Patent Publication Number: US-2017349497-A1

Title: Porous ceramic structure and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-111136 filed on Jun. 2, 2016, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a porous ceramic structure, and more particularly relates to a porous ceramic structure suitable for achieving a reduction in thermal conductivity of a component containing the porous ceramic structure, as well as to a method of manufacturing such a porous ceramic structure. 
     Description of the Related Art 
     As a filler that is filled in a heat insulating material or a film, compositions and hollow particles and the like have been described in Japanese Laid-Open Patent Publication No. 2010-155946, Japanese Laid-Open Patent Publication No. 2004-010903, and Japanese Laid-Open Patent Publication No. 2010-064945. 
     Japanese Laid-Open Patent Publication No. 2010-155946 describes a curable organopolysiloxane composition, which is capable of forming a porous organopolysiloxane cured product having low thermal conductivity. 
     Japanese Laid-Open Patent Publication No. 2004-010903 describes the formation of a film having low thermal conductivity, by using a coating material in which hollow particles with low thermal conductivity are used. 
     Japanese Laid-Open Patent Publication No. 2010-064945 discloses a method in which additive particles are adsorbed on surfaces of base particles by an electrostatic interaction, thereby producing nanocoated composite particles, and further manufacturing a composite material through an ordinary powder metallurgy process by use of the composite particles. 
     SUMMARY OF THE INVENTION 
     With the technology described in Japanese Laid-Open Patent Publication No. 2010-155946 and Japanese Laid-Open Patent Publication No. 2004-010903, the reduction in thermal conductivity is insufficient. With the technology described in Japanese Laid-Open Patent Publication No. 2010-064945, since it is intended to manufacture a composite material by powder metallurgy, it is kept in mind that fine particles with a particle diameter on the order of nanometers (nm) are coated on the base particles. Therefore, the distance between the base particles becomes short, and in this case as well, the reduction in thermal conductivity is insufficient. 
     If the particles added to the adhesive are small, it is difficult to uniformly disperse the particles in the adhesive. Further, since it is necessary to fire an adhesive to which particles have been added in advance to form a bulk body, and thereafter place the adhesive on the object, for example, it becomes difficult to place the adhesive in a partial area of the object, and it is difficult to place the adhesive along a complex shape. 
     The present invention has been made in consideration of the aforementioned problems, and has the object of providing a porous ceramic structure as well as a method of manufacturing the porous ceramic structure, in which it is possible to achieve low thermal conductivity, together with installing the porous ceramic structure directly on an object using an adhesive or the like, and further, it is possible to facilitate installation of a bulk body. 
     [1] A porous ceramic structure according to a first present invention includes one sheet, and a porous ceramic aggregate bonded on the sheet, wherein the porous ceramic aggregate includes a plurality of porous ceramic particles. 
     [2] In the first present invention, the porous ceramic aggregate preferably is a member disposed on an object, and a planar shape of the porous ceramic aggregate as viewed from an upper surface thereof preferably is the same as a planar shape, as viewed from an upper surface thereof, of a region within the object where the porous ceramic aggregate is intended to be placed. 
     [3] In the first present invention, from among the plurality of porous ceramic particles included within the porous ceramic aggregate, there may exist at least one porous ceramic particle for which a planar shape as viewed from an upper surface thereof is a polygonal shape surrounded by a plurality of straight lines. 
     [4] In this case, from among the plurality of porous ceramic particles included within the porous ceramic aggregate, preferably a percentage of the porous ceramic particles including a curve in the planar shape as viewed from the upper surface thereof is less than or equal to 50%. 
     [5] Further, the porous ceramic aggregate may include a portion in which five or more porous ceramic particles are arranged with one apex each facing toward each other. 
     [6] In the first present invention, a gap between adjacent ones of the porous ceramic particles may be greater than or equal to 0.1 μm and less than or equal to 10 μm. 
     [7] In the first present invention, side surfaces of adjacent ones of the porous ceramic particles preferably face each other in parallel, and include a portion where an angle of inclination of a side surface of one of the adjacent porous ceramic particles is less than or equal to 45 degrees with respect to a normal line that is normal to the sheet. 
     [8] In the first present invention, preferably, number densities of the porous ceramic particles within the porous ceramic aggregate are different, and a ratio of a maximum value and a minimum value of the number densities defined by maximum number density/minimum number density is greater than 1.2. 
     [9] In the first present invention, preferably, sizes of planar shapes of the plurality of porous ceramic particles are different, and a ratio of a maximum value and a minimum value of the sizes of the planar shapes defined by the maximum value/the minimum value is greater than 1.2. 
     [10] In the first present invention, preferably, a thickness of the plurality of porous ceramic particles included within the porous ceramic aggregate is less than or equal to 1000 μm, and a variation in the thickness is less than or equal to 10%. 
     [11] In the first present invention, a porosity of the porous ceramic particles preferably is 20%˜99%. 
     [12] In the first present invention, the porous ceramic particles preferably have an average pore diameter of less than or equal to 500 nm. 
     [13] In the first present invention, a thermal conductivity of the porous ceramic particles preferably is less than 1.5 W/mK. 
     [14] In the first present invention, a heat capacity of the porous ceramic particles preferably is less than or equal to 1000 kJ/m 3 K. 
     [15] A method of manufacturing a porous ceramic structure according to a second present invention, the porous ceramic structure including one sheet, and a porous ceramic aggregate bonded on the sheet, wherein the porous ceramic aggregate includes a plurality of porous ceramic particles, the method including a green body manufacturing step of manufacturing a green body, a firing step of firing the green body to thereby manufacture a sintered body, a bonding step of bonding the sintered body to the sheet, and a dividing step of dividing the sintered body into a plurality of porous ceramic particles. 
     [16] In the second present invention, there may further be included a step of forming a plurality of cuts in the green body before firing the green body. 
     [17] In the second present invention, in the green body manufacturing step, the green body preferably is manufactured by applying a slurry on a film having a mirror surface, and tape-casting the slurry. 
     Owing to the porous ceramic structure according to the present invention, it is possible to achieve a low thermal conductivity, together with installing the porous ceramic structure directly on an object using an adhesive or the like, and further, it is possible to facilitate installation of a bulk body. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which preferred embodiments of the present invention are shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a porous ceramic structure according to an embodiment of the present invention; 
         FIG. 2A  is a plan view showing an example in which a porous ceramic aggregate is constituted by one type of planar shape; 
         FIG. 2B  is a plan view showing an example in which a porous ceramic aggregate is constituted by two types of planar shapes; 
         FIG. 2C  is a plan view showing an example in which a porous ceramic aggregate is constituted by three types of planar shapes; 
         FIG. 3A  is a plan view showing an example in which a curve is included in the planar shapes of two porous ceramic particles, respectively; 
         FIG. 3B  is a plan view showing an example in which curves are included in the planar shapes of six porous ceramic particles, respectively; 
         FIG. 4A  is a cross-sectional view showing a case in which a gap formed between porous ceramic particles is narrow; 
         FIG. 4B  is a cross-sectional view showing a case in which a gap formed between porous ceramic particles is wide; 
         FIG. 4C  is a cross-sectional view showing a case in which a gap formed between porous ceramic particles is a mixture of a narrow gap and a wide gap; 
         FIG. 5A  is a cross-sectional view showing a case in which an angle of inclination of a side surface of the porous ceramic particles is less than or equal to 45 degrees; 
         FIG. 5B  is an explanatory diagram showing a problem point for a case in which an angle of inclination of a side surface of the porous ceramic particles is greater than 45 degrees; 
         FIG. 5C  is an explanatory diagram illustrating a definition of the angle of inclination for a case in which side surfaces of the porous ceramic particle are bent; 
         FIG. 6  is a process diagram showing a first method of manufacturing the porous ceramic structure according to an embodiment of the present invention; 
         FIG. 7  is a schematic diagram showing an example of a doctor blade device; 
         FIG. 8  is a process diagram showing a second method of manufacturing the porous ceramic structure according to an embodiment of the present invention; 
         FIG. 9A  is a process diagram showing a state in which the porous ceramic structure is placed on an object; 
         FIG. 9B  is a process diagram showing a state in which a sheet is peeled off from the porous ceramic structure; 
         FIG. 9C  is a process diagram showing a state in which a resin material is coated on the porous ceramic aggregate disposed on the object; 
         FIG. 10  is a cross-sectional view with partial omission showing a bulk body together with the object; 
         FIG. 11A  is an explanatory diagram with partial omission showing a state in which a plurality of particles are dispersed in a slurry according to a conventional example; and 
         FIG. 11B  is an explanatory diagram with partial omission showing a state in which the slurry is dried, fired, and solidified into a bulk body. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An Example of a porous ceramic structure according to the present invention will be described below with reference to  FIGS. 1 to 11B . In the present specification, the tilde symbol “˜” which indicates a numerical range is used with the implication that the numerical values written before and after the tilde symbol are included therein as a lower limit value and an upper limit value of the numerical range. 
     As shown in  FIG. 1 , for example, the porous ceramic structure  10  according to the present embodiment includes one sheet  12 , and a porous ceramic aggregate  14  bonded on the sheet  12 . The porous ceramic aggregate  14  includes a plurality of porous ceramic particles  16 . In this instance, the term “bonded” implies that a member is fixed in a peelable state, and refers to a state in which the fixed state is released due to changes that occur over time or by the addition of external factors, whereby a bonded object is separated. Accordingly, a state in which the object is fixed by an adhesive force, and also a state in which the object is firmly fixed temporarily at a bonding interface are included. The sheet  12  and the porous ceramic aggregate  14  may be bonded together using a specialized material such as an adhesive or the like between the sheet  12  and the porous ceramic aggregate  14 . 
     The term “porous” may refer to a state that is neither dense nor hollow, as well as a state composed of a plurality of pores or grains. Moreover, the term “dense” refers to a state in which a plurality of fine grains are bonded without gaps, having no pores. The term “hollow” refers to a state in which the interior is hollow, and in which an outer shell portion thereof is dense. 
     The porous ceramic particles  16  preferably have an aspect ratio greater than or equal to 3. More preferably, the aspect ratio is greater than or equal to 5, and even more preferably, is greater than or equal to 7. In this case, the aspect ratio is defined by the maximum length La divided by the minimum length Lb, or La/Lb. In this instance, the maximum length La refers to a maximum length on a widest surface (in this case, a single main surface  16   a ) from among the plurality of surfaces constituting the porous ceramic particles  16 . Assuming that the widest surface is a square, a rectangle, a trapezoid, a parallelogram, or a polygon (pentagon, hexagon, etc.), the maximum length La corresponds to the length of a longest diagonal line, whereas if the widest surface is circular, the maximum length La corresponds to the length of a diameter, and if the widest surface is an ellipse, the maximum length La corresponds to the length of a major axis of the ellipse. On the other hand, as shown in  FIG. 1 , the minimum length Lb refers to the thickness to of the porous ceramic particles  16 . 
     The minimum length Lb preferably is 50˜500 μm, more preferably, is 55˜400 μm, even more preferably is 60˜300 μm, and particularly preferably, is 70˜200 μm. 
     Concerning the sheet  12 , for example, a resin-made sheet or a film having an adhesive strength can be used, and a sheet or film is preferable that becomes peelable due to temporal change or due to external factors such as heat, electricity, or external forces or the like. 
     The porous ceramic aggregate  14  is placed as a bulk body  20  on an object  22 , by being coated with a resin material  18  (matrix) such as an adhesive, as will be described later (see  FIGS. 9C and 10 ). 
     In this case, rather than placing individual porous ceramic particles  16  on the object  22 , it is easier to collectively transfer a plurality of the porous ceramic particles  16  together onto the object  22 , which also makes it easy to control the gaps between the porous ceramic particles  16 . 
     A planar shape of the porous ceramic aggregate  14  as viewed from the upper surface is preferably the same as the planar shape as viewed from the upper surface of a region of the object  22  where the porous ceramic aggregate  14  is intended to be placed (hereinafter referred to as an installation area of the object  22 ). In this instance, the installation area of the object  22  is a concept that includes a portion of the object  22 . The term “same” as used above includes a case of being entirely the same, or a case of being similar to the planar shape of the installation area of the object  22 . In this instance, the similar relationship implies a shape obtained by enlarging the planar shape of the installation region of the object  22  by 1.1˜2.0 times, or a shape obtained by reducing such a planar shape by 1.1˜2.0 times. In accordance with this feature, a plurality of porous ceramic particles  16  can be transferred onto objects  22  of various shapes without causing a loss of material (a loss of the porous ceramic particles  16 ). 
     Further, among the plurality of porous ceramic particles  16  included within the porous ceramic aggregate  14 , there may exist at least one porous ceramic particle  16  for which the planar shape as viewed from the upper surface thereof is a polygonal planar shape surrounded by a plurality of straight lines  24  (see  FIGS. 2A to 3B ). Naturally, the planar shapes of all of the porous ceramic particles  16  may be in the form of polygonal shapes surrounded by a plurality of straight lines  24 . 
     For example, as shown in  FIG. 2A , one type of planar shape may be used, or as shown in  FIG. 2B , two types of planar shapes may be used. Further, as shown in  FIG. 2C , three types of planar shapes may be used. 
     In the example of  FIG. 2A , a case is shown in which the planar shapes of all of the porous ceramic particles  16  are quadrilateral shapes. In the example of  FIG. 2B , a case is shown in which the porous ceramic aggregate  14  is constituted by a combination of quadrilateral shapes and triangular shapes, and an example is shown in which six triangular shapes are arranged on an inner side and six quadrilateral shapes are arranged on an outer side. In  FIG. 2C , a case is shown in which the porous ceramic aggregate  14  is constituted by a combination of triangular shapes, quadrilateral shapes, and a pentagonal shape, and an example is shown in which one pentagonal shape, two triangular shapes, and five quadrilateral shapes are arranged thereon. 
     Further, as shown in  FIGS. 3A and 3B , among the plurality of porous ceramic particles  16  included within the porous ceramic aggregate  14 , a percentage of the porous ceramic particles  16  including a curve  26  in the planar shapes thereof as viewed from the upper surface may be greater than 0% and less than or equal to 50%. 
     If the planar shapes are solely linear, the porous ceramic particles  16  tend to be easily shifted upon transferring the plurality of porous ceramic particles  16  onto the object  22 . However, as a result of the curves  26  existing partially within the porous ceramic aggregate  14 , it is unlikely for such shifting to occur, and it also becomes possible to uniformly transfer the plurality of porous ceramic particles  16  onto the object  22 . 
     In the case of determining the percentage of the porous ceramic particles  16  including a curve  26  in the planar shape thereof as viewed from the upper surface, such a percentage may be determined by counting the total number Nz of porous ceramic particles  16  on the sheet  12 , and the total number Nw of porous ceramic particles  16  including a curve  26  in the planar shape thereof, and then performing the calculation (Number Nw/Number Nz)×100 (%). 
     In  FIG. 3A , the planar shapes of seven of the porous ceramic particles  16  (the porous ceramic particles  16  indicated by ( 1 ) to ( 7 ) in  FIG. 3A ) out of nine of such porous ceramic particles  16  are of a quadrilateral shape, whereas the planar shapes of the remaining two porous ceramic particles  16  (the porous ceramic particles  16  indicated by ( 8 ) and ( 9 ) in  FIG. 3A ) have curves  26  therein, respectively. In  FIG. 3B , the planar shapes of eighteen of the porous ceramic particles  16  (the porous ceramic particles  16  indicated by ( 3 ) to ( 14 ), ( 16 ) to ( 18 ), and ( 20 ) to ( 22 ) in  FIG. 3B ) out of twenty-four of such porous ceramic particles  16  are of a quadrilateral shape, whereas the planar shapes of the remaining six porous ceramic particles  16  (the porous ceramic particles  16  indicated by ( 1 ), ( 2 ), ( 15 ), ( 19 ), ( 23 ) and ( 24 ) in  FIG. 3B ) have curves  26  therein, respectively. 
     In addition, as shown in  FIG. 2B , the porous ceramic aggregate  14  may include a portion  27  in which five or more porous ceramic particles  16  are arranged with one apex each facing toward each other. Owing thereto, the plurality of porous ceramic particles  16  are easily arranged along a surface shape of the object  22 , even if curved surfaces or irregularities are formed locally on the surface of the object  22 . 
     It is preferable for the gap d (see  FIGS. 4A to 4C ) formed between adjacent ones of the porous ceramic particles 16 to be greater than or equal to 0.1 μm and less than or equal to 10 μm. In accordance therewith, it is easy to transfer the plurality of porous ceramic particles  16  onto the object  22 , and moreover, it becomes possible to uniformly transfer the plurality of porous ceramic particles  16  onto the object  22 . In this instance, the gap d refers to a narrowest gap from among the gaps between adjacent ones of the porous ceramic particles  16 . More specifically, with the gap d shown in  FIG. 4A  and the gap d shown in  FIG. 4B , the gap d shown in  FIG. 4A  is narrow and the gap d shown in  FIG. 4B  is wide. On the other hand, in the case where a wide gap db and a narrow gap da are mixed, as with the gaps d shown in  FIG. 4C , the narrow gap da is defined as the gap d between the porous ceramic particles  16 . Such a gap d is obtained by measuring with an optical microscope the space between adjacent ones of the porous ceramic particles  16  in the porous ceramic aggregate  14  that is bonded on the sheet  12 . 
     Furthermore, as shown in  FIG. 5A , among the adjacent porous ceramic particles  16 , the angle of inclination θ of the side surface of one of the porous ceramic particles  16  is preferably less than or equal to 45 degrees with respect to a normal line  28  that is normal to the sheet  12 , i.e., greater than or equal to 0 degrees and less than or equal to 45 degrees, and more preferably, is greater than 0 degrees and less than or equal to 45 degrees. In the case that the side surfaces of adjacent porous ceramic particles  16  lie parallel to each other, and if the angle of inclination θ is greater than 45 degrees, as shown in  FIG. 5B , cases may occur in which the peripheries of the porous ceramic particles  16  become chipped and fragments  17  are scattered. More specifically, by setting the inclination angle θ to be greater than or equal to 0 degrees and less than or equal to 45 degrees, when transferring a plurality of the porous ceramic particles  16  onto the object  22 , or when handling the porous ceramic structure  10 , the porous ceramic particles  16  are unlikely to become cracked or chipped, and defects are few upon formation of the bulk body  20 . Moreover, the aforementioned angle of inclination θ may also include the meaning of a vertical plane. The angle of inclination θ is obtained by measuring with an optical microscope the angle of inclination θ between adjacent ones of the porous ceramic particles  16  in the porous ceramic aggregate  14  that is bonded on the sheet  12 . 
     Moreover, the gap formed between adjacent porous ceramic particles  16  is not necessarily a linear gap. For example, as shown in  FIG. 5C , cases may also occur in which a portion of the gap is bent (bent in a convex shape or bent in a concave shape). In such a case, when viewed in a vertical cross section of the porous ceramic particle  16 , the angle of inclination θ is defined by the angle formed between a straight line Lx connecting the upper end and the lower end of the side surface of the porous ceramic particle  16 , and the normal line  28  that is normal to the sheet  12 . 
     Further, the number densities of the porous ceramic particles  16  preferably differ by location in the porous ceramic aggregate  14 . Further, the sizes of respective planar shapes of the plurality of porous ceramic particles  16  preferably are different. 
     For example, at a portion where the surface of the object  22  is flat, the number density is small (the size of the porous ceramic particles  16  is large), and at a portion where the surface of the object  22  is a curved surface and within the surrounding vicinity thereof, the number density is large (the size of the porous ceramic particles  16  is small). Hence, when the plurality of porous ceramic particles  16  is transferred onto the object  22 , it is possible to arrange the plurality of porous ceramic particles  16  in following relation to the surface of the object  22 . 
     The ratio of the maximum value and the minimum value of the number density (maximum number density/minimum number density) is preferably greater than 1.2. 
     The number density can be calculated in the following manner. More specifically, in the porous ceramic aggregate  14  that is bonded on the sheet  12 , ten arbitrary fields of view are observed with an optical microscope, and the number of porous ceramic particles  16  contained within each field of view is measured. In relation to each of such fields of view, for example, a square region of 3 mm×3 mm can be adopted. 
     In addition, by dividing the number of the porous ceramic particles  16  included within each measured visual field by the area of the visual field (=9 mm 2 ), the number density per unit area (number/mm 2 ) is calculated. By comparing the number densities corresponding to the ten individual fields of view, the maximum number density and the minimum number density are extracted, and the ratio thereof (maximum number density/minimum number density) is calculated. 
     Further, the ratio (maximum value/minimum value) of the maximum value and the minimum value of the sizes of the planar shapes of the porous ceramic particles  16  preferably is greater than 1.2. 
     The sizes of the planar shapes of the porous ceramic particles  16  can be calculated in the following manner. More specifically, in the porous ceramic aggregate  14  that is bonded on the sheet  12 , ten arbitrary fields of view are observed respectively with an optical microscope. In addition, for each field of view, five arbitrary straight lines are drawn respectively, and the length of line segments within the porous ceramic particles  16  that cross the straight lines are measured, and an average value thereof is taken to represent the size of the porous ceramic particles  16  within the field of view. The sizes of the porous ceramic particles  16  within the ten fields of view are compared, a maximum value and a minimum value of the sizes of the porous ceramic particles  16  are extracted, and the ratio thereof (maximum value/minimum value) is calculated. 
     A thickness ta (see  FIG. 5A ) of the plurality of porous ceramic particles  16  included within the porous ceramic aggregate  14  is preferably less than or equal to 1000 μm, and a variation in the thickness ta is preferably less than or equal to 10%. The thickness ta can be measured using a constant pressure thickness measuring device or the like. 
     In accordance with this feature, as shown in  FIGS. 9A to 10 , in the case that the porous ceramic aggregate  14  is coated entirely with a resin material  18  (matrix) such as an adhesive or the like to thereby form the bulk body  20 , coating of the entire porous ceramic aggregate  14  with the resin material  18  is facilitated, and it becomes easy to make the thickness of the resin material  18  on portions of the porous ceramic particles  16  uniform. This also contributes to a lower thermal conductivity of the bulk body  20 . 
     The porosity of the porous ceramic particles  16  preferably is 20%˜99%. The pores include at least one of closed pores and open pores, and may include both closed pores and open pores. Further, the shape of the pores, i.e., a surface shape of openings thereof, may be of any shape including a square shape, a quadrilateral shape, a triangular shape, a hexagonal shape, a circular shape, etc., or an irregular shape. 
     The average pore diameter preferably is less than or equal to 500 nm, and more preferably, is 10˜500 nm. This dimension is effective to inhibit the occurrence of lattice vibrations (phonons), which is a primary cause of thermal conductivity. 
     The porous ceramic particles  16  have a structure in which fine grains are connected in three dimensions. A grain diameter of the fine grains is preferably 1 nm˜5 μm. More preferably, the grain diameter is 50 nm˜1 μm. The porous ceramic particles  16 , which are composed of fine grains having such a grain size range, effectively achieve a low thermal conductivity, since the occurrence of lattice vibrations (phonons), which is a primary cause of heat conduction, is inhibited. The fine grains may be a grain composed of one crystalline grain (a single crystalline grain), or a grain composed of a large number of crystalline grains (a polycrystalline grain). Stated otherwise, the porous ceramic particles  16  preferably are aggregations of fine grains having grain diameters lying within the aforementioned ranges. The grain diameter of the fine grains is determined by measuring, from an image of an electronic microscopic observation, the size (a diameter in the case of spherical grains, or a maximum diameter otherwise) of one grain of the grain groups that make up a framework of the porous ceramic particles  16 . 
     The thermal conductivity of the porous ceramic particles  16  is preferably less than 1.5 W/mK, more preferably, is less than or equal to 0.7 W/mK, even more preferably, is less than or equal to 0.5 W/mK, and particularly preferably, is less than or equal to 0.3 W/mK. 
     The heat capacity of the porous ceramic particles  16  preferably is less than or equal to 1000 kJ/m 3 K, more preferably, is less than or equal to 900 kJ/m 3 K, even more preferably, is less than or equal to 800 kJ/m 3 K, and particularly preferably, is less than 500 kJ/m 3 K. 
     The constituent material of the porous ceramic particles  16  preferably contains a metal oxide, and more preferably, consists only of a metal oxide. This is because, if such a metal oxide is contained therein, the thermal conductivity tends to be lower, due to the fact that the ion binding property between metal and oxygen is stronger compared to the case of a non-oxide (for example, a carbide or nitride) of a metal. 
     In this case, the metal oxide preferably is an oxide of one element or a composite oxide of two or more elements selected from the group consisting of Zr, Y, Al, Si, Ti, Nb, Sr, La, Hf, Ce, Gd, Sm, Mn, Yb, Er, and Ta. This is because, if the metal oxide is an oxide or a composite oxide of such elements, heat conduction due to lattice vibrations (phonons) is unlikely to occur. 
     Specific examples of the material include ZrO 2 —Y 2 O 3  to which Gd 2 O 3 , Yb 2 O 3 , Er 2 O 3 , etc., is added. As further specific examples thereof, there may be cited ZrO 2 —HfO 2 —Y 2 O 3 , ZrO 2 —Y 2 O 3 —La 2 O 3 , ZrO 2 —HfO 2 —Y 2 O 3 —La 2 O 3 , HfO 2 —Y 2 O 3 , CeO 2 —Y 2 O 3 , Gd 2 Zr 2 O 7 , Sm 2 Zr 2 O 7 , LaMnAl 11 O 19 , YTa 3 O 9 , Y 0.7 La 0.3 Ta 3 O 9 , Y 1.08 Ta 2.76 Zr 0.24 O 9 , Y 2 Ti 2 O 7 , LaTa 3 O 9 , Yb 2 Si 2 O 7 , Y 2 Si 2 O 7 , Ti 3 O 5 , and the like. 
     Next, with reference to  FIGS. 6 to 8 , a first manufacturing method and a second manufacturing method for manufacturing the porous ceramic structure  10  will be described. 
     Initially, the first manufacturing method will be described. First, in step S 1  of  FIG. 6 , a pore forming agent, a binder, a plasticizer, and a solvent are added to and mixed with a constituent material powder of the aforementioned porous ceramic particles  16  in order to prepare a casting slurry  36  (see  FIG. 7 ). 
     Thereafter, in step S 2 , the casting slurry  36  is subjected to a vacuum defoaming treatment, whereby the viscosity of the slurry is adjusted, followed by carrying out tape casting in order to manufacture a cast body  30  (green sheet, green body) (green body manufacturing step). For example, as shown in  FIG. 7 , the casting slurry  36  is introduced onto a ceramic release type polyester film  34  of a doctor blade device  32 , and the cast body  30  (green sheet) is manufactured by a doctor blade  38 , such that a thickness thereof becomes a specified thickness after firing. 
     Thereafter, in step S 3  of  FIG. 6 , the cast body  30  (green sheet) is separated from the polyester film  34  and picked up. Since the surface of the ceramic release type polyester film  34  is a mirror surface, from among the surface of the cast body  30 , the surface from which the polyester film  34  has been peeled (hereinafter referred to as a peeled surface  30   a ) also becomes a mirror surface. Thereafter, in step S 4 , the picked cast body  30  is fired, whereby a sheet-shaped sintered body  40  is obtained (firing step). Next, in step S 5 , the sintered body  40  is bonded on the sheet  12  (bonding step). As noted above, the peeled surface  30   a  of the cast body  30  is in the form of a mirror surface, and therefore, an end surface  40   a  of the sintered body  40  (the surface of the peeled surface  30   a ) after the firing process also is in the form of a mirror surface. Accordingly, by bonding the end surface  40   a  of the sintered body  40  on the sheet  12 , the sintered body  40  becomes bonded firmly to the sheet  12 . 
     Thereafter, in step S 6 , the sintered body  40  is divided into a plurality of porous ceramic particles  16  (dividing step). Consequently, a porous ceramic structure  10  having one sheet  12 , and a porous ceramic aggregate  14  bonded to the sheet  12  and made up of a plurality of porous ceramic particles  16  is obtained. A surface modification treatment may be performed on the sintered body  40  after the firing step, or may be performed on the porous ceramic particles  16  after the dividing step. Such a surface modification treatment is a treatment (principally a treatment to make permeation of the resin material unlikely) for controlling the degree of penetration of the resin material  18  (matrix: see  FIGS. 9C and 10 ) such as an adhesive or the like into the porous ceramic particles  16 . 
     The above-described dividing step in step S 6  divides the sintered body  40  into a plurality of small pieces, or stated otherwise, a plurality of porous ceramic particles  16 . Of course, in the dividing step, such division can be carried out by various methods. For example, a knife may be pressed against the sintered body  40  in order to cut (divide) the sintered body  40  into a plurality of porous ceramic particles  16 , or the sintered body  40  may be cut with a laser into a plurality of the porous ceramic particles  16 , or the like. In this case, from the fact that the sintered body  40  is firmly bonded to the sheet  12 , when division is performed, peeling of the sintered body  40  and the porous ceramic particles  16  from the sheet  12  is prevented. 
     Next, the second manufacturing method will be described with reference to  FIG. 8 . In the second manufacturing method, in steps S 101  to S 103 , in the same manner as in the aforementioned steps S 1  to S 3 , preparation of the casting slurry  36 , manufacturing of the cast body  30 , and picking up of the cast body  30  are performed. 
     Thereafter, in step S 104 , by carrying out laser machining or press machining, a plurality of cutting lines (cuts)  42  are formed from the upper surface of the cast body  30 . 
     Thereafter, in steps S 105  to S 107 , in the same manner as in the aforementioned steps S 4  to S 6 , the picked cast body  30  is fired, whereby a sheet-shaped sintered body  40  is obtained. In addition, the sintered body  40  is bonded onto the sheet  12  and divided into a plurality of the porous ceramic particles  16 . 
     Consequently, a porous ceramic structure  10  having one sheet  12 , and a porous ceramic aggregate  14  bonded to the sheet  12  and made up of a plurality of porous ceramic particles  16  is obtained. Moreover, in the second manufacturing method as well, a surface modification treatment may be performed on the sintered body  40  after the firing step, or may be performed on the porous ceramic particles  16  after the dividing step. 
     Next, a method of constructing a single bulk body  20  using the porous ceramic structure  10  will be described with reference to  FIGS. 9A to 9C and 10 . 
     First, as shown in  FIG. 9A , an adhesive  44  is coated on the object  22 . The porous ceramic structure  10  is placed on the adhesive  44  that has been coated on the object  22 . In this case, the porous ceramic structure  10  is placed in such a manner that the adhesive  44  on the object  22  and the porous ceramic aggregate  14  face toward each other. 
     Then, as shown in  FIG. 9B , for example, the sheet  12  is heated and the sheet  12  is peeled off, whereby the porous ceramic aggregate  14  is transferred onto the adhesive  44  of the object  22 . 
     Thereafter, as shown in  FIGS. 9C and 10 , the porous ceramic aggregate  14  is coated entirely with a resin material  18  (matrix) such as an adhesive or the like, thereby forming the bulk body  20 . More specifically, the bulk body  20  is installed on the object  22 . 
     Conventionally, as shown in  FIG. 11A , since particles  52  added to a slurry  50  are small, it is difficult to uniformly disperse the particles  52  in the slurry  50 . Therefore, as shown in  FIG. 11B , when the slurry  50  is solidified into a bulk body  54 , due to the fact that the plurality of particles  52  are not uniformly dispersed in the adhesive  56  upon solidification of the slurry  50 , many regions  58  exist where only the adhesive  56  is present, which has a thermal conductivity higher than that of the particles  52 , and thus, the reduction in thermal conductivity of the bulk body  54  is insufficient. 
     In contrast thereto, in the present embodiment, the porous ceramic structure  10 , which includes the porous ceramic aggregate  14  composed of the plurality of porous ceramic particles  16  bonded on the sheet  12 , is placed on the object  22 . Thereafter, the sheet  12  is peeled off, and the porous ceramic aggregate  14  is transferred onto the object  22 . Then, the porous ceramic aggregate  14  is coated with the resin material  18  (matrix) such as an adhesive or the like to thereby constitute the bulk body  20 . 
     Therefore, it is possible to uniformly disperse and arrange the plurality of porous ceramic particles  16  in the resin material  18 . In addition, since regions composed of only the resin material  18  having a thermal conductivity higher than that of the porous ceramic particles  16  are narrowed, the thermal conductivity of the bulk body  20  can be suppressed and remain low. Moreover, the thermal conductivity can be equalized within the bulk body  20 , there is no need to change or modify the bulk body  20  corresponding to the location where the bulk body  20  is installed, the process of arranging the bulk body  20  can be simplified, and the number of steps required therefor can be reduced. 
     Further, since the sintered body  40  bonded to the sheet  12  is divided into a plurality of porous ceramic particles  16 , unlike the case of the conventional technique, a plurality of the porous ceramic particles  16  can be arranged uniformly on the object  22 . In addition, even in the case that the surface of the object  22  is of an irregular shape (warped or the like) or a curved surface, the plurality of porous ceramic particles  16  can be easily arranged along a surface shape of the object  22 , and the degree of freedom of design can be enhanced. Further, since the porous ceramic structure  10  is composed of the sheet  12  and the porous ceramic aggregate  14  having the plurality of porous ceramic particles  16  that are bonded on the sheet  12 , handling of the porous ceramic structure  10  is facilitated, while in addition, the operation of transferring the plurality of porous ceramic particles  16  onto the object  22  is simplified. This is advantageous in terms of simplifying the manufacturing process. 
     Preferably, the adhesive strength (JIS Z0237) of the sheet  12  is greater than or equal to 1.0 N/10 mm, the tensile elongation (JIS K7127) of the sheet  12  is greater than or equal to 0.5%, and the thickness of the sheet  12  is less than or equal to 5 mm. Consequently, the following effects can be obtained. 
     (a) The higher the adhesive strength, the more firmly the porous ceramic particles  16  can be fixed. 
     (b) As the tensile elongation increases, it is possible to follow the curved surface. 
     (c) As the thickness thereof is thinner, it becomes easier to follow the curved surface. 
     In greater detail, the adhesive strength of the sheet  12  exhibits the following properties. More specifically, the adhesive strength at the time that the porous ceramic particles  16  are retained is greater than or equal to 1.0 N/10 mm, and the adhesive strength at the time of peeling the porous ceramic particles  16  is less than or equal to 0.1 N/10 mm. 
     The method of evaluating the adhesive strength of the sheet  12  is the same as the method used for evaluating the adhesive strength of an adhesive tape. In particular, the sheet  12  is attached to a stainless steel plate, and the sheet  12  is pulled at an angle of 180 degrees or 90 degrees, whereupon the force applied when peeling the sheet  12  off from the stainless steel plate is regarded as the adhesive force (adhesive strength). 
     Further, the sheet  12  is formed by applying an adhesive to a base material (support). In this case, as the type of base material, preferably a material is selected from among the following. 
     More specifically, when the porous ceramic particles  16  are transferred onto the planar object  22 , it is preferable to use a film, metal foil, paper, or the like as the base material. In this case, since the base material of the sheet  12  is stiff, it is possible to dispose the sheet  12  in the form of a film without wrinkles with respect to the planar object  22 . 
     In the case of transferring the porous ceramic particles  16  onto an object  22  having a curved surface (convex surface, concave surface, irregular surface) shape, it is preferable to use a cloth, a rubber sheet, foam or the like as the base material. In this case, since the base material of the sheet  12  is soft and stretchable, it is possible to dispose the sheet  12  in following relation to the curved surface shape of the object  22 . 
     Further, by application of heat, water, a solvent, light (ultraviolet light), or microwaves, the adhesive strength of the sheet  12  can be weakened and the sheet  12  can be easily peeled off. At this time, the adhesive strength of the sheet  12  is preferably weaker than the adhesive strength of the adhesive  44  that is used between the object  22  and the porous ceramic structure 10. 
     EXAMPLES 
     A confirmation was carried out concerning the thermal conductivity, a smallness of loss of material, a smallness of positional shifting of the porous ceramic particles  16 , ease of following the curved surface, and the likelihood of cracking or chipping of the porous ceramic particles  16  when transferring them onto the object  22  for each of various bulk bodies  20 , for cases in which the bulk bodies  20  were constituted using the porous ceramic structures  10  according to Examples 1 to 8, and porous ceramic structures according to Comparative Examples 1 and 2. 
     Example 1 
     Porous ceramic particles  16  each having a porosity of 60% and a thickness of 60 μm were used as the plurality of porous ceramic particles  16  constituting the porous ceramic structure  10 , and a bulk body  20  according to Example 1 was prepared according to the above-described first manufacturing method. More specifically, at first, a porous ceramic structure  10  including a sheet  12  and a plurality of porous ceramic particles  16  bonded to one surface of the sheet  12  was used. Then, after coating an adhesive  44  (thermal conductivity 2 W/mK) onto an object  22 , the plurality of porous ceramic particles  16  were transferred onto the adhesive  44  of the object  22  using the sheet  12 , and by application of heat thereto, the sheet  12  was peeled off. After coating the transferred particles on the object with a resin material  18  (matrix) from above, the resin material  18  was solidified, and the bulk body  20  was installed on the surface of the object 22. 
     &lt;Manufacturing of Porous Ceramic Structure  10 &gt; 
     In Example 1, a porous ceramic structure  10  for use in measuring porosity, and a porous ceramic structure  10  for use as a bulk body were manufactured in the following manner. The porous ceramic structures of the later-described Examples 2 to 8, and Comparative Example 2 were also manufactured in a similar manner. 
     First, a pore forming agent (latex particles or melamine resin particles), a polyvinyl butyral resin (PVB) as a binder, DOP (dioctyl phthalate) as a plasticizer, and xylene and 1-Butanol as solvents were added to yttria-partially-stabilized zirconia powder, and mixed in a ball mill for 30 hours in order to prepare a casting slurry  36 . The casting slurry  36  was subjected to a vacuum defoaming treatment, whereby the viscosity thereof was adjusted to 4000 cps, and thereafter, the cast body  30  (green sheet) was produced by the doctor blade device  32  such that a thickness thereof after firing was 60 μm. Thereafter, the cast body  30  was fired at 1100° C. for 1 hour in order to obtain the sintered body  40 . Thereafter, the sintered body  40  was bonded onto the upper surface of the sheet  12 . Furthermore, the sintered body  40  was divided into a plurality of the porous ceramic particles  16 . More specifically, a porous ceramic structure  10  was manufactured, in which a porous ceramic aggregate  14  made up of a plurality of porous ceramic particles  16  was bonded on the sheet  12 . 
     The planar shape of the porous ceramic aggregate  14  on the sheet  12  is a square shape having a length of 100 mm and a width of 100 mm, and the area of one of the porous ceramic particles  16  is about 0.25 mm 2 . More specifically, the porous ceramic structure  10  is formed in a state with roughly 40000 of the porous ceramic particles  16  being arrayed on the sheet  12 . 
     In the porous ceramic structure  10  according to Example 1, the planar shape of the porous ceramic aggregate  14  made up from the plurality of porous ceramic particles  16  as viewed from the upper surface is different from the planar shape of a region within the object  22  where the porous ceramic aggregate  14  is intended to be placed, as viewed from the upper surface. In the porous ceramic structure  10 , the planar shapes of the plurality of porous ceramic particles  16  that make up the porous ceramic structure  10  were all in the form of polygonal shapes surrounded by straight lines  24 . The angles of inclination θ of the side surfaces of the respective porous ceramic particles  16  exceeded 45 degrees, respectively, and was less than or equal to 50 degrees with respect to the normal line  28  that is normal to the sheet  12 . Further, the thickness to of the porous ceramic particles  16  was 45-55 μm, and the variation in thickness was 10%. The gap d between the porous ceramic particles  16  was 5˜10 μm, the ratio of the maximum number density to the minimum number density (maximum number density/minimum number density) was 1.15, and the ratio of the maximum value and the minimum value of the sizes of the planar shapes (maximum value/minimum value) was 1.15. Further, there were portions where, at a maximum, four porous ceramic particles  16  were arranged with one apex each facing toward each other. 
     Example 2 
     The bulk body  20  according to Example 2 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which the planar shape of the porous ceramic aggregate  14  made up from the plurality of porous ceramic particles  16  as viewed from the upper surface is the same as the planar shape of a region within the object  22  where the porous ceramic aggregate  14  is intended to be placed as viewed from the upper surface. 
     Example 3 
     The bulk body  20  according to Example 3 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which, from among the plurality of porous ceramic particles  16 , the percentage Pa of the porous ceramic particles including a curve  26  in the planar shape thereof as viewed from the upper surface is greater than 0% and less than or equal to 50%. 
     Example 4 
     The bulk body  20  according to Example 4 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used which includes a portion  27  (see  FIG. 2B ) in which five porous ceramic particles  16  are arranged with one apex each facing toward each other. 
     Example 5 
     The bulk body  20  according to Example 5 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which the angle of inclination θ of the side surfaces of the plurality of porous ceramic particles  16  constituting the porous ceramic aggregate  14  is greater than or equal to 0 degrees and less than or equal to 45 degrees with respect to a normal line  28  that is normal to the sheet  12 . 
     Example 6 
     The bulk body  20  according to Example 6 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which the ratio of the maximum number density to the minimum number density (maximum number density/minimum number density) of the plurality of porous ceramic particles  16  making up the porous ceramic aggregate  14  is 1.25. 
     Example 7 
     The bulk body  20  according to Example 7 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which the ratio (maximum value/minimum value) of the maximum value and the minimum value of the sizes of the planar shapes of the plurality of porous ceramic particles  16  making up the porous ceramic aggregate  14  is 1.25. 
     Example 8 
     The bulk body  20  according to Example 8 was manufactured in the same manner as in Example 1, except for the feature that, as the porous ceramic structure  10 , a porous ceramic structure  10  was used in which the thickness ta of the plurality of porous ceramic particles  16  making up the porous ceramic aggregate  14  is 47.5 to 52.5 μm, and the variation in thickness is 5%. 
     Comparative Example 1 
     As shown in  FIG. 1A , a bulk body  54  according to Comparative Example 1 was manufactured by preparing a slurry 50 containing particles  52  (commercially available porous ceramic particles) having a porosity of 90% and a particle diameter of 50 μm, polystyrene resin fine particles, and water, and thereafter pouring the slurry  50  into a mold, and then after drying, performing firing and solidifying to obtain the bulk body  54 . 
     Comparative Example 2 
     A plurality of porous ceramic particles  16  each having a porosity of 60% and a thickness ta of 47.5˜52.5 μm were bonded directly on the object  22  with an adhesive  44  and without using the sheet  12 , and after coating the particles bonded on the object with a resin material  18  (matrix) from above, the resin material  18  was solidified to thereby prepare a bulk body  20  according to Comparative Example 2. 
     In Table 1 appearing below, there is shown a compositional breakdown of Examples 1 to 8 and Comparative Examples 1 and 2. Note that, in Table 1, the upwardly pointing arrows “↑” indicate that the content thereof is the same as the examples shown above. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Percentage 
                 Number 
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                 including 
                 of 
                   
                   
                   
                   
                 Number 
               
               
                   
                 Planar Shape of 
                 Curve 
                 Facing 
                 Angle of 
                 Thickness 
                 Thickness 
                 Gap 
                 Density 
                 Size 
               
               
                   
                 Aggregate 
                 Pa 
                 Apexes 
                 Inclination θ 
                 ta (μm) 
                 Variation 
                 (μm) 
                 Ratio 
                 Ratio 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 Differs from 
                 0% 
                 4 
                 45° &lt; θ ≦ 50° 
                 45~55 
                 10% 
                 5~10 
                 1.15 
                 1.15 
               
               
                   
                 Planar Shape of 
               
               
                   
                 Base Material 
               
               
                 Example 2 
                 Same as Planar 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
               
               
                   
                 Shape of Base 
               
               
                   
                 Material 
               
               
                 Example 3 
                 Differs from 
                 0% &lt; Pa ≦ 50% 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
               
               
                   
                 Planar Shape of 
               
               
                   
                 Base Material 
               
               
                 Example 4 
                 ↑ 
                 0% 
                 5 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
               
               
                 Example 5 
                 ↑ 
                 ↑ 
                 ↑ 
                  0° ≦ θ ≦ 45° 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
               
               
                 Example 6 
                 ↑ 
                 ↑ 
                 ↑ 
                 45° &lt; θ ≦ 50° 
                 ↑ 
                 ↑ 
                 ↑ 
                 1.25 
                 ↑ 
               
               
                 Example 7 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 1.15 
                 1.25 
               
               
                 Example 8 
                 ↑ 
                 ↑ 
                 ↑ 
                 ↑ 
                 47.5~52.5 
                  5% 
                 ↑ 
                 ↑ 
                 1.15 
               
            
           
           
               
               
            
               
                 Comparative 
                 Particles with particle diameters of 50 μm dispersed within adhesive 
               
               
                 Example 1 
               
               
                 Comparative 
                 Large number of porous ceramic particles individually bonded on base material 
               
               
                 Example 2 
               
               
                   
               
            
           
         
       
     
     [Measurement Method, Method of Calculation, and Evaluation Standards] 
     &lt;Measurement of Porosity&gt; 
     With respect to Examples 1 to 8, ten porous ceramic particles  16  were selected at random from among the plurality of porous ceramic particles  16  constituting a porous ceramic structure  10  for use in measuring porosity, and the selected porous ceramic particles  16  were embedded in a resin. The resin was polished until producing an observation site at which the porous ceramic particles  16  could be observed with an electron microscope, to thereby obtain a resin-filled polished surface. Then, an electron microscopic observation (image analysis) was performed on the resin-filled polished surface. From such an image analysis, the respective porosities of the ten porous ceramic particles  16  were calculated, and the average value of the ten porous ceramic particles  16  was taken as the porosity of the porous ceramic particles  16 . Concerning Comparative Example 2, ten porous ceramic particles  16  for use in measuring porosity were selected, and the porosity of the porous ceramic particles  16  was determined by the same method as described above. 
     &lt;Measurement of Average Pore Diameter&gt; 
     The average pore diameter of the porous ceramic particles  16  was measured using an automated porosimeter (trade name “Autopore 9200”) manufactured by Shimadzu Corporation. 
     &lt;Method of Measuring Thermal Conductivity of Bulk Body  20  and Evaluation Criteria&gt; 
     At first, the density of the bulk body  20  was measured with a mercury porosimeter. Next, the specific heat of the bulk body  20  was measured using a DSC (Differential Scanning calorimeter) method. Next, the thermal diffusivity of the bulk body  20  was measured using a laser flash method. Thereafter, the thermal conductivity of the bulk body  20  was calculated from the following relational expression: 
       Thermal Diffusivity×Specific Heat×Density=Thermal Conductivity
 
     Then, based on the following evaluation criteria, the thermal conductivities of Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated. 
     A: Less than or equal to 0.9 W/mK 
     B: Greater than or equal to 1.0 W/mK and less than or equal to 1.4 W/mK 
     C: Greater than or equal to 1.5 W/mK and less than or equal to 1.9 W/mK 
     D: Greater than or equal to 2.0 W/mK 
     &lt;Method of Measuring Gap d Between Porous Ceramic Particles  16 &gt; 
     The gaps d between the plurality of porous ceramic particles  16  that make up the porous ceramic aggregate  14  were measured respectively with an optical microscope. 
     &lt;Method of Measuring Thickness ta of Porous Ceramic Particles  16 &gt; 
     The thicknesses ta of the plurality of porous ceramic particles  16  that make up the porous ceramic aggregate  14  were measured respectively with an optical microscope. 
     &lt;Method of Measuring Angle of Inclination θ of Side Surfaces of Porous Ceramic Particles  16 &gt; 
     The angles of inclination θ of the plurality of porous ceramic particles  16  that make up the porous ceramic aggregate  14  were measured respectively with an optical microscope. 
     &lt;Method of Calculating Percentage of Porous Ceramic Particles  16  Including a Curve  26  in the Planar Shape&gt; 
     A total number of the plurality of porous ceramic particles  16  constituting the porous ceramic aggregate  14 , and the number of the porous ceramic particles  16  including a curve  26  in the planar shape thereof were determined, and the value (number/total number)×100 (%) was calculated. 
     &lt;Determination of Percentage of Number Density of Porous Ceramic Particles  16 &gt; 
     In the porous ceramic aggregate  14  that is bonded on the sheet  12 , ten arbitrary fields of view were observed with an optical microscope, and the number of porous ceramic particles  16  contained within each field of view was measured. In relation to each of such fields of view, for example, a square region of 3 mm×3 mm was adopted. In addition, by dividing the number of the porous ceramic particles  16  included within each measured visual field by the area of the visual field (=9 mm 2 ), the number density per unit area (number/mm 2 ) was calculated. By comparing the number densities corresponding to the ten individual fields of view, the maximum number density and the minimum number density were extracted, and the ratio thereof (maximum number density/minimum number density) was calculated. 
     &lt;Method of Determining the Percentage of the Sizes of the Planar Shapes of the Porous Ceramic Particles  16 &gt; 
     In the porous ceramic aggregate  14  that is bonded on the sheet  12 , ten arbitrary fields of view were observed with an optical microscope. In addition, for each field of view, five arbitrary straight lines were drawn respectively, the length of line segments within the porous ceramic particles  16  that cross the straight lines were measured, and an average value thereof was taken to represent the size of the porous ceramic particles  16  within the field of view. The sizes of the porous ceramic particles  16  within the ten fields of view were compared, a maximum value and a minimum value of the sizes of the porous ceramic particles  16  were extracted, and the ratio thereof (maximum value/minimum value) was calculated. 
     [Evaluation of Smallness of Loss of Material] 
     The number Na of porous ceramic particles  16  existing on the object  22  was confirmed using an optical microscope, and the percentage of the number Na with respect to the total number Nz of porous ceramic particles  16  on the sheet  12 , or more specifically, the value (Number Na/Total Number Nz)×100 (%), was determined. In addition, Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated on the basis of the following Evaluation Standards. 
     A: Greater than or equal to 95% 
     B: Greater than or equal to 85% and less than 95% 
     C: Less than 85% 
     [Evaluation of Smallness of Positional Shifting of Porous Ceramic Particles  16 ] 
     Among the porous ceramic particles  16  present on the object  22 , the porous ceramic particles  16  having a largest amount of positional shifting were confirmed with an optical microscope, and the amount of positional shifting was measured. In addition, Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated on the basis of the following Evaluation Standards. 
     A: Amount of shifting less than 0.5 mm 
     B: Amount of shifting greater than or equal to 0.5 mm 
     [Evaluation of Ease of Following Curved Surface of Object  22 ] 
     The number Nb of the porous ceramic particles  16  whose peripheral portion remains floating from among the porous ceramic particles  16  existing on the object  22  was confirmed with an optical microscope, and the percentage of the number Nb with respect to the total number Nz of porous ceramic particles  16  on the sheet  12 , or more specifically, the value (Number Nb/Total Number Nz)×100 (%), was determined. In addition, Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated on the basis of the following Evaluation Standards. 
     A: Less than 5% 
     B: Greater than or equal to 5% 
     [Evaluation of Likelihood of Cracking or Chipping of Porous Ceramic Particles  16  at a Time of Transfer Thereof onto the Object  22 ] 
     The number Nc of porous ceramic particles  16  lacking peripheral portions from among the porous ceramic particles  16  existing on the object  22  was confirmed using an optical microscope, and the percentage of the number Nc with respect to the total number Nz of porous ceramic particles  16  on the sheet  12 , or more specifically, the value (Number Nc/Total Number Nz)×100 (%), was determined. In addition, Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated on the basis of the following Evaluation Standards. 
     A: Less than 5% 
     B: Greater than or equal to 5% 
     &lt;Evaluation Results&gt; 
     Evaluation results of Examples 1 to 8 and Comparative Examples 1 and 2 are shown below in Table 2. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Resistance 
               
               
                   
                   
                   
                   
                   
                 to 
               
               
                   
                   
                   
                   
                 Ease of 
                 Cracking/ 
               
               
                   
                 Low 
                 Small 
                 Small 
                 Following 
                 Chipping 
               
               
                   
                 Thermal 
                 Material 
                 Positional 
                 Curved 
                 Upon 
               
               
                   
                 Conductivity 
                 Loss 
                 Shifting 
                 Surface 
                 Transfer 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 B 
                 B 
                 B 
                 B 
                 B 
               
               
                 Example 2 
                 B 
                 A 
                 B 
                 B 
                 B 
               
               
                 Example 3 
                 B 
                 B 
                 A 
                 B 
                 B 
               
               
                 Example 4 
                 B 
                 B 
                 B 
                 A 
                 B 
               
               
                 Example 5 
                 A 
                 B 
                 B 
                 B 
                 A 
               
               
                 Example 6 
                 B 
                 B 
                 B 
                 A 
                 B 
               
               
                 Example 7 
                 B 
                 B 
                 B 
                 A 
                 B 
               
               
                 Example 8 
                 A 
                 B 
                 B 
                 B 
                 A 
               
               
                 Comparative 
                 D 
                 C 
                 A 
                 A 
                 A 
               
               
                 Example 1 
               
               
                 Comparative 
                 C 
                 B 
                 A 
                 B 
                 B 
               
               
                 Example 2 
               
               
                   
               
            
           
         
       
     
     As can be understood from Table 2, in Comparative Example 1, the thermal conductivity was greater than or equal to 2.0 W/mK. In the bulk body  54  according to Comparative Example 1, it is considered that the reason the thermal conductivity was increased is because there were many regions  58  in which only the adhesive  56  was present. In Comparative Example 2 as well, the thermal conductivity was greater than or equal to 1.5 W/mK. In the bulk body  54  according to Comparative Example 2, this is considered to be due to the fact that, since the porous ceramic particles  16  were bonded individually to the object  22 , wide gaps occurred between the porous ceramic particles  16 , and many regions existed in which only the resin material  18  was present. 
     In contrast thereto, in any of Examples 1 to 8, the thermal conductivity was low at less than or equal to 1.4 W/mK, and in particular, in Examples 5 and 8, the thermal conductivity was extremely low at 0.9 W/mK. This is considered to be due to the fact that, since the plurality of porous ceramic particles  16  were uniformly dispersed in the resin material  18 , and regions composed of only the resin material  18  having a high thermal conductivity were narrowed, the thermal conductivity of the bulk body  20  can be suppressed to remain at a low value. 
     Among Examples 1 to 8, concerning the smallness of the loss of the material, the loss of material was lowest in Example 2. Concerning the smallness of positional shifting, the amount of shifting was smallest in Example 3. Concerning the ease of following the curved surface of the object  22 , a high evaluation therefor was indicated in Examples 4, 6 and 7. Concerning the likelihood of cracking or chipping, cracking or chipping was most unlikely to occur in Example 5. 
     The porous ceramic structure and the method of manufacturing the same, according to the present invention, are not limited to the above-described embodiments, and it is a matter of course that various configurations can be adopted therein without departing from the scope of the present invention. 
     In the above examples, the porous ceramic aggregate  14  is coated with the resin material  18  when the bulk body  20  is manufactured. However, alternatively, a portion of the porous ceramic aggregate  14  may be coated with the resin material  18  to thereby form the bulk body  20 , or the bulk body  20  may be formed merely by installing the porous ceramic aggregate  14  on the object  22  without using the resin material  18 .