Glass-ceramics process for their preparation and use

Process for the preparation of glass ceramics from a powder mixture which has the formula:

• SiO2—Me2′″O3—Me″O
• wherein Me″ is selected from the group consisting of Ca, Ba, Mg, Zn and mixtures thereof;
• wherein Me′″ is selected from the group consisting of Al, B and mixtures thereof and the weight percent of each of SiO2;
• Me2′″O3;
• and Me″O is:
• SiO2=30-65%;
• Me′″O3=5-less than 20%;
• and
• Me″O=5-40% wherein:
• the starting materials are submitted to grinding, mixing and pressing steps for the production of porcelain stoneware to form a pressed powder mixture, and then firing said pressed powder mixture as follows:
• starting from room temperature said pressed powder mixture is heated by increasing the temperature from room temperature at the rate of 10°-30° C. per minute up to 350° C., to eliminate organic impurities, and thereafter increasing the temperature at a rate of 10°-30° C. per minute up to the Tg;
• maintaining the Tg temperature for 0-120 minutes and thereafter increasing the temperature at a rate of 10°-30° C. per minute up to the Tc where it is maintained for 0-several hours and optionally increasing the temperature at a rate of 10°-30° C. per minute up to the next Tc and up to the final Tc;
• and after the highest Tc has been reached, cooling the glass ceramic down to room temperature.