DE842966C - High temperature coefficient resistor and process for its manufacture - Google Patents

Description

Resistance with high temperature coefficient and method of its Manufacture The invention relates to resistors and especially small ones Fine-film resistors and processes for their production.

Fine-film resistors, especially those made of materials, their resistance fluctuates strongly with temperature and these are commonly referred to as thermal resistances are effective as a bolometer for displaying ultra-red rays and as a fast heat sensitive devices have been used. The layers forming the resistance, which are used in such devices are so far made of a grain material has been produced, the outermost grain size of which is about a hundredth of the desired The strength of the finished paper and which one is only temporarily effective Binder is mixed; the mixture is in a thin layer on an optical Spread out flat and dry. The dry layer is then removed from the backing and depending on the type of material at a temperature between iioo and fired at 145o ° C.

Even if this procedure has certain merits having, so it tends to require fairly close control. one The problems that arise are the tendency of the leaflets, especially the thinner leaflets that they bulge during the sintering process. -These Appearance likes. on uneven shrinkage in the top and bottom layers of the leaflet during the firing process, which is due to a slight difference the density of these two layers in the unfired flake. the Density fluctuations are caused by leaving the particles in the liquid Mixture will settle out when the mixture is initially spread out in the form of a film will. Another difficulty has arisen from the fact that the products of several Manufacturing processes have characteristics that extend beyond the narrow limits for the devices in which the resistors are used, are to be adhered to. These belong to these characteristics Noise, the specific resistance and the temperature coefficient of resistance of the Unity and its stability. One aim of the invention is to simplify the manufacture of fine-film resistors. Another goal is to reduce of noise and in the improvement of the stability as well as in the recoverability and in the uniformity of such fine-film resistors. The invention has as Another aim to reduce the tendency of fine-film resistors to become during of the firing process to bulge.

The invention has as a special feature the production of a non porous, homogeneous resistance film made from a mixture of two different Groups of grain sizes of the resistor material consists. Another feature of the Invention consists in the production of the liquid mixture of resistor material, from which the fine layers are obtained in such a way that initially a temporary effective binder made of a long chain polymer with particles of resistance material is mixed which with respect to the polymer chain length have such dimensions that a gel mixture is formed, the gel in the Extension of a polymer chain from one particle to an adjacent particle arises. Resistance particles of larger grain size are added to this mixture, which is kept in suspension by the gel during the production of the resistance layer whereby a film of uniform density is obtained.

The above and other objects and features of the invention will be clearer and more fully understandable from the following detailed description of an embodiment, in conjunction with the drawing.

Fig. I shows a sectional view of an embodiment of the fine-film resistor according to the invention; Fig. 2 shows a diagram showing the of the Resistance particles in an unfired layer of occupied volume as a function the grinding time for a species for making such resistances; Fig.3 shows a curve showing the relationship between percent shrinkage, which is caused by the firing of the resistor platelets and the firing temperature; Fig. 4 shows a temperature curve as a function of time, with representation of firing processes that are used to produce platelet resistances.

The curves and the specific procedure described below refer to a resistor plate, which consists of manganese and nickel oxide, which are combined in the atomic ratio of manganese to nickel between 2.0: i and 4.0: i are. It should be noted, however, that other material compositions within the scope of Invention and that the description is for the purpose of illustration only is based on this composition. Such other materials include or several oxides of manganese, nickel, cobalt, copper, iron, zinc, and uranium.

To produce a mixture for resistor plates, 6 g of the thermal resistance material with a grain size on the order of i to 1.5 microns in diameter (nickel and manganese oxide can be used in this grain size range be prepared by keeping their carbonates at 6oo ° C for a period of 2 hours calcined) in a high-speed ball mill, with 6 g of one temporary binding agent and 12 cc of a solvent; the resistor material is ground to the order of a hundredth of the original grain size, which requires 6 hours of grinding time when preparing nickel-manganese oxide material shall be. After that, another 7 g of the resistor material is added with a grain size on the order of 2 microns (nickel and manganese oxide with this grain size will be obtained in the usual way by calcining their carbonates at goo ° C for 16 hours) added to the mixture, which is then ground for a further hour, so that the total grinding time is 7 hours. A fine layer of this prepared one Mixture is then on a smooth surface, e.g. B. on an optical plane spread to a thickness of a few microns. This can be done by spraying or expediently by spreading the mixture over part of the area with the help of a @in suitable Distance guided straight edge happen. The fine layer and the support are then placed in a dust free atmosphere and given the volatile solvent opportunity given to evaporation.

The dried fine layer is then removed from the optical surface, what can be done, for example, by soaking with water at 25 ° C by on this way the leaflet swells and separates from the glass surface. The shift will then dried and cut into pieces or flakes of suitable size and shape cut as it is for their use in the electrical devices for which the material is needed is required; cutting up can with Any suitable device, e.g. B. by means of a pair of scissors, or with a thin knife or razor blade.

The raw or untreated rolling papers obtained in this way are even if you let them exist as large pieces, extremely tough and able be handled without special precautions. Furthermore, these leaflets stratified in high piles and autgeliol> ^ n for long periods of time without that harmful effects become noticeable; in this way will their manufacture extremely relieved. Another associated with this toughness and stability The advantage is that the untreated papers are sold immediately and sent to the Producers of devices for which such electrical elements are intended, can be sent; it is left to the producers, the distillers and Carry out the sintering process yourself, as the special firing conditions in certain Determine the electrical characteristics of the elements.

Each flake or piece of the fine layer is then placed on a Flat surface made of refractory material, which consists of a sintered Disc may consist of aluminum oxide. So far the uniform heat distribution over the leaflet had been required to fine layers of the prescribed To produce evenness, and for this purpose it was requested <leave the supporting surface possessed good thermal conductivity and a large area with respect to the leaflet or the fine layer had. If these conditions also help treat this Leaflets made from two grain sizes are desired, an acceptable one may be Flatness can be achieved without the expensive setup of the old process, which consisted of platinum plates coated with aluminum oxide, which were removed after each firing process had to be provided with a new coating. For example, a powerful Aluminum oxide plate used for these purposes and clean and after each firing process just to be polished.

After the leaflets have been applied, a plurality of these contact surfaces is created with the interposition of suitable spacers, which are a mechanical individual vibration of the leaflets during the firing process, stacked on top of each other and then for the purpose of removing the temporarily active binder and for the purpose of sintering placed in an oven. If polyvinyl butyrate is used as a binder, so it can be driven off by depolymerization by changing the temperature can gradually rise to about 400 ° C. After the binder is driven off is, the temperature according to curve A according to Figure 4 up to a Tempcratur between 100 and 1300 ° C are increased, in a period of about one hour; then gradually cools down to a cooking temperature of about 86o ' C, which is maintained for 16 hours; then the leaves are left in to cool in the oven. Another type of procedure can be used to measure the temperature of the peak temperature corresponding to the cooling rate of the furnace without Let the cooking time decrease at a low temperature; it is also possible to have a low one Use peak temperature for sintering, for example 103o ° C for nickel-manganese oxide material in connection with a cooking treatment lasting 16 to 64 hours at the peak temperature. The main factors to consider when choosing the heat treatment to be applied Points to note depend on the stability of the final device; this stability is greater with longer cooking times. That gives a stoichiometric one Composition of the material, with higher temperatures the proportion of oxygen degrade in the material.

The leaflet 11 produced in this way is according to the The illustration in FIG. 1 is provided with electrodes 12. These electrodes can go through Application of a metallic paste to the two faces of the leaf and heating of the paste until it hardens and bonds with the leaflet. One there is another possibility of attaching the electrodes to the platelet resistors in that a finely crushed precious metal with a suitable, temporarily effective binder and an appropriate solvent is mixed and that a composite leaflet is built up in such a way that a thin layer is formed Apply electrode material to a flat surface, this layer dries on it a layer of resistance material applies, the latter dries, a second electrode layer applies, and the resulting double-sided coated structure burns to a To produce a structure which is similar to that of Fig. I. After that, additions are made 14 attached to the electrode layers by means of drops of a soft Glass-platinum powder mixture to complete the unit, which is now can be accommodated in a suitable housing, not shown.

The details of the preparation of the mixture will now be dealt with will. The grain size range of 1 to 1.5 microns is required with consideration on the special mill used, which consists of a cubic steel container with inner Dimensions of almost 38 mm and for walche 130 g chrome steel balls of 1.5 mm diameter and 20 g chrome steel balls with 2.2 mm diameter 'as working equipment to be used. The particles are crushed by the impact effect by the container performs a reciprocating motion at an amplitude of 5o mm and a speed of 50o strokes per minute.

The main action of the mill is to break down the particles into such small dimensions and in the wetting of the grain surface with the temporary effective binding agent, before an adsorbed air or Gas layer which would reduce the density of the final mixture. Another effect on surface gases appears to be that the adsorbed layer present, both large and small Particles of the mixture are removed. When the smaller particles up to the order of magnitude 1o-8 cm in diameter be crushed and that temporarily effective binder is appropriately selected, the polymeric one Chain structure in the binder such that a single chain is adjacent particles and causes the formation of a gel structure. The binder can for example from a polyvinyl butyral syrup with the following proportions by weight consist: i8.7% plastic polyvinyl butyral, 65.3% ethyl alcohol, i2% ISO-propyl alcohol and 4% amyl acetate; a suitable solvent therefor may be in the following composition are produced: So volume percent amyl acetate and So volume percent methyl alcohol. The gel obtained in the manner explained has a sufficiently high viscosity, around relatively large particles (for example, those with a diameter of approx. cm) to be kept in suspension during the smearing and drying process of the film.

Other suitable binders include isobutyl methacrylate, cellulose acetate butyrate and the same kind of long carbon chain binder polymers, which in one Soluble in organic solvents and not treated with halogens.

The main features of these binders are: that they have long polymer chains that do not affect the resistance material chemically, after heating to a temperature below that at which the material sinters, leave no residue, have high mechanical strength and from the flat surface on which the resistor films dried can be removed.

The larger particles in the mixture act as seeds into which some of the smaller particles penetrate during the sintering process. Your even Distribution across the leaflet greatly increases the shrinkage uniformity during the burning process. Another effect that comes with the use of large particles in connection with smaller particles is that the larger Particles cause a slightly greater density in the unfired mixture, which in less shrinkage and consequently less tendency to warp affects during the burning process.

The aforementioned tendency to warp caused by uneven distribution of larger particles and accordingly uneven density in the thickness direction of the resistor plate is caused significantly by the manufacturing process small particles are narrowly reduced by the illustrated complete grinding. If the Particles having a size of 10 cm or less, and a binder with a polymer chain on the order of 500 to 1500 angstrom lengths is used there is an immediate expansion of the polymer chain from particle to particle other neighboring particles, whereas such a structure does not come about, if the particles are somewhat larger, for example 10 times the size.

The feeding of the larger particles and their subsequent grinding for a period of about one hour for the purpose of even distribution in the mixture and for the purpose of removing the adsorbed surface gas layer increases the density of the treated material considerably, as indicated by the hump in the curve according to FIG 2 is illustrated which shows the volume fraction of unfired flake that occupied by the thermal resistance material as a function of milling time illustrated. If only one grain size range is used, leave earlier ones Measurements recognize that the compaction does not exceed a value of 52%, and this value is only reached with a grinding time of 15 hours. The infliction of the larger particles therefore provides an approximately 10 percent increase in compaction and therefore a material which has a greater density of the overall mixture.

Other effects associated with the use of two grain sizes in the resistor material mixture show up in the firing process of the material. The graph of the percentage snuff that results from results, depending on the firing temperature, is shown in Fig. 3. L, denotes the length of a unit edge before burning, and L is the length of the same edge after burning. The manganese-nickel-oxide flakes with which these data were obtained were approximately 11.5 microns thick in the unfired state, so that they shrank to about 10 microns after the firing process was complete. The curve according to FIG. 3 shows the shrinkage which resulted from the heating of a test piece according to the firing process curve shown in FIG. 4 up to the desired temperature and subsequent rapid cooling to the ambient temperature.

Micrographic examinations for the preparation of the curve according to Fig. 3 samples used, which immediately after reaching the in question Temperature were cooled and therefore represent a transition state, are made to facilitate the explanation of this curve. The shrinkage in the temperature range from 700 to 830 ° C is the incorporation of the smaller particles in their neighbors and to a lesser extent, the adsorption of the smaller particles into the larger particles attributable to. On the samples that have been fired up to these temperatures Pores and cavities detectable, but which largely disappear when that Material is brought along the curve in the range of 85o to 10o ° C. Up to around 100o ° C there is only a slight change in size in the larger particles, but they develop crystallographic surfaces as the temperature rises. The smaller particles, which also tend to have crystallographic surfaces to develop, grow in this area quickly until they are separated from the larger particles are no longer distinguishable. The cavities, which are partly due to adsorption The small particles that have arisen in larger particles will be to a large extent decreased; this results in strong shrinkage at these higher temperatures. The effects observed above about 100 ° C are attributable to the grain growth, which is very rapid at these temperatures, and also recrystallization processes; none of these phenomena are consistent with the original particle size of the raw material tied together.

The heat treatments used in the manufacture of flakes for resistors were applied and not related to the explained crystal investigations stand, extend to cooking times at elevated temperatures, from which a waitere reduction of the cavities and therefore a b ° ssc-rcr contact between the Particles and better electrical properties result. Because of this reduction of the cavities, greater shrinkage takes place in these bodies, and thus would the shrinkage curve as a function of temperature for any treatment, which includes a cooking time, lie to the left of the curve according to FIG. 3. Two firings including cooking times are shown in FIG. 1. The one illustrated by curve B. Process is of particular interest in making platelet resistors Made of nickel-manganese oxide with grain sizes ranging from 10-6 cm and 10-4 cm in diameter, since it has been shown that a heat treatment of such material to zri one Temperature of about 103o ° C and a cooking time of 16 hours at this temperature delivers a body that is essentially pore-free when under investigation Conditions takes place, which provide a resolving power of points, which closer than 5 x 10 cm to each other.

It has been found that sintering this type of mixture at lower Temperatures takes place than with similar materials made after the earlier calcination processes have been won. This lowering of the sintering temperature is explained by the higher free energy, which is associated with the large surface area of the fine Particles in (learn G @ mixed is connected, and from the breaking process used. The Grinding causes an increase in the free energy of the powder due to the fact that greater area is offered when crushing a given mixture of powder will. The area, and therefore the surface free energy, increases as does the particle size decreases, so that in the case of the fine particles of resistor material in the order of magnitude from 10 "cm in diameter, which corresponds to the order of magnitude of 50 to 100 atomic diameters, the free energy of these particles is of the order of 1 or 2c'11, the heat of sublimation matters. This amount of energy is larger than it normally is: in conventional sintering processes is available. An advantage that arises from the possibility of sintering resistance materials at these lower temperatures is that the end product is lighter is controllable because the higher sintering temperature required earlier was, often enough, urp undesired deviations from the stoichiometric composition of the resistance material, which in turn changes the of resistance causes. Another advantage of this low sintering temperature consists in the elimination of any inclination of the resistance body on the contact surfaces sticking to it and eliminating the losses it causes.

Claims (6)

PATENT CLAIMS: i. Process for the production of a lamellar, temperature-dependent, electrically conductive device, characterized in that that oxide particles with diameters on the order of io-e cm with oxide particles in the order of magnitude of 10-4 cm in diameter. 2. Procedure according to Claim i, characterized in that the oxide particles are of the smaller order of magnitude mechanically processed in a binder for a period of, for example, 6 hours whereupon the oxide particles of the higher order are added and the Mixture mechanically processed for a further period of, for example, one hour will. 3. The method according to claim 2, characterized in that the oxide particles consist of nickel, manganese, cobalt, copper, iron, zinc or uranium oxide and as a liquid binder, soluble and not in an organic solvent long carbon chain polymers treated with halogens are used, for example polyvinyl butyral, isobutyl methacrylate or cellulose acetate butyrate. . 4. The method according to claim 2 and 3, characterized in that the mechanical Processing the oxide particles in the liquid binder in the presence of a solvent carried out for the binder and continued for such a period of time, that essentially all of the surface gas layer is on the larger particles is removed so that the mixture is then uniformly on a flat surface Thickness is spread and the solvent is given the opportunity to evaporate, and that the dry film thus obtained is brought into the desired shape, then up to the temperature required to drive off the binder and then heated to the temperature required for sintering the material. 5. Method according to claim 4, characterized in that the device initially to drive off the binder is gradually heated to about 400 ° C, whereupon heating to a temperature of about 1,000 to within about an hour 1300 ° C increased and then decreased to about 86o ° C and at this level for a longer period of about 16 hours is maintained and that thereafter the device is cooled in the furnace according to its cooling rate. 6. Procedure according to claim 4, characterized in that the device initially gradually is heated to about 400 ° C, followed by heating to one in about an hour Temperature is increased from about 100 to 1300 ° C and that then the device in the oven accordingly whose cooling rate is cooled will. . Method according to claim q, characterized in that the device gradually is heated to about 40o ° C, followed by heating to 103o ° in about an hour C and at this temperature for a longer period of time from about 16 to 64 hours is held and that then the device in the oven accordingly whose cooling rate is cooled. B. Heat sensitive, electrical Conductive oxide material which, according to the method of one of the preceding claims manufactured .is.