|Frequently Asked Questions|
Silica gel now comes in many colours then ?
Yes, now it does. Silica gel comes in either non-indicating or self-indicating forms. Non-indicating silica gel is white and stays white as it adsorbs moisture. Self-indicating silica gels have traditionally been impregnated with a moisture sensitive cobalt chloride indicator. This gives a blue silica gel which slowly changes colour as it adsorbs moisture until it becomes pink. New self-indicating silica gels feature a number of other colours (because they have different moisture sensitive indicators), but all have the same purpose - to indicate when the silica gel is saturated and unable to take up any more moisture.
Does silica gel comes ready to use ?
Yes. The silica gel does not need to be 'generated' before use. It is always sold (loose or in sachets) in a dry condition, ready for use.
How long can silica gel be stored ?
Almost indefinitely. The key to retaining a sachets usefulness is to keep it under air tight conditions until it needs to be used. Silica gel will adsorb moisture from any environment, so a sachet left out in the open will immediately start taking up water vapour. Although the moisture uptake rate is not fast, small sachets can be vulnerable to such exposure, as they do not have a large moisture holding capacity. It is recommended that they are not left open to the atmosphere for longer than 15 minutes. Larger sachets should not be removed from their packaging more than 1 hour before they are required for use. The shelf life of silica gel in a sealed environment can safely be said to be between 4 and 12 months. Practical experience has shown that it can often far exceed this.
How much water vapour can silica gel hold ?
Silica gel will adsorb up to 40% of its own weight in moisture.
Can silica gel be used anywhere ?
Theoretically yes, but it is really only effective in an enclosed environment. In a situation where new air (and moisture) is constantly being introduced, an unpractical amount of silica gel will likely be needed to keep the Relative Humidity at low levels.
What is Relative Humidity ?
Air will always contain water vapour. At any given temperature there will be a saturation point at which no more moisture can be retained (any excess will condense). The Relative Humidity of air is the actual moisture content expressed as a percentage of this saturation content. The aim of using silica gel is to keep the Relative Humidity at levels below 50% of the saturation capacity. At these levels, corrosion and mould growth will not be promoted. Problems are often caused if the temperature drops as the saturation content of air at the new temperature becomes much lower.
Is silica gel dangerous ?
Non-indicating (white) silica gel is non-toxic and non-flammable, it is very inert with a very high melting point. It is very much like sand and thus can safely be sent by any means of transport.
Self-indicating (blue) silica gel has been reclassified by the European Union and as of 01/07/2000 is classified as toxic. New safe self-indicating silica gels are now available.
How can silica gel work when it's inside a sachet ?
The materials used to make silica gel sachets are specifically chosen to be breathable. Water vapour passes through them to be adsorbed by the silica gel.
Why are there so many different size sachets ?
The larger the item that is being protected, the more silica gel is needed. A range of sachets allows for a single sachet to be used in most cases.
And which size sachet should I use ?
It will depend on the application. For a well sealed item, a rule of thumb is that 5 grams of silica gel are needed for every cubic foot of volume of the package. This converts to 170 grams per cubic meter.
Can you get non-indicating and self-indicating silica gel sachets ?
Yes. The blue - self-indicating silica gels can be seen through the sachet material.
How is silica gel regenerated ?
Self-indicating silica gels when they have become saturated can be regenerated by heating at 100 - 120°C until they return to their original colours. The heating literally drives off the adsorbed moisture. Regeneration can be carried out repeatedly, although eventually the crystals will lose their colour. When regenerating self-indicating silica gel sachets, only the minimum necessary heat should be used. This will prevent the sachet material from deteriorating. Although non-indicating silica gel can be regenerated in exactly the same way, it is not apparent when the silica gel is regenerated other than by checking its weight - it will return to its original dry weight when completely regenerated.