Phase Transitions in Two-Dimensional Systems of Janus-like Particles on a Triangular Lattice

We studied the phase behavior of two-dimensional systems of Janus-like particles on a triangular lattice using Monte Carlo methods. The model assumes that each particle can take on one of the six orientations with respect to the lattice, and the interactions between neighboring particles were weighted depending on the degree to which their A and B halves overlap. In this work, we assumed that the AA interaction was fixed and attractive, while the AB and BB interactions varied. We demonstrated that the phase behavior of the systems considered strongly depended on the magnitude of the interaction energies between the AB and BB halves. Here, we considered systems with non-repulsive interactions only and determined phase diagrams for several systems. We demonstrated that the phase diagram topology depends on the temperature at which the close-packed systems undergo the orientational order–disorder transition.     

Kinetics of Solid Polymorphic Phase Transitions of CL‐20

Solid‐solid phase transitions of the CL‐20 polymorphs ε→γ, α→γ, and β→γ were studied isothermally at ambient pressure by transmission FT‐IR spectroscopy and analyzed by multivariate regression. Activation energies as function of the extent of conversion were obtained using the model‐free isoconversional method. The apparent activation energies for all three solid phase transformations were about 210 kJ/mol at 5% conversion, and compared well with the calculated lattice energies. The apparent activation energies increased to a maximum of about 400 kJ/mol at 40%, 80% and 60% conversion for ε→γ, α→γ, and β→γ, respectively, and then decreased. The mechanisms of the phase transitions of CL‐20 appear to be quite complex. Comparisons are made with the phase transitions of HMX.     

Dynamics of Ultrafast Phase Transitions in (001) Si on the Shock-Wave Front

We demonstrate an ultrafast (<0.1 ps) reversible phase transition in silicon (Si) under ultrafast pressure loading using molecular dynamics. Si changes its structure from cubic diamond to β-Sn on the shock-wave front. The phase transition occurs when the shock-wave pressure exceeds 11 GPa. Atomic volume, centrosymmetry, and the X-ray-diffraction spectrum were revealed as effective indicators of phase-transition dynamics. The latter, being registered in actual experimental conditions, constitutes a breakthrough in the path towards simple X-ray optical cross-correlation and pump-probe experiments.     

Some Observations on the Role of Dopants in Phase Transitions in Zirconia from Atomistic Simulations

Attempts to calculate the free energy of the polymorphs of zirconia are reported. The results suggest a theoretical basis for the phase transitions in terms of the removal of lattice instabilities (evidenced by imaginary phonon frequencies). Dopant stabilization of the higher symmetry structures is seen to arise because of changes to the phonon frequencies due to the different mass and effective charge of the dopant.     

还原焰烧成分相花釉的研制与形成机理探讨

针对还原焰烧成陶瓷西餐具的需要，对还原焰分相花釉的釉料组成、工艺条件、外观效果、低倍结构作了实验研究，并进一步探讨了分相花釉的形成机理。     

PG-TAM二元体系固-固相变的贮热性能及相变动力学研究

利用差示扫描量热法(DSC)测试了三羟甲基乙烷(PG)和三羟甲基氨基甲烷(TAM)二元体系的贮热性能包括相转变温度和相变焓.利用步冷曲线法研究相变与时间的关系,从而证明固-固相变符合阿仑尼乌斯方程,计算得到相变反应级数和表观活化能.     

乌洛托品气相生产工艺及生成反应的影响因素简

本文结合生产实际情况介绍乌洛托品气相法生产工艺和生成反应的影响因素,对气相法生产乌洛托品工艺有一定的参考意义.     

垂直管内两相流流型的实验研究

为正确预测气井井筒气液两相流动规律,在多相流实验平台上开展了不同管径(28、60 mm)和不同压力(0.10、0.50 MPa)下空气/水两相流流型实验,利用高速摄像机再现了泡状流、段塞流、搅动流和环状流的流型结构和过渡现象,绘制了实验流型图,对比了管径、压力对流型过渡的影响以及分析了环状流形成与液滴夹带的关系,在气液两相流实验的基础上,以环状流形成过程为例,从流型的物理现象着手,对环状流形成的机理进行了定义和数学建模,从而建立了产液气井两相流流型转变组合机理模型。将该组合机理模型和不同管径、不同压力下的实验结果进行对比,发现新模型均能正确预测各流型间的转变条件,具有一定的通用性。     

Third Phase Formation in the Extraction of Th(NO3)4 by Tri-n-Butyl Phosphate and Tri-iso-Amyl Phosphate in n-Dodecane and n-Tetradecane from Nitric Acid Media

Binary solutions of tri-n-butyl phosphate (TBP) or tri-iso-amyl phosphate (TiAP) in n-dodecane or n-tetradecane (1.1 M) as diluents have been investigated for third phase formation in the extraction of Th(NO₃)₄ from its solutions with 1 M or 5 M HNO₃ as a function of equilibrium aqueous phase Th(IV) concentration ([Th(IV)]_aq,eq) at 303 K. Extraction isotherms for the extraction of Th(IV) and HNO₃ have been generated with respect to [Th(IV)]_aq,eq. The difference in density between the third phase and the diluent-rich phase as well as the diluent-rich phase and the pure diluent, ratio of volume of the diluent-rich phase to that of the third phase have also been determined over a wide range of [Th(IV)]_aq,eq in the triphasic region. An attempt has also been made to determine the extractant concentrations in the third phase and the diluent-rich phase in the extraction of Th(NO₃)₄ by the above solvents from its saturated solutions with 1 M and 5 M HNO₃.     

Plutonium Third Phase Formation in the 30% TBP/Nitric Acid/Hydrogenated Polypropylene Tetramer System

Abstract

A study on plutonium third phase formation in 30% TBP/nitric acid/hydrogenated polypropylene tetramer (HPT) was performed. Characterization studies of HPT indicate its composition to be a mixture of many highly branched alkanes with a volatility close to n‐undecane. This composition results in about a factor of two better resistance to Pu(IV) third phase formation than dodecane. At 7 M nitric acid in the aqueous phase, the presence of Pu(VI) was observed to substantially reduce the organic phase metal concentration necessary to induce phase splitting in both diluents. Spectroscopic investigation of mixed valence systems also suggest a prominent role for Pu(VI) in the formation of the dense organic phase. Accumulation of Pu(VI) in the heavy phase, as well as certain spectral features, suggest that Pu(VI) is forming a different species, possibly a plutonyl trinitrato, with a strong tendency to form third phase.     

Mechanochemical Formation of Metal–Ceramic Composites

A mechanical activation technique has been used to form composites of alumina with titanium carbide, nitride, or carbonitride, both with and without elemental iron. The composites were formed by reacting elemental aluminum with either ilmenite (FeTiO₃) or rutile (TiO₂) concentrates in the presence of carbon and/or nitrogen in a ball-mill at ambient temperature. The reaction was complete for the ilmenite samples after milling but was completed only for rutile under hot pressing conditions. Microhardness measurements indicated that the composites had hardnesses in the range 19–30 GPa (1740–2750 VHN), with only a small variation within each sample. Elemental mapping of the pressed pellets indicated that titanium and aluminum were evenly distributed on a submicrometer level whereas iron tended to coalesce into <20 μm particles in the presence of TiC. The coalescence decreased with the carbon content of the hard material until iron was evenly distributed with TiN. A superstoichiometric amount of aluminum led to the formation of iron–aluminum phases which decreased the iron coalescence. The XRD crystallite size of the alumina was 30–50 nm and was 25–50 nm for the titanium phases, confirming the extremely fine microstructure.     

十二烷基磺酸钠/异辛烷/正构醇/水微乳状液的相行为及其结构转变的研究

The forming mechanism of microemulsion of sodium dodecyl sulfonate.alcohols,water and isooctane was studied,with particular emphasis on the effect of molecular weight and concentration of alocohols.Phase diagram of the four components,alcohol, sodium dodecyl sulfonate,water and isooctane,was used as a means of study,through which the microemulsion regions were determined.Phase diagram of sodium dodecyl sulfonate/n-pentanol/isooctane/water system at km=2(km=Wn-pentanol/WSDS)is presented. The variation of conductivities of different microemulsion samples with water was measured.From the conductivities we investigated a change in structure from water droplets in oil(W/O)at low water content to liquid crystal at intermediate water content and a structure of oil droplets in water(O/W)at high water content.     

Cristobalite Phase Formation in Glass/Ceramic Composites

The effect of several different aluminum-containing ceramic additions to borosilicate glass on suppressing cris-tobalite precipitation has been examined. The results showed that mullite or aluminum nitride suppresses cristo-balite formation more effectively than alumina or spinel. Although both follow a simple rule of mixtures, glass/mullite composites can be fabricated with lower dielectric constants than glass/alumina composites, while maintaining a thermal expansion coefficient close to Si. Electron micro-analysis using X-ray energy dispersive spectroscope showed that the measured interdiffusion coefficient between alumina and glass is in good agreement with the data which have already been published.     

Double pyrovanadates CaMgV2O7: Formation mechanism,phase structure,and thermodynamic properties

A double pyrovanadate CaMgV₂O₇ sample was synthesized via a facile solid-state route under an air atmosphere. The nonequilibrium formation pathways of the CaMgV₂O₇ were investigated via powder X-ray diffraction. A multistep reactions path (metavanadates–pyrovanadates–double pyrovanadate CaMgV₂O₇) was proposed to describe the formation of the CaMgV₂O₇ considering the thermodynamic and kinetic factors. The cell unit parameters of the CaMgV₂O₇ sample indicated the crystallization according to a monoclinic system with space group P12/c1(14), and the lattice parameters of a = 6.756 Å, b = 14.495 Å, c = 11.253 Å, β = 99.12, and V = 108.806 Å³. X-ray photoelectron spectroscopy also confirmed the +5 oxidation state vanadium in CaMgV₂O₇. The endothermic effects at 1033 and 1143 K were related to the incongruent melting and liquidus temperatures of CaMgV₂O₇, respectively. The comprehensive thermodynamic properties of CaMgV₂O₇ were established in both low- and high-temperature regions, utilizing a physical property measurement system and multi-high-temperature calorimetry (96 lines). The heat capacity (200 J mol K⁻¹) and entropy (198 J mol K⁻¹) at 298.15 K were computed based on the low-temperature heat capacity values, and the enthalpy of formation at 298.15 K was also estimated. The fitted high-temperature capacity can be used to obtain the changes in the enthalpy, entropy, and Gibbs free energy. This study is part of building a reliable thermodynamic database of the CaO–MgO–V₂O₅ system.     

Third Phase Formation in the Extraction of Zirconium(IV) by TRPO in Kerosene

The third phase formation in the extraction of zirconium(IV) from nitric acid media by TRPO(trialkyl phosphine oxide)/kerosene was studied. The limiting organic concentrations (LOC) of Zr(IV) under various experimental conditions were determined. Low temperature and high nitric acid concentrations (> 3 M) were found to facilitate the third phase formation, while increasing the concentration of TRPO or adding phase modifier (TBP) into the organic phase resulted in increased LOC of Zr(IV). When the third phase appeared, the conductivity in the organic phase changed sharply, indicating the change of aggregating behavior in the organic phase. FT-IR spectra were used to illustrate the interaction of TRPO with HNO₃ or Zr(IV), and the composition of the two organic phases indicated by FT-IR spectra was consistent with a diluent-enriched light phase and a zirconium/TRPO-concentrated heavy phase.     

The Deformation of Rigid Gels of One-Step Polyamide Networks and Their Constituent Stiff Segments

Abstract

When a gel of rigid polyamide network is prepared in solution by a single step polymerization, some of its stiff segments are straight and others are bent. The motional freedom of the majority of the segments is greatly constrained by having fully or mostly reacted multifunctional rigid branchpoints at both their ends. A minority of the segments are less constrained because they are attached to the network at one end only. We believe that a most efficient mechanism for bending of constrained straight stiff polyamide segments is by a pair of syn-anti interconversions occurring in the same segment. For polyamides these are the least energy consuming changes in which 180° rotations around the ring-to-carbonyl or ring-to-nitrogen bonds take place at an activation energy as low as 4 kcal/mol. In this way, significant translations of one branchpoint relative to the other take place without any torsions of the moving branchpoint and with the bent portions of the stiff segment defining no or almost no “cone of rotation” in space. Conversely, the most efficient straightening mechanism for constrained bent stiff segments is the reversal of the above process, i.e., two placement interconversions occurring per segment. Stiff segments attached to the network at only one end can easily deform by a single inter-conversion, of course.

During macrodeformation the gels maintain constant volume. In this deformed state, the size of the populations of straight and bent stiff segments changes from the relaxed state. In the directions where the stressed sample increases its dimensions, the population of straight segments grows at the expense of the bent segments. In the perpendicular directions where the dimensions of the gel decrease, the population of bent segments increases at the expense of the straight ones. The inability of straight stiff segments to stretch results in increases in modulus with deformation. After the stress is removed the populations of straight and bent segments revert back to their original size. From the above it is obvious that the deformation of rigid gels is not affine. Similarities exist between deformation and swelling, except for the fact that in the swollen gel the population of straight segments increases isotropically throughout the sample which is not the case in the deformed gel. The strong effects of network imperfections are discussed in the context of rigid network swelling.     

Phase Transitions of Branched Fatty-Acid Calcium Salt/Water Systems

Calcium (Ca) salts of fatty acids are powder materials, which exhibit lubricant, hydrophobic, and bactericidal properties. These physical and biological properties depend on the chemical structure of the alkyl chain of the fatty acids. In this study, the phase behavior of iso-stearic acid Ca salt/water binary systems was studied, and the effect of the branched structure in the alkyl chain was analyzed. Herein, calcium chloride is added to the iso-stearic acid aqueous solution. The state of the binary systems changed with the molar ratio (R) of [Ca²⁺]/[iso-stearic acid]. Precipitation occurred when R was more than 0.05, whereas the mixture changed from a micelle phase (W_m) to an oil phase (O) through a liquid crystalline phase (LC) when R was less than 0.01. The polarized microscopy images and small-angle X-ray scattering profiles showed that the LC is in a lamellar liquid crystalline state. In addition, we evaluated the crystal structure of the precipitated material. These results showed that the iso-stearic acid Ca salt was in the amorphous state. In contrast, the n-stearic acid Ca salt formed only the W_m and gel phases. These findings suggest that the branched structure of fatty acids induces loose intermolecular packing of liquid crystalline structures.     

Na2XO4(X=Cr、MO、W)固-固相变贮热的测定

利用DTA－TG热分析技术研究了无机塑晶材料Na2XO4(X=Cr、Mo、W)的热性能，实验数据表明，三种材料是一种有前途的固－固相变贮热材料，其固－固相变贮热的机理是随着温度升高，三种晶体的晶格发生畸变，晶型由低对称的晶系向高对称的晶系转变，同时引入振动和转动无序，从而吸收热量。     

Diffusionless Cubic-to-Tetragonal Phase Transition and Microstructural Evolution in Sintered Zirconia–Yttria Ceramics

Microstructural changes associated with the diffusionless cubic-to-tetragonal phase transition ( c–t ') in sintered ZrO₂–Y₂O₃ ceramics with 4 to 20 mol% Y₂O₃ are investigated. Ceramics containing 4 to 7 mol% Y₂O₃ that are quickly cooled from high temperatures experience cubic-to-tetragonal transformation by a diffusionless mechanism. The TEM diffraction pattern of the transformation product, t '-ZrO₂, reveals (112) reflections that are suppressed in the c -ZrO₂ phase. The microstructural features of the t '-ZrO₂ phase include antiphase boundaries and a twinned substructure in the (112) dark-field images. The (112) reflections result from the displacement of oxygen atoms in the lattice during phase transformation. With increasing Y₂O₃ content, the antiphase domain size, the tetragonality of the lattice, and the intensity of the (112) reflections decrease. When the Y₂O₃ content reaches 8 mol% or more, the (112) reflections appear, but the dark-field image shows no antiphase boundary, and the tetragonality decreases to 1. In ceramics with 14 to 20 mol% Y₂O₃, no suppressed reflection appears because the c–t transformation is fully suppressed. A model of the lattice structure is calculated and the intensity of diffraction determined experimentally; on this basis, the mechanism of diffusionless c–t 'transformation is discussed.     

Tetragonal-to-Monoclinic Phase Transitions in Nanocrystalline Rare-Earth-Stabilized Zirconia Prepared by a Mild Hydrothermal Method

Nanocrystalline 4-mol%-Sc₂O₃-stabilized zirconia (4ScSZ) and 4-mol%-Y₂O₃-stabilized zirconia (4YSZ) powders were prepared by a mild urea-based hydrothermal method. The as-prepared 4ScSZ and 4YSZ powders behaved with different tetragonal–monoclinic ( t – m ) transitions on calcination at temperatures between 400° and 1400°C. For the as-calcined 4ScSZ samples, the monoclinic phase fraction varies discontinuously with increasing temperature, i.e., first increases, then decreases, and finally increases again; whereas the monoclinic phase content reduces monotonously for the as-calcined 4YSZ samples, and only tetragonal phase is present over 1000°C. Such interesting results can be explained satisfactorily by considering the combined influences of crystallite size effect, microstrain, and the stabilization effect of the dopant. The microstrain relaxation is mainly responsible for the unusual phase transition in the 4ScSZ samples, while for the 4YSZ samples, the microstrain effect and crystallite size effect can be masked by the stabilization effect of the Y₂O₃ dopant due to its stronger stabilization capability.