NON-LINEAR RESISTANCE ELEMENT
United States Patent 3715701
A varistor whose ceramic body contains bismuth oxide and antimony oxide containing semiconducting titanium oxide having a relatively low C-value and a low β value.
US Patent References:
Non-linear electric resistor
Fotland - May 1959 - 2885521
Semiconductive capacitor and the method of manufacturing the same
Saburi - January 1967 - 3299332
Non-linear electric resistor
Fotland - May 1959 - 2885521
Semiconductive capacitor and the method of manufacturing the same
Saburi - January 1967 - 3299332
Inventors:
Yperman, Jean Michel Baudry Ghislain (Woluwe, BE)
Rapaille, Jean Rodolphe (Brussels, BE)
Rapaille, Jean Rodolphe (Brussels, BE)
Application Number:
05/116922
Publication Date:
02/06/1973
Filing Date:
02/19/1971
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Export Citation:
Assignee:
U.S. Philips Corporation (New York, NY)
Primary Class:
Other Classes:
252/520.200
International Classes:
C04B35/46; H01C7/115; H01C7/105; H01C7/10
Field of Search:
338/20-25 313/238 252/520
Primary Examiner:
Duggan D. F.
Claims:
What is claimed is
1. A non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semiconducting titanium oxide, wherein the ceramic body contains per mol of titanium oxide 0.005-0.1 mol of bismuth oxide and 0.001-0.05 mol of antimony oxide.
2. A non-linear resistance element as claimed in claim 1, wherein the ceramic body contains per mol of titanium oxide 0.03-0.05 mol of bismuth oxide and 0.004-0.01 mol of antimony oxide.
1. A non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semiconducting titanium oxide, wherein the ceramic body contains per mol of titanium oxide 0.005-0.1 mol of bismuth oxide and 0.001-0.05 mol of antimony oxide.
2. A non-linear resistance element as claimed in claim 1, wherein the ceramic body contains per mol of titanium oxide 0.03-0.05 mol of bismuth oxide and 0.004-0.01 mol of antimony oxide.
Description:
The invention relates to a non-linear resistance element having a large voltage dependence of the resistance and in which the resistance body comprises sintered ceramic ferroelectric material. Such non-linear resistance elements are sometimes referred to as varistors.
For such a resistance element the relation between current intensity and voltage may be defined by the formula:
V = C. I β.
In this formula V represents the voltage across the resistor in Volts, I represents the current through the resistor in amperes, C represents the voltage across the resistor at I = 1 amp. and β represents a number smaller than 1.
Known varistors are manufactured by sintering fine particles of silicon carbide and a ceramic binder and/or a conducting material, for example, graphite. Varistors thus manufactured with a conducting binder have a comparatively small electric resistance, that is to say, a relatively small value for C and a relatively large value for β. Varistors manufactured from silicon carbide and a non-conducting binder have a comparatively large electric resistance, that is to say, a relatively large value for C and a relatively small value for β. In both cases the value of β lie between 0.15 and 0.30 in practice.
In known silicon carbide varistors, the value of β is often dependent on V; at comparatively low values of V, β is larger than at comparatively high values of V. This has drawbacks for certain applications inter alia, for voltage stabilization, rendering small motor free from interference (limitation of the over-voltage) and protection of collectors in small motors (tape recorders, record players).
The object of the present invention is to provide a varistor in which the value of β is not dependent or is only dependent to a slight extent on the value of V. A further object of the invention is to provide a varistor whose values of β are small also at low values of C. Such a varistor is particularly suitable for the said applications.
The invention relates to a non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semi-conducting titanium oxide and is characterized in that the ceramic body contains per mol of titanium oxide, 0.005-0.1 and preferably 0.03-0.05 mol of bismuth oxide and 0.001-0.05 and preferably 0.004-0.01 mol of antimony oxide.
Resistance bodies for non-linear resistance elements according to the invention may be manufactured, for example, in the following manner. A mixture of TiO 2 , Bi 2 O 3 and Sb 2 O 3 , or of compounds which change into these oxides upon heating, is homogeneized by wet grinding in a porcelain ball mill. After grinding the mass obtained is dried. After mixing with an organic binder, for example, polyvinylacetate, bodies are moulded from the mass. These bodies are brought into a furnace and heated in air at a temperature of between 1,350°C and 1,600°C during, for example, 10 to 30 minutes. The ceramic resistance bodies thus obtained may be provided with electrodes in known manner, for example, by first vapor depositing in vacuo a layer consisting of chromium and nickel, which contains for example 20 percent of chromium, on the surfaces of the body on which the electrodes are to be provided and subsequently by vapor depositing likewise in vacuo on this layer a layer of solderable metal, for example, silver.
A more detailed description of the manufacture of a resistance element according to the invention will be described hereinafter by way of example.
79.9 g (1 mol) TiO 2 , 19.8 g (0.04 mol) Bi 2 O 3 and 1.45 g (0.0005 mol) Sb 2 0 3 were introduced in a porcelain ball mill with 350 mls of ethanol and mixed and ground for 15 hours. Subsequently the mixture was dried in a furnace at 50°C. The dried mixture was then mixed with 40 mls of a mixture obtained by mixing 45 g of polyvinyl acetate , 1,000 mls of methylethylketone and 10 mls of dibutylphthalate. Subsequently cylindrical bodies (thickness 1.0 mm, diameter 5.6 mm) were moulded from the mass obtained. These bodies were introduced into a furnace and heated in air at 1,490°C for 5 minutes. After cooling the end-faces of the cylindrical bodies were provided with electrodes in the known manner mentioned above.
The electrical properties of the varistor thus manufactured and those of varistors manufactured in a similar manner whose compositions of the ceramic resistance bodies are different are shown in the table together with these compositions.
It was found that varistors according to the invention can be improved in some respects (lowβ -values), by incorporating lead oxide (PbO 2 or PbO) or an oxide of barium, strontium or calcium in the ceramic resistance body up to a quantity of 0.1 mol of these oxides per 1 mol of titanium oxide (TiO 2 ). Resistance bodies according to the invention containing PbO 2 , BaO, SrO or CaO may be manufactured in accordance with the above-mentioned method. The desired quantity of one or more of these oxides or of compounds which change into these oxides upon heating are added to the starting mixture containing TiO 2 , Bi 2 O 3 and Sb 2 O 3 .
The following table shows data of different Examples of non-linear resistance elements according to the invention. The columns 1, 2, 3, and 4 state the quantities of oxides contained in the resistance body in addition to TiO 2 . The quantities of these oxides are stated in mol per mol of TiO 2 . The resistance body according to Example 1, thus contains 0.005 mol of Sb 2 O 3 and 0.05 mol of Bi 2 O 3 per mol of TiO 2 . Columns 5 and 6 show the sintering temperature (in °C) and sintering period (in minutes), respectively. Columns 7 and 8 show the voltage V (in Volts) at which a current of 1 mA is reached and the associated value of β , respectively. Column 9 shows the numbers of the examples. ##SPC1##
As can be seen from the table varistors are obtained in all cases for which a low β value has been measured at a relatively low C-value. Varistors having β values of from 0.11-0.14 in combination with V-values of from 25-75 are very suitable for the previously mentioned applications.
The drawing shows an embodiment of a non-linear resistance element according to the invention. This element consists of a cylindrical ceramic resistance body 1 whose end-faces 2 and 3 are provided with electrodes 4 and 5 by vapor depositing in vacuo successively a layer of chrome-nickel alloy and a layer of silver. Supply wires 8 and 9 are provided by means of solder 6 and 7.
For such a resistance element the relation between current intensity and voltage may be defined by the formula:
V = C. I β.
In this formula V represents the voltage across the resistor in Volts, I represents the current through the resistor in amperes, C represents the voltage across the resistor at I = 1 amp. and β represents a number smaller than 1.
Known varistors are manufactured by sintering fine particles of silicon carbide and a ceramic binder and/or a conducting material, for example, graphite. Varistors thus manufactured with a conducting binder have a comparatively small electric resistance, that is to say, a relatively small value for C and a relatively large value for β. Varistors manufactured from silicon carbide and a non-conducting binder have a comparatively large electric resistance, that is to say, a relatively large value for C and a relatively small value for β. In both cases the value of β lie between 0.15 and 0.30 in practice.
In known silicon carbide varistors, the value of β is often dependent on V; at comparatively low values of V, β is larger than at comparatively high values of V. This has drawbacks for certain applications inter alia, for voltage stabilization, rendering small motor free from interference (limitation of the over-voltage) and protection of collectors in small motors (tape recorders, record players).
The object of the present invention is to provide a varistor in which the value of β is not dependent or is only dependent to a slight extent on the value of V. A further object of the invention is to provide a varistor whose values of β are small also at low values of C. Such a varistor is particularly suitable for the said applications.
The invention relates to a non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semi-conducting titanium oxide and is characterized in that the ceramic body contains per mol of titanium oxide, 0.005-0.1 and preferably 0.03-0.05 mol of bismuth oxide and 0.001-0.05 and preferably 0.004-0.01 mol of antimony oxide.
Resistance bodies for non-linear resistance elements according to the invention may be manufactured, for example, in the following manner. A mixture of TiO 2 , Bi 2 O 3 and Sb 2 O 3 , or of compounds which change into these oxides upon heating, is homogeneized by wet grinding in a porcelain ball mill. After grinding the mass obtained is dried. After mixing with an organic binder, for example, polyvinylacetate, bodies are moulded from the mass. These bodies are brought into a furnace and heated in air at a temperature of between 1,350°C and 1,600°C during, for example, 10 to 30 minutes. The ceramic resistance bodies thus obtained may be provided with electrodes in known manner, for example, by first vapor depositing in vacuo a layer consisting of chromium and nickel, which contains for example 20 percent of chromium, on the surfaces of the body on which the electrodes are to be provided and subsequently by vapor depositing likewise in vacuo on this layer a layer of solderable metal, for example, silver.
A more detailed description of the manufacture of a resistance element according to the invention will be described hereinafter by way of example.
79.9 g (1 mol) TiO 2 , 19.8 g (0.04 mol) Bi 2 O 3 and 1.45 g (0.0005 mol) Sb 2 0 3 were introduced in a porcelain ball mill with 350 mls of ethanol and mixed and ground for 15 hours. Subsequently the mixture was dried in a furnace at 50°C. The dried mixture was then mixed with 40 mls of a mixture obtained by mixing 45 g of polyvinyl acetate , 1,000 mls of methylethylketone and 10 mls of dibutylphthalate. Subsequently cylindrical bodies (thickness 1.0 mm, diameter 5.6 mm) were moulded from the mass obtained. These bodies were introduced into a furnace and heated in air at 1,490°C for 5 minutes. After cooling the end-faces of the cylindrical bodies were provided with electrodes in the known manner mentioned above.
The electrical properties of the varistor thus manufactured and those of varistors manufactured in a similar manner whose compositions of the ceramic resistance bodies are different are shown in the table together with these compositions.
It was found that varistors according to the invention can be improved in some respects (lowβ -values), by incorporating lead oxide (PbO 2 or PbO) or an oxide of barium, strontium or calcium in the ceramic resistance body up to a quantity of 0.1 mol of these oxides per 1 mol of titanium oxide (TiO 2 ). Resistance bodies according to the invention containing PbO 2 , BaO, SrO or CaO may be manufactured in accordance with the above-mentioned method. The desired quantity of one or more of these oxides or of compounds which change into these oxides upon heating are added to the starting mixture containing TiO 2 , Bi 2 O 3 and Sb 2 O 3 .
The following table shows data of different Examples of non-linear resistance elements according to the invention. The columns 1, 2, 3, and 4 state the quantities of oxides contained in the resistance body in addition to TiO 2 . The quantities of these oxides are stated in mol per mol of TiO 2 . The resistance body according to Example 1, thus contains 0.005 mol of Sb 2 O 3 and 0.05 mol of Bi 2 O 3 per mol of TiO 2 . Columns 5 and 6 show the sintering temperature (in °C) and sintering period (in minutes), respectively. Columns 7 and 8 show the voltage V (in Volts) at which a current of 1 mA is reached and the associated value of β , respectively. Column 9 shows the numbers of the examples. ##SPC1##
As can be seen from the table varistors are obtained in all cases for which a low β value has been measured at a relatively low C-value. Varistors having β values of from 0.11-0.14 in combination with V-values of from 25-75 are very suitable for the previously mentioned applications.
The drawing shows an embodiment of a non-linear resistance element according to the invention. This element consists of a cylindrical ceramic resistance body 1 whose end-faces 2 and 3 are provided with electrodes 4 and 5 by vapor depositing in vacuo successively a layer of chrome-nickel alloy and a layer of silver. Supply wires 8 and 9 are provided by means of solder 6 and 7.