Everything about Thoria totally explained
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Thorium dioxide (ThO
2), also called
thorium(IV) oxide (IUPAC) is a white, crystalline powder. It was formerly known as
thoria or
thorina. It is produced mainly as a by-product of
lanthanide and
uranium production
[1].
Chemistry
The compound is
radioactive due to the radioactivity of
thorium. Thorium dioxide can be used as a
nuclear fuel. (Refer to the article of
thorium for more information on this application.)
The high
thermal stability of thorium dioxide allows applications in flame spraying and high temperature ceramics. Thorium dioxide was the primary ingredient in the
X-ray contrast medium
Thorotrast. Use of Thorotrast was abandoned when it was found to be a
carcinogen, sometimes causing
cholangiocarcinoma. Today,
barium sulfate is the standard X-ray contrast agent.
Thoria has the
fluorite crystal structure. Few other binary dioxides have this structure:
uranium dioxide,
hafnium dioxide and
cerium dioxide, not to mention
plutonium dioxide. The
band gap of thoria is about 6
eV.
Applications
Thorium dioxide is used as a stabilizer in
tungsten electrodes in
TIG welding,electron tubes, and aircraft engines. As an alloy, thoriated tungsten metal isn't 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.
A major use in the past was in
gas mantles of lanterns, which were frequently composed of 99 percent ThO
2 and 1%
cerium(IV) oxide. Even as late as the 1980s it was estimated that about half of all ThO
2 produced (several hundred tonnes per year) was used for this purpose
[1]. Some mantles still use thorium, but
yttrium oxide (or sometimes
zirconium oxide) is used increasingly as a replacement.
Thorium dioxide was formerly added to
glasses during manufacture to increase their
refractive index, producing
thoriated glass with up to 40% ThO
2 content. These glasses were used in the construction of high-quality
photographic lenses. However, the radioactivity of the thorium caused both a safety and pollution hazard and self-degradation of the glass (turning it yellow or brown over time).
Lanthanum oxide has replaced thorium dioxide in almost all modern high-index glasses.
The melting point of thorium oxide is 3300°C - the highest of all oxides. Only a few elements (including
tungsten and
carbon) and a few compounds (including
tantalum carbide) have higher melting points.
Thorium oxide is a Welsbach material. It has been suggested
[2] that these chemicals could be sprayed into the upper atmosphere to reflex sunlight and thus lower the global temperature.
The
Ruzicka large ring synthesis uses thorium oxide as catalyst.
Further Information
Get more info on 'Thoria'.
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