Patent Application
20160089724
The present invention concerns a new method for producing metal powders, metal alloy powders, intermetallic powders and/or their hydride powders, by a simplified, cost efficient process, preferably by performing the reduction reaction of metal oxides under hydrogen gas protection, using specific reducing agents and specific reduction conditions.
Powder metallurgical (PM) techniques are well established routes for efficient production of complex metal based components. These techniques are commonly used in applications where alloys based on iron, stainless steel, copper or nickel are required. However, the use of PM techniques where material such as titanium, chromium and tantalum are required has so far been limited due to lack of availability of corresponding powders of high quality.
Titanium metal base alloys and non-titanium metal base alloy powders are amongst the advanced materials, which are key to performance improvements and have many favorable properties such as high strength to weight ratio, good ductility and fracture toughness, high corrosion resistance and high melting point, making them important engineering materials for many applications in aerospace, chemical processing industry, architecture, and terrestrial systems. However, a major concern with titanium-based materials is high cost compared to competing materials.
The present invention relates to a cost effective production of metal powders, metal alloy powders, intermetallic powders and/or their hydride powders, resulting in high levels of purity.
The conventional method of producing titanium alloy powder today involves producing titanium sponge by the Kroll process, vacuum arc melting the sponge followed by gas atomising. The Kroll process involves the reaction of TiO2 and carbon under chlorine gas at temperatures around 800° C., thus forming titanium chloride, TiCl4.
TiCl4 produced in the reaction is in the form of liquid and must first be purified by distillation. This means that this process is complex and uses products difficult to handle, such as Mg and/or chlorine.
There have been many attempts to produce titanium alloys in a more cost efficient way, but attempts so far require the use of more than one heat treatment step, lasting for several hours.
U.S. Pat. No. 6,264,719 discloses a method of producing a titanium-alumina composite, which results in the formation of Al2O3 particles in a Ti-rich metallic or intermetallic phase.
JP 05299216 relates to the preparation of rare earth based alloy magnetic material, and describes a method in which a rare earth oxide, a reducing agent, and a metal are mixed, a reduction-diffusion reaction treatment is conducted in a hydrogen-containing reducing atmosphere, and the obtained cake-like reaction product is cooled. The reducing atmosphere is switched to an inert gas atmosphere when the cake-like reaction product is cooled. This switch is conducted in the temperature window of 770 to 870° C. Conducting the switch in this specific temperature window is said to lead to the rare earth alloy product having good magnetic characteristics. In particular, conducting the switch in this temperature window is said to be important to ensure that the product does not contain any undesirable metal hydride product.
There is no suggestion that any intermediate metal hydride product that may form during the reduction step would have any useful attributes.
WO2008/010733 describes a process for producing titanium alloy powders. In a first heat treatment step TiO2 and Al powder are mixed and heat-treated to form a TiAl/Al2O3 metal matrix ceramic composite material. Said composite is further reduced in a second heat treatment step using CaH2.
Attempts have also been made to produce various metal powders from their metal oxides by using the so-called self-ignition synthesis method. (Akiyama et al). These methods usually lead to products which suffer from low purity.
Consequently, there is still a need for a more cost efficient process to produce high quality metal powders, metal alloy powders, intermetallic powders and/or their hydride powders, with high purity.
The present invention is based on the realization that it is possible to completely reduce metal oxides under hydrogen atmosphere, using calcium and/or calcium hydride granules or powders, at a specified temperature to obtain pure metal or metal alloy powders at a high rate. Surprisingly, it has been found that the process of the invention, particularly in the context of the preferred metal oxides discussed herein, enables excellent control over the reaction conditions, meaning that there is no need to take extra steps that may have been employed in previous methods. Such extra steps may include the provision of “buffer” substances that do not contribute to the reaction step, to act as a buffer during heat absorption/generation in order to avoid sharp rises/falls in temperature. The process of the invention also enables the preparation of metal powders, metal alloy powders, intermetallic powders and/or their hydride powders, which are of a very high quality, particularly in terms of purity and particle size distribution. The process may be applied to the production of a wide range of metal containing powders, such as metal powders, metal hydride powders, and/or metal alloy powders.
As starting materials, metal oxides, in powder form, are mixed with a reducing agent, such as calcium or magnesium in powder form or in the form of granules. The powder mixture should preferably not be compacted. The powder mixture is heated to a temperature in the range of 1000° C. to 1500° C., and kept under a hydrogen atmosphere. This results in the formation of metal hydrides which are optionally subsequently dehydrated under a vacuum, or under an inert gas atmosphere (e.g. argon).
The invention is defined in the claims.
The final product is of a higher purity than what is achieved with previously known technologies. This makes it possible to use the resulting metal powder in a variety of different applications within the powder metallurgy industry.
The invention will now be described by way of non-limitative example only, with reference to the accompanying drawings, in which:
The above XRD pattern showed that titanium was the first major phase of material, but in the same time showed calcium titanium oxide as the second phase of material. This means that the reduction reaction process was not successfully processed under the above mentioned conditions.
The present invention provides a process for manufacturing metal containing powder, the process comprising the steps of:
In one aspect the metal containing powder is a metal hydride powder or a hydride of a metal alloy or intermetallic. In this aspect, the invention provides a process as defined above, wherein metal hydride powder is recovered.
The present invention provides a process for manufacturing metal hydride powder, comprising the steps of;
In another aspect the metal containing powder is a metal powder, a metal alloy or an intermetallic. In this aspect, the invention provides a process as defined above, further further comprising between steps (b) and (c):
In one aspect, step (a) comprises mixing at least one metal oxide powder with Ca or Mg granules and/or calcium hydride or magnesium hydride in granule or powder form to form a mixture.
Said at least one metal oxide is preferably chosen from oxides of:
In one embodiment said at least one metal oxide is chosen from oxides of Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Hf, Ta, rare earth metals, Th, U, and/or Si. In another embodiment oxides which may be used as starting material are oxides of Al, In, Sb, Sn, Ge, Bi, and/or Pb. In another embodiment oxides which may be used as starting material are oxides of Ti, Cr, Al, V, La, Nb and/or Ta.
The above preferences for the metal(s) present in the metal oxide(s) apply correspondingly to the metal(s) present in the product.
The temperature range in which to maintain the mixture under an H2 atmosphere is preferably between 1000° C. and 1500° C., more preferably 1020° C. and 1400° C., more preferably 1020° C. and 1300° C., more preferably 1020° C. and 1200° C., still more preferably 1020° C. and 1100° C.
The time for which the mixture is maintained under an H2 atmosphere is preferably 1-10 hours, more preferably 1-5 hours, more preferably 2-4 hours and most preferably around 3 hours.
More particularly, the invention provides a process for manufacturing metal hydride powder, comprising the steps of:
The invention also provides a process for manufacturing metal powder, comprising steps a) and b) above, followed by;
In this regard, step d) involves maintaining the mixture under a temperature of from 1000° C. to 1500° C., preferably 1020° C. to 1400° C., more preferably 1020° C. to 1300° C., yet more preferably 1020° C. to 1200° C., and yet more preferably still 1020° C. to 1100° C. Typically, the temperature maintained in step d) is substantially the same as that used in step b).
The mixture is maintained under an Ar atmosphere preferably for around 1 hour, but this may vary between 20 minutes and 5 hours, preferably 40 minutes to 3 hours, preferably 50 minutes to 2 hours, still more preferably 55 minutes to 80 minutes.
Optionally, the ratio between number of oxygen atoms in said metal oxide and the number of calcium atoms (O:Ca) is in the range of 1:1.7-1.1 or 1:1.5-1:1.1 or 1:1.5-1:1.05, or 1:1.4-1:2, or 1:1.2.
Optionally, said metal oxide powder is TiO2 powder and said powder mixture is maintained in step b) under an H2 atmosphere, at a temperature between 1020° C. and 1100° C. for around 3 hours.
The invention also includes the metal powder or metal hydride powder produced according to the above methods.
In one aspect the invention provides a metal powder or metal hydride powder wherein the metal is as defined herein subject to being other than Ti. The invention includes a metal powder or metal hydride powder so produced, wherein the metal is Ti, Cr, Nb, or Ta. In a particularly preferred aspect the metal is Cr.
The invention includes a metal powder or metal hydride powder so produced, wherein the metal is substantially free from oxygen.
The invention includes a metal powder or metal hydride powder so produced, having an amount of oxygen lower than 0.35% by weight.
The term “metal oxide” may also include metal particles that contain substantial amounts of oxygen in the form of dissolved oxygen, oxide inclusions and/or oxide coatings, in such amounts that make them unfit for use in production using PM techniques.
The Ca or Mg granules are preferably in the size range of 0.03-2 mm. Ca hydride (CaH2) and/or magnesium hydride granules in the same size range may also be used.
As defined herein, the term “powder” is meant to describe a collection of particles having a size range of 50 nm-1 mm.
Particle size distribution X50 (sometimes denoted D50) is also known as the median diameter or the medium value of the particle size distribution, and is the value of the particle diameter at 50% in the cumulative distribution. The particle size distribution of the products produced by the present method typically has an X50 of less than 40 μm, or less than 35 μm, or less than 25 μm, or less than 20 μm. Particle size and size distribution may be determined by e.g. light scattering.
The X50 distribution is discussed at pages 216-218 of “Metals Handbook”, 9th Edition, Volume 7, Powder Metallurgy, American Society for Metals, Metals Park, Ohio 44073, ISBN 0-87170-013-1.
The amount of contaminants (e.g. oxygen or nitrogen) in the final product may be determined by combustion analysis and detection by way of IR absorption (to determine oxygen levels) or by thermic conductivity (to determine nitrogen levels).
The starting materials may, in addition to only one metal oxide, also include one or more additional metal containing reagents, which could be one or more metals or metal oxides (preferably metal oxides). In that case, the final product may be a metal alloy or an intermetallic compound. Preferably it is a metal alloy. The term “metal powder” is therefore meant to include pure metals, metal alloys and also intermetallic compounds. In this regard, elemental metal powders such as iron, aluminum, nickel, copper etc, may be added to the reaction mix to provide a source of additional elements (e.g. to provide alloying elements). Oxides of these elements may also be used, e.g. Fe3O4. The resulting end product is a metal alloy powder or intermetallic compound powder. In a preferred embodiment, the metal oxide powder is TiO2 powder.
Similar considerations apply to embodiments of the invention in which the product is a hydride, i.e. wherein the product of step b is recovered (without the subsequent possible steps of switching to an Ar atmosphere, cooling under Ar atmosphere, and then recovering metal powder). Thus, the starting materials may, in addition to only one metal oxide, also include one or more additional metal containing reagents, which could be one or more metals or metal oxides (preferably metal oxides). In that case, the final product may be a metal alloy hydride or an intermetallic hydride compound. In this regard, elemental metal powders such as iron, aluminum, nickel, copper etc, may be added to the reaction mix to provide a source of additional elements (e.g. to provide alloying elements). Oxides of these elements may also be used, e.g. Fe3O4. The resulting end product is a hydride of a metal alloy or intermetallic compound (in powder form).
Said one or more additional metal containing reagents are preferably included in the reaction mixture in powder or granular form, most preferably powder form.
When the product of the method of the invention is a hydride, the hydrogen may be part of a substantially regular crystalline structure, but alternatively the hydrogen may be contained within the metal(s) in the form of a solid solution.
As a general rule, percentages given in connection with the content of a given component in an alloy preferably indicate percentages by weight, and percentages given in connection with the content of a given component of an intermetallic compound preferably indicate percentages by mol. Unless indicated otherwise, percentage figures mentioned herein follow this general rule.
The metal oxides may be present on the surface of metal particles or components, e.g. as a surrounding layer on a metal particle having been exposed to oxidizing conditions.
The powder mixture in step b is preferably maintained under an H2 atmosphere, at a temperature between 1020° C. and 1100° C., preferably for 3 hours.
It is preferred to perform the reduction under conditions which will avoid the initiation of a strong exothermic reaction. In this sense, a “strong” exothermic reaction is interpreted as an un-controlled, thermal runaway reaction. It is believed that such an uncontrolled exothermic reaction (e.g. self-ignition combustion synthesis) leads to less pure material.
These unwanted reactions can be avoided by e.g. using a specific ratio between oxygen and calcium, and optionally maintaining the reactants in non-compacted form. Furthermore, the reduction reaction should ideally take place under hydrogen atmosphere. In case a compacted form of reactants is to be used, this should ideally be in the form of thin plates, pellets, or granules.
The resulting powders may be subjected to a drying step to remove water. The resulting metal powder typically has a particle size less than 25 μm. Furthermore, the metal powder is of high purity, having an oxygen content lower than 0.35%, by weight.
The equipment used to perform the experimental work was as follows:
Any type of furnace suitable for working under temperatures for the reduction reaction, i.e. up to 1500° C. may be used. The furnace should also be fitted with means for supplying various types of gases, or in some cases applying vacuum. For the work herein, a muffle open furnace was used to perform the heat treatment processes to achieve the reduction reaction of the oxides being used at different stages of work.
A rectangular cross section crucible with a flat base was used. The crucible was made of high temperature resistant material such as e.g. chromium nickel steel (253 MA). The crucible was introduced to the furnace at each heat treatment process.
The heat treatment was performed at different temperatures and time according to the examples below. The real temperature of the furnace was measured using a thermocouple to compare it with the set temperature. The difference in temperature between real temperature and set temperature was below 10° C.
Containers filled with water were used for washing. The intermediate product after heat treatment was added to the water and washed. The containers were equipped with stirrers to stir the mixture of water and the intermediate material. Acetic acid was added to the slurry with continuous stirring.
After washing, the resulting powder were dried to yield the final product. Starting materials used for making different metals, metal hydrides and their alloy powder were as follows:
99%
98%
98%
99%
Calcium hydride may be prepared from its elements by direct combination of calcium and hydrogen at 300 to 400° C. Calcium granules were obtained from Mashinostroitelny Zavod (Elektrostal, Moskovskaya oblast,144001, Russia).
The amount of contaminants (e.g. oxygen or nitrogen) was determined by combustion analysis, followed by detection by way of IR absorption (to determine oxygen levels) or by thermic conductivity (to determine nitrogen levels). The io instrument used was a LECO TC436DR.
Comparative example of preparation of titanium from TiO2 powder and calcium granules as starting materials.
100 g TiO2 in powder form, 99% purity, 325 mesh, (Aldrich) was mixed with 130 g grams of calcium granules 0.4-2 mm (Mashinostroitel'nyi zavod, Russia). The powder and granules were mixed thoroughly and placed in a crucible as described above. The mixture was heated at 1100° C. during 2 hrs under argon gas in an open muffle furnace. The resulting titanium powder particles had a particle size with X50 of 35 μm, and formed agglomerates. The oxygen content was 2.7%, nitrogen content 0.38%, and hydrogen content 0.26%. The XRD pattern showed that titanium is the first major phase of material, and also showed that calcium titanium oxide is the second phase of material. This means that the reduction reaction process was not fully processed under the above mentioned conditions.
The calcium content was 2.9% as shown by ICP analysis.
This example was carried out with the above mentioned heat treatment conditions with the only exception of heating being carried out under hydrogen gas and for 2hrs also, and then switched to argon gas. The resulting titanium powder particles had a particle size with X50 of 117.64 μm, and did not form agglomerates. The oxygen content was 0.30%, nitrogen content 0.08%, and hydrogen content 0.28%. XRD pattern showed that titanium was obtained without impurities. This confirms that heat treatment of the TiO2 and calcium granules at the same heat treatment conditions but under hydrogen gas protection and then performing the dehydrogenation under argon atmosphere was successful.
The calcium content was 0.25% as shown by ICP analysis.
The mixture was heated at 1100° C. during 2 hrs under hydrogen gas in an open muffle furnace. After heating, the mixture was cooled for one hour under argon atmosphere.
The resulting titanium powder particles had a particle size with X50 of 20.06 μm, and did not form agglomerates. The oxygen content was 0.27%, nitrogen content 0.016%, and hydrogen content 0.17%. XRD pattern showed that titanium was obtained without impurities.
The calcium content was 0.22% as shown by ICP analysis.
100 grams of TiO2 in powder form (Aldrich) was mixed with 145 grams of calcium hydride granules, size of 0.4-2 mm (Höganäs AB). The mixture of powders and granules was heated at 1100° C. during 2 hrs under hydrogen gas in an open muffle furnace. After heating, the mixture was cooled for one hour under hydrogen atmosphere.
The resulting titanium hydride powder particles had a particle size with X50 of 6.35 μm, and did not form agglomerates. The oxygen content was 0.17%, nitrogen content 0.73%, and hydrogen content 3.63%. XRD pattern showed that titanium hydride was obtained without impurities.
The calcium content was 0.17% as shown by ICP analysis.
The mixture was heated at 1100° C. during 2 hrs under hydrogen gas in an open muffle furnace. Both heating and cooling sessions were performed under hydrogen gas protection.
The resulting chromium metal powder particles had a particle size with X50 of 5.93 μm, and did not form agglomerates. The oxygen content was 0.08%, nitrogen content 0.003%, and hydrogen content 0.006%. XRD pattern showed that chromium was obtained without impurities.
The calcium content was 0.004% as shown by ICP analysis.
100 grams of TiO2 in powder form(Aldrich) was mixed with 145 grams of calcium hydride powder at −325 mesh(Aldrich). The mixture was heated at 1100° C. during 2 hrs under hydrogen gas in an open muffle furnace. Both heating and cooling sessions were maintained under hydrogen gas protection.
The resulting titanium hydride powder particles had a particle size with X50 of 8.06 μm, and did not form agglomerates. The oxygen content was 0.12%, nitrogen content 0.72%, and hydrogen content 3.42% . XRD pattern showed that titanium io hydride was obtained without impurities.
The calcium content was 0.19% as shown by ICP analysis.
135 grams of TiO2 in powder form(Aldrich) was mixed with 19 grams of Al powder(Aldrich) was mixed with 141.7 grams of calcium granules (Mashinostroitel'nyi zavod, Russia).
The mixture was heated at 1100° C. during 2 hrs under hydrogen gas, followed by argon gas, in an open muffle furnace.
The resulting Ti19Al powder particles had a particle size with X50 of 16.4 μm, and did not form agglomerates. The oxygen content was 0.28%, nitrogen content 0.03%, and hydrogen content 0.27%. XRD pattern showed that Ti19Al was obtained without impurities.
The calcium content was 0.03% as shown by ICP analysis.
103.5 grams of TiO2 in powder form (Aldrich) was mixed with 100 grams of Fe3O4 powder(Aldrich) was mixed with 218.1 grams of CaH2 powder (Aldrich). The mixture was heated at 1100° C. during 3hrs under hydrogen gas, in an open muffle furnace. Both heating and cooling processing steps were maintained under hydrogen gas protection.
The resulting ferrotitanium powder particles had a particle size with X50 of 10.69 μm, and did not form agglomerates. The oxygen content was 0.13%, nitrogen content 0.06%, and hydrogen content 2.07%. XRD pattern showed that ferro titanium hydride powder was obtained without impurities.
The calcium content was 0.026% as shown by ICP analysis
150 grams of TiO2 in powder form (Aldrich) was mixed with 7.1 grams of V2O5 powder and 6 gram of Al(Aldrich) powders were mixed with 245 grams of CaH2 granules (Höganäs AB) size of 0.4-<2 mm.
The mixture was heated at 1100° C. during 3 hrs under hydrogen gas, then switched to argon gas environment, in an open muffle furnace. The switching of gases was performed in the open muffle furnace, with no need for transfer to another furnace for the dehydrogenation processing step.
The resulting Ti6Al4V powder particles had a particle size with X50 of 9.73 μm, and did not form agglomerates. The oxygen content was 0.24%, nitrogen content 0.05%, and hydrogen content 0.08%. XRD pattern showed that Ti6Al4V was obtained without impurities.
The calcium content was 0.017% as shown by ICP analysis
55.5 grams of La2O3 in powder form (Aldrich) was mixed with 100 grams of Ni powder were mixed with 43 grams of CaH2 granules (Höganäs AB) size of 0.4-2 mm.
The mixture was heated at 1080° C. for a period of 6 hrs under hydrogen gas protection, then switched to argon gas environment, in an open muffle furnace. Switching gases performed in the same furnace, with no need for another furnace foe dehydrogenation processing step.
The resulting LaNi5 powder particles had a particle size with X50 of 9.57 μm, and did not form agglomerates. The oxygen content was 0.17%, nitrogen content 0.08%, and hydrogen content 0.04%. XRD pattern showed that LaNi5 was obtained without impurities.
The calcium content was 0.06% as shown by ICP analysis
Niobium metal powder was produced using heat treatment at 1050° C. of the starting materials Nb2O5 and CaH2 granules (as 1.2 of the stoichiometric ratio) for 2 hrs under hydrogen followed by switching gases for the cooling session to be performed under argon gas protection.
Tantalum metal powder from Ta2O5 and CaH2 granules (as 1.2 of the stoichiometric ratio). Heat treatment was at 1050° C. for 2 hrs. Heating was under hydrogen gas protection followed by switching to argon gas environment (in the same furnace without changing the furnace) for the dehydrogenation. SEM micrographs showed that the material is consisted of different sizes of agglomerates. These agglomerates were mostly consisted of very fine size particles but with few big sizes of the large agglomerates. In general the agglomerates were of very fine particles sizes as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1309173.1 | May 2013 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/060462 | 5/21/2014 | WO | 00 |
