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 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.
A major use in the past was in gas mantles of lanterns, which were frequently composed of 99 percent 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. 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% ThO2 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 known oxides. Only a few elements (including tungsten and carbon) and a few compounds (including tantalum carbide) have higher melting points.).
Thorium dioxide is a Welsbach material. It has been suggested that these chemicals could be sprayed into the upper atmosphere to reflect sunlight and thus lower the global temperature.
Thorium dioxide is a catalyst in many chemical reactions, including the Ruzicka large ring synthesis, petroleum cracking, conversion of ammonia to nitric acid and preparation of sulfuric acid.
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.
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