Study of dielectric and optical properties of agro-food wastes derived glasses and glass ceramics

Abstract

Glasses play a very important role in modern life due to their applications in electronics, medical, communication, microwave, optoelectronics, etc.1–4 Basically, glasses are completely disordered materials, which exhibit lack of the periodic arrangement of atoms.5 However, they look like mechanically solid. According to Zachariasen's and Sun's criteria, some selected materials can only form glasses after rapid cooling from their molten state.1,6 The properties of the glasses depend on their initial composition, their amount and local arrangement of the structural units. So, proper selection of glass composition could be tailored the properties according to need and application. In recent times, researchers have been reported that the ashes of appropriate agro-food wastes could use as the resources materials to synthesize the oxide glasses and glass-ceramics for numerous applications.7,8 Since, some of the ashes of agricultural waste contain SiO2 as the major component along with minor alkali and alkaline-earth metals oxides, which are essential constituents to modify the properties of silicate glasses.9,10 Therefore, ashes of the agro-food waste could be used to synthesize the inexpensive silicate-based glasses and glass-ceramics to check their suitability in various applications.11–13 Various synthesis techniques have been employed such as sol-gel, solid-state reaction, and melt-quench to synthesize glasses and glass-ceramics.14,15 In the present study, the melt-quench technique is used to synthesize the glasses/glass-ceramics from various agro-food wastes ashes. For this purpose, Rice husk ash (RHA), sugarcane leave ash (SCLA), wheat straw ash (WSA), peanut shell ash (PSA) and eggshell powder (ESP) are taken as the initial ingredients. Above mentioned ashes/powder exhibit SiO2, CaO, MgO, as major components along with Na2O, TiO2, K2O, and Fe2O3 as minor components or traced elements.16–20 These waste ashes exhibit more or less similar constituents, which are required to synthesize silicate glasses and glass-ceramics. However, RHA, SCLA, and WSA have required very high temperature for melting, since, the ashes of these agro-wastes contain up to ~70 weight percentage (wt%) of silica along with some xvii other element oxides. The addition of ESP in different ashes not only modifies the network of the silicate structure but also decreases the melting point; since ESP has ~97-98 wt% (CaO) with a small amount of alkali oxides such as Na2O, K2O, which act as the modifiers in silicate glasses. So, appropriate wt% of RHA, SCLA, PSA, WSA and ESP have been used to synthesize the glasses and glass-ceramics for the present study. The as-quenched glasses and glass-ceramics are characterized and tested using various experimental techniques. The present work of the thesis includes the characterization of these agro-food waste ashes derived glasses and glass-ceramics to study their structural, thermal, optical, and dielectric properties for better applications such as non-linear optics, wide-band gap semiconductors and light-emitting diodes (LEDs), substrate for the solar-energy production, microelectronics. Some selected glasses are used for interaction study with interconnecting materials to check their applicability as the sealant materials in solid oxide fuel cells (SOFCs). Based on the above properties, This thesis work has been divided into six chapters along with references. Chapter 1 deals with a brief introduction related to the production of different wastes and their disposable process in developing countries. Rapid growth of population, the demand for food is increased day by day, which inherently responsible to create more and more wastes. It is well-known that the rest of the consuming part of any kind of staple food or vegetable is considered as the agro or biowastes. Now a day, agricultural-food wastes are found in the excess amounts due to a lack of knowledge and scientific methods to dispose of them properly. Presently, these wastes are being used as conventional applications like animal feed, mud houses, bio-fertilizers, etc. In recent times, these wastes have been used in civil construction and power generation as fuel.21,22 During heat-generation in power plants, sugarcane industries, and other small scale industries. The ashes of the agro-food waste have been produced as secondary by-products. These secondary bio-products are used as resource materials like RHA, SCLA, WSA to prepare the glasses and glass-ceramics due to contained silica with other trace elements.23 Silica is xviii required a higher melting temperature to convert glass. On the other hand, ESP is a direct source of CaO with a small amount of trace elements, which act as the modifier and reduced the melting temperature of the final melts of the above ashes. The role of different components presented in agro-food wastes is discussed as the glass former, modifier and intermediate oxides and their influences on various properties of glasses. Furthermore, different methods of glass and their applications in modern life have also been summarized. In the last, the chapter ends with the motivation of the present study. Chapter 2 reviews the literature and gives an idea about the agro-food waste ashes derived glasses and glass-ceramics. Normally, the agro-food wastes have been used in various applications. The advancement in various techniques/methods for the effective use of agro-food wastes is also discussed. Based on the advancement and available the objectives of the present study are given at the end of this chapter. Chapter 3 is related to synthesize and characterization details of glasses and glass-ceramics. The glasses were prepared by taking the required stoichiometric amounts of different agro-food waste ashes in the wt%. These ashes were first sintered at 1000 °C for 2 h and mixed together using an agate mortar-pestle to make a homogenous mixture. Then, ashes and ESP were mixed and melted at 1550 °C followed by quenching in the air on copper plates. The synthesis parameters and characterization of the as-prepared glasses and glass-ceramics have been discussed in detail in this chapter. Four different glass series have been synthesized using different agro-food wastes ashes/powder. In these series, the different sources of silica along with variable ESP (CaO) content are chosen. The technical details of the various characterization and testing techniques are given. These techniques X-rays diffraction (XRD), differential thermal analyzer (DTA), thermo-gravimetric analyzer (TGA), Dilatomerty, UV-Visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Photoluminescence spectroscopy (PL), Scanning electron microscopy (SEM) with attached energy dispersive xix spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and impedance analyzer are used in this chapter. Chapter 4 the interpretations of the data obtained from various characterization techniques have been discussed. It has been found that the glasses and glass-ceramics could be made using the different components of the waste ashes. Physical properties like color appearance, density and molar volume of the samples have been calculated and discussed in light of variation in compositions. The direct band gap decreases by adding the ESP on the cost of RHA/SCLA/WSA. Optical studies indicate that Urbach energy increases with ESP content in all the selected glasses. Mass loss with respect to temperature is observed very less, which shows the good thermal stability of the samples. CTE lies from 6-16×10-6/K, which could be exploited to use the selected sample as the sealant in solid oxide fuel cells (SOFCs). The obtained results are also discussed and compared with mineral oxides derived glasses and glass-ceramics of similar composition. The dielectric properties of agro-food waste ashes are comparable as obtained glasses from mineral oxides. Chapter 5 contains the conclusions drawn from the present research work and offers recommendations for future direction. Interestingly, agro-food waste ashes derived glasses and glass-ceramics are having comparable or better thermal, optical and dielectric properties. These materials are not only inexpensive but also open new avenues of research and innovations. Most of the ashes of the agro-food waste-derived glasses exhibit an optical band gap in the wide semiconductor range. So, these developed materials find applications in the field of the energy sector. Some glasses and glass-ceramics are shown independent dielectric behaviors with temperature and frequency, which can be used in microelectronic and semiconductor devices. Some of the samples are shown better sealing properties at various thermal cycles as compared to similar mineral-derived glasses and glass-ceramics. xx These waste ashes derived glasses and glass-ceramics can be used as biomaterials, catalytic materials to remove toxic and heavy metal from drinking water. Most importantly, agro-food waste ashes are sustainable and abundantly available. So, in the future, these wastes can be used as resource materials to generate many cost-effective value-added engineering materials.