JPS5810450B2 - Electrical contact material and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical contact material used for electrical contacts and a method for manufacturing the same.

It is an object of the present invention to provide a new and effective contact material for electrical contacts that exhibits desirable rapid resistance to arc extinguishing characteristics, has relatively low contact resistance, and is simple to manufacture.

The present invention provides a mixture of silver and up to 3% by weight of at least one substance selected from the group consisting of tellurium or tellurium and lithium.

According to a feature of the invention, there is provided an electrical contact material containing 2.5 to 20% by weight cadmium oxide as outlined above.

The present invention also includes a step of preparing irregular silver powder having a particle size of about 350 mesh or less, a step of preparing a coprecipitated cadmium-tellurium powder having a particle size of about 75 microns or less, and mixing the silver powder and cadmium-tellurium powder. a step of heating the mixed powder in a reducing atmosphere to form a silver-cadmium alloy powder in which cadmium telluride is dispersed on the surface of the alloy powder particles; and a step of internally oxidizing the alloy powder. a step of reoxidizing cadmium and cadmium telluride, a step of sieving the reoxidized alloy powder to reduce the powder particle size to 100 mesh or less, a step of compressing the alloy powder into a desired shape, and a step of sintering the compacted compact. Provided is a method of manufacturing an electrical contact material including the following.

According to a feature of the invention, before the sieving step, a lithium compound solution of up to 3% by weight is added to the alloy powder to form a slurry, and the solution concentration is adjusted so that substantially equal volumes of liquid and powder are mixed. air drying the slurry at high temperatures; and heating the dry powder in air to decompose the lithium compounds thereby forming lithium oxide particles on the surface of the alloy powder particles. There is provided a method comprising the foregoing.

The foregoing and other features according to the invention will be better understood from the following specific embodiments of the invention.

The electrical contact material according to the invention, which is particularly suitable for low-duty media, consists of a mixture of silver and tellurium or tellurium and lithium in an amount of up to 3% by weight.

The amount of tellurium or tellurium and lithium added is preferably in the range of 0.01 to 1.5% by weight.

Therefore, silver forms the majority of the contact material and it is necessary that the contact material be manufactured such that the additional material is uniformly dispersed within the matrix material.

The particle size of the silver powder is preferably 350 mesh or less.

This is to increase the ratio of surface area to volume to facilitate alloying and internal oxidation.

Lithium and tellurium can be added to the matrix alone or together.

Lithium, a low work related material, reduces the electronic work function of the contact material at discrete locations within the contact material, resulting in propagation of arc corrosion when contact is established between electrical contacts.

This low work function material also reduces the arc voltage when the contact between electrical contacts is broken and causes weld embrittlement.
This results in the breakdown of the weld that is formed when contact is established between the electrical contacts.

Tellurium causes embrittlement of the silver matrix, particularly of the grain boundaries, thereby promoting failure of the weld formed when contact is established between electrical contacts.

However, if tellurium is not used in an amount of 3% by weight or less,
This is preferable because the matrix embrittlement effect is too large.

Also, arc corrosion is improved when lithium is used as a partial substitute for tellurium at the same time as tellurium, but its content is 3.
% by weight or less.

Cadmium oxide in the aforementioned steel-based electrical contact materials can be added to concentrations of 2.5 to 20% by weight.

Cadmium oxide is susceptible to formation when contact is established between electrical contacts, resulting in embrittlement of the weld, and cadmium still present in the sterilizing arc will destroy the contact between electrical contacts made from this silver-based material. The steam acts to lower the average electron energy in the arc, change the electron energy distribution in the arc, and remove high-energy electrons.

Cadmium oxide is added to suppress arc discharge and increase welding resistance, but if the amount exceeds 20% by weight, it is not preferable for practical use because the contact becomes too brittle.

The aforementioned lithium-containing electrical contact materials are particularly used in the manufacture of electrical contacts used for the switching of arbitrary loads, often, but not necessarily, capacitive loads, but also in fact eliminating contact closure.

When the electrical contacts used in these switch applications are made of pure materials or alloys of elements with the same electronic work function, contact closure discharge occurs between the points most protruding from the contact surface, and the actual discharge The position is largely controlled by the distribution of the cathode contacts.

The actual initiation of discharge is accompanied by field electron emission from the protruding end when the contact is closed.

The protruding end severely deforms the electric field in its vicinity, increasing the electric field value to a value at which electron emission occurs.

Damage and roughening of the contact surface occurs in the area where each discharge occurs, resulting in a higher protrusion in that area, so that subsequent discharges are more likely to occur in the same area, resulting in A Excessive corrosion occurs in the case of the , switch, and mass transfer occurs in the case of the , switch, resulting in pips and craters in the latter case, resulting in the contacts sticking together.

This corrosion concentration in the contact surface area is prevented by the lithium-containing electrical contact material according to the invention, in which the low electron work function material lithium, homogeneously distributed within the contact material, alternates against arc initiation. This is because it provides a mechanism.

This is because electrons are much more easily released by this low electron work function material at low field strengths compared to the high electron work function material silver.

Therefore, the location of the low electronic work function material in the silver contact material acts just like a protrusion in the pure material or alloy with respect to electron emission.

These two processes therefore compete with each other during contact use.

In fact, the highest protrusion containing lithium sites provides the arc starting electrons.

The resulting discharge destroys the initial shape of the protrusion and roughens its surrounding area, but the lithium locations are completely destroyed and removed.

The subsequent discharge is therefore initiated from the next highest protrusion containing the lithium site, and so on.

Therefore, in the case of known materials, the lithium is well dispersed in the contact material so that corrosion is sufficient to form on the contact surfaces, and when these corroded surfaces are removed, an undesired concentration in one area then occurs. In contrast, it spreads to a considerable extent in the bulk of the contact material.

Furthermore, lithium is very easily ionized during discharge and easily excited to an optical state that results in photon emission.

Therefore, the addition of lithium to an electrical contact material significantly increases the tendency for inelastic collisions of electrons to occur in an arc initiated between electrons, resulting in a significant decrease in the average electron energy and the relative number of high-energy electrons.

Therefore, electron bombardment of the contacts is less intense at lower heating, reducing volatilization and corrosion.

This advantageous effect occurs both in the case of an arc that occurs when the contacts are closed, and also for the arc that occurs when the contacts are opened.

The production of electrical contact materials consisting of silver, cadmium oxide and tellurium is best carried out by powder metallurgy techniques, and to achieve a completely homogeneous dispersion of tellurium in the contact material, tellurium is chemically co-precipitated with cadmium. It is best added in the form of a compound.

A co-precipitated compound of cadmium and tellurium is produced by a) carefully dissolving the required amount of cadmium oxide and tellurium oxide powder in hot concentrated nitric acid using the minimum necessary amount of acid, and b) heating the above solution to dissolve the oxides. c) precipitating the insoluble cadmium-tellurium compound from the solution using a sodium carbonate solution in a known manner; d) settling the fine white precipitate formed and precipitating it with distilled water. e) washing the precipitate on the filter bed with distilled water and acetone and then drying the mouth liquid in an air oven at 60°C; f) passing the precipitate into a suitable Cadmium oxide and cadmium and tellurium are decomposed by heating in a container at about 450° C. for about 2 hours in a furnace operated in air (the temperature of the furnace is raised to the above level in about 1 hour), and cadmium oxide and cadmium and tellurium are a process of producing a finely divided powder mixture of mixed oxides in which the oxides of
At this time, the color of the powder mixture is at a low tellurium level, i.e. 0.01
range from chocolate brown to orange at high tellurium levels, i.e. 1.5% by weight; g) Re-washing the decomposed precipitate to remove traces of sodium impurities and drying the washed precipitate at approximately 100°C a drying step, during which the color of the precipitate changes to light yellow during washing and drying due to water conservation, and h) the washed decomposed precipitate is recalcined in air at about 450°C for about 2 hours to obtain hydration water. It can be obtained by a method including a step of removing.

The resulting co-precipitated powder, in which cadmium and tellurium are completely and uniformly dispersed in precisely known amounts, is sieved through a 75 micron screen and used to make silver-cadmium oxide-tellurium contact materials.

Commercially available cadmium oxide and tellurium oxide powders with a minimum analysis value of 99% can be used to prepare the co-precipitated compounds; a common commercially available cadmium oxide material is "reagent grade" cadmium oxide powder manufactured by Hopkins and Williams Limited. It is.

The cadmium oxide powder, which is produced by burning cadmium and condensing the smoke produced by the combustion, is cubic and has a particle size of less than 1 micron.

According to chemical analysis, the powder has the following composition: Cadmium oxide (as CdO) min. 99.0
% chloride (ct) up to 0',
005% sulfate (SO4) max. 0.005
% Iron (Fe) Maximum 0.001% Potassium (K) Maximum 0.002% Sodium (Na) Maximum 0.01% Small amounts of additional substances C1, SO4, Fe, and Na are made from materials containing this CaO powder. It was found that there was no significant effect on the performance of the electrical contacts.

. Commercially available powders need to be stored clean and dry to prevent moisture absorption.

The powder can be stored using a desiccator.

Therefore, in the method for producing a silver-cadmium oxide-tellurium electrical contact material according to the present invention, irregular silver is used.

The powder is intimately mixed with the co-precipitated cadmium-tellurium powder in the desired proportions, diluted if necessary with cadmium oxide powder, such as the commercially available cadmium oxide powder described above.

The size and shape of the powder particles are of paramount importance in the production of optimal silver-based contact materials, and economically it is preferred that they be as fine as possible.

For this purpose, irregular silver powder with a particle size of less than 350 meshes and cadmium-tellurium powder with a particle size of less than 75 microns are used.

The use of fine powders results in fine, homogeneously dispersed substance mixtures as electrical contact materials produced.

A common commercially available silver material that can be used is "Sesco" silver powder manufactured by Sheffield Smelting Company, a subsidiary of Angel Bird Industries.

This silver powder, which is a commercially pure precipitated powder, has an irregular shape, a particle size of less than 300 mesh, and an apparent density of 1.9 g/c.
It is a powder particle of c.

This material also has (I) a geometric mean linear intercept of 17.8 microns (standard deviation 2.0) and (
11) Geometric mean linear intercept of the polished area is 4.1 microns (standard deviation 2.0).

This commercially available silver powder is sieved to remove powder grains of 350 mesh or more before use in the method according to the invention.

Of note, this commercial material must be stored clean and dry to prevent moisture absorption, contamination, and surface corrosion.

Powder storage can be carried out, for example, using a desiccator.

Intimate mixing of the component powders can be achieved by dry tumble milling.

In order to mix these powders by dry tumble milling, it is important to observe the following conditions: a) The component powders must have the aforementioned particle sizes.

b) The powder needs to be stored in a desiccator or by other means to prevent moisture absorption and surface corrosion.

c) The mixing amount is maximum 50 g, the actual mixing time depends on the particle size of the mixture.

d) Cadmium oxide composition is 2.5 to 20% by weight.

e) The volume of the drum is approximately 2 to 10 times the volume of the mixed powder so as not to restrict the movement of the powder.

f) The relative humidity inside the drum is between 0 and 70%, and the humidity inside the drum is between 10 and 30°C.

g) The rotational speed of the drum is such that the powder moves continuously during mixing.

Increasing the rotational speed of the drum reduces the time required to achieve good mixing and reduces the tendency of the oxide to agglomerate.

However, when the rotational speed becomes excessive, mixing is hindered due to the influence of centrifugal forces.

h) The powder mixing time generally depends on the cadmium oxide content of the powder mixture, the higher the cadmium oxide content, the longer the mixing time.

For example, for a cadmium oxide content of 2.5% by weight, the mixing time is around 12 hours, while for a cadmium oxide content of 10% by weight.
Alternatively, at 15% by weight, the mixing time is about 24 hours.

Using substantially shorter mixing times than those described above, especially for powders with high moisture content, results in incomplete breakdown of agglomerates in the oxide powder.

On the other hand, excessive continuous mixing times, especially under humid conditions, for example well over 100 hours, tend to degrade mixing due to the growth of cadmium oxide aggregates.

It should be noted, however, that the most important variable in finely and uniformly dispersing cadmium oxide and tellurium in the contact material is the absolute and relative dimensions of the component powder particles, and the optimal mixing plan is largely determined by this factor. be done.

The general mixing conditions for the powder with a mixing volume of 50 to 1000 g and a cadmium oxide composition of 2.5 to 15% by weight are as follows: a) The drum volume was about 2 to 10 times the volume of the mixed powder. .

b) Mixing was carried out at 20°C (range 17-23°C) at a relative temperature of approximately 60% (range 45-65%).

c) The drum rotated at 160r,p,m.

d) Mixing time was 24 hours.

It has been found that these mixing conditions result in a homogeneously mixed composite powder with the particular powder used.

If the cadmium oxide component has an excess of moisture and a consequent tendency to agglomerate, it is necessary to pass the powder through a 350 mesh sieve after the 24 hour tampling operation and then subject the sieved powder mixture to a further 24 hour tampling operation.

After mixing, the powder is placed in a suitable flat container, such as a quartz tray, to a depth of 1 cm or less, and then heated to 200-700° C. in a hydrogen atmosphere.

At all points in this temperature range, the hydrogen reduces the cadmium oxide to cadmium, which diffuses into the pot to form a silver-cadmium alloy powder, with very fine cadmium telluride particles on the surface of the alloy powder particles. distributed.

At temperatures above 321° C., cadmium is in a liquid state, and homogenization of the alloy is accompanied by a liquid phase mechanism.

The final stage of homogenization involves a solid state diffusion step.

Sintering of the alloy particles also occurs, but should be avoided as much as possible.

However, the sintering is loose and easily destroyed by sieving.

The presence of submicron telluride particles makes it very easy to break the loosely sintered product into powder, especially when the tellurium content is above about 0.2% by weight.

After sieving through a 500 μm screen, the alloy is in the form of small agglomerates.

A temperature of 400° C. is suitable for the reduction step, while avoiding excessive sintering as well as cadmium loss due to volatilization.

The temperature of 400°C should be maintained for 1 hour and the mixed powder is brought to this temperature at a rate of 200°C/hour.

The reduction process can be made continuous by using a belt furnace.

In such cases, an automatic mixing sieve device can be used.

Next, the sieved alloy powder is internally oxidized to reoxidize the cadmium and fine cadmium telluride particles, converting the cadmium to cadmium oxide and the fine cadmium telluride particles to a composite oxide containing cadmium and tellurium.

This can be done by passing the powder through a belt furnace under subatmospheric, subatmospheric or superatmospheric pressure in a suitable oxidizing atmosphere such as air or oxygen.

The temperature can range from 350°C to the melting point of the alloy, but the preferred temperature is 600°C.

The oxidation time depends on the oxygen partial pressure of the furnace atmosphere used, the cadmium content of the alloy, the operating temperature, and the size of the alloy powder grains.

These factors can be calculated by known methods, taking into account the fact that the alloy powder produced by the method of the invention is finer than conventional alloy powders.

The internally oxidized alloy powder is then sieved to a fineness suitable for subsequent use.

When the material is sieved to less than 100 mesh, the powder has an apparent density of about 15% of the theoretical density and has good flow properties.

The reason why the final particle size is 100 mesh or less is to provide sufficient surface area for rapid sintering of the high-density material.

The alloy powder is then compacted using a mold at a compression rate of 40 tons per square inch to form the desired shape, such as the electrical contact to be manufactured.

The compression molded body is heated for 600 minutes in air, oxygen or inert atmosphere.
℃ to the melting point of the substance (960.5°C), but a temperature of 930°C is preferred.

Sintering times ranging from a few minutes to 24 hours or more can be used, with 1 to 2 hours being preferred.

The density of the contact material can be increased if necessary by a stamping or coining operation at a pressure of 45 tons per square inch.

The following electrical contact materials were manufactured using a co-precipitated compound of cadmium and tellurium.

The powder mixture used to generate the coprecipitated compound was 55.009
cdo10.313gTeO2 and 55. OOgcd
o/9.381gTeO2.

Ag-11 wt% CdO-0,01 wt% TeAg-1
1% by weight CdO - 0,05% by weight TeAg - 11% by weight CdO - 0,25% by weight TeAg - 11% by weight CdO
- 1,50% Te by weight All of the above materials were subjected to weld resistance tests to measure the weld strength distribution and average weld strength between dome contacts closing at 70 cIrL/sec while capacitive discharge was applied at a peak current of 950 Amps. .

During these tests contact bounce was reduced to less than 0.2 milliseconds.

Materials containing 0.25 and 1.50 wt.% tellurium (Te) showed significant improvement in weld resistance compared to Ag-11 wt.% CdO without Te, and the average weld strength was lower than that of these two tellurium-containing materials. is about 1 magnitude lower than that of materials that do not contain tellurium.

Materials containing 0.05 and 0.01 wt% Te also showed improved weld resistance, albeit to a lesser extent, compared to the tellurium-containing strong materials.

The silver-cadmium oxide-lithium-tellurium electrical contact material was manufactured using the internally oxidized silver-cadmium oxide-tellurium alloy powder (tellurium is combined with cadmium and exists as a composite oxide) prepared as described above. This can be done by powder metallurgy.

A lithium compound solution of up to 3% by weight is added to this powder mixture to form a slurry.

The concentration of the solution is adjusted so that equal volumes of liquid and powder are mixed to form a slurry.

Preferably, the lithium compound is added to the powder mixture as a propatool solution.

This alcohol base aids in wetting the powder compared to water,
Makes drying easier.

The slurry is then dried in air at about 60° C. to obtain an internally oxidized silver-cadmium-tellurium alloy powder with small crystals of lithium compounds unevenly formed on the powder particle surface.

The dry powder mixture is then sieved to reduce the powder particle size to less than 100 mesh.

This sieving operation effectively destroys large cakes that may form during the slurry drying process.

The lithium compound, preferably lithium nitrate, is then decomposed by passing the dry powder mixture into a suitable flat container, such as a quartz tray, to a depth of less than 1 cIrL in air and through a belt furnace operated at 700°C. The powder mixture, which splits about 15 times to pass through the furnace, is held at this temperature for about 2 minutes.

It has been found that for materials containing 0.01% by weight or more of lithium, it is necessary to pass the powder mixture through the furnace multiple times in order to completely decompose the lithium compound.

The obtained powder material consists of a silver-cadmium oxide-tellurium alloy powder in which lithium oxide particles are dispersed on the surface of the powder particles and internally oxidized.

The characteristics of the electrical contacts made from this AgCd0+Te+Li material are that the addition of lithium, especially at a low lithium concentration of 0.01% by weight, improves the corrosion rate.
The characteristics are virtually identical to those of electrical contacts made from +Te material.

The specific embodiments and examples of the invention described above are merely illustrative and do not limit the scope of the invention.

Claims (1)

Claims: 1. Silver, consisting of a mixture of 2.5-20% by weight of cadmium oxide in the form of homogeneously distributed silver-cadmium oxide alloy particles and 0.01-3% by weight of tellurium in the form of its oxide. . An electrical contact material, wherein the tellurium oxide is present on the surface of the silver-cadmium oxide alloy particles and is uniformly distributed throughout the contact material. 2 silver, consisting of a mixture of 2.5-20% by weight of cadmium oxide in the form of homogeneously distributed silver-cadmium oxide alloy particles and a total of 0.01-3% by weight of tellurium and lithium in the form of oxides, An electrical contact material characterized in that the tellurium and lithium oxides are present on the surface of the silver-cadmium oxide alloy particles and are uniformly distributed throughout the contact material. 3 Prepare irregular silver powder with a particle size of 350 mesh or less;
Co-precipitated cadmium-tellurium compound powder of about 75 microns or less is prepared; the silver powder and the cadmium-containing powder are thoroughly mixed with 2.5 to 20% by weight of cadmium oxide and 3% by weight or less of tellurium to form a fine powder. forming a uniformly dispersed mixture; heating this powder mixture in a reducing atmosphere to form a silver-cadmium alloy powder in which fine cadmium telluride particles are dispersed on the surface of the silver-cadmium alloy powder terminal; this alloy powder; internally oxidize to reoxidize cadmium and cadmium telluride; sieve the reoxidized alloy powder to a particle size of 100 mesh or less; compress this powder mixture into a desired shape; compress the compact in air. A method for producing an electrical contact material, characterized by various steps of sintering. 4 Prepare irregular silver powder with a particle size of 350 mesh or less;
Co-precipitated cadmium-tellurium compound powder having a particle size of about 75 microns or less is prepared; the silver powder and the cadmium-containing powder are mixed with 2.5 to 20% by weight of cadmium oxide and 3% by weight of tellurium.
Mix to obtain a fine and uniformly dispersed mixture by weight% or less; heat this powder mixture in a reducing atmosphere to form fine cadmium telluride particles dispersed on the surface of the silver-cadmium alloy powder particles. A silver-cadmium alloy powder is formed, and the alloy powder is internally oxidized to reoxidize cadmium and cadmium telluride; adding a solution containing an amount of a lithium compound to form a slurry, adjusting the concentration of the solution to mix substantially equal volumes of liquid and powder; air drying the slurry at an elevated temperature; and drying. The powder is heated in air to decompose the lithium compounds, thereby forming particles in the form of oxides of lithium on the alloy powder particles; the powder mixture is sieved to reduce the particle size to 1.
00 mesh or less; compressing the powder mixture into a desired shape; and sintering the compressed compact in air.