Kinetic studies of aluminum formation in the caustic side solvent extraction (CSSX) process

This project focused on aluminum precipitation within the Caustic Side Solvent Extraction (CSSX) process at the Savannah River Site (SRS). The CSSX process uses a solvent to separate cesium. In the scrubbing section, the solvent containing cesium is scrubbed with 0.05 M nitric acid to remove soluble sodium and potassium ions. During scrubbing, aluminum precipitation has been observed. Solids precipitation is of concern as solids might erode centrifugal contactor internals and/or plug transfer pipelines. Hence, it is important to identify conditions under which solids precipitation may occur and identify an operating region where solids precipitation is minimized. Room temperature experiments on the CSSX scrubbing process were conducted. Experimental results were compared with predictions from ESP (Environmental Simulation Program). The order and specific rate for the reversible aluminum precipitation reaction were obtained as a function of initial stream dilution and % carryover. The reaction was first order based on regression results

Tribological and mechanical characterizations of polyelectrolyte multilayer nanoassemblies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, June 2005.Includes bibliographical references.Over the last decade, the sequential layer-by-layer assembly of oppositely charged polyelectrolytes has received much interest for the deposition of film architectures, ranging from tens to hundreds of nanometers in thickness, that can be precisely tuned as a function of the processing conditions. The resulting polyelectrolyte multilayer (PEM) constructs are being investigated as biomaterials, photonic structures, electrochemical devices, and separation membranes. There is a distinct lack of literature, however, on the friction-and-wear behavior of these nanocoatings, and their exploitation in systems with tribological problems of practical relevance. In addition, their mechanical properties, crucial for the success of almost all applications being studied, have not been systematically characterized. This thesis focuses on the elucidation of the tribological and mechanical properties of PEMs composed predominantly of weak polyelectrolytes--poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). In general, the friction coefficients of PAH/PAA PEM-coated substrates were at least marginally higher than those exhibited by their uncoated counterparts, in the absence of substrate wear. The films, however, demonstrated a significant capacity for wear prevention of underlying substrates in the dry state, and also in the presence of bovine calf serum, used to simulate joint synovial fluid. In the latter case, a significant decrease in wear rates, in tests using a clinically relevant number of cycles and articulation pattern, pointed to the efficacy of PEM-coated systems for wear reduction in total joint replacement prostheses; wear particle- induced implant loosening remains a major cause of revision surgeries.(cont.) To tune the frictional response of PEMs without compromising their wear-retarding behavior, various strategies were explored; these included surface capping with a block co-polymer, in-situ synthesis of silver nanoparticles in the films, and assembly of composites containing PAH and multi-wall carbon nanotubes. The engineered coatings find possible applications in microelectromechanical systems (MEMS) where friction, wear, and stiction can be detrimental to device performance. Nanoindentation was employed to probe the mechanical behavior of these ultra-thin films. It was demonstrated that the modulus and hardness of PAH/PAA PEMs could be tuned as a function of the pH of the polyelectrolyte solutions used for their assembly. The mechanical response of these structures was superior to either parent polyelectrolyte and also commercially used polymeric systems. The mechanical properties were studied at ambient conditions and in the presence of a liquid medium.by Prem Venkatachalam Pavoor.Ph.D

AUTHENTICATED CHECK IN TECHNIQUES FOR MEETING SPACES

Current methods for usage of resources related to office space rely on prompt booking and releasing of office spaces, in addition to honest check ins. However, no-shows to a meeting, not releasing a resource when done or when not being used, occupying a space without booking it or checking in, or occupying someone else’s resource can cause problems that may require more than existing check in techniques provide. To address such issues, proposed herein are authenticated check in and locked resource techniques to ensure proper usage of office space and resources through authenticating the users who are authorized to join and check in to meetings using a meeting\u27s roster

Smooth Muscle Cell Phenotype Modulation and Contraction on Native and Cross-Linked Polyelectrolyte Multilayers

Smooth muscle cells convert between a motile, proliferative “synthetic ” phenotype and a sessile, “contractile ” phenotype. The ability to manipulate the phenotype of aortic smooth muscle cells with thin biocompatible polyelectrolyte multilayers (PEMUs) with common surface chemical characteristics but varying stiffness was investigated. The stiffness of (PAH/ PAA) PEMUs was varied by heating to form covalent amide bond cross-links between the layers. Atomic force microscopy (AFM) showed that cross-linked PEMUs were thinner than those that were not cross-linked. AFM nanoindentation demonstrated that the Young’s modulus ranged from 6 MPa for hydrated native PEMUs to more than 8 GPa for maximally cross-linked PEMUs. Rat aortic A7r5 smooth muscle cells cultured on native PEMUs exhibited morphology and motility of synthetic cells and expression of the synthetic phenotype markers vimentin, tropomyosin 4, and nonmuscle myosin heavy chain IIB (nmMHCIIB). In comparison, cells cultured on maximally cross-linked PEMUs exhibited the phenotype markers calponin, smooth muscle myosin heavy chain (smMHC), myocardin, transgelin, and smooth muscle R-actin (smActin) that are characteristic of the smooth muscle “contractile ” phenotype. Consistent with those cells being “contractile”, A7r5 cells grown on cross-linked PEMUs produced contractile force when stimulated with a Ca2+ ionophore

Compact Polyelectrolyte Complexes: “Saloplastic” Candidates for Biomaterials

Precipitates of polyelectrolyte complexes were transformed into rugged shapes suitable for bioimplants by ultracentrifugation in the presence of high salt concentration. Salt ions dope the complex, creating a softer material with viscous fluid-like properties. Complexes that were compacted under the centrifugal field (CoPECs) were made from poly(diallyldimethyl ammonium), PDADMA, as polycation, and poly(styrene sulfonate), PSS, or poly(methacrylic acid), PMAA, as polyanion. Dynamic mechanical testing revealed a rubbery plateau at lower frequencies for PSS/PDADMA with moduli that decreased with increasing salt concentration, as internal ion pair cross-links were broken. CoPECs had significantly lower modulii compared to similar polyelectrolyte complexes prepared by the “multilayering ” method. The difference in mechanical properties was ascribed to higher water content (located in micropores) for the former and, more importantly, to their nonstoichiometric polymer composition. The modulus of PMAA/PDADMA CoPECs, under physiological conditions, demonstrated dynamic mechanical properties that were close to those of the nucleus pulposus in an intervertebral disk