Passivated magnesium material, in particular passivated magnesium, and method for producing same

Abstract

The present invention relates to a method for passivating a magnesium material, comprising the step of coating the magnesium material with urea, wherein the magnesium material is magnesium, a magnesium alloy containing at least 50 wt.% magnesium or a mixture of magnesium and one or more such magnesium alloys, and wherein the magnesium material is coated by mixing the magnesium material with urea particles. In addition, the present invention relates to passivated magnesium material, in particular magnesium, obtainable by the method, in the form of particles of magnesium material, which is coated with a coating containing urea or consisting of urea, and to the use of passivated magnesium material for producing pyrotechnics, sheathed welding electrodes, refractory products, cored wires or desulphurisation agents for pig iron and / or steel desulphurisation.

Description

[0001] Passivated magnesium material, in particular passivated magnesium, and process for its production

[0002] The present invention relates to a process for passivating magnesium material, such as in particular magnesium, to passivated magnesium material, in particular passivated magnesium, obtainable by the process, and to the use of passivated magnesium material.

[0003] Magnesium has a wide range of uses, including as a desulfurizer for pig iron and steel, whereas magnesium alloys are particularly used in the automotive industry, for example in the manufacture of dashboards, seat brackets, transmission housings, and steering systems. However, magnesium and magnesium alloys with a high magnesium content are highly flammable, which limits the use of these magnesium materials, particularly their use in the form of small particles or chips. Therefore, such magnesium material is usually passivated beforehand, which is typically achieved by coating the magnesium material particles with a coating that reduces or even prevents their flammability. For some time, passivation was primarily carried out with melamine.However, melamine is suspected of being carcinogenic, which is why it has been classified as a substance of very high concern by the EU and is therefore no longer permitted as a passivating agent. Therefore, melamine must be replaced with other passivating agents, which are, however, less effective than melamine.

[0004] Against this background, the object of the present invention is to provide a method for passivating magnesium material, such as in particular magnesium and / or a magnesium alloy containing at least 50% by weight of magnesium, in which a passivating agent is used which is largely harmless to health, but which is as effective or at least almost as effective as melamine with regard to reducing the flammability of the magnesium material.

[0005] According to the invention, this object is achieved by a method for passivating a magnesium material, which comprises the step of coating the magnesium material with urea, wherein the magnesium material is magnesium, a magnesium alloy containing at least 50 wt.% magnesium or a mixture of magnesium and one or more such magnesium alloys, and wherein the coating is carried out by mixing the magnesium material with urea particles.

[0006] This solution is based on the surprising discovery that urea, which is harmless to health, is an extremely effective passivating agent for magnesium material, and especially for magnesium. Therefore, even comparatively small amounts of urea in the coating of the magnesium material are sufficient to achieve effective passivation against burning. Without wishing to be bound by any theory, it is believed that this is due to the fact that urea decomposes in endothermic reactions at temperatures just below 200°C, thereby extracting energy from the environment. So that in the event of a fire, burning magnesium material cools down quickly and the burning of the magnesium material is quickly stopped. A further advantage of the process according to the invention is that the passivated magnesium material obtained, unlike uncoated magnesium material, is not hazardous material and can therefore be transported easily.

[0007] According to the invention, the magnesium material is coated with urea. This includes coating exclusively with urea or with a mixture containing urea. For the purposes of the present invention, coating means that urea or a urea-containing mixture adheres to at least part of the magnesium material, in particular to part of the particles of the magnesium material, over the entire surface or in part. For example, more than 1 wt.%, in particular more than 5 wt.%, such as 1 to 100 wt.% or 5 to 60 wt.% or 10 to 40 wt.% of all magnesium material particles are fully or partially coated with urea or a urea-containing mixture, whereas the remaining part of the particles is uncoated.In this context, "partially" means that urea or a urea-containing mixture adheres to a portion of the surface of a magnesium material particle, such as 1 to 90%, in particular 5 to 70%, such as 10 to 60% of the surface of a magnesium material particle. This adhesion can involve any type of chemical, physical, adhesive, or ionic bond, meaning that the urea is bonded to the surface of the magnesium material particle in some way. Typically, this bond is adhesive, with the urea sticking to the surface of the magnesium material particle.

[0008] According to the invention, a magnesium material is coated in the method. For the purposes of the present invention, magnesium material means magnesium and any alloy which consists of at least 50% by weight of magnesium. In principle, in the case of a magnesium alloy, the present invention is not particularly restricted with regard to the further alloy constituent(s). Good results are obtained in the case of magnesium alloys in particular when the magnesium material is a magnesium alloy containing at least 50% by weight of magnesium or a mixture of magnesium with at least one magnesium alloy containing at least 50% by weight of magnesium, wherein the at least one magnesium alloy contains, in addition to magnesium, at least one element selected from the group consisting of aluminum, zinc, silicon, manganese, strontium, rare earths, and any mixtures of two or more of the aforementioned elements.Preferably, the at least one magnesium alloy contains 60 to 99 wt.% magnesium and one or more elements selected from the group consisting of aluminum, zinc, silicon, manganese, strontium, rare earths, and any mixtures of two or more of the aforementioned elements. Particularly preferably, the at least one magnesium alloy consists of 60 to 99 wt.% magnesium and the remainder to 100 wt.% of one or more elements selected from the group consisting of aluminum, zinc, silicon, manganese, strontium, rare earths, and any mixtures of two or more of the aforementioned elements. Preferred examples of rare earths are cerium and yttrium.

[0009] The magnesium material is particularly preferably magnesium. For the purposes of the present invention, magnesium is understood to mean a metal that contains at least 99% by weight, preferably at least 99.5% by weight, particularly preferably at least 99.8% by weight, very preferably at least 99.9% by weight, and most preferably at least 99.95% by weight, such as in particular 100% by weight of magnesium, with any remainder to 100% by weight being impurities.

[0010] In particular, fine-grained magnesium materials, i.e. those in the form of comparatively small particles, are highly flammable, which is why passivation of such fine-grained magnesium materials in particular is advantageous. Therefore, in the process according to the invention, it is preferred to coat particulate magnesium materials, such as in particular magnesium and / or magnesium alloy, preferably with an average d50 particle size of 0.01 to 10 mm and particularly preferably with an average d50 particle size of 0.5 to 5 mm. For example, the magnesium material, such as in particular magnesium, can be coated in the form of powder with an average d50 particle size of 0.01 to 10 mm, in the form of granules with an average d50 particle size of 0.01 to 10 mm, or in the form of chips with an average chip length of 0.01 to 10 mm.In the process according to the invention, magnesium material, such as in particular magnesium, is particularly preferably coated in the form of powder with an average d50 particle size of 0.5 to 5 mm, in the form of granules with an average d50 particle size of 0.5 to 5 mm, or in the form of chips with an average chip length of 0.5 to 5 mm. Average particle size d50 is understood to be the value for the particle diameter below which 50% of the particles present fall. The average particle size d50 can be determined in particular by laser diffractometry. In contrast, chip length refers to the longest extension of a chip along a straight line, and thus average chip length refers to the average value of all chip lengths.Particularly preferably, at least 80% and particularly preferably at least 90% of all powder or granulate particles have a particle size of 0.01 to 10 mm and preferably of 0.5 to 5 mm and at least 80% and particularly preferably at least 90% of all chips have a chip length of 0.01 to 10 mm and preferably of 0.5 to 5 mm.

[0011] In principle, the magnesium materials can only be coated with urea. Good results are obtained in this embodiment, especially when the coating is carried out by mixing the magnesium material with urea with an average d50 particle size of 10 nm to 20 mm, preferably from 2 pm to 20 mm, particularly preferably from 10 pm to 20 mm, very particularly preferably from 50 pm to 10 mm, and most preferably from 500 pm to 1.6 mm.

[0012] In order to improve the wettability of the magnesium material or the coatability of the magnesium material, it is proposed in a further development of the inventive concept to carry out the coating by mixing the magnesium material with a mixture of urea and at least one additive, wherein the at least one additive is selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkali metal phosphates, alkali metal nitrates, alkali metal sulfates, alkaline earth metal oxides, alkaline earth metal carbonates, alkaline earth metal phosphates, alkaline earth metal nitrates, alkaline earth metal sulfates and any mixtures of two or more of the aforementioned compounds.

[0013] Particularly preferably, the at least one additive in this embodiment of the present invention is selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates and any mixtures of two or more of the aforementioned compounds.

[0014] Good results are obtained in this embodiment of the present invention in particular when the at least one additive is selected from the group consisting of calcium oxide, magnesium oxide, calcium carbonate, magnesium carbonate and any mixtures of two or more of the aforementioned compounds.

[0015] According to a particularly preferred embodiment of the present invention, calcium oxide, magnesium oxide, calcium carbonate, or a mixture of calcium oxide and magnesium oxide is used as at least one additive, most preferably a mixture of calcium oxide and magnesium oxide. In the latter variant, the weight ratio of calcium oxide to magnesium oxide is preferably 10:1 to 1:1, more preferably 5:1 to 1:1.

[0016] In the above embodiment of the present invention, it is particularly preferred that both the urea and the at least one additive in the mixture used for coating each have an average d50 particle size of 10 nm to 20 mm, preferably from 2 pm to 20 mm, particularly preferably from 10 pm to 20 mm, very particularly preferably from 50 pm to 10 mm, and most preferably from 500 pm to 1.6 mm. Good results are achieved in particular when the weight ratio of urea to the at least one additive in the mixture used to coat the magnesium material is 1:1 to 1:10.

[0017] According to a further preferred embodiment of the present invention, the step of coating the magnesium material with urea or with a mixture of urea and at least one additive is carried out at room temperature. Alternatively, the coating step can also be carried out at slightly elevated temperatures of 24 to 50°C or at slightly reduced temperatures of 1 to 22°C.

[0018] As explained above, in the process according to the invention even a small amount of urea in the coating is sufficient to effectively reduce the flammability of the magnesium material. Therefore, in a further development of the inventive concept, it is proposed to carry out the coating by mixing the magnesium material with urea or with a mixture of urea and at least one additive, wherein the urea or the mixture of urea and at least one additive is added to the magnesium material in an amount of 0.1 to 10 wt.% based on 100 wt.% of the magnesium material, so that preferably coated magnesium material is obtained in which the amount of urea contained in the coating, based on 100 wt.% of the magnesium material, is 0.1 to 10 wt.% and preferably 0.5 to 3 wt.%. Usually, not the entire amount of urea or urea used is used.Mixture of urea and at least one additive to bind to the magnesium material.

[0019] According to a further aspect, the present invention relates to passivated magnesium material in the form of particles of magnesium material coated with a coating containing or consisting of urea. The particles can be, in particular, powder particles, granulate particles, chips, or the like.

[0020] The coating of the magnesium material preferably contains at least one additive selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkali metal phosphates, alkali metal nitrates, alkali metal sulfates, alkaline earth metal oxides, alkaline earth metal carbonates, alkaline earth metal phosphates, alkaline earth metal nitrates, alkaline earth metal sulfates, and any mixtures of two or more of the aforementioned compounds. The coating of the magnesium material preferably contains at least one additive selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates, and any mixtures of two or more of the aforementioned compounds. Particularly preferably, the coating of the magnesium material contains, in addition to urea, calcium oxide, magnesium oxide, calcium carbonate, or a mixture of calcium oxide and magnesium oxide as an additive.

[0021] According to a further preferred embodiment of the present invention, the particles are magnesium particles with an average d50 particle size of 0.01 to 10 mm, and particularly preferably with an average d50 particle size of 0.5 to 5 mm. Particularly preferred are magnesium powder particles with an average d50 particle size of 0.01 to 10 mm, and preferably 0.5 to 5 mm, magnesium granulate particles with an average d50 particle size of 0.01 to 10 mm, and preferably 0.5 to 5 mm, or magnesium chips with an average chip length of 0.01 to 10 mm, and preferably 0.5 to 5 mm.

[0022] Good results are particularly obtained when the amount of urea contained in the coating, based on 100 wt.% of the magnesium material, is 0.1 to 10 wt.%, and preferably 0.5 to 3 wt.%. Finally, the present invention relates to the use of the passivated magnesium material described above for producing pyrotechnics, coated welding electrodes, refractory products, flux-cored wires, or desulfurizing agents for pig iron and / or steel desulfurization.

[0023] The present invention will now be explained by means of examples which are merely illustrative and do not limit the present invention.

[0024] Example 1

[0025] 97 parts of magnesium particles with a purity of 99.95 wt% and a dso particle size of 5 mm were mixed with 3 parts of a mixture of 80 wt% urea with a dso particle size of 1 mm and 20 wt% calcium oxide with a dso particle size of 1 mm at room temperature to produce urea-coated magnesium.

[0026] The ability of the coated magnesium to support a fire was then tested according to UN Test N.1. A mold measuring 250 mm in length and with a triangular cross-section with a height of 10 mm and a width of 20 mm was filled with the coated magnesium, and the coated magnesium was ignited. A progressive smoldering was observed, with the reaction dying out after 140 mm of the total test length of 200 mm. Thus, the flammability of the magnesium was significantly reduced by the urea-containing coating, and the coated magnesium met the criteria for a material that does not fall under the classification as a dangerous good. Example 2

[0027] The procedure was as in Example 1, except that a mixture of 86 parts of magnesium particles with a purity of 99.95 wt.% and with a d50 particle size of 5 mm and 12 parts of a magnesium-aluminium

[0028] An alloy containing 70 wt% magnesium and 30 wt% aluminum with a dso particle size of 5 mm was mixed with 2 parts of a mixture of 80 wt% urea with a dso particle size of 1 mm and 20 wt% calcium oxide with a dso particle size of 1 mm at room temperature to produce urea-coated magnesium material.

[0029] After igniting the magnesium material in the mold, a progressive glow was observed, with the reaction dying out after 120 mm of the total measuring distance of 200 mm. Therefore, the flammability of the magnesium material was considerably reduced by the urea-containing coating and the

[0030] Magnesium material met the criteria for a material that does not fall under the conditions of a dangerous good.

Claims

Patent claims 1. A method for passivating a magnesium material comprising the step of coating the magnesium material with urea, wherein the magnesium material is magnesium, a magnesium alloy containing at least 50 wt.% magnesium, or a mixture of magnesium and one or more such magnesium alloys, and wherein the coating is carried out by mixing the magnesium material with urea particles.

2. The method according to claim 1, wherein the magnesium material is a magnesium alloy which contains, and preferably consists of, at least 50% by weight of magnesium and at least one element selected from the group consisting of aluminum, zinc, silicon, manganese, strontium, rare earths and any mixtures of two or more of the aforementioned elements.

3. The method of claim 1, wherein the magnesium material is magnesium.

4. Method according to one of the preceding claims, wherein the magnesium material is in particulate form and is preferably coated in the form of powder with an average d50 particle size of 0.01 to 10 mm and preferably of 0.5 to 5 mm, in the form of granules with an average d50 particle size of 0.01 to 10 mm and preferably of 0.5 to 5 mm or in the form of chips with an average chip length of 0.01 to 10 mm and preferably of 0.5 to 5 mm.

5. The method according to any one of the preceding claims, wherein the coating is carried out by mixing the magnesium material with urea having an average d50 particle size of 10 nm to 20 mm, preferably from 2 pm to 20 mm, particularly preferably from 10 pm to 20 mm, very particularly preferably from 50 pm to 10 mm and most preferably from 500 pm to 1.6 mm.

6. The method according to any one of claims 1 to 4, wherein the coating is carried out by mixing the magnesium material with a mixture of urea and at least one additive, wherein the at least one additive is selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkali metal phosphates, alkali metal nitrates, alkali metal sulfates, alkaline earth metal oxides, alkaline earth metal carbonates, alkaline earth metal phosphates, alkaline earth metal nitrates, alkaline earth metal sulfates and any mixtures of two or more of the aforementioned compounds.

7. The method according to claim 6, wherein the at least one additive is selected from the group consisting of alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates and any mixtures of two or more of the aforementioned compounds, wherein the at least one additive is preferably calcium oxide, magnesium oxide, calcium carbonate or a mixture of calcium oxide and magnesium oxide.

8. The method according to claim 6 or 7, wherein the urea and the at least one additive in the mixture used for coating each have an average d50 particle size of 10 nm to 20 mm, preferably from 2 pm to 20 mm, particularly preferably from 10 pm to 20 mm, very particularly preferably from 50 pm to 10 mm and most preferably from 500 pm to 1.6 mm.

9. The method according to any one of claims 6 to 8, wherein the weight ratio of urea to the at least one additive in the mixture used to coat the magnesium material is 1:1 to 1:

10.

10. The method according to any one of the preceding claims, wherein the coating is carried out by mixing the magnesium material with urea or with a mixture of urea and at least one additive, wherein the urea or the mixture of urea and at least one additive is added to the magnesium material in an amount of 0.1 to 10 wt.% based on 100 wt.% of the magnesium material, so that preferably coated magnesium material is obtained in which the amount of urea contained in the coating, based on 100 wt.% of the magnesium material, is 0.1 to 10 wt.% and preferably 0.5 to 3 wt.%. 11 . Passivated magnesium material in the form of particles of magnesium material coated with a coating containing or consisting of urea.

12. Passivated magnesium material according to claim 11, wherein the coating further contains an alkali metal oxide, an alkali metal carbonate, an alkaline earth metal oxide, an alkaline earth metal carbonate or a mixture of two or more thereof, and the coating preferably contains calcium oxide, magnesium oxide, calcium carbonate or a mixture of calcium oxide and magnesium oxide.

13. Passivated magnesium material according to claim 11 or 12, wherein the particles are magnesium powder particles with an average d50 particle size of 0.01 to 10 mm and preferably 0.5 to 5 mm, magnesium granulate particles with an average d50 particle size of 0.01 to 10 mm and preferably 0.5 to 5 mm or magnesium chips with an average chip length of 0.01 to 10 mm and preferably 0.5 to 5 mm.

14. Passivated magnesium material according to one of claims 11 to 13, wherein the amount of urea contained in the coating, based on 100 wt.% of the magnesium material, is 0.1 to 10 wt.% and preferably 0.5 to 3 wt.%.

15. Use of magnesium material according to any one of claims 11 to 14 for the manufacture of pyrotechnics, coated welding electrodes, refractory products, flux-cored wires or desulfurizing agents for pig iron and / or steel desulfurization.