Kinetics and mechanism of the low-energy β-a phase transition of the second kind in 2,4-dinitroanisole

In this work, comprehensive studies of 2,4-dinitroanisole(2,4DNAN) were carried out using powder thermorentgenography of the internal standard. The time of the complete polymorphic transition in the solid phase β→a in 2,4DNAN under various combinations of conditions has been determined. It has been established that, regardless of the season of manufacture of the substance, when it is stored for 8-9months, with a change in ambient temperature from minus 30℃ to plus 30℃, a complete polymorphic transition β→a occurs. When stored in conditions below minus 5℃, polymorphic transition does not occur. When stored in conditions above plus 30℃ in a closed container, polymorphic transition occurs within 3 weeks. The polymorphic transition is accompanied by a decrease in density by 1.3%-1.5% and an increase in melting temperature by 10-12℃, depending on the degree of purity of the starting substance. The activation energy of the molecular rearrangement was 68-70 k J/mol(16.5 ± 3 kcal/mol). The mechanism of polymorphic transition has been evaluated, which is presumably based on internal homodiffusion and energy transfer to the surface of the mass of powder particles and the product. The average activation energy of the polymorphic transition process was 110 ± 6.2 k J/mol(26.2 kcal/mol). In an open container, reactions proceed by a homogeneous mechanism, and in a closed container by a heterogeneous mechanism involving the gas phase.

Simulation of bacterial flagellar phase transition by non-convex and non-local continuum modeling

Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths and helix radii.When subjected to the frictional force of flowing fluid,the filament changes between a left-handed normal phase and a right-handed semi-coiled phase via phase nucleation and growth.This paper develops non-local finite element method(FEM) to simulate the phase transition under a displacement-controlled loading condition(controlled helix-twist).The FEM formulation is based on the Ginzburg-Landau theory using a one-dimensional non-convex and non-local continuum model.To describe the processes of the phase nucleation and growth,viscosity-type kinetics is also used.The non-local FEM simulation captures the main features of the phase transition:two-phase coexistence with an interface of finite thickness,phase nucleation and phase growth with interface propagation.The non-local FEM model provides a tool to study the effects of the interfacial energy/thickness and loading conditions on the phase transition.

Mechanical analysis of phase transition experiments of the bacterial flagellar filament

Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.

Structural modification in swift heavy ion irradiated muscovite mica

Two-layer monoclinic （2M） muscovite mica sheets with a thickness of 12 μm are irradiated with Sn ions at room temperature with electronic energy loss （dE/dx）e of 14.7 keV/nm. The ion fiuence is varied between 1 ×10^11 and 1 ×10^13 ions/cm^2. Structural transition in irradiated mica is investigated by x-ray diffraction （XRD）. The main diffraction peaks shift to the high angles, and the inter-planar distance decreases due to swift heavy ion （SHI） irradiation. Dehydration takes place in mica during SHI irradiation and mica with one-layer monoclinic （1M） structure is thought to be generated in 2M mica after SHI irradiation. In addition, micro stress and damage cross section in irradiated mica are analyzed according to XRD data. High resolution transmission electron microscopy （HRTEM） is used on the irradiated mica to obtain the detailed information about the latent tracks and structural modifications directly. The latent track in mica presents an amorphous zone surrounded by strain contrast shell, which is associated with the residual stress in irradiated mica.

Effect of hydration on the elasticity of mantle minerals and its geophysical implications

Recent studies have shown that major nominally anhydrous minerals in the Earth's mantle, such as olivine, pyroxene and garnet, can incorporate considerable amounts of water as structurally bound hydroxyl. Even a small amount of water is present in mantle minerals, it can strongly affect a number of physical properties, including density, sound velocity, melting temperature, and electrical conductivities. The presence of water can also influence the dynamic behavior, lead to lateral velocity heterogeneities, and affect the material circulation of the Earth's deep interior. In particular, seismic studies have reported the existence of low-velocity zones in various locations of the Earth's upper mantle and transition zone, which has been expected to be associated with the presence of water in the region. In the past two decades, the effect of water on the elasticity and sound velocities of minerals at relevant pressure-temperature(P-T) conditions of the Earth's mantle attracted extensive interests. Combining the high P-T experimental and theoretical mineralogical results with seismic observations provides crucial constraints on the distribution of water in the Earth's mantle. In this study, we summarize recent experimental and theoretical mineral physics results on how water affects the elasticity and sound velocity of nominally anhydrous minerals in the Earth's mantle, which aims to provide new insights into the effect of hydration on the density and velocity profile of the Earth's mantle, which are of particular importance in understanding of water distribution in the region.

Ca^2+ doping effects in(K,Na,Li)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics

Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.