A mullite sintered body according to the present invention has an impurity element content of 1% by mass or less and contains sintered mullite grains having an average grain size of 8 μm or less. When a surface of the mullite sintered body is finished by polishing, pores in the surface have an average largest pore length of 0.4 μm or less. The surface preferably has a center line average surface roughness (Ra) of 3 nm or less. The surface preferably has a maximum peak height (Rp) of 30 nm or less. The number of pores in the surface is preferably 10 or less per unit area of 4 μm×4 μm.

A mullite sintered body according to the present invention has an impurity element content of 1% by mass or less and contains sintered mullite grains having an average grain size of 8 μm or less. When a surface of the mullite sintered body is finished by polishing, pores in the surface have an average largest pore length of 0.4 μm or less. The surface preferably has a center line average surface roughness (Ra) of 3 nm or less. The surface preferably has a maximum peak height (Rp) of 30 nm or less. The number of pores in the surface is preferably 10 or less per unit area of 4 μm×4 μm.

A joined body 10 includes a ceramic body 12, a metal member 14, and a joint portion 15 that joins the ceramic body 12 and the metal member 14 together. The joint portion 15 includes a first joint layer 16 joined to the ceramic body 12 and a second joint layer 18 joined to the metal member 14. The first joint layer 16 is disposed on the ceramic body 12 side and contains an alloy that contains Fe and Cr as main components, and a compound having a thermal expansion coefficient of 4.0×10.sup.−6 (/° C.) or lower is dispersed in the first joint layer 16. The second joint layer 18 is disposed on the metal member 14 side, contains an alloy that contains Fe and Cr as main components, and has a larger thermal expansion coefficient than the first joint layer 16.

A method of preparing a substrate having a wetting surface, including confirming the presence of an open, interconnected pore network in a ceramic substrate to be wetted with a first metal, filling the open, interconnected pore network with a second metal,

exuding the second metal to coat the surface of the substrate, and wetting the substrate with the first metal. The ceramic substrate is not decomposed by the first metal and the ceramic substrate is not decomposed by the second metal.

A ceramic structure 10 includes a heater electrode 14 within a disk-shaped AlN ceramic substrate 12. The heater electrode 14 contains a metal filler in the main component WC. The metal filler (such as Ru or RuAl) has a lower resistivity and a higher thermal expansion coefficient than AlN. An absolute value of a difference |ΔCTE| between a thermal expansion coefficient of the AlN ceramic substrate 12 and a thermal expansion coefficient of the heater electrode 14 at a temperature in the range of 40° C. to 1000° C. is 0.35 ppm/° C. or less.

A heat conduction member includes: a cylindrical ceramic body, a metal pipe on the outer periphery side of the cylindrical ceramic body, and an intermediate member held between the cylindrical ceramic body and the metal pipe. The cylindrical ceramic body has passages passing through from one end face to the other end face and allowing the first fluid to flow therethrough. The intermediate member is made of material having at least a part having a Young's modulus of 150 Gpa or less. The first fluid is allowed to flow through the inside of the cylindrical ceramic body while the second fluid having lower temperature than that of the first fluid is allowed to flow on the outer peripheral face side of the metal pipe to perform heat exchange between the first fluid and the second fluid.

A ceramic-metal substrate in which the ceramic substrate has a low content of an amorphous phase. The ceramic-metal substrate includes a ceramic substrate and on at least one side of the ceramic substrate a metallization. The ceramic-metal substrate has at least one scribing line, at least one cutting edge, or both at least one scribing line and at least one cutting edge. Amorphous phases extend parallel to the scribing line and/or the cutting edge in a width of at most 100 μm or of at least 0.50 μm.

There are provide a metal/ceramic bonding substrate wherein the bonding strength of an aluminum plate bonded directly to a ceramic substrate is higher than that of conventional metal/ceramic bonding substrates, and a method for producing the same. The metal/ceramic bonding substrate is produced by a method including the steps of: arranging a ceramic substrate 10 in a mold 20; putting the mold 20 in a furnace; lowering an oxygen concentration to 25 ppm or less and a dew point to −45° C. or lower in the furnace; injecting a molten metal of aluminum into the mold 20 so as to allow the molten metal to contact the surface of the ceramic substrate 10; and cooling and solidifying the molten metal to form a metal plate 14 for circuit pattern of aluminum on one side of the ceramic substrate 10 to bond one side of the metal plate 14 for circuit pattern directly to the ceramic substrate 10, while forming a metal base plate 12 of aluminum on the other side of the ceramic substrate 10 to bond the metal base plate 12 directly to the ceramic substrate 10.

To prevent braze stain and improve solder bondability of a semiconductor chip without deteriorating bondability between a metal plate and a ceramic substrate: a producing method of a power-module substrate by braze-bonding a metal plate which is blanked by press working on a metal raw-plate on one surface of a ceramic substrate: in the metal plate, a height of burrs is 0.021 mm or smaller, a thickness of a fracture surface is 0.068 mm or larger; the metal plate is stacked on the ceramic substrate so as to stack a surface thereof on a side at which the burrs are generated is in contact with the one surface of the ceramic substrate and brazed.

To prevent braze stain and improve solder bondability of a semiconductor chip without deteriorating bondability between a metal plate and a ceramic substrate: a producing method of a power-module substrate by braze-bonding a metal plate which is blanked by press working on a metal raw-plate on one surface of a ceramic substrate: in the metal plate, a height of burrs is 0.021 mm or smaller, a thickness of a fracture surface is 0.068 mm or larger; the metal plate is stacked on the ceramic substrate so as to stack a surface thereof on a side at which the burrs are generated is in contact with the one surface of the ceramic substrate and brazed.