JPS5914233B2 - Molybdenum electrode rod for glass melting - Google Patents

Description

[Detailed description of the invention] The present invention relates to a molybdenum electrode rod for glass melting.

In the glass industry, the electric melting method has high thermal efficiency and great cost advantages; it does not emit NOx or SOx and can reduce air pollution; it is easy to operate and control, and the quality is stable. It offers many advantages in terms of productivity, quality, work environment, etc., including being suitable for mass production of high-quality glass.

However, the electric melting method described above uses a rod-shaped electrode made of metal molybdenum manufactured by a powder metallurgy method. In other words, molybdenum electrode rods are superior in terms of ease of use, longevity, and impact on glass quality, and molybdenum electrode rods manufactured by vacuum arc melting are prone to breakage during plastic processing or handling processes. This is because molybdenum electrode rods manufactured by powder metallurgy are less susceptible to breakage and less likely to cause defects in glass foaming, whereas molybdenum electrode rods manufactured by powder metallurgy are more likely to cause cracking or defective glass foaming. However, molybdenum electrode rods manufactured by the above powder metallurgy method have a limit to their densification through sintering, are easily oxidized through the voids, and are susceptible to oxidation during use (usually at temperatures of 1200 to 1600°C).
The growth of crystal grains tends to be accelerated by recrystallization. However, there is a drawback in that oxides with a low ionization tendency in the molten glass components selectively infiltrate these grain boundaries, causing detachment of the crystal grains, resulting in electrode wear. This consumption of the electrodes results in the contamination of molybdenum components into the molten glass, and therefore it is difficult to apply this method in cases where high purity is required for quality control. In this way, improvements in the wear resistance of molybdenum electrode rods manufactured by the above powder metallurgy method have been studied, including selecting the grain size of the raw molybdenum powder, making it a highly dense sintered body, increasing the processing ratio to make it finer, and adding zinc oxide to it. Attempts have been made to prevent grain boundary infiltration by adding additives to suppress crystal growth. However, it cannot be said that the abrasion resistance and long life of the above-mentioned electrode rods are sufficiently satisfactory in practical use. There is a pressing need to find a solution to the demand for electrode rods. As a result of repeated studies in view of the above points, the present inventors found that electrode rods made of molten molybdenum exhibit excellent abrasion resistance when the content of oxygen and analkali metal impurities is kept to a very small level, and that the electrode rods are made of molten molybdenum. The present invention aims to provide a molybdenum electrode rod for glass melting that can be applied to melting methods over a long period of time.

The present invention will be described in detail below. The present invention is a molybdenum electrode rod for glass melting, which is made of molten molybdenum and has a content of oxygen and alkali metal impurities of 5 OPF or less. The molybdenum electrode rod for glass melting according to the present invention can be manufactured as follows. That is, metal molybdenum powder, granules or molded bodies prepared by adding a deoxidizing agent such as carbon to metal molybdenum powder are melted, and if necessary, remelted.
, This increases the refining effect. This melting process eliminates the voids and bubbles in the raw molybdenum metal, essentially achieving theoretical density, and reducing the oxygen content and impurity content of alkali metal elements such as potassium and sodium to below 50PF. Oxidic acid and low alkali dissolved molybdenum can be obtained. To further explain this molybdenum dissolution, the above molybdenum dissolution can be carried out by electron beam dissolution,
A plasma melting method or a vacuum arc melting method is suitable.
In other words, electrons are bombarded and heated by a high-voltage electron beam in a high vacuum.
The one-line melting method has a good refining effect, and can be used to remove not only high vapor pressure substances such as alkali metal elements and molybdenum oxides contained in the material (material to be melted), but also substances that cause coloration, such as iron and nickel, which have a higher vapor pressure than molybdenum. It can also be refined to remove impurities. In contrast to the above-mentioned electron beam melting, the plasma melting method requires a low vacuum to be maintained in order to continue the plasma, and the refining effect is somewhat inferior.
A molybdenum melt with a low alkaline content is obtained. Furthermore, in the case of vacuum arc melting, the refining effect is generally inferior (compared to plasma melting), so it is necessary to repeat the vacuum arc melting process to obtain a molybdenum melt with the required low oxygen and alkali content. There is. Table 1 shows the results of measuring the impurity content of an example of dissolved molybdenum obtained by each of these dissolution methods. In addition, the amount of impurities in the table is shown in units, and for reference, the case of molybdenum electrode rods conventionally used for glass melting is also shown.〇 As mentioned above, since it is made by melting, it has high density and oxygen content. The molybdenum electrode rod for glass melting according to the present invention, in which the alkali metal content is suppressed to 50 or less, performs the required function as a current-carrying glass melting electrode for a long period of time.

That is, even when the molybdenum electrode rod according to the present invention is applied to electrical melting of glass, damage due to infiltration is suppressed, exhibits excellent wear resistance, and always performs the required electrode function.
The reason why the molybdenum electrode rod according to the present invention has excellent wear resistance and maintains a long life is considered to be as follows. Molybdenum is used as an electrode rod for glass melting and is heated to 1100℃.
If it is kept at a high temperature for a long time, it will recrystallize, and the initial
The crystal grain size, which was about
As the grains grow, the grain surface area decreases in almost inverse proportion to the grain size, and the total grain boundary surface area after recrystallization is 1
/1000 or so. On the other hand, alkali metal elements and oxygen have almost no solubility in molybdenum, so they exist at grain boundaries, and as the grain boundary surface area decreases, they come to exist in a concentrated form at the remaining grain boundaries. Since the impurities such as oxygen and alkali metal elements concentrated in the grain boundaries have a low melting point, when the glass is melted, they promote infiltration of the glass and cause selective erosion, resulting in particle detachment and attrition loss. invite However, in the molybdenum electrode rod according to the present invention, since the content of the above-mentioned oxygen and alkali metal elements is extremely small, infiltration and corrosion are suppressed as described above, and it is thought that it exhibits excellent wear resistance. . Next, examples of the present invention will be described.

An electron beam melted molybdenum electrode rod (cutting process) having an alkali metal content of 15 PF, an oxygen content of 17 PF, and a carbon content of 15 PF 1 (no adverse effects are observed up to a carbon content of about 100 PF) was prepared.

On the other hand, three types of glasses having the composition ratios (wt%) shown in Table 2 were prepared, and 0.3% by weight of arsenic oxide was added to each glass as a bubble breaker.

The molybdenum electrode rod was used to melt each of the above-mentioned glass components, and the glass components were electrically melted (about 1450° C.).

After 50 hours of current melting, the current melting was stopped and cooled, and the state of the molybdenum electrode rod, that is, the state of molybdenum eluting into the glass and the state of glass penetrating into the molybdenum metal, was observed. In the case of the electrode rod used for electric melting of borosilicate glass in the above case, only a slight black layer was observed on the surface, and when looking at the cross section of the electrode rod, glass infiltration into the grain boundaries was observed. The area was about 0.02m1 at most.

In this regard, in the case of conventionally used molybdenum electrode rods (current melting under the same conditions), a black layer of about 5 to 10 ml was observed on the surface, and glass infiltration into the grain boundaries was 0.1 to 0.
．． This is a remarkable difference from the fact that the depth reached 21 tm.Furthermore, in the case of the molybdenum electrode rod used for electric melting of lead-containing glass, a black layer with a thickness of 2 to 3171 mm was observed on the surface, but the reduction of lead was not observed. In the case of the molybdenum electrode used conventionally, The formation of a black layer and the reductive precipitation of lead were 10 nm or more, and the glass infiltration into the crystal grain boundaries in the electrode cross section reached a depth of 0.5 mm, which is a remarkable difference.

As described above, the low-oxygen, low-alkali molybdenum electrode rod according to the present invention had excellent performance against surface infiltration and grain boundary infiltration despite the crystal grains being large, on the order of several ml.

Claims (1)

[Claims] 1. A molybdenum electrode rod for glass melting, which is made of molten molybdenum and has an oxygen content of 50 ppm or less and an alkali metal impurity content of 50 ppm or less.