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.
