Search

In the present study, CFD were used to investigate the effect of a new type of rotary kiln on the velocity field, temperature field, material component distribution, and NOx concentration distribution in poor oxygen (18% O2), normal oxygen (21% O2), oxygen-enriched (24% O2, 27% O2, 30% O2) and full oxygen (100% O2) combustion conditions. The reliability of the simulations was demonstrated by grid independence and the thermal calibration data of the cement plant. The results revealed that the dual recirculation zone could strengthen the burner's stabilizing effect. The local low-temperature zone near the burner could prolong the burner nozzle's service life. Furthermore, the increase in oxygen concentration would change the flame length; the flame length under oxygen enrichment and full oxygen were significantly shorter than that under oxygen depletion. The highest temperature in the kiln was directly proportional to the oxygen concentration. The average temperature changes were relatively smooth, resulting in poor combustion uniformity in the kiln. The maximum temperature of poor oxygen combustion below 1730 K is not conducive to the intensified production of clinker. Full oxygen combustion can maximize the combustion temperature in the kiln and is accompanied by a significant increase in CO2 and thermal NOx concentration. As the oxygen concentration increased from 21% to 27%, the temperature in the kiln rapidly increased, and NOx slowly increased; when the O2 concentration was greater than 27%, the temperature slowly increased, and NOx rapidly increased. Therefore, oxygen-enriched conditions should be controlled by 27%, and the NOx emission reduction effect would be more obvious. [ABSTRACT FROM AUTHOR]

An anisotropic plasticity model for the description of nonisotropic mechanical behaviors of porous media is presented. This model is developed using bounding surface plasticity theory within the critical state framework. The inherent and stress-induced anisotropy has been accounted for by an anisotropic variable, which is employed with the consideration of both irrecoverable deformation and stress state. The evolution of anisotropy has been described by both rotational and distortional hardening rules. The rotational hardening rule is proposed for the consideration of bounding surface inclination induced by inherent or induced anisotropy. The distortional hardening rule is developed to capture the varying shape of bounding surface associated with the accumulation of irrecoverable deformation and anisotropy. This model has been validated through modeling the stress–strain responses of porous media under various loading conditions, including triaxial drained/undrained compression/extension tests on both isotropically and anisotropically consolidated samples. Good agreement between model simulation and experimental results has been achieved for all cases taken into consideration, demonstrating the capability of the proposed model. [ABSTRACT FROM AUTHOR]

• The 4D-LSM is further developed by implementing JHB constitutive model. • The JHB-4D-LSM was verified by modelling Brazilian tests and dynamic spalling tests. • JHB-4D-LSM is applied to study penetration in both thin plate targets and thick B 4 C under various impact velocities. • Good agreement among numerical simulation and numerical/ analytic results demonstrates the capability of JHB-4D-LSM. The imbedded linear constitutive model in four-dimensional lattice spring model (4D-LSM) is not sufficient or accurate enough to solve the dynamic problems with high-speed impacts. In order to produce a more realistic prediction of dynamic fracture process in brittle materials, the capability of four-dimensional lattice spring model (4D-LSM) has been further extended by implementing Johnson-Holmquist-Beissel (JHB) model. This is achieved by defining the micromechanical constitutive model parameters of 4D-LSM through the macro-scale strength parameters in JHB model, with an incremental form of 4D-LSM being developed. The incremental JHB-4D-LSM model is verified by modelling dynamic Brazilian tests and dynamic spalling tests, with good agreement between modelling results by JHB-4D-LSM and theoretical/numerical solutions in literature being obtained. For the demonstration of model application, the proposed JHB-4D-LSM model is applied to simulate and analyse the problems of projectile penetration with various initial impact speeds. Reasonable numerical modelling results indicate that, the proposed JHB-4D-LSM model can be served a promising tool to predict projectile penetration behaviour of brittle materials. [ABSTRACT FROM AUTHOR]

In this study, pure-phase Cd7P10 crystals are prepared by the reaction of elements at high pressures in a large-volume cubic press. The synthetic Cd7P10 samples are characterized by powder X-ray diffraction, scanning electron microscopy and diamond indentation method. The results show that orthorhombic Cd7P10 grains with a size of over 70 μm could be obtained and that the high pressure well-sintered Cd7P10 compacts have a Vickers hardness value of 8.9 GPa under a load of 49 N. The pressure–temperature formation region of Cd7P10 is determined up to 5 GPa and 1500°C, and the formative mechanism under high pressures is discussed. Our results exhibit a novel route for synthesizing bulk semiconductor polystalline Cd7P10 compacts. [ABSTRACT FROM AUTHOR]

Abstract: Well-crystallized graphite and high energy ball-milled graphite were treated under 16GPa and temperatures up to 2500°C. Our experiments indicated that the ball-milled graphite can completely transform to nano-polycrystalline diamond (NPD) at 2100°C, while the well-crystallized graphite required 2500°C. The samples were characterized by X-ray diffraction, optical microscope, scanning electron microscope, and Vickers indenter hardness test. We found that high pressure not only made the conversion of graphite to NPD thermodynamically preferred, but also reduced the needed activation energy barrier. By analyzing thermodynamics and kinetics of the transformation, we suggested a low boundary for NPD forming region based on the phase diagram of carbon, and the formation mechanisms of Nano-polycrystalline diamond. [Copyright &y& Elsevier]

Abstract: High pressure in situ differential thermal analysis (DTA) was applied to study phase transitions of Na0.5Bi0.5TiO3 (NBT) up to 5GPa. DTA analysis at room temperature with pressure as the variable indicated NBT samples have two pressure induced phase transformations at about 0.7GPa and 2.5GPa respectively. Below 0.7GPa, two temperature induced phase transitions could be observed at around 220°C and 520°C as it was reported at ambient pressure. But under a pressure higher than 0.7GPa, these two temperature induced phase transitions would not happen. In situ electrical resistance measurements showed that the resistance of NBT changes smoothly, and the tendency is similar to that of electrical insulators like pyrophyllite. We suggest that the pressure induced phase transitions at 0.7GPa and 2.5GPa are both insulator to insulator phase transitions. [Copyright &y& Elsevier]

Single-phase BC4N can be formed at high pressure and temperature, starting with either a mixture of diamond and cubic boron nitride or graphite and hexagonal boron nitride. The samples exhibit extreme Vickers hardness (85±4GPa), reaching the hardness of single crystal diamond. Within a random solid solution model, the X-ray diffraction patterns of cubic BC x N solid solutions were calculated. The results indicate that the prepared B–C–N materials are continuous solid solutions with a zinc-blende structure. [Copyright &y& Elsevier]

Abstract: This work presents a comprehensive study on phase transition in NaGaO2 under high pressure and temperature (P–T) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO2 could undergo a structural phase transition from orthorhombic - NaGaO2 to hexagonal - NaGaO2 under high pressure and temperature. The pressure–temperature phase boundaries of NaGaO2 were determined up to 5 GPa and 2073 K. The hexagonal - NaGaO2 sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition from - to - NaGaO2 was observed above 473 K under normal-pressure condition. The high-pressure melting curve of NaGaO2, for the first time, was measured by using in-situ thermal measurement. [Copyright &y& Elsevier]

Quantitative measurements of pressure gradients have been made in the pyrophyllite and magnesium oxide (MgO) pressure-transmitting mediums using large-volume cubic apparatus. The relationships of pressure gradients along the axis of symmetry of the pyrophyllite and MgO cubes versus corresponding cell pressures have been established at room temperature. Our experimental results indicated that the pressure gradients increase as the cell pressure increases and that the pressure gradient in the MgO pressure-transmitting medium is about twice as high as that in the pyrophyllite pressure-transmitting medium at the same cell pressure. When the cell pressure reaches 5.5 GPa, the pressure gradient along the axis of symmetry of the pyrophyllite cube is about 50 MPa/mm. When the cell pressure reaches 7.7 GPa, the pressure gradient along the axis of symmetry of the MgO cube is about 140 MPa/mm. The experimental data obtained in the present work not only adapt to the cubic apparatus but also provide reference for the tetrahedral press and the double-stage multi-anvil apparatus (the octahedral compression). [ABSTRACT FROM PUBLISHER]

Phase transitions of the title compound are investigated by high pressure in situ DTA up to 5 GPa. [ABSTRACT FROM AUTHOR]