US 2645700 A
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F. J. MORIN July 14, 1953 SEMICONDUCTOR OF MIXED NICKEL, MANGANESE, AND IRON OXIDES 2 Sheets-Sheet 1 Filed Aug. 27, 1949 0 9 0 a 0 I.-I X 0 N 2 8 F Q M -wm N 0 2m -3 2 mm W F m N 3A w. T 0 5 Z Y S -w O 8 7 6 5 4 3 w m w w w m FIG-3 $Y$TEM NI M773 OX-NIFOz 0x 3.36% .3 Quiz: m
/v I/EN TOR EJ. MOP/N BVW 40 so .00 aroma 7DNIFI2 0x ATTORNEY July 14, 1953 FQ'J. MOR lN 2 6 5,7
SEMICONDUCTOR OF MIXED NICKEL, MANGANESE, AND IRON OXIDES Filed Aug. 2'7, 1949 2 Sheets-Sheet 2 a l0 sys7u NI M19 Ox- N/ F0 0x l I l I 0 I0 20 3o 1 40 so so so 00 4 ran/c I, All F1 0x FIG. 5
CENT/GRADE DEGREES t 1 I l I I 1 0 I0 a0 40 so so a0 ATOMIC 70 N1 Fe 0x INVENTOIQ F J. MOP/N A TTORNEV Patented July 14, 1953 SEMICONDUCTOR OF MDIED NICKEL, MANGANESE, AND IRON OXIDES Francis J. Morin, Berkeley Heights, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 27, 1949, Serial N 0. 112,805
This invention relates to thermally sensitive semiconductors and to methods of making them. In some of its more specific aspects it relates to resistors comprising certain metal-oxygen compositions and to methods of combining such compositions to obtain particular resistance characteristics.
The semiconductor. resistors particularly involved in this invention are those whose resist ance varies greatly with changes in temperature and which are commonly known as thermistors. Where this term is employed, it is to be understood that resistors of this nature are intended. The principal characteristics of such devices are the specific resistance, commonly designated p, the temperature coefficient of resistance a, and the temperature dependence factor ,8 which unlike a. is a constant and is independent of temperature. The mathematical expression relating the specific resistance p, temperature dependence factor and the absolute temperature T is as follows:
=constant e (1) The temperature coefficient of resistance a is usually obtained from the relationship Applying this equation to 1) there is obtained Thermistors having particular temperature coefiicients of resistance are sometimes necessary in the proper operation of a circuit. While a wide range of coefiicients are disclosed in the,
materials of the art, these materials are compounded from a large variety of constituents some of which are required only rarely and therefore not generally kept in stock.
One object of this, invention is to enable the manufacture of resistor bodies from a mixture of a limited number of constituent oxides whose temperature coefficient of resistance is reproducibleand can be varied over a wide range, and whose structure is that of a stable compound.
Another object of this invention is to improve methods of forming resistor bodies from finely divided particles.
3 Claims. (01. 201 63) In accordance with one feature of this inven- H tion, the resistor materials comprise combinations of the oxides of nickel, manganese and iron.
Another feature of this invention resides in controlling the relative amounts of. the constituent oxides of nickel, manganese and iron in the material to obtain a desired resistance-temperature coefficient and specific resistance.
A further feature of this invention resides in a method of applying a coating of a wax binder to the individual particles making up the resistor body by precipitating the wax out of a suspension and onto the particles.
In one of its more specific aspects, this invention involves the compounding of two stable compounds, which may be of the spinel-type, which are mutually soluble in all proportions to produce a system having a single phase throughout the composition range. The resulting mixture thus has stable electrical characteristics which depend upon' relative proportions of the component metals.
Further objects and features of this invention will be understood from the following detailed description with reference to the accompanying drawings in which:
Fig. 1 is a sectional view of a resistor illustrative of one embodiment of this invention;
Fig. 2 is a curve showing the specific resistance of one mixture of the material at 25 C. as a func- I tion-of the NiFezOx present in a composition;
- Fig. 3. shows the relationship between the temperature dependence factor B and the composition of the NiMn2O -NiFezOx mixture;
Fig. 4 is a curve showing the specific resistance of a NiMmOx-NiFe4Ox mixture at 25 C, as a.
function of the NiFeiOX content; and
Fig. 5 is a curve showing the relationship .be--
tween the temperature dependence factor 5 and the composition of the NiMn4OXNiFe4OX mix-- ture.
Resistors having particularly desirable temperature-resistance characteristics compounded.
perature coefficient which can be varied by controlling the proportions of the components.
Thermistor materials composed of three oxide mixtures of nickel, manganese and iron can be produced with the extremely stable spinel-type cubic structure and with a variety of temperature dependence factors by maintaining the ratio of the constituent oxides of the final product such that the number of Mn atoms plus Fe atoms to the number of Ni atoms will be in the range from 2 to inclusive. The specific resistance and temperature dependence factors of compounds at these limits are disclosed in the curves of Figs. 2 to 5, the resultant mixtures having a constant ratio of nickel atoms to the combined iron and manganese atoms, the iron atoms being varied from zero to 90 per cent of the total of the two. These mixtures in eifect are compounded of the combination of two mutually soluble spinel-type compounds in all proportions from zero to 90 per cent of NiFQZOx in the mixture of NlMI'lZOx and NiFeQOX and from zero to 90 percent of NiFeiOx in the mixture of NiMniOX and NiFeiCx.
The end products of the mixtures have been characterized as having an indefinite quantity of oxygen represented by the symbol OX. This has been done since the quantity of oxygen varies with the partial pressure of oxygen and temperature conditions under which the mixture of the oxides is sintered to form the solid solution. The 3 materials disclosed here have all been sintered at 1200 C. in air at atmospheric pressure. Further temperature treatments and their eifects upon the characteristics of thermistors produced from these compounds are disclosed in the ap- 1 plication of George T. Loman, Serial No. 118,590, filed September 1, 1949.
As disclosed in the curves of Figs. 2 and 3, by proportioning the atomic per cent of the NlFBZGx in th system of NiMmOx and NiFezOX the value of the temperature dependence factor B can be varied from the order of 3500 C. to the order of 4600 C. while the specific resistance at 25 C. varies between 3X10 and 2 10 ohm centimeters.
At the other extreme of the mixtures, i. e., in i the NiMmOX and NiFeiik system, the temperature dependence factor [3 as disclosed in Fig. and the specific resistance at C. as shown in Fig. 4 plotted against the atomic per cent of NiFeiOX varies between 3700 C. and 5800 C. and between 2 10 and 2X16 ohm centimeters.
Resistors of these materials may be made in the forms of beads, rods, or as disclosed in Fig. 1, discs 19 having electrodes 12 and i3 securing leads i i and it to the body portion.
The basic elements employed in the mixing of the body material are NiO, MI12O3 and F6203 particles of the order of one micron in diameter which are mixed in a colloid mill with a solution which may be either slightly acidic or basic, for example distilled water slightly acidified with acetic acid, in order to improve the Wetting of the oxide particles and therefore the intimacy of mixing. Considering a per cent NiFe2OX mixture in the NiMnzOx and NiFezox system as exemplary, the following quantities of oxides are mixed:
18.67 grams of MO 19.73 grams of M11203 19.96 grams of F8203 The quantities of oxides which must be mixed to obtain the desired ratio of the number of metal atoms in any other mixture may be determined 4 in the well-known manner by considering the atomic weight of the elements.
Aft r the oxides are thoroughly mixed, a binder in a liquid suspension is added, the liquid being of such a nature and concentration as to be neutralized by the solution originally employed in mixing and produce a water soluble salt. In the case of an acetic acid solution, for example, a petroleum wax in an amine, such as trietha-nolamine, emulsifying agent is added to the mixture in the mill. The acid in the original mixture neutralizes the emulsifying agent in the binder causing the wax to precipitate from th emulsion and to coagulate on the oxide particles. The resulting mixture is then removed from the mill and the salt solution filtered off. After the solution is removed the resulting cake is in condition for pressing to the desired resistor form.
The resistor of Fig. l is constructed by pressing the dried cake into discs, for example discs of one-half inch diameter containing about 1 gram of material. High densities are attainable in this pressing operation since the wax not only acts as a binder but also lubricates the particles so they readily slide over each other to reduce the voids in the pressed body. Then the pressed body is mounted in a holder buried in 129 mesh alundum and heated to about 300 C. until the wax binder is evaporated and all binder residue is removed. Next the body is sintered in air for 16 hours at 1299" C. and is allowed to cool in air to room temperature.
To complete the unit, electrodes 12 and 13 are applied to the sintered body H), for example by coating the surfaces with a metallic paste comprising finely divided metal particles, a binder and a solvent and then curing the paste at an elevated temperature to form a stable and tough layer on the body faces. Contact to the electrodes can be made in several ways, including soldering, by mechanical pressure, or as disclosed in the drawing by embedding leads It and i5 in the electrode paste prior to curing it.
What is claimed is:
l. A conductive device consisting essentially of a sintered body of the combined oxides of nickel, manganese and iron having a specific resistance and temperature coefficient of resistance dependent upon the atomic ratio of the constituent metals, said atomic ratio falling between the limits of En +Fe and spaced electrodes connected to the body.
2. A conductive device comprising a sintered body consisting essentially of combined oxides of nickel, manganese and iron in the proportions of one atom of nickel, one atom of manganese, and one atom of iron, and spaced electrodes connected to said body.
3. A conductive device comprising a sintered body consisting essentially of a first spinel type compound consistmg essentially of the oxides of nickel and manganese in solid solution with a second spinel type compound consisting essentially of the oxides of nickel and iron, the atomic ratio of the nickel to the manganese in said first compound falling between the limits of 1:2 and 1:4, the atomic ratio of nickel to iron in the second compound falling between the limits of 1:2 and 1:4, and spaced electrodes connected to said body.
of 2.0 and 4.0
FRANCIS J. MORIN.
(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Meyer et a1 May 25, 1937 Fisher June 1, 1937 Janssen' Oct. 29, 1940 Grisdale Oct. 14, 1941 Dearborn Feb. 24, 1942 Number 6 Name Date Bugel Oct. 5, 1943 Vaughan May 9, 1944 Becker et a1. Jan. 28, 1947 Wejnarth July 13, 1948 OTHER REFERENCES Snoek, Magnetic & Electrical Properties of the Binary Systems MO F6203, Physica III, No. 6 June 1936, pages 481-482.