Methods for forming ceramic cores are disclosed. A ceramic core formed using the method of the present application includes a silica depletion zone encapsulating an inner zone. The inner zone includes mullite and the silica depletion zone includes alumina. The method includes heat-treating a ceramic body in a non-oxidizing atmospheric condition for an effective temperature and time combination at a pressure less than 10.sup.2 atmosphere to form the silica depletion zone at a surface of the ceramic core.

Methods for forming ceramic cores are disclosed. A ceramic core formed using the method of the present application includes a silica depletion zone encapsulating an inner zone. The inner zone includes mullite and the silica depletion zone includes alumina. The method includes heat-treating a ceramic body in a non-oxidizing atmospheric condition for an effective temperature and time combination at a pressure less than 10.sup.2 atmosphere to form the silica depletion zone at a surface of the ceramic core.

A machined ceramic article having an initial surface defect density and an initial surface roughness is provided. The machined ceramic article is heated to a temperature range between about 1000 C. and about 1800 C. at a ramping rate of about 0.1 C. per minute to about 20 C. per minute. The machined ceramic article is heat-treated in air atmosphere. The machined ceramic article is heat treated at one or more temperatures within the temperature range for a duration of up to about 24 hours. The machined ceramic article is then cooled at the ramping rate, wherein after the heat treatment the machined ceramic article has a reduced surface defect density and a reduced surface roughness.

A machined ceramic article having an initial surface defect density and an initial surface roughness is provided. The machined ceramic article is heated to a temperature range between about 1000 C. and about 1800 C. at a ramping rate of about 0.1 C. per minute to about 20 C. per minute. The machined ceramic article is heat-treated in air atmosphere. The machined ceramic article is heat treated at one or more temperatures within the temperature range for a duration of up to about 24 hours. The machined ceramic article is then cooled at the ramping rate, wherein after the heat treatment the machined ceramic article has a reduced surface defect density and a reduced surface roughness.

Provided is a hexagonal boron nitride powder that can achieve higher thermal conductivity when added as a filler to resin. A plasma treatment method of plasma-treating a hexagonal boron nitride powder under reduced pressure comprises: storing the hexagonal boron nitride powder in a treatment container; supplying a plasma generating gas into the treatment container and maintaining inside of the treatment container at a pressure lower than atmospheric pressure; applying high frequency waves to an electrode installed outside the treatment container while rotating the treatment container about a central axis of the treatment container as a rotation axis in a state in which the rotation axis of the treatment container is inclined with respect to horizontal, to plasma-treat the hexagonal boron nitride powder in the treatment container; and cooling one or both of the treatment container and the electrode during the plasma treatment.

One aspect relates to a composite, including a ceramic body having a first layer surface and a second layer surface and at least one cermet conductor that electrically connects the surfaces. The composite includes a first layer with the first layer surface, a first ceramic, a first hole and a first cermet element in the first hole, a second layer with the second layer surface, a second ceramic, a second hole and a second cermet element in the second hole, and an intermediate layer that is located between the first and the second layer. The intermediate layer includes an intermediate layer ceramic, an intermediate hole and one intermediate cermet element in the intermediate hole. A projection of the cross-section of the first hole and a projection of the cross section of the second hole onto a plane P.sub.x,y are arranged offset to each other.

One aspect relates to a composite, including a ceramic body having a first layer surface and a second layer surface and at least one cermet conductor that electrically connects the surfaces. The composite includes a first layer with the first layer surface, a first ceramic, a first hole and a first cermet element in the first hole, a second layer with the second layer surface, a second ceramic, a second hole and a second cermet element in the second hole, and an intermediate layer that is located between the first and the second layer. The intermediate layer includes an intermediate layer ceramic, an intermediate hole and one intermediate cermet element in the intermediate hole. A projection of the cross-section of the first hole and a projection of the cross section of the second hole onto a plane P.sub.x,y are arranged offset to each other.

A process for marking a surface of a refractory ceramic part, known as the surface to be marked. The part has a microstructure of grains including more than 50% by mass of ZrO.sub.2, bound by a silicate binder phase, and a total porosity of less than 5% by volume. The process involves irradiation of the surface with a laser beam. The beam is emitted by a laser device set to comply with relationship: a.V.sup.2+b.F.sup.2+c.VF+d.V+e. F+f<0, in which: a=10.sup.4. D+2?10.sup.6, b=0.5?10.sup.6. D?150?10.sup.6, c=0.5?10.sup.6. D?300?10.sup.6, d=5?10.sup.3. D?2.5?10.sup.6, e=?5?10.sup.3. D+2.0?10.sup.6, and f=?5?10.sup.9. D+1.8?10.sup.12. V is expressed in mm/second, D is expressed in mm and F is expressed in kHz.

A process for marking a surface of a refractory ceramic part, known as the surface to be marked. The part has a microstructure of grains including more than 50% by mass of ZrO.sub.2, bound by a silicate binder phase, and a total porosity of less than 5% by volume. The process involves irradiation of the surface with a laser beam. The beam is emitted by a laser device set to comply with relationship: a.V.sup.2+b.F.sup.2+c.VF+d.V+e. F+f<0, in which: a=10.sup.4. D+2?10.sup.6, b=0.5?10.sup.6. D?150?10.sup.6, c=0.5?10.sup.6. D?300?10.sup.6, d=5?10.sup.3. D?2.5?10.sup.6, e=?5?10.sup.3. D+2.0?10.sup.6, and f=?5?10.sup.9. D+1.8?10.sup.12. V is expressed in mm/second, D is expressed in mm and F is expressed in kHz.

The present invention relates to an information storage medium and a method for long-term storage of information.