A solid composition contains a first material and a powder and satisfies requirements 1 and 2. Requirement 1: |dA(T)/dT| satisfies 10 ppm/° C. or more at least at −200° C. to 1,200° C. A is (an a-axis lattice constant of a crystal in the powder)/(a c-axis lattice constant of a crystal in the powder), obtained from X-ray diffractometry of the powder. Requirement 2: C is 0.04 or more. C is (a log differential pore volume when a pore diameter of the solid composition is B in a pore distribution curve of the solid composition)/(a log differential pore volume corresponding to a maximum peak intensity in the pore distribution curve of the solid composition). B is (a pore diameter giving a maximum peak intensity in the pore distribution curve of the solid composition)/2. The pore distribution curve of the solid composition shows a relationship between the pore diameter and the log differential pore volume.

A solid composition contains a first material and a powder and satisfies requirements 1 and 2. Requirement 1: |dA(T)/dT| satisfies 10 ppm/° C. or more at least at −200° C. to 1,200° C. A is (an a-axis lattice constant of a crystal in the powder)/(a c-axis lattice constant of a crystal in the powder), obtained from X-ray diffractometry of the powder. Requirement 2: C is 0.04 or more. C is (a log differential pore volume when a pore diameter of the solid composition is B in a pore distribution curve of the solid composition)/(a log differential pore volume corresponding to a maximum peak intensity in the pore distribution curve of the solid composition). B is (a pore diameter giving a maximum peak intensity in the pore distribution curve of the solid composition)/2. The pore distribution curve of the solid composition shows a relationship between the pore diameter and the log differential pore volume.

A thermally-insulating composite material with co-shrinkage in the form of an insulating material formed by the inclusion of microballoons in a matrix material such that the microballoons and the matrix material exhibit co-shrinkage upon processing. The thermally-insulating composite material can be formed by a variety of microballoon-matrix material combinations such as polymer microballoons in a preceramic matrix material. The matrix materials generally contain fine rigid fillers.

Provided herein are methods for making a freeze-cast material having a internal structure, the methods comprising steps of: determining the internal structure of the material, the internal structure having a plurality of pores, wherein: each of the plurality of pores has directionality; and the step of determining comprises: selecting a temperature gradient and a freezing front velocity to obtain the determined internal structure based on the selected temperature gradient and the selected freezing front velocity; directionally freezing a liquid formulation to form a frozen solid, the step of directionally freezing comprising: controlling the temperature gradient and the freezing front velocity to match the selected temperature gradient and the selected freezing front velocity during directionally freezing; wherein the liquid formulation comprises at least one solvent and at least one dispersed species; and subliming the at least one solvent out of the frozen solid to form the material.

A method to form a machinable ceramic matrix composite comprises forming a porous ceramic multilayer on a surface of a fiber preform. In one example, the porous ceramic multilayer comprises a gradient in porosity in a direction normal to the surface. In another example, the porous ceramic multilayer includes low-wettability particles having a high contact angle with molten silicon, where an amount of the low-wettability particles in the porous ceramic multilayer varies in a direction normal to the surface. After forming the porous ceramic multilayer, the fiber preform is infiltrated with a melt, and the melt is cooled to form a ceramic matrix composite with a surface coating thereon. An outer portion of the surface coating is more readily machinable than an inner portion of the surface coating. The outer portion of the surface coating is machined to form a ceramic matrix composite having a machined surface with a predetermined surface finish and/or dimensional tolerance.

A method to form a machinable ceramic matrix composite comprises forming a porous ceramic multilayer on a surface of a fiber preform. In one example, the porous ceramic multilayer comprises a gradient in porosity in a direction normal to the surface. In another example, the porous ceramic multilayer includes low-wettability particles having a high contact angle with molten silicon, where an amount of the low-wettability particles in the porous ceramic multilayer varies in a direction normal to the surface. After forming the porous ceramic multilayer, the fiber preform is infiltrated with a melt, and the melt is cooled to form a ceramic matrix composite with a surface coating thereon. An outer portion of the surface coating is more readily machinable than an inner portion of the surface coating. The outer portion of the surface coating is machined to form a ceramic matrix composite having a machined surface with a predetermined surface finish and/or dimensional tolerance.

Provided is an exhaust gas purifying filter used with a HC purifying catalyst supported thereon. Numerous pores are formed in partitions of the exhaust gas purifying filter. In a cross-section of the partition, pores are open at a passage surface, having an open end of which the opening diameter is 50 μm or larger. In the cross-section of the partitions, the partitions include a narrow part where a pore diameter is 5 μm or more and the pore diameter becomes a minimum in a region. In the cross-section of the partitions, the region is positioned between a pair of virtual lines L.sub.1 and L.sub.2 extending from opposing sides of the opening end to a passage surface positioned opposite to the opening end along the wall thickness direction X, Z. The pore diameter at the narrow part is 6% or more and less than or equal to 20% of the opening diameter.

Provided is an exhaust gas purifying filter used with a HC purifying catalyst supported thereon. Numerous pores are formed in partitions of the exhaust gas purifying filter. In a cross-section of the partition, pores are open at a passage surface, having an open end of which the opening diameter is 50 μm or larger. In the cross-section of the partitions, the partitions include a narrow part where a pore diameter is 5 μm or more and the pore diameter becomes a minimum in a region. In the cross-section of the partitions, the region is positioned between a pair of virtual lines L.sub.1 and L.sub.2 extending from opposing sides of the opening end to a passage surface positioned opposite to the opening end along the wall thickness direction X, Z. The pore diameter at the narrow part is 6% or more and less than or equal to 20% of the opening diameter.

Provided herein are methods for making a freeze-cast material having a internal structure, the methods comprising steps of: determining the internal structure of the material, the internal structure having a plurality of pores, wherein: each of the plurality of pores has directionality; and the step of determining comprises: selecting a temperature gradient and a freezing front velocity to obtain the determined internal structure based on the selected temperature gradient and the selected freezing front velocity; directionally freezing a liquid formulation to form a frozen solid, the step of directionally freezing comprising: controlling the temperature gradient and the freezing front velocity to match the selected temperature gradient and the selected freezing front velocity during directionally freezing; wherein the liquid formulation comprises at least one solvent and at least one dispersed species; and subliming the at least one solvent out of the frozen solid to form the material.

Methods of manufacturing a ceramic honeycomb body having a honeycomb structure with a matrix of intersecting walls, and a skin disposed on an outer peripheral portion of the matrix where the skin has a first average porosity and the interior portion of the matrix has a second average porosity that is greater than the first average porosity. The methods include coating at least the skin with a fluid formulation containing a sintering aid and subsequently firing the honeycomb structure. In certain embodiments, a glass layer is formed in the skin or in regions of the walls directly adjacent to the skin. In certain embodiments, the coating is applied to a green honeycomb structure, and in other embodiments the coating is applied to a ceramic honeycomb structure. Other honeycomb bodies and methods are described.