Thorium dioxide

Chemical compound

Thorium dioxide

Names
IUPAC names

Thorium dioxide
Thorium(IV) oxide

Other names

Thoria
Thorium anhydride

Identifiers

CAS Number

* 1314-20-1 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:37339

ChemSpider |

* 14124

ECHA InfoCard | 100.013.842
EC Number |

* 215-225-1

Gmelin Reference

| 141638

PubChem CID

* 14808

UNII |

* 9XA7X17UQC Y

UN number | 2910 2909

CompTox Dashboard (EPA)

* DTXSID0051657

InChI

* Key: ZCUFMDLYAMJYST-UHFFFAOYSA-N

* InChI=1S/2O.Th

SMILES

* O=[Th]=O

Properties

Chemical formula

| ThO2
Molar mass | 264.037 g/mol[1]
Appearance  | white solid[1]
Odor | odorless
Density | 10.0 g/cm3[1]
Melting point | 3,350 °C (6,060 °F; 3,620 K)[1]
Boiling point | 4,400 °C (7,950 °F; 4,670 K)[1]

Solubility in water

| insoluble[1]
Solubility | insoluble in alkali
slightly soluble in acid[1]

Magnetic susceptibility (χ)

| −16.0·10−6 cm3/mol[2]

Refractive index (nD)

| 2.200 (thorianite)[3]
Structure

Crystal structure

| Fluorite (cubic), cF12

Space group

| Fm3m, No. 225

Lattice constant

a = 559.74(6) pm[4]

Coordination geometry

| Tetrahedral (O2−); cubic (ThIV)
Thermochemistry

Std molar
entropy (S⦵298)

| 65.2(2) J K−1 mol−1

Std enthalpy of
formation (ΔfH⦵298)

| −1226(4) kJ/mol
Hazards
GHS labelling:[5]

Pictograms

Signal word

| Danger

Hazard statements

| H301, H311, H331, H350, H373

Precautionary statements

| P203, P260, P261, P264, P270, P271, P280, P301+P316, P302+P352, P304+P340, P316, P318, P319, P321, P330, P361+P364, P403+P233, P405, P501
NFPA 704 (fire diamond)  |

Flash point | Non-flammable
Lethal dose or concentration (LD, LC):

LD50 (median dose)

| 400 mg/kg
Related compounds

Other anions

| Thorium(IV) sulfide

Other cations

| Hafnium(IV) oxide
Cerium(IV) oxide

Related compounds

| Protactinium(IV) oxide
Uranium(IV) oxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)

Infobox references

Chemical compound

Thorium dioxide (ThO2), 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.[4] 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 °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.[6] All thorium compounds, including the dioxide, are radioactive because there are no stable isotopes of thorium.

## Structure and reactions

[edit]

Thoria exists as two polymorphs. One has a fluorite crystal structure. This is uncommon among binary dioxides. (Other binary oxides with fluorite structure include cerium dioxide, uranium dioxide and plutonium dioxide.)[clarification needed] The band gap of thoria is about 6 eV. A tetragonal form of thoria is also known.

Thorium dioxide is more stable than thorium monoxide (ThO).[7] Only with careful control of reaction conditions can oxidation of thorium metal give the monoxide rather than the dioxide. At extremely high temperatures, the dioxide can convert to the monoxide either by a disproportionation reaction (equilibrium with liquid thorium metal) above 1,850 K (1,580 °C; 2,870 °F) or by simple dissociation (evolution of oxygen) above 2,500 K (2,230 °C; 4,040 °F).[8]

## Applications

[edit]

### Nuclear fuels

[edit]

Thorium dioxide (thoria) can be used in nuclear reactors as ceramic fuel pellets, typically contained in nuclear fuel rods clad with zirconium alloys. Thorium is not fissile (but is "fertile", breeding fissile uranium-233 under neutron bombardment); hence, it must be used as a nuclear reactor fuel in conjunction with fissile isotopes of either uranium or plutonium. This can be achieved by blending thorium with uranium or plutonium, or using it in its pure form in conjunction with separate fuel rods containing uranium or plutonium. Thorium dioxide offers advantages over conventional uranium dioxide fuel pellets, because of its higher thermal conductivity (lower operating temperature), considerably higher melting point, and chemical stability (does not oxidize in the presence of water/oxygen, unlike uranium dioxide).

Thorium dioxide can be turned into a nuclear fuel by breeding it into uranium-233 (see below and refer to the article on thorium for more information on this). The high thermal stability of thorium dioxide allows applications in flame spraying and high-temperature ceramics.

### Alloys

[edit]

Thorium dioxide is used as a stabilizer in tungsten electrodes in TIG welding, electron tubes, and aircraft gas turbine engines. As an alloy, thoriated tungsten metal is not easily deformed because the high-fusion material thoria augments the high-temperature mechanical properties, and thorium helps stimulate the emission of electrons (thermions). It is the most popular oxide additive because of its low cost, but is being phased out in favor of non-radioactive elements such as cerium, lanthanum and zirconium.

Thoria-dispersed nickel finds its applications in various high-temperature operations like combustion engines because it is a good creep-resistant material. It can also be used for hydrogen trapping.[9][10][11][12][13]

### Catalysis

[edit]

Thorium dioxide has almost no value as a commercial catalyst, but such applications have been well investigated. It is a catalyst in the Ruzicka large ring synthesis. Other applications that have been explored include petroleum cracking, conversion of ammonia to nitric acid and preparation of sulfuric acid.[14]

### Radiocontrast agents

[edit]

Thorium dioxide was the primary ingredient in Thorotrast, a once-common radiocontrast agent used for cerebral angiography, however, it causes a rare form of cancer (hepatic angiosarcoma) many years after administration.[15] This use was replaced with injectable iodine or ingestable barium sulfate suspension as standard X-ray contrast agents.

### Lamp mantles

[edit]

Main article: Gas mantle

Another major use in the past was in gas mantle of lanterns developed by Carl Auer von Welsbach in 1890, which are composed of 99% ThO2 and 1% cerium(IV) oxide. Even as late as the 1980s it was estimated that about half of all ThO2 produced (several hundred tonnes per year) was used for this purpose.[16] Some mantles still use thorium, but yttrium oxide (or sometimes zirconium oxide) is used increasingly as a replacement.

### Glass manufacture

[edit]

Yellowed thorium dioxide lens (left), a similar lens partially de-yellowed with ultraviolet radiation (centre), and lens without yellowing (right)

When added to glass, thorium dioxide helps increase its refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments.[17] The radiation from these lenses can darken them and turn them yellow over a period of years and degrade film, but the health risks are minimal.[18] Yellowed lenses may be restored to their original colourless state by lengthy exposure to intense ultraviolet radiation. Thorium dioxide has since been replaced by rare-earth oxides such as lanthanum oxide in almost all modern high-index glasses, as they provide similar effects and are not radioactive.[19]

## References

[edit]

1. ^ a b c d e f g Haynes, p. 4.95
2. ^ Haynes, p. 4.136
3. ^ Haynes, p. 4.144
4. ^ a b Yamashita, Toshiyuki; Nitani, Noriko; Tsuji, Toshihide; Inagaki, Hironitsu (1997). "Thermal expansions of NpO2 and some other actinide dioxides". J. Nucl. Mater. 245 (1): 72–78\. Bibcode:1997JNuM..245...72Y. doi:10.1016/S0022-3115(96)00750-7.
5. ^ "Thorium dioxide". pubchem.ncbi.nlm.nih.gov.
6. ^ Emsley, John (2001). Nature's Building Blocks (Hardcover, First ed.). Oxford University Press. pp. 441. ISBN 978-0-19-850340-8.
7. ^ He, Heming; Majewski, Jaroslaw; Allred, David D.; Wang, Peng; Wen, Xiaodong; Rector, Kirk D. (2017). "Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations". Journal of Nuclear Materials. 487: 288–296\. Bibcode:2017JNuM..487..288H. doi:10.1016/j.jnucmat.2016.12.046.
8. ^ Hoch, Michael; Johnston, Herrick L. (1954). "The Reaction Occurring on Thoriated Cathodes". J. Am. Chem. Soc. 76 (19): 4833–4835\. doi:10.1021/ja01648a018.
9. ^ Mitchell, Brian S (2004). An Introduction to Materials Engineering. and Science for Chemical and Materials. John Wiley & Sons. p. 473\. ISBN 978-0-471-43623-2.
10. ^ Robertson, Wayne M. (1979). "Measurement and evaluation of hydrogen trapping in thoria dispersed nickel". Metallurgical and Materials Transactions A. 10 (4): 489–501\. Bibcode:1979MTA....10..489R. doi:10.1007/BF02697077. S2CID 137105492.
11. ^ Kumar, Arun; Nasrallah, M.; Douglass, D. L. (1974). "The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys". Oxidation of Metals. 8 (4): 227–263\. doi:10.1007/BF00604042. hdl:2060/19740015001. ISSN 0030-770X. S2CID 95399863.
12. ^ Stringer, J.; Wilcox, B. A.; Jaffee, R. I. (1972). "The high-temperature oxidation of nickel-20 wt.% chromium alloys containing dispersed oxide phases". Oxidation of Metals. 5 (1): 11–47\. doi:10.1007/BF00614617. ISSN 0030-770X. S2CID 92103123.
13. ^ Murr, L. E. (1974). "Interfacial energetics in the TD-nickel and TD-nichrome systems". Journal of Materials Science. 9 (8): 1309–1319\. Bibcode:1974JMatS...9.1309M. doi:10.1007/BF00551849. ISSN 0022-2461. S2CID 96573790.
14. ^ Stoll, Wolfgang (2012) "Thorium and Thorium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim. doi:10.1002/14356007.a27_001
15. ^ Thorotrast. radiopaedia.org
16. ^ Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1425, 1456. ISBN 978-0-08-022057-4.
17. ^ Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC Press. ISBN 978-0-8493-0485-9.
18. ^ Oak Ridge Associated Universities (1999). "Thoriated Camera Lens (ca. 1970s)". Retrieved 29 September 2017.
19. ^ Stoll, W. (2005). "Thorium and Thorium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. p. 32\. doi:10.1002/14356007.a27_001. ISBN 978-3-527-31097-5.

## Cited sources

[edit]

* Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.

* v
* t
* e

Thorium compounds

Th(II)|

* ThC2
* ThCl2
* ThI2
* ThO

Th(III)|

* ThCl3
* ThF3
* ThI3

Th(IV)|

* ThO2
* Th(OH)4
* ThC
* ThCl4
* ThF4
* ThI4
* ThSiO4
* ThOF

* Th(C2O4)2
* ThS2
* ThSe2
* Th(SeO4)2
* Th(NO3)4
* Th(C8H8)2
* Th(HCOO)4
* Th(CH3COO)4
* ThP7

* v
* t
* e

Oxides

Mixed oxidation states|

* Antimony tetroxide (Sb2O4)
* Boron suboxide (B12O2)
* Carbon suboxide (C3O2)
* Chlorine perchlorate (Cl2O4)
* Chloryl perchlorate (Cl2O6)
* Cobalt(II,III) oxide (Co3O4)
* Dichlorine pentoxide (Cl2O5)
* Iron(II,III) oxide (Fe3O4)
* Lead(II,IV) oxide (Pb3O4)
* Manganese(II,III) oxide (Mn3O4)
* Mellitic anhydride (C12O9)
* Praseodymium(III,IV) oxide (Pr6O11)
* Silver(I,III) oxide (Ag2O2)
* Terbium(III,IV) oxide (Tb4O7)
* Tribromine octoxide (Br3O8)
* Triuranium octoxide (U3O8)

+1 oxidation state|

* Aluminium(I) oxide (Al2O)
* Copper(I) oxide (Cu2O)
* Caesium monoxide (Cs2O)
* Dibromine monoxide (Br2O)
* Dicarbon monoxide (C2O)
* Dichlorine monoxide (Cl2O)
* Gallium(I) oxide (Ga2O)
* Iodine(I) oxide (I2O)
* Lithium oxide (Li2O)
* Mercury(I) oxide (Hg2O)
* Nitrous oxide (N2O)
* Potassium oxide (K2O)
* Rubidium oxide (Rb2O)
* Silver oxide (Ag2O)
* Thallium(I) oxide (Tl2O)
* Sodium oxide (Na2O)
* Water (hydrogen oxide) (H2O)

+2 oxidation state|

* Aluminium(II) oxide (AlO)
* Barium oxide (BaO)
* Berkelium monoxide (BkO)
* Beryllium oxide (BeO)
* Boron monoxide (BO)
* Bromine monoxide (BrO)
* Cadmium oxide (CdO)
* Calcium oxide (CaO)
* Carbon monoxide (CO)
* Chlorine monoxide (ClO)
* Chromium(II) oxide (CrO)
* Cobalt(II) oxide (CoO)
* Copper(II) oxide (CuO)
* Dinitrogen dioxide (N2O2)
* Disulfur dioxide (S2O2)
* Europium(II) oxide (EuO)
* Germanium monoxide (GeO)
* Iron(II) oxide (FeO)
* Iodine monoxide (IO)
* Lead(II) oxide (PbO)
* Magnesium oxide (MgO)
* Manganese(II) oxide (MnO)
* Mercury(II) oxide (HgO)
* Nickel(II) oxide (NiO)
* Nitric oxide (NO)
* Niobium monoxide (NbO)
* Palladium(II) oxide (PdO)
* Phosphorus monoxide (PO)
* Polonium monoxide (PoO)
* Protactinium monoxide (PaO)
* Radium oxide (RaO)
* Silicon monoxide (SiO)
* Strontium oxide (SrO)
* Sulfur monoxide (SO)
* Thorium monoxide (ThO)
* Tin(II) oxide (SnO)
* Titanium(II) oxide (TiO)
* Vanadium(II) oxide (VO)
* Yttrium(II) oxide (YO)
* Zirconium monoxide (ZrO)
* Zinc oxide (ZnO)

+3 oxidation state|

* Actinium(III) oxide (Ac2O3)
* Aluminium oxide (Al2O3)
* Americium(III) oxide (Am2O3)
* Antimony trioxide (Sb2O3)
* Arsenic trioxide (As2O3)
* Berkelium(III) oxide (Bk2O3)
* Bismuth(III) oxide (Bi2O3)
* Boron trioxide (B2O3)
* Californium(III) oxide (Cf2O3)
* Cerium(III) oxide (Ce2O3)
* Chromium(III) oxide (Cr2O3)
* Cobalt(III) oxide (Co2O3)
* Curium(III) oxide (Cm2O3)
* Dinitrogen trioxide (N2O3)
* Dysprosium(III) oxide (Dy2O3)
* Einsteinium(III) oxide (Es2O3)
* Erbium(III) oxide (Er2O3)
* Europium(III) oxide (Eu2O3)
* Gadolinium(III) oxide (Gd2O3)
* Gallium(III) oxide (Ga2O3)
* Gold(III) oxide (Au2O3)
* Holmium(III) oxide (Ho2O3)
* Indium(III) oxide (In2O3)
* Iron(III) oxide (Fe2O3)
* Lanthanum oxide (La2O3)
* Lutetium(III) oxide (Lu2O3)
* Manganese(III) oxide (Mn2O3)
* Neodymium(III) oxide (Nd2O3)
* Nickel(III) oxide (Ni2O3)
* Phosphorus trioxide (P4O6)
* Praseodymium(III) oxide (Pr2O3)
* Promethium(III) oxide (Pm2O3)
* Rhodium(III) oxide (Rh2O3)
* Samarium(III) oxide (Sm2O3)
* Scandium oxide (Sc2O3)
* Terbium(III) oxide (Tb2O3)
* Thallium(III) oxide (Tl2O3)
* Thulium(III) oxide (Tm2O3)
* Titanium(III) oxide (Ti2O3)
* Tungsten(III) oxide (W2O3)
* Vanadium(III) oxide (V2O3)
* Ytterbium(III) oxide (Yb2O3)
* Yttrium(III) oxide (Y2O3)

+4 oxidation state|

* Americium dioxide (AmO2)
* Berkelium(IV) oxide (BkO2)
* Bromine dioxide (BrO2)
* Californium dioxide (CfO2)
* Carbon dioxide (CO2)
* Carbon trioxide (CO3)
* Cerium(IV) oxide (CeO2)
* Chlorine dioxide (ClO2)
* Chromium(IV) oxide (CrO2)
* Curium(IV) oxide (CmO2)
* Dinitrogen tetroxide (N2O4)
* Germanium dioxide (GeO2)
* Iodine dioxide (IO2)
* Iridium dioxide (IrO2)
* Hafnium(IV) oxide (HfO2)
* Lead dioxide (PbO2)
* Manganese dioxide (MnO2)
* Molybdenum dioxide (MoO2)
* Neptunium(IV) oxide (NpO2)
* Nitrogen dioxide (NO2)
* Niobium dioxide (NbO2)
* Osmium dioxide (OsO2)
* Platinum dioxide (PtO2)
* Plutonium(IV) oxide (PuO2)
* Polonium dioxide (PoO2)
* Praseodymium(IV) oxide (PrO2)
* Protactinium(IV) oxide (PaO2)
* Rhenium(IV) oxide (ReO2)
* Rhodium(IV) oxide (RhO2)
* Ruthenium(IV) oxide (RuO2)
* Selenium dioxide (SeO2)
* Silicon dioxide (SiO2)
* Sulfur dioxide (SO2)
* Technetium(IV) oxide (TcO2)
* Tellurium dioxide (TeO2)
* Terbium(IV) oxide (TbO2)
* Thorium dioxide (ThO2)
* Tin dioxide (SnO2)
* Titanium dioxide (TiO2)
* Tungsten(IV) oxide (WO2)
* Uranium dioxide (UO2)
* Vanadium(IV) oxide (VO2)
* Zirconium dioxide (ZrO2)

+5 oxidation state|

* Antimony pentoxide (Sb2O5)
* Arsenic pentoxide (As2O5)
* Bismuth pentoxide (Bi2O5)
* Dinitrogen pentoxide (N2O5)
* Diuranium pentoxide (U2O5)
* Neptunium(V) oxide (Np2O5)
* Niobium pentoxide (Nb2O5)
* Phosphorus pentoxide (P2O5)
* Protactinium(V) oxide (Pa2O5)
* Tantalum pentoxide (Ta2O5)
* Tungsten pentoxide (W2O5)
* Vanadium(V) oxide (V2O5)

+6 oxidation state|

* Chromium trioxide (CrO3)
* Molybdenum trioxide (MoO3)
* Polonium trioxide (PoO3)
* Rhenium trioxide (ReO3)
* Selenium trioxide (SeO3)
* Sulfur trioxide (SO3)
* Tellurium trioxide (TeO3)
* Tungsten trioxide (WO3)
* Uranium trioxide (UO3)
* Xenon trioxide (XeO3)

+7 oxidation state|

* Dichlorine heptoxide (Cl2O7)
* Manganese heptoxide (Mn2O7)
* Rhenium(VII) oxide (Re2O7)
* Technetium(VII) oxide (Tc2O7)

+8 oxidation state|

* Iridium tetroxide (IrO4)
* Osmium tetroxide (OsO4)
* Ruthenium tetroxide (RuO4)
* Xenon tetroxide (XeO4)
* Hassium tetroxide (HsO4)

Related|

* Oxocarbon
* Suboxide
* Oxyanion
* Ozonide
* Peroxide
* Superoxide
* Oxypnictide

Oxides are sorted by oxidation state. Category:Oxides

Authority control databases: National |

* United States
* Israel

|

*[CID]: Compound ID
*[EPA]: U.S. Environmental Protection Agency
*[H301]: H301: Toxic if swallowed
*[H311]: H311: Toxic in contact with skin
*[H331]: H331: Toxic if inhaled
*[H350]: H350: May cause cancer
*[H373]: H373: May cause damage to organs through prolonged or repeated exposure
*[P203]: P203: Obtain, read and follow all safety instructions before use.
*[P260]: P260: Do not breathe dust/fume/gas/mist/vapours/spray.
*[P261]: P261: Avoid breathing dust/fume/gas/mist/vapours/spray.
*[P264]: P264: Wash ... thoroughly after handling.
*[P270]: P270: Do not eat, drink or smoke when using this product.
*[P271]: P271: Use only outdoors or in a well-ventilated area.
*[P280]: P280: Wear protective gloves/protective clothing/eye protection/face protection.
*[P301+P316]: P301+P316: IF SWALLOWED: Get immediate emergency medical help.
*[P302+P352]: P302+P352: IF ON SKIN: Wash with soap and water.
*[P304+P340]: P304+P340: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing.
*[P316]: P316: Get immediate emergency medical help.
*[P318]: P318: If exposed or concerned, get medical advice.
*[P319]: P319: Get medical help if you feel unwell.
*[P321]: P321: Specific treatment (see ... on this label).
*[P330]: P330: Rinse mouth.
*[P361+P364]: P361+P364: Take off immediately all contaminated clothing and wash it before reuse.
*[P403+P233]: P403+P233: Store in a well ventilated place. Keep container tightly closed.
*[P405]: P405: Store locked up.
*[P501]: P501: Dispose of contents/container to ...
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