CA1064223A - Method of making goethite powder - Google Patents
Method of making goethite powderInfo
- Publication number
- CA1064223A CA1064223A CA182,127A CA182127A CA1064223A CA 1064223 A CA1064223 A CA 1064223A CA 182127 A CA182127 A CA 182127A CA 1064223 A CA1064223 A CA 1064223A
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- Canada
- Prior art keywords
- ferrous
- hydroxide
- powder
- goethite
- mixing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
- G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
- G11B5/70652—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides gamma - Fe2 O3
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G49/00—Compounds of iron
- C01G49/02—Oxides; Hydroxides
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
- G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
- G11B5/70647—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides with a skin
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/42—Magnetic properties
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Dermatology (AREA)
- General Health & Medical Sciences (AREA)
- Hard Magnetic Materials (AREA)
- Compounds Of Iron (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of malding goethite powder in which a ferrous hydroxide suspension is stirred for about three hours in an inert atmosphere and then is oxidized to form goethite powder.
A method of malding goethite powder in which a ferrous hydroxide suspension is stirred for about three hours in an inert atmosphere and then is oxidized to form goethite powder.
Description
BACKGROUND OF THE INVENrION
Field of the Invention . _ This invention relates to a method of making goethite powder and more particularly to a method of making goethite powder useful for making maghemite powder of high coercivity.
_escription of the Prior Art In a magnetic tape suitable for use with a tape recorder, ~ ;
a video tape recorder and the like, acicular maghemite powder (or gamma-Fe203 powder) is widely used. However, as the coercivity (Hc) of conventional acicular maghemite powder is under 400 oersteds, it is t not suitable for high density recording. -Acicular maghemite powder made by the known route of :~ -reducing and oxidizing goethite powder (or alpha-FeOOH powder) has ~ -a coercivity which depends on the particle size, the particle shape, 1 and the particle size uniformity of the goethite powder used as the .j . , starting material.
Heretofore, two methods have commonly been employed for making conventional goethite powder. One of these methods involves bubbling air through a solution of iron sulfate and sodium hydroxide to ~- ~
. ,--, '.
form goethite powder and sulfuric acid, and then the resulting sulfuric acid i8 changed to iron sulfate by iron. One disadvantage of this ~ method is that excessive time (typically ranging from several days to ;~ several months) are required for the formation of goethite. Another ' ~ disadvantage of this method is that the coercivity (Hc) of the maghemite - powder derived from the resulting goethite by the above indicated knavn , ' *
Field of the Invention . _ This invention relates to a method of making goethite powder and more particularly to a method of making goethite powder useful for making maghemite powder of high coercivity.
_escription of the Prior Art In a magnetic tape suitable for use with a tape recorder, ~ ;
a video tape recorder and the like, acicular maghemite powder (or gamma-Fe203 powder) is widely used. However, as the coercivity (Hc) of conventional acicular maghemite powder is under 400 oersteds, it is t not suitable for high density recording. -Acicular maghemite powder made by the known route of :~ -reducing and oxidizing goethite powder (or alpha-FeOOH powder) has ~ -a coercivity which depends on the particle size, the particle shape, 1 and the particle size uniformity of the goethite powder used as the .j . , starting material.
Heretofore, two methods have commonly been employed for making conventional goethite powder. One of these methods involves bubbling air through a solution of iron sulfate and sodium hydroxide to ~- ~
. ,--, '.
form goethite powder and sulfuric acid, and then the resulting sulfuric acid i8 changed to iron sulfate by iron. One disadvantage of this ~ method is that excessive time (typically ranging from several days to ;~ several months) are required for the formation of goethite. Another ' ~ disadvantage of this method is that the coercivity (Hc) of the maghemite - powder derived from the resulting goethite by the above indicated knavn , ' *
- 2- ~ ~
~".. ," ........ . ... , ~ . . ,, ."
' , ' ~ '';' 10~;42;23 route, is un~er 370 oersteds.
The other of thesc methods involves bubbling air through an aqueous solution of ferrous salt and alkaline hydroxide to form goethite powder. The maghemite powder derived from such resulting gcethite by the above indicated known route generally has a higher coercivity (Hc) than the maghemite powder derived from the goethite obtained by the preceding two-st~ge metho~. However, one disadvantage of the second method is that about 10 to 20 hours are required for the formation of goethite. Another disadvantage of this second method is that the hydroxide is apt to gel and be non-uniform, particularly if a suspension of ferrous hydroxide of high density is used, thereby making it is very difficult to form a geothite powder with uniform particle size.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a method for making '~
a goethite powder using an aqueous ferrous hydroxide suspension.
The suspension is stirred for a relatively brief period of time in an inert gaseous atmosphere. Thereafter, the resulting suspension is cq~idized with oxygen to form goethite powder.
An object of this invention is to provide an improved 'J method of making a goethite powder suitable for use as a starting ~ -material for making an acicular maghemite powder preferably in a short time.
Another object of this invention is to provide a method of making a goethite powder suitable for use as a starting material 40r ', . ,;
10~42Z3 making an acicular maghemite powder of high coercivity (pref-erably over 400 oersteds).
A further object of this invention is to provide a method of making goethite powder with uniform particle size by a step of stirring ferrous hydroxide suspension in an inert atmosphere.
More particularly there is provided a method of making acicular goethite powder comprising the steps of:
a) forming a ferrous hydroxide suspension by mixing an aqueous solution of an alkali hydroxide selected from the group consisting of potassium hydroxide and sodium hydroxide ~ ~ -with an aqueous solution of a ferrous salt selected from the group consisting of ferrous chloride and ferrous sulfate;
b) continuously stirring the resulting mixture simultan-: eously throught said mixing and after said mixing for a total period of from 2 to 5 hours to produce a milk-white ferrous hydroxide suspension; `- ~;
steps a) and b) being carried out under an inert gaseous - ~ -atmosphere and at a temperature within the range from 60 to 80C; and c) oxidizing said milk-white ferrous hydroxide suspen~
sion with an oxygen containing gas, at a temperature within the range from 50 to 80C when the alkali hydroxide is ; potassium hydroxide and from 40 to 60C when the alkali hydrox-ide is sodium hydroxide, for a period of from 4 to 6.5 hours s; to form yellow goethite powder.
Other and further aims, objects, purposes, advantages, utilities, and eatures will be apparent to those skilled in ~-the art from a reading of the present specification and -drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph showing the relationship between the ~
~ 4 ~ ~; -E
time of stirring in a nitrogen atmosphere and the time required for a reaction according to the embodiment of Example 1 here- -inbelow;
Figure 2 is a graph showing the relationship between ~ .
the time of stirring in a nitrogen atmosphere and the coercivity (Hc) of a resulting maghemite powder according to such Example .
1 embodiment; ;
Figure 3 is a graph showing the relationship between the time of stirring in a nitrogen atmosphere and the time required ~-for a reaction according to the embodiment of Example 2 of this ~
invention hereinbelow; ~ ~ .
Figure 4 is a graph showing the relationship between -the time of stirring in a nitrogen atmosphere and the --coercivity (Hc) of a resulting ma~hemite powder according to such Example 2 embodiment of this invention; and - -.~ ,. ... .
, :' -., ;.
~ :
,:" ~
.-, .. ,. ~.
.. :. ~.
. .
.~ ~
.~ -.
;; .' ~
`' ,:,`.- :' -.~.
'~ J ~-.
:' ~
~ - 4a -': ',~`, ', ~ ; ~' .
' ~ ' 10~4223 Figure S is a gr~ph showing the relationship between the mol ratio of OH--tO Fe~ (OH /Fe~) and the coercivity (Hc) of a maghemite powder derived from a goethite powder wluch is prepared by the teachings of the present invention.
EMBODIMENI S
The present invention is further illustrated by reference to the following Examples. Those skilled in the art will appreciate that other and further embodiments are obvious and within the spirit and scope of this invention from the teachings of these present Examples taken with the accompanying specification and drawings.
EXAMP~E 1 -~
An alkaline solution including potassium hydroxide in an amount of 392 grams (7. 0 moles) mixed with 800 milliliters of water was charged to a reaction vessel.
279 grams (1. 4 moles) of ferrous chloride (FeC12 4H2O) dissolved into 400 milliliters of water was gradually added to the alkaline solution with stirring to form a colloidal suspension of ferrous hydrox-ide. Previously, an inert gas, for example, a nitrogen gas was passed, ;
as by bubbling, through the alkaline solution a~ a flow rate of 3.0 liters ~ -per minute to remove oxygen therein.
~ub~
As the ferrous chloride was added, nitrogen gas was tsparged) Into and through the resulting solution in a reaction vessel while keeping the temperature at 80C with continuous stirring using this procedure, a covering or blanket of the nitrogen gas was maintained .
- .. . . . .. . , , -, . . .,. ",, : ~ :
., .
~ 064Z23 over the surface of the resulting liquid reaction system. This bubbling was continued until a milk-white, uniform colloidal ferrous hydroxide was obtained. The time required for the re- ~
action (as measured from the commencement of reacting alkali ~ --hydroxide with the ferrous chloride to a point when formation of this colloidal ferrous hydroxide was deemed complete) was about three hours.
Next, the nitrogen gas was switched over to air, and air sparging was commenced at a flow rate of 5.0 l/min, through the resulting liquid reaction system at the temperature of 80C
with continuous stirring to form a yellow goethite in 4.5 hours.
After rinsing with water, the goethite material was filtered, dried and pulverized to obtain 120 grams of yellow goethite powder. The particles of this yellow goethite powder were acicular, about 0.5 mlcrons in length, and about 20 in acicular ratio, where the acicular ratio value is obtained by ,i .
dividing the average length of the particle by the average - .
diameter of the particle. Moreover, the uniformity of the ~
particle size of the goethite powder was good. -` 0 2.0 grams of this goethite powder was reduced at a temperature of 350C with the passing of hydrogen gas thereover at a flow rate of 1.0 l/min for one hour, after which the . ~ - .
: resulting product was oxidized by passing air thereover at a temperature of 230C for one hour. As a result, a brown maghemite ` powder (gamma-Fe2O3 powder) was obtained. The coercivity (Hc), squareness ratio (Rs) and saturation magnetization of this resulting gamma-Fe2O3 were 466 oersteds, 55~, and 69.5 emu/g, respectively.
~ 2.0 more grams of the same goethite powder was reduced ; 30 :,'~ . ., ... .
'''' .
,., ,~.
, ~ .. . ..... ,,. ~
., .. - . .:
' ' '. , ' ' ' , at a temperature of 380C with the passing of hydrogen gas there-over at a flow rate of l.0 l/min for one hour, after which the resulting product was oxidized by passing air thereover at a temperature of 250C for one hour, to produce a maghemite powder.
The coercivity (Hc), squareness ratio (Rs) and saturation mag-netization of such gamma-Fe2O3 were 480 oersteds, 55%, and 65.1 emu/g, respectively.
Referring to Figure 1, there is seen a graph which shows the relationship between the time of stirring in the nitrogen atmosphere and the required reaction time at (a) a constant density of the suspension comprising the liquid reaction system (b) a constant reaction temperature and (c) a constant flow rate of air. In this graph, the axis of the abscissas shows the time of stirring in the nitrogen atmosphere, and the axis of ordinates shows the required reaction time. The curve a shows the varia-tions of the time required for the formation of the goethite after the beginning of the oxidation reaction, and the curve _ shows the variations of the time of stirring in the nitrogen atmosphere plus the time required for the formation of goethite after the beginning of the oxidation reaction.
In this Example, the time of the end of the oxidative reaction between air and colloidal ferrous hydroxide (that is, the time when the ferrous (Fe++) ions are substantially consumed) was decided in the following manner: A sample of 5 millilters of the reacting liquid reaction system was taken out from the reaction vessel every ten minutes after the beginning of such oxidative reaction (this is, after commencement of ferrous chloride ~-, addition to potassium hydroxide " :' .
''~ ' `
- 7 - ~ `
''', . : ~ ~; ' " ' ,,~ ' ~ ' '` ' ; ' ~
,. . ... .
10~4'~Z3 with n~tro~en blo~ving), and the sa.nl-lc was added to a dilute hydro-chlonc a~id solution from which oxygen had been removed to prevent oxidation by the passing o~ nitrogen gas therethrougll, and the unreacted ferrous hydroxide in sucll sa.nple was dissolved therein. The amount of hydrochloric aeid in this dilute solution was adjusted so that the Ptl of the resulting solution was in the range from one to seven. Then, the Ferrous ions Fe+t in the resulting solution were detected by using a sensitive Fe~ ion detecting pa~er. The paper used was and is available commercially as Merckoquant Fe~, a trade mark of E-Merck Company. The time when no ferrous ion Fe~ could be so detected in such a sample was regarded a3 the time of the end of the oxida~ive reac~ion.
Figure 2 shaws the relationship between the time of stirring in the nitrogen atmosphere and the coercivity(Hc) of the gamma-Fe203 derived from the resulting goethite powder as the starting material.
As shown by Figure 2, it is prefera~le to stir the solution for a time interval of from about 2 to 5 hours in an inert (e. g., oxygen free) gas in order to obtain the desired goethite powder product for use as a starting material for the gamma-Fe203 of high coercivity, for example, - over 440 oersteds.
~ .
EXAMPLE 2 ~ -For the comparison, the following conventional method of making goethite powder and the property of the gamma-Fe203 obtained in the same method, is described in the following example:
The a~ueous solution of ferrous chloride was mixed with ., .
-8- .
10~i4Z23 the aqueous solution of po~assium hydro~cicic and sdrr~d at the tcmpera-ture of 80C with the passing of air at a floN rate of 5.0 l/min. ln this case, there was not the stirring trea~mcnt in the incrt a mosphere as in the method of the invention. In 9.5 hours, the reaotion ended and yellow goethite was formed. Aftcr rinsing with watcr, the material was filtered, dried and pulverized to obtain 120 grams of goethite pawder. The particles of the resulting goethite po~vder were acicular, a~out 0. 8 microns in length and a~out 10 in acicular ratio.
As in the Example 1 of the invention, 3.0 grams of the goethite powder was reduced at the temperature of 350~C by hydrogen gas and then it was oxidized at the temperature of 230C by air to --form the gamma-Fe2O3. The coercivity (Hc), squareness ratio (Rs) and saturation magnetization c;~ of the resulting gamma-Fe2O3 were 387 oersteds, 54% and 67.1 emu/g, respectively. As understood -from this results, the coercivity (Hc) of the gamma-Fe2O3 a_cording to the method of this invention is higher than that of the gamma Fe2O3 ~ ~Y
according to the conventional method. -~
An alkaline solution including sodium hydro~de in an . -~
amount of 256 grams (6.4 moles) mixed with 600 milliliters of water ;~
was charged to a reaction vessel.
445 grams (1. 6 moles) of ferrous sulfate (FeS04 7H2O) dissolved into 600 milliliters of water was gradually added to the alkaline solution with sarring to form suspensioll of ferrous hydro~cide.
Previously, a nitrogen gas was passed through the alkaline solution at a , :
,' , .
.
, 9 ~;........... . : . . . .
: - ,~ . . , , , ,, . .:
-:.......... : . . ::, .' ~ .' ', , 10~4'~23 flow rate of 2.0 l/min to remove oxygen therein. Simultaneously, and in the manner of Example 1, nitrogen (N2) gas was sparged into the resulting suspension maintained at a temperature of 60 C with continuous stirring until milk-white uniform colloidal ferrous hydroxide was obtained. The time required for this reaction was about three hours.
After that, the nitrogen gas was switched over to air which, at a flow rate of 1.0 l/min, was passed through the resul-ting suspension maintained at a temperature of 60C with contin-10 uous stirring to form by oxidation yellow goethite in 6.5 hours.
After rinsing with water, the material was filtered, dried and pulverized to obtain 140 grams of yellow goethite powder. The particles of the yellow goethite powder were acicular, about 0.5 microns in length and about 20 in acicular ratio (measured as in Example 1). Moreover, the uniformity of the particle size of the goethite powder was good.
2.0 grams of this goethite powder was reduced at a temperature of 350C with the passing therethrough of hydrogen gas at a flow rate of 1.0 l/min for one hour, and then the produce 20 was oxidized by air passing therethrough at a temperature of 250C for one hour. As the result, the brown powder of gamma-Fe2O3 was obtained. The coercivity (Hc~, squareness ratio (Rs), and saturation magnetization of this gamma-Fe2O3 powder was 458 oersteds, 55% and 65.6 emu/g, respectively. -Referring to Figure 3, there is seen a graph showing the relationship in this example between the time of stirring ~' in the nitrogen atmosphere and the required reaction time at st (a) a constant density of the :
- 10 - ~
. ., . - -, . .~ ~, , " , , . ~ ~ . ., ,~,: .
.
10~4~23 reaetioll suspension, (b) a constant reaction temperaturc, and (c) a constant flow rate of air. In this graph, the axis of abscissas shows the time of stirring in the nitrogen atmosphcre and the ax~s of ordi-na~es sho~s the required ~me. A curve a shows the variations of the time required for the formation of the goethite after the beginning of the air oxidative reaction, and a curve b shows the variations of the time of stirring in the nitrogen atmosphere plus the time required for the formation of the goethite after the beginning o the oxidative reaction.
Figure 4 shows the relationship in this Example between the time of stirring in the nitrogen atmosphere and the coercivity (Hc) of the gamma-Fe203 powder derived from the resulting goethite powder as the starting material. As shown in Figure 4, it is preferable to stir the solution for 2 to 4 hours in the nitrogen gas in order to obtain a -desired goethite powder for use as the starting material for the ~ ~ -gamma-Fe203 of high coercivity, for example, over 440 oersteds.
In Example 1 and Example 3, the amounts of potassium hydroxide (KOH) and ferrous chloride (FeC12 4H20), and sodium hydro~de (NaOH) and ferrous sulfa-~e (FeS04 7H20), were varied; in other words, the mo~ ratio of OH ion to Fe~ ion (OH /Fe~) was varied.
,~ .
An alkaline solution including potassium hydroxide in an - amount of 336 grams (6.0 moles) mixed with 900 milQliters of water was charged to a reaction vessel.
. ... .
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.. . . . . .
334 grams (1.2 moles) of ferrous aulfate (FeSO4.7H2O) dissolved into 500 milliliters of water was gradually added to the alkaline solution with stirring to form a suspension of ferrous hydroxide. Previously, a nitrogen gas was passed through the alkaline solution at a flow rate of 3.0 l/min to remove oxygen therein. Simultaneously, in a manner similar to Example 1, nitrogen gas was sparged into the resulting suspension at a tem-perature of 80C with continuous stirring until the milk-white uniform colloidal ferrous hydroxide was obtained. The time required for this reaction was about three hours.
After that, the nitrogen gas was switched over to air which, at a flow rate of 5.0 l/min, was passed through the re-sulting suspension at the temperature of 80C with continuous stirring to form by oxidation yellow geothite in 4.0 hours.
After rinsing with water, the material was filtered, dried and pulverized to obtain 109 grams of yellow goethite ; powder. The particles of the yellow goethite powder were acicular, about 0.4 microns in length and about 15 in acicular ratio (measured as in Example 1). Moreover, the uniformity of the 2Q particle size of the goethite powder was good.
. .;.
2.0 grams of this goethite powder was reduced at a temperature of 370C with the passing of hydrogen gas there-through at a flow rate of 1.0 l/min for one hour, and then the product was oxidized by passing air therethrough at a temperature of 250C for one hour. A brown powder of gamma-Fe2O3 was obtained.
The coercivity (Hc), squareness ratio (Rs), and saturation mag-netization of this gamma-Fe2O3 powder was 447 oersteds, 55%, and 72.0 emu/g, respectively. ;
', , r,-, An alkaline solution including sodium hydra~cide in an amount of 270 grams (7. 0 moles) mixed with 800 milliliters of water was charged to a reaction vessel.
279 grams (1.4 moles) of ferrous chloride (FeC12 4H2O) dissolved into 500 milliliters of water was gra~ually added to the alkaline solution with stirring to form a suspension of ferrous hydroxide.
~ ,, Previously, a nitrogen gas was passed through the alkaline solution a~ ~:
a flow ra~e of 3. 0 l/min to remove oxygen therein. Simultaneously, a rdtrogen gas was passed through the resulting suspension at a temper-ature of 60C with continucJus strong stirring by ultrasonic means for 2.5 hours to obtain milk-white uniform colloidal ferrous hydro.Yide.
After that, the nitrogen gas was switched over to air which, at a flow rate o 2. 0 l/min, was passed through the resulting suspension -at a temperature of 60C with continuous ultrasonic stirring to form yellaw goethite in 4. 0 hours.
After rinsing with water, this product material was filtered, ~-dried and pulverized to obtain 120 grams of yellow goethite powder.
The particles of the yellow goethite powder were acicular, about 0. 5 ~'~ .
~- microns in length, and about 20 in acicular ratio (measured as in ~`
Example 1). Moreover, the uniformity of the particle size of the goethite powder was good.
2. 0 grams af this goethite pa,vder was reduced at a temperature of 360C with the pas~ing there~hrough of hydrogen gas at a flov rate of 1.0 l/min for one hour, and then the product was 03ddized by air passing therethraugh at a temperature of 250C for , ' -13^
l"," ~ , `.- ` - ` `':, ` ;, ` . ., ` :
. . ` . ` . ` ~.
.. . ..
~ 0~4223 one hour. As tl1e rcsult, a brown powdcr of gamma-Fe203 was obta ncd. The coercivity (Hc), squareness ra~o (Rs), and satura~ion magnetization ~ig~ r,3 of this gamma-Fe203 was 455 oersteds, 55%, and 71. 2 emu/gJ respectively.
The relationships between the variations of the mol ratio and the coercivity (Hc) were examined in gamma-Fe203 powder derived from goethite powder produced by the method aI this invention used as the starting material. The results are illustrated by the curves shawn in Figure 5. Here, a curve a shows the case of a goethite derived from potassium hydroxide and ferrous chloride, and a curve b shows ~ -the case of goethite derived from sodium hydroxide and ferrous sulfate. -Figure 5 illustrates thaL gamma-Fe203 powder having higher coerdvity (Hc) than a ^onventional gamma-Fe203 powder can be obtained by having a mol ratio (OH /Fe~) of over 2.5, and gamma-Fe203 p~wder having a coercivity (Hc) of over 440 oersteds can be obtained by ha~Ting a mol ratio (OH /Fe~) ranging from 3. 2 to 4.5, in the case of goethite powder derived from potassium hydroxide (KOH) and ferrous chloride - .
(FeC12 4H20); this case is called the "KOH-FeC12 method" herein.
Figure S further illustrates that gamma-Fe203 powder having higher `~
coercivity (Hc) than the conventional gamma-Fe203 powder can be obtained by having a mol ratio (OH /Fe~) of over 3, and gamma-Fe2o3 powder having coercivity (Hc) of over 440 oersteds can be obtained by ha~ing a mol ratio ranging from 3. 8 to 5. 8, in the case of gaethite powder derived from sodium hydroxide (NaOH) and ferrous sulfate r ;''' ' ' `'`: ' ~ . .
:~ ' ~0~4Zz3 (FeS04-71-120); this case is callcd the "NaO~ FeSO4 method" herein.
While in the above examples, go~thite powder produced by the process of this inven~on is used as a starting material for making acicular gamma-Fe203 p~wder, it will be appreciated that, of course, such may also be used as starting ma;erial for ma~.dng acicular magnetite powder, as above indicated.
DESCRIPrION OF THE PREFÆRRED EMBODIMENIS
The present invention is directed to a method of ma'.cing goethite powder. The method involves the step of mixing an aqueous solution of a water soluble ferrous salt with an aqueous solution of an aLkali hydroxide to form a ~errous hydroxide. During such mixing, the liquid rea_tant system is stirred in an inert (non-oxidative) atmosphere.
`The resulting colloidal ferrous hydroxide suspension is then oxidized, `
with an oxygen containing gas to convert the ferrous hydroxide to goethite powder.
Preferably, the alkali hydroxide is sodium hydroxide or potassium hydroxide. Preferably, the ferrous salt is ferrous sulfate or ferrous chloride. Preferably, the stirring time for the mixture of lakali hydroxide and ferrous salt ranges from about 2 to 5 hours with -a time of from about 2 to 4 hours being more preferred when ferrous sulfate is employed as the ferrous salt. Preferably, the mol ratio of OH- ions to Fe~ ions (OH /Fe~) is over about 2. 5, and when, more preferably, sodium hydroxide and ferrous sulfa~e are used, such mol ratio of OH ion to Fe~ ion (OH~/Fe~) ranges from about 3. 8 to 5. 8, and when, more preferably, potassium hydroxide and ferrous chloIide '; -15- .
, ..... . , , , , , . ., . . ~ , , are used, such mol ratio of OH /Fe++ range~ from about 3.2 to 4.5.
Preferably, the mixing of alkali hydroxide and of ferrous salt, and the stirring of the liquid reaction system and the oxidation to goethite are carried out at a temperature in the range where goethite formation is promoted and magnetite formation is substan-tially prevented; thus, a temperature range of from about 40 to 60C is more preferred for a sodium hydroxide and ferrous sulfate system and a temperature range of from about 50 to 80C is more preferred for potassium hydroxide and ferrous chloride system.
In accordance with the teachings of this invention, the solution including ferrous hydroxide is stirred for several hours -~
while simultaneously being prevented from being oxidized, which permits one to obtain a uniform and finely divided, colloidal sized ferrous hydroxide aqueous suspension. The method of this invention has a number of advantages among which are the following: -(1) Reaction time is shortened. An oxidative reaction time required for the formation of goethite powder is unexpectedly and even remarkably shortened by stirring in an inert (non-oxidizing) gaseous (preferably nitrogen) atmosphere in accord with the present invention. Even the combined time of stirring in such a gaseous atmosphere plus the oxidative reaction time, ; as illustrated by Figure 1 and Figure 3, is characteristically shorter by a maximum of about 2 hours in the KOH-FeC12 embodiment and by a maximum of about 4.5 hours in the NaOH-FeSO4 embodiment, both compared to the reaction time in the case where no stirring treatment in such inert atmosphere is performed.
., ... :
, . . .
~: . .. . : - :
.
(2) The coercivity (Hc) o~ the resulting maghemite po~der is increased. Maghemite powder (gamma-Fe203 powder) derived from a goethite pc)\vder prepared a_cording to the method of the present invention, unexpectedly has a high coercivity (Hc) characteristically in the range from about 440 to 480 oersteds by a suitable or appropriate selection of striving time in inert (preferably nitrogcn) a~mosphere.
As illustrated by Figure 2 and Figure 4, such a high coercivity (Hc) can be obtained by stirring for about 2 to 5 hours in the inert atmosphere in the KOH-FeC12 embodiment and by stirring for about 2 to 4 hours in the inert a;mosphere in the NaOH-FeSO4 embodiment. Moreover, by a suitable selection of the mol ratio OH~/Fe+~ in a goethite powder made by the present invention and used as the starang material for maldng a gamma-Fe2O3 powder, one can produce a higher maghemite p~wder coercivity than in a conventional maghemite powder. As shown by Figure 5, a mol ratio (OH /Fe~) of over about 2. 5 may be selected in the KOH-FeC12 embodiment, and a mol ra~io (OH~/Fe+~) of over a~out 3 may be selected in the NaOH-FeSO4 embodiment. Thus, preferably, at a mol ratio (OH /Fe+t) of 3.2 to 4.5 in the KOH-FeC12 embodiment, and at a mol ratio (OH-/Fe+~) of 3. 8 to 5. 8 in the Na~H-FeS04 embodiment, a goethite powder is produced which, when used as a starting material for making a gamma-Fe2O3 powder, produces a gamma-Fe203 powder having a coercivity (Hc) of over about 440 oersteds. ,
~".. ," ........ . ... , ~ . . ,, ."
' , ' ~ '';' 10~;42;23 route, is un~er 370 oersteds.
The other of thesc methods involves bubbling air through an aqueous solution of ferrous salt and alkaline hydroxide to form goethite powder. The maghemite powder derived from such resulting gcethite by the above indicated known route generally has a higher coercivity (Hc) than the maghemite powder derived from the goethite obtained by the preceding two-st~ge metho~. However, one disadvantage of the second method is that about 10 to 20 hours are required for the formation of goethite. Another disadvantage of this second method is that the hydroxide is apt to gel and be non-uniform, particularly if a suspension of ferrous hydroxide of high density is used, thereby making it is very difficult to form a geothite powder with uniform particle size.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a method for making '~
a goethite powder using an aqueous ferrous hydroxide suspension.
The suspension is stirred for a relatively brief period of time in an inert gaseous atmosphere. Thereafter, the resulting suspension is cq~idized with oxygen to form goethite powder.
An object of this invention is to provide an improved 'J method of making a goethite powder suitable for use as a starting ~ -material for making an acicular maghemite powder preferably in a short time.
Another object of this invention is to provide a method of making a goethite powder suitable for use as a starting material 40r ', . ,;
10~42Z3 making an acicular maghemite powder of high coercivity (pref-erably over 400 oersteds).
A further object of this invention is to provide a method of making goethite powder with uniform particle size by a step of stirring ferrous hydroxide suspension in an inert atmosphere.
More particularly there is provided a method of making acicular goethite powder comprising the steps of:
a) forming a ferrous hydroxide suspension by mixing an aqueous solution of an alkali hydroxide selected from the group consisting of potassium hydroxide and sodium hydroxide ~ ~ -with an aqueous solution of a ferrous salt selected from the group consisting of ferrous chloride and ferrous sulfate;
b) continuously stirring the resulting mixture simultan-: eously throught said mixing and after said mixing for a total period of from 2 to 5 hours to produce a milk-white ferrous hydroxide suspension; `- ~;
steps a) and b) being carried out under an inert gaseous - ~ -atmosphere and at a temperature within the range from 60 to 80C; and c) oxidizing said milk-white ferrous hydroxide suspen~
sion with an oxygen containing gas, at a temperature within the range from 50 to 80C when the alkali hydroxide is ; potassium hydroxide and from 40 to 60C when the alkali hydrox-ide is sodium hydroxide, for a period of from 4 to 6.5 hours s; to form yellow goethite powder.
Other and further aims, objects, purposes, advantages, utilities, and eatures will be apparent to those skilled in ~-the art from a reading of the present specification and -drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph showing the relationship between the ~
~ 4 ~ ~; -E
time of stirring in a nitrogen atmosphere and the time required for a reaction according to the embodiment of Example 1 here- -inbelow;
Figure 2 is a graph showing the relationship between ~ .
the time of stirring in a nitrogen atmosphere and the coercivity (Hc) of a resulting maghemite powder according to such Example .
1 embodiment; ;
Figure 3 is a graph showing the relationship between the time of stirring in a nitrogen atmosphere and the time required ~-for a reaction according to the embodiment of Example 2 of this ~
invention hereinbelow; ~ ~ .
Figure 4 is a graph showing the relationship between -the time of stirring in a nitrogen atmosphere and the --coercivity (Hc) of a resulting ma~hemite powder according to such Example 2 embodiment of this invention; and - -.~ ,. ... .
, :' -., ;.
~ :
,:" ~
.-, .. ,. ~.
.. :. ~.
. .
.~ ~
.~ -.
;; .' ~
`' ,:,`.- :' -.~.
'~ J ~-.
:' ~
~ - 4a -': ',~`, ', ~ ; ~' .
' ~ ' 10~4223 Figure S is a gr~ph showing the relationship between the mol ratio of OH--tO Fe~ (OH /Fe~) and the coercivity (Hc) of a maghemite powder derived from a goethite powder wluch is prepared by the teachings of the present invention.
EMBODIMENI S
The present invention is further illustrated by reference to the following Examples. Those skilled in the art will appreciate that other and further embodiments are obvious and within the spirit and scope of this invention from the teachings of these present Examples taken with the accompanying specification and drawings.
EXAMP~E 1 -~
An alkaline solution including potassium hydroxide in an amount of 392 grams (7. 0 moles) mixed with 800 milliliters of water was charged to a reaction vessel.
279 grams (1. 4 moles) of ferrous chloride (FeC12 4H2O) dissolved into 400 milliliters of water was gradually added to the alkaline solution with stirring to form a colloidal suspension of ferrous hydrox-ide. Previously, an inert gas, for example, a nitrogen gas was passed, ;
as by bubbling, through the alkaline solution a~ a flow rate of 3.0 liters ~ -per minute to remove oxygen therein.
~ub~
As the ferrous chloride was added, nitrogen gas was tsparged) Into and through the resulting solution in a reaction vessel while keeping the temperature at 80C with continuous stirring using this procedure, a covering or blanket of the nitrogen gas was maintained .
- .. . . . .. . , , -, . . .,. ",, : ~ :
., .
~ 064Z23 over the surface of the resulting liquid reaction system. This bubbling was continued until a milk-white, uniform colloidal ferrous hydroxide was obtained. The time required for the re- ~
action (as measured from the commencement of reacting alkali ~ --hydroxide with the ferrous chloride to a point when formation of this colloidal ferrous hydroxide was deemed complete) was about three hours.
Next, the nitrogen gas was switched over to air, and air sparging was commenced at a flow rate of 5.0 l/min, through the resulting liquid reaction system at the temperature of 80C
with continuous stirring to form a yellow goethite in 4.5 hours.
After rinsing with water, the goethite material was filtered, dried and pulverized to obtain 120 grams of yellow goethite powder. The particles of this yellow goethite powder were acicular, about 0.5 mlcrons in length, and about 20 in acicular ratio, where the acicular ratio value is obtained by ,i .
dividing the average length of the particle by the average - .
diameter of the particle. Moreover, the uniformity of the ~
particle size of the goethite powder was good. -` 0 2.0 grams of this goethite powder was reduced at a temperature of 350C with the passing of hydrogen gas thereover at a flow rate of 1.0 l/min for one hour, after which the . ~ - .
: resulting product was oxidized by passing air thereover at a temperature of 230C for one hour. As a result, a brown maghemite ` powder (gamma-Fe2O3 powder) was obtained. The coercivity (Hc), squareness ratio (Rs) and saturation magnetization of this resulting gamma-Fe2O3 were 466 oersteds, 55~, and 69.5 emu/g, respectively.
~ 2.0 more grams of the same goethite powder was reduced ; 30 :,'~ . ., ... .
'''' .
,., ,~.
, ~ .. . ..... ,,. ~
., .. - . .:
' ' '. , ' ' ' , at a temperature of 380C with the passing of hydrogen gas there-over at a flow rate of l.0 l/min for one hour, after which the resulting product was oxidized by passing air thereover at a temperature of 250C for one hour, to produce a maghemite powder.
The coercivity (Hc), squareness ratio (Rs) and saturation mag-netization of such gamma-Fe2O3 were 480 oersteds, 55%, and 65.1 emu/g, respectively.
Referring to Figure 1, there is seen a graph which shows the relationship between the time of stirring in the nitrogen atmosphere and the required reaction time at (a) a constant density of the suspension comprising the liquid reaction system (b) a constant reaction temperature and (c) a constant flow rate of air. In this graph, the axis of the abscissas shows the time of stirring in the nitrogen atmosphere, and the axis of ordinates shows the required reaction time. The curve a shows the varia-tions of the time required for the formation of the goethite after the beginning of the oxidation reaction, and the curve _ shows the variations of the time of stirring in the nitrogen atmosphere plus the time required for the formation of goethite after the beginning of the oxidation reaction.
In this Example, the time of the end of the oxidative reaction between air and colloidal ferrous hydroxide (that is, the time when the ferrous (Fe++) ions are substantially consumed) was decided in the following manner: A sample of 5 millilters of the reacting liquid reaction system was taken out from the reaction vessel every ten minutes after the beginning of such oxidative reaction (this is, after commencement of ferrous chloride ~-, addition to potassium hydroxide " :' .
''~ ' `
- 7 - ~ `
''', . : ~ ~; ' " ' ,,~ ' ~ ' '` ' ; ' ~
,. . ... .
10~4'~Z3 with n~tro~en blo~ving), and the sa.nl-lc was added to a dilute hydro-chlonc a~id solution from which oxygen had been removed to prevent oxidation by the passing o~ nitrogen gas therethrougll, and the unreacted ferrous hydroxide in sucll sa.nple was dissolved therein. The amount of hydrochloric aeid in this dilute solution was adjusted so that the Ptl of the resulting solution was in the range from one to seven. Then, the Ferrous ions Fe+t in the resulting solution were detected by using a sensitive Fe~ ion detecting pa~er. The paper used was and is available commercially as Merckoquant Fe~, a trade mark of E-Merck Company. The time when no ferrous ion Fe~ could be so detected in such a sample was regarded a3 the time of the end of the oxida~ive reac~ion.
Figure 2 shaws the relationship between the time of stirring in the nitrogen atmosphere and the coercivity(Hc) of the gamma-Fe203 derived from the resulting goethite powder as the starting material.
As shown by Figure 2, it is prefera~le to stir the solution for a time interval of from about 2 to 5 hours in an inert (e. g., oxygen free) gas in order to obtain the desired goethite powder product for use as a starting material for the gamma-Fe203 of high coercivity, for example, - over 440 oersteds.
~ .
EXAMPLE 2 ~ -For the comparison, the following conventional method of making goethite powder and the property of the gamma-Fe203 obtained in the same method, is described in the following example:
The a~ueous solution of ferrous chloride was mixed with ., .
-8- .
10~i4Z23 the aqueous solution of po~assium hydro~cicic and sdrr~d at the tcmpera-ture of 80C with the passing of air at a floN rate of 5.0 l/min. ln this case, there was not the stirring trea~mcnt in the incrt a mosphere as in the method of the invention. In 9.5 hours, the reaotion ended and yellow goethite was formed. Aftcr rinsing with watcr, the material was filtered, dried and pulverized to obtain 120 grams of goethite pawder. The particles of the resulting goethite po~vder were acicular, a~out 0. 8 microns in length and a~out 10 in acicular ratio.
As in the Example 1 of the invention, 3.0 grams of the goethite powder was reduced at the temperature of 350~C by hydrogen gas and then it was oxidized at the temperature of 230C by air to --form the gamma-Fe2O3. The coercivity (Hc), squareness ratio (Rs) and saturation magnetization c;~ of the resulting gamma-Fe2O3 were 387 oersteds, 54% and 67.1 emu/g, respectively. As understood -from this results, the coercivity (Hc) of the gamma-Fe2O3 a_cording to the method of this invention is higher than that of the gamma Fe2O3 ~ ~Y
according to the conventional method. -~
An alkaline solution including sodium hydro~de in an . -~
amount of 256 grams (6.4 moles) mixed with 600 milliliters of water ;~
was charged to a reaction vessel.
445 grams (1. 6 moles) of ferrous sulfate (FeS04 7H2O) dissolved into 600 milliliters of water was gradually added to the alkaline solution with sarring to form suspensioll of ferrous hydro~cide.
Previously, a nitrogen gas was passed through the alkaline solution at a , :
,' , .
.
, 9 ~;........... . : . . . .
: - ,~ . . , , , ,, . .:
-:.......... : . . ::, .' ~ .' ', , 10~4'~23 flow rate of 2.0 l/min to remove oxygen therein. Simultaneously, and in the manner of Example 1, nitrogen (N2) gas was sparged into the resulting suspension maintained at a temperature of 60 C with continuous stirring until milk-white uniform colloidal ferrous hydroxide was obtained. The time required for this reaction was about three hours.
After that, the nitrogen gas was switched over to air which, at a flow rate of 1.0 l/min, was passed through the resul-ting suspension maintained at a temperature of 60C with contin-10 uous stirring to form by oxidation yellow goethite in 6.5 hours.
After rinsing with water, the material was filtered, dried and pulverized to obtain 140 grams of yellow goethite powder. The particles of the yellow goethite powder were acicular, about 0.5 microns in length and about 20 in acicular ratio (measured as in Example 1). Moreover, the uniformity of the particle size of the goethite powder was good.
2.0 grams of this goethite powder was reduced at a temperature of 350C with the passing therethrough of hydrogen gas at a flow rate of 1.0 l/min for one hour, and then the produce 20 was oxidized by air passing therethrough at a temperature of 250C for one hour. As the result, the brown powder of gamma-Fe2O3 was obtained. The coercivity (Hc~, squareness ratio (Rs), and saturation magnetization of this gamma-Fe2O3 powder was 458 oersteds, 55% and 65.6 emu/g, respectively. -Referring to Figure 3, there is seen a graph showing the relationship in this example between the time of stirring ~' in the nitrogen atmosphere and the required reaction time at st (a) a constant density of the :
- 10 - ~
. ., . - -, . .~ ~, , " , , . ~ ~ . ., ,~,: .
.
10~4~23 reaetioll suspension, (b) a constant reaction temperaturc, and (c) a constant flow rate of air. In this graph, the axis of abscissas shows the time of stirring in the nitrogen atmosphcre and the ax~s of ordi-na~es sho~s the required ~me. A curve a shows the variations of the time required for the formation of the goethite after the beginning of the air oxidative reaction, and a curve b shows the variations of the time of stirring in the nitrogen atmosphere plus the time required for the formation of the goethite after the beginning o the oxidative reaction.
Figure 4 shows the relationship in this Example between the time of stirring in the nitrogen atmosphere and the coercivity (Hc) of the gamma-Fe203 powder derived from the resulting goethite powder as the starting material. As shown in Figure 4, it is preferable to stir the solution for 2 to 4 hours in the nitrogen gas in order to obtain a -desired goethite powder for use as the starting material for the ~ ~ -gamma-Fe203 of high coercivity, for example, over 440 oersteds.
In Example 1 and Example 3, the amounts of potassium hydroxide (KOH) and ferrous chloride (FeC12 4H20), and sodium hydro~de (NaOH) and ferrous sulfa-~e (FeS04 7H20), were varied; in other words, the mo~ ratio of OH ion to Fe~ ion (OH /Fe~) was varied.
,~ .
An alkaline solution including potassium hydroxide in an - amount of 336 grams (6.0 moles) mixed with 900 milQliters of water was charged to a reaction vessel.
. ... .
",, . ... . . " , __ .. ..
.. . . . . .
334 grams (1.2 moles) of ferrous aulfate (FeSO4.7H2O) dissolved into 500 milliliters of water was gradually added to the alkaline solution with stirring to form a suspension of ferrous hydroxide. Previously, a nitrogen gas was passed through the alkaline solution at a flow rate of 3.0 l/min to remove oxygen therein. Simultaneously, in a manner similar to Example 1, nitrogen gas was sparged into the resulting suspension at a tem-perature of 80C with continuous stirring until the milk-white uniform colloidal ferrous hydroxide was obtained. The time required for this reaction was about three hours.
After that, the nitrogen gas was switched over to air which, at a flow rate of 5.0 l/min, was passed through the re-sulting suspension at the temperature of 80C with continuous stirring to form by oxidation yellow geothite in 4.0 hours.
After rinsing with water, the material was filtered, dried and pulverized to obtain 109 grams of yellow goethite ; powder. The particles of the yellow goethite powder were acicular, about 0.4 microns in length and about 15 in acicular ratio (measured as in Example 1). Moreover, the uniformity of the 2Q particle size of the goethite powder was good.
. .;.
2.0 grams of this goethite powder was reduced at a temperature of 370C with the passing of hydrogen gas there-through at a flow rate of 1.0 l/min for one hour, and then the product was oxidized by passing air therethrough at a temperature of 250C for one hour. A brown powder of gamma-Fe2O3 was obtained.
The coercivity (Hc), squareness ratio (Rs), and saturation mag-netization of this gamma-Fe2O3 powder was 447 oersteds, 55%, and 72.0 emu/g, respectively. ;
', , r,-, An alkaline solution including sodium hydra~cide in an amount of 270 grams (7. 0 moles) mixed with 800 milliliters of water was charged to a reaction vessel.
279 grams (1.4 moles) of ferrous chloride (FeC12 4H2O) dissolved into 500 milliliters of water was gra~ually added to the alkaline solution with stirring to form a suspension of ferrous hydroxide.
~ ,, Previously, a nitrogen gas was passed through the alkaline solution a~ ~:
a flow ra~e of 3. 0 l/min to remove oxygen therein. Simultaneously, a rdtrogen gas was passed through the resulting suspension at a temper-ature of 60C with continucJus strong stirring by ultrasonic means for 2.5 hours to obtain milk-white uniform colloidal ferrous hydro.Yide.
After that, the nitrogen gas was switched over to air which, at a flow rate o 2. 0 l/min, was passed through the resulting suspension -at a temperature of 60C with continuous ultrasonic stirring to form yellaw goethite in 4. 0 hours.
After rinsing with water, this product material was filtered, ~-dried and pulverized to obtain 120 grams of yellow goethite powder.
The particles of the yellow goethite powder were acicular, about 0. 5 ~'~ .
~- microns in length, and about 20 in acicular ratio (measured as in ~`
Example 1). Moreover, the uniformity of the particle size of the goethite powder was good.
2. 0 grams af this goethite pa,vder was reduced at a temperature of 360C with the pas~ing there~hrough of hydrogen gas at a flov rate of 1.0 l/min for one hour, and then the product was 03ddized by air passing therethraugh at a temperature of 250C for , ' -13^
l"," ~ , `.- ` - ` `':, ` ;, ` . ., ` :
. . ` . ` . ` ~.
.. . ..
~ 0~4223 one hour. As tl1e rcsult, a brown powdcr of gamma-Fe203 was obta ncd. The coercivity (Hc), squareness ra~o (Rs), and satura~ion magnetization ~ig~ r,3 of this gamma-Fe203 was 455 oersteds, 55%, and 71. 2 emu/gJ respectively.
The relationships between the variations of the mol ratio and the coercivity (Hc) were examined in gamma-Fe203 powder derived from goethite powder produced by the method aI this invention used as the starting material. The results are illustrated by the curves shawn in Figure 5. Here, a curve a shows the case of a goethite derived from potassium hydroxide and ferrous chloride, and a curve b shows ~ -the case of goethite derived from sodium hydroxide and ferrous sulfate. -Figure 5 illustrates thaL gamma-Fe203 powder having higher coerdvity (Hc) than a ^onventional gamma-Fe203 powder can be obtained by having a mol ratio (OH /Fe~) of over 2.5, and gamma-Fe203 p~wder having a coercivity (Hc) of over 440 oersteds can be obtained by ha~Ting a mol ratio (OH /Fe~) ranging from 3. 2 to 4.5, in the case of goethite powder derived from potassium hydroxide (KOH) and ferrous chloride - .
(FeC12 4H20); this case is called the "KOH-FeC12 method" herein.
Figure S further illustrates that gamma-Fe203 powder having higher `~
coercivity (Hc) than the conventional gamma-Fe203 powder can be obtained by having a mol ratio (OH /Fe~) of over 3, and gamma-Fe2o3 powder having coercivity (Hc) of over 440 oersteds can be obtained by ha~ing a mol ratio ranging from 3. 8 to 5. 8, in the case of gaethite powder derived from sodium hydroxide (NaOH) and ferrous sulfate r ;''' ' ' `'`: ' ~ . .
:~ ' ~0~4Zz3 (FeS04-71-120); this case is callcd the "NaO~ FeSO4 method" herein.
While in the above examples, go~thite powder produced by the process of this inven~on is used as a starting material for making acicular gamma-Fe203 p~wder, it will be appreciated that, of course, such may also be used as starting ma;erial for ma~.dng acicular magnetite powder, as above indicated.
DESCRIPrION OF THE PREFÆRRED EMBODIMENIS
The present invention is directed to a method of ma'.cing goethite powder. The method involves the step of mixing an aqueous solution of a water soluble ferrous salt with an aqueous solution of an aLkali hydroxide to form a ~errous hydroxide. During such mixing, the liquid rea_tant system is stirred in an inert (non-oxidative) atmosphere.
`The resulting colloidal ferrous hydroxide suspension is then oxidized, `
with an oxygen containing gas to convert the ferrous hydroxide to goethite powder.
Preferably, the alkali hydroxide is sodium hydroxide or potassium hydroxide. Preferably, the ferrous salt is ferrous sulfate or ferrous chloride. Preferably, the stirring time for the mixture of lakali hydroxide and ferrous salt ranges from about 2 to 5 hours with -a time of from about 2 to 4 hours being more preferred when ferrous sulfate is employed as the ferrous salt. Preferably, the mol ratio of OH- ions to Fe~ ions (OH /Fe~) is over about 2. 5, and when, more preferably, sodium hydroxide and ferrous sulfa~e are used, such mol ratio of OH ion to Fe~ ion (OH~/Fe~) ranges from about 3. 8 to 5. 8, and when, more preferably, potassium hydroxide and ferrous chloIide '; -15- .
, ..... . , , , , , . ., . . ~ , , are used, such mol ratio of OH /Fe++ range~ from about 3.2 to 4.5.
Preferably, the mixing of alkali hydroxide and of ferrous salt, and the stirring of the liquid reaction system and the oxidation to goethite are carried out at a temperature in the range where goethite formation is promoted and magnetite formation is substan-tially prevented; thus, a temperature range of from about 40 to 60C is more preferred for a sodium hydroxide and ferrous sulfate system and a temperature range of from about 50 to 80C is more preferred for potassium hydroxide and ferrous chloride system.
In accordance with the teachings of this invention, the solution including ferrous hydroxide is stirred for several hours -~
while simultaneously being prevented from being oxidized, which permits one to obtain a uniform and finely divided, colloidal sized ferrous hydroxide aqueous suspension. The method of this invention has a number of advantages among which are the following: -(1) Reaction time is shortened. An oxidative reaction time required for the formation of goethite powder is unexpectedly and even remarkably shortened by stirring in an inert (non-oxidizing) gaseous (preferably nitrogen) atmosphere in accord with the present invention. Even the combined time of stirring in such a gaseous atmosphere plus the oxidative reaction time, ; as illustrated by Figure 1 and Figure 3, is characteristically shorter by a maximum of about 2 hours in the KOH-FeC12 embodiment and by a maximum of about 4.5 hours in the NaOH-FeSO4 embodiment, both compared to the reaction time in the case where no stirring treatment in such inert atmosphere is performed.
., ... :
, . . .
~: . .. . : - :
.
(2) The coercivity (Hc) o~ the resulting maghemite po~der is increased. Maghemite powder (gamma-Fe203 powder) derived from a goethite pc)\vder prepared a_cording to the method of the present invention, unexpectedly has a high coercivity (Hc) characteristically in the range from about 440 to 480 oersteds by a suitable or appropriate selection of striving time in inert (preferably nitrogcn) a~mosphere.
As illustrated by Figure 2 and Figure 4, such a high coercivity (Hc) can be obtained by stirring for about 2 to 5 hours in the inert atmosphere in the KOH-FeC12 embodiment and by stirring for about 2 to 4 hours in the inert a;mosphere in the NaOH-FeSO4 embodiment. Moreover, by a suitable selection of the mol ratio OH~/Fe+~ in a goethite powder made by the present invention and used as the starang material for maldng a gamma-Fe2O3 powder, one can produce a higher maghemite p~wder coercivity than in a conventional maghemite powder. As shown by Figure 5, a mol ratio (OH /Fe~) of over about 2. 5 may be selected in the KOH-FeC12 embodiment, and a mol ra~io (OH~/Fe+~) of over a~out 3 may be selected in the NaOH-FeSO4 embodiment. Thus, preferably, at a mol ratio (OH /Fe+t) of 3.2 to 4.5 in the KOH-FeC12 embodiment, and at a mol ratio (OH-/Fe+~) of 3. 8 to 5. 8 in the Na~H-FeS04 embodiment, a goethite powder is produced which, when used as a starting material for making a gamma-Fe2O3 powder, produces a gamma-Fe203 powder having a coercivity (Hc) of over about 440 oersteds. ,
(3) Uniformity of particle size in the resulting goethite.
The uniformity of a paracle size of the resulting goethite powder is unexpectedly improved by stirring the solution including ferrous hydroxide ... ... .. . . . . . .. . . .. . . . . . .. . . . . . . . . .... .... ..
: -- , 10~4223 in an inert (non-oxida~ive) gascous (prefcra~1y nitrogcn) a~mosphere-This procedure makes uniform, ~gralncd fcrrous hydroxide particles.
Such improved uniformity is confirmed by clcctron-microsCopy. The size of the ferrous hydroxide particlcs in aqueous suspension produced in accord with this invention cannot be mcasured bcca;lse the ferrou.s hydroxide quickly o~idizes in air, and, therefore, when such a 8US-pension becomes milk-white in color, the sarring of the suspension may be ended, which also indicates tha~ the ferrous (Fe~) ions have been substantially completely consumed. In a magnetic tape made using a gamma-Fe203 powder derived from a goethite powder produced according to the method of the present invention, the orienta~ion of such gamma-Fe203 powder is observed to be improved and the printing level such is observed to be desirably low.
The uniformity of a paracle size of the resulting goethite powder is unexpectedly improved by stirring the solution including ferrous hydroxide ... ... .. . . . . . .. . . .. . . . . . .. . . . . . . . . .... .... ..
: -- , 10~4223 in an inert (non-oxida~ive) gascous (prefcra~1y nitrogcn) a~mosphere-This procedure makes uniform, ~gralncd fcrrous hydroxide particles.
Such improved uniformity is confirmed by clcctron-microsCopy. The size of the ferrous hydroxide particlcs in aqueous suspension produced in accord with this invention cannot be mcasured bcca;lse the ferrou.s hydroxide quickly o~idizes in air, and, therefore, when such a 8US-pension becomes milk-white in color, the sarring of the suspension may be ended, which also indicates tha~ the ferrous (Fe~) ions have been substantially completely consumed. In a magnetic tape made using a gamma-Fe203 powder derived from a goethite powder produced according to the method of the present invention, the orienta~ion of such gamma-Fe203 powder is observed to be improved and the printing level such is observed to be desirably low.
(4) Ease of oxidative reaction temperature control.
In general, the higher the temperature of the goethite oxida~ve reaction with oxygen bearing ga3 (preferably air), the higher the coerci-vity (Hc) and the better the magnetic properties obtained. Ho~qever, characteristically, yellow goethite is not formed, but black magnetite is obtained as a reaetion product, at reaction temperatures of over 70C
when sodium hydroxide is used as the allcali, and at the temperature of over 90C when potassium is used as the alkali. Therefore, the temperature of an oxidative reaction by the passing, for example, of air through a ferrous hydroxide suspension produced by this invention, may be normally about 40 to 60~C when sodium hydroxide is used, and normally about 50 to 80C when potassium hydroxide is used. On the other hand, a ferrous ion in a solution of ferrals salt is inherently -, ~,,.
-18- ~
~ . . i . ~-.
10~4Z23 unstable and i8 apt to be converted to a ferric iU~I in hot water, and a har alkali solution can be dangerals. Therefore, a solution of ferrous salt and an alkali hydr~xide solution are preferably mixed at the relatively l~w temperatures indicated.
Preferably, in the practice of this invention, a solution of ferrals salt and a solution o~ alkali hydroxide are mixed at a relatively low temperature, stirred in a nitrogen atmosphere to prevent oqddation, then hea~ed up to a higher temperature before the oxidative reaction is started. Such a procedure favors the desired better results ob-tained with the practice of the present invention in comparison to the conventional maghemite preparation method in which heating and air bubbling are started at the same time when the solution of ferrous salt and the alkaline solution are mixed.
The concentration of alkali hydroxide in a starting solution prior to the mixing of such with a ~tarting solution of solublé ferrals salt can range very widely; typically, one may employ in such f~om about 6.0 to i2.0 mols of dissolved alkali hydroxide per liter of water. Similarly, the concentration o~ ferrals salt in a ~tar~ing solution prior to the mixing of such with a starting solution of alkali hydroqdde ;
can range very widely; typically, one may employ in such from about 1.2 to 3.0 mols of water soluble, dissolved ferrous salt per liter o water.
While for purposes of the present invention it is preferred to rnix a 301ution o ferrous salt with a ~olution of alkali hydrc~ide simultanea~sly with stirring, it is also preferred to compbte such mixing while ~tirring is still being continued; thu~, a typical mixing `
.. ~ .
~ ' .'' ':
~ - 19~
y,s -, .. , , . ... , . , ,, " , ...
. . . , - , , , . . . .
" . . . . . .
; ,~ ., ,. - .
, . .
0~4;~z3 ~' , çe~,l 2¦,~3 time ranges from about D 7 to g.~. 3 ~0 oE the total stirring time.
While air constitutes a preferred oxygen-containing gas for purposes of accomplishing oxidation of ferrous hydroxide to gaethite, those skilled in the art will appreciate that any oxygen containing ga~
may be used in such oxida~ion reaction to achieve a contacting between oxygen gas and colloidal particles of ferrous hydroxide suspended in water. Pllre oxygen may be employed, for example, or predetermined mixtures of oxygen with inert gasses may be employed, such as mixtures of oxygen and nitrogen, or the like, a~ those skilled in the art will appreciate.
Preferably, the oxidation reaction i8 conducted until the ferrals ions are substantially completely consumed, although, for certain purposes, some residual amounts of ferrous ions may be present at the termination of an oxidation reaction. Any convenient qualita~ve or quantitative technique may be employed to determine or set the end pdnt o the axidative reaction.
After formation of yellow goethite particles in water in accordance with the teachings of this invention, the resulting mixture comprised of such goethite particles, water, and dissolved materials is ;..................................................................... ~
!,." conveniently filtered to. separate such goethite and these separated solids are thereafter dried and pclwdered. Drying may be accomplished by ~` ` any convenient means. Por example, air drying of the solids at a ~-s~t-2~ ~73 temperature in the range from about 80c toi~4~may be employed. ~;, The dried powder is then pulverized by any convenient means. For example, a mortar and pestle may be used, a3 those sldlled in the art will appreciate. ' ;- ~ ;
t :
~,., . -.
In general, the higher the temperature of the goethite oxida~ve reaction with oxygen bearing ga3 (preferably air), the higher the coerci-vity (Hc) and the better the magnetic properties obtained. Ho~qever, characteristically, yellow goethite is not formed, but black magnetite is obtained as a reaetion product, at reaction temperatures of over 70C
when sodium hydroxide is used as the allcali, and at the temperature of over 90C when potassium is used as the alkali. Therefore, the temperature of an oxidative reaction by the passing, for example, of air through a ferrous hydroxide suspension produced by this invention, may be normally about 40 to 60~C when sodium hydroxide is used, and normally about 50 to 80C when potassium hydroxide is used. On the other hand, a ferrous ion in a solution of ferrals salt is inherently -, ~,,.
-18- ~
~ . . i . ~-.
10~4Z23 unstable and i8 apt to be converted to a ferric iU~I in hot water, and a har alkali solution can be dangerals. Therefore, a solution of ferrous salt and an alkali hydr~xide solution are preferably mixed at the relatively l~w temperatures indicated.
Preferably, in the practice of this invention, a solution of ferrals salt and a solution o~ alkali hydroxide are mixed at a relatively low temperature, stirred in a nitrogen atmosphere to prevent oqddation, then hea~ed up to a higher temperature before the oxidative reaction is started. Such a procedure favors the desired better results ob-tained with the practice of the present invention in comparison to the conventional maghemite preparation method in which heating and air bubbling are started at the same time when the solution of ferrous salt and the alkaline solution are mixed.
The concentration of alkali hydroxide in a starting solution prior to the mixing of such with a ~tarting solution of solublé ferrals salt can range very widely; typically, one may employ in such f~om about 6.0 to i2.0 mols of dissolved alkali hydroxide per liter of water. Similarly, the concentration o~ ferrals salt in a ~tar~ing solution prior to the mixing of such with a starting solution of alkali hydroqdde ;
can range very widely; typically, one may employ in such from about 1.2 to 3.0 mols of water soluble, dissolved ferrous salt per liter o water.
While for purposes of the present invention it is preferred to rnix a 301ution o ferrous salt with a ~olution of alkali hydrc~ide simultanea~sly with stirring, it is also preferred to compbte such mixing while ~tirring is still being continued; thu~, a typical mixing `
.. ~ .
~ ' .'' ':
~ - 19~
y,s -, .. , , . ... , . , ,, " , ...
. . . , - , , , . . . .
" . . . . . .
; ,~ ., ,. - .
, . .
0~4;~z3 ~' , çe~,l 2¦,~3 time ranges from about D 7 to g.~. 3 ~0 oE the total stirring time.
While air constitutes a preferred oxygen-containing gas for purposes of accomplishing oxidation of ferrous hydroxide to gaethite, those skilled in the art will appreciate that any oxygen containing ga~
may be used in such oxida~ion reaction to achieve a contacting between oxygen gas and colloidal particles of ferrous hydroxide suspended in water. Pllre oxygen may be employed, for example, or predetermined mixtures of oxygen with inert gasses may be employed, such as mixtures of oxygen and nitrogen, or the like, a~ those skilled in the art will appreciate.
Preferably, the oxidation reaction i8 conducted until the ferrals ions are substantially completely consumed, although, for certain purposes, some residual amounts of ferrous ions may be present at the termination of an oxidation reaction. Any convenient qualita~ve or quantitative technique may be employed to determine or set the end pdnt o the axidative reaction.
After formation of yellow goethite particles in water in accordance with the teachings of this invention, the resulting mixture comprised of such goethite particles, water, and dissolved materials is ;..................................................................... ~
!,." conveniently filtered to. separate such goethite and these separated solids are thereafter dried and pclwdered. Drying may be accomplished by ~` ` any convenient means. Por example, air drying of the solids at a ~-s~t-2~ ~73 temperature in the range from about 80c toi~4~may be employed. ~;, The dried powder is then pulverized by any convenient means. For example, a mortar and pestle may be used, a3 those sldlled in the art will appreciate. ' ;- ~ ;
t :
~,., . -.
Claims (8)
OR PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:
1. A method of making acicular goethite powder comprising the steps of:
a) forming a ferrous hydroxide suspension by mixing an aqueous solution of an alkali hydroxide selected from the group consisting of potassium hydroxide and sodium hydroxide with an aqueous solution of a ferrous salt selected from the group consisting of ferrous chloride and ferrous sulfate;
b) continuously stirring the resulting mixture simultane-ously throughout said mixing and after said mixing for a total period of from 2 to 5 hours to produce a milk-white ferrous hydroxide suspension;
steps a) and b) being carried out under an inert gaseous atmosphere and at a temperature within the range from 60° to 80°C; and c) oxidizing said milk-white ferrous hydroxide suspension with an oxygen containing gas, at a temperature within the range from 50° to 80°C when the alkali hydroxide is potassium hydroxide and from 40° to 60°C when the alkali hydroxide is sodium hydroxide, for a period of from 4 to 6.5 hours to form yellow goethite powder.
a) forming a ferrous hydroxide suspension by mixing an aqueous solution of an alkali hydroxide selected from the group consisting of potassium hydroxide and sodium hydroxide with an aqueous solution of a ferrous salt selected from the group consisting of ferrous chloride and ferrous sulfate;
b) continuously stirring the resulting mixture simultane-ously throughout said mixing and after said mixing for a total period of from 2 to 5 hours to produce a milk-white ferrous hydroxide suspension;
steps a) and b) being carried out under an inert gaseous atmosphere and at a temperature within the range from 60° to 80°C; and c) oxidizing said milk-white ferrous hydroxide suspension with an oxygen containing gas, at a temperature within the range from 50° to 80°C when the alkali hydroxide is potassium hydroxide and from 40° to 60°C when the alkali hydroxide is sodium hydroxide, for a period of from 4 to 6.5 hours to form yellow goethite powder.
2. The method of Claim 1 wherein the alkali hydroxide is sodium hydroxide and the ferrous salt is ferrous sulfate.
3. The method of Claim 1 wherein the alkali hydroxide is potassium hydroxide and the ferrous salt is ferrous chloride.
4. The method of Claim 1, 2 or 3 wherein the mixing is effected so that the mole ratio of OH- to Fe++ ions is over 2.5.
5. The method of Claim 2 wherein the mixing is effected so that the mole ratio of OH- to Fe++ ions is over 3.
6. The method of Claim 2 wherein the mixing is effected so that the mole ratio of OH- to Fe++ ions is within the range from 3.8 to 5.8.
7. The method of Claim 2, 5, or 6 wherein the total period of said continuous stirring is from 2 to 4 hours.
8. The method of Claim 3 wherein the mixing is effected so that the mole ratio of OH- to Fe++ ions is within the range from 3.2 to 4.5.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP47098511A JPS5221720B2 (en) | 1972-09-30 | 1972-09-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1064223A true CA1064223A (en) | 1979-10-16 |
Family
ID=14221659
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA182,127A Expired CA1064223A (en) | 1972-09-30 | 1973-09-28 | Method of making goethite powder |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5221720B2 (en) |
| CA (1) | CA1064223A (en) |
| DE (1) | DE2349112A1 (en) |
| GB (1) | GB1437409A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS53127400A (en) * | 1977-04-13 | 1978-11-07 | Nippon Telegr & Teleph Corp <Ntt> | Production of goethite |
| JPS54110999A (en) * | 1978-02-20 | 1979-08-30 | Nippon Telegr & Teleph Corp <Ntt> | Preparation of magnetic particulates |
| CH637212A5 (en) * | 1980-04-29 | 1983-07-15 | Schweizerische Beratungsstelle | APPARATUS FOR ADJUSTING A SAFETY MOUNT MOUNTED ON A SKI. |
-
1972
- 1972-09-30 JP JP47098511A patent/JPS5221720B2/ja not_active Expired
-
1973
- 1973-09-26 GB GB4504473A patent/GB1437409A/en not_active Expired
- 1973-09-28 CA CA182,127A patent/CA1064223A/en not_active Expired
- 1973-09-29 DE DE19732349112 patent/DE2349112A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2349112A1 (en) | 1974-04-04 |
| GB1437409A (en) | 1976-05-26 |
| JPS5221720B2 (en) | 1977-06-13 |
| JPS4957397A (en) | 1974-06-04 |
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