Silicon Dioxide

Grades and forms

Silicon dioxide in food supplements is amorphous silica, used mainly as an excipient: a glidant, an anti-caking agent and a carrier for liquid actives. Manufacturers buying silicon dioxide powder in bulk choose between a few types. Each is made differently and behaves differently in a blend.

• Precipitated silica: produced by precipitation from a soluble silicate solution. It is a common choice for anti-caking and for carrying liquids.
• Fumed (pyrogenic) silica: produced by high-temperature flame hydrolysis. It is very fine and light, and is often called colloidal silicon dioxide. It is the usual glidant in capsule and tablet blends.
• Silica gel: a porous form. It is chosen where moisture adsorption is the main job.

Three things decide the choice. The first is the function: flow, liquid loading or moisture control. The second is the compliance standard your customer requires, such as the EU food-additive specification or a pharmacopoeia grade. The third is handling on your line. The specification sheet states the type, assay, loss on drying and ignition, particle size and contaminant limits. SoleChem sends it with the certificate of analysis alongside the quote. Ask for the grade you need in the quote form.

EU regulatory status

Silicon dioxide can appear in a food supplement in two legal roles. Each role has its own rules.

As a food additive. Silicon dioxide is authorised under Regulation (EC) No 1333/2008. Annex II sets the conditions by food category, including food supplements. Annex III covers additives in other additives and in nutrient preparations. Purity criteria are laid down in Regulation (EU) No 231/2012. The conditions and specifications for this additive have been under review, so check the current consolidated texts before you fix a formula.

In the ingredients list, an additive is declared by its functional class, followed by its name or E number. This follows Annex VII of Regulation (EU) No 1169/2011. The same regulation requires the word “nano” after an ingredient present as an engineered nanomaterial. Whether a given grade falls under that definition must be assessed for that grade. See the labelling guide for the wider rules.

As a source of silicon. Silicon is listed among the minerals in Annex I of Directive 2002/46/EC. Check in the consolidated Annex II whether silicon dioxide is listed as a permitted source before declaring silicon on the label. The permitted forms guide explains how the annexes work. Maximum amounts of silicon in supplements are set nationally and differ by member state, as the maximum levels guide explains.

Formulation notes

Capsules. A small addition of fumed silica improves powder flow into capsule bodies on dosator and tamping machines. Better flow narrows fill-weight variation. It works in both gelatin and HPMC shells. See ingredients for capsules.

Tablets. In direct-compression blends, silicon dioxide acts as a glidant alongside fillers such as dicalcium phosphate. Sieve or pre-blend it to break up agglomerates, and add it near the end of blending. More notes are in ingredients for tablets.

Powders. In hygroscopic sachet and tub blends, it reduces caking by adsorbing surface moisture. It is practically insoluble in water, so it leaves a haze in drinks. Avoid it where the product must dissolve to a clear solution. See ingredients for powders.

Carrier for liquids. Porous grades can adsorb oily or liquid actives and turn them into a free-flowing powder. The achievable loading depends on the grade. Confirm it in trials.

Handling. The powder is fine, light and dusty, and it can carry a static charge. Use dust extraction and follow the safety data sheet.

Silicon content. Pure SiO2 contains 46.7 % silicon by mass. This is calculated from the molar mass of 60.084 g/mol and the standard atomic weight of silicon. To declare 10 mg of silicon per serving, you need about 21.4 mg of silicon dioxide, before correcting for assay and moisture. The elemental content calculator does this arithmetic for other claims.