Eggshell is a biomaterial source of calcium compounds, such as calcium carbonate, calcium oxide, and calcium hydroxide, which are useful in many industries, such as the pharmaceutical, dental, and medical industries; filler manufacture (for ink, paint, rubber, animal feed, pesticides, cosmetic, and food industries), cement and construction, and catalyst and adsorbent industries. Tangboriboon et al. [1] studied the preparation of CaSiO3 dielectric material from eggshells with a CaO:SiO2 molar ratio of of 1:1 by the sol-gel process. The obtained CaSiO3 was wollastonite, which was of the triclinic or anorthic phase formation. The dielectric constant and electrical conductivity of triclinic CaSiO3 were 62.59 ± 0.44 and 8.00529 × 10−4 (Ω·m)−1, respectively, at 25 °C and 1 MHz. In addition, Parande et al. [2] described the effect of addition of eggshell particles into Mg–Zn on the corrosion, damping, and mechanical properties. They suggested that mechanical properties of the Mg–Zn-ES composites were superior due to absence of corrosion, high hardness, and high strength suitable for orthopedic applications. In addition, Tangboriboon et al. [3] described the duck eggshell that was used to prepare meso- and nano-particulate calcium phosphate and hydroxyapatite. The duck eggshell is an important CaCO3 source, which is a potential candidate for the synthesis of calcium hydroxyapatite, useful in various bioceramic applications, such as bone tissue engineering, drug delivery, and bone void fillers for orthopedic restoration. Oladele et al. [4] synthesized hydroxyapatite from chicken eggshell waste based high density polyethylene (HDPE) biocomposites for biomedical implants. Eggshell can enhance the mechanical properties (flexural strength, Young's modulus, yield strength, wear resistance, and fracture toughness) of HDPE. Boronat et al. [5] suggested the preparation of a biocomposite of PE biopolymer and eggshell. They found that eggshell increased the mechanical properties of the bio-PE matrix in terms of stiffness, hardness, flexural strength, and tensile modulus because eggshell enhanced the interaction between the PE matrix and the eggshell filler. Meanwhile, there are many million tons of eggshell waste generated daily [6]. At present, many researchers are interested in trying to use wastes from natural sources and recycled waste, such as biological wastes, biofibers, industrial wastes, biodegradable materials [7], and nontoxic materials [8], as starting materials. In addition, encouragement of environmental understanding in industrial applications is becoming more prevalent [9], with sustainable development [10] and eco-efficiency being considered as major responsibilities in many countries [9]. Furthermore, advanced manufacturing technology or “smart” technology plays an important role in enabling the development of materials to revolutionize global manufacturing [11].
Superconducting materials are a superior option to induce electric current to flow indefinitely. There are two types of superconductors: type I (metals, rare earth metals, and alloys, including aluminum, lead, mercury, TaSi2, chromium, rhenium, palladium, tin, Nb3Sn, and Ba8Si40); and type II (such as metal oxide compounds or ceramic compounds YBa2Cu3O7 (YBCO) and GdBa2Cu3O
The objective of this work was to synthesize a superconductor yttrium barium copper oxide (YBCO) with or without the addition of calcium oxide (CaO) from a commercial source or from eggshell. The physical (color, microstructure, and phase formation), chemical (functional group), thermal (thermal reaction and residual mass), and electrical (capacitance, electrical conductivity, dielectric constant, and dielectric loss) properties were measured and reported according to the standardization methods.
The chemical substances – yttrium oxide (Y2O3), barium chloride (BaCl2), copper oxide (CuO), caustic soda (NaOH), and quicklime (CaO) – were supplied by Ajax Finechem Co., Ltd. Waste eggshell was gathered from the local restaurant at the Kasetsart University, Bangkok, Thailand. Dried eggshell was ground to a fine powder using a rapid porcelain mill for 1 h and calcined at the firing temperature of 900 °C for 2 h.
Superconductor sample preparation for measurement of electrical properties of disk-like samples:
The formulas of superconducting samples with/without adding calcium oxide (CaO) were prepared to be five formulas via sol-gel process, as indicated by the data in Table 1. The precursor solution was prepared by mixing four solutions by controlling the stoichiometry. Each precursor was prepared from the chemical substances (Y2O3, BaCl2, CuO, and CaO) by dissolving in the solvent. Four types of solvents were used, including water (H2O), ethyl alcohol (C2H5OH), or hydrochloric acid (HCl), before mixing the precursors together by stirring at room temperature following Eq. (1). The stoichiometric ratio of Y2O3:BaCl2:CuO: CaO was 1:2:3:1 based on the molar mass.
Formulas for preparation of superconductor samples.
Y2O3 in 9.93 cm3 ethanol (C2H5OH) | 2.26 g | 2.26 g | 2.26 g | 2.26 g | 2.26 g |
BaCl2 in 10.80 cm3 water | 4.16 g | 4.16 g | 4.16 g | 4.16 g | 4.16 g |
CuO in 8.37 cm3 HCl | 4.77 g | 4.77 g | 4.77 g | 4.77 g | 4.77 g |
CaO in 8.37 cm3 HCl (commercial grade) | – | – | – | 2.24 | 2.24 |
CaO in 8.37 cm3 HCl (eggshell) | – | 2.24 g | 2.24 g | – | – |
NaOH (pH) | – | – | Adjust the pH to 11 | – | Adjust the pH to 11 |
Encoded sample | YBa2Cu3O7− |
YCaBa2Cu3O7− |
YBa2Cu3O7− |
YCaBa2Cu3O7− |
YCaBa2Cu3O7− |
Firing temperature (°C) | |||||
900 | YBCO-900-ref | YCaBCO-900-eggshell | YCaBCO-NaOH-900-eggshell | YCaBCO-900-com grade | YCaBCO-NaOH-900-com grade |
1,000 | YBCO-1000-ref | YCaBCO-1000-eggshell | YCaBCO-NaOH-1000-eggshell | YCaBCO-900-com grade | YCaBCO-NaOH-1000-com grade |
YBCO, yttrium barium copper oxide.
The solubility testing of raw materials was done according to Table 2. To make yttrium oxide solution precursor, barium chloride solution precursor, calcium oxide solution precursor, and copper oxide solution precursor, we had to choose a suitable solvent. Yttrium oxide (Y2O3) was easily soluble in ethanol but slightly solubility in hydrochloric acid, while barium chloride had excellent soluble in water. Both calcium oxide (CaO) and copper oxide (CuO) were easily soluble in hydrochloric acid. The calcium oxide was obtained from firing eggshell at a firing temperature of 900 °C for 2 h, as shown in Eq. (2). The fired eggshell was mainly constituted by calcium oxide (CaO), which was in the form of soft, fine, white powder and was odorless. The average particle size of the CaO from eggshell was 3.04 μm. The carbon dioxide (CO2) gas diffused out of the chemical reaction.
Density values and solubility data of chemical substances used for preparation of superconductors.
Yttrium oxide (Y2O3) | 5.03 | – | ✓ | Slightly soluble |
Barium chloride (BaCl2) | 3.10 | ✓ | – | – |
Calcium oxide (CaO) from eggshell, pH 12 | 2.46 | – | – | ✓ |
Calcium oxide (CaO), commercial grade, pH 12.6 | 3.34 | – | – | ✓ |
Copper oxide (CuO) | 6.51 | – | – | ✓ |
Remark: “–” = insoluble.
“✓” = good solubility.
Sodium hydroxide (NaOH) was used to adjust the pH and to accelerate gel formation in the third and the fifth formulas. All powder samples had a light green–blue color when they were dried in an oven at 110 °C for 3 days. After that, the dry samples were fired at 900 °C or 1,000 °C for 30 h at a heating rate of 10 °C/min to obtain superconductor samples. The first formula without adding CaO and specifying firing at 900 °C and 1,000 °C yielded products labeled as YBCO-900-ref and YBCO-1000-ref, respectively. The second and fourth formulas were used for sample preparation by adding CaO from eggshell and commercial grade product, respectively. Further, the third and the fifth formulas were used for preparation with CaO from eggshell and commercial grade CaO, along with NaOH, labeled as YCaBCO-NaOH-firing temperature (900 °C or 1,000 °C)-CaO from eggshell or commercial grade product.
The dried precursors were studied based on the thermal reaction to select the suitable firing temperature by using an STA from room temperature (25 °C) to 1,000 °C with a heating rate of 10 °C/min, as shown in Figure 3. The residual mass values of YCaBCO-eggshell and YCaBCO-com grade were analyzed approximately at 75.76% and 71.08%, respectively. In addition, both dried precursor samples with added CaO from eggshell and commercial grade CaO had four sharp peaks and displayed endothermic peaks at 147.3 °C, 315.0 °C, 393.6 °C, and 459.3 °C, respectively. The obtained STA results of Figures 3A and 3B had the same behaviors. In addition, the displayed endothermic peaks caused by the decomposition of the organic matter and other intermediate components of YCaBCO were in the range of 200–600 °C. From the differential thermal analysis (DTA) curve of both samples with/without the addition of CaO, we obtained the suitable temperature for preparation of the superconducting YBCO and YCaBCO with CaO (from eggshell and commercial grade product) at the same range (850–1,000 °C). The thermogravimetric analysis (TGA) results of YCaBCO with added CaO from eggshell and commercial grade CaO showed that it had the approximately 30–40 wt% weight loss at temperatures ranging from room temperature (27 °C) to 1,100 °C. Furthermore, the study by Harabor et al. [19] presented the DSC curves of samples on heating in air and in the temperature range of 20–1,000 °C. Ochsenkühn-Petropulu et al. [20] characterized the temperature to be in the range of 20–1,080 °C and discovered the endothermic reactions caused by the organic decomposition of Y-Ba-Cu salt, BaCO3, and YBCO at 180 °C, 450 °C, and 850 °C, respectively.
The characteristics of obtained samples with/without the addition of CaO into YBCO were fine and black-colored powders that were odorless, as shown in Figure 4. The densities of YBCO (without the addition of CaO) and YCaBCO (with CaO from eggshell fired at 900 °C) were 6.87 ± 0.53 g/cm3 and 6.10 ± 0.06 g/cm3, respectively. The theoretical density of the superconductor (YBCO or YBa2Cu3O7) without the addition of CaO was 6.30 g/cm3, and it was characterized as a solid black powder, insoluble in water, with a melting temperature >1,000 °C, and a perovskite structure, as shown in Figure 5 [15].
YCaBCO powder with added calcium oxide (CaO):
Perovskite structure of superconductor YBCO [15]. YBCO, yttrium barium copper oxide.
The FTIR spectra of the superconductors with/without the addition of CaO measured in the wave number range of 500–4,000 cm−1 are shown in Figure 6. The YBCO sample without adding CaO was fired at 900 °C for 30 h, and the functional groups were measured by FTIR. YBCO had many small peaks in the range of 500–750 cm−1. Many peaks appeared at 482 cm−1 belonging to Y-Cu-O and Ba-O, around 500 cm−1 for
The XRD peak patterns of the YBCO superconductors with/without CaO addition before and after firing in the temperature range of 10°–90° were characterized as shown in Figure 7. The dried gel samples of YBCO and YCaBCO before firing had XRD peak patterns corresponding with the JCPDS file numbers 00-035-0690 (copper chloride, CuCl2, monoclinic form), 00-035-1258 (calcium copper chloride hydrate, Cu3(OH)6CaCl2·H2O, hexagonal form), 00-046-0946 (barium chloride hydrate, BaCl2·0.5H2O), and 00-047-0703 (calcium oxide hydrate, tetragonal). The XRD peak pattern of YBCO-900-ref without the addition of CaO corresponded with the JCPDS file peak pattern no. 01-079-1613 of yttrium barium copper oxide (YBa2Cu3O7) with an orthorhombic structure, as shown in Figure 8 [15]. The highest five peaks of YBCO-900-ref appeared as in the YBCO standard pattern at 32.769° (110), 33.111° (103), 46.561° (020), 47.479° (200), and 58.909° (213). The YCaBCO doped with CaO from eggshell and commercial grade product and fired at 900 °C or 1,000 °C showed XRD peak patterns corresponding with the standard peak patterns of JCPDS file numbers 01-082-0268 (Y0.9Ca0.1Ba2Cu4O8), 01-084-1853 (Y2Cu2O5), and 01-079-1613 (YBa2Cu3O7). The crystal structures of (Y0.9Ca0.1)Ba2Cu4O8, Y2Cu2O5, and YBa2Cu3O7 in Figure 7 had an orthorhombic phase formation, with densities of 6.14 g/cm3, 5.41 g/cm3, and 6.47 g/cm3, respectively; these were close to the obtained experimental density values (6.10 ± 0.06 g/cm3). Furthermore, the phase formation of the superconductor YCaBCO samples, with added CaO from commercial grade product and eggshell and then fired at 1,200 °C, had the XRD peaks of barium oxide (BaO) and YBa2Cu3O6 caused by decomposition of barium chloride to barium oxide. Therefore, the excess firing temperature changed the phase formation of these superconductors. Furthermore, Amoudeh et al. [18] and Ozabaci [22] suggested that the XRD peak patterns of YBCO had polycrystalline structure with orthorhombic phase formation. The asymmetrical orthorhombic structure affected its electrical properties such as inducing polarization at the electromagnetic frequency and increasing oxygen absorption during the critical current density.
Spectra of raw materials and superconducting materials measured by FTIR. FTIR, Fourier transform infrared spectroscopy.
Patterns of the X-ray peaks of superconductor samples prior to and after firing.
The SEM micrographs of CaO from eggshell, YBCO-900-ref, YCaBCO-900-eggshell, YCaBCO-900-com grade, YCaBCO-NaOH-900-eggshell, and YCaBCO-NaOH-900-com grade at a magnification of 1,000× were analyzed and reported as shown in the Figure 9. SEM microstructure of CaO obtained from the fired eggshell showed agglomeration. The obtained superconductor without the addition of CaO (YBCO-900-ref) and fired at 900 °C was an irregular solid black powder. Further, the SEM microstructures of YCaBCO-900-eggshell, YCaBCO-900-com grade, YCaBCO-NaOH-900-eggshell, and YCaBCO-NaOH-900-com grade showed grain connectivity, grain agglomeration, and grain growth, being characterized as a solid black powder; the obtained powder was hard and brittle with a random orientation. Adding CaO from eggshell supported good orientation and rectangular-like grains, and facilitated the filling-in of pores, as shown in Figures 9C and 9E. Furthermore, CaO from the eggshell affected the agglomeration and grain growth of the superconductor YCaBCO (Figures 9C and 9E) more than for the superconductor with added commercial grade CaO (Figures 9D and 9F).
Microstructures of calcium oxide and superconductor samples observed using SEM at 1,000× magnification:
Table 3 and Figures 10 and 11 exhibit the electrical properties (capacitance, electrical conductivity, dielectric constant, and dielectric loss) of the specimens (raw materials and superconductors with and without the addition of CaO) at electromagnetic frequencies ranging from 500 Hz to 1 × 106 Hz at room temperature (27°C). The electrical conductivity values of CuO, Y2O3, BaCl2, CaO (commercial grade), and CaO (eggshell) at 500 Hz and 27 °C were 1,960.00 ± 18.70 S/m, 236.00 ± 9.04 S/m, 1,200.00 ± 16.10 S/m, 185.00 ± 2.30 S/m, and 8,700.00 ± 38.70 S/m, respectively. The dielectric constants of CuO, Y2O3, BaCl2, CaO (commercial grade), and CaO (eggshell) at 500 Hz and 27 °C were 8.334 ± 0.080, 71.366 ± 2.706, 13.808 ± 0.184, 94.627 ± 1.189, and 1.966 ± 0.009, respectively. The addition of CaO from a commercial grade product or eggshell powder resulted in greater values for the electrical conductivity, capacitance, and dielectric constant of the superconductors, better than in the starting materials, at magnitudes of approximately 104–105, 102, and 102–103, respectively. Comparison of the superconductor YBCO with added CaO from commercial grade product and eggshell with the sample of YCaBCO showed that the capacitance and the dielectric constant of the superconductors with added CaO from eggshell were higher than those of samples with added commercial grade CaO. However, the electrical conductivity of these superconductors with added CaO from the eggshell was close to that of the samples with added commercial grade CaO. When the electrical frequency increased from 500 Hz to 1 × 106 Hz, the values of electrical conductivity and dielectric constant decreased—as shown in Figures 10 and 11—and these results were consistent with the polarization theory of materials versus the electromagnetic frequency, as suggested by Waheed et al. [7] (see Figure 12). Therefore, the superconductors YBCO and YCaBCO with/without the addition of CaO from eggshell had electrical conductivity and dielectric constant values close to the theoretical values. On comparison with the electrical properties (electrical conductivity and dielectric constant versus the electromagnetic frequency) of the superconductor YCaBCO, samples doped with CaO from eggshell and commercial grade product showed the same tendency as in theory. In addition, the superconductor YCaBCO with added CaO had an orthorhombic crystal structure that increased oxygen absorption due to the increase in the surface – volume ratio, un-symmetrical structure (a ≠ b), and the critical current density. The superconductor with CaO from eggshell (YCaBCO) had electrical properties (both conductivity and dielectric constant) better than that of the superconductor (YBCO) without added CaO, as shown in Figure 11. Adding sodium hydroxide (NaOH) to the superconductor YCaBCO, to adjust the pH for gel formation as a basic catalyst – for firing at 900 °C or 1,000 °C, increased the electrical properties of their structures, as shown in Figures 10 and 11. Furthermore, all superconductor samples with and without the addition of CaO from either commercial source or eggshell had low loss in their dielectric values, which offers an important advantage over dielectric materials, making them suitable as superconducting materials in various industries.
Electrical properties due to polarization at various electromagnetic frequencies [7].
Electrical properties of raw materials and superconductor samples measured at room temperature (27 °C), (±SD), n = 3.
CuO | 1.0 × 106 | 5.63 ± 0.42 | 7.08 ± 0.010 | 1.158 ± 0.087 | 0.122 ± 0.053 |
Y2O3 | 1.0 × 106 | 64.75 ± 0.29 | 0.622 ± 0.003 | 13.526 ± 0.061 | 0.128 ± 0.057 |
BaCl2 | 1.0 × 106 | 21.88 ± 0.63 | 1.83 ± 0.052 | 4.535 ± 0.130 | 0.155 ± 0.068 |
CaO (commercial grade) | 1.0 × 106 | 55.37 ± 2.71 | 0.743 ± 0.035 | 11.794 ± 0.578 | 0.130 ± 0.056 |
CaO (from eggshell) | 1.0 × 106 | 0.47 ± 0.01 | 87.90 ± 1.720 | 0.099 ± 0.002 | 0.168 ± 0.073 |
YBCO-900-ref | 1.0 × 106 | 107.59 ± 0.46 | (5.40 ± 0.02) × 106 | 24.341 ± 0.103 | 0.159 ± 0.069 |
YBCO-1000-ref | 1.0 × 106 | 257.25 ± 1.70 | (2.26 ± 0.01) × 106 | 58.200 ± 0.400 | 0.159 ± 0.070 |
YCaBCO-900-eggshell | 1.0 × 106 | 132.02 ± 0.90 | (4.28 ± 0.03) × 106 | 30.740 ± 0.200 | 0.213 ± 0.010 |
YCaBCO-1000-eggshell | 1.0 × 106 | 121.50 ± 1.30 | (4.63 ± 0.05) × 106 | 28.391 ± 0.300 | 0.213 ± 0.090 |
YCaBCO-NaOH-900-eggshell | 1.0 × 106 | 177.84 ± 0.40 | (3.42 ± 0.008) × 106 | 38.47 ± 0.10 | 0.171 ± 0.010 |
YCaBCO-NaOH-1000-eggshell | 1.0 × 106 | 145.65 ± 1.47 | (4.09 ± 0.04) × 106 | 32.11 ± 0.32 | 0.171 ± 0.074 |
YCaBCO-900-com grade | 1.0 × 106 | 130.32 ± 1.21 | (4.43 ± 0.04) × 106 | 29.70 ± 0.28 | 0.159 ± 0.069 |
YCaBCO-1000-com grade | 1.0 × 106 | 118.55 ± 0.87 | (4.78 ± 0.04) × 106 | 27.51 ± 0.20 | 0.159 ± 0.069 |
YCaBCO-NaOH-900-com grade | 1.0 × 106 | 177.84 ± 0.42 | (3.42 ± 0.01)×106 | 38.47 ± 0.09 | 0.171 ± 0.007 |
YCaBCO-NaOH-1000-com grade | 1.0 × 106 | 146.83 ± 2.38 | (4.30 ± 0.07)×106 | 30.55 ± 0.50 | 0.161 ± 0.071 |
SD, standard deviation; YBCO, yttrium barium copper oxide.
Yttrium calcium barium copper oxide (YCaBa2Cu3O7−