caking (chemical engineering) on:
[Wikipedia]
[Google]
[Amazon]
Caking is a powder's tendency to form lumps or masses. The formation of lumps interferes with packaging, transport, flowability, and consumption. Usually caking is undesirable, but it is useful when pressing powdered substances into pills or briquettes. Granular materials can also be subject to caking, particularly those that are hygroscopic such as salt, sugar, and many chemical fertilizers.
Anticaking agent
An anticaking agent is an additive placed in powdered or granulated materials, such as table salt or confectioneries, to prevent the formation of lumps (caking) and for easing packaging, transport, flowability, and consumption. Caking mechanisms d ...
s are commonly added to control caking.
Caking properties must be considered when designing and constructing bulk material handling equipment. Powdered substances that need to be stored, and flow smoothly at some time in the future, are often pelletize
Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, plastics, waste materials, and more. The process ...
d or made into pills.
Mechanism
Caking mechanisms depend on the nature of the material. Caking is a consequence of chemical reactions of grain surfaces. Often these reactions involve adsorption of water vapor or other gases. Crystalline solids often cake by formation of liquid bridge between microcrystals and subsequent fusion of a solid bridge. Amorphous materials can cake byglass transition
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubb ...
s and changes in viscosity. Polymorphic phase transitions can also induce caking. The caking process can involve electrostatic attractions or the formation of weak chemical bonds between particles.
Anticaking agents
Anticaking agents are chemical compounds that prevent caking. Some anticaking agents function by absorbing excess moisture or by coating particles and making them water-repellent.Calcium silicate
Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·SiO2. It is also referred to by the shortened trade name Cal-Sil or Calsil. It occurs naturally as the mineral larnite.
...
(CaSiO3), a common anti-caking agent added to table salt, absorbs both water and oil. Anticaking agents are also used in non-food items such as road salt, fertilisers, cosmetics, synthetic detergent
A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more ...
s, and in manufacturing applications.
References