Elsevier

Journal of Non-Crystalline Solids

Volume 498, 15 October 2018, Pages 262-271
Journal of Non-Crystalline Solids

Crystallization kinetics of machinable glass ceramics produced from volcanic basalt rock

https://doi.org/10.1016/j.jnoncrysol.2018.06.041Get rights and content

Highlights

  • The possibilities of using basalt for machinable glass-ceramic material production were investigated. > Mica phase crystallization effects on basalt crystallization were observed. > Formation of mica and other phases providing machinable properties, transformations among these phases depending on compositions were investigated.

Abstract

This study investigates the utilization of basalt in manufacturing machinable glass ceramics. As the fluorine and potassium phases, MgF2 and K2O added into basalt are responsible for the machinability of glass ceramics. Three different compositions containing 80%, 85%, and 90% basalt, with K2O and MgF2 as the remainder, were mixed and melted in an alumina crucible at 1500 °C. Glass samples were obtained by casting the melt into a graphite mould. Glass ceramics were prepared through subsequent crystallization heat treatment of the obtained glass. Compositional and mechanical characterizations were carried out via XRD-SEM and hardness/fracture toughness and machinability tests respectively. The effect of change in the obtained phases with basalt composition on the machinability of glass ceramics was investigated. Furthermore, crystallization kinetics of the glasses were investigated by differential thermal analysis (DTA) using the Kissinger kinetic model with several different heating rates. This study reports that basalt can be utilized in the production of machinable glass ceramics only if the basalt ratio is justified. The results showed that good machining performance was observed in low-basalt content conditions (B80), When the basalt content increased (B85 and B90), the machining capability decreased markedly. Furthermore, the crystallization activation energies decreased with increase in basalt content.

Introduction

Glass ceramic materials are crystalline materials produced by controlled heat treatment of appropriate glasses. The crystalline phases depending on the glass system type and residual glass structure make up these materials. Although glass ceramic materials having high hardness and toughness compared to glasses can be used for some applications that are important in terms of mechanical behaviour, they are still inadequate for use in machining and drilling applications. Fluorine has been utilized in glass ceramic systems to improve the aforementioned properties, which has been commercialized under the name of fluormica and used in dental bio-implant applications. These materials are known to have favourable combinations of thermal, mechanical and biomedical properties due to their laminated structure, which enables them to be cut and drilled [1]. The unique microstructure of an interlocking plate provides the desirable machinability, and deformation occurs along with the interfaces between layers while being machined. These laminar structures provide excellent machinability and preserve the body against cracking and mechanical damages [2]. Commercial mica glass ceramics are produced from pure oxides along with certain compositions. For instance, a commercial machinable glass ceramic MACOR® consists of 46% SiO2, 17% MgO, 16% Al2O3, 10% K2O 7% B2O3 and 4% F. A literature analysis on machinable glass ceramics reveals that studies were more focused on the effect of additives on the mechanical, thermal and machining behaviours of these commercial systems.

Basalt is a grey to black, fine-grained volcanic rock that is formed by magmatic movement and subsequent sudden cooling of magma in atmospheric conditions. As it occupies approximately 2.5 million square kilometres on earth, it is cheap and readily available. Basalt, containing SiO2 and Al2O3 as the major oxides with approximately 40–55% and 10–20% respectively, consists of SiO2, Al2O3, Fe2O3, CaO, MgO and other oxides such as K2O and TiO2. It can be used for glass ceramic production via its high silica content. Basalt-based glass ceramics exhibit good abrasion, wear and chemical resistance. They can be used when the transport of material causes mechanical or chemical abrasion as well as mineral wool for heat, noise and fire insulation [3]. Basalt-based glass ceramic products are commercial materials, and diverse glass ceramic phases can be produced from basalt because it has many different oxides. Some modifications and additions in basalt composition provide different glass ceramic phases and systems formation. In terms of machinable glass ceramic phases, basalt has similar elements compared to these phases. For example, Phlogopite is one of the major phases for machinable glass ceramics. Its chemical formula consists of K, Mg, Al, F and Si elements; except for F, the other oxides are in the basalt composition [4, 5, 6].

In the study, the possibility of using basalt for machinable glass ceramic material production was investigated. Basalt, which is used for glass ceramic production, includes high amounts of SiO2 and earth alkaline metal oxides such as CaO and MgO. Diopside is one of the major crystalline phases from studies of basalt-based glass ceramic systems, and there are investigations on the machining capability of glass ceramics containing the Diopside phase. In terms of chemical composition, basaltic rocks can be used for machinable glass ceramic production. As the phases that impart machinability to glass ceramics are mica-based phases, we modified the basalt composition by additives including fluorine to obtain the required phases. Thus, mica phase crystallization effects on basalt crystallization were observed, and the formation of mica and other phases that provide machinable properties and transformations among these phases depending on compositions were investigated in the current study.

Section snippets

Experimental procedure

Basalt rocks obtained from Central Anatolia Konya region of Turkey were used in this study. Basalts crushed by a jaw crusher were milled by a ring miller and then sieved to obtain the particulate size of −75 μm, and the obtained powders were characterized by using Perkin-Elmer 2300 atomic absorption spectroscopy. The chemical composition of the basalt powder is given in Table 1. MgF2 and K2O were mixed with basalt to provide mica phase formation. The compositions, sample codes, and heat

XRD analysis results of the glass ceramic samples

The XRD patterns of glass ceramic samples depending on the basalt content and crystallization temperature can be seen in Fig. 1. Thermal behaviours and phases developed were given in Table 3. Phlogopite (KMg3AlSi3O10OHF-01-073-1657), Fluorphlogopite (KMg3(Si3Al)O10F2-01-076-0816), Sanidine (KAlSi3O8-01-074-0700), Augite (Ca(Mg,Fe)Si2O6-00-024-0203) and Diopside (Ca(Mg,Al)(Si,Al)2O6-00-041-1370) phases were determined depending on the crystallization temperature and the compositions. The XRD

Conclusion

In the current study, a novel machinable glass ceramic was produced from the volcanic rock basalt. The investigations of the machinability and crystallization properties were the main objective for this study. Phlogopite, Fluorphlogopite, Sanidine, Augite and Diopside phases were observed in the XRD patterns of glass ceramics depending on the treatment temperatures and additives to basalt. The mica phases, such as Phlogopite and Fluorphlogopite, provide good machining performance for the glass

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