Methods for producing wavelength converters are described. The methods include sintering a mixture consisting essentially of first particles and second particles to form a sintered article. In embodiments the first particles consist essentially of particles of -SiAlON or precursors thereof, and the second particles consist essentially one or more sintering aids or precursors thereof. In embodiments the sintered article has a density that is greater than or equal to about 90% of a theoretical bulk density of the mixture, and is configured to convert primary light incident thereon to secondary light, wherein the secondary light exhibits a peak with a full width half maximum of greater than 0 to about 60 nanometers (nm) within a wavelength range of about 495 nm to about 600 nm.

A sintered material includes a first material and a second material, the first material being partially stabilized ZrO.sub.2 having a crystal grain boundary or crystal grain in which 5 to 90 volume % of Al.sub.2O.sub.3 is dispersed with respect to a whole of the first material, the second material including at least one of SiAlON, silicon nitride and titanium nitride, the sintered material including 1 to 50 volume % of the first material.

To provide a sintered material having excellent oxidation resistance, as well as excellent abrasion resistance and chipping resistance. A sintered material containing a first compound formed of Ti, Al, Si, O, and N is provided.

A sintered molded article includes a ceramic of /-sialon having a grain boundary phase, the grain boundary phase containing at least one hard material formed in situ as an additional phase. A method for the production of the sintered molded article uses at least the following compounds as a starting material: Si.sub.3N.sub.4, AlN, and, if applicable, Al.sub.2O.sub.3, at least one oxide of the rare earths, and at least one oxide of the element titanium.

A SiAlON composite includes a SiAlON phase including -SiAlON phase, -SiAlON phase and grain boundary phase. The SiAlON composite is prepared from a starting powder mixture including a silicon nitride powder and at least one powder providing aluminum, oxygen, nitrogen, yttrium (Y) and erbium (Er) to the SiAlON composite. The SiAlON composite contains the SiAlON phase of at least 90 vol %, z-value of the -SiAlON phase ranges between 0.27 and 0.36 and thermal diffusivity of the SiAlON composite is equal to or greater than 2.4 (mm.sup.2/sec) and equal to or less than 5.2 (mm.sup.2/sec).

A method for producing a composite of cubic boron nitride dispersed in a SiAlON ceramic. This method involves mixing silicon nitride nanoparticles, aluminum nitride nanoparticles, silica nanoparticles, calcium oxide nanoparticles, and cubic boron nitride microparticles to produce a mixture. The cubic boron nitride may be coated with nickel. The mixture is sintered to produce the composite, and this sintering may involve spark plasma sintering and/or sintering at a relatively low temperature. The composite may comprise a mixture of Ca--SiAlON and -SiAlON ceramic reinforced by boron nitride in either or both cubic and hexagonal phases.

To provide a sintered material having excellent oxidation resistance, as well as excellent abrasion resistance and chipping resistance. A sintered material containing a first compound formed of Ti, Al, Si, O, and N is provided.

A mullite-containing sintered body according to the present invention contains mullite and at least one selected from the group consisting of silicon nitride, silicon oxynitride, and sialon. It is preferable that the mullite-containing sintered body have a thermal expansion coefficient of less than 4.3 ppm/ C. at 40 C. to 400 C., an open porosity of 0.5% or less, and an average grain size of 1.5 m or less.