US3696039A - Process for the production of ferromagnetic chromium dioxide - Google Patents

Process for the production of ferromagnetic chromium dioxide Download PDF

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Publication number
US3696039A
US3696039A US32648A US3696039DA US3696039A US 3696039 A US3696039 A US 3696039A US 32648 A US32648 A US 32648A US 3696039D A US3696039D A US 3696039DA US 3696039 A US3696039 A US 3696039A
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Prior art keywords
chromium
chromium oxide
dioxide
chromium dioxide
temperature
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US32648A
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Fritz Rodi
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Bayer AG
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Bayer AG
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    • 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
    • G11B5/70636—CrO2
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G37/00—Compounds of chromium
    • C01G37/02—Oxides or hydrates thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-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
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • 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
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • 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

Definitions

  • the obtained finely divided chromium oxide in which the average oxidation state of the chromium is in the range of from 3 to 4 is heated together with an oxidising agent under hydrothermal conditions at a temperature of from 50 C. to 400 C. and at a pressure of from 50 to 500 kg./cm. optionally in the presence of a substance, which acts as a modifier.
  • This invention relates to a process for the production of high-grade ferromagnetic chromium dioxide for magnetogram carriers.
  • chromium dioxide crystallising in the rutile lattice can be obtained in the pure form by the decomposition of chromic acid under hydrothermal conditions.
  • the products thus obtained are in the form of coarse particles, the coercive forces being below 100 [oe.]; accordingly, they are unsuitable for numerous application, for example magnetic recording processes.
  • US. patent specification No. 3,278,263 relates to a process by which it is possible to produce chromium dioxide which is free from modifiers and has outstanding properties.
  • Chromium oxides and chromium oxide hydrates in which the average valency of the chromium is in the range of from 3 to 4, are oxidised into chromium dioxide under hydrothermal conditions.
  • Chromium oxide hydrate produced in this way is dehydrated and tempered at a temperature in the range of from 200 C. to 1000 C. and thus converted into a chromium oxide with chromium in the average oxidation state of between 3 and 4.
  • Chromic acid is preferably used as an oxidising agent for oxidation into chromium dioxide under hydrothermal conditions. Chromic acid is also converted into chromium dioxide under the reaction conditions so that an excess of the oxidising agent does not have any harmful effects.
  • This invention provides a process for the production of ferromagnetic chromium dioxide by heating finely divided chromium oxide in which the average oxidation state of the chromium is between 3 and 4, with an oxidising agent, optionally in the presence of a substance acting as a modifier, under hydrothermal conditions at a temperature of from 50 to 400 C. and at a pressure of from 50 to 500 kg./cm. in which a finely divided chromium oxide is used which has been obtained by dehydrating and tempering a precipitated chromium oxide hydrate green, prepared by reducing a chromate or polychromate solution with an organic substance at a temperature of from 300 to 400 C. and under a pressure of from 250 to 350 kg./cm.
  • this invention relates to an improved process for the production of ferromagnetic chromium dioxide, wherein a chromate or polychromate solution is reduced by an organic substance at a temperature of from 300 C. to 400 C. and at a pressure of from 250 to 350 kgJcm. to form chromium oxide hydrate green, wherein the resulting chromium oxide hydrate green is dehydrated and tempered to produce finely divided chromium oxide in which the average oxidation state of the chromium is in the range of from 3 to 4, and wherein the chromium oxide is heated with an oxidising agent under hydrothermal conditions at a temperature of from 50 C. to 400 C. and at a pressure of from 50 to 500 kg./cm.
  • a certain type of chromium oxide hydrate green is obtained by reducing an aqueous chromate or polychromate solution, e.g. a solution of sodium chromate or soduim dichromate, under pressure with an organic substance and, for the purposes of the invention, this will be referred to as precipitated chromium oxide hydrate green. It has surprisingly been found that this precipitated chromium oxide hydrate green is eminently suitable as a starting material for the reaction to produce chromium dioxide. Substances with a reducing effect are used as the organic substances such as, for example, molasses, formaldehyde, formates, lignite powder. The reducing agent should be present in a quantity sufficient to guarantee a quantitative reaction of the dichromate into chromium oxide hydrate green.
  • chromium oxide hydrate green for example guignet green
  • guignet green a comprehensive list of commercial chromium oxide hydrate green pigments can be found, for example, in H. Kittel, Pigmente, Stuttgart, 1960, pp. 293-297.
  • chromium dioxide In order to obtain chromium dioxide with the required properties, it is advisable to dehydrate and temper the precipitated chromium oxide hydrate green before oxidation under pressure.
  • the dehydration or tempering temperature may be in a range from 300 to 900 C.
  • the extremely finely divided needle-shaped particles of the chromium oxide hydrate green are converted into isometric finely divided particles of chromium oxide.
  • the chromium oxide thus prepared is distinguished by the uniform size of its particles and their limited tendency towards agglomeration, and thus meets the ideal requirements for conversion into chromium dioxide.
  • the chromium oxide prepared by dehydrating precipitated chromium oxide hydrate green is intimately mixed with water and chromic acid and treated under pressure.
  • the ratio by weight of chromium oxide to chromic acid should be in the range from 1:1 to 1:5. If too little chromic acid is present, not all the chromium oxide used is converted into ferromagnetic chromium dioxide. If too much chromic acid is used, it is solely the chromium dioxide crystallising in the rutile lattice that is formed, as shown by X-ray photographs, the particles, however, being too large and hence the magnetic values unsatisfactory.
  • the quantity of water used can be varied within a wide range.
  • reaction temperature during the pressure treatment may be in a range of from 50 to 400 C., preferably of from 200 to 400 C. and the reaction pressure in a range of from 50 to 500 kg./cm. Although higher temperatures and pressure can be used, they do not produce any improvement in the products and involve the use of fairly expensive pressure apparatus.
  • the reaction time is not critical and can amount to a few hours.
  • the modifiers known from the literature referred to above may be used as modifiers, especially oxides and/or fluorides of manganese, cobalt, iron, niobium, ruthenium, arsenic, antimony, vanadium, tellurium and so on, of the kind described in British patent specifications Nos. 859,- 937 and 1,073,483. It is preferred to use the oxide-forming compounds of tellurium and/or antimony.
  • the tellurium may also be used in the elementary form or in the form of an alloy with antimony.
  • a combination of a tellurium or antimony compound with an iron-containing compound may also be used.
  • the TeO or SbgOgcontent of the end product should not exceed 0.5% by weight. If a relatively large quantity of the modifier is used, the material becomes too finely divided and the magnetic properties deteriorate.
  • the remanent magnetising values for the chromium dioxide prepared as described in the foregoing are between 400 and 500 [gauss cm. -g.-
  • the coercive forces are governed by the particle size and can readily be varied by adjusting the chromium oxide/chromic acid ratio and by adding modifiers, in a range of from 200 to 550 [oe.].
  • chromium dioxide accumulates in the form of needle-like particles.
  • the length of the needles may be varied from 0.1 to 2 11.111. and their width from 0.015 to 0.1 am.
  • the chromium oxide used as the starting material obtained by dehydrating and tempering precipitated chromium oxide hydrate green has a favourable particle size distribution and a limited tendency towards agglomeration, the individual particles of the chromium dioxide obtained from it are also very uniform in shape and size. The process can be controlled so that as large a number of particles as possible is in the optimum particle size range.
  • the favourable particle size distribution has a beneficial effect upon a number of properties.
  • unusually high print-through values of up to 60 [db.] were found on sound tapes that had been produced from the chromium dioxide obtained by the process according to the invention.
  • the chromium dioxide has another qualitative feature: due to the relatively low Curie point of 126 C., the magnetic properties, for example the remanent magnetisation, are governed to some extent by temperature even at relatively low temperatures. This effect is undesirable because it is able to vary the characteristic of the tapes and can lead to disturbances during operation. Due to the favourable particle size distribution, the dependence upon temperature of the magnetic characteristics at temperatures of practical interest is minimal in the chromium dioxide produced in accordance with the invention.
  • the precipitated chromium oxide hydrate green was tempered for 2 hours at 700 C. in a rotating tubular oven. As a result it was converted with loss of water (20% weight loss) into a-Cr O which was found by measurement to have a BET surface of 24 m. g.
  • a print-through of 56 [db.] was determined on the tape in accordance with DIN 45 519.
  • COMPARISON EXAMPLE A The use of chromium oxide hydrate according to U.S. patent specification No. 3,278,263 as starting material for the production of chromium dioxide.
  • Example 1a Like the precipitated chromium oxide hydrate green in Example 1a, the preparation was heated fortwo hours at 700 C. in a rotating tubular oven.
  • the chromium oxide obtained in this Way had a specific surface of 19.8 mfi/g.
  • the magnetisation temperature in C. was plotted on the abscissa and, on the ordinate, the remanent magnetisation at 22 C. in percent based on the remanent magnetisation, after magnetisation at 22 C.
  • the solid-line curve shows the values obtained for the product according to Example 1, whilst the chainline curve shows the values obtained for the product of Comparison Example A.
  • EXAMPLE 2 (a) Precipitated chromium oxide hydrate green according to Example 1a was tempered for two hours at 700 C. in a mufiie furnace. After tempering, the product had a BET surface of 23 mF/g.
  • Chromium dioxide with the following magnetic data was obtained:
  • the average needle length was measured at 0.24 ,um. from photographs taken with an electron microscope, and at approximately 0.5,um. for the preparations according to Examples 1b and 2b. The greater fineness in the division of the product caused by the addition of tellurium is also reflected in the greater coercive force.
  • EXAMPLE 4 143.5 g. of chromium oxide prepared in accordance with Example 2'.) and l g. of Sb O were stirred into a suspension of 287 g. of chromic acid in 110 ml. of water and the mixture heated in the autoclave under the conditions described in Example lb.
  • The' chromium dioxide thus prepared had the following magnetic data:
  • COMPARISON EXAMPLE B (a) Commercial guignet green (Reading Green and Marvell) was tempered for 2 hours at 700 C. in a rotating tubular oven. After tempering, the product had a specific surface according to BET of 24 m. g.
  • a product of this kind is unsuitable on account of its poor magnetic properties.
  • X-ray photographs show that the product contains Cr O in addition to Cr0 Unlike precipitated chromium oxide hydrate green, guignet green is not suitable for use as a starting material in the production of chromium dioxide.
  • a process for the production of ferromagnetic chromium dioxide wherein a chromate or dichromate solution is subjected to the action of an organic substance at a temperature of from 300 C. to 400 C. and at a pressure of from 250 to 350 kg./cm. said organic substance being a reducing agent for the chromate and dichromate under said conditions, to form chromium oxide hydrate green, wherein the resulting chromium oxide hydrate green is dehydrated at a temperature of 300 C. to 900 C.
  • chromium oxide in which the average oxidation state of the chromium is in the range of from 3 to 4, and wherein the chromium oxide is heated with chromic acid under hydrothermal conditions at a temperature of from 50 C. to 400 C. and at a pressure of from 50 to 500 kg./cm.2.
  • a process according to claim 2, wherein the substance acting as a modifier is tellurium or a compound thereof in an amount such that the modifier oxide content of the end product of the oxidation of the chromium oxide does not exceed 0.5 by weight.
  • a process according to claim 2, wherein the substance acting as a modifier is antimony or a compound thereof in an amount such that the modifier oxide content of the end product of the oxidation of the chromium oxide does not exceed 0.5% by weight.
  • a process according to claim 2, wherein the substance acting as a modifier is a combination of tellurium or a compound thereof and an iron-containing compound in an amount such that the modifier oxide content of the end product of the oxidation of the chromium oxide does not exceed 0.5% by weight.
  • a process according to claim 2, wherein the substance acting as a modifier is a combination of antimony or a compound thereof and an iron-containing compound in an amount such that the modifier oxide content of the end product of the oxidation of the chromium oxide does not exceed 0.5 by weight.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Nanotechnology (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Inorganic Chemistry (AREA)
  • Composite Materials (AREA)
  • Hard Magnetic Materials (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
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US32648A 1969-05-02 1970-04-28 Process for the production of ferromagnetic chromium dioxide Expired - Lifetime US3696039A (en)

Applications Claiming Priority (1)

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DE19691922409 DE1922409A1 (de) 1969-05-02 1969-05-02 Verfahren zur Herstellung von ferromagnetischem Chromdioxid

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US (1) US3696039A (fr)
JP (1) JPS4828274B1 (fr)
BE (1) BE749818A (fr)
CA (1) CA932944A (fr)
CH (1) CH545252A (fr)
DE (1) DE1922409A1 (fr)
FR (1) FR2041805B1 (fr)
GB (1) GB1316664A (fr)
NL (1) NL7006481A (fr)
SE (1) SE345649B (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3911095A (en) * 1972-06-30 1975-10-07 Montedison Spa Preparation of ferromagnetic chromium dioxide having granulometric and magnetic characteristics varying within wide limits as well as a new chromium dioxide of particular granulometric characteristics
DE2648305A1 (de) * 1975-10-31 1977-05-12 Montedison Spa Verfahren zur herstellung von ferromagnetischem chromdioxid
US4741895A (en) * 1986-03-25 1988-05-03 Basf Aktiengsellschaft Preparation of chromium(III) oxide

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4698220A (en) * 1986-03-28 1987-10-06 E. I. Du Pont De Nemours And Company Partitioned reduction process for ferromagnetic chromium dioxide
US4769165A (en) * 1987-01-20 1988-09-06 E. I. Du Pont De Nemours And Company Process for synthesis of ferromagnetic chromium dioxide
DE3728453A1 (de) * 1987-08-26 1989-03-09 Basf Ag Verfahren zur herstellung von modifiziertem, ferromagnetischem chromdioxid

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3911095A (en) * 1972-06-30 1975-10-07 Montedison Spa Preparation of ferromagnetic chromium dioxide having granulometric and magnetic characteristics varying within wide limits as well as a new chromium dioxide of particular granulometric characteristics
DE2648305A1 (de) * 1975-10-31 1977-05-12 Montedison Spa Verfahren zur herstellung von ferromagnetischem chromdioxid
US4741895A (en) * 1986-03-25 1988-05-03 Basf Aktiengsellschaft Preparation of chromium(III) oxide

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FR2041805B1 (fr) 1974-04-26
DE1922409A1 (de) 1970-11-12
FR2041805A1 (fr) 1971-02-05
SE345649B (fr) 1972-06-05
BE749818A (fr) 1970-10-30
JPS4828274B1 (fr) 1973-08-30
CA932944A (en) 1973-09-04
NL7006481A (fr) 1970-11-04
GB1316664A (en) 1973-05-09
CH545252A (de) 1973-12-15

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