Thick coatings by thermo‐chemical deposition in spouted beds

Abstract

Spouted beds are an established way of coating nuclear fuel microspheres with pyrolytic carbon or silicon carbide by high‐temperature thermochemical reactions. In recent years, similar coatings have aroused particular interest as bio‐compatible materials. This paper describes the differences between these two applications, and the changes that must be made to the coating process and furnace to control both the overall surface of the bed material and its increase in volume. It is shown that a satisfactory control can be achieved by continuous feeding of small particles, followed by the continuous withdrawal of variously coated particles. Experiments on two columns with internal diameter of 0.08 and 0.14 m, respectively, showed that segregation phenomena may occur, depending on the flow dynamics, and that the way in which a steady state is brought about will depend on the position of the discharge pipe in the bed. Les lits “spoutés” constituent un moyen courant pour recouvrir des microsphères de combustible nucléaire de carbone pyrolytique ou de carbure de silicum, en employant des réactions thermochimiques à température élevée. Durant les dernières années, les recouvrements du type précité ont suscité un intérět particulier en raison de leur biocompatibilité.

Utilização do leito de jorro para a aplicação de revestimento entérico em cápsulas gelatinosas duras

“…Esse processo tem sido amplamente empregado para a aplicação de revestimento em produtos químicos, agrícolas e farmacêuticos, tais como sementes, agrotóxicos, fertilizantes, compostos nucleares e comprimidos (Porter, 1978;Doane et al, 1977;Salman, 1989;Salman et al, 1989;Piccinini, Rovero, 1983;Oliveira, 2002). Em particular, tem sido atribuída a esse processo a vantagem de formação de camada altamente uniforme em curto tempo de processamento, devido, principalmente, às excelentes condições de transferência de calor e de massa no interior do equipamento (Kucharski, Kmiec, 1983).…”

Synthese von Kohlenstoffschichten auf der Oberfläche feindisperser Mikroglaskugeln in einer Strahlschicht

“…In der Literatur sind allerdings nur wenige Arbeiten zu finden, in denen die Beschichtung in einem Strahlschichtapparat durchgeführt wurde. P I C C I N I N I und R O V E R O [45] benutzen einen Strahlschichtapparat für die Beschichtung von Glaskugeln mit Partikeldurchmessern von d p = 550 lm bis d p = 1240 lm und & p = 2667 kg/m 3 mit pyrolytischem Kohlenstoff oder Siliciumcarbid bei hochtemperaturthermochemischer Reaktion 1) .…”