FR2641156A1 - - Google Patents

Abstract

High temperature heating element, method of manufacturing such an element and its application, in particular for incandescent spark plugs for the automotive industry. Heating element characterized in that it comprises a heating conductor 2 made of molybdenum disilicide with which, where appropriate, different amounts of material have been mixed in order to adjust the electrical resistance and / or to improve the adaptation of the thermal expansion coefficients.

Description

"High temperature heating element, method of

  manufacture of such an element and application of that

  The present invention relates to a high-temperature heating element comprising a support for the automotive industry.

  aluminum nitride to which a conductive

heater.

  The high temperature heating elements are used, as is known, in a very

  extended in the automotive industry for the manufacture of

  ceramic devices in particular.

  to bind incandescent candles or incandescent

  for example, using means to facilitate the

starting diesel engines.

  For example, according to DE-OS 12 483, a ceramic heating device is known.

  formed of a heating element and a sintered body

  placed with a mixture of MoSi2 powder and Si3N4 powder, a support in a sintered, ceramic, insulating element

  electrically as well as a feeding device

  electrical power. In the heating device, known, the heating element consists of a sintered body formed of a mixture of MoSi 2 powder and Si 3 N 4 powder, the average diameter of the Si 3 N 4 powder particles being

  greater than that of MoSi2 powder particles.

  DE-OS 33 42 753 also discloses a ceramic heating device used for example as an incandescent spark plug for diesel engines and for which a mixture of MoSi 2 and Si 3 N 4 is used for the production of the sintered parts of the engine.

  heating body made of ceramic material.

  DE-OS 30 11 297 also discloses high temperature heating elements formed of a silicon nitride ceramic body.

  (sialon) made of aluminum nitride and silicon carbide

  which is embedded in a metal body in the form of a plate or wire, the metal being

tungsten or molybdenum.

  According to DE-OS 33 35 144,

  an intake burner for an internal combustion engine

  dull having a heating installation formed of a tungsten heating resistor embedded in ceramic. The ceramic may be for example

silicon nitride (Si3N4).

  Furthermore, according to US Pat. No. 4,035,613, heating elements of cylindrical shape are known from

  refractory ceramic material such as aluminum oxide

  and a form of resistance applied to this element and giving off heat, this resistant element consisting of a conductive metal paste, for example a paste of

  molybdenum-manganese or tungsten paste.

  According to Japanese Patent Publication 54-

  109 536, there is also known a heating ceramic material for incandescent candles, this means being formed of platelets of ceramic material in

  discs on which are printed

  resistant molybdenum, tungsten or manganese

ganèse.

  Finally, according to DE-OS 33 07 109, an installation is known for injecting fuel into combustion chambers, in particular chambers of combustion.

  combustion of diesel engines, this installation com-

  taking an injector with downstream an incandescent element wetted by the jet of fuel thus injected;

  this incandescent element is provided on the front face

  it is located on the side of the combustion chamber of the injector and is surrounded by a channel with walls capable of being heated, to ensure the passage and partial evaporation of the fuel jet thus injected. The incandescent element can be in matter

  ceramic and the heating element can be a coating-

  metal coating applied to the surface of the material

ceramic.

  AlN ceramic supports are also generally known which are characterized by high thermal conductivity, good electrical insulation up to high temperatures, high hardness, good mechanical properties and good resistance to temperature variations, to be printed using the thick film technique

  using thick film pastes in the same way

  to the printing of ceramic supports.A1203.

  The disadvantage of the heating elements in

  known ceramic material is that it can not be

  permitted to very high temperatures because these elements are not sufficiently refractory, do not have sufficient resistance to temperature shocks and layers of heating conductors printed on the ceramic support do not hang well and / or can not be achieved inexpensively. The present invention proposes to remedy these drawbacks and for this purpose relates to a heating element at high temperature characterized in that

  includes a heating conductor in disilicide of

  lybdenum to which were mixed, where appropriate,

  different amounts of material to adjust the

  electrical resistance and / or to improve adaptation

  thermal expansion coefficients.

  The heating element according to the invention can be produced inexpensively thanks to the relatively inexpensive heating materials and

  can be used up to very high temperatures

  in the order of 1400 ° C; the disilicide of molybdenum

  not on aluminum nitride clings much better than on silicon nitride; a regular distribution of the temperature is achieved thanks to the good thermal conductivity of the support. In addition,

  the element is very resistant to thermal shock.

  The manufacture of a heating element

  high temperature according to the invention is preferably

  to be printed on an aluminum nitride support, according to the thick film technique,

  a heating conductor formed of a. disinfecting paste

  re molybdenum which may contain if necessary

  up to 40% by volume of material defining the

  electrical resistance and / or improving the adaptation of the coefficients of thermal expansion and in that the support thus printed is sintered at temperatures between 1600 ° C. and 1800 ° C. under an atmosphere

  of protective gas then let it age.

  The manufacture of a heating element

  high temperature according to the invention can be se-

  In another advantageous development, for example by printing on an aluminum nitride support, according to the thick-film technique, a heating conductor formed of a molybdenum disilicide paste.

  which may contain up to 40% in

  a material defining the electrical resistance and / or improving the adaptation of the coefficients of thermal expansion, and in that, on the aluminum nitride support having thus received an impression, at least one other nitride support is applied. a-luminium and sintered the supports thus combined into

  sandwich with the heating conductor, drowned.

  As an aluminum nitride support which can be printed using the thick film technique with a molybdenum disilicide paste, it is

  aluminum nitride sheets should be used

  which, with the exception of aluminum nitride,

  minium, contain binders that decompose or

  vaporize at the sintering temperature, that is,

  means AlN media, uncooked, pressed, or

sintered ports.

  The thickness of the aluminum nitride support

  nium can be variable; it is preferably between 0.3 and 3 mm, in particular between 0.5 and 2

mm.

  Where appropriate, the aluminum nitride supports may contain additives such as, for example, relatively small amounts of

  favoring sintering, for example Y203.

  The typical materials added to molybdenum disilicures to achieve a better

  electrical resistance and / or to improve the

  the coefficients of thermal expansion are

  aluminum oxide and aluminum nitride.

  A high temperature heating element according to the invention is used for the manufacture of

  heating devices of ceramic material corresponding

  to the most different types and the most variable applications. It is particularly important for the automotive industry, the heating element being used for the manufacture of incandescent candles, incandescent or other elements as well as

  intake burner, to facilitate, for example, the de-

  diesel engines. This means that one

  high temperature heating element according to the invention can be integrated into a fastening element of

  construction known usually and to be connected to a

  seems to power supply, generally-known.

  The manufacture of a heating element

  the temperature according to the invention is preferably

  on multipurpose machine. Advantageously

  the width of a heating element is included

  between 3 and 10 mm and the length between 10 and 50 mm.

  When the heating element according to the invention

  tion is applied to an incandescent candle it is

  preferably in the form of a pre-

  rotation symmetry and the conductive path

  in disilicide of molybdenum is printed on a

  massive aluminum nitride rod for example in ni-

  aluminum tress pressed hot or on a sheet

  rolled up to form a solid rod.

  In the case of an incandescent candle, the diameter of the heating element is advantageously between 3 and 6 mm, the protruding length of 10

  at 30 mm and the length of the rod between 20 and 60 mm.

  According to another characteristic of the invention

  The sintered material is aged by annealing.

under an oxidizing atmosphere.

  According to another characteristic of the invention

  The sintered material is annealed for about two hours under a N 2 atmosphere at 5 - 40% H 2

  temperatures between 1600 ° C and 1800 ° C.

  According to another characteristic of the invention

  tion, sintering is carried out for about two

  hours at a temperature of the order of 1600 to 1800C.

-2641156

  According to another characteristic of the invention

  tion, nitride support foils are used

aluminum or platelets.

  Drawings. The present invention will be described hereinafter in more detail with the aid of three exemplary embodiments of the invention shown in the accompanying drawings and described hereinafter. Thus: FIG. 1 shows a first embodiment of a heating element according to the invention

  formed of a relatively rigid AlN carrier sheet

  of. FIGS. 2a and 2b show a second exemplary embodiment of a heating element according to the invention comprising an AlN support sheet,

  flexible, represented in a simplified manner.

  - Figure 3 is a sectional view of an incandescent candle with a heating element according to the invention.

  Description of the exemplary embodiments.

  The high temperature heating element according to the invention, represented in a simplified manner and

  greatly enlarged in Figure 1, consists of a

  port 1, for example a commercial AlN sheet, having a thickness for example of 1 mm, on which was printed by screen printing, preferably by a

  printing by transparency or stamp, the conductor

  heater 2 as well as the contact surfaces 3a and 3b. In the example shown, the heating conductor has a meander shape. The heating conductor can however have any other shape. For printing, a molybdenum disilicide paste having the following composition was used: 69.8% by weight of commercial MoSi 2 powder 30.2% by weight of cutting oil 6.0% by weight of ethyl cellulose 79, 0% by weight of α-terpinol and 15.0% by weight of benzyl alcohol. On the support thus printed,

  after drying the layer forming the heating element

  fant, a second support 4, not printed, having substantially the same thickness, so that the contact surfaces 3a, 3b can not be covered. The supports thus joined were sintered at a pressure

  of 5 mbar at a temperature of 1600 ° C under an atmosphere of

  nitrogen sphere N2 containing 10% hydrogen H2

  during two hours. Support 4 served as protector

against oxidation.

  However, it was not possible to use

  printed medium 1 with support 4 if the support

  port 1 on which the driver was printed

  Fig. 2 was subjected to a protective gas atmosphere including forming gas for sintering at temperatures between 1600 ° C and 1800 ° C and then subjected to a pre-aging process. The process

  For example, pre-aging may consist of

  cook under oxidizing atmosphere the printed support and sintered for 2 to 6 hours. Such treatment results in the formation of a protective layer of SiO2 silica which protects the heating conductor, in a very

  to a large extent against oxidizing atmospheres and

  ductrices. Whether the printed support i is coated or not with a second support 4, in each case the heating conductors are strongly attached to the AlN supports

  on which they were made.

  The contact surfaces can be metal-

  in the usual way. For example, the contact between the heating conductor can be made using thick-layer pastes, which burn in the protective gas and which are based on Cu, Ni or Au or

  still by non-electrical separation of Ni or Cu.

  The heating element shown diagrammatically in FIGS. 2a and 2b differs from the heating element shown schematically in FIG. 1, mainly in that the AlN support is formed of a flexible, uncured AlN5 sheet. After printing the heating conductor 6 and the contact surfaces 7a and 7b, a layer of a thickness of about 25 μl of a paste of 25 μm was printed on the portion of the sheet 5 which carries the heating conductor 6. AlN powder and an organic binder for example

  ethylcellulose or α-terpinol or benzyl alcohol

lic.

  The printed medium as shown schematically

  Figure 2a has been rolled up to result in the shape shown in Figure 2b. The wound element

  was sintered for about 2 hours at a temperature of

  re in the range of 1600 to 1800 ° C. Then we metallized

the contact surfaces 7a and 7b.

  The incandescent candle shown in FIG. 3 mainly consists of a box or candle body 8, a heating element 9 formed of the aluminum nitride rod 10 on which the heating conductor 11 in molybdenum disilicide has been printed. of the bushing 12 (terminal -) brazed to the aluminum nitride rod 10, and through which the aluminum nitride rod 10 has been pressed into the body 8 of the spark plug; the spark plug also comprises the sleeve 13 soldered to the aluminum nitride rod (+ terminal) of the insulation 14 of the heating element 11 relative to the + terminal, of the insulating washer

  15, the circular nut 16 and the connecting pin are

17.

Claims (1)

1) High temperature heating element comprising an aluminum nitride support on which a heating conductor is applied, characterized in that it comprises a heating conductor (2) made of molybdenum disilicide. Various amounts of material have been mixed, if necessary, to adjust the electrical resistance and / or to improve the adaptation of the thermal expansion coefficients. 2e) high temperature heating element according to claim 1, characterized in that it comprises a heating conductor (2) molybdenum disilicide, printed on the support (1) according to the technique of thick layers, and if necessary, one or more materials have been added to adjust the electrical resistance and / or to improve the adaptation of the coefficients of thermal expansion, in quantities which, relative to the dough used for printing, go up to 40% by weight. 3 ') high temperature heating element according to any one of claims 1 and 2, characterized in that it consists of a heating conductor (2) formed of a mixture of molybdenum disilicide and aluminum oxide and / or aluminum nitride. 4 ') Process for the manufacture of a high temperature heating element according to any one of Claims 1 to 3, characterized in that an aluminum nitride support (1) is printed, according to technique of thick layers, a heating conductor (2) formed of a molybdenum disilicide paste optionally containing up to 40% in volume of material for adjusting the electrical resistance and / or improving the adapting the coefficients of thermal expansion and in that the printed medium is sintered at temperatures between 1600 ° C. and 1800 ° C. under a protective gas atmosphere, and is then aged. 5 ') Process according to claim 4, characterized in that the sintered material is aged by annealing under an oxidizing atmosphere. 6. Process according to claim 5, characterized in that the sintered material is annealed for about two hours under an atmosphere of N 2 at 5% H 2 at temperatures between 1600 ° C and 18 ° C.   7) Method for producing a heating element   at high temperature according to claims 1 to   3, characterized in that it prints on a support in   aluminum nitride (1), a heating element (2) forms   of a molybdenum disilicide paste according to   technique of thick layers, this paste containing   up to 40% by volume of material   to regulate the electrical resistance and / or improve the adaptation of the coefficients of thermal expansion and in that on the support thus printed in aluminum nitride, another support is also applied made of aluminum nitride and that we sinter the supports   sandwiched together with the interposition of heater.   8 ') Process according to claim 7, characterized   in that sintering is carried out during   two hours at a temperature of about 1600 to 1800C,   9 ') Process according to any one of the   Claims 4 to 8, characterized in that aluminum nitride support sheets or wafers are used. 10 ') Application of heating elements to   high temperature according to any of the claims   cations i to 3, for the production of heating devices of ceramic material including candles   incandescent and incandescent elements for the in-   automotive industry characterized in that the diameter of the heating element is advantageously between 3 and 6 mm, the projecting length of 10 to 30 mm and   the length of the rod between 20 and 60 mm.