Pressure Dependence Of Modes Research Articles

Structural and chemical properties of the nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate under pressure

The structural and chemical properties of the bi-molecular, hydrogen-bonded, nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate C(3)H(12)N(12)O(2) (TAG-MNT) have been investigated at room pressure and under high pressure isothermal compression using powder x-ray diffraction and Raman and infrared spectroscopy. A stiffening of the equation of state and concomitant structural relaxation between 6 and 14 GPa are found to correlate with Raman mode disappearances, frequency discontinuities, and changes in the pressure dependence of modes. These observations manifest the occurrence of a reversible martensitic structural transformation to a new crystalline phase. The onset and vanishing of Fermi resonance in the nitrimine group correlate with the stiffening of the equation of state and phase transition, suggesting a possible connection between these phenomena. Beyond 15 GPa, pressure induces irreversible chemical reactions, culminating in the formation of a polymeric phase by 60 GPa.

Splat Problem for Control of Thermal Spray Process

Some kinds of metallic powder particles were thermally sprayed onto the mirror polished metallic substrate surface and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature increasing and ambient pressure decreasing. That is, the flattening behavior changed transitionally from splash shape to disk one on that critical temperature and pressure range, respectively. A transition temperature, Tt, and transition pressure, Pt, were defined and introduced, respectively for those critical conditions. Correspondingly, the coating adhesion property changed transitionally on that critical temperature and pressure range, respectively. Three dimensional transition curvature by combining both transition temperature and transition pressure dependence was proposed as a practical and effective controlling principle of the thermal spray process. The fact that the dependence of both transition temperature and transition pressure on the sprayed particle material had similar tendency indicated that the dynamic wetting of the substrate by the molten particles seemed to be a domination in the flattening.

Splash Splat to Disk Splat Transition Behavior in Plasma-Sprayed Metallic Materials

A variety of metallic powder particles were thermally sprayed onto the mirror polished metallic substrate surface and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature and ambient pressure. That is, the flattening behavior changed transitionally on that critical temperature and pressure range, respectively. A transition temperature, T t, and transition pressure, P t, were defined and introduced, respectively for those critical conditions. The fact that the dependence of both transition temperature and transition pressure on the sprayed particle material had similar tendency indicated that the wetting of the substrate by the molten particles seemed to be a domination in the flattening. Three-dimensional transition curvature by combining both transition temperature and transition pressure dependence was proposed as a practical and effective controlling principle of the thermal spray process.

粒子偏平挙動解析による溶射プロセスの制御化

A variety of metallic or ceramic powder particles were thermally sprayed onto the mirror polished metallic substrate surface and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature and ambient pressure. That is, the flattening behavior changed transitionally from a distorted shape with splash to a disk shape without splash on that critical temperature and pressure range, respectively. The results indicate that instead of the ordinal particle oriented factors, such as particle's velocity and temperature, particle/substrate interface oriented factors like substrate temperature and ambient pressure affect more the flattening behavior of the sprayed particle. A transition temperature, Tt, and transition pressure, Pt, were defined and introduced, respectively for those critical conditions. The fact that the dependence both of transition temperature and transition pressure on the sprayed particle material had similar tendency indicated that the wetting of the substrate by the molten particles seemed to be domination in the flattening. Three dimensional transition curvature by combining both transition temperature and transition pressure dependence was proposed as a practical and effective controlling principle of the thermal spray process.

Three-dimensional transition map of flattening behavior in the thermal spray process

Abstract Many kinds of both metallic and ceramic powder particles were plasma-sprayed onto the mirror-polished metallic substrate surface, and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature and ambient pressure. That is, the flattening behavior changed transitionally on that critical temperature and pressure range, respectively. We defined and introduced a transition temperature, T t, and transition pressure, P t, respectively, for those critical conditions. The role of the related factors (such as solidification of the bottom surface of the splat, desorption of adsorbates on the substrate surface and wetting at interface) on the transition behavior in the flattening was clarified from several points of views. The fact that the dependence both of transition temperature and transition pressure on the sprayed particle material had a similar tendency indicated that the wetting of the substrate by the molten particles seemed to be a domination in the flattening. A three-dimensional transition map by combining both transition temperature and transition pressure dependence was proposed as a controlling principle of the thermal spray process.

Pressure Induced Phase Transformations in Silica

ABSTRACTSilica, SiO2, is one of the most widely studied substance because of its complex and unusual properties. We have used a recently developed 2-body interaction force field [1] to study the structural phase transformations in silica under various pressure loading conditions. The specific transformations we studied are the a-quartz to stishovite, coesite to stishovite and fused glass to a dominantly six-coordinated dense glassy phase. Molecular dynamics simulations are performed under constant loading rates ranging from 0.1 GPa/ps to 1.0 GPa/ps, with final pressures upto 100 GPa and at temperatures of 300, 500, and 700 K. We observe the crystal to crystal transformations to occur reconstructively, whereas it occurs in a smooth and displacive manner from glass to a stishovite-like phase confirming earlier conjectures.[2] We studied the dependence of transition pressure on the loading rate and the temperature to elucidate the shock loading experiments. We also studied the unloading behavior of each transformation to assess the hysterisis effect.

PVT-studies on polymeric and oligomeric compounds

The pressure dependence of transitions in perfluorododecyloctane-F12H8-and in perfluorododecylhexadecane-F12H16)-has been measured from 10 to 200 MPa, from room temperature up to 220° C. The two transitions within this range-the transition of the alkane block from crystalline to mesomorphic, Tss, and the transition to melt, Tm-exhibit different pressure coefficients. As a pecularity, for F12H16 Tss and Tm superimpose at 10 MPa, in accordance to atmospheric pressure DSC data. Pressure dependences of transitions are given as well as their melting enthalpies.

Pressure dependence of transitions

Empirical observations indicate that secondary transitions, T sec, in polymers exhibit smaller pressure dependence than do glass transitions, T g . To explain these results, we have formulated a molecular model, known as the isosegmental model, which relates the pressure dependence of polymer transitions to the number of polymer segments involved in the transition. The model predicts a linear relation between the pressure dependence of T sec and T g and the number of polymer segments involved. This prediction is supported by experimental results.

Pressure Dependence of Transitions and Relaxations in Polytetrafluoroethylene

The ultrasonic absorption and linear thermal expansion behavior of polytetrafluoroethylene in a hydrostatic high pressure vessel (piston and compound cylinder type) capable of achieving 16,000 kg/cm2 are measured in the temperature from -30°C to 200°C and in the pressure from 1 atm. to 5,000 kg/cm2. Ultrasonic (5 Mc/s carrier frequency) attenuation maxima at atmospheric pressure are found at about -12°C, 30°C, 50°C, 130°C and 140°C, and pressure dependence of these maxima is found as about 10, 9, 28, 13, and 25 degrees per 1,000 kg/cm2, respectively. From these facts and the dispersion map, the third, fourth and fifth peaks indicate important informations of existence of segmental motion in amorphous regions (primary dispersion), crystalline dispersion and grain-boundary dispersion, respectively. By a thermodynamical consideration and the thermal expansion behavior, the second peak is defined as the one due to the 30°C transition.