TWI844671B - Radiation-resistant inorganic materials and their fibers - Google Patents

Abstract

The subject of the present invention is to provide an inorganic material having excellent radiation resistance and excellent melt-spinning properties. In an inorganic material containing SiO ₂ , Al ₂ O ₃ , CaO and Fe ₂ O ₃ as components, an inorganic material having excellent melt-spinning property and excellent radiation resistance can be produced by making the mass percentage of the above components in the inorganic material as oxides within the following ranges, wherein: i) the total content of SiO ₂ and Al ₂ O ₃ is 40 mass % or more and 70 mass % or less; ii) Al ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) (mass ratio) is within the range of 0.15 to 0.40; iii) the content of Fe ₂ O ₃ is 16 mass % or more and 25 mass % or less; iv) the content of CaO is 5 to 30 mass %.

Description

Radiation-resistant inorganic materials and their fibers

The present invention relates to a novel inorganic material having excellent radiation resistance and its fiber. More specifically, it relates to a radiation resistance inorganic material having excellent melt-spinning property and its fiber.

Due to the Great East Japan Earthquake that struck eastern Japan in March 2011, nuclear power plants were damaged and a huge amount of manpower and resources had to be invested in decommissioning furnaces and handling radioactive waste.

On the other hand, after the Great East Japan Earthquake, safety restrictions on nuclear reactors were strengthened, resulting in the closure of many nuclear power plants and an increase in the proportion of thermal power generation. Coal is used in large quantities as a fuel for thermal power generation, but this produces a large amount of fly ash. In the past, fly ash was disposed of as waste, but in recent years it has gradually been used as a concrete admixture, resulting in a decrease in waste. However, there are concerns that most of this utilization depends on the cement field, and if the demand for cement stagnates, the amount of fly ash that is disposed of will increase again. Therefore, exploring new uses for fly ash has become an urgent issue. Furthermore, the composition of fly ash varies depending on the raw material coal and the place of production (power plant, country).

As an example of high utilization of fly ash, Japanese Patent Application Laid-Open No. 6-316815 (hereinafter referred to as Patent Document 1) discloses a fly ash fiber characterized by containing 20-40% Al ₂ O ₃ , 35-50% SiO ₂ , 15-35% CaO, 3-12% Fe ₂ O ₃ and 2-5% MgO. The same document states: "The content of Fe ₂ O ₃ also contained in the fly ash fiber is 3-12%. The content is preferably as small as possible. In addition, if the Fe ₂ O ₃ content increases, the coloring degree of the fly ash fiber increases and is not good. Therefore, when the Fe ₂ O ₃ content is 12% or more, there are many problems and it must be avoided" (the same document, paragraph [0054]). In addition to fly ash fibers, for example, regarding mineral fibers, Japanese Patent Publication No. 2018-531204 (hereinafter referred to as Patent Document 2) discloses a mineral fiber comprising Al ₂ O ₃ , SiO ₂ , CaO, MgO, and Fe ₂ O ₃ as components, and characterized in that the Fe ₂ O ₃ content is 5 to 15%. The same document states: "The increase in iron content tends to color the mineral fiber, which is particularly undesirable in applications where the mineral fiber is kept visible" (the same document, paragraph [0005]). Patent Document 1 and Patent Document 2 have in common that they both have Al ₂ O ₃ , SiO ₂ , CaO and Fe ₂ O ₃ as essential components, and both state that the content of Fe ₂ O ₃ must be limited to a specified amount or less (12% or less in Patent Document 1, 15% or less in Patent Document 2). In addition, Japanese Patent Application Laid-Open No. 60-231440 (hereinafter referred to as Patent Document 3) and Japanese Patent Application Laid-Open No. 10-167754 (hereinafter referred to as Patent Document 4) disclose a glass and a vitrified material, wherein the glass is characterized in that it has Al ₂ O ₃ , SiO ₂ , CaO and Fe ₂ O ₃ as essential components, and the content of each oxide component is within a specific range. In addition, Materials Research Bulletin 36 (2001) 1513-1520 (hereinafter referred to as non-patent document 2) describes the relationship between the iron oxide (Fe ₂ O ₃ ) content and magnetic properties of goethite (FeOOH) industrial waste as a sample. Furthermore, none of Patent Documents 1, 2, 3, 4 and Non-Patent Document 2 mentions radiation resistance. Here, as mentioned above, radiation-resistant materials are indispensable in the treatment of damaged nuclear power generation facilities, the treatment of radioactive waste or radioactive soil, or the treatment of radioactive waste. As a radiation-resistant material, basalt fiber made of basalt has attracted attention, but as far as the inventor knows, there is no literature discussing the relationship between its composition and radiation resistance. In addition, the scientific chronology (hereinafter referred to as non-patent document 1) introduces the types and composition of basalt as follows (Table 1).

[Table 1] ＜Types and composition of basalt Source: Chronology of science＞ Element Alkaline basalt Flood basalt Oceanic island basalt Seafloor basalt Island arc basalt SiO ₂ 45.4 50.01 50.51 50.68 51.9 Al ₂ O ₃ 14.7 17.08 13.45 15.6 16 _{Fe2O3 ​} 4.1 - 1.78 - - FeO 9.2 10.01 9.59 9.85 9.56 CaO 10.5 11.01 11.18 11.44 11.8 MnO - 0.14 0.17 - 0.17 MgO 7.8 7.84 7.41 7.69 6.77 _TiO2 3 1 2.63 1.49 0.8 _Na2O 3 2.44 2.28 2.66 2.42 _K2O 1 0.27 0.49 0.17 0.44 _{P2O5 ​} - 0.19 0.28 0.12 0.11 Total 98.7 99.99 99.77 99.7 100 In addition, a review article on basalt fiber (International Journal of Textile Science 2012, 1 (4): 19-28, non-patent document 3) records SiO ₂ : 52.8%, Al ₂ O ₃ : 17.5, Fe ₂ O ₃ : 10.3, CaO: 8.59% as the representative composition of basalt. [Prior Art Document] [Patent Document]

[Patent document 1] Japanese Patent Publication No. 6-316815 [Patent document 2] Japanese Patent Publication No. 2018-531204 [Patent document 3] Japanese Patent Publication No. 60-231440 [Patent document 4] Japanese Patent Publication No. 10-167754 [Non-patent document]

[Non-patent document 1] Chronology of Science 2019 Edition (Edited by National Astronomical Observatory of Japan) [Non-patent document 2] Materials Research Bulletin 36 (2001) 1513-1520 [Non-patent document 3] International Journal of Textile Science 2012, 1 (4): 19-28

[The problem that the invention wants to solve]

As described above, to the best of the knowledge of the inventors, there has been no research on inorganic materials containing SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ as main components for the purpose of improving radiation resistance. Therefore, the inventors have been committed to improving the radiation resistance of inorganic materials containing SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ as main components, and in particular, have been committed to developing radiation-resistant inorganic materials with excellent melt-spinnability. [Technical means for solving the problem]

As a result, it was found _that in _an inorganic material with _{SiO2 and Al2O3} as the main components, when the total of _SiO2 and _Al2O3 is within a specific range, the ratio _{of Al2O3} to the total of _SiO2 and _Al2O3 is within a specific range, and when _Fe2O3 and CaO are contained in specific amounts respectively, the radiation resistance and melt-spinning properties are excellent. As _a result, a material suitable for use in radiation-irradiated areas was completed. That is, the present invention is an inorganic material suitable for use in a radiation irradiated part, which is an inorganic material containing SiO ₂ , Al ₂ O ₃ , CaO and Fe ₂ O ₃ as components, and the mass percentage of each component in the inorganic material in terms of oxide conversion is: i) the total content of SiO ₂ and Al ₂ O ₃ is 40 mass % or more and 70 mass % or less; ii) the ratio (mass ratio) of Al ₂ O ₃ in the total of SiO ₂ and Al ₂ O ₃ is in the range of 0.15 to 0.40; iii) the content of Fe ₂ O ₃ is 16 mass % or more and 25 mass % or less; iv) the content of CaO is 5 mass % or more and 30 mass % or less. Hereinafter, the above i) to iv) may be abbreviated as "the four requirements of the present invention regarding the composition". Specific examples of the radiation irradiated portion using the inorganic material of the present invention are as follows.

Furthermore, in the present invention, there is no substantial difference between the component ratio in the blended mixture of each raw material and the component ratio in the material after the mixture is _melted . Therefore, the component ratio in the blended mixture can be used as the material component ratio. The inorganic material of the present invention is obtained by adjusting the blending ratio of the raw materials in such a way that the ratio of _SiO2 , _{Al2O3 , Fe2O3 and} CaO in the components is within the above range, and then melting to form the final inorganic material. As described below, if the raw materials are blended in such a way that they are within the above range, the raw materials will melt at a temperature that is not too high, and the melt has a moderate viscosity, so the melt-spinning property is excellent. In addition, the obtained inorganic material becomes one with very excellent radiation resistance.

The total content of SiO ₂ and Al ₂ O ₃ in the inorganic material of the present invention is 40 mass % or more and 70 mass % or less. In the following description, SiO ₂ is sometimes referred to as the S component, and the content of SiO ₂ is sometimes represented as [S]. Similarly, Al ₂ O ₃ is sometimes referred to as the A component, and the content of Al ₂ O ₃ is sometimes represented as [A]. When the total of [S] and [A] is outside the above range, that is, it is less than 40 mass % or exceeds 70 mass %, the melting temperature of the material becomes higher, or the viscosity of its melt becomes higher, or conversely, the melt viscosity becomes too low, and the melt spinnability becomes poor.

In the inorganic material of the present invention, the ratio of Al ₂ O ₃ to the total of SiO ₂ and Al ₂ O ₃ ([A]/([A]+[S])) (mass ratio) must be in the range of 0.15 to 0.40. If this requirement is outside the above range, that is, if it is less than 0.15 or exceeds 0.40, the material will also become poor in melt spinnability.

In the inorganic material of the present invention, the content of Fe ₂ O ₃ must be 16 mass % or more and 25 mass % or less. If the content of Fe ₂ O ₃ is less than 16 mass %, the radiation resistance of the material will deteriorate. On the other hand, if the content exceeds 25 mass %, the viscosity of the melt will be too low to form fibers. Hereinafter, Fe ₂ O ₃ is sometimes referred to as the F component, and the content of Fe ₂ O ₃ is sometimes expressed as [F].

In the inorganic material of the present invention, the content of CaO is preferably 5% by mass or more and 30% by mass or less. If the content of CaO is less than 5% by mass, the melting start temperature of the material will be high, which is not good from the perspective of energy saving. The content of CaO is preferably 10% by mass or more. On the other hand, if the content exceeds 30% by mass, the viscosity of the melt will be too low to form fibers. Hereinafter, CaO is sometimes referred to as component C, and the content of CaO is sometimes expressed as [C].

When obtaining the inorganic material of the present invention, as long as the ratio of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ and CaO is within the above range, the raw materials are not restricted. Therefore, compounds of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ and CaO can be prepared as the starting raw materials, but in terms of raw material cost, it is preferred to use a silicon dioxide source rich in SiO ₂ , an aluminum oxide source rich in Al ₂ O ₃ , an iron oxide source rich in Fe ₂ O ₃ , and a calcium oxide source rich in CaO as the starting raw materials. As the silicon dioxide source, there can be listed: amorphous silicon dioxide, silica sand, fumed silicon dioxide, volcanic ash, but it is not limited to them. As an aluminum oxide source, in addition to aluminum oxide, mullite and other minerals can be listed, but it is not limited to them. As a source of silicon dioxide and an aluminum oxide source (silicon aluminum source), kaolinite, montmorillonite, feldspar, and zeolite can be listed, but it is not limited to them. As an iron oxide source, iron oxide, iron hydroxide, and iron ore can be listed, but it is not limited to them. As a calcium oxide source, in addition to calcium carbonate, calcite, dolomite, and other minerals can be listed, but it is not limited to them.

In addition, thermal power generation waste or metal refining waste can also be effectively used as one of the silicon dioxide sources, aluminum oxide sources, iron oxide sources, or calcium oxide sources. As the above-mentioned thermal power generation waste, fly ash or coal ash can be used. Since fly ash or _coal ash is rich in _SiO2 and _Al2O3 , it is suitable as a silicon aluminum source. However, since _{the Fe2O3} content in fly ash and coal ash is relatively small, it is difficult to obtain the inorganic material of the present invention only by this. However, the inorganic material of the present invention can be obtained at a low cost by adding an appropriate amount of iron oxide source. Furthermore, since coal gasification slag (CGS) produced as a waste of coal gasification combined cycle (IGCC) has a chemical composition roughly equivalent to that of fly ash, it can be a source of silicon and aluminum. Since coal gasification slag is granular, it has the advantage of excellent operability. As the metal refining waste listed above, steel slag or copper slag can be listed. Since the CaO content of steel slag is relatively high, it can be used as a calcium oxide source. Steel slag includes blast furnace slag, converter slag, and reduction slag. Since copper slag has a high _Fe2O3 content, it can be used as an iron _oxide source. Therefore, fly ash, coal slag, or coal gasification slag can be appropriately used as a silicon aluminum source, copper slag can be used as an iron oxide source, and steel slag can be used as a calcium oxide source. In a preferred embodiment, most of the silicon aluminum source, iron oxide source, and calcium oxide source can be provided by industrial waste. In addition, volcanic rocks represented by basalt and andesite can also be used as a silicon aluminum source.

The inorganic material of the present invention does not exclude the inclusion of inevitable impurities contained in the raw materials. Examples of such impurities include MgO, _Na2O , _K2O , _TiO2 , _CrO2 , and the like.

Since the inorganic material of the present invention is rich in amorphous properties, in the melt-spinning fiber, there is basically no strength reduction caused by the peeling of the crystalline phase/amorphous phase interface, and a high-strength fiber can be obtained. Here, the amorphous degree as a measure of amorphous properties can be calculated by the following formula (1) through the X-ray diffraction (XRD) spectrum. Amorphous degree (%) = [Ia/(Ic+Ia)]×100 (1) (In formula (1), Ic is the sum of the integrated values of the scattering intensity of the crystalline peak when performing X-ray diffraction analysis on the above-mentioned inorganic material, and Ia is the sum of the integrated values of the scattering intensity of the amorphous halo). The degree of amorphization of the inorganic material of the present invention also depends on its composition, but generally shows a value of more than 90%. In the case of a higher degree of amorphization, it can also reach more than 95%. In the highest case, the fiber becomes substantially composed of only amorphous phase. Here, substantially composed of only amorphous phase means that only amorphous halo can be seen in the X-ray diffraction spectrum, and no peak of the crystalline phase can be seen.

The radiation resistance of the material composed of the inorganic material of the present invention can be known by comparing the Vickers hardness of the material before and after radiation irradiation. In addition, the radiation resistance can also be evaluated by comparing the tensile strength and the porosity of the material before and after radiation irradiation. The porosity of the material can be measured by the positron mutual destruction method. [Effects of the invention]

Compared to existing inorganic materials containing _SiO2 , _Al2O3 , CaO and _Fe2O3 as components, the inorganic material of the present invention has excellent _radiation resistance _and excellent _{melt-spinnability because the total of SiO2 and Al2O3 , the ratio of Al2O3 to} the total of _SiO2 and _Al2O3 , the content of _Fe2O3 and the content of CaO are within specific ranges.

The content of the present invention is specifically described below by means of test examples. In the following test examples (Example, Comparative Example), the following were used as a silicon dioxide source, an aluminum oxide source, a silicon aluminum source, an iron oxide source, and a calcium oxide source. <Silicon dioxide source> ·Silicon dioxide: Test agent (expressed as SiO ₂ (test agent) in Tables 6 to 9 below) <Alumina source> ·Alumina: Test agent (expressed as Al ₂ O ₃ (test agent) in Tables 6 to 9 below) <Iron oxide source> ·Iron (III) oxide: Test agent (expressed as Fe ₂ O ₃ (test agent) in Tables 6 to 9 below) ·Copper slag: Copper slag produced by a copper refinery in Japan (expressed as FA (10) in Table 3 below) <Calcium oxide source> ·Calcium oxide: Test agent (expressed as CaO (test agent) in Tables 6 to 9 below) · Blast furnace slag: Blast furnace slag produced by steel mills in Japan (indicated as FA(13) in Table 3 below) · Reduced slag: Reduced slag produced by steel mills in Japan (indicated as FA(14) in Table 3 below) <Silicon aluminum source> · Fly ash: 12 samples discharged from thermal power plants in Japan (indicated as FA(1) to FA(9), FA(12) in Tables 2 and 3 below) · Coal gasification slag: Samples discharged from coal gasification combined power plants in Japan (indicated as FA(11) in Table 3 below) · Volcanic rock: Basaltic rock with a particularly high iron oxide content mined from Akita Prefecture and Fukui Prefecture (indicated as BA(1), BA(2) in Table 4 below)

The compositions of FA(1) to FA(14), BA(1) and BA(2) are shown in Tables 2, 3 and 4. Furthermore, component analysis was performed by fluorescent X-ray analysis.

[Table 2] ＜Fly ash composition, unit: mass %＞ Element FA (1) FA (2) FA (3) FA (4) FA (5) FA (6) Fe ₂ O ₃ [F] 10 5 5 9 10 14 SiO ₂ [S] 53 61 57 72 51 59 Al ₂ O ₃ [A] 13 25 18 11 18 25 CaO[C] 17 0 3 3 12 1 other 7 9 17 5 9 1

[Table 3] ＜Fly ash and slag composition, unit: mass %＞ Element FA (7) FA (8) FA (9) FA (10) FA (11) FA (12) FA (13) FA (14) Fe ₂ O ₃ [F] 9 13 15 55 9 1 0 1 SiO ₂ [S] 62 60 59 35 54 73 34 19 Al ₂ O ₃ [A] 18 15 15 5 11 twenty two 13 17 CaO[C] 3 5 3 2 17 0 42 55 other 8 7 8 3 9 4 11 8 Remarks Copper slag Coal gasification slag Blast furnace slag Reduced slag

[Table 4] <Volcanic rock composition, unit: mass %> Element BA (1) BA (2) Fe ₂ O ₃ [F] 19 18 SiO ₂ [S] 46 25 Al ₂ O ₃ [A] 11 10 CaO[C] 17 3 other 7 44

<Preparation of Powder Raw Materials> In the following test examples, a silicon dioxide source, an aluminum oxide source, an iron oxide source, and a calcium oxide source were pulverized and prepared so that SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ and CaO were in a predetermined ratio for testing.

<Evaluation of melt-spinnability> In addition, the evaluation of the melt-spinnability of the blend is based on a melt-spinning test using an electric furnace. The outline of the test is shown in Figure 1. In Figure 1, the height (H) of the electric furnace (1) is 60 cm, the outer diameter (D) is 50 cm, and it has an opening (4) with a diameter (d) of 10 cm in the center. On the other hand, 30 g of the blend is added to a Tamman tube (2) with an inner diameter (φ) of 2.1 cm and a length of 10 cm. Furthermore, a hole with a diameter of 2 mm is opened in the center of the bottom of the Tamman tube (2). In the melt test, the Tamman tube (2) is held at a specified position in the opening (4) of the electric furnace by a hanger (3). If the dope is melted by heating, the dope will flow and fall from the bottom of the Tamman tube due to its own weight, and solidify when it contacts the outside atmosphere to become fiber. The electric furnace is heated according to a prescribed heating program, and the maximum temperature reached in the furnace is preset to 1350°C. At this time, it is confirmed in advance that the temperature inside the Tamman tube (melt) follows a temperature that is approximately 50°C lower than the temperature in the furnace. In the present invention, as an indicator for evaluating melt-spinnability, the melt flows and falls to form a yarn before the temperature in the furnace reaches 1350°C, that is, the melting temperature of the sample is below 1300°C and the melt has a melt viscosity suitable for forming a yarn. This indicator is set as an allowable level. The melting behavior of the sample is roughly divided into the groups represented by A to D below. <Evaluation level> A: Fibers are formed. B: Although the melted and softened sample is about to flow out from the bottom of the Tamman tube, the viscosity is high and it does not fall down by its own weight, and no filaments are formed. C: Since the melting of the sample has not started or the melting is insufficient, no filaments flow out from the bottom of the Tamman tube. D: The sample melts, but the melt viscosity of the melt is too low, and it only becomes droplets and does not form fibers. <Heat resistance test> The inorganic fiber composed of the material of the present invention also has excellent heat resistance. Differential thermal analysis (DTA) was performed to evaluate the heat resistance.

[Previous test] After appropriately mixing a silicon dioxide source, an aluminum oxide source, an iron oxide source, and a calcium oxide source, four samples with different contents of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , and CaO were prepared for melt spinning tests. Samples 3 and 4 met all the requirements of the present invention as described above, but samples 1 and 2 lacked the requirement iii) regarding the Fe ₂ O ₃ content (Table 5). All samples showed good melt spinning properties. Using cobalt 60 as a radiation source, the obtained fiber samples were subjected to a radiation irradiation test under the condition of a gamma ray irradiation dose of 50 kGy, and the tensile strength before and after irradiation was measured to determine its retention rate. The results are shown in Table 5. Figure 3 plots the relationship between the iron oxide (Fe ₂ O ₃ ) content in the sample and the fiber strength retention rate after radiation exposure. It can be clearly seen that if the iron oxide (Fe ₂ O ₃ ) content in the material is above 15%, the retention rate of tensile strength after radiation exposure will be significantly increased.

[table 5] Ingredients in the sample Sample 1 Sample 2 Sample 3 Sample 4 Fe ₂ O ₃ [F] 3 11 16 19 SiO ₂ [S] 51 52 48 42 Al ₂ O ₃ [A] 12 18 12 14 CaO[C] 20 9 17 13 other 14 10 7 12 [S]＋[A] 63 70 60 56 [A]/([S]＋[A]) 0.19 0.26 0.20 0.25 [F] 3 11 16 19 [C] 20 9 17 13 Fiber strength retention after radiation exposure (%) 30 58 99 99 Melt spinnability A A A A

[Example 1] 30 parts by mass of FA (1) and 70 parts by mass of BA (1) were mixed. This sample has the same composition as Sample 3 used in the above-mentioned previous test. The component ratios of this sample are: [S] + [A]: 60% by mass, [A]/([S] + [A]): 0.20, [F]: 16% by mass, [C]: 17% by mass (Table 6). The results of the melt spinning test showed that within 5 hours after the furnace temperature reached 1350°C, extremely fine fibers (mineral fibers) with a diameter of less than 50 μm could be obtained. The obtained fibers have a strength that is not easily broken even when stretched by hand. The fiber sample was irradiated under the following conditions. ＜High-radiation irradiation test＞ Using the nuclear reactor (thermal neutron reactor, BR2) installed at the More Institute in Belgium, the fiber samples were subjected to ultra-high-dose radiation irradiation tests. The gamma-ray irradiation dose was 5.85 GGy. This dose is equivalent to the radiation dose emitted by general high-level radioactive waste in about 1,000 years.

The following XRD analysis and Vickers hardness test were performed on the fiber samples after irradiation and the fiber samples without irradiation. <XRD analysis> The XRD spectra of the fiber samples before and after irradiation are shown in Figure 2 (before irradiation: left figure, after irradiation: right figure, the vertical axis represents the diffraction intensity in arbitrary units (a.u.)). In addition, since the sample after irradiation can emit radiation, a hemispherical protective cover with a limited opening is set on the sample support only in this case. The reason is that the range of the measured incident angle of the spectrum data of the sample after irradiation (right figure of Figure 2) becomes narrower. In the XRD spectra of the fiber samples before and after irradiation, only amorphous haloes can be seen, and no peaks of the crystalline phase can be seen. In other words, it can be seen that: before and after irradiation, it is essentially composed of only amorphous phases, and amorphous properties can be maintained even after irradiation.

<Vickers hardness test> Vickers hardness test was conducted on fiber samples before and after irradiation. The test equipment used was Reichert-Jung Microduromat 4000E and Leica Telatom 3 optical microscope. Considering that the width of the fiber sample is about 20 μm, the force applied to the sample surface was set to 10 gF (0.098 N). The results of 17-point measurement of each sample before and after irradiation were 723±24 kgF/mm ² before irradiation and 647±19 kgF/mm ² after irradiation. Considering that the Vickers hardness retention rate after irradiation became 89% and the gamma ray irradiation dose was 5.85 GGy, it can be said that the above values are extremely high. As mentioned above, the material has excellent radiation resistance. For comparison, the retention rate (89%) of this test is plotted in Figure 3 shown above. Although the determination method of strength retention is different, it is worth noting that the sample with 16% iron oxide content maintains a strength retention rate of nearly 90% even when irradiated with an ultra-high radiation dose of about 100,000 times that of the previous test mentioned above.

[Example 2] The sample was adjusted according to the raw material blending ratio shown as Example 2 in Table 6. The component ratio of this sample is: [S] + [A]: 60 mass%, [A]/([S] + [A]): 0.25, [F]: 19 mass%, [C]: 13 mass% (Table 6). The result of the melt spinning test is that within 5 hours after the furnace temperature reaches 1350°C, the sample melts and falls, and an extremely fine fiber (mineral fiber) with a diameter of less than 50 μm can be obtained. The obtained fiber sample is the same as Example 1, and is essentially composed of only an amorphous phase, and is not easily broken even when stretched by hand. Furthermore, the amorphous property can be maintained even after irradiation, and the Vickers hardness retention rate is also at the same level as that of Example 1. As described above, the radiation resistance of this material is very excellent.

[Example 3] The sample was adjusted according to the raw material blending ratio shown in Table 6 as Example 3. The composition ratio of this sample is: [S] + [A]: 56 mass%, [A]/([S] + [A]): 0.20, [F]: 18 mass%, [C]: 25 mass% (Table 6). The result of the melt spinning test is that within 5 hours after the furnace temperature reaches 1350°C, the sample melts and falls, and an extremely fine fiber (mineral fiber) with a diameter of less than 50 μm can be obtained. The obtained fiber sample is the same as Example 1, and is essentially composed of only an amorphous phase, and is not easily broken even when stretched by hand. The amorphous property can be maintained even after irradiation, and the Vickers hardness retention rate is at the same level as that of Example 1. As described above, the radiation resistance of this material is very excellent.

[Comparative Example 1 to Comparative Example 8] The samples were adjusted according to the raw material blending ratios shown in Table 6 as Comparative Examples 1 to 8. All of them lacked any one of the "four requirements of the present invention related to the composition". The result was that none of the samples was fiberized within 5 hours after the furnace temperature reached 1350°C (Table 6).

[Table 6] Unit Embodiment 1 Embodiment 2 Embodiment 3 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Raw material blending ratio FA (1) Quality% 30 - - - - - 17 - - - - FA (2) - - - - - - - - 53 11 - FA (3) - - - - 70 - - - - - - FA (4) - - 62 - - - - 67 - - - FA (5) - 46 - - - - - - - - 40 FA (6) - - - 100 - - - - - - - BA (1) 70 46 - - - - - - - - 10 BA (2) - - - - - 100 - - - - - SiO ₂ (reagent) - - - - - - 67 17 - 33 - Al ₂ O ₃ (reagent) - 2 4 - - - - - 27 33 10 Fe ₂ O ₃ (reagent) - 6 12 - 30 - 17 17 20 twenty two 15 CaO (reagent) - - twenty three - - - - - - - 25 Composition ratio [S]＋[A] Quality% 60 60 56 84 53 35 78 72 73 76 43 [A]/([S]＋[A]) Quality Ratio 0.20 0.25 0.20 0.30 0.24 0.29 0.02 0.10 0.55 0.47 0.42 [F] Quality% 16 19 18 14 34 18 19 twenty three twenty three twenty three twenty one [C] 17 13 25 1 2 3 3 2 0 0 32 Evaluation items Radiation resistance Very good Very good Very good Poor Melt spinnability A A A C C C B C C C C

[Examples 4 to 11] Fly ash FA (7) was selected as the silicon aluminum source, and the "four requirements of the present invention regarding the composition" were met. As required, additional doping reagents SiO ₂ (S), Al ₂ O ₃ (A), Fe ₂ O ₃ (F), and CaO (C) were added to conduct tests (Table 7, Examples 4 to 11). The melt spinning properties were excellent. The radiation resistance was also very excellent as in Example 1. [Table 7] Unit Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Raw material blending ratio FA (7) Quality% 44 72 53 64 62 57 72 53 FA (8) - - - - - - - - FA (9) - - - - - - - - FA (10) - - - - - - - - FA (11) - - - - - - - - FA (12) - - - - - - - - BA (1) - - - - - - - - BA (2) - - - - - - - - SiO ₂ (reagent) 6 9 14 - 8 7 9 7 Al ₂ O ₃ (reagent) - - - 5 - - - - Fe ₂ O ₃ (reagent) 15 12 14 13 12 18 13 11 CaO (reagent) 15 5 15 15 15 15 4 26 Composition ratio [S]＋[A] Quality% 42 68 58 58 59 54 68 50 [A]/([S]＋[A]) Quality Ratio 0.20 0.20 0.17 0.30 0.20 0.20 0.20 0.20 [F] Quality% 19 18 19 19 18 twenty three 19 16 [C] 17 7 17 17 17 17 7 28 Evaluation items Radiation resistance Very good Very good Very good Very good Very good Very good Very good Very good Melt spinnability A A A A A A A A

Fly ash FA (7) was selected as a silicon-aluminum source, and additional doping reagents SiO ₂ (S), Al ₂ O ₃ (A), Fe ₂ O ₃ (F), and CaO (C) were added to conduct experiments (Table 8, Comparative Examples 9 to 16). Comparative Examples 9 to 16 all lacked any one of the "four requirements of the present invention related to the composition". If the value of [S] + [A] does not reach the lower limit of requirement i), the viscosity of the melt is too low, and as a result, filaments cannot be formed (Comparative Example 9). On the other hand, if the value of [S] + [A] exceeds the upper limit of requirement i), the viscosity of the melt is too high, so the falling action caused by gravity, which is a prerequisite for filament formation, does not occur, and fibers cannot be formed (Comparative Example 10). When the value of [A]/([S]+[A]) does not reach the lower limit of requirement ii), the viscosity of the melt is too low, and as a result, filaments cannot be formed (Comparative Example 11). On the other hand, when the value of [A]/([S]+[A]) exceeds the upper limit of requirement ii), the viscosity of the melt is too high, so the falling motion caused by gravity, which is a prerequisite for filament formation, does not appear (Comparative Example 12). The result of X-ray diffraction (XRD) spectrum is that in Comparative Example 12, the formation of a crystalline phase believed to be derived from an _{Al2O3 -} rich phase is observed (Figure 4). When the value of [F] does not reach the lower limit of requirement iii), the radiation resistance is poor (Comparative Example 13). On the other hand, if the value of [F] exceeds the upper limit of requirement iii), the viscosity of the melt is too low, and as a result, fibers cannot be formed (Comparative Example 14). When the value of [C] does not reach the lower limit of requirement iv), the viscosity of the melt is too low, and as a result, fibers cannot be formed (Comparative Example 15). On the other hand, if the value of [C] exceeds the upper limit of requirement iv), the viscosity of the melt is too high, and fibers cannot be formed (Comparative Example 16).

[Table 8] Unit Comparative Example 9 Comparative Example 10 Comparative Example 11 Comparative Example 12 Comparative Example 13 Comparative Example 14 Comparative Example 15 Comparative Example 16 Raw material blending ratio FA (7) Quality% 40 76 32 53 66 53 74 49 FA (8) - - - - - - - - FA (9) - - - - - - - - FA (10) - - - - - - - - FA (11) - - - - - - - - FA (12) - - - - - - - - BA (1) - - - - - - - - BA (2) - - - - - - - - SiO ₂ (reagent) 5 10 19 - 9 7 10 6 Al ₂ O ₃ (reagent) - - - 14 - - - - Fe ₂ O ₃ (reagent) 15 9 20 14 8 twenty two 12 12 CaO (reagent) 15 3 25 15 15 15 0 30 Composition ratio [S]＋[A] Quality% 38 72 44 58 63 50 70 46 [A]/([S]＋[A]) Quality Ratio 0.20 0.20 0.13 0.42 0.20 0.20 0.20 0.20 [F] Quality% 19 16 twenty three 19 14 27 19 16 [C] 17 5 26 17 17 17 3 32 Evaluation items Radiation resistance Poor Melt spinnability D B D B A D B D

Next, we tried formulas in which the silicon aluminum source, iron oxide source, and calcium oxide source are mostly composed of thermal power generation waste (fly ash, coal ash) or metal refining waste (steel slag, copper slag), or volcanic rocks as natural resources (Table 9, Examples 12 to 18). All of them meet the "four requirements of the present invention related to the composition" and have excellent melt spinning properties. The radiation resistance is also very excellent.

[Table 9] Unit Embodiment 12 Embodiment 13 Embodiment 14 Embodiment 15 Embodiment 16 Embodiment 17 Embodiment 18 Raw material blending ratio FA (7) Quality% - - 50 - - 30 45 FA (8) 50 - - - - - - FA (9) - 33 - - - - - FA (10) - - 30 - 40 30 25 FA (11) - - - 33 - - - FA (12) - - - - 50 - - FA (13) - - - - - 18 - FA (14) - - - - - - 10 BA (1) 50 67 7.5 67 2.5 twenty two 20 BA (2) - - - - - - - SiO ₂ (reagent) - - - - - - - Al ₂ O ₃ (reagent) - - - - - - - Fe ₂ O ₃ (reagent) - - - - - - - CaO (reagent) - - 12.5 - 7.5 - - Composition ratio [S]＋[A] Quality% 62 61 56 48 65 56 61 [A]/([S]＋[A]) Quality Ratio 0.20 0.20 0.20 0.19 0.21 0.21 0.22 [F] Quality% 16 18 twenty two 17 twenty three twenty one twenty two [C] 14 14 16 17 9 16 11 Evaluation items Radiation resistance Very good Very good Very good Very good Very good Very good Very good Melt spinnability A A A A A A A

FIG4 shows the XRD spectra of a series of melt samples. Samples whose values of [A]/([S]+[A]) do not exceed the upper limit of requirement ii) of the present invention (Comparative Example 11, Example 6) are amorphous, but in Comparative Example 12, which exceeds the upper limit of the requirement, the formation of a crystalline phase believed to be derived from an _{Al2O3 -} rich phase is observed. In addition, when the value of [F] changes to a range near the upper limit of requirement iii) of the present invention, the material is also amorphous (Comparative Example 13, Examples 8, 9, Comparative Example 14). FIG5 shows the thermograms (DTA curves) of the differential thermal analysis of the inorganic fibers obtained in a series of experiments. The inorganic fiber of the present invention has stable thermal properties up to about 800°C (at least close to 700°C), and its melting temperature is above 1200°C. [Industrial Applicability]

Since the inorganic material of the present invention has excellent radiation resistance, it can be used in the fields of nuclear energy, aerospace, and medicine. By using it in the radiation-irradiated parts of equipment, machines, and components in these fields, the radiation degradation of the radiation-irradiated parts can be suppressed. As equipment, machines and components in the field of nuclear energy, the following can be listed: · Equipment, machines and components used for nuclear power generation; · Equipment, machines and components used for mining and processing of uranium ore; · Equipment, machines and components used for secondary processing of nuclear fuel (including conversion, concentration, reconversion, forming and MOX manufacturing of the same fuel); · Equipment, machines and components used for storing, processing and reprocessing used nuclear fuel; · Equipment, machines and components used for storing, processing and disposing of radioactive waste; · Machines and components for transporting uranium ore, secondary processed nuclear fuel, used nuclear fuel or radioactive waste; · Other nuclear-related equipment, machines and components. As more specific examples of the equipment, machines, and components for the above-mentioned nuclear power generation, there can be listed: nuclear reactor buildings (including research furnaces and test furnaces), nuclear reactor storage containers, nuclear reactor facility internal piping, and waste furnace treatment robots. As equipment, machines, and components in the field of aerospace, there can be listed: · Space base buildings, space stations, artificial satellites, planetary exploration satellites, space suits, etc. As equipment, machines, and components in the field of medicine, there can be listed: · Medical devices using particle rays. Since the inorganic material of the present invention has excellent melt-spinning properties, it is suitable for use in inorganic fibers for fiber-reinforced composites. Depending on the purpose, it can be processed into coarse yarn, chopped strands, woven fabrics, prepregs, non-woven fabrics, etc. As the base material (fiber-reinforced material) of the above-mentioned composite material, there can be listed: resin, cement. As the resin, well-known thermoplastic resins and thermosetting resins can be used. Another example of the use of the inorganic material of the present invention is the use as a material for three-dimensional printing. That is, if the powder of the inorganic material of the present invention is mixed with wax, resin and other carriers as a material for three-dimensional printing, it can be made into a component with excellent radiation resistance without being restricted by the shape. The above examples of use are exemplified for the purpose of showing the usefulness of the present invention, and are not intended to limit the scope of the present invention.

1: Electric furnace 2: Tamman tube 3: Hanging rod 4: Opening 5: Fiber D: Electric furnace outer diameter H: Electric furnace height d: Electric furnace opening diameter

[Figure 1] is a schematic diagram showing the outline of the evaluation test of the melt-spinnability of the inorganic material of the present invention and an enlarged view of the melt-spun fiber. [Figure 2] is the XRD spectrum of the melt-spun fiber of the inorganic material of Example 1 before and after radiation irradiation. [Figure 3] is a diagram showing the relationship between the iron oxide content in the inorganic material and the radiation resistance. [Figure 4] is a diagram showing a number of examples of XRD spectra of the inorganic fiber of the example and the comparative example. [Figure 5] is a diagram showing a number of examples of DTA curves of the inorganic fiber of the example and the comparative example according to the differential thermal analysis.

Claims (17)

A radiation-resistant inorganic material comprises _SiO2 , _Al2O3 , CaO and _Fe2O3 as components, wherein the mass _percentages of the above components in the above _{inorganic material in terms of oxide conversion are as follows: i) the total content of SiO2 and Al2O3 is 40} mass _% or more and 70 mass% or less; ii) the mass ratio of _{Al2O3 /} ( _{SiO2 + Al2O3} ) is in the range of 0.15-0.40; iii) the content of _Fe2O3 is 16 mass% or more and 25 mass% or less; and iv) the content of _CaO is 5-30 mass%. For example, the radiation-resistant inorganic material in claim 1 is used for the part irradiated by radiation. A fiber composed of the radiation-resistant inorganic material of claim 1 or 2. A fiber-reinforced composite material reinforced with the fiber of claim 3. The fiber-reinforced composite material of claim 4 is a fiber-reinforced resin. The fiber-reinforced composite material in claim 4 is fiber-reinforced cement. A method for producing radiation-resistant inorganic fibers comprises melt-spinning a mixture of a silicon dioxide source, an aluminum oxide source, a _{calcium oxide source and an iron oxide source, wherein the mass percentages of SiO2, Al2O3 , CaO and Fe2O3} in the mixture as oxides are as _follows : i) the total content of _SiO2 and _Al2O3 is 40 mass% or more and 70 mass% _or less; ii) the mass ratio _{of Al2O3} /( _{SiO2 + Al2O3} ) is in the range of 0.15-0.40; iii) the content of _Fe2O3 is 16 mass% or more and 25 mass% or less; and iv) the content of CaO is 5-30 mass%. The method for manufacturing radiation-resistant inorganic fibers as in claim 7 is for use in the part irradiated by radiation. A method for producing radiation-resistant inorganic fibers as claimed in claim 7 or 8, wherein fly ash is used as a silicon dioxide source or an aluminum oxide source. The method for producing radiation-resistant inorganic fibers as claimed in claim 9, wherein the iron oxide source is copper slag. The method for producing radiation-resistant inorganic fibers as claimed in claim 10, wherein the calcium oxide source is steel slag. The method for producing radiation-resistant inorganic fibers as claimed in claim 7 or 8, wherein the silicon dioxide source or aluminum oxide source is basalt or andesite. The method for manufacturing a radiation-resistant inorganic material as claimed in claim 12, wherein the iron oxide source is copper slag. The method for manufacturing a radiation-resistant inorganic material as claimed in claim 13, wherein the calcium oxide source is steel slag. An inorganic material is used in a radiation irradiated part, the inorganic material contains _{SiO2 , Al2O3 ,} CaO and _Fe2O3 as components _, and the mass percentages of the above components in the above _inorganic material in terms of oxide conversion are as follows: i) the total content of _SiO2 and _Al2O3 is ₄₀ mass% or more and 70 _mass % or less; ii) the mass ratio of _Al2O3 /( _SiO2 + _Al2O3 ) is in the range of 0.15-0.40; iii) the content of _Fe2O3 is 16 mass% or more and 25 mass% or less; and iv) the content of _CaO is 5-30 mass%. For example, the use of inorganic materials in radiation-irradiated parts as in claim 15, wherein the radiation-irradiated parts are any of the following: a) nuclear reactor buildings, nuclear reactor storage containers, piping in nuclear reactor facilities, or waste reactor processing robots; b) space base buildings, space stations, artificial satellites, planetary exploration satellites, or space suits; c) medical devices using particle radiation. A method for suppressing radiation degradation of a fiber-reinforced composite material of a radiation-irradiated portion is disclosed. The method is for suppressing radiation degradation of a fiber-reinforced composite material constituting a radiation-irradiated portion, wherein the fiber is made into an inorganic fiber containing _{SiO2 , Al2O3} , CaO and _Fe2O3 as _components ; and the mass percentages of the above components in the inorganic fiber as converted into oxides are as _follows : i) the total content of _SiO2 and _Al2O3 is 40 mass% or more and ₇₀ mass% _or less; ii) the mass ratio of _Al2O3 /( _{SiO2 + Al2O3} ) is in the range of 0.15-0.40; iii) the content of _Fe2O3 is 16 mass% or more and 25 mass% or less; and iv) the content of CaO is 5-30 mass%.