LUDOX® AS-40 is an ammonium-stabilized dispersion of negatively charged, amorphous colloidal silica particles with an average particle size of approximately 22 nanometers. LUDOX® AS-40 particles have a high surface area, rich in silanol groups. This makes LUDOX® AS-40 an excellent binder for metals, oxides, siliceous materials, and polymers with reactive functional groups.

Standard colloidal silica grades such as LUDOX® HS-40 and TM-40 are stabilized with sodium ions that can act as a flux at high temperatures. Since LUDOX® AS-40 is stabilized with ammonium ions rather than sodium, it is better suited for use in applications such as vacuum-formed fibrous shapes and refractory manufacturing. LUDOX® AS-40 is also ideal in catalyst applications where the presence of sodium stabilizing ions is detrimental, such as zeolites and emission-control products. When included in water-based coating formulations, LUDOX® AS-40 becomes an integral component of the polymer matrix and increases the durability, antiblocking, and antisoiling properties.