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Autoignition temperature
Lowest temperature at which a substance spontaneously combusts
Lowest temperature at which a substance spontaneously combusts
The autoignition temperature (often called self-ignition temperature, spontaneous ignition temperature, minimum ignition temperature, or shortly ignition temperature, formerly also known as kindling point) of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is decreased.
Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed pyrophoric.
Autoignition temperatures of liquid chemicals are typically measured using a 500 ml flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.
When measured for plastics, 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.
Autoignition time equation
The time t_\text{ig} it takes for a material to reach its autoignition temperature T_\text{ig} when exposed to a heat flux q'' is given by the following equation:
:t_\text{ig} = \frac{\pi}{4} k \rho c \left [ \frac{T_\text{ig} - T_0}{q''} \right]^2,
where k = thermal conductivity, ρ = density, and c = specific heat capacity of the material of interest, T_0 is the initial temperature of the material (or the temperature of the bulk material).
Autoignition temperature of selected substances
Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally the autoignition temperature for hydrocarbon/air mixtures decreases with increasing molecular mass and increasing chain length. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons.
| Substance | Autoignition | Note | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Barium | 550 C | last1=Laurendeau | first1=N. M. | last2=Glassman | first2=I. | title=Ignition Temperatures of Metals in Oxygen Atmospheres | journal=Combustion Science and Technology | date=1971-04-01 | volume=3 | issue=2 | pages=77–82 | doi=10.1080/00102207108952274 | language=en}} |
| Bismuth | 735 C | Pressure | C | C}} | |||||||||
| Butane | 405 C | ||||||||||||
| Calcium | 790 C | Pressure | C | C}} | |||||||||
| Carbon disulfide | 90 C | ||||||||||||
| Diesel or Jet A-1 | 210 C | ||||||||||||
| Diethyl ether | 160 C | ||||||||||||
| Ethanol | 365 C | url=http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html | title=Fuels and Chemicals - Autoignition Temperatures | publisher=engineeringtoolbox.com}} | |||||||||
| Gasoline (Petrol) | 247 - | ||||||||||||
| Hydrogen | 535 C | ||||||||||||
| Iron | 1315 C | Pressure | C | C}} | |||||||||
| Lead | 850 C | Pressure | C | C}} | |||||||||
| Leather / parchment | 200 - | last1=Cafe | first1=Tony | title=PHYSICAL CONSTANTS FOR INVESTIGATORS | url=http://www.tcforensic.com.au/docs/article10.html | website=tcforensic.com.au | publisher=TC Forensic P/L. | access-date=11 February 2015}} | |||||
| Magnesium | 635 C | Magnesium | B | B}} | |||||||||
| Magnesium | 473 C | Magnesium | B | B}} | |||||||||
| Methane | 537 C | ||||||||||||
| Molybdenum | 780 C | Pressure | C | C}} | |||||||||
| Paper | 218 - | url=http://www.tcforensic.com.au/docs/article10.html | title=Physical Constants for Investigators | author=Tony Cafe | journal=Journal of Australian Fire Investigators}} (Reproduced from "Firepoint" magazine) | ||||||||
| Phosphorus (white) | 34 C | Phosphorus | A | A}} | |||||||||
| Silane | 21 C | or below | |||||||||||
| Strontium | 1075 C | Pressure | C | C}} | |||||||||
| Tin | 940 C | Pressure | C | C}} | |||||||||
| Triethylborane | -20 C |
| Under standard conditions for pressure. |
|---|
References
References
- (29 March 2023). "Auto-Ignition Temperature: Understanding the Science behind Spontaneous Combustion". To Chemistry Journal.
- E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.
- S. Grynko, "Material Properties Explained" (2012), {{ISBN. 1-4700-7991-7, p. 46.
- Principles of Fire Behavior. {{ISBN. 0-8273-7732-0. 1998.
- Zabetakis, M. G. (1965), Flammability characteristics of combustible gases and vapours, U.S. Department of Mines, Bulletin 627.
- (1971-04-01). "Ignition Temperatures of Metals in Oxygen Atmospheres". Combustion Science and Technology.
- "Butane - Safety Properties". Wolfram|Alpha.
- "Diethyl Ether - Safety Properties". Wolfram|Alpha.
- "Fuels and Chemicals - Autoignition Temperatures". engineeringtoolbox.com.
- "PHYSICAL CONSTANTS FOR INVESTIGATORS". TC Forensic P/L..
- "Flammability and flame retardancy of leather". Leather International / Global Trade Media.
- Tony Cafe. "Physical Constants for Investigators". Journal of Australian Fire Investigators.
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