Estimating the creep behavior of polycarbonate with changes in temperature and aging time

Thermoplastic resins are typically used without any kind of physical aging treatment. For such materials, creep behavior and physical aging, which depend on time and temperature, occur simultaneously. The effects of these processes are evident after quenching and are recorded in the material as a thermal history. This history strongly influences mechanical properties and creep behavior in particular. Thus, a more thorough understanding of the physical aging process is desirable. We examined the creep deformation of polycarbonate (PC) to reveal the effects of physical aging on creep behavior. The effects were dependent on both time and temperature. The relationship between physical aging and creep behavior exemplified superposition principles with regard to time and both pre-test aging time and pre-test aging temperature. The superposition principles allowed the calculation of creep deformations at a given temperature; the calculated results were corroborated by experimental data.     

Energy Savings through Microwave Selective Heating of Pd/AC Catalyst Particulates in a Fixed‐Bed Reactor

Microwave radiation is a novel energy source to drive chemical reactions. In conventional reactors, however, the heat created either escapes through uninsulated reactor walls, or the microwave radiation is attenuated by insulated walls. Here, microwave selective heating of Pd catalyst particles supported on activated carbon particulates was examined in a fixed‐bed reactor using a novel vacuum‐filled Dewar‐like double‐walled continuous‐flow reactor. This reactor was developed toward energy savings in performing such organic reactions as the transformation of the hydride methyl cyclohexane to toluene.     

Acidic property of BEA zeolite synthesized by seed-directed method

The acidic property of a BEA zeolite prepared by a seed-directed synthesis (SDS) method without organic structure directing agent (OSDA) was analyzed by a method of ammonia infrared/mass spectroscopic temperature-programmed desorption. The number of Brønsted acid sites on the SDS-BEA zeolite was larger than that on a conventional BEA zeolite synthesized from using OSDA. The enthalpy of ammonia desorption, distributed mainly in a range between 115 and 145 kJ mol^?1, was in agreement with the acid strength region generated by isomorphous substitution of Si⁴⁺ by Al³⁺ in the BEA framework. These observations confirm that the microstructure around the incorporated Al in the SDS-BEA zeolite was equivalent to that in the conventional one.     

Acceleration of the Rate of Silver Nanoparticle Formation Using Microbubbles in a Sonochemical Process

The effect of the addition of microbubbles on the formation of silver nanoparticles produced in an ultrasonic radiation-mediated process was investigated. The addition of microbubbles with an area-based median diameter of 26.0?µm and a bubble volume density of 0.18?cm³/L significantly increased the silver nanoparticle formation rate during the sonochemical process. The size distribution of the silver nanoparticles was largely unaffected by the addition of the microbubbles. The influence of changes in the microbubble volume density on the formation of the silver nanoparticles was also investigated; it was confirmed that the rate of formation of the silver nanoparticles increased moderately with increasing volume density. The gradient in absorption spectra was approximately 30 times larger for the case when microbubbles (median diameter: 28.3?µm) were added at 0.74?cm³/L, compared with the case without microbubbles. The results suggested that the microbubbles provided reaction sites similar to cavitation bubbles in the ultrasonic reaction.     

Heat Capacity of Dilute 3He–4He Films on Graphite

The heat capacity of dilute ³He–⁴He films is measured to clarify whether the second adsorbed layer of ⁴He films on graphite solidify into the so-called “4/7 phase.” The ³He areal density is fixed at 0.2 nm^?2, whereas the ⁴He areal density is gradually increased. The measured heat capacities suddenly decrease with an increasing areal density approaching that of the 4/7 phase. Above the areal density of the 4/7 phase, the heat capacities do not reduce completely to zero and have finite values. The behavior of the heat capacity does not change over a rather wide areal density regime, although it suddenly increases or recovers at around the areal density of the third-layer promotion. These behaviors can be interpreted as the separation of ³He–⁴He mixture films into a ³He-rich phase and a ⁴He-rich phase, with the ³He-rich phase solidifying into the 4/7 phase and the ⁴He-rich phase remaining fluid below the areal density of the third-layer promotion. These observations strongly suggest that a ⁴He film adsorbed on a graphite surface does not solidify into the 4/7 phase.     

Analysis and modeling of char particle combustion with heat and multicomponent mass transfer

A char combustion model suitable for a large-scale boiler/gasifier simulation, which considers the variation of physical quantities in the radial direction of char particles, is developed and examined. The structural evolution within particles is formulated using the basic concept of the random pore model while simultaneously considering particle shrinkage. To reduce the computational cost, a new approximate analytical boundary condition is applied to the particle surface, which is approximately derived from the Stefan–Maxwell equations. The boundary condition showed reasonably good agreement with direct numerical integration with a fine grid resolution by the finite difference method under arbitrary conditions. The model was applied to combustion in a drop tube furnace and showed qualitatively good agreement with experiments, including for the burnout behavior in the late stages. It is revealed that the profiles of the oxygen mole fraction, conversion, and combustion rate have considerably different characteristics in small and large particles. This means that a model that considers one total conversion for each particle is insufficient to describe the state of particles. Since our char combustion model requires only one fitting parameter, which is determined from information on the internal geometry of char particles, it is useful for performing numerical simulations.