Method for Obtaining Coloured Metal-Containing Powder, the Powder Obtained Thereof and its Use as Metallic Pigment

Abstract

A method for producing a coloured metal-containing powder, which can be used as a metallic pigment, said method comprising: preparing a bulk metal-containing material in the form of powder (which acts as a particle substrate), which is a ferromanganese (FeMn) powder; and heating said material up to a temperature ranging from 100° C. to 1000° C. in a container, in the presence of oxygen. Preferably, the bulk powder is a refined FeMn powder. It is also an object of the disclosure the coloured metal-containing powder obtainable by means of the disclosed method, in the absence of surface modifiers, wherein it can have a blue, purple/violet and gold colour, or any intermediate tonality, depending on the metal oxide content. Said oxides are present forming an outer layer on the particles of the powder. The disclosure also refers to the use of the powder as a metallic pigment.

Claims

1. A method for producing a composite coloured metal-containing powder, wherein the method comprises the following steps, in the absence of surface modifiers: a) preparing a bulk metal-containing material in the form of powder which acts as a particle substrate by means selected from the group consisting of: a.1) grinding or milling a raw metal-containing material into powder, directly; a.2) grinding or milling a raw metal-containing material into powder, and classifying the milled powder into fractions; and a.3) classifying a raw metal-containing material powder into fractions, directly without grinding or milling; wherein the bulk metal-containing material is a ferromanganese powder selected from the group consisting of: a high Carbon FeMn, a refined medium Carbon FeMn and a refined low Carbon FeMn; having an elongated shape and an homogeneous particle size selected from the group of fractions consisting of: 125-250 μm, 60-125 μm, 45-60 μm, 20-45 μm, from higher than 0 μm to 20 μm, and from higher than 0 μm to 10 μm, wherein less than 10% by weight of the powder has a size lower that the lower limit of the particle range, and that less than 10% by weight of the powder has a size higher that the higher limit of the particle range; and b) heating the bulk metal-containing powder up to a temperature ranging from 100° C. to 1000° C. in a rotating furnace, in the presence of oxygen during a heating time needed for obtaining the metal-containing powder having one colour selected from the group consisting of: any intermediate tonality between the original colour of the bulk metal-containing powder and gold; gold, violet, blue, and any intermediate tonality between said colours; wherein the heating time is inversely related to the temperature and directly related to the particle size of the bulk powder.

2. The method according to claim 1, wherein the bulk metal-containing material is a refined medium Carbon FeMn or a refined low Carbon FeMn comprising at least in the composition: Mn in an amount between 78-84% w/w of the total composition; Fe in an amount between 13-22% w/w of the total composition; Si in an amount equal or less than 1.5% w/w of the total composition; C in an amount equal or less than 1.5% w/w of the total composition; P in an amount equal or less than 0.250% w/w of the total composition; and S in an amount equal or less than 0.015% w/w of the total composition.

3. The method according to claim 1, wherein the bulk metal-containing powder is made of particles having a planar shape.

4. The method according to claim 3, wherein the bulk metal-containing powder is made of particles having a flake shape.

5. The method according to claim 1, wherein the heating step b) is carried out in the presence of an atmosphere containing oxygen selected from the group consisting of: air, air enriched with O.sub.2, a mixture of N.sub.2 and O.sub.2, pure oxygen; and air with H.sub.2O.

6. A coloured metal-containing powder obtainable by means of the method disclosed in claim 1, wherein said powder is made of composite particles having an elongated shape and an outer layer of amorphous manganese oxides and/or iron oxides of the MnFeO.sub.x type surrounding the surface thereof, the oxide content being defined by the following formula: (Mn.sub.2-xFe.sub.x)O.sub.3, wherein 0≤x≤2.

7. The coloured metal-containing powder according to claim 6, having a content of oxygen equal or lower than 27% by weight of the total composition of the powder.

8. The coloured metal-containing powder according to claim 6, wherein the powder has a refractive index comprised between 2.16 and 3.22.

9. The coloured metal-containing powder claim 6, wherein the outer layer has a thickness of between 0.10 to 4.00 μm.

10-12. (canceled)

13. A process for giving metallic finish to products by utilizing the coloured metal-containing powder of claim 6.

14. The process according to claim 13, wherein the product is selected from the group consisting of: ceramic products, ceramic surfaces, paints, coatings, plastics, printing materials and cosmetics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1: Image taken from an electronic microscope of a FeMn bulk powder prepared in a) for carrying out the heating step b) according to the disclosure, wherein the flat shape of the particles can be clearly seen. The powder has a particle size range higher than 0 and lower than 20 microns.

[0066] FIG. 2: Image taken from an electronic microscope of a FeMn bulk powder prepared in a) for carrying out the heating step b) according to the disclosure, wherein the flat shape of the particles can be clearly seen. The powder has a particle size between 20-45 microns.

[0067] FIG. 3: Image taken from an electronic microscope of a FeMn bulk powder prepared in a) for carrying out the heating step b) according to the disclosure, wherein the flat shape of the particles can be clearly seen. The powder has a particle size between 45-60 microns.

[0068] FIG. 4: Image taken from an electronic microscope of a FeMn bulk powder prepared in a) for carrying out the heating step b) according to the disclosure, wherein the flat shape of the particles can be clearly seen. The powder has a particle size between 60-120 microns.

[0069] FIG. 5: Image taken from an electronic microscope of a FeMn bulk powder prepared in a) for carrying out the heating step b) according to the disclosure, wherein the flat shape of the particles can be clearly seen. The powder has a particle size between 125-250 microns.

[0070] FIG. 6: XRD pattern of a sample of metal-containing powder that is a FeMn sample, having a blue colour. It can be clearly seen the peaks of Mn ° (see black line), in this case Fe is in solid solution. Four different samples (FeMn having a particle size between 60-120 microns, without treatment; blue FeMn having a particle size between 60-120 microns; purple FeMn having a particle size between 60-120 microns; and gold FeMn having a particle size between 60-120 microns) characterized by the XRD shows similar results: no crystalline oxides are detected, or they appear in a low percentage so that the diffraction it produces is shielded by the metal peaks. In the case of the XRD of FIG. 6, the spectrum of the claimed material is shown, and one can see that this is common spectrum of MnO.sub.2; and the Mn as the only crystalline metallic species. Hence, the Fe is in solid solution within the Mn amorphous structure. No peaks of oxides can be seen.

[0071] FIG. 7: Spectra EDS of the surface of a grain of FeMn Blue powder obtained according to the Example 4 procedure. It is observed the peaks from left to right: peak of oxygen and secondary peak of Mn, forming a double peak; small peak of silicon; very intense peak of Mn; primary peak of Fe (Ka); and secondary peak of Fe (Kb).

[0072] FIG. 8: SEM image showing a cross section of a grain of coloured powder according to Example 4, i.e. a FeMn blue powder, after polishing. Analysis was carried out via EDS in different points of the grain to compare compositions: position of measurement points 7, 8, 9 and 10 is highlighted in the Figure.

[0073] FIG. 9: Spectra analysis of four points on the surface of the sample feMn blue powder of Example 4, after polishing.

[0074] FIG. 10: Diffraction index of the formed layer of oxides (Mn, Fe)Ox in coloured metal-containing powders to different wavelengths.

[0075] FIG. 11: Graph showing the relationship between the heating time in step b) and the content of oxygen in the surface of ferromanganese material prepared in the form of plates.

[0076] FIG. 12: TEM image of a violet FeMn particle obtained in Example 7.

[0077] FIG. 13: TEM image of a gold FeMn particle obtained in Example 7.

[0078] FIG. 14: TEM image of a blue FeMn particle obtained in Example 7.

DETAILED DESCRIPTION

Examples

Example 1: Method for Obtaining a Golden Metal-Containing Powder According to the Disclosure

[0079] 1 kg of refined LC FeMn bulk powder having an average particle size equal or below 250 microns is classified by sieving at 45-60 microns, and charged on a tray located inside a furnace in the form of a thin layer of around 0.5 cm. The heating step was carried out on air atmosphere, at 250° C. and during 3 hours. A golden coloured metal-containing powder was obtained.

Example 2: Method for Obtaining a Golden Metal-Containing Powder According to the Disclosure

[0080] 1 kg of refined LC FeMn bulk powder having an average particle size equal or below 250 microns is classified by sieving at 60-125 microns and is charged on a tray located inside a furnace in the form of a thin layer of around 0.5 cm. The heating step was carried out on air atmosphere, at 325° C. and during 15 minutes. A golden coloured metal-containing powder was obtained.

Example 3: Method for Obtaining a Purple/Violet Metal-Containing Powder According to the Disclosure

[0081] 1 kg of refined LC FeMn bulk powder having an average particle size equal or below 250 microns is classified by sieving at 125-250 microns and is charged on a tray located inside a furnace in the form of a thin layer of around 0.5 cm. The heating step was carried out on air atmosphere, at 250° C. and during 5 hours. A purple coloured metal-containing powder was obtained.

Example 4: Method for Obtaining a Blue Metal-Containing Powder According to the Disclosure

[0082] 1 kg of refined LC FeMn bulk powder having an average particle size equal or below 250 microns is classified by sieving at 125-250 microns and is charged on a tray located inside a furnace in the form of a thin layer of around 0.5 cm. The heating step was carried out on air atmosphere, at 250° C. and during 19 hours. A blue coloured metal-containing powder was obtained.

Example 5: Relationship Between the Parameters Controlled in the Claimed Method: Characterization of a Colouring (Gold, Violet and Blue) FeMn in the Form of a Plate

[0083] The following experiment was carried out in order to check and analyse the relationship between the different parameters implied in the process of the disclosure. With this aim, different samples of ferromanganese material were prepared in the form of a plate, and the outer surface was analysed (i.e. analysis in the surface as deep as 1.50 μm).

[0084] Therefore, after selecting a piece of FeMn alloy, 30×10×3 mm plates were sawn, which after a cleaning and degreasing process were polished and subjected to heat treatments in atmospheric electric furnaces according to step b) of the process of the claimed disclosure. The treatment conditions were the following ones: [0085] Treated plate having golden colour: FeMn alloy plate stays at 350° C. during 90 minutes under air atmosphere conditions. [0086] Treated plate having purple/violet colour: FeMn alloy plate treated at 350° C. during 120 minutes under air atmosphere conditions. [0087] Treated plate having blue colour: FeMn alloy plate stays at 350° C. during 180 minutes under air atmosphere conditions.
Table 2 shows the results obtained in the EDS analysis with an electron beam excitation at 2 KeV, which reaches areas of the sample with depths of about 1.5 microns.

TABLE-US-00002 TABLE 2 Superficial EDS analysis of the FeMn coloured plates Temp Time O Mn Fe Si Al Sample (° C.) (min) (%) (%) (%) (%) (%) Metallic NA 0 3.35 ± 2.09 76.88 ± 2.04 18.17 ± 0.34 1.45 ± 0.14 0.16 ± 0.10 (original) Gold 350 90 22.45 ± 3.63 60.90 ± 3.60 14.95 ± 1.03 0.97 ± 0.15 0.62 ± 0.13 Violet 350 120 31.50 ± 5.00 48.22 ± 2.77 11.34 ± 1.22 0.90 ± 0.20 0.40 ± 0.10 Blue 350 180 47.50 ± 2.80 41.33 ± 1.99 9.94 ± 0.60 0.86 ± 0.07 0.36 ± 0.06

[0088] Representing the oxygen content in the outer surface as deep as 1.50 microns vs. the heating time, see FIG. 11, it is observed a significant correlation between the two parameters: the higher the heating time, the higher the oxygen content (in the surface of the material). This result confirms that the oxide thickness in the surface is controlled by controlling the heating time, and thus it is possible to reach an intended colour for the FeMn material, as desired.

Example 6: Characterization of the Coloured Metal-Containing Powders Obtained in Examples 1-4

[0089] The golden, violet and blue powders, as well as a sample of the bulk, raw metallic powder that was used as starting material, were subjected to Optical microscopy by light reflected (OMLR) and characterised by EDS microanalysis, result being shown in the following table. This analysis is useful to show the trend, even though the absolute values could not be specified. An example of spectra EDS analysis is shown in FIG. 7, wherein the surface of a FeMn blue powder is taken as an example.

TABLE-US-00003 TABLE 3 EDS analysis of the powders prepared according to Examples 1-4, and compared with the composition of the FeMn raw material before starting the process Wt % FeMn FeMn gold FeMn violet FeMn blue Oxygen Traces 3.49 ± 0.35 3.91 ± 0.30 4.76 ± 0.20 Si°  1.3 ± 0.29 0.87 ± 0.10 0.36 ± 0.08 0.34 ± 0.06 Mn° 79.42 ± 0.29  76.71 ± 0.41  76.34 ± 0.41  74.69 ± 0.27  Fe° 19.03 ± 0.28  18.93 ± 0.30  19.38 ± 0.34  20.31 ± 0.22  (Mn.sub.2-xFe.sub.x)O.sub.3, where 0 ≤ × ≤ 2* <0.3  11.50 12.63 15.06 *These values were obtained by stoichiometric calculation.

[0090] These results show that, for a particle size of 60-120 microns, the amorphous oxide content can reach the 15% by weight of the total composition, increasing in the following order: Gold, Purple/Violet and Blue.

[0091] FIG. 8 show a SEM-EDS image of the powder named FeMn blue colour, which corresponds to a cross section of one of the grains, analysed on the basis of four different points: Spectrum 7, Spectrum 8, Spectrum 9 and Spectrum 10. FIG. 9 shows the results of the analysis in every point of analysis.

TABLE-US-00004 TABLE 4 Semiquantitative EDS analysis of four points on the surface of a grain of FeMn blue powder after polishing Spectrum Spectrum Spectrum Spectrum Wt % 7 8 9 10 Oxygen Traces 9.04 ± 0.53 0.30 ± 0.20 43.87 ± 0.71  Si° 2.42 ± 0.33 0.69 ± 0.14 0.90 ± 0.30 1.27 ± 0.25 Mn° 79.12 ± 0.93  71.02 ± 0.53  80.0 ± 0.90 42.41 ± 0.64  Fe° 18.48 ± 0.52  14.26 ± 0.35  18.9 ± 0.54 12.45 ± 0.45 

[0092] In FIG. 9 it can be seen that the oxygen peak is not observed in spectra of point 7 and 9, however, it is very remarkable in points 8 and 10, which are near to the border of the grain. This result evidences that the Fe and/or Mn oxides are forming an outer layer, and that they are not present in the inner part of the particles of the powder. Depending on time, the thickness increases.

[0093] In order to measure the thickness of the oxide layer for the different intended colours, it was made the assumption that as Fe and Mn oxides are less dense than the metal alloy, hence their transparency to electron jets will be higher, and therefore TEM images of the particles can visualise these oxide layers (see FIGS. 3, 4 and 5). Table 5 shows the oxide layer thickness measurements on the different colours.

TABLE-US-00005 TABLE 5 Thickness of the oxide layer in different colour particles according to the TEM images (μm) Sample Thickness (μm) Gold 1.16 Violet 1.75 Blue 2.31

TABLE-US-00006 TABLE 6 Effect of particle size on heating time (T = 35° C.) Particle size Colour 120-250 microns 20-45 microns Blue 240 min 150 min Gold  30 min  30 min Violet/Purple  60 min  60 min

TABLE-US-00007 TABLE 7 Effect of temperature on heating time (particle size = 120-250 microns) Temperature Colour 275° C. 350° C. Blue NA 240 min Gold 120 min  30 min Violet/Purple 615 min  60 min
Using coloured powders from examples 1-4 with Rama spectroscopy to the following conclusions: [0094] the oxide formed on the powder particles has a typical MnO.sub.2 spectrum. [0095] no isolated Fe oxides are detected. Iron is in solid solution in the Mn structure. [0096] the intensity of the Raman peaks increases in the metallic-golden-violet-blue direction. Therefore the oxide layer must also increase.

TABLE-US-00008 TABLE 8 Intensity of the Raman peak of the oxide layer on particles (a.u.) Sample Intensity (u.a.) Metallic  48 Gold 102 Violet 154 Blue 258

[0097] In order to check the relationship between the oxygen content and the specific surface of the particles, they were measured both of them in three different size cuts (45-60 μm, 60-90 μm and 90-120 μm) for the golden colour material or powder, which was obtained in three different sizes: 45-60 μm, 60-90 μm and 90-120 μm.

TABLE-US-00009 TABLE 9 Oxygen content (%) vs specific surface (m.sup.2/g), analysing three different sizes of golden powder Oxygen Specific Particle size content (%) Surface (m.sup.2/g)  45-60 μm 0.67 0.24  60-90 μm 0.53 0.12 90-120 μm 0.52 0.06

[0098] According to these results, one can confirm that, for the same colour, the higher the specific surface area, the higher the oxygen content. And that said content is proportionate to the surface. That is the evidence that the metal oxides are only present in the outer surface of the particles.

Example 7: Method for Obtaining Gold, Violet and Blue Metal-Containing Powders According to the Disclosure

[0099] 10 kg of refined LC FeMn bulk powder having an average particle size equal or below 250 microns is milled with a jet mill to below 20 microns. The obtained material was charged on three trays located inside a furnace in the form of a thin layer of around 0.5 cm. The heating step was carried out on air atmosphere, at 320° C. and during 60, 120 and 240 minutes to obtain powders with gold, purple and blue colours, respectively. Results obtained (TEM image of the particles) are shown in FIGS. 12 (violet particles), 13 (gold particles) and 14 (blue particles).

Disclosure

[0100] The present application discloses the following objects of the disclosure:

[0101] 1. A method for producing a composite coloured metal-containing powder, characterised in that said method comprises, in the absence of surface modifiers: [0102] a) preparing a bulk metal-containing material in the form of powder which acts as a particle substrate; wherein the bulk material is a ferromanganese powder; and [0103] b) heating the bulk powder up to a temperature ranging from 100° C. to 1000° C.—in a container, in the presence of oxygen.

[0104] 2. The method according to disclosure 1, wherein the bulk metal-containing material is prepared by means selected from the group consisting of: [0105] a.1) by grinding or milling a raw metal-containing material into powder, directly; [0106] a.2) by grinding or milling a raw metal-containing material into powder, and classifying the milled powder into fractions; and [0107] a.3) classifying a raw metal-containing material powder into fractions, directly without grinding or milling.

[0108] 3. The method according to any one of disclosures 1 or 2, wherein the bulk metal-containing material is selected from the group of ferromanganese materials consisting of: a high Carbon FeMn, a refined medium Carbon FeMn and a refined low Carbon FeMn.

[0109] 4. The method according to disclosure 3, wherein the bulk metal-containing material is a refined medium Carbon FeMn or a refined low Carbon FeMn comprising at least in the composition: [0110] Mn in an amount between 78-84% w/w of the total composition; [0111] Fe in an amount between 13-22% w/w of the total composition; [0112] Si in an amount equal or less than 1.5% w/w of the total composition; [0113] C in an amount equal or less than 1.5% w/w of the total composition; [0114] P in an amount equal or less than 0.250% w/w of the total composition; and [0115] S in an amount equal or less than 0.015% w/w of the total composition.

[0116] 5. The method according to any one of disclosures 1 to 4, wherein the powder of bulk metal-containing material prepared in step a) has a particle size lower than 2 mm.

[0117] 6. The method according to any one of disclosures 1 to 5, wherein the powder of bulk metal-containing material prepared in step a) has any fraction or range of particle size below 1 mm and shows an homogeneous particle size, wherein less than 10% by weight of the powder has a size lower that the lower limit of the particle range, and less than 10% by weight of the powder has a size higher that the higher limit of the particle range.

[0118] 7. The method according to disclosure 6, wherein the powder of bulk metal-containing material prepared in step a) has an homogeneous particle size selected from the group of fractions consisting of: 125-250 μm, 60-125 μm, 45-60 μm, 20-45 μm, from higher than 0 μm to 20 μm, and from higher than 0 μm to 10 μm, wherein less than 10% by weight of the powder has a size lower that the lower limit of the particle range, and that less than 10% by weight of the powder has a size higher that the higher limit of the particle range.

[0119] 8. The method according to any one of disclosures 1 to 7, wherein the bulk metal-containing powder is made of particles having a flake shape.

[0120] 9. The method according to any one of disclosures 1 to 8, wherein the heating step b) is carried out in the presence of an atmosphere containing oxygen selected from the group consisting of: air, air enriched with O.sub.2, a mixture of N.sub.2 and O.sub.2 and pure oxygen.

[0121] 10. A coloured metal-containing powder obtainable by means of the method disclosed in any one of the preceding disclosures, characterised in that said powder is made of composite particles having an outer layer of amorphous manganese oxides and/or iron oxides of the MnFeO.sub.x type surrounding the surface thereof, the oxide content being defined by the following formula: (Mn.sub.2-xFe.sub.x)O.sub.3, wherein 0≤x≤2.

[0122] 11. The coloured metal-containing powder according to disclosure 10, having a content of oxygen equal or lower than 27% by weight of the total composition of the powder.

[0123] 12. The coloured metal-containing powder according to any one of disclosures 10 or 11, wherein the powder has a refractive index comprised between 2.16 and 3.22.

[0124] 13. Use of the coloured metal-containing powder defined in any one of disclosures 10 to 12, as a colouring additive.

[0125] 14. The use of the coloured metal-containing powder according to disclosure 13, as a metallic pigment.

[0126] 15. The use of the coloured metal-containing powder according to any one of disclosures 13 or 14, as an additive for one of the products selected from the group consisting of: ceramic products, ceramic surfaces, paints, coatings, plastics, printing materials and cosmetics.