Acicular ferromagnetic alloy particles and process for producing said particles

Acicular ferromagnetic alloy particles doped with silicon, chromium and nickel and optionally magnesium and a process for producing said particles comprising heating at 300.degree. to 500.degree. C. under reducing atmosphere acicular particles of .alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel and optionally magnesium or acicular particles of .alpha.-ferric oxide doped with silicon, chromium and nickel and optionally magnesium obtained by dehydrating the acicular particles of .alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel and optionally magnesium are disclosed herein.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to acicular ferromagnetic alloy particles of 
improved particle properties, especially large specific surface and 
improved magnetic properties, especially high coercive force and large 
saturation magnetization which are suitable as a magnetic material for use 
in magnetic recording media. And, the present invention relates to a 
process for producing such acicular ferromagnetic alloy particles. 
Recently, the improvements such as the miniaturizing and weight-lightening, 
the long-time recording and the like of the reproducing apparatus for 
magnetic recording, for example, video tape recorder, has been 
dramatically progressed. Accompanied by such improvements, the necessity 
for improving the qualities of the magnetic recording media such as 
magnetic tape, magnetic disk and the like has been more and more 
increasing. Especially, the magnetic recording media of high signal to 
noise ratio, little chroma noise and improved frequency characteristic 
have been requested. To fulfill such a request, the improvements of the 
magnetic material has been also requested since the above-mentioned 
specific properties of magnetic recording media depend upon the specific 
properties of the magnetic material, as described hereinafter. 
To increase the signal to noise ratio of the recording media, the noise 
level due to the recording medium should be lowered. For that purpose, the 
micronization of the particle size of the magnetic particles and the 
improvements of their dispersibility in the vehicle and their orientation 
and packing in a coating medium are essential. Since the improvement of 
the latter brings also the surface smoothness to the recording media, such 
an improvement is important. 
To reduce the chroma noise, the improvement of the surface smoothness of 
the recording medium is important, which depends upon the dispersibility 
in the vehicle and the orientation and packing in a coating medium of the 
magnetic particles. 
To improve the frequency characteristic, the improvements of coercive force 
and residual magnetic flux density of the recording medium are important, 
each of which depends upon the coercive force and the saturation 
magnetization of the magnetic particles. Further, the latter depends upon 
their dispersibility in a vehicle and their orientation and packing in a 
coating medium. 
As clear from the above-mentioned, it is necessary that the magnetic 
particles have excellent acicularity and the particle size thereof is 
uniform without the contamination of the dentrites and the apparent 
density thereof is as possible as large to improve their dispersibility in 
the vehicle and their orientation and packing in a coating medium. In 
addition, the specific surface area of the magnetic particle which is an 
index of the particle size and the coercive force as well as the 
saturation magnetization thereof are necessarily as large as possible. 
As the magnetic material ferromagnetic iron oxide particles are 
conventionally employed in magnetic media, but the ferromagnetic iron 
oxide particles are not satisfactory in both their particle properties and 
their magnetic properties. The improved magnetic materials are acicular 
ferromagnetic iron particles and acicular ferromagnetic alloy particles 
obtained by heating acicular particles of .alpha.-iron(III) oxide 
hydroxide, acicular .alpha.-ferric oxide particles, each of these 
containing metal(s) different from iron in a flow of reducing gas at about 
350.degree. C. Although the thus-obtained particles have relatively 
satisfactory magnetic properties, they have not excellent acicularity and 
uniformity in particle size and the dentrites are coexistent therein. This 
is due to the .alpha.-iron(III) oxide hydroxide as a starting material. 
The most representative process for producing the acicular particles of 
.alpha.-iron(III) oxide hydroxide comprises blowing an oxygen-containing 
gas into an aqueous suspension containing precipitated ferrous hydroxide 
obtained by adding an aqueous alkali solution in an amount more than the 
equivalent into an aqueous solution of a ferrous salt at a temperature of 
lower than 80.degree. C. and at a pH of over 11 to effect the oxidation. 
However, the thus-obtained acicular particles of .alpha.-iron(III) oxide 
hydroxide are around 0.5 to 1.5 .mu.m in length of long axis and their 
axial ratio is at most 10:1 and the dentrites are coexistent therein. One 
of this cause is in that the particle sizes of both the flock of ferrous 
hydroxide which is the precursor of the acicular particles of 
.alpha.-iron(III) oxide hydroxide and the ferrous hydroxide particles 
themselves which constitute the flock of ferrous hydroxide are not 
uniform. Further, the other cause, is in that the stage of the formation 
of the nuclei of the acicular particles of .alpha.-iron(III) oxide 
hydroxide and the stage of the growth of the nuclei of acicular particles 
proceed simultaneously since the contact of ferrous hydroxide with 
dissolved oxygen to form the nuclei of the acicular particles of 
.alpha.-iron(III) oxide hydroxide is partial and uneven. 
A method for preparing the acicular particles of .alpha.-iron(III) oxide 
hydroxide which have the uniformity in particle size and do not contain 
the dentrites is to add a water-soluble silicate such as sodium silicate, 
potassium silicate and the like in an amount of 0.1 to 1.7 atomic % 
calculated as the ratio of Si to Fe(II) and based on the amount of ferrous 
hydroxide in the suspension (hereinafter referred to as simply "calculated 
as the ratio of Si/Fe(II)") into the aqueous alkali solution or the 
aqueous suspension containing ferrous hydroxide in advance of the blowing 
of an oxygen-containing gas into the aqueous suspension containing ferrous 
hydroxide (refer to Japanese Patent Publication Nos. 8461/80 and 
32652/80). By such an addition of the water-soluble silicate, the minute 
flocks of ferrous hydroxide and the minute particles of ferrous hydroxide 
can be obtained with uniform particle size, and further the nuclei of the 
acicular particles of .alpha.-iron(III) oxide hydroxide grow after the 
formation of the nuclei thereof is completed. Accordingly, the 
thus-obtained acicular particles of .alpha.-iron(III) oxide hydroxide have 
excellent acicularity and the particle size thereof is uniform without the 
contamination of the dentrites, they being to be said a favorable starting 
material. As a result, the acicular ferromagnetic alloy particles obtained 
by reducing the favorable starting material have also the uniformity in 
particle size without the contamination of the dentrites and so the 
apparent density thereof is satisfactory. The other properties such as the 
dispersibility, the orientation and the like except the specific surface 
area are also satisfactory. As the specific surface area of these magnetic 
particles is around 20 m.sup.2 /g, however, they are undesirable on the 
whole. 
Accordingly, the object of the present invention is to provide the acicular 
ferromagnetic alloy particles having the above-mentioned specific 
properties necessary for use as the magnetic recording medium. 
Another object of the present invention is to provide a process for 
producing such acicular ferromagnetic alloy particles. 
These and other objects of the present invention will become more apparent 
from the following description. 
The foregoing and the other objects of the present invention will be 
accomplished by the use of the .alpha.-iron(III) oxide hydroxide doped 
with silicon, chromium and nickel as the starting material.

DETAILED DESCRIPTION OF THE INVENTION 
The acicular ferromagnetic alloy particles doped with silicon, chromium and 
nickel according to the present invention have large specific surface area 
while maintaining the excellent acicularity and the uniform particle size, 
and high coercive force as well as large saturation magnetization. The 
acicular ferromagnetic alloy particles doped with silicon, chromium and 
nickel of the present invention can be prepared by using the acicular 
particles of .alpha.-iron(III) oxide hydroxide doped with silicon, 
chromium and nickel or the acicular .alpha.-ferric oxide particles doped 
with silicon, chromium and nickel obtained by heating the acicular 
particles of .alpha.-iron(III) oxide hydroxide as the starting material 
particles and reducing these particles. The .alpha.-iron(III) oxide 
hydroxide doped with silicon, chromium and nickel used as the starting 
material particles can be obtained in forming the acicular particles of 
.alpha.-iron(III) oxide hydroxide doped with silicon by further adding a 
water-soluble chromium salt and a water-soluble nickel salt into the 
aqueous solution of the ferrous salt, the aqueous alkali solution, the 
aqueous suspension containing ferrous hydroxide in advance of the blowing 
of an oxygen-containing gas or the aqueous suspension containing ferrous 
hydroxide during the blowing of an oxygen-containing gas. 
As mentioned above, the acicular ferromagnetic alloy particles doped with 
silicon, chromium and nickel of the present invention have large specific 
surface area and high coercive force. Moreover, to improve the specific 
surface area and the coercive force a water-soluble magnesium salt can be 
added in a similar manner. Namely, the water-soluble magnesium salt is 
added into the aqueous solution of the ferrous salt, the aqueous alkali 
solution, the aqueous suspension containing ferrous hydroxide in advance 
of the blowing of the oxygen-containing gas or the aqueous suspension 
containing the ferrous hydroxide during the blowing of the 
oxygen-containing gas, to form the acicular particles of .alpha.-iron(III) 
oxide hydroxide doped with silicon, chromium, nickel and magnesium which 
used as the starting material particles. Reducing the thus-formed 
particles, the acicular ferromagnetic alloy particles doped with silicon, 
chromium, nickel and magnesium having the improved specific surface area 
and coercive force can be obtained. 
Based upon the experimental results obtained by the inventors of the 
present invention, the conditions and the effects of the addition of the 
water-soluble chromium salt, the water-soluble nickel salt and the 
water-soluble magnesium salt will be described as follows while referring 
to the attached drawings. 
FIG. 1 shows the relation between the specific surface area of the acicular 
ferromagnetic alloy particles and the added amount of the water-soluble 
chromium salt. The acicular ferromagnetic alloy particles used are the 
acicular ferromagnetic alloy particles doped with silicon and chromium 
obtained by oxidizing the aqueous suspension of pH 13.8 and containing 
ferrous hydroxide which is prepared by adding 300 l of an aqueous solution 
of ferrous sulfate at a concentration of 1.2 mol/liter into 400 l of an 
aqueous sodium hydroxide solution containing sodium silicate in an amount 
of 0 to 1.0 atomic % calculated as the ratio of Si to Fe(II) and based on 
the amount of the ferrous hydroxide in the suspension (hereinafter 
referred to as simply "calculated as the ratio of Si/Fe(II)") and chromium 
sulfate in an amount of 0 to 5.0 atomic % calculated as the ratio of Cr to 
Fe(II) and based on the amount of the ferrous hydroxide in the suspension 
(hereinafter referred to as simply "calculated as the ratio of Cr/Fe(II)" 
by blowing air at 45.degree. C. at a rate of 1000 liters per minute 
thereinto to form the acicular particles of .alpha.-iron(III) oxide 
hydroxide doped with silicon and chromium followed by reducing at 
430.degree. C. for 4.0 hours. 
Curves a, b and c in the drawing indicate the case of no-addition of 
silicate, the case of the addition of 0.35 atomic % of silicate calculated 
as Si/Fe(II) and the case of the addition of 1.0 atomic % of silicate 
calculated as Si/Fe(II), respectively. As shown in FIG. 1, there is a 
tendency of the increase of the specific surface area of the particle with 
the increase of the amount of the added water-soluble chromium salt, 
chromium sulfate. This tendency is more clear when the silicate is added 
in combination with the chromium salt. 
The acicular ferromagnetic alloy particles doped with silicon and chromium 
have excellent acicularity and uniformity in particle size without the 
contamination of the dentrites, and further they have large specific 
surface area. The synergistic effect of silicon and chromium is considered 
to give these advantages. However, with the added amount of the chromium 
salt, the coercive force of the ferromagnetic alloy particles doped with 
silicon and chromium tends to fall. 
FIG. 2 shows the relation between the coercive force of the acicular 
ferromagnetic alloy particles and the added amount of the water-soluble 
nickel salt. The acicular ferromagnetic alloy particles used are the 
acicular ferromagnetic alloy particles doped with silicon, chromium and 
nickel obtained by oxidizing the aqueous suspension of pH 14.0 and 
containing ferrous hydroxide which is prepared by adding 300 l of an 
aqueous solution of ferrous salt at a concentration of 1.2 mol/liter into 
400 l of an aqueous sodium hydroxide solution containing sodium silicate 
in an amount of 0.35 atomic % calculated as Si/Fe(II), chromium sulfate in 
an amount of 0.5 atomic % calculated as Cr/Fe(II) and nickel sulfate in an 
amount of 0 to 7.0 atomic % calculated as the ratio of Ni to Fe(II) and 
based on the amount of the ferrous hydroxide in the suspension 
(hereinafter referred to as simply "calculated as the ratio of Ni/Fe(II)") 
by blowing air at 45.degree. C. at a rate of 1000 liter per minute 
thereinto to form the acicular particles of .alpha.-iron(III) oxide 
hydroxide doped with silicon, chromium and nickel followed by reducing at 
420.degree. C. for 4.0 hours. 
As shown in FIG. 2, there is a tendency of the increase of the coercive 
force of the particles with the increase of the added amount of the 
water-soluble nickel salt, nickel sulfate while maintaining the large 
specific surface area. These advantages are considered to be owing to the 
synergistic effect of silicon, chromium and nickel. 
FIG. 3 shows the relation between the coercive force of the acicular 
ferromagnetic alloy particles and the added amount of the water-soluble 
magnesium salt and FIG. 4 shows the relation between the specific surface 
area thereof and the added amount of the water-soluble magnesium salt. The 
ferromagnetic alloy particles used are the ferromagnetic alloy particles 
doped with silicon, chromium, nickel and magnesium obtained by oxidizing 
the aqueous suspension of pH 14.0 and containing ferrous hydroxide which 
is prepared by adding 300 l of an aqueous solution of ferrous sulfate at a 
concentration of 1.2 mol/liter into 400 l of an aqueous sodium hydroxide 
solution containing sodium silicate in an amount of 0.35 atomic % 
calculated as Si/Fe(II), chromium sulfate in an amount of 0.50 atomic % 
calculated as Cr/Fe(II), nickel sulfate in an amount of 3.0 atomic % 
calculated as Ni/Fe(II) and magnesium sulfate in an amount of 0 to 15.0 
atomic % calculated as the ratio of Mg to Fe(II) and based on the amount 
of the ferrous hydroxide in the suspension (hereinafter referred to as 
simply "calculated as the ratio of Mg/Fe(II)") by blowing air at 
50.degree. C. at a rate of 1000 l per minute thereinto to form the 
acicular particles of .alpha.-iron(III) oxide hydroxide doped with 
silicon, chromium, nickel and magnesium followed by reducing at 
420.degree. C. for 4.5 hours. 
As shown in FIGS. 3 and 4, there is a tendency of the increases in both 
coercive force and specific surface area of the particles with the 
increase of the added amount of the water-soluble magnesium salt, 
magnesium sulfate. These advantages are considered to be owing to the 
synergistic effect of silicon, chromium, nickel and magnesium. 
Now the condition for carrying out the process of the present invention 
will be explained in detail as follows. 
To obtain the acicular ferromagnetic alloy particles of the present 
invention, the acicular particles of .alpha.-iron(III) oxide hydroxide 
doped with silicon, chromium and nickel (and if desired magnesium) should 
be firstly formed. For that purpose, a water-soluble chromium salt and a 
water-soluble nickel salt (and if desired a water-soluble magnesium salt) 
in addition to a water-soluble silicate are added in forming the acicular 
particles of .alpha.-iron(III) oxide hydroxide. 
The water-soluble chromium salt to be used in the process of the present 
invention includes chromium sulfate, chromium chloride and the like. 
The amount of water-soluble chromium salt to be used is 0.1 to 5.0 atomic % 
calculated as Cr/Fe(II). In the case where the added amount is less than 
0.1 atomic % calculated as Cr/Fe(II), the effect of increasing the 
specific surface area of the particles which is the object of the addition 
of water-soluble chromium salt is not attained. While, in the case where 
the added amount is more than 5.0 atomic %, although the large specific 
surface area can be obtained, it is not so favorable because of the 
greatly reduced coercive force and saturation manetization of the 
thus-obtained acicular ferromagnetic alloy particles. 
The water-soluble nickel salt to be used in the process of the present 
invention includes nickel sulfate, nickel chloride, nickel nitrate and the 
like. 
The amount of water-soluble nickel salt to be used is 0.1 to 7.0 atomic % 
calculated as Ni/Fe(II). In the case where the added amount is less than 
0.1 atomic % calculated as Ni/Fe(II), the effect of improving the coercive 
force of the particles which is the object of the addition of 
water-soluble nickel salt is not exhibited satisfactorily. While, in the 
case where the added amount is more than 7.0 atomic % calculated as 
Ni/Fe(II), although the large coercive force can be obtained it is not so 
favorable because of the contamination of the undesirable non-acicular 
particles. 
The water-soluble magnesium salt to be used in the present invention 
includes magnesium sulfate, magnesium chloride and the like. 
The amount of water-soluble magnesium salt to be used is 0.1 to 15.0 atomic 
% calculated as Mg/Fe(II). In the case where the added amount is less than 
0.1 atomic % calculated as Mg/Fe(II), the effect of improving the specific 
surface area and the coercive force of the particles which is the object 
of the addition of water-soluble magnesium salt can be obtained 
satisfactorily. While, in the case where the added amount is more than 
15.0 atomic % calculated as Mg/Fe(II), although the improved specific 
surface area and coercive force can be obtained, it is not so favorable 
because of the greatly reduced saturation magnetization of the particles. 
These water-soluble salts should be present when the nuclei of the acicular 
particles of .alpha.-iron(III) oxide hydroxide are formed, and accordingly 
the addition of these water-soluble salts may be carried out into the 
aqueous solution of the ferrous salt, the aqueous alkali solution, the 
aqueous suspension containing ferrous hydroxide in advance of the blowing 
of the oxygen-containing gas or the aqueous suspension containing ferrous 
hydroxide during the blowing of the oxygen-containing gas. Even if the 
water-soluble salt is added in the stage where the formation of the nuclei 
of the acicular particles of .alpha.-iron(III) oxide hydroxide are 
completed, any satisfactory effects can not be obtained. The thus added 
water-soluble salts are economically diffused into the acicular particles 
of .alpha.-iron(III) oxide hydroxide, and each doped amount of chromium 
and nickel and optionally magnesium in the particles is substantially same 
as the added amount of each of the water-soluble salts, as clearly shown 
in the following Tables. 
In the next step, the thus-prepared acicular particles of .alpha.-iron(III) 
oxide hydroxide doped with silicon, chromium and nickel (and magnesium if 
desired) are heat-treated at 300.degree. to 500.degree. C. in a flow of 
reducing gas. In the case of the heat-treating temperature of not higher 
than 300.degree. C., the reduction reaction progresses very slowly and 
requires long time. On the other hand, in the case of the temperature of 
not lower than 500.degree. C., the deformation of the acicularity of the 
particles and the sintering between the particles are caused. Accordingly, 
both the temperature of heat-treatment of not higher than 300.degree. C. 
and the temperature of not less than 500.degree. C. are not favorable. 
Now the advantage of the present invention will be summarized as follows. 
According to the present invention, the acicular ferromagnetic alloy 
particles of superior specific properties can be obtained. The acicular 
ferromagnetic alloy particles of the present invention have the improved 
particle properties, especially excellent acicularity and uniformity in 
particle size without the contamination of the dentrites, high apparent 
density and large specific surface area. Besides, they have the improved 
magnetic properties, especially high coercive force and large saturation 
magnetization. Accordingly, the particles of the present invention are 
favorably suitable as the magnetic material for recording of high quality, 
high output, high sensitivity and high recording density, which are at 
present most keenly required. 
In addition, when the acicular ferromagnetic alloy particles according to 
the present invention is used in the production of magnetic paint, they 
exhibit superior dispersibility in a vehicle and superior orientation and 
packing in a coating medium contributing to the production of the 
preferable magnetic recording media. 
Now the present invention will be described by the examples and the 
comparative examples. 
The length of long axis and the axial ratio (long axis: short axis) of the 
particle in the examples and comparative examples were measured by 
electron microscope photograph and indicated as the mean value, 
respectively. 
The specific surface area of the particle was measured by the BET method. 
The apparent density of the particle was measured by "Pigment Test Methods" 
of JIS K 5101-1978. 
The amounts of Si, Cr, Ni and Mg in the particle was measured by the X-ray 
fluorescent analysis according to "General Rules in X-ray fluorescence 
Analysis" of JIS K 0119-1979 while using an X-ray fluorescence analytical 
apparatus, Model 3063M (RIKAGAKU-DENKI-KOGYO Co. Ltd. of Japan). 
The magnetic properties of the magnetic tape were determined under the 
external magnetic field of 10 KOe. 
PREATION OF STARTING MATERIAL TICLES 
EXAMPLE 1 
Into 400 liters of an aqueous 5.45 N sodium hydroxide solution in which 152 
g of sodium silicate (corresponding to 28.55 % by weight of SiO.sub.2) to 
contain 0.20 atomic % calculated as Si/Fe(II), 644 g of chromium sulfate 
to contain 0.50 atomic % calculated as Cr/Fe(II) and 2884 g of nickel 
sulfate to contain 3.0 atomic % calculated as Ni/Fe(II) had been added, 
300 liters of an aqueous solution of ferrous sulfate at a concentration of 
1.20 mol/liter was added, whereby a formation of an aqueous suspension of 
Fe(OH).sub.2 containing silicon, chromium and nickel ions was carried out 
at a temperature of 45.degree. C. and pH of 14.0. Into the thus-prepared 
aqueous suspension, air was blown at a rate of 1000 liters/minute for 6.3 
hours at 50.degree. C. to form acicular particles of .alpha.-iron(III) 
oxide hydroxide doped with silicon, chromium and nickel. The termination 
of the oxidation reaction was determined by the blue colour reaction test 
of Fe(II) with red prussiate solution after extracting a portion of the 
reaction solution and acidifying it with hydrochloric acid. 
The reaction mixture was then filtered to recover the thus formed acicular 
particles of .alpha.-iron(III) oxide hydroxide doped with silicon, 
chromium and nickel, and the particles were washed with water, a part of 
which was dried and pulverized to be specimens for analysis and electron 
microscope photographic observation. 
According to the X-ray diffraction, the thus obtained acicular particles of 
.alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel 
gave the same diffraction pattern as that of the authentic particles of 
.alpha.-iron(III) oxide hydroxide, and the results of X-ray fluorescence 
analysis of the specimen indicated the presence of silicon in an amount of 
0.204 atomic % calculated as Si/Fe(II), chromium in an amount of 0.496 
atomic % calculated as Cr/Fe(II) and nickel in an amount of 3.02 atomic % 
calculated as Ni/Fe(II). From these results, it is considered that the 
acicular particles of .alpha.-iron(III) oxide hydroxide contain silicon, 
chromium and nickel ions in the crystal lattice. 
FIG. 5 shows the electron microscope photograph of 20000 times in 
magnification of the acicular particles of .alpha.-iron(III) oxide 
hydroxide doped with silicon, chromium and nickel. As is seen in FIG. 5, 
the thus obtained particles was 0.50 .mu.m in length and the axial ratio 
of 28:1 on the average, and the particle size thereof was uniform without 
the contamination of dentrites. 
EXAMPLES 2 TO 13 
In the same manner as in Example 1 except for variously changing the kind 
and the concentration of aqueous solution of ferrous salt, the 
concentration of aqueous sodium hydroxide solution and the kind and the 
amount of water-soluble silicate, water-soluble chromium salt and 
water-soluble nickel salt and the time of addition thereof as shown in 
Table 1, the acicular particles of .alpha.-iron(III) oxide hydroxide doped 
with silicon, chromium and nickel were prepared, the main condition for 
the preparation and the properties of the particles being also shown in 
Tables 1 and 2. 
However, in Example 5 the formation of the aqueous suspension of 
Fe(OH).sub.2 was carried out at a temperature of 40.degree. C. and the 
formation of the acicular particles of .alpha.-iron(III) oxide hydroxide 
was carried out at a temperature of 45.degree. C. 
EXAMPLE 14 
Into 400 liters of an aqueous 5.46 N sodium hydroxide solution in which 379 
g of sodium silicate (corresponding to 28.55% by weight of SiO.sub.2) to 
contain 0.50 atomic % calculated as Si/Fe(II), 644 g of chromium sulfate 
to contain 0.50 atomic % calculated as Cr/Fe(II), 2884 g of nickel sulfate 
to contain 3.0 atomic % calculated as Ni/Fe(II) and 4473 g of magnesium 
sulfate to contain 5.0 atomic % calculated as Mg/Fe(II) had been added, 
300 liters of an aqueous solution of ferrous sulfate at a concentration of 
1.20 mol/liter was added, whereby the formation of an aqueous suspension 
of Fe(OH).sub.2 containing silicon, chromium, nickel and magnesium ions 
was carried out at a temperature of 45.degree. C. and pH of 13.8. 
The thus-prepared aqueous suspension was treated in the same manner as in 
Example 1 except for the change of the blowing time of air to 5.1 hours to 
form the acicular particles of .alpha.-iron(III) oxide hydroxide doped 
with silicon, chromium, nickel and magnesium. 
According to the X-ray diffraction, the thus obtained acicular particles of 
.alpha.-iron(III) oxide hydroxide doped with silicon, chromium, nickel and 
magnesium gave the same pattern as that of the authentic particles of 
.alpha.-iron(III) oxide hydroxide, and the results of X-ray fluorescence 
analysis indicated the presence of silicon in an amount of 0.504 atomic % 
calculated as Si/Fe(II), chromium in an amount of 0.498 atomic % 
calculated as Cr/Fe(II), nickel in an amount of 3.03 atomic % calculated 
as Ni/Fe(II) and magnesium in an amount of 4.98 atomic % calculated as 
Mg/Fe(II). From these results, it is considered that the acicular 
particles of .alpha.-iron(III) oxide hydroxide contain silicon, chromium, 
nickel and magnesium ions in the crystal lattice. 
FIG. 6 shows the electron microscope photograph of 20000 times in 
magnification of the acicular particles of .alpha.-iron(III) oxide 
hydroxide doped with silicon, chromium, nickel and magnesium. As seen in 
FIG. 6, the thus obtained particles was 0.55 .mu.m in length and the axial 
ratio of 33:1 on the average, and the particle size thereof is uniform 
without the contamination of dentrites. 
EXAMPLES 15 TO 28 
In the same manner as in Example 14 except for variously changing the kind 
and the concentration of aqueous solution of ferrous salt, the 
concentration of aqueous sodium hydroxide solution and the kind and the 
amount of water-soluble silicate, water-soluble chromium salt, 
water-soluble nickel salt and water-soluble magnesium salt and the time of 
addition thereof as shown in Table 3, the acicular particles of 
.alpha.-iron(III) oxide hydroxide doped with silicon, chromium, nickel and 
magnesium were prepared, the main condition for the preparation and the 
properties of the particles being also shown in Tables 3 and 4. 
COMATIVE EXAMPLE 1 
In the same manner as in Example 1, however, without adding sodium 
silicate, chromium sulfate and nickel sulfate, the acicular particles of 
.alpha.-iron(III) oxide hydroxide were prepared under the conditions shown 
in Table 1. The specific properties of the product is shown in Table 2. 
FIG. 7 shows the electron microscope photograph of 20000 times in 
magnification of the acicular particles of .alpha.-iron(III) oxide 
hydroxide. 
As is seen in FIG. 7, the thus obtained particles was 0.45 .mu.m in length 
and the axial ratio of 9:1 on the average. Their particle size was not 
uniform and the dentrites were found therein. 
PREATION OF ACICULAR .alpha.-FERRIC OXIDE TICLES 
EXAMPLE 29 
3000 g of the acicular particles of .alpha.-iron(III) oxide hydroxide doped 
with silicon, chromium and nickel obtained in Example 5 were heat-treated 
in the air at 300.degree. C. to obtain the acicular particles of 
.alpha.-ferric oxide doped with silicon, chromium and nickel. 
As a result of the X-ray fluorescent analysis of the thus obtained 
particles, it was detected that silicon, chromium and nickel were present 
therein in an amount of 0.256 atomic % calculated as Si/Fe(II), 0.499 
atomic % calculated as Cr/Fe(II) and 5.03 atomic % calculated as 
Ni/Fe(II), respectively. 
According to electron microscope photographic observation, the length of 
the thus obtained particle was 0.38 .mu.m and the axial ratio thereof was 
30:1 on the average, and the particle size thereof was uniform without the 
contamination of the dentrites. 
EXAMPLE 30 
In the same manner as in Example 29, the acicular particle of 
.alpha.-ferric oxide doped with silicon, chromium, nickel and magnesium 
were prepared while using the acicular particles of .alpha.-iron(III) 
oxide hydroxide doped with silicon, chromium, nickel and magnesium 
obtained in Example 15. 
As a result of the X-ray fluorescent analysis of the thus obtained 
particles, it was detected that silicon, chromium, nickel and magnesium 
were therein in an amount of 0.350 atomic % calculated as Si/Fe(II), 0.498 
atomic % calculated as Cr/Fe(II), 4.98 atomic % calculated as Ni/Fe(II) 
and 3.02 atomic % calculated as Mg/Fe(II), respectively. 
According to electron microscope photographic observation, the length of 
the thus obtained particles was 0.65 .mu.m and the axial ratio of the 
particle was 45:1 on the average, and the particle size thereof was 
uniform without the contamination of the dentrites. 
PREATION OF ACICULAR FERROMAGNETIC ALLOY TICLES OR ACICULAR 
FERROMAGNETIC IRON TICLES 
EXAMPLE 31 
In a 3-liter rotary retort, 100 g of the acicular particles of 
.alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel 
obtained in Example 1, was placed, and hydrogen gas was passed through the 
retort at a rate of 35 liters/minute and at 390.degree. C. while rotating 
the retort to carry out the reduction of the particles therein. After the 
reduction was over, the product was once soaked in toluene and toluene was 
evaporated to form a stable oxidized membrane on the surface of the 
particles in order to prevent the sudden oxidation when the product was 
put out from the retort into the ambient air. The thus produced acicular 
ferromagnetic alloy particles doped with silicon, chromium and nickel 
showed the same X-ray diffraction pattern of a single phase of 
body-centered cubic lattice as that of iron, and as a result of 
fluorescent X-ray analysis, 0.203 atomic % calculated as Si/Fe(II) of 
silicon, 0.498 atomic % calculated as Cr/Fe(II) of chromium and 3.02 
atomic % calculated as Ni/Fe(II) of nickel were detected in the product. 
Accordingly, it is considered that iron, silicon, chromium and nickel are 
in a state of solid solution. 
FIG. 8 shows the electron microscope photograph of 20000 times in 
magnification of the acicular ferromagnetic alloy particles doped with 
silicon, chromium and nickel. As is seen in FIG. 8, the thus obtained 
particles was 0.28 .mu.m in length and the axial ratio of 8:1 on the 
average, and the particle size thereof was uniform without the 
contamination of dentrites. The specific surface area and the apparent 
density of the particles were 38.6 m.sup.2 /g and 0.43 g/ml, respectively. 
And the particles had 1130 Oe of coercive force and 164.5 emu/g of 
saturation magnetization. 
EXAMPLES 32 TO 44 
In the same manner as in Example 31 except for variously changing the kind 
of the starting material particles and the temperature of reduction, the 
acicular ferromagnetic alloy particles doped with silicon, chromium and 
nickel were obtained, the specific properties of the product being shown 
in Table 5. 
The products of Examples 32 to 44 were uniform in particle size without the 
contamination of dentrites according to the electron microscope 
photographic observation. 
EXAMPLE 45 
In the same manner as in Example 31, the acicular ferromagnetic alloy 
particles doped with silicon, chromium, nickel and magnesium were prepared 
while using the acicular .alpha.-iron(III) oxide hydroxide particles doped 
with silicon, chromium, nickel and magnesium obtained in Example 14 and 
the temperature of reduction of 400.degree. C. 
The thus produced acicular ferromagnetic alloy particles doped with 
silicon, chromium, nickel and magnesium showed the same X-ray diffraction 
pattern of a single phase of body-centered cubic lattice as that of iron, 
and as the result of fluorescent X-ray analysis, 0.506 atomic % calculated 
as Si/Fe(II) of silicon, 0.499 atomic % calculated as Cr/Fe(II) of 
chromium, 3.03 atomic % calculated as Ni/Fe(II) of nickel and 4.96 atomic 
% calculated as Mg/Fe(II) of magnesium were detected in the product. 
Accordingly, it is considered that iron, silicon, chromium, nickel and 
magnesium are in a state of solid solution. 
FIG. 9 shows the electron microscope photograph of 20000 times in 
magnification of the acicular ferromagnetic alloy particles. As is seen in 
FIG. 9, the thus obtained particles was 0.24 .mu.m in length and the axial 
ratio of 9:1 on the average and the particle size thereof was uniform 
without the contamination of dentrites. The specific surface area and the 
apparent density of the particles were 45.6 m.sup.2 /g and 0.46 g/ml, 
respectively. And the particles had 1300 Oe of coercive force and 155.2 
emu/g of saturation magnetization. 
EXAMPLES 46 TO 60 
In the same manner as in Example 45 except for variously changing the kind 
of the starting material particles and the temperature of reduction, the 
acicular ferromagnetic alloy particles doped with silicon, chromium, 
nickel and magnesium were obtained, the specific properties of the product 
being shown in Table 6. 
The products of Examples 46 to 60 were uniform in particle size without the 
contamination of the dentrites according to the electron microscope 
photographic observation. 
COMATIVE EXAMPLE 2 
In the same manner as in Example 31, the acicular ferromagnetic iron 
particles were prepared while using the acicular .alpha.-iron(III) oxide 
hydroxide particles obtained in Comparative Example 1. As is seen in FIG. 
10, the electron microscope photograph of 20000 times in magnification of 
the product, the length of the particle was 0.20 .mu.m and the axial ratio 
of the particles was 2:1. The deformation of acicularity of the particles 
and the non-uniformity in particle size were also found. And the specific 
surface area and the apparent density of the particles were 15.8 m.sup.2 
/g and 0.17 g/ml, respectively. Their magnetic properties were inferior, 
the coercive force and the saturation magnetization being 704 Oe and 160.3 
emu/g. 
PRODUCTION OF MAGNETIC TAPE 
EXAMPLE 61 
A magnetic paint was prepared by compounding the acicular ferromagnetic 
alloy particles doped with silicon, chromium and nickel obtained in 
Example 31, a suitable amount of a dispersing agent, a copolymer of vinyl 
chloride and vinyl acetate, thermoplastic polyurethane and a mixed solvent 
comprising toluene, methyl ethyl ketone and methyl isobutyl ketone in a 
predetermined composition and by introducing the mixture to a ball mill 
and mixing to disperse therein for 8 hours. After adding the mixed solvent 
to the thus prepared magnetic paint to be a suitable viscosity, the paint 
was applied onto a polyester film and dried according to the ordinary 
method to produce a magnetic tape. The coercive force (Hc), the residual 
magnetic flux density (Br), squareness ratio (Br/Bm), and the orientation 
ratio of the thus obtained magnetic tape were 1030 Oe, 3720 Gauss, 0.706 
and 1.66, respectively. 
EXAMPLES 62 TO 90 AND COMATIVE EXAMPLE 3 
In the same manner as in Example 61 except for variously changing the kind 
of the acicular ferromagnetic particles, the magnetic tapes were produced. 
The specific properties of the thus obtained magnetic tapes are shown in 
Table 7. 
3 TABLE 1 
Production of acicular particles of .alpha.-FeO(OH) doped with Si, Cr 
and Ni Aqueous Fe(II) Aqueous NaOH Water-soluble Si salt Water-soluble 
Cr salt Water-soluble Ni salt Examples solution solution Time Time 
Time Reac- and Concen- Used Concen- Used Added of Added of Added of 
tion Comparative tration amount tration amount amount addi- amount 
addi- amount addi- time Example Kind (mol/l) (l) (N) (l) Kind (atomic 
%) tion* Kind (atomic %) tion* Kind (atomic %) tion* (hour) 
Example 1 FeSO.sub.4 1.20 300 5.45 400 Sodium 0.20 B Cr.sub.2 
(SO.sub.4).sub.3 0.50 B NiSO.sub.4 3.0 B 6.3 silicate Example 2 " 
" " 5.48 " Sodium 0.50 " " 0.70 " " 5.0 " 6.9 silicate Example 3 " 
" " 6.24 " Sodium 0.35 " " 3.00 " " 4.0 " 6.8 silicate Example 4 " 
" " 6.21 " Sodium 0.20 " " 1.0 " " 2.0 " 7.0 silicate Example 5 " 
" " 5.47 " Sodium 0.25 " " 0.5 " " 5.0 " 6.0 silicate Example 6 " 
1.68 " 7.20 " Sodium 1.00 " " 0.30 " " 5.0 " 7.9 silicate Example 
7 " " " 7.18 " Sodium 0.50 " " 0.60 A " 4.0 " 9.3 silicate Example 
8 " " " 7.16 " Sodium 0.40 " " 0.60 B " 3.0 A 9.5 silicate Example 
9 " " " 7.18 " Sodium 0.50 " " 0.70 A " 3.0 " 9.3 silicate Example 
10 " 1.20 " 6.21 " Potas- 0.35 " " 0.50 B " 4.0 B 6.9 sium 
silicate Example 11 " " " 6.20 " Sodium 0.20 C " 0.30 C " 3.0 C 7.0 
silicate Example 12 " " " 6.25 " Sodium 0.50 B " 1.0 D " 3.0 D 6.3 
silicate Example 13 FeCl.sub.2 1.68 " 7.16 " Sodium 0.35 " CrCl.sub.3 
0.5 B NiCl.sub.2 4.0 B 9.9 silicate Comparative FeSO.sub.4 1.2 " 
5.30 .spsb.1 -- -- -- -- -- -- -- -- -- 12.0 
*A: Watersoluble salt was added to an aqueous Fe(II) solution. 
B: Watersoluble salt was added to an aqueous alkali solution. 
C: Watersoluble salt was added to an aqueous suspension of Fe(OH).sub.2 i 
advance of the blowing of an oxygencontaining gas. 
D: Watersoluble salt was added to an aqueous suspension of Fe(OH).sub.2 
during the blowing of an oxygencontaining gas. 
TABLE 2 
__________________________________________________________________________ 
Particle properties of acicular particles of .alpha.-FeO(OH) 
doped with Si, Cr and Ni 
Examples 
and Length of 
Axial ratio 
Comparative 
Si/Fe(II) 
Cr/Fe(II) 
Ni/Fe(II) 
long axis 
(long axis: 
Example 
(atomic %) 
(atomic %) 
(atomic %) 
(.mu.m) 
short axis) 
__________________________________________________________________________ 
Example 1 
0.204 0.496 3.02 0.50 28:1 
Example 2 
0.505 0.695 5.04 0.45 25:1 
Example 3 
0.355 2.990 4.03 0.40 20:1 
Example 4 
0.203 0.996 2.05 0.44 28:1 
Example 5 
0.257 0.497 5.01 0.38 30:1 
Example 6 
1.030 0.298 5.02 0.45 25:1 
Example 7 
0.500 0.596 4.00 0.60 25:1 
Example 8 
0.403 0.600 3.03 0.60 28:1 
Example 9 
0.505 0.698 3.04 0.55 28:1 
Example 10 
0.354 0.495 4.02 0.55 30:1 
Example 11 
0.204 0.296 3.03 0.60 35:1 
Example 12 
0.504 0.996 3.05 0.45 30:1 
Example 13 
0.354 0.496 4.02 0.50 28:1 
Comparative 
-- -- -- 0.45 9:1 
Example 1 
__________________________________________________________________________ 
3 TABLE 3 
Production of acicular particles of .alpha.-FeO(OH) doped with Si, Cr, 
Ni and Mg Water-soluble Water-soluble Water-soluble Water-soluble 
Aqueous Fe(II) Aqueous NaOH Si salt Cr salt Ni salt Mg salt solution 
solution Added Time Added Time Added Time Added Time Reac- Concen- U 
sed Concen- Used amount of amount of amount of amount of tion 
tration amount tration amount (atom- addi- (atom- addi- (atom- addi- 
(atom- addi- time Examples Kind (mol/l) (l) (N) (l) Kind (ic %) tion* 
Kind (ic %) tion* Kind (ic %) tion* Kind ic %) tion* (hour) 
Example 14 FeSO.sub.4 1.20 300 5.46 400 Sodium 0.50 B Cr.sub.2 
(SO.sub.4).sub.3 0.50 B NiSO.sub.4 3.0 B MgSO.sub.4 5.0 B 5.1 
silicate Example 15 " 1.68 " 7.64 " Sodium 0.35 " " 0.50 " " 5.0 " " 3.0 
" 8.8 silicate Example 16 " " " 7.26 " Sodium 0.50 " " 1.0 " " 4.0 
" " 2.0 " 9.0 silicate Example 17 " " " 7.31 " Sodium 0.20 " " 0.3 
" " 2.0 " " 7.0 A 10.4 silicate Example 18 " " " 7.51 " Sodium 
0.50 " " 0.7 " " 3.0 " " 10.0 B 8.0 silicate Example 19 " 1.20 " 
6.49 " Sodium 0.35 " " 0.4 " " 2.0 " " 15.0 " 5.3 silicate Example 
20 " " " 6.42 " Sodium 0.20 " " 3.0 " " 4.0 " " 5.0 " 6.5 silicate 
Example 21 " " " 6.26 " Sodium 1.00 " " 0.30 " " 3.0 " " 1.0 " 4.2 
silicate Example 22 " 1.68 " 7.10 " Sodium 0.35 " " 0.60 A " 3.0 " " 4.0 
" 8.8 silicate Example 23 " " " 7.47 " Sodium 0.20 " " 0.50 B " 
3.0 A " 5.0 " 8.5 silicate Example 24 FeCl.sub.2 " " 7.29 " Sodium 
0.35 " CrCl.sub.3 0.50 " NiCl.sub.2 3.0 B MgCl.sub.2 5.0 " 8.8 
silicate Example 25 FeSO.sub.4 " " 7.47 " Potas- 0.35 " Cr.sub.2 
(SO.sub.4).sub.3 0.50 " NiSO.sub.4 3.0 " MgSO.sub.4 5.0 " 8.8 sium 
silicate Example 26 " " " 7.46 " Sodium 0.20 " " 0.40 A " 3.0 A " 
5.0 A 9.0 silicate Example 27 " 1.2 " 6.51 " Sodium 0.20 C " 0.50 
C " 3.0 C " 5.0 C 8.6 silicate Example 28 " " " 6.42 " Sodium 0.20 
B " 0.50 D " 3.0 D " 3.0 D 8.8 silicate 
*A: Watersoluble salt was added to an aqueous Fe(II) solution. 
B: Watersoluble salt was added to an aqueous alkali solution. 
C: Watersoluble salt was added to an aqueous suspension of Fe(OH).sub.2 i 
advance of the blowing of an oxygencontaining gas. 
D: Watersoluble salt was added to an aqueous suspension of Fe(OH).sub.2 
during the blowing of an oxygencontaining gas. 
TABLE 4 
__________________________________________________________________________ 
Particle properties of acicular particles of .alpha.-FeO(OH) doped with 
Si, Cr, Ni and Mg 
Length of 
Axial ratio 
Si/Fe(II) 
Cr/Fe(II) 
Ni/Fe(II) 
Mg/Fe(II) 
long axis 
(long axis: 
Examples 
(atomic %) 
(atomic %) 
(atomic %) 
(atomic %) 
(.mu.m) 
short axis) 
__________________________________________________________________________ 
Example 14 
0.504 0.498 3.03 4.98 0.55 33:1 
Example 15 
0.353 0.495 5.00 3.00 0.65 45:1 
Example 16 
0.502 0.994 4.04 2.01 0.60 35:1 
Example 17 
0.203 0.296 2.01 6.98 0.60 40:1 
Example 18 
0.505 0.695 3.04 10.02 0.62 37:1 
Example 19 
0.354 0.398 2.01 14.94 0.60 35:1 
Example 20 
0.205 2.970 4.02 4.97 0.64 35:1 
Example 21 
1.060 0.299 3.05 1.01 0.60 33:1 
Example 22 
0.356 0.600 3.04 4.00 0.63 40:1 
Example 23 
0.207 0.496 3.01 5.05 0.60 40:1 
Example 24 
0.355 0.498 3.02 4.97 0.65 40:1 
Example 25 
0.353 0.497 3.02 4.98 0.65 40:1 
Example 26 
0.201 0.317 3.04 5.02 0.62 35:1 
Example 27 
0.206 0.496 3.03 5.02 0.65 40:1 
Example 28 
0.206 0.496 3.03 4.96 0.65 40:1 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Properties of acicular ferromagnetic alloy particles doped with Si, Cr 
and Ni 
Kind of Magnetic 
particles properties 
to be Satura- 
treated 
Reduc- 
Particle Properties tion Coer- 
Examples 
(Examples 
tion Specific 
magneti- 
cive 
and and Temper- Length of 
Axial ratio 
surface 
zation 
force 
Comparative 
Comparative 
ature 
Si/FE(II) 
Cr/Fe(II) 
Ni/Fe(II) 
long axis 
(long axis: 
area .sigma.s) 
(Hc) 
Example 
Example 
(.degree.C.) 
(atomic %) 
(atomic %) 
(atomic %) 
(.mu.m) 
short axis) 
(m.sup.2 /g) 
(emu/g) 
(Oe) 
__________________________________________________________________________ 
Example 31 
Example 1 
390 0.203 0.498 3.02 0.28 8:1 38.6 164.5 
1130 
Example 32 
Example 2 
400 0.501 0.696 5.01 0.25 9:1 39.6 164.4 
1200 
Example 33 
Example 3 
350 0.353 2.99 4.04 0.30 8:1 41.6 150.6 
965 
Example 34 
Example 4 
420 0.202 0.998 2.01 0.25 9:1 37.5 155.4 
1030 
Example 35 
Example 5 
400 0.254 0.496 5.03 0.20 11:1 43.7 165.8 
1305 
Example 36 
Example 6 
470 1.020 0.297 5.02 0.25 9:1 35.6 156.3 
1080 
Example 37 
Example 7 
380 0.503 0.598 4.03 0.25 8:1 36.4 162.4 
980 
Example 38 
Example 8 
340 0.402 0.600 3.02 0.25 8:1 37.4 156.3 
960 
Example 39 
Example 9 
400 0.501 0.696 3.03 0.25 8:1 35.6 166.5 
975 
Example 40 
Example 10 
380 0.354 0.499 4.03 0.30 10:1 40.0 165.2 
1145 
Example 41 
Example 11 
390 0.202 0.300 3.02 0.30 10:1 38.8 162.4 
1180 
Example 42 
Example 12 
400 0.502 1.00 3.00 0.25 9:1 39.7 156.3 
1050 
Example 43 
Example 13 
400 0.353 0.498 4.02 0.28 10:1 38.4 165.4 
1120 
Example 44 
Example 29 
390 0.253 0.499 5.02 0.20 12:1 44.8 166.3 
1302 
Comparative 
Comparative 
380 -- -- -- 0.20 2:1 15.8 160.3 
704 
Example 2 
Example 1 
__________________________________________________________________________ 
TABLE 6 
__________________________________________________________________________ 
Properties of acicular ferromagnetic alloy particles doped with Si, Cr, 
Ni and Mg 
Magnetic Properties 
Satura- 
Kind of Reduc- 
Particle Properties tion 
particles 
tion Si/ Cr/ Ni/ Mg/ Specific 
matneti- 
to be Temper- 
Fe(II) 
Fe(II) 
Fe(II) 
Fe(II) 
Length of 
Axial ratio 
surface 
zation 
Coercive 
treated 
ature (atomic 
(atomic 
(atomic 
(atomic 
long axis 
(long axis: 
area (.sigma.s) 
force (Hc) 
Examples 
(Examples) 
(.degree.C.) 
%) %) %) %) (.mu.m) 
short axis) 
(m.sup.2 /g) 
(emu/g) 
(Oe) 
__________________________________________________________________________ 
Example 45 
Example 14 
400 0.506 
0.499 
3.03 
4.96 
0.24 9:1 45.6 155.2 1300 
Example 46 
Example 15 
400 0.354 
0.500 
5.01 
3.01 
0.40 12:1 44.0 165.4 1290 
Example 47 
Example 16 
430 0.503 
0.998 
4.05 
2.02 
0.35 9:1 42.0 157.2 1092 
Example 48 
Example 17 
350 0.202 
0.295 
2.01 
6.97 
0.35 11:1 40.0 132.6 1160 
Example 49 
Example 18 
400 0.509 
0.697 
3.03 
10.01 
0.35 10:1 44.3 133.7 1225 
Example 50 
Example 19 
450 0.352 
0.400 
2.02 
14.95 
0.30 10:1 39.4 128.4 1230 
Example 51 
Example 20 
470 0.203 
2.980 
4.01 
4.99 
0.25 7:1 47.4 134.3 1060 
Example 52 
Example 21 
430 1.080 
0.301 
3.06 
1.02 
0.30 9:1 35.6 148.2 1120 
Example 53 
Example 22 
380 0.357 
0.601 
3.05 
4.01 
0.30 11:1 45.0 153.6 1100 
Example 54 
Example 23 
380 0.206 
0.495 
3.01 
5.06 
0.30 12:1 46.0 155.5 1130 
Example 55 
Example 24 
380 0.357 
0.497 
3.03 
4.95 
0.28 12:1 45.3 157.4 1285 
Example 56 
Example 25 
380 0.353 
0.499 
3.00 
4.99 
0.26 12:1 44.6 154.6 1310 
Example 57 
Example 26 
340 0.204 
0.399 
3.06 
5.03 
0.30 10:1 40.3 149.5 1120 
Example 58 
Example 27 
400 0.205 
0.501 
3.02 
5.02 
0.28 11:1 43.5 157.6 1305 
Example 59 
Example 28 
400 0.208 
0.496 
3.01 
4.98 
0.30 12:1 44.2 160.3 1300 
Example 60 
Example 29 
400 0.351 
0.501 
4.99 
3.03 
0.30 13:1 44.6 163.6 1295 
__________________________________________________________________________ 
TABLE 7 
__________________________________________________________________________ 
Properties of Tape 
Kind of magnetic 
Residual 
Examples 
particles 
Coercive 
magnetic Orientation 
ExampleComparativeand 
Example)Comparative(Examples and 
(Oe)(Hc)force 
(Gauss)(Br)flux density 
(Br/Bm)ratioSquareness 
##STR1## 
__________________________________________________________________________ 
Example 61 
Example 31 
1030 3720 0.706 1.66 
Example 62 
Example 32 
1084 3660 0.710 1.72 
Example 63 
Example 33 
854 3550 0.686 1.64 
Example 64 
Example 34 
950 3610 0.692 1.68 
Example 65 
Example 35 
1155 3920 0.746 2.03 
Example 66 
Example 36 
990 3610 0.701 1.68 
Example 67 
Example 37 
863 3590 0.694 1.66 
Example 68 
Example 38 
852 3560 0.688 1.63 
Example 69 
Example 39 
860 3620 0.692 1.68 
Example 70 
Example 40 
1011 3740 0.724 1.90 
Example 71 
Example 41 
1066 3690 0.712 1.84 
Example 72 
Example 42 
942 3660 0.701 1.69 
Example 73 
Example 43 
1010 3690 0.711 1.73 
Example 74 
Example 44 
1164 3900 0.744 2.04 
Example 75 
Example 45 
1186 3670 0.713 1.70 
Example 76 
Example 46 
1150 3860 0.740 2.13 
Example 77 
Example 47 
975 3764 0.697 1.68 
Example 78 
Example 48 
1012 3920 0.751 2.36 
Example 79 
Example 49 
1096 3485 0.708 1.71 
Example 80 
Example 50 
1100 3230 0.734 1.80 
Example 81 
Example 51 
910 3596 0.684 1.66 
Example 82 
Example 52 
992 3602 0.716 1.75 
Example 83 
Example 53 
963 3724 0.714 1.75 
Example 84 
Example 54 
986 3860 0.725 1.94 
Example 85 
Example 55 
1140 3624 0.738 2.10 
Example 86 
Example 56 
1175 3700 0.742 2.30 
Example 87 
Example 57 
980 3940 0.754 2.40 
Example 88 
Example 58 
1170 3742 0.734 2.11 
Example 89 
Example 59 
1183 3790 0.741 2.25 
Example 90 
Example 60 
1155 3812 0.754 2.42 
Comparative 
Comparative 
569 2230 0.553 1.20 
Example 3 
Example 2 
__________________________________________________________________________