Investigation of production possibilities of machinable glass-ceramic materials from basalts

INVESTIGATION OF PRODUCTION POSSIBILITIES OF MACHINABLE GLASS-CERAMIC MATERIALS FROM BASALTS SUMMARY Keywords: Natural rock, basalt, glass, melting, sintering, Glass-ceramic, machinable glass-ceramic, Production of machinable glass-ceramics is provided by heat treatment of glass which obtained after melting and casting process, with controlled nucleation and crystallization. Having proper microstructure and micro hardness value that allows machinability after a suitable nucleation and crystallization heat treatments differs machinable glass-ceramics from other all glass-ceramics. In addition to machinability, machinable glass ceramics also have good mechanical and electrical properties. The aim of this study is that researching possibilities of production of machinable glass-ceramics from natural rocks. To achieve this, three different compositions are prepared by adding MgF2 and K2O to basalt being a volcanic rock to obtain machinability properties. By using this compound, machinable glass-ceramics are produced by melting and sintering methods. These compounds are grinded and mixed for1 hour in ball mill. After grinding process, some of this compound is melted by keeping at 1500°C in Alumina pot for one hour, and then molded into graphite mould. To relieve internal strain occurred during the melting process, casted glass samples are annealed at 600°C for 1 hour. Heat treatment temperatures required to obtain glass-ceramics are determined by analyzing of DTA, and glasses are transformed to glass-ceramics by heating at these temperature. Scanning electron microscope (SEM) is used in order to make micro-structural characterization and XRD is used to analyze phases, micro-hardness test for determining hardness values of the specimens and machinability tests are also applied. In economically production of glass-ceramics from raw materials by sintering methods, compound is sieved from 75 μm sifter and undersize grain is used in production. 200 mm in diameter cylindrical samples are compressed with 100 MPa pressure by using these compounds. Pressed samples is heat treated at 900, 1000 and 1100 ○C to supply transition from glass to glass-ceramics. SEM and XRD analyzes, density, hardness, fracture toughness, water absorption, porosity and machinability tests were performed on the sintered glass-ceramic samples produced. At the end of characterization studies, that is determined Ferroan-phlgopite [K(Mg,Fe+2)3]AlSi3O10(F,OH)2] which provides machinability is crystallized in all melted and sintered samples