Molten titanium

This comprehensive survey of the title topic is in three parts, the first dealing with the theoretical background and laboratory studies, with 29 references. The second part, with 21 references deals with case histories and experimental studies of industrial vapour explosions. These involved the systems molten titanium-water, molten copper-water, molten aluminium-water, smelt-water, water-various cryogenic liquids, molten salt-water and molten uranium dioxide-liquid sodium. In the third part (with a further 26 references) is discussion of the various theories which abound, and the general conclusion that superheated liquids most likely play a major role in all these phenomena [1]. A further related publication covers BLEVEs and pressure let-down explosions [2],... 

Although no definite cause could be ascertained, it was generally agreed that there was a bum-through of the cmcible (possibly by misdirection of the arc). This allowed water (under pressure) to enter the cmcible and contact the molten titanium. A minor (steam) explosion resulted and the burst disc blew. The heavy electrode was lifted up and then fell back into the water-titanium mix. A later, final explosion resulted when the cmcible fell on the floor to allow a water-titanium contact. 

Since cmcible failures have occurred in numerous instances in the industry—with minor steam explosions, the violence of the event described above is believed to be due to the electrode falling into the water-metal mixture. Somehow, the steam-liquid water-molten titanium mixture changed character from a relatively slow increase in pressure to a sharp shock wave. 

One might note the striking similarity between Cases I and II. In both, a crucible failure allowed water to enter and mix with molten titanium. Steam (and hydrogen) formed and the pressure increased so as to bulge the crucible and rupture the safety discs. Tamping the water-metal mix by the fall of the electrode then caused a major explosion. No injuries resulted in the Case II incident because the vault walls provided protection. No data were available to allow an estimation of blast pressures, but as described, the vault construction maintained its integrity and the wave was forced to exit from the bottom. 

The most important apphcation of this metal is as control rod material for shielding in nuclear power reactors. Its thermal neutron absorption cross section is 46,000 bams. Other uses are in thermoelectric generating devices, as a thermoionic emitter, in yttrium-iron garnets in microwave filters to detect low intensity signals, as an activator in many phosphors, for deoxidation of molten titanium, and as a catalyst. Catalytic apphcations include decarboxylation of oxaloacetic acid conversion of ortho- to para-hydrogen and polymerization of ethylene. 

As fluxes for MEM of titanium, the reactive compositions on the base of halogenides of alkali and alkali-earth metals are used. Halogenide fluxes allow the electroslag process to be easily set and provide its stability within the wide range of melting conditions. Rate of dissolution of harmful inclusions of nitrides of titanium in these fluxes much exceeds their rate of dissolution in molten titanium [4], Thus, the premises for dissolution and grinding of hard a-phase type inclusions are created. 

Because of the expense of this process, schemes using electrolysis of molten titanium salts, similar to the production of aluminium, have been widely investigated. To date, none of these has worked well. Although metal can be produced in this way, it is often dendritic in form, and very reactive, oxidising on contact with air. The various valence states of titanium found in melts ( A+, 3- - and 2- -) lower the efficiency of the methods and contribute to unreliable results. 

Gas atomization process (GAP) Atomization of molten titanium by a jet of inert gas Sumitomo Titanium Corp. n.a. Near-spherical Porosities... 

Gas-atomization process. In this process, the atomization of molten titanium is performed by a jet of inert gas, usually hehum or argon. The particles exhibit a spherical shape. 

Casting. Titanium castings can be produced by investment or graphite-mold methods. Casting must be done in a vacuum furnace because of the high chemical reactivity of molten titanium metal with oxygen and nitrogen. 

Proprietary lost wax ceramic shell systems have been developed by the several fotmdries engaged in titanivim casting manufacture. Of necessity, these shell systems must be relatively inert to molten titanium and cannot be made with the conventional foimdiy ceramics used in the ferrous and nonferrous industries. Usually, the face coats are made with special re actoiy oxides and appropriate binders. After the initial face coat ceramic is applied to the wax pattern, more traditional refractoiy systems are used to add shell strength om repeated backup ceramic coatings. Regardless of face coat composition, some metal/mold reaction inevitably occurs from titanium reduction... 

The skull may be due to cooling (for example, a molten material in contact with a water-cooled copper hearth) or the formation of a reaction layer (such as molten titanium in contact with a carbon liner, giving a TiC skull). 

---