Dryers are equipment used in laboratories to dry residues of liquids into solid materials. They do not involve any chemical transformation, but merely a mass transformation in the material being dried.
A dryer consists of a container with thick glass walls and a lid. The lower part of the container is separated from the upper part by a perforated ceramic disc, above which the materials to be dried are placed. Below it, a hygroscopic material, such as silica gel, acts as a dehydrating agent. It has the task of absorbing the water molecules in the drying of the treated material.
Cobalt salts are added to the hygroscopic substance, which have the characteristic of changing colour from blue to pink depending on their degree of hydration. After drying, the silica gel must be kept in an oven for several hours. Of paramount importance is not to allow external moisture to penetrate the interior of the dryers. For this reason, the lid and edges are provided with frosted edges that are coated with lubricants. Some dryer models are equipped with a valve on the lid, to be connected to a pump, so that the air inside can be removed. Making the inside of the instrument vacuum-packed favours the evaporation of the water present in the material to be dried.
Their use can, for example, follow the filtration of a solid material in order to separate it and the residual water inside. it is important to note, however, that dryers may not be sufficient to remove traces of water from an almost dry material. It is often necessary to precede their use with prior heating of the material. In addition, a desiccator can be used to protect hygroscopic materials that react with the water contained in moisture. The materials inside dryers react to contact with air as soon as they are opened. Consequently, dryers are not suitable for storing materials that react violently or quickly with atmospheric moisture, such as alkaline metals.
Fields of application
Dryers are commonly used in laboratories. However, they also find application in the industrial field. For example, industrial dryers are used in the processing of wood or powdered materials.