A simple shape with
many sides
The myriad of tiny spheres found in every vial of LUDOX® colloidal silica offer many surprisingly useful capabilities. The silicon dioxide nanoparticles that comprise colloidal silica have been a mainstay for scientists, engineers, and manufacturers for the better part of a century. Take a brief tour of just a few of these powerful properties of colloidal silica and the applications that they enable.
Room to grow
One size
doesn't fit all
Beating the heat
Looking for a reaction
A clear view
A potentially valuable vehicle
Room to grow
The manufacturing process for LUDOX® colloidal silica provides tight and consistent control over the final diameter of the resulting nanoparticles. This is valuable because different applications benefit from the narrow distributions and product consistency.
A silicate is added to a water tank under conditions that promote nanoparticle growth.
Particle growth continues until the optimal size is reached.
Smaller particles are ideal binders for applications such as catalysis and investment casting, as they offer a high surface-area-to-volume ratio and higher stabilizing alkali content. Larger particles are useful for adding friction to surfaces, for example, to increase the coefficient of friction between paper surfaces such as multi-walled bags, corrugated boxes and linerboard.
One size doesn’t fit all
For many applications, LUDOX® colloidal silica users want a formulation where every single nanoparticle is essentially identical in size, a property known as monodispersity. But some applications benefit from a little more variety.
The total proportion of empty space between packed monodisperse particle formulations is typically about 35%.
In contrast, a polydisperse colloidal silica, which contains a range of different sizes, can pack more efficiently, reducing this empty volume to as little as 5-10%.
It can be useful to tune this ‘void space’ in the context of filtration. By controlling the porosity of a layer of colloidal silica, the size of the molecules that can pass through can be regulated.
Beating the heat
Colloidal silica is a form of synthetic amorphous silica, which has very good high-temperature stability. When used in combination with other compounds that are similarly stable, one can produce materials that can withstand remarkably high temperatures—up to 1,500 degrees Celsius or more. This is useful when generating catalysts for industrial use or for casting metals with very high melting points.
A typical procedure for preparation of investment casting shells entails mixing a dispersion of colloidal silica with grains of a refractory material such as alumina or zircon, which is then heated to evaporate off the water.
As the water evaporates, the refractory grains and silica particles become more densely packed and form strong covalent bonds with each other, creating a robust and heat-tolerant network.
The resulting materials are useful as a casting shell for metals like titanium or steel.
Looking for a reaction
The outer surfaces of LUDOX® colloidal silica particles are normally covered with hydroxyl groups. These groups can form hydrogen bonds with other compounds, yielding mixtures with unique and specialized properties. These hydroxyl groups can undergo ionization, introducing electrostatic properties, as well as condensation reactions with silane chemical groups to produce functionalized surfaces.
When colloidal silica is combined with water-based polyurethane dispersions, it yields dried films with distinctive physical properties such as increased stiffness.
The electrostatic properties of colloidal silica surfaces can also enable fine control over fluid flow. For example, the combination of cationic colloidal silica and anionic polysaccharides has been used to generate 3D-printable bioinks for crafting biocompatible ear prostheses.
A clear view
Synthetic amorphous silica has a refractive index—a measure of how quickly light travels through solid material—of 1.46. This is just slightly higher than that of water (1.33), and considerably higher than that of air (1.00). LUDOX® colloidal silica preparations can yield ultra-clear coatings depending on the formulation.
Light bends when it travels between substances with different refractive indexes. When colloidal silica is dispersed in water, the transparency of the resulting sol depends on the particle size. For particles less than about 20 nm, the sols can be quite transparent, while much larger particles, as in the image shown, yield opaque sols.
If the particles are fused or embedded in a polymer with a matching refractive index, the resulting material achieves excellent transparency regardless of the particle size, while also retaining the durability and other benefits of the silica nanoparticles.
Preparations of colloidal silica can produce clear coatings that protect surfaces like wood without interfering with the natural beauty of the grain.
A potentially valuable vehicle
The core material of LUDOX® colloidal silica– synthetic amorphous silica– is relatively inert and non-hazardous. A number of researchers see clear promise using colloidal silica-based capsules for agricultural applications such as the delivery of pesticides and fertilizers to crops.
Colloidal silica can form nanocapsules that contain molecular cargos.
Colloidal silica-based capsules can gradually release compounds through pores between nanoparticles.
Discover how LUDOX® colloidal silica is an essential part of everyday life
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Colloidal Silica Coatings in Food-Contact Applications
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Filtration
Colloidal silica
Active agricultural ingredient
Encapsulation
Soil application
Slow release
Silicate
Discover LUDOX® colloidal silica in investment casting
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Colloidal silica particle
Refractory grain
The information contained herein is based on our testing and experience and is offered for the user’s consideration, investigation and verification. WARRANTIES EXPRESSED OR IMPLIED, regarding results obtained from the use of our products, ARE DISCLAIMED since customer operating and use conditions vary and are beyond our control. Test methods are available on request. GRACE® and LUDOX® are trademarks, registered in the United States and/or other countries, of W. R. Grace & Co.-Conn. TALENT TECHNOLOGY TRUST™ is a trademark of W. R. Grace & Co.-Conn. This trademark list has been compiled using available published information as of the publication date of this brochure and may not accurately reflect current trademark ownership or status. © 2021 W. R. Grace & Co.-Conn. All rights reserved.