Nevertheless, this process remains attractive because of its superiority to the Kroll process in terms of the form and purity of the generated metal deposit.

Because these industrial issues have remained unresolved, large-scale Ti smelting using the Hunter process for industrial purposes has been discontinued since 1993, with the exception of the production of some electronic materials ( Fig.В 5.1). Furthermore, recovering the by-product, NaCl, from the aqueous solution requires additional energy. Therefore, NaCl should be removed by leaching in an aqueous solution. Because the vapor pressure of NaCl is lower than that of MgCl 2 ( pВ° NaClВ =В 3В Г—В 10 в€’3В atm, pВ° MgCl 2В =В 1В Г—В 10 в€’2В atm at 1200В K ), it is difficult to efficiently separate NaCl by vacuum distillation. Fig.В 5.8 shows the vapor pressures of various chlorides. The main issues in industrial application of the Hunter process are the separation of the produced Ti and NaCl, and the reproduction of Na metal. Unlike that in the Kroll process, the Ti produced here is in a powder form referred to as sponge fines this serves as an inexpensive feed material in powder metallurgy ( Chapters 10 and 12 Chapter 10 Chapter 12). Ti is leached with dilute hydrochloric acid (HCl) to remove NaCl and trace amounts of remaining Na metal.

The Ti adheres to the inner wall of the container to a lesser extent than that in the Kroll process and the level of contamination by Fe and other elements originating from the container wall is relatively low. The major motivation behind employing the two-step operation is that Na reduction generates a larger amount of heat compared with Mg ( Fig.В 5.6) in addition, controlling the vapor pressure of Na metal is difficult ( Fig.В 5.8).ДЇig.В 5.9 shows a schematic diagram of the reduction container used in the Hunter process.

(5.5) TiCl 2 ( l, in NaCl ) + 2 Na ( l ) в†’ Ti ( s ) + 2 NaCl ( l ) Thus, R&D into sodium reduction processes continues to this day. However, the process remains attractive because of its superiority to the Kroll process in terms of the form and purity of the metal deposit produced. Because these industrial issues have remained unresolved, with the exception of the production of some electronic materials, large-scale titanium smelting using the Hunter process for industrial purposes has been discontinued since 1993. Since the vapor pressure of NaCl is lower than the vapor pressure of MgCl 2 ( p NaClВ =В 3В Г—В 10 в€’В 3В atm, p MgCl 2В =В 1В Г—В 10 в€’В 2В atm at 1200В K ), it is difficult to efficiently separate NaCl by distillation. Figure 2.9.21 shows the vapor pressures of various chlorides. The main problem for the industrial application of the Hunter process is the separation of the titanium produced and NaCl, as well as the reproduction of sodium metal. The major reasons for employing the two-step operation are that the sodium reduction generates a larger amount of heat compared to the use of magnesium and controlling the vapor pressure of sodium metal is difficult. Next, TiCl 2 in molten sodium chloride (NaCl) is transferred to another container and then reduced to titanium metal with additional sodium reductant. In contrast, the two-step operation starts by first reducing TiCl 4 to titanium dichloride (TiCl 2) with half of the stoichiometric amount of sodium necessary. In the one-step operation, the stoichiometric amount of sodium metal necessary for the reduction of TiCl 4 is reacted in one installment, and TiCl 4 is reduced directly to titanium metal in a single reaction container. The operation mode in the Hunter process is either a one- or two-step operation. The Hunter process shares the same steps as the Kroll process for producing TiCl 4, but it reduces TiCl 4 with a sodium reductant. Okabe, in Treatise on Process Metallurgy: Industrial Processes, 2014 2.9.2.1.3.1 Hunter Process

Mindustry large vs small walls