Iron-silicon magnetic powder core and preparation method and application thereof

Abstract

The invention discloses an iron-silicon magnetic powder core and a preparation method and application thereof.The preparation method of the iron-silicon magnetic powder core comprises the following steps that S1, annealing treatment is conducted on iron-silicon alloy powder at the temperature of 900-1200 DEG C, and annealed iron-silicon alloy powder is obtained; s2, the annealed iron-silicon alloy powder and a phosphating agent are mixed, and phosphated iron-silicon alloy powder is obtained; s3, mixing the phosphorized iron-silicon alloy powder and resin to obtain coated iron-silicon alloy powder; and S4, mixing the coated iron-silicon alloy powder and a release agent, carrying out compression molding, and carrying out heat treatment to obtain the iron-silicon magnetic powder core. Wherein the iron-silicon alloy powder comprises the following elements in percentage by mass: 5.005%-6.550% of Si and Ce, and the balance of Fe and inevitable impurities; the mass ratio of Si to Ce is 100: (0.075-1). The prepared iron-silicon magnetic powder core has the characteristics of low magnetic loss and high direct current superposition.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and more specifically, to an iron-silicon magnetic powder core, its preparation method, and its application. Background Technology

[0002] Ferrosilicon magnetic powder cores are an important type of magnetic powder core material with excellent comprehensive performance and large usage. They have advantages such as high resistivity, low magnetic loss, high saturation magnetic induction intensity, good DC superposition characteristics, and excellent temperature stability. This material is mainly processed into inductor devices such as PFC inductors, output filter inductors, and common mode inductors, which are widely used in modern server power supplies, communication power supplies, industrial power supplies, on-board chargers, and DC-DC converters with high current and high frequency.

[0003] Currently, inductor devices are developing rapidly towards high frequency, miniaturization, high power and high reliability, which directly requires the core material - iron-silicon magnetic powder core - to make continuous breakthroughs in low magnetic loss and high DC superposition characteristics.

[0004] Therefore, developing a method for preparing iron-silicon magnetic powder cores with low magnetic loss and high DC superposition characteristics is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an iron-silicon magnetic powder core, its preparation method and application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing an iron-silicon magnetic powder core, comprising the following steps: S1. Anneal the iron-silicon alloy powder at 900-1200℃ to obtain annealed iron-silicon alloy powder; S2. Mix the annealed iron-silicon alloy powder and the phosphating agent to obtain phosphated iron-silicon alloy powder; S3. Mix the phosphated iron-silicon alloy powder and resin to obtain the coated iron-silicon alloy powder; S4. Mix the coated iron-silicon alloy powder and the release agent, press them into shape, and perform heat treatment to obtain the iron-silicon magnetic powder core; In step S1, the iron-silicon alloy powder comprises, by mass percentage, the following elements: 5.005%-6.550% Si and Ce, with the balance being Fe and unavoidable impurities; the mass ratio of Si to Ce is 100:(0.075-1).

[0007] In this invention, by annealing the iron-silicon alloy at 900-1200℃ and using a specific mass ratio of Si and Ce elements, the magnetic loss of the iron-silicon magnetic powder core can be reduced and the DC superposition characteristics of the iron-silicon magnetic powder core can be improved.

[0008] Specifically, annealing iron-silicon alloys at 900-1200℃ can remove quenching stress and numerous lattice defects, which is beneficial for reducing magnetic losses and improving DC superposition characteristics of iron-silicon magnetic powder cores. Furthermore, the addition of Si and Ce elements in specific mass ratios can not only significantly increase the resistivity and reduce eddy current losses of iron-silicon magnetic powder cores, but also reduce coercivity and hysteresis losses by decreasing the magnetocrystalline anisotropy and magnetostriction coefficient, thus further contributing to reduced magnetic losses and improved DC superposition characteristics. In addition, the addition of a specific amount of Ce can inhibit the formation of ordered phases in the iron-silicon alloy, improve the plasticity and toughness of the iron-silicon alloy powder, making it easier to press and mold, and significantly improve the density and DC superposition characteristics of the iron-silicon magnetic powder core. At the same time, the addition of a specific amount of Ce can also promote the formation of a dense SiO2 film and refine the oxide film grains to block ion diffusion and purify harmful impurities, thereby improving the high-temperature oxidation resistance of the iron-silicon alloy, enabling the iron-silicon alloy to withstand annealing treatment at high temperatures of 900-1200℃, which is conducive to better reducing the magnetic loss of the iron-silicon magnetic powder core and improving the DC superposition characteristics of the iron-silicon magnetic powder core.

[0009] Preferably, the mass ratio of Si to Ce is one of 100:0.075, 100:0.080, 100:0.085, 100:0.090, 100:0.095, 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, or 100:1, or a range between any two of them.

[0010] Preferably, the mass ratio of Si to Ce is 100:(0.3-0.7).

[0011] Preferably, the method for preparing the iron-silicon alloy powder includes: A1. Weigh the raw materials according to the composition ratio of the iron-silicon alloy powder, heat and melt them to obtain the alloy melt; A2. Pour the molten alloy into the tundish, allowing it to flow into the atomization chamber through the bottom guide pipe. Use nitrogen to atomize the molten alloy to obtain alloy droplets. Cool and solidify to obtain iron-silicon alloy powder.

[0012] More preferably, in step A1, the heating and melting temperature is 1590-1660℃.

[0013] More preferably, in step A1, the heating and melting are carried out under the protection of nitrogen.

[0014] More preferably, in step A2, the pressure of the nitrogen gas is 3.2-5.2 MPa.

[0015] Preferably, in the iron-silicon alloy powder, the unavoidable impurities include at least one of the elements C, O, P, and S.

[0016] More preferably, the mass percentage of element C is ≤0.020%.

[0017] More preferably, the mass percentage of the O element is ≤0.030%.

[0018] More preferably, the mass percentage of the P element is ≤0.040%.

[0019] More preferably, the mass percentage of the S element is ≤0.020%.

[0020] Preferably, in step S1, the annealing temperature is one of 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or a range between any two.

[0021] Preferably, in step S1, the annealing temperature is 1000-1100℃.

[0022] Preferably, in step S1, the annealing process takes 0.5-7 hours.

[0023] More preferably, in step S1, the annealing time is one of or between any two of the following: 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, and 7h.

[0024] More preferably, in step S1, the annealing process takes 0.5-5 hours.

[0025] Preferably, in step S1, the vacuum degree of the annealing process is 10. -3 -10 -2 MPa, specifically 10 MPa -3 MPa.

[0026] Preferably, in step S1, the heating rate of the annealing treatment is 3-10℃ / min, specifically 5℃ / min.

[0027] In step S2 of the present invention, the phosphating agent includes, but is not limited to, phosphoric acid.

[0028] Preferably, in step S2, the mass ratio of the annealed iron-silicon alloy powder to the phosphating agent is 100:(0.1-1).

[0029] Preferably, in step S2, the mass ratio of the annealed iron-silicon alloy powder to the phosphating agent is one of 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, or 100:1, or any value between the two.

[0030] Preferably, in step S3, the resin includes at least one of silicone resin, phenolic resin, and epoxy resin.

[0031] More preferably, in step S3, the resin includes silicone resin and phenolic resin, and the mass ratio of the silicone resin and phenolic resin is 1:(0.2-6), specifically 1:(0.2-5).

[0032] More preferably, in step S3, the resin includes silicone resin and phenolic resin, and the mass ratio of the silicone resin and phenolic resin is one or any combination of 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.3, 1:1.5, 1:1.8, 1:2, 1:2.3, 1:2.5, 1:2.8, 1:3, 1:3.3, 1:3.5, 1:3.8, 1:4, 1:4.3, 1:4.5, 1:4.8, 1:5, 1:5.5, and 1:6.

[0033] More preferably, in step S3, the resin includes silicone resin and phenolic resin, and the mass ratio of the silicone resin to the phenolic resin is 1:(1.5-3.5).

[0034] Preferably, in step S3, the mass ratio of the phosphated iron-silicon alloy powder to the resin is 100:(0.1-2).

[0035] Preferably, in step S3, the mass ratio of the phosphated iron-silicon alloy powder to the resin is one of or between any two of the following: 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, 100:1.1, 100:1.2, 100:1.3, 100:1.4, 100:1.5, 100:1.6, 100:1.7, 100:1.8, 100:1.9, and 100:2.

[0036] In step S4 of the present invention, the release agent includes, but is not limited to, zinc stearate.

[0037] Preferably, in step S4, the mass ratio of the coated iron-silicon alloy powder to the release agent is 100:(0.1-0.5).

[0038] Preferably, in step S4, the mass ratio of the coated iron-silicon alloy powder to the release agent is one of 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5 or any value between the two.

[0039] Preferably, in step S4, the pressing pressure is 1500-2000 MPa.

[0040] More preferably, the pressing pressure is one of 1500MPa, 1600MPa, 1700MPa, 1800MPa, 1900MPa, 2000MPa or any combination thereof.

[0041] Preferably, the pressing and molding time is 5-20 seconds, specifically 10 seconds.

[0042] Preferably, in step S4, the temperature of the heat treatment is 550-850℃, specifically 550-750℃.

[0043] Preferably, in step S4, the temperature of the heat treatment is one of 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, or any value between two of them.

[0044] Preferably, in step S4, the heat treatment time is 1-3 hours.

[0045] Preferably, in step S4, the heat treatment time is one of 1h, 1.5h, 2h, 2.5h, 3h or any range between two of them.

[0046] Preferably, in step S4, the heat treatment is carried out in an inert gas protective atmosphere.

[0047] In this invention, the inert gas includes, but is not limited to, at least one of nitrogen and argon.

[0048] Secondly, the present invention provides an iron-silicon magnetic powder core, which is prepared by the above-described preparation method.

[0049] Thirdly, the present invention provides an application of iron-silicon magnetic powder cores in inductor devices.

[0050] In this invention, the inductor device includes, but is not limited to, at least one of PFC (Power Factor Correction) inductor, output filter inductor, and common mode inductor.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, by annealing the iron-silicon alloy at 900-1200℃ and using a specific mass ratio of Si and Ce elements, the magnetic loss of the iron-silicon magnetic powder core can be reduced and the DC superposition characteristics of the iron-silicon magnetic powder core can be improved.

[0052] Specifically, annealing iron-silicon alloys at 900-1200℃ can remove quenching stress and numerous lattice defects, which is beneficial for reducing magnetic losses and improving DC superposition characteristics of iron-silicon magnetic powder cores. Furthermore, the addition of Si and Ce elements in specific mass ratios can not only significantly increase the resistivity and reduce eddy current losses of iron-silicon magnetic powder cores, but also reduce coercivity and hysteresis losses by decreasing the magnetocrystalline anisotropy and magnetostriction coefficient, thus further contributing to reduced magnetic losses and improved DC superposition characteristics. In addition, the addition of a specific amount of Ce can inhibit the formation of ordered phases in the iron-silicon alloy, improve the plasticity and toughness of the iron-silicon alloy powder, making it easier to press and mold, and significantly improve the density and DC superposition characteristics of the iron-silicon magnetic powder core. At the same time, the addition of a specific amount of Ce can also promote the formation of a dense SiO2 film and refine the oxide film grains to block ion diffusion and purify harmful impurities, thereby improving the high-temperature oxidation resistance of the iron-silicon alloy, enabling the iron-silicon alloy to withstand annealing treatment at high temperatures of 900-1200℃, which is conducive to better reducing the magnetic loss of the iron-silicon magnetic powder core and improving the DC superposition characteristics of the iron-silicon magnetic powder core. Detailed Implementation

[0053] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0054] In the following examples, experimental methods without specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer. Unless otherwise specified, all raw materials and reagents used are commercially available from the general market. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.

[0055] The reagents used in the various embodiments and comparative examples of this invention are as follows: Silicone resin, SILRES® REN 60, Wacker Chemie, Germany; Phenolic resin, SUMILITERESIN® PR-12603, Sumitomo, Japan; Epoxy resin, EP 6220, Baigo.

[0056] Example 1 This embodiment provides an iron-silicon magnetic powder core, the preparation method of which includes the following steps: S1. Under a vacuum degree of 10 -3 The iron-silicon alloy powder was heated to 1050℃ under the conditions of MPa and heating rate of 5℃ / min, and then annealed at 1050℃ for 3h to obtain annealed iron-silicon alloy powder. S2. Add the annealed iron-silicon alloy powder and phosphating agent (phosphoric acid) to the organic solvent acetone, stir and mix until the acetone is completely evaporated, and dry at 80°C for 1 hour to obtain the phosphated iron-silicon alloy powder. S3. Add the phosphated iron-silicon alloy powder and resin to the organic solvent acetone, stir and mix until the acetone is completely evaporated, and dry at 80°C for 1 hour to obtain the coated iron-silicon alloy powder. S4. Mix the coated iron-silicon alloy powder and the release agent (zinc stearate), press at 1800MPa for 10s to obtain a magnetic powder core matrix (ring, outer diameter Φ20 mm, inner diameter Φ10 mm, thickness 2 mm), and perform heat treatment at 650℃ for 2h in an inert nitrogen atmosphere to obtain the iron-silicon magnetic powder core. In step S1, the iron-silicon alloy powder, by mass percentage, comprises the following elements: 5.700% Si and Ce, with the balance being Fe and unavoidable impurities; the mass ratio of Si to Ce is 100:0.7; the unavoidable impurities include 0.013% C, 0.021% O, 0.034% P, and 0.015% S; the preparation method of the iron-silicon alloy powder includes: A1. Weigh the raw materials according to the composition ratio of the iron-silicon alloy powder, add them to the medium-frequency induction furnace, and first evacuate to 8×10⁻⁶. -3 MPa, then nitrogen gas is introduced, and the mixture is heated at 1650℃ for 1 hour to obtain an alloy melt; A2. Pour the molten alloy into a 1200℃ tundish, and let the molten alloy flow into the atomization chamber through the bottom guide pipe. Use high-pressure nitrogen gas of 4.6MPa to atomize the molten alloy to obtain alloy droplets. Cool and solidify to obtain iron-silicon alloy powder. In step S2, the mass ratio of the annealed iron-silicon alloy powder to the phosphating agent (phosphoric acid) is 100:0.5, and the volume ratio of the acetone to the mass ratio of the annealed iron-silicon alloy powder is 10mL:1g. In step S3, the resin includes an organosilicon resin and a phenolic resin in a mass ratio of 1:3.5, the mass ratio of the phosphated iron-silicon alloy to the resin is 100:1, and the volume ratio of the acetone to the mass ratio of the phosphated iron-silicon alloy powder is 10 mL:1 g. In step S4, the mass ratio of the coated iron-silicon alloy powder to the release agent (zinc stearate) is 100:0.3.

[0057] Examples 2-4 and Comparative Examples 1-2 Examples 2-4 and Comparative Examples 1-2 provide different iron-silicon magnetic powder cores and their preparation methods. The difference between them and Example 1 is that the mass ratio of Si to Ce is different, while the rest is the same as Example 1, as shown in the table below: Table 1. Mass ratios of Si and Ce in Examples 1-4 and Comparative Examples 1-2 Examples 5-8 and Comparative Examples 3-4 Examples 5-8 and Comparative Examples 3-4 provide different iron-silicon magnetic powder cores and their preparation methods. The difference between them and Example 1 is that the annealing temperature in step S1 is different. The rest is the same as Example 1, as shown in the table below: Table 2 shows the annealing temperatures of Examples 1, 5-8, and Comparative Examples 3-4. Examples 9-11 Examples 9-11 provide different iron-silicon magnetic powder cores and their preparation methods. The difference between them and Example 1 is that the annealing time in step S1 is different, while the rest is the same as Example 1, as shown in the table below: Table 3. Annealing time for Examples 1 and 9-11 Examples 12-19 Examples 12-19 provide different iron-silicon magnetic powder cores and their preparation methods. The difference between them and Example 1 is that the mass ratio of organosilicon resin and phenolic resin in step S3 is different. The rest are the same as in Example 1, as shown in the table below: Table 4. Mass ratio of silicone resin and phenolic resin in Examples 1, 12-19 Note: In the table above, "1:3.5 (epoxy resin)" in Example 16 means that epoxy resin is used instead of phenolic resin, and "all epoxy resin" in Example 19 means that epoxy resin is used instead of silicone resin and phenolic resin.

[0058] Examples 20-22 Examples 20-22 provide different iron-silicon magnetic powder cores and their preparation methods. The difference between them and Example 1 is that the heat treatment temperature in step S4 is different, while the rest is the same as Example 1, as shown in the table below: Table 5. Temperatures of heat treatment in Examples 1 and 20-22 Example 23 This embodiment provides an iron-silicon magnetic powder core and its preparation method. The difference between this embodiment and Embodiment 1 is that the mass percentage of each element in the iron-silicon alloy powder is different, while the rest is the same as in Embodiment 1, as detailed below: In step S1, the iron-silicon alloy comprises, by mass percentage, the following elements: 5.005% Si and Ce, with the balance being Fe and unavoidable impurities; the mass ratio of Si to Ce is 100:0.7, and the unavoidable impurities include 0.015% C, 0.024% O, 0.035% P, and 0.016% S.

[0059] Example 24 This embodiment provides an iron-silicon magnetic powder core and its preparation method. The difference between this embodiment and Embodiment 1 is that the mass percentage of each element in the iron-silicon alloy powder is different, while the rest is the same as in Embodiment 1, as detailed below: In step S1, the iron-silicon alloy comprises, by mass percentage, the following elements: 6.550% Si and Ce, with the balance being Fe and unavoidable impurities; the mass ratio of Si to Ce is 100:0.7, and the unavoidable impurities include 0.018% C, 0.028% O, 0.036% P, and 0.017% S.

[0060] Performance testing The following performance tests were performed on the iron-silicon magnetic powder cores of each embodiment and comparative example: 1. Magnetic loss test: The magnetic loss (in mW / cm²) of the iron-silicon magnetic powder core was measured using a BH analyzer (SY-8218) from Iwasaki, Japan, under conditions of 100 mT, 50 kHz, and 25 °C. 3 ); 2. Magnetic permeability test: Under conditions of 100mT and 50KHz, the inductance value L (unit: H) of the iron-silicon magnetic powder core was tested and recorded using an Agilent 4284A LCR tester. Then, the effective permeability D1 of the iron-silicon magnetic powder core was calculated from the inductance value, thus obtaining the permeability data of the iron-silicon magnetic powder core. 3. DC superposition characteristic test: A test system was built using an Agilent 4284A LCR tester and a DC power supply. A 50kHz sinusoidal signal with an effective value of 1V was input to the AC winding. A constant current was supplied to the DC bias winding through the DC power supply to make the DC bias field H=100Oe. The inductance value L (unit: H) of the iron-silicon magnetic powder core was measured and recorded. Then, the effective permeability D2 of the iron-silicon magnetic powder core under the DC superposition characteristic condition was calculated using the inductance value, and D (%) was calculated according to the following formula: D (%) = (D2 / D1) × 100%; D1 was obtained through the above-mentioned "2. Magnetic permeability test"; The larger the D (%), the stronger the DC superposition characteristic of the iron-silicon magnetic powder core. The experimental results are shown in the table below: Table 6 Performance test results of the iron-silicon magnetic powder cores of each embodiment and comparative example. As shown in Table 6, the iron-silicon magnetic powder core prepared by this invention has low magnetic loss and high DC superposition characteristics, and also has high permeability, with magnetic loss ≤600.0 mW / cm. 3 DC superposition characteristics ≥74.0%, magnetic permeability ≥55.0%.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an iron-silicon magnetic powder core, characterized in that, Includes the following steps: S1. Anneal the iron-silicon alloy powder at 900-1200℃ to obtain annealed iron-silicon alloy powder; S2. Mix the annealed iron-silicon alloy powder and the phosphating agent to obtain phosphated iron-silicon alloy powder; S3. Mix the phosphated iron-silicon alloy powder and resin to obtain the coated iron-silicon alloy powder; S4. Mix the coated iron-silicon alloy powder and the release agent, press them into shape, and perform heat treatment to obtain the iron-silicon magnetic powder core; In step S1, the iron-silicon alloy powder comprises, by mass percentage, the following elements: 5.005%-6.550% Si and Ce, with the balance being Fe and unavoidable impurities; the mass ratio of Si to Ce is 100:(0.075-1).

2. The method for preparing the iron-silicon magnetic powder core as described in claim 1, characterized in that, Includes at least one of the following (1)-(4): (1) The mass ratio of Si to Ce is 100:(0.3-0.7); (2) In step S1, the annealing temperature is 1000-1100℃; (3) In step S1, the annealing process takes 0.5-7 hours; (4) In step S3, the resin includes at least one of silicone resin, phenolic resin and epoxy resin.

3. The method for preparing the iron-silicon magnetic powder core as described in claim 2, characterized in that, Includes at least one of the following (1)-(2): (1) In step S1, the annealing process takes 0.5-5 hours; (2) In step S3, the resin includes silicone resin and phenolic resin, and the mass ratio of silicone resin to phenolic resin is 1:(0.2-5).

4. The method for preparing the iron-silicon magnetic powder core as described in claim 3, characterized in that, In step S3, the resin includes silicone resin and phenolic resin, and the mass ratio of the silicone resin to the phenolic resin is 1:(1.5-3.5).

5. The method for preparing the iron-silicon magnetic powder core as described in claim 1, characterized in that, Includes at least one of the following (1)-(5): (1) In step S2, the phosphating agent includes phosphoric acid; (2) In step S2, the mass ratio of the annealed iron-silicon alloy powder to the phosphating agent is 100:(0.1-1); (3) In step S3, the mass ratio of the phosphated iron-silicon alloy powder to the resin is 100:(0.1-2); (4) In step S4, the release agent includes zinc stearate; (5) In step S4, the mass ratio of the coated iron-silicon alloy powder to the release agent is 100:(0.1-0.5).

6. The method for preparing the iron-silicon magnetic powder core as described in claim 5, characterized in that, The pressing pressure is 1500-2000 MPa.

7. The method for preparing the iron-silicon magnetic powder core as described in claim 1, characterized in that, Includes at least one of the following (1)-(2): (1) In step S4, the temperature of the heat treatment is 550-850℃; (2) The preparation method of the iron-silicon alloy powder includes: A1. Weigh the raw materials according to the composition ratio of the iron-silicon alloy powder, heat and melt them to obtain the alloy melt; A2. Pour the molten alloy into the tundish, allowing it to flow into the atomization chamber through the bottom guide pipe. Use nitrogen to atomize the molten alloy to obtain alloy droplets. Cool and solidify to obtain iron-silicon alloy powder.

8. The method for preparing the iron-silicon magnetic powder core as described in claim 1, characterized in that, In step S4, the temperature of the heat treatment is 550-750℃.

9. A type of iron-silicon magnetic powder core, characterized in that, It is prepared by any of the preparation methods described in claims 1-8.

10. An application of the iron-silicon magnetic powder core as described in claim 9 in an inductor device.

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