A method of producing a metal-containing composition.

(54) NAME Process for the preparation of a single-phase composition comprising metal (56) PUBLICATIONS INCLUDED:

US Al 4,961,529 (B23K 1/012), US Al 5,330,701 (B22F 9/00) (57) SUMMARY:

The present invention relates to a process for preparing a single-phase composition M- <A_:X_r, where n is within a range C.3 - 3.2 and where z is within a range 0.8 1.2, where further M is at least one metal of the group Ti (titanium), Sc (scandium), V (vanadium), Cr (chromium) , Zr (zirconium), Nb (niob) and Ta (tantalum) of metals and where X is at least one of the non-metals C (Carbon) and N (nitrogen) and where A is at least one of the elements Si (silicon), Al (aluminum) and Sn (tin) or a compound of said substances so that the final desired compound's components Μ- <Α.Χ- are present, the process further comprising forming a powdery mixture of said metal, non-metal and the latter element or compound of said substances and igniting said powdery mixture under inert atmosphere so that dissociation is not promoted, with constituents reacting.

The invention is characterized in that the reaction temperature is caused to be maintained at or above that at which constituent components are reacted but below the temperature at which the associated composition dissociates.

In particular, the invention relates to the manufacture of the single-phase material Ti; SiC_;.

The numbers in brackets indicate international identification code, INID code. The letter within the clamp indicates the internatiNnefl document code.

521 882

Summary

The present invention relates to a process for preparing a single phase composition M_{n +}iA_zX_n, where n is in a range 0.8 - 3.2 and where z is in a range 0.8 1.2, where further M is at least one metal of the group Ti (titanium), Sc (scandium), V (vanadium), Cr (chromium), Zr (zirconium), Nb (niob) and Ta (tantalum) of metals and where X is at least one of the non-metals C (Carbon) and N (nitrogen) and where io A is at least one of the elements Si (silicon), Al (aluminum) ) and Sn (tin) or a compound of said substances so that the final desired compound's components M_{n +}iA_zX_n are present, wherein the process further comprises forming a powdery mixture of said metal, non-metal and the latter element or compound of said substances, and igniting said powdery mixture under inert atmosphere so that dissociation is not promoted, with constituents reacting.

The invention is characterized in that the reaction temperature is caused to be maintained at or above that at which constituents are reacted but below the temperature at which the single-phase composition dissociates.

The invention relates primarily to the manufacture of the single-phase material

Ti₃Sic₂.

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The present invention relates to a process for making a single-phase composition comprising metal. In particular, the invention relates to the preparation of titanium silicon carbide as well as compound compounds in the same family.

Oxygen-free combustion synthesis, also called SHS (Self-propagating)

High Temperature Synthesis), is widely used to make intermetallic products and ceramic compositions.

According to the SHS technique, a mixture of two or more materials is ignited locally by an intense heat source. This may, for example, be a glow coil or other heating element, a laser beam or an electron beam. The local ignition results in a local reaction by a strongly exothermic reaction. In this way, excess energy is released which ignites the surrounding part of the material and finally all the material. This chain reaction is very rapid and, when the reaction is controlled, provides a very effective way of mass-producing intermetals and ceramics. The highest temperature the system can reach is the adiabatic temperature.

Since the middle of the nineteenth century many attempts have been made to produce Ti₃Sic₂. Pampuch et al (R. Pampuch et al. Solid Combustion Synthesis of Ti₃Sic₂, J. EUR. CERAM. SOC., 5,283-87 (1989) and others ignited a mixture of Ti, Si and C in powder form in an inert atmosphere. The result was

Ti₃Sic₂ + about 10 - 30% of other phases such as TiC, TiSi₂ also SiC.

Goesmann et al. (F. Goesmann et al. Preparation of Ti₃Sic₂ by Electron-Beam-Ignited Solid-State Reaction, J. Amer. Ceram

Soc., 81,11,3025-28 (1998)) believed that SHS did not result

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521 882 is a predominantly simple phase consisting of Ti₃Sic₂ therefore, because of the very high temperature of the reaction, overgassing of metallic silicon exceeds 2000 ° C. Goesmann started with a mixture of Ti and SiC with a chemical composition of Ti₃Sic₂ + 12.5% ​​by weight of excess silicon. He used an electron beam to ignite the mixture. The mixture was treated in three stages, namely heat treatment at 800 ° C, ignition at 900 ° C and then a heat treatment at 1600 ° C to cause excess silica to degass. This method resulted in less than 8% secondary phases in the sample.

In our own US patent application no. 09 / 469,893 of December 1999, we have shown that the oxygen content of the atmosphere affects the thermal stability of Ti₃Sic₂ in the formation as well as in the subsequent sintering by forming gaseous SiO, which is somewhat fundamentally different from silica evaporation due to high temperature.

Thus, it has proved difficult to produce titanium silicon carbide in the aforementioned manner without obtaining other reaction products.

It was stated above that the invention also relates to compositions in the same family. The family can be drawn as a single-phase composition M₃SiZ₂, where M is at least one metal, Z is at least one of the elements C (Carbon) and N (nitrogen).

The present invention solves the problem of high titanium silicon carbide manufacturing costs.

The present invention thus relates to a process for preparing a single-phase composition M_{n +}iA_zX_n, according to an SHS procedure, where n is in the range 0.8 - 3.2 and where z is in a range 0.8 - 1.2, where further M is at least one metal of the group Ti (titanium), Sc (scandiK: \ Patent \ 01005 lse \ Final submission.inl 03-09-26.doc

521 882 µm), V (vanadium), Cr (chromium), Zr (zirconium), Nb (niob) and Ta (tantalum) of metals and where X is at least one of the non-metals C (Carbon) and N (nitrogen) and where A is at least one of the elements Si (silicon), Al (aluminum) and Sn (tin) or a compound of said substances so that the final desired compound components M_{n + 1}A_zX_n are present, wherein the method further comprises forming a powdery mixture of said metal, non-metal and the latter element or compound of said substances, and igniting said powdery mixture under inert atmosphere so that dissociation is not promoted, wherein constituents react and are characterized by, causing the reaction temperature to be maintained at or above that to which constituent components are reacted but below the temperature at which the single-phase composition dissociates by the desired compound M_{n +}iA_zX_n is added in a pre-reacted state, which material thus acts as a heat sink.

The invention is further described below, partly in connection with three examples.

Process for preparing a single-phase composition Μ_{+ η}ιΑ_ζΧ_η, where n is in the range 0.8 - 3.2 and where z is in the range 0.8 - 1.2, where further M is at least one metal of the group Ti (titanium), Sc (scandium), V (vanadium), Cr (chromium), Zr (zirconium), Nb (niob) and Ta (tantalum) of metals and where X is at least one of the non-metals C (Carbon) and N (nitrogen) and where A is at least one of the elements Si (silicon), Al (aluminum) ) and Sn (tin) or a compound thereof, so that the final desired compound components M_n+ iA_zX_n exists. A powdery mixture of said metal, non-metal and the latter element or compound is formed and ignited said powdery mixture so that it reacts under an inert atmosphere. Inert atmosphere

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521 882 includes an atmosphere of sufficiently low partial oxygen pressure to prevent dissociation.

According to the invention, the reaction temperature is kept at or above that to which constituents are reacted but below the temperature at which the single-phase composition dissociates.

Thus, the essential step of the invention is to realize that the temperature should be kept down, but still above a certain level, during the reaction.

It is preferred to manufacture the single-phase composition Ti₃Sic₂In this way.

In a very preferred embodiment, the temperature is kept down by pre-reacting Ti₃Sic₂ is added, which material thus acts as a heat sink.

It is preferred that up to about 25% by weight of Ti₃Sic₂used as a heat sink.

It is also possible to use other methods to keep the temperature down during the reaction, namely, for example, controlled cooling of the input material.

Some examples are given below.

Example 1

Ti, SiC and graphite powder were mixed to produce a stoichiometric mixture for Ti₃Sic₂. This mixture was mixed with 12% by weight of pre-reacted Ti₃Sic₂.

The mixture was placed in a reaction vessel under an argon flow of 0.5 l / min. The powder bed was about 20 cm thick.

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521 882

The bed was ignited by a molybdenum disilicide element located at the bottom of the reaction vessel. The bed components reacted.

After cooling, the powder was removed from the vessel. The bed was easy to crush.

Samples from the bed were analyzed by X-ray diffraction.

It was found that the bed contained about 2-4% by weight of TiC.

Example 2.

Same example as Example 1, but instead 25% by weight of reacted Ti₃Sic₂ the mixture was added.

It was found that after ignition and cooling, the bed contained 15-20% by weight of TiC.

Example 2 shows, inter alia, that excessive dilution of pre-reacted material results in an incomplete reaction, where the bed requires heat treatment at 1400 ° C for 8 hours to provide a single-phase material.

Example 3.

The same examples as Example 2, where Ti, Si and graphite powder were mixed together with 25% by weight of reacted Ti₃Sic₂ the mixture was added.

It was found that after ignition and cooling down, the bed contained 25-30% by weight of TiC.

After the bed was heat-treated at 1400 ° C for 8 hours, the bed contained less than 2% by weight of TiC.

This example shows that Si can be used instead of SiC.

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A number of embodiments have been described above. However, it is obvious that other means of keeping the temperature within the range described, than the methods described, are included in the invention.

Thus, the present invention is not to be considered limited to the above embodiments but can be varied within the scope of the appended claims.

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521 882