DE3729693A1 - Process for preparing fine barium ferrite particles - Google Patents

Abstract

An aqueous solution containing Fe<3+> and Ba<2+> ions or a suspension containing the corresponding hydroxides is subjected, at ambient pressure in an alkaline solution of relatively high concentration, to a wet reaction and thus gives fine barium ferrite particles which are distinguished by their particle size distribution and their magnetic properties such as the coercive force or the magnetisation per unit weight. According to the invention, the aqueous solution or suspension contains not only Fe<3+> and Ba<2+> ions but use is likewise made of the starting material ions of elements lowering the coercive force or of elements increasing the coercive force, so as to thus be able to control the coercive force of the fine barium ferrite particles prepared, so that it is finally possible to prepare fine barium ferrite particles having a coercive force making them suitable for use in magnetic recording materials or as permanent magnets.

Description

The invention relates to a method for manufacturing fine barium ferrite particles used as permanent magnet material or magnetic particles for magnetic recording materials with vertical magnetization are used will.

Barium ferrite is already long enough as a permanent magnet material Lich known in such a way that his particles under Cast formation of permanent magnets of various shapes and sinter or in rubber to form so-called Can mix in rubber magnets.

On the other hand, research work and Investigations regarding the possible use of barium ferrite particles as magnetic powder for magnetic Vertical magnetization recording materials in progress.

Barium ferrite particles have a flat, hexagonal Plate shape with easily magnetizable axes that run perpendicular to the surface of the platelet, so that this in the development of magnetic recording materials with vertically magnetized magnet layer are indispensable.

In the conventional magnetic recording medium You have materials with longitudinal magnetization on the usefulness of the barium ferrite particles again to reflect with the progress in the field of To keep pace with high density recording. So  are z. B. Studies have been done on barium ferrite particles as magnetic particles for high-density disks or daughter tapes that are used for magnetic transmission of the information recorded on the main tape will be used.

The magnetic recording materials with magneti magnetized layer, which is this barium ferrite part Chen use, have compared to magnetic Recording materials with a thin metal layer or so-called vapor-deposited metal strips a variety of benefits. For example, you have a excellent high-density recording behavior and can be used in larger quantities with a conventional continuous coating device will. The risk of corrosion is also very low, because the particles are made of an oxide magnetic material, while looking at interfacial technology for Magnetic head materials like the conventional systems can operate.

The barium ferrite particles for permanent magnet materials or magnetic recording materials have so far been used usually made using a dry process.

After the dry process, barium ferrite according to fol gender implementation produced:

→ 6 Fe ₂ O ₃ + BaCO ₃ → BaO.6 Fe ₂ O ₃

The barium ferrite obtained is then in a ball mill, a vibrating mill or an attritor Formation of fine barium ferrite particles crushed.  

However, the wet process is unsuitable because the Barium ferrite particles do not exceed a certain limit worth can be reduced while the Particle size distribution is small and coarse Particles or contaminants from the ball mill in the end product will inevitably be mixed.

To overcome these disadvantages, one has recently Investigations regarding a river or glass kri installation process, a hydrothermal process using an autoclave or process using organic metal salts, such as alkoxides, carried out.

However, these procedures are complicated because of the Operations, low productivity and in the amount of production costs driven is unsuitable. Finally, in the hydrothermal process Autoclave used, so this process to manufacture large quantities is not suitable.

In summary, it can be said that this has been so far knew wet process for the production of barium ferrite particles due to the small particle size and part distribution of the size of the barium ferrite particles obtained and the addition of coarse-grained particles or impurities is not suitable, while the flow ratio drive, glass crystallization process, the hydrothermal procedure with the autoclave or the procedure with organic metal salts, such as alkoxides, also due to the low productivity and increased manufac is unsuitable.

It is therefore an object of the invention to be a powerful method for producing barium ferrite particles, which have a small particle size, free from are mixed impurities and in terms of Particle size distribution and the magnetic behavior over possess inherent properties.

Another object of the invention is to provide a Process for the production of barium ferrite particles which one does not have to use a high pressure vessel for the production of larger quantities is suitable for sheep fen.

It is a further object of the invention to provide a method to create barium ferrite particles, where it is possible to use the coercive force of the herge set barium ferrite particles to control so that barium ferrite particles with a moderate coercive force will hold so that these as magnetic particles for Ma gnet recording materials suitably used can be.

Finally, there is another object of the invention therein a process for making barium ferrite to create particles where it is possible to create the Coercive force of the barium ferrite particles produced in order to obtain particles that are considered Permanent magnets can be used suitably.

These tasks are accomplished with the method according to the invention Renium for the production of barium ferrite particles in reverse exercise pressure solved, it has been found that a wet reaction in an alkaline medium is increased Concentration of great benefit for this procedure is.  

The invention provides a process for producing fine barium ferrite particles which consists in an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions, a suspension containing the corresponding hydroxides or a mixture thereof at ambient pressure and an alkali concentration of 6 to 20 mol / l is subjected to a wet reaction and the barium ferrite product obtained is subjected to a heat treatment in air.

The invention further provides a process for the manufacture of fine barium ferrite particles, which consists in that an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions as well as ions of the elements reducing the coercive force, a suspension containing the corresponding hydroxides or a mixture thereof is subjected to a wet reaction at ambient pressure and an alkali concentration of 6 to 20 mol / l and the barium ferrite product obtained is subjected to a heat treatment in air.

Finally, the invention provides a process for the production of fine barium ferrite particles, which consists in an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions as well as ions of elements which increase the coercive force, a suspension containing the corresponding hydroxides or a mixture thereof is subjected to a wet reaction at ambient pressure and an alkali concentration of 6 to 20 mol / l and the barium ferrite product obtained is subjected to a heat treatment in air.

If the aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or a suspension containing their hydroxides in an alkaline solution of an increased concentration is subjected to a wet reaction, fine barium ferrite particles are produced even at ambient pressure.

The barium ferrite particles obtained have a small one Size and an excellent particle size distribution on, being free of admixtures of coarse-grained part Chen or impurities are what can be attributed to it lead is that they are made by the wet process have been.

If the ions of the coercive force-lowering elements such as Co ²⁺ ions are previously added to the aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or the suspension containing their hydroxides, it becomes possible to reduce the coercive force of the to lower obtained barium ferrite particles.

On the other hand, if ions of elements which increase the coercive force, such as Al ³⁺ ions, are previously added to the aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or to the suspension containing their hydroxides, it becomes possible to add the coercive force of the obtained barium ferrite particles.

Fig. 1 shows the X-ray diffraction diagram in accordance with an embodiment of the invention barium ferrite particles obtained before heat treatment.

Fig. 2 shows the X-ray diffraction diagram in accordance with an embodiment of the invention barium ferrite particles obtained after the heat treatment.

Fig. 3 shows a diagram of the results of the thermal analysis of the barium ferrite particles obtained according to an embodiment of the invention.

Fig. 4 shows the X-ray diffraction pattern in accordance with another embodiment of the invention barium ferrite particles produced before the heat treatment.

Fig. 5 shows the X-ray diffraction pattern of the barium ferrite particles produced according to another embodiment of the invention after the heat treatment.

Fig. 6 is a graph showing changes in magnetic behavior caused by changes in the substitution amounts of cobalt and titanium.

Fig. 7 shows the X-ray diffraction diagram of the treatment before the Wärmebe according to another embodiment of the invention barium ferrite particles obtained.

Fig. 8 shows the X-ray diffraction pattern of the barium ferrite particles obtained according to a further embodiment of the invention after the heat treatment.

Fig. 9 shows the graph of the results of the analysis of the Thermoana according to another embodiment of the invention barium ferrite particles obtained.

An aqueous, Fe ³⁺ -, and Ba ²⁺ ion-containing solution, which is according to the invention used as a starting material, is prepared by a water-soluble Fe ³⁺ - salt, such as ferric chloride FeCl ₃ · n H ₂ O or iron nitrate Fe (NO ₃ ) ₃ · 6 H ₂ O and a water-soluble Ba ²⁺ salt, such as barium chloride BaCl ₂ · 2 H ₂ O, barium nitrate Ba (NO ₃ ) ₂ , barium acetate Ba (CH ₃ COO) ₂ · H ₂ O or barium hydroxide Ba ( OH) ₂ · 8 H ₂ O, Ba (OH) ₂ can be dissolved in pure water. The starting material is not limited to the aqueous solutions of these water-soluble salts, but it can comprise, for example, a liquid suspension containing water-insoluble hydroxides, such as iron hydroxide, or a mixture of the water-soluble salts and water-insoluble hydroxides.

The molar ratio Fe / Ba des in the aqueous mentioned Fe or Ba containing solution or suspension preferably in the range from 9 to 12, in particular in the Range from 10.5 to 11.8.

To control the coercive force, ions of the elements reducing the coercive force can be added to the already mentioned aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or to the liquid suspension containing the corresponding hydroxides, so that a Part of the Fe ³⁺ ions is replaced by ions of these elements which reduce the coercive force. By adding these ions of the elements which lower the coercive force, the coercive force Hc or the magnetization per specific weight σ g can be kept at a predetermined value, so that barium ferrite particles which are suitable as magnetic powder for magnetic recording materials are produced.

The ions of the elements which reduce the coercive force include Co ²⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Nb ⁵⁺ , Cu ²⁺ , Ni ²⁺ or Zn ²⁺ ions. Above all, two different ions of the elements reducing the coercive force can be used in combination to reduce the coercive force. If, for example, two different ions of the elements which reduce the coercive force are used in combination, such as Co ²⁺ / Ti ⁴⁺ , Co ²⁺ / Zr ⁴⁺ or Co ²⁺ / Nb ⁵⁺ , the composition of the barium ferrite corresponds to the following Formula:

BaFe _{12-2 x} Co _x M _x O ₁₉

wherein M is Ti ⁴⁺ , Zr ⁴⁺ or Nb ⁵⁺ ions, provided that when M = Nb ⁵⁺ , M _x in the formula is Nb _{4 x / 5} ; Similar meanings continue to be used in the description. The amount of substitution x is preferably in the range of 0.4 x 0.9. The ^{amount of} Co ²⁺ substitution and that of the Ti ⁴⁺ , Zr ⁴⁺ or Nb ⁵⁺ ions can of course be different in each case.

The ions of these elements which reduce the coercive force can, similarly as in the case of the already mentioned Fe ³⁺ or Ba ²⁺ ions, to the already mentioned aqueous solution or suspension in the form of the corresponding water-soluble salts or in the form of the corresponding water-insoluble hydroxides to be added.

To increase the coercive force Hc or magnetization σ g, on the other hand, ions from the elements increasing the coercive force can be added to the aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or to the liquid suspension containing the corresponding hydroxides, so that the Fe ³⁺ ions are partially replaced by the ions of these elements which increase the coercive force.

The ions of the elements which increase the coercive force include Al ³⁺ and Ga ³⁺ ions, it being sufficient for some of the Fe ³⁺ ions to be replaced by at least one of these ions. The ions of the coercive force-increasing elements, similar to the ions of the coercive force-lowering elements already mentioned, can be added in the form of water-soluble salts, such as aluminum chloride or gallium chloride, or as a suspension in the form of water-insoluble hydroxides. The ratio of the concentrations of the added aluminum ions (Al ³⁺ ) or gallium ions (Ga ³⁺ ) to the concentration of the barium ions (Ba ²⁺ ) is preferably in the range from 0.3 to 3.5.

In the wet reaction, an alkali is added such that the alkali concentration in the solution or suspension is 6 to 20 moles per liter and the resulting solution or suspension is heated to the boiling point at ambient pressure. In this case, the alkali can be added little by little to the aqueous Fe ³⁺ and Ba ²⁺ ions containing the solution or suspension, or the aqueous solution or suspension containing Fe ³⁺ and Ba ²⁺ ions can otherwise be added gradually and after added to the alkali solution. Although the type of alkali to be used is not critical to the invention, alkali metal hydroxides such as sodium, potassium or lithium hydroxide are used. These alkalis can be added as they are or in the form of an aqueous alkali solution in pure water. Otherwise, the alkalis can be added partly as they are and partly in the form of the aqueous alkali solution. It has been shown that the alkali concentration (OH ^- ) with a uniform course of the reaction is preferably in the range from 6 to 20 mol / l.

The product obtained after the wet reaction mentioned is washed Reaction product with waser, filters, dries and performs a heat treatment in the air for improvement of the magnetic properties.

The temperature during the heat treatment is preferred wise not more than 700 ° C.

From the above explanations it can be seen that the aqueous solution containing Fe ³⁺ and Ba ²⁺ ions or the suspension containing the corresponding hydroxides in an alkaline solution of higher concentration is subjected to a wet reaction, so that fine barium ferrite particles with excellent crystallinity be produced at ambient pressure.

If you then use the powder to improve the magneti undergoes heat treatment properties, so the particle size of the reaction product remains hold so that you are extraordinary in this way fine barium ferrite particles with excellent particles can produce size distribution.

Since it is not necessary according to the invention, a high pressure to use vessel, one can barium ferrite particles in produce larger quantities with higher productivity len.

Since the process is also a wet reaction process is carried out, one avoids the risk that Verun cleaning or coarse-grained particles mixed in will.  

Since part of the Fe according to the invention also by the Coercivity-lowering elements, such as Co, are replaced the reduction of the coercive force is made possible so that barium ferrite particles with an appropriate height of coercive force for use as magnetic particles for magnetic recording materials can be obtained.

Since part of the Fe according to the invention through the coercive force-increasing elements, such as Al or Ga, are replaced, the increase in the coercive force is made possible so that Barium ferrite particles, suitably as permanent gneten can be used.

example 1

0.115 mol of iron chloride and 0.01 mol of barium chloride are dissolved ridin a Teflon beaker in 50 ml of pure water. Man separately dissolves 40 g sodium hydro in 70 ml pure water xid and gradually sets the resulting solution with stirring to the previously described solution. Man then continues to add 50 g of sodium hydroxide to the resulting added to the mixture and leaves the resulting solution react at the boiling point for 8 hours. While the reaction is added to the reaction system in such an amount that the by the Water evaporation caused water loss is compared so that excessive fluctuations in the Avoided alkali concentration of the reaction system will.  

The result obtained after completion of the reaction is given Reaction product gradually in 2 l of pure water and removes the excess water by decanting. Fresh water is added after decanting added. These measures are repeated until the pH has reached a neutral range at which one filters the reaction product and the Filtra tion product in a drying device at a Temperature of 100 ° C for 2 days and nights dry, so that one finally finishes Obtained particles as a reaction product.

Fig. 1 shows an X-ray diffraction pattern of the fine particles obtained by the above-mentioned method using a copper target and a monochrometer in the X-ray tube. Since the X-ray diffraction pattern is similar to that of 27-1029 on the JCPDS card and the Miller indices can be assigned to the individual diffraction peaks, the particles could be identified as barium ferrite particles of the hexagonal system. When these barium ferrite particles were examined under a transmission electron microscope, it was found that the particles had a particle size of 0.1 μm.

A heat treatment is carried out with these barium ferrite particles in air at a temperature of 900 ° C. for 2 hours. Fig. 2 shows the X-ray diffraction diagram of the particles obtained after the heat treatment. Although the individual peaks of the diffraction diagram have become sharper after the heat treatment, the diffraction diagram is similar to that shown in Fig. 1, so that it can be seen that the particles consist only of hexagonal barium ferrite.

Fig. 3 shows the results of the thermal analysis of the barium ferrite particles obtained after the heat treatment just described. In this diagram, the results of the thermogravimetric analysis are expressed by TG and the results of the differential thermal analysis are expressed by DTA. This diagram shows a heat absorption peak for DTA near 100 ° C, which may be due to the desorption of adsorbed water, during which a corresponding weight loss for TG can be recorded.

The magnetic properties of the reaction product before and after the heat treatment are measured on the other hand with a vibration test magnetometer (VSM) with the intensity of the external magnetic field of 15 k Oe. Thereafter, it can be seen that the coercive force Hc of the reaction product improved from a value of 60 Oe before the heat treatment to a value of 3320 Oe after the heat treatment at a temperature of 900 ° C for two hours, during which the magnetization per specific gravity σ g of the reaction product has similarly improved from a value of 9 before the heat treatment to a value of 59.5 emu / g after the heat treatment.

Example 2

It is dissolved in 500 ml of pure water 0.0575 mol of iron nitrate Fe (NO ₃ ) ₃ .9 H ₂ O. 25 ml of concentrated ammonia water are added to the resulting aqueous solution, so that iron hydroxide can precipitate out, which is then filtered and filtered washes with water. The precision is transferred to a 250 ml Teflon beaker. 0.005 mol of barium hydroxide Ba (OH) ₂ .8H ₂ O, 600 g of sodium hydroxide and pure water are filled into this beaker so that the contents of the beaker give 100 ml. The mixture obtained is allowed to react at the boiling point for 8 hours. Additional water is occasionally added to the reaction system during the reaction in order to compensate for the water loss caused by water evaporation, so that changes in the alkali concentration in the reaction system are avoided.

The one obtained after completion of the reaction is added Gradually add the reaction solution to 2 liters of pure water. Man removes the supernatant by decanting and fills with fresh water. These measures are repeated like this long until the pH reaches a neutral range , where you filter the precipitate and in a Drying device at a temperature of 100 ° C dry for 2 consecutive days and nights net, so that you eventually get fine particles as a reak tion product.

These fine particles could be identified by their X-ray diffraction diagram, which is similar to that shown in Fig. 1, as barium ferrite particles of the hexagonal system. The particles have a coercive force Hc of 50 Oe and a magnetization per specific weight of 8 emu / g.

A heat treatment is carried out with these barium ferrite particles at a temperature of 900 ° C. in air for two hours. The particles obtained after the heat treatment according to their X-ray diffraction pattern are only hexagonal barium ferrite, which is similar to that shown in FIG. 2. The coercive force Hc is 4500 Oe and the magnetization per specific weight σ g 62 emu / g, which finally indicates that the magnetic properties of the barium ferrite fine particles could be improved by the heat treatment.

Example 3

Place 400 g in a 1 liter stainless steel beaker Sodium hydroxide and dissolves in 300 ml of pure water.

Dissolve in 300 ml of pure water to form a mixed aqueous solution 0.075 mol of barium chloride and 0.8625 mole of ferric chloride.

The aqueous sodium hydroxide solution is heated with stirring solution. It is added to this heated aqueous solution little by little the mixed one just mentioned Solution and leave the resulting mixture on the boil Stir point for 8 hours. One adds during the Implementation add water from time to time to the caused by the water evaporation desire to compensate for excessive fluctuations in the alkali concentration of the reaction system avoided will.

The reaction product is gradually put into one 5 l beaker filled with 4 l of pure water. You wash the reaction product with water by decanting, filtered and dried in a dryer a temperature of 200 ° C for 2 consecutive the days and nights.

The fine barium ferrite part obtained in this way Chen show an X-ray diffraction pattern that corresponds to that of the Reaction product before the heat treatment according to the  previous example 1 is similar. The after the Heat treatment at a temperature of 900 ° C during Particles obtained for 2 hours show an X-ray tube tion diagram that follows that of the barium ferrite particles the heat treatment according to Example 1 is similar.

The magnetic properties of these heat-treated barium ferrite particles are measured using a vibration sample magnetometer (VSM) which has an external magnetic field of 15 kOe. From this it can be seen that the coercive force Hc 3400 Oe and the magnetization per specific weight σ g are 59.8 emu / g, whereas the magnetization per specific weight σ g from an assumed undetermined large external magnetic field is 71.8 emu / g.

Example 4

It is dissolved in 60 ml of pure water in a teflon beaker 0.100 mol of iron chloride, 0.01 mol of barium chloride, 0.0075 moles of cobalt chloride and 0.0075 moles of a titanium chloride solution based on titanium. It is dissolved in 70 ml pure water 40 g sodium chloride and adds the obtained Solution with stirring gradually to that just mentioned aqueous solution. You add to the resulting solution continue 50 g of sodium hydroxide and leaves the resulting Solution at the boiling point with stirring for 8 hours react. During the implementation one occasionally adds Make-up water to add to the water supply compensate for water loss caused by vaporization, thus excessive fluctuations in the alkali concentration tion of the reaction system can be avoided.  

The one obtained after completion of the reaction is given Gradually add the reaction solution to 2 l of pure water. Man removes the supernatant by decanting and fills with fresh water. You repeat these measures until the pH has reached a neutral range at which the precipitate is then filtered and at 120 ° C Dried overnight, so that you get fine particles receives as a reaction product.

The X-ray diffraction pattern of the fine particles obtained using a copper target and a monochrometer in the X-ray tube is shown in FIG. 4. This X-ray diffraction pattern is similar to that of the 27-1029 of the JCPDS card and the Miller indices can be transferred to the respective diffraction peaks. The fine particles are therefore identified as barium ferrite particles of the hexagonal system.

A heat treatment is carried out with the barium ferrite particles just mentioned in air at a temperature of 900 ° C. for 2 hours. The X-ray diffraction chart obtained after the heat treatment is shown in FIG. 5. The X-ray diffraction diagram after the heat treatment shows that the barium ferrite peaks are much more pronounced than in the diffraction diagram from FIG. 4.

The magnetic properties are measured after heat treatment with a vibration sample magnetometer (VSM) with an external magnetic field of 15 kOE, with a value of 670 Oe for the coercive force Hc and a value of 61.8 emu / for the specific gravity σ g. g receives.

Example 5

Fine barium ferrite particles are prepared by the method similar to that in Example 1, with the difference that with changing x values 0.115-0.02 x mol iron chloride, 0.01 mol barium chloride, 0.01 x mol cobalt chloride, 01 x mol of a titanium chloride solution, based on titanium, is used.

A heat treatment is carried out with the barium ferrite particles obtained in a muffle furnace in air at a temperature of 900 ° C. for 2 hours. The X-ray diffraction diagram after the heat treatment is similar to the diagram shown in FIG. 5. The magnetic properties of the particles after the thermal treatment, which are measured with the VSM with an external magnetic field of 15 kOe, are shown in FIG. 6. It can be seen from this figure that the larger the value x , the smaller the coercive force shown by curve A in FIG . The magnetization per specific weight is expressed by curve B in FIG. 6. The slope is steeper for the coercive force. Thus, there is proof that the coercive force and the magnetization per specific weight can be controlled to prescribed values by the addition amounts x of Co and / or Ti.

Example 6

0.5 mol of iron chloride, 0.05 mol, is dissolved in a beaker Barium chloride, 0.0375 mol cobalt chloride and 0.0375 mol a titanium chloride solution, based on titanium, in 300 ml pure water. Incidentally, it is dissolved in 300 ml of pure water 150 g of sodium hydroxide and adds the resulting solution  gradually with stirring to the just mentioned aq solution. The resulting solution is transferred to a 1 liter stainless steel cup. One inserts Stir 150 g of sodium hydroxide gradually to the Add solution and omits the resulting mixture Warming in a jacket heater to boiling react point for 8 hours. During the implementation you occasionally add make-up water to the through water loss caused by water evaporation to compensate for excessive fluctuations in the Alkaline concentration in the reaction system can be avoided.

The reaction mixture is poured after completion of the order gradually put in 2 l of pure water. One removes by decanting the supernatant liquid and adds add fresh water to the remaining precipitate. These measures are now repeated until the pH of the solution reaches a neutral range in which you then filter the solution and that Filtration product overnight at a temperature of Dries 120 ° C to form fine barium ferrite particles.

These barium ferrite particles are subjected to heat treatment at a temperature of 900 ° C in air for two hours. An X-ray diffraction chart of these barium ferrite particles is then made and found to be similar to that shown in FIG .

The magnetic properties of the barium ferrite particles after the heat treatment are measured using a VSM which has an external magnetic field of 15 kOe. A value of 634 Oe is obtained for the coercive force Hc and a value of 59.4 emu / g for the magnetization per specific weight σ g.

Example 7

0.51 mol of iron chloride, 0.05 mol of barium chloride, 0.0375 mol of cobalt chloride and 0.0375 mol of a titanium chloride solution, based on titanium, are dissolved in 300 ml of water in a 1 liter beaker. Fine barium ferrite particles are obtained and heat treatment is carried out using this aqueous solution as a raw material, and the method of the previous example 6 is further used. A diffraction pattern of the barium ferrite particles is obtained and found to be similar to that shown in FIG .

The magnetic properties of the barium ferrite fine particles are measured after the heat treatment using a VSM which has an external magnetic field of 15 kOe. A value of 648 Oe is obtained for the coercive force Hc and a value of 56.9 emu / g for the magnetization per specific weight σ g.

Example 8

Fine barium ferrite particles are produced and subjected to heat treatment by using 0.115-0.02 x mol of iron chloride, 0.1 mol of barium chloride, 0.01 x mol of cobalt chloride and 0.01 x mol of a zirconium chloride solution as starting material with substitution values for Fe ^{3 +} of 0.7 and 0.75 and otherwise carries out the measures of the previous example 4. The X-ray diffraction pattern of the fine barium ferrite particles is made and is found to be similar to that shown in FIG .

Example 9

Fine barium ferrite particles are prepared and subjected to heat treatment by using 0.115-0.02 x mol of iron chloride, 0.01 mol of barium chloride, 0.01 x mol of cobalt chloride and 0.0667 x mol of a niobium chloride solution based on niobium as the starting material with substitution values for Fe ^{³ +} of 0.7 and 0.75 and otherwise carries out the measures of the previous example 4. The X-ray diffraction pattern of the barium ferrite fine particles is made and found to be similar to that shown in FIG .

One measures using a VSM which is an external one Magnetic field of 15 kOe, the magnetic eigen properties of those obtained according to Examples 8 and 9 fine barium ferrite particles after the heat treatment. The results are shown in Table 1 below refer to.

Table 1

From Table 1 it can be seen that the coercive force of the barium ferrite particles produced are extraordinary takes small values from 710 to 770 Oe, so that these particles advantageously as magnetic particles can be used for magnetic recording media. When considering zirconium chloride and niobium chloride compared to their coercive force, that's how niobium works chloride in the direction, a lower coercive force to have as zirconium chloride. The magnetization per specific weight ranges from 58 to 59 emu / g and, in contrast to the coercive force, it works Zirconium chloride in the direction, a lower degree own netization than the niobium chloride.

Example 10

Fine barium ferrite particles are prepared and subjected to heat treatment by adding 0.115-0.02 x mol of iron chloride, 0.01 mol of barium chloride, 0.01 x mol of a titanium chloride solution based on titanium, and 0.01 x mol of copper chloride Starting materials and substitution values for Fe ³⁺ of 0.7 and 0.75 are used and otherwise the reaction stages of the previous example 4 are adopted. The X-ray diffraction pattern of the obtained barium ferrite fine particles is similar to that shown in FIG. 5.

Example 11

Fine barium ferrite particles are prepared and subjected to heat treatment by using 0.115-0.02 x mol of iron chloride, 0.01 mol of barium chloride, 0.01 x mol of a titanium chloride solution based on titanium, and 0.01 x mol of nickel chloride as starting materials and Substitution values x for Fe ³⁺ of 0.7 and 0.75 are used and otherwise follows the reaction steps of the previous example. The X-ray diffraction pattern obtained from the barium ferrite particles produced is similar to that shown in FIG. 5.

Example 12

Fine barium ferrite particles are produced and subjected to heat treatment by using 0.115-0.02 x mol of iron chloride, 0.01 mol of barium chloride, 0.01 x mol of a titanium chloride solution based on titanium, and 0.01 x mol of zinc chloride as starting materials and Values for x of the substitution amount for Fe ³⁺ of 0.7 and 0.75 are used and otherwise follows the reaction steps of the previous example 4. The X-ray diffraction pattern obtained from the barium ferrite particles produced is similar to that shown in FIG. 5.

One measures using a VSM with an external one Magnetic field of 15 kOe the magnetic properties after heat treatment according to the previous one Examples 10 to 12 obtained barium ferrite particles. The results are shown in Table 2.  

Table 2

From Table 2 it can be seen that the coercive force of the barium ferrite particles produced in the range of 1600 to 2700 Oe, which are relatively small values although larger than those in the previous ones Examples 8 and 9 are values obtained. Compares the addition elements copper, nickel and zinc in In terms of their relative influence on the coercive copper, copper ranks first, followed by nickel and zinc. The magnetizations per specific weight are in the range of 40 to 56 emu / g, with the values are highest when replaced by copper and these become progressively lower when iron goes through Nickel chloride and zinc chloride is replaced.  

Example 13

Place 400 g in a 1 liter stainless steel beaker Sodium hydroxide and dissolves in 300 ml of pure water. In addition, 0.75 mol is dissolved in 300 ml of pure water Iron chloride, 0.075 mol barium chloride, 0.0563 mol Cobalt chloride and 0.0563 mol of titanium chloride and represents a mixed solution.

The first aqueous solution is heated with stirring Sodium hydroxide solution. It is then added to this aqueous one Solution the mentioned mixed solution drop by drop and after and leaves the resulting mixture on react to the boiling point for 8 hours. During the Implementation one occasionally adds make-up water to thus the one caused by water evaporation Compensate for water loss, thus excessive fluctuation gene in the alkali concentration of the reaction system be avoided.

The reaction product is gradually put into one 5 liter beaker containing 4 liters of pure water. One removes by decanting the supernatant liquid and adds then add new water and decant. These Process steps are repeated until the pH of the solution is in the neutral range at which filter the precipitate, wash and overnight a temperature of 120 ° C in a drying device dries.

The fine barium ferrite part obtained in this way Chen show an X-ray diffraction pattern that is similar corresponding to the reaction product before the heat treatment the previous example 4. One submits  these fine particles of heat treatment and measure using a VSM with an external magnetic field of 15 kOe the magnetic properties of the obtained Product. The results are shown in Table 3 remove.

Table 3

Example 14

0.01 mol of barium chloride is placed in a teflon beaker, 0.085 moles of iron chloride and 0.03 moles of aluminum chloride and dissolves with stirring in 60 ml of pure water and receives a mixed solution.

In addition, 40 g of sodium are dissolved in 60 ml of pure water hydroxide and adds the resulting aqueous with stirring Solution gradually to the aforementioned mixed Solution.

50 g of sodium hydroxide are added to the mixture obtained and leaves the resulting product to the boiling point react for 8 hours. Adds during implementation  you occasionally add make-up water so that the through water loss caused by water evaporation to compensate for excessive fluctuations in the Avoided alkali concentration of the reaction system will.

The reaction product is gradually added to 2 l pure water and removed by decanting the over standing liquid and then fill up with new water and decanted again. These process steps will be Repeated until the pH of the solution in the neutral range where the precipitate filtered and in a dryer at a Temperature of 200 ° C dry for 2 days and nights net.

The X-ray diffraction pattern of the particles produced, which was made using a copper target and a monochrometer in the X-ray tube, is shown in FIG. 7. Since this diagram is similar to that of the 27-1029 of the JCPDS card, the particles could be identified as barium ferrite. These barium ferrite particles are examined with a transmission electron microscope, and it is found that they have a size of 0.1 μm.

These barium ferrite particles are subjected to a heat treatment at a temperature of 900 ° C. for 2 hours in air. The X-ray diffraction pattern after this treatment is shown in Fig. 8. The diffraction diagram after the heat treatment is similar to that shown in Fig. 7, although the respective peaks are sharper. The particles are therefore hexagonal barium ferrite, which no longer contains any other crystals.

A thermal analysis is carried out with the fine barium ferrite particles obtained after the heat treatment. The results are shown in Fig. 9, where TG expresses the results of thermogravimetric analysis and DTA expresses that of differential thermal analysis. It can be seen from this figure that a heat absorption peak, which is most likely attributable to water adsorption, is in the vicinity of 110 ° in the case of the DTA, while a corresponding weight reduction for TG has occurred.

The magnetic properties of these heat-treated barium ferrite particles are measured with a VSM with an external magnetic field of 15 kOe. A value of 5000 Oe is obtained for the coercive force Hc and a value of 60.5 emu / g for the magnetization σ g per specific weight. The magnetization per specific weight σ g in an undetermined large external magnetic field is 71.0 emu / g.

Example 15

Place 400 g in a 1 liter stainless steel beaker Sodium hydroxide and dissolves in 300 ml of pure water. In addition, 0.075 mol is dissolved in 300 ml of pure water Barium chloride, 0.75 mol iron chloride and 0.1125 mol Aluminum chloride and receives a mixed solution.

The former aqueous is heated with stirring Sodium hydroxide solution. You add to this watery Solution drop by drop the mentioned mixed  Solution and leave the resulting mixture on the boil react point for 8 hours. During this order Settlement you occasionally add make-up water to thus the one caused by water evaporation Compensate for water loss, thus excessive swan in the alkali concentration of the reaction system be avoided.

The reaction product is gradually put into one 5-liter beaker containing 4 liters of pure water, thus wash by decanting, followed by filtration and a drying process follows.

The barium ferrite particles thus obtained show an X-ray diffraction pattern similar to that shown in Fig. 7, while those subjected to heat treatment at a temperature of 900 ° C for 2 hours show an X-ray diffraction pattern similar to that in Fig. 7 . 8 is shown.

The magnetic properties of these heat-treated barium ferrite particles are measured with a VSM with an external magnetic field of 15 kOe. A value of 5080 Oe is obtained for the coercive force Hc and a value of 60.3 emu / g for the magnetization per specific weight σ g. The magnetization per specific weight σ g for an assumed undetermined large external magnetic field is 71.3 emu / g.

Example 16

Put 0.01 mol of barium chloride in a Teflon beaker, 0.095 mol of iron chloride and 0.02 mol of gallium chloride and dissolves with stirring in 60 ml of pure water and receives thus a mixed solution.  

One poses according to the one shown in the previous example method using this mixed solution fine barium ferrite particles.

The barium ferrite fine particles thus produced give an X-ray diffraction pattern similar to that shown in FIG. 7. The same barium ferrite particles which had been heat-treated at a temperature of 900 ° C for two hours give an X-ray diffraction pattern similar to that shown in FIG. 8.

The magnetic properties of the heat-treated barium ferrite particles are measured with a VSM with an external magnetic field of 15 kOe and a value of 5120 Oe is obtained for the coercive force Hc and a value of 57.7 emu / g for the magnetization per specific weight σ g . The magnetization per specific weight σ g for an assumed, indefinitely large external magnetic field is 70.3 emu / g.

It is prepared according to that in Examples 14 and 15 shown methods and using different Al and Ga quantities of samples of various fine barium ferrite particles. The magnetic properties are measured of the fine barium ferrite particles produced samples (sample numbers: BF-1 to BF-7). The one in the example 14 shown synthesis follows, with the sub decided that the amount of sodium hydroxide for sample BF-6 Is 55 g. The examples are listed in Table 4 leads.  

Table 4

It can be seen from this table that the substitution by Al ³⁺ or Ga ³⁺ effectively improves the coercive force.

Claims (5)

1. Process for the production of fine barium ferrite particles, characterized in that an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions, a suspension containing the corresponding hydroxides or a mixture thereof at ambient pressure and an alkali concentration of 6 to 20 Mol / liter is subjected to a wet reaction and the barium ferrite product obtained is heat-treated in air. 2. Process for the production of fine barium ferrite particles, characterized in that an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions and ions of the elements which reduce the coercive force, a suspension containing the corresponding hydroxides or a mixture thereof Ambient pressure and an alkali concentration of 6 to 20 mol / liter is subjected to a wet treatment and the barium ferrite product obtained is heat-treated in air. 3. The method according to claim 2, characterized in that at least one of the ions of Co ²⁺ -, Ti ⁴⁺ -, Zr ⁴⁺ -, Nb ⁵⁺ -, Cu ²⁺ -, Ni ²⁺ - and Zn ² Group comprising ⁺ ions as ions of elements which reduce the coercive force. 4. A process for the production of fine barium ferrite particles, characterized in that an aqueous solution containing Fe ³⁺ and Ba ²⁺ ions and ions of the elements which increase the coercive force, a suspension containing the corresponding hydroxides or a mixture thereof Ambient pressure and an alkali concentration of 6 to 20 mol / liter is subjected to a wet treatment and the barium ferrite product obtained is heat-treated in air. 5. The method according to claim 4, characterized in that at least one of the ions of the Al ³⁺ - and Ga ³⁺ ions comprising group is used as ions of the elements which increase the coercive force.