If moisture is present in a desiccator enclosure, probable causes are:
- It is trapped in the desiccator enclosure when it was sealed or there were water molecules on or inside the contents in the enclosure
- Moisture leakage, i.e. moisture (humidity) entered the desiccator due to a leaky seal, porous enclosure material or the enclosure was not properly sealed
- If the enclosure is equipped with a breather valve, moisture/humidity can enter the desiccator enclosure when the valve opens
Desiccators employ one of four basic types of technologies: standard desiccant, automatic desiccant regeneration, gas purge or vacuum.
Moisture in the air is absorbed by a desiccant, which is an adsorbent substance that attracts water vapor molecules. The molecules are collected and held on the desiccant's surface. Common types include silica gel, activated alumina, clay (Montmorillonite) and molecular sieves. Once the desiccant is saturated with water vapor molecules, the desiccant must be regenerated via heating or replaced. This kind of desiccator offers the flexibility to use any type of desiccant, and is usually the most economical choice.
Automatic Desiccant Regeneration:
To provide a low–humidity environment and prevent desiccant saturation, this type of desiccator employs heaters or electric fans that continually regenerate the desiccant. Automatic regeneration desiccant models require minimal monitoring, offer more precise humidity control vs. standard desiccators and can be equipped with silica gel desiccant beads that last for thousands of regeneration cycles.
Gas Purge Desiccators:
In gas purge desiccators, a continual flow of inert gas displaces the moisture–rich atmosphere inside the desiccator. These desiccators commonly use dry nitrogen as the purge gas. They can reach the desired humidity level much quicker than standard or automatic desiccant regeneration desiccators and provide a dust–free environment. Gas purge desiccators are suitable for many applications, including cleanrooms. Many models offer stopcocks that allow the option of disconnecting the purge gas stream and using standard desiccants.
These desiccators use a vacuum pump to remove air that contains moisture. They are regarded as superior to other types if total dry storage is required. Vacuum desiccators are common in cleanroom applications and provide a dust–free environment. Many models offer a stopcock so that the vacuum pump can be disconnected to use regular desiccants.
Selecting a Desiccator
Design factors to consider when purchasing a desiccator include, but may not be limited to:
- Type of desiccator
- How much interior volume is required in the desiccator
- Available space in your lab
- Required level of moisture control and protection
- Required/desired length of time between recharge, if using a desiccator with rechargeable desiccant
- Whether or not a breather valve or humidity indicator is required
- Required dusting protection
- Tolerable desiccator leakage rate