As the need for more economically advantageous and environmentally friendly material synthesis methods rise, there remains a significant need to set standard methods of characterization for materials derived from these processes.
The conversion of agricultural waste ashes (AWA) to raw resource materials not only improves air and water pollution and agricultural land fertility but also provides a new source for glass and glass-ceramic materials, whose application in electronic devices continues to grow with continuous improvements in the engineering technology of this field. In a recent study published in Ceramics International, a group of researchers from Thepar University and ABES Institute of Technology in India analyzed heat-treated samples of sugarcane leaves and rice husk ash that were used to synthesize glass and glass-ceramic materials.
The Transformation of Agricultural Wastes to Engineering Resource Materials
When agricultural wastes such as rice husk, sugarcane leaves, and corn husks are burned, their ash contains a variety of useful constituents. These constituents include silica, which typically accounts for about 80% of agricultural waste ashes (AWA), as well as metal oxides including calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na2O) and potassium oxide (K2O). The silica that is extracted from agricultural waste ash can be utilized to form raw high-performance materials such as glasses, refractories, capacitors, glass sealants, biological ceramics, fibers, optical cavities and much more1.
During the melt-quench process of extracting silica, various gases are formed from the organic contents that are present within the agricultural wastes, which prove to be even more useful for glass and glass-ceramics as they improve the inherent porosity of the materials. While this porosity can limit thermal conductivity and dielectric density, it also has the potential to enhance properties including sensing and absorption of sound waves for future microelectronic devices, dielectric resonant antennas, and oscillators, etc.
This transformation process is a highly economical and renewable way to produce high content silica while simultaneously ensuring environmental protection by converting large amounts of agricultural waste for useful purposes. The dumping of AWA is associated with not only decreasing the fertility of agricultural fields, but the lightweight and small particle size of these ashes can also contaminate the air and nearby water supplies.
Characterization of Agricultural Waste-Derived Glass and Glass Ceramics
Previously employed analytical techniques that have been used to characterize the structural and dielectric properties of glasses and glass-ceramics derived from different agricultural waste ashes include elemental analysis by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. In the Ceramics International study, the researchers utilized a combination of x-ray diffraction (XRD), scanning electron microscopy (SEM) and UV/visible photoluminescence spectroscopy to characterize the properties of glass and glass-ceramics derived from sugarcane leaves and rice husk ashes.
X-ray Diffraction (XRD)
Through this analytical method, the researchers determined that higher contents of rice husk ash were unable to form glasses, as these materials exhibit crystalline phases that are indexed with cristobalite, silica dioxide (SiO2) and tridymite. Since rice husk content, which is associated with containing a higher percentage of SiO2 as compared to sugarcane leaves ash, the higher content of rice husk ash was found to also increase the amount of cristobalite. Therefore, the researchers determined that rice husk ashes require higher temperatures to melt and form glass materials.
Scanning Electron Microscopy (SEM)
SEM images taken of the samples in this study demonstrated a high amount of porosity, which may be attributed to the presence of crystalline phases like cristobalite and tridymite that were previously confirmed by XRD.
UV/Visible and Photoluminescence Spectroscopy
Photoluminescence (PL) spectra of the heat-treated samples was recorded in the 235-425 nm region, in which the glass and glass-ceramics materials that were analyzed in this study exhibited a wide range of intensity emission peaks from the blue to the red spectral region2. The broad PL data indicates that these materials exhibit a broad distribution of the energy levels, which may be a result of the disordered structure of the silica network combined with the presence of other trace elements. With the highest bands presented at 410—425 nm, the researchers concluded that the wide-band gap and good refractive index of the heat-treated samples allow for their useful application in power generation materials, as well as materials utilized for high temperature and ultra-violet blue (LEDs) purposes.
References:
- Danewalia, S. S., Sharma, G., Thakur, S., & Singh, K. (2015). Agricultural wastes as a resource of raw materials for developing low dielectric glass-ceramics. Scientific Reports. DOI: 10.1038/srep24617.
- Sharma, G., Arya, S. K., & Singh, K. (2018). Optical and thermal properties of glasses and glass-ceramics derived from agricultural wastes. Ceramics International. DOI: 10.1016/j.ceramint.2017.10.027.
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