properties of ductility, strength, hardness, electrical resistivity, creep resistance, specific corrosion resistance, and combinations thereof. In addition to the ASTM specifications, titanium alloys are also produced to meet aerospace and military specifications (SAE-AMS, MIL-T), ISO standards, and country-specific specifications, as well as proprietary end-user specifications for aerospace, military, medical, and industrial applications. Titanium powder is manufactured using a flow production process known as the Armstrong process that is similar to the batch production Hunter process. A stream of titanium tetrachloride gas is added to a stream of molten sodium; the products (sodium chloride salt and titanium particles) is filtered from the extra sodium. Titanium is then separated from the salt by water washing. Both sodium and chlorine are recycled to produce and process more titanium tetrachloride. Fabrication All welding of titanium must be done in an inert atmosphere of argon or helium to shield it from contamination with atmospheric gases (oxygen, nitrogen, and hydrogen). Contamination causes a variety of conditions, such as embrittlement, which reduce the integrity of the assembly welds and lead to joint failure. Titanium is very difficult to solder directly, and hence a solderable metal or alloy such as steel is coated on titanium prior to soldering. Titanium metal can be machined with the same equipment and the same processes as stainless steel. Forming and forging Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account of the tendency of the metal to springback. This is especially true of certain high-strength alloys. Exposure to the oxygen in air at the elevated temperatures used in forging results in formation of an brittle oxygen-rich metallic surface layer called "alpha case" that worsens the fatigue properties, so it must be removed by milling, etching, or electrochemical treatment. Applications Titanium is used in steel as an alloying element (ferro-titanium) to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content. Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum, and other metals. Titanium mill products (sheet, plate, bar, wire, forgings, castings) find application in industrial, aerospace, recreational, and emerging markets. Powdered titanium is used in pyrotechnics as a source of bright-burning particles. Pigments, additives, and coatings About 95% of all titanium ore is destined for refinement into titanium dioxide (), an intensely white permanent pigment used in paints, paper, toothpaste, and plastics.