JP2006308081A - Valve member and its manufacturing method as well as valve using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a valve member whose mechanical property such as strength and destruction toughness and heat shock resistance are improved. <P>SOLUTION: The valve member for liquid formed of a silicon nitride sintered body has a groove or a hole portion as at least part of a liquid flow path. The silicon nitride sintered body forming the valve member has a crystal phase containing silicon nitride as a main component, and a grain boundary phase containing a first metal silicide of a first metal element of at least one type of Fe, Cr, Mn, Co, Ni, Ti, Zr and Cu and a second metal silicide of a second metal element having a higher melting point than the first metal element. The density of each of the first metal silicide and the second metal silicide on the surface of the groove or the hole portion is lower than that of the inside of the silicon nitride sintered body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to valve members such as valve bodies and valve boxes for closing and controlling fluids such as corrosive gases, liquids containing solids, corrosive liquids, and powders in various chemical plants, steel, flue gas desulfurization, etc. And a valve using the same.

  Conventionally, there are a valve body, a valve box and the like as a valve member used for a valve. For example, in a ball valve 101 as shown in FIG. 7, a ceramic ball valve body 102 as shown in FIG. 6 is used. The driving force for opening and closing the ball valve body 102 is transmitted from the end of the stem 104 to the rectangular groove 105 having a rounded corner at the ball valve body 102. As a result, a complicated tensile stress is generated in the ball valve body 102 in the vicinity of the groove 105.

  In other words, when slurry or the like adheres to the portion of the valve seat 106 that holds the ball valve body 102 and seals between the ball valves 101, the opening / closing force that drives the ball valve body 102 increases, and stress generated in the ceramic portion. May exceed material strength and break.

  For this reason, in order to improve the material strength, ceramics such as alumina, partially stabilized zirconia, silicon carbide, and silicon nitride containing 90% by mass or more of an alumina component are used. In particular, it is known that silicon nitride is strong against a thermal shock load and is not easily damaged by a rapid temperature change. For example, Patent Documents 1 and 2 show a ball valve body 102 using a silicon nitride sintered body.

Further, as a silicon nitride sintered body satisfying mechanical properties and thermal properties such as strength and fracture toughness required when used as the ball valve body 102 and thermal shock resistance strength, Patent Document 3 discloses Fe as an impurity. In addition, it has been proposed to suppress variation in characteristics with high strength by adding a small amount of W. Patent Document 4 discloses a silicon nitride-based sintered body in which crystal grains of at least one metal silicide of W, Mo, Cu, Mn, Fe and Nb are dispersed in a grain boundary phase. Document 5 describes a silicon nitride-based sintered body in which a compound composed of a refractory metal—Fe—Si—O is formed in the grain boundary phase. Further, Patent Document 6 contains particles composed of silicides such as W and Fe and Ti compounds (nitrides, carbonitrides, carbonitrides) in the grain boundary phase, and silicides such as W and Fe are incorporated into Ti compounds. A silicon nitride-based sintered body aggregated around each of the above has been proposed.
Japanese Patent Laid-Open No. 5-60251 JP 2001-74149 A Japanese Patent Laid-Open No. 5-148031 Japanese Patent Laid-Open No. 2001-206774 JP 2001-106576 A JP-A-11-267538

  However, when the silicon nitride-based sintered body of Patent Documents 3 to 6 is used as a valve member such as the ball valve body 102, it usually has a metal silicide in the grain boundary phase of the silicon nitride-based sintered body. When mechanical stress is applied under the force of compression, tension, torsion, etc., the stress tends to concentrate on the metal silicide in the grain boundary phase. For this reason, the metal silicide with concentrated stress acts as a fracture source and a crack occurs between the silicon nitride crystal and the metal silicide, and as a result, there is a problem that the valve member is likely to be damaged during long-term use. Was.

  Further, since the metal silicide is uniformly dispersed in the valve member, the concentration of the metal silicide is likely to be substantially equal between the inside and the surface. This allows metal silicides with low mechanical strength and thermal shock resistance to easily degrade these characteristics of the valve member itself, especially when used in flue gas desulfurization equipment in thermal power plants in cold regions. It was easily damaged and was not sufficient for thermal shock load (heat shock).

  In order to solve the above problems, the valve member of the present invention is a valve member for liquid comprising a groove or hole made of a silicon nitride sintered body and constituting at least a part of a liquid flow path, The silicon nitride sintered body constituting the valve member includes a crystal phase mainly composed of silicon nitride and at least one first metal element selected from Fe, Cr, Mn, Co, Ni, Ti, Zr, and Cu. And a grain boundary phase containing a second metal silicide composed of a silicide of a second metal element having a melting point higher than that of the first metal element. Or each density | concentration of the said 1st metal silicide in the surface of a hole part and a 2nd metal silicide is lower than the inside of the said silicon nitride sintered body, It is characterized by the above-mentioned.

  Further, the present invention is characterized in that the valve member is a spherical body having a through hole in a central portion.

  Furthermore, the valve member of the present invention is characterized in that the metal element is at least one of Fe and Cu.

  Furthermore, the valve member of the present invention is characterized in that the first metal silicide is contained in an amount of 0.01 to 10% by mass in terms of the total of Fe and Cu.

  The valve member of the present invention is characterized in that the grain boundary phase contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table.

  Furthermore, the valve member of the present invention is characterized in that the second metal element is at least one of W and Mo.

  And the manufacturing method of the valve member of this invention is a manufacturing method of the valve member in any one of the above, Comprising: The silicon nitride powder which is predetermined raw material powder, and at least 1 metal element among melting | fusing point is 1000 degreeC or more A raw material preparation step of preparing a raw material powder by mixing a metal compound (excluding Si), a forming step of forming a formed body of the raw material powder and an organic binder, and substantially nitrogen gas and argon Obtained from a degreasing step of degreasing the organic binder in an atmosphere composed of a gas or a mixed gas thereof to produce a degreased body, and a firing step of firing the degreased body in a non-oxidizing atmosphere containing nitrogen gas After that, the obtained sintered body is immersed in an aqueous solution having a pH of 3 or less, or exposed to a gas comprising a halide, and then the outer surface is polished.

  The valve of the present invention is characterized by using the valve member.

  The valve member according to the present invention includes a crystalline phase mainly composed of silicon nitride and a silicide of at least one first metal element of Fe, Cr, Mn, Co, Ni, Ti, Zr and Cu. 1 metal silicide and a grain boundary phase containing a second metal silicide composed of a silicide of a second metal element having a melting point higher than that of the first metal element, and the surface of the upper groove or the hole. Since the concentration of each of the first metal silicide and the second metal silicide is lower than the inside, when the fluid is inserted into the groove or the hole, a valve member that is hard to adhere to the fluid and has excellent corrosion resistance is provided. It becomes possible to do.

  In addition, since the metal element is at least one of Fe and Cu, the occurrence of cracks in the grain boundary phase can be suppressed even when a large strain occurs in the ball valve body due to mechanical stress or thermal stress. It becomes possible to prevent the valve member from being damaged.

  In addition, since the first metal silicide is contained in an amount of 0.01 to 10% by mass in terms of the total of Fe and Cu, the fracture toughness of the grain boundary phase can be increased even at a high temperature. Even when stress is applied, it can be suppressed.

  Further, since the grain boundary phase contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table, the mechanical strength can be improved even at high temperatures.

  Furthermore, in the valve member of the present invention, since the second metal element is at least one of W and Mo, the mechanical characteristics and the thermal shock resistance can be further improved.

  And it is a manufacturing method of the valve member in any one of the above, A silicon nitride powder which is predetermined raw material powder, A metal compound which consists of at least one metal element (except Si) whose melting point is 1000 ° C or more, A raw material production step for producing a raw material powder by mixing, a molding step for producing a molded body comprising the raw material powder and an organic binder, and an atmosphere substantially comprising nitrogen gas, argon gas, or a mixed gas thereof A sintered body obtained after being obtained from a degreasing step in which the organic binder is degreased to produce a degreased body and a firing step in which the degreased body is fired in a non-oxidizing atmosphere containing nitrogen gas. Is immersed in an aqueous solution having a pH of 3 or less, or exposed to a gas comprising a halide, and then the outer surface is polished.

  Next, the valve of the present invention has a high strength, a high hardness, a high strength with little deterioration in strength even when it is repeatedly used at a high temperature by a manufacturing method characterized by using any one of the valve members described above. It is possible to provide a valve member having fracture toughness.

  Hereinafter, embodiments of the present invention will be described in detail.

  Examples of the valve member of the present invention include a valve box and a valve body. These embodiments and valves using these are shown in FIGS. 1 (a) to 1 (m). 1 (a) to 1 (e) are valve casings, (f) to (j) are valve bodies, (k) to (m) are valve casings of FIGS. 1 (a) to (e). The valve | bulb obtained by inserting the valve body of (j) is shown.

  A valve box that is a valve member of the present invention will be described with reference to FIGS. The valve box 21 is made of a silicon nitride sintered body having a prismatic outer shape, and has a long hole portion 22 inside the longitudinal direction, and a hole portion that penetrates the long hole portion 22 in a direction perpendicular to the longitudinal direction. 23a, 23b, and 23c. The valve box 21 is integrally formed by joining a valve box main body 21a and a sealing body 21b with screws, an adhesive, or the like. Both the valve box body 21a and the sealing body 21b are made of a silicon nitride sintered body.

  Further, as shown in FIGS. 1F to 1J, the valve body has a groove 24b formed in a part in the longitudinal direction of the valve body 24a, and the valve box 21 and the valve body 24 are combined. A valve can be obtained.

  This valve is demonstrated based on FIG.1 (k)-(m). In FIG. 1 (k), the outer diameter of the valve 26 in a state where the valve body 24 is inserted into the valve box 21 is slightly smaller than the inner diameter of the elongated hole portion 22 of the valve box 21. The valve body 24 is inserted inside the valve body 24a and can be rotated in the long hole portion 22 while improving the airtightness therebetween. Further, a counterbore (not shown) is formed on the outer peripheral portion of the valve body 24a in contact with the sealing body 21b, and a heat-resistant seal ring (not shown) for improving airtightness is provided on the counterbore, thereby providing the valve box 21. And the confidentiality between the valve body 24 can be enhanced.

  An example of how to use the valve 26 will be described. The valve 26 is fixed so that the longitudinal direction of the valve 26 is perpendicular to the gravity. That is, in FIG. 1 (k), the valve box 22 is fixed with the hole 23a on the upper side and the holes 23b and 23c on the lower side. The liquid is injected into the groove 24b from the hole 23a, and the groove 24b is filled with the liquid. Next, when the valve body 24 is rotated 180 ° in the long hole portion 22 and the groove 24b is lowered, the liquid in the groove 24b is discharged by gravity from the hole portion 23c. Further, when the valve body 24 is rotated 180 ° in the long hole portion 22, the original state shown in FIG. 1 (k) is obtained. Similarly, the liquid is filled from the hole portion 23a into the groove 24b, and the liquid is repeatedly supplied from the hole portion 23c. Can be released in a certain amount.

  FIG. 2A is a perspective view of a ball valve body showing another embodiment of the valve member according to the present invention, and FIG. 2B is a cross-sectional view showing a cross section of the ball valve according to the present invention. Further, FIG. 3 is a schematic view showing an outline of the assembly of the ball valve according to the present invention.

  The ball valve body which is another embodiment of the valve member of the present invention is formed of a silicon nitride-based sintered body as shown in FIG. 2 (a) and has a spherical shape with a through hole 7 in the central portion. It has a groove 5 for connection when used as a ball valve as shown in FIG. The ball valve 1 using the ball valve body 2 can be opened and closed via a stem 4 that transmits a driving force to the groove 5 of the ball valve body 2 by an actuator 30. The ball valve body 2 is sandwiched and accommodated between a valve box 6b having a spherical portion receiving surface which also serves as a valve seat and a socket 6a, is held from both sides, and is rotatable by a stem 4.

  Further, an O-ring 9 is disposed between the valve box 6b and the socket 6a so that the internal fluid is not leaked. A valve seat is disposed on the end face of the valve box 6b and the socket 6a, and a cylindrical body gland 8b having a bottomed portion and a socket presser 8a are disposed so as to surround the outside of the valve seat. It is concluded. Further, in order to obtain a certain distance from the ground 8b at the lower part of the actuator 30, a yoke 31 having a through hole is interposed at the center and fixed to the ground 8b. The stem 4 passes through the through hole of the yoke 31. Is freely rotatable.

  And when the through-hole 7 of the ball valve body 2 is assembled to the ball valve 1 body, when it matches the opening provided in the center of the gland 8b, the valve box 6b, the socket 6a, and the socket presser 8a, It has a structure that can pass through. When the through hole 7 of the ball valve body 2 does not coincide with the opening, the fluid is stopped so that the ball valve body 2 can be rotated to open and close. A hole 7 is formed. Although the through-hole 7 is shown as a round hole in FIG. 1, it may be formed as a triangular hole as shown in FIG. 5, and the flow rate can be adjusted with opening and closing. In general, these are managed by CV values. The groove 5 has a substantially rectangular shape, and the corner portion preferably has a curved surface with a radius of curvature of R 0.5 mm to 2 mm.

  Here, as shown in FIGS. 1A to 1M and 2A, the valve bodies 2 and 24 and the valve box 21 which are the valve members of the present invention include the valve bodies 2 and 24 and the valve box 21. The formed silicon nitride sintered body is composed of a crystalline phase mainly composed of silicon nitride and a silicide of at least one first metal element of Fe, Cr, Mn, Co, Ni, Ti, Zr and Cu. And a grain boundary phase containing a second metal silicide composed of a silicide of a second metal element having a melting point higher than that of the first metal element, and on the surface of the through hole. It is important that the concentrations of the first metal silicide and the second metal silicide are lower than the inside.

  Thereby, even when a large thermal stress is applied to the valve bodies 2 and 24 and the valve box 21 due to exposure to a high-temperature fluid, the grain boundary phase containing the first metal silicide and the second metal silicide and the silicon nitride It is possible to suppress the development of microcracks at the interface with the crystal, and to improve the thermal characteristics such as thermal shock resistance, even if a high temperature fluid flows in, it can be damaged by a thermal shock load (heat shock). It is possible to obtain a ball valve body 2 that is not present.

  FIG. 4 shows a schematic diagram of the surfaces of these valve bodies 2 and 24 and the valve box 21 observed with an SEM (scanning electron microscope). A silicon nitride crystal 12 as a main component, and a first metal made of silicide of at least one first metal element of Fe, Cr, Mn, Co, Ni, Ti, Zr and Cu in the grain boundary phase 20 It includes a silicide 16 and a second metal silicide 18 made of a silicide of a second metal element having a melting point higher than that of the first metal element.

The grain boundary phase 20 refers to a region surrounded by the silicon nitride crystals 12.

  The silicon nitride crystal 12 is mainly formed in a needle shape, and includes β-type silicon nitride crystal or β′-sialon crystal having the same crystal structure as β-type silicon nitride.

As the first metal silicide _{16, FeSi 2, FeSi, Fe} 3 Si, Fe 5 Si 3, CrSi 2, Cr 3 Si, MnSi, CoSi 2, NiSi, Ni 2 Si, TiSi 2, ZrSi 2, Cu 2 Si Etc. The second metal silicide is preferably at least one selected from WSi ₂ , W ₅ Si ₃ , WSi ₃ , W ₂ Si ₃ and MoSi ₂ .

Moreover, as the second metal element, Mo, Ta, Nb, and W are preferable. As the second metal silicide 18 made of silicide of these metal elements, MoSi ₂ , Mo ₅ Si ₃ , TaSi ₂ , Ta ₅ Si ₃ , Nb ₅ Si ₃ , WSi ₂ , W ₅ Si ₃ , WSi ₃ , W ₂ Si _{3 and the} like. Since these second metal silicides 18 have a very high melting point, they are particularly strongly bonded to the silicon nitride crystal 12 and are thermodynamically stable even when exposed to a high temperature fluid. Therefore, even when a large thermal stress is applied to the valve bodies 2 and 24 and the valve box 21 due to exposure to a high-temperature fluid, the grain boundary phase including the first metal silicide 16 and the second metal silicide 18 is present. The microcrack is prevented from progressing at the interface between the silicon nitride crystal 20 and the silicon nitride crystal 12. As a result, thermal characteristics such as thermal shock resistance can be further improved. At the same time, the surface 24b of the groove 24b, the surface 26a of the elongated hole portion 22, the surfaces 26c to 26e of the hole portions 21a to 21c, and the first metal silicide 16 and the second metal silicide 18 on the surface 7a of the through hole 7 respectively. By lowering the concentration from the inside, when exposed to a high-temperature fluid, the first metal silicide 16 and the second metal silicide 18 contained in the interior can improve the mechanical characteristics and the thermal characteristics. it can.

The reason why the concentrations of the first and second metal silicides 16 and 18 on the surface 26a to 26e of the hole and the surface 7a of the through hole 7 are made lower than the inside is that the high-temperature fluid is suddenly changed by opening and closing the valve. This is because a thermal shock load (heat shock) is generated when the gas flows into the groove 24b or the through hole 7, and there is a fear of breakage. In particular, the valve 26 and the ball valve 1 used in a flue gas desulfurization apparatus such as a thermal power plant may be used outdoors, and in that case, it is not uncommon to be exposed to zero. When high temperature lime slurry flows into the cooled valve 26 and ball valve 1, temperature distribution occurs in the valve box 21, valve body 24, and ball valve body 2, and as a result, damage may occur.

  In the ball valve 1, when the valve is closed, the spherical portion remains in contact with the fluid, so the temperature does not change so much. When the valve is opened, the spherical portion hardly contacts the fluid, so the temperature does not change. The surface 7a of the through hole 7 is less susceptible to thermal shock load (heat shock).

  Further, even when a highly corrosive fluid is inserted, the first and second metal silicides 16 and 18 having low corrosion resistance maintain the high corrosion resistance because the concentration of the surface 7a is lower than the inside. Therefore, it is difficult for erosion to occur from voids existing on the surface, and it is possible to use the fluid without adhering to the portion and inhibiting the flow. In particular, since the metal silicide impairs the corrosion resistance, it is preferable that the concentrations on the surface 26a to 26e of the hole and the surface of the through hole 7 are lower than the inside.

  Further, the silicon nitride sintered body constituting the valve box 21, the valve body 24, and the ball valve body 2 may be a sintered body or may be subjected to processing such as polishing after sintering. In any case, the concentration of the first and second metal silicides 16 and 18 on the surface 7a may be lower than the inside.

  In addition, the inside of the valve box 21 is the outer surface of the valve box 21, the surface 26a of the elongated hole 22, the surfaces of the holes 23a to 23c, and the vicinity of the surface in a range from these surfaces to a depth of 0.2 mm. It is a part excluding. The inside of the valve body 24 is a portion excluding the outer surface of the valve box 24, the surface of the groove 24b, and the vicinity of the surface in a range from these surfaces to a depth of 0.2 mm. The inside of the ball valve body 2 is a portion excluding the surface 7a of the through hole 7, the outer surface of the ball valve body 2, and the vicinity of the surface that is a range from these surfaces to a depth of 0.2 mm.

  Hereinafter, the surface 26 a of the long hole 22 of the valve box 21, the holes 23 a to 23 c, the surface 26 b of the groove 24 b of the valve body 24, and the surface 7 a of the through hole 7 of the ball valve body 2 are collectively referred to as a surface. The valve box 21, the valve body 24, and the ball valve body 2 are collectively referred to as a valve member.

  Here, as a method for comparing the concentration of the metal silicide inside the valve box 21, the valve body 24, and the ball valve body 2, which are the valve members of the present invention, the first and second metal silicides 16 and 18 are: A case where Fe silicide and Cu silicide are included will be described as an example.

For example, it is performed as follows using a fluorescent X-ray analyzer. First, the surface and the surface polished at a predetermined position are each irradiated with X-rays, and the intensity of fluorescent X-rays (characteristic X-rays) of each element of Fe and Cu generated thereby is as follows: taking measurement. Fluorescent X-rays (characteristic X-rays) of each element of Fe and Cu are incident on a high-resolution proportional counter, amplified by an amplification circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (Fe, Cu) to be measured are specified, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements is output. In order to make the measurement conditions the same, the area of the sample, the intensity of X-rays to be irradiated, the time for counting fluorescent X-rays, and the like are the same. The counts of the fluorescent X-rays of the elements Fe and Cu on the surface thus measured are C _Fe1 and C _Cu1 , and the counts of the fluorescent X-rays of the elements Fe and Cu inside are C _Fe2 and C _Cu2 . To do. Furthermore, the inside of the valve member is analyzed by an X-ray diffraction method, a micro X-ray diffraction method, a transmission electron microscope, or the like to confirm that a crystal phase made of a metal silicide is contained.

If the surface contains the first and second metal silicides 16 and 18, the crystal phase can be confirmed by analyzing with an X-ray diffraction method, a micro X-ray diffraction method, a transmission electron microscope, or the like. it can. The ratio of the metal silicide concentration between the surface and the interior is calculated from C _Fe1 / C _{Fe2 for Fe} silicide and C _Cu1 / C _Cu2 for Cu silicide. In the valve member of the present invention, the fact that the concentration of the metal silicides 16 and 18 on the surface is lower than the inside means that at least one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 is smaller than 1. Define. Thus, when the first and second metal silicides 16 and 18 include a plurality of metal elements, when the concentration of at least one of the first and second metal silicides 16 and 18 is lower than the inside at the surface, It is defined that the concentration of the metal silicide on the surface 7a of the through hole 7 is lower than the inside. Further, the concentration of the metal silicide is 1 / n (n is an arbitrary numerical value larger than 1) compared to the inside, which is smaller one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2. It is defined as a case of 1 / n or less. However, the case where the first and second metal silicides 16 and 18 are not present on the surface of the valve member is also one of the preferred embodiments of the present invention. In this case, the values of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 are zero. It is defined as

  In order to reduce the concentration of the first and second metal silicides 16 and 18 on the surface of the valve member of the present invention, details will be described later in the manufacturing method. First, silicon nitride obtained by a general method is used. After obtaining a sintered body containing as a main component, the concentration of the metal silicide on the surface can be reduced by immersing in an aqueous solution having a pH of 3 or less or by exposing to a gas comprising a halide. When immersed in an aqueous solution, the pH and the immersion time are changed, and the lower the pH and the longer the immersion time, the lower the concentration of metal silicide on the surface. When exposed to a gas comprising a halide such as fluorine or chlorine, the exposure time is changed, and the longer the exposure time, the lower the concentration of metal silicide on the surface. Alternatively, it is preferable that the through-holes 7 are formed by burning and not ground.

  When the valve member is the ball valve body 2, it is preferable that the surface roughness of the outer surface of the ball valve body 2 is 0.4 μm or less in terms of arithmetic average roughness (Ra). This is because when the value is larger than 0.4 μm, the torque at the time of operation is high, and when the fluid is a fluid containing powder or the like, it is easy to bite between the ball valve body 2 and the valve seat. Since it sometimes cannot be operated smoothly, it is preferably 0.4 μm or less, and more preferably 0.2 μm or less. Furthermore, from the viewpoint of fluid leakage, the arithmetic average roughness (Ra) is preferably 0.4 μm or less.

  The silicon nitride sintered body constituting the valve member preferably has a void occupancy ratio of 1% or less and a maximum void diameter of 10 μm or less. When the fluid is a fluid containing powder or the like, a void is formed. This prevents the fluid from sticking to the surface and does not impair the operability. Preferably, the void occupation ratio is 0.8% or less, and the maximum void diameter is 5 μm or less, and further 2 μm or less.

  Moreover, it is preferable that the 1st metal element contained in the silicon nitride sintered body 3 which comprises the valve member of this invention is at least 1 among Fe and Cu.

  Thus, when the first metal element is at least one of Fe and Cu, it is preferable to contain 0.01 to 10% by mass of the first metal silicide in terms of the total conversion of Fe and Cu.

  Accordingly, the first metal silicide 16 having not only excellent mechanical characteristics and thermal characteristics but also high fracture toughness can be generated in the grain boundary phase 20, so that when stress is applied to the valve member, Even when a large strain is generated in the entire valve member due to mechanical stress or thermal stress, the occurrence of cracks in the grain boundary phase 20 can be suppressed, and the valve member can be prevented from being damaged.

  If the content of the first metal element is large, the amount of the metal element present in the silicon nitride as an impurity increases and the mechanical characteristics are deteriorated, so that problems such as breakage of the valve member are likely to occur. . Moreover, when it is less than a lower limit, it becomes difficult to form a metal silicide, the adjacent layer of the metal silicide in the silicon nitride-based sintered body 3 becomes difficult to exist, and the silicon nitride-based sintered body 3 constituting the valve member does not exist. Mechanical properties and thermal shock resistance are reduced.

  In particular, when these valve members are used in flue gas desulfurization equipment, etc., high-temperature lime slurry suddenly flows in, so that a thermal shock load is applied. It is feared that the remaining fluid expands and a pressing force is applied from the inner periphery, but it can be used without any problem against these mechanical stresses and thermal stresses.

  The grain boundary phase 20 preferably contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table. As a result, since the liquid phase is generated at low temperature during firing, the crystal 12 of the silicon nitride-based sintered body is fine and has a uniform particle size. As a result, the ball having excellent thermal shock resistance and high mechanical strength. The valve body 2 can be obtained. The amorphous phase can be generated in the sintered body by, for example, adding an oxide of Group 3 element (hereinafter referred to as RE) of the periodic table and aluminum oxide powder in the manufacturing process, and then molding and firing. it can.

Preferably, the silicon nitride sintered body constituting the valve member contains 1 to 20% by mass of RE in terms of RE ₂ O ₃ and 0.1 to 10% by mass of Al in terms of Al ₂ O ₃ . The Group 3 element means at least one element selected from Sc, Y, lanthanoid elements, and actinoid elements.

  The RE is preferably at least one of Y, Er, Yb, and Lu. This tends to produce a liquid phase at a low temperature during firing and to reduce the difference between the thermal expansion coefficient of the resulting amorphous phase and the thermal expansion of the silicon nitride crystals. For this reason, not only the silicon nitride crystals are fine and uniform in particle size, but even when mechanical stress or thermal stress is applied at high temperature, the difference in thermal expansion coefficient between silicon nitride and the grain boundary phase 20 Generation of microcracks in the grain boundary phase can be suppressed. As a result, the mechanical strength at high temperature can be improved while maintaining the thermal shock resistance. Thereby, the oxidation resistance in a high-temperature oxidizing atmosphere can also be improved.

  When RE is Y, it is possible to control the material composition of the silicon nitride-based sintered body with high accuracy because it is possible to suppress the evaporation of RE during firing more than when RE is other than Y. Since it can reduce, it is especially preferable.

Furthermore, it is preferable that the grain boundary phase 20 contains at least one of an apatite phase, a borastite phase, and a disilicate phase. Thereby, the mechanical strength of the valve member can be further improved. The apatite phase is a compound represented by RE ₅ (Si ₄ ) ₃ N, the borastite phase is represented by RESiO ₂ N, and the disilicate phase is represented by RE ₂ Si ₂ O ₇ . Moreover, when the grain boundary phase 20 contains an apatite phase or a borastite phase, high temperature strength, high temperature creep resistance, and thermal shock resistance are improved. Further, when the grain boundary phase contains a disilicate phase, the oxidation resistance at high temperatures is improved.

  In order to measure the amount of the grain boundary phase 20 on the surface 7a of the through-hole 7 with respect to the amount of the grain boundary phase 20 inside the valve member containing RE and Al, for example, the following is performed using a fluorescent X-ray analyzer.

The surface of the valve member and the polished surface of the valve member are each irradiated with X-rays, and the intensity of fluorescent X-rays (characteristic X-rays) of each element of RE and Al generated thereby is measured as follows. . Fluorescent X-rays (characteristic X-rays) of each element of RE and Al are incident on a high-resolution proportional counter, amplified by an amplifier circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (RE, Al) to be measured are designated, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements is output. In order to make the measurement conditions the same, the area of the sample, the intensity of X-rays to be irradiated, the time for counting fluorescent X-rays, and the like are the same. The counts of the fluorescent X-rays of the RE and Al elements on the surface 7a thus measured are C _RE1 and C _Al1 , the internal RE and the fluorescent X-ray counts of the Al elements are C _RE2 and C _Al2 , respectively. To do.

However, when a plurality of fluorescent X-rays of RE are detected, the total number of fluorescent X-rays of the plurality of REs is defined as C _RE1 and C _RE2 for the surface 7a and the inside, respectively. The ratio between the surface 7a and the internal concentration for each of _RE and Al is calculated by C _RE1 / C _{RE2 for RE} and C _Al1 / C _{Al2 for Al} . In the silicon nitride-based sintered body constituting the ball valve body 2, the fact that the grain boundary phase 20 containing RE and Al is present on the surface less than the inside of the valve member means that the C _RE1 / C _RE2 , C _Al1 / It is defined as a case where at least one of C _Al2 is smaller than 1. However, when the grain boundary phase 20 containing RE and Al does not exist on the surface 7a, the values of C _RE1 / C _RE2 and C _Al1 / C _Al2 are set to zero.

Moreover, it is preferable that the ratio of Si and RE contained in the grain boundary phase 20 is 0.2 to 10 in terms of a molar ratio of SiO ₂ / RE ₂ O ₃ . Thereby, the mechanical characteristics of the valve member can be further improved. It is more preferable that the molar ratio of SiO ₂ / RE ₂ O ₃ is 0.2 to 4 in order to improve the sinterability of the silicon nitride sintered body. This molar ratio can be determined as follows. Let G (mass%) be the total of the amount of oxygen (mass%) contained in RE ₂ O ₃ and Al ₂ O ₃ converted to volume% by the above method. The total oxygen content in the silicon nitride sintered body is measured with an oxygen analyzer manufactured by LECO, and G (mass%) is subtracted from the total oxygen content (mass%), and the remaining oxygen content (mass%) is determined as SiO. Converted to ₂ amount (mass%). The ratio of the amount of SiO ₂ (% by mass) and the content (% by mass) of RE ₂ O ₃ in terms of mass is defined as the ratio of Si to RE in terms of the molar ratio of SiO ₂ / RE ₂ O ₃ .

The ratio of Al to RE contained in the grain boundary phase 20 is preferably 0.2 to 5 in terms of a molar ratio of Al ₂ O ₃ / RE ₂ O ₃ . This is because the sinterability of the silicon nitride sintered body can be further improved and the fracture toughness can be improved. More preferably, it is 0.4 to ₃ in terms of a molar ratio of Al ₂ O ₃ / RE ₂ O ₃ . The molar ratio of Al to RE can be measured by ICP emission spectroscopic analysis as follows.

The content (mass%) of RE and Al in the silicon nitride sintered body is measured by ICP emission spectroscopic analysis, and this content is converted into the content (mass%) in terms of RE ₂ O ₃ and Al ₂ O _3. Convert. Further, using the content and theoretical density of RE ₂ O ₃ and Al ₂ O ₃ in terms of mass (for example, Y ₂ O ₃ is 5.02 g / cm ³ , Al ₂ O ₃ is 3.98 g / cm ³ ), The content of RE ₂ O ₃ and Al ₂ O ₃ in terms of volume% is determined.

  Further, the second metal element is preferably at least one of W and Mo, and the content of the second metal silicide 18 is preferably 0.1 to 3% by mass. This facilitates formation of the adjacent phase 14 in which the first metal silicide 16 and the second metal silicide 18 are in contact with each other, thereby concentrating mechanical stress and thermal stress on the first and second metal silicides 16 and 18. Therefore, it is possible to further improve the mechanical characteristics and thermal shock resistance.

Further, FeSi _2, WSi ₂ is preferably selected as the second metal silicide 18 as the first metal silicide 16. This is because the Fe silicide and the W silicide are close in crystal structure, so that the adjacent phase 14 is remarkably easily formed. Accordingly, the content of the adjacent phase 14 with respect to the grain boundary phase 20 is increased, and as a result, the mechanical characteristics and thermal characteristics, particularly mechanical strength and thermal shock resistance are further improved.

  Furthermore, the crystal 12 of the silicon nitride-based sintered body is composed of needle-like crystals, the needle-like crystals have a major axis having an average diameter of 30 μm or less, and the needle-shaped crystals having a minor axis having a minor axis of 2 μm or less. Is preferred. Thereby, since the acicular crystal suppresses the progress of fine cracks more effectively, it can be a silicon nitride sintered body with improved fracture toughness and improved mechanical strength. In particular, in order to further improve mechanical properties such as mechanical strength, it is preferable that the average diameter of the major axis of the needle-like crystal is 15 μm or less. This is because when the average particle size exceeds 15 μm, the fracture toughness cannot be remarkably improved, so that the mechanical strength cannot be remarkably improved.

  There are various methods for measuring the average grain size of the silicon nitride crystal 12 as follows. That is, the cross-section of the valve member is mirror-polished, this mirror surface is taken in a SEM (scanning electron microscope) photograph, and the method of measuring the long diameter of the silicon nitride crystal 12 in the SEM photograph is combined with an X-ray microanalyzer. Then, the silicon nitride crystal 12 is identified and the major axis of the crystal is measured, or the major axis is measured after removing the grain boundary phase 20 on the mirror-finished valve member surface from the surface by etching by heat treatment or chemical etching. In any case, it is calculated by averaging a plurality of measured long diameter data.

  Further, when the valve member is the ball valve body 2, the grain boundary phase 20 contains at least one metal silicide of a metal element having a melting point of 1400 ° C. or higher, and contains less than 20 volume% of the grain boundary phase 20. Is preferred. As a result, the metal silicides 16 and 18 having excellent creep resistance at high temperatures are generated in the grain boundary phase during firing in the course of manufacturing the ball valve body 2. As a result, deformation can be suppressed during firing performed in the process of manufacturing the ball valve body 2, so that the ball valve body 2 with high dimensional accuracy can be obtained. In particular, the through holes 7 and the grooves 5 can be formed by being burned out.

  Further, when the content of the grain boundary phase 20 is 20% by volume or more, deformation is likely to occur during the firing step, which makes it difficult to produce a ball valve body with high dimensional accuracy, which is not preferable. Moreover, when the grain boundary phase 20 exceeds 15 volume% and is less than 20 volume%, deformation cannot be remarkably reduced. Further, when the grain boundary phase is less than 5% by volume, it is necessary to fire at a high temperature in order to obtain a dense ball valve body 2, and since the silicon nitride crystal 12 becomes partially coarse when fired at a high temperature, mechanical Strength and wear resistance cannot be remarkably improved. For this reason, the content of the grain boundary phase is particularly preferably 5 to 15% by volume.

  The adjacent phase may be in a state where the first and second metal silicides 16 and 18 are in contact with each other, and thereby mechanical stress and heat are applied to the first and second metal silicides 16 and 18. The stress concentration can be suppressed, and as a result, the mechanical characteristics and thermal shock resistance of the valve member can be further improved, and one of the first and second metal silicides 16 and 18 is one of the other metal silicides. It is more preferable that a part or the whole is surrounded.

  Further, the adjacent phase includes the first metal silicide 16 and the second metal silicide 18, and further, the first metal element constituting the first metal silicide 16 and the second metal silicide 18. It is preferable to have a third metal silicide composed of a plurality of metal components including a metal element. Since the third metal silicide is similar in crystal structure to the first and second metal silicides 16 and 18, not only the adjacent phase is easily formed, but also the adjacent phase is thermodynamically stable. This is because when used as a valve member at a high temperature, the adjacent phase is less likely to undergo phase transformation, and mechanical properties and thermal shock resistance at high temperatures are improved.

  Next, the manufacturing method of the valve member of this invention is demonstrated.

  For example, first, a raw material production step of producing a raw material powder by mixing a silicon nitride powder, which is a predetermined raw material powder, and a metal compound composed of at least one metal element (except Si) having a melting point of 1000 ° C. or higher; A molding step for producing a molded body comprising the raw material powder and an organic binder, and degreasing the organic binder in an atmosphere substantially composed of nitrogen gas, argon gas, or a mixed gas thereof to obtain a degreased body. After being obtained from a degreasing step to be produced and a firing step in which the degreased body is fired in a non-oxidizing atmosphere containing nitrogen gas, the obtained sintered body is immersed in an aqueous solution having a pH of 3 or less, or a halide. After having exposed to the gas which consists of, the process which grind | polishes an outer surface can make the density | concentration of the surface metal silicide lower than an inside. Thereby, mechanical characteristics and thermal shock resistance can be improved.

  Furthermore, the manufacturing method of the ball valve 1 of the present invention will be specifically described.

  For example, first, a raw material preparation step of preparing a raw material powder by mixing a silicon nitride powder and a metal compound composed of at least one metal element (excluding Si) having a melting point of 1000 ° C. or higher, and the raw material powder and an organic bond A degreasing step for producing a degreased body by degreasing the organic binder in an atmosphere substantially composed of nitrogen gas, argon gas, or a mixed gas thereof; A sintered body is manufactured by a manufacturing method including a baking step of baking the degreased body in a non-oxidizing atmosphere containing nitrogen gas. This sintered body is a silicon nitride-based sintered body mainly composed of β-type silicon nitride crystal or β′-sialon crystal having the same crystal structure as β-type silicon nitride. Moreover, it is preferable that the metal element mentioned above is chosen as at least 1 metal element among melting | fusing point of 1000 degreeC or more.

  Next, an immersion process in which the obtained sintered body is immersed in an aqueous solution having a pH of 3 or less, or an exposure process in which the sintered body is exposed to a gas composed of a halide.

In the dipping process, the metal silicide present on the surface of the sintered body is reacted with an aqueous solution having a pH of 3 or less to remove at least a part thereof from the surface of the sintered body. Examples of the aqueous solution having a pH of 3 or lower include aqueous solutions of HCl, HNO ₃ , H ₂ SO ₄ , HF, H ₂ O ₂ , and HClO ₄ and aqueous solutions obtained by mixing at least two of them. Among these aqueous solutions, HCl aqueous solution alone or mixed acid aqueous solution as HNO ₃ + H ₂ SO ₄ , HF + HNO ₃ + H ₂ SO ₄ , HF + H ₂ O ₂ , HF + HNO ₃ , HNO ₃ + HF, HNO ₃ + HF + H ₂ SO ₄ , HNO ₃ + HF It is preferable to use any aqueous solution of HNO ₃ + HF + HClO ₄ . By immersing the sintered body in the aqueous solution, the metal silicide is removed from the surface of the sintered body. Among the aqueous solutions, an aqueous HCl solution that can improve economy and safety in the manufacturing process is particularly preferable. The reason why water is contained in the aqueous solution having a pH of 3 or less used in the dipping process is to improve the economy and safety in the production process. The time for exposing the sintered body to an aqueous solution having a pH of 3 or less is preferably 5 minutes or more.

In the exposure step, the sintered body is exposed to a halide. As the halide, a gas composed of fluoride is preferable. In particular, ClF ₃ , CF ₂ Cl ₂ , CFCl ₃ , CF ₃ Cl, CF ₄ , A gas containing any of NF ₃ , SF ₆ , SiF ₄ , BF ₃ , PF ₃ , and PF ₅ is preferable. Thereby, the metal silicide contained in the surface of the sintered body is removed. In particular, metal silicides containing W and Mo as metal silicides can be efficiently removed. More preferably, an air stream of these halides is formed, and the sintered body is exposed to the air stream for 1 minute or more.

  The reason why the immersion step or the exposure step is selected as a method for reducing the metal silicide on the surface of the sintered body will be described. There are many methods for reducing the metal silicide on the surface of the silicon nitride-based sintered body, and among these, it is preferable to use the immersion step and the exposure step. As another method for removing the metal silicide present on the surface of the silicon nitride sintered body, for example, sodium oxide and the sintered silicon nitride sintered body may be any one of Au, Fe, Ni, Ag, and Zr. There is a method of heating to about 500 ° C. in a metal container made of such. However, this method has a problem that the container is easily eroded, a problem that a metal component contained in the container is fixed to the silicon nitride sintered body, a problem that the sodium oxide used is fixed to the silicon nitride sintered body, and the like. There is. For this reason, this method cannot be used as a method for removing metal silicide from the surface of a silicon nitride-based sintered body for use as a valve member.

  Further, in order to control the concentration of the metal silicide on the surface to ½ or less compared to the inside, for example, an aqueous solution having a pH of 2.5 or less is used as the aqueous solution, and the sintered body is immersed in this solution for 10 minutes or more. Or exposed to a gas containing at least one of fluorine and chlorine for 20 minutes or more.

  Furthermore, when using at least one metal compound of Fe and Cu as a metal compound composed of at least one metal element (excluding Si) having a melting point of 1000 ° C. or higher, Fe silicide, Cu is used in the sintered body. By controlling the content of Fe and Cu so that the silicide contains 0.01 to 10% by mass in terms of the total of Fe and Cu, the fracture toughness of the grain boundary phase can be increased even at higher temperatures. Even when thermal stress is applied at a higher temperature, it is possible to manufacture a valve member that is difficult to break.

Further, by adding an oxide (RE ₂ O ₃ ) of group 3 element (RE) of the periodic table and aluminum oxide to the raw material powder, a liquid phase is generated at a low temperature in the firing step, and the grain boundary phase Can contain an amorphous phase composed of RE, Al and O. As a result, it is possible to manufacture a valve member having a fine silicon nitride crystal and a uniform particle size, excellent thermal shock resistance, and high mechanical strength. In addition, in order to make the silicon nitride crystals fine and uniform throughout the sintered body by uniformly dispersing the amorphous phase in the grain boundary phase, it is the highest in the firing step. After passing through the temperature, it is preferable that the rate of temperature decrease to 800 ° C. is greater than 100 ° C./hour.

Furthermore, by using at least one of _{Y 2 O 3, Er 2 O} 3, Yb 2 O 3, Lu 2 O 3 as the _RE 2 _{O 3,} with improved mechanical strength and oxidation resistance at high temperatures A valve member can be manufactured. Further, in the firing step, the rate of temperature decrease is set to be greater than 200 ° C./hour, so that the ratio of Si and RE contained in the grain boundary phase is 0.2 to 10 in terms of the molar ratio of SiO ₂ / RE ₂ O _3. Therefore, the ball valve body 2 with further improved mechanical characteristics can be manufactured.

Further, RE ₂ O ₃ and aluminum oxide should be added to the raw material powder so that the ratio of Al to RE in the sintered body is 0.2 to 5 in terms of molar ratio of Al ₂ O ₃ / RE ₂ O _3. Thus, the amorphous phase can be uniformly formed over the entire grain boundary phase, and uneven distribution of the amorphous phase can be suppressed, so that the ball valve body 2 with improved sinterability and improved fracture toughness is obtained. Can be manufactured.

Further, by setting the specific surface area of the degreased body to 1 to 30 m ² / g, the silicon nitride crystals contained in the sintered body are made of needle-like crystals, and the average diameter of the major axis of the needle-like crystals is 30 μm or less. The average particle diameter of the minor axis of the acicular crystal can be 2 μm or less. As a result, the ball valve body 2 having improved fracture toughness and further improved mechanical strength can be produced.

  Further, it is preferable to control the content of the grain boundary phase contained in the sintered body to less than 20% by volume by controlling the content of the compound other than silicon nitride contained in the raw material powder, Therefore, the ball valve body 2 with high dimensional accuracy can be manufactured.

  In addition, it is preferable to continuously perform the degreasing step, the nitriding step, and the firing step in the same furnace because the manufacturing cost of the silicon nitride sintered body is particularly reduced.

  Further, in order to make the ball valve body 2 spherical, after obtaining the above-mentioned manufacturing method while leaving a grinding and polishing margin on the outer diameter, grinding and polishing may be performed, and after grinding and polishing, There is no problem even if the above manufacturing method is performed. Preferably, after the above manufacturing method, it is preferable to perform grinding / polishing to add dimensional accuracy. This is because, when the ball valve is closed, the spherical surface is a surface that comes into contact with the fluid, but since it always comes into contact with the fluid, In addition, the temperature at which the fluid is in contact with the fluid remains the same even when it is open to closed.) Compared to the through-hole 7, it is less susceptible to rapid temperature changes, and the shape is not a structure that generates tensile strength. Therefore, it is not necessary to make the concentration of the metal silicide lower than the inside by the manufacturing method as in the present invention. In addition, the more the metal silicide, the easier it is to slide the valve seat during the operation of the ball valve body, and the movement becomes better. Therefore, it is preferable that the spherical portion is subjected to grinding and mirror finishing after performing the above manufacturing method. .

  In order to improve the mechanical characteristics by densifying the obtained silicon nitride-based sintered body, the maximum temperature in the firing step is preferably 1600 ° C. or higher. By firing at 1600 ° C. or higher, a dense ball valve body 2 having a relative density of 97% or higher can be produced, and mechanical characteristics can be improved. In order to suppress the decrease in mechanical strength by suppressing abnormal grain growth of silicon nitride crystals, the upper limit of the maximum firing temperature is preferably set to 1850 ° C.

  Next, in order for the first metal silicide 16 to be the adjacent phase 14 formed so as to surround the second metal silicide 18, the first metal element is made larger than the second metal element, and In the powder mixing step, the first metal element is added in a total amount of 0.2 to 10% by mass and the second metal element is added in a total amount of 0.1 to 3% by mass in the silicon nitride sintered body. The addition amount of the metal element compound and the second metal element compound is controlled.

  When the first and second metal elements are mixed as impurities during the manufacturing process, the contents of the first and second metal elements may be controlled by removing the impurities. Specifically, for example, when the metal Fe component is mixed in the raw material powder due to wear of the machine used in the powder mixing step, after the powder mixing step, a magnetic field is applied to the powder to adsorb the Fe component, By removing, the content of Fe finally contained in the valve member can be controlled.

  Further, by setting the average particle size of the powder composed of the first metal element compound to 1 to 20 μm and the average particle size of the powder composed of the second metal element compound to 0.1 to 5 μm, the surrounding first metal Since the content of silicide can be increased, the ball valve body 2 having further excellent mechanical characteristics can be manufactured.

More preferably, the average particle diameter of the silicon nitride crystals contained in the valve member is adjusted by setting the average particle size of the Si powder as a starting material to 2 to 50 μm and the specific surface area of the defatted body to ² to 30 m ² / g. The particle size is controlled to 15 μm or less. If the average particle size of the Si powder is less than 2 μm, a large amount of heat is generated due to the rapid nitridation reaction of the Si powder during the nitriding process, so that the temperature of the nitride rapidly increases, and large silicon nitride crystals are formed in the nitriding process As a result, the silicon nitride crystal grows abnormally in the baking process, so that the average grain size may exceed 15 μm. Further, when the average particle diameter of the Si powder exceeds 50 μm, large Si particles are nitrided in the nitriding process to generate large silicon nitride crystals, and the large silicon nitride crystals further grow abnormally in the firing process. The particle size may exceed 15 μm. By setting the specific surface area of the degreased body to ² to 30 m ² / g, it is possible to suppress a large amount of heat generation due to the rapid nitriding reaction of the Si powder in the nitriding step, and even when large silicon nitride crystals are generated in the nitriding step. Since the grain growth of the silicon nitride crystal is suppressed during firing, it becomes possible to control the average grain size of the major axis of the silicon nitride body crystal to 15 μm or less.

  In addition, by setting the average particle size of the powder made of the first metal element compound to 0.1 to 5 μm and the average particle size of the powder made of the second metal element compound to 1 to 30 μm, the surrounding second metal Since the content of silicide can be increased, the ball valve body 2 having further excellent thermal shock resistance can be manufactured.

  The average particle diameter of the particles constituting the compound of the first and second metal elements can be determined by measuring the particle diameter of each particle by, for example, SEM photographs and averaging these particle diameters.

  As mentioned above, although embodiment of this invention was described, this invention is not limited only to this embodiment, In the range which does not deviate from the summary of this invention, in addition to what was improved and changed, other valve members It can also be applied to.

First, as shown in Table 1, ball valve bodies were produced from silicon nitride sintered bodies having various grain boundary phases, and a thermal shock test was performed.

Metal compound powders (powder 1 and powder 2) shown in Table 1, high-purity silicon nitride (Si ₃ N ₄ ) powder (average particle size 1 μm, α conversion 90%) as raw material powder, high-purity Si powder (average A mixed powder was prepared by mixing a Y ₂ O ₃ powder having a particle diameter of ₃ μm, an average particle diameter of 1 μm, and an Al ₂ O ₃ powder having an average particle diameter of 0.7 μm. At this time, the powder 1 and the powder 2 which are metal compound powders are wet pulverized using water, the average particle size of the powder after the wet pulverization is set to 0.8 to 1 μm, and then dried to prepare a premixed powder. After the production, a sample that had undergone a premixing step for producing a premixed powder and a raw material powder was also produced. The obtained mixed powder, ethanol, and silicon nitride grinding media were put into a barrel mill and mixed. Thereafter, polyvinyl alcohol (PVA) was added and mixed as an organic binder to the obtained slurry, and granulated with a spray dryer. The obtained granulated powder was degreased by maintaining the compact in a nitrogen atmosphere at 600 ° C. for 3 hours so as to have a substantially spherical surface. In Table 1, the content of the metal compound powder is converted into a metal element, and the mass ratio of the Si powder is converted into Si ₃ N ₄ . Moreover, it was 10-15 m < ² > / g when the specific surface area of the degreased body was measured by the BET method.

The obtained degreased body was placed in a carbon mortar whose surface was covered with sintered silicon crystal particles of silicon nitride, and the nitrogen-containing partial pressure of 150 kPa consisting essentially of nitrogen was at 1050 ° C. for 20 hours. Nitriding is carried out by sequentially holding at 1250 ° C. for 10 hours, and further heating and holding for 3 hours at 1500 ° C. in a nitrogen partial pressure of 120 kPa, 10 hours at 1770 ° C., and 3 hours at 1800 ° C. in a nitrogen partial pressure of 200 kPa. Then, the temperature was lowered at 200 ° C./hour and fired to obtain a sintered body made of a β-type silicon nitride sintered body. The produced sintered body was surface-treated using an immersion process or an exposure process shown in Table 1 to obtain a ball valve body 2 (outer diameter φ80 mm) of the present invention. The dipping process was a method of dipping in a hydrochloric acid aqueous solution having a pH shown in Table 1 for a predetermined time, washing with water, and drying. In the exposure step, the sample was placed in a chamber, and the sample was exposed for a predetermined time while flowing a CF ₄ gas into the chamber, followed by washing with water and drying.

  The following evaluation was performed using the ball valve body sample which is the sample of the present invention produced as described above.

  First, the crystal phase of the grain boundary phase on the surface of the spherical surface in the sample was examined, and when the metal boundary was included in the grain boundary phase, this crystal structure was identified. That is, a sample was processed using an ion thinning device manufactured by Technology-Linda, a lattice image by electron beam diffraction of a grain boundary phase was observed using a transmission electron microscope JEM2010F manufactured by JEOL, and the lattice image was analyzed. When a plurality of metal silicides were contained in one sample, the crystal structure of the metal silicide contained most was identified.

  Moreover, the density | concentration of the metal silicide of the surface which mirror-polished the surface of the sample and the inside of the sample was measured as follows using the X-ray microanalyzer (JEOL Co., Ltd. JXA-8600M).

The intensity of fluorescent X-rays (characteristic X-rays) of metal elements (E _M ) such as Fe and Cu generated by irradiating the sample surface and the mirror-polished surface of the sample respectively with X-rays as follows: Measured. Fluorescent X-rays (characteristic X-rays) of each metal element (E _M ) were incident on a high-resolution proportional counter, amplified by an amplifier circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (Fe, Cu, etc.) to be measured were designated, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements was output. In order to make the measurement conditions the same, the area of the sample, the intensity of the irradiated X-ray, the time for counting the fluorescent X-rays, and the like were made the same.

The count number of the fluorescent X-rays of each metal element on the sample surface measured in this way is, for example, C _Fe1 and C _Cu1 for Fe and Cu, and the count number of fluorescent X-rays of each element of Fe and Cu inside the sintered body is C. _Fe2 and _CCu2 were used. The ratio of the concentration of the metal silicide inside and on the surface of the sintered body was calculated by C _Fe1 / C _Fe2 for Fe silicide and C _Cu1 / C _Cu2 for Cu silicide, for example. The ratio between the surface and the interior was similarly determined for other metal silicides. When the metal silicide contains a plurality of metal elements, the concentration of the metal silicide on the sintered body surface is lower than the inside of the sintered body when the concentration of at least one metal silicide is lower than the inside on the surface. did. Further, the concentration of the metal silicide is 1 / n (n is an arbitrary numerical value larger than 1) compared to the inside, for example, the smaller one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 Was 1 / n or less.

  Moreover, after putting the ball valve body of a sample into a thermostat and maintaining the temperature of 225 degreeC, it dropped in 25 degreeC water, gave the thermal shock, and confirmed the presence or absence of the crack or a crack.

The results are shown in Table 2.

The concentration ratio between the surface and the inside of the metal silicide in the grain boundary phase of the silicon nitride sintered body constituting the ball valve body is 0.7 or less, the average grain size is 23 μm or less, the bending strength is 750 MPa or more, and the fracture toughness The value was as high as 5.5 MPa · m ^1/2, and no cracks or cracks occurred. In particular, even when a sample containing either Fe silicide or Cu silicide was added, no cracks or cracks occurred.

In addition, the sample containing the adjacent phase had a particularly high bending strength of 840 MPa or more and a fracture toughness value of 6.5 MPa · m ^1/2 or more. Although not shown in the table, an amorphous phase containing RE, Al, and O was present in the grain boundary phase of all the samples of the present invention.

On the other hand, as a comparative example, when a metal compound composed of a metal element having a metal silicide with a lower surface concentration than the inside but having a melting point of less than 1000 ° C. is used, no metal silicide is present (sample No. 17 to 19, 20-22) had a bending strength of 650 MPa or less and a fracture toughness of 4.8 MPa · m ^1/2 or less.

(A)-(d) is a top view of the valve box which is a valve member of this invention, (e) is sectional drawing of (b). (F)-(i) is a top view of the valve box which is a valve member of this invention, (j) is sectional drawing of (g). (K) is a top view of the valve | bulb which consists of the valve box of (a)-(e) and the valve body of (f)-(j), (j), (m) is sectional drawing of (k). (A) is a perspective view which shows the ball valve body which concerns on this invention, (b) is sectional drawing which shows the cross section of the ball valve which concerns on this invention. It is the schematic which shows the outline of the assembly of the ball valve concerning this invention. It is a schematic diagram which shows the SEM observation photograph of the cross section of the silicon nitride sintered compact which comprises the ball valve body which concerns on this invention. It is a perspective view which shows the ball valve body which concerns on this invention. It is a perspective view which shows the conventional ball valve body. It is sectional drawing which shows the conventional ball valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 101 ... Ball valve 2, 102 ... Ball valve body 3 ... Silicon nitride type sintered body 4, 104 ... Stem 4a ... End part 5, 105 ... Groove 6, 106 ... ..Valve seat 7, 107... Through hole 7a, 107a... Surface 12: Silicon nitride crystal 14: Adjacent phase 16: First metal silicide 18: Second metal silicide 20: Grain boundary phase 21: Valve box 21a: Valve box body 21b: Sealing body 22: Slots 23a-23c: Hole 24: Valve body 24a: Valve body 24b: Groove 26: Valves 26a-26e: Surface

Claims (8)

A liquid valve member comprising a silicon nitride sintered body and having a groove or a hole constituting at least part of a liquid flow path, wherein the silicon nitride sintered body constituting the valve member is nitrided A first metal silicide comprising a crystalline phase mainly composed of silicon, a silicide of at least one first metal element of Fe, Cr, Mn, Co, Ni, Ti, Zr and Cu, and the first And a grain boundary phase containing a second metal silicide composed of a silicide of a second metal element having a melting point higher than that of the metal element, and the first metal silicide on the surface of the groove or hole, and A valve member characterized in that each concentration of the second metal silicide is lower than the inside of the silicon nitride sintered body. The said valve member is a spherical body provided with the through-hole in the center part, The valve member characterized by the above-mentioned. The valve member according to claim 1 or 2, wherein the first metal element is at least one of Fe and Cu. The valve member according to claim 3, wherein the first metal silicide is contained in an amount of 0.01 to 10% by mass in terms of total Fe and Cu. The valve member according to any one of claims 1 to 4, wherein the grain boundary phase contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table. The valve member according to any one of claims 1 to 5, wherein the second metal element is at least one of W and Mo. The method for producing a valve member according to any one of claims 1 to 6, wherein silicon nitride powder and a metal compound comprising at least one metal element (except Si) having a melting point of 1000 ° C or higher are mixed. Degreasing the organic binder in an atmosphere substantially consisting of nitrogen gas, argon gas, or a mixed gas thereof, and a step of obtaining a raw material powder; a step of obtaining a molded body comprising the raw material powder and an organic binder; To obtain a degreased body, a step of firing the degreased body in a non-oxidizing atmosphere containing nitrogen gas to obtain a sintered body, and whether the obtained sintered body is immersed in an aqueous solution having a pH of 3 or less. Or a step of polishing the outer surface after exposure to a gas comprising a halide, and a method for producing a valve member. A valve using the valve member according to any one of claims 1 to 6.

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