Tim Aerts

Fabrication and chromatographic performance of porous-shell pillar-array columns.

We report on a new approach to obtain highly homogeneous silica-monolithic columns, applying a sol-gel fabrication process inside a rectangular pillar-array column (1 mm in width, 29 microm in height and 33.75 mm in length) having a cross-sectional area comparable to that of a 200 microm diameter circular capillary. Starting from a silicon-based pillar array and working under high phase-separation-tendency conditions (low poly(ethylene glycol) (PEG)-concentration), highly regular silica-based chromatographic systems with an external porosity in the order of 66-68% were obtained. The pillars, 2.4 microm in diameter, were typically clad with a 0.5 microm shell layer of silica, thus creating a 3.4 microm total outer pillar diameter and leaving a minimal through-pore size of 2.2 microm. After mesopore creation by hydrothermal treatment and column derivatization with octyldimethylchlorosilane, the monolithic column was used for chip-based liquid-chromatographic separations of coumarin dyes. Minimal plate heights ranging between 3.9 microm (nonretaining conditions) and 6 mum (for a retention factor of 6.5) were obtained, corresponding to domain-size-reduced plate heights ranging between 0.7 and 1.2. The column permeability was in the order of 1.3 x 10(13) m(2), lower than theoretically expected, but this is probably due to obstructions induced by the sol-gel process in the supply channels.

Experimental Study And Modelling Of HeatTransfer During Anodizing In A Wall-jet Set-up

Anodizing of aluminium is an electrochemical surface treatment yielding the formation of an alumina film, the characteristics of the formed oxide strongly depending on the considered anodizing conditions. Heat transfer has an important influence on the anodizing process, which can be explained by considering the production of heat near the aluminium anode, combined with the significant influence of the local electrode temperature on the process of oxide formation. The influences of temperature and heat transfer on the growth of the anodic oxide film during anodizing of high purity Al are studied on a laboratory scale in a wall-jet electrode reactor. The impinging jet configuration of the reactor creates a non-uniformly accessible electrode with variable convection as a function of the radial position on the anode. The influence of the resulting nonuniform heat transfer on the local temperature of the electrode is monitored by local temperature measurements on the backside of the aluminium anode, whereas its influence on local film growth is evaluated by means of FEG-SEM surface and cross sectional analyses. A comparison between the simulated and experimentally acquired data is presented. The controlled and known electrolyte flow in the wall-jet reactor enable numerical simulations of the convection which supply additional information on the encountered conditions of heat transfer. The anodizing process itself is simulated using a model based on the high field theory.