Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 µm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity.
Non-metallic inclusions have been shown frequently to lead to crack initiation in superelastic Nitinol fatigue specimens. While prior studies suggested that both carbide (TiC) and oxide (Ti 4 Ni 2 O x ) inclusions can develop in superelastic Nitinol alloys, questions remain on whether or how the chemistry and morphology of these non-metallic inclusions are affected by the melting and subsequent tube manufacturing process. In the present study, samples of Ti-55.8wt.%Ni alloy were taken from tubes fabricated from materials of various VIM and VAR melt processes. Additional samples were taken from various stages of the tube drawing process for studying the stringer formation. Our results suggest that both carbide and oxide inclusions are present in VIM/VAR materials and the oxide break-down during tube drawing appears to be the primary mechanism for stringer formation. Carbides in VIM materials generally remain as isolated particles during tube fabrication while the primary inclusion of oxide in the VAR material explains its higher stringer density. In addition, the carbide inclusion has been confirmed to contain a noticeable amount of oxygen; hence, we suggest the ''Ti(C, O)'' nomenclature. Further study on the role of oxygen on carbide and oxide formation in VIM/VAR materials may be beneficial for improving the future melt quality of NiTi alloys.
Globally, kidney failure has consistently been a major health problem. The number of patients suffering from kidney failure is radically increasing. Some studies forecast an exponential growth in the number of kidney failure patients during the coming years. This emphasizes the importance of hemodialysis (HD) membranes. Current dialysis membranes (cellulose based and synthetic polymer membranes) have irregular pore shapes and sizes, nonuniform pore distribution and limited reusable capability, which leads to low efficiency of toxin removal. New alumina membranes with uniform, controllable and well-structured nanoscale pores, channeled pores aligned perpendicular to the membrane plane, high porosity, high thermal and chemical resistance, and better mechanical properties are certainly preferable to currently used membranes. Determination of transport properties of alumina membranes will assist in the development of the alumina membranes for enhancing hemodialysis. Experiments were performed to evaluate hydraulic permeability, solute diffusive permeability, sieving coefficient, and clearance of four solutes (urea, creatinine, Vancomycin, and inulin) for alumina membrane. Based on comparison of these values against those of polyethersulfone (PES) membranes, transport performance of alumina membrane was determined. Hydraulic conductivity of the alumina membrane was approximately twice that of the PES membrane and inulin sieving coefficient for alumina membrane is approximately 21% higher than that for PES membrane. Alumina membrane has higher solute clearances and no albumin leakage, which makes it an effective replacement for current dialysis membranes.
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