JP2007119296A - Heat-resistant container made of iridium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-wall heat-resistant container having long service life, usable at a higher temperature than heretofore and applicable to a Bridgman crucible or the like. <P>SOLUTION: This heat-resistant thin container made of iridium has a thickness of ≤0.3 mm and is formed by electrolysis of a molten salt including iridium salt. In the constituent material of the container, it is preferable that the total content of impurity elements except noble metals is ≤100 ppm and further, that of noble metals except iridium is ≤10,000 ppm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin heat-resistant container made of iridium. Specifically, the present invention relates to a container used in a high-temperature environment such as a Bridgeman crucible or a sample cell of a thermal analyzer.

Like a crucible (ampoule) used in the Bridgeman method, which is one of the single crystal manufacturing methods, and a sample cell used in thermal mass-differential heat (TG-DTA) analysis for analyzing the state of a substance in the heated state For such a small heat-resistant container, a thin heat-resistant container made of platinum or a platinum alloy is often used. In these applications, the container is often exposed to a relatively high temperature environment, and in addition to a decrease in strength of the container itself and a change in mass due to oxidation, high temperature strength and corrosion resistance are required in order to prevent contamination of the contents. And platinum has high corrosion resistance and heat resistance, and has high strength even if it is thin.
JP 2003-171198 A

  However, even a conventional container made of platinum or a platinum alloy may break or deform with use. This is often due to an increase in use time due to long-term use and repeated use, rather than a problem of high or low use temperature.

  Further, conventional platinum or platinum alloy containers may not be able to sufficiently meet future demands in the above-described applications. For example, in the field of single crystal manufacturing by the Bridgman method, single crystal production of materials having a temperature of about 1000 ° C. or lower has been the mainstream so far, but the Bridgman method can produce single crystals with few lattice defects. Since there is an advantage, the expansion of the applicable material is examined in the future, and the application to high melting point single crystal materials such as sapphire and rutile is being studied. On the other hand, platinum has sufficient durability up to a high temperature of about 1000 to 1500 ° C. However, high temperature heating of 2000 ° C. or more is necessary in the production of a single crystal of sapphire, and platinum or a platinum alloy cannot be used.

  Therefore, an object of the present invention is to provide a long heat-resistant container that can be used at a higher temperature than a conventional thin-walled heat-resistant container.

  The most common countermeasure effective for the above problem is a material change. The inventors of the present invention studied to use iridium (pure iridium) as a constituent material instead of conventional platinum and platinum alloys. Iridium has a melting point of over 2400 ° C., can be used at a higher temperature than platinum, and has sufficient mechanical properties.

  On the other hand, when iridium is used as a thin heat-resistant container, there is a problem of workability as a problem to be cleared. Although iridium has high strength, it has an inferior workability, and plastic processing to a thin plate or cylinder is difficult. Further, when processing a thinned material as much as possible into a container shape, cracks and cracks are likely to occur during the process (cutting, bending, etc.), and welding is also difficult.

  Iridium is a high-strength material, but even if it is applied to a heat-resistant container such as a Bridgman crucible, it does not always enable long-term use. In the case of Bridgman crucibles, etc., the stress applied in the process of use is the sum of the weight of the container itself and the weight of the internal single crystal (sample in the case of an analyzer cell), but it is not so large. In addition, the method of applying stress is static. As described above, a material subjected to a static low stress load is not simply high in strength (creep rupture strength) but has flexibility (even if the rupture strength is low, the durability time is long or the durability temperature is low). Be high).

  Therefore, the present inventors have further studied to find a product having improved high processability and a high temperature characteristic corresponding to a statically loaded container while applying iridium, and arrived at the present invention. did.

  That is, the present invention is an iridium heat-resistant container made of iridium and having a thickness of 0.3 mm or less and formed by molten salt electrolysis of a molten salt containing an iridium salt.

  Molten salt electrolysis is an electrocasting method using molten salt as an electrolyte, and is a method of depositing metal (iridium) in the electrolyte on the cathode surface and recovering bulk metal. In this molten salt electrolysis, a precipitate following the size and shape of the cathode can be obtained, and the thickness can also be adjusted by the electrolysis conditions (current density, electrolysis time). Therefore, the shape of the product can be easily controlled, and a thin container can be manufactured without being aware of the workability of the material.

  Furthermore, iridium produced by molten salt electrolysis has a material that is preferable as a high-temperature heat-resistant container in its material properties, and it has a low breaking strength and is softer than a material that has undergone normal casting, rolling, etc., but it has a long breaking time. Has characteristics. As a cause of this, the present inventors have found that iridium produced by molten salt electrolysis has a relatively large crystal grain size, and since there are very few impurities as described later, there is little segregation of impurities at the grain boundaries. This is considered to be due to the tendency that intragranular slip has priority over intergranular slip when a load is applied.

  The iridium container produced by molten salt electrolysis according to the present invention is made of high-purity iridium with a low impurity content and has very few internal defects. This is because the electrolytic method is a separation precipitation method using a precipitation potential difference. Here, in the present invention, the total concentration of impurity elements excluding noble metals is preferably 100 ppm or less, and the total concentration of noble metals excluding iridium (platinum, gold, silver, ruthenium, palladium, osmium) is 10000 ppm or less. Is more preferable.

  Here, as a molten salt for depositing iridium by molten salt electrolysis, it is natural to include an iridium salt, but a solvent salt containing a molten salt such as a chloride or a cyanide is preferable. These solvent salts play a role as ionic conductors in the electrolysis process, and by electrolyzing the mixed molten salt containing such solvent salts, the molten salt temperature can be efficiently reduced while reducing the operating temperature. It becomes possible to deposit iridium. As the solvent salt, it is preferable to use a mixed salt of three kinds of chlorides of sodium chloride, potassium chloride and cesium chloride. These mixed salts can easily dissolve the iridium salt. By using this mixed molten salt, it is possible to obtain a precipitate having a small internal stress and containing no impurities. The composition of the mixed molten salt is preferably in the range of 25 to 35 mol% sodium chloride, 20 to 30 mol% potassium chloride, 40 to 50 mol% cesium chloride, 30 mol% sodium chloride, 24.5 mol% potassium chloride, 45 cesium chloride. It is particularly preferable that the amount be 5 mol%. This is because the iridium salt is easily dissolved within this range.

  In addition, as molten salt temperature at the time of molten salt electrolysis, it is preferable to set it as 450-650 degreeC, and it is especially preferable to set it as 500-550 degreeC. If the temperature is lower than 450 ° C., the molten salt tends to solidify and it is difficult to maintain the molten state. If the temperature exceeds 650 ° C., continuous precipitates cannot be obtained. Moreover, the reason why the range of 500 to 550 ° C. is optimized is that the surface properties (surface roughness) of the precipitate can be improved.

As for the electrolysis conditions, the dimensions of the container to be produced, is adjusted to a more thicker, preferably the current density 1-5A / dm ^2. This is because if it is less than 1 A / dm ² , the deposition rate becomes slow and the electrolysis time increases, and if it exceeds 5 A / dm ² , the surface properties of the precipitate are disturbed and the thickness distribution of the container becomes uneven. . The electrolysis time is preferably 5 to 24 hours.

  As described above, according to the present invention, by using iridium as a constituent material, it is possible to meet a demand for use at a high temperature that cannot be handled by a conventional heat-resistant container. In the present invention, although it is made of iridium having poor processability, it is made into a thin container by molten salt electrolysis, and the production efficiency is good. And the container manufactured by molten salt electrolysis has a (mechanical) characteristic required for the heat-resistant container used under a static stress load.

  The heat-resistant container according to the present invention can be applied as a heat-resistant container for sample cells, after heaters, lids, etc. for TG-DTA analyzers, in addition to Bridgeman crucibles for single crystal production.

  Embodiments of the present invention will be described below. In this embodiment, the iridium container was manufactured by the electrocasting method using the mixed molten salt containing an iridium salt. The composition of the mixed molten salt used in the present embodiment is as shown in Table 1.

  Electrocasting was performed using the mixed molten salt as an electrolyte. The electrocasting was performed using the molten salt electrolysis apparatus 10 shown in FIG. As shown in FIG. 1, the molten salt electrolysis apparatus 10 serves as a cylindrical container 11 having an open upper surface, a flange 12 having an electrode insertion port serving as a lid of the cylindrical container, a graphite electrolytic cell 13, and a mold. A cathode rotating means 14 is provided. The cylindrical container 11 can be separated into two chambers by a gate valve 15, and the upper chamber serves as a preliminary exhaust chamber when the cathode 16 is loaded or taken out. Note that rod-shaped graphite having a diameter of 50 mm and a length of 150 mm is used for the cathode. During electrolysis, the iridium anode 1 was laid so as to be in contact with the bottom of the electrolytic cell 13, and the distance between the anode and the cathode was set to 50 mm. In addition, current was supplied to the iridium anode 1 in contact with the electrolytic cell by supplying current to the electrolytic cell 13. In the present embodiment, the iridium electrode is used as the soluble anode as the electrode facing the cathode, but an insoluble anode can also be used. However, it is preferable to use a soluble anode in order to more efficiently deposit iridium. This is because, according to the soluble anode, replenishing noble metal ions from the anode makes it possible to maintain a constant iridium ion concentration in the solution and obtain uniform precipitates without replenishing iridium salts from the outside.

The electrocasting conditions in this embodiment were a bath temperature of 530 ° C., a cathode current density of 2 A / dm ^2, and electrolytic deposition with a deposition time of 12 hours. The iridium precipitate was peeled off from the cathode after pickling. By the above operation, an iridium container having an inner diameter of 50 mm, a thickness of 0.25 mm, and a length of 100 mm was obtained.

  Next, a test piece was cut out from the manufactured container and subjected to a high temperature creep test and a high temperature tensile test. In any test, as a comparison, an iridium plate material manufactured by melting and rolling was also tested.

FIG. 2 shows the results of the high temperature creep test. In this test, the load was changed at a test temperature of 1600 ° C., the rupture time was measured, and a stress-rupture time curve was created. From FIG. 2, it can be seen that the iridium material produced by molten salt electrolysis produced in this embodiment has a different slope of the stress-rupture time curve from the comparative melt-rolled material. And the iridium material manufactured by molten salt electrolysis has the rupture time in a low load area longer than the melt rolling material. Stress iridium material of the present embodiment - the rupture time curve is shown by ^{y = 33.7x -0.15,} in the comparative example are shown in ^{y = 71.7x -0.33,} produced by molten salt electrolysis The slope of the stress-rupture time curve of the iridium material is smaller than that of the melt-rolled material. According to the present inventors, the slope of the straight line when the stress-rupture time characteristics of an iridium material produced by molten salt electrolysis is logarithmically displayed as shown in the figure is -0.10 to -0. It is in the range of 20.

  3 and 4 show the appearance of fracture surfaces of both materials after creep rupture. From this figure, it can be seen that the iridium material obtained by molten salt electrolysis is broken within the grains. Further, it was confirmed that this material has a large elongation and breaks by a mechanism different from that of the melt-rolled material.

  Next, Table 2 shows the results of the high temperature tensile test. In this test, the test temperature is 1200 ° C. The temperature was 1500 ° C. 5 and 6 show the results of a tensile test at each temperature. Table 2 shows characteristic values such as tensile strength and elongation measured in this test.

  As can be seen from FIG. 3, at any test temperature, the molten salt electrolyte material is inferior in strength, such as tensile strength and yield stress, to the melt-rolled material, but the elongation is remarkably large and has ductility. According to the inventors, when a plurality of tests were performed on the molten salt electrolytic material, the yield stress was 35 to 65 MPa and the elongation was 80 to 110% at a test temperature of 1200 ° C., and the yield stress was 10% at 1500 ° C. It has been confirmed that the elongation is in the range of 80 to 100% at ˜25 MPa.

  Next, an iridium container according to the present embodiment was used as a Bridgman crucible, and a single crystal production test was conducted. Single crystal production was performed by pre-sintering high-purity alumina powder (5N) and encapsulating it in an iridium crucible with single crystal seeds. Then, the crucible was inserted into a cylindrical electric furnace having a hot zone of 2100 ° C. and 100 mm, and the crucible was lowered at a descending speed of 3 mm / h. Thereafter, the crucible for cooling the electric furnace was taken out.

  When the appearance of the crucible taken out was observed, no extreme deformation was observed, and no breakage such as a crack was observed on the surface. Then, the crucible was broken and the internal sapphire single crystal was recovered and observed for appearance, but the surface had the appearance of a clean single crystal material.

The figure which shows the structure of a molten salt electrolysis apparatus. The figure which shows the stress-rupture time curve in a high temperature creep test. The photograph which shows the fracture surface after high temperature creep rupture of molten salt electrolyte material. A photograph showing a fracture surface of a melted and rolled material after high temperature creep rupture. The figure which shows the result of a high temperature tensile test (1200 degreeC). The figure which shows the result of a high temperature tensile test (1500 degreeC).

Claims (5)

A thin heat-resistant container made of iridium and having a thickness of 0.3 mm or less,
An iridium heat-resistant container formed by molten salt electrolysis of a molten salt containing an iridium salt. The iridium heat-resistant container according to claim 1, wherein the total concentration of impurity elements excluding noble metals is 100 ppm or less. The heat-resistant container made of iridium according to claim 1 or 2, wherein the total concentration of noble metals excluding iridium is 10,000 ppm or less. The Bridgman crucible which consists of an iridium heat-resistant container of any one of Claims 1-3. The heat-resistant cell for thermal analyzers which consists of an iridium heat-resistant container of any one of Claims 1-3.