Editing Thorium dioxide (section)

{{short description|Chemical compound}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 433232426
| Name = Thorium dioxide
| ImageFile = Fluorite-unit-cell-3D-ionic.png
| ImageSize =
| ImageName =
| IUPACName = Thorium dioxide<br>Thorium(IV) oxide
| OtherNames = Thoria<br>Thorium anhydride
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 1314-20-1
| ChEBI = 37339
| ChemSpiderID = 14124
| EC_number = 215-225-1
| Gmelin = 141638
| PubChem = 14808
| UNNumber = 2910 2909
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 9XA7X17UQC
| InChI = 1S/2O.Th
| StdInChIKey = ZCUFMDLYAMJYST-UHFFFAOYSA-N
| SMILES = O=[Th]=O
  }}
|Section2={{Chembox Properties
| Formula = ThO<sub>2</sub>
| MolarMass = 264.037&nbsp;g/mol<ref name=crc1/>
| Appearance = white solid<ref name=crc1/>
| Odor = odorless
| Density = 10.0&nbsp;g/cm<sup>3</sup><ref name=crc1>Haynes, p. 4.95</ref>
| Solubility = insoluble<ref name=crc1/>
| SolubleOther = insoluble in [[alkali]]<br>slightly soluble in [[acid]]<ref name=crc1/>
| MeltingPtC = 3350
| MeltingPt_ref=<ref name=crc1/>
| BoilingPtC = 4400
| BoilingPt_ref=<ref name=crc1/>
| RefractIndex = 2.200 (thorianite)<ref>Haynes, p. 4.144</ref>
| MagSus = &minus;16.0·10<sup>−6</sup>&nbsp;cm<sup>3</sup>/mol<ref>Haynes, p. 4.136</ref>
  }}
|Section3={{Chembox Structure
| CrystalStruct = [[Fluorite structure|Fluorite]] (cubic), [[Pearson symbol|''cF12'']]
| SpaceGroup = Fm<u style="text-decoration:overline">3</u>m, No. 225 
| Coordination = Tetrahedral (O<sup>2−</sup>); cubic (Th<sup>IV</sup>)
| LattConst_a = 559.74(6) pm<ref name=Yamashita>{{Cite journal | title = Thermal expansions of NpO<sub>2</sub> and some other actinide dioxides | journal = J. Nucl. Mater. | volume = 245 | issue = 1 | year = 1997 | pages = 72–78 |author1=Yamashita, Toshiyuki |author2=Nitani, Noriko |author3=Tsuji, Toshihide |author4=Inagaki, Hironitsu | doi = 10.1016/S0022-3115(96)00750-7 | bibcode = 1997JNuM..245...72Y }}</ref>
  }}
|Section4={{Chembox Thermochemistry
| DeltaHf = &minus;1226(4) kJ/mol
| Entropy = 65.2(2)&nbsp;J&thinsp;K<sup>&minus;1</sup>&thinsp;mol<sup>&minus;1</sup>
  }}
|Section7={{Chembox Hazards
| GHS_ref=<ref>{{cite web |title=Thorium dioxide |url=https://pubchem.ncbi.nlm.nih.gov/compound/14808#section=Safety-and-Hazards |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref>
| GHSPictograms = {{GHS06}}{{GHS08}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|301|311|331|350|373}}
| PPhrases = {{P-phrases|203|260|261|264|270|271|280|301+316|302+352|304+340|316|318|319|321|330|361+364|403+233|405|501}}
| ExternalSDS = 
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = RA
| FlashPt = Non-flammable
| LD50 = 400&nbsp;mg/kg
  }}
|Section8={{Chembox Related
| OtherAnions = [[Thorium(IV) sulfide]]
| OtherCations = [[Hafnium(IV) oxide]]<br/>[[Cerium(IV) oxide]]
| OtherFunction = 
| OtherFunction_label = 
| OtherCompounds = [[Protactinium(IV) oxide]]<br/>[[Uranium(IV) oxide]]
  }}

}}
'''Thorium dioxide''' (ThO<sub>2</sub>), also called '''thorium(IV) oxide''', is a crystalline solid, often white or yellow in colour. Also known as '''thoria''',  it is mainly a by-product of [[lanthanide]] and [[uranium]] production.<ref name=Yamashita/> [[Thorianite]] is the name of the mineralogical form of [[thorium]] dioxide. It is moderately rare and crystallizes in an isometric system. The melting point of thorium oxide is 3300&nbsp;°C – the highest of all known oxides. Only a few elements (including [[tungsten]] and [[carbon]]) and a few compounds (including [[tantalum carbide]]) have higher melting points.<ref>{{cite book | last = Emsley | first = John | title = Nature's Building Blocks | edition = Hardcover, First | publisher = [[Oxford University Press]] | year = 2001 | pages = [https://archive.org/details/naturesbuildingb0000emsl/page/441 441] | isbn = 978-0-19-850340-8 | url = https://archive.org/details/naturesbuildingb0000emsl/page/441 }}</ref>  All thorium compounds, including the dioxide, are radioactive because there are no stable [[isotopes of thorium]].