JPS5968906A - Method of producing voltage nonlinear resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an IP method for manufacturing a voltage non-linear resistor that is mainly composed of zinc oxide and is used in lightning arresters and surge absorbers.
It is something to do.

Conventionally, when producing a zinc oxide voltage nonlinear resistor, the general f is the main component of zinc oxide, and additives such as bismuth oxide and cobalt oxide are also used as oxide powder raw materials.

These various powders are mixed by adding water and using a ball mill or the like, and after drying, a suitable binder is added to form granules, which are then subjected to fless molding and fired at a temperature of around 7.200°C to obtain a sintered body.

After forming a polished electrode on the dough, an element is obtained. Among these processes, the granulation process to form granules is required for mass production.
Add a binder of PVA (polyvinyl alcohol) to the tornado reactor.

Dry granules are often produced using drying equipment such as spray dryers.

It is well known that various electrical characteristics of voltage nonlinear resistors vary greatly depending on the manufacturing method and manufacturing parameters thereof. For example, in the case of the mixing process, there are nearly 10 types of trace additives other than the main ingredients, and the density of each powder is quite different (zinc oxide density: left A g/ct/I, bismuth oxide density gqF!/crl, Silicon oxide density, 21
1/cd, etc.), it is quite difficult to achieve sufficiently uniform mixing.

Poor mixing deteriorates the uniformity of the ceramic itself, which in turn causes problems such as voltage non-linearity, lifespan, and failures in various durability tests.

Although there is little mention of ensuring uniformity of mixing, for example, a method has been proposed in which an aqueous solution of additive ions is added to zinc oxide powder and mixed, as described in Japanese Patent Application Laid-Open No. 1997-97090.

This mixture is well mixed in a microscopic sense, and the resulting sintered body has a well-uniformed particle size and fewer defects, as well as current-voltage characteristics and lifespan characteristics, compared to those using ordinary powder as a starting material. etc. are also excellent. Although the method of mixing these salts gives the device excellent properties, it has been found that there are problems in the drying method of the slurry in the actual manufacturing process.

6. Figure 1 shows a microstructure model of a voltage nonlinear resistor whose main component is zinc oxide. In the figure,
The fine structure of the resistor includes particles 1 mainly composed of zinc oxide, a boundary layer mainly composed of bismuth oxide, and particles 3 of spinel or the like produced when antimony oxide is added. The source of voltage nonlinearity is thought to be related to electrical barriers existing between zinc oxide particles or in a boundary layer between zinc oxide and bismuth oxide.

Depending on the magnitude of the voltage applied to the barrier K, (1) ohmic region, (λ) Schottky region, (3) tunnel region, and (
(i) A region where the resistance of zinc oxide particles dominates the current-voltage characteristics. In the case of lightning arresters, although it depends on the energizing conditions, the leakage current region roughly corresponds to the (,2) region, and the current region (/θKA-) is defined as the so-called limiting voltage.
corresponds to areas (3) and (da).

In other words, an element with excellent protection characteristics has a current stability (lifetime) in the range (, 2) < , (,?) or (
It is desirable that the limiting voltage related to the region 4t) be as small as possible.

From the previous studies on the fine+vIII structure and the reaction mechanism, we have found that bismuth oxide (or compounds that form bismuth oxide at high temperatures, such as bismuth nitrate) becomes a liquid phase during firing and promotes the crystal growth of zinc oxide particles. , chromium, and other ions are dissolved in solid solution, and zinc oxide particles are present as a solid solution. Kono (ruto, nickel, manganese, chromium,
Aluminum oxide ions are dissolved in zinc oxide particles, but some of them form spinel particles together with antimony oxide (or substances that decompose at high temperatures to become antimony oxide, such as antimony tartrate). From this, it can be seen that the components dissolved in zinc oxide particles are mainly related to the large current region ((,?) and (4') above), do not easily react with zinc oxide like bismuth oxide, and are Those that do exist are mainly related to the low current region ((1) and (2) above). It is thought that the spinel particles of the second phase are involved in the distribution of various ions to the zinc oxide portion and the bismuth oxide portion.

Now, when preparing aqueous solutions of various salts, nitrates such as nickel, cobalt, manganese, and chromium dissolve well in water, and antimony tartrate is also easily soluble, while nitrate of bismuth is slightly insoluble in water. It causes scuttling in an oxide state, but by adding concentrated nitric acid to lower the pH, the scuttling disappears and it dissolves in 1-1-. Bismuth ions exist stably in nitric acid with a sufficiently high concentration of 1, but when this solution is reacted with Zinc oxide powder, nitric acid reacts with zinc oxide quickly according to the following equation, so Z
nO+ 2HNOy → Zn (No,)
, + T)H of the HxO solution becomes large and bismuth ions immediately form scuttling. In other words, an aqueous solution of bismuth nitrate containing nitric acid appears to be a sloppy aqueous solution, but when this aqueous solution is mixed with zinc oxide powder, it immediately forms a scuttling L7 solid phase, so it is similar to mixing with other added ionic components. It cannot be handled as such, and it causes problems in uniform dispersion.

In particular, when these 11 slurries are allowed to stand and dry, all but the bismuth ions become evaporated to dryness from the aqueous solution, but the bismuth is dried from the same phase as a scuttling substance, and this density is extremely high. Due to this fact, it is extremely difficult to obtain a highly uniform dry powder for bismuth nine.
It was found that this deteriorated the current-voltage characteristics on the low current side and had a negative impact on the life characteristics.

Although we have mainly talked about the use of bismuth nitrate here, the same is true when bismuth chloride is used in an alcoholic solution because if there is a large amount of water, it will undergo hydrolysis and form the same phase. In any case, since it is difficult to mix bismuth ion powder with zinc oxide in a solution state, it is necessary to dry it in the best possible mixed state even if this precipitate occurs. I found out that Collisu's first A was improved to other large widths.

This invention is the first of its kind to have the above-mentioned knowledge, and in the production of a voltage nonlinear resistor that also contains zinc oxide as a main component, zinc oxide powder, an aqueous metal salt solution of an additive, and a part of the additive are used. Voltage non-straight III comprising the step of homogenizing the mixed slurry containing the reaction precipitate by stirring or agitation, and immediately drying the mixed slurry into a fine solid to obtain the resistor raw material powder.
! i! 4F (in the antibody production method).

As a method for drying in a better mixed state, several methods using a spray dryer, fluidized bed/JLI heater, freeze dryer, etc. are preferably used, but any method is a method for rapid drying. is desirable. Here, a case where a spray dryer is used and a case where a freeze-drying method is used will be explained based on examples.

Example The case where a laboratory type spray dryer is used will be explained.

Nickel nitrate? , t g , cobalt nitrate 7, s;
1. Prepare a solution by dissolving chromium nitrate s,,zg and manganese nitrate 1g5y in lθθml of water, and mix this with 10θy
and zinc oxide powder to form a slurry. The obtained slurry is mixed for about 30 minutes using a stirrer or the like. Next, tartaric acid/3
1! and antimony oxide JZI were dissolved in 700 g of water and added to the slurry, and stirring was continued in the same manner.

Bismuth nitrate SSg in water/θrIIt and concentrated nitric acid lθm)
This solution is slowly added to the stirring slurry containing zinc oxide, etc.

After 1υ stirring for about 3 minutes, the slurry is sent from the liquid transfer pump of the spray dryer to start drying. In the present invention, as a matter of course, the slurry is constantly stirred during drying. FIG. 2 shows a schematic diagram of the two-fluid nozzle type commercially available spray dryer used.

Air heater7. Drying chamber, exhaust fan9. cyclo 7
/θ, compressor//, product container lλ and/,
Including 7th prize. The operating conditions in this experiment were: hot air inlet temperature 10°C, chamber exhaust air temperature 10°C, dry air amount 0. !
m"7 minutes, nozzle discharge pressure 3~, and liquid delivery amount lθml 7 minutes.

The unrecovered rate of the resistor raw material powder obtained was about 7θ%.

This powder is granulated using standard ceramic techniques.

After molding, it was fired. An aluminum electrode was formed by thermal spraying and the current-voltage characteristics were measured.

In addition, the case where the device was created using spray-dried powder is A.
As a sample, and as a comparative example, an element was prepared starting from a powder that had been dried in an oven, etc. by keeping the slurry still without spray drying, and a case where all oxide powder was used for the zinc oxide powder. Shown as sample C. Note that the manufacturing steps for samples A, B, and C are all the same except that the dry powder was not prepared.

The shrinkage percentage of the element obtained by firing at /jθ°C for a period of time is shown in the table below.

A element B element C element 35 (%), 2 pieces (%) tg (%) It is clear that the KA sample and the B sample shrunk more than the C sample, and the ceramic inside the element was caused by the addition of various salts in the form of an aqueous solution. It can be seen that the reactivity of various reactions in the production process has improved.

FIG. 3 shows the measurement results of the current-voltage characteristics of the three types of samples mentioned above. It can be seen that sample A exhibits the best characteristics in the entire current range, sample B has poorer characteristics in the low current region, and sample C has poorer characteristics in both the large current and small current regions.

Note that the fluidized bed dryer is similar to the spray dryer, and the current and voltage characteristics of the obtained devices were also similar.

Example λ A case will be described in which a method already known as the freeze-drying method is used. For example AJII, Ceram, sac
, BuJ, J.

This is the method described in S/Volume/S9 page (t? 7.2). A conceptual diagram of this method is shown in Figure 1.

The dryer in the figure uses, for example, dry ice, a cold agent/f using acetone, etc., and a hexane solution/jf.

It includes a stirring device such as a stirrer/6, a mixed slurry/7 containing all the additives such as various salts, zinc oxide, and bismuth compounds described in Example 1. Send nitrogen gas from the nozzle
Put the fine mist-like slurry from y into a hexane solution and freeze it instantly. The frozen slurry will accumulate at the bottom of the hexane solution, so collect it on a mesh and quickly dry it under reduced pressure. The degree of vacuum is about 10-'~/0-'wgH.

When we examine the current-voltage characteristics of a device made from the thus dried resistor raw material powder using the usual ceramic method as Sample D, we find that it has almost the same characteristics as Sample A shown in Figure 3. This was confirmed.

As mentioned above, 1. In order to increase the homogeneity of ceramics and improve current-voltage characteristics, slurry consisting of various ion aqueous solutions, bismuth autoprecipitates, and the king of zinc oxide is homogenized by stirring without leaving it still, and then finely dried and solidified. By manufacturing a voltage nonlinear resistor using this as a raw material, improvements in its characteristics were realized.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the fine structure of a voltage non-linear applied body, Fig. 2 is a schematic diagram of a spray dryer used in this invention, and Fig. 3 is a current/voltage diagram of devices manufactured by the method of this invention and the conventional method. The characteristic diagram, Figure q, is a schematic diagram of the freeze-drying method used in the present invention. In the figure, l...particles whose main component is zinc butyride, co...boundary layer whose main component is bismuth liquefaction, 3...spinel particles, da...
Sample slurry, 3. Slurry transport pump, 6. Nozzle, 7.
・Air heater, za...drying chamber, wa...exhaust fan, I
Q...Cyclone, //...Compressor, lj and 1
3.Product storage container, /Da.Dry ice-acetone (cold agent), lj.Hexane solution, /A.Stirring device, 17.Mixed slurry, /Ir..Nitrogen scum, /9.. Nozzle, -〇...insulation material. Agent Shin Kuzuno - yfE) Figure 1 Flame Figure 3 Denmaru (/cvlL&)

Claims (1)

[Scope of Claims] In the production of a voltage nonlinear resistor containing zinc oxide as a main component, a mixed slurry containing zinc oxide powder, an aqueous metal salt solution of an additive, and a reaction precipitate of a part of the additive is used. A method for manufacturing a voltage non-linear resistor, comprising the steps of homogenizing by stirring or agitation and immediately drying the mixed slurry into a fine solid to obtain the resistor raw material powder. (g) A method for manufacturing a voltage nonlinear resistor according to claim 1, which is performed by utilizing evaporation in a dry spray dryer or a fluidized bed heater. (3) The method for manufacturing a voltage nonlinear resistor according to claim 7, wherein drying is performed using sublimation in a freeze dryer.