Claims:We Claim:

1.A glass ceramic comprising of CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition wherein atleast 75% of said CaO- MgO-Al2O3-SiO2 (CMAS) is sourced from steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material.

2. The glass ceramic as claimed in claim 1, wherein said CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition include based on the total content of said steel ladle slag, said MgO containing spent refractory, said ZrO2 containing spent refractory, said fluorspar, said SiO2 rich material and said Al2O3 rich material, the content of steel ladle slag is from 15-25 wt%, the content of MgO containing spent refractory is from 2-5 wt.%, the content of ZrO2 containing spent refractory is from 7-10 wt.%, the content of fluorspar is from 5-8%; the content of SiO2 rich material is from 40-45 wt.% and content of Al2O3 rich material is from 5-13 wt.% and with said ZrO2 containing spent refractory based nucleating agent source.

3. The glass ceramic as claimed in any one of claims 1 or 2 wherein, the CMAS system glass ceramic composition contain said steel ladle slag composition comprising:
45-50 wt.% of CaO;
8-15 wt.% of MgO;
12-35 wt.% of Al2O3;
5-22 wt.% of SiO2; and
1-4 wt.% of Fe2O3.

4. The glass ceramic as claimed in any one of claims 1 to 3 wherein, the CMAS system glass ceramic composition contain said MgO containing spent refractory comprising:
80-93 wt.% of MgO;
3-6 wt.% of Al2O3;
2-3 wt.% of SiO2; and
<1 wt.% of CaO.

5. The glass ceramic as claimed in any one of claims 1 to 4 wherein, the CMAS system glass ceramic composition contain said ZrO2 containing spent refractory comprising:
92-95 wt.% of ZrO2;
1-2 wt.% of MgO; and
0.8-1.6 wt.% of CaO.

6. The glass ceramic as claimed in any one of claims 1 to 5, wherein the CMAS system glass ceramic composition optionally comprises at least one of the components selected from the group consisting of K2CO3 and boric acid; wherein the content of K2CO3 is from 0.1-5 wt.% and the content of boric acid is 0.1-5 wt.%.

7. The glass ceramic as claimed in any one of claims 1 to 4, wherein the CMAS system glass ceramic composition contain said steel ladle slag which is a slag generated after secondary refining of primary steel and is sourced from Al-killed, Si-killed or Al and Si-killed ladle furnace (LF) slag or a combination thereof.

8. The glass ceramic as claimed in any one of claims 1 to 7, wherein the CMAS system glass ceramic composition include said MgO containing spent refractory which is sourced from lime kiln, electric arc furnace (EAF), basic oxygen furnace (BOF), steel ladle or a combination thereof.

9. The glass ceramic as claimed in any one of claims 1 to 8, wherein the CMAS system glass ceramic composition include said ZrO2 containing spent refractory which is sourced from tundish nozzle, sub-entry nozzle or a combination thereof.

10. The glass ceramic as claimed in any one of claims 1 to 9, wherein the CMAS system glass ceramic composition include said SiO2 rich material which is sourced from spent silica refractory, river sand, quartz, quartzite or a combination thereof.

11. The glass ceramic as claimed in any one of claims 1 to 10, wherein the area fraction of the crystalline phase of the CMAS system based glass ceramic is 83-95%. and include diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) phases.

12. The glass ceramic as claimed in any one of claims 1 to 11, which is adapted selectively in form suitable for capacitor, inductor, resistor, transformer or hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC).

13. A method for producing the glass ceramic as claimed in claims 1 to 12 comprising:
mixing 15-25 wt.% of steel ladle slag; 2-5 wt.% of MgO containing spent refractory; 7-10 wt.% of ZrO2 containing spent refractory; 5-8 wt.% of spar; 40-45 wt.% of SiO2 rich material; and 5-13 wt.% Al2O3 rich material to form a mixture;
melting the mixture by arcing in a graphite crucible to form a molten glass;
quenching the molten glass by air to room temperature to form a parent glass; and
annealing to 850-1100 °C to produce the CMAS system based glass ceramic; wherein the annealing is performed at a temperature range of 850-1100 °C, preferably between 900-1000 °C for 2 hours.

Dated this the 19th day of May, 2020
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION
The present invention belongs to a glass ceramic composition and method of preparing the same by using solid waste derived from a steel plant and natural raw materials. More particularly, the present invention related to a CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition and method of preparing the same. The CMAS system based glass ceramic composition contains the steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material as essential components and which is used for fabrication of capacitor, inductor, resistor, transformer or hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC).

BACKGROUND OF THE INVENTION
Glass ceramics are fine-grained polycrystalline materials produced by controlled crystallization under heat treatment. Generally, a glass ceramic is not completely crystalline and the microstructure contains 50-95 volume % crystalline phase with the rest being residual glass. Glass ceramics are often produced in two steps, viz., formation of a parent glass by melting process followed by cooling and reheating the same in a second step for crystallization. In most of the cases, nucleating agents are added to the base composition that help in controlled crystallization. The most common nucleating agents are TiO2 and ZrO2. Other materials used as nucleating agents include P2O5, platinum group, noble metals and few fluorides. Glass ceramics are broadly divided into seven types of materials, i) Mica glass ceramics, ii) Mica apatite glass ceramics, iii) Leucite glass ceramics, iv) Leucite apatite glass ceramics, v) Lithium disilicate glass ceramics, vi) Apatite containing glass ceramics, and vii) ZrO2-containing glass ceramics.

Industrial wastes account for a major portion of all solid wastes being landfilled in India, and are therefore becoming a major environmental concern. These solid wastes may contain heavy metal contaminants which require proper disposal methods to prevent leaching of the heavy metal contaminants into water supplies. Handling and disposal of such industrial wastes may require additional cost and is also hazardous to the environment. There has been focused attention on reducing landfilling and on regulations that prevent leachable toxic materials from being disposed of in landfills. Substantial efforts have, therefore, been made to develop safe recycled products out of these solid wastes.

In the recent past, the industrial wastes are being utilized in various industries such as cement industry, steel industry etc. Similarly, extensive research has been carried out on the production of glass ceramics from industrial waste, owing to some of their physicochemical properties that can be exploited to obtain new materials for various applications. Thus, they are opening new resources of not only providing an alternate solution to environmentally unfavourable waste disposal, but also helping in conserving the natural resources.

For example, Chinese Patent CN104724929A and CN104478220 dated 13th Nov 2014 by Changrong et. al. proposes a method for using high-alkalinity steel slag of ladle furnace (LF) or VOD furnace for preparing CMAS based microcrystalline glass. Because of the composition of steel slag, no nucleating agent is required. This reduces production cost.

However, the process of crystallization is generally affected by nucleating agent via two mechanisms. Firstly, it can support the crystallization by forming a metastable liquid-liquid phase separation, which has to be the starting point for the internal crystallization of the glass. Secondly, small crystalline precipitates can also act as heterogeneous nucleation sites for further crystallization of the glass matrix.

Therefore, it is an object of the present invention to use industrial waste to prepare glass ceramic wherein the nucleating agent is also from industrial waste. Furthermore, there is a need to develop a method for manufacturing porous glass ceramics which is environment friendly, cost effective and has superior mechanical and chemical properties.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to develop a glass ceramic including CMAS system from solid wastes generated in steel plant such as steel ladle slag and spent refractories as the main ingredient.

Another object of the present invention is to use the spent ZrO2 refractory as the nucleating agent.
A still further object of the present invention is directed to develop a glass ceramic involving steel ladle slag of Si-killed steel and spent refractories as the main ingredient in order to recycle and utilize steel plant process waste, so as to close the sustainable production loop.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided for a glass ceramic comprising of CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition wherein atleast 75% of said CaO- MgO-Al2O3-SiO2 (CMAS) is sourced from steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material.

According to an aspect in the glass ceramic as above, the said CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition include based on the total content of said steel ladle slag, said MgO containing spent refractory, said ZrO2 containing spent refractory, said fluorspar, said SiO2 rich material and said Al2O3 rich material, the content of steel ladle slag is from 15-25 wt%, the content of MgO containing spent refractory is from 2-5 wt.%, the content of ZrO2 containing spent refractory is from 7-10 wt.%, the content of fluorspar is from 5-8%; the content of SiO2 rich material is from 40-45 wt.% and content of Al2O3 rich material is from 5-13 wt.% and with said ZrO2 containing spent refractory based nucleating agent source.

According to another aspect in the glass ceramic as above, the CMAS system glass ceramic composition contain said steel ladle slag composition comprising:
45-50 wt.% of CaO;
8-15 wt.% of MgO;
12-35 wt.% of Al2O3;
5-22 wt.% of SiO2; and
1-3 wt.% of Fe2O3.

According to another aspect in the glass ceramic as above, the CMAS system glass ceramic composition contain said the MgO containing spent refractory comprising:
80-93 wt.% of MgO;
3-6 wt.% of Al2O3;
2-3 wt.% of SiO2; and
<1 wt.% of CaO.

According to another aspect in the glass ceramic as above, the CMAS system glass ceramic composition contain said ZrO2 containing spent refractory comprising:
92-95 wt.% of ZrO2;
1-2 wt.% of MgO; and
0.8-1.5 wt.% of CaO.

According to yet another aspect in the glass ceramic as above the CMAS system glass ceramic composition optionally comprises at least one of the components selected from the group consisting of K2CO3 and boric acid; wherein the content of K2CO3 is from 0.1-5 wt.% and the content of boric acid is 0.1-5 wt.%.

According to a further aspect in the glass ceramic as above, the CMAS system glass ceramic composition contain said steel ladle slag which is a slag generated after secondary refining of primary steel and is sourced from Al-killed, Si-killed or Al and Si-killed ladle furnace (LF) slag or a combination thereof.

According to yet another aspect in the glass ceramic as above, the CMAS system glass ceramic composition include said MgO containing spent refractory which is sourced from lime kiln, electric arc furnace (EAF), basic oxygen furnace (BOF), steel ladle or a combination thereof.

According to a further aspect in the glass ceramic as above, the CMAS system glass ceramic composition include said ZrO2 containing spent refractory which is sourced from tundish nozzle, sub-entry nozzle or a combination thereof.

According to yet another aspect in the glass ceramic as above, the CMAS system glass ceramic composition include said SiO2 rich material which is sourced from spent silica refractory, river sand, quartz, quartzite or a combination thereof.

According to another aspect in the glass ceramic as above, the area fraction of the crystalline phase of the CMAS system based glass ceramic is 83-95%. and include diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) phases.

According to another aspect in the glass ceramic as above, which is adapted selectively in form suitable for capacitor, inductor, resistor, transformer or hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC).

According to yet another aspect of the present invention a method of producing the glass ceramic as above comprising:

(i) providing of a parent glass by melting process involving CaO- MgO-Al2O3-SiO2 (CMAS) system glass ceramic composition involving atleast 75% of said CaO- MgO-Al2O3-SiO2 (CMAS) sourced from steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material ,followed by cooling and reheating the same ;and
(ii) obtaining said glass ceramic including desired crystalline phase of 83-95% form said parent glass involving said spent ZrO2 refractory as the nucleating agent.

According to yet further aspect of the present invention, the method as above comprising:
mixing 15-25 wt.% of steel ladle slag; 2-5 wt.% of MgO containing spent refractory; 7-10 wt.% of ZrO2 containing spent refractory; 5-8 wt.% of spar; 40-45 wt.% of SiO2 rich material; and 5-13 wt.% Al2O3 rich material to form a mixture;
melting the mixture by arcing in a graphite crucible to form a molten glass;
quenching the molten glass by air to room temperature to form a parent glass; and
annealing to 850-1100 °C to produce the CMAS system based glass ceramic; wherein the annealing is performed at a temperature range of 850-1100 °C, preferably between 900-1000 °C for 2 hours.

According to yet further aspect of the present advancement there is provide for the method as above wherein the parent glass is annealed to form diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) phases.

BRIEF DESCRIPTION OF THE NON LIMITING ACCOMPANYING DRAWINGS
Embodiments are illustrated by way of example and are not limited in the accompanying figures.

Fig. 1A illustrates photographs of parent glass.

Fig. 1B illustrates photographs of CMAS system based glass ceramic.

Fig. 2 illustrates DSC curve of the parent glass showing the characteristic temperatures for the crystallization process at a heating rate of 10 °C/min.

Fig. 3 illustrates microstructure of (a) parent glass, (b) CMAS system based glass ceramic annealed at 900 °C, and (c) CMAS system based glass ceramic annealed at 950 °C.

Fig. 4 illustrates XRD patterns of the parent glass and the CMAS system based glass ceramic after annealing at 900 °C and 950 °C for 2 hours.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The accompanying figure together with the detailed description below forms part of the specification and serves to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accompanying drawings, like and/or corresponding elements are referred to by like reference numbers.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts.

Before describing in detail embodiments that are in accordance with the invention, it should be observed that the embodiments reside primarily for a CMAS system based glass ceramic composition and in method steps related to manufacturing the CMAS system based glass ceramic.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article or composition that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article or composition. An element proceeded by "comprises...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article or composition that comprises the element.

The present invention, in particular, differs from the prior art by way of developing a glass ceramic in the CaO- MgO-Al2O3-SiO2 (CMAS) system using solid wastes of steel plant such as steel ladle slag and spent refractories from steel plant as the main ingredients with spent ZrO2 refractory as the nucleating agent, thus providing a sustainable solution for recycling process waste and developing a product for technical applications. The CMAS system based glass ceramic composition is manufactured using waste materials. The waste materials are selected from a group that includes steel ladle slag and spent refractories. CaO–MgO–Al2O3–SiO2 (CMAS) is one of the most useful glass-ceramic systems due to their good chemical and mechanical properties.

The present invention has advantages in that a product can be developed using solid wastes generated in steel plant, which has up till now being disposed as a waste, can be recycled and the glass ceramic can be used for technical applications such as capacitor, inductors, resistors, transformers, hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC). Low temperature means that the sintering temperature is below 1,000 °C. It is thus possible by way of the present invention to provide a glass ceramic using appropriate proportion of steel plant wastes, thereby reducing the disposal and environmental concerns.

The present invention provides a CMAS system based glass ceramic composition comprising a mixture containing steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material as essential components. The total content of steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material in the mixture is at least 75 wt%. Based on the total content of steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material, the content of steel ladle slag is from 15-25 wt.%, the content of MgO containing spent refractory is from 2-5 wt.%, the content of ZrO2 containing spent refractory is from 7-10 wt.%, the content of fluorspar is from 5-8 wt.%, the content of SiO2 rich material is from 40-45 wt.% and content of Al2O3 rich material is from 5-13 wt.%.

The ZrO2 containing spent refractory acts as a nucleating agent.

The steel ladle slag comprising 45-50 wt.% of CaO; 8-15 wt.% of MgO; 12-35 wt.% of Al2O3; 5-22 wt.% of SiO2; and 1-3 wt.% of Fe2O3. The steel ladle slag is a slag generated after secondary refining of primary steel. The steel ladle slag is sourced from Al-killed, Si-killed or Al and Si-killed ladle furnace (LF) slag or a combination thereof. The steel ladle slag generated in steel ladle after secondary refining process acts as a source of CaO.

The MgO containing spent refractory comprising 80-93 wt.% of MgO; 3-6 wt.% of Al2O3; 2-3 wt.% of SiO2; and <1 wt.% of CaO. The MgO containing spent refractory is sourced from lime kiln, electric arc furnace (EAF), basic oxygen furnace (BOF), steel ladle or a combination thereof.

The ZrO2 containing spent refractory comprising 92-95 wt.% of ZrO2; 1-2 wt.% of MgO; and 0.8-1.5 wt.% of CaO. The ZrO2 containing spent refractory is sourced from tundish nozzle, sub-entry nozzle or a combination thereof.

The CMAS system based glass ceramic composition optionally comprising in the mixture at least one of the components selected from the group consisting of K2CO3 and boric acid; wherein the content of K2CO3 is from 0.1-5 wt.% and the content of boric acid is 0.1-5 wt.%.

The SiO2 rich material is sourced from spent silica refractory, river sand, quartz, quartzite or a combination thereof.

The Al2O3 rich source is sourced from calcined Al2O3, tabular Al2O3 or combination thereof.

The total content of steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material and Al2O3 rich material in the mixture is at least 95 wt.%.

The area fraction of the crystalline phase of the CMAS system based glass ceramic is 83-95%.

The CMAS system based glass ceramic is used for fabrication of capacitor, inductor, resistor, transformer or hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC).

A further object of the present invention is directed to develop a glass ceramic by melting the mixture through arcing process followed by air quenching to room temperature and further annealing at high temperature to produce the glass ceramic.

A method of preparing a CMAS system based glass ceramic by using steel ladle slag and spent refractories is disclosed, which comprising firstly, mixing 15-25 wt.% of steel ladle slag; 2-5 wt.% of MgO containing spent refractory; 7-10 wt.% of ZrO2 containing spent refractory; 5-8 wt.% of fluorspar; 40-45 wt.% of SiO2 rich material; and 5-13 wt.% of Al2O3 rich material to form a mixture. Secondly, melting the mixture by arcing in a graphite crucible to form a molten glass. When the parent glass is annealed, diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) phases are formed. Thirdly, quenching the molten glass by air to room temperature to form a parent glass. Lastly, annealing to 850-1100 °C to produce the CMAS system based glass ceramic. The annealing is performed at a temperature range of 850-1100 °C, preferably between 900-1000 °C. The annealing is performed for 2 hours. The annealing temperature range was decided based on the Differential Scanning Calorimetry (DSC) results by heating the parent glass from room temperature to 1200 °C at a heating rate of 10 °C/min in N2 atmosphere.

The CMAS system based glass ceramic is grinded and dry mixing the ingredients to a size less than 0.5 mm.

The glass ceramic so produced is suitable for fabrication of capacitor, inductors, resistors, transformers, hybrid circuit as Low Temperature Co-Fired Ceramics (LTCC). Low temperature means that the sintering temperature is below 1,000 °C.

The invention will now be illustrated by means of the following example. However, the following example is only for explaining the present invention in more detail, but scope of the present invention is not limited to the particular embodiments only.

Example 1: Composition
The ingredients used for the present invention were steel ladle slag, MgO containing spent refractory, ZrO2 containing spent refractory, fluorspar, SiO2 rich material, Al2O3 rich material, K2CO3 and boric acid were used as starting materials. The chemical composition of each component is shown in Table 1.

Table 1: Chemical composition of ingredients (wt.%)
Source CaO Al2O3 SiO2 MgO ZrO2 K2O B2O3 CaF2 Fe2O3
Ladle Slag 45-50 12-35 5-22 8-15 1-3
MgO containing spent refractory <1 3-6 2-3 80-93 <1
ZrO2 containing spent refractory 0.8-1.5 1-2 92-95
Fluorspar 8-10 85-90
SiO2 rich material 1-2 95-98 <1
Al2O3 rich material =98
K2CO3 =99
Boric Acid =99

18% by weight of ladle slag from Si-killed steel, 2.8% by weight of MgO containing spent refractory from lime kiln, 8.4% by weight of spent ZrO2 containing refractory from tundish nozzle, 8% by weight of fluorspar, 42% by weight of SiO2 rich material from river sand, 11.6% by weight of calcined Al2O3 rich material, 4.8% by weight of K2CO3 and 4.4% by weight of boric acid were used as a starting material.

Example 2: Composition

Firstly, mixing the composition as given in example 1 to form a mixture. Secondly, melting the mixture by arcing in a graphite crucible to form a molten glass. When the parent glass is annealed, diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) phases are formed. The glass ceramic consisted of 45.5% diopside, 10.5% baddeleyite and 28.9% anorthite phases with an area fraction of crystalline phase 88%. The batch was melted by arcing in a graphite crucible at a current of 100 A. Thirdly, quenching the molten glass by air to room temperature to form a parent glass. The parent glass has 9.16 wt.% CaO, 15.10 wt.% Al2O3, 45.77 wt.% SiO2, 7.32 wt.% MgO, 8.46 wt.% ZrO2, 3.44 wt.% K2O, 2.75 wt.% B2O3 and 7.55 wt.% CaF2. Lastly, annealing to 850-1100 °C to produce the CMAS system based glass ceramic. The annealing is performed at a temperature range of 850-1100 °C, preferably between 900-1000 °C. The parent glass was annealed at 950 °C for 2 hours. The annealing temperature range was decided based on the Differential Scanning Calorimetry (DSC) results by heating the parent glass from room temperature to 1200 °C at a heating rate of 10 °C/min in N2 atmosphere.

Example 3: Results
Fig. 1A illustrates photographs of parent glass. The parent glass is transparent as illustrated in Fig. 1 A. Fig. 1B illustrates photographs of the CMAS system based glass ceramic. The glass ceramic is opaque as illustrated in Fig. 1B.

In-formation about the crystallization process of the parent glass was obtained by di?erential scanning calorimetry (DSC). The annealing temperature range was decided based on the Differential Scanning Calorimetry (DSC) results by heating the parent glass from room temperature to 1200 °C at a heating rate of 10 °C/min in N2 atmosphere. Fig. 2 illustrates the DSC curve of the parent glass at a heating rate of 10 °C/min. It was observed that the crystallization process does not get completed when the annealing temperature was maintained at 900°C. As the temperature was increased to 950 °C, a dense microstructure of the crystalline phases is formed. Further increase in temperature to 1000 °C results in grain growth of the crystalline phases.

Fig. 3 illustrates microstructure of (a) parent glass, (b) CMAS system based glass ceramic annealed at 900 °C, and (c) CMAS system based glass ceramic annealed at 950 °C. Fig. 4 illustrates XRD patterns of the parent glass and the CMAS system based glass ceramic after annealing at 900 °C and 950 °C for 2 hours. The microstructure of the parent glass prepared reveals an amorphous structure which is supported by the XRD data. The parent glass, when annealed at 900 °C for 2 hours, revealed partial crystallization in the glassy matrix with white coloured star-shaped baddeleyite crystals of nanometer size as shown in Fig. 3b that had nucleated and grown in the bulk. When annealed at 950°C, their size grew to 3-4 µm as shown in Fig. 3c. In addition, crystallization of diopside, that had started at 900 °C, grew into large crystals having a length of 15-30 µm and width of about 4-6 µm at 950 °C. The amorphous phase nearly disappeared as the sintering temperature was raised to 950 °C. These findings were further confirmed by the XRD results which reveal formation of diopside and beddeleyite phases in 900 °C annealed samples with a decrease in the characteristic hump for amorphous phase. Diopside (CaMgSi2O6), anorthite (CaAl2Si2O8) and baddeleyite (ZrO2) were formed as the main phases in 950 °C annealed sample. As the temperature increased during annealing, the glass viscosity decreased and the crystallization rate accelerated. Sintering of the parent glass and crystallization occurred simultaneously, leading to decrease in the glassy phase.