Corrosion Behavior Of Ti₂AlX（X=C Or N） Ceramics And Electrochemical Properties Of The Products

MAX phase has the nature of both metals and ceramics,it has been received abroad attention in recent years.The acid corrosion behavior of MAX ceramics has been well known.The corrosion products of MAX phase,due to its unique two-dimensional sheet structure,MXene has great advantages in terms of physical and chemical properties.However,there are few studies on alkali corrosion behavior of MAX ceramics,the corrosion mechanism and product properties have not yet been clarified.In this work,the Ti₂AlC and Ti₂AlN ceramics were synthesized by pressureless sintering,and were etched by acid or alkali solution respectively.The crystalline phase,size and morphology of the products were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and the electrochemical performance were explored through the constant current charge/discharge experimental,cyclic voltammograms（CV）,the results are as follows:The Ti₂AlC and Ti₂AlN ceramic powders obtained by pressureless sintering have good crystallinity and dense lamellar morphology.The grain size are between 5-10?m and 5?m,respectively.Ti₂AlC showed the good selective corrosion behavior under conditions of6M/H⁺,1.2M/F^-,and 35°C for 36h.The Ti₂AlC ceramics exhibited an accordion-like and could be exfoliated two-dimensional nano-sheets.At the same time,under the current density of 100mA g^-1,the specific capacity of charge-discharge can reach 241mAh g^-1.The value is close to its theoretical specific capacity of Ti₂C(250 mAh g^-1),and showed good rate performance and cycle stability.At first the products of Ti₂AlC were mostly non-stoichiometric potassium titanate.With the increase of concentration and time,the morphology of the product became banded,coarsed,and then curled into the rods.When the concentration was fixed on 10M,the corrosion time was 24h,the products were lamellar C-K₂Ti₄O₉ composites,which showed excellent electrochemical performance.With the current density of 100 mA g^-1,after 700 cycles of charge and discharge,the specific capacity could reach 314 mAh g^-1.The value has been improved to the experimental value of Ti₂C significantly.Due to the extremely unstable Ti-N structure,theselective etch of Ti₂AlN was difficult to achieve in HF acid.And similarly to Ti₂AlC,the alkali corrosion products of Ti₂Al N was also potassium titanate.The difference is that the products had tunnel-structure of K₂Ti₈O₁₇ whiskers.Because of the closeness structure,The K₂Ti₈O₁₇ exhibited a weaker electrochemical performance than C-K₂Ti₄O₉.The specific capacity was less than 200 mAh g^-1 at 100 mA g^-1,and the cycle performance was relatively poor.In order to design the structure,we have investigated the doping modification of Ti₂Al N ceramics on Al-site.When the A-site was doped three elements of 0.05Ga/0.03In/0.02Sn,the Ti₂AlN prefored obviously solid solution effect.Under the effect of HCl solution,the corrosion products was free-distributed two-dimensional thin sheets with the thickness of less than 50nm and exhibited good peeling behavior.At the same time,highly textured Ti₂Al N ceramic was successfully fabricated by edge-free spark plasma sintering（EFSPS）of Ti₂AlN discs followed by thermal explosion（TE）.Due to the highly preferred orientation of grains,the textured ceramics exhibited excellent anisotropy in physical and chemical properties...