JPH03122053A - Production of graphite crucible for oxygen and nitrogen analysis - Google Patents

Abstract

PURPOSE:To obtain a graphite crucible for oxygen and nitrogen analysis capable of giving stable and reliable analytic results at a low cost by adding and kneading a specific amount of a thermosetting resin to carbon powder, molding the mixture in the form of a crucible and baking the formed mixture in a non-oxidizing atmosphere at a prescribed temperature. CONSTITUTION:100 pts.wt. of carbon powder (e.g. coke powder) is mixed and kneaded with 15-50 pts.wt. of a thermosetting resin (e.g. benzylic ether-type phenolic resin). The kneaded mixture is molded in the form of a crucible and banked at >=2,000 deg.C in a non-oxidizing atmosphere to obtain the objective graph ite crucible for the analysis of oxygen and nitrogen. A crucible having dense texture and high dimensional accuracy can be produced by this process. Since the dimension of each part is uniform between the crucibles, there is no differ ence of the heat-generation between the crucibles when the graphite crucible is heated by passing electric current through the crucible in analysis and, accord ingly, a stable analytic results can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a graphite crucible that is used to analyze oxygen and nitrogen contained in metals and ceramics, and that provides stable and reliable measurement results. .

[Conventional technology]

Conventionally, to analyze oxygen and nitrogen in metals or ceramics, a graphite crucible made of graphite material processed and formed using a lathe, a drill press, or the like has been used.

[Problem to be solved by the invention]

However, the graphite crucible for analysis is disposable for each sample, and when a standard sample is analyzed using the graphite crucible, there is a problem in that the measured values are not stable and vary depending on the crucible used.

As a result of various studies on the above-mentioned problems, the inventors of the present invention found that the thickness, weight, etc. of the crucible were not constant during processing and molding, resulting in variations in electrical resistance, etc., and that the entire graphite crucible was electrically heated. In this case, it is thought that the cause is variation in the temperature heated by each crucible.

The present invention was made based on the above idea, and aims to provide a method for manufacturing a graphite crucible for oxygen and nitrogen analysis, which can accurately measure the amount of oxygen and nitrogen in metals or ceramics. .

[Means to solve the problem]

In order to achieve the above object, in the method for manufacturing a graphite crucible for oxygen and nitrogen analysis according to the present invention, 15 to 50 parts by weight of a thermosetting resin is added to 100 parts by weight of carbon powder, kneaded, and the mixture is placed in a crucible. After forming into a shape, under a non-oxidizing atmosphere,
Calcinate at a temperature of 2500°C or higher.

The carbon powder used in the method of the present invention is preferably a powder of coke, graphite, etc., and has a particle size of 500 μm or less, particularly 200 μm or less. When the particle size exceeds 500 μm, the density of the produced crucible decreases.

Further, as the thermosetting resin, phenol resin, furan resin, etc. can be used, but benzylic ether type phenol resin is particularly preferred because injection molding is easy. This resin has a low viscosity and has a slow rate of increase in viscosity when maintained at the molding temperature, so it can be molded stably.

The above benzylic ether type phenol resin is produced as follows.

That is, a phenol compound and an aldehyde represented by RCHO (R is H or a hydrocarbon group) are mixed in a ratio of about 1:1 to 3 using a metal salt catalyst, such as a salt of zinc, cobalt, manganese, tin, etc. Obtained by reaction. This resin has properties intermediate between resol and 7volac.

These resins are usually used after being diluted with a solvent such as acetone or ethanol.

The mixing ratio of carbon powder and resin is 100 parts by weight of the former and 15 to 50 parts by weight of the latter as non-volatile content excluding the solvent. If the amount of resin is less than 15 parts by weight, injection molding becomes difficult and cracks are likely to occur in the formed product, while if it exceeds 50 parts by weight, shrinkage during firing will be large and the dimensional stability of the product after firing will be affected. It is easy to chip or crack during firing (
Become.

The carbon powder and resin are kneaded using a conventional pressurized kneader or the like. The kneaded material is cured in advance at about 100° C., and the solidified material is crushed and used for molding.

The molding method is preferably injection molding, and as shown in FIG.

Next, this formed body is exposed to a non-oxidizing atmosphere such as nitrogen.
The resin is fired at a temperature of 2500'C or higher to carbonize and graphitize it. If the firing temperature is less than 2500° C., problems will arise in the oxidation resistance, heat spalling resistance, electrical conductivity, etc. of the crucible. There is no particular upper limit on the temperature, but industrially it is 3000℃.
The extent is the limit.

The normal operating temperature of the graphite crucible in this analytical method is 2
The temperature is approximately 400-2600°C, but when measuring special components such as boron, it is used at 2700-3000'C. Therefore, it is particularly preferable that the firing temperature is 2700° C. or higher.

Carbonized thermosetting resin is hard carbon. Hard carbon is dense, has a small non-surface area, is oxidation resistant, and has excellent impermeability. This property increases the resistance of the sample to a graphite crucible and prevents it from being damaged during analysis when it is heated to 500 mt.

In addition, by molding by injection molding, a molded article with uniform dimensions of each part can be easily obtained. Due to this lack of variation in dimensions, there is no difference in calorific value between individual crucibles when the graphite crucibles are heated with electricity during analysis, and stable analytical values can be obtained.

〔Example〕

Next, the present invention will be specifically explained by showing Examples and Comparative Examples.

Examples 1 to 7 First, a benzylic ether type phenol resin was produced as follows.

That is, formalin (1.5 mol in terms of CH, O) was added at a ratio of 37 wt% to 1.0 mol of Fer/-, and as a catalyst, 0.005 mol of zinc acetate anhydride was added at 100'C. The mixture was allowed to react for 2 hours.

After the reaction was completed, water was removed by vacuum dehydration to reduce the water content to 1 wt % to obtain a Fer/Fell resin.

The physical properties of the obtained resin are Viscosity 12,000 CP Non-volatile content 80% Moisture 0.9% Met.

In addition, artificial graphite (manufactured by Showa Denko K.K., U
Using 30 μm powder (average particle size: 10 μm) of FG), the above benzylic ether type phenol resin was added to it in the respective ratios /f! Using a 30Q pressure kneader (manufactured by Moriyama Seisakusho Co., Ltd.), the pressurization pressure was 1 kg/
cm', and kneaded for 60 minutes at room temperature. This kneaded paste was breculated at +00°C for 20 minutes and then crushed in a hammer mill to obtain a coloring material.

Molding was carried out using a 65-ton thermosetting resin injection molding machine (manufactured by Meiki Seisakusho Co., Ltd.) under conditions of a mold temperature of 190° C. and a total mold clamping pressure of 50 tons.

The molded product has the shape shown in Figure 1, and the dimensions of each part are as follows.
a: 14.6mmφ, b: 13mmφ, C゛1.3mm
5d + 20.0mmSe: 6. On+mφ・
It was set to f゛3mm.

This formed body was prepared in a nitrogen atmosphere at a temperature of about 5°C according to a conventional method.
The temperature was raised at a heating rate of hr, and the graphite crucibles were produced by firing at each temperature t.

Prepare 7 of these crucibles and set them in a simultaneous oxygen and nitrogen analyzer (manufactured by LECO, TC-436).
pm, amount of nitrogen contained, 68±3 ppm) was analyzed, and variations in analytical values due to the crucible used were investigated.

Example 8.9 The same as Examples 1 to 7 except that powder of calcined coke (manufactured by Nippon Mining Co., Ltd., Petrocoke) with a maximum particle size of 100 μm and an average particle size of 40 μm was used instead of the artificial graphite powder. Made it the same.

Comparison f+ 1.2 Same as Examples 1 to 7 except that the firing temperature was 2300°C.

Comparative Example 3 Same as Example 8.9 except that the firing temperature was 2300°C.

Comparative Example 4 The same measurements as in Examples 1 to 7 were performed except that a commercially available graphite crucible (made by machining a normal graphite material, manufactured by Hitachi Chemical Co., Ltd.) was used.

The results of Examples 1 to 9 and Comparative Examples 1 to 4 are collectively shown in Table 1.

As is clear from Table 1, the crucibles produced by the method of the present invention have little variation and can provide highly reliable analytical values.

Example 10 A lead crucible was made with 30 nuts under the conditions of No. 5 in Table 1, and +f1 was added to a, b, c, and d of the formed shape shown in Figure 1.
``The dimensions and weight of the U part were measured.

Further, as shown in FIG. 2, a copper electrode 2 made of a 20 mmφ round bar was brought into contact with the crucible, a constant current of 1 ampere was applied, and the voltage drop was measured by the four-terminal method.

Comparative Example 5 Measurement was carried out in the same manner as in Example 10, except that a commercially available graphite crucible for oxygen and nitrogen analysis was used.

Example 10. The results of Comparative Example 5 are shown in Table 2.

Table 2 It can be seen from Table 2 that the voltage drop variance of the graphite crucible made by the method of the present invention is much smaller.

〔Effect of the invention〕

As described above, the method for manufacturing a graphite crucible according to the present invention does not require any post-processing, and can be obtained at a low cost with higher dimensional accuracy and significantly smaller variance in voltage drop than commercially available graphite crucibles. .

When measuring the content of oxygen and nitrogen in the fields of metal materials, ceramic materials, superconducting materials, electronic materials, etc., this analytical crucible is disposable for each sample measurement, and the number of crucibles consumed is large. The present invention, which makes it possible to supply an inexpensive and high-performance graphite crucible for analysis, will greatly contribute to the industrial world.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a formed body formed by the method of the present invention, and FIG. 2 is an explanatory diagram of a method for measuring the voltage drop in a crucible.

Claims (1)

[Claims] After adding 15 to 50 parts by weight of a thermosetting resin to 100 parts by weight of carbon powder and kneading the mixture, molding it into the shape of a crucible,
A method for producing a graphite crucible for oxygen and nitrogen analysis, which comprises firing at a temperature of 2500° C. or higher in a non-oxidizing atmosphere.