One aspect of the heat insulator of the present invention includes a porous sintered body having a porosity of 70 vol % or more and less than 91 vol %, and pores having a pore size of 0.8 μm or more and less than 10 μm occupy 10 vol % or more and 70 vol % or less of the total pore volume, while pores having a pore size of 0.01 μm or more and less than 0.8 μm occupy 5 vol % or more and 30 vol % or less of the total pore volume. The porous sintered body is formed from an MgAl.sub.2O.sub.4 (spinel) raw material and fibers formed of an inorganic material, the heat conductivity of the heat insulator at 1000° C. or more and 1500° C. or less is 0.40 W/(m.Math.K) or less, and the weight ratio of Si relative to Mg in the porous sintered body is 0.15 or less.

One aspect of the heat insulator of the present invention includes a porous sintered body having a porosity of 70 vol % or more and less than 91 vol %, and pores having a pore size of 0.8 μm or more and less than 10 μm occupy 10 vol % or more and 70 vol % or less of the total pore volume, while pores having a pore size of 0.01 μm or more and less than 0.8 μm occupy 5 vol % or more and 30 vol % or less of the total pore volume. The porous sintered body is formed from an MgAl.sub.2O.sub.4 (spinel) raw material and fibers formed of an inorganic material, the heat conductivity of the heat insulator at 1000° C. or more and 1500° C. or less is 0.40 W/(m.Math.K) or less, and the weight ratio of Si relative to Mg in the porous sintered body is 0.15 or less.

A coated member includes a heat-shielding coating layer made of a zirconia-dispersed silicate in which ytterbia-stabilized zirconia is precipitated as a dispersed phase in a matrix phase which is any one of a rare earth disilicate, a rare earth monosilicate, and a mixed phase of the rare earth disilicate and the rare earth monosilicate. The rare earth disilicate is a (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd. The rare earth monosilicate is Y.sub.2SiO.sub.5, [Ln.sub.1].sub.2SiO.sub.5, a (Y.sub.1-b[Ln.sub.1]b).sub.2SiO.sub.5 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-d[Ln.sub.2].sub.d).sub.2SiO.sub.5 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd.

A coated member includes a heat-shielding coating layer made of a zirconia-dispersed silicate in which ytterbia-stabilized zirconia is precipitated as a dispersed phase in a matrix phase which is any one of a rare earth disilicate, a rare earth monosilicate, and a mixed phase of the rare earth disilicate and the rare earth monosilicate. The rare earth disilicate is a (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd. The rare earth monosilicate is Y.sub.2SiO.sub.5, [Ln.sub.1].sub.2SiO.sub.5, a (Y.sub.1-b[Ln.sub.1]b).sub.2SiO.sub.5 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-d[Ln.sub.2].sub.d).sub.2SiO.sub.5 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd.

A method that includes introducing a suspension comprising a coating material and a carrier into a heated plume of a thermal spray device. The coating material may include silicon or a silicon alloy. The method further includes directing the coating material using the heated plume toward a substrate that includes a ceramic or a ceramic matrix composite and depositing the coating material to form a bond coat directly on the substrate such that the bond coat defines a porosity of less than about 3 percent by volume.

A method that includes introducing a suspension comprising a coating material and a carrier into a heated plume of a thermal spray device. The coating material may include silicon or a silicon alloy. The method further includes directing the coating material using the heated plume toward a substrate that includes a ceramic or a ceramic matrix composite and depositing the coating material to form a bond coat directly on the substrate such that the bond coat defines a porosity of less than about 3 percent by volume.

A ceramic component is provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and a boron-doped refractory compound, such as about 0.001% to about 85% by volume of the boron-doped refractory compound (e.g., about 1% to about 60% by volume of the boron-doped refractory compound). A coated component is also provided that includes a CMC component defining a surface; a bond coating directly on the surface of the CMC component, with the bond coating comprises a silicon-containing material and a boron-doped refractory compound (e.g., about 0.1% to about 25% of the boron-doped refractory compound); a thermally grown oxide layer on the bond coating; and an environmental barrier coating on the thermally grown oxide layer.

A ceramic component is provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and a boron-doped refractory compound, such as about 0.001% to about 85% by volume of the boron-doped refractory compound (e.g., about 1% to about 60% by volume of the boron-doped refractory compound). A coated component is also provided that includes a CMC component defining a surface; a bond coating directly on the surface of the CMC component, with the bond coating comprises a silicon-containing material and a boron-doped refractory compound (e.g., about 0.1% to about 25% of the boron-doped refractory compound); a thermally grown oxide layer on the bond coating; and an environmental barrier coating on the thermally grown oxide layer.

A coating method includes depositing a slurry including a coarsely particulate ceramic and a finely particulate ceramic on a base material configured with an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material; forming a bond coating by performing a heat treatment on the base material on which the slurry has been deposited; and forming a top coating by thermally spraying a ceramic onto the bond coating. The oxide-based ceramics matrix composite is an alumina silica type oxide-based ceramics matrix composite. The coarsely particulate ceramic and the finely particulate ceramic are alumina-based powder.

A coating method includes depositing a slurry including a coarsely particulate ceramic and a finely particulate ceramic on a base material configured with an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material; forming a bond coating by performing a heat treatment on the base material on which the slurry has been deposited; and forming a top coating by thermally spraying a ceramic onto the bond coating. The oxide-based ceramics matrix composite is an alumina silica type oxide-based ceramics matrix composite. The coarsely particulate ceramic and the finely particulate ceramic are alumina-based powder.