Titanium vapours, reaction with

Attempts have been made to carry out the sodium reduction of titanium tetrachloride in other ways. For example, the reaction of the two vapours at a temperature of about 2000°C to give molten, or massive solid, titanium metal.2 - This reaction can be carried out in a vessel lined with sponge as in the National Smelting Company s patent applicable to titanium or zirconium. Alternatively, the low-temperature fluidization process has been used, in which titanium tetrachloride vapour reacts with a dispersion of 1 to 2 per cent of molten sodium, in a bed of titanium sponge and sodium chloride reaction products, at 200°C to 600°C, fluidized with a flow of pure argon. It is not known that these, or similar processes, have been operated on a commercial scale yet. 

The dichloride is more difficult to produce in bulk but it can be tolerated as an impurity in the trichloride. Although the reaction equilibrium favours trichloride formation at low temperatures, a temperature of 1000°C is necessary for a reasonable reaction rate. A satisfactory technique is to boil titanium tetrachloride and allow the vapour, mixed with hydrogen, to pass over a tungsten fllament sheathed in silica and heated to 1000-1100°C. The trichloride product condenses on the walls of the reactor. The excess tetrachloride is condensed under reflux and the liquid dissolves the less volatile trichloride and carries it to the still. When the reaction has proceeded sufficiently, the excess tetrachloride is distilled away, leaving the trichloride in the form of a purple coloured crystalline deposit. This process is operated on a relatively small scale (about 0 5 tons per annum if run continuously), the reactor being of stainless-steel with a single glass condenser. 

Thus, the chlorination of titanium raw stock in salt melt helps to build very productive apparatuses and avoid labour-intensive operations of preparing and backing bricks, partially increases the conditions for further condensation of the vapour and gas mixture, considerably reduces the concentration of carbon oxide in outlet gases and helps to withdraw the non-chlorinated residue from the reactive zone continuously. Disadvantages of chlorination in salt melt include increased losses of titanium with discharge melt (because small particles of the furnace charge are carried away with reaction gases) and increased amounts of solid chlorides. 

Emission from electronically excited TiO molecules has been observed by Palmer and co-workers from the reaction of titanium tetrachloride or tetrabromide with potassium vapour in the presence of oxygen [277] and of nitrous oxide [278]. The potassium atoms presumably strip the halogen atoms from the titanium tetrahalide, and the titanium atoms then react with the oxygen or nitrous oxide producing electronically excited TiO molecules. 

A rather elaborate machine is required to perform this process. The glass plates and lenses are supported on a heated horizontal rotating disk having a maximum speed of 60 r-p-m. Burners or gas-mixer nozzles are supported and geared to sweep back and forth horizontally across the work pieces, one depositing 2, and the other SiC>2. Mixed oxides can be formed by the simultaneous operation of two nozzles so that 2 and SiC>2 are deposited alternately in very thin films. The titanium dioxide nozzle has two inlets for dry air, one for a mixture of dry air and titanium tetrachloride vapour and one for moist air. To prevent chemical reaction of TiCU with humid air inside the nozzle a concentric curtain of dry air between these two reaction partners is maintained. The glasses to be coated are exposed to a temperature of about 250°C and the mixture from the burner reacts on the heated surface to form 2 film... 

There are two well known ways of carrying out reactions of the type of eq. (11.8), with and without continuous nucleation. With continuous nucleation, a very fine powder is formed, that has to be separated. Well known examples are the preparation of pure titania from titanium tetrachloride and the burning of iron chlorides to iron oxides. Without continuous nucleation, the solid is precipitated on an existing surface. This can be a flat surface, such as in chemical vapour... 

The reaction is carried out in the vapour phase by passing a mixture of o-xylene and air over a catalyst such as vanadium pentoxide supported on silica and promoted with titanium dioxide at about 400°C. The exit gases are cooled and the phthalic anhydride is collected and purified by distillation under reduced pressure. 

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