Method for creating phase equilibrium diagram

Abstract

To provide a method for creating a phase equilibrium diagram, capable of obtaining a phase relationship obtained by applying maximum fractional crystallization action, easily preparing a raw material molding and stably holding a melt in the formation process of a solidified material for measuring composition distribution.SOLUTION: A method for creating a phase equilibrium diagram comprises: a step (1) of irradiating the upper surface of a raw material molding obtained by mixing and molding two or more kinds of solid materials with infrared light to melt the upper surface of the raw material molding and slowly cool and solidify the obtained melt; and a step (2) of measuring the composition distribution of the solidified material obtained in the step (1) to create a phase equilibrium diagram on the basis of the measurement result.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for creating a phase equilibrium diagram. [Background technology]

[0002] There is a great social demand for the development of new materials to meet the sophistication of next-generation science and technology, such as the shift away from fossil fuels and high-capacity, high-speed communication technology. In general, the development of new materials is carried out through an organic link between the search for new substances, the growth of single crystals of the target substance, the measurement of physical properties, and applied research.

[0003] Phase equilibrium research, which aims to discover new materials, is an important field that supports the foundations of materials science and sometimes attracts a great deal of attention due to the discovery of a series of new materials. Although the elements that exist on Earth are limited, there is a high possibility that unknown and useful compounds will be discovered in the compounds that are produced by combining them, such as three-component or multi-component systems.

[0004] Many methods have been proposed for studying phase equilibrium, but they can be broadly classified into static and dynamic methods. Static methods hold a system at a given temperature until it reaches a completely equilibrium state, and attempt to obtain a phase diagram based on the state at that time. Examples of static methods include the quenching method and the fractionation method.

[0005] Dynamic methods, which involve changing the temperature, pressure, etc., and observing the accompanying changes in state to obtain a phase diagram, include thermal analysis methods. This method, for example, involves measuring the heat generation or endothermic temperature of a sample while increasing the temperature at a constant rate or slowly cooling it down, in order to determine the phase change. If the rate of temperature increase is increased, it becomes easier to identify the state change, but errors will occur in the measurement of the change temperature. Therefore, it is desirable to increase the rate of increase as slowly as possible, but if it is too slow, there is a risk that slight changes will be overlooked. For these reasons, the quenching method has become the mainstream method for studying phase equilibrium.

[0006] 1) Phase equilibrium study using quenching method To determine what compounds are present in a system consisting of substance A and substance B and to clarify their properties by investigating their melting points, a typical method is to prepare samples with different mixture ratios of A and B, place small amounts of each mixture ratio sample in a platinum crucible or other container and heat it to a specified temperature. Once it is determined that the reaction has progressed and equilibrium has been reached, the sample is rapidly cooled as is and the presence or absence of products and the melting properties of the compounds produced are examined to obtain information on phase equilibrium. This method is called the quenching method. In order to obtain information as accurately as possible using the quenching method, samples with different mixture ratios are subjected to various temperature changes and the changes in state of each are carefully examined. The more the mixture ratio is changed, the more accurate the results.

[0007] Figure 1 shows a schematic diagram of an experiment to obtain information on the phase equilibrium of a two-component system of substance A and substance B. The composition ratio is changed by 5%, and for each, the temperature is increased by 100°C from 1000°C, and the sample is left at each temperature until it reaches equilibrium, and then it is rapidly cooled to prepare the test sample.

[0008] Even if, in order to reduce the number of experiments, samples with different composition ratios were placed individually in crucibles and processed under the same temperature conditions to produce quenched samples, there would still be 152 positions where the dotted lines in Figure 1 intersect, meaning that the number of samples to be examined would be 152. It is clear that it would take an enormous amount of time and effort to perform structural examinations on each of these samples using powder X-ray diffraction, optical microscopes, etc.

[0009] Naturally, with a rough mixing ratio, accuracy decreases and the risk of missing important reactions increases. In addition, the reaction rate of powdered raw materials tends to be slow at low temperatures and fast at high temperatures, and the time required to reach equilibrium increases as the temperature decreases. Therefore, if accuracy of the results is required, the number of experiments and the time required for the experiments will increase exponentially. Furthermore, when the number of constituent elements increases to a three-component or four-component system, for example, in a three-component system consisting of A, B, and C, in addition to the three two-component systems AB, BC, and AC, a huge number of samples with different mixing ratios of each of the three components ABC must be subjected to quenching experiments, and the overall effort and time required will be orders of magnitude greater than that of a two-component system.

[0010] As already mentioned, the quenching method is based on a powder reaction, and requires a long time to reach equilibrium. Furthermore, containers such as crucibles impose restrictions on the atmosphere and temperature. For example, platinum, a typical crucible material, cannot be used in a reducing atmosphere, and its maximum operating temperature is limited to about 1600°C. It is possible to increase the maximum operating temperature by adding rhodium, but even so, it is limited to about 1800°C.

[0011] On the other hand, the method using a melt has the advantage of being able to shorten the reaction time. Also, the method using a floating zone, which allows experiments without using a crucible, which has many experimental constraints, has been considered.

[0012] 2) Phase equilibrium study method using maximum fractionation Bowen clarified the correlation between fractional crystallization and phase equilibrium, established the reaction principle, and pointed out the importance of considering fractional crystallization when melting and crystallizing magma, which is important in geoscience (Non-Patent Document 1). This indicates that when the liquid or solid phase generated during melting or crystallization of any composition is removed from the reaction system for some reason, a result different from that obtained in an equilibrium system may be obtained depending on the degree of removal. For example, during crystallization, the generated solid phase floats or precipitates due to the difference in density with the liquid, and the reaction with the liquid is suppressed. Fractional crystallization also occurs when the temperature of the system drops suddenly, the diffusion inside the solid phase cannot keep up, a reaction edge is formed on the surface, and the reaction with the inside of the solid phase cannot be made.

[0013] Therefore, in fractional crystallization, the composition of the liquid changes depending on the amount of solid phase removed from the system, the reaction time, and other factors, so a huge number of reaction systems can occur. Bowen called the most complete system of fractional crystallization, that is, crystallization under conditions in which re-reaction between the crystallized solid phase and the liquid is completely suppressed, maximum fractionation. In maximum fractional crystallization, only the precipitation of the solid phase from the liquid phase continues unilaterally, and re-reaction between the liquid and the solid phase must be suppressed, and the temperature in the solid phase must be low enough to move away from the interface with the liquid. The precipitation state of the solid phase obtained under such conditions should completely reflect the phase equilibrium diagram.

[0014] Incidentally, the above-mentioned fractional crystallization utilizes a reaction in an environment completely different from that of the quenching method, which assumes that the temperature of the entire system is homogeneous, because the temperature of the solid phase away from the interface between the solid and liquid phases is lower than the interface temperature. For this reason, it is sometimes misunderstood that a reaction in an environment where the temperature is not homogeneous is not at equilibrium. This is not only due to a simple lack of understanding of the correlation between fractional crystallization and phase equilibrium diagrams, but is also due to the fact that no experimental method had been established up until then that could theoretically perform maximum fractional crystallization with good reproducibility.

[0015] Tiller was the first to propose an experimental method for studying phase equilibrium using this fractional crystallization (Non-Patent Document 2). Tiller's idea is a method that uses normal freezing (although he uses the term controlled solidification), and Phann, who established a refining method using the zone melting method, also describes a similar idea (Non-Patent Document 3).

[0016] Figure 2 shows a conceptual diagram of a mechanism known as normal freezing, or unidirectional solidification. When a sample with melting point P is placed in a long, narrow container 10 and placed at the position shown in Figure 2(A), the sample melts completely and becomes liquid 11. When this container 10 is slowly moved to the left, the molten sample solidifies after passing the melting point position, resulting in the state shown in Figure 2(B). When the container 10 is left stationary in this position, an equilibrium state is reached within the container 10 with the solid 12 and liquid 11 in contact, with the melting point position serving as the interface 13.

[0017] In the case of unidirectional solidification, the liquid phase and the solid phase are completely separated by the interface 13, and the temperature in the solid phase decreases the further away from the interface 13, meaning that solidification of the system proceeds with this interface 13 moving slowly. At this time, the liquid phase is stirred and has a homogenous concentration, and there is no crystallization in the liquid phase or incorporation of the liquid phase into the solid phase.

[0018] First, a liquid phase of the desired composition is formed and slowly crystallized by unidirectional solidification as shown in Figure 2. During this process, if the position and temperature of the solid-liquid interface are accurately measured and recorded in some way while the liquid phase is thoroughly stirred, the relationship between composition and position can be determined after all the liquid phase has solidified, and this can be used to determine the relationship between temperature and composition, and hence the solidus and liquidus. At this time, the system must satisfy the following three conditions:

[0019] (i) The solid and liquid phases can be considered to coexist in equilibrium at their interface even as the solid phase continues to grow. (ii) There is no change in composition due to diffusion within the solid phase. (iii) The liquid phase is thoroughly mixed and its composition can be considered homogeneous. Based on this idea, Tiller et al. have investigated the phase equilibrium of the binary system Bi2Te3-Bi2Se3 (Non-Patent Document 2).

[0020] As mentioned above, the phase equilibrium research method using fractional crystallization does not use powder reactions but melt reactions, and should be far superior to the quenching method, but in reality, this method has not been used much and there have been few successful examples. Pfann gives the following two reasons for this (Non-Patent Document 3).

[0021] a) It is difficult to measure the position of the solid-liquid interface in relation to its temperature and composition. b) The liquid must always be homogeneous, but in the zone melting method using a conventional cylindrical vessel, it is difficult to stir the liquid, making it difficult to achieve a homogeneous liquid.

[0022] Furthermore, at that time, quantitative analysis methods for small parts of solid samples had not been established, and the methods for analyzing experimental results were insufficient, so it was not possible to establish detailed correspondences with phase equilibrium diagrams, and it seems that applications had to be limited to determining eutectic compositions that do not require analysis of small parts. In this situation, the development of the EPMA (Electron Probe Micro Analyzer) as a device for analyzing the composition of solid samples was significant. This device irradiates an electron beam and measures the characteristic X-rays emitted from the sample to determine the composition of an unknown sample. It was a groundbreaking device that could quantitatively analyze the composition of microscopic areas of less than a few micrometers by narrowing the electron beam diameter.

[0023] The development of a phase equilibrium research method that applies maximum fractionation by applying the floating zone method, which can hold the melt by its own surface tension without using a crucible, has been eagerly awaited. The floating zone slow cooling method (Non-Patent Document 4) has been developed as a method that satisfies this requirement. This method is derived from the process of research into single crystal growth by the floating zone melting method. In the case of single crystal growth, as shown in FIG. 3, a raw material rod 20 made of powder of the starting composition molded into a round rod is hung on the upper shaft, and the lower end of the raw material rod 20 is locally heated and melted by irradiation with infrared rays 21, and then joined to a rod-shaped seed single crystal (seed rod) 22 arranged below to form a floating zone (melted region) 23 (FIG. 3(a)). While stably maintaining the floating zone (melted region) 23, the upper and lower shafts are moved downward at the same time to continue melting the raw material and generating a single crystal 24 by solidification from the melt (FIG. 3(b)), and a round rod-shaped single crystal 24 is grown (FIG. 3(c)).

[0024] When conducting phase equilibrium research, as shown in Figure 4, raw material rods 30, 30 molded into a round bar shape are placed on the upper and lower shafts, respectively, and a floating zone (molten area) 33 is formed in the same manner as in the single crystal manufacturing method (Figure 4 (a)), and then slowly cooled. At this time, the amount of the floating zone (molten area) 33 decreases, so the upper and lower shafts are slightly moved in opposite directions so that the width and height of the melt, i.e., the floating zone (molten area) 33, become the same (Figure 4 (b)). By this operation, a sample is obtained in which melted and then solidified parts (solidified parts) 34, 34 are formed at each of the opposing ends of the raw material rods 30, 30 (Figure 4 (c)). By examining the composition distribution of the solidified parts 34, 34 using an EPMA device, knowledge about phase equilibrium when maximum fractionation is applied can be obtained.

[0025] 3) Principle of the floating zone annealing method In the floating zone melting method, the melt is held by the surface tension of the melt itself, so there is no need to use a container such as a crucible. Therefore, there are no experimental constraints such as temperature, atmosphere, and chemical reactions that are imposed when using a crucible. Furthermore, the melt zone formed can be stirred by rotating the upper and lower support shafts in opposite directions, so the composition of the melt zone can be kept uniform. The temperature of the melt formed between the upper and lower feed rods (seed single crystals) is the highest, and the temperature drops rapidly as it moves away from these, so the maximum fractionation effect is naturally applied. This provides an experimental environment with extremely favorable conditions for phase equilibrium research methods that apply maximum fractionation effect.

[0026] In light of the above background, a new phase equilibrium research method named the slow cooling float zone (SCFZ method) was established (Non-Patent Document 4). This method experimentally makes it possible to perform maximum fractionation, which has the least reaction between the liquid and the precipitated solid phase, among the fractional crystallization methods established by Bowen (Non-Patent Document 1), and thereby aims to obtain phase equilibrium diagrams quickly and accurately. This floating zone slow cooling method was born from research into single crystal growth of decomposed melting compounds using the floating zone method, and applies the techniques of single crystal growth throughout sample preparation, melting and solidification experiments, characterization of solidified samples, and uses similar equipment. The floating zone slow cooling method has many advantages, such as not requiring a crucible and the fact that temperature measurement errors do not affect the results very much.

[0027] For example, if substances A and B have the phase relationship shown in Figure 5, and a mixture of composition D1 is placed in a suitable crucible and the temperature is raised, substance A and reaction product C coexist in a solid state at temperature T1. When the temperature exceeds T2, liquid begins to form, and at temperature T3, solid A and liquid (composition D3) coexist, with the mass ratio of solid A to liquid at this time being S2:L2. As the temperature increases further, the amount of liquid formed increases, and at temperature T4, the mass ratio of solid A to liquid (composition D2) is S1:L1. When the temperature exceeds T5 and reaches T6, the mixture is completely dissolved.

[0028] To clarify the above relationship using the quenching method, it is necessary to carry out heating, holding, and quenching experiments at least 10 times for a sample with the same composition D1. In general, the phase relationship shown in Figure 5 is unknown, and in such cases, the accuracy of the results will deteriorate unless many more quenching experiments are carried out. To know the phase equilibrium relationship of the entire two-component system of substances A and B, samples with different mixture ratios of A and B must be prepared and quenching experiments must be carried out several times or more for each, which requires a huge amount of time and effort.

[0029] On the other hand, there is a report on the phase equilibrium of the MgO-TiO2 binary system (Non-Patent Document 4) as an example of investigating phase relationships using the floating zone slow cooling method. According to this report, a composition with a molar ratio of MgO:TiO2 = 80:20 was melted as the starting composition, and a solidified material was produced while maintaining maximum fractionation. The solidified bar obtained was then cut into two vertically, and the surface was polished. The state of the sample is shown in Figure 6. It can be seen from the figure that multiple different textures form a chemical zone structure.

[0030] The following findings were obtained from one experiment in which the composition distribution of the sample in Figure 6 was measured using an EPMA. a) The composition of the solidified material was initially MgO, then Mg2TiO4, MgTiO3, and finally a eutectic of MgTiO3 and MgTi2O5. b) Both Mg2TiO4 and MgTiO3 are decomposing melting materials. c) MgTiO3 has a solid solution region, and the solubility limit is 3%. d) As the temperature decreases, the solubility limit of MgTiO3 solid solutions decreases. In other words, a phenomenon called exsolution occurs. e) MgTiO3 and MgTi2O5 form a eutectic with a molar ratio of 39:61.

[0031] The above findings were obtained from just one floating zone slow cooling experiment. In order to discover decomposition melting properties such as Mg2TiO4 and MgTiO3 using the quenching method, a considerable number of detailed quenching experiments are required. Furthermore, the existence of the solid solution region of MgTiO3 and the exsolution phenomenon are extremely difficult to discover using the quenching method, and these properties were completely unknown in some previous reports (Non-Patent Documents 5 and 6).

[0032] As can be seen from the examples of reports shown in Figure 7, the results obtained by the quenching method are completely different. In none of them was the existence of a solid solution region in MgTiO3 or the phenomenon of exsolution detected. From these examples, it is easy to understand how excellent the floating zone slow cooling method is for phase equilibrium experiments.

[0033] 4) Limitations of the floating zone annealing method As mentioned in the previous section, the floating zone slow cooling method is a method that can provide detailed knowledge about many phase relationships with a small number of experiments, and is a groundbreaking method that can provide clear experimental results, particularly regarding the presence of solid solution regions and accurate detection of solid solution limits, as well as the presence or absence of exsolution phenomena in solid solution regions. However, since the floating zone slow cooling method was reported, there have been almost no reports of phase equilibrium research results using this method. There are several possible reasons why the floating zone slow cooling method has not become more widespread.

[0034] A) The experimental equipment required will be several pieces of equipment described below, which will cost a considerable amount of money overall. Equipment for forming raw powder into rod shape A device that heats and sinters rod-shaped samples to produce straight, dense sintered rods. ·Single crystal manufacturing equipment using the floating zone method - Cutting and polishing equipment for the solidified rods obtained ·EPMA (Electron Probe Microanalyzer) Equipment a) In order to form a stable melt, it is necessary to establish the conditions for producing a highly dense raw material rod. (c) In order to stably form the floating zone and slowly cool it to obtain a solidified rod, it is necessary to maintain heating conditions that match the ever-decreasing amount of molten material and to establish conditions for optimally controlling the relative positions of the upper and lower raw material rods. For example, in systems containing heavy elements such as lead and bismuth, it is difficult to form a melt, making it difficult to apply the floating zone slow cooling method. e) The formation of a stable melt was difficult due to the existence of a solid-liquid coexistence region. This tendency became more pronounced in multi-component systems.

[0035] Among the above several factors, factors d) and e) in particular are essential problems with the floating zone annealing method. Factor d) is a problem that inevitably arises when the specific gravity of the constituent elements is high, while factor e) is a problem that becomes particularly important when investigating the phase relationship of a multi-component system.

[0036] In Figure 5, a melt is formed when a raw material rod of composition D1 is locally heated to a temperature T6 indicated by point P. At this time, the temperatures of the upper and lower raw material rods drop rapidly as they move away from the maximum temperature T6 in the center in the vertical direction. If this is illustrated, it will appear as shown in Figure 8.

[0037] If the composition of the raw material rod shown in the schematic diagram of Figure 8 is D1 in Figure 5, when it is heated by irradiating infrared rays, infrared absorption begins near the surface of the raw material rod, and the raw material rod liquefies. As the amount of infrared rays is absorbed and decreases as it progresses deeper into the liquid that is formed, the temperature inside the raw material rod is lower than the surface. Therefore, if the temperature near the center of the raw material rod is raised to T6 to completely liquefy the solid, the temperature decreases as it moves away from the center, but a region where solid and liquid coexist is formed between T5 and T2. The solid that coexists and floats with the liquid loses its ability to hold the liquid, so the liquid in this state is extremely easy to fall overall. This tendency becomes stronger as the system becomes more multi-component, and the applicability of the stable floating zone slow cooling method deteriorates. [Prior art documents] [Non-patent literature]

[0038] [Non-Patent Document 1] NL Bowen: Amer. J. Sci., 33 (1912) 55l. [Non-Patent Document 2] WA Ti11er: Trans. AIME,215(1959)555. [Non-Patent Document 3] WG Phann: “Zone Melting” 2nd ed. (Robert E. Krieger Co. New York,1978). [Non-Patent Document 4] I. Shindo: J. Crystal Growth,50(1980)839. [Non-Patent Document 5] LW Coughanour and VA DeProsse: J. Research Natl. Bur. Standards,51(1953)85. [Non-Patent Document 6] F. Massazza and E. Sirchia: Chime. Ind. (Milan), 40 (1958) 376. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0039] In the floating zone cooling method, a series of steps is required: prepare a starting material rod of any composition of any substance, heat it locally with infrared rays to form a melt (liquid), form a stable floating zone by surface tension, and then slowly cool and solidify the melt while stably holding it as a whole. For this reason, when the specific gravity of the formed melt is high or depending on the combination of constituent elements in a multi-component system, it may be difficult to form a stable floating zone, making it virtually impossible to apply the floating zone cooling method. In addition, it is necessary to prepare the raw material rod, sinter it, produce infrared single crystals, cut the solidified sample, and use a polishing device, and so on, which means that expensive research facilities are required overall.

[0040] In view of the above-mentioned conventional techniques, the present invention aims to provide a method for creating a phase equilibrium diagram, which not only provides a phase relationship using maximum fractional crystallization, but also allows for easy preparation of a raw material molded body and enables stable retention of a melt during the process of forming a solidified material for measuring composition distribution. [Means for solving the problem]

[0041] As shown in Figure 9, when a raw material molded body 40 made of any composition is irradiated with infrared rays 41 from the top surface, it is heated and melted to form a molten liquid 42, and then slowly cooled, the temperature of the part irradiated with the infrared rays rises, but the temperature decreases as it moves away from the irradiation position, so that the maximum fractionation effect is applied during solidification. The above is the principle of the newly developed top surface melting and slow cooling method.

[0042] The present inventors have found that the above problems can be solved by utilizing this top surface melting and slow cooling method, and have completed the present invention. The present invention relates to, for example, the following [1] to [8].

[0043] [1] A step (1) of mixing two or more solid substances, molding the mixture, irradiating an upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting melt to solidify it; A step (2) of measuring the composition distribution of the solidified material obtained in the step (1) and creating a phase equilibrium diagram based on the measurement results. A method for constructing a phase equilibrium diagram, including:

[0044] [2] The method for creating a phase equilibrium diagram according to [1] above, wherein the means for irradiating infrared rays is an infrared lamp or a laser oscillator.

[0045] [3] A melting apparatus of an infrared concentrated heating type, in which a raw material molded body is placed in a sample chamber, an atmospheric gas is introduced into the sample chamber, and in this state, infrared rays are irradiated from an infrared irradiation means onto the raw material molded body to heat and melt the raw material molded body, thereby obtaining a molten liquid, A raw material molded body supporting member that supports the raw material molded body from below is provided, a vibration generator for applying vibration to the raw material molded body, the vibration generator being disposed at a lower portion of the raw material molded body support member; The infrared ray irradiation means is configured to irradiate the raw material molded body with infrared rays from directly above or obliquely above. Prepare The method for creating a phase equilibrium diagram according to the above [1] or [2], wherein in the step (1), the upper surface of the raw material molded body is melted using the melting device.

[0046] [4] The method for creating a phase equilibrium diagram according to [3] above, wherein the melting apparatus is an inclined laser heating infrared single crystal manufacturing apparatus.

[0047] [5] The method for creating a phase equilibrium diagram according to any one of the above [1] to [4], wherein in the step (1), if bubbles remain in the melt, the bubbles are removed.

[0048] [6] The method for creating a phase equilibrium diagram according to any one of [1] to [5] above, wherein in the step (1), the melt is slowly cooled while suppressing the occurrence of cell growth.

[0049] [7] The method for creating a phase equilibrium diagram according to any one of the above [1] to [6], wherein the ratio of the two or more solid substances is changed and the step (1) is repeated multiple times.

[0050] [8] A method for producing a solidified material for measuring composition distribution used in creating a phase equilibrium diagram, comprising the steps of: mixing two or more solid substances, molding the mixture, irradiating the upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting molten liquid to solidify it. Effect of the Invention

[0051] According to the method for creating a phase equilibrium diagram of the present invention, a raw material molded body can be easily prepared, and the melt can be stably maintained during the process of forming a solidified material for measuring composition distribution, thereby obtaining a phase relationship that applies maximum fractional crystallization.

[0052] The top-surface melting and slow cooling method used in the present invention is a highly versatile method that requires low-cooling equipment and can be applied to a variety of systems, including systems containing heavy metals such as lead and bismuth, and multi-component systems, to which the floating-zone slow cooling method has been difficult to apply. Therefore, according to the method for creating phase equilibrium diagrams of the present invention using the top-surface melting and slow cooling method, it is possible to create phase equilibrium diagrams for a variety of systems, including systems containing heavy metals and multi-component systems, at low cost. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is a schematic diagram of a phase equilibrium experiment in a two-component system of substances A and B. [Diagram 2] FIG. 2 is a schematic diagram of directional solidification. [Diagram 3] Figure 3 is a schematic diagram of the growth of a rod-shaped single crystal by the floating zone method, where (a) shows the state at the start of growth, (b) shows the state during growth, and (c) shows the state at the end of growth. [Figure 4] Figure 4 is a schematic diagram of the floating zone annealing method. (a) shows the state at the start of melting, (b) shows the state during annealing, and (c) shows the state at the end. [Diagram 5] FIG. 5 is a hypothetical diagram showing the melting and solidification of a two-component mixture of substances A and B with composition D1. [Figure 6] FIG. 6 is a cross-sectional view of a solidified bar obtained in a floating zone slow cooling experiment. [Figure 7] Figure 7 shows two different reports on the phase diagram of the MgO-TiO2 binary system, which were investigated by the quenching method. (a) is a report by Coughanour et al. (Non-Patent Document 5), and (b) is a report by Massazza et al. (Non-Patent Document 6). [Figure 8] FIG. 8 is a schematic diagram showing an assumed up-down state when the floating zone is formed using the raw material rod of composition D1 in FIG. [Figure 9] FIG. 9 is a conceptual diagram of a method for producing a solidified material to be used for measuring composition distribution while maintaining maximum fractionation effect by the top-melting and slow-cooling method. [Figure 10] FIG. 10 shows cell growth occurring during growth. [Figure 11] Figure 11 shows a schematic diagram of the upper surface melting and slow cooling device. (a) shows a method using a xenon lamp, and (b) shows a method using a laser heating device. [Figure 12] FIG. 12 is a detailed view of the chamber. [Figure 13] FIG. 13 is a conceptual diagram of a tilted laser heating single crystal manufacturing apparatus with a top-melting phase equilibrium research function added. [Figure 14] FIG. 14 is a conceptual diagram showing an example of a method for preparing a sample for measuring the composition distribution of a solidified material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] The present invention will now be described in further detail. [How to create a phase equilibrium diagram] The method for creating a phase equilibrium diagram according to the present invention comprises the steps of: A step (1) of mixing two or more solid substances, molding the mixture, irradiating an upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting melt to solidify it; The method is characterized by including a step (2) of measuring the composition distribution of the solidified material obtained in the step (1) and creating a phase diagram based on the measured composition distribution.

[0055] ≪Process (1)≫ Step (1) is a step of mixing two or more solid substances, molding the mixture, irradiating the upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting molten liquid to solidify it.

[0056] (Solid substance) The solid substance is a raw material for obtaining a measurement sample (solidified material) for composition analysis. The solid substance is not particularly limited as long as it is a substance that melts when heated by infrared irradiation, but from the viewpoint of heating by infrared irradiation, it is preferable to use an insulating substance that has infrared absorption ability and is difficult to apply other methods such as high-frequency induction. Furthermore, the solid substance may be a substance containing a heavy metal element such as lead or bismuth, to which the floating zone cooling method is difficult to apply.

[0057] The solid substances are of two or more kinds, and there is no limit to the number of kinds, but from the viewpoint of obtaining information on phase relationships from the composition distribution of the solidified material, the number of kinds is preferably 2 to 5 kinds, and more preferably 2 to 3 kinds.

[0058] The combination of the solid substances is not particularly limited, and an example thereof is a ternary system of aluminum oxide (Al2O3), zirconium oxide (ZrO2) and yttrium oxide (Y2O3). The solid substance is preferably in the form of a powder from the viewpoint of producing a raw material molded body in which two or more solid substances are uniformly mixed.

[0059] (Raw material molded body) The shape of the raw material molded body is preferably a right columnar shape such as a cylindrical shape or a square columnar shape, in consideration of ease of handling and ease of production.

[0060] In step (1), the upper surface of the raw material molded body is melted to form a melted region (melt), and the melt is stored in the unmelted portion of the raw material molded body. The depth of the melted region is preferably about 5 mm from the viewpoint of forming a sufficient amount of solidified material for measuring the composition distribution. In order to store the melt, the length of the raw material molded body in the direction perpendicular to the upper surface of the raw material molded body (hereinafter referred to as the "axial direction") is, for example, 6 mm or more, preferably 8 mm or more. The upper limit of the axial length of the raw material molded body may be, for example, 12 mm or less from the viewpoint of not wasting the solid material.

[0061] When the raw material molded body is a straight column, the cross-sectional area in the axial direction (which is also the area of ​​the upper surface of the raw material molded body) is, for example, 10 mm 2 More than 50mm, preferably 50mm 2 More preferably, it is 100 mm or more. 2 If the area is within this range, the upper surface of the raw material molded body can be melted, and then a sufficient amount of solidified material can be formed for measuring the composition distribution in step (2). 2 It may be the following.

[0062] The raw material molded body can be obtained by thoroughly mixing two or more of the solid substances and then molding them. There are no particular limitations on the molding method, and any conventionally known molding method can be used.

[0063] In the present invention, the amount of raw material required to obtain a measurement sample (solidified material) is overwhelmingly smaller than when a phase equilibrium diagram is created using the floating zone slow cooling method. In addition, when using the floating zone slow cooling method, the melt formed needs to be stably held between the upper and lower raw material rods by the surface tension of the melt itself, so the raw material rod, which is the raw material molded body, needs to be manufactured with high density and high precision. In contrast, in the present invention, the melt formed only needs to be held (reserved) on the upper surface of the raw material molded body, so the raw material molded body is easier to manufacture than when using the floating zone slow cooling method.

[0064] (Melting and slow cooling of the upper surface of the raw material molded body) In step (1), the upper surface of the raw material molded body is melted by irradiation with infrared rays, and the resulting melt is slowly cooled. By doing so, at a predetermined temperature, the formed liquid phase and the solid phase that coexists in equilibrium with each other are in contact with each other, while the temperature of the solid phase away from the solid-liquid interface is maintained lower than the interface temperature, and a solidified product is produced by maximum fractional crystallization. In other words, step (1) is a process in which the upper surface of the raw material molded body is melted by irradiation with infrared rays, the resulting melt is slowly cooled, and a solidified product is produced by maximum fractional crystallization.

[0065] As a method for forming a melt under such conditions, for example, a method of forming a melt by locally heating the upper surface of the raw material molded body by concentrating infrared rays from an infrared lamp such as a halogen lamp or a xenon lamp with an elliptical mirror, and a method of forming a melt by irradiating a laser beam onto the upper surface of the raw material molded body. When irradiating a laser beam, the in-plane intensity distribution of the laser beam is usually a Gaussian distribution (normal distribution). In this way, when the raw material molded body is locally heated to form a melt, the temperature drops rapidly with distance from the solid-liquid interface in contact with the melt, and as a result, maximum fractional crystallization occurs when the melt is slowly cooled and solidified.

[0066] If the entire top surface of the raw material molded body melts, it becomes difficult to retain the molten liquid, so it is preferable to adjust the infrared irradiation conditions, the size of the raw material molded body, etc. so that only the central area of ​​the top surface of the raw material molded body melts and the surrounding area does not melt.

[0067] A preferred method for slowly cooling the melt is to gradually reduce the amount of infrared radiation. With this method, the cooling rate of the melt can be adjusted by adjusting the amount of radiation. The slower the cooling rate, the more accurate the phase equilibrium diagram created in step (2) based on the composition distribution of the solidified material can be.

[0068] Explaining with reference to FIG. 9, as shown in FIG. 9(A), infrared rays 41 are irradiated onto the upper surface of the raw material molded body 40, melting the upper surface of the raw material molded body 40 and forming a melt 42. Next, as shown in FIG. 9(B), the amount of infrared rays 41 is reduced, and the low-temperature region (I) 43 solidifies. When the amount of infrared rays 41 is further reduced, a region (II) 44 having a different composition from the region (I) 43 solidifies, as shown in FIG. 9(C). The infrared irradiation is continued until all the melt is solidified, and it is preferable to gradually cool the sample to room temperature at a rate of about 100° C. per hour. A sudden temperature change may make the obtained solidified sample fragile, making it difficult to prepare a sample for the subsequent composition distribution analysis.

[0069] Furthermore, in the present invention, the upper surface of the raw material molded body is locally heated to form a melt, and the formed melt is maintained on the upper surface of the raw material molded body; in other words, the melt is stored in the unmelted parts of the raw material molded body, thereby completely preventing the melt from falling, which is a concern when the floating zone slow cooling method is applied.

[0070] An example of an apparatus applicable to the top surface melting and slow cooling method, i.e., the melting and slow cooling of the top surface of the raw material molded body in step (1), is an infrared concentrated heating melting apparatus in which the raw material molded body is placed in a sample chamber made of transparent quartz, an atmospheric gas is introduced into the sample chamber, and in this state, infrared rays are irradiated from an infrared irradiating means onto the raw material molded body to heat and melt the raw material molded body to obtain a molten liquid, the infrared irradiating means being configured to irradiate infrared rays onto the raw material molded body from directly above or obliquely above. The infrared irradiating means may be one or more.

[0071] Fig. 11 shows a conceptual diagram of an apparatus 50 applicable to such an upper surface melting and slow cooling method. Fig. 11(a) shows an apparatus using a xenon lamp 52 as an infrared ray irradiation means, i.e., an irradiation source of infrared rays 51, and Fig. 11(b) shows an example using a laser oscillator 53 as an irradiation source of infrared rays 51. In the apparatus using a xenon lamp 52, it is also possible to use a halogen lamp instead of the xenon lamp 52.

[0072] The infrared irradiation means (xenon lamp 52, laser oscillator 53) is located directly above raw material molded body 55 in the apparatus depicted in Figures 11(a) and 11(b), but may be located diagonally above raw material molded body 55.

[0073] The raw material molded body 55 is placed in an atmosphere control chamber 56 made of transparent quartz. An atmosphere supply pipe 59 constituting an atmosphere supply system, and an exhaust pipe 60 constituting an external exhaust system are attached. The atmosphere supply system and the external exhaust system work together to regulate the atmosphere inside the chamber 56. The atmosphere inside the chamber 56 is circulated by an atmosphere circulator 61, and fine particles that have evaporated and solidified from the raw material molded body 55 are trapped by a filter 62 as the atmosphere circulates, preventing them from adhering to the inner wall of the chamber 56 and deteriorating the transmittance of infrared rays 51.

[0074] As shown in FIG. 12, an exhaust pipe 63 connected to an external vacuum exhaust device may be attached to the chamber 56 so that the inside of the chamber 56 can be evacuated to a vacuum. Figures 11 and 12 are conceptual diagrams of an apparatus applicable to the top surface melting and slow cooling method, i.e., the melting and slow cooling of the top surface of the raw material molded body in step (1) (the illustration of the infrared irradiation means is omitted in Figure 12). Infrared irradiation means such as a xenon lamp 52 and a laser oscillator 53 are depicted above raw material molded body 55, but the infrared irradiation means may also be provided diagonally directly above raw material molded body 55.

[0075] Furthermore, it is possible to incorporate the same functions as these devices into an inclined laser heating infrared single crystal manufacturing device. Figure 13 shows a conceptual diagram of this case.

[0076] FIG. 13(a) is a conceptual diagram of the heating section of an inclined laser heating infrared single crystal manufacturing apparatus, in which a laser beam (infrared) 73 is irradiated from an obliquely upward direction by a laser oscillator 72 onto the lower end of a raw material rod 71 to melt the lower end, and the molten raw material is solidified on a seed single crystal 74 arranged below the raw material rod 71 to manufacture a single crystal. In FIG. 13(a), reference numeral 75 denotes a transparent quartz tube (sample chamber). FIG. 13(b) shows a schematic diagram of obtaining a solidified sample by the top melting and slow cooling method, i.e., step (1), in which a vibration generator 76 is inserted into the lower part of a seed single crystal support shaft 78 (not shown in FIG. 13(a)) at the lower part in FIG. 13(a), a laser beam (infrared) 73 is irradiated by the laser oscillator 72 onto a raw material molded body 77 to melt it and form a melt, and then the melt is slowly cooled while being vibrated by the vibration generator 76 to obtain a solidified sample.

[0077] As the inclined laser heating infrared single crystal manufacturing apparatus, for example, a floating zone melting apparatus disclosed in International Publication No. 2009 / 081811 can be used. In this case, the raw material molded body is attached to the upper part of a shaft-shaped growth crystal support part, which is a member that supports the raw material molded body from below, a vibration generator is added to the lower part, and a transparent quartz tube is set. Then, a melted region is formed on the upper surface of the raw material molded body using only the upper downward infrared irradiation means, and the melted region is solidified according to the method already described to prepare a sample for composition distribution analysis.

[0078] Step (1) may be carried out multiple times by varying the ratio of the two or more solid substances, thereby obtaining more detailed information on the phase relationships.

[0079] (Removal of air bubbles) When bubbles are generated in the melt, it is preferable to remove the bubbles. In principle, it is possible to remove the bubbles remaining in the melt by stirring the melt using, for example, a stirring rod, but it is technically difficult to stir the melt formed on the upper surface of the raw material molded body by irradiating infrared rays while controlling the atmosphere.

[0080] Therefore, for example, the atmosphere in which the raw material molded body is melted can be arbitrarily controlled in accordance with the characteristics of the raw material molded body, thereby making it possible to remove the bubbles in the melt. This method makes it possible to remove the bubbles extremely easily.

[0081] Specifically, when the solid substances are aluminum oxide (Al2O3), zirconium oxide (ZrO2) and yttrium oxide (Y2O3), for example, it was found that the internal gases of the bubbles formed in the melt on the upper surface of the raw material molded body are nitrogen gas and oxygen gas when examining the phase relationship of these ternary systems. It is considered that the nitrogen gas was contained in the air when the raw material molded body was produced, was taken into the raw material molded body as it was, was released, and remained in the melt. Similarly, it is considered that the oxygen gas contained in the air of the atmosphere and the raw material melted, and since the oxygen content in the liquid is less than that in the solid oxide and the liquid oxide, the excess was released during melting and remained in the melt.

[0082] It was confirmed that when the atmosphere was changed to argon gas, the partial pressures of nitrogen gas and oxygen gas in the atmosphere and those in the melt were significantly different, and therefore the nitrogen gas and oxygen gas were released from the melt into the surrounding atmosphere, thereby removing the bubbles.

[0083] (Melting effect and suppression of cell growth) When a solid is formed from a melt, it is desirable for the surface of the solid being formed to be flattened along the temperature gradient. However, if fluctuations in composition occur near the surface of the solid, this directly leads to fluctuations in the melting point, causing uneven growth and the formation of areas with low melting points. In such areas, solidification is slower than in the surrounding areas, so low-melting-point components that are expelled from the surrounding areas as they solidify gather there, further lowering the melting point and sometimes exhibiting a structure shape in which cells (bundles) are gathered in a direction parallel to the growth direction. This is referred to as cell growth occurring, and the structure that is formed is called a cell-grown structure.

[0084] Figure 10 shows the Y3Fe4GaO grown by infrared floating zone melting method. 12 This is a diagram of growth striations observed in a single crystal when observed with an optical microscope. In Fig. 10, the growth direction of the single crystal is from bottom to top, reflecting the results of growth experiments in which the growth rate was changed from 1 mm per hour to 2 mm per hour near the center of the figure. As a result of the faster growth rate, a lamellar pattern indicative of typical cellular growth can be observed in the upper half of Fig. 10.

[0085] In step (1), it is preferable to suppress the occurrence of cell growth, which can increase the accuracy of the process of inferring phase equilibrium relationships from composition distribution analysis.

[0086] The cause of cell growth during solidification of the melt is the layer of high solvent concentration that occurs at the solid-liquid interface as the melt solidifies. This is called the "boundary layer." Therefore, any effort to reduce the boundary layer will directly lead to the prevention of cell growth.

[0087] Specifically, the following measures are effective: -Slows down the solidification rate. -Stir the melt to reduce the boundary layer.

[0088] Although it is difficult to directly stir the melt, an effective method is to apply mechanical vibrations to the raw material molded body to disturb the boundary layer and produce a stirring effect. For example, in systems containing silicon dioxide (SiO2), the viscosity of the melt is likely to become high, making cell growth extremely likely to occur, and it was found that cell growth can be prevented if the solidification rate is slow, at 0.01 mm per hour or less. However, at such a slow solidification rate, there are cases where the solidification rate is inevitably faster locally due to the influence of ambient temperature fluctuations, causing cell growth. In such cases, by applying mechanical vibration to the raw material molded body, it is possible to solidify the entire melt while preventing cell growth, even if the solidification rate is increased by an order of magnitude or more.

[0089] ≪Process (2)≫ Step (2) is a step of measuring the composition distribution of the solidified material obtained in step (1) and creating a phase equilibrium diagram based on the measurement results (knowledge regarding phase equilibrium). The method for measuring the composition distribution of the solidified material is not particularly limited, and a conventionally known method, for example, a method for measuring the composition distribution using an EPMA device, can be applied.

[0090] FIG. 14 shows an example of a method for preparing a sample to be used for measuring the composition distribution of the solidified material. FIG. 14(A) shows a raw material molded body 80 that has been subjected to step (1). A solidified material 81 is formed in the upper center of the raw material molded body 80 by step (1). As shown in FIG. 14(B), this raw material molded body 80 is accommodated in a raw material molded body accommodation container 82 that is slightly larger than the raw material molded body 80, and a curable resin 83 is filled in the space between the raw material molded body 80 and the raw material molded body accommodation container 82. An example of the raw material molded body accommodation container 82 is a glass tube. After the curable resin 83 is cured, as shown in FIG. 14(C), the raw material molded body 80 together with the raw material molded body accommodation container 82 is cut in the axial direction so that the solidified material 81 appears on the cut surface, and then the cut surface is polished as necessary to obtain a sample 84 for measuring the composition distribution of the solidified material.

[0091] The method for creating a phase equilibrium diagram based on the measurement results of the composition distribution of the solidified material is not particularly limited, and any conventionally known method can be used.

[0092] [Method of manufacturing solidified materials for measuring composition distribution used in creating phase equilibrium diagrams] The method for producing a composition distribution measurement sample used for creating a phase equilibrium diagram according to the present invention includes the steps of: The method includes a step (1) of mixing two or more solid substances, molding the mixture, irradiating an upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting melt to solidify the mixture. It is characterized by the following.

[0093] The solidified material produced in step (1) is used as a sample for measuring composition distribution, which is used to create a phase equilibrium diagram. The details of step (1) are as described above. [Explanation of symbols]

[0094] 10 containers 11 liquid 12 Solid 13 Interface 20 Raw material rod 21 Infrared 22 Seed single crystal 23 Melting zone (floating zone) 24 Single crystal 30 Raw material rod 31 Infrared 33 Molten zone (floating zone) 34 Solidification section 40 Raw material molded body 41 Infrared 42 Melt 43 Area (I) 44 Area (II) 50 Apparatus applicable to the upper surface melting and slow cooling method 51 Infrared 52 Xenon lamp 53 Laser Oscillator 54 Elliptical Mirror 55 Raw material molded body 56 Atmospheric Control Chamber 57 Support rod 58 Vibration Generator 59 Atmosphere supply pipe 60 Exhaust pipe of external exhaust system 61 Atmosphere Circulator 62 Filters 63 Vacuum exhaust system exhaust pipe 71 Raw material rod 72 Laser Oscillator 73 Laser Light 74 Seed single crystal 75 Transparent quartz tube 76 Vibration Generator 77 Raw material molded body 78 Seed single crystal support shaft 80 Raw material molded body 81 Solidified materials 82 Raw material molded body container 83 Curing resin 84 Sample for measuring composition distribution of solidified material

Claims

1. A step (1) of mixing two or more solid substances, molding the mixture, irradiating an upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting melt to solidify it; and A step (2) of measuring the composition distribution of the solidified material obtained in the step (1) and creating a phase equilibrium diagram based on the measurement results. A method for constructing a phase equilibrium diagram, including:

2. 2. The method for creating a phase equilibrium diagram according to claim 1, wherein the means for irradiating infrared rays is an infrared lamp or a laser oscillator.

3. A melting apparatus of an infrared concentrated heating type, in which a raw material molded body is placed in a sample chamber, an atmospheric gas is introduced into the sample chamber, and in this state, infrared rays are irradiated from an infrared irradiation means onto the raw material molded body to heat and melt the raw material molded body, thereby obtaining a molten liquid, A raw material molded body supporting member that supports the raw material molded body from below is provided, a vibration generator for applying vibration to the raw material molded body, the vibration generator being disposed at a lower portion of the raw material molded body support member; The infrared ray irradiating means is configured to irradiate the raw material molded body with infrared rays from directly above or obliquely above. Prepare 2. The method for creating a phase equilibrium diagram according to claim 1, wherein in the step (1), the upper surface of the raw material molded body is melted using the melting device.

4. 4. The method for creating a phase equilibrium diagram according to claim 3, wherein the melting apparatus is a gradient laser heating infrared single crystal manufacturing apparatus.

5. 2. The method for creating a phase equilibrium diagram according to claim 1, wherein in the step (1), if bubbles remain in the melt, the bubbles are removed.

6. 2. The method for creating a phase equilibrium diagram according to claim 1, wherein in the step (1), the melt is slowly cooled while suppressing the occurrence of cell growth.

7. 2. The method for creating a phase equilibrium diagram according to claim 1, wherein the step (1) is repeated multiple times by changing the ratio of the two or more solid substances.

8. A method for producing a solidified material for measuring composition distribution used in creating a phase equilibrium diagram, comprising the steps of: mixing two or more solid substances, molding the mixture, irradiating an upper surface of the raw material molded body with infrared rays to melt the upper surface of the raw material molded body, and then slowly cooling the resulting molten liquid to solidify it.

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