Entropy change-induced elastic softening of lithiated materials

To understand the ＂elastic softening＂ of Li-Si alloys for the development of Li-ion batteries, the effect of stress-induced change of entropy on the mechanical properties of lithiated materials is examined within the theories of thermodynamics and linear elasticity, An approach is presented whereby the change of Gibbs free energy is governed by the change of the mixture entropy due to stress-induced migration of mobile atoms, from which the contribution of the change of the mixture entropy to the apparent elastic modulus of lithiated materials is determined. The reciprocal of the apparent elastic modulus of a lithiated material is a linear function of the concentration of mobile Li-atoms at a stress-free state and the square of the mismatch strain per unit mole fraction of mobile Li-atoms.

Thermodynamics of Phase Equilibria in FeO-TiO2-Al_(2)O_(3)System

This scientific paper discusses the information on the structure of the three-component system FeO-TiO_(2)-Al_(2)O_(3),which is necessary for the creation of heat-resistant oxide materials.The structure of binary systems:FeO-Al_(2)O_(3),FeO-TiO_(2),and Al_(2)O_(3)-TiO_(2)is described,and the data on the FeO-TiO_(2)-Al_(2)O_(3)system are presented.The thermodynamic data of all compounds of the system are given,on the basis of which the change in the Gibbs free energy in the temperature range of 800-1900 K for twenty-one exchange reactions was calculated.It has been established that the triangulation of the FeO-TiO_(2)-Al_(2)O_(3)system changes in five temperature ranges:up to 1408 K(TiO_(2)exists in the polymorphic modification-anatase),1408-1537 K(TiO_(2)exists in the polymorphic modification-rutile and pseudobrookite is stable),1537-1630 K(thialite is stable),1630-2076 K(rearrangement cannot occur)and above 2076 K(the presence of the stoichiometric compound Al_(4)TiO_(8)is allowed).Two-phase equilibria up to 1408 K are stable:Al_(2)O_(3)-FeTiO_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1408-1537 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1537-1630 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),FeAl_(2)O_(4)-Fe_(2)TiO_(4),and FeAl_(2)O_(4)-Al_(2)TiO_(5);in the temperature range of 1630-2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),Al_(2)TiO_(5)-FeTiO_(3),FeTiO_(3)-Al_(2)O_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);over 2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),FeTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-FeTiO_(3),Al_(4)TiO_(8)-Fe_(2)TiO_(4),Al_(4)TiO_(8)-FeO,and Al_(4)TiO_(8)-FeAl_(2)O_(4).

Thermodynamic Modeling of MgO-Al_(2)O_(3)-TiO_(2) System

This scientific paper gives consideration to the information on the structure of the triple component system,in particular MgO-Al_(2)O_(3)-TiO_(2) that serves as a basis for the production of thermal resistance materials.The structure of such binary systems as MgO-Al_(2)O_(3),Al_(2)O_(3)-TiO_(2),MgO-TiO_(2) was described and the data available for the MgO-Al_(2)O_(3)-TiO_(2) system were given.Thermodynamic data on all the system compounds were also presented and used for the computation of a change in the free Gibbs energy in the temperature range form 800 K to 1900 K for the basic exchange reactions.It was established that the triangulation of the MgO-Al_(2)O_(3)-TiO_(2) system was changed in the three temperature intervals:in the temperature range lower than 1537 K TiO_(2) existed as the polymorphous modification,i.e.anatase;in the temperature range from 1537 K to 2076 K TiO_(2) existed as a polymorphous modification in form of rutile and tialite was stable;and at the temperatures above 2076 K the availability of stochiometric compound of Al4TiO_(8) was possible.In the temperature range lower than 1537 K the two-phase equilibra of Al_(2)O_(3)-MgTi2O_(5),Mg-MgALCU MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable;in the temperature range from 1537 K to 2076 K the two-phase equilibria of MgTigO_(5)-AlgTiO_(5),MgTiO_(3)-Al_(2)TiO_(5),MgTiO_(3)-Al_(2)O_(3),MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable,and above 2076 K the MgTi_(2)O_(5)-Al_(2)TiO_(5),MgTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-MgTiO_(3),Al_(4)TiO_(8)-Mg_(2)TiO_(4),Al_(4)TiO_(8)-Mg0,and Al_(4)TiO_(8)-MgAl_(2)O_(4) systems were stable.

Electron beam surface heating-diffusion bonding:An effective joining method for aluminum alloy metal-matrix composite with high SiC volume

As a novel method to reduce the temperature during electron beam welding,and to subsequently inhibit interfacial reaction between SiC and Al matrix,the electron beam surface heating-diffusion bonding is proposed for joining SiC particle reinforced aluminum alloy metal-matrix composite of 45 vol.%SiC/2024 Al.The defocused electron beam was used to heat the base metal surface,and the simultaneous pressure was applied to the butt surface to achieve bonding.The base metals were successfully joined by diffusion.The maximum temperature of the whole joint was effectively decreased to less than 650°C.The Gibbs free energy change of interfacial reaction was calculated,meaning a positive value reaching 218 kJ/mol and a consequently prominent inhibitory effect on the formation of brittle Al_(4)C_(3)that was proved by microstructural observation.The tensile strength for the bonded joint was increased by 35%compared to that for ordinary welded joint.When the TC4 layer was added,TiC strengthening particles were formed with the deficiency of Al_(4)C_(3),corresponding to the significantly increased tensile strength of 63%of base metal(154 MPa).