JP6520168B2 - Iron nitride based magnetic powder and bonded magnet using the same - Google Patents

Description

The present invention relates to an iron nitride-based magnetic powder having a Fe ₁₆ N ₂ compound phase as a main phase, maintaining high saturation magnetization, and having high coercivity. Furthermore, a bonded magnet using the iron nitride magnetic powder is provided.

In recent years, Nd-Fe-B based magnets are widely used as magnets for motors of electric vehicles, hybrid vehicles and the like. However, rare earths typified by Nd are raw materials for high-value-added components that support industrial fields, and demand is expanding in recent years, so there is concern that resource exhaustion and raw material prices may be unstable. . Furthermore, the growing demand in developing countries and the high degree of reliance on specific producing countries due to their uneven distribution have led to problems with securing stable supply.

In order to avoid the above problems, it is required to develop high-performance magnets from elements (iron, nitrogen) which are inexhaustible in nature without using rare earth.

Fe-N compounds, in particular Fe ₁₆ N _2, are attracting attention as one of the materials exhibiting a saturation magnetization larger than that of Fe.

In Patent Document 1, an iron nitride-based magnetic powder is synthesized by a method of synthesizing iron oxide by a coprecipitation method, and reducing and nitriding it. However, due to the low coercivity of the obtained iron nitride powder, its use as a magnetic material for motor applications where high coercivity and high saturation magnetization are required is difficult.

JP, 2009-84115, A

The present invention has been made in view of the above, and an object thereof is to provide an iron nitride-based magnetic powder having a high coercive force and a bonded magnet using the magnetic powder.

That is, the present invention is an iron nitride-based magnetic powder containing Fe ₁₆ N ₂ particles as a main component, wherein the Fe ₁₆ N ₂ particles of the iron nitride-based magnetic powder have a disk-like anisotropic shape elongated in the easy magnetization axis direction. The present invention relates to an iron nitride-based magnetic powder having a shape aspect ratio of 2 to 8 expressed by an average particle major axis / an average particle minor axis of the Fe ₁₆ N ₂ particles and a bonded magnet using the iron nitride-based magnetic powder. .

Further, the present invention relates to the iron nitride-based magnetic powder and the bonded magnet using the iron nitride-based magnetic powder, wherein the average particle major diameter of the Fe ₁₆ N ₂ particles is 30 to 150 nm.

Since the shape of the Fe ₁₆ N ₂ particles constituting the iron nitride-based magnetic powder is a disk-shaped anisotropic shape having a long axis in the direction of easy magnetization, the Fe ₁₆ N ₂ particles have shape anisotropy and are favorable. Coercivity can be obtained.

By setting the shape aspect ratio of the Fe ₁₆ N ₂ particles to 2 to 8, the iron nitride-based magnetic powder can obtain good coercivity.

By setting the average particle long diameter of the Fe ₁₆ N ₂ particles to 30 to 150 nm, the iron nitride-based magnetic powder can obtain even better coercivity.

According to the present invention, the iron nitride-based magnetic powder containing the Fe ₁₆ N ₂ phase is composed of Fe ₁₆ N ₂ particles, and the Fe ₁₆ N ₂ particles have shape anisotropy, and the average particle length / average diameter When the shape aspect ratio represented by the particle minor diameter is 2 to 8, since it has shape magnetic anisotropy in addition to the magnetocrystalline anisotropy, good coercivity can be obtained.

Further, by setting the average particle major axis of the Fe ₁₆ N ₂ particles to 30 to 150 nm, a further favorable coercive force can be obtained.

Hereinafter, preferred embodiments of the present invention will be described. The present invention is not limited by the contents of the embodiments and examples described below. In addition, the components shown in the embodiments and examples described below may be combined as appropriate or selected as appropriate.

In the iron nitride based magnetic powder according to the present embodiment, the main phase is made of Fe ₁₆ N ₂ particles. In addition to the main phase _may have a _{Fe 2 O 3, Fe 3 O} 4 and iron oxide phase such as FeO.

The iron nitride-based magnetic powder according to the present embodiment may have a main phase of an Fe ₁₆ N ₂ compound phase and may contain an Fe ₄ N compound phase. In addition, it may have a phase composed of an oxide on the surface of the iron nitride based magnetic particles.

The Fe ₁₆ N ₂ particles may contain a transition metal such as Mn, Ni, Co, Ti, Zn or the like.

In the iron nitride-based magnetic powder according to the present embodiment, the shape of Fe ₁₆ N ₂ particles as the main phase is a disk-like anisotropic shape having a long axis in the direction of easy magnetization.

The iron nitride-based magnetic powder according to the present embodiment has a shape aspect ratio of 2 to 8 represented by the average particle major axis / average particle minor axis of the Fe ₁₆ N ₂ particles. When the shape aspect ratio of the Fe ₁₆ N ₂ particles is less than 2, sufficient shape anisotropy can not be obtained, and therefore the coercivity is not sufficient and when the shape aspect ratio exceeds 8, Fe ₁₆ N _Because the crystal structure of the _two particles is distorted, it does not have a sufficient coercive force. Also preferably, the average particle length of the Fe ₁₆ N ₂ particles is 30 to 150 nm. By setting the average particle long diameter in this range, the ratio of particles having a single magnetic domain critical diameter or more can be reduced, and a better coercivity can be obtained.

The suitable manufacturing method of the iron nitride type magnetic powder which concerns on this embodiment is described. The iron nitride-based magnetic powder according to the present embodiment is obtained by synthesizing iron oxide particles and then subjecting the iron oxide particles to a reduction treatment and a nitriding treatment in order, followed by calendering the iron nitride-based magnetic particles.

The iron oxide particles can be produced by mixing an aqueous iron salt solution containing a ferrous salt and / or a ferric salt with an aqueous alkaline solution, followed by aging and washing.

As said iron salt, a sulfate, a chloride, nitrate etc. can be mentioned, You may use it combining these suitably. Also, their hydrates can be used.

As the aqueous alkali solution, one or more of aqueous sodium hydroxide solution, aqueous ammonia, aqueous ammonia salt solution, and aqueous urea solution can be used, but it is not limited thereto.

In addition, after iron oxide production, in-liquid aging reaction such as hydrothermal treatment with an autoclave may be performed to improve crystallinity and control particle size and particle shape.

After the production of iron oxide, the aqueous solution is filtered, and if necessary, washing treatment such as water washing can be performed to recover iron oxide particles.

The iron oxide particles cover the particle surface with a Si compound in order to suppress sintering of the particles due to reduction treatment. As the Si compound, colloidal silica, a silane coupling agent, a silanol compound or the like can be used.

The coating amount of the Si compound is 0.1% by mass or more and 20% by mass or less in terms of Si based on iron oxide particles. If the amount is less than 0.1% by mass, the effect of suppressing sintering between particles can not be sufficiently obtained during heat treatment, so that the finally obtained iron nitride-based magnetic particles become large. If it exceeds 20% by mass, the effect of suppressing sintering between particles during heat treatment becomes excessive, and the finally obtained iron nitride-based magnetic particles become smaller. In addition, the nonmagnetic component is increased, which is not preferable. A more preferable surface coverage is 0.15% by mass to 15% by mass, and still more preferably 0.2% by mass to 10% by mass.

The iron oxide particles preferably have an average particle size of 10 nm or more and 150 nm or less. By setting the average particle diameter to this range, it is possible to set the average particle major diameter of the finally obtained disk-shaped anisotropic shaped Fe ₁₆ N ₂ particles to 30 to 150 nm.

The iron oxide particles are not limited to magnetite, γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, β-FeOOH, γ-FeOOH, FeO, and the like.

The particle shape of the iron oxide particles may be spherical, needle-like, granular, spindle-like, rectangular or the like.

Next, reduction processing of the obtained iron oxide particles is performed to obtain iron particles. The temperature of the reduction treatment is 200 to 400 ° C. When the temperature of the reduction treatment is less than 200 ° C., the iron oxide particles are not sufficiently reduced. When the temperature of the reduction treatment exceeds 400 ° C., the iron oxide particles are sufficiently reduced, but this is not preferable because sintering between particles proceeds. More preferably, it is 230 to 350 ° C.

Although the time of a reduction process is not specifically limited, 1 to 96 hours are preferable. If it exceeds 96 hours, depending on the reduction temperature, sintering will proceed and it will be difficult to advance the subsequent stage nitriding treatment. The reduction does not proceed sufficiently in less than one hour. More preferably, it is 2 to 72 hours.

The atmosphere of the reduction treatment is a hydrogen atmosphere.

Next, the iron particles obtained are subjected to a nitriding treatment to obtain iron nitride-based magnetic particles. The temperature of the nitriding treatment is 100 to 200 ° C. When the temperature of the nitriding treatment is less than 100 ° C., the nitriding does not proceed sufficiently. When the temperature of the nitriding treatment exceeds 200 ° C., the nitriding progresses excessively, and the magnetic properties are degraded. More preferably, it is 120-180 ° C.

Although the time of the nitriding treatment is not particularly limited, 1 to 48 hours are preferable. If it exceeds 48 hours, depending on the nitriding temperature, the magnetic properties deteriorate. In less than one hour, sufficient reduction can often not be achieved. More preferably, it is 3 to 24 hours.

The atmosphere for the nitriding treatment is preferably an NH ₃ atmosphere, and in addition to NH ₃ , N ₂ , H _{2 and the} like may be mixed.

At this time, the iron nitride based magnetic particles may have an iron oxide phase on the surface of the particles.

The obtained iron nitride-based magnetic particles are mixed with an organic solvent sufficiently dehydrated, and a dispersant is further added to prepare a slurry containing iron nitride-based magnetic particles.

As the organic solvent, a single liquid or mixed liquid using any one or more of alkanes such as hexane, cyclohexane and octane, and ketones such as cyclohexanone and MEK can be used, but not limited to this .

As the dispersant, any one or more of oleic acid, oleylamine, trioctylamine and the like can be used, but it is not limited thereto.

The addition amount of the dispersant is 0.1% by mass or more and 5% by mass or less with respect to the iron nitride-based magnetic particles. By setting the amount of the dispersing agent in this range, it is possible to control the shape aspect ratio represented by the average particle major axis / average particle minor axis of the iron nitride magnetic particles at the subsequent calendering process.

The slurry containing the iron nitride-based magnetic particles is treated with a particle calendar processing machine to flatten the iron nitride-based magnetic particles, thereby producing a slurry containing iron-nitride-based magnetic particles in an anisotropic disk shape.

At this time, a magnetic field is applied in a direction perpendicular to the calendar direction of the particle calendar processor. The iron nitride-based magnetic particles rotate in the magnetic field, and the direction of easy magnetization of the iron nitride-based magnetic particles and the direction of the magnetic field application become the same. As a result, it is possible to produce iron-nitride-based magnetic particles of an anisotropic disk shape long in the direction of easy magnetization axis.

The shape aspect ratio represented by the average particle major axis / average particle minor axis of the disk-shaped anisotropic iron nitride-based magnetic particles is set to 2 to 8. When the amount of the dispersant in the slurry is less than 0.1% by mass with respect to the iron nitride-based magnetic particles, the shape of the iron nitride-based magnetic particles is significantly deformed during calendering, and the shape aspect ratio exceeds 8 and further nitriding This is not preferable because it produces connected particles of iron magnetic particles. In addition, when the amount of the dispersant in the slurry exceeds 5% by mass with respect to the iron nitride-based magnetic particles, the viscosity of the slurry containing the iron nitride-based magnetic particles decreases, and the pressure is applied to the iron nitride-based magnetic particles at the time of calendering. However, it is not preferable because the shape aspect ratio is less than 2 and the iron nitride-based magnetic particles can not have sufficient shape magnetic anisotropy.

Next, the obtained slurry containing the disc-shaped anisotropic iron nitride-based magnetic particles can be dried at 100 ° C. for 20 hours to produce an iron nitride-based magnetic powder.

A bonded magnet can be obtained using the iron nitride based magnetic powder obtained by the present embodiment. Hereafter, the manufacturing method is described.

First, an example of a method of manufacturing a bonded magnet using the iron nitride based magnetic powder obtained by the present embodiment will be described. The resin binder containing the resin and the magnetic powder are kneaded, for example, by a pressure kneader such as a pressure kneader to prepare a compound magnet composition (composition). Resins include thermosetting resins such as epoxy resins and phenol resins, styrene-based, olefin-based, urethane-based, polyester-based and polyamide-based elastomers, ionomers, ethylene propylene copolymer (EPM), ethylene-ethyl acrylate copolymer There is a thermoplastic resin such as coalescence. Among them, a thermosetting resin is preferable, and an epoxy resin or a phenol resin is more preferable, as a resin used in compression molding. The resin used for injection molding is preferably a thermoplastic resin. Further, if necessary, a coupling agent and other additives may be added to the bonded magnet compound.

Further, the content ratio of the magnetic powder to the resin in the bond magnet preferably includes, for example, 0.5% by mass or more and 20% by mass or less of the resin with respect to 100% by mass of the magnetic powder. When the content of the resin is less than 0.5% by mass with respect to 100% by mass of the magnetic powder, the shape retention tends to be impaired, and when the content of the resin exceeds 20% by mass, sufficiently excellent magnetic properties are obtained. It tends to be difficult to obtain.

After preparing the above-described bonded magnet compound, the bonded magnet compound including the magnetic powder and the resin can be obtained by injection molding the bonded magnet compound. When a bonded magnet is produced by injection molding, the bonded magnet compound is heated to the melting temperature of the binder (thermoplastic resin) as necessary to bring it into a fluidized state, and then the bonded magnet compound has a predetermined shape. It injects in the mold and performs molding. Then, it cools and takes out the molded article (bond magnet) which has a predetermined shape from a metal mold | die. Thus, a bonded magnet is obtained. The method of manufacturing the bonded magnet is not limited to the above-described injection molding method. For example, the bonded magnet containing a magnetic powder and a resin may be obtained by compression molding a bonded magnet compound. When producing a bonded magnet by compression molding, after preparing the above-mentioned bonded magnet compound, the bonded magnet compound is filled in a mold having a predetermined shape, and pressure is applied to have a predetermined shape from the mold Take out the molded product (bond magnet). When molding the bonded magnet compound with a mold and taking it out, it is carried out using a compression molding machine such as a mechanical press or hydraulic press. Thereafter, it is placed in a furnace such as a heating furnace or a vacuum drying furnace and hardened by applying heat to obtain a bonded magnet.

The shape of the bonded magnet obtained by molding is not particularly limited, and may be changed to, for example, a flat plate shape, a columnar shape, or a ring shape in cross section depending on the shape of a mold to be used. Further, the obtained bonded magnet may be plated or coated on its surface to prevent deterioration of the oxide layer, the resin layer and the like.

When the compound for a bonded magnet is formed into a predetermined shape, the molded product obtained by applying a magnetic field is oriented in a certain direction. As a result, the bonded magnet is oriented in a specific direction, so that a more magnetically anisotropic bonded magnet can be obtained.

Next, the iron nitride-based magnetic powder according to the present invention will be described in more detail using Examples and Comparative Examples, but the present invention is not limited to the embodiments shown in the Examples.

Example 1 First, 167 g of iron sulfate heptahydrate (FeSO ₄ · 7 H ₂ O) and 85 g of iron chloride hexahydrate (FeCl ₃ · 6 H ₂ O) are dissolved in ion-exchanged water, and an iron salt aqueous solution is dissolved. Made. After holding 600 g of a 2.5 mol aqueous ammonia solution at 30 ° C. and adding the previously prepared iron salt aqueous solution, the temperature is controlled to be constant at 70 ° C. as an in-liquid aging reaction, and after stirring for 30 minutes, centrifuge The reaction mixture was washed three times with 2 L of ion-exchanged water to prepare an iron oxide slurry.

To the above-mentioned iron oxide slurry, 5.0 g of tetraethoxysilane, 21 g of ethanol and 78 g of diethylene glycol monobutyl ether were added to carry out Si deposition treatment. The iron oxide slurry was dried at 85 ° C. for 24 hours to prepare iron oxide particles containing Fe ₂ O ₃ .

2 g of the iron oxide particles were placed in a baking boat and allowed to stand in a heat treatment furnace. The furnace was filled with nitrogen gas, and while flowing hydrogen gas at a flow rate of 1 L / min, the temperature was raised to 250 ° C. at a temperature rising rate of 5 ° C./min and held for 48 hours for reduction treatment. Thereafter, the supply of hydrogen gas was stopped, and the temperature was lowered to 140 ° C. while flowing nitrogen gas at a flow rate of 2 L / min. Subsequently, nitriding treatment was performed at 140 ° C. for 24 hours while flowing ammonia gas at 0.2 L / min. Thereafter, the temperature was lowered to 50 ° C. while flowing nitrogen gas at a flow rate of 2 L / min, air replacement was carried out for 24 hours, and iron nitride based magnetic particles were obtained.

100 g of the obtained iron nitride-based magnetic particles were mixed with 60 g of fully dehydrated octane, and 3 g of oleylamine as a dispersant was further added to prepare a slurry containing iron nitride-based magnetic particles. The obtained slurry containing iron nitride based magnetic particles was charged into a particle calendering machine to flatten the iron nitride based magnetic particles to obtain a slurry containing disc-shaped anisotropic iron nitride based magnetic particles. At this time, in order to obtain an iron nitride-based magnetic particle in the shape of a circular disk that is long in the easy magnetization direction, a magnetic circuit with electromagnets is installed above and below the calendar roll, and a magnetic field is applied in the direction perpendicular to the pressure direction of the calendar. It occurred.

Next, the obtained slurry containing the disc-shaped anisotropic iron nitride-based magnetic particles was dried at 200 ° C. for 20 hours to produce an iron nitride-based magnetic powder.

(Examples 2, 3, 4, 5) The same method as in Example 1 except that the amount of tetraethoxysilane added to the iron oxide slurry was 4.0, 2.5, 1.0, and 0.5 g. An iron nitride based magnetic powder was produced.

(Examples 6, 7 and 8) The amount of tetraethoxysilane added to the iron oxide slurry is 4.0, 2.5 and 1.0 g, and the amount of oleylamine added to the slurry containing iron nitride based magnetic particles is 5 g An iron nitride-based magnetic powder was produced in the same manner as in Example 1 except that

(Examples 9, 10, 11) The amount of tetraethoxysilane added to the iron oxide slurry is 4.0, 2.5, 1.0 g, and the amount of oleylamine added to the slurry containing iron nitride magnetic particles is 1 g An iron nitride-based magnetic powder was produced in the same manner as in Example 1 except that

Comparative Examples 1 and 2 An iron nitride-based magnetic powder was produced in the same manner as in Example 3 except that the amount of oleylamine added to the slurry containing the iron nitride-based magnetic particles was changed to 7 and 0.5 g.

Comparative Example 3 An iron nitride based magnetic powder was produced in the same manner as in Example 3 except that the slurry containing the iron nitride based magnetic particles was not subjected to the particle calendering treatment.

The constituent phase, relative density, particle long diameter, shape aspect ratio, residual magnetic flux density (Br) and coercivity (HcJ) of the iron nitride-based magnetic powder thus obtained were measured by the following method. The results are shown in Table 1.

«Constituent phase of iron nitride based magnetic powder»
The constituent phase of the obtained iron nitride-based magnetic powder was identified using a powder X-ray diffractometer (XRD, manufactured by Rigaku RINT-2500).

<< Particle major axis of iron nitride magnetic powder, shape aspect ratio >>
The obtained iron nitride-based magnetic powder is weighed in a disc-shaped case of 66 mm, paraffin with a melting point of 50-52 ° C. is added, and heating is performed with a hot plate. When the paraffin melts, standing for 10 minutes in a magnetic field of 20 kOe did. While applying a magnetic field, the paraffin was allowed to cool and solidify to produce a paraffin containing an iron nitride-based magnetic powder. As shown in FIG. 1, the paraffin containing iron nitride-based magnetic powder 1 obtained, carved to exit cross-section in a direction perpendicular to the direction of the applied magnetic field 2. In the case of a bonded magnet, the bonded magnet is cut out so that its cross section is perpendicular to the magnetic orientation direction. The obtained cross section was observed with a magnetic field electron microscope (TEM, JEM-2000FX manufactured by Nippon Denshi K.K.). Select 1000 particles from the TEM observation image, set the longest diameter 3 as the longest diameter of the chord through the particle center, and make the diameter 4 perpendicular to the particle long diameter through the particle center The diameter was taken and the average value of each was calculated. Moreover, it was set as the shape aspect ratio represented by average particle major axis / average particle minor axis.

<< Saturation Magnetization (σs) and Coercivity (HcJ) of Iron Nitride-Based Magnetic Powders >>
The saturation magnetization (σs) and the coercivity (HcJ) of the obtained iron nitride-based magnetic powder were determined from the measurement results of the demagnetization curve using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.). An iron nitride magnetic powder having a coercive force (HcJ) of 2.3 kOe or more was accepted.

In all the examples and comparative examples, it was confirmed that the Fe ₁₆ N ₂ phase is the main phase.

As in Examples 1, 2, 3, 4 and 5, the average particle length of the iron nitride magnetic powder is 26 nm, 31 nm, 72 nm, 148 nm, 156 nm aspect ratio is 4.1, 4.3, 4.1, 4 In the cases of .2 and 4.3, it was confirmed that the coercivity (HcJ) was 2.3 kOe or more. In particular, when the average particle major axis was in the range of 30 to 150 nm, good characteristics with a coercive force (HcJ) of 2.5 kOe or more were obtained.

As in Examples 6, 7 and 8, in the case where the average particle major axis of the iron nitride magnetic powder is 32 nm, 68 nm, 148 nm and the aspect ratio is 2.1, 2.2, 2.1, the coercivity (HcJ) is It was confirmed that it was 2.5 kOe or more.

As in Examples 9, 10 and 11, when the average particle major axis of iron nitride based magnetic powder is 35 nm, 74 nm and 147 nm, and the aspect ratio is 8.0, 7.9 and 8.0, the coercivity (HcJ) is It was confirmed that it was 2.6 kOe or more.

As in Comparative Example 1, when the average particle major axis of the iron nitride magnetic powder is 68 nm and the aspect ratio is 1.5, a coercivity (HcJ) of 2.2 kOe, which is sufficiently high, can not be obtained. The It is considered that when the aspect ratio of the Fe ₁₆ N ₂ particles in the iron nitride magnetic powder is less than 2, the Fe ₁₆ N ₂ particles do not have sufficient shape anisotropy, so the coercivity is lowered.

As in Comparative Example 2, when the average particle length of the iron nitride magnetic powder is 73 nm and the aspect ratio is 8.3, a coercivity (HcJ) of 2.2 kOe can not be obtained, which is sufficiently high. The This is considered to be because when the aspect ratio of the Fe ₁₆ N ₂ particles in the iron nitride based magnetic powder exceeds 4, the crystal structure of the Fe ₁₆ N ₂ particles in the iron nitride based magnet is distorted, and the coercive force is lowered. .

As in Comparative Example 3, when the average particle length of the iron nitride-based magnetic powder is 71 nm and the aspect ratio is 1, a sufficiently high coercivity (HcJ) of 2.0 kOe could not be obtained. It is considered that this is because the Fe ₁₆ N ₂ particles in the iron nitride-based magnetic powder were not calendered, and therefore the effect of improving the coercive force by shape anisotropy was not obtained.

As described above, the iron nitride-based magnetic powder according to the present invention is useful as a magnet that does not use rare earth because it has a sufficient coercive force.

It is the schematic of the cross section which shaved off the paraffin containing iron nitride type | system | group magnetic powder according to this invention in the direction orthogonal to the magnetic field direction.

1 iron nitride-based magnetic powder end
2 Magnetic field application direction
3 particle long diameter
4 particle minor diameter

Claims (3)

An iron nitride-based magnetic powder containing an Fe ₁₆ N ₂ phase, wherein the shape of the Fe ₁₆ N ₂ particles constituting the iron nitride-based magnetic powder is a disk-like anisotropic shape having a long axis in the direction of easy magnetization;
In the cross section perpendicular to the easy magnetization axis of the _Fe 16 _{N 2} particles, the _Fe 16 _N around the passing length of the chord of the ₂ particles the longest diameter and the particle diameter, of the _Fe 16 _{N 2} particles Iron nitride-based iron having a shape minor aspect ratio of 2 to 8 represented by the average particle major axis / average particle minor axis of the Fe ₁₆ N ₂ particles , wherein the diameter which intersects the center and intersects perpendicularly to the particle major axis is the particle minor axis Magnetic powder. The iron nitride-based magnetic powder according to claim 1, wherein an average particle major diameter of Fe ₁₆ N ₂ particles constituting the iron nitride-based magnetic powder is 30 to 150 nm. Bonded magnet using the iron nitride system magnetic powder according to claim 1 or 2.

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