JPS5837855B2 - graphite crucible - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a graphite crucible for analyzing gas components in metals, and in particular, the present invention relates to a graphite crucible for analyzing gas components in metals.
The present invention relates to a graphite crucible used in a so-called direct current heating type extraction furnace in which the crucible itself generates heat by flowing Joule heat generated during the flow.

This type of graphite crucible heats and melts a sample placed in the crucible, and generates the components such as nitrogen and hydrogen as gas as they are, and also reacts oxygen with carbon, which is a predominant ingredient in the graphite crucible, to oxidize it into monoxide. Since carbon gas is extracted as carbon gas, in order to effectively produce and extract this gas, the temperature of the bottom surface of the crucible where the sample is placed must be adjusted to the maximum temperature within the crucible (approximately It is important to design the temperature so that the temperature is 3000°C.

In graphite crucibles used in the direct current heating method, heat generation is based on Joule heat, and Joule heat is proportional to the density of the current flowing through that part, so the inner bottom surface is heated to 3000°C.
In order to heat the crucible to high temperatures, it is necessary to devise the structure and shape of the crucible so that the current density near the inner bottom surface increases accordingly.

Conventionally, it was the first graphite crucible with this kind of innovation.
As shown in the figure, there is a structure in which a columnar body 2 is protruded from a bottom part 1.

In the graphite crucible having this structure, the columnar body 2 is shaped to have a small diameter, and the thickness of the bottom portion 1 and the wall thickness of the cylindrical side wall 3 are appropriately selected. The current density in the vicinity is made to be high.

By the way, although the graphite crucible having this structure has the above-mentioned advantages, it also has the following disadvantages.

First, since the bottom part 1 has a columnar body 2 with a small diameter, simply placing it on the lower electrode 4 is unstable and may fall over, and the contact area is sufficient to stably supply a large current. Therefore, it is necessary to form an insertion hole 4a in the lower electrode 4 into which the columnar body 2 is inserted.

Moreover, in order to maintain good contact with the columnar body 2, the insertion hole 4a needs to be formed to have the same size and shape as the outer diameter of the columnar body 2 so that the columnar body 2 can be fitted tightly. High precision processing technology is required.

Furthermore, since the columnar portion 2 having the highest heating temperature is fitted into the fitting hole 4a, the edge portion 4b of the fitting hole 4a is exposed to extremely high temperatures, and is subject to severe wear and tear due to the high temperature.

As the crucible is used more frequently, this wear and tear causes poor contact between the crucible and the electrodes, making the current flowing unstable, and eventually leading to a situation where the inner bottom surface cannot be raised to the target temperature.

As a result, the expensive heat-resistant alloy electrode 4 must be replaced, and the cost of spare parts is quite high.

Furthermore, as described above, since the columnar body 2 is manufactured so as to fit tightly into the insertion hole 4a without any gaps, unless the crucible is accurately positioned, the columnar body 2 will not fit into the insertion hole 4a.
The crucible cannot be inserted into the crucible, and the crucible must be lifted straight upwards to remove it, making the crucible exchange operation extremely difficult and unsuitable for automation.

In addition, as a graphite crucible with a different idea, conventionally the 5th crucible
As shown in the figure, the connecting part between the outside of the cylindrical side wall 11 and the bottom part 12 is largely chamfered, and the contact area between the bottom part 12 and the lower electrode (not shown) is reduced by having a chamfered part 13. There is.

In the graphite crucible having this structure, the end area of the bottom part 2 is made smaller than the end area of the cylindrical side wall 11, so that the current density near the center of the bottom part becomes high.

Compared to a graphite crucible with a structure in which a columnar body is formed protruding from the bottom, a graphite crucible with this structure is considerably improved in terms of processing surface, stability, automation, and heating efficiency is improved because the bottom of the crucible is heated directly. However, there is no improvement at all in that the contact area with the lower electrode is extremely heated and the lower electrode is severely worn out.

SUMMARY OF THE INVENTION An object of the present invention is to provide an extremely useful graphite crucible which eliminates all of these drawbacks and whose inner bottom surface can be heated to a temperature sufficient to heat and melt a sample.

Embodiments of the present invention will be described below based on the drawings. In FIG. An annular depression 24 is provided in the vertically intermediate portion of the curved surface to form a small diameter portion 23e.

Reference numeral 25 denotes an upper electrode, which is placed on the upper end of the graphite crucible 21 with an appropriate pressing force applied thereto, and a passage for injecting an inert gas such as helium gas into the internal space A of the crucible; 25a is the formal precept.

26 is a lower electrode, and the lower end surface 23a of the crucible bottom 23 is brought into contact with the upper surface of the lower electrode.

Although not shown, the lower electrode 26 and the upper electrode 25 are cooled by circulating a coolant therein.

27 is an extraction furnace power source that generates high current (800A to 1200A).

In this configuration, when the extraction furnace power supply 27 is connected to both electrodes 25 and 26, the high current generated by the power supply 27 is transferred to the upper electrode 25.
5, flows through the side wall 22 and bottom 23 of the graphite crucible 21 to the lower electrode 26.

The flow of this current is schematically shown by streamlines P in the figure.

In this case, an annular recess 24 is provided in the vertically intermediate portion of the outer surface of the bottom portion 23, and a small diameter portion 23e is formed. The diameter is smaller than that of the part.

Therefore, the current concentrates in this small diameter portion 23e, and the current density becomes the highest.As a result, this small diameter portion 23e generates the maximum power, and a small area including this small diameter portion 23e & the inner bottom surface 23b as the center. B (area drawn by crossing diagonal lines in FIG. 3) has a higher temperature than other parts.

Therefore, the sample placed on the inner bottom surface 23b is effectively heated and melted, and gas components in the sample are generated and extracted.

On the other hand, since the bottom portion 23C below the small diameter portion 23e has the same diameter as the bottom portion 23d above the small diameter portion 23e, the current passing through the small diameter portion 23e is transferred to the bottom portion 23c. It spreads again at , and flows to the lower electrode 26 through the entire lower surface thereof.

By the way, in this bottom portion 23c, the amount of heat generated is low due to the spread of the current, and the large surface area also provides a certain degree of heat dissipation, so that the temperature is maintained at a relatively low temperature.

Therefore, the lower electrode 26 is not exposed to high temperatures as in the conventional case, and its wear and tear is drastically reduced.

The most desirable dimensions of the graphite crucible 21 having the above structure are shown in FIG. 3: DI = 14 mm, D2 = 5
mm, D3 = 1 4ii, H = 1 9mm, T
I = 1.2mm, T2 = 3mm, T3 = 1m
It is m.

The dimension D3 can be made somewhat smaller than D1, or can be made larger, taking into consideration the heat resistance of the lower electrode 26.

In addition, the dimensions of D2 and T2-Ta are such that the crucible has sufficient strength to withstand pressure and compression by both the upper and lower electrodes 25 and 26, and that the small area B can reach the maximum temperature. It was determined through testing to satisfy two conditions.

As a result of setting a graphite crucible with this size as shown in Fig. 2 and passing a current, the result is that in small area B, 3400
°C, 2800 to 3000 °C in the cylindrical side wall 22
A temperature distribution of approximately 600° C. was obtained on the lower surface of the bottom portion 23.

The temperature in the small region B is high enough to ripen and melt the sample that has been introduced, and the temperature at the lower surface of the bottom is such that the lower electrode 26 made of, for example, a chromium or copper alloy is not worn out at all. The temperature is low.

Next, FIG. 4 shows another embodiment of the present invention, in which the inner bottom surface 23b of the roof 21 is formed to be inclined.

This configuration is suitable for heating and melting fine samples such as chips or fruit particles.

That is, when such a sample is put into the crucible, it naturally flows down according to the slope of the inner bottom surface 23b, so that it can be collected in one place near the center.

The heat generation temperature near the center is higher than other parts, so the sample is uniformly heated and melted near the high temperature center.

Similarly, in the illustrated example, the lower surface 23f of the bottom portion 23d is inclined to be approximately parallel to the inner bottom surface 23b, but this is because the thickness of the bottom portion 23d is made approximately uniform, and the current density is reduced in the central portion. This is to prevent the temperature from increasing excessively and to make the temperature distribution within the small region B as uniform as possible.

Next, FIG. 5 shows another embodiment of the present invention.

In this embodiment, the shapes of the recess 24 and the small diameter portion 23e are slightly different from those of the previous embodiment, as is clear from FIG.

In this way, the depression 24 and the small diameter portion 23e can have various shapes.

As explained above, the present invention is a graphite crucible consisting of a cylindrical side wall and a bottom, in which an annular depression is provided in the vertically intermediate portion of the outer peripheral surface of the bottom to form a small diameter portion. It produces various effects all at once.

■ Since it has a small diameter part in the vertical middle part of the bottom that acts to increase the current density, the inner bottom surface reliably generates heat to the target temperature and effectively heats and melts the sample put in.

■ Since the annular recess is provided in the middle part of the outer circumferential surface of the bottom in the vertical direction, the lower surface of the bottom can be made sufficiently wide, and the stability of the crucible itself is good, and the current exchange with the lower electrode is improved. A large contact area can be maintained without any problems.

Furthermore, since the crucible only needs to be simply placed on the flat surface of the lower electrode and no strict positioning is required, automation of the crucible replacement operation becomes extremely easy.

■ Since the crucible is simply placed on the lower electrode, there is no need to form a hole with high dimensional accuracy on the lower electrode.
Since the manufacturing process of the lower electrode becomes simple and there is no need to use special materials, it greatly contributes to reducing the cost of the electrode.

■ Since the bottom part below the vertical middle part of the bottom where the annular depression is formed has a large cross-sectional area, the amount of heat generated in this part is small, so the lower electrode is not exposed to high temperature, and its Wear and tear are drastically reduced.

This makes it possible to stably supply the current to the crucible even if the crucible is used many times, allowing the expensive lower electrode to be used for a long period of time.

As a result, the number of spare parts and the number of electrode replacements are reduced, and the costs associated with maintaining and managing the device are significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a front sectional view showing a state in which a conventional graphite crucible is set on the upper and lower electrodes, FIG. 2 is a front sectional view showing a state in which a graphite crucible according to an embodiment of the present invention is set in the upper and lower electrodes, and FIG. The figure is a front sectional view of the graphite crucible shown in Figure 2,
5 is a front sectional view showing another embodiment of the present invention, FIG. 5 is a front sectional view showing another conventional example, and FIG. 6 is a front sectional view showing another embodiment of the present invention. 21...Graphite crucible, 22... Cylindrical side wall, 23.
...Bottom, 23e...small diameter portion, 24...annular recess.

Claims (1)

[Claims] 1 In a graphite crucible consisting of a cylindrical side wall and a bottom,
A graphite crucible in which a small-diameter portion is formed by providing an annular depression in the vertically intermediate portion of the outer circumferential surface of the bottom portion.