FR2498503A1 - - Google Patents

Abstract

PROCESS FOR COMBINING SILICON CARBIDE PARTS OBTAINED BY REACTION-FRITTING AND METAL PARTS; THE SILICON CARBIDE PART 1 IS FIXED ON THE METAL PART 2 USING A BINDER 3 CONSTITUTED BY SILICON AND A METAL, THE JOINT BEING THEN HEATED.

Description

Process To join pieces of silicon carbide obtained by

  frittaae-reaction and pieces of iron or other metal, as well as an ionization electrode manufactured according to this process.

  The invention relates to a method for joining parts

  these silicon carbide obtained by sintering-reaction

  and pieces of iron or other metal.

  The contact meeting of ceramic semiconductor elements of the silicon carbide type has always been

  problematic. Among the processes known for carrying out

  tion of electrical and mechanical transitions we can

  cite metal-to-metal bonds by projection of mete

  rates melted in a flame or by withdrawal. During the u

  use of high temperatures, for example

  erasures between 600-700OC, the molten metal projected by the flame can be eliminated by burning, and other bonds, such as metal bonds on metal by shrinkage, are unstable mechanically by

  following significant thermal effects.

  The invention proposes to provide a method for establishing a secure and heat-resistant connection between metal parts and silicon carbide parts. According to the invention, the piece of silicon carbide is fixed to the piece of iron or other metal using a

  binder consisting of silicon and a metal, then in heating

fant the bond.

  Preferably, the binder is a eutectic mixture of silicon and the metal used, for example iron. As a result, a thermally stable electrical and mechanical connection is obtained between the carbide part of

silicon and the iron part.

  The use of an ionization electrode is known for controlling the flame of oil or gas burners. Such electrodes are based on the known principle that the electrode, for example an iron electrode, is brought into the flame region, which has the effect that the flame ionizes the path between the arrival of -2- fuel from the burner and the electrode so it

  can circulate an electric current. In the case of burn-

  their blue flame emitting no visible light

  ble, an ultraviolet detector was used. However, such a detector is not often usable, for example when the burner is surrounded by a recirculation chamber. In such burners,

  therefore an ionization electrode which however

  given the disadvantage that the material degrades, this is why it has a relatively short lifespan due to the very high temperature of the flame, which typically in blue flame burners is

  in the range from 1400 to 15000C.

  The invention therefore further proposes to provide a

  more resistant electrode. This is obtained according to the in-

  vention thanks to the fact that the electrode has the shape of a rod and that at least the part of the rod which penetrates into the flame is constituted by a semiconductor material of carbide of

  silicon obtained by reaction-sintering.

  Advantageously, the semiconductor material extends over a length such that the connection with the metal part is substantially outside

  of the flame region. Taking into account the fragile-

  the electrode block, the electrode should be as short as possible. On the other hand, the high temperature poses problems with regard to the attachment to the metal part of the electrode. Even outside the flame the bond is subjected to a temperature

  high of about 600-7000C. In the case of such temperatures

  erasures, the following method can be used in particular

  vant the invention to join the metal part of

  the ionization electrode and the carbide rod

  cium. By fixing the end of the electrode to the metal part according to the invention, that is to say using

  a binder consisting of silicon and iron, pre-

  ferect a eutectic mixture of silicon and iron, a resistant electrode is obtained. The eutectic system -3- binds to the silicon carbide rod as well as

the iron piece.

  The link as such can be obtained

  thanks to the fact that the silicon carbide rod is placed

  created in an iron rod recess, that a mixture of silicon powder and iron powder is placed in

  the space between the carbide rod

  cium and the iron rod, and that the part is then heated to more than 12000C. One can use for example a 1/1 ratio for the mixture. Thereby the powder of

  silicon and iron powder form a eutecti mixture, -

  that that binds with the silicon carbide rod and the

iron piece.

  If necessary, the metal part agglomerated by sintering can completely surround the rod with silicon carbide. As a result, a mechanically stable part is obtained which is easy to handle because the sintered envelope protects the somewhat fragile silicon carbide ceramic rod. The part of the sintered metal part which is subjected to the action of the flame is naturally degraded, but it remains

  however a part which surrounds the stable rod in car-

  silicon bure in the region a little far from the flame where the temperature is only 700-8000C. Therefore, only the part which is directly in the high temperature part of the flame is attacked

by corrosion.

  In addition, the metal electrode may include

  a weakened area outside the sintered part.

  This makes it possible to give the fragile end, located furthest to the outside of the electrode, an inclination by

  relative to the rest of the electrode, in a position

  hated, without damaging this part.

  According to another embodiment, a metal body

  lique is threaded on at least the end of the silicon carbide rod and the two parts are joined by sintering by bringing them to a temperature of 11000C. The sintering causes a certain shrinkage, while in the transition region an intimate mechanical and electrical connection is obtained which also resists in the case of high temperatures. If in this case also the temperature is brought above 1200WC, we obtain a eutectic system which gives a further transition

  more stable and good electrical contact.

  The part thus produced is brazed, welded or fixed

  in another way the parts of the electrode move away

gaining from the flame area.

  Preferably, the agglomeration by sintering of the

  metal part is carried out with simultaneous compaction

  born, possibly isostatic compaction. This gives a very compact transition surface and

  solid of the metal part agglomerated by sintering.

  The present invention will be better understood using

  of the following description of several embodiments

  preferred but nonlimiting sation shown in the accompanying drawings in which Figure 1 shows an ionization electrode comprising a rod of silicon carbide, housed in an iron mount;

  FIG. 2 represents the finished electrode manufactured

  quée following the process illustrated in Figure 1; FIG. 3 represents an ionization probe in which the silicon carbide rod is completely surrounded by a metallic material agglomerated by sintering; Figures 4 and 5 show the probe of Figure 3 after some use; and FIG. 6 represents two examples a and b of a rod of silicon carbide provided with a metal part

  agglomerated by sintering and having undergone a shrinkage.

  A silicon carbide ceramic rod is made

  briquetted in a known manner, preferably by sintering-

  reaction of a mixture of silicon carbide (SiC) and graphite with silicon (Si) liquid at high temperature, the free graphite reacting with silicon -5- to give silicon carbide. Figure 1 illustrates how such a piece of silicon carbide 1

  according to the invention can be combined with an electrical part

  metal trode 2 made of iron. The silicon carbide rod is placed in a bore 7 made in the iron rod. The intermediate space between the bore and the rod is filled with a mixture 3 of silicon powder and iron, for example in a 1/1 ratio. Instead, a powder of an already prepared mixture of silicon and iron, for example a eutectic mixture, can be placed in the intermediate space. The whole part with the ceramic rod is now heated above 1200WC where the powder mixture forms a eutectic system and binds both to the silicon carbide rod and to the iron. As a binder, other metallic compounds can also be used, for example a mixture of silicon

and nickel.

  FIG. 2 represents the completed electrode 1, 2, manufactured according to the method of FIG. 1. The iron part 2 integral with the silicon carbide rod is a connecting piece which can now be fixed from

  desired way on the rest 4 of the electrode rod 5.

  FIG. 3 illustrates a process in which iron powder is compacted around a rod of silicon carbide, for example by isostatic compacting, that is to say by compacting with an identical pressure on all sides. Then the whole part is brought to around 12000C, preferably beyond 1200-12201C, to

  after which the iron powder is sintered and simulated

  the silicon in the silicon carbide rod diffuses into the iron powder and a molten mass is formed (eutectic system) which forms a thermally stable mechanical and electrical connection

  between the silicon carbide rod and the iron powder.

  Such an electrode is more robust and better supports transport and handling than the rod following the

Figures 1 or 2.

  -6- As seen in Figures 4 and 5, the part

  of the metal sleeve which penetrates into the dispa-

  rait slowly by corrosion and only the rod remains

stable in silicon carbide.

  In FIG. 4 we can also see how the rod 4 can be fitted behind the connecting piece 2 of the

  ceramic rod in silicon carbide 1, of weakened zones

  - blies 6 which can for example extend as desired either over the entire periphery of the rod or only over

  part of the perimeter. It thus becomes possible to adapt-

  ter the inclination of the silicon carbide rod relative to the rest of the electrode, by simple manual bending at the weakened zone, under existing conditions, without damaging the outer ceramic part

  brittle. Other embodiments of the electrode may

  They may also have such a weakened area.

  FIG. 6 represents, in two embodiments,

  tion a and b, how a metal part 8, here an annular part, can undergo a withdrawal on the rod in

  silicon carbide and be sintered.

  Many other embodiments and methods

  for compaction and sintering of parts are approxi-

  sageable and applicable according to the present invention.

-7-

Claims (9)

Claims   1. Method for joining carbide parts of si-   silicon obtained by reaction sintering and pieces of iron or other metal, characterized in that the piece of silicon carbide (1) is fixed to the piece of iron or other metal (2) using a binder ( 3) consisting of silicon and a metal, and the bond is then heated. 2. Method according to claim 1, characterized in that the binder is a eutectic mixture of silicon and iron.   3. Electrode made of an essential material-   metal element for flame control by ionization during the operation of oil and gas burners, manufactured according to the method of claim 1 or 2, characterized in that the electrode (5) has the shape of a rod and that '' at least the end of the rod which penetrates   in the flame is made up of a semiconductor material   silicon carbide tor obtained by reaction sintering.   4. Electrode according to claim 3, character-   sée in that the semiconductor material extends over a length such that the connection with the metal part (2) is located substantially outside the flame region. 5. Method for manufacturing an electrode according to claim 3 or 4, characterized in that the connection is effected because the silicon carbide rod (1) is placed in a recess (7) of an iron rod, that in the intermediate space between the silicon carbide rod and the iron rod is placed a mixture (3) of silicon powder and iron powder, and that the piece   is then heated above 12000C.   6. Method for manufacturing an electrode according to the   claim 3 or 4, characterized in that the metal piece   sintered liquor completely surrounds the stem made of silicon carbide (1).   7. Electrode according to any one of the claims   - 8 - 3 to 5, characterized in that the metal electrode has a weakened zone (6) outside the sintered part.   8. Method for manufacturing an electrode according to claim 3 or 4, characterized in that a metal part (8) is threaded on at least the end of the silicon carbide rod, and that the two parts   are combined by sintering while being brought to a temperature ture greater than 11000C.   9. Method according to one of claims 1, 2,   6, 7 and 8, characterized in that the agglomeration by fried-   tage of the metal part takes place with compaction   simultaneous, possibly isostatic compaction.