1. bookVolume 39 (2021): Issue 3 (September 2021)
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2083-134X
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Bio-dielectric based on superconductors yttrium calcium barium copper oxide (YCaBa2Cu3O7−x) from eggshell as calcium oxide source via sol-gel process

Published Online: 30 Dec 2021
Volume & Issue: Volume 39 (2021) - Issue 3 (September 2021)
Page range: 305 - 318
Received: 23 Apr 2021
Accepted: 23 Apr 2021
Journal Details
License
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English
Abstract

Eggshell is a rich source of calcium that is a dielectric material used for doping in a superconductor. Yttrium calcium barium copper oxide (YxCa1−xBa2Cu3O7) was prepared using the sol-gel process and fired at 900 °C or 1,000 °C. The stoichiometric ratio of the raw materials Y2O3:BaCl2:CuO:CaO was 1:2:3:1 based on the molar mass. The obtained YCaBCO had an orthorhombic crystal structure composed of distorted oxygen-deficient perovskite. The orthorhombic structure was unsymmetrical, providing a substantial increase in the physical electromagnetic properties of the superconductor. The YBCO-900-reference analyzed using an impedance analyzer in the range from 500 Hz to (1 × 106) Hz and at room temperature (27 °C) had the following values for capacitance, electrical conductivity, and dielectric constant ± standard error: 8,286.70 ± 28.49 pF, (3.60 ± 0.01) × 107 S/m, and 1,874.794 ± 6.446, respectively. The YCaBCO-900-eggshell (YxCa1−xBa2Cu3O7) analyzed at 500 Hz at room temperature (27 °C) had high values for capacitance, electrical conductivity, and dielectric constant, namely, 8,540.10 ± 2.00 pF, (1.32 ± 0.00) × 108 S/m, and 1,988.540 ± 0.500, respectively. Furthermore, the YCaBCO-900-eggshell had electrical properties (capacitance, conductivity, and dielectric constant values) higher than those of YCaBCO-900-commercial grade measured under the same conditions. The YCaBCO-900-com grade had capacitance of 8,225.75 ± 0.73 pF, electrical conductivity of (1.40 ± 0.01) × 108 S/m, and dielectric constant of 1,874.59 ± 0.17, respectively. Therefore, eggshell is an alternative dielectric material useful for doping in yttrium barium copper oxide (YBCO) to form YCaBCO, thus causing an increase in its electrical properties. The obtained superconductor is a candidate that could be applied in many industries.

Keywords

Introduction

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 GdBa2Cu3Ox) [12]. Superconductors have special properties and exhibit special behaviors such as the Meissner effect, as shown in Figure 1 [13]. In addition, the other outstanding property of superconductors is their diamagnetic behavior, suitable for use in a variety of applications such as inducing opposite direction of magnetic fields, low magnetic susceptibility, and manufacture of perfect diamagnetic devices such as strong-field superconducting magnets, nuclear magnetic resonance (NMR) machines, magnetic resonance imaging (MRI) machines, low-loss power cables, microwave devices [14], power transmission lines, magnetic bearings, delay lines, levitated vehicles, and magnetic levitation (maglev) trains [15]. There are many processes, such as sol-gel process [16], solid-state reaction, wet chemical process, thin/thick film coating, electro-spinning, vapor deposition using chemical vapor (CVD) or physical vapor (PVD) [17], sputtering, and inductive coupled plasma (ICP), which can be used to prepare superconductors [18]. Adding a calcium atom in the superconductor (YBCO) structure induces high electrical conductivity [17] and decreases the critical temperature (TC) [18]. Over doping of Ca atoms into YBCO grains results in a low TC due to the segregation of the calcium atoms at the grain boundary caused by the diffusion process [13].

Fig. 1

(A) Meissner effect of superconductor materials; (B) superconducting materials at temperature (T) below a critical temperature (Tc) [13].

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.

Experimental
Materials and 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.

Instrumentation

An X-ray diffractometer (XRD; Bruker, AXS analyzer-D8 Discover) with a VANTEC-1 detector and a double-crystal wide-angle goniometer was used to measure the phase composition and crystallinity at a scan speed of 5°/min with increments in 2θ of 0.05° or 0.03° from 10° to 90°, using CuKα radiation at a λ value of 0.15406 nm. The standard X-ray diffraction patterns were measured according to the international standards (Joint Committee on Powder Diffraction Standards, JCPDS).

A scanning electron microscope (SEM; JEOL, 5200) was used to characterize the microstructures of YCaBCO samples. The samples were coated with gold at a thickness of 0.1 μm to induce electrical conductivity. The electrical voltage was accelerated to 15 kV and subjected to 1,000x magnification.

Fourier transform infrared (FTIR) spectroscopy (Perkin Elmer, Bruker Alpha E) was used to characterize the chemical-functional groups of superconductors in the range 500–4,000 cm−1. The samples were prepared and mixed using potassium bromide (KBr) as a reference substance in the wave number range of 500–4,000.

A simultaneous thermal analyzer (STA; Netzsch 409) was utilized to measure the thermal reaction, decomposition temperature, and thermal stability. The superconductor specimens were measured at the heating rate of 10 °C/min under air conditioned from room temperature (25 °C) to 1,000 °C.

An impedance analyzer (dielectric test fixture: Hewlett Packard 4248A) was used to measure the electrical properties (capacitance, electrical conductivity, dielectric constant, and dielectric loss) in the frequency range of 500 Hz – 1 MHz at room temperature. The obtained powder sample after firing was pressed into a disk-shaped mold with thickness of 0.5–1.0 mm, as shown in Figure 2.

Fig. 2

Superconductor sample preparation for measurement of electrical properties of disk-like samples: (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-1000-eggshell, (E) YCaBCO-900-com grade, (F) YCaBCO-1000-com grade, (G) YCaBCO-NaOH-900-eggshell, and (H) YCaBCO-NaOH-1000-eggshell. YBCO, yttrium barium copper oxide; YCaBCO, yttrium calcium barium copper oxide.

Sample preparation

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.

Y2O3+3CuO+CaO+2BaCl2YCaBa2Cu3O7x+2Cl2 \begin{array}{*{35}{l}}{{\text{Y}}_{2}}{{\text{O}}_{3}}+3\text{CuO}+\text{CaO}+2\text{BaC}{{\text{l}}_{2}} \\ \to \text{YCaB}{{\text{a}}_{2}}\text{C}{{\text{u}}_{3}}{{\text{O}}_{7-x}}+2\text{C}{{\text{l}}_{2}} \\ \end{array}

Formulas for preparation of superconductor samples.

Sample Formula 1 Formula 2 Formula 3 Formula 4 Formula 5
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−z (ref.) YCaBa2Cu3O7−z (CaO from eggshell) YBa2Cu3O7−z (CaO from eggshell) YCaBa2Cu3O7−z (commercial grade CaO) YCaBa2Cu3O7−z (commercial grade CaO)
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.

CaCO3ΔCaO+CO2 \text{CaC}{{\text{O}}_{3}}\xrightarrow{\Delta }\text{CaO}+\text{C}{{\text{O}}_{2}}

Density values and solubility data of chemical substances used for preparation of superconductors.

Chemical substance Density (g/cm3) H2O Ethanol (C2H5OH) HCl
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.

Results and discussion
Characteristics of starting materials and superconductors with/without addition of calcium oxide (CaO)

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.

Fig. 3

(A) STA of superconductors with added calcium oxide (CaO) from eggshell. (B) STA of super-conductors with added commercial grade calcium oxide (CaO). STA, simultaneous thermal analysis.

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].

Fig. 4

YCaBCO powder with added calcium oxide (CaO): (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-NaOH-900-eggshell, (E) YCaBCO-900-com grade, and (F) YCaBCO-900-com grade. YBCO, yttrium barium copper oxide.

Fig. 5

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 ν (Cu-O), at 528 cm−1 for ν (Cu-O), at 550 cm−1 and 692 cm−1 for ν (Ba-Cu-O), at 565 cm−1 and 588 cm−1 for ν (Y-O) and ν (Y-O-Y), and at 1,420 cm−1 for strong ν (C=O). The obtained FTIR spectra of the YCaBCO samples fired at 900 °C had a peak at 1,250–1,500 cm−1 for ν (C-O) and were close to the FTIR result of YBCO-900-ref. However, the FTIR spectra of the YCaBCO samples fired at 1,000 °C had no peak for ν (C-O) at 1,250–1,500 cm−1. The YCaBCO samples fired at 900 °C and 1,000 °C showed sharp peaks at 1,480–1,600 cm−1 due to ν(C=O) and ν(C=C), respectively. The other peak of the YCaBCO samples fired at 900°C and 1,000 °C was at 3,450–3,500 cm−1 for ν (O-H) due to the water molecule in their structures. Furthermore, Thuy et al. [21] described the FTIR results of YBCO showing a sharp peak at 565 cm−1 for Y2O3 and BaCO3, assigned to ν (Y-O) and ν (Ba-O), respectively, while Ozabaci [22] suggested peaks of YBCO assigned at 588 cm−1, 1,026 cm−1, 1,085 cm−1, and 1,216 cm−1 for ν (Y-O-Y). The strong absorption bands of YBCO located at 591 cm−1 and 701 cm−1 were assigned to the vibration of Cu-O. In addition, Hamadneh et al. [23] reported bands at 1,660 cm−1, 2,382 cm−1, as well as a broad band peak at 2,800–3,100 cm−1, belonging to ν (C=O), ν (C-O), and ν (O-H), respectively.

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.

Fig. 6

Spectra of raw materials and superconducting materials measured by FTIR. FTIR, Fourier transform infrared spectroscopy.

Fig. 7

Patterns of the X-ray peaks of superconductor samples prior to and after firing.

Fig. 8

(A) and (B) Orthorhombic and (C) tetragonal structure of superconductor (YBCO) with and without addition of CaO [15]. YBCO, yttrium barium copper oxide.

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).

Fig. 9

Microstructures of calcium oxide and superconductor samples observed using SEM at 1,000× magnification: (A) calcium oxide from eggshell, (B) YBCO-900-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-900-com grade, (E) YCaBCO-NaOH-900-eggshell, (F) YCaBCO-NaOH-900-com grade. SEM, scanning electron microscope; YBCO, yttrium barium copper oxide.

Electrical properties of superconductors with/without addition of calcium oxide

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.

Fig. 10

(A) Conductivity of samples versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples versus electromagnetic frequency from 500 Hz to 1 MHz.

Fig. 11

(A) Conductivities of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz.

Fig. 12

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.

Sample Frequency(Hz) Capacitance (pF) Electrical conductivity (S/m) Dielectric constant Dielectric loss
CuO 0.5 × 102 40.53 ± 0.39 1,960.00 ± 18.700 8.334 ± 0.080 1.511 ± 0.671
CuO 1.0 × 106 5.63 ± 0.42 7.08 ± 0.010 1.158 ± 0.087 0.122 ± 0.053
Y2O3 0.5 × 102 341.63 ± 12.95 236.00 ± 9.040 71.366 ± 2.706 1.529 ± 0.663
Y2O3 1.0 × 106 64.75 ± 0.29 0.622 ± 0.003 13.526 ± 0.061 0.128 ± 0.057
BaCl2 0.5 × 102 66.63 ± 0.89 1,200.00 ± 16.100 13.808 ± 0.184 1.478 ± 0.641
BaCl2 1.0 × 106 21.88 ± 0.63 1.83 ± 0.052 4.535 ± 0.130 0.155 ± 0.068
CaO (commercial grade) 0.5 × 102 444.19 ± 5.58 185.00 ± 2.30 94.627 ± 1.189 1.685 ± 0.730
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) 0.5 × 102 9.40 ± 0.04 8,700.00 ± 38.700 1.966 ± 0.009 1.795 ± 0.777
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 0.5 × 102 8,286.70 ± 28.49 (3.60 ± 0.01) × 107 1,874.794 ± 6.446 1.351 ± 0.585
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 0.5 × 102 8,326.70 ± 28.00 (7.60 ± 0.01) × 107 1,883.910 ± 6.400 1.351 ± 0.590
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 0.5 × 102 8,540.10 ± 2.00 (1.32 ± 0.00) × 108 1,988.540 ± 0.500 0.534 ± 0.030
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 0.5 × 102 9,765.30 ± 47.00 (1.15 ± 0.01) × 108 2,281.880 ± 11.00 0.534 ± 0.230
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 0.5 × 102 14,622.02 ± 1.10 (8.31 ± 0.01) × 107 3,163.23 ± 0.20 1.635 ± 0.110
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 0.5 × 102 10,838.78 ± 233 (1.10 ± 0.02) × 108 2,389.53 ± 51.40 1.635 ± 0.715
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 0.5 × 102 8,225.75 ± 0.73 (1.40 ± 0.01) × 108 1,874.59 ± 0.17 1.351 ± 0.585
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 0.5 × 102 9,484.85 ± 57.47 (1.19 ± 0.01) × 108 2,200.69 ± 13.33 1.351 ± 0.585
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 0.5 × 102 14,821.33 ± 215 (8.70 ± 0.10)×107 3,022.77 ± 43.93 1.483 ± 0.064
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 0.5 × 102 10,213.51 ± 9.27 (1.24 ± 0.001)×108 2,125.19 ± 1.93 1.483 ± 0.644
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.

Conclusion

Yttrium calcium barium copper oxide (YCaBa2Cu3O7−x) with added CaO from eggshell prepared via the sol-gel process acted as a biodielectric, and this has potential applications in the manufacture of a superior bio-based superconducting material. The limitation in doping with CaO is that it should follow the stoichiometric ratio of 1:2:3:1 for Y2O3:BaCl2:CuO:CaO based on the molar mass. The obtained superconductor YCaBa2Cu3O7−x was a solid black powder with a density of 6.10 ± 0.06 g/cm3, consistent with the theoretical density (6.30 g/cm3). Its asymmetrical crystal structure of the orthorhombic form (YCaBa2Cu3O7−x) induced polarization at electromagnetic frequency and increased oxygen absorption in relation to the critical current density. The values of the capacitance, electrical conductivity, and dielectric constant of the superconductor YCaBCO-900-eggshell measured at 500 Hz at room temperature (27 °C) were 8,540.10 ± 2.00 pF, (1.32 ± 0.00) × 108 S/m, and 1,988.540 ± 0.500, respectively, better than those of YBCO-900-ref and YCaBCO-900-com grade. Further, the capacitance, electrical conductivity, and dielectric constant of the superconductor YCaBCO-900-com grade, measured under the same conditions 500 Hz and 27 °C, were equal to 8,225.75 ± 0.73 pF, (1.40 ± 0.01) × 108 S/m, and 1,874.59 ± 0.17, respectively. Therefore, CaO prepared from eggshell can function as a feasible-alternative dielectric product for producing a superior and sustainable bio-superconducting material.

Fig. 1

(A) Meissner effect of superconductor materials; (B) superconducting materials at temperature (T) below a critical temperature (Tc) [13].
(A) Meissner effect of superconductor materials; (B) superconducting materials at temperature (T) below a critical temperature (Tc) [13].

Fig. 2

Superconductor sample preparation for measurement of electrical properties of disk-like samples: (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-1000-eggshell, (E) YCaBCO-900-com grade, (F) YCaBCO-1000-com grade, (G) YCaBCO-NaOH-900-eggshell, and (H) YCaBCO-NaOH-1000-eggshell. YBCO, yttrium barium copper oxide; YCaBCO, yttrium calcium barium copper oxide.
Superconductor sample preparation for measurement of electrical properties of disk-like samples: (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-1000-eggshell, (E) YCaBCO-900-com grade, (F) YCaBCO-1000-com grade, (G) YCaBCO-NaOH-900-eggshell, and (H) YCaBCO-NaOH-1000-eggshell. YBCO, yttrium barium copper oxide; YCaBCO, yttrium calcium barium copper oxide.

Fig. 3

(A) STA of superconductors with added calcium oxide (CaO) from eggshell. (B) STA of super-conductors with added commercial grade calcium oxide (CaO). STA, simultaneous thermal analysis.
(A) STA of superconductors with added calcium oxide (CaO) from eggshell. (B) STA of super-conductors with added commercial grade calcium oxide (CaO). STA, simultaneous thermal analysis.

Fig. 4

YCaBCO powder with added calcium oxide (CaO): (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-NaOH-900-eggshell, (E) YCaBCO-900-com grade, and (F) YCaBCO-900-com grade. YBCO, yttrium barium copper oxide.
YCaBCO powder with added calcium oxide (CaO): (A) YBCO-900-ref, (B) YBCO-1000-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-NaOH-900-eggshell, (E) YCaBCO-900-com grade, and (F) YCaBCO-900-com grade. YBCO, yttrium barium copper oxide.

Fig. 5

Perovskite structure of superconductor YBCO [15]. YBCO, yttrium barium copper oxide.
Perovskite structure of superconductor YBCO [15]. YBCO, yttrium barium copper oxide.

Fig. 6

Spectra of raw materials and superconducting materials measured by FTIR. FTIR, Fourier transform infrared spectroscopy.
Spectra of raw materials and superconducting materials measured by FTIR. FTIR, Fourier transform infrared spectroscopy.

Fig. 7

Patterns of the X-ray peaks of superconductor samples prior to and after firing.
Patterns of the X-ray peaks of superconductor samples prior to and after firing.

Fig. 8

(A) and (B) Orthorhombic and (C) tetragonal structure of superconductor (YBCO) with and without addition of CaO [15]. YBCO, yttrium barium copper oxide.
(A) and (B) Orthorhombic and (C) tetragonal structure of superconductor (YBCO) with and without addition of CaO [15]. YBCO, yttrium barium copper oxide.

Fig. 9

Microstructures of calcium oxide and superconductor samples observed using SEM at 1,000× magnification: (A) calcium oxide from eggshell, (B) YBCO-900-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-900-com grade, (E) YCaBCO-NaOH-900-eggshell, (F) YCaBCO-NaOH-900-com grade. SEM, scanning electron microscope; YBCO, yttrium barium copper oxide.
Microstructures of calcium oxide and superconductor samples observed using SEM at 1,000× magnification: (A) calcium oxide from eggshell, (B) YBCO-900-ref, (C) YCaBCO-900-eggshell, (D) YCaBCO-900-com grade, (E) YCaBCO-NaOH-900-eggshell, (F) YCaBCO-NaOH-900-com grade. SEM, scanning electron microscope; YBCO, yttrium barium copper oxide.

Fig. 10

(A) Conductivity of samples versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples versus electromagnetic frequency from 500 Hz to 1 MHz.
(A) Conductivity of samples versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples versus electromagnetic frequency from 500 Hz to 1 MHz.

Fig. 11

(A) Conductivities of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz.
(A) Conductivities of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz. (B) Dielectric constants of samples with/without the addition of CaO from eggshell versus electromagnetic frequency from 500 Hz to 1 MHz.

Fig. 12

Electrical properties due to polarization at various electromagnetic frequencies [7].
Electrical properties due to polarization at various electromagnetic frequencies [7].

Formulas for preparation of superconductor samples.

Sample Formula 1 Formula 2 Formula 3 Formula 4 Formula 5
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−z (ref.) YCaBa2Cu3O7−z (CaO from eggshell) YBa2Cu3O7−z (CaO from eggshell) YCaBa2Cu3O7−z (commercial grade CaO) YCaBa2Cu3O7−z (commercial grade CaO)
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

Density values and solubility data of chemical substances used for preparation of superconductors.

Chemical substance Density (g/cm3) H2O Ethanol (C2H5OH) HCl
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

Electrical properties of raw materials and superconductor samples measured at room temperature (27 °C), (±SD), n = 3.

Sample Frequency(Hz) Capacitance (pF) Electrical conductivity (S/m) Dielectric constant Dielectric loss
CuO 0.5 × 102 40.53 ± 0.39 1,960.00 ± 18.700 8.334 ± 0.080 1.511 ± 0.671
CuO 1.0 × 106 5.63 ± 0.42 7.08 ± 0.010 1.158 ± 0.087 0.122 ± 0.053
Y2O3 0.5 × 102 341.63 ± 12.95 236.00 ± 9.040 71.366 ± 2.706 1.529 ± 0.663
Y2O3 1.0 × 106 64.75 ± 0.29 0.622 ± 0.003 13.526 ± 0.061 0.128 ± 0.057
BaCl2 0.5 × 102 66.63 ± 0.89 1,200.00 ± 16.100 13.808 ± 0.184 1.478 ± 0.641
BaCl2 1.0 × 106 21.88 ± 0.63 1.83 ± 0.052 4.535 ± 0.130 0.155 ± 0.068
CaO (commercial grade) 0.5 × 102 444.19 ± 5.58 185.00 ± 2.30 94.627 ± 1.189 1.685 ± 0.730
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) 0.5 × 102 9.40 ± 0.04 8,700.00 ± 38.700 1.966 ± 0.009 1.795 ± 0.777
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 0.5 × 102 8,286.70 ± 28.49 (3.60 ± 0.01) × 107 1,874.794 ± 6.446 1.351 ± 0.585
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 0.5 × 102 8,326.70 ± 28.00 (7.60 ± 0.01) × 107 1,883.910 ± 6.400 1.351 ± 0.590
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 0.5 × 102 8,540.10 ± 2.00 (1.32 ± 0.00) × 108 1,988.540 ± 0.500 0.534 ± 0.030
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 0.5 × 102 9,765.30 ± 47.00 (1.15 ± 0.01) × 108 2,281.880 ± 11.00 0.534 ± 0.230
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 0.5 × 102 14,622.02 ± 1.10 (8.31 ± 0.01) × 107 3,163.23 ± 0.20 1.635 ± 0.110
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 0.5 × 102 10,838.78 ± 233 (1.10 ± 0.02) × 108 2,389.53 ± 51.40 1.635 ± 0.715
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 0.5 × 102 8,225.75 ± 0.73 (1.40 ± 0.01) × 108 1,874.59 ± 0.17 1.351 ± 0.585
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 0.5 × 102 9,484.85 ± 57.47 (1.19 ± 0.01) × 108 2,200.69 ± 13.33 1.351 ± 0.585
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 0.5 × 102 14,821.33 ± 215 (8.70 ± 0.10)×107 3,022.77 ± 43.93 1.483 ± 0.064
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 0.5 × 102 10,213.51 ± 9.27 (1.24 ± 0.001)×108 2,125.19 ± 1.93 1.483 ± 0.644
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

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