Process for producing ferromagnetic powder

Ferromagnetic powders comprising cobalt and/or nickel are produced by reducing cobalt and/or nickel salts in an aqueous solution containing hypophosphite ions while applying a magnetic field.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
This invention relates to a process for producing powders of ferromagnetic 
metals, and more particularly to a process for producing powders of 
ferromagnetic metals having a square hysteresis loop suited for use in 
magnetic recording tape, a high coercive force and high maximum residual 
flux density. 
2. DESCRIPTION OF THE PRIOR ART 
Feroxide ferromagnetic powders, such as .gamma.-Fe.sub.2 O.sub.3 and 
Fe.sub.3 O.sub.4 hitherto used for producing magnetic recording tape, are 
not suited for recording signals of ultra-short wave lengths (less than 10 
.mu.) or high density magnetic recording since the coercive force and the 
maximum residual flux density thereof are insufficient. 
Recently, many studies have been made to find ferromagnetic materials 
having magnetic properties suited for high density magnetic recording. 
Suitable ferromagnetic metal powders discovered include pure metal powders 
such as Co powder or Ni powder, and alloy powders composed mainly of at 
least two metals selected from Co, Ni and Fe. 
These ferromagnetic powders are produced by the following known processes: 
1. Reducing the oxalate of a metal capable of forming the ferromagnetic 
body in flowing H.sub.2 gas at high temperatures. (see Japanese Patent 
Publications 11412/61, 22230/61, 8027/65, 14818/66 and 22394/68) 
2. Reducing goethite or accicular .gamma.-Fe.sub.2 O.sub.3 in flowing 
H.sub.2 gas at high temperatures. (see Japanese Patent Publications 
3862/60 and 20939/64) 
3. Evaporating a ferromagnetic metal in an inert gas atmophere. (see 
"Applied Physics" vol. 40, No. 1, p, 110 (1971)) 
4. Reducing a salt of a metal capable of forming the ferromagnetic body in 
a solution of the salt using a borohydride. (see Japanese Patent 
Publications 20116/68 and 26555/63, and "Television", Vol. 19, No. 1, p, 
19 (1965)) 
5. Decomposing a carbonyl of a metal capable of forming the ferromagnetic 
body. (see U.S. Pats. Nos. 2,983,997, 3,172,776, 3,200,007, and 3,228,882) 
6. Electrolytically depositing a ferromagnetic metal using an Hg cathode 
and separating the deposited metal from Hg by heating. (see Japanese 
Patent Publications 15525/64 and 8123/65) 
According to processes (1) and (2) the volume of the metal powder is 
decreased during the high temperature reducing treatment, thus causing 
intergranular voids or aperatures, sintering of the powder, activation of 
the powder surface and deformation of the powder shape are caused during 
the reducing treatment at temperatures higher than 300.degree. C in the 
flowing H.sub.2 gas, thus causing irregular dispersion of the 
ferromagnetic powder in a binder and causing the ferromagnetic powder to 
exhibit insufficient ferromagnetic properties. 
According to processes (1), (2) and (3) the metal powder after the reducing 
or evaporating treatment poses a danger of ignition due to the highly 
active powder surface, and accordingly treating and handling of the metal 
powder are very disadvantageousfrom the commercial viewpoint. 
Although wet processes (4), (5) and (6) eliminate the inherent defects of 
dry processes (1), (2) and (3), the ferromagnetic metal powder obtained, 
for example by process (4), is accicular and easily broken during mixing 
and dispersing in a binder, thus lowering the orientation property in a 
magnetic field. This is observed as an inferior squareness ratio (Br/Bs). 
In addition, processes (5) and (6) require careful handling or poisonous 
and dangerous materials such as metal carbonyls and mercury. 
SUMMARY OF THE INVENTION 
Therefore, one object of this invention is to eliminate the aforesaid 
defects and problems in conventional processes and to provide a novel 
process for producing ferromagnetic metal powder having a square 
hysteresis loop ratio whereby the coercive force may be easily controlled 
as desired. 
The process of the present invention is characterized in reducing nickel 
and/or cobalt salts in an aqueous solution which contains hypophosphite 
ions and an organic solvent while applying a magnetic field to the aqueous 
solution. While nickel and/or cobalt salts are the main components which 
form the ferromagnetic product, small proportions of other materials to be 
incorporated into the ferromagnetic material may be present. 
DETAILED DESCRIPTION OF THE INVENTION 
The term "salts of metals indispensably containing Co or Ni as the main 
component and capable of forming the ferromagnetic body" means metal salts 
containing indispensably Co and/or Ni as the main component and a very low 
amount of La, Ce, Nd, Sm, Al, S, Cr, Mn, Fe, Cu, Zn and so on, e.g., 0.1 - 
10%, preferably 0.1 - 5%, by weight, for improving the magnetic 
properties. Among these metal salts there can be exemplified sulfates, 
chlorides, nitrates, formates, acetates, sulfamates and hypophosphates of 
the metals. 
Preferred systems thus comprise 0.1 - 5% by weight of the salts of metals 
which improve the magnetic properties set out above, balance Co and/or Ni, 
and, as explained below, low proportion of phosphate derived from the 
hypophosphite ions present. The invention includes, however, embodiments 
of Co and/or Ni plus several percent of phosphorous without such metals 
which improve the powder properties. 
According to the process of this invention, these metal salts are dissolved 
in water and a reducing reaction is conducted in the aqueous solution. The 
concentration of the aqueous solution must be such that the metal ions in 
the solution are not in a state of supersaturation. Too high a 
concentration of the metal ions requires an excess amount of complexing 
agent and increases the production cost of the ferromagnetic powder. On 
the other hand, too low a concentration of the metal ions reduces the 
yield of the ferromagnetic alloy powder and the efficiency of the process. 
Therefore, the concentration of metal ions the aqueous solution is usually 
in the range of 0.001 - 1 mol of metal ions per liter, more preferably 
0.001 - 0.5 mol/l. 
Hypophosphite ion is present in the aqueous solution together with the 
metal salts. The hypophosphite ion provides the reducing action, and is 
formed by dissolving a compound such as hypophophorous acid, an alkali 
metal hypophosphite such as potassium or sodium hypophosphite, an alkaline 
earth metal hypophosphite such as magnesium, calcium or barium 
hypophosphite, or a bivalent metal hypophosphite such as nickel 
hypophosphite, cobalt hypophosphite, iron hypophosphite, ferric 
hypophosphite, zinc hypophosphite, manganese hypophosphite, lead 
hypophosphite, cerium hypophosphite or cerous hypophosphite in the aqueous 
solution, or a mixture thereof. The reaction between the hypophosphite ion 
and the metal salts causes the deposition of the ferromagnetic metal or 
alloy. The amounts of materials added to the aqueous solution which 
provide hypophosphite ion preferably range from 0.001 mol/liter to 10 
mol/liter, most preferably 0.01 to 2 mol/liter. The concentration of the 
materials yielding hypophosphite ions in the aqueous solution is not 
restricted to this range but may be changed in accordance with changes of 
the reaction temperature, pH and the kind of the metal salts. Usually, 
however, the reaction temperature is from about 65.degree. C to about 
95.degree. C and the pressure is from about 0.5 to about 5 atmospheres. 
Pressure is not overly critical. The pH is greater than 5, preferably 8 - 
12. 
In addition to the metal salts, water hypophosphite ion and an organic 
solvent, other components such as a pH buffering agent, complexing agent 
or pH buffering/complexing agent can be added to modify the reaction 
conditions used. The ph buffering agent can be added to prevent changes in 
pH during the course of the reaction, and the complexing agent can be 
added to prevent any precipitation during reaction. The pH 
buffer/complexing agent serves both functions. 
As examples of suitable pH buffering and complexing agents, there are 
formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 
acrylic acid, trimethylacetic acid, benzoic acid, chloracetic acid or like 
monocarboxylic acids or monocarboxinates. 
Examples of complexing agents which can be used in the present invention 
include succinic acid, malonic acid, maleic acid, itaconic acid, 
p-phthalic acid and like dicarboxylic acids and dicarboxylic acid metal 
esters, or glycolic acid, lactic acid, salicylic acid, tartaric acid, 
citric acid or like oxycarboxylic acids and metal oxycarboxylic acid 
esters. 
Representative of the metal esters of monocarboxylic acids, dicarboxylic 
acids or oxycarboxylic acids referred to above are those wherein the metal 
is an alkali metal such as sodium, potassium, etc., or an alkaline earth 
metal such as magnesium, calcium, etc. 
Boric acid, carbonic acid, sulfurous acid and like acids may be used as 
pH-buffering and adjusting agents. The pH buffering agent, complexing 
agent, etc. are usually added to elevate the pH to a pH greater than pH 5, 
preferably pH 8 - 12. 
Other inorganic acids, organic acids, ammonium and alkali hydroxides can be 
used as the pH adjusting materials, e.g., inorganic acids such as sulfuric 
acid, hydrochloric acid or nitric acid, organic acids such as acetic acid, 
succinic acid, malonic acid, maleic acid, itaconic acid or p-phthalic 
acid, alkali metal hydroxides such as sodium hydroxide or potassium 
hydroxide, etc. 
These compounds can be added to the aqueous solution to assist the reducing 
reaction. Some of these compounds may effect two or more actions, for 
example, some of them serve not only as a complexing agent but also as a 
pH buffer. 
By adding ions of precious metals, such as Pd, Au, Ag or Pt, to the 
reaction bath as nuclei to initiate the reaction and adding the organic 
solvent, which is peculiar to this invention, to the reaction bath, the 
ferromagnetic metal powder can be reduced and deposited directly from the 
reaction bath. Usually the initiator is used in an amount of from 1 
.times. 10.sup.-6 to 1 .times. 10.sup.-1 moles per liter, preferably 1 
.times. 10.sup.-5 to 1 .times. 10.sup.-3 moles per liter. 
There is no particular limitation on the types of organic solvents which 
can be used in the present invention to percipitate the ferromagnetic 
powders. The organic solvent must, of course, have a melting point lower 
than the reaction temperature and must be completely soluble in the 
aqueous solution. Further, the organic solvent must not react with any of 
the components of the aqueous bath at the reaction temperature. Other than 
this, any organic solvent which is not unduly volatile may be used. 
However, by using certain organic solvents as explained in detail below, 
extremely preferred results are obtained in that the characteristics of 
the ferromagnetic powder obtained can be adjusted by the selection of the 
solvent or solvents used. 
Examples of organic solvents added to the reaction bath include methyl 
alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, benzyl alcohol, 
furfuryl alcohol, ethylene glycol and like alcohols; acetone, methyl ethyl 
ketone, diethyl ketone, methyl isobutyl ketone and like ketones; phenol, 
cresol and like phenols; benzene toluene, xylene and like aromatic 
hydrocarbons; tetrachloroethylene, carbon tetrachloride, halogenated 
hydrocarbon such as tetrachloroethylene, carbon tetrachloride, Freon, and 
the like; methyl formate, methyl acetate, ethyl acetate, butyl acetate, 
ethyl propionate, ethyl butyrate, methyl tartarate and like esters between 
a lower fatty acid such as formic acid, acetic acid, glacial acetic acid, 
propionic acid, glycolic acid, etc. and an alcohol; ethylene diamine, 
pyridine, triethanolamine and like amines; formic acid, acetic acid, 
propionic acid and like lower fatty acids. These organic solvents must 
have the melting point lower than the temperature of the reacting bath. 
The amount of organic solvent or mixture thereof which is added to the 
reacting bath is preferably in the range of 0.01 - 5 mol/l of all other 
components of the bath, i.e., the aqueous bath without organic solvent. 
The addition of the alochols, ketones, phenols, esters, aromatic 
hydrocarbons or amines to the reaction bath improves the squareness ratio 
of the hysteresis loop resulting ferromagnetic metal or alloy powder. The 
addition of the alcohols or esters to the reaction bath increases the 
coercive force of the resulting ferromagnetic metal or alloy powder, and 
the coercive force can be adjusted in the range of 700 - 1200 o.e. by 
controlling the amount of the alcohol or ester. On the other hand, the 
halogenated hydrocarbons, the lower fatty acids and the phenols improve 
the squareness ratio of the hysteresis loop but decrease the coercive 
force. 
The coercive force can be controlled to be within the range of 300 - 700 
o.e. by changing the amount of the halogenated hydrocarbons, the lower 
fatty acids or the phenols. In order to obtain ferromagnetic metal or 
alloy particles having the desired magnetic properties, a suitable organic 
solvent or mixture of solvents is selected. 
The organic solvent may be added to the reaction bath at any time before or 
after the start of the reducing reaction, but preferably it is added at 
the start of the reducing reaction. 
Preferred solvents within the above classes are alcohols of from 1 to 10 
carbon atoms, ketones of the formula 
##STR1## 
wherein R is C.sub.n H.sub.2n+1, R' is C.sub.m H.sub.2m+1, n is an integer 
of from 1 to 4 and m is an integer of from 1 to 4, phenols where the 
aromatic nucleous has from 1 to 3 hydroxyl groups, aromatic hydrocarbon 
wherein the benzene ring has an alkyl group having from 1 to 3 carbon 
atoms, chlorinated hydrocarbons wherein the hydrocarbon contains from 1 to 
3 carbon atoms substituted with from 1 to 4 chlorine atoms, and lower 
fatty acids having from 1 to 10 carbon atoms. 
The magnetic field applied to the reaction bath can be a direct current 
magnetic field, a pulsing magnetic field or an alternating current 
magnetic field, and the pulsing magnetic field is effective to reduce the 
size of the resulting ferromagnetic powder without worsening the 
uniformity or toughness of the resulting ferromagnetic powder. Generally a 
magnetic field of 10 - 10,000 oersteds (oe), preferably 500 - 5,000 oe, 
provides best results. 
Preferred bounds exist for the magnetic field used, i.e., a pulsing field 
of 10 - 10,000 oe, preferably 500 - 5,000 oe, and a pulsing time of 0.1 
milli second - 10 seconds with and internal time of 1/10 - 100 times the 
pulsing time. The magnetic field is applied during the whole reaction 
period. 
In the case that the ferromagnetic metal powder obtained under a pulsing 
magnetic field is used to produce a recording tape, the surface of the 
tape is improved for such use and the electromagnetic performance of the 
tape is greatly improved, i.e., the information conversion capability. 
The effective pH for the reducing reaction of the process of this invention 
is greater than 5, preferably from 8 - 12. 
The temperature for the reducing reaction is not particularly restricted, 
but reaction is usually conducted between -10.degree. to 100.degree. C, 
preferably 65.degree. to 95.degree. C. 
The ferromagnetic metal powder obtained by the process of this invention 
has the coercive force (Hc) of more than 300 oe and a saturated magnetism 
(4.pi.IS) of more than 8,000 G/cc, and comprises as a main component Co 
and/or Ni and several percent of P, e.g., usually 0.5 - 15 percent by 
weight based on powder weight. The desired grain size of the ferromagnetic 
metal or alloy powder is obtained by changing the reacting conditions, 
e.g., at higher temperatures larger grains are obtained. The grain size is 
generally 100A to 2.mu. at the temperature ranges provided above. 
According to the process of this invention the squareness ratio of the 
hysteresis loop of the ferromagnetic metal or alloy powder obtained is 
remarkably increased, the coercive force can be controlled within the 
range of 300 - 1200 oe by selecting the kind of the organic solvent, the 
grain size of the powder can be kept uniform, the ratio of the length to 
the width of the powder grains can be increased, and the strength and 
toughness of rod shaped powder grain is increased, whereby the dispersion 
of the powder in a binder and the magnetic orientation of the powder after 
coating are much improved, and a magnetic recording material made from the 
ferromagnetic metal powder has an extremely high squareness ratio. 
The magnetic properties of the ferromagnetic metal or alloy powder obtained 
by the process of this invention are further improved by heating in a 
non-oxidizing environment, e.g., in a vacuum or in a flowing N.sub.2, 
CO.sub.2 CO or H.sub.2 gas stream and the oxidation resistance of the 
ferromagnetic powder can be improved by heating the latter in an 
atmosphere containing very small amounts of moisture and oxygen. The 
conditions used are the same described on Japanese Patent Publication No. 
16052/1972 (published December 5, 1972), that is, heating temperature at 
greater than 100.degree. C, preferably more than 200.degree. C for 30 
minutes - 24 hours at a pressure less than 100 torr. 
The ferromagnetic powders of this invention preferably have a grain size 
distribution with the range of 100A - 2 .mu..

Particular embodiments of this invention will now be illustrated by several 
examples and comparative examples, where operation was always under 
atmospheric pressure unless otherwise indicated. All grain sizes were 
determined using an electron microscope and X-ray diffraction. 
EXAMPLE 1 
__________________________________________________________________________ 
Liquid A Liquid B Liquid C Liquid D 
__________________________________________________________________________ 
Co chloride 
10g 
Na hypo- Pd chloride n-Butyl 
Na tartarate 
50g 
phospharite 
20g 0.03% aqueous 
alcohol 
50cc 
Boric acid 
15g 
Water 50cc 
solution (by) 
Water 300cc weight) 10cc 
__________________________________________________________________________ 
Liquid A, Liquid B and water were mixed with each other to obtain 500 cc of 
an aqueous solution and the pH of the solution was adjusted to 8.5 - 9.0 
by adding an aqueous caustic soda solution. Liquid C was then added to the 
resulting solution while keeping the temperature of the solution at 
90.degree. C, a direct current magnetic field of 2,000 Gauss was applied 
to the solution and the solution agitated. Liquid D was successively added 
to the solution and the pH of the solution obtained was again adjusted to 
8.5 - 9.0, continuing magnetic field application and agitation until the 
precipitation was complete. H.sub.2 gas bubbles occurred while reacting 
because of the use of hypophosphite. The precipitate caused by the 
reducing reaction was washed with water and dried to obtain 2.4 g of 
ferromagnetic alloy powder. The mean length of the powder grains was 1.2 
.mu. and the ratio of the length to the width of the grains was about 8:1, 
each grain being shaped like a rod. The coercive force and the saturated 
magnetism were 650 oe and 15,000 G/cc, respectively. 
The ferromagnetic metal powder obtained was dispersed in a coating liquid 
containing a binder composed mainly of a vinyl chloride vinyl acetate 
copolymer in an amount of 3 times the amount of powder by weight (8% by 
weight in butylacetate of binder (6 g) and ferromagnetic metal powder (2 
g), and the dispersion was coated on a plastic film to produce a magnetic 
recording tape. The squareness ratio of the hysteresis loop of the 
magnetic recording tape was 0.85. 
COMATIVE EXAMPLE 1 
A ferromagnetic alloy powder was produced according to the same process as 
described in Example 1 except Liquid D was not added to Liquid A, Liquid B 
and Liquid C. The amount of powder produced was also 2.4 g, but the powder 
had a mean grain length of 2.5 .mu. and a ratio of length to width of 
about 6:1. The powder grain was thus shaped like a large rod. The magnetic 
properties of the ferromagnetic alloy powder were almost equal to those of 
the powder obtained in Example 1. 
The squareness ratio produced with this ferromagnetic metal powder was 
0.70. Although the magnetic properties of this powder were almost equal to 
those of the powder obtained in Example 1, the magnetic properties of the 
resulting magnetic tape made from this powder were considerably reduced as 
compared with those of the magnetic tape made from the powder in Example 
1. This result was considered to be caused by the difference between the 
grain sizes of the powders, and therefore both magnetic layers on both 
tapes were inspected and compared by a scanning type electron microscope. 
As a result of electron microscope inspection it was found the powder of 
Example 1 exhibited grains of a slender rod like shape and a uniform grain 
size distribution, and the grains were scarcely broken after being mixed 
with and dispersed in the binder to produce the magnetic tape but the 
powder of Comparative Example 1 exhibited grains shaped like rough of rods 
and a varying grain size distribution, and the grains were broken after 
being mixed with and dispersed in the binder, thus bringing out the 
remarkable difference between the squareness ratios of both magnetic 
tapes. 
As particularly described above, the addition of the alcohol to the 
reacting system just at the start of the reducing reaction is effective to 
render the grain size uniform, to increase the ratio of the length to the 
width of the grain, to minimize the length of the grain and to render the 
rod shaped powder grain strong and tough. 
COMATIVE EXAMPLE 2 
A ferromagnetic metal powder was produced as in Example 1 except that a 
magnetic field was not applied. 
The coercive force and the saturated magnetism of the ferromagnetic powder 
obtained were 440 oe and 14,000G, respectively, and the length of each 
powder grain was about 0.1 .mu.. The powder grain was very fine but 
granular. The squareness ratio of the magnetic tape produced by dispersing 
the ferromagnetic powder into the binder was less than 0.5. 
The addition of the organic solvent thus turned out to be effective only 
when the magnetic field was applied. 
The total reaction time was 10 minutes. The product had the following 
composition: 
Co: 82.3% 
P: 9.6% 
the product contained a small amount of hydroxide and oxide. 
EXAMPLE 2 
A ferromagnetic metal powder was produced according to the same process as 
in Example 1 except for changing the time that Liquid D was added. The 
results are given below. 
1. Liquid D was added to the solution mixture before the addition of Liquid 
C. The squareness ratio of the resulting ferromagnetic powder was 0.75. 
The addition of Liquid D in this sequence did not cause such a remarkable 
effect, but the magnetic properties were slightly improved as compared 
with the case of not using Liquid D. 
2. Liquid D was added to the solution mixture together with Liquid C. The 
squareness ratio of the resulting ferromagnetic powder, the mean grain 
size and the ratio of the length to the width of the grain were 0.80, 1.2 
.mu. and 7:1, respectively. The grain size was uniform. The addition of 
Liquid D turned out to be fully effective. 
3. Liquid D was added before the generation of H.sub.2 gas bubbles in the 
reaction bath and after the addition of Liquid C. The squareness ratio of 
the resulting ferromagnetic powder, the mean grain size and the ratio of 
the length to the width of the grain were 0.85, 1.3 .mu. and 8:1, 
respectively. The grain size was uniform, and the addition of Liquid D 
turned out to be very effective. 
4. Liquid D was added to the reaction immediately after the generation of 
H.sub.2 gas bubbles therein. The squareness ratio of the resulting 
ferromagnetic powder, the mean grain size and the ratio of the length to 
the width of the grain were 0.85, 1.2 .mu. and 8:1, respectively. The 
grain size was almost uniform. The effect of the addition of Liquid D was 
fully recognized. 
5. Liquid D was added to the reaction bath after the generation of H.sub.2 
gas bubbles therein by the addition of Liquid C. The squareness ratio of 
the resulting ferromagnetic powder, the mean grain size and the ratio of 
the length to the width of the grain were 0.85, 1.4 .mu. and 8:1, 
respectively. The distribution of the grain size was not so smooth and 
uniform. 
The addition of the organic solvent is preferably carried out at the same 
time as, or immediately after, the addition of Liquid C. The most 
preferred results will be obtained by adding the organic solvent in the 
period between the addition of Liquid C and the start of the H.sub.2 gas 
bubble generation due to the hypophosphite. This results in the production 
of a ferromagnetic powder having a satisfactory squareness ratio and a 
uniform grain size distribution. The time to add Liquid B and to add 
Liquid C may be reversed with the same results. 
EXAMPLE 3 
______________________________________ 
Liquid A 
Ni acetate 6 g 
Co acetate 10 g 
Na tartarate 50 g 
Boric acid 15 g 
Water 300 cc 
Liquid B 
Na hypophosphite 20 g 
Water 50 cc 
Liquid C 
Pd chloride 0.03% aq. solution 
15 cc 
Liquid D 
Alcohols 50 cc 
______________________________________ 
(methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, benzy 
alcohol, furufuryl alcohol or ethylene glycol as shown in Table 1) 
Liquid A, Liquid B and water were mixed with each other to obtain 500 cc of 
an aqueous solution, and the pH of this solution was adjusted to 9.0 by 
adding an aqueous caustic soda solution. Liquid C was then added to the 
resulting solution keeping the temperature at 90.degree. C. A direct 
current magnetic field of 2,000G was applied to the solution throughout 
the precipitation and the solution also agitated throughout the 
precipitation. Liquid D was then added to the solution and the pH was 
adjusted to be 8.5 - 9.0. 
The precipitate caused by the reducing reaction was washed with water and 
dried to obtain the ferromagnetic metal powder which exhibited a uniform 
grain size distribution and a large ratio of length to width of the powder 
grain. The powder grains were observed to be very fine, strong and tough. 
The resultant ferromagnetic metal powder was dispersed in a binder (8% by 
weight butylacetate solution of ferromagnetic metal powder 5 g and 
vinylchloride vinylidene chloride copolymer 5 g) and formed into a 
magnetic recording tape. The squareness ratio and the coercive force of 
the magnetic tape were greater than 0.8 and greater than 7000 oe, 
respectively, as shown in Table 1. 
It will be apparent from this example that the addition of the alcohols to 
the reaction bath yields good magnetic properties, and especially the 
addition of the lower alcohols yields a ferromagnetic metal powder having 
an excellent squareness ratio. 
Comparing the specimens of Example 1 with those of Example 2 in a case of 
using butyl alcohol, the ferromagnetic powder obtained from the Co-Ni 
containing bath exhibited a higher coercive force than that of the 
ferromagnetic powder obtained from the Co containing bath. 
Table 1 
______________________________________ 
Squareness 
Grain size 
Coercive force 
ratio 
Organic solvent 
(.mu.) (oe) (Br/Bs) 
______________________________________ 
*-- 2.5 600 0.70 
methyl alcohol 
1.0 900 0.88 
ethyl alcohol 
1.1 850 0.86 
isopropyl alcohol 
1.2 800 0.86 
n-butyl alcohol 
1.2 720 0.85 
benzyl alcohol 
1.5 700 0.80 
furfuryl alcohol 
1.5 710 0.82 
ethylene glycol 
1.7 720 0.80 
*n-butyl alcohol 
1.2 650 0,85 
______________________________________ 
*Comparative specimens in Example 1. 
Product 
Reaction 
composition* 
time Co Ni P 
Organic solvent 
(min.) (%) (%) (%) Note 
______________________________________ 
-- 12 83.5 -- 9.2 Comparative 
Example 1 
methyl alcohol 
10 56.2 35.7 5.0 Example 3 
ethyl alcohol 
10 56.0 35.8 4.8 Example 3 
isopropyl alcohol 
10 56.5 35.8 4.7 Example 3 
n-butyl alcohol 
10 56.7 35.7 4.6 Example 3 
benzyl alcohol 
12 56.7 35.9 4.4 Example 3 
furfuryl alcohol 
12 56.9 36.0 4.4 Example 3 
ethylene glycol 
15 56.2 36.0 4.6 Example 3 
n-butyl alcohol 
10 85.0 -- 8.6 Comparative 
Example 1 
______________________________________ 
In each case, the product contained a small amount of a hydroxide and an 
oxide. 
EXAMPLE 4 
______________________________________ 
Liquid A 
Ni sulfamate 5 g 
Co sulfamate 10 g 
Boric acid 15 g 
Water 300 cc 
Liquid 3 
Na hypophosphite 20 g 
Water 50 cc 
Liquid C 
Chloroauric acid (0.03% aq. solution) 
20 cc 
Liquid D 
Acetone 20 cc 
______________________________________ 
Liquid A, Liquid B and water were mixed with each other to obtain 500 cc of 
an aqueous solution, and the pH of this solution was adjusted to 9.0 C by 
adding an aqueous caustic soda solution. Liquid C was then added to the 
resulting solution keeping the temperature at 90.degree. C and applying a 
direct current magnetic field of 2000G to the solution while agitating the 
solution. Liquid D was added to the solution immediately after H.sub.2 
bubbles were generated in the reaction bath and the pH of the solution was 
again adjusted to 8.5 - 9.0. The magnetic field was applied throughout the 
precipitation in combination with agitation. The precipitate caused by the 
reducing reaction was washed with water and dried to obtain the 
ferromagnetic alloy powder, which was composed of rod shaped grains having 
a mean grain size of 1.5 .mu. and a length: width ratio of about 15:1. The 
coercive force and the saturated magnetism (4.pi.IS) of the alloy powder 
were 1,200 oe and 11,000 Gcc, respectively. This ferromagnetic metal 
powder was dispersed in a binder and formed into a magnetic tape which 
exhibited a squareness ratio of 0.85. 
Upon inspection of the ferromagnetic alloy powder by a scanning type of 
electron microscope, a uniform distribution of the powder grain was 
observed. 
The total reaction time was 10 minutes. The product had the following 
composition: Co (62.3%), Ni (30.2%), P (4.0%) and contained a small amount 
hydroxide and oxide. 
COMATIVE EXAMPLE 3 
A ferromagnetic alloy powder was produced according to the process of 
Example 4 except a magnetic field was not applied to the reaction bath. 
The coercive force and the saturated magnetism of the obtained 
ferromagnetic alloy powder were 480 oe and 11,000G, respectively. The 
grains were very fine but granular (having from a size of 0.1 .mu.). The 
squareness ratio of the magnetic tape produced from this ferromagnetic 
alloy powder dispersed in the binder was less than 0.5. 
It will be apparent from these results that the effect of the addition of 
the organic solvent is brought out by the application of the magnetic 
field. 
EXAMPLE 5 
Ferromagnetic alloy powders were produced, following the procedures of 
Examples 1 and 4 but by changing the kind of magnetic field, i.e., using; 
1. a pulsing magnetic field; 2. an alternating current magnetic field, and 
3. ultrasonic waves and a direct current magnetic field. 
The grain size and the squareness ratio of the magnetic hysteresis loop of 
the alloy powders obtained were measured. 
The results are shown in Table 2 (according to the process of Example 1 
where total reaction time was 10 minutes) and Table 3 (according to the 
process of Example 4 where total reaction time was 10 minutes. 
Table 2 
______________________________________ 
Grain 
size Squareness 
Magnetic field applied (.mu.) ratio 
______________________________________ 
Direct current magnetic field(2000G) 
1.2 0.85 
Direct current magnetic field(1000G) 
1.0 0.85 
+ultrasonic waves (40KHZ) 
Alternating current magnetic field 
1.0 0.85 
(50HZ, 2000G) 
Pulsed magnetic field* 
(1 sec,10) 1.0 0.85 
" (1 sec,1) 0.8 0.82 
" (1 sec,1/5) 0.5 0.80 
" (1 sec,1/10) 0.3 0.60 
" (1 sec,1/100) 
0.2 &lt;0.50 
" (100msec,**,10) 
0.6 0.85 
" (100msec,1) 0.5 0.84 
" (100msec,1/5) 
0.4 0.82 
" (100msec,1/10) 
0.3 0.70 
" (10msec,1) 0.4 0.83 
" (10msec,1/5) 0.3 0.81 
" (10msec,1/10) 
0.3 0.80 
" (1msec,1) 0.3 0.82 
" (1mesc,1/5) 0.2 0.80 
______________________________________ 
*all pulsed magnetic field values were of 2000G 
**msec means milliseconds 
The numerals in the parentheses for the pulse magnetic field show the pulse 
width and the ratio of pulse width to the interval between pulses. For 
example, (10msec, 1/5) means the magnetic field where the field was 
applied for 10m sec and stopped for 1/5 .times. 10m sec, (1 sec, 10) means 
1 second pulses spaced by 10 second intervals, etc. 
The numerals in the middle column of "grain size" indicate the length of 
the rod shaped powder grain. 
Table 3 
______________________________________ 
Grain 
size Squareness 
Magnetic field applied (.mu.) ratio 
______________________________________ 
Direct current magnetic field 
1.5 0.85 
Direct current magnetic field(1000G) 
1.2 0.84 
+ ultrasonic wave (40KHZ) 
Alternating current magnetic field 
1.2 0.84 
(50 HZ, 2000G) 
Pulsed magnetic field 
(1 sec,10) 1.3 0.85 
" (1 sec,1) 0.9 0.84 
" (1 sec,1) 0.9 0.84 
" (1 sec,1/5) 0.6 0.80 
" (1 sec,1/10) 0.3 0.65 
" (1 sec,1/1000) 
0.2 &lt;0.50 
" (10msec,1) 0.5 0.82 
" (10msec,1/5) 0.3 0.80 
" (10msec,1/10) 
0.3 0.70 
______________________________________ 
*all pulsed magnetic fields were of 2000G 
It will be apparent from the results shown in Table 2 and Table 3 that the 
application of a pulsed magnetic field or an alternating current magnetic 
field or the combined application of a direct current magnetic field and 
ultrasonic waves are effective for reducing the size and shortening the 
powder grain length. The application of a pulsed magnetic field is 
especially effective, and the shorter the pulse width is, the finer the 
powder grains obtained are. 
The accicularity of the powder grains was sharply reduced at a pulse width 
of 1m sec - 1 sec and at a ratio of the pulse width to the interval of 
less than 1/10. 
The strength and toughness of the powder grains formed with the application 
of a pulsed magnetic field were excellent, as well as those formed with 
the application of a direct current magnetic field. 
The squareness ratio of a magnetic tape produced from the ferromagnetic 
metal powders dispersed in a binder was greater than 0.8, and the pulse 
width/interval ratio was more than 1/5. Inspection of the powder grains by 
a scanning electron microscope showed that the grain size distribution was 
smooth and uniform. 
EXAMPLE 6 
______________________________________ 
Liquid A 
Ni sulfate 6 g 
Co sulfate 10 g 
Na citrate 50 g 
Boric acid 300 cc 
Liquid B 
Na hypophosphite 20 
Water 50 cc 
Liquid C 
Pd chloride 0.03% aq. solution 
20 cc 
Liquid D 
Organic solvent (see Table 4) aqueous solution 
50 cc 
______________________________________ 
(5 - 20 g of organic solvent was dissolved in water to obtain 50 cc of 
solution) 
Liquid A, Liquid B and water were mixed with each other to obtain 500 cc of 
an aqueous solution, and an aqueous caustic soda solution was added to the 
obtained solution to adjust the pH to 9.0. Then Liquid D was added to the 
solution while agitating and keeping the latter at 90.degree. C. A direct 
current magnetic field of 2,000G was applied during the precipitation. 
While Liquid D was added to the solution the pH was adjusted to 8.5 - 9.0. 
The reducing reaction was continued until precipitation was completed, and 
the precipitate then washed with water and dried to obtain the 
ferromagnetic alloy powder. 
The grain size, the coercive force and the squareness ratio of the 
hysteresis loop of the alloy powder obtained were measured and the results 
are shown in Table 4. 
Table 4 
______________________________________ 
Grain Reaction 
size Coercive Squareness 
time 
Organic solvent 
(.mu.) force(oe) ratio(Br/Bs) 
(min.) 
______________________________________ 
phenol 10 g 
1.6 640 0.85 10 
phenol 20 g 
1.2 700 0.90 10 
cresol 20 g 
1.5 600 0.83 10 
hydroquinone 20g 
1.6 580 0.80 12 
pyrocatechol 10g 
1.9 530 0.78 15 
pyrocatechol 20g 
1.8 400 0.82 15 
pyrogallol 1.9g 440 0.76 20 
pyrogallol 10 g 
1.8 380 0.80 20 
pyrogallol 20 g 
1.8 300 0.80 20 
______________________________________ 
It will be apparent from Table 4 that the ferromagnetic alloy powders 
produced using phenol as the organic solvent exhibited excellent magnetic 
properties, i.e., a tape formed as in Example 1 using the 20 g phenol 
ferromagnetic powder system showed a coercive force of 700 oe, a 
squareness ratio of 0.90, and a favorable grain orientation with a smooth 
tape surface. 
EXAMPLE 7 
A ferromagnetic alloy powder was produced under the same conditions as in 
Example 6 except for replacing Liquid D with various fatty acids, carbon 
tetrachloride, Freon or hydrocarbons. The grain size, coercive force and 
the squareness ratio of the hysteresis loop of the obtained ferromagnetic 
alloy powder were measured. The results are shown in Table 5 along with 
the fatty acids, hydrocarbons, carbon tetrachloride and Freon used. 
Table 5 
______________________________________ 
Grain Reaction 
size Coercive Squareness 
time 
Organic solvent 
(.mu.) force(oe) ratio(Br/Bs) 
(min.) 
______________________________________ 
formic acid 20cc 
1.6 500 0.82 15 
glacial acetic 
1.6 530 0.80 15 
acid 10cc 
glacial acetic 
1.5 400 0.81 15 
acid 20cc 
propionic acid 
1.3 560 0.82 15 
20cc 
*capric acid 20cc 
2.0 350 0.60 15 
glycolic acid 10cc 
1.3 550 0.82 15 
glycolic acid 20cc 
1.2 450 0.81 15 
**oleic acid 20cc 
-- -- -- 60 
benzene 20cc 
1.9 590 0.83 10 
toluene 20cc 
1.6 600 0,85 10 
xylene 20cc 
1.5 600 0.85 10 
carbon tetra- 
1.3 450 0.79 15 
chloride 10cc 
carbon tetra- 
1.0 300 0.80 15 
chloride 20cc 
***Freon 10cc 
1.2 520 0.80 15 
***Freon 20cc 
1.0 350 0.80 15 
______________________________________ 
*the grain shape became rectangular 
**the alloy powder was not precipitated 
***a mixed solvent of Freon-113 (CCl.sub.2 FCClF.sub.2 made by E. I. Du 
Pont de Nemours & Co., Inc.) and methylene chloride (CH.sub.2 Cl.sub.2) 
(50.5 : 49.5 by volume) was used 
It was concluded from the results in Table 5 that higher fatty acids 
insoluble in water are not suitable for producing a ferromagnetic alloy 
powder having a high orientation (see U.S. Pat. No. 2,711,901) or a good 
squareness ratio. 
On the other hand, lower fatty acids soluble in water and having a low 
melting point generally reduced the coercive force of the ferromagnetic 
alloy powder, and accordingly a coercive force between 400 oe and 600 oe 
could be obtained by controlling the amount of the lower fatty acid. 
The addition of aromatic hydrocarbons brought out a good squareness ratio 
and a stable coercive force in the resulting ferromagnetic powders. The 
addition of the halogenated hydrocarbon was effective to control the 
coercive force to be in the range of 300 - 600 oe. 
Thus, the addition of organic solvents substantially insoluble in water or 
having a boiling point lower than that reaction temperature brings out the 
effects peculiar to the process of this invention. 
EXAMPLE 8 
Ferromagnetic alloy powders were produced under the same conditions as in 
Example 6 except for replacing Liquid D with methylethyl ketone, 
methylisobutyl ketone or a like ketone or esters. The grain size, the 
coercive force and the squareness ratio of the hysteresis loop of the 
obtained ferromagnetic alloy powders were measured and are listed in Table 
6 along with the materials used to form Liquid D. 
Table 6 
______________________________________ 
Grain size 
Coercive Squareness 
Organic solvent 
(.mu.) force (oe) 
ratio 
______________________________________ 
methylethyl ketone 10cc 
1.6 1,000 0.85 
methylethyl ketone 20cc 
1.5 1,180 0.84 
methylisobutyl ketone 10cc 
1.5 1,050 0.83 
methylisobutyl ketone 20cc 
1.4 1,200 0.84 
diethyl ketone 20cc 
1.8 950 0.85 
ethyl formate 20cc 
1.2 780 0.83 
methyl acetate 10cc 
1.2 730 0.82 
methyl acetate 20cc 
1.6 930 0.83 
ethyl acetate 20cc 
1.4 960 0.83 
butyl acetate 10cc 
1.5 910 0.82 
butyl acetate 20cc 
1.6 1,000 0.80 
ethyl malonate 10cc 
2.0 830 0.82 
diethyl phthalate 10cc 
1.7 700 0.80 
______________________________________ 
It will be apparent from Table 6 that the ferromagnetic alloy powders 
produced using ketones other than acetone used in Example 4 exhibited an 
excellent squareness ratio and a high coercive force as did the alloy 
powders in Example 4. The addition of the esters was also effective as 
compared to the ketones, and the addition of methyl acetate and butyl 
acetate brought out an especially favorable squareness ratio and a 
coercive force of 1,000 oe. 
The total reaction time = 15 min. in each case. 
EXAMPLE 9 
Ferromagnetic metal powders were obtained under the same conditions as in 
Example 6 except for replacing Liquid D with an amine. The addition of the 
amine yielded a stable coercive force and an excellent squareness ratio in 
the resulting ferromagnetic metal powders. The ferromagnetic alloy powder 
produced using triethanolamine exhibited a squareness ratio of 0.85 and a 
coercive force of 600 oe. Hc can be obtained at constant values and the 
reproducibility of Hc is stable. 
Table 7 
______________________________________ 
Grain Reaction 
size Coercive Squareness 
time 
Amine (.mu.) force(oe) 
ratio (min.) 
______________________________________ 
triethanolamine 10g 
1.2 600 0.85 12 
triethanolamine 20g 
1.1 600 0.85 12 
ethylenediamine 10cc 
1.5 600 0.82 10 
ethylenediamine 20cc 
1.3 600 0.82 15 
______________________________________ 
EXAMPLE 10 
Ferromagnetic metal powers were obtained under the same conditions as in 
Example 3 except for further adding very small amounts of special elements 
to the reacting bath. The resultant ferromagnetic metal powder exhibited a 
coercive force higher than that obtained in Example 3. More particularly, 
the addition of La, Ce, Nd, Sm or like rare earth elements and Al, S, Cr, 
Mn, Fe, Cu or Zn increased the coercive force. The combination of a 
suitable organic solvent and small amounts of these elements was very 
effective to even further increase the coercive force. 
Table 8 
__________________________________________________________________________ 
Alcohol Isopropyl alcohol 
(Reaction time:15min) 
(Reaction time:10min) 
Amount 
Grain size 
Coercive 
Grain size 
Coercive 
Additive (g) (.mu.) 
force(oe) 
(.mu.) 
force(oe) 
__________________________________________________________________________ 
-- -- 2.5 600 1.2 800 
LaCl.sub.3 . 6H.sub.2 O 
0.2 2.0 750 1.0 880 
CeCl.sub.3 . 7H.sub.2 O 
0.3 2.0 750 1.0 850 
NdCl.sub.3 . 6H.sub.2 O 
0.2 2.0 850 0.8 1,000 
SmCl.sub.3 . 6H.sub.2 O 
0.2 2.0 800 0.9 1,000 
Al.sub.2 (SO.sub.4).sub.3 . 18H.sub.2 O 
1.0 2.1 650 1.3 850 
CS(NH.sub.2).sub.2 
0.01 2.5 670 1.2 900 
CrO.sub.3 0.2 1.8 660 0.8 830 
MnSO.sub.4 . 5H.sub.2 O 
0.3 2.3 640 1.1 860 
FeSO.sub.4 . 7H.sub.2 O 
0.5 2.0 700 1.0 850 
CuSO.sub.4 . 5H.sub.2 O 
0.1 2.2 720 1.1 900 
ZnSO.sub.4 . 7H.sub.2 O 
0.5 2.3 750 1.3 840 
3CdSO.sub.4 . 8H.sub.2 O 
0.05 2.5 580 1.5 760 
RhSO.sub.4 
0.01 2.4 600 1.2 800 
WO.sub.3 0.03 2.5 550 1.2 650 
__________________________________________________________________________ 
While this invention has been described with reference to particular 
embodiments thereof, it will be understood that the numerous modifications 
may be made by those skilled in the art without actually departing from 
the spirit and scope of this invention, and therefore the appended claims 
are intended to cover all such equivalent variations as coming within the 
true spirit and scope of this invention.