Oxide Polishing Suspensions

Oxides

A wide selection, even water-free
For final polishing of certain materials, especially for metals, silica suspensions have replaced alumina suspensions. This is mainly due to the chemical-mechanical material removal that results in nearly deformation free surfaces.

We offer a wide selection of silica suspensions manufactured for different requirements and for polishing different materials.

· Various grain structures
· Acidic and basic reacting suspensions with pH ranging from 3.5 to 10
· Grain size distribution from 0.2 µm to 0.050 µm (120 to 50 nm)
· Unique system to prevent crystal formation
· Water-free suspensions

Silica suspensions were originally developed to polish silicon wafers. The action is chemical-mechanical. The sample surface is etched, and the resulting layer is removed by means of the soft silica leaving the surface almost without deformation.
As in wafer polishing, this is best achieved by adding an oxidation agent to the suspension just before application. Hydrogen peroxide or acids/bases combined with a salt are frequently used.
The etching agent applied is often the same as that used for etching of the finished specimen. The oxidation or etching agent must be added just before application, since it may otherwise cause changes such as flocculation or coagulation in the silica suspension.

Grain structure

We offer both types Usually, only two types of amorphous silica are used for polishing suspensions.

Fumed Silica

Is manufactured in an oxidation process in a flame. This type of silica primarily contains particles with a diameter of nano-size, which may, however, form aggregates of varying sizes. In our suspensions, the mean aggregate size is 0.2 µm to 0.1 µm, which is considered the appropriate size for final polishing. Sedimentation may occur and the bottle should therefore be carefully shaken before use.

Colloid Silica

is manufactured as an aqueous precipitation which produces relatively few aggregates as compared to the oxidation process described above. The most frequent particle size is 20-100 nm. Our colloidal silica suspension has been ultrafiltered before bottling in order to remove as many aggregates as possible, and the particle size in this product (D50) is approx. 50 nm. This illustration shows the difference between fumed (particle aggregates) and colloidal (individual particles) silica:

pH

From 3.5 to 10
In order to work with suspensions which are as stable as possible, pH must be adjusted in relation to the addition of oxidation or etching agent. Our fumed silica is available with both acidic and basic formulations corresponding to the two applications.

Crystal formation

At last a system that effectivly stops the formation of crystal
One problem in connection with silica suspensions is the forming of crystals after use. When the liquid in the suspension evaporates after preparation, the silica content is concentrated leading to precipitation of crystals which cannot be dissolved by adding new suspension. The crystals will be deposited in the polishing cloth which will have to be discarded.
We have developed a very efficient method of limiting the precipitation of crystals. According to this method, the evaporation of water is reduced and – something quite new – our colloidal silica suspension allows precipitated crystals to be redissolved thus prolonging the life of the polishing cloth.

Water-free

Again a product unique to Aptex
We offer a non-aqueous version of our fumed silica suspension. Instead of water we have used ethane diol. The polishing action of this silica suspension is not chemical-mechanical as that of the other silica suspensions, since polishing is made in a non-aqueous environment where the notion of etchings and oxidations is irrelevant.
The polishing action of the suspension is therefore purely mechanical and consequently cannot be expected to provide quite the same polishing results as traditional silica suspensions. Nevertheless, the results are superior to anything else achievable in a non-aqueous environment.

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