Theautoignition temperature (often calledself-ignition temperature,spontaneous ignition temperature,minimum ignition temperature, or shortlyignition temperature, formerly also known askindling point) of asubstance is the lowesttemperature at which itspontaneously ignites in a normal atmosphere without an external source of ignition, such as aflame orspark.[1] This temperature is required to supply theactivation energy needed forcombustion. The temperature at which a chemical ignites decreases as thepressure is decreased.[2]
Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termedpyrophoric.
Autoignition temperatures of liquid chemicals are typically measured using a 500-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described inASTM E659.[3]
When measured forplastics, autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this is ASTM G72.[4]
The time it takes for a material to reach its autoignition temperature when exposed to aheat flux is given by the following equation:[5]
wherek =thermal conductivity,ρ = density, andc =specific heat capacity of the material of interest, is the initial temperature of the material (or the temperature of the bulk material).
Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation includepartial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally the autoignition temperature for hydrocarbon/air mixtures decreases with increasingmolecular mass and increasingchain length. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons.[6]
| Substance | Autoignition[D] | Note |
|---|---|---|
| Barium | 550 °C (1,022 °F) | 550±90[1][C] |
| Bismuth | 735 °C (1,355 °F) | 735±20[1][C] |
| Butane | 405 °C (761 °F) | [7] |
| Calcium | 790 °C (1,450 °F) | 790±10[1][C] |
| Carbon disulfide | 90 °C (194 °F) | [8] |
| Diesel orJet A-1 | 210 °C (410 °F) | [9] |
| Diethyl ether | 160 °C (320 °F) | [10] |
| Ethanol | 365 °C (689 °F) | [8] |
| Gasoline (Petrol) | 247–280 °C (477–536 °F) | [8] |
| Hydrogen | 535 °C (995 °F) | |
| Iron | 1,315 °C (2,399 °F) | 1315±20[1][C] |
| Lead | 850 °C (1,560 °F) | 850±5[1][C] |
| Leather /parchment | 200–212 °C (392–414 °F) | [9][11] |
| Magnesium | 635 °C (1,175 °F) | 635±5[1][B][C] |
| Magnesium | 473 °C (883 °F) | [8][B] |
| Methane | 537 °C (999 °F) | |
| Molybdenum | 780 °C (1,440 °F) | 780±5[1][C] |
| Paper | 218–246 °C (424–475 °F) | [9][12] |
| Phosphorus (white) | 34 °C (93 °F) | [8][A][B] |
| Silane | 21 °C (70 °F) | [8]or below |
| Strontium | 1,075 °C (1,967 °F) | 1075±120[1][C] |
| Tin | 940 °C (1,720 °F) | 940±25[1][C] |
| Triethylborane | −20 °C (−4 °F) | [8] |
| A On contact with anorganic substance,melts otherwise. |
| B There are two distinct results in the published literature. Both are separately listed in this table. |
| C At 1atm. The ignition temperature depends on the air pressure. |
| D Understandard conditions for pressure. |
