IMPROVED TEMPERATURE-STABLE SOFT-MAGNETIC POWDER

Abstract

A soft-magnetic powder coated with a silicon-based coating, wherein the silicon-based coating comprises at least one fluorine containing composition of formula (I), Si.sub.1-0.75c MCO.sub.2-0.5c F.sub.d (I), wherein c is in the range of 0.01 to 0.5, d is in the range of 0.04 to 2, and M is B or Al.

Claims

1-16. (canceled)

17. A process for coating a soft-magnetic powder, the coating comprising at least one fluorine containing composition containing a composition of formula (I):
1. Si.sub.1-0.75cM.sub.cO.sub.2-0.5cF.sub.d   (I): wherein c is in the range of 0.01 to 0.5, d is in the range of 0.04 to 2, and M is B or Al, wherein the soft-magnetic powder is mixed with a silicon-based solution containing at least one soluble fluorination agent, wherein the at least one soluble fluorination agent is a compound of formula (II)
[Q][MF.sub.4]  (II) wherein M is B or Al; and Q is a cationic group selected from H.sup.+, Na.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+ or [NR.sup.1.sub.4].sup.+, wherein R.sup.1 is independently selected from the group consisting of —H, -C.sub.1-12-alkyl, -C.sub.2-12-alkenyl, and -C.sub.6-18-aryl, each of which may be substituted with at least one group represented by the formula —OR.sup.2, wherein R.sup.2 is independently selected from —H, -C.sub.1-12-alkyl, -C.sub.2-12-alkenyl, and -C.sub.1-18-aryl.

18. The process as claimed in claim 17, wherein the soft-magnetic powder is mixed with a silicon-based solution and the at least one soluble fluorination agent is added after at least partial treatment of the soft-magnetic powder with the silicon-based solution.

19. The process as claimed in claim 17, wherein the at least one soluble fluorination agent is a compound of formula (II)
[Q][MF.sub.4]  (II) wherein M is selected from B, and Q is cationic group selected from H.sup.+ or [NR.sup.1.sub.4].sup.+, wherein R.sup.1 is independently selected from the group consisting of —H, -C.sub.1-12-alkyl, -C.sub.2-12-alkenyl, and -C.sub.6-18-aryl, each of which may be substituted with at least one group represented by the formula —OR.sup.2, wherein R.sup.2 is independently selected from —H, -C.sub.1-12-alkyl, -C.sub.2-12-alkenyl, and -C.sub.1-18-aryl.

20. The process as claimed in claim 17, wherein the soluble fluorination agent is selected from the group consisting of HBF.sub.4, [NH.sub.4][BF.sub.4], and [(R.sup.4—O—R.sup.3).sub.x—NH.sub.3-x][BF.sub.4], wherein R.sup.3 represents a group of the formula —(C.sub.nH.sub.2n+p)—; n is an integer from 1 to 6, p is an integer selected from 0 and −2, R.sup.4 is selected from —H or —(C.sub.mH.sub.2m+q)—CH.sub.3, m is an integer from 0 to 6, q is an integer selected from 0 and −2, with the proviso that when m=0 then q=0, and x is an integer selected from 1 to 3.

21. The process as claimed in claim 17, wherein the soluble fluorination agent has a solubility in ethanol at 0° C. of at least 15 wt.-%.

22. The process as claimed in claim 17, wherein the soluble fluorination agent is added during treatment with the silicon-based solution or immediately after the treatment with the silicon-based solution.

23. The process as claimed in claim 17, wherein 0.1 to 10 mmol of fluorination agent per kg of soft-magnetic powder is added to the silicon-based solution.

24. The process as claimed in claim 17, wherein the silicon-based solution contains a silicon alkoxide, which is added in one or more steps to the reaction mixture.

25. A soft-magnetic powder coated with a silicon-based coating obtained by the process according to claim 17.

26. A soft-magnetic powder coated with a silicon-based coating, wherein the silicon-based coating comprises at least one fluorine containing composition of formula (I):
Si.sub.1-0.75cM.sub.cO.sub.2-0.5cF.sub.d   (I) wherein c is in the range of 0.01 to 0.5, d is in the range of 0.04 to 2, the index c and the index d have the following relation: d=4c and M is B or Al.

27. The soft-magnetic powder as claimed in claim 26, comprising at least one fluorine containing composition of formula (I), wherein M is B.

28. The soft-magnetic powder as claimed in claim 26, wherein the silicon-based coating comprises between >5 to 45 wt.-%, of the at least one fluorine containing composition of formula (I).

29. The soft-magnetic powder as claimed in claim 26, wherein the silicon-based coating comprises 20 to 35 wt.-%, of the at least one fluorine containing composition of formula (I).

30. The soft-magnetic powder as claimed in claim 26, wherein the fluorine component of the fluorine containing composition is embedded within a SiO.sub.2-matrix and/or bonded to a surface of a SiO.sub.2-coating.

31. The soft-magnetic powder as claimed in claim 26, wherein the silicon-based coating has an average thickness of 2 to 100 nm.

32. The soft-magnetic powder of as claimed in claim 26, wherein the soft magnetic powder comprises 0.1 to 10 wt % of the silicon based coating based on the total weight of the soft magnetic powder.

33. An electronic component comprising the soft-magnetic powder as claimed in claim 26.

Description

EXAMPLES

Coating of Metal Powder—General Procedure A (Preparation Using a Planetary Mixer)

[0080] In a heatable planetary mixer 2700 kg carbonyl-iron-powder as for instance available from BASF with a purity of 99.5 g of iron content per 100 g and an average particle size d50 between 4.5 and 5 μm is added. The mixer is equipped with a condenser and flushed with argon to obtain an inert atmosphere. While stirring, 480 g ethanol is added. Subsequently, 75 wt.-% of the total amount of TEOS is added (the total amount of TEOS used in each experiment is given in Tables 1 to 6 below). Then, 80 wt.-% of the total amount of an aqueous NH.sub.3 solution having a concentration of 5 wt.-% NH.sub.3 is added (the total amount of the aqueous NH.sub.3 solution used in each experiment is given in Tables 1 to 6 below). Now the temperature is raised to 60° C. while stirring. After stirring at this temperature for about 2 hours, the fluorination agent is added to the reaction mixture in form of a solution in ethanol with a concentration of about 10 to 15 wt.-%. The temperature is maintained while the remaining 25 wt.-% of TEOS and the remaining 20 wt.-% of the NH.sub.3 solution is added over a time of about one hour. The mixture is stirred for further 45 minutes. The condenser is taken off and the product is stirred another hour. During that time the inert gas stream is increased to 600 l/h, already taking some solvent off. After one hour the temperature is raised to 90° C. and the product is stirred under the increased inert gas stream until being dry. The coated carbonyl-iron-powder is obtained as a gray powder.

Coating of Metal Powder—General Procedure B (Preparation in a Flask)

[0081] 355 g ethanol is added to a flask equipped with a homogenizer (rotor/stator homogenizer available from Polytron®) and a condenser and flushed with argon to obtain an inert atmosphere. The homogenizer is set to 2000 rpm. While stirring, 500 g carbonyl-iron-powder as for instance available from BASF with a purity of 99.5 g of iron content per 100 g and an average particle size d50 between 4.5 and 5 μm is added. The homogenizer speed is increased to 6000 rpm. Subsequently, 68 wt.-% of the total amount of TEOS is added (the total amount of TEOS used in each experiment is given in Table 7 below). Then, 100 wt.-% of the total amount of an aqueous NH.sub.3 solution having a concentration of 2.5 wt.-% NH.sub.3 is added (the total amount of the aqueous NH.sub.3 solution used in each experiment is given in Table 7 below). Now the temperature is raised to 45° C. for 20 min, then to 55° C. for 20 min and finally to 65 min for 20 min while stirring. After stirring at this temperature for about 1 further hour, the fluorination agent is added to the reaction mixture in form of a solution in ethanol with a concentration of about 10 to 15 wt.-%. The temperature is maintained while the remaining 32 wt.-% of TEOS is quickly added. The mixture is stirred for 1 further hour. The product is stirred for about 3 hours at 95° C. at an inert gas stream of 600 l/h and 47 rpm in a planetary mixer until the solvent is taken off. The dried coated carbonyl-iron-powder is obtained as a gray powder.

Mixing with Epoxy Resin

[0082] 100 g of the coated carbonyl iron powder (CIP) were mixed with epoxy resin, e.g. Epikote™ 1004 available from Momentive, by dissolving 2.8 g epoxy resin in 15 to 20 mL of solvent (methylethylketone or acetone) and addition of 0.14 g of dicyandiamide, e.g. Dyhard® 100SH available from Alzchem, as hardener. In a glass beaker the coated CIP is stirred together with the epoxy formulation using a dissolver mixer at 1000 R/min. After mixing the slurry is poured in an aluminum plate, which is then put in a fume hood for 8 h. The resulting dry CIP epoxy plate is milled in a knife mill for 10 seconds to yield the ready to press powder. It comprises 2.8 wt.-% of epoxy resin.

Molding and Wiring of Ring Core

[0083] 6.8 g (±0.1 g) of the ready to press powder is put into a steel mold of ring type with an outer diameter of 20.1 mm and an inner diameter of 12.5 mm resulting in a height of approximately 5-6 mm. The ready to press powder is molded at 440 MPa for a couple of seconds. From the exact mass and height of the ring the density of the ring core is calculated. The ring core is wired with 20 windings of an isolated 0.85 mm copper wire, e.g. Isodraht available from Multogan 2000MH 62, for determination of the permeability and resistivity.

Measurement of Permeability and Resistivity

[0084] An LRC meter was used to measure permeability of a ring core. All measurements were done at 100 kHz with 0V DC bias. The test AC current of 10 mA was applied to the ring core.

[0085] To measure the resistivity of the pressed parts, a power supply was connected in series to a voltmeter and a sample. 298 Volts were applied to a multimeter and the sample connected in series. Voltage reading of a multimeter was used to estimate the resistance of the sample using following equation.

R.sub.sample=R.sub.meter×(V.sub.PS−V.sub.meter)/V.sub.meter,

where R.sub.sample is the resistance of the cylinder, R.sub.meter is the internal resistance of the meter, V.sub.PS is the applied voltage from power supply (=298 V), and V.sub.meter is the reading from the voltmeter.

Temperature Stability

[0086] Before the temperature stability test can start the epoxy is cured. This is done by placing the ring cores in oven set to 70° C. After 2 h the ring cores are placed into a second oven set to 155° C. After 2 h the ring cores are taken out for resistivity testing.

[0087] Now the ring cores are placed again into an oven set to 180° C. for an amount of time. The temperature stability after 24 h e.g. is measured after additional 24 h of temperature treatment at 180° C. The ring core is labeled as temperature stable if the measured voltage is about 0 V after 24 h at 180° C. and ≤30 V, preferably ≤25 V, and in particular ≤20 V, after 48 h at 180° C. In a further preferred embodiment, the measured voltage is preferably ≤70 V, more preferred ≤30 V, and in particular ≤10 V after 120 h at 180° C.

Test Results

[0088] After temperature treatment of the compacted samples the permeability and the resistivity were determined as described above. The results are given in Tables 1 to 7. Corrosion testes are summarized in Table 8.

[0089] In Table 1, examples E-1 to E-3 and Comparative Examples C-1 and C-2 are summarized. The examples and comparative examples allow the comparison of coated carbonyl iron powder (CIP) using different fluorination agents under otherwise identical conditions. As can be seen from the results, all compounds exhibit good to excellent properties with respect to permeability as well as heat resistance after the specified amounts of time.

[0090] As demonstrated by Examples E-4 to E-8 shown in Table 2, the fluorination agents in accordance with the present invention allow a considerable reduction of the amounts used for achieving excellent results in resistivity. Starting from 9.6 mmol fluorination agent per 1 kg of CIP, the amount typically employed in EP 2 871 646 A1, the amount of fluorination agent may be reduced by about 30% to 6.70 mmol/kg without negative effects on heat stability if HBF.sub.4 is used. In fact, the reduction results in slight improvements with respect to resistivity after 48 h.

[0091] Table 3 demonstrates different reaction conditions by means of different ratios of TEOS, ammonia and floriation agent which allow influencing the product properties. As can be seen, particularly good properties with respect to resistivity as well as permeability are achieved if the molar ratio of ammonia to TEOS is within the range of 1:1.1 to 1:1.8.

[0092] Examples E-16 to E-19 in Table 4 demonstrate that the amount of fluorination agent may be significantly reduced, if [NH.sub.3EtOH][BF.sub.4] is used, compared to BF3.NH.sub.2—CH.sub.2—Ph (cf. Comparative Example CE-4).

[0093] Table 5 shows that using [NH.sub.3EtOH][BF.sub.4] as fluorination agent allows a further reduction of the used amount of SiO.sub.2 and fluorination agent compared to BF.sub.3.—NH.sub.2—CH.sub.2—Ph. In particular, the amount of fluorination agent may be reduced by about 65 mol-%, the amount of TEOS may be reduced by 10 mol-% and the amount of NH.sub.3 solution can be reduced by 20 wt.-% when [NH.sub.3EtOH][BF.sub.4] is used compared to BF.sub.3.—NH.sub.2—CH.sub.2—Ph without significant deterioration of the product properties.

[0094] Table 6 compares the use of [NH.sub.3EtOH][BF.sub.4] as fluorination agent with the known fluorination agent BF.sub.3.—NH.sub.2—CH.sub.2—Ph in different combinations with respect to the amounts of SiO.sub.2 and NH.sub.3 solution whereas the amount of fluorine atoms is kept approximately constant in the example pairs CE-6/E25, CE-7/E26, CE-8/E-7, and CE-9/E8. As can be seen from these examples and comparative examples, the comparative examples using BF.sub.3.—NH.sub.2—CH.sub.2—Ph typically result in higher voltages after exposing the prepared ring core to an increased temperature (i.e. higher resistivity). On the other hand, the test specimen using BF.sub.3.—NH.sub.2—CH.sub.2—Ph often exhibit a lower permeability. By contrast, the examples according to the present invention using [NH.sub.3EtOH][BF.sub.4] exhibit a unique combination of comparably high permeability and low resistivity (i.e. measured voltage) after exposing to an increased temperature. For example, by comparing the examples which exhibit a permeability of about 17 (+/−0.05) (i.e. examples E-26, CE-8 and CE-9) it is evident that according to the present invention a similar permeability is achieved while the resistivity is distinctly lower after 48 h at 180° C. (15 V for E-26, 143 V for CE-8 and 105 V for CE-9).

[0095] Table 7 shows the test results of two Examples E-29 and E-30 which were both exposed to 180° C. for 120 h. both examples show excellent results with respect to permeability, as well as resistivity.

TABLE-US-00001 TABLE 1 Examples E-1 to E-3 and Comparative Examples CE-1 and CE-2 prepared according to General procedure A. Amount Amount Amount fluori- fluori- SiO.sub.2 with nation nation respect Fluori- Amount agent agent with Voltage Voltage to total nation Fluori- [wt.-% with respect to measured measured Amount Amount weight agent nation respect to total weight after 24 h after 48 h TEOS TEOS of CIP (solution agent total weigh of CIP Permeability at180° C. at 180° C. Ex. No [g] [mol] [mmol/kg] in ethanol) [g] of CIP] [mmol/kg] (dry) [V] [V] E-1 96.9 0.46 172.28 HBF.sub.4 22.68 0.084 9.57 16.63 0.00 4.34 (solution of 10 wt.-%) E-2 96.9 0.46 172.28 NH.sub.4BF.sub.4 27.00 0.100 9.57 15.9 0 5.1 (solution of 10 wt.-%) E-3 96.9 0.46 172.28 [BF.sub.4][H.sub.3N—CH.sub.2—Ph] 30.30 0.167 8.63 17.70 0.02 28.28 (solution of 15 wt.-%) CE-1 96.9 0.46 172.28 H.sub.2SiF.sub.6 24.80 0.138 9.57 16.10 0.00 3.50 (solution of 15 wt.-%) CE-2 96.9 0.46 172.28 BF.sub.3•NH.sub.2—CH.sub.2—Ph 30.30 0.167 9.57 16.4 0 19 (solution of 15 wt.-%)

TABLE-US-00002 TABLE 2 Examples E-4 to E-8 prepared according to General procedure A. Amount Amount Amount fluori- fluori- SiO.sub.2 with nation nation respect Fluori- Amount agent agent with Voltage Voltage to total Amount nation Fluori- [wt.-% with respect to measured measured Amount Amount weight NH.sub.3 agent nation respect to total weight after 24 h after 48 h TEOS TEOS of CIP solution (solution in agent total weigh of CIP Permeability at 180° C. at 180° C. Ex. No. [g] [mol] [mmol/kg] [g] ethanol) [g] of CIP] [mmol/kg] (dry) [V] [V] E-4 96.9 0.46 172.28 134.9 HBF.sub.4 22.7 0.084 9.57 16 0 3.9 (solution of 10 wt.-%) E-5 96.9 0.46 172.28 134.9 HBF4 18.1 0.067 7.65 16.1 0 3.4 (solution of 10 wt.-%) E-6 96.9 0.46 172.28 134.9 HBF.sub.4 15.9 0.059 6.70 15.9 0 3.8 (solution of 10 wt.-%) E-7 96.9 0.46 172.28 134.9 HBF.sub.4 13.5 0.050 5.74 16.3 0 30 (solution of 10 wt.-%) E-8 96.9 0.46 172.28 134.9 HBF.sub.4 11.3 0.042 4.78 17.1 0.8 83 (solution of 10 wt.-%)

TABLE-US-00003 TABLE 3 Examples E-9 to E-15 and Comparative Example CE-3 prepared according to General procedure A. Amount Amount Amount fluor- fluori- SiO.sub.2 with ination nation respect Fluori- Amount agent agent with Voltage Voltage to total Amount nation Fluori- [wt.-% with respect to measured measured Amount Amount weight NH.sub.3 agent nation respect to total weight after 24 h after 48 h TEOS TEOS of CIP solution (solution in agent total weigh of CIP Permeability at 180° C. at 180° C. Ex. No. [g] [mol] [mmol/kg] [g] ethanol) [g] of CIP] [mmol/kg] (dry) [V] [V] E-9 96.9 0.46 172.28 94.4 HBF.sub.4 15.93 0.059 6.70 17.2 0.14 39 (solution of 10 wt.-%) E-10 96.9 0.46 172.28 107.9 HBF.sub.4 15.93 0.059 6.70 17.5 0 3 (solution of 10 wt.-%) E-11 87.2 0.41 155.05 134.9 HBF.sub.4 18.09 0.067 7.65 16.8 0 9 (solution of 10 wt.-%) E-12 77.5 0.37 137.82 134.9 HBF.sub.4 22.68 0.084 9.57 17.5 0.5 63 (solution of 10 wt.-%) E-13 82.4 0.39 146.43 134.9 HBF.sub.4 20.41 0.076 8.63 16.6 0.23 46 (solution of 10 wt.-%) E-14 96.9 0.46 172.28 101.2 HBF.sub.4 15.93 0.059 6.70 16.3 0 3.3 (solution of 10 wt.-%) E-15 87.2 0.41 155.05 107.9 (solution of 18.09 0.067 7.65 16.4 0 — 10 wt.-%) CE-3 96.9 0.46 172.28 134.9 BF.sub.3•NH.sub.2—CH.sub.2—Ph 30.30 0.167 9.57 16.4 0 19 (solution of 15-wt.-%)

TABLE-US-00004 TABLE 4 Examples E-16 to E-19 and Comparative Example CE-4 prepared according to General procedure A. Amount Amount Amount fluori- fluori- SiO.sub.2 with nation nation respect Fluori- Amount agent agent with Voltage Voltage to total Amount nation Fluori- [wt.-% with respect to measured measured Amount Amount weight NH.sub.3 agent nation respect to total weight after 24 h after 48 h TEOS TEOS of CIP solution (solution in agent total weigh of CIP Permeability at 180° C. at 180° C. Ex. No. [g] [mol] [mmol/kg] [g] ethanol) [g] of CIP] [mmol/kg] (dry) [V] [V] E-16 96.9 0.46 172.28 134.9 [NH.sub.3EtOH][BF.sub.4] 28.08 0.104 5.30 16.55 0.00 1.6 (solution of 10 wt.-%; molar ratio N:B = 1.785:1) E-17 96.9 0.46 172.28 134.9 [NH.sub.3EtOH][BF.sub.4] 22.68 0.084 4.24 16.5 0 7.5 (solution of 10 wt.-%; molar ratio N:B = 1.785:1) E-18 96.9 0.46 172.28 101.2 [NH.sub.3EtOH][BF.sub.4] 22.68 0.084 4.24 16.51 0 0.5 (solution of 10 wt.-%; molar ratio N:B = 1.785:1) E-19 87.2 0.41 155.05 107.9 [NH.sub.3EtOH][BF.sub.4] 22.68 0.084 4.24 16.85 0 5.15 (solution of 10 wt.-%; molar ratio N:B = 1.785:1) CE-4 96.9 0.46 172.28 134.9 BF.sub.3•NH.sub.2—CH.sub.2—Ph 30.30 0.167 9.57 16.7 0 11 (solution of 15 wt.-%)

TABLE-US-00005 TABLE 5 Examples E-20 to E-24 and Comparative Example CE-5 prepared according to General procedure A. Amount Amount Amount fluori- fluor- SiO.sub.2 with nation ination respect Fluori- Amount agent agent with Voltage to total nation Fluori- [wt.-% with respect to measured Amount Amount weight Amount NH.sub.3 agent nation respect to total weight after 48 h TEOS TEOS of CIP solution (solution of agent total weigh of CIP Permeability at 180° C. Ex. No. [g] [mol] [mmol/kg] [g] 15 wt.-%) [g] of CIP] [mmol/kg] (dry) [V] E-20 96.9 0.46 172.28 134.9 [NH.sub.3EtOH][BF.sub.4] 14.22 0.079 4.70 16.43 0.85 (molar ratio N:B = 1.3:1) E-21 87.2 0.41 155.05 107.9 [NH.sub.3EtOH][BF.sub.4] 17.01 0.063 3.76 17.2 4 (molar ratio N:B = 1.3:1) E-22 96.9 0.46 172.28 101.2 [NH.sub.3EtOH][BF.sub.4] 14.85 0.055 3.29 17.8 9.5 (molar ratio N:B = 1.3:1) E-23 87.2 0.41 155.05 101.2 [NH.sub.3EtOH][BF.sub.4] 17.01 0.063 3.76 17.7 11 (molar ratio N:B = 1.3:1) E-24 87.2 0.41 155.05 107.9 [NH.sub.3EtOH][BF.sub.4] 14.85 0.055 3.29 17.6 15 (molar ratio N:B = 1.3:1) CE-5 96.9 0.46 172.28 134.9 BF.sub.3•NH.sub.2—CH.sub.2—Ph 30.3 0.167 9.57 17.1 16.5

TABLE-US-00006 TABLE 6 Examples E-25 to E-28 and Comparative Examples CE-6 to CE-9 prepared according to General procedure A. Amount Amount Amount fluori- SiO.sub.2 with fluori- nation respect Fluori- nation agent to total Amount nation agent [wt.-% with Amount Amount weight NH.sub.3 agent [g] respect to TEOS TEOS of CIP solution (solution of (15 wt. % in total weight Ex. No. [g] [mol] [mmol/kg] [g] 15 wt.-%) Ethanol) of CIP] CE-6 96.9 0.46 172.28 134.9 BF.sub.3•NH.sub.2—CH.sub.2—Ph 30.3 0.167 E-25 96.9 0.46 172.28 134.9 [NH.sub.3EtOH][BF.sub.4] 21.76 0.121 (molar ratio N:B = 1.3:1) CE-7 87.2 0.41 155.05 101.2 BF.sub.3•NH.sub.2—CH.sub.2—Ph 15.77 0.087 E-26 87.2 0.41 155.05 101.2 [NH.sub.3EtOH][BF4] 11.38 0.063 (molar ratio N:B= 1.3:1) CE-8 87.2 0.41 155.05 107.9 BF.sub.3•NH.sub.2—CH.sub.2—Ph 13.94 0.077 E-27 87.2 0.41 155.05 107.9 [NH.sub.3EtOH][BF.sub.4] 9.95 0.055 (molar ratio N:B= 1.3:1) CE-9 89.1 0.43 160.22 101.2 BF.sub.3•NH.sub.2—CH.sub.2—Ph 19.7 0.109 E-28 89.1 0.43 160.22 101.2 [NH.sub.3EtOH][BF.sub.4] 14.22 0.079 (molar ratio N:B = 1.3:1) Amount fluori- Amount nation fluorine agent with atoms with Voltage Voltage respect to respect to measured measured total weight total weight after 24 h after 48 h of CIP of CIP Permeability at 180° C. at 180° C. Ex. No. [mmol/kg] [mmol/kg] (dry) [V] [V] CE-6 9.57 28.71 16.3 0 8 E-25 7.19 28.76 15.25 0 0.25 CE-7 4.98 14.94 16.6 0.5 77 E-26 3.76 15.04 17.05 0 15 CE-8 4.4 13.2 16.95 1.4 143 E-27 3.29 13.16 16.45 0 37 CE-9 6.22 18.66 17 0.2 105 E-28 4.7 18.8 16.2 0 3

TABLE-US-00007 TABLE 7 Examples E-29 and E-30 prepared according to General Procedure B Amount Amount SiO.sub.2 with fluori- respect nation to total Amount agent Amount Amount weight NH.sub.3 Fluori- [g] TEOS TEOS of CIP solution nation (15 wt. % in Ex. No. [g] [mmol] [mmol/kg] [g] agent ethanol) E-29 17 81.6 163.21 60 [NH.sub.3EtOH][BF.sub.4] 2.6 E-30 17 81.6 163.21 60 [NH.sub.3EtOH][BF.sub.4] 2.6 Amount Amount fluori- fluori- nation nation agent agent with Voltage Voltage Voltage [wt.-% with respect to measured measured measured respect to total weight after 48 h after 96 h after 120 h total weight of CIP Permeability at 180° C. at 180° C. at 180° C. Ex. No. of CIP] [mmol/kg] (dry) [V] [V] [V] E-29 0.078 4.7 16.65 0 0 1.1 E-30 0.078 4.7 17.2 0 0 0.5

Corrosion Tests

[0096] Corrosion of different stainless steel materials was tested by exposing the samples (dimensions: 50×20×2 mm) of the stainless steel materials (tested materials include according to DIN EN 10027-2: 1.4541, 1.4571, 1.4462, 1.0425) to the respective additive solution at T=60° C. for 4×7 days wherein the solution is replaced by a fresh solutions every week. The test was carried out in a PTFE vessel equipped. The test results are summarized in Table 8.

TABLE-US-00008 TABLE 8 Results of the corrosion tests Additive solution pH corrosion [NH.sub.3EtOH][BF.sub.4] (15 wt.-% in ethanol) 6 no BF.sub.3•NH.sub.2—CH.sub.2—Ph (15 wt.-% in ethanol) 4 no/little HBF4 (3 wt. % in ethanol) 3 little HBF4 (10 wt. % in ethanol) 3 little/strong HBF4 (10 wt. % in water) 0-1 strong

[0097] As can be seen, a solution of HBF4.results in little to strong corrosion of stainless steel materials depending on the solvent used. By contrast, BF.sub.3.—NH.sub.2—CH.sub.2—Ph (15 wt.-% in ethanol) and [NH.sub.3EtOH][BF.sub.4] (15 wt.-% in ethanol) show substantially no or little corrosion. From the view-point of product purity, NH.sub.3EtOH][BF.sub.4] and BF.sub.3.—NH.sub.2—CH.sub.2—Ph are therefore preferred in the process for coating a soft-magnetic powder compared to HBF.sub.4. However, the latter one may be used in low concentrations (i.e. 3 wt.-% in ethanol).

[0098] From the above, the advantages of the present invention may be summarized as follows. The use of a fluorination agent according to formula (II) in a process for coating a soft-magnetic powder, wherein coating comprising at least one fluorine containing composition containing a composition of formula (I), allows the provision of a coated soft-magnetic powder having a higher permeability at a comparable resistivity compared to known fluorination agents. On the other hand, a higher resistivity at comparable permeability may be achieved. Moreover, the fluorination agent according to the present invention is more stable in solution, less prone to precipitate from solution (i.e. has a higher solubility), shows an improved material compatibility (in particular with regard to corrosion) and an improved manageability.