E-ISSN:2583-9152

Research Article

Glass-Ceramics

Journal of Condensed Matter

2023 Volume 1 Number 1 Jan-Jun
Publisherwww.thecmrs.in

Optical and Mechanical Properties of Lithium Aluminosilicate Glass-ceramics

Kumar A1*, Chakrabarti A2, Chatterjee S3, Shekhawat M4, Molla A5
DOI:10.61343/jcm.v1i01.5

1* Anil Kumar, Department Of Physics, Seth G L Bihani S D Pg College, Sri Ganganagar 335001, Rajasthan, India.

2 Anirban Chakrabarti, Department of SolidState Physics , Indian Association for the Cultivation of Science, Kolkata 700032, West Bengal, India.

3 Shaona Chatterjee, Specialty Glass Division, CSIR Central Glass and Ceramic Research Institute, Kolkata700032, West Bengal, India.

4 Manoj S Shekhawat, Department of Physics, Engineering College Bikaner, Bikaner 334004, Rajasthan, India.

5 Atiar Rahaman Molla, Specialty Glass Division, CSIR Central Glass and Ceramic Research Institute, Kolkata700032, West Bengal, India.

These glasses prepared by melt-quench technique. High transparency (>80%) in the visible wavelength range has been observed in the material by UV-VIS-NIR spectrometry. FTIR spectra indicated the presence of Si-O as well as Al-O bonds in the glass-ceramics. The LAS glass ceramics showed moderate flexural strength (~80 MPa) and young’s modulus (~50 GPa). Microstructural characterization of the heat-treated glass ceramics by FESEM and TEM showed nano-crystalline spherical particles of 30-40 nm, which provided a rationale for its high transparency and good mechanical properties that may open up possibilities for newer applications.

Keywords: Lithium Aluminosilicate glasses, TEM, FESEM

Corresponding Author How to Cite this Article To Browse
Anil Kumar, , Department Of Physics, Seth G L Bihani S D Pg College, Sri Ganganagar 335001, Rajasthan, India.
Email: 		Kumar A, Chakrabarti A, Chatterjee S, Shekhawat M, Molla A, Optical and Mechanical Properties of Lithium Aluminosilicate Glass-ceramics. J.Con.Ma. 2023;1(1):24-28.
Available From
https://jcm.thecmrs.in/index.php/j/article/view/5

Manuscript Received Review Round 1 Review Round 2 Review Round 3 Accepted
2023-05-10 2023-05-15 2023-05-20 2023-05-25 2023-06-01
Conflict of Interest Funding Ethical Approval Plagiarism X-checker Note
None Nil Yes 18.67%

© 2023by Kumar A, Chakrabarti A, Chatterjee S, Shekhawat M, Molla Aand Published by Condensed Matter Research Society. This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/ unported [CC BY 4.0].

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Introduction

Lithium Aluminosilicate glass-ceramics are of great scientific as well as commercial interest because they have exceptional thermal stability, high mechanical strength, optical transparency and good chemical durability [1]. LSA are used in telescope, cooktop panels and optical stability [2]. The beta quartz or beta spodumene used in these glass ceramics serves as their basis. The extremely small thermal expansion characteristic is primarily caused by the positive expansion of the remaining glass phase and the volume fraction of the β-quartz solid solution crystals that are well matched in one direction [3-5]. The characteristics of multiphase systems depend on the microstructure, the microproperties, and the relative amounts of the different phases. Thermal expansion, strength, mechanical characteristics, and other properties of glasses are primarily determined by temperature and time of heat treatment, which in turn affects crystal volume fraction, crystal morphologies, and other factors [6] of the ceramic glasses. Most important crystallization kinetics of the lithium aluminium silicate glasses have been investigated greatly by many researchers [7,8]. It found that crystallization process influenced by a three-dimensional (3-D) diffusion reaction mechanism. It has also been exhibited method for controlling the characteristics of a glass-ceramic using the microstructure and compositions of phases [9,10]. Glass-ceramic technology has become a significant commercial technique as a result of retaining both of these properties through controlled heat treatments [11]. Hu et al [12,13] investigated the expansion behaviour of lithium aluminium silicate glass ceramics apart from different number of additives. B2O3 doped LAS glass ceramics are also reported for their thermos-mechanical properties [14]. Recently, Arvind et al studied thermo-mechanical characteristics of LAS glass ceramics [15]. Anmin et al investigated glass ceramics with high quartz solid solution, spodumene and spodumene-diopside fracture toughness, flexural strength, and thermal shock resistance [16]. They gave experimental evidences that show how to change crystal phases in a glass-ceramics which alter thermal expansion and mechanical characteristics.

This paper examines the effect of microstructure, phases present and crystallite

sizes on the optical and mechanical characteristics of LAS glass ceramics. The properties of glass ceramics are correlated with the microstructure and phases present.

Experimental

The ceramic glass with composition (weight percentage) of 26.31 Al2O3, 55.85 SiO2, 3.31 Li2O, 6.98 P2O5, 2.23 TiO2, 1.82 ZrO2, 1.51 ZnO, 0.56 K2O, 0.30 MgO, 0.93 As2O3, and 0.20 Na2O was prepared with high-purity chemicals. The method used for preparation of glass was melt-quench technique. The glass sample was mixed thoroughly by a mixer. and was melted in platinum crucible in a furnace at high temperature about 1600°C for 4-6 hour (in air) and stirring with a silica glass rod. The prepared melt glass was transferred in an iron mold which was already preheated at 1000°C, after this sample annealed at 675 °C for 2 hours. After cooling the furnace sample take out from the furnace. Now the prepared glass was cut as per desired shape and dimension. After this glass block was optically polished for the heat-treatment and other various characterization measurements.

A high resolution field emission scanning electron microscope (FESEM) was used to investigate the microstructure. For this we used heat-treated glass–ceramics samples. Samples etched in hydrofluoric acid (HF) solution and coated with a thin carbon film. The transmission electron microscope (TEM) images and selected area electron diffraction (SAED) of powdered glass ceramic sample were collected from field emission gun instrument.

The indentation fracture toughness and hardness property of glass ceramic specimens were determined using micro-indentation on polished surface of samples. At an indent load of 0.3 kg, micro-indentations were made using a Clemax microhardness tester (Canada) built with a conical Vicker's indenter. For each sample under the same loading circumstances, about ten indents were obtained. Using an optical microscope, the Vickers indents' diagonals were meticulously measured, and the hardness was then determined using the formula for the Vickers geometry.

jcm_05_1.jpg
Where Hv is Vickers hardness number (VHN) in unit of Kg/mm2, P is normal load in unit of Kg, and d is


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average length of indentation in unit of mm. The following equation is utilized to determine fracture toughness which was proposed by Antis et. al [17]:

jcm_05_2.jpg

Results and Discussion

The transmission characteristic obtained for glass and glass-ceramic derived from the same glass by heat-treatment are shown in Figure 1. From the spectra it is seen that the transmission for glass in wavelength region 200-1100 nm is more compared to the glass-ceramics. The cut-off wavelength (λcut-off) for glass as well as glass ceramics was observed at 350 nm. In both the cases transmittivity were attained higher than 80%, however, the transmission for glass is higher than that of the glass-ceramics. Due to the crystals formation, the scattering of light is obtained more in glass ceramic compared to precursor glass which does not have any crystals. This remarkable transmittivity of glass ceramic is obtained due to formation of nano-crystals. Due to the small and homogeneous size of the crystals in the GC product, which determines around 30-40 nm, and as birefringence in β-quartz (ss) and refractive index difference between crystals and residual glass are negligible, there is almost no or minimal scattering of visible light. As a result, these glass-ceramics are very clear and appropriate for a wide range of technical and home applications.

jcm_05_3.jpg
Figure 1: Transmission spectra of lithium aluminosilicate precursor glass and glass-ceramics. (Thickness of glass = 2 mm).

jcm_05_4_a.jpg   
Figure 2: Optical microscope images of indent impressions taken on a) LAS glass and b) LAS glass-ceramics at 0.3 kg load.

The hardness of glass ceramic samples (heat-treated) is determined by collecting micro indentation for 0.3 kg of indent load and calculating the hardness impressions average diagonal length. The optical microscope image of indent impression was obtained for the sample at 0.3 kg load as illustrated in Figure 2. The image of optical microscope shows an indent impression on the surface of sample and spread of radial cracks from the corners of indent.

The hardness is obtained as 6.08 ± 0.49 GPa for the glass sample. Whereas, hardness value of the glass-ceramics derived from the same glass is 5.87 ± 0.7 GPa. It has been observed that glass-ceramic is less hard than that of the corresponding precursor glass. As such, the hardness value measured is comparable with the data reported in the literature for this material. The fundamental


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mechanical characteristics i.e. flexural strength (3-point) and glass-ceramics elastic modulus were determined. The experimental data show that a moderate strength (76.08 ± 7.94 MPa) and E-modulus (47± 2.27 MPa) could be measured in glass-ceramic samples. In previously reported research papers on GC of this system, such comprehensive measurements of all fundamental mechanical characteristics are not given. Data measured for the present system on hardness, indentation fracture toughness, flexural strength and E-modulus have been provided in Table 1.

Table 1: Mechanical Properties of Lithium Aluminosilicate Glass and Glass-ceramics

SampleHardness (GPa)at 3 kg loadIndented fracture toughness (MPa m0.5)Flexural Strength (MPa)Elastic Modulus (GPa)
LAS Glass6.08 ± 0.490.89 ± 0.09--
LAS Glass-ceramics5.87 ± 0.70.95 ± 0.1976.08 ± 7.9447 ± 2.27

Flexure strength and E-modulus measured for the presently investigated glass-ceramic nano-composite is found relatively low compared to the values reported by the earlier researchers [12,16-17]. The existence of large internal stresses in the glass-ceramics may be the cause of this low strength value. Circumferential tensile strains in the remaining glass phase are probably going to form around any crystals that are present that have a very low thermal expansion coefficient. These stresses will probably reduce the overall strength of the glass-ceramic even if they do not result in microcracking. It has been predicted that glass-ceramics with low-expansion crystal phases have a tendency to be weaker than those with high expansion crystal phases. The presence of anisotropic crystal phases such as β-quartz (ss) may also be responsible for the generation of unfavourable boundary stresses between the crystal and glass phases and it can cause a catastrophic reduction of mechanical strength.

Conclusions

The lithium aluminosilicate glass-ceramics and several characteristics of the material were studied. A number of characterizing techniques, including FESEM, TEM, and FTIRTS were used for characterization of microstructure; optical characteristics of glass samples as well as glass-ceramics have been determined using prism coupler and UV-Vis spectrophotometer. In the glasses and glass-ceramics transmittivity was obtained

more than 80%, however, the percentage transmission of glass was little higher than GC. The hardness value of 6.08 ± 0.49 GPa is found for the glass sample, whereas, hardness value of the glass-ceramics derived from the same glass is 5.87 ± 0.7 GPa. The experimental data reflect that a combination of moderate strength (76.08 ± 7.94 MPa) and E-modulus (47 ± 2.27 MPa) could be obtained in the glass-ceramic samples. This inferior mechanical property is probably due to the presence of anisotropic, ultra-low thermal expansion β-quartz (ss) crystals in the glass-ceramics.

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