United States Patent: 3644207

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United States Patent	3,644,207
Baba , et al.	February 22, 1972

LITHIUM-TITANIUM-ZINC FERRITES

Abstract

Microwave ferrites with narrow resonance linewidths, good temperature performance, low losses, low costs, and rectangular hysteresis loops are made from a lithium-titanium ferrite containing a small amount of zinc. In addition, small amounts of copper or manganese can be present in the ferrites.

Inventors:	Baba; Paul D. (San Carlos, CA), Argentina; Giltan Michael (Belmont, CA)
Assignee:	Ampex Corporation (Redwood City, CA)
Appl. No.:	04/863,372
Filed:	October 2, 1969

Current U.S. Class: 252/62.59 ; 252/62.6; 252/62.61; 252/62.62

Current International Class: C04B 35/26 (20060101); C04b 035/26 ()

Field of Search: 252/62.59,62.6,62.61,62.62

References Cited [Referenced By]

U.S. Patent Documents


3065182	November 1962	Aghajanian
3177145	April 1965	Brownlow
3483126	December 1969	Sara et al.

Primary Examiner: Levow; Tobias E.
Assistant Examiner: Cooper; J.

Claims

We claim:

1. A lithium-titanium-zinc ferrite having the formula: Li.sub.0 .sub.675 Fe.sub.1 .sub.475 Ti.sub.0 .sub.55 Cu.sub.0 .sub.1 Mn.sub.0 .sub.1 Zn.sub.0 1 O.sub.4.

Description

The invention described herein was made in the course of a contract with the United States Department of Air Force.

SUMMARY OF THE INVENTION

At the present time, garnets are ordinarily employed at microwave frequencies. However, garnets are expensive and have poor temperature performance. Although it has been suggested that ferrites might be used, the losses have been high, the densities have been low or the coercive forces have been too high. In accordance with the present invention, these difficulties are obviated by employing at microwave frequencies, ferrites which have narrow resonance linewidths, good temperature performance, low losses, low costs and rectangular hysteresis loops. This is accomplished by making a ferrite containing lithium and titanium with a small amount of zinc. Copper and manganese may also be present.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following preparative procedure is used in compounding ferrite materials in accordance with the present invention:

Oxides of the constituent metal ions are generally employed when possible. In instances where the chemical instability of the oxide of a particular metal ion causes said oxide to be an impure and unreliable compound, the anhydrous carbonate of the metal ion is used. The raw materials are weighted out in stoichiometric proportions and are wet mixed for 1 hour or more in a ball mill. The resulting slurry is then dried at around 100.degree. C. and the dried raw material mixture is then forced through a standard 20-mesh screen for ease of handling.

The screened oxide mixture is then loaded into refractory boats. The boats are placed in a box-type furnace, and heated to a predetermined temperature. The exact temperature can vary from 700.degree. to 900.degree. C. The object of this step is twofold: the primary object is to provide sufficient energy to react the oxide mixture to a 70 percent ferrite 30 percent oxide mixture by a solid state reaction. The secondary objective is the simple thermal decomposition of any carbonates used.

The reacted mixture is generally characterized by a relatively large predominant particle size. Before the mixture can be shaped and sintered into a single phase ferrite body the particle size must be reduced. Ball milling is employed in essentially the same manner as outlined above. The ferrite-oxide slurry is then dried at around 80.degree. C. to a fine powder.

The powder is then mixed with a binder as is well known to those skilled in the art. Wide latitude is permissible in the selection of binders. A typical binder is polyvinyl alcohol.

The addition of the binder can be carried out in the second ball milling step, or in an additional step employing any sort of method facilitating uniform distribution of the substance used as a binder. The binder impregnated powder is then shaped in tool steel dies with enough pressure to facilitate uniform compaction.

The pressed shapes are then sintered at temperatures ranging from 950.degree. to 1,150.degree. C. in atmospheres of oxygen or air.

The novel ferrites of the present invention have the following composition. ##SPC1##

The following nonlimiting examples illustrate various preferred embodiments of the invention. In the examples, Examples 1 and 3 illustrate compositions which contain zinc while Examples 2 and 4 show substantially the same composition without the addition of zinc, showing the beneficial effect of the zinc addition.

EXAMPLE 1

A ferrite having the composition where x= 0.7, y= 0, z= 0 and w= 0.1 was prepared by the above procedure. The reaction step was performed at 900.degree. C. The sintering step was performed at 1,100.degree. C. in an oxygen atmosphere. The ferrite had a coercive force of 2.26 oersteds, a remanence of 709 gauss, a saturation magnetization of 825 gauss, a magnetic loss of 0 decibels per inch, a dielectric loss of 0.7 decibels per inch, a resonance linewidth of 360 oersteds, and a density of 3.64 grams per cubic centimeter.

EXAMPLE 2

A ferrite was made where x= 0.7, y= 0, z=0 and w= 0. It has a coercive force of 3.42 oersteds, a remanence of 384 gauss, a saturation magnetization of 610 gauss, a magnetic loss of 0.93 decibels per inch, a dielectric loss of 0.63 decibels per inch, a resonance linewidth of 425 oersteds, and a density of 3.48 grams per cubic centimeter.

Example 1 contains zinc while Example 2 does not contain zinc. The material of Example 1 is superior because it exhibits a lower coercive force, a higher remanence, a lower magnetic loss, a narrower resonance linewidth, and a higher density than does 2.

EXAMPLE 3

A ferrite was made where x= 0.55, y= 0.1, z= 0.1 and w= 0.1. It has a coercive force of 4.02 oersteds, a remanence of 670 gauss, a saturation magnetization of 915 gauss, a dielectric loss of 0.52 decibels per inch, a resonance linewidth of 375 oersteds, and a density of 4.02 grams per cubic centimeter.

EXAMPLE 4

A ferrite was made where x= 0.55, y= 0.1, z= 0.1 and w=0. It had a coercive force of 5.15 oersteds, a remanence of 535 gauss, a saturation magnetization of 661 gauss, a dielectric loss of 0.58 decibels per inch, a resonance linewidth of 550 oersteds, and a density of 3.09 grams per cubic centimeter.

Example 3 contains zinc while Example 4 does not contain zinc. The material of Example 1 is superior because it exhibits a lower coercive force, a higher remanence, a lower dielectric loss, a narrower linewidth, and higher density than does 4.

* * * * *

Current U.S. Class:	252/62.59 ; 252/62.6; 252/62.61; 252/62.62
Current International Class:	C04B 35/26 (20060101); C04b 035/26 ()
Field of Search:	252/62.59,62.6,62.61,62.62