Patent Publication Number: US-2010130343-A1

Title: Ceramics sliding member for use in pure water

Description:
TECHNICAL FIELD 
     The present invention relates to a ceramics sliding member for use as a bearing, a mechanical seal, etc. of rotary machinery in ultrapure water having an electrical resistivity of 10 M•·cm or higher or pure water having an electrical resistivity of 1 M•·cm or higher. 
     BACKGROUND ART 
     Canned motor pumps, as an example of rotary machinery, generally include two radial slide bearings which support the respective opposite ends of a main shaft and two thrust slide bearings which bear thrust loads acting on the main shaft in opposite axial directions at loaded and non-loaded sides thereof. Ceramics bearings, which are of excellent wear resistance and corrosion resistance, are widely used in the art as such slide bearings. Slide bearings (ceramics bearings) are lubricated and a motor is cooled by a fluid which is handled by the motor pump and self-circulated in the motor pump. 
     Many rotary machines are of such a structure that fixed and rotatable parts have end surfaces or sliding surfaces which come into contact with each other in operation. Sliding members, such as slide bearings, seal members, etc., are used as parts in regions where rotors and stators are held in mechanically sliding relation to each other. For example, a slide bearing includes a rotatable member fixed to a main shaft and rotatable in unison with the main shaft, and a fixed member fixed to a casing, the rotatable member and the fixed member being configured to make sliding contact with each other. In general, one of the rotatable and fixed members of the ceramics bearing is made of silicon carbide (SiC), and the other of a carbon material (C), or both the rotatable and fixed members are made of SiC. SiC is in the form of α-SiC having a wurtzite crystal structure including a hexagonal crystal system. 
     Ceramic seal members made of α-SiC are also widely used as seal members to provide a watertight seal between a main shaft and a casing of rotary machinery. In other words, ceramics sliding members, such as ceramics bearings, ceramic seal members, etc., are widely used in rotary machines. 
     SiC may be manufactured by several methods. Among those methods is a sintering method, which is of utmost important, capable of manufacturing SiCs having various characteristics depending on starting materials and sintering conditions. The SiCs that are manufactured are put to practical use. These SiCs are materials which are generally of excellent wear resistance in addition to excellent thermal, chemical, and mechanical characteristics, and are widely used as sliding members such as bearings, mechanical seals, etc. 
     DISCLOSURE OF INVENTION 
     For example, some canned motor pumps handle tap water having an electrical resistivity of 0.01 M•·cm or higher as a handled fluid and employ ceramics bearings as slide bearings. In such canned motor pumps, the ceramics bearings can be in service for a long time while sliding surfaces of the ceramics bearings (slide bearings) are being effectively lubricated by tap water (handled fluid). Other canned motor pumps handle pure water having an electrical resistivity of 1 M•·cm or higher or ultrapure water having an electrical resistivity of 10 M•·cm or higher as a handled fluid, and employ ceramics bearings as slide bearings. In those other canned motor pumps, however, when sliding surfaces of the ceramics bearings are lubricated by pure water or ultrapure water (handled fluid), the sliding surfaces gradually develop sliding wear marks in the pure water or ultrapure water, leading to wear which is considered to be sliding damage to the sliding surfaces. 
     Table 1 shown below illustrates the results of a frictional wear test in which members of α-SiC were caused to slide against each other at a peripheral speed of 7.59 m/s while being pressed under a pressure of 0.5 MPa for 100 hours in the presence of handled fluids having different electrical resistivities (tap water, pure water, and ultrapure water). 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Electrical 
                 Results of 
                   
                   
               
               
                 resistivity 
                 frictional wear 
               
               
                 (M• · cm) 
                 test 
                 Remarks 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0.01 
                 ◯ 
                 No damage 
                 Tap water 
               
               
                 1 
                 Δ 
                 Slight damage 
                 Pure water 
               
               
                 2 
                 Δ 
                 Slight damage 
                 Pure water 
               
               
                 14 
                 X 
                 Damage 
                 Ultrapure water 
               
               
                 18 
                 X 
                 Damage 
                 Ultrapure water 
               
               
                   
               
            
           
         
       
     
     The cause of the results is not necessarily clear. However, when sliding surfaces of ceramic bearings are held in sliding contact with each other in the presence of tap water, it is considered that a silicon-based hydroxide or gel-like silicon-based hydrate is formed as a lubricating film on the sliding surfaces to protect the sliding surfaces. It is also considered that no such film is formed on sliding surfaces when the sliding surfaces of ceramic bearings are held in sliding contact with each other in the presence of pure water or ultrapure water which contains extremely low dissolved oxygen. 
     As described above, SiC (α-SiC) has excellent properties for use as a sliding material. If SiC (α-SiC) is used as the material of bearings of rotary machinery which handles pure water or ultrapure water, however, it often encounters damage trouble of unknown cause. The damage may occur not only to the sliding portions of SiC sliding members, but also to the fluid-contact portions of the sliding members. 
     Attention was paid to the erosion resistance of an SiC sintered body because of the damaged state thereof, and the following test was conducted. As a result of the test, it has been found that the erosion resistance differs depending on the properties of the SiC crystal system and the structure. It has also been revealed that the damage to SiC is not simple erosion, but erosive and corrosive damage. Specifically, when a fluid having a certain current speed is caused to impinge upon a specimen comprising an SiC sintered body, no damage is caused to the SiC if the fluid is tap water having an electrical resistivity of 0.01 M•·cm. On the other hand, damage is caused to the SiC if the fluid is ultrapure water having an electrical resistivity of 10 M•·cm. 
     The cause of the results is not necessarily clear. However, it is considered as one cause that when ultrapure water is caused to impinge upon the SiC sintered body at a certain current speed, the grain boundary of the SiC crystal is damaged, causing SiC particles to drop off. It is also considered that when the surface is significantly roughened by the drop-off of SiC particles, bearings and seal members of rotary machinery, which incorporate the SiC sintered body, tend to cause abnormally high torques. 
     The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide a ceramics sliding member for use in pure water which can be used stably over a long period of time while minimizing damage due to erosion or the like when used in pure water or ultrapure water. 
     The present invention provides a ceramics sliding member for use in ultrapure water or pure water, the ceramics sliding member being made of an SiC sintered body, wherein the SiC sintered body includes β-SiC at a ratio of 20% or more thereto and has an average crystal structure whose aspect ratio is 2 or greater. 
     It has been confirmed that an SiC ceramics sliding member, which includes β-SiC at a ratio of 20% or more thereto and has an average crystal structure whose aspect ratio is 2 or greater, can be used stably over a long period of time while minimizing damage due to erosion or the like when used in ultrapure water for a long time. This is considered to be due to the fact that an SiC sintered body containing β-SiC, which is of a zincblende structure and has a cubic crystal system, has an SiC crystal structure liable to become acicular, and since this tendency is stronger as the proportion of β-SiC in the SiC sintered body is greater, the acicular crystals are strongly intertwined with each other, exhibiting good frictional wear characteristics under strict sliding conditions, and that with respect to the erosion resistance, the acicular crystals are strongly intertwined with each other to minimize the drop-off of SiC particles, and as the aspect ratio (vertical-to-horizontal ratio) of the SiC crystal structure is greater, many crystals are strongly intertwined with each other to minimize the drop-off of SiC particles. 
     Preferably, the SiC sintered body has a maximum crystal particle diameter of 200 μm and an average crystal particle diameter of 20 μm or smaller. 
     It has been confirmed that a SiC ceramics sliding member whose maximum crystal particle diameter is 200 μm and average crystal particle diameter is 20 μm or smaller is almost not roughened on its surface and have a good surface state even when used in ultrapure water over a long period of time. This is considered to be due to the fact that as the crystal particle diameter is smaller, SiC particles are less liable to drop off the SiC sintered body, so that the SiC sintered body is damaged more uniformly and prevents the fluid from entering deeply thereinto, further reducing damage thereto and minimizing the surface roughening. 
     Preferably, the proportion of β-SiC in SiC of SiC material powder before being sintered is 90% or greater. 
     When SiC material powder in which the proportion of β-SiC in SiC is 90% or greater is sintered, an SiC sintered body in which the proportion of β-SiC in SiC is 20% or greater is easily manufactured. 
     According to the present invention, a ceramics sliding member can be used stably over a long period of time while minimizing damage due to erosion or the like of not only a sliding surface, but also a fluid-contacting surface, even when the ceramics sliding member is used in pure water or ultrapure water for a long time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a canned motor pump incorporating ceramics sliding members according to an embodiment of the present invention, which are applied to ceramic bearings; 
         FIG. 2  is a schematic view of an erosion test apparatus; and 
         FIG. 3  is a cross-sectional view showing a portion of a rotary machine for use in pure water which incorporates ceramics sliding members according to another embodiment of the present invention, which are applied to ceramic seal members. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described below with reference to the drawings. 
       FIG. 1  shows a canned motor pump incorporating ceramics sliding members according to an embodiment of the present invention, which are applied to ceramic bearings. As shown in  FIG. 1 , the canned motor pump comprises a suction casing  1 , a discharge casing  5 , and an outer tube  9  interconnecting the suction casing  1  and the discharge casing  5 . The suction casing  1 , the discharge casing  5 , and the outer tube  9  have ledges  1   a ,  9   a ,  9   b ,  5   a  extending outwardly from outer circumferential surfaces of open ends thereof. The suction casing  1  and the outer tube  9  are integrally connected to each other by cast flanges  20 ,  20  made of cast iron or the like which grip the adjacent ledges  1   a ,  9   a  and bolts  45  tightened to fasten the flanges  20 ,  20  to each other. Similarly, the discharge casing  5  and the outer tube  9  are integrally connected to each other by cast flanges  21 ,  21  made of cast iron or the like which grip the adjacent ledges  5   a ,  9   b  and bolts  45  tightened to fasten the flanges  21 ,  21  to each other. The suction casing  1 , the discharge casing  5 , and the outer tube  9  jointly make up a pump casing which houses a canned motor  22  therein. 
     The suction casing  1  comprises a substantially frustoconical main body  2  and a suction nozzle  3  extending from the main body  2  toward a suction side. Essentially as is the case with the suction casing  1 , the discharge casing comprises a frustoconical main body  6  and a discharge nozzle  7  extending from the main body  6  toward a discharge side. 
     The suction casing  1  houses therein an inner casing  10  comprising a vessel-like main body  11  and a hollow cylindrical suction side member  12  extending from the main body  11  toward the suction side. A seal member  18  comprising an elastic member, such as an O-ring or the like, is interposed between the main body  11  and the suction side member  12 . A guide device  13 , which provides guide vanes or volute, is disposed in the main body  11  of the inner casing  10 . The guide device  13  has a faucet joint portion which is fitted in a motor frame  23  of the canned motor  22 . The motor frame  23  of the canned motor  22  is of high rigidity. Since the guide device  13  is supported by the motor frame  23 , the inner casing  10  is supported by the motor frame  23  of the canned motor  22  which is of high rigidity. 
     The suction side member  12  of the inner casing  10  has an end extending to a position near the suction nozzle  3 . A seal member  14  is disposed in a gap between the end of the suction side member  12  of the inner casing  10  and the suction nozzle  3  of the suction casing  1 . The seal member  14  provides a seal between the suction side (low-pressure side) and the discharge side (high-pressure side). 
     Impeller  15  is housed in the inner casing  10  and fixed to and supported on a main shaft  16  of the canned motor  22 . A suction flange  48  and a discharge flange  49  are fixed respectively to the suction nozzle  3  and the discharge nozzle  7  with intermediate rings  46 ,  46  interposed respectively therebetween. 
     The motor frame  23  of the canned motor  22  comprises a substantially cylindrical frame outer barrel  24  and frame side plates  25 ,  26  disposed respectively in opposite openings of the frame outer barrel  24 . The frame outer barrel  24  has a plurality of axially extending radial ribs  24   a  on an outer circumferential surface thereof. The ribs  24   a  are integrally formed on the frame outer barrel  24  by pressing. The ribs  24   a  have respective outer side surfaces fitted against the inner circumferential surface of the outer tube  9  of the pump casing. The ribs  24  and the outer tube  9  are integrally joined to each other by spot welding or the like where they are fitted with each other. 
     A stator  27  and a rotor  28  are disposed in the motor frame  23 . The rotor  28  is supported by the main shaft  16 , and a cylindrical can  29  is fitted in the stator  27 . Between the frame side plate  25  and the main shaft  16 , there is disposed a ceramics bearing (ceramics sliding member)  30  as a radial slide bearing. 
     The ceramics bearing (ceramics sliding member)  30  comprises an inner ring  51  serving as a rotatable member which is fixed to the main shaft  16  for rotation in unison with the main shaft  16 , and an outer ring  52  serving as a fixed member which is fixed to the frame side plate  25 . Both the inner ring (rotatable member)  51  and the outer ring (fixed member)  52  of the ceramics bearing  30  comprise an SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater. 
     In this example, both the inner ring  51  and the outer ring  52  comprise an SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater. However, only one of the inner ring  51  and the outer ring  52  may comprise an SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater. 
     Using an erosion test apparatus shown in  FIG. 2 , an erosion test was conducted on specimens comprising various SiC sintered bodies having different crystal systems and crystal structures. The results of the erosion test are shown in Table 2. The erosion test apparatus shown in  FIG. 2  is configured such that an ejection nozzle  106  ejects water (ultrapure water or tap water) delivered from a water pump  104  toward a surface of a specimen  102  that is vertically held by a holder  100 . The water ejected from the ejection nozzle  106  had a current speed of 28 m/s and a temperature of 30° C. The erosion test was conducted for a test time of 100 h. The distance from the ejection nozzle  106  to the test piece  102  was 25 mm. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                   
                   
                   
                 Crystal particle 
                 Eroded 
                   
               
               
                   
                 Material 
                 β-SiC 
                 Aspect 
                 diameter (μm) 
                 quantity 
                 Surface state 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Water type 
                 powder 
                 ratio (%) 
                 ratio 
                 Average 
                 Maximum 
                 (mm 3 ) 
                 after test 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Ultra- 
                 β-SiC 
                 20 
                 2-4 
                 5 
                 10 
                 ◯ 
                 Δ 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.006 
                 Slightly 
               
               
                 water 
                   
                   
                   
                   
                   
                   
                 roughened 
               
               
                 Ultra- 
                 β-SiC 
                 60 
                  6-30 
                 20 
                 200 
                 ◯ 
                 ◯ 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.010 
                 Almost not 
               
               
                 water 
                   
                   
                   
                   
                   
                   
                 roughened 
               
               
                 Ultra- 
                 β-SiC 
                 5 
                  2-15 
                 20 
                 200 
                 Δ 
                 X 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.017 
                 Roughened 
               
               
                 water 
               
               
                 Ultra- 
                 β-SiC 
                 100 
                   1-1.5 
                 3 
                 15 
                 Δ 
                 ◯ 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.018 
                 Almost not 
               
               
                 water 
                   
                   
                   
                   
                   
                   
                 roughened 
               
               
                 Ultra- 
                 β-SiC 
                 0 
                  4-30 
                 100 
                 500 
                 X 
                 X 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.037 
                 Highly 
               
               
                 water 
                   
                   
                   
                   
                   
                   
                 roughened 
               
               
                 Ultra- 
                 α-SiC 
                 0 
                 1-2 
                 10 
                 15 
                 X 
                 X 
               
               
                 pure 
                   
                   
                   
                   
                   
                 0.040 
                 Highly 
               
               
                 water 
                   
                   
                   
                   
                   
                   
                 roughened 
               
               
                 Tap 
                 α-SiC 
                 0 
                 1-2 
                 10 
                 15 
                 ◯ 
                 ◯ 
               
               
                 water 
                   
                   
                   
                   
                   
                 0    
                 No 
               
               
                   
                   
                   
                   
                   
                   
                   
                 abnormality 
               
               
                   
               
            
           
         
       
     
     In Table 2, the aspect ratio and the crystal particle diameter represent values obtained when arbitrary portions of structure photographs (about 70 mm×about 90 mm) were taken at magnifications ×100 and ×500, and measured. The crystal particle diameter represents numerical values indicating longer ones of vertical and horizontal particle diameters. The β-SiC ratio represents the ratio of β-SiC in the SiC sintered bodies after they are sintered. 
     It can be seen from Table 2 that those specimens (SiC sintered bodies), which include β-SiC at a ratio of 20% or more in the SiC sintered body and have an average crystal structure whose aspect ratio is 2 or greater, have an eroded quantity of 0.010 (mm 3 ) or smaller, and can be used stably over a long period of time while minimizing damage due to erosion or the like when used in ultrapure water for a long time. This is considered to be due to the fact that an SiC sintered body containing β-SiC, which is of a zincblende structure and has a cubic crystal system, has an SiC crystal structure liable to become acicular, and since this tendency is stronger as the proportion of β-SiC in the SiC sintered body is greater, the acicular crystals are strongly intertwined with each other, exhibiting good frictional wear characteristics under strict sliding conditions, and that with respect to the erosion resistance, the acicular crystals are strongly intertwined with each other to minimize the drop-off of SiC particles, and as the aspect ratio (vertical-to-horizontal ratio) of the SiC crystal structure is greater, many crystals are strongly intertwined with each other to minimize the drop-off of SiC particles. 
     It can also be seen that those specimens (SiC sintered bodies) whose maximum crystal particle diameter is 200 μm and average crystal particle diameter is 20 μm or smaller are almost not roughened on their surfaces and have a good surface state after the test. This is considered to be due to the fact that as the crystal particle diameter is smaller, SiC particles are less liable to drop off the SiC sintered body, so that the SiC sintered body is damaged more uniformly and prevents the fluid from entering deeply thereinto, further reducing damage thereto and minimizing the surface roughening. Consequently, it is preferable that the inner ring  51  and the outer ring  52  be made of an SiC sintered body whose maximum crystal particle diameter is 200 μm and average crystal particle diameter is 20 μm or smaller. 
     Even if the starting material of an SiC sintered body consists of β-SiC material powder, the SiC sintered body contains not only β-SiC, but also α-SiC. It is known that the proportion of β-SiC varies depending on sintering conditions or the like. If an SiC sintered body contains a crystal structure of β-SiC in part, then it contains another structure of α-SiC. If the proportion of β-SiC in SiC of SiC material powder before being sintered is 90% or greater, then it is easy to manufacture an SiC sintered body in which the proportion of β-SiC in SiC is 20% or greater. 
     A bearing housing  32  is detachably mounted on the frame side plate  26  with an elastic body  44  interposed therebetween. The bearing housing  32  holds an outer ring  33  and a fixed ring  34 , respectively. The outer ring  33  is configured to slide against an inner ring  35  fixedly mounted on the main shaft  16 . The outer ring  33  and the inner ring  35  jointly make up a ceramics bearing (radial slide bearing) which is similar in structure to the above-described ceramics bearing (ceramics sliding member)  30 . 
     A thrust disc  36  is fixed to the end of the main shaft  16  near the discharge side. The thrust disc  36  has a rotatable ring  37  disposed in confronting relation to and slidable against the fixed ring  34 . The fixed ring (fixed member)  34  and the rotatable ring (rotatable member)  37  jointly make up a ceramics bearing (ceramics sliding member)  39  as a thrust slide bearing. As is the case with the inner ring  51  and the outer ring  52  of the ceramics bearing  30 , the fixed ring  34  and the rotatable ring  37  of the ceramics bearing (thrust slide member)  39  are made of a SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater, or preferably a SiC sintered body whose maximum crystal particle diameter is 200 μm and average crystal particle diameter is 20 μm or smaller. Alternatively, one of the fixed ring  34  and the rotatable ring  37  may be made of a SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater. 
     An end plate  40 , which serves as a filter, is fixed to the frame side plate  26 . The end plate  40  has a rectifier  41  projecting in a substantially semispherical shape and having a plurality of slits  42  defined therein which extend radially outwardly. The rectifier  41  of the end plate  40  is of a substantially semispherical shape extending along the streamlines of flows in the discharge casing  5 . The fluid, which is discharged from the impeller  15 , passes through a passage  50  defined between the outer tube  9  and the frame outer barrel  24  and flows into the discharge casing  5 . Thereafter, the fluid is rectified by the rectifier  41  and guided into the discharge port. 
     The radial slits  42  that are defined in the rectifier  41  function as a filter which traps and removes foreign matter in the fluid when the fluid flows through the slits  42  into the canned motor  22 . Since the slits  42  are defined along the directions of the flows, the foreign matter trapped by the slits  42  is moved in the directions of the flows because of the current speed of the fluid, and then removed from the slits  42 , which are thus prevented from becoming clogged. In other words, the slits  42  are shaped to have a self-cleaning action. The end plate  40  also serves as a presser plate for secure the bearing housing  32  to the frame side plate  26 . 
     Operation of the canned motor pump will be described below. The fluid drawn in from the suction nozzle  3  passes through the suction side member  12  of the inner casing  10  and flows into the impeller  15 . The fluid is discharged from the impeller  15  as they rotate, and flows through the guide device  13  which changes the direction of the fluid from the centrifugal direction to the axial direction. Thereafter, the fluid flows into the passage  50  defined between the outer tube  9  and the frame outer barrel  24  of the canned motor  22 , and then flows through the passage  50  into the discharge casing  5 . Subsequently, the fluid is rectified by the rectifier  41  of the end plate  40 , and then discharged from the discharge nozzle  7  that is integral with the discharge casing  5 . 
     A gap is defined between a main plate  15   a  of the impeller  15  and the frame side plate  25 . When the impeller  15  rotates, disc friction occurs in the gap, developing a pressure reducing effect in the gap. Therefore, a circulatory path is formed for the fluid which flows through the slits  42  in the end plate  40  into the canned motor  22  to pass through openings  32   a  in the bearing housing  32  and then through the gap between the rotor  28  and the can  29  of the stator  27  and from openings  25   a  in the frame side plate  25  to the rear side of the main plate  15   a  of the impeller  15 , as indicated by arrows. While the handled fluid is circulating in the canned motor  22 , the handled fluid lubricates the sliding surfaces of the ceramics bearings  30 ,  38 ,  39 , and simultaneously cools the canned motor  22 . 
     Even if the handled fluid comprises pure water having an electrical resistivity of 1 M•·cm or higher or ultrapure water having an electrical resistivity of 10 M•·cm or higher, any wear caused to the slide surfaces and fluid-contacting surfaces of the ceramics bearings  30 ,  38 ,  39  is suppressed to a minimum, making it possible for the ceramics bearings  30 ,  38 ,  39  to be used stably over a long period of time. 
     In the above embodiment, the ceramic sliding members are incorporated in the canned motor pump, which includes the ceramics bearings, as the ceramics bearings. However, the ceramic sliding members may be incorporated in rotary machines, which includes ceramic seal members of SiC, as ceramics seal members. 
       FIG. 3  shows a portion of a rotary machine for use in pure water which incorporates ceramics sliding members according to another embodiment of the present invention, which are applied to ceramic seal members. In this embodiment, a sleeve  62  is mounted on a rotatable shaft  60 , and the periphery of the sleeve  62  is sealed by a mechanical seal  68  comprising a movable seal member  64  and a stationary seal member  66  which have respective end faces configured to make sliding contact with each other. In this embodiment, both the movable seal member  64  and the stationary seal member  66  are made of a SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater, or preferably a SiC sintered body whose maximum crystal particle diameter is 200 μm and average crystal particle diameter is 20 μm or smaller. Alternatively, only one of the movable seal member  64  and the stationary seal member  66  may be made of a SiC sintered body including β-SiC at a ratio of 20% or more to SiC and having an average crystal structure whose aspect ratio is 2 or greater, and the other of SiC or another ceramics. 
     According to this embodiment, even if the handled fluid comprises pure water having an electrical resistivity of 1 M•·cm or higher or ultrapure water having an electrical resistivity of 10 M•·cm or higher, any wear caused to the slide surfaces and fluid-contacting surfaces of the movable seal member  64  and the stationary seal member  66  of the mechanical seal  68  is suppressed to a minimum, making it possible for the mechanical seal  68  to be used stably over a long period of time. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a ceramics sliding member for use as a bearing, a mechanical seal, etc. of rotary machinery in ultrapure water having an electrical resistivity of 10 M•·cm or higher or pure water having an electrical resistivity of 1 M•·cm or higher.