Effect of E-44 Epoxy Resin and Pyrolysis Temperature on the Adhesion Strength of SiBCN Ceramic

An adhesive of the SiBCN ceramic was synthesized through the polymer derived ceramics(PDC)route.Meanwhile with higher adhesion strength and simpler process condition,the polyborosilazane(PSNB)was modified by E-44 epoxy resin.The E-44 epoxy resin was used to promote the oxidation process of SiBCN,in other words,to produce more amount of SiO2-B2O3 glasses.The phase composition,elemental analysis,chemical bonds and microstructure were investigated by using X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and scanning electron microscope(SEM)measurements.The E-44 modified adhesives were cured at 120℃in air for 2 h,and were pyrolyzed at 1200,1400,and 1500℃for 2 h in air,respectively.The highest adhesion strength of the modified adhesive was up to 5.33,12.23,and 12.50 MPa after being heat treated at 1200,1400,and 1500℃,respectively.Finally,we proposed an adhesion model and revealed the adhesion mechanism of SiBCN ceramic.

Nanoindentation responses of NiCoFe medium-entropy alloys from cryogenic to elevated temperatures

NiCoFe alloy,a medium-entropy alloy,shows potential for applications in extreme environments.However,there is a theoretical barrier concerning the unclear understanding of its high-temperature dislocation motion mechanism.The load response exhibits distinct signatures relevant to thermal activation,most notably a decrease in critical force(i.e,softening)from cryogenic to elevated temperatures,e.g.,from 200 to 1000 K.The onset of plasticity is characterized by the nucleation of stacking faults and prismatic loops at low temperatures,whereas the surface nucleation of Shockley partial dislocations dominates plasticity at elevated temperatures.We show that thermal effects lead to non-uniform atom pile-ups and control the rate of phase transformation with increasing indentation depth.The findings in this work extend the understanding of the mechanical response of NiCoFe alloys under indentation at different temperatures,shedding light on the underlying dislocation motion mechanisms and surface deformation characteristics.The observed transformation-induced plasticity mechanism has implications for the properties of medium-entropy alloys and their potential applications in extreme environments.

Synthesis of Non-oxide Porous Ceramics Using Random Copolymers as Precursors

In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.

BN/SiBCN light-leakage-proof coatings of silica optical fiber for long term sensors at high temperatures

SiBCN and BN/SiBCN light-leakage-proof coatings were prepared on silica optical fibers for sensing applications at high temperatures.Scanning electron microscopy was used to characterize the surface morphology and microstructure of the coated fiber.Mechanical and optical properties of the coated fiber were characterized by Raman,optical and tensile tests.Compared with the original fiber,the tensile strength of Si BCN and BN/Si BCN coated fiber show an increase of about 60%and 90%at room temperature,respectively.In addition,the tensile strength of BN/Si BCN coated silica optical fiber was increased by about 42%at 700°C.It has been found that the improvement of the strength of BN/Si BCN coated silica optical fiber is related to the healing of defects and residual compressive stress in fibers.From the light transmittance performance of the coated fiber,it was found that BN/Si BCN double coating could be an ideal total reflection solution to protect silica optical fiber from light leakage during high temperature sensing operation.