Supersonic Nozzle Flow Simulations for Particle Coating Applications: Effects of Shockwaves,Nozzle Geometry,Ambient Pressure,and Substrate Location upon Flow Characteristics

Characteristics of supersonic flow are examined with specific regard to nano-particle thin-film coating. Effects of shockwaves, nozzle geometry, chamber pressure, and substrate location were studied computationally. Shockwaves are minimized to reduce fluctuations in flow properties at the discontinuities across diamond shock structures. Nozzle geometry was adjusted to ensure optimal expansion (i.e., P _exit = P _ambient), where shock formation was significantly reduced and flow kinetic energy maximized. When the ambient pressure was reduced from 1 to 0.01316 bar, the nozzle’s diverging angle must be increased to yield the optimum condition of minimized adversed effects. Beyond some critical distance, substrate location did not seem to be a sensitive parameter on flow characteristics when P _amb = 0.01316 bar; however, overly close proximity to the nozzle exit caused flow disturbances inside the nozzle, thereby adversely affecting coating gas flow.     

Continued self-similar breakup of drops in viscous continuous phase in agitated vessels

Drop breakup in viscous liquids in agitated vessels occurs in elongational flow around impeller blade edges. The drop size distributions measured over extended periods for impellers of different sizes show that breakup process continues up to 15–20 h, before a steady state is reached. The size distributions evolve in a self-similar way till the steady state is reached. The scaled size distributions vary with impeller size and impeller speed, in contrast with the near universal scaling known for drop breakup in turbulent flows. The steady state size of the largest drop follows inverse scaling with impeller tip velocity. The breadth of the scaled size distributions also shows a monotonic relationship with impeller tip velocity only.     

Electrical behavior of silver particulate films deposited on 8 MeV electron beam irradiated softened polystyrene substrates

Results of the investigations carried out on the electrical behavior of silver particulate films deposited on electron beam irradiated polystyrene (PS) coated substrates held at a temperature of 455 K in a vacuum of 8 × 10⁻⁶ torr at a constant deposition rate of 0.4 nm/s are reported. It is known that when metals are evaporated on to softened polymer substrates, subsurface particulate structures are formed whose morphology is dependent on deposition parameters. Further, it was shown that the morphology is dependent on polymer-metal interaction. The present work demonstrates that the polymer-metal interaction can be brought about in inert polymers like PS by electron irradiation. The results indicate that the films deposited on PS irradiated to a dose of 20 and 25 kGy gives rise to smaller clusters with smaller inter-cluster separation, better suited for sensor applications. The induced polymer-metal interaction is attributed to the creation of free radicals due to the 8 MeV electron irradiation.     

Evaluation of the physical and mechanical properties of high drug load formulations: Wet granulation vs. novel foam granulation

The purpose of this study was to evaluate the influences of intrinsic drug mechanical properties and different granulation binder delivery processes on the physical and mechanical properties of high drug load granulations after wet granulation. Formulations (80% w/w) of acetaminophen (APAP), metformin and aspirin, which are brittle, viscoelastic, and ductile, respectively; were granulated by high-shear wet granulation. Two modes of binder delivery for wet granulation, either conventional or binder foam, were investigated. Particle size, surface area and pore size of the granulations were characterized. Compacts were prepared at a solid fraction of 0.9 under tri-axial decompression and Hiestand indices (worst-case bonding index (BI_w) and brittle fracture index (BFI)) of the compacts were determined. APAP formulations exhibited the smallest geometric mean particle sizes (d_g) and showed only slight differences in d_g values between the two granulation processes. Binder delivery mode affected mechanical properties of the granulated model drugs differently. Foam granulation appeared to enhance the granule plasticity for APAP while aspirin showed a mixed deformation mechanism based on both its high BI_w and high BFI values. The higher BI_w value for aspirin after foam granulation may be attributed to improved binder distribution among particles during granulation. On the other hand, conventional wet granulation improved the plasticity of metformin as measured by the higher BI_w and lower BFI values. Therefore, conventional wet granulation process conferred advantages in manufacturability and product quality for metformin; as compared to foam granulation which did not enhance plasticity for metformin. Based on this study, a wet granulation process can be selected based on knowledge of the intrinsic drug mechanical properties.     

Full-Scale Testing of Procedures for Assembling Trunnion-Hub-Girder in Bascule Bridges

To simulate a trunnion-hub-girder (THG) assembly for bascule bridges, two full-scale laboratory tests were conducted for quantifying stresses at previously observed failure locations and for identifying a favorable assembly procedure. One assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. Using AP#1, development of cracks on the hub was observed in one THG assembly, and, in yet another assembly, the trunnion got stuck in the hub before full insertion could take place. Large hoop stresses and low temperatures were observed at the trunnion-hub interface when the trunnion-hub assembly was cooled for insertion into the girder. Since fracture toughness of THG parts decreases with temperature, allowable crack lengths were small. In an alternative assembly procedure, AP#2, where the hub is shrink fitted into the girder first, followed by cooling the trunnion and shrink fitting it into the hub-girder assembly, the allowable crack length was determined to be double the allowable crack length of AP#1. Hence, for the given full-scale geometry and interference values, assembly procedure AP#2 was found to be better than AP#1.     

Modeling of the solubility of alumina in the NaF-AlF<Subscript>3</Subscript> system at 1300 K

The experimentally well-known alumina solubility in the range of acidic to neutral cryolite-base melts has been modeled thermodynamically in terms of several oxyfluoride solutes. For an acidic melt, cryolite ratio r=1.5, the dominant solute is monoxygen Na₂Al₂OF₆. In a less acidic regime, dioxygen Na₂Al₂O₂F₄ is dominant, whereas for neutral compositions (r=3), Na₄Al₂O₂F₆ starts to gain importance. The fit of the model to the experimental solubility data is virtually perfect. The values of the equilibrium constants for the formation of the individual solutes are reported. The formation and conversion of these oxyfluoride complexes serve as an effective buffer opposing change in the melt basicity.     

Low energy oblique ion beam sputtering induced surface engineering of polyethylene terephthalate

ABSTRACT

In the present work, the self-organized pattern formation with simultaneous surface smoothing of Polyethylene terephthalate (PET) by 40 keV Ar+ ions irradiation has been discussed. The effect of most important experimental parameter i.e. ion beam incidence that control these processes has been discussed by varying off normal incidences from 30⁰ to 50⁰. The changes in surface topography have been studied using Atomic Force Microscopy (AFM). It has been investigated from AFM analysis that oblique ion beam induced sputtering significantly reduced the surface roughness with simultaneous formation of some hillock and hole like structures.