Calcined ferrite, sintered ferrite magnet and its production method

Abstract

A method comprising the steps of mixing raw material powders to a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula of Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, wherein 1xy, x and y are values in a region defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy, y and z, and n representing a molar ratio meet 0.5y1, 0.2z<0.25, and 5.2<n<5.6; calcining the raw material powder mixture; pulverizing the calcined body; molding the calcined powder; and sintering the resultant green body; 0.1% or more and less than 1.5% by mass of SiO.sub.2 being added to the raw material powder mixture, the calcined body or the calcined powder; and 0-2% by mass (as CaO) of CaCO.sub.3 being added to the calcined body or the calcined powder.

Claims

1. A calcined ferrite comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, wherein 1xy, x and y are values in a region defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy; and y and z, and n representing a molar ratio are values meeting 0.5y1, 0.2z<0.25, and 5.2<n<5.6.

2. A method for producing a sintered ferrite magnet comprising the steps of mixing raw material powders to a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, wherein 1xy, x and y are values in a region defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy; and y and z, and n representing a molar ratio are values meeting 0.5y1, 0.2z<0.25, and 5.2<n<5.6, thereby obtaining a raw material powder mixture; calcining said raw material powder mixture to obtain a calcined body; pulverizing said calcined body to obtain calcined powder; molding said calcined powder to obtain a green body; and sintering said green body to obtain a sintered body; 0.1% or more and less than 1.5% by mass of SiO.sub.2 being added to 100% by mass of said raw material powder mixture, said calcined body or said calcined powder; and 0-2% by mass (as CaO) of CaCO.sub.3 being added to 100% by mass of said calcined body or said calcined powder.

3. A method for producing a sintered ferrite magnet comprising the steps of mixing raw material powders to a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, wherein 1xy, x and y are values in a region defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy; and y and z, and n representing a molar ratio are values meeting 0.5y1, 0z<0.25, and 5.2<n<5.6, thereby obtaining a raw material powder mixture; calcining said raw material powder mixture to obtain a calcined body; pulverizing said calcined body to obtain a calcined powder; molding said calcined powder to obtain a green body; and sintering said green body to obtain a sintered body; a raw material powder of Co being added to said calcined body or said calcined powder, such that said z meets 0.2z<0.25 as a whole; 0.1% or more and less than 1.5% by mass of SiO.sub.2 being added to 100% by mass of said raw material powder mixture, said calcined body or said calcined powder; and 0-2% by mass (as CaO) of CaCO.sub.3 being added to 100% by mass of said calcined body or said calcined powder.

4. A sintered ferrite magnet produced by the method recited in claim 2, which comprises metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, wherein 1xy, x and y are values in a region defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate f: (0.221, 0.289, 0.490), a coordinate g: (0.221, 0.221, 0.558), a coordinate h: (0.295, 0.147, 0.558), a coordinate i: (0.346, 0.147, 0.507) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy; and y and z, and n representing a molar ratio are values meeting 0.5y1, 0.147z<0.25, and 3.88n<5.6, said sintered ferrite magnet having a residual magnetic flux density B.sub.r (mT) and an intrinsic coercivity H.sub.cJ (kA/m) at 23 C. meeting the relation of B.sub.r+H.sub.cJ/4535.5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a ternary diagram showing the composition range of the calcined body of the present invention.

(2) FIG. 2 is a ternary diagram showing the composition range of the sintered ferrite magnet of the present invention.

(3) FIG. 3 is a graph showing the relation between a molar ratio n and B.sub.r and H.sub.cJ in calcined bodies for the sintered ferrite magnets of Samples 1-6 in Example 1.

(4) FIG. 4 is a graph showing the relation between a molar ratio n and B.sub.r and H.sub.cJ in calcined bodies for the sintered ferrite magnets of Samples 7-10 in Example 1.

(5) FIG. 5 is a graph showing the relation between a molar ratio n and B.sub.r and H.sub.cJ in calcined bodies for the sintered ferrite magnets of Samples 11-18 in Example 1.

(6) FIG. 6 is a graph showing the relation between H.sub.cJ and B.sub.r in sintered ferrite magnets in Example 1.

(7) FIG. 7 is a ternary diagram showing the compositions of calcined bodies of Samples in Example 2 and the composition range of the calcined body of the present invention.

(8) FIG. 8 is a graph showing the relation between H.sub.cJ and B.sub.r in sintered ferrite magnets in Example 2.

(9) FIG. 9 is a graph showing the relation between y and B.sub.r and H.sub.cJ in calcined bodies for sintered ferrite magnets in Example 3.

(10) FIG. 10 is a graph showing the relation between H.sub.cJ and B.sub.r in sintered ferrite magnets in Example 3.

(11) FIG. 11 is a graph showing the relation between z and B.sub.r and H.sub.cJ in calcined bodies for sintered ferrite magnets in Example 4.

(12) FIG. 12 is a graph showing the relation between z and H.sub.k/H.sub.cJ in calcined bodies for sintered ferrite magnets in Example 4.

(13) FIG. 13 is a graph showing the relation between H.sub.cJ and B.sub.r in sintered ferrite magnets in Example 4.

(14) FIG. 14 is a graph showing the relation between H.sub.cJ and B.sub.r in sintered ferrite magnets in Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) [1] Calcined Ferrite

(16) The calcined ferrite of the present invention comprises metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z,
wherein 1xy, x and y are values in a region I defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy (see FIG. 1); and y and z, and n representing a molar ratio are values meeting

(17) 0.5y1,

(18) 0.2z<0.25, and

(19) 5.2<n<5.6.

(20) Using the calcined ferrite of the present invention, it is possible to produce a sintered ferrite magnet having high B.sub.r and high H.sub.cJ at a low cost.

(21) The calcined ferrite of the present invention comprises as a main phase a ferrite phase having a hexagonal M-type magnetoplumbite structure. In general, a compound determining the properties (physical properties, magnetic properties, etc.) of a magnetic material is defined as main phase. A main phase in the calcined ferrite of the present invention, namely, a ferrite phase having a hexagonal M-type magnetoplumbite structure, determines the basic character such as properties of the calcined ferrite of the present invention.

(22) Having a hexagonal M-type magnetoplumbite structure means that a hexagonal M-type magnetoplumbite structure is mainly observed in an X-ray diffraction pattern of the calcined ferrite measured under a general condition.

(23) A ternary diagram of FIG. 1 indicates a Ca content (1xy), a La content (x) and a (Sr+Ba) content (y), x+y+(1xy) being 1, plotted in an equilateral triangle, with a base side as an axis for the Ca content (1xy), a right side as the La content (x), and a left side as the (Sr+Ba) content (y). An arbitrary point (, , ) in the ternary diagram indicates a distance from the base side, a distance from the right oblique side, and a distance from the left oblique side.

(24) Reasons for limiting the ratios of the elements will be explained below.

(25) 1xy representing the Ca content is in a range of 0.231xy0.4, when 1xy, x and y are in the above region I. When 1xy is less than 0.23 or more than 0.4, foreign phases such as an orthoferrite phase, a perovskite phase, etc. are easily formed, undesirably resulting in low magnetic properties.

(26) x representing the La content is in a range of 0.3x0.47, when 1xy, x and y are in the above region I. When x is less than 0.3, foreign phases such as a spinel ferrite phase, etc. are easily formed, undesirably resulting in low magnetic properties. When x exceeds 0.47, foreign phases such as an orthoferrite phase, a hematite phase, etc. are easily formed, undesirably resulting in low magnetic properties.

(27) y representing the total amount of Sr and Ba contained is in a range of 0.2y0.4, when 1xy, x and y are in the above region I. When y is less than 0.2 or more than 0.4, foreign phases such as an orthoferrite phase, SrFeO.sub.3, BaFe.sub.2O.sub.4, etc. are easily formed, undesirably resulting in low magnetic properties.

(28) y representing a ratio of Sr to (Sr+Ba) is in a range of 0.5y1. Less than 0.5 of y undesirably reduces magnetic properties, particularly H.sub.cJ.

(29) z representing the Co content is in a range of 0.2z<0.25. Because Co is expensive, its amount is preferably as small as possible to suppress a raw material cost, but less than 0.2 of z undesirably reduces magnetic properties, particularly H.sub.cJ. When z is 0.25 or more, foreign phases such as a spinel ferrite phase, etc. are easily formed, undesirably resulting in drastically reduced magnetic properties, particularly rectangularity of a demagnetization curve.

(30) n represents a molar ratio of (Fe+Co) to (Ca+La+Sr+Ba), expressed as 2n=(Fe+Co)/(Ca+La+A). The molar ratio n is 5.2<n<5.6. 5.2 or less or 5.6 or more of n undesirably reduces magnetic properties.

(31) Though the above composition indicates the atomic ratios of metal elements, a composition including oxygen (O) is represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y)Fe.sub.2n-zCo.sub.zO.sub.,
wherein 1xy, x and y are values in a region I defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy (see FIG. 1); and y and z, and n representing a molar ratio are values meeting
0.5y1,
0.2z<0.25, and
5.2<n<5.6;
and =19 in a stoichiometric composition in which La and Fe are trivalent, and Co is divalent, with x=z, and n=6.

(32) In the oxygen-including composition of the calcined ferrite, the molar number of oxygen differs depending on the valences of Fe and Co, the value of n, etc. Also, a ratio of oxygen to the metal elements varies depending on the valence of oxygen, the valences of Fe and Co in the ferrite phase, etc. Accordingly, an actual molar number of oxygen may be deviated from 19. In the present invention, the composition is expressed by the atomic ratios of metal elements, which most easily define the composition.

(33) [2] Production method of sintered ferrite magnet

(34) The Production Method of the Sintered Ferrite Magnet of the Present invention comprises the steps of

(35) mixing raw material powders to a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z,
wherein 1xy, x and y are values in a region I defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy (see FIG. 1); and y and z, and n representing a molar ratio are values meeting

(36) 0.5y1,

(37) 0.2z<0.25, and

(38) 5.2<n<5.6,

(39) thereby obtaining a raw material powder mixture;

(40) calcining the raw material powder mixture to obtain a calcined body;

(41) pulverizing the calcined body to obtain a calcined powder;

(42) molding the calcined powder to obtain a green body; and

(43) sintering the green body to obtain a sintered body;

(44) 0.1% or more and less than 1.5% by mass of SiO.sub.2 being added to 100% by mass of the raw material powder mixture, the calcined body or the calcined powder; and

(45) 0-2% by mass (as CaO) of CaCO.sub.3 being added to 100% by mass of the calcined body or the calcined powder.

(46) In this method, all raw material powders (excluding SiO.sub.2 and CaCO.sub.3 as sintering aids) are added before calcining. This method is thus called prior-addition method.

(47) Another method of the present invention for producing a sintered ferrite magnet comprises the steps of

(48) mixing raw material powders to a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y)Fe.sub.2n-zCo.sub.z,
wherein 1xy, x and y are values in a region I defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy (see FIG. 1); and y and z, and n representing a molar ratio are values meeting
0.5y1,

(49) 0z<0.25, and

(50) 5.2<n<5.6,

(51) thereby obtaining a raw material powder mixture;

(52) calcining the raw material powder mixture to obtain a calcined body;

(53) pulverizing the calcined body to obtain a calcined powder;

(54) molding the calcined powder to obtain a green body; and

(55) sintering the green body to obtain a sintered body;

(56) a raw material powder of Co being added to the calcined body or the calcined powder, such that the above z meets 0.2z<0.25 as a whole;

(57) 0.1% or more and less than 1.5% by mass of SiO.sub.2 being added to 100% by mass of the raw material powder mixture, the calcined body or the calcined powder; and

(58) 0-2% by mass (as CaO) of CaCO.sub.3 being added to 100% by mass of the calcined body or the calcined powder.

(59) In this method, (a) all raw material powders (excluding a raw material powder of Co, and SiO.sub.2 and CaCO.sub.3 as sintering aids) are entirely added before calcining; or (b) part of a raw material powder of Co and total amounts of all other raw material powders than Co (excluding SiO.sub.2 and CaCO.sub.3 as sintering aids) are added before calcining, and all or remaining part of the raw material of Co is added to the calcined body or calcined powder after calcining and before molding, such that the value of z meets 0.2z<0.25 as a whole (hereinafter referring to as post-addition method).

(60) In the present invention, any of the prior-addition method and the post-addition method can produce a sintered ferrite magnet described below. Each step will be explained below.

(61) (a) Mixing Step of Raw Material Powders

(62) Prepared are metal-containing raw material powders having a composition comprising metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y)Fe.sub.2n-zCo.sub.z,
wherein 1xy, x and y are values in the region I in a ternary diagram of x, y, and 1xy (see FIG. 1); and y and z, and n representing a molar ratio are values meeting

(63) 0.5y1,

(64) 0.2z<0.25, and

(65) 5.2<n<5.6.

(66) Each raw material powder may be oxide, carbonate, hydroxide, nitrate, chloride, etc. of each metal, irrespective of its valence. Solutions of raw material powders may be used. Ca compounds may be carbonate, oxide, chloride, etc. of Ca. La compounds may be oxides such as La.sub.2O.sub.3, hydroxides such as La(OH).sub.3; carbonates such as La.sub.2(CO.sub.3).sub.3.8H.sub.2O, etc. Compounds of the element A may be carbonates, oxides, chlorides, etc. of Ba and/or Sr. Iron compounds may be iron oxide, iron hydroxide, iron chloride, mill scale, etc. Co compounds may be oxides such as CoO, Co.sub.3O.sub.4, etc.; hydroxide such as CoOOH, Co(OH).sub.2, Co.sub.3O.sub.4.m.sub.1H.sub.2O (m.sub.1 is a positive number), etc.; carbonate such as CoCO.sub.3, etc.; and basic carbonates such as m.sub.2CoCO.sub.3.m.sub.3Co(OH).sub.2.m.sub.4H.sub.2O, etc. (m.sub.2, m.sub.3 and m.sub.4 are positive numbers).

(67) As described above, an entire amount of a raw material powder of Co (for example, Co.sub.3O.sub.4 powder) may be added in the mixing step of raw material powders (before calcining) (prior-addition method), or part or all of a raw material powder of Co may be added after calcining and before molding (post-addition method).

(68) During calcining, up to about 1% by mass of a B-containing compound such as B.sub.2O.sub.3, H.sub.3BO.sub.3, etc. may be added, if necessary, to accelerate a reaction. Particularly, the addition of H.sub.3BO.sub.3 is effective to improve H.sub.cJ and B.sub.r. The amount of H.sub.3BO.sub.3 added is preferably 0.3% by mass or less, most preferably about 0.2% by mass. Less than 0.1% by mass of H.sub.3BO.sub.3 has a small effect of improving B.sub.r, and more than 0.3% by mass of H.sub.3BO.sub.3 reduces B.sub.r. Also, because H.sub.3BO.sub.3 has an effect of controlling the shape and size of crystal grains during sintering, it may be added after calcining (before fine pulverization and before sintering), or both before and after calcining.

(69) The prepared raw material powders are mixed to provide a raw material powder mixture. The raw material powders may be mixed in a wet or dry manner. Stirring with media such as steel balls enables more uniform mixing of raw material powders. In wet mixing, water is preferably used as a solvent. To increase the dispersibility of raw material powders, known dispersants such as ammonium polycarboxylate, calcium gluconate, etc. may be used. The mixed raw material slurry may be calcined as it is or after dewatering.

(70) (b) Calcining Step

(71) The raw material powder mixture obtained by dry or wet mixing is heated in an electric furnace, a gas furnace, etc., to form a ferrite compound having a hexagonal M-type magnetoplumbite structure by a solid-phase reaction. This process is called calcining, and the resultant compound is called calcined body.

(72) The calcining step is conducted preferably in an atmosphere having an oxygen concentration of 5% or more. At an oxygen concentration of less than 5%, abnormal grain growth, the formation of foreign phases, etc. occur. The more preferred oxygen concentration is 20% or more.

(73) In the calcining step, a solid-phase reaction forming a ferrite phase proceeds more as the temperature is elevated. At a calcining temperature of lower than 1100 C., unreacted hematite (iron oxide) remains, resulting in low magnetic properties. At a calcining temperature exceeding 1450 C., crystal grains excessively grow, needing too much time for pulverization. Accordingly, the calcining temperature is preferably 1100-1450 C., more preferably 1200-1350 C. The calcining time is preferably 0.5-5 hours.

(74) When H.sub.3BO.sub.3 is added before calcining, a ferritization reaction is accelerated, so that calcining can be conducted at 1100-1300 C.

(75) (c) Addition of Sintering Aid

(76) SiO.sub.2 and CaCO.sub.3 are added as sintering aids. 0.1% or more and less than 1.5% by mass of SiO.sub.2 is added to 100% by mass of the raw material powder mixture, the calcined body or the calcined powder, after mixing the raw material powders and before molding. Namely, 0.1% or more and less than 1.5% by mass of SiO.sub.2 is added to 100% by mass of the raw material powder mixture (addition pattern 1), to 100% by mass of the calcined body (addition pattern 2), or to 100% by mass of the calcined powder (addition pattern 3), or in combination of these three patterns. When addition is conducted with the above patterns combined, SiO.sub.2 is added such that the total amount of SiO.sub.2 added in these patterns is 0.1% or more and less than 1.5% by mass.

(77) 0-2% by mass (as CaO) of CaCO.sub.3 is added to 100% by mass of the calcined body or powder after calcining and before molding. Namely, 0-2% by mass of CaCO.sub.3 is added to 100% by mass of the calcined body (addition pattern 4), or to 100% by mass of the calcined powder (addition pattern 5), or in both addition patterns 4 and 5. When CaCO.sub.3 is added in both patterns 4 and 5, the total amount of CaCO.sub.3 added in the patterns 4 and 5 should be 0-2% by mass.

(78) In the addition pattern 1 in which SiO.sub.2 is added to the raw material powder mixture, the timing of addition may be before, during or after the preparation of the raw material powder mixture. When SiO.sub.2 is added after the preparation, a raw material powder mixture is then further added. When SiO.sub.2 or CaCO.sub.3 is added to the calcined body (patterns 2 or 4) or to the calcined powder (patterns 3 or 5), a pulverization step may be conducted after adding sintering aids to the calcined body obtained by the calcining step; sintering aids may be added during the pulverization step; or the calcined powder after pulverized may be mixed with sintering aids and then molded.

(79) The addition of 1.5% or more by mass of SiO.sub.2 lowers H.sub.cJ, undesirably resulting in low B.sub.r and H.sub.k/H.sub.cJ. Though SiO.sub.2 is most preferably added to the calcined body, part of SiO.sub.2 may be added before calcining (in the mixing step of raw material powders) as described above. With SiO.sub.2 added before calcining, the size of crystal grains can be controlled during calcining.

(80) 0-2% by mass (as CaO) of CaCO.sub.3 is added to 100% by mass of the calcined body. The addition of CaCO.sub.3 improves B.sub.r and H.sub.cJ. More than 2% by mass of CaCO.sub.3 added undesirably lowers B.sub.r and H.sub.k/H.sub.cJ. In the present invention, the amount of CaCO.sub.3 added is expressed by an amount as CaO. The amount of CaCO.sub.3 added can be determined from the amount as CaO by the equation of (molecular weight of CaCO.sub.3amount as CaO)/molecular weight of CaO. For example, when 1.5% by mass (as CaO) of CaCO.sub.3 is added, the amount of CaCO.sub.3 added is [40.08 (atomic weight of Ca)+12.01 (atomic weight of C)+48.00 (atomic weight of O3)=100.09 (molecular weight of CaCO.sub.3)]1.5% by mass (amount as CaO)/[40.08 (atomic weight of Ca)+16.00 (atomic weight of O)=56.08 (molecular weight of CaO)]=2.677% by mass.

(81) Because the CaLaCo ferrite of the present invention contains Ca as a main phase component, the addition of SiO.sub.2 as a sintering aid makes it possible to form a liquid phase without adding CaCO.sub.3, enabling sintering. Though the present invention can be performed without adding CaCO.sub.3, CaCO.sub.3 is preferably added to prevent decrease in H.sub.cJ.

(82) In addition to SiO.sub.2 and CaCO.sub.3 described above, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, etc. can be added to improve magnetic properties, after calcining, or before molding as described below. Each is preferably 5% by mass or less.

(83) (d) Pulverization Step

(84) The calcined body is pulverized by a vibration mill, a ball mill, an attritor, etc. to provide a calcined powder. The calcined powder preferably has an average particle size of about 0.4-0.8 m (measured by an air permeation method). In the pulverization step, either dry pulverization or wet pulverization may be conducted, though both are preferably combined.

(85) Wet pulverization is conducted using water and/or a non-aqueous solvent (an organic solvent such as acetone, ethanol, xylene, etc.) as a dispersion medium. The wet pulverization prepares a slurry of the calcined powder in a dispersion medium. 0.2-2% by mass, as a solid component ratio, of known dispersant and/or surfactant are preferably added to the slurry. After the wet pulverization, the slurry is preferably concentrated and blended.

(86) In WO 2008/105449 A, a heat-treating and repulverizing step comprising a first fine pulverization step, a step of heat-treating powder obtained by the first fine pulverization step, and a second fine pulverization step of repulverizing the heat-treated powder is conducted as the pulverization step, thereby making the particle sizes of crystal grains smaller to increase the density of a magnet, and further controlling the shapes of crystal grains to improve magnetic properties. However, the present invention provides a sintered ferrite magnet having high B.sub.r and H.sub.cJ without the heat-treating and repulverizing step, by carrying out the above method on the calcined ferrite having the above composition.

(87) (e) Molding Step

(88) The slurry after the pulverization step is press-molded in a magnetic field or without a magnetic field, while removing a dispersion medium. Press-molding in a magnetic field can align the crystal orientations of powder particles, thereby drastically improving magnetic properties. Further, a dispersant and a lubricant may be added in an amount of 0.01-1% by mass each to improve orientation. Before molding, the slurry may be concentrated, if necessary. The concentration is preferably conducted by centrifugal separation, filter pressing, etc.

(89) (f) Sintering step

(90) The green body obtained by press-molding is degreased, if necessary, and then sintered. The sintering is conducted in an electric furnace, a gas furnace, etc. The sintering is preferably conducted in an atmosphere having an oxygen concentration of 10% or more. Less than 10% of the oxygen concentration causes abnormal grain growth, the formation of foreign phases, etc., thereby deteriorating magnetic properties. The oxygen concentration is more preferably 20% or more, most preferably 100%. The sintering temperature is preferably 1150-1250 C. The sintering time is preferably 0.5-2 hours. A sintered magnet obtained by the sintering step has an average crystal grain size of about 0.5-2 m.

(91) The sintered ferrite magnet is subjected to known production steps such as machining, cleaning, inspection, etc.

(92) [3] Sintered Ferrite Magnet

(93) The sintered ferrite magnet of the present invention produced by the above method comprises metal elements of Ca, La, Sr, Ba, Fe and Co, whose atomic ratios are represented by the general formula:
Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y)Fe.sub.2n-zCo.sub.z,
wherein 1xy, x and y are values in a region II defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate f: (0.221, 0.289, 0.490), a coordinate g: (0.221, 0.221, 0.558), a coordinate h: (0.295, 0.147, 0.558), a coordinate i: (0.346, 0.147, 0.507) and a coordinate e: (0.470, 0.200, 0.330) in a ternary diagram of x, y, and 1xy (see FIG. 2); and y and z, and n representing a molar ratio are values meeting

(94) 0.5y1,

(95) 0.147z<0.25, and

(96) 3.88<n<5.6;

(97) the sintered ferrite magnet having a residual magnetic flux density B.sub.r (mT) and an intrinsic coercivity H.sub.cJ (kA/m) at 23 C. meeting the relation of B.sub.r+H.sub.cJ/4535.5. The ternary diagram shown in FIG. 2 is the same as shown in FIG. 1, except for a region indicating the composition range.

(98) The sintered ferrite magnet of the present invention comprises as a main phase a ferrite phase having a hexagonal M-type magnetoplumbite structure. In general, a magnetic material, particularly a sintered magnet is composed of pluralities of compounds, and a compound determining its properties (physical properties, magnetic properties, etc.) is defined as a main phase. A main phase in the present invention, namely, a ferrite phase having a hexagonal M-type magnetoplumbite structure, determines the basic properties such as physical properties, magnetic properties, etc. of the sintered ferrite magnet of the present invention.

(99) Having a hexagonal M-type magnetoplumbite structure means that a hexagonal M-type magnetoplumbite structure is mainly observed in an X-ray diffraction pattern of the sintered ferrite magnet measured under a general condition.

(100) The sintered ferrite magnet of the present invention comprises a grain boundary phase containing Si. In the present invention, 0.1% or more and less than 1.5% by mass of SiO.sub.2 and 0-2% by mass (as CaO) of CaCO.sub.3 are added to 100% by mass of the calcined body in the production process as described above. SiO.sub.2 and CaCO.sub.3 mainly constitute the grain boundary phase. Accordingly, the grain boundary phase contains Si. Because it is difficult to observe the grain boundary phase by an X-ray diffraction pattern, it is preferably observed by a transmission electron microscope, etc.

(101) In the present invention, the grain boundary phase observed in an arbitrary cross section of the sintered ferrite magnet includes a linear grain boundary phase existing between main phases, which may be called two-grain boundary phase by those skilled in the art; and a grain boundary phase having a substantially polygonal (triangular) or irregular shape existing among three or more main phases, which may be called triplet-junction grain boundary phase by those skilled in the art.

(102) The sintered ferrite magnet of the present invention may contain a third phase containing a higher atomic ratio of La than in the main phase, in addition to the main phase and the grain boundary phase. The term third phase means a phase different from the main phase (first phase) and the grain boundary phase (second phase), but does not define its ratio, the order of precipitation, etc. The third phase is not indispensable in the present invention, meaning that the presence or absence of the third phase does not change the construction and effects of the present invention. The sintered ferrite magnet of the present invention may contain foreign phases (spinel phase, etc.) and impurity phases observed in trace amounts (about 5% or less by mass) by X-ray diffraction, etc. The quantitative determination of foreign phases by X-ray diffraction can be conducted by such a method as Rietveld analysis.

(103) The sintered ferrite magnet of the present invention has a high residual magnetic flux density B.sub.r (mT) and an high intrinsic coercivity H.sub.cJ (kA/m) at 23 C., which meet the relation of B.sub.r+H.sub.cJ/4535.5. Accordingly, the sintered ferrite magnet can be made fully thin for motors recently used in electric parts for automobiles.

(104) The present invention will be explained in further detail by Examples below, without intention of restricting the present invention thereto.

Example 1

(105) CaCO.sub.3 powder, La(OH).sub.3 powder, SrCO.sub.3 powder, BaCO.sub.3 powder, Fe.sub.2O.sub.3 powder and Co.sub.3O.sub.4 powder were mixed to compositions represented by the metal element composition formula (by atomic ratio) of Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z as shown in Table 1, and 0.1% by mass of H.sub.3BO.sub.3 powder was added to 100% by mass of each resultant mixture to prepare each raw material powder mixture. Each raw material powder mixture was wet-ball-milled for 4 hours, dried, granulated, and then calcined at 1250 C. for 3 hours in the air. Each resultant calcined body was coarsely pulverized to coarse powder by a hammer mill. Table 1 shows the compositions of calcined bodies.

(106) 100% by mass of each coarse powder was mixed with 0.7% by mass (as CaO) of CaCO.sub.3 powder, and 0.6% by mass of SiO.sub.2 powder, wet-ball-milled with water as a dispersion medium, and then finely pulverized to an average particle size of 0.6 m (measured by an air permeation method). Each resultant finely pulverized powder slurry was molded under pressure of about 50 MPa in a magnetic field of about 1.3 T in parallel with a compression direction, while removing the dispersion medium. Each resultant green body was sintered at about 1200 C. for 1 hour in the air to obtain each sintered magnet.

(107) The measurement results of B.sub.r and H.sub.cJ of the sintered magnets are shown in Table 1 and FIGS. 3-6. In Table 1, Samples with * are Comparative Examples. Samples 11-18 are Comparative Examples, which are based on the composition of Sample 13 described in Example of WO 2008/105449 A. The composition of Sample 13 used as Comparative Example is a typical composition of WO 2008/105449 A, because it is a base for many samples (Samples 29-40, 51-58, 64-79, 82, 85-92, 93-94, 101-102, 103-104, 131-136, 137-139, and 146-157) in Examples.

(108) TABLE-US-00001 TABLE 1 Sample 1-x-y x y y yy y(1-y) z n 1* 0.275 0.385 0.340 1.000 0.340 0 0.24 5.2 2 0.275 0.385 0.340 1.000 0.340 0 0.24 5.3 3 0.275 0.385 0.340 1.000 0.340 0 0.24 5.4 4 0.275 0.385 0.340 1.000 0.340 0 0.24 5.5 5* 0.275 0.385 0.340 1.000 0.340 0 0.24 5.6 6* 0.275 0.385 0.340 1.000 0.340 0 0.24 5.8 7* 0.375 0.385 0.240 1.000 0.240 0 0.24 5.2 8 0.375 0.385 0.240 1.000 0.240 0 0.24 5.3 9 0.375 0.385 0.240 1.000 0.240 0 0.24 5.4 10 0.375 0.385 0.240 1.000 0.240 0 0.24 5.5 11* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.0 12* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.2 13* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.4 14* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.6 15* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.8 16* 0.200 0.390 0.410 1.000 0.410 0 0.3 5.9 17* 0.200 0.390 0.410 1.000 0.410 0 0.3 6.0 18* 0.200 0.390 0.410 1.000 0.410 0 0.3 6.2 B.sub.r H.sub.cJ Sample (mT) (kA/m) B.sub.r + H.sub.cJ/4 1* 456.2 236.0 515.2 2 454.6 334.4 538.2 3 453.5 393.3 551.8 4 452.7 407.5 554.6 5* 447.0 352.0 535.0 6* 430.1 363.9 521.1 7* 454.0 239.0 513.8 8 453.6 330.1 536.1 9 454.7 366.9 546.4 10 444.9 364.4 536.0 11* 448.8 217.4 503.1 12* 454.6 222.6 510.2 13* 456.1 259.3 520.9 14* 454.8 348.4 541.9 15* 453.4 360.8 543.6 16* 451.2 301.4 526.6 17* 442.5 319.5 522.4 18* 428.8 310.3 506.4 Note: *indicates Comparative Example.

(109) FIGS. 3, 4 and 5 show the relation between a molar ratio n and B.sub.r and H.sub.cJ in calcined bodies for the sintered ferrite magnets of Samples 1-6, 7-10 and 11-18. In each figure, square points indicate B.sub.r, and triangular points indicate H.sub.cJ. In a ternary diagram of x, y, and 1xy expressing the composition of each calcined body, Samples 1-6 (FIG. 3) are (x, y, 1xy)=(0.385, 0.340, 0.275) in the region I, and Samples 7-10 (FIG. 4) are (x, y, 1xy)=(0.385, 0.240, 0.375) similarly in the region I, but Samples 11-18 are (x, y, 1xy)=(0.390, 0.410, 0.200) outside the region I.

(110) FIG. 6 shows the relation between H.sub.cJ and B.sub.r in Samples 1-18, with a dotted line of B.sub.r+H.sub.cJ/4=535.5. B.sub.r+H.sub.cJ/4 is 535.5 or more in an region on the upper right side from the line, and 535.5 or less in a lower left region. Square points indicate Samples 1-6 [(x, y, 1xy)=(0.385, 0.340, 0.275)], diamond points indicate Samples 7-10 [(x, y, 1xy)=(0.385, 0.240, 0.375)], and circular points indicate Samples 11-18 [(x, y, 1xy)=(0.390, 0.410, 0.200)]. The sintered ferrite magnets of the present invention (Samples 2-4 and 8-10) are indicated by black points.

(111) As shown in Table 1 and FIG. 3, at (x, y, 1xy)=(0.385, 0.340, 0.275) in the region I shown in FIG. 1, 5.2<n<5.6 provides a sintered ferrite magnet with high B.sub.r and high H.sub.cJ, but 5.2 or less of n provides low H.sub.cJ, and 5.6 or more of n provides lowered B.sub.r. Also, as shown in Table 1 and FIG. 4, at (x, y, 1xy)=(0.385, 0.240, 0.375) in the region I shown in FIG. 1, 5.3n5.5 provides a sintered ferrite magnet with high B.sub.r and high H.sub.cJ. By these results, the molar ratio n is limited to 5.2<n<5.6 in the calcined body of the present invention. On the other hand, as shown in Table 1 and FIG. 5, at (x, y, 1xy)=(0.390, 0.410, 0.200) outside the region I shown in FIG. 1, the maximum H.sub.cJ tends to be low, and the value of n providing the maximum H.sub.cJ and drastically reducing B.sub.r tends to be large (n5.6).

(112) Because a typical composition in Examples of WO 2008/105449 is (x, y, 1xy)=(0.390, 0.410, 0.200), the molar ratio n providing the maximum H.sub.cJ is in a range of n5.6. This result agrees with those shown in Tables 5 and 7 in WO 2008/105449 A. Samples 51-58 in Table 5 in WO 2008/105449 A are based on the composition of Sample 13 with the value of 12z (corresponding to 2n in the present invention) changed, and as shown in Table 7 in WO 2008/105449 A, the maximum H.sub.cJ is obtained in Sample 13, namely at 12z=12.00 (n=6), and the maximum B.sub.r is obtained in Sample 54, namely at 12z=11.8 (n=5.9). Though higher B.sub.r and H.sub.cJ are obtained in Examples of WO 2008/105449 A than in this Example, their values of B.sub.r and H.sub.cJ cannot simply be compared, because production conditions, etc. are different between this Example and Examples of WO 2008/105449 A.

(113) As shown in Table 1 and FIG. 6, all sintered ferrite magnets (black points) formed from the calcined bodies of the present invention, in which 1xy, x and y are in the region I shown in FIG. 1, and 5.2<n<5.6, meet the condition that B.sub.r+H.sub.cJ/4 is 535.5 or more, indicating excellent magnetic properties with high B.sub.r and high H.sub.cJ. Among Samples 11-18, which are Comparative Examples based on the composition described in Example of WO 2008/105449 A, Samples 14 and 15 meet the condition that B.sub.r+H.sub.cJ/4 is 535.5 or more. However, the Co content (z) is 0.3 in any of Samples 11-18, more than in Examples of the present invention [Co content (z)=0.24]. This makes sintered ferrite magnets more expensive, despite as high magnetic properties as in Examples of the present invention. Thus, using the calcined bodies of the present invention, sintered ferrite magnets having excellent magnetic properties with high B.sub.r and high H.sub.cJ can be obtained inexpensively.

(114) As described above, the calcined bodies of the present invention, in which 1xy, x and y are in the region I shown in FIG. 1, and 5.2<n<5.6, provide sintered ferrite magnets having high B.sub.r and high H.sub.cJ. On the other hand, sintered ferrite magnets having high magnetic properties are obtained at n5.6 in WO 2008/105449 A, different from the present invention.

Example 2

(115) Sintered magnets were produced in the same manner as in Example 1, except that raw material powders were mixed to the metal element composition formula (by atomic ratio) of Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z shown in Table 2. The compositions of the calcined bodies of Samples 3, 9 and 19-37 and the composition range of the calcined body in the present invention are shown in a ternary diagram of FIG. 7. The measurement results of B.sub.r and H.sub.cJ of the resultant sintered magnets are shown in Table 2 and FIG. 8. In Table 2, Samples with * are Comparative Examples.

(116) TABLE-US-00002 TABLE 2 Sample 1-x-y x y y yy y(1-y) z n 19* 0.425 0.385 0.190 1.000 0.190 0 0.24 5.4 9 0.375 0.385 0.240 1.000 0.240 0 0.24 5.4 20 0.325 0.385 0.290 1.000 0.290 0 0.24 5.4 3 0.275 0.385 0.340 1.000 0.340 0 0.24 5.4 21* 0.225 0.385 0.390 1.000 0.390 0 0.24 5.4 22* 0.175 0.385 0.440 1.000 0.440 0 0.24 5.4 23* 0.375 0.285 0.340 1.000 0.340 0 0.24 5.4 24 0.325 0.335 0.340 1.000 0.340 0 0.24 5.4 25* 0.225 0.435 0.340 1.000 0.340 0 0.24 5.4 26* 0.175 0.485 0.340 1.000 0.340 0 0.24 5.4 27* 0.275 0.285 0.440 1.000 0.440 0 0.24 5.4 28* 0.275 0.335 0.390 1.000 0.390 0 0.24 5.4 29 0.275 0.435 0.290 1.000 0.290 0 0.24 5.4 30* 0.275 0.485 0.240 1.000 0.240 0 0.24 5.4 31 0.375 0.335 0.290 1.000 0.290 0 0.24 5.4 32* 0.425 0.335 0.240 1.000 0.240 0 0.24 5.4 33 0.275 0.42 0.305 1.000 0.305 0 0.24 5.4 34 0.325 0.42 0.255 1.000 0.255 0 0.24 5.4 35 0.375 0.42 0.205 1.000 0.205 0 0.24 5.4 36 0.275 0.45 0.275 1.000 0.275 0 0.24 5.4 37 0.325 0.45 0.225 1.000 0.225 0 0.24 5.4 B.sub.r H.sub.cJ Sample (mT) (kA/m) B.sub.r + H.sub.cJ/4 19* 454.3 319.0 534.1 9 454.7 366.9 546.4 20 454.0 384.8 550.2 3 453.5 393.3 551.8 21* 450.6 337.0 534.9 22* 450.0 313.3 528.3 23* 446.4 255.0 510.2 24 451.0 380.4 546.1 25* 448.8 328.7 531.0 26* 449.3 308.1 526.3 27* 449.4 243.4 510.3 28* 448.7 309.9 526.2 29 453.3 341.0 538.6 30* 450.8 330.9 533.5 31 453.4 333.0 536.7 32* 453.1 288.8 525.3 33 451.2 361.2 541.5 34 452.5 374.9 546.2 35 451.8 384.6 548.0 36 452.0 344.8 538.2 37 452.0 357.6 541.4 Note: *indicates Comparative Example.

(117) FIG. 7 shows a region I of 1xy, x and y in the calcined body of the present invention, which is defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330); and circular and square points of 1xy, x and y of Samples 3, 9 and 19-37, in a ternary diagram of x, y, and 1xy. The compositions of the calcined ferrites of the present invention are shown by black square points, and those of Comparative Examples are shown by circular points.

(118) FIG. 8 shows the relation between H.sub.cJ and B.sub.r in Samples 3, 9 and 19-37, with a dotted line of B.sub.r+H.sub.cJ/4=535.5. B.sub.r+H.sub.cJ/4 is 535.5 or more in a region on the upper right side of this line, and 535.5 or less on the lower left side. In the figure, black square points indicate the sintered ferrite magnets of the present invention, and circular points indicate the sintered ferrite magnets of Comparative Examples.

(119) It is clear from Table 2 and FIGS. 7 and 8 that using calcined bodies, in which 1xy, x and y were in the region I defined by a coordinate a: (0.470, 0.297, 0.233), a coordinate b: (0.300, 0.392, 0.308), a coordinate c: (0.300, 0.300, 0.400), a coordinate d: (0.400, 0.200, 0.400) and a coordinate e: (0.470, 0.200, 0.330) in the ternary diagram of FIG. 7, and y, z and n met the requirements of the present invention, sintered ferrite magnets (shown by black square points in the figure) having excellent magnetic properties with high B.sub.r and high H.sub.cJ were obtained. All sintered ferrite magnets met B.sub.r+H.sub.cJ/4 of 535.5 or more.

Example 3

(120) Sintered magnets were produced in the same manner as in Example 1, except that raw material powders were mixed to the metal element composition formula (by atomic ratio) of Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z shown in Table 3. The measurement results of B.sub.r and H.sub.cJ of the sintered magnets are shown in Table 3 and FIGS. 9 and 10. In Table 3, Samples with * are Comparative Examples.

(121) TABLE-US-00003 TABLE 3 Sample 1-x-y x y y yy y(1-y) z n 3 0.275 0.385 0.340 1.000 0.340 0 0.24 5.4 38 0.275 0.385 0.340 0.882 0.300 0.040 0.24 5.4 39 0.275 0.385 0.340 0.735 0.250 0.090 0.24 5.4 40 0.275 0.385 0.340 0.588 0.200 0.140 0.24 5.4 41* 0.275 0.385 0.340 0.412 0.140 0.200 0.24 5.4 42* 0.275 0.385 0.340 0.265 0.090 0.250 0.24 5.4 43* 0.275 0.385 0.340 0.118 0.040 0.300 0.24 5.4 44* 0.275 0.385 0.340 0 0 0.340 0.24 5.4 B.sub.r H.sub.cJ B.sub.r + Sample (mT) (kA/m) H.sub.cJ/4 3 453.5 393.3 551.8 38 451.8 371.0 544.5 39 448.1 366.6 539.8 40 449.0 350.3 536.6 41* 450.2 335.7 534.1 42* 449.7 324.1 530.7 43* 448.2 320.1 528.2 44* 446.2 312.5 524.3 Note: *indicates Comparative Example.

(122) FIG. 9 shows the relation between y and B.sub.r and H.sub.cJ in calcined bodies for the sintered ferrite magnets of Samples 3 and 38-44. These samples of the calcined bodies had a composition (x, y, 1xy)=(0.385, 0.340, 0.275), which was in the region I in the ternary diagram of x, y, and 1xy shown in FIG. 1. In the figure, square points represent B.sub.r, and triangular points represent H.sub.cJ. FIG. 10 shows the relation between H.sub.cJ and B.sub.r in the sintered ferrite magnets of Samples 3 and 38-44, with a dotted line of B.sub.r+H.sub.cJ/4=535.5. B.sub.r+H.sub.cJ/4 was 535.5 or more in a region on the upper right side of this line, and 535.5 or less in a region on the lower left side. The sintered ferrite magnets of the present invention are indicated by black square points, and the sintered ferrite magnets of Comparative Examples are indicated by circular points.

(123) As shown in Table 3 and FIG. 9, though 0.412 or less of y in the calcined body provides low H.sub.cJ, 0.5y1 provides a sintered ferrite magnet with high B.sub.r and high H.sub.cJ. By these results, y is limited to 0.5y1 in the calcined body. It is clear from FIG. 10 that all the sintered ferrite magnets of the present invention with 0.5y1 (shown by black square points in the figure) meet B.sub.r+H.sub.cJ/4=535.5 or more, providing excellent magnetic properties with high B.sub.r and high H.sub.cJ.

Example 4

(124) CaCO.sub.3 powder, La(OH).sub.3 powder, SrCO.sub.3 powder, BaCO.sub.3 powder, Fe.sub.2O.sub.3 powder and Co.sub.3O.sub.4 powder were mixed to the ratios shown in Table 4 (the values of z are shown in the column of When Mixed) in the metal element composition formula (by atomic ratio) of Ca.sub.1-x-yLa.sub.x(Sr.sub.yBa.sub.1-y).sub.yFe.sub.2n-zCo.sub.z, and 100% by mass of the mixed powders were mixed with 0.1% by mass of H.sub.3BO.sub.3 powder to obtain a raw material powder mixture. The molar ratio n was 5.4 (when mixed) in Samples 3 and 45-49 (prior-addition method), and 5.4 (when Co.sub.3O.sub.4 powder was added during fine pulverization, namely in a mixture of the calcined body and Co.sub.3O.sub.4 powder without a sintering aid) in Samples 50-54 (post-addition method). Incidentally, n was 5.38 (when mixed) in Sample 50, 5.355 (when mixed) in Sample 51, 5.33 (when mixed) in Sample 52, 5.305 (when mixed) in Sample 53, and 5.28 (when mixed) in Sample 54. Each raw material powder mixture was wet-ball-milled for 4 hours, dried, granulated, and then calcined at 1250 C. for 3 hours in the air. Each resultant calcined body was coarsely pulverized by a hammer mill to obtain coarse powder.

(125) 100% by mass of each coarse powder was mixed with 0.7% by mass (as CaO) of CaCO.sub.3 powder and 0.6% by mass of SiO.sub.2 powder, as well as Co.sub.3O.sub.4 powder in such an amount as having z shown in the column of When Finely Pulverized in Table 4, wet-ball-milled with water as a dispersion medium, and then finely pulverized to an average particle size of 0.6 m (measured by an air permeation method). The finely pulverized powder slurry was molded under pressure of about 50 MPa in a magnetic field of about 1.3 T in parallel with a compression direction, while removing the dispersion medium. The resultant green body was sintered at about 1200 C. for 1 hour in the air, to obtain sintered magnets.

(126) The measurement results of B.sub.r, H.sub.cJ and H.sub.k.H.sub.cJ.sup.1(H.sub.k/H.sub.cJ) of the sintered magnets are shown in Table 4 and FIGS. 11-13. In Table 4, Samples with * are Comparative Examples. FIG. 11 shows the relation between z and B.sub.r and H.sub.cJ, with square points representing B.sub.r, and triangular points representing H.sub.cJ. FIG. 12 shows the relation between z and H.sub.k/H.sub.cJ. In H.sub.k/H.sub.cJ, H.sub.k represents the value of H at a position in the second quadrant at which J is 0.95 B.sub.r in a curve of J (intensity of magnetization) to H (intensity of magnetic field).

(127) TABLE-US-00004 TABLE 4 z When When Finely Sample 1-x-y x y y yy y(1-y) Mixed Pulverized 45* 0.275 0.385 0.340 1.000 0.340 0 0.18 0 46 0.275 0.385 0.340 1.000 0.340 0 0.2 0 47 0.275 0.385 0.340 1.000 0.340 0 0.22 0 48 0.275 0.385 0.340 1.000 0.340 0 0.23 0 3 0.275 0.385 0.340 1.000 0.340 0 0.24 0 49* 0.275 0.385 0.340 1.000 0.340 0 0.25 0 50 0.275 0.385 0.340 1.000 0.340 0 0.2 0.04 51 0.275 0.385 0.340 1.000 0.340 0 0.15 0.09 52 0.275 0.385 0.340 1.000 0.340 0 0.1 0.14 53 0.275 0.385 0.340 1.000 0.340 0 0.05 0.19 54 0.275 0.385 0.340 1.000 0.340 0 0 0.24 B.sub.r H.sub.cJ Sample (mT) (kA/m) H.sub.k/H.sub.cJ B.sub.r + H.sub.cJ/4 45* 451.8 332.5 0.943 534.9 46 452.6 358.9 0.905 542.3 47 453.1 373.4 0.857 546.4 48 452.9 381.5 0.818 548.3 3 453.5 393.3 0.842 551.8 49* 453.9 390.0 0.761 551.4 50 450.8 389.6 0.834 548.2 51 447.8 394.2 0.822 546.3 52 447.9 387.1 0.811 544.7 53 447.8 393.8 0.832 546.2 54 447.1 393.6 0.818 545.5 Note: *indicates Comparative Example.

(128) FIG. 13 shows the relation between H.sub.cJ and B.sub.r in Samples 3 and 45-54, with a dotted line of B.sub.r+H.sub.cJ/4=535.5. B.sub.r+H.sub.cJ/4 was 535.5 or more in a region on the upper right side of the line, and 535.5 or less in a region on the lower left side. The sintered ferrite magnets of the present invention are indicated by black square points, and the sintered ferrite magnets of Comparative Examples are indicated by circular points.

(129) As shown in Table 4 and FIG. 11, a calcined body meeting 0.2z<0.25 provides a sintered ferrite magnet with high B.sub.r and high H.sub.cJ. As shown in Table 4 and FIG. 12, Sample 49 (z=0.25) of Comparative Example has so drastically reduced H.sub.k/H.sub.cJ that it cannot provide recently demanded thin sintered ferrite magnets, despite high B.sub.r and high H.sub.cJ. By these results, z in the calcined body is limited to 0.2z<0.25.

(130) As shown in FIG. 13, all the sintered ferrite magnets of the present invention (shown by black square points in the figure) obtained from the calcined bodies with 0.2z<0.25 had excellent magnetic properties with high B.sub.r and high H.sub.cJ, meeting B.sub.r+H.sub.cJ/4=535.5 or more. Further, high B.sub.r and high H.sub.cJ were obtained by any of the prior-addition method in which all of Co was added during mixing, and the post-addition method in which part or none of Co was added during mixing and then remaining part or all of Co was added during fine pulverization.

Example 5

(131) CaCO.sub.3 powder, La(OH).sub.3 powder, SrCO.sub.3 powder, BaCO.sub.3 powder, Fe.sub.2O.sub.3 powder and Co.sub.3O.sub.4 powder were mixed to a metal element composition of Ca.sub.0.275La.sub.0.385Sr.sub.0.340Fe.sub.10.56Co.sub.0.24 (by atomic ratio), and 100% by mass of the mixed powders were then mixed with 0.1% by mass of H.sub.3BO.sub.3 powder to prepare a raw material powder mixture. The raw material powder mixture was wet-ball-milled for 4 hours, dried, granulated, and then calcined at 1250 C. for 3 hours in the air. The calcined body was coarsely pulverized by a hammer mill to obtain a coarse powder.

(132) CaCO.sub.3 powder and SiO.sub.2 powder in amounts shown in Table 5 were added to 100% by mass of the coarse powder. The amount of CaCO.sub.3 powder added is expressed by the amount of CaO. Next, fine pulverization was conducted by a wet ball mill with water as a dispersion medium, to an average particle size of 0.6 m (measured by an air permeation method). The finely pulverized powder slurry was molded under pressure of about 50 MPa in a magnetic field of about 1.3 T in parallel with a compression direction, while removing the dispersion medium. The resultant green body was sintered at about 1200 C. for 1 hour in the air, to obtain a sintered magnet.

(133) The measurement results of B.sub.r and H.sub.cJ of the sintered magnet are shown in Table 5 and FIG. 14. In Table 5, Samples with * are Comparative Examples. FIG. 14 shows the relation between H.sub.cJ and B.sub.r in Samples 3 and 55-64, with a dotted line of B.sub.r+H.sub.cJ/4=535.5. B.sub.r+H.sub.cJ/4 is 535.5 or more in a region on the upper right side of the line, and 535.5 or less in a region on the lower left side. Black square points indicate the sintered ferrite magnets of the present invention, and circular points indicate the sintered ferrite magnets of Comparative Examples.

(134) TABLE-US-00005 TABLE 5 CaO SiO.sub.2 B.sub.r H.sub.cJ B.sub.r + Sample (% by mass) (% by mass) (mT) (kA/m) H.sub.cJ/4 55 0 0.2 459.4 324.6 540.6 56 0.1 0.2 458.3 316.0 537.3 57 0.2 0.3 454.8 349.5 542.2 58 0.3 0.4 455.3 381.1 550.6 59 0.5 0.5 451.8 404.7 553.0 3 0.7 0.6 453.5 393.3 551.8 60 1.1 0.8 443.4 434.1 551.9 61 1.5 1.2 437.7 400.5 537.8 62 1.8 1.2 439.4 411.5 542.3 63* 2.1 1.2 440.8 345.6 527.2 64* 1.5 1.5 428.4 336.7 512.6 Note: *indicates Comparative Example.

(135) As shown in Table 5 and FIG. 14, high B.sub.r and H.sub.cJ were obtained in wide ranges of CaCO.sub.3 (as CaO) and SiO.sub.2, providing sintered ferrite magnets having excellent magnetic properties with B.sub.r+H.sub.cJ/4=535.5 or more. However, 2.1% or more by mass (as CaO) of CaCO.sub.3 and 1.5% or more by mass of SiO.sub.2 lower B.sub.r and H.sub.cJ, failing to provide recently demanded thin sintered ferrite magnets.

Example 6

(136) The sintered ferrite magnets of Sample 3 in Example 1, Samples 31 and 32 in Example 2, and Samples 55, 61 and 63 in Example 5 were subjected to component analysis by an ICP atomic emission spectrometer (ICPV-1017 available from Shimadzu Corporation), to determine the atomic ratios of metal elements and the molar ratios n. The results are shown in Table 6. In the atomic ratios of metal elements and the molar ratios n determined from component analysis, the amount of SiO.sub.2 is expressed by a ratio (% by mass) to 100% by mass of the total amount of CaCo.sub.3, La(OH).sub.3, SrCO.sub.3, Fe.sub.2O.sub.3, and Co.sub.3O.sub.4.

(137) TABLE-US-00006 TABLE 6 Sample 1 x y x y y yy 3 0.352 0.349 0.299 0.990 0.296 31 0.441 0.301 0.258 0.988 0.255 33* 0.484 0.301 0.214 0.991 0.212 55 0.280 0.383 0.337 0.988 0.333 61 0.417 0.310 0.273 0.989 0.270 63* 0.457 0.290 0.253 0.988 0.250 SiO.sub.2 Sample y(1 y) z n (% by mass) 3 0.003 0.215 5.06 0.57 32 0.003 0.213 4.96 0.57 33* 0.002 0.212 4.98 0.57 56 0.004 0.236 5.48 0.24 62 0.003 0.190 4.50 1.10 64* 0.003 0.177 4.23 1.09 Note: *indicates Comparative Example.

(138) It is clear that in the sintered ferrite magnets of the present invention, the values of 1xy, x and y are in the region II shown in FIG. 2, and those of y and z and n representing a molar ratio meet 0.5y1, 0.147z<0.25, and 3.88n<5.6.

Effect of the Invention

(139) The use of the calcined ferrite of the present invention can provide a sintered ferrite magnet having high B.sub.r and high H.sub.cJ. Because the Co content can be reduced than in conventional CaLaCo ferrites, sintered ferrite magnets having high B.sub.r and high H.sub.cJ can be obtained inexpensively.

(140) Because the sintered ferrite magnet of the present invention has a high residual magnetic flux density B.sub.r (mT) and a high intrinsic coercivity H.sub.cJ (kA/m) at 23 C., meeting the relation of B.sub.r+H.sub.cJ/4535.5, it can be made fully thin.

(141) The sintered ferrite magnets of the present invention can provide parts for automobile electric parts, electric equipments, etc., such as various motors, electric generators, speakers, etc., which have high performance with reduced size and weight.