JPS621598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining reaction-sintered silicon carbide workpieces to iron or metal workpieces.

Bonding of silicon carbide type ceramic semiconductor devices has always been a problem. Known methods for producing electrical and mechanical transitions include flame sprayed metal connections or shrink-fit metal connections. When high temperatures are applied, e.g. temperatures of 600-700°C, flame sprayed metals may burn out and other joints, such as shrink-fit metal joints, may become mechanically damaged as a result of high thermal effects. It is unstable.

The present invention discloses a method for reliably and thermally stably bonding a metal member and a silicon carbide workpiece.

According to the invention, a silicon carbide workpiece is bonded to a metal or iron workpiece using a silicon-metal bond and the bond is then fixed by heating.

The binder is preferably a eutectic mixture of silicon and the metal used, for example iron. This provides a thermally stable mechanical and electrical connection between the silicon carbide workpiece and the iron workpiece.

It is known to use ionizing electrodes to monitor the flame when operating oil and gas burners. Such electrodes are based on the known principle that an electrode, for example an iron electrode, is guided into a flame, which ionizes the area between the fuel inlet of the burner and the electrode in such a way that a current flows. Blue flame burners, which do not emit visible light, used ultraviolet detectors. However, UV detectors often cannot be used, for example if the burner is surrounded by a recirculation chamber. Therefore,
Turning electrodes are used in such burners, but
It has the disadvantage that the material disintegrates and therefore said electrodes only have a relatively short service life due to the very high flame temperatures, which are typically in the range 1400-1500 DEG C. in blue flame burners.

The invention therefore has the objective of disclosing a more stable electrode. According to the invention, such an electrode is obtained when the electrode is shaped like a rod and at least the portion of the rod that is inserted into the flame is made of a reactively sintered silicon carbide semiconductor material.

It is advantageous if the semiconductor material has an extension such that the connection to the metal part is located primarily outside the flame area. Considering the fragility of the electrode unit, make the electrode as short as possible. However, high temperatures cause problems at the joints that contact the metal parts of the electrodes. The temperature at the joint is approximately 600-700℃ even if it is outside the flame.
exposed to high temperatures. In particular, at such temperatures the method of the invention can be applied to the bonding of the metal part of the ionization electrode and the silicon carbide rod. According to the invention, a durable electrode is obtained by fixing the electrode end to a metal part using a binder of silicon and iron, in particular a eutectic mixture of silicon and iron. The eutectic mixture combines with the silicon carbide rod and also with the iron workpiece.

For bonding, a silicon carbide rod is inserted into the hole of the iron rod, a mixture of silicon powder and iron powder is charged into the gap between the silicon carbide rod and the iron rod, and then the workpiece is
This can be done by heating above .degree. In this case, for example, a mixing ratio of 1:1 can be applied. Thereby, the silicon powder and the iron powder form a eutectic mixture, which is bonded to the silicon carbide rod and the iron workpiece.

Optionally, the metal workpiece sintered onto the silicon carbide rod may cover the entire rod. This results in a mechanically stable workpiece that is easy to handle because the sintered mantle protects the ceramic silicon carbide rod, which is somewhat susceptible to destruction. That part of the sintered metal workpiece subjected to the action of the flame clearly disintegrates, but the part that covers the silicon carbide rod remains stable in an area somewhat distant from the flame, where the temperature is 700-800°C. Therefore, only the parts located directly in the hot part of the flame are corroded.

Furthermore, the metal electrode may have a weak point outside the sintered part. This allows the extremely fragile end of the electrode to be bent to a desired position without damaging this part.

Another embodiment is to sinter the metal body by moving it over at least the end of the silicon carbide rod and heating both parts to a temperature of 1100°C. The sintering then produces a type of shrink fit, in which a tight mechanical and electrical connection is achieved at the same time in the transition zone, which is stable even at high temperatures. Also in this case
When increasing the temperature above 1200° C., a eutectic mixture is obtained which produces a more stable transition zone and a better electrical anchorage.

The workpiece thus produced is hard soldered, welded or otherwise secured to an electrode member remote from the flame.

It is advantageous if the metal workpiece is sintered at the same time by compression molding, optionally by isostatic compression molding. A very tight and hard transition surface of the sintered metal workpiece is thereby obtained.

Some advantageous embodiments of the invention will be explained in more detail with reference to the accompanying drawings.

Ceramic silicon carbide rods are prepared in a known manner, in particular by reaction sintering of a mixture of silicon carbide (SiC) and graphite with liquid silicon at high temperatures, whereby the free graphite reacts with the silicon and is converted into silicon carbide. Manufactured by FIG. 1 shows such a silicon carbide workpiece 1 combined with a ferrous metal electrode member 2 according to the invention. A silicon carbide rod is placed in the hole 7 in the iron rod material. The void between the rod 1 and the iron bar stock 2 is filled with a mixture 3 of silicon powder and iron powder (for example in a 1:1 ratio). The cavity can instead be filled with powder of a mixture already prepared from silicon and iron, for example a eutectic mixture. The entire workpiece with ceramic rods is heated to a temperature above 1200°C. The powder mixture thereby forms a eutectic mixture and combines with the silicon carbide rod and also with the iron. It is also possible to use other metal binders as binders, for example mixtures of silicon and nickel.

FIG. 2 represents the electrode ends 1, 2 manufactured by the method described in connection with FIG. The iron part 2 of the silicon carbide rod is a connecting part, which can be attached to the electrode rod 5 as desired.
It can be fixed to the remaining part 4 of.

Figure 3 shows a workpiece obtained by compression molding iron powder around a silicon carbide rod, for example, by isostatic compression molding, that is, compression molding by applying the same amount of pressure from the entire surface. . The entire workpiece is then heated to approximately 1200°C, in particular above 1200-1220°C. This causes the iron powder to sinter, and at the same time the silicon in the silicon carbide rod diffuses into the iron powder, creating a melt (eutectic mixture) that is thermally stable between the silicon carbide rod and the iron powder. form a good mechanical and electrical bond.
Such electrodes are durable and are better resistant to transport and handling than bars according to FIGS. 1 or 2.

As shown in FIGS. 4 and 5, that portion of the metal sleeve inserted into the flame gradually corrodes and wears away, leaving behind only a stable silicon carbide rod.

Furthermore, FIG. 4 shows that the ceramic silicon carbide rod 1 can be provided with a weak point 6 behind the joint 2, which can be provided, for example, over the entire circumference of the rod or, if desired, on a part of the circumference. It's good to be able to do it. This allows the slope of the silicon carbide rod corresponding to the electrode to be adapted to the actual situation by simply bending it manually at this weak point, without damaging the outer part of the ceramic. Other embodiments of the electrode may also be provided with such a weakened portion.

In the two embodiments a and b of FIG. 6, a metal workpiece 8, which is an annular workpiece, is shrink-fitted onto a silicon carbide rod and sintered. Many other embodiments and methods for compression molding and sintering a workpiece are possible, all of which are encompassed by the inventive concept.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an ionizing electrode with a silicon carbide rod inserted into a steel holder, FIG. 2 is a diagram of the electrode according to FIG. 1 as manufactured, and FIG. 4 and 5 are illustrations of the sensor according to FIG. 3 after several uses, and FIG. 6 shows a silicon carbide rod with sintered and FIG. 2 is a view of two embodiments a and b showing a fitted metal workpiece; DESCRIPTION OF SYMBOLS 1...Silicon carbide workpiece, 2...Metal or iron workpiece, 3...Binder, 5...Electrode, 6...Weak part, 7...Hole, 8...Metal workpiece.

Claims (1)

[Claims] 1. A silicon carbide workpiece 1 is bonded to a metal or iron workpiece 2 using a bonding agent 3 made of silicon and metal, and then the bonded portion is heated and fixed. A method of bonding a reactively sintered silicon carbide workpiece and an iron or metal workpiece. 2. The method of claim 1, wherein the binder is a eutectic mixture of silicon and iron. 3. The method according to claim 1 or 2, wherein the metal workpiece is simultaneously sintered by compression molding, and optionally by isostatic compression molding.