Патент USA US2407751код для вставки
Patented Sept. 17, 1946 2,407,750 UNITED STATES PATENT OFFICE 2,407,750 TEMPERATURE SENSITIVE RESISTOR Frederick Gordon Smith, Toronto, Ontario, Can' ada, assignor to Research Consultants Limited, Toronto, Ontario, Canada, a corporation of On tario No Drawing. ‘ Application February 23, 1944, Serial No. 523,571 14 Claims. (Cl. 201--76) 2 This invention relates to a family of temper ature sensitive resistance materials and particu larly to resistors constructed of such materials which thereby provide a very high negative tem perature coe?icient of resistance. It is a general object of the present invention to provide improved resistors and resistance ma written as follows: group IIA of the periodic table of elements ex perature in atmosphere thereby combining the metals in group IIA of the periodic table of elements, excluding mercury, and. the general formula expressive of these titanates may be MO.TiO2 where M is magnesium, zinc, cadmium or berryl terials having high, uniform and stable negative lium. Each of these compounds is a true titanate temperature coe?icients of resistance. and comprises a single crystalline phase which More particularly it is an object of the inven 10 for the magnesium compound is orthorhombic tion to provide temperature sensitive resistors and for the zinc compound is cubic. composed of true titanates of certain metals of The several compounds are prepared by com group II of the periodic table of elements. bining one molecule of the monoxide of the base An important object of the invention consists metal with one molecule of titanium dioxide in the provision of resistors of one crystalline 15 (T102) . The constituent oxides in powdered form phase composed of titanates of the metals in are carefully mixed and heated to a high tem eluding mercury. A further object of the invention consists in ingredients. The several compounds may be pre pared by sintering at a temperature below their the provision of a family of titanate resistors 20 respective melting points or they may be melted. providing a wide range of resistance coeflicients A temperature of 1300" C. is sufficient to melt the which overlap so as to permit the selection of cadmium titanate; 14000 C. is su?‘lcient to melt resistance ranges for any desired purpose. the zinc titanate; 1650" C. is suilicient to melt An important feature of each of the resistors the magnesium titanate. is its extremely wide variation in resistance with Each of these titanates is a hard, strong, stable temperature change together with extreme sta crystalline compound unchanging in oxygen or bility in air or oxygen up to the melting point air up to its melting point which in the case of the material which melting point is above the of the magnesium compound is approximately melting points of most metals and of most ma- 1610“ C. The zinc compound melts somewhat terials in commercial usage whereby the resistors 30 above 1300° C. whereas the cadmium compound may form the essential element of resistance begins to decompose slightly above 1000" C. thermometers or the like. Each of the compounds can be worked in air An extremely important feature of each of the with any kind of combustion torch without de materials is the fact that it is composed of one composition. They can also be melted in plati single crystalline phase so that it can be formed num crucibles and poured or cast in any desired into minute resistors without causing any ob form like metal. Each of the compounds is clear, servable change in the temperature coe?icient transparent, and almost colorless. Following any of resistance, and which permits positive dupli Working to change the shape or size of a mass cation of the resistance curve at any time. of the material it‘ is preferably heat treated to Other and further objects and features of the a dull red heat in air or in oxygen after being invention will be more fully understood by those brought to its ?nal form to make certain that skilled in the art upon a consideration of the fol all of the titanium present is in the tetravalent lowing speci?cation wherein are disclosed several form. exemplary embodiments of the invention with the The material is non-reactive with platinum understanding that such changes and modi?ca even at temperatures above the melting point tions may be made therein as fall within the of the material which permits the use of platinum scope of the appended claims without departing crucibles and platinum wire for terminals or heat- ‘ from the spirit of the invention. ing elements for the resistors. An important The ‘resistance materials of the present inven-' ' feature is “that the thermal expansion of the tion are in a chemical sense titanates of the 50 serveral resistor materials is so similar to that 2,407,750 4 n a coeilicient in terms of the "temperature rise or of platinum that no cracking takes place when fall required to respectively decrease or increase the resistance compound is cast about the ends the resistance by a factor of two.” This temper of platinum wires which are to act as terminals. ature change will be herein termed the “half re The compositions are cheap to manufacture 5 sistance temperature.” The following tabulation both because of the simple process of forming has been determined by experiment with the sev them and because of the ready availability at eral resistors low prices of the basic materials. Pure titanium dioxide is readily available at a low price and the Half resistance temperature ' same is true of the required oxides of magnesium, 1 0 Critical tem zinc, cadmium and beryllium. Below critical ' Above critical perature As has been previously mentioned the resistors temperature temperature constructed in accordance with this invention have extremely high negative temperature co efficients which makes them available for a num ber of important uses some of which will later °C. MgOfl‘iOL 15 ZnO.Ti 2.. Cd0.TiOz.. _ _ . °C. 34 30 14 °C. 55 76 94 780 560 350 be explained, but before going into detail as to the range of resistance with temperature changes Because of the constant temperature coefficient it might be well to point out some of the advan of resistance above or below the critical tempera tages-of the new resistor materials. There is no ture, standard scales may be prepared for meas aging of the material in the sense that with 20 uring or recording devices for temperature which change in age there is no change in resistance can be made to read in ohms, when the tempera~ or temperature coe?icient of resistance such as ture of the resistor is changed to vary its resist is commonly the case with mixed oxide resistors. ance, or in degrees of temperature when the re Resistors constructed of the new materials sistor is used as a thermometer. It will be ap 25 have extremely low “thermal noise” (variation parent in either case, that if the same titanate of total resistance due to variation of contact reresistor species is used, one calibration point only sistance between the granules of powdered or is needed to ?x the instrument reading to the cor compressed resistors) which is a common fault rect resistance or temperature. With mixed ox of powdered carbon and mixed oxide resistors. ide and carbon resistors however, the tempera Because of their stability in air titanate re 3 0 ture coefficient changes with small changes in sistors do not require vacuum or gas ?lled en composition and/or particle sizes, .so that a full velopes. recording scale must of necessity be prepared for Each titanate resistor occurs only in one crys each and every resistor which is required to per talline phase and hence can be made in any de sired small size with no observable change in the 01 form quantitatively in measuring instruments. A single magnesium titanate resistor may be used to provide the equivalent of a complete se— temperature coe?icient of resistance. In this connection it may be pointed out that resistors ries of resistances from what is commonly re~ using the new materials have been prepared garded as an excellent insulator having a specific complete with platinum leads having a total 40 resistance of 1014 ohms at room temperature to a weight of only .001 grams. With two phase re good conductor of 50 ohms speci?c resistance at sistors, or powdered oxide resistors and carbon 1600” C. This extremely wide range is not shown types, the temperature coefficient changes with the physical size, especially as the total mass ap proaches the size of the individual phases or grains. This improvement is extremely impor by any previously known temperature sensitive resistors. A number of uses for the resistors of the pres ent invention have already been mentioned but tant because in certain types of calorimeters, several additional speci?c uses may be pointed small mass and hence small heat capacity of the out herein. In a great many ?elds and particu temperature measuring device is an advantage larly in radio, ?xed resistors for use at room tem permitting much superior results in use. 59 perature are desired which have very high actual Each of the titanate compounds mentioned resistances of the order of one or more megohms. herein. has an extremely high speci?c resistance By varying the physical dimensions of a resistor at atmospheric temperature and each shows a unit composed of one of the titanate composi relatively rapid lowering of speci?c resistance tions the following ranges may be constructed. with increase in temperature. The curve of tem— 55 Ohms perature coeiiicient of resistance of each of these Magnesium titanate ________________ __ ION-1013 titanates shows a point of in?ection the tempera Zinc titanate _______________________ __ 1013-4010 ture of which may be termed the “critical” tem Cadmium titanate _________________ __ 1012-109 perature. This coeflicient is less negative above the critical temperature than it is below the criti 60 An extremely important feature of such meg cal temperature but for all temperatures above ohm resistors is the ability to readily determine and all temperatures below the critical tempera the exact resistance without the necessity of ac ture the coe?icient in each case remains con curately measuring such extremely high resist stant. ances which require very careful work and ex— Except at the point of in?ection mentioned 65 pensive equipment. With materials of the con above the relationship between resistance and stant temperature coefficient of those of the pres temperature in any of the compounds may best ent invention, the resistor may be brought to a be illustrated by the formula convenient constant elevated temperature below its critical temperature and the relatively low re where R is the resistance in ohms, a is a constant 70 sistance measured by simple standard methods. Then the resistance at room temperature canbe dependent on the physical dimensions of the simply calculated from the known temperature resistor element, 6 is the base of Naperian log coe?icient of resistance. arithms, b is the temperature coef?cient of re Where variable resistors are required, the re sistance and T is the absolute temperdture. It is however, more convenient to express the 75 sistance across the terminals attached to a 2,407,750 5 6 titanate resistor may be made to vary continu ously by varying continuously the temperature of the resistor material between the two electrodes. A simple construction permitting this comprises a suitable sized portion of the resistance material with electrodes having their ends coaxially dis posed and separated by several millimeters and with a thin platinum wire disposed in the mate rial at right angles to the direction of the elec trode wires and between and separate therefrom, with both the electrodes and the heating wire in good electrical and thermal contact with the re sistor material. With this arrangement, if the great accuracy at low temperatures is not required the magnesium titanate can be used to cover the whole range. I claim: 1. A negative resistance-temperature coe?icient resistance material consisting of a titanate of a metal exclusive of mercury of group IIA of the periodic table of elements. 2. A negative resistance-temperature coe?icient resistance material consisting of magnesium titanate. 3. A negative resistance-temperature coeiiicient resistance material consisting of zinc titanate. terminations of the electrodes are as close to 4. A negative resistance-temperature coe?icient gether as stated above, and therefore close to the 15 resistance material consisting of cadmium ti heating wire, and if the temperature of the outer tanate. part of the resistor is low due to thermal radia 5. The method of making a negative resist tion then there will be a rapid change in the re ance-temperature coe?‘icient resistance material sistance across the electrodes when the tempera ture of the heating wire is suddenly changed. This results partially from the closeness of the ends of the electrodes to the heating wire and partially to the property of the titanate resistor of conducting heat more rapidly when hot than when cold which permits a large thermal gradient to exist in such material. The thermal inertia of the resistor element may be made very small by employing a small element with thin electrodes and heating wire. The temperature of the heat comprising mixing ?nely divided titanium dioxide in molecular proportions with a ?nely divided monoxide of a metal selected from the group containing magnesium, zinc and cadmium, and combining the oxides into a true titanate by heat ing the mixture to a melting temperature. 6. The method of making a negative resist ance-temperature coeiiicient resistance material comprising mixing ?nely divided titanium dioxide in molecular proportions with a ?nely divided ing wire is controllable by varying the voltages 30 monoxide of a metal selected from the group containing magnesium, zinc and cadmium, com across its terminals by standard methods and by bining the oxides into a true titanate by heating calibrating the voltage against the resistance across the resistor electrodes any desired resist ance may be obtained by applying a known volt age across the heating wire. ‘ the mixture to a melting temperature and heat treating the mixture at a dull red heat to con vert all titanium present to the tetravalen-t form. 35 7. The method of making a resistor having a The upper limit of the temperature of the re negative resistance-temperature coe?icient com sistor element in the neighborhood of its electrode prising melting and casting in atmosphere about terminations is approximately 800° C. and thus two spaced terminal conductors a bead of a the available ranges of resistance for the three titanates resistor species modi?ed as above will 40 titanate of a metal selected from the group con be as follows: sisting of magnesium, zinc and cadmium and sub sequently heat treating the bead until it is a clear, Ohms transparent substantially colorless mass. 0°—B00° 0°-560° 560°-800° 0°-350° MgO.'I'iO2 ________________ __ ZnO.TiO2 _________________ __ ZnO.TiO-2 _________________ __ CdO.TiO2 _________________ __ 1016-105 1013-104 105-103 1013-104 negative resistance-temperature coe?icient com prising melting and casting in atmosphere about 350°-800° CdO.TiO2 _________________ __ 105 --102 the spaced ends of a pair of platinum wires a bead 8. The method of making a resistor having a of a single crystalline phase of a metallic titanate For use in circuits where the heating potential and treating the bead to reduce all titanium and that across the resistor must be electrically therein to the tetravalent form. separated various obvious arrangements may be 50 9. An electrical resistor formed as a shaped, resorted to. self-bonded, coherent, monolithic, single crystal The use of the titanate resistors for resistance line phase structure consisting of a chemical thermometers will be handled in a more or less compound having the formula MO.TiO2 where M conventional manner by measuring the voltage is magnesium, zinc or cadmium. drop across the variable resistor in series with 55 10. An electrical resistor consisting of a me a ?xed resistance or by measuring the current tallic titanate whose curve of negative resistance ?owing through the resistor at a constant voltage, temperature coe?icient contains a de?nite point etc. Because of the tremendous changes in re of in?exion at a critical temperature above which sistance available with relatively small changes the coei?cient is less negative than below. in temperature the measuring equipment required 11. An electrical resistor consisting of a me may be quite elementary and cheap and even if tallic titanate whose curve of negative resistance its accuracy is not high nevertheless it will indi temperature coeii‘icient contains a de?nite point cate thermal readings to relatively close toler of in?exion at a critical temperature above and ances. below which the coe?icient is constant. Magnesium titanate is most useful for measur 12. An electric resistance element containing ing temperatures from about 745 to 1600° C., a titanium and magnesium in a single crystalline range which includes most commercial furnace phase. temperatures used in the ceramic, glass and 13. An electric resistance element of mono metallurgical arts. Zinc titanate is most useful lithic form and of su?icient size to be used alone in the temperature range from room tempera containing titanium and zinc, said element be ture to 560° C. and cadmium titanate, from room ing of a single crystalline phase. temperature to 350° C. It will thus be seen that 14. An electric resistance element containing the three materials permit temperature measure titanium and cadmium. ments ranging from zero to 1600° C. but where FREDERICK GORDON SMITH.