JPS5849003B2 - Method for manufacturing voltage nonlinear resistance material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on a sintered body of titanium oxide, dioptic oxide, and bismuth oxide, whose resistance value is highly dependent on voltage, and whose characteristics are caused by the voltage resistance of the sintered body itself. The present invention relates to a method of manufacturing a nonlinear resistance material.

In recent years, with the rapid progress and spread of audio equipment, control equipment, and small power equipment, the prevention of noise caused by small electric motors, protection from overvoltage, and protection of relay contacts have become important issues.
It has become to.

However, since these devices are generally becoming less expensive, this point needs to be taken into consideration when solving the above-mentioned problems.

As voltage nonlinear resistance materials, silicon carbide sintered varistors, selenium and cuprous oxide varistors, zinc oxide sintered varistors, and the like are known.

By the way, the electric current characteristics of a varistor are generally expressed by the formula It is expressed as

Here, ■ is the voltage applied to the varistor, ■ is the current flowing through the varistor, and C is a constant corresponding to the voltage when a predetermined current flows.

The index α is a non-linear coefficient and can be determined by the following equation.

Here ■, and ■2 are the given currents ■1 and I2, respectively.
is the voltage at .

A resistor with α=1 is a normal resistor that follows Ohm's law, and it can be said that the larger α is, the better the voltage nonlinearity is. It can be used as a guideline.

Furthermore, the desirable value for C varies depending on the use of the varistor, but for low voltage varistors, it is preferable that the C value is low and that a value suitable for the use can be easily achieved.

Among the known varistors that have been used so far, silicon carbide varistors are manufactured by baking silicon carbide particles with a particle size of around 100μ in clay, and their voltage nonlinearity is due to the voltage dependence of the resistance between particles. Tame, C
The value of can be adjusted by changing the thickness of the varistor, that is, the number of grain boundaries in the direction of current flow.

However, in the case of low-voltage applications, the C value per grain boundary is high, so the number of grain boundaries must be reduced, and reducing the number of grain boundaries causes the problem of lower voltage resistance. .

1. Also, this product has a relatively small non-linearity index α of 3 to 7, and because the silicon carbide is hard, the mold used for molding suffers from severe wear and is difficult to form into precise shapes. .

On the other hand, selenium and cuprous oxide based varistors have a nonlinear index α
is as small as 2 to 3, and has the disadvantage that the limiting voltage cannot be increased, so it cannot be said to be a satisfactory material.

Furthermore, zinc oxide-based varistors generally have a large non-linearity index α of 10 to 50, and the particle diameter can be made as small as about 10μ, so the voltage range can be changed from 10 to IOOOV. Since zinc oxide is chemically unstable, it is subject to deterioration of nonlinearity over time, and it also has the disadvantage of being labor-intensive and expensive to manufacture.

In order to improve these drawbacks of conventional varistors,
A material made by adding niobium oxide and bismuth oxide as additives to titanium oxide and sintering it was proposed.

This has the advantage that the nonlinear index α is higher than that of silicon carbide-based varistors, selenium, or cuprous oxide-based varistors, and that a desired C value can be achieved without changing the α value.

However, this method has the disadvantage that it is difficult to uniformly disperse the additive components niobium oxide and bismuth oxide into the sintered body, resulting in variations in quality.

The inventors of the present invention have conducted intensive research to overcome these drawbacks and develop a titanium oxide-based voltage nonlinear resistance material with stable quality. By adding niobium oxide to a powder mixture of

That is, the present invention uses niobium oxide of 0.002 to 0.09
Mol% (Nb205 equivalent), bismuth oxide 0.05-1
In producing a voltage non-linear resistance material having a 0 molar width (Bi203 equivalent) and a structure of titanium oxide residue, a predetermined amount of the niobium oxide raw material is made into a solution with a concentration of 0.001 to 2φ, and other raw materials are mixed. The present invention provides a method characterized in that the powder is added to a powder mixture, thoroughly mixed, and then sintered.

The niobium oxide raw material used in the present invention may be any niobium compound that can be converted into niobium oxide by calcination, as long as it becomes a solution when dissolved in water or other volatile solvent.

As such a nioptic compound, for example, Nb(OH)
Examples include 2Cl3, NbCl5, Nb6Cl14.7H20.

However, what is particularly suitable for practical use is one obtained by treating metallic niobium with hydrofluoric acid and dissolving it in sulfuric acid.

These niopium oxides need to be used as a solution with a concentration of 0.001 to 2φ in order to mix uniformly with the powder mixture of other precepts.

1. As titanium oxide raw materials and bismuth oxide raw materials,
Usually powdered titanium oxide and bismuth oxide are used, but
In addition, it is also possible to use a substance that can form titanium oxide or bismuth oxide upon firing.

These are used as powders with an average particle size of about 5 to 300 μm.

To produce a voltage nonlinear resistance material by the method of the present invention, for example, a solution containing a predetermined amount of a niobium oxide raw material is added to a powder mixture in which titanium oxide raw material powder and bismuth oxide raw material powder are mixed at a predetermined ratio. and mix thoroughly using a wet ball mill or the like.

Next, after drying this mixture, it is calcined overnight at a temperature of 800 to 1000°C, and the calcined body is crushed.

A suitable binder such as polyvinyl alcohol, CMC, etc. is added to this pulverized material, formed into granules, further press-molded into a suitable shape, and heated in air or an inert atmosphere for 11 hours.
Sinter at a temperature of 00 to 1400°C.

At this time, the calcination step can be omitted unless it is particularly necessary.

The material obtained by the method of the present invention has a niobium oxide content of 0.002 to 0.09 mole φ when converted to Nb205,
Bismuth oxide content 0.05 when converted to Bi203
It has a composition of ~10 moles and a titanium oxide (Ti02) residue.

Good nonlinearity cannot be obtained when the niopium oxide content is less than 0.002 mol φ.

On the other hand, if this exceeds 0.09 mol φ, no particular improvement in nonlinearity is observed, and in addition, nonlinearity in a high current region decreases.

On the other hand, if the bismuth oxide content is less than 0.05 moles or more than 10 moles, good nonlinearity cannot be obtained.

In the voltage nonlinear resistance material obtained by the method of the present invention, the voltage nonlinearity depends on the sintered body itself, so by changing the thickness in the direction of current flow, the desired value can be obtained without changing the α value. It has the characteristic that the C value can be easily achieved.

In addition, since the C value per unit thickness is low, low voltage devices can be easily produced, and the device can be made homogeneous, reliability such as voltage resistance is high.

Since the α value can be made significantly larger than that of silicon carbide-based varistors, it has advantages such as being able to be used in a wide range of applications, and requiring fewer types of raw material components, making it possible to lower the price.

Next, the voltage nonlinear resistance material obtained by the method of the present invention can be used at a low voltage of 3 to 12.3 V and the nonlinear index α can be made thicker, so it can be used as a noise prevention element for a micromotor. It is suitable as

The noise in this micromotor is caused by the spark phenomenon that occurs between the commutator and the brushes.

More specifically, in motors that generally use a commutator, the commutator is usually shaped like a cylinder with several commutator pieces attached at predetermined intervals, and there is a space between each commutator piece. There will always be a gap in the insulating layer.

Therefore, when the commutator is rotating, the brushes jump across the gaps between the commutator pieces and move on to the next commutator piece. Due to the presence of large self-inductance of the rotor, spike-like voltage sparks occur.

This spark causes electrical noise and tends to wear out the commutator and brushes, shortening the life of the motor.

By the way, these spike-like sparks are a bipolar oscillating voltage, the peak value of which is 20 to 50 times the motor power supply voltage, the connection time is 00 μs apart from the button, and has a high frequency of 2 to 5 MHz, so these In order to eliminate the A varistor element with characteristics is required.

The voltage nonlinear resistance material obtained by the method of the present invention has all of these characteristics, and the device provided with electrodes is said to be extremely suitable for noise prevention in micromotors. be able to.

The electrode in this case may be either non-ohmic or ohmic, as long as it does not impair the properties of the specified material.
As the mounting method, any method such as baking, plating, vapor deposition, sputtering, thermal spraying, etc. can be used.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Fluoric acid and several drops of nitric acid are added to 10 g of metallic niobium to completely dissolve it, and this solution is once evaporated to dryness.

Next, this residue was dissolved in hydrofluoric acid]00TLl, and then diluted with water.
000 yd to prepare a solution with a niobium concentration of 10,000 ppm, add sulfuric acid to 100 ml of this solution, heat treat it, and further dilute with water to 1,000 ml to obtain a 10% sulfuric acid solution with a niobium concentration of 1,000 ppm.

Next, titanium oxide powder (average particle size] 0 μ or less) and bismuth oxide powder (average particle size 10
The above-mentioned niobium solution was added to the mixture with niobium (μ or less), and thoroughly mixed using a wet ball mill.

After drying this mixture, it was placed in an electric furnace and calcined at about 1,000°C for 30 minutes.

After pulverizing the calcined material to pass 48 mesh,
2 polyvinyl alcohol per total weight as a binder
After adding it in the ratio of 100 ml to 100 ml and making it into grains, it was made into 16 m in diameter.
It was shaped like a disc with a thickness of 1.2 m and a thickness of 1.2 m.

The shaped body was then fired at about 1300° C. for 1 hour to obtain a desired nonlinear resistance material.

Silver-baked electrodes were provided on both sides of the various materials thus obtained, and voltage-current characteristics were measured.

The results are shown in the table below.

In the table, the C value is the voltage when a current of 10 mA/1 is passed (
V/distance).

As can be seen from this table, the oxides of niobium and bismuth are converted into the form of Nb205 and Bi203, respectively.
In the range of 0.002 to 0.09 mol and 0.05 to 10 mol, α exceeds 5, and reaches 10 at high values, which is a sufficiently high α value compared to silicon carbide varistors.

Furthermore, the C value per unit thickness also shows a wide range of values, making it suitable as a varistor for low voltage applications.

Example 2 The element obtained in Example 1 was attached between the coils of a micromotor at each working voltage (approximately 80φ of the applied voltage), and the noise cut voltage was measured using an oscilloscope.

The results are shown in the table below. Example 3 Voltage nonlinear resistance material (4) with a composition of 0.05 mol of niobium oxide, 0.5 mol of bismuth oxide, and 99.45 mol of titanium oxide (Fe203-based material), SnO2
Using ZnO type material (C') and ZnO type material 0, working voltage 5V
A noise cut test was conducted in the same manner as in Example 2 on a micromotor for use in a commercial vehicle.

The noise cut state for each sample is shown in the attached drawing.

As is clear from this figure, the material of the present invention exhibits superior properties compared to materials used for conventional noise cutting.

[Brief explanation of the drawing]

The drawing is an oscillograph diagram showing the noise cutting state when the material of the present invention and the known material are used as a noise prevention element of a micromotor.

Claims (1)

[Claims] 1 Acid f Hiniop 0.002-0.09 mol (Nb2
05 conversion 3I), bismuth oxide 0.05 to 10 molar width (B
In producing a voltage non-linear resistance material having a combination of titanium oxide (i203 equivalent) and titanium oxide residue, a predetermined amount of niobium oxide raw material is added as a solution with a concentration of 0.001 to 2% to a powder mixture of other raw materials. A method characterized by sintering after mixing thoroughly.