Ultrasonic is an eco-friendly, safe, and inexpensive technology[1,2] that is used as a versatile tool in a wide range of scientific and technological applications such as biology, chemistry, physics, medicine, materials science and industrial applications[8–11]. One of the ultrasonic applications is the synthesis of nanoparticles. The waves propagated in the aqueous solution form transient bubbles that explode, causing the nanostructures to disperse and form. Epoxy resins are thermoset polymers that have interesting properties such as high chemical resistance, good tensile strength, compressive and flexural strength, good thermal resistance, and acceptable solubility[14–16]and then incorporated into PiP-DOPO through in situ reaction, resulting in the formation of the hybrids (PD-rGO. These polymers have received a lot of attention today due to their interesting properties and have many applications, including in the electronics, aerospace, and coating industries[17–19]. Xia et al  synthesized polyaniline nanoparticles using ultrasonic waves. They found that the use of ultrasonic waves increased the polymerization rate of aniline, which was very slow under normal conditions. Ultrasonic radiation also emits HCL molecules and improved the degree of doping. Song et al  synthesized magnesium hydroxide nanoparticles using the ultrasonic method. Their results showed that ultrasonic waves can limit the growth of magnesium hydroxide crystals in each lattice plate and improve the hydrophobicity of magnesium hydroxide nanoparticles. Rahmawati et al 400 and 400 kHz. The stirring rates performed in the synthesis process are varied from 500 to 900 rpm. The qualitative analysis by using X-Ray Diffractometer (XRD synthesized Fe3O4 nanoparticles using ultrasonic methods. Their results showed that using the deby sherer equation, the size of the Fe3O4 crystal from 21 to 25 nm depended on the ultrasonic frequency and the stirring speed. D. Gopi et al  synthesized hydroxyapatite nanoparticles by ultrasonic method. They investigated the time of ultrasonic irradiation on the size of nanoparticles in the presence of hollow spheres of glycine-acrylic acid. The results showed that the particle size decreases with increasing ultrasonic irradiation time. Therefore, the use of ultrasonic is an easy way to obtain nanoparticles, high quality anlppd with a suitable morphology. Mahdavi et al  investigated the effects of ultrasonic waves on the morphology and structure of ZnO nanoparticles. They observed that the purity of the samples increased with increasing ultrasonic wave power and irradiation time. Ultrasonic waves not only improve structure and morphology but also reduce grain size and prevent agglomeration. Alizadeh et al  used the ultrasonic method to synthesize CDs/TiO2 nanoparticles. They used the response surface methodology to optimize the shell thickness and found that the strength of ultrasonic waves and time had the greatest effect on the nanoparticle size. Utara et al  synthesized barium titanate nanoparticles using ultrasonic at 25 ° C and atmospheric pressure without calcination. The results showed that a more uniform and regular structure formed with increasing ultrasonic time. Other researchers have synthesized ferritic and magnetic nanoparticles for various applications[27–31]. Lee et al.  fabricated a polymer-based composite using electrospinning technique and nanocarbon reinforcement and investigated its thermal, mechanical, and electrical properties. Hoon oh et al. whether or not the reflective wave from an incident electromagnetic wave can be nullified. In this research, by blending conductive carbon black with the binder matrix of glass/epoxy composite, a radar absorbing structure (RAS constructed a radar-absorbing structure using glass/epoxy composite and carbon black in the X-band frequency range. Their system was designed to display the optimal amount of absorption for the X band in the range of 8.2 to 12 GHz. ISA et al  investigated the effect of fiber type and its composition on the thermal, mechanical and physical properties of polyester composites. The results showed that the composite with Kevlar reinforcer has the highest tensile strength and the composite with handmade nylon fiber reinforcer has the lowest tensile strength. The composition of the fibers also improved the thermal properties of the composite and had a positive effect on water absorption and density. Xu Ma et al  worked on the synthesis of degradable hyper branched epoxy resin and found that not only simultaneously elongation, tensile properties, modulus, flexural strength and impact resistance were increased about 50%, 64.8%, 70.4%, 38.1% and 93.7% respectively, but also their low temperature resistance improves.
In this paper, nanoparticles were first fabricated using the ultrasonic method as green and ecofriendly method and their properties were investigated. These nanoparticles were then added to the epoxy resin and the mechanical properties consist of ultimate tensile strength and toughness of the nanocomposites were investigated and compared with each other and epoxy polymer.
MATERIALS AND METHODS
To produce nanoparticles by ultrasonic method, first 0.97 g of iron nitrate per 0.3 g of cobalt sulfate, 0.92 g of iron nitrate per 0.3 g of nickel sulfate, and 1.2 g of iron nitrate per 0.3 g of copper sulfate were poured into 150 ml of distilled water and mixed with a stirrer for 20 minutes. The solution was then immersed in an ultrasonic device for 20 minutes. While the solution was in the ultrasonic device, 1 molar sodium hydroxide solution was slowly added to the main solution to bring the pH to 11. In the next step, the solution was centrifuged and placed in the oven to dry the nanoparticles and be ready for use in the next steps. Fig. 2 shows a schematic of the ultrasonic method.
To produce the polymer matrix composite, 5% by weight of the nanoparticles were first added to the epoxy resin and mixed together for 20 minutes. The produced composites were then placed in a vacuum apparatus for 20 minutes and placed in a room for two hours to de-bubble and eliminate pores. In the next step, the composites were poured into the mold and placed according to the standard at room temperature and then in the furnace to find the necessary mechanical properties. To evaluate the mechanical properties of the samples, nanocomposites made with a thickness of 4 mm according to the ASTM D638 standard and at a speed of 0.5 mm/min were tested. All tests were repeated three times and their mean was reported.
RESULTS AND DISCUSSION
To identify the phase, XRD analysis was taken from the generated samples, which is shown in Figs. 2-4. Fig. 2 illustrates the X-ray diffraction pattern (XRD) of cobalt ferrite nanoparticles (CoFe2O4) nanoparticles, the pattern has a suitable agreement with pure material standard using JCPDS: 00-022-1086 and Miller indexes include (220), (311), (400), (422), (511), (440) are observed in the pattern and approve purity of the phase in this rapid and simple reaction. XRD pattern of nickel ferrite nanoparticles (NiFe2O4) is shown in Fig. 3, also this spectrum has appropriate accordance with pure standard using JCPDS: 01-086-2267 and by miller indexes: (220), (311), (222), (400), (422), (440), (622), (444). Fig. 4 depicts the XRD pattern of copper ferrite nanoparticle (CuFe2O4) with JCPDS: 00-034-0425 and by miller indexes: (202), (311), (004), (224), (333), and (440).
An electron scan microscope was used to evaluate the morphology and particle size, with different magnifications showing Figs. 5 to 7. Fig 5 shows an electron scanning microscope image of cobalt ferrite nanoparticles with different magnifications and a work distance of 4.96 mm. Fig. 6 shows an electron scanning microscope image of nickel ferrite nanoparticles. The images confirm the formation of nanoparticles with a fine and uniform structure. Scanning electron microscope images with magnifications of 100 and 200 kx and work distances of 4.77 and 4.84 mm and at scales of 200 and 500 nm of copper ferrite nanoparticles are also shown in Fig. 7.
Figs. 8 to10 show the infrared absorption spectroscopy of cobalt ferrite, nickel ferrite, and copper ferrite nanoparticles. Peaks in areas 588, 624, and 438 related to metal-oxygen bonding, peaks in areas 1119-1631, 1117-1537, and 1124-1629 related to synthetic precursors, and wide peaks in areas 3425, 3445, and 3422 related to oxygen-hydrogen bonding.
Fig. 11 shows the stress-strain diagrams of the composites and the base polymer. As can be seen, after adding nanoparticles to the epoxy resin and their uniform distribution, the final tensile strength of the composites has significantly improved compared to the base polymer, which can be due to the homogeneous distribution of nanoparticles in the matrix of epoxy resin and adhesion between epoxy resin and nanoparticles. Also, by adding nanoparticles to the epoxy resin, the toughness of the composite has improved compared to the base polymer. The UTS and toughness values are 75.93539 MPa and 4.326422 Mj/m3 for epoxy/CoFe2O4 nanocomposite, 81.79603 MPa and 4.861615 Mj/m3 for epoxy/NiFe2O4 nanocomposite, 76.6423 MPa and 4.91496 Mj/m3 for epoxy/CuFe2O4 composite, and 64.43333 MPa and 3.76838 Mj/m3 for pure polymer, respectively. The highest ultimate tensile strength was observed in epoxy/NiFe2O4 nanocomposite and the lowest ultimate tensile strength was observed in the pure epoxy polymer. Also, the highest toughness was observed in epoxy/CuFe2O4 composite and the lowest toughness was observed in the pure epoxy polymer. The changes of which are shown in Fig. 12. Also, the highest ultimate tensile strength was observed in the nanocomposite fabricated with nickel ferrite nanoparticles.
In this paper, different ferrite nanoparticles were first produced in a very simple, inexpensive, and practical method and their properties were investigated. Then nanocomposites were produced with these nanoparticles and their tensile properties were investigated. Based on the results of this paper, ultrasonic is a suitable method for the production of nanoparticles with a uniform and fine-grained structure, and the nanoparticles produced to comply with standard peaks. According to the results of the tensile test of the samples, the composites produced, in addition to better ultimate tensile strength than the base polymer, also have better toughness. The highest ultimate tensile strength was obtained in nanocomposites fabricated with nickel ferrite nanoparticles and the highest toughness value was obtained in nanocomposites made of copper ferrite nanoparticles.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.