Loss on ignition
Encyclopedia
Loss on Ignition is a test used in inorganic analytical chemistry
, particularly in the analysis of mineral
s. It consists of strongly heating ("igniting"
) a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change. This may be done in air, or in some other reactive or inert atmosphere. The simple test typically consists of placing a few grams of the material in a tarred, pre-ignited crucible
and determining its mass, placing it in a temperature-controlled furnace for a set time, cooling it in a controlled (e.g. water-free, CO2-free) atmosphere, and redetermining the mass. The process may be repeated to show that mass-change is complete. A variant of the test in which mass-change is continually monitored as temperature is changed, is thermogravimetry
.
The loss on ignition is reported as part of an elemental or oxide analysis of a mineral. The volatile materials lost usually consist of "combined water" (hydrate
s and labile hydroxy-compounds) and carbon dioxide
from carbonates. It may be used as a quality test, commonly carried out for minerals such as iron ore. For example, the loss on ignition of a fly ash
consists of contaminant unburnt fuel.
In pyroprocessing
industries such as lime
, calcined bauxite
, refractories
or cement
manufacture, the loss on ignition of the raw material is roughly equivalent to the loss in mass that it will undergo in a kiln
. Similarly for minerals the loss on ignition represents the actual material lost during smelting or refining in a furnace or smelter. The loss on ignition of the product indicates the extent to which the pyroprocessing was incomplete. ASTM tests are defined for limestone and lime and cement among others.
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
, particularly in the analysis of mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s. It consists of strongly heating ("igniting"
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
) a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change. This may be done in air, or in some other reactive or inert atmosphere. The simple test typically consists of placing a few grams of the material in a tarred, pre-ignited crucible
Crucible
A crucible is a container used for metal, glass, and pigment production as well as a number of modern laboratory processes, which can withstand temperatures high enough to melt or otherwise alter its contents...
and determining its mass, placing it in a temperature-controlled furnace for a set time, cooling it in a controlled (e.g. water-free, CO2-free) atmosphere, and redetermining the mass. The process may be repeated to show that mass-change is complete. A variant of the test in which mass-change is continually monitored as temperature is changed, is thermogravimetry
Thermogravimetry
Thermogravimetry is a branch of physical chemistry, materials research, and thermal analysis...
.
The loss on ignition is reported as part of an elemental or oxide analysis of a mineral. The volatile materials lost usually consist of "combined water" (hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
s and labile hydroxy-compounds) and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
from carbonates. It may be used as a quality test, commonly carried out for minerals such as iron ore. For example, the loss on ignition of a fly ash
Fly ash
Fly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal...
consists of contaminant unburnt fuel.
In pyroprocessing
Pyroprocessing
Pyroprocessing is a process in which materials are subjected to high temperatures in order to bring about a chemical or physical change. Pyroprocessing includes such terms as ore-roasting, calcination and sintering...
industries such as lime
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
, calcined bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
, refractories
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
or cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
manufacture, the loss on ignition of the raw material is roughly equivalent to the loss in mass that it will undergo in a kiln
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
. Similarly for minerals the loss on ignition represents the actual material lost during smelting or refining in a furnace or smelter. The loss on ignition of the product indicates the extent to which the pyroprocessing was incomplete. ASTM tests are defined for limestone and lime and cement among others.