Theory and application of Sinter-Crystallization

The sinter-crystallization of glass powders or grains is an alternative technique for manufacture of glass-ceramics. This method is developing dynamically and gives possibility to extend the application range of these advanced materials in different fields of medicine, electronics, military industry, building industry or vitrification of nuclear and industrial wastes.
During sinter-crystallization the densification and the phase formation occur simultaneously and take place in the same temperature range. As a result, the information for the relationship between these two processes is fundamental for the understanding and the control of synthesis of these materials. However, up to now, these two processes are studied separately and different opinions for the correct selection of parent glass and suitable production cycle exist; a general theory, which successfully explains the different types of sinter-crystallization yet is not developed.
The main aim of this project is to create a common theory, explaining the various cases of sinter-crystallization, which is based on the crystallization ability of parent glasses and on the size of used fraction.

This can simplify the future research of this type of glass-ceramics and might contribute for the improvement of their properties.
In the frame of the project, different simultaneous in-situ experiments for a parallel evaluation of the sintering and the crystallization with suitable model glasses are planned, as well as complex examination of the structure of the obtained samples. Together with techniques, such as SEM, DTA and high temperature XRD, in the project will be used unique for Bulgaria methods as contactless optical dilatometry, 3D computed tomography and gas pycnometry. The sinter-crystallization will be carried out by conventional heat-treatment and buy using ceramics microwave ovens, which is a prerequisite for improvement of the mechanical properties. Some of the simultaneous experiments will be performed for first time in the world.
In the team of project are included leading European scientists in the field of glass-ceramic and ceramics, as well as experts for each of the used experimental techniques. More than one third of the participants in the project are junior researchers, PhD students and post-doctoral fellows.

Expected results

  • The main part of the studies, related to the present project, is based on experiments with different model of glasses obtained especially for the purposes of the present project.
  • In these studies will be used a combination of different research techniques. Very stimulating are the “in situ” isothermal and non-isothermal evaluations of the sintering and the crystallization shrinkages, which will be performed by optical contactless dilatometer, high-temperature XRD and DTA.
  • Other intriguing research is related to the evaluation of the structure and morphology of the obtained glass-ceramics, which will be examined in details by contemporaneous analysis of results obtained with 3D XRD computed tomography and SEM.
  • New ceramics with enhanced crystallinity, forming crystallization induced porosity during the cooling, will be also investigated.
  • The obtained experimental results will be used to develop theoretical approach, which can distinguish the three main cases of the sinter-crystallization, as well as, to create a relationship between the sintering ability and the tendency to form crystallization induced porosity. The model will be based on the hypothesis for formation of hard shell, which thickness depends on the crystallization ability.