JPH0154314B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for surface metallization of metal oxides, and in particular to such a method at low temperatures. Metallizing the surface of metal oxides is an important issue in order to facilitate the bonding and fixation of metal oxides and metals, and in particular metallization at low temperatures is economically important. This is also necessary in order not to affect the properties of the metal oxide body. [Prior Art] Conventionally, when a metal oxide product such as a ferrite vibrator is bonded and fixed to another metal body, an organic adhesive such as an epoxy adhesive has been used. However, such adhesives are weak against high temperatures and vibrations, and tend to cause problems such as the adhesive portion peeling off. On the other hand, the surface of the metal oxide is metallized and the metal oxide is bonded and fixed to another metal body by brazing. In this case, as a method for surface metallization of metal oxides,
The Mo-Mn method is known. This method works with Mo and
Mn powder is applied onto the surface of the metal oxide, sintered in a hydrogen atmosphere, and then nickel plated and diffused to obtain a metallized surface. However, in this Mo-Mn method, the sintering temperature is as high as 1400 to 1500°C, and the process is complicated. In addition, as a method of brazing metal oxides together or metal oxides and metals, it is possible to braze titanium foil and brazing material (Ag, Cu, Ni) without taking the step of metallizing the soldering surface of the metal oxide in advance. or their alloys)
The foil is sandwiched between the substrates to be brazed and heated to 900 to 950°C to braze. This is called the active metal method.
Although the mechanism by which brazing is performed in this manner is not completely understood, it is thought that Ti reduces the metal oxide during heating, and the reduced metal and the solder material form an alloy. In fact, the oxygen absorption capacity of Ti, that is, its reducibility, suddenly increases above its phase transformation temperature, as shown in the data by PHMorton (edited by the Welding Society of Japan, Welding Handbook, February 1961, p. 861). ,figure
48.4 and its explanation) etc. The present inventor has already proposed a method for metallizing the surface of an oxide metal by effectively utilizing the large oxygen absorption ability of Ti above the phase transformation temperature in the earlier patent application No. 55-101291. No. (Japanese Unexamined Patent Publication No. 57-27985). In the method of the earlier application, an alloy of copper and titanium or silver solder and titanium is prepared, this titanium alloy is brought into contact with the surface of the metal oxide whose surface is to be metallized, and in this state, the titanium phase is formed in a non-oxidizing atmosphere. Heating to a temperature near the transformation point (750-950℃), thereby
The metal oxide in the surface layer of the metal oxide is reduced with titanium. [Problems to be solved by the invention] In the method of the same prior application, compared to the Mo-Mn method,
Surface metallization of oxide metals takes place at much lower temperatures. However, considering the economics of thermal energy and the effect on the heating of the metal oxide body,
It cannot be said that the processing temperature is still sufficiently low. Therefore, the present invention provides a method for surface treatment of metal oxides, which enables heat treatment at a temperature that does not deteriorate the material and which can obtain a reduced layer having a sufficient thickness for bonding with a brazing filler metal or the like. The purpose is to [Means and effects for solving the problem] As a result of various studies on methods for further lowering the surface metallization treatment temperature, the present inventor has developed an alloy of copper and titanium or silver solder and titanium in the method of the above-mentioned prior application. It has been found that the processing temperature can be lowered by making it into a fine powder. Industrially produced titanium is usually in the form of titanium plates, foils, or sponge-like particles. When these forms of titanium are alloyed by absorbing copper or silver solder by heating in vacuum, as shown in the above-mentioned earlier application, unless heated to a temperature close to the phase transformation point, metal oxides will form. Although sufficient surface metallization of the metal oxide is not achieved, when the alloy is brought into contact with the metal oxide surface as a fine powder, it can be heated to temperatures close to, but well below, the phase transformation point, but above 450°C. Surface metallization was achieved. That is, in the present invention, a fine powder of an alloy of copper and titanium or a silver solder and titanium is prepared, the fine powder of the titanium alloy is brought into contact with the surface of a metal oxide whose surface is to be metallized, and the temperature is lower than 750°C in a non-oxidizing atmosphere. This is a method of metallizing the surface of a metal oxide by heating it to a relatively low temperature of 450°C or higher. Of course, the purpose of surface oxidation can be achieved even if the processing temperature is above the phase transformation temperature, but sufficient surface oxidation is achieved at a temperature below this temperature, so it is possible to achieve economic efficiency in thermal energy and to prevent deterioration of the material quality of the material being processed. The temperature was set below the phase transformation temperature for reasons such as avoidance. For the same reason, the temperature is preferably 750°C or lower. If the treatment temperature is below 450°C, metallization will be extremely poor, so a temperature of at least 450°C is required. The smaller the alloy fine powder, the better, with a particle size of 100 to 200.
The thickness of the reduced layer that provides sufficient bonding strength can be obtained below the mesh. In the present invention, by making the alloy used for reducing the metal oxide into a fine powder, the reducibility of titanium is fully exhibited, and surface metallization can be achieved at lower temperatures. It is thought that the It is obvious that the surface metallization method of the present invention can be applied to all metal oxides that have a smaller affinity for oxygen than titanium. Such metals include FDRichadson and JHE Jeffes, I.Iron
In the paper Steel Inst., 160, 261 (1948)
As is clear from the graph showing the relationship between the standard free energy of formation of oxides and temperature shown in Fig. 1, Fe, Ni, Zn, Cu, Pb, Sn, Co, K, V,
Examples include Na, Mn, Cr, Si, etc. [Example] Hereinafter, an example in which the present invention is applied to metallizing nickel ferrite will be described in detail with reference to the drawings. Example 1 First, five types of titanium fine powder with various particle sizes were prepared, namely, 40 mesh, 60 to 100 mesh, and 100 to 200 mesh.
Titanium fine powder of 200 to 350 mesh and 325 mesh or less was prepared, and an alloy fine powder with copper powder (325 mesh) was formed. Actually, the above-mentioned fine titanium powder and copper powder were mixed in a ratio of 8:2 and held at 900° C. for 10 minutes in a vacuum.
As a result, copper was absorbed into the titanium fine powder, and titanium alloy fine powder of various particle sizes, which was an alloy of copper and titanium, was obtained. This fine alloy powder of copper and titanium was filled into a fireproof container 1 as shown in FIG. 1, and a nickel ferrite plate 2 was embedded in this fine alloy powder 3. In this state, treatment was performed at 700° C. and 750° C. for 30 minutes each in an argon atmosphere. The thickness of the reduced layer of the ferrite plate 2 thus reduced was examined using an optical microscope. The results are shown in Table 1.

[Table] As a result, the smaller the titanium particle size, the more
It was shown that the reducing capacity was significantly increased. In general, it has been found that sufficient bonding strength can be obtained if the thickness of the reduced layer is 30 μm or more, so
It has been found that metallization layers of sufficient thickness can be obtained even at very low processing temperatures, such as 700°C, by using titanium alloys with grain sizes of ~200 mesh or less. Example 2 As is clear from the results of Example 1, it was found that the smaller the particle size of the titanium alloy fine powder, the greater its reducing ability. Therefore, a titanium alloy with a size of 325 mesh or less, which is the smallest alloy powder of copper and titanium, was filled into a fireproof container 1 as shown in Figure 2, and a rod-shaped sample 2 of nickel ferrite (9 mm x 20 mm x 30 mm) was prepared.
The surface of the alloy was embedded in this fine alloy powder. In this state, each temperature from 457°C to 850°C was maintained in an argon atmosphere for 30 minutes. After this process is completed, the metallized surfaces of each of the two samples are joined using high temperature solder (Cd-Zn, melting point 280-320℃).
The joint strength was examined by a three-point bending test. The results are shown in Table 2.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, surface metallization that provides a reduced layer with increased joint strength such as brazing can be achieved with good uniformity at a much lower temperature than conventional metallization methods. Therefore, it is very advantageous because it is economical because it requires less thermal energy, and it is possible to prevent the deterioration of the oxide body due to heat. In addition, since the present invention uses fine powder, local metallization is possible without embedding it in the alloy, for example, by making the fine powder alloy into a paste, coating, spraying, etc. This is an extremely rational metallization method because it enables electrode production and local bonding with metal, which were difficult with conventional techniques, and reduces the amount of alloy used.

[Brief explanation of drawings]

The figure shows different embodiments of the present invention.
The figure is a perspective view showing a processing method in the case of the first embodiment, and FIG. 2 is a perspective view showing the case in the second embodiment. 1... Fireproof container, 2... Nickel ferrite,
3...Titanium alloy fine powder.

Claims (1)

[Claims] 1. Prepare fine alloy powder of copper and titanium or silver solder and titanium with a particle size of 100 mesh or less, and add the metal oxide whose surface you want to metallize (however, as a metal, the affinity for oxygen is smaller than that of titanium). Bringing the fine powder of the titanium alloy into contact with the surface,
The oxide metal in the surface layer of the metal oxide is reduced by heating to a relatively low temperature within the temperature range of 450°C to 750°C in a non-oxidizing atmosphere, thereby metallizing the surface layer. A method for surface metallization of a metal oxide, characterized by controlling the thickness of the metal oxide to 30 μm or more.