the lithium diffusion. The full plastic flow makes the abnormal lithium concentration distribution possible, i.e., the concentration at the lithium inlet can be lower than the concentration at the interface(downstream). The increase in the thickness of the active layer during charging is much larger than the eigen-stretch due to lithiation, and this excess thickening is found to be caused by the lithiation induced plastic yield.

Interdiffusion in the Fe_2O_3-TiO_2 system

Interdiffusion in the Fe203-TiO2 system was investigated by the diffusion couple method in the temperature range of 1323 to 1473 K. The diffusion concentration curves of Ti4＋ cations were obtained by electron probe microanalysis, according to which the Boltzmann-Matano method optimized by Broeder was used to calculate the interdiffusion coeffi- cients. The interdiffusion coefficients almost increased linearly with the mole fraction of Ti4＋ cations increasing, and they were in the range of 10-12-10-11cm2-s-1. The increase of temperature could also lead to the increase of the interdiffusion coefficients at a constant concentration of Ti4＋ cations. It was also found that the thickness growth of the diffusion layer obeyed the parabolic rate law.

DIFFUSION REACTIONS BETWEEN Cu AND NbTi-ALLOY

Diffusion reaction of superconductig composite NbTi/Cu assembled both mechanically and metallurgically,diffusion couples Ti/Cu and Nb/Cu have/been studied by means of EPMA.The results indicate that the initial interface state of the composite NbTi/Cu significantly affects the forming process of intermetallic compounds at the interface.In comparison with the metallurgically bound composite,the intermetallic com- pounds forms at a higher temperature in mechanically bound one.Therefore.the mechanical hinding process is beneficial to the production of NbTi/Cu superconducting composite. No intermetallic compounds have been observed in Nb/Cu system.The morphology of intermetallic phases and the sequence in which they form in Ti/Cu system are somewhat different from that in NbTi/Cu.The relationship between the thickness of compound layer and annealing time obeys the rule of y^(1.5) ∝ t.

Anisotropic diffusion of volatile pollutants at air-water interface

The volatile pollutants that spill into natural waters cause water pollution. Air pollution arises from the water pollution because of volatilization. Mass exchange caused by turbulent fluctuation is stronger in the direction normal to the air-water interface than in other directions due to the large density difference between water and air. In order to explore the characteristics of anisotropic diffusion of the volatile pollutants at the air-water interface, the relationship between velocity gradient and mass transfer rate was established to calculate the turbulent mass diffusivity. A second-order accurate smooth transition differencing scheme （STDS） was proposed to guarantee the boundedness for the flow and mass transfer at the air-water interface. Simulations and experiments were performed to study the trichloroethylene （C2HC13） release. By comparing the anisotropic coupling diffusion model, isotropic coupling diffusion model, and non-coupling diffusion model, the features of the transport of volatile pollutants at the air-water interface were determined. The results show that the anisotropic coupling diffusion model is more accurate than the isotropic coupling diffusion model and non-coupling diffusion model. Mass transfer significantly increases with the increase of the air-water relative velocity at a low relative velocity. However, at a higher relative velocity, an increase in the relative velocity has no effect on mass transfer.

Formation of Intermetallic Compound in Iron-Aluminum Alloys

The mechanism of iron and aluminum intermetallics formation in the reactive sintering of iron and aluminum mixing powders has been studied by investigating iron aluminum diffusion couples.The couples were treated at 600℃,700℃,800℃,900℃ and 1000℃ respectively.It was found that an Al rich intermetallics FeAl 3 has formed in iron adjacent to the interface of iron and aluminum by aluminum diffusion into iron at 600℃ (below the eutectic temperature),and that in the case above 700℃ (above the eutectic temperature) there was a liquid,an intermetallics Fe 2Al 5 has formed in both side of the interface.The diffusion of iron and aluminum atoms is companied with the Fe Al reaction during the treatment under the both conditions.The diffusion coefficients of iron and aluminum and the activation energy were determined.The mechanism of the intermetallics formation in the couples is also discussed.

ISOTHERMAL SECTION AT 1000 AND 1100℃ OF Fe-Mn-Al PHASE DIAGRAM

Phase equilibria at Fe-Mn side of isothermal section at 1000 and 1100℃ in Fe-Mn- Al system have been determined using the diffusion couple technique and metallography. A three-phase,α+γ+β,region was found at 1000℃.The method of solid/gas diffusion couple used to determine equilibrium phase composition is believed to be feasible for the system containing volatile component.

Experimental Determination of Solid Solubility of Ce、La、Nd、Sm in Fe or Ni

The solid solubility of Ce、La、Sm and Nd in Fe or N i at various temperature was determined by means of a diffusion-couple method with the aid of an electron probe microanalyzer.Two methods,namely area method and whole range method,were proposed for data processing in the present paper.The principle and re- lated problems in the experimental determination of the solid solubility of rare-earth elements in Fe or Ni by use of the above mentioned methods were also discussed.

ISOTHERMAL SECTION OF W-Ni-Cu SYSTEM AT 1017℃

The isothermal section of the W-Ni-Cu ternary system at 1017℃ was determined by means of diffusion couple specimens,EMPA and X-ray diffraction.Body-centered tetragonal Ni_4W and orthorhombic NiW but no NiW_2 observed in the W-Ni binary sys- tem at this temperature.The solubility ranges of W and Cu in Ni_4W are 16.95- 20.51 at.-% and 0-4.36 at.-%,respectively.The maximum solubility of W in γ(Ni) is 13.11 at.-%.

Cluster synchronization in a network of non-identical dynamic systems

Cluster synchronization in a network of non-identical dynamic systems is studied in this paper, using two-cluster synchronization for detailed analysis and discussion. The results show that the common intercluster coupling condition is not always needed for the diffusively coupled network. Several sufficient conditions are obtained by using the Schur unitary triangularization theorem, which extends previous results. Some numerical examples are presented for illustration.

A MFE method combined with L1-approximation for a nonlinear time-fractional coupled diffusion system

In this paper,a nonlinear time-fractional coupled diffusion system is solved by using a mixed finite element(MFE)method in space combined with L1-approximation and implicit second-order backward difference scheme in time.The stability for nonlinear fully discrete finite element scheme is analyzed and a priori error estimates are derived.Finally,some numerical tests are shown to verify our theoretical analysis.

The effect of oxygen concentration on the coupled neurons:Rich spiking patterns and synchronization

The dynamical microenvironments play a crucial role in neuronal spiking patterns.In this paper,we investigated the effect of oxygen concentration on different synchronous spiking patterns of two coupled neuron models by including dynamical ion concentration.Two coupling modes of electrical diffusive coupling and potassium diffusive coupling were considered.In these two cases,oxygen concentration exhibited an important role in the synchronous spiking patterns between two coupled neurons,and extremely rich electrical activities were observed.For the potassium diffusive coupling,differential synchronous patterns of oscillation state(OS),synchronous epileptic seizure state(SSZ)and synchronous spreading depression state(SSD)as well as SZ and SD bursting states were generated.For the electrical diffusive coupling,differential synchronous patterns of resting state(RS),SSZ and SSD were observed.

Solubility and diffusivity of CO2 in n-butanol ＋ N235 system and absorption mechanism of CO2 in a coupled reactionextraction process

The absorption of CO2 in insoluble organic amine is crucial for understanding the mechanism of coupled reaction-extraction-crystallization process between aqueous chloride and CO2. In this study, the solubility and diffusivity of CO2 in n-butanol＋ N235 system were measured and reported. The absorption of CO2 in the system is a physical absorption behavior and the solubility of CO2 decreases with the increase of the mass fraction of N235. The diffusivity of CO2 increases firstly and then decreases with the increase in the mass fraction of N235. Moreover, the absorption mechanism of CO2 in the coupled reaction-extraction-crystallization process was investigated and identified by experiments. The results indicated that in the coupled reaction-extraction-crystallization process, CO2 is absorbed by the aqueous phase rather than by the organic phase and further transferred into the aqueous phase.

Mechanisms of interfacial reactions between 316L stainless steel and MnO-SiO_(2) oxide during isothermal heating

Diffusion couple experiments were performed to study the thermodynamic and kinetic mechanisms of interfacial reactions between the 316L stainless steel and the composite MnO-SiO_(2) oxide during isothermal heating at 1473 K(1200℃)for 1,3,5,and 10 h and at 1173,1273,1373,1473,and 1573 K(900,1000,1100,1200,and 1300℃)for 3 h.Compositional variations in the 316L stainless steel and the composite MnO-SiO_(2) oxide in the vicinity of the steel-oxide interface in each diffusion couple specimen were determined.Before and after isothermal heating,thermodynamic equilibria between the oxide and steel at the interface were estimated in accordance with the calculation of the Gibbs free energy change in the interfacial steel-oxide reactions.The diffusion coefficients of Mn,Cr,and Si in 316L stainless steel under different experimental conditions were quantitatively acquired.The results showed that solid-state interfacial reactions occurred between the Cr in the 316L stainless steel and composite MnO-SiO_(2) oxide during isothermal heating,which resulted in the depletion of Cr and accumulation of Si and Mn in the steel in the vicinity of the steel-oxide interface.The widths of the Crdepleted zone,Mn-accumulated zone and Si-accumulated zone all showed increasing trends with increasing isothermal heating temperature and time.The average values of the diffusion coefficients of Mn,Cr,and Si in the steel at 1473 K(1200℃)were 1.21×10^(^(-14))±2.96×10^(-15),1.69×10^(-14)±2.54×10^(-15),and 1.00×10^(-14)±1.96×10^(-15) m^(2)s^(-1),respectively,and they continued to increase with increasing isothermal heating temperature.

High-throughput development and applications of the compositional mechanical property map of the β titanium alloys

By a combination of the nanoindentation and electron probe microanalysis(EPMA)techniques,the traditional diffusion couple technique is extended to map the mechanical property of β-type Ti alloys over a wide composition range,which can be utilized to develop very versatile novel bio-Ti alloys for hard tissue re placements in arti ficial bones,joints,and dental implants.To create complete single-phase composition ranges of Ti-based bcc solid solution,12 types of bcc Ti-Nb-Zr-Mo/Ti-Nb-Zr-Ta quaternary diffusion couples were fabricated and annealed at 1273 K for 25 h.In this way,the composition-mechanical property relationships in the vast composition space of Ti-based alloys were established using EPMA and nanoindentation probes.Notably,the measured composition-dependent Young’s moduli,hardness,and elastic recovery as well as the derived ratio of hardness to Young’s modulus,and the ratio of the cube of hardness to the square of Young’s modulus,in the developed compositional mechanical property database,were visualized in a five-dimensional scatter plot.This enables an effective tool to screen the Ti-Nb-Zr-based alloys fororthopedic and dental applications according to different clinical requirements,and to rationalize the fundamental mechanical relationships in the rapid development of β-Ti alloys.

Pseudo-spinodal mechanism approach to designing a near-βhigh-strength titanium alloy through high-throughput technique

The main reason for the high strength in near-βtitanium alloys is the ultrafine precipitation of the acicular secondary a phase in theβmatrix.The purpose of this study is to use the pseudo-spinodal mechanism to obtain the ultrafine a phase for the design of a new high-strength near-γtitanium alloy.Thermodynamic calculations and TC21-(TC21+15 Mo)diffusion couple composition gradient experiments were used to demonstrate that TC21+3 Mo alloy can undergo a pseudo-spinodal decomposition to obtain the ultrafine a phase,resulting in a high-strength alloy.By adjusting the heat treatment process to obtain a bimodal microstructure,the alloy exhibits a good balance between ultimate tensile strength(1351 MPa)and plasticity(8.5%strain).Thus,it was demonstrated that the pseudospinodal mechanism combined with a high-throughput diffusion couple technique is an effective method for designing high-strength titanium alloys.