JP3317129B2 - Voltage non-linear resistance ceramic composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a voltage non-linear resistance ceramic composition.

[0002]

2. Description of the Related Art A conventional voltage non-linear resistance porcelain (hereinafter referred to as "varistor element") composition has obtained electrical characteristics suitable for each application by adding various trace additives to zinc oxide as a main component. When a high varistor voltage (V _{1 mA / mm} ) is required in addition to the basic performance of the varistor, the thickness of the element is increased or the amount of silicon oxide added as a sub-component is controlled. On the other hand, when a low varistor voltage is required, titanium oxide or tin oxide may be used as a method of reducing the thickness of the element or a method of increasing the zinc oxide crystal grain size of the sintered body and reducing the number of crystal grain boundaries per unit thickness. A method of controlling a sub-component such as addition of a compound is generally known.

[0003]

In the case of a low-voltage varistor element having such a conventional structure, when the element thickness is reduced, the mechanical strength of the element is reduced, which is not practical. For this reason, a method of securing the required thickness and increasing the crystal grain size of zinc oxide in the sintered body is used. However, it is difficult to increase the crystal grain size and to make the grain size uniform, which causes a variation in the varistor voltage. Was the cause.

An object of the present invention is to solve such a problem and to provide a varistor element which suppresses variations in varistor voltage and has stable characteristics.

[0005]

In order to achieve the above object, the present invention uses a material in which impurities in titanium oxide contained as a sub-component are controlled to 0.004% or less of iron in terms of oxide. Things. This controls the reaction between the liquid phase and zinc oxide generated during the sintering process, promotes uniform grain growth, and suppresses the number of grain boundaries in the sintered body.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is characterized in that iron as a trace impurity contained in titanium oxide in an additive added to zinc oxide as a main component and contained as an additive is converted into oxide. A material controlled to 0.004% or less is used. The titanium oxide promotes the reaction between liquid-phase bismuth oxide and solid-phase zinc oxide that appears during the sintering process of the varistor element, and has a function of assisting the uniform growth of the crystal grain size of zinc oxide. Among these, iron content must be suppressed to a certain level or less in order to inhibit the function of titanium oxide.

The invention according to claim 2 of the present invention is characterized in that the potassium content of trace impurities contained in the cobalt oxide in the additive, which is added to zinc oxide as the main component, is 0.0003% in terms of oxide. The materials controlled below are used. The cobalt oxide forms a stable interface state by forming a solid solution with zinc oxide as a main component, and has a function of controlling a crystal grain boundary layer in the sintered body. In this, the potassium content must be controlled to a certain level or less in order to inhibit the function of cobalt oxide.

(Embodiment 1) An embodiment of the present invention will be described below.

Bismuth oxide 0.70 mol%, cobalt oxide 0.30 m
ol%, manganese oxide 0.95 mol%, antimony oxide 0.05 mol%, chromium oxide 0.05 mol%, nickel oxide 0.05 mol%, titanium oxide 0.50 mo
1% and 0.0018 mol% of aluminum nitrate were weighed and mixed to obtain a varistor composition having a varistor voltage V _{1 mA / mm} of 25 V. The materials used at this time were each of a quasi-reagent grade. Among them, titanium oxide, in particular, contained iron, which is a trace impurity contained therein, in an amount of 0.1% in terms of oxide.
004% or less, and cobalt oxide used was a material in which potassium as a trace impurity was controlled to 0.0003% or less in terms of oxide. Ten lots of the varistor composition were prepared. Each of these granulated powders was pressed at a pressure of 800 kg / cm ² at a diameter of 13 m.
After molding into a disk having a thickness of 1.2 mm and a thickness of 1.2 mm, a sintered body was formed at a temperature of 1260 ° C. A varistor element was completed by baking silver electrodes on both sides of the sintered body. The varistor voltage V _{1 mA / mm} of the varistor element thus obtained was measured, and the results are shown in (Table 1). In addition, the results when titanium oxide and cobalt oxide were not specifically controlled as described above were also shown.

[0010]

[Table 1]

As is clear from Table 1, titanium oxide,
The varistor voltage V _{1 mA / mm} of a varistor element made of a material in which cobalt oxide is specially controlled shows a stable value with little variation between lots. On the other hand, when the varistor element is prepared using a material that is not particularly controlled, the varistor voltage V _{1 mA / mm} of the varistor element varies greatly between lots.
Further, after polishing the varistor element obtained by controlling the amount of impurities contained in the titanium oxide and the cobalt oxide, the sintered body particle size of the zinc oxide was 50 to 6 in optical microscope observation.
It has been confirmed that it is as large as 0 μm and uniform.

(Embodiment 2) For zinc oxide as a main component,
Bismuth oxide 0.70 mol%, cobalt oxide 0.30 mol%, manganese oxide 0.95 mol as subcomponents
%, Antimony oxide 0.05 mol%, chromium oxide 0.
05 mol%, nickel oxide 0.05 mol%, titanium oxide 0.50 mol%, aluminum nitrate 0.0018 mol
% Were weighed and mixed, and the varistor voltage V
The varistor composition was _{1 mA / mm} of 25 V. The materials used at this time were the same as those in Embodiment 1,
Among them, (1) only titanium oxide, and the iron content of trace impurities contained therein was 0.002% and 0.004% in terms of oxide, respectively.
%, 0.006%, and 0.008%, respectively, and the other materials are not specifically controlled.

(2) Only cobalt oxide and potassium, a trace impurity contained therein, are converted to oxides in amounts of 0.00
01%, 0.0003%, 0.0005%, and 0.1%.
When a material controlled to 0010% is used and other materials are not specially controlled. Each of the devices formed into a diameter of 13 mm and a thickness of 1.2 mm was subjected to the same treatment as in the first embodiment, and the varistor voltage V _{1 mA / mm} was evaluated.
The results are shown in (Table 3).

[0014]

[Table 2]

[0015]

[Table 3]

As is clear from Table 2, when the iron content in the titanium oxide is more than 0.004%, the varistor voltage increases rapidly and the variation also increases. Also in Table 3, it can be seen that, when the potassium content in the cobalt oxide is more than 0.0003%, the varistor voltage increases and the variation increases.

[0017] Titanium oxide and cobalt oxide are difficult to avoid from being mixed with iron and potassium, respectively, in the material manufacturing method.
Since the material is very expensive, a range that can be industrially produced and that does not adversely affect the performance of the varistor element is determined. This promotes the grain growth of zinc oxide, stabilizes the spinel phase in the grain boundaries formed by the reaction of the subcomponents, and can control the fluctuation of the varistor voltage V1 _{mA / mm} .

[0018]

As described above, the present invention uses a material in which impurities in titanium oxide contained as subcomponents are controlled so that iron content is 0.004% or less in terms of oxide. That is, the titanium oxide has a function of promoting the reaction between liquid-phase bismuth oxide and solid-phase zinc oxide appearing in the sintering process of the varistor element, and assisting the uniform growth of the crystal grain size of the zinc oxide. The voltage variation can be suppressed.

Claims (2)

(57) [Claims] 1. A voltage non-linear resistance comprising zinc oxide as a main component and trace amounts of bismuth oxide, antimony oxide, chromium oxide, cobalt oxide, manganese oxide, nickel oxide, titanium oxide and aluminum nitrate added as accessory components. A voltage non-linear resistance ceramic composition, wherein a material in which an impurity in the titanium oxide in the subcomponent is controlled to 0.004% or less in terms of an oxide in terms of oxide is used. 2. The impurities in the cobalt oxide in the secondary component,
2. The voltage non-linear resistance ceramic composition according to claim 1, wherein a material whose potassium content is controlled to 0.0003% or less in terms of oxide is used.