JPS62158161A - Ceramic heating element - 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 [Field of Industrial Application] The present invention relates to a heating element made of oxide-based ceramic which has high strength and hardness and excellent wear resistance and corrosion resistance.

[Conventional technology]

Traditionally, metal heating elements such as nichrome and kanthal alloy, silicon carbide, and lanthanum chromite (LaC) have been used as heating elements.
Ceramic heating elements mainly composed of rOa) are known.

The former metal heating element cannot be used as a high-temperature heating element due to its heat resistance, and a ceramic heating element mainly made of silicon carbide or lanthanum chromite is used exclusively as a resistor for high-temperature heating.

However, such ceramic heating elements have the drawback of being relatively weak against thermal shock and having poor bondability with metal connections. Furthermore, since the ceramic heating element has a high specific resistance, it is difficult to use it at low voltage.

To address this issue, the applicant focused on alumina ceramics that are resistant to thermal shock, and used Mo2 as a conductive agent.
A heating element with improved resistivity by adding carbides such as C, ZrC, NbC, TaC, WC, and Cr2Ca was developed in JP-A-1988-
No. 127260.

[Problem that the invention seeks to solve]

However, since the terminals of such oxide-based ceramic heating elements have insufficient bonding properties with the electrodes, the contact resistance between the electrodes and the heating element increases, which may cause poor continuity or abnormal heat generation at the joints. In addition, since the carbide added as a conductivity imparting agent is easily oxidized, there is also a problem in oxidation resistance, which is a factor that shortens the life of the heating element itself.

The problem to be solved by the present invention is to create a stable heating element using an oxide ceramic heating element that has improved heat resistance and oxidation resistance as well as improved joints, and can be used even at low voltages. The goal is to establish its use as a

[Means for solving problems]

The present invention provides that the resistivity of the oxide ceramic sintered body, which is an insulating ceramic, can be controlled by controlling the addition of carbide, nitride, boride, or a composite thereof as a conductivity imparting agent, In addition, this heating element is based on the knowledge that even if the terminal portions are metallized after sintering, there is no adverse effect on the specific resistance of the heating element body, and a heating element with no change in contact resistance can be obtained.

Oxide ceramics include not only alumina but also single oxides such as zirconium oxide, magnesium oxide, chromium oxide, titanium oxide, and mullite.

Composite oxides such as zircon and spinel can be applied.

In addition, examples of the conductivity imparting agent include IVa in the periodic table.

At least one member selected from the group consisting of Va, VTa group carbides, nitrides, borides, or composites thereof,
Contain it as appropriate depending on the capacity of the heater.

As the content of these conductivity-imparting components increases, the electrical resistivity tends to decrease, but as the amount of carbides, nitrides, and borides that are difficult to sinter increases, the sintering temperature becomes higher (necessarily). This is not preferable because the crystal grain size becomes coarse, the strength decreases, and the incidence of coarse spots increases.

On the other hand, if the content of the conductivity imparting agent is too small, the specific resistance of the heating element, which is a sintered body, becomes too large, resulting in a
- Exceeds the mouth, making it unsuitable as a heating element.

These conductivity-imparting components need to be set in a range of 15.0 to 40.0% by volume. By adjusting these conductivity-imparting components within this range, the specific resistance of the sintered body can be arbitrarily adjusted as a heating element.

In addition, when adding the same amount of conductive agents, nitrides, borides, or their composites have lower specific resistance than carbides, and ceramic heating elements with excellent heat resistance and oxidation resistance can be produced. Obtainable.

In addition, the terminal portion of such a ceramic heating element can be subjected to metallization treatment without any effect on the specific resistance adjusted by blending the conductivity imparting agent.

The metallization treatment is performed by forming a first layer consisting of Ti, Cu, and Mn, and a Mo layer or a Ni plating layer on the first layer, and then, if necessary, applying a layer to the metallized portion. Terminals are formed by plating oxidation-resistant conductive material, Ag+Cu, Au, etc., or brazing Ag-W, Ag-WC, Cu-W with a composition similar to ceramic in the thermal expansion coefficient to the metallized part. do.

When manufacturing the main body heat generating part of the heat generating element of the present invention, what should be done? I
Even if gO or other known oxide-based sintering aids are added, sintering can be accelerated without affecting the specific resistance value of the heating element. Furthermore, by including such a sintering aid, a dense and homogeneous sintered body that is particularly desirable as a heating element can be obtained.

When producing the heating element of the present invention, various raw material powders having an average particle diameter of 3 μm or less, preferably 1.5 μm or less are blended in a predetermined amount, pulverized and mixed in a ball mill, and then dried and sized. Obtain raw material for sinterability.

Further, the conductivity-imparting components of carbides, nitrides, borides, and composites thereof are uniformly dispersed in the sintered body as particles with an average particle size of 3 μm or less, more preferably 1.5 μm or less,
In addition, conductivity can be obtained by blending at least an amount that forms a net structure, and the effect as a conductivity imparting component is exhibited.

For sintering, sintering is performed in a non-oxidizing atmosphere at a pressure of 10 kg/d or less, and the theoretical density is 95 in a non-oxidizing atmosphere.
% or more, then hot isostatic press (hereinafter referred to as 11P) method, 100-300 kg/
aI! Any sintering method can be applied, such as the method of true press sintering under the pressure of There is a need.

Furthermore, since the heating element of the present invention has high mechanical strength as well as thermal shock resistance, it can also be used as a thin plate-shaped heating element. Shaping and sintering of this heating element having a thin plate shape is performed by cutting a sheet manufactured by the doctor blade method to a predetermined size and then secretly sintering it while processing it into the desired shape, or by slip casting method to create a simple shape. It can be manufactured by making it into a curved shape or a complicated shape, or by canting an extruded round or square bar into a predetermined shape and sintering it.

Further, in the ceramic heating element of the present invention, the end portion of the heating element body is metallized for attachment of electrodes to improve electrical connection with the electrodes.

Various methods can be applied for this metallization treatment, but in particular Ti:Cu with Ti, Cu and Mn as essential components.
: Mn in weight ratio of 20-70:20-70, respectively
: Apply the mixture at a ratio of 2 to 20 to the end of the heating element body, place a 10 thin plate on top of it, fire it in a vacuum atmosphere, and bond it with the ceramic element at the same time, and further form a Ni plating layer. let Furthermore, if left as is, oxidation may occur in the metallized portion, and depending on the application, the metallized portion may be coated with an oxidation-resistant conductive material, Ag, or Cu.

It is preferable to plate with Au or the like or to braze a metal plate with good electrical conductivity.

The metal plate mentioned above should preferably have a component with a coefficient of thermal expansion close to that of the ceramic heating element, specifically Ag- or Ag-WC.
, Cu-W, etc., can prevent the ceramic heating element from cracking due to differences in thermal expansion coefficients.

〔Example〕

Example 1 Hachi1203 with a purity of 99.9% and an average particle size of 0.5 μm
and carbides, nitrides, and borides of groups rVa, Va, and Via of the periodic table with an average particle diameter of 2 μm or less as conductivity imparting agents, and composites thereof as sintering aids with an average particle diameter of 99.9%. 0.5 μm? A predetermined amount of IgO was weighed and mixed by pulverization in a wet ball mill for 20 hours at the mixing ratio shown in Table 1. This mixed powder is dried and sized into 50x50mm+
100 to 300 kg/filled at the optimum sintering temperature of 1350°C to 1800°C in a graphite mold with a height of 60 cm.
By applying a pressure of ad and holding it for 60 minutes, then removing the pressure and allowing it to cool, it becomes 50X5 with a theoretical density of 98.5% or more.
A sintered body of 0×5 mm was obtained. Each sintered body was cut and ground using a diamond grindstone to prepare each test piece, which was subjected to various tests. A specimen of 3 x 4 x 4Q*m ground with a diamond grinding wheel was used as a sample for physical property investigation, and a sample of 0-5 x 3 x 30 m was used as a heating element.
It was cut and ground on a thin plate of 500 m in diameter and used for testing.

The results of these tests are shown in Table 1.

Example 2 Among the samples shown in Example 1, materials corresponding to the various samples shown in Examples 2 to 15 were cut into a 5x1.0x50 plate shape, and the terminal portion was made of Ti: Cu: Mn
A paste mixture with a weight ratio of 45:45:10 was applied, dried, a 0.5 am thick Mn layer was placed on top of the paste, and the mixture was kept at 1300°C for 30 minutes in a 10-10-HH vacuum. The ends are metallized. Next, Ni plating with a thickness of 10 μm was applied to the top of the 1o layer. Furthermore, a terminal was formed by brazing Ag-W with a thickness of 1 inch on the top thereof.

As a result of raising the temperature of these heating elements with a voltage of 12 V, the temperature reached 500° C. or higher within 10 seconds.

As a result of using these as resin cutting heaters, there was no corrosion due to molten resin compared to metal heaters, and both were rated 3.
The lifespan was more than twice as long, and the power consumption was 40% or less.

Table 1 [Effects of the Invention] The heating element of the present invention has excellent strength, heat resistance, oxidation resistance, and corrosion resistance, has a relatively low specific resistance, and can be used at low voltage.

Furthermore, the bondability of the terminal connection portion is extremely good, and the contact resistance value is as low and stable as that of a metal heating element.

Therefore, the heating element according to the present invention is suitable as a heating element in all fields, such as heaters for hot air generators, various heating element elements for military use, heaters for heating furnaces, heaters for resin processing, heaters for textile processing, and for use in OA machines. Can be used for

Claims (1)

[Claims] 1. The heating element body contains 15.0 to 40.0% by volume of at least one member selected from the group consisting of carbides, nitrides, borides, and composites thereof of groups IVa, Va, and VIa of the periodic table. 1. A ceramic heating element comprising a sintered body of an oxide-based ceramic containing an oxide-based ceramic, and having a terminal portion which is metallized at the end of the heating element main body.