JP2013018099A - Method of manufacturing porous structure, and porous structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a porous structure capable of increasing the polished amount of a workpiece.SOLUTION: This method of manufacturing the porous structure 10 including a porous metal 20 having an open pore structure includes: a first step of forming an abrasive grain layer 30 including abrasive grains 31 on the surface of the framework of the porous metal 20; and a second step of cutting the surface of the porous metal 20 on the framework surface of which the abrasive grain layer is formed to remove a part of the abrasive grain layer 30 so as to increase the area of the abrasive grain layer 30 on the cut surface. The step of forming the abrasive grain layer 30 is a step of electroplating.

Description

  The present invention relates to a method for producing a porous structure used for a processing tool or the like and a porous structure.

  Formed by adding a thickener and diamond abrasive grains to a base metal such as molten aluminum as a polishing tool, adding a foaming agent while stirring them, and cooling and solidifying the fired metal material A fired metal wheel having a large number of bubbles and having a large number of diamond abrasive grains protruding on the surface is known (see, for example, Patent Document 1). This foaming metal wheel has a mesh-like skeleton formed in three dimensions, and the skeleton is formed by mixing diamond abrasive grains in a base metal.

JP-A-1-193173

  However, in the metal wheel of Patent Document 1, not only the surface of the skeleton but also diamond abrasive grains are mixed inside the base metal. For this reason, diamond abrasive grains cannot be protruded from the surface of the skeleton at a high density, and the amount of grinding or polishing of the workpiece cannot be increased.

  The present invention has been made paying attention to these problems, and an object of the present invention is to provide a porous structure manufacturing method and a porous structure capable of increasing the amount of grinding or polishing of a workpiece. .

In order to achieve the above object, a method for producing a porous structure according to the first aspect of the present invention comprises:
A method for producing a porous structure composed of a porous metal having an open pore structure,
A first step of forming an abrasive layer containing abrasive grains on the surface of the porous metal skeleton;
The surface of the porous metal having the abrasive layer formed on the surface of the skeleton is scraped to remove a part of the abrasive layer, thereby increasing the area of the abrasive layer on the scraped surface. Process,
It is characterized by providing.

  In the second step of the method for producing a porous structure, the surface of the porous metal having an abrasive layer formed on the surface of the skeleton is shaved, and a part of the skeleton of the porous metal is further removed. You may make it do.

  In the method for manufacturing a porous structure, the first step may be an electroplating step.

  In the method for producing a porous structure, the porous metal may be one metal selected from the group consisting of Ni, Cu, Zn, Al, Au, Ag, Fe, and Co, or an alloy thereof, or two or more thereof. You may form with the alloy containing a metal.

  In the method for manufacturing a porous structure, the abrasive grains may be formed of superabrasive grains selected from the group consisting of diamond and cubic boron nitride (CBN).

In the manufacturing method of the porous structure, the abrasive grains are alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), ceria (CeO ₂ ), titania (TiO ₂ ), magnesia (MgO And an oxide selected from the group consisting of:

In the method for producing a porous structure, the abrasive grains may be formed of a carbide selected from the group consisting of silicon carbide (SiC) and boron carbide (B ₄ C).

In the method for manufacturing a porous structure, the abrasive grains may be formed of a nitride selected from the group consisting of aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ).

In the method for producing a porous structure, the abrasive grains are selected from the group consisting of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), titania (TiO ₂ ), and magnesia (MgO). You may form with the complex oxide of 2 or more types of oxides.

The porous structure according to the second aspect of the present invention for achieving the above object is
A porous structure composed of a porous metal having an open pore structure,
Forming an abrasive layer containing abrasive grains on the surface of the porous metal skeleton;
Manufactured by increasing the area of the abrasive layer on the scraped surface by scraping the surface of the porous metal on which the abrasive layer is formed on the surface of the skeleton,
It is characterized by that.

  ADVANTAGE OF THE INVENTION By this invention, the manufacturing method and porous structure of a porous structure which can increase the grinding amount or polishing amount of a to-be-processed object can be provided.

It is a perspective view which shows the porous structure which concerns on embodiment of this invention. It is an enlarged photograph which shows the porous structure which concerns on embodiment of this invention. It is an enlarged view which shows the cross section of the frame | skeleton of the porous structure which concerns on embodiment of this invention. 1 is a perspective view schematically showing a skeleton of a porous structure according to an embodiment of the present invention. (A) is the schematic diagram which looked at the frame | skeleton of the state before cutting the porous structure which concerns on embodiment of this invention from the IV direction of FIG. 4, (b) is the frame | skeleton of the state cut | disconnected to the surface 11B 4 is a schematic view of the skeleton in a state of being cut down to the surface 11C from the IV direction of FIG. 4. (A) is the VV sectional view of Drawing 4 showing typically the frame of the state where the porous structure concerning an embodiment of the present invention was shaved to 11D, (b) is the state shaved to 11E 5 is a VV cross-sectional view of FIG. 4 schematically showing the skeleton of FIG. It is a figure of the porous structure manufacturing apparatus which manufactures the porous structure which concerns on embodiment of this invention. (A) is a schematic diagram which shows the state before shaving the porous structure which concerns on embodiment of this invention, (b) is a schematic diagram which shows the state which shaved the porous structure to the surface 11a (C) is a schematic diagram which shows the state which shaved the porous structure to the surface 11b. It is sectional drawing which shows typically the frame | skeleton of the porous structure which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below. In addition, embodiment described below is for description and does not restrict | limit the scope of the present invention. Therefore, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.

  As shown in FIG. 1, the porous structure 10 is formed in a rectangular parallelepiped shape, for example, and can use the side surface 101, the upper surface 102, etc. as work surfaces for polishing or the like. As shown in FIGS. 1 and 2, the porous structure 10 is formed by a three-dimensional network structure 10 a (see the gray portion in FIG. 2). In addition, open pores 21 (see black portions in FIG. 2) are formed between the mesh-like skeletons 10a. The open pores are pores that communicate from one surface to the other surface located on the opposite side.

  More specifically, as shown in FIG. 3, the skeleton 10 a of the porous structure 10 includes a porous metal 20 and an abrasive layer 30 that covers the surface of the porous metal 20. Further, abrasive grains 31 are taken into the abrasive grain layer 30. Some abrasive grains, for example, abrasive grains 31a, are fixed to the porous metal 20 via the base material 30a in a state of protruding from the abrasive grain layer 30 toward the open pores 21. Further, other abrasive grains, for example, 31b are fixed to the porous metal 20 via the base material 30a in a state of being buried in the abrasive grain layer 30. In the present embodiment, the abrasive grains 31 are formed with an average particle diameter of 3 μm, and the abrasive grain layer 30 is formed with a thickness of about 16 to 17 μm.

  Hereinafter, each element which comprises the porous structure 10 which concerns on this embodiment is demonstrated. In the present embodiment, a material having a Mohs hardness greater than the Mohs hardness of the base metal 30 a of the porous metal 20 and the abrasive grain layer 30 is selected as the abrasive grain 31. The Mohs hardness in the present invention is a standard material corresponding to each of ten hardness indices. The standard material of Mohs hardness 1 is talc, 2 is gypsum, 3 is calcite, 4 is fluorite, 5 is apatite, 6 is orthoclase, 7 is quartz, 8 is topaz, 9 is corundum, and 10 is diamond. The Mohs hardness determines the corresponding Mohs hardness by scratching the surface of the substance to be measured with a standard material of the Mohs hardness and examining the presence or absence of scratches.

  The porous metal 20 is made of nickel (Ni, Mohs hardness: 3 to 4), and has an open pore structure in which a network skeleton is formed in three dimensions. The porous metal 20 is formed in a rectangular parallelepiped shape (see FIG. 1). The porous metal 20 is made of copper (Cu, Mohs hardness: 2-4), zinc (Zn, Mohs hardness: 2-3), aluminum (Al, Mohs hardness: 2-3) in addition to nickel (Ni). ), Gold (Au, Mohs hardness: 2-3), silver (Ag, Mohs hardness: 2-3), iron (Fe, Mohs hardness: 4-5), cobalt (Co, Mohs hardness: 5-6) You may form from the metal of 1 type selected from the group which consists of, or its alloy, or the alloy containing 2 or more types of metals.

  Moreover, what was formed by the various manufacturing method as the porous metal 20 can be used. For example, the surface of a three-dimensional network porous body such as a foam, a nonwoven fabric, or a mesh body as a base material is imparted with conductivity by carbon coating, chemical plating, or vapor deposition, then electroplated, and then fired to form the above-mentioned base. A material obtained by burning a material and forming a three-dimensional network skeleton by a metal layer can be used.

The abrasive grains 31 are made of diamond (Mohs hardness: 10), and the average particle diameter is 3 μm. The average particle size was measured by image analysis of a SEM (scanning electron microscope) photograph of the abrasive grains, but it can also be performed using other methods such as a particle size measuring instrument. The abrasive grains 31 include, in addition to diamond, superabrasive grains such as cubic boron nitride (CBN, Mohs hardness: 10), alumina (Al ₂ O ₃ , Mohs hardness: 8 to 9), zirconia (ZrO ₂ , Mohs hardness: 7-9), silica (SiO _2, Mohs hardness: 6-7), ceria (CeO _2, Mohs hardness: 5-7), titania (TiO _2, Mohs hardness: 5-8), magnesia (MgO , Oxides such as Mohs hardness: 5-6), carbides such as silicon carbide (SiC, Mohs hardness: 8-9), boron carbide (B ₄ C, Mohs hardness: 8-9), aluminum nitride (AlN, Mohs) Hardness: 6-8) and nitrides such as silicon nitride (Si ₃ N ₄ , Mohs hardness: 5-7) may be used. The abrasive grains 31 are two or more oxides selected from the group consisting of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), titania (TiO ₂ ), and magnesia (MgO). It may be formed from the complex oxide.

  The base material 30a of the abrasive grain layer 30 is formed from nickel (Ni). The base material 30a of the abrasive grain layer 30 is not only nickel (Ni) but also copper (Cu), zinc (Zn), aluminum (Al), gold (Au), silver (Ag), cobalt (Co), You may form from the metal of 1 type selected from the group which consists of iron (Fe), its alloy, or the alloy containing 2 or more types of metals.

  Next, the operation when the work surface (see 101 and 102 in FIG. 1) of the porous structure 10 according to the present embodiment is shaved will be described with reference to FIGS. The skeleton 10a illustrated in FIG. 4 is the skeleton 10a in the vicinity of the work surface. The surfaces 11A to 11E are surfaces that define the outer shape of the porous structure 10 (virtual surfaces formed by circumscribing the plurality of skeletons 10a). And surface 11A-11E is a surface used as a work surface for grinding | polishing, when it is used as a grindstone like the side surface 101 of the porous structure 10, for example. For the sake of simplicity, the skeleton 10a shown in FIG. 4 has an X portion parallel to the surfaces 11A to 11E, which are work surfaces, and a Y portion perpendicular thereto. The surfaces 11A to 11E are all parallel.

  First, the X portion parallel to the surfaces 11A to 11C in the skeleton 10a will be described.

  As shown in FIG. 5A, in the portion X, the abrasive grain layer 30 incorporating the abrasive grains 31 is formed on the entire periphery of the porous metal 20 before the surface 11A is cut. And in the area | region B1, the abrasive grain 31 protrudes from the surface 11A.

  When the surface 11A is shaved and a part of the abrasive layer 30 is removed, a surface 11B is newly formed as shown in FIG. At this time, the abrasive grains 31 protrude from the surface 11B in the region B2. And since the area of area | region B2 in the surface 11B of FIG.5 (b) is larger than the area of area | region B1 in the surface 11A of Fig.5 (a), when the workpiece was grind | polished with the surface 11B, it grind | polished with the surface 11A. Larger polishing than possible.

  Further, when the surface 11B is cut, a part of the abrasive grain layer 30 and the porous metal 20 is removed, and a new surface 11C is formed as shown in FIG. At this time, since the area of the region B3 in the surface 11C of FIG. 5C is larger than the area of the region B1 in the surface 11A of FIG. 5A, when the workpiece is polished by the surface 11C, the surface 11A is polished. It is possible to polish larger than the case.

  In this way, in the skeleton parallel to the work surface, the number of abrasive grains that come in contact with the workpiece increases after the cutting, compared to before the abrasive layer is cut. The amount increases.

  Next, the Y portion perpendicular to the surfaces 11A to 11E in the skeleton 10a will be described.

  As shown in FIG. 6A, an abrasive grain layer 30 incorporating abrasive grains 31 is formed around the porous metal 20 in the Y portion. And in the area | region C1 of Fig.6 (a), the abrasive grain 31 protrudes from the surface 11D.

  When the surface 11D is cut, both the porous metal 20 and the abrasive layer 30 are worn, and a new surface 11E is formed as shown in FIG. At this time, the area of the region C2 on the surface 11E of FIG. 6B is substantially the same as the area of the region C1 on the surface 11D of FIG. Therefore, the amount of abrasive grains 31 protruding from the surface 11D in the region C1 and the amount of abrasive particles 31 protruding from the surface 11E in the region C2 are substantially the same. Therefore, the polishing amount of the workpiece is also substantially the same.

  Next, a method for manufacturing the porous structure 10 according to this embodiment will be described. In detail, the manufacturing method of the porous structure 10 which formed the abrasive grain layer 30 containing the abrasive grain 31 which consists of the diamond on the porous metal 20 which consists of nickel by the electroplating method (electrodeposition method) is demonstrated. .

  First, in order to remove oil and fat on the metal surface of the porous metal 20 to be plated, degreasing is performed, and then water washing is performed. Then, in order to remove the oxide layer on the metal surface of the porous metal 20, acid treatment is performed, and then washed with water.

  Next, a plating solution 52 containing nickel sulfate, nickel chloride, and boric acid is stored in the electrodeposition tank 51 of the porous structure manufacturing apparatus 50 shown in FIG. Then, diamond abrasive grains 31 having an average particle diameter of 3 μm are mixed in the plating solution 52. Here, an additive may be added to adjust the state of the diamond abrasive grains 31 in the liquid.

  Next, the porous metal 20 to be plated and the electrolytic metal 55 made of nickel are immersed in the plating solution 52, the porous metal 20 is connected to the negative terminal of the energizing means 60, and the electrolytic metal 55 is energized by the energizing means 60. Connect to the positive terminal.

  A voltage is applied between the porous metal 20 and the electrolytic metal 55 from the energizing means 60 to deposit the abrasive grains 31 mixed in the plating solution 52 on the surface of the porous metal 20, and the dissolved electrolytic metal 55 The surface of the porous metal 20 is plated, and the abrasive grain layer 30 incorporating the abrasive grains 31 is grown.

  Then, the abrasive grain layer 30 is formed to a thickness of about 16 to 17 μm, and the plated porous metal 200 is taken out from the plating solution 52, washed with water, and dried.

  As shown in FIG. 8A, the abrasive grain layer 30 is formed with a uniform thickness on the surface of the skeleton of the plated porous metal 200 taken out from the plating solution 52. At this time, the abrasive grains 31 protrude from the surface 110 in the region D1 of the surface 110 defining the outer shape of the plated porous metal 200 (a virtual surface formed by circumscribing a plurality of skeletons). . 8A shows 20a, 20b, 20c, which are skeletons parallel to the surface 110 (see the X part in FIG. 4), among the skeletons of the porous metal 200 plated with the abrasive grain layer 30. Only 20d, 20e, 20f... Are schematically shown.

  Then, the surface 110 (see FIG. 8A) of the porous metal 200 is shaved, and as shown in FIG. 8B, a part of the abrasive grain layer 30 is removed to form the surface 11a. In this way, the porous structure 10 is manufactured. The thickness removed by shaving is smaller than the thickness of the abrasive layer 30. At this time, the abrasive grains 31 protrude from the surface 11a in the region D2 of the surface 11a. Further, the surface 110 of the plated porous metal 200 is scraped using a grindstone, a sandpaper, or a porous structure already manufactured according to the present invention.

In the porous structure 10 manufactured as described above, the area (region D2) of the abrasive grain layer 30 on the surface 11a after the surface 110 is shaved is the state before the surface 110 is shaved (FIG. 8A )) Larger than the area (region D1) of the abrasive grain layer 30 on the surface 110. By scraping the surface of the porous metal on which the abrasive layer is formed, the number of abrasive grains in contact with the workpiece can be increased, so that the amount of grinding or polishing of the workpiece can be increased. .
Further, in the Y portion perpendicular to the work surface (see FIG. 4), the polishing amount of the workpiece is substantially the same before and after cutting, and in the X portion (see FIG. 4) parallel to the work surface, the workpiece is ground before cutting. The amount of polishing of the workpiece can be increased later. Therefore, in the entire porous structure, the amount of grinding or polishing of the workpiece can be increased after cutting.

  In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible.

  The porous structure 10 of FIG. 8B of the above embodiment can be further shaved. FIG. 8C shows a state in which the surface 11b is newly formed by further cutting the porous structure 10 to cut not only the abrasive grain layer 30 but also the skeleton 20a. Here, the surface 11b defining the outer shape of the porous structure 10 is formed by the skeletons 20c, 20d, 20e, and 20f. The skeletons 20c, 20d, 20e, and 20f are skeletons that did not form a surface that defines the outer diameter of the plated porous metal 200 before the surface 110 of the plated porous metal 200 was shaved. is there. At this time, the abrasive grains 31 protrude in the region D3 of the surface 11b. Since the area (region D3) of the abrasive layer 30 on the surface 11b in FIG. 8C is larger than the area (region D1) of the abrasive layer 30 on the surface 110 in FIG. 8A, the amount of grinding of the workpiece Alternatively, the polishing amount can be further increased.

  Moreover, in the said embodiment, although the porous structure 10 was formed in the rectangular parallelepiped shape, it is not limited to this, For example, you may form in the sheet form or the ring shape.

  Moreover, in the said embodiment, although the abrasive grain layer 30 was formed with about 16-17 micrometers thicker than the average particle diameter of 3 micrometers of the abrasive grain 31, it is not limited to this. As shown in FIG. 9, the abrasive grain layer 30 may be formed with about 1.5 μm which is 1/2 of the average grain diameter of 3 μm of the abrasive grain 31. It suffices that the thickness 31 does not fall off from the abrasive layer 30. In this case, since the abrasive layer 30 is sufficiently thin with respect to the thickness of the skeleton of the porous metal 20, the porous structure 10 can be easily deformed into a desired shape.

  Moreover, in the said embodiment, although the abrasive grain 31 was formed with the average particle diameter of 3 micrometers, it is not limited to this, Abrasive grain of various magnitude | sizes can be used. For example, when forming a porous structure with a small amount of polishing of a workpiece, abrasive grains having a small average particle diameter (for example, an average particle diameter of about 0.1 μm) can be used. Further, if the porous metal open pores are not blocked, abrasive grains having a large average particle diameter can be used. For example, when the pore diameter of the porous metal open pores is large (for example, the pore diameter is 2 mm), Abrasive grains having a large average particle diameter (for example, an average particle diameter of about 800 μm) can be used. By using abrasive grains having a large average particle diameter, the amount of grinding or polishing of the workpiece can be further increased.

  Moreover, in the said embodiment, although the abrasive grain layer 30 was formed by the electroplating method, it is not limited to this, You may be formed by the electroless-plating method. Specifically, first, degreasing is performed in order to remove oil and fat on the metal surface of the porous metal 20 to be plated, and then water washing is performed. Then, in order to remove the oxide layer on the metal surface of the porous metal 20, acid treatment is performed, and then washed with water. Next, a plating solution containing nickel sulfate and sodium hypophosphite is stored in the plating tank, and abrasive grains 31 taken into the plating coating are mixed in the plating solution. Then, the porous metal 20 is immersed in the plating solution. The abrasive grains 31 mixed in the plating solution are deposited on the surface of the porous metal 20, and the surface of the porous metal 20 is plated to grow the abrasive grain layer 30 incorporating the abrasive grains 31. Thereafter, the abrasive grain layer 30 is formed to a desired thickness, for example, about 15 μm, and the porous metal 20 on which the abrasive grain layer 30 is formed is taken out of the plating solution, washed with water, and dried. The porous structure 10 is manufactured as described above. Thereby, the porous structure 10 can be manufactured more easily without using electricity.

  Moreover, in the said embodiment, although the porous metal 20 was formed by giving electroconductivity after giving electroconductivity to a foam etc., it is not limited to it, For example, it foams to a base metal. Those formed by adding an agent can also be used. In this case, first, the base metal is melted, and an active metal such as calcium or strontium is added and stirred to thicken the base metal. Then, titanium hydride or the like is added to the molten metal as a foaming agent, and the titanium hydride is decomposed by heating and stirring to generate molecular or atomic hydrogen in the molten metal. Hydrogen gas bubbles are formed, which are gradually grown and dispersed in the metal. Thereafter, a metal porous body having a three-dimensional network skeleton formed by cooling and solidifying can also be used.

  For the porous metal 20, for example, a paint in which metal powder or alloy powder is suspended and dispersed in water or an organic solvent is produced, and this paint is impregnated and applied to a porous material such as a foamed resin having communication holes. After forming a film made of metal powder or alloy powder, it is formed by burning and extinguishing at a temperature below the melting point of the metal or alloy impregnated with porous material and sintering the metal powder or alloy powder. You can also.

DESCRIPTION OF SYMBOLS 10 Porous structure 10a Skeleton 20 Porous metal 20a, 20b, 20c, 20d, 20e, 20f Skeleton 21 Open pore 30 Abrasive grain layer 30a Base material 31 Abrasive grain 31a Abrasive grain 31b Abrasive grain 50 Porous structure manufacturing apparatus 51 Electrodeposition bath 52 Plating solution 55 Electrolytic metal 101 Side surface 102 Upper surface 200 Plated porous metal

Claims (10)

A method for producing a porous structure composed of a porous metal having an open pore structure,
A first step of forming an abrasive layer containing abrasive grains on the surface of the porous metal skeleton;
The surface of the porous metal having the abrasive layer formed on the surface of the skeleton is scraped to remove a part of the abrasive layer, thereby increasing the area of the abrasive layer on the scraped surface. Process,
A method for producing a porous structure, comprising:   2. In the second step, the surface of the porous metal having an abrasive layer formed on the surface of the skeleton is shaved, and a part of the skeleton of the porous metal is further removed. The manufacturing method of the porous structure as described in 2.   The method for producing a porous structure according to claim 1 or 2, wherein the first step is an electroplating step.   The porous metal is formed of one metal selected from the group consisting of Ni, Cu, Zn, Al, Au, Ag, Fe, and Co or an alloy thereof or an alloy containing two or more metals. The method for producing a porous structure according to any one of claims 1 to 3.   The porous structure according to any one of claims 1 to 4, wherein the abrasive grains are formed by superabrasive grains selected from the group consisting of diamond and cubic boron nitride (CBN). Production method. The abrasive is an oxide selected from the group consisting of alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), ceria (CeO ₂ ), titania (TiO ₂ ), and magnesia (MgO). The method for producing a porous structure according to any one of claims 1 to 4, wherein the porous structure is formed by: The porous structure according to any one of claims 1 to 4, wherein the abrasive grains are made of a carbide selected from the group consisting of silicon carbide (SiC) and boron carbide (B ₄ C). Body manufacturing method. The porous material according to any one of claims 1 to 4, wherein the abrasive grains are formed of a nitride selected from the group consisting of aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ). Method for manufacturing the structure. The abrasive grain is a composite of two or more oxides selected from the group consisting of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), titania (TiO ₂ ), and magnesia (MgO). It forms with an oxide, The manufacturing method of the porous structure of any one of the Claims 1 thru | or 4 characterized by the above-mentioned. A porous structure composed of a porous metal having an open pore structure,
Forming an abrasive layer containing abrasive grains on the surface of the porous metal skeleton;
Manufactured by increasing the area of the abrasive layer on the scraped surface by scraping the surface of the porous metal on which the abrasive layer is formed on the surface of the skeleton,
A porous structure characterized by that.