A novel thermal plasma process for fumed silica production was investigated. The novelty was the result of the method used for silica decomposition which consisted of transferring an arc (Ar or Ar/H2) to a silica anode. The primary objective was to examine the effect of current (150--250 A), plasma gas flow rate (10--20 lpm Ar) and plasma gas composition (0--2.8% H2) on the rate of silica decomposition. The decomposition rate (0.09--1.8 g/min) was determined to be a heat transfer limited process which occurred below the arc root where the surface had attained its boiling point. The decomposition rate was not affected by plasma gas flow rate since convective heat transfer was reduced by the counter flow of decomposition products (SiO(g) and O2) from the anode surface. Increasing current increased the decomposition rate because the heat input to the anode due to electron flow and arc radiation was increased. Adding H2 to the plasma gas increased the decomposition rate because of an increase in radiative heat transfer to the anode, a reduction in the theoretical energy requirement for decomposition and a consumption of O2 which lowered the boiling point. A mathematical model was developed to simulate the behavior of the silica anode. The predicted decomposition rates were of the same order of magnitude as those observed experimentally. A secondary objective was to examine the effect of oxidation zone parameters including SiO(g) concentration (0.09--3.24%) and temperature (1414--1801 K) of the reactor exit gas and steam flow rate (46--71 g/min) on powder properties. The oxidation zone was where SiO(g) was quenched with steam to generate fumed silica. The specific surface area of the powders (104--257 m2/g) increased with increasing steam flow rate due to the higher quench rates. The high H2O (g) concentration in the oxidation zone produced surface hydroxyl densities which approached saturation (7.85 Si-OH/nm2). The powders had typical characteristics associated with
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34906 |
| Date | January 1998 |
| Creators | Addona, Tony. |
| Contributors | Munz, R. J. (advisor), Proulx, P. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001610569, proquestno: NQ44335, Theses scanned by UMI/ProQuest. |
Page generated in 0.0021 seconds