Mold for glass forming and methods for forming glass using a mold

A mold for glass forming, wherein the mold comprises a ceramic material comprising from 50 to 80% by weight of aluminum nitride and from 20 to 50% by weight of hexagonal boron nitride, based on the total weight of the ceramic material,

• and wherein the mean grain size of the aluminum nitride in the ceramic material is from 1.0 to 5.0 μm,
• and wherein the density of the ceramic material is at least 85% of the theoretical density of the ceramic material,
• and wherein the ceramic material further comprises boron oxide (B2O3) in an amount of up to 2% by weight, based on the total weight of the ceramic material,
• and wherein the ceramic material has a hardness of from 50 to 300 HBW 2.5/62.5, wherein the hardness is measured by the Brinell method according to DIN EN ISO 6506-1 (2013),
• and wherein the mold has a contact surface having a surface roughness Ra of at least 0.2 μm and at most 2.0 μm,
• and wherein the mean grain size of the aluminum nitride in the ceramic material is determined by measuring the grain size of aluminum nitride on scanning electron microscopy (SEM) micrographs with a magnification of 10,000× of polished samples, wherein the longest diameter of each individual aluminum nitride grain is measured and the mean grain size is calculated as the average value of the longest diameter of 50 individual aluminum nitride grains,
• and wherein the theoretical density of the ceramic material is calculated by the density of the pure aluminum nitride, which is 3.26 g/cm3, and the density of the pure hexagonal boron nitride, which is 2.25 g/cm3, and the respective fractions of aluminum nitride and hexagonal boron nitride in the ceramic material,
• and wherein the surface roughness of the contact surface is measured according to ISO 4287 (1997).