Optimization of glass-ceramic crystallization based on DTA exotherm analysis.
OBJECTIVE
Crystallization of glass-ceramics is traditionally achieved through a two-stage heat treatment consisting of an isothermal nucleation stage followed by an isothermal growth stage. A method for determining a more efficient heat treatment schedule for a glass-ceramic material using a thermal analysis technique is proposed. The goal of an optimized heat treatment schedule is the production of a glass-ceramic with a desired microstructure (number of crystals per volume) in the shortest amount of time.


METHODS
The proposed method involves differential thermal analysis (DTA) to measure glass crystallization exotherm characteristics which are correlated with the population density of growing crystals, and therefore, to the effectiveness of any prior heat treatment. Traditional thermal processing parameters were investigated and optimized. A method for generating a more efficient heat treatment schedule composed of a series of increasing heating rates was also demonstrated.


RESULTS
The thermal analysis method measured a significant effect upon the number density of crystals generated as a function of several experimental variables. Micrographs from samples crystallized with a more time-efficient heat treatment schedule were shown to have equivalent crystal number densities compared to those crystallized with a more time consuming, traditional schedule.


CONCLUSIONS
This work demonstrated that a rapid thermal analysis method was capable of measuring the relative effectiveness of heat treatment schedules to generate crystalline populations. A novel heat treatment schedule was developed based on progressive adjustment of processing heating rates to generate the maximum crystal population in the shortest amount of time.
Parsell
D E
DE
Department of Dental Biomaterials, University of Florida, College of Dentistry, Gainesville, USA.
Anusavice
K J
KJ
D002516:Ceramics / Q000737:chemistry*; D003198:Computer Simulation; D003460:Crystallization; D003776:Dental Porcelain / Q000737:chemistry; D004055:Differential Thermal Analysis; D005898:Glass / Q000737:chemistry; D006358:Hot Temperature; D013674:Technology, Dental / Q000379:methods*; D013816:Thermodynamics
D003776:Dental Porcelain