DE1571285C - Lithium ferrite storage core and process for its manufacture - Google Patents

Description

The invention relates to a storage core made from a vanadium and a divalent metal oxide Lithium ferrite.

It is known that storage cores made of ferrite based on manganese-magnesium and vanadium oxide, in particular Vanadium pentoxide to be added. For this purpose, the base ferrite can be mixed with an ammonium vanadate solution before sintering are impregnated. The known addition of vanadium oxide increases the sintering temperature and the signal resolution of the memory cores improved. It will but the coercive force of the ferrite is increased by the addition. This may be due to the fact that the known ferrites based on manganese-magnesium with the addition of vanadium oxide no composition that could result in a pure spinel.

Lithium ferrite has a practically rectangular hysteresis loop and has a coercive force with a very low temperature coefficient. As a result, the memory in which such a core is used can be exposed to large temperature differences without the coercive force being significantly affected / Despite this low temperature coefficient of the coercive force, the use of lithium ferrite for memory cores has been limited until now because the value of the coercive force compared to other common ferrites in lithium ferrite is relatively high. In order to produce a sufficiently dense lithium ferrite with a coercive force comparable to that of other ferrites, temperatures above 1150 ^° C. would be required for sintering the lithium ferrite. Below 1150 ^° C., the lithium ferrite grains do not grow in such a way that the material acquires the required density. At 1150 ° C or above, however, rapid evaporation of the lithium occurs, which of course changes the composition of the ferrite. The resulting loss of lithium significantly reduces the rectangular quality of the hysteresis loop of the material. They also represent Co, Ni, Cu and Zn, as is commonly found in ferrites of spinel structure. Preferably, χ is in the range from 0.005 to 0.025. The amount of the metal cation M is chosen so that the valences are exactly balanced in the end product. The divalent metal cation is needed because of the presence of the vanadium, which has a valence of +5. Lithium vanadates or vanadate hydrates can be used as lithium vanadium salts. Usable lithium vanadates include: lithium _{orthovanadate Li 3} VO ₄ , lithium metavanadate LiVO ₃ , lithium pyrovanadate LIjV ₂ O ₇ , lithium oxyorthovanadate

Li ₂ O- _{2 Li 3} VO ₄ H ₂ O

without being limited to it. The vanadate hydrates are the orthovanadate hydrates

Li ₃ VO ₄ · 8 H ₂ O and Li ₃ "VO ₄ · H ₂ O into consideration.

Lithium vanadium salts have many advantages over the common vanadium pentoxide. They are generally of lower density than vanadium pentoxide; therefore they take up a larger volume per vanadium atom and are easier to mix. In addition, some of the lithium _{vanadium salts, such as Li 3} VO ₄ and LuV ₂ O ₇ , have higher melting points than the vanadium pentoxide, and their effects can therefore be more easily controlled.

Example I

A mixture containing vanadium was made according to the formula mentioned

f ⁺ Fe ₂ ³ J _ _3x O ₄

f _x

The object of the invention is to provide a memory core of the type mentioned at the outset, which with low Temperature coefficient of its coercive force has a decreased coercive force.

To achieve this object, the storage core according to the invention is characterized by its composition '.

manufactured. The value of χ was chosen to be 0.01. The ingredients were: 0.235 mol (17.36 g) lithium carbonate Li ₂ CO ₃ , 0.01 mol (1.358 g) lithium ortho-

... .. "~ - vanadate Li ₃ VO ₄ , 0.02 mol (1.49 g) nickel oxide and

The composition of the storage cores at 40 is 1.235 moles (197.2 g) of iron oxide Fe ₂ O ₃ . As grinding media λ. ¹ ! " ¹ ^ ^{v <} ? ^N 9! W to batch. Different. A substance was selected in which all of the named

Ingredients were insoluble. Isopropyl alcohol has proven to be suitable for this purpose. The mixture was then milled for hours. The resulting sludge was removed from the mill and dried. Then it was sieved and exposed to a temperature of 760 ^° _{C. for about 2 hours.} The mass was then ground again in a ball mill and the sludge was dried again

. ". 50 and sifted .. Then the mass was used for pressing

where χ is the value _; Does not exceed 0.05 and M -prepared by having a binder and a lubricant being at least one divalent cation. were admitted. A polyvinyl chloride was used as a binder

The storage core according to the invention is characterized by a weight ratio of 27% to alcohol in that the temperature coefficient is given. The lubricant consisted of V, weight «:" Coercive force is about as low as with pure 55 percent stearic acid.
Lithium ferrite, but that its coercive force compared to "~" ~

pure lithium ferrite is reduced to about half. It is characteristic of the composition of the invention Memory core that it enables the formation of pure spinel structures.

The vanadium is preferably used in the components from which the storage core is sintered The form of a lithium vanadium salt is added in such an amount that the resulting mixture of the formula

MJs Vr Ml _x ⁺ Fe |; _ _3x O ₄

enough; therein M preferably represents at least one divalent cation from the group Mg, Mn, Fe,

r arinic acid.

From the binder and lubricant-containing dust cores were pressed to the desired shape and gesintert- Here, samples having sintering temperatures 982-1068 ⁰ C made to determine the effect of sintering temperature on the final product. It was found that the Tpm pera.tur was lower than that for materials without τ; thium vanadium salts required, the min ^ J. 1150 ⁰ C. . at least

In the process, lithium can be prevented and compounds of divalent metallic metals are used in the case of Erhit

are compounds of divalent metal and Kati turns ^"gene, which when heated ^ver Οχ, Αμ ^11" are, for example oxalates, nitrates, Hydro "Η °

'and carbonates of lithium and of the divalent metal cation into consideration.

The amount and type of binders and lubricants for making the cores according to the above Examples are known. The weight proportion of the materials increases with the size of the items to be manufactured Cores. Certain compositions can serve the dual purpose of lubricants and binders serve, such as polyethylene glycol.

Example II

The above example was repeated, the x values in the above formula being varied so that different amounts of lithium vanadium salts were present. In Table 1 below are Properties of various compositions listed.

In Table 1, H _{c means} the coercive force, / ₆ // _w is the maximum interference ratio, where I _{b is} the maximum amplitude of an interference pulse and I _{w is} the amplitude of a write pulse _{, uV t} is the read voltage of the undisturbed one, dV _z is the Reading voltage of the disturbed zero, i _s is the switching time in microseconds, the temperature range is in ⁰ C.

ίο represents the useful temperature range for the core. The core used had an outer diameter of 1.27 mm and an inner diameter of 0.76 mm and was 0.38 mm high. The rise time t _{r of} the current pulses was 0.5 microseconds. The temperature was 25 ° C.

properties of

Table!
M _2x Fe ₂₁₅ _ _3x O ₄ storage cores (25 ° C)

Sintering temperature ( ⁰ C).
H _c (Amp.Wdgn)

hßyt '■ ·· ■ ·

MF ₁ (mV)

dV _z (mV)

i _s (μδεο)

Temperature range ( ⁰ C)

1100

1.7
■ 1.12 _n "

80
7th

1.05 -25 to 125

χ = 0.014

= 0.65

1068

0.80
0.520
0.800
70
5

1.05
-50 to 100

χ = 0.02

1040
0.70

0.44

OJQ = 0.63

60
5.5
.1.05
-50 to 75

A very important factor that emerges from the table is that, without the presence of vanadium, the coercive force of lithium ferrite is extremely high, namely at a value of 1.7, which indicates an excessive current requirement for the magnetic reversal of the core. By using the vanadium this value has been reduced considerably to an amount less than half for χ equal to 0.02. If one also wanted to reduce the coercive force of the core in the column for χ equal to 0, ie without the presence of vanadium, the sintering temperature would have to be increased to over 1150 ° C. As already mentioned, such a temperature has a destructive effect because it causes evaporation of the lithium and gives rise to cores with uncontrollable, poor properties.

Table 1 also shows that the read voltage of the disturbed zero dV _{c is} significantly reduced in the presence of vanadium. Nickel was used as the divalent metal cation.

As already mentioned, other metal cations also result, as they are found in Eerriten with a pure spinel structure finds good results. Equally favorable results are obtained by using one of the others above enumerated lithium vanadates or orthovanadate hydrates according to the procedure of Example I. used.

B e i s ρ i e 1 III

In order to show the excellent properties of the cores in more detail, smaller ones were also added Cores manufactured and tested. These cores had an outer diameter of 0.76 mm, an inner diameter of 0.51 now and a height of 0.178 mm. The changes in the properties of this Cores with the temperature under normal operating conditions are shown in Table 2 below written down. The composition of the cores was:

Lio.s V _o , o2 Ni _o , o2 Fe _{2> 47} O ₄

^ (mV) Table 2 dK _z (mV) t _s fcsec) MmA) 0.76 temperature 24 2.7 0.63 ■ 550 0.73 (° C) 30th 2.7 0.62 530 0.704 -50 35 ' 2.6 0.61 510 0.675 -25 39 2; 6 0.60 490 0.650 0 42 2.5 0.59 470 0.620 +25 45 .2.5 0.58 450 0.593 + 50 48 2.5 0.57 430 0.565 +75 51 2.5 0.56 410 + 100 + 125

Sintering temperature = 1040 ° C, (l _H aiti _{mp uisWschreibim P} uis) = 363 mA / 725 mA, pulse rise time t _r = 0.2

Of particular note is that the disturbed reading voltage dV _x nearly doubled over the wide temperature range from -50 to + 125 ⁰ C, which indicates the extraordinary value of the composition of such temperature ranges out. As can be seen from the tables, the other properties of the cores remain roughly constant in the broad temperature range.

Claims (5)

Patent claims: 1. Storage core made of a vanadium and a
lithium ferrite containing divalent metal oxide, characterized by the composition τ + ^L1 0. 0.5 ^iVi 2x wherein χ does not exceed 0.05 and M is at least one divalent cation. 2. memory core according to claim 1, characterized in that M from the group Mg, Mn, Fe, Co, Ni, Cu, Zn is selected. 3. Memory core according to claim 1 or 2, characterized in that χ is in the range from 0.005 to 0.025. . 4. memory core according to claim 3, characterized in that χ is equal to 0.01. 5. A method for producing a memory core according to any one of the preceding claims, characterized in that characterized in that known starting components of lithium ferrite are lithium vanadate or a lithium orthovanadate hydrate mixed in and the mixture in a known manner is sintered. 6: The method according to claim 5, characterized in that that the sintering takes place below 1100 ° C.