WO1992000593A1 - Procede de fabrication d'un varistor d'oxyde metallique a capacite energetique amelioree - Google Patents

Procede de fabrication d'un varistor d'oxyde metallique a capacite energetique amelioree Download PDF

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Publication number
WO1992000593A1
WO1992000593A1 PCT/SE1991/000453 SE9100453W WO9200593A1 WO 1992000593 A1 WO1992000593 A1 WO 1992000593A1 SE 9100453 W SE9100453 W SE 9100453W WO 9200593 A1 WO9200593 A1 WO 9200593A1
Authority
WO
WIPO (PCT)
Prior art keywords
metal oxide
varistor
metallic salt
envelope
salt solution
Prior art date
Application number
PCT/SE1991/000453
Other languages
English (en)
Inventor
Teddy Boije
Paul Merkelbach
Ragnar Österlund
Original Assignee
Asea Brown Boveri Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asea Brown Boveri Ab filed Critical Asea Brown Boveri Ab
Publication of WO1992000593A1 publication Critical patent/WO1992000593A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
    • H01C7/102—Varistor boundary, e.g. surface layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
    • H01C7/105—Varistor cores
    • H01C7/108—Metal oxide

Definitions

  • the invention relates to a method of manufacturing a metal oxide varistor, the energy capability of which has been improved by arranging it such that the current displacement, which normally arises, especially in connection with high impulse currents, close to the edges of the electrodes is avoided. More particularly, the invention relates to a method of achieving a high resistance zone close to the envelope surface of a metal oxide varistor, thereby preventing the harmful effects which normally arise in connection with the above-mentioned current displacement.
  • Varistors comprising a body of metal oxide powder, preferably of zinc oxide, with or without stabilizing additives and with electrodes connected at the end surfaces are used because of their nonlinear, voltage-dependent resistivity in current-limiting applications such as, for example, surge diverters . It is known that, at high impulse currents, an increased current density is obtained close to the edges of the electrodes . To avoid this current dis ⁇ placement, which may lead to local overheating of the varis ⁇ tor close to the edge of the electrode and hence to break ⁇ down, it is known to prove the metal oxide varistor with a high resistance surface zone which comprises the region f close to the edge of the electrodes. In this way, the current displacement is prevented and the current is
  • the high resistance surface zone is achieved by applying a paste layer of a suitable material, for example Si ⁇ 2 , B2O3, Bi 2 ⁇ 3 , Sb 2 ⁇ 3 , In2 ⁇ 3 , or mixtures thereof, onto a metal oxide varistor, preferably a zinc oxide varistor. Thereafter, the varistor with the applied layer is sintered, thus obtaining a high resistance layer with a thickness of some 20 or 30 ⁇ m.
  • the high resistance layer is accomplished partly by diffusion from the applied layer into the metal oxide varistor, partly by the applied layer sintering to the metal oxide varistor.
  • a metal oxide varistor with a high resistance surface zone of 2-6 mm and hence improved energy capability is manufactured by supplying a metallic salt solution to the surface and causing it to penetrate into the metal oxide varistor so that a zone with enhanced resistivity is formed close to the surface of the metal oxide varistor during the final sintering.
  • a metal oxide varistor is formed from a metal oxide powder which is presintered at a low temperature, 400-600°C. The forming and the presintering are carried out such that a high porosity is formed. The pores are open, permitting the metallic salt solution supplied to the envelope surface, with tne aid of the capillary forces, to penetrate into the desired depth, 2-6 mm, in the metal oxide varistor.
  • the metallic salt solution may be supplied to the pre- sintered, porous metal oxide varistor by dipping, spraying, rolling, or in some other suitable way.
  • the depth of penetration and hence the amount of absorbed metallic salt and the thickness of the zone are controlled by the porosity of the varistor.
  • the porosity may be varied by the forming of the varistor and/or by varying the amount of organic additives. Since the forming of varistors preferably takes place by pressing, the porosity is varied by adapting the compacting pressure and the amount of added pressing aid.
  • the resistivity in the surface layer may be controlled by the choice of the metal included in the metallic salt as well as by the concentration of the metallic salt solution.
  • salt solutions are used in which the salt upon sintering is decomposed into a metal oxide and a volatile compound which escapes at the sintering temperature, for example solutions of nitrate, sulphate, or carbonate.
  • the salt solution is suitably prepared into a concentration of 10-80%, expressed as a percentage by weight, preferably 20- 60%.
  • a metal oxide powder substantially consisting of zinc oxide with the usual stabilizing additives and pressing aids, which is manufactured in a known manner, for example according to the description of European patent application EP 0029749, was pressed and presintered at 500°C into a cylindrical varistor body with a porosity of 30-50%.
  • a 25 per cent chromium nitrate solution was added to the envelope surface of the presintered porous body by spraying, whereupon sintering of the varistor body was completed at 1100-1300°C for 2-10 h. After the sintering, the two end surfaces were metallized in a known manner and the electrodes applied.
  • the ability to withstand repeated energy impulses with a * duration of 2 ms and an amplitude of 550 to 1200 A was con ⁇ siderably improved compared with corresponding varistor bodies to which no chromiun nitrate solution had been added.
  • the energy absorption capacity for blocks manufactured according to the invention was improved by 70-80% relative to blocks to which no chromium nitrate solution had been added. At the same time, the spread in the test result was considerably smaller for blocks manufactured according to the invention.
  • Presintered varistor bodies were manufactured in the same way as in Example 1 and a 50% magnesium nitrate solution was added to the bodies before the final sintering of the varis ⁇ tor in the same way as in Example 1. Also in this case, a considerable improvement of the ability to withstand repea ⁇ ted energy impulses was noted.
  • the energy absorption capacity for blocks manufactured according to the invention was improved by 20-30% relative to blocks to which no chromium nitrate solution had been added. At the same time, the spread in the test result was considerably smaller for blocks manufactured according to the invention.

Landscapes

  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
  • Apparatuses And Processes For Manufacturing Resistors (AREA)

Abstract

Procédé de production d'un varistor d'oxyde métallique à capacité énergétique améliorée. On dispose des électrodes en contact avec les surfaces d'extrémité du varistor, ces surfaces d'extrémité étant revêtues de métal. On apporte aux surfaces enveloppantes un matériau à résistance élevée pour former une zone à résistivité élevée à proximité de la surface enveloppante. D'après l'invention, on façonne une poudre d'oxyde métallique en corps cylindrique et on soumet celui-ci à un traitement thermique à 400-600 °C pour obtenir une porosité de 30-50 %, les pores proches des surfaces enveloppantes étant ouverts. On recouvre les surfaces enveloppantes d'une solution de sels métalliques par pulvérisation, trempage, peinture ou procédé équivalent. La solution de sels métalliques pénètre à une profondeur de 2-6 mm, et, ensuite, le corps du varistor, avec son apport de sels métalliques, est finalement fritté à 1100-1300 °C.
PCT/SE1991/000453 1990-06-28 1991-06-25 Procede de fabrication d'un varistor d'oxyde metallique a capacite energetique amelioree WO1992000593A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9002277-3 1990-06-28
SE9002277A SE466826B (sv) 1990-06-28 1990-06-28 Saett att framstaella en metalloxidvaristor med foerbaettrad energihaallfasthet

Publications (1)

Publication Number Publication Date
WO1992000593A1 true WO1992000593A1 (fr) 1992-01-09

Family

ID=20379886

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1991/000453 WO1992000593A1 (fr) 1990-06-28 1991-06-25 Procede de fabrication d'un varistor d'oxyde metallique a capacite energetique amelioree

Country Status (3)

Country Link
AU (1) AU8209991A (fr)
SE (1) SE466826B (fr)
WO (1) WO1992000593A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1244115A2 (fr) * 2001-03-20 2002-09-25 Abb Ab Procédé de fabrication d'une varistance à base d'oxide de métal

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5095007A (en) * 1990-10-24 1992-03-10 Ahluwalia Gurpreet S Alteration of rate and character of hair growth

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2365232B2 (de) * 1972-12-29 1977-12-08 Matsushita Electric Industrial Co, Ltd, Kadoma, Osaka (Japan) Verfahren zur herstellung eines aufgrund der zusammensetzung seiner masse selbst spannungsabhaengigen gesinterten widerstandes
EP0074177A2 (fr) * 1981-08-24 1983-03-16 General Electric Company Varistance en oxyde métallique à tension de claquage et capacité contrôlables
US4700169A (en) * 1984-03-29 1987-10-13 Kabushiki Kaisha Toshiba Zinc oxide varistor and method of making it

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2365232B2 (de) * 1972-12-29 1977-12-08 Matsushita Electric Industrial Co, Ltd, Kadoma, Osaka (Japan) Verfahren zur herstellung eines aufgrund der zusammensetzung seiner masse selbst spannungsabhaengigen gesinterten widerstandes
EP0074177A2 (fr) * 1981-08-24 1983-03-16 General Electric Company Varistance en oxyde métallique à tension de claquage et capacité contrôlables
US4700169A (en) * 1984-03-29 1987-10-13 Kabushiki Kaisha Toshiba Zinc oxide varistor and method of making it

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1244115A2 (fr) * 2001-03-20 2002-09-25 Abb Ab Procédé de fabrication d'une varistance à base d'oxide de métal
EP1244115A3 (fr) * 2001-03-20 2004-01-02 Abb Ab Procédé de fabrication d'une varistance à base d'oxide de métal

Also Published As

Publication number Publication date
SE9002277D0 (sv) 1990-06-28
SE9002277L (sv) 1991-12-29
SE466826B (sv) 1992-04-06
AU8209991A (en) 1992-01-23

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