A composition having nanoparticles of a refractory-metal carbide or refractory-metal nitride and a carbonaceous matrix. The composition is not in the form of a powder. A composition comprising a metal component and an organic component. The metal component is nanoparticles or particles of a refractory metal or a refractory-metal compound capable of decomposing into refractory metal nanoparticles. The organic component is an organic compound having a char yield of at least 60% by weight or a thermoset made from the organic compound. A method of combining particles of a refractory metal or a refractory-metal compound capable of reacting or decomposing into refractory-metal nanoparticles with an organic compound having a char yield of at least 60% by weight to form a precursor mixture.

This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

A composition having nanoparticles of a boron carbide and a carbonaceous matrix. The composition is not in the form of a powder. A composition comprising boron and an organic component. The organic component is an organic compound having a char yield of at least 60% by weight or a thermoset made from the organic compound. A method of combining boron and an organic compound having a char yield of at least 60% by weight, and heating to form boron carbide or boron nitride nanoparticles.

The present invention relates to a method of manufacturing a ceramic article (3) from a metal or metal matrix composite preform (1) provided by 3D-printing or by 3D-weaving. The preform (1) is placed in a heating chamber (2), and a predetermined time-temperature profile is applied in order to controllably react the preform (1) with a gas introduced into the heating chamber (2). The metal, the gas and the time-temperature profile are chosen so as to induce a metal-gas reaction resulting in at least a part of the preform (1) transforming into a ceramic. Preferred embodiments of the invention comprises a first oxidation stage involving a metal-gas reaction in order to form a supporting oxide layer (5) at the surface of the metal, followed by a second stage in which the heating chamber (2) is heated to a temperature above the melting point of the metal to increase the kinetics of the chemical reaction. The invention also relates to a number of advantageous uses of a ceramic article manufactured as described.

A porous ceramic composition having improved thermal stability is comprised of ceramic grains bonded together by grain boundary phase comprised of silica, yttrium and oxygen wherein the amount of alkali metals, alkaline earth metals and other transition metals not including rare earth metals is at most 2% by weight of the grain boundary phase.

Color unevenness generated on a surface of a silicon nitride substrate is reduced. A silicon nitride substrate formed by nitriding silicon containing in a sheet-shaped green body includes a first surface and a second surface opposite to the first surface. In this case, when color difference between a center and an edge of at least one surface of the first surface and the second surface is expressed to be E*ab, a relation E*ab1.5 is established.