Adhesion strength of tetrahydrofuran hydrates is dictated by substrate stiffness

Understanding the hydrate adhesion is important to tackling hydrate accretion in petro-pipelines.Herein,the relationship between the Tetrahydrofuran(THF)hydrate adhesion strength(AS)and surface stiffness on elastic coatings is systemically examined by experimental shear force measurements and theoretical methods.The mechanical factor-elastic modulus of the coatings greatly dictates the hydrate AS,which is explained by the adhesion mechanics theory,beyond the usual factors such as wettability and structural roughness.Moreover,the hydrate AS increases with reducing the thickness of the elastic coatings,resulted from the decrease of the apparent surface elastic modulus.The effect of critical thickness for the elastic materials with variable elastic modulus on the hydrate AS is also revealed.This study provides deep perspectives on the regulation of the hydrate AS by the elastic modulus of elastic materials,which is of significance to design anti-hydrate surfaces for mitigation of hydrate accretion in petro-pipelines.

BaTiO_(3)-based ceramics with high energy storage density

BaTiO_(3)ceramics are difficult to withstand high electric fields,so the energy storage density is relatively low,inhabiting their applications for miniaturized and lightweight power electronic devices.To address this issue,we added Sr_(0.7)Bi_(0.2)TiO_(3)(SBT)into BaTiO_(3)(BT)to destroy the long-range ferroelectric domains.Ca^(2+)was introduced into BT-SBT in the form of CaTiO_(3)(CT),which has the effect of inhibiting the movement of A-site defects to reduce dielectric loss and refining the grains to increase the breakdown field strength.In addition,we have increased the density and grain uniformity of ceramics by repeated rolling of the green samples through the viscous polymer processing(VPP),to further increase the breakdown electric field.The BT-SBT-CT ceramics exhibit the high recoverable energy storage density of 4.0 J·cm^(-3)under electric field of 480 kV·cm^(-1).Its recoverable energy storage density varies by less than 8%in the temperature range of 30-150℃,indicating good temperature stability of the energy storage performance.In this work,the energy storage performance of barium titanate-based ceramics was greatly improved by transforming ferroelectrics into relaxor ferroelectrics and VPP method,which can bring new inspiration for the research of energy storage ceramics.

High-efficiency dielectric capacitors based on BaTi_(0.5)Hf_(0.5)O_(3) films

Film dielectric capacitors enabled with large breakdown field strength and high energy density play a key role for compact and integrated power systems.Nevertheless,the energy storage efficiency is always sacrificed as we tried to increase the energy density.This trade-off between energy density and efficiency means significant energy dissipation and thermal effects,which will lead to a deterioration ofthe reliability and lifetime of the dielectric capacitors.

Mechanical properties and enhancement mechanisms of titanium-graphene nanocomposites

Molecular dynamics(MD)simulations of the titanium-graphene nanocomposites(TiGNCs)under uniaxial tension are carried out to investigate the mechanical properties and reinforcement mechanism of graphene in composites.It is found that introduction of mechanically robust graphene limits the strain-induced dislocation and araorphization and thereby highly improves the mechanical properties of metallic titanium that are greatly affected by the crystal stacking orientation of graphene and titanium layers.The thickness of titanium layers,interface interaction and working temperature play an important role in the mechanical strength and elastic moduli of composites.The results show the mechanical properties of TiGNCs are monotonically enhanced with reduction of the titanium layer thickness and working temperature,and the Young5s modulus obtained by MD simulation are higher than that predicted by the rule of mixture(ROM)due to consideration of interfacial interaction in computational calculation.In addition,once the critical thickness of titanium layer is reached,graphene wrinkles are induced in composites because of Poisson's effect induced large lateral compression stress in the interface region.This study provides helpful insights into fundamental understanding reinforcing mechanism of graphene and ultimately contribute to the optimal design and performance of mechanically robust graphene-based metallic composites.

DIELECTRIC RELAXATION IN RELAXOR FERROELECTRICS

In this review the dielectric properties of relaxor ferroelectrics are discussed and compared withthe properties of normal dielectrics and ferroelectrics. We try to draw a general picture ofdielectric relaxation starting from a textbook review of the underlying concepts and pay attentionto common behavior of relaxors rather than to the features observed in specific materials. We hopethat this general approach is beneficial to those physicists, chemists, material scientists and deviceengineers who deal with relaxors. Based on the analysis of dielectric properties, a comprehensivedefinition of relaxors is proposed: relaxors are defined as ferroelectrics in which the maximum inthe temperature dependence of static susceptibility occurs within the temperature range ofdielectric relaxation, but does not coincide with the temperature of singularity of relaxation timeor soft mode frequency.