Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Reexamination Certificate
2002-05-13
2003-10-28
Wyszomierski, George (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
C075S360000, C075S364000
Reexamination Certificate
active
06638336
ABSTRACT:
FIELD OF INVENTION
The present invention relates to titanium powder manufactured by crushing and grinding titanium sponge produced by metallo-thermic reduction of titanium chlorides. More particularly, the invention is directed to the cost-cutting and energy-saving manufacture of titanium powder by the improved process of magnesium-reduction of TiCl
4
including vacuum separation (vacuum distillation) from magnesium and magnesium chlorides followed by the improved process of grinding and hydro-metallurgical treating of the ground sponge.
BACKGROUND OF THE INVENTION
Titanium powder for commercial use, is presently produced by a hydride-dehydride (HDH) process, as disclosed in U.S. Pat. No. 6,168,644, by gas atomization, or by the plasma-rotating electrode process, as disclosed in U.S. Pat. No. 6,136,060. Raw materials for HDH process are titanium metal obtained by re-melting and processing titanium sponge, or ready-crushed titanium sponge itself, as disclosed in JP 10096003, 1998. These raw materials are hydrogenated, then, the brittle hydrogenated titanium is ground to the desired powder size that is dehydrogenated by vacuum heating. Essentially, the titanium powder production is a multi-step, energy-consumable, high-cost industrial process including the manufacture of titanium sponge, which is the most expensive part of the technology.
Numerous disclosures for magnesium-reducing TiCl
4
and subsequent processing of the obtained titanium sponge are present in the art, starting from U.S. Pat. No. 2,205,854 granted to Wilhelm Kroll in 1940. Most developments were directed to improve the quality of the sponge by diminishing the final content of magnesium, chlorine, oxygen, and iron contaminants. Various processes have been developed during the last two decades for energy-saving, cost-effective, sponge-related technologies.
For example, Russian patent 2,061,585, 1994, describes the manufacture of titanium powder by (a) magnesium-thermic reduction of titanium chlorides in a reactor, (b) preliminary distillation of the reaction mass to the content of magnesium chloride of 5-12%, (c) cooling of obtained sponge block in argon, (d) crushing and grinding the sponge into the powder having a particle size of 0-12 mm, (e) preliminary drying of the powder at <250° C., (f) cooling and additional grinding, (g) final distillation of the powder from magnesium chloride residues by vacuum separation, (h) hydro-metallurgical treatment, (i) final drying, and (j) final grinding of titanium powder.
In spite of saving time and energy of sponge production, this process is not cost-effective when considering titanium powder as the final product. In this process, the first stage of vacuum separation is carried out at 1020° C., which results in a solid sintered block of the reaction mass and increases the time of sponge distillation. Double-stage vacuum separation accompanied by multi-stage drying and grinding increases the process time and electric energy consumption, and significantly decreases the powder productivity. Besides, multi-stage hot drying increases the content of gaseous impurities in the obtained powder.
Periodic removal of exhaust magnesium chloride from the reactor bottom and cooling a reaction interface by argon flow (disclosed in JP 59001646, 1984) reduced the time of sponge production, but neither the cost nor the energy of the entire process of powder manufacture is gained.
The same result, insignificant to powder cost, was reached in the process disclosed in JP 61012836, 1986 which increases the sponge yield by predetermined blowing of TiCl
4
at the temperature of <600° C. under argon into molten magnesium.
The electric power consumption was decreased by 20% using a condensing vessel in the reactor for removing unreacted magnesium and residual magnesium chloride from the reaction zone as disclosed in JP 03047929, 1991. This energy savings related only to sponge production and does not reflect on the total production cost because the obtained ductile sponge needs to be hydrated/dehydrated with the repetition of the multi-stage processing.
An attempt at producing titanium powder directly by the magnesium-thermic reduction of TiCl
4
and eliminated all expenses involved with sponge production was made by Uda T. with colleagues (2
nd
Int. Conf on Process. Mater. and Properties, TMS
, 2000, p. 31-36). This method looks promising for the future but presently, it is far from an industrial scale. Incidentally, some rather expensive rare-earth metals (e.g., Dy and Ho) are involved in the process.
Productivity of the magnesium-thermic process was increased by the preliminary cleaning of TiCl
4
and accelerated the supply into the reactor as disclosed in Russian patent 2,145,979, 2000. This method also related only to the sponge production and results mostly in the sponge quality.
A way of accelerating the distillation stage was offered by Sandier R. A. and Kholmovskaya N. A. (
Izv. Akad Nauk USSR, Met
., 1967, 6, p. 58-62). According to this, the oxide impurities are partially soluble in fused MgCl
2
at a higher temperature, therefore the reduction process should be carried out at more elevated temperature and simultaneously increase feeding the reactor with TiCl
4
to obtain a porous titanium sponge, which facilitates the removal of fused MgCl
2
together with oxygen dissolved in it. Unfortunately, the higher temperature results in additional power consumption.
The supply of hot argon through the reaction mass can also speed up the distillation process by vaporizing the magnesium and magnesium chloride in gaseous form, as disclosed in the U.S. Pat. No. 3,880,652. But additional expenses involved with heating and supplying high-temperature argon override the savings on production cost during the distillation stage.
The manufacture of high-purity titanium sponge lumps is disclosed in recent JP 2001262246, 2001. The process includes crushing the titanium sponge to a particle size of 2-50 mm and heat-treating at a reduced argon pressure of 600-1100° C. Crushing and heat treatment are repeated several times until the desired purity of coarse titanium is reached. This method is ineffective for commonly used titanium, and requires HDH processing to obtain the powder for industrial purposes.
All other known methods of producing titanium powder directly from magnesium-reduced sponge have the same drawback: cost and energy savings are only realized for one or two stages, but not for the continuous multi-stage process, which makes none of these processes cost effective.
Not one conventional process comprises the sponge production adjusted specially to subsequent powder manufacture: sponge lumps are ductile and need to be treated by HDH process.
OBJECTS OF THE INVENTION
The object of the invention is to establish a continuous cost-effective process to produce as-reduced titanium powder from titanium sponge obtained by the magnesium-thermic process specially adjusted to subsequent powder manufacturing.
Another objective of the present invention is to control the structure of the reaction mass block to facilitate and accelerate the sponge distillation from magnesium and magnesium chloride residues.
It is yet another objective to produce brittle sponge metal to provide crushing lumps and grinding titanium powder with additional HDH processing.
Another objective of the invention is to find energy-saving combinations of the process stages to achieve a cost effective method for the entire technology.
The nature, utility, and further features of this invention will be more apparent from the following detailed description with respect to preferred embodiments of the invented technology.
SUMMARY OF THE INVENTION
The invention relates to the manufacture of titanium powder by magnesium-thermic reduction of titanium chlorides followed by thermal-vacuum distillation, crushing, grinding. and hydro-metallurgical treatment of the obtained titanium sponge. While the use of magnesium-thermic reduced sponge has previously been contemplated in the titanium powder production as mentioned above, problems related to
Andreev Anatoli E.
Drozdenko Victor A.
Froes Francis H.
Ivasishin Orest M.
Moxson Vladimir S.
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