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Cavitation process for products from precursor halides

Cavitation process for products from precursor halides description/claims

This invention pertains to substantially ambient temperature preparation of metals, metal alloys and compounds, ceramic materials, and metal matrix-ceramic composite materials from hydride precursors in an anhydrous liquid medium using cavitation processing. Suitable alkali or alkaline earth metals may be dispersed by cavitation in the liquid medium for reduction of precursor halides. For example, titanium and titanium alloys and compounds, platinum alloys and transition metal silicides may be prepared. In an illustrative example, the practice pertains to the addition of titanium chloride or mixtures of titanium chloride with other precursor halides to a cavitated liquid containing the reductant material to produce titanium metal or titanium alloys or compounds.

Titanium and its metal alloys are examples of materials that currently are relatively expensive to produce. Titanium alloys can be used in forms such as castings, forgings, and sheets for preparing articles of manufacture. Titanium based materials can be formulated to provide a combination of good strength properties with relatively low weight. For example, titanium alloys are used in the manufacture of airplanes. But the usage of titanium alloys in automotive vehicles has been limited because of the cost of titanium compared to ferrous alloys and aluminum alloys with competitive properties.

Titanium-containing ores are beneficiated to obtain a suitable concentration of TiO2. In a Chloride Process the titanium dioxide (often the rutile crystal form) is chlorinated in a fluidized-bed reactor in the presence of coke (carbon) to produce titanium tetrachloride (TiCl4), a volatile liquid at room temperature. Traditionally, metallic titanium was produced in batch processes from the high temperature reduction of titanium tetrachloride (TiCl4) with sodium or magnesium metal. Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter by heating TiCl4 with sodium in a steel bomb at 700-800° C. The first, and still the most widely used, process for producing titanium metal on an industrial scale is the Kroll Process. In the Kroll Process, magnesium at 800° C. to 900° C. is used as the reductant for TiCl4 vapor and magnesium chloride is produced as the byproduct. Both of these processes produce titanium sponge and necessitate repetitive energy intensive vacuum arc remelting steps for purification of the titanium. These processes can be used for the co-production of titanium and one or more another metals (an alloy) when the alloying constituent can be introduced in the form of a suitable chloride salt (or other suitable halide salt) that undergoes the sodium or magnesium reduction reaction with the titanium tetrachloride vapor. These high temperature and energy-consuming processes yield good quality titanium metal and metal alloys but, as stated, these titanium materials are too expensive for many applications such as in components for automotive vehicles.

The Armstrong/ITP process also uses alkali metals or alkaline earth metals to reduce metal halides in the production of metals. The Armstrong process can run at lower temperatures and can operate as a continuous process for producing a metal or metal alloy (such as titanium or titanium alloy) powder. However, the projected cost of the metal is still high, too high for many automotive applications.

A lower cost process is needed for the production of titanium and titanium alloys and compounds. It would be particularly beneficial if a lower cost process could be provided that had applicability to other metals and their alloys and compounds.

Titanium metal (as an example) may be produced by reduction of a titanium halide (for example, titanium tetrachloride) with a reductant metal in a liquid reaction medium at close-to-ambient temperatures and at close-to-atmospheric pressure. The reduction of the precursor halide in the reaction medium is assisted using suitable cavitation practices, for example a sonochemical process or high-shear mixing. The process may also be used to simultaneously reduce other precursor halides with a titanium halide to produce alloys or compounds of titanium or titanium metal matrix composite materials. Further, the process may be used to produce many other materials in many forms depending on the selection of the precursor halide or combinations of precursor halides.

The reaction medium is an anhydrous, suitably low vapor pressure liquid that is not reactive with the precursor halide(s) or the reductant metal(s). Anhydrous liquid hydrocarbons such as decalin, tetralin, decane, dodecane, and hexadecane are examples of suitable reaction medium materials. Liquid silicon-containing oils, such as polydimethylsilanes, and room temperature ionic liquids are also examples of suitable reaction medium materials. The liquid medium may be infused or covered with dry and substantially oxygen-free and water-free inert gas such as helium or argon to provide an inert atmosphere during processing.

The reductant for the precursor halide(s) is suitably one or more of the alkali or alkaline earth metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, and barium. A preferred reductant is a low-melting point mixture of the reactants that can be dispersed, by application of ultrasonic vibrations to the liquid, as colloidal bodies in the liquid medium at a near-to-ambient temperature. For example, eutectic mixtures of sodium and potassium, such as Na0.22K0.78 and Na0.44K0.56 are liquid at about room temperature and are effective reductants for precursor halides. One or more precursor halides, such as titanium tetrachloride, are then added to the reaction medium, with its dispersed reductants, and reduced to a predetermined product. When the precursor halide(s) includes a titanium halide the product may, for example, may be titanium metal or a mixture of titanium and other metals, or titanium containing alloy or a titanium compound.

The process uses cavitation processes (preferably sonochemical practices) to disperse the reductant material in the liquid medium and to promote the reduction of the precursor halides. A suitable vessel containing the liquid medium is subjected to ultrasonic vibrations, using a transducer that generates sound waves in the liquid at a frequency usually greater than about 20 kilohertz. The sonic energy causes the repeated formation, growth, and collapse of tiny bubbles within the liquid, generating localized centers of very high temperature and pressure, with extremely rapid cooling rates to the bulk liquid. It is preferred that the liquid medium have a relatively low vapor pressure at processing temperatures so that the medium contributes little vapor to the high temperature regions in the cavitation bubbles. Meanwhile, the introduction of the inert gas into the liquid facilitates the formation of the cavitation bubbles with small atoms that will not be reactive at the high temperature in the bubbles.

This cavitation processing first disperses the reductant metal in the hydrocarbon liquid and then promotes the reaction of the reducing metal with the precursor halide(s) when they are brought into contact with the liquid. The reduced halide yields particles of metal, metal alloy, metal compound, metal matrix ceramic composite, or the like, depending on the composition of the halide starting materials (of course, when the precursor halide is, or contains, a non-metal such as carbon tetrachloride or silicon tetrachloride, the product then may be a non-metal). The metal content of the reducing medium is oxidized to a corresponding alkali metal or alkaline earth metal halide salt(s). The reaction usually proceeds over a period of minutes to several hours and usually provides an essentially quantitative yield of the metal constituents of the halide(s) being treated.

Thus, as an example, titanium tetrachloride liquid is passed into hexadecane containing finely dispersed Na0.22K0.78 and the products are titanium metal, sodium chloride, and potassium chloride.

The solids are separated from the reaction medium and the salt is separated from the metal product (or other predetermined product). The temperature of the liquid medium increases somewhat from an ambient starting temperature, but typically only to a temperature of the order of 60° C. to about 100° C. The reaction may be conducted as a batch process or on a continuous basis.

Examples of products of this process using, for example, titanium-containing halide vapor include titanium metal, mixtures of titanium with other metals for alloy formation such as aluminum and/or vanadium, and titanium compounds such as titanium silicide (TiSi2). Other metals such as platinum and zirconium may be produced along with their alloys and compounds. Non-metal halide precursors such as carbon tetrachloride or silicon tetrachloride may be used in the process. The products are often produced initially as very small particles. Often the product is amorphous or of very small crystal size.

An obvious advantage of this practice for producing, for example, metals, metal alloys and metallic compounds, inter-metallic compounds metal matrix ceramic composites, and the like is that the process may be conducted at temperatures that are close to ambient temperatures and with relatively low consumption of energy.

FIG. 1 is a flow diagram illustrating an embodiment of the invention as it is applied to the production of titanium metal starting with titanium tetrachloride as the halide precursor.

FIG. 2 is a schematic illustration of apparatus for the sonochemical reduction of titanium chloride using a mixture of sodium and potassium dispersed in a hydrocarbon liquid.

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