ABSTRACT
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Summary and Conclusions . . . . . . . . . . . . . . . . . . . 100
Preparation of Silica Aquasols by
Electrodialysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Silica Sol Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Technical Field . . . . . . . . . . . . . . . . . . . . . . . . . 102
Background Art . . . . . . . . . . . . . . . . . . . . . . . . 102
Theory of the Invention . . . . . . . . . . . . . . . . 103
Summary of the Invention . . . . . . . . . . . . . . . . 103
Detailed Description of the Invention . . . . . . . 104
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Nucleation . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Particle Growth . . . . . . . . . . . . . . . . . . . . . . 107
Analytical Procedures . . . . . . . . . . . . . . . . . 107
Example I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Example II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Example III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Example IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Electrodialysis Unit . . . . . . . . . . . . . . . . . . . . . . . 114
Flow of Liquids within the Cell and Electrical
Connections of Electrodes . . . . . . . . . . . . . . . 114
Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Materials of Construction . . . . . . . . . . . . . . . . . . 115
Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Analytical Procedures . . . . . . . . . . . . . . . . . . . . . 115
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Discussion of Results . . . . . . . . . . . . . . . . . . . . . . . . 117
Influence of Process Variables . . . . . . . . . . . . . . 117
Effect of Temperature . . . . . . . . . . . . . . . . . . . . . 117
Effect of Sodium Silicate Concentration in the
Nucleation of Silica Sols . . . . . . . . . . . . . . . . . . 122
Effect of Change of Temperature
During the Process . . . . . . . . . . . . . . . . . . . . . . . 122
Concentration of Sodium Silicate at the
Time of Initial Nucleation, SSN, and at the
Point of Temperature Increase . . . . . . . . . . . . . 124
Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Appendix C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Concentrated aqueous silica sols of small silica particles about 10 nm or less in diameter and uniformly
sized are prepared by a process for maintaining a constant number of silica nuclei particles prior to the
deposition process. The process for maintaining a constant number of silica nuclei particles in the sol con-
sists of forming the particles at a pH 8-10.5 and a low temperature then heating the sol through a transition
temperature to a deposition temperature maintaining the pH, removing alkali metal ions and simultaneously
adding alkali metal silicate from the system at a rate such that the number of silica particles in the sol
remains constant while the temperature is being raised.
