Design and characterization of asymmetrical porous nickel membranes

Abstract

As an alternative to organic membranes, ceramic membranes are suitable for the chemical industry due to their intrinsic thermal, chemical and mechanical stability. The centrifugal dispositioning technique has the advantage that it produces membranes that are asymmetrical with a smooth inner surface. In this study, nickel powders were used in the place of regular a-alumina powders to produce an asymmetrical porous membrane, and to determine its characteristics. Sub-micron nickel powders can be produced by the hydrothermal reduction of a nickel salt with hydrazine. The particles obtained are of the correct size and size distribution and can be processed to be suitable for centrifugal dispositioning. Dispersants like polyacrylamide-codiallyldimethylammoniumchloride, polyvinylpirrolidone (PVP) and ammonium-polymetacrylate (APMA) were investigated to determine their ability to stabilize Ni powder in an aqueous dispersion. Nickel powder manufactured by the hydrothermal reduction of a nickel salt with hydrazine were moulded into a tubular membrane by means or the centrifugal dispitioning technique. A stable dispersion was made with PAAco with little agglomeration or segregation. The membranes were successfully removed from the stainless steel moulds without breakage of the membrane. The greencasted membranes obtained were sintered without membrane failure, where after they were subjected to numerous tests to determine their characteristics. SEM photographs were taken from the Inner surface and cross-sections to determine the morphology of the membranes. It was demonstrated that a change in the crystal phase occurred at 1200°C, changing the morphology as well as the membrane characteristics. The nickel membrane shrinkage during the sintering experiments was found to increase linearly. It was shown with mercury intrusion that the bimodal pore size distribution of the membranes decreased with increasing sintering temperature, while larger pores were exchanged for smatter pores. It was found that water permeation varied from 5 to 69 L.m-2.h-1.bar-1, depending on the sintering temperature (950°C to 1250°C) of the membrane. The water permeation decreased linearly with increasing sintering temperature.