Titanium is well known for its excellent resistance to corrosion; it is almost as resistant as platinum, being able to withstand attack by acids, moist chlorine gas, and by common salt solutions. Pure titanium is not soluble in water but is soluble in concentrated acids. A metallic element, it is also well-known for its high strength-to-weight ratio. It is a light, strong metal with low density that, when pure, is quite ductile (especially in an oxygen-free environment), easy to work, lustrous, and metallic-white in colour. The relatively high melting point of this element makes it useful as a refractory metal. Commercially pure grades of titanium have an ultimate tensile strength equal to that of intermediate strength high strength low alloy steels, but are 43% lighter; it is 60% heavier than aluminium, but more than twice as strong as 6061-T6 aluminium alloy; these numbers can vary quite substantially due to different alloy compositions and processing variables. They are included as guidelines only.
This metal forms a passive and protective oxide coating (leading to corrosion-resistance) when exposed to elevated temperatures in air but at room temperatures it resists tarnishing. The metal, which burns when heated in air 610 °C or higher (forming titanium dioxide) is also one of the few elements that burns in pure nitrogen gas (it burns at 800 °C and forms titanium nitride). Titanium is resistant to dilute sulfuric and hydrochloric acid, along with chlorine gas, chloride solutions, and most organic acids. It is paramagnetic (weakly attracted to magnets) and has a very low electrical resistivity and thermal conductivity.
Experiments have shown that natural titanium becomes very radioactive after it is bombarded with deuterons, emitting mainly positrons and hard gamma rays. The metal is a dimorphic allotrope with the hexagonal alpha form changing into the cubic beta form very slowly at around 880 °C. When it is red hot the metal combines with oxygen, and when it reaches 550 °C it combines with chlorine. It also reacts with the other halogens and absorbs hydrogen.