Editing Autoignition temperature

{{Short description|Lowest temperature at which a substance spontaneously combusts}}

The '''autoignition temperature''' or '''self-ignition temperature''', often called '''spontaneous ignition temperature''' or '''minimum ignition temperature''' (or shortly '''ignition temperature''') and formerly also known as '''kindling point''', of a [[Chemical substance|substance]] is the lowest [[temperature]] at which it [[Spontaneous combustion|spontaneously ignites]] in a normal atmosphere without an external source of ignition, such as a [[flame]] or [[Spark (fire)|spark]].<ref name="LAURENDEAU"/> 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.<ref>{{cite journal | url=https://www.purkh.com/articles/autoignition-temperature-understanding-the-science-behind-spontaneous-combustion-101934.html#:~:text=Pressure%20can%20influence%20the%20auto,aerospace%20or%20deep%2Dsea%20exploration | title=Auto-Ignition Temperature: Understanding the Science behind Spontaneous Combustion | journal=To Chemistry Journal | date=29 March 2023 | volume=10 | issue=1 | pages=1 | last1=Lin | first1=Guanyou }}</ref> 

*Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed [[Pyrophoricity|pyrophoric]].

Autoignition temperatures of liquid chemicals are typically measured using a {{convert|500|ml|adj=on}} flask placed in a temperature-controlled oven in accordance with the procedure described in [[ASTM International|ASTM]] E659.<ref>E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.</ref>

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.<ref>S. Grynko, "Material Properties Explained" (2012), {{ISBN|1-4700-7991-7}}, p. 46.</ref>

==Autoignition time equation==
The time <math>t_\text{ig}</math> it takes for a material to reach its autoignition temperature <math>T_\text{ig}</math> when exposed to a [[heat flux]] <math>q''</math> is given by the following equation:<ref>Principles of Fire Behavior. {{ISBN|0-8273-7732-0}}. 1998.</ref>

:<math>t_\text{ig} = \frac{\pi}{4} k \rho c \left [ \frac{T_\text{ig} - T_0}{q''} \right]^2, </math>

where ''k'' = [[thermal conductivity]], ''ρ'' = density, and ''c'' = [[specific heat capacity]] of the material of interest, <math>T_0</math> 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 [[Catenation|chain length]]. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons.<ref>Zabetakis, M. G. (1965), Flammability characteristics of combustible gases and vapours, U.S. Department of Mines, Bulletin 627.</ref>

{| class="wikitable sortable"
|-
! Substance !! data-sort-type="number" | Autoignition{{ref label|standCond|D|D}}!!scope="col" class="unsortable"  |Note
|-
| [[Barium]] || {{convert|550|C|F|sortable=on|abbr=on}} ||550±90<ref name="LAURENDEAU">{{cite journal |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}}</ref>{{ref label|Pressure|C|C}}
|-
| [[Bismuth]] || {{convert|735|C|F|sortable=on|abbr=on}} || 735±20<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Butane]] || {{convert|405|C|F|sortable=on|abbr=on}} || <ref>{{cite web |url=http://www.wolframalpha.com/input/?i=butane|title=Butane - Safety Properties |publisher=Wolfram&#124;Alpha}}</ref>
|-
| [[Calcium]] || {{convert|790|C|F|sortable=on|abbr=on}} || 790±10<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Carbon disulfide]] || {{convert|90|C|F|sortable=on|abbr=on}} ||  <ref name=ETB/>
|-
| [[Diesel fuel|Diesel]] or [[Jet fuel|Jet A-1]] || {{convert|210|C|F|sortable=on|abbr=on}} || <ref name=TCForensics/>
|-
| [[Diethyl ether]] || {{convert|160|C|F|sortable=on|abbr=on}} || <ref>{{cite web |url=http://www.wolframalpha.com/input/?i=diethyl+ether|title=Diethyl Ether - Safety Properties |publisher=Wolfram&#124;Alpha}}</ref>
|-
| [[Ethanol]] || {{convert|365|C|F|sortable=on|abbr=on}} || <ref name=ETB>{{citation |url=http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html |title=Fuels and Chemicals - Autoignition Temperatures |publisher=engineeringtoolbox.com}}</ref>
|-
| [[Gasoline]] (Petrol) || {{convert|247|-|280|C|F|sortable=on|abbr=on}} || <ref name=ETB/>
|-
| [[Hydrogen]] || {{convert|535|C|F|sortable=on|abbr=on}} ||
|-
| [[Iron]] || {{convert|1315|C|F|sortable=on|abbr=on}} || 1315±20<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Lead]] || {{convert|850|C|F|sortable=on|abbr=on}} || 850±5<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Leather]] / [[parchment]] ||{{convert|200|-|212|C|F|sortable=on|abbr=on}} || <ref name=TCForensics>{{cite web|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}}</ref><ref name=LeatherInt>{{cite web|title=Flammability and flame retardancy of leather|url=http://www.leathermag.com/features/featureflammability-and-flame-retardancy-of-leather/|website=leathermag.com|publisher=Leather International / Global Trade Media|access-date=11 February 2015}}</ref>
|-
| [[Magnesium]] || {{convert|635|C|F|sortable=on|abbr=on}} || 635±5<ref name="LAURENDEAU"/>{{ref label|Magnesium|B|B}}{{ref label|Pressure|C|C}}
|-
| [[Magnesium]] || {{convert|473|C|F|sortable=on|abbr=on}} || <ref name=ETB/>{{ref label|Magnesium|B|B}}
|-
| [[Methane]] || {{convert|537|C|F|sortable=on|abbr=on}} || 
|-
| [[Molybdenum]] || {{convert|780|C|F|sortable=on|abbr=on}} || 780±5<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Paper]] ||{{convert|218|-|246|C|F|sortable=on|abbr=on}} || <ref name=TCForensics/><ref>{{cite journal |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)</ref>
|-
| [[Allotropes of phosphorus#White phosphorus|Phosphorus (white)]]|| {{convert|34|C|F|sortable=on|abbr=on}} ||  <ref name=ETB/>{{ref label|Phosphorus|A|A}}{{ref label|Magnesium|B|B}}
|-
| [[Silane]] || {{convert|21|C|F|sortable=on|abbr=on}} ||  <ref name=ETB/> <small>or below</small>
|-
| [[Strontium]] || {{convert|1075|C|F|sortable=on|abbr=on}} || 1075±120<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Tin]] || {{convert|940|C|F|sortable=on|abbr=on}} || 940±25<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}}
|-
| [[Triethylborane]] || {{convert|-20|C|F|sortable=on|abbr=on}} || <ref name=ETB/>
|}
{|
|-
|{{note label|Phosphorus|A|A}} On contact with an [[organic substance]], [[Melting|melts]] otherwise.
|-
|{{note label|Magnesium|B|B}} There are two distinct results in the published literature. Both are separately listed in this table.
|-
|{{note label|Pressure|C|C}} At 1 [[Atmosphere (unit)|atm]]. The ignition temperature depends on the air pressure.
|-
|{{note label|standCond|D|D}}Under [[standard conditions for temperature and pressure|standard conditions for pressure]].
|}

==See also==
* [[Fire point]]
* [[Flash point]]
* [[Gas burner]] (for flame temperatures, combustion heat energy values and ignition temperatures)
* [[Spontaneous combustion]]

==References==
{{Reflist}}
{{Refbegin}}
{{Refend}}

== External links ==
* [http://www.fire.nist.gov/bfrlpubs/fire03/art015.html Analysis of Effective Thermal Properties of Thermally Thick Materials].

{{Firelighting}}
{{Authority control}}

{{DEFAULTSORT:Autoignition Temperature}}
[[Category:Chemical properties]]
[[Category:Fire]]
[[Category:Threshold temperatures]]

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