DE1248240B - Heat head for block mold - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

1 249 240

Int. Cl .:

COIg

/U.N

German class: 12 η -45/12

Number: 1249240

File number: A 48115 IV a / 12 η

Filing date: January 14, 1965

Opened on: September 7, 1967

The invention relates to a method for producing ferromagnetic NiMnO ₃ with an ilmenite structure.

Recently, ferromagnetic compositions have come into use in many fields. The mixture NiMnO ₃ , which is a complex compound of oxides of manganese and nickel, is of particular importance. The mixture has a rhombohedral ilmenite type crystal structure. It is also ferrimagnetic up to a temperature of 164 ° C. The pulverized material has a high coercive force of about 400 oersted. The coercive force can be increased to over 1000 Oersted by cold working. Since the material NiMnO _{3 has} no loss properties at high frequencies and has a relatively high coercive force, it is particularly useful for magnetic tapes or for highly permanent magnets.

To date, however, other ferromagnetic crystalline oxides have been more widely used than the ferromagnetic NiMnO ₃ , although these other compounds do not necessarily have the excellent properties of NiMnO ₃ . The reason why the NiMnO _{3 is} not so widespread is that it is extremely difficult to manufacture with the previously used methods. The previous production process for NiMnO ₃ is described in US Pat. No. 2,770,523; it works with the reactivity of NiO and MnO ₂ in a high pressure vessel at 500 ⁰ C and 1000 atm pressure. This process presents great difficulties and provides an extremely low yield. In addition, the product created in this way does not have a high degree of purity. Therefore, the possibilities of NiMnO ₃ could not be fully exploited.

The object of the invention is to provide a method of the type mentioned at the beginning which allows the ferromagnetic NiMnO ₃ with an ilmenite structure to be produced in high purity and which can be carried out easily.

To achieve this object of soluble nickel and manganese salts is precipitated, a mixture of nickel and Manganoxalaten and this mixture is heated to a temperature of 600-780 ⁰ C in an aqueous solution.

The soluble nickel and manganese salts used are preferably nickel acetate and manganese acetate, and oxalic acid is added to the aqueous solution to precipitate the oxalates. The molar ratio Mn: (Ni + Mn) in the aqueous solution of the soluble nickel and manganese salts is preferred set between 0.50 and 0.53.

It has proven to be particularly expedient to use methods for producing ferromagnetic NiMnO ₃ with an ilmenite structure

Applicant:

Ampex Corporation,

Redwood City, Calif. (V. St. A.)

Representative:

Dipl.-Ing. F. Weickmann,

Dr.-Ing. A. Weickmann,

Dipl.-Ing. H. Weickmann

and Dipl.-Phys. Dr. K. Fincke, patent attorneys,

Munich 27, Möhlstr. 22nd

Named as inventor:
Donald Guy Wickham,
Los Altos, Calif. (V. St. A.)

Claimed priority:

V. St. v. America 6 February 1964 (342 938)

when the aqueous solution of the nickel and manganese salts is boiling before the addition of the oxalic acid is heated; the precipitated oxalates are then preferably dried.

In the following, embodiments of Invention cited with reference to the drawing. It shows

F i g. 1 is a graph showing the loss of manganese in moles per liter of solution during coprecipitation of nickel and manganese oxides,

F i g. 2 shows a state diagram of the system NiO - Mn ₂ O ₃ - O ₂ .

The inventive method was ₂ O ₃ -O ₂ oxygen pressures of 0.21 and 1.00 at temperatures at 600-1200 ⁰ C obtained in the course of a thorough investigation of the system NiO Mn. In Fig. Figure 2 is a complete state diagram for this system that has been derived. From this figure it can be seen that the

709 640/369

1 249 240

certain, considered magnetic state Ni ₂ -J) MnJ) O ₃ exists for a certain narrow range of ρ and for temperatures between 700 and about 805 ⁰ C depending on the value of ρ and the oxygen pressure. The state would have to be stable under higher oxygen pressures even at higher temperatures; however, this has not been investigated.

As can be seen from the state diagram in FIG. 2, a single-phase substance with the composition NiMnO ₃ cannot exist at temperatures above 760 ± 5 ° C. under an air atmosphere. At this temperature range or below, the previously customary process for producing the substance mixture in which the oxides NiO and Mn ₂ O ₃ are reacted with one another cannot be used. These individual oxides are resistant (difficult to melt) and react extremely slowly. It is therefore necessary to mix the nickel and manganese in atomic proportions in a form that can then be converted into an oxide. According to the method of the invention, this is done by simultaneous precipitation of nickel and manganese oxalates from aqueous solutions of soluble nickel and manganese salts.

The state diagram of FIG. 2 is the key to the limits of the temperature ranges and the values for the production of the mixture of substances NiMnO ₃ by the method according to the invention. Example I which now follows describes the production and analysis of the samples which were used to set up a state diagram of the NiO - Mn ₂ O ₃ - O _{2 system} .

example 1

The acetates Ni (OAc) ₂ · 4H ₂ O and Mn (OAc) ₂ · 4H ₂ O were freshly crystallized from acetic acid, dried in air and stored in tightly closed bottles. According to the desired molar ratio /?, Which is defined as Mn: (Ni + Mn), the amounts by weight of the salts were weighed out. The total number of moles (Ni-j-Mn) was made equal to 0.1 + C, with C being a small correction for the manganese that remained in solution after the oxalates precipitated. The acetates were approximately 4 ml / dissolved in 400 ° _o acetic acid solution. While this solution was being heated and vigorously stirred, 100 ml of an oxalic acid solution containing the equivalent amount of oxalic acid plus an excess of 0.3 g was quickly added. Then the mixture of the precipitated oxides and the solution was boiled for 10 minutes with stirring. After cooling, the oxalates were separated off on a filter, washed and dried.

To check the value of C , the filtrate was evaporated to dryness, the residue was ^{ignited at 700 °} C. and weighed _{as Mn 2} O _3. A very exact value for C is not easy to predict, but the results show that an intermediate value for C can be used to better control the composition of the precipitate. It can be seen from FIG. 1, in which the values of C found are plotted, that C is a function of R. In the trials, there was a variation in C for a constant value of R due to the difficulty in controlling some variables such as the effectiveness of the stirring and the rate at which oxalic acid was added.

Example II

As in the previous example, a number of oxide samples with different, within U-values within a range. The oxides were turned into a slow glow

so oxygen atmosphere at a temperature between 400 and 500 ⁰ C degraded. Then the samples were heated to controlled temperatures between 600 and 1150 ⁰ C long enough time to e; n equilibrium between the solid phases and the atmo-

* 5 sphere - either air or pure oxygen - bring about.

X-ray diffraction patterns were taken from each oxide sample. Next up was that Oxidation capacity of each oxide sample is determined by

the sample was dissolved in an excess of a normal solution of vanadium sulfate in sulfuric acid. The excess was _{titrated with a KMnO 4} standard solution, phosphoric acid serving as the catalyst. The oxidizing power was expressed in equivalents per

Grams of the substance are counted, with an equivalent being the amount required ^{to convert one mole of V 4+} into V ^6+.

The evaluation of the X-ray powder images showed that six phases were included. These phases are in the diagram of FIG. 2 shown. The solid lines belong in the state diagram to an oxygen partial pressure of 0.21 at in air, while the dashed lines for an oxygen pressure of 1 at are. There could also be a third coordinate, the oxygen content indicate each phase; but this seems unnecessary.

Since the invention only deals with one phase of the

In the diagram concerned, namely with the NiMnO ₃ phase, only the oxidizing capacity and the X-ray data for this particular phase are recorded in the following table. It can be seen that the values of the oxidizing capacity of the substance mixture lie within the values calculated on the basis of ideal chemical formulas. This allows a very simple chemical method to be used to precisely determine the boundary lines of the individual phases.

Tabel

Λ = Mn: (Ni + Mn)

structure

Ignition temperature

( ⁰ C)

Atmosphere can oxidize
(Equivalents / 100 g)

attempt

theory

Lattice constants
(+ 0.002 Ä)

0.500
0.525
0.525

Ilmenite
Ilmenite
Ilmenite

780
684

743

O ₂

air

O ₂ 1.226
1.238
1,236

1,237
1,239
1,239

4.904
4.908

13.57 (hexane)
13.61

Claims (2)

1 249 240 5 6 The above examples briefly explain the invention. Subsequently, further samples were heated in a free process according to the invention for the production of oxide stream of oxygen for 8 hours at 780 ° C, samples that serve to provide a complete state. that the obtained diagram of the system NiO - Mn ₂ O ₃ - O _{2 from} sample had a composition that can be passed through exactly. The resulting state diagram in FIG. 5 is given the formula Ni ²⁺ Mn ⁴⁺ O ₃ . A sample fig. 2 shows a range in which the desired analysis showed 36.14 percent by weight nickel, 34.01 gemagnetic ilmenite material NiMnO _{3 is} present. weight percent manganese and an oxidizing capacity By evaluating this phase diagram, 1.230 equivalents for 100 g. The formula one, the ratio of the values corresponding to the formation of the mixture of substances NiMnO ₃ would be 36.32 ° / ₀ Ni, required components and the required IO 33.99 ° / ₀ Mn and 1.237 equivalents per 100 g of oxy temperatures and the atmospheric conditions dation ability. The x-ray diffraction patterns determine. It is particularly noteworthy that the analysis showed that the sample had the ilmenite crystal structure of the desired mixture of substances over a range of hexagonal lattice constants ₀ = 4.904 Ä Ä values. As can be seen, and c ₀ = 13.57 A. R can vary from 0.5 to about 0.53. Before the invention, which was explained in detail above, it was not possible to use the mixture of substances to produce other oxides with an ilmenite structure NiMnO ₃ over a range of values, provided that they are closely related and this made it much more difficult to obtain the mixture of substances to the limits of phase e in the diagram of produce in pure quantities. F i g. 2 hold. So if the formula of the substance The exact example _{below describes the mixture is Ni 2} - ^ MnJ ₁ O ₃ , ρ can range from 1 to 1.06 Process for the preparation of the product NiMnO ₃ vary if one considers the whole i? Range for the according to the invention, taking advantage of the ab phase e , as shown in the state diagram directed and in the F i g. 1 and 2 is shown. The procedure is under varying Results. of temperatures along the borderline between B eis ρ ie 1 III * ⁵ ^ ^en B ^ere ' ^cnen e and k of the diagram carried out. The temperature limit between these areas can be In order to obviously not exceed the substance in the oxalate compounds when adding them, it has proven to be most beneficial to want to obtain the desired ilmenite structure. When to run out of nickel and manganese acetates. For example, the acetate is /> = 1.06, R = 0.53 in the context that is, the starting materials in the approach of a phase diagram of Fig. 2. For this value is, mixture of substances according to the invention. 0.100 mol or, as can be seen, a pure ilmenite phase in air above -24.81 g nickel acetate and 0.1023 mol or 25.07 g half 705 ° C not stable. If ρ = 1, is a pure manganese were not dissolved in 800 ml of 4% acetic acid Ilmenitphase above 760 ⁰ C in air or solution. Like F i g. 2 shows the resulting 81O ⁰ C in pure oxygen has stable. The final product has been found to have a 1: 1 molar ratio where R is 0.5. 35 put that the oxides, once on Tempe-F i g. 1 shows that at R = 0.5 C a temperature above 600 ⁰ C was heated, at a lower value of 0.0023 mol; consequently, temperatures are initially stable. The lower range, on excess of manganese acetate equal to these moles- the material can be heated to keep an amount present. After dissolving the acetates in the satisfactory product to be delivered, the substances cannot be identified with an acetic acid solution to a degree of certainty. The oxides should be heated to all-boiling temperature. During the boiling and generally ^{heated to temperatures above 600 °} C., with vigorous stirring, 200 ml of an aqueous solution containing 0.2023 moles of oxaline, so that they are stable at lower temperatures, were quickly added. 2 can contain acid plus 1 g excess, that is 26.50 g. that is, the method according to the specification in use. As a result, the mixed oxalates of nickel 45 were precipitated on the simultaneous precipitation of manganese and manganese. Like F i g. 1 indicates, nickel oxalates advantageously remain in an amount of approximately 0.0023 moles of manganese carried in under such conditions that a ferromagnetic of the solution remains. This was the reason why ilmenite crystal structure arises,
originally the excess was added in the presence of the nickel acetate used as starting substances, so that the Ni: Mn-50 soluble salts, it is advantageous to use the nickel and manganese ratio of the precipitate very close to the nominal acetate, as already mentioned above described, value 1 comes close. After 10 minutes of digestion because the reaction products in the final solution, the precipitate was filtered off, are insoluble with pure water. Other soluble salts are also washed and dried in air. can be used for which, without claim to complete The mixed oxalate was used in a convenient way to include carbonates, nitrates, sulfates, and the like, moderate container, for example in a boat from Regarding the oxalic acid, which is used to make the soluble ones Silica, heated. To convert other containers from a salt into oxalates, it should be mentioned that these inert materials such as platinum are suitable. the saline solution in a stoichiometric, based on the The container was placed in a tube made of borosilicate glass, converting it into oxalates in a coordinated amount. introduced with about 96 * / o SiO ₂ . For the tube suitable 60 is given. A slight excess of oxalic acid Also Hartfeuerpoizjllan or another heat- is beneficial to a complete transfer in stable material in the manner of gas discharge to ensure the oxalates,
to roar. The estate then slowly became under one free flow of pure oxygen up to a temper- claims: temperature of 78O ⁰ C heated. Then the sample from 65 1. Method for the production of ferromagnetic taken out of the furnace and placed in an agate NiMnO ₃ with ilmenite structure, thereby Grind mortar, being carefully marked that from an aqueous was not to contaminate them with foreign matter. Solution of soluble nickel and manganese salts 1 249 Mixture of nickel and manganese oxalates is precipitated and this mixture at a temperature is heated between 600 and 780 ° C. 2. The method according to claim 1, characterized in that the soluble nickel and manganese salts Nickel acetate and manganese acetate are used and to precipitate the oxalates of the aqueous Oxalic acid is added. 3. The method according to claim 1 or 2, characterized in that the molar ratio Mn: (Ni + Mn) in the aqueous solution of the soluble nickel and manganese salts between 0.50 and 0.53 is set. 4. The method according to claim 2, characterized in that the aqueous solution of the nickel and manganese salts are heated to boiling temperature prior to the addition of the oxalic acid. 5. The method according to claim 4, characterized in that that the precipitated oxalates are dried. 1 sheet of drawings 709 640/369 8.67 © Bundesdruckerei Berlin