CeAlO₃ nanoparticle synthesis through combustion-assisted method and structural property assessment in Nano-CeAlO₃ polymer composites

ABSTRACT

This study explores enhancing epoxy polymers with cerium aluminate (CeAlO₃) nanoparticles via a solution combustion process. CeAlO₃ loading (0.5 to 2.5 wt.%) significantly influences resulting composite properties. Characterization techniques confirm CeAlO₃ presence, porous spherical morphology, and formation. FTIR spectroscopy identifies functional groups, while TGA shows excellent thermal stability below 200 °C, with minimal mass loss, and stability at 900 °C. The composites exhibit enhanced properties, with maximum tensile strength at 0.5 wt.%, a linear increase in tensile modulus up to 2.5 wt.%, and maximum compressive strength at 0.5 wt.%, with increasing modulus at higher filler loadings. These findings suggest CeAlO₃-filled epoxy composites hold promise for high-temperature applications, emphasizing the importance of low filler concentrations for optimal structural properties. Overall, this research underscores the potential of CeAlO₃ nanoparticles in advancing epoxy-based materials across various industries.

KEYWORDS:

• CeAlO₃ nanoparticles
• epoxy-resin & hardener
• material characterization methods
• polymer nanocomposites
• epoxy polymers

Introduction

The combustion synthesis method is widely employed for producing uniformly sized, finely dispersed crystalline oxides, metals, and alloys homogeneously [1]. This method offers the advantage of bypassing the need for intermediate preparation steps, making it a quick, straightforward, and time-efficient process. It is particularly versatile, enabling the synthesis of various metal-based materials, including nitrides, perovskites, oxides, carbides, and alloys, which find applications across diverse fields [2]. Among the different combustion processes, the solution combustion method stands out, especially when it comes to producing metal oxide nanoparticles. It offers the flexibility to tailor the qualities of oxides for a wide range of applications by adjusting the metal composition during synthesis. The solution combustion route is advantageous in generating homogeneous products with lower ignition temperatures.

The solution combustion method of nanoparticle synthesis is a chemical technique employed to produce nanoparticles, which are extremely small particles typically in the range of 1 to 100 nanometers. This approach involves a rapid and highly exothermic reaction between metal salts or metal-containing compounds and a suitable fuel, often an organic compound. This reaction takes place within a liquid medium, typically a solvent, leading to the formation of suspended nanoparticles within the solution [3,4]. In the solution combustion process, organic molecules containing functional groups, such as glycine, serve as fuels, while metal nitrates act as oxidisers. When the fuel-metal nitrate mixture is heated, it undergoes an extremely exothermic combustion reaction, producing fine solid powder and significant quantities of gaseous byproducts. The shape and size of the resulting nanoparticles are often strongly influenced by the type and quantity of the fuel in the reaction mixture. In certain cases, the choice and amount of fuel can even induce phase changes and the formation of metastable phases [4,5]. Cerium Aluminate (CeAlO₃) nanoparticles, a significant inorganic material, have widespread applications in catalysis, superconductors, and ceramics. They are used as catalysts and electrode-active materials for processes like carbon monoxide oxidation, hydrocarbon reactions, phenol degradation in supercritical water, and nitrous oxide decomposition with ammonia [6–12].

The solution combustion method is a chemical process utilised to fabricate nanoparticles, which are minute particles typically measuring between 1 to 100 nanometers in size. This technique involves a rapid and highly exothermic reaction between metal salts or compounds containing metals and a suitable fuel, often an organic compound. This reaction occurs within a liquid medium, commonly a solvent, resulting in the formation of suspended nanoparticles within the solution. In the solution combustion process, organic molecules containing functional groups, like glycine, act as fuels, while metal nitrates serve as oxidisers. Upon heating the mixture of fuel and metal nitrate, an extremely exothermic combustion reaction ensues, yielding fine solid powder along with significant amounts of gaseous byproducts. The shape and size of the resultant nanoparticles are frequently influenced by the type and quantity of the fuel incorporated into the reaction mixture. In specific instances, the selection and proportion of the fuel can even trigger phase transitions and the formation of metastable phases. One notable application of nanoparticles synthesised through this method is in the production of cerium aluminate (CeAlO₃) nanoparticles, which find extensive use in various fields such as catalysis, superconductors, and ceramics. These nanoparticles serve as catalysts and electrode-active materials in numerous processes including carbon monoxide oxidation, hydrocarbon reactions, phenol degradation in supercritical water, and nitrous oxide decomposition with ammonia [13–19].

Various-sized fillers are frequently used to reinforce polymers, aiming to enhance their properties and overcome some of the limitations inherent to polymers, thereby broadening their application potential. Traditional polymer composites have given way to a novel approach employing nanoscale fillers to augment the mechanical, physical, and chemical attributes of polymers. Nanofillers can be classified into three main categories: two-dimensional (2D) layered materials such as silicate and graphene, one-dimensional (1D) materials like carbon nanofibers and nanotubes, and fibrous or zero-dimensional (0D) materials such as quantum dots and spherical silica [20–24]. Nano-metal oxide polymer composites incorporate minute metal particles into a conventional polymer matrix. Incorporating metal oxide nanoparticles into polymers leads to significant improvements in properties, including increased toughness, enhanced mechanical strength, improved thermal conductivity, and elevated electrical conductivity. Typically, less than 5% by weight of metal oxide nanoparticles are incorporated into the polymer matrix due to their remarkable efficiency in influencing the properties of the polymer composites [25–30].

Incorporating metal oxide nanoparticles into polymer composites imparts unique qualities to these materials, making them suitable for a wide range of applications. Notably, metal oxide nanoparticles like CeAlO₃ exhibit distinctive optical properties, which are contingent on both their size and shape. This renders them promising candidates for applications such as heterogeneous catalysis, and more. The present work is focused on the synthesis of metal oxide-polymer nanocomposites using CeAlO₃ nanoparticles. The present study aims to synthesise composite materials comprising nano-CeAlO₃ and epoxy, varying the quantities of synthesised CeAlO₃ nanoparticles. To assess these materials, various characterisation techniques were employed, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Thermogravimetric Analysis (TGA), Photoluminescence (PL), Mechanical properties utilised using Universal Testing Machine (UTM). Experiments were conducted to investigate the influence of CeAlO₃ nanoparticle loading on polymer curing time, thermal properties, optical properties, and mechanical properties. These characteristics are crucial when using these nanocomposites as strengthening materials [31,32].

The even and consistent dispersion of nanoparticles throughout the epoxy matrix plays a crucial role in making a polymer composite distinct and improving its overall mechanical characteristics. Several studies have highlighted that incorporating low concentrations of nano-fillers, typically ranging from 0.5 wt.% to 2.5 wt.%, results in a substantial enhancement in mechanical properties. In specific investigations, CeAlO₃ was employed as a nanofiller in epoxy, demonstrating its capability to enhance surface damage under multi-scratching conditions after viscoelastic recovery. Researchers noted that the addition of nanoparticles increased the stiffness of epoxy. The impact of CeAlO₃ concentration on the mechanical properties of epoxy was thoroughly examined. Tensile properties, including ultimate tensile strength and tensile modulus, as well as compressive properties, such as compressive strength and compressive modulus, showed significant improvements. The introduction of CeAlO₃ also contributed to enhanced crack resistance, particularly up to a 2.5wt% concentration in epoxy. However, a further increase in filler content resulted in a decline in mechanical properties. These findings underscore the delicate balance required in optimising the concentration of CeAlO₃ for achieving the desired improvements in epoxy mechanical performance [33–35].

Over the past decade, polymer nanocomposites have garnered considerable attention from both industry and academia. These materials represent a novel category of multiphase substances characterised by the dispersion of an ultrafine phase typically ranging from 1 to 100 nanometers. They offer an intriguing blend of inorganic-organic or organic-organic components, presenting not only promising technological applications but also serving as valuable systems for investigating fundamental scientific principles on a scale intermediate between nano- and microscale. Numerous experimental studies have revealed that polymer nanocomposites exhibit novel and often enhanced properties that surpass those of individual phases or conventional composite materials. These improvements encompass mechanical characteristics such as increased tensile strength and modulus, reduced thermal expansion coefficients, and enhanced solvent resistance. Moreover, the inclusion of nanoparticles generally augments the elastic modulus without compromising rheological behaviour or processing efficiency, while also influencing the optical properties of the polymer matrix. The distinctive conformation of polymers within the nanoparticle host galleries, coupled with specific polymer-surface interactions not typically observed in bulk materials, significantly alters local and global polymer dynamics. This confinement effect profoundly impacts chain dynamics and contributes to the observed synergistic enhancements in material properties. Despite these advancements, the underlying mechanisms driving these improvements remain incompletely understood. Current theories suggest that nanoparticle effects stem from optically confined polymer matrices, quantum size phenomena, and Coulombic charging effects arising from ultrafine sizes, morphologies, and interfacial interactions between phases [36–47].

CeAlO₃ nanoparticles and nano-CeAlO₃ polymer composites are incredibly versatile materials with significant applications, especially in the aerospace sector. They possess distinct properties, including size-dependent optical and catalytic characteristics, which are highly valuable in modern technology. To fully harness their potential in aerospace applications, a comprehensive set of analytical techniques is required for their characterisation. This includes using SEM and EDX for examining surface morphology and elemental composition, XRD for studying crystal structures, FTIR for identifying functional groups, TGA for assessing thermal stability, PL for assessing Luminescence spectra, UTM for assessing mechanical properties, and this characterisation process enables tailoring these materials to meet the specific demands of the aerospace industry. In aerospace applications, these materials excel under extreme conditions and seamlessly integrate into critical components such as engine parts, heat shields, and structural elements. They contribute to enhanced safety and durability while also serving as effective reinforcing agents for polymers, thus improving the thermal properties of materials used in aircraft construction. This results in reduced weight, improved fuel efficiency, and enhanced overall performance of aerospace systems [48]. The incorporation of CeAlO₃ nanoparticles in the synthesis of CeAlO₃ nanoparticles and nano-CeAlO₃ epoxy composite materials is aimed at enhancing the composite’s properties and expanding its applications across various fields [49]. The integration of nanofillers into polymer matrices represents a promising strategy to enhance resistance against chemical degradation and environmental challenges. This advancement is particularly valuable for applications exposed to harsh chemicals and extreme conditions, commonly encountered in industrial and outdoor settings. This approach holds substantial potential for addressing durability concerns in demanding operational environments [50].

In terms of applications, polymer composites incorporating CeAlO₃ and similar nano-fillers are being employed in the aerospace industry for the manufacturing of components such as aircraft panels, wings, and structural elements [51]. These advanced materials contribute to the development of lightweight yet robust structures, improving fuel efficiency and overall aircraft performance. The enhanced polymer composites designed for food packaging find diverse applications. The improved mechanical properties contribute to the packaging’s increased robustness, offering superior protection for the contents within. Furthermore, the heightened resistance to cracks observed in these composites proves particularly valuable in averting the formation of fractures that may endanger the packaging’s reliability, thereby ensuring the safety and quality of the packaged food [52,53].

Materials and methods

Materials

The precursor salt of Cerium nitrate hexahydrate (Ce(NO₃)₃. 6H₂O, ≥ 90 %), Aluminium nitrate nonahydrate (Al(NO₃)₃ · 9H₂O ≥ 90 %) and Glycine (CH₂NH₂COOH) were obtained from Sigma-Aldrich. The Araldite epoxy resin XIN-100 IN and Araldite hardener XIN-900 IN were used as received. Metal precursor solutions were created using deionised water.

Synthesis of CeAlO₃ nanoparticles

CeAlO₃ nanoparticles were synthesised via the solution combustion method, where Glycine was employed as a combustion enhancer along with Cerium nitrate hexahydrate precursor salt. The fuel-to-nitrate ratio (F/N) was held at 0.3, requiring the dissolution of 4.34 g of Cerium Nitrate Hexahydrate, 7.5 g of Aluminium nitrate nonahydrate, and 1.8 grams of Glycine dissolved in 100 mL of deionised water. The reaction mixture was consistently agitated on a heated plate. As the heating process advanced, it resulted in the release of gases, including carbon dioxide, water vapour, and nitrogen dioxide (distinguished by its reddish-brown hue and potent odour), leading to the formation of a gel. Within a short period after gel formation, the reaction spontaneously reached completion through self-ignition combustion, producing a fine, porous powder. Subsequently, the ultimate product underwent a 3-hour calcination process at 600 °C in a muffle furnace.

Preparation of nano CeAlO₃ polymer-epoxy composite

A specified quantity of epoxy was measured and subjected to sonication for 45 minutes along with CeAlO₃ using a 200 W ultrasonicator, which caused the epoxy’s temperature to rise to 60 °C. Different weight percentages (wt.%) of CeAlO₃, specifically 0.5, 1.0, 1.5, 2.0, and 2.5 wt.%, were prepared and mixed during sonication. Following cooling to room temperature, a mixture of epoxy and hardener was prepared and cast into a mould. The mixture was left to dry at ambient temperature for 24 hours. To obtain Pristine epoxy, a combination of 90 % resin and 10 % hardener by volume was mixed. The same process was repeated to produce polymer composites infused with various proportions of CeAlO₃. After the drying process, epoxy and nano-CeAlO₃ polymer epoxy composites were obtained. The thickness of both the pristine epoxy and epoxy composites was measured using a digital vernier calliper, and it was determined that the average thickness for both was approximately 3 mm.

Material characterization techniques

The elemental composition and morphology analysis of CeAlO₃ nanoparticles and nano-CeAlO₃ polymer composites were carried out using a Hitachi S-3400 scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) and the INCA EDS detector. X-ray diffraction (XRD) measurements were conducted using an X-ray diffractometer with a tube voltage and current set at 40 kV and 40 mA. X-ray diffraction data collection was performed using a Bruker D8 ADVANCE from Germany. A Cu Kα (λ=1.5406 Å) source with a Ni filter was employed to generate X-rays. Data was collected over the 2θ range from 10 to 90 degrees, with a step size of 0.02 degrees. FTIR Spectral data was recorded as a percentage of transmittance, with a bandwidth of 5 nm, and were acquired using the ALPHA FT-IR instrument (Bruker) over a range of 4000 to 500 cm⁻¹ in ECO-ATR transmittance mode. A total of 64 scans were performed during the FTIR analysis, with a resolution of 4 cm⁻¹. Thermal properties were evaluated using a Thermal Analyzer-STA 449 F5 Jupiter, employing N₂ gas as the sweeping gas within a SiC furnace. The mass loss data was collected over a temperature range of 30 to 900 ℃ for CeAlO₃ nanoparticles, using a heating rate of 10 ℃/min, and maintaining gas flow rates of 20 mL/min for Gas Flow (protective) and 50 mL/min for Gas Flow (purge2). For the TGA experiments, an empty Al₂O₃ crucible was employed as a reference, while an Al₂O₃ crucible filled with the sample was used for the CeAlO₃ nanoparticle analysis. The same experimental parameters were applied to the nano-CeAlO₃ epoxy polymer composites, except for the heating temperature, which ranged from 30 to 600 ℃. The F2700 fluorescence spectrometer was used for examining the fluorescence properties of composites comprising CeAlO₃ and Epoxy. The mechanical properties, including tensile and compressive strength, were evaluated utilising the Wance Universal Tensile Testing Machine (UTM). Tensile properties were assessed following the ASTM D638 standard testing procedure, with a crosshead speed of 10 mm-min-1. Compression properties were tested according to the ASTM D695 standard, with a testing speed of 2 mm-min⁻¹. Three samples were taken and tested for each composite composition, and the reported values represent the averages.

Results and discussion

FE-SEM and EDX analysis

The CeAlO₃ nanoparticles shown in Figure 1 predominantly display a spherical shape [54]. Figure 1 illustrates the pure CeAlO₃ nanoparticles, which are spherical, porous, and tend to aggregate. These CeAlO₃ nanoparticles have sizes falling within the range of 44.57 to 74.66 nm. The agglomeration of particles is primarily attributed to the high surface energy and substantial surface area of the nanoparticles. At the nanoscale, large Van der Waals surface charges contribute to this agglomeration phenomenon [55–59]. In Figure 2, SEM images depict (a) pristine epoxy and epoxy- CeAlO₃ polymer composites with varying CeAlO₃ contents of (b) 0.5 wt.%, (c) 1.0 wt.%, (d) 1.5 wt.%, (e) 2.0 wt.%, and (f) 2.5 wt.%.

Figure 1. Scanning electron microscopy (SEM) images depicting cerium aluminate nanoparticles synthesized through the solution combustion method.

Figure 2. The scanning electron microscopy (SEM) images of (a) the pristine epoxy and epoxy- CeAlO₃ polymer composites with different CeAlO₃ content, specifically (b) 0.5 wt.%, (c) 1.0 wt.%, (d) 1.5 wt.%, (e) 2.0 wt.%, and (f) 2.5 wt.%.

Figure 2 reveals that at lower concentrations, the nanoparticles are evenly distributed within the epoxy matrix. However, as the nanofiller content increases, agglomeration becomes more evident, with larger clusters forming in some of the images. The extent of aggregation of CeAlO₃ nanoparticles rises with higher filler content. Achieving a uniform dispersion of nanofillers within an epoxy polymer poses a significant challenge in the development of polymer composites [60–62]. Furthermore, this increased agglomeration subsequently affects the thermal characteristics of the polymer composite.

In Figure 3, the EDX spectrum displays seven prominent peaks, approximately at 0.3 keV, corresponding to the O element, the peaks at 1.6 KeV attributed to the Al element, and peaks at 0.85, 4.9, 5.1, 5.2, and 5.4 keV, attributed to the Ce element. Furthermore, EDX analysis was utilised to investigate potential impurities and provide information about the elemental composition of the synthesised CeAlO₃ nanoparticles, as illustrated in Figure 3. The detailed elemental composition of CeAlO₃ can be found in Table 1.

Figure 3. An EDX graph showcasing the existence of Ce, Al, and O elements.

Table 1. The elemental composition of CeAlO₃ nanoparticles that was measured using energy dispersive X-ray (EDX).

Element	Weight %	Atomic %
Ce	37.38	7.61
Al	26.51	28.03
O	36.11	64.37

XRD analysis of CeAlO₃ and epoxy-CeAlO₃ composites

The X-ray diffraction (XRD) patterns of the CeAlO₃ nanoparticles, depicted in Figure 4, display distinct peaks. These patterns prominently feature specific angles at 2θ values of approximately 16.9°, 28.9°, 33.3°, 47.8°, 56.65°, 70.0°, and 77.3°. Each of these angles corresponds to distinct crystal planes within the CeAlO₃ crystal structure, namely the (100), (111), (110), (111), (200), (210), and (211) planes, respectively. The sample of CeAlO₃ displayed a high degree of crystallinity, closely matching the CeAlO₃ crystal structure as per the JCPDS file JCPDS 48–1548. The Scherrer equation, considering the Full Width at Half Maximum (FWHM) of peaks, X-ray wavelength, and diffraction angles, was employed to determine the crystallite size of CeAlO₃. This approach involved analysing X-ray diffraction (XRD) patterns and their correlation with the atomic arrangement within the crystals. Wider peaks suggest a greater degree of size variation [63,64].

Figure 4. The XRD pattern of cerium aluminate nanoparticles synthesized using the solution combustion method with a lattice plane for each peak.

The average size of crystallites (D) was calculated using the Debye–Scherrer formula [64], as represented in Equation (1)(1) $\mathit{D}=0.9\mathit{\lambda }/\mathit{\beta cos\theta }$(1) .

(1) $\mathit{D}=0.9\mathit{\lambda }/\mathit{\beta cos\theta }$(1)

In the analysis, λ signifies the wavelength of the X-ray source (0.15418 nm), specifically corresponding to Cu K-alpha radiation. The parameter β denotes the Full Width at Half Maximum (FWHM), and θ represents the diffraction angle in the determination of crystallite size using the Debye–Scherrer formula. The computed mean crystallite size was established at 53.32 nm [65]. This measurement falls within the range of particle sizes obtained from the SEM data.

In the composite polymer with nano-CeAlO₃, you can find aggregated clusters that reach sizes of up to 500 nm. With an increase in the concentration of CeAlO₃ in the nano-CeAlO₃ polymer composite from 0.5% to 2.5% by weight, there is a corresponding elevation in saturation levels, leading to a reduction in the distance between CeAlO₃ molecules among the particles. The XRD patterns of the polymer composite, containing CeAlO₃ nanoparticles ranging from 0.5 to 2.5 wt.%, reveal prominent and strong peaks, reflecting the extent of CeAlO₃ integration into the epoxy matrix, as depicted in Figure 5. The strength of the peaks in the polymer composites is influenced by the amount of CeAlO₃ loading. The augmentation of CeAlO₃ loading from 0.5% to 2.5 wt.% leads to an increase in peak intensity, signifying enhanced crystallinity and a greater presence of CeAlO₃ in the polymer composites. However, the peak position remains consistent even with increasing CeAlO₃ loading. Figure 4 illustrates that the XRD analysis reveals the slightly amorphous nature of epoxy, with a crystallinity level of 90%. In Figure 5, the XRD patterns of the nano-CeAlO₃ polymer composites, containing varying amounts of CeAlO₃ from 0.5 to 2.5 wt.%, demonstrate the crystalline nature of epoxy. This is apparent from the peak observed around 2θ = 28.9°, corresponding to the epoxy (111) crystal plane. Additionally, a few peaks around 18.1 and 28.7° become more prominent as the amount of CeAlO₃ nanoparticles incorporated into the composite increases [66–70].

Figure 5. The X-ray diffraction (XRD) pattern illustrates (a) the pristine epoxy and nano- CeAlO₃ polymer composites with different concentrations of CeAlO₃ impregnated at (b) 0.5 wt.%, (c) 1.0 wt.%, (d) 1.5 wt.%, (e) 2.0 wt.%, and (f) 2.5 wt.%.

Fourier-transform infrared spectroscopy (FTIR)

The FTIR spectra depicted in Figures 6 and 7 exhibit distinctive peaks for CeAlO₃ within the range of 4000 to 1300 cm⁻¹, corresponding to the stretching vibrations of CeAlO₃. The peak at 3700 cm⁻¹ in the spectrum is associated with O-H stretching vibrations, indicating the presence of water molecules adsorbed on the surface of CeAlO₃. The peaks detected at 3773 cm⁻¹ in the FTIR spectrum indicate the presence of surface hydroxyl groups. The range of 3000–1200 cm⁻¹ exhibits peaks associated with C-H groups (as summarised in Table 2). The FTIR spectrum revealed peaks at approximately 1217 and 1068 cm⁻¹, implying the presence of C-O groups. This observation aligns with previous research [71–75]. The intensity of the CeAlO₃ stretching vibration peak is observed to increase with the rise in the weight percentage of CeAlO₃ in the polymer composites, thereby suggesting a direct correlation between peak intensity and the quantity of CeAlO₃ in the composite. The peak within the range of 1600–1500 cm⁻¹ is an indicator of the presence of a C=C group. Figure 7 within the FTIR spectra reveals peaks at approximately 1300 cm⁻¹ and 800 cm⁻¹, which can be associated with C-O stretching vibrations. Additionally, a peak at approximately 1236 cm⁻¹ points to the existence of a C-N group. The Peaks within the 800–500 cm⁻¹ range denote the presence of C-H groups, contributing to a more comprehensive view of the material’s structural features. The peaks at 2937 and 2918 cm⁻¹ are indicative of the presence of C-H groups, and their intensity exhibits an upward trend with the increasing weight of CeAlO₃ nanoparticles in the polymer composites [67,76,77].

Figure 6. The FTIR spectrum of CeAlO₃ nanoparticles illustrates vibrational modes or functional groups.

Figure 7. The FTIR spectra encompass (a) pristine epoxy and nano-CeAlO₃ polymer composites with varying loads of CeAlO₃ nanoparticles at (b) 0.5 wt.%, (c) 1.0 wt.%, (d) 1.5 wt.%, (e) 2.0 wt.%, and (f) 2.5 wt.%.

Table 2. FTIR peaks and respective functional groups.

Sample	Wavenumber (cm^−1)	Functional groups
CeAlO3 nanoparticles	3773	O-H stretching vibrations
	3000–1300	C-H group
	1200–1000	C-H group
Nano- CeAlO3 polymer composites	2937 and 2918	Presence of a C-H group
	1600–1500	C=C group
	1236	C-N group
	1170 and 1024	C-O stretching vibrations
	827 and 554	C-H group

Thermogravimetric analysis (TGA)

The CeAlO₃ nanoparticles underwent Thermo Gravimetric Analysis (TGA) across a temperature range spanning from 30 to 900 °C. According to the data presented in Figure 8, it was observed that, at 900 °C, the residual mass of the CeAlO₃ nanoparticles remained at an impressive 94.88 %. During the decomposition process, merely 5.2 % of the initial mass was lost at this high temperature, and at the lower end of the spectrum (200 °C), there was only a minimal loss of mass. The outstanding thermal stability of the CeAlO₃ nanoparticles positions them as excellent candidates for applications requiring exposure to high temperatures. This exceptional thermal stability is substantiated by the large residual mass that remains at 900 °C. The great surface area and crystallinity of CeAlO₃ nanoparticles contribute significantly to their remarkable thermal stability and structural integrity. The crystalline nature of these nanoparticles also indicates that they can maintain their structural integrity even when subjected to elevated temperatures [78–80]. The nano-CeAlO₃ polymer composites underwent measurements to determine the transition temperature values at 250 °C. From Figure 9, and Table 3 the polymer composite samples displayed different levels of residual mass at 200 °C for various CeAlO₃ loadings: 91% for 0–0.5 wt.%, 88% for 1.0 wt.%, 93% for 1.5 wt.%, 88% for 2.0 wt.%, and 95% for 2.5 wt.%. Across all CeAlO₃ loadings, the residual mass varied from 88% to 95%, suggesting minimal substance breakdown at this temperature. The inclusion of CeAlO₃ nanoparticles had a notable impact on the thermal stability of the epoxy matrix. The significant thermal stability exhibited by CeAlO₃ nanoparticles, functioning as a thermal barrier, played a pivotal role in preventing the degradation of the epoxy matrix, as indicated by the substantial residual mass [81].

Figure 8. Thermogravimetric analysis of CeAlO₃ nanoparticles reveals the percentage weight loss relative to temperature.

Figure 9. Thermogravimetric analysis of CeAlO₃ nanoparticles embedded in an epoxy polymer composite illustrates the percentage mass loss with respect to temperature.

Table 3. The remaining mass of CeAlO₃ nanoparticles and epoxy polymer composites were impregnated with CeAlO₃ at 250 °C.

S.No	Samples	CeAlO3 Weight (%)	Residual Mass at 200 °C (%)
1	CeAlO3	-	97.3
(a)	(a) Pristine epoxy	0.0	91.37
(b)	(b) Epoxy + 0.5 wt.% CeAlO3	0.5	91.37
(c)	(c) Epoxy + 1.0 wt. % CeAlO3	1.0	88.98
(d)	(d) Epoxy + 1.5 wt. % CeAlO3	1.5	93.07
(e)	(e) Epoxy + 2.0 wt. % CeAlO3	2.0	88.77
(f)	(f) Epoxy + 2.5 wt. % CeAlO3	2.5	95.01

Photoluminescence (PL)

Photoluminescence spectroscopy was employed to investigate the light emission properties of CeAlO₃ when exposed to specific wavelengths. Electrons in CeAlO₃ samples can be excited from their ground state to higher energy levels upon light exposure, resulting in a broad band of photoluminescence centred between 240 and 420 nm, corresponding to red light emission. This red emission is attributed to the release of photons during the recombination of excited electrons with holes at oxygen vacancies. Various factors, such as excitation wavelength, temperature, and the presence of defects or impurities, can influence the intensity and structure of the photoluminescence spectrum. Analysis of CeAlO₃ polymer composite spectra revealed multiple peaks between 400 and 800 nm shown in Figure 10. Peak shifting, where the peak location moves towards longer wavelengths as the excitation wavelength increases, was observed, indicating the re-absorption of photons by nanoparticles, causing a redshift in the photoluminescence peak [82].

Figure 10. The spectral luminescence of CeAlO₃ nanoparticles.

The confirmation that light recombination results in a hole with a single ionised electron in the valence band is supported by the intensity of a single ionised oxygen vacancy, leading to the red emission peak at 600 nm. Energy transfer between CeAlO₃ nanoparticles and the polymer composite explains this phenomenon [83]. The study suggests the potential for designing red-emitting optoelectronic devices using CeAlO₃ nanoparticles loaded polymer composites. The increase in intensity varies with the amount of CeAlO₃ loading intensity into the epoxy polymer. Figure 11 shows the increase in the conducting properties of the composite. The integration of CeAlO₃ nanoparticles into epoxy polymer not only increases intensity but also improves the conducting property of the composite upon irradiation. Consequently, these composites find applications in electronics, providing better thermal qualities for reinforcement. Furthermore, polymer nanocomposites, incorporating CeAlO₃ nanoparticles, demonstrate enhanced barrier properties, making them suitable for protective applications such as food packaging, thereby expanding their capabilities for safeguarding various products.

Figure 11. Luminescent spectra for (a) pristine epoxy, (b) epoxy + 0.5 wt.% CeAlO₃, (c) epoxy + 1.0 wt.% CeAlO₃, (d) epoxy + 1.5 wt.% CeAlO₃, (e) epoxy + 2.0 wt.% CeAlO₃, and (f) epoxy + 2.5 wt.% CeAlO₃.

Mechanical properties

The Mechanical properties of a polymer matrix composite were examined using a universal testing machine (UTM). Tensile and compressive strength values were recorded and tabulated in Tables 4 and 5, respectively. The results are represented in Figures 12–15. The primary focus of the study was to assess the impact of CeAlO₃ filler concentration on the mechanical properties of the polymer matrix, particularly exploring tensile strength variations within the filler loading range of 0 to 2.5% weight. Figure 12 defines the influence of CeAlO₃ loading on tensile strength within epoxy-CeAlO₃ nanocomposites. Table 4 reveals a good enhancement in tensile strength values with the addition of nanofillers. Notably, a noticeable increase of 30% was observed for nanocomposites containing 0.5 wt.% CeAlO₃ compared to the pristine epoxy matrix. This can be attributed to the establishment of favourable interfacial tension between CeAlO₃ and the epoxy matrix at the specified CeAlO₃ concentration [84].

Figure 12. The tensile strength of nanocomposites consists of epoxy and CeAlO₃ at various concentrations.

Figure 13. The tensile modulus of nanocomposites consists of epoxy and CeAlO₃ at various concentrations.

Figure 14. The compressive strength of nanocomposites consisting of epoxy and CeAlO₃ at various concentrations.

Figure 15. The compressive modulus of nanocomposites consisting of epoxy and CeAlO₃ at various concentrations.

Table 4. Tensile properties of nanocomposites synthesised.

% of CeAlO3	Thickness (mm)	Tensile strength (N/mm^2)	Tensile modulus (N/mm^2)
0.0	2.8	11.11	73.03
0.5	2.9	18.43	398.37
1.0	3.0	17.36	444.06
1.5	2.9	20.07	563.67
2.0	2.8	18.37	634.88
2.5	3.0	16.06	674.09

Table 5. Compressive properties of nanocomposites synthesised.

% of CeAlO3	Thickness (mm)	Compressive strength (N/mm^2)	Compressive modulus (N/mm^2)
0.0	2.8	95.31	3556
0.5	2.9	99.19	3969
1.0	3.0	76.52	4009
1.5	2.9	74.33	4313
2.0	2.8	61.74	4998
2.5	3.0	59.03	5216

A subsequent increase in the filler loading beyond 0.5 wt.% resulted in a decreasing trend in tensile strength. This phenomenon can be elucidated by the adverse effects of nanofiller agglomeration, wherein an excessive concentration led to a suboptimal dispersion within the polymer matrix. The resultant agglomeration detrimentally impacted the mechanical properties, notably causing a decrease in tensile strength. This investigation highlights the relationship between filler concentration, dispersion, and ensuing mechanical properties in polymer matrix composites. The findings affirm the importance of optimising filler content to utilise the beneficial effects on material strength while avoiding the adverse outcomes linked to the clumping together of particles [78,85,86].

The interaction between the polymer matrix and nanofiller is more potent than that of the pure polymer, demonstrating increased strength compared to the pristine polymer.

Figure 13 depicts the variation in tensile modulus within epoxy-CeAlO₃ nanocomposites. The tensile modulus increased linearly with the rise in filler concentration, as evidenced by both Table 4 and in Figure 13. The epoxy reached its highest strength in epoxy-2.5wt.% CeAlO₃ composite, signifying the efficacy of incorporating nanoparticles into the epoxy matrix, resulting in heightened stiffness of the composite. This observation underscores the effectiveness of the polymer matrix-nanofiller interface, displaying a greater intensity compared to the original polymer. Examining the impact of filler loading on the compressive strength of the epoxy polymer is tabulated in Table 5 and Figure 14 showing the improved trend. The epoxy-0.5wt.% CeAlO₃ nanocomposite exhibited superior compressive strength when compared to the pristine epoxy, demonstrating an enhancement of approximately 10%. However, as the nanofiller loading increased, a linear reduction in compressive strength was observed. This decrease is associated with the possible liberation of free radicals during the homo-polymerisation process when epoxy and nanofiller load, resulting in reduced interactions between the epoxy matrix and nanofiller. The subsequent linear decrease in compressive strength beyond 0.5wt.% CeAlO₃ can be attributed to the agglomeration of CeAlO₃ nanoparticles [87–89].

Figure 15 depicts changes in compressive modulus within epoxy-CeAlO₃ nanocomposites. Higher filler loading in the epoxy-CeAlO₃ nanocomposite results in a notably greater compressive modulus compared to the original epoxy. Specifically, the epoxy-2.5wt.% CeAlO₃ nanocomposite demonstrated a substantial enhancement of approximately 45% in compressive modulus. This increase in compressive modulus was consistently observed with an increased loading of CeAlO₃ [90].

The future scope of this research involves a more detailed exploration of the CeAlO₃ nanoparticle content, seeking an optimal balance between increased material properties and economical efficiency. Additionally, delving into the compatibility of these composites with diverse polymer matrices and analysing their performance across varied environmental conditions could unveil novel applications. Further investigation into the fundamental mechanisms underlying the observed peak shifting and photoluminescence behaviour could contribute to tailoring luminescent materials with precision. Addressing scalability and manufacturability considerations is paramount for the practical integration of these findings into industrial applications [91].

The SEM analysis provided insights into the homogeneous distribution of CeAlO₃ nanoparticles within the epoxy, manifesting as well-defined spherical particles. This uniform dispersion is pivotal for enhancing mechanical properties, rendering these composites well-suited for aerospace and automotive industries where lightweight yet robust materials are imperative. TGA results underscored minimal mass loss below 250 °C for nano-CeAlO₃ polymer composites, signifying exceptional thermal stability. This thermal toughness positions these composites favourably for high-temperature applications, such as aerospace components or the construction of materials resistant to elevated temperatures [92]. The study suggests that adding CeAlO₃ nanoparticles to epoxy makes it better in certain ways, and this improvement depends on how much CeAlO₃ is added. The experimental outcomes showcase that the good binding of CeAlO₃ nanoparticles into epoxy polymer composites can yield materials endowed with a diverse spectrum of applications [93]. These range from the development of high-strength aerospace components to the formulation of thermally stable adhesives.

The application of CeAlO₃ as a nanofiller in epoxy matrices has shown promise in enhancing the stiffness of polymers used in aerospace components. This increased stiffness is particularly beneficial for structural elements that require strength and durability while remaining lightweight. Studies have also investigated the impact of CeAlO₃ on crack resistance and overall mechanical performance. Improved crack resistance is crucial in aerospace applications where structural integrity is paramount, and materials must withstand varying stresses, including vibrations, impacts, and extreme temperature fluctuations [94].

The use of CeAlO₃ as a nanofiller in epoxy for food packaging purposes has shown promising results. Studies indicate that the inclusion of CeAlO₃ enhances the surface durability of the polymer under various conditions, including multiscratching scenarios [95]. This improved surface performance contributes to the overall integrity of the packaging material, ensuring it can withstand potential stresses during handling, transportation, and storage [92,96]. Moreover, investigations into the mechanical properties of polymer composites with CeAlO₃ reveal positive outcomes. Tensile properties, such as ultimate tensile strength and tensile modulus, exhibit significant improvements, enhancing the material’s ability to withstand tensile forces. Compressive properties, including compressive strength and compressive modulus, also benefit from the incorporation of CeAlO₃, contributing to the material’s capacity to withstand compression forces. The applications of such enhanced polymer composites in food packaging are diverse [97].

Conclusion

In this research, CeAlO₃ nanoparticles were synthesised using the solution combustion method and then incorporated into an epoxy matrix through ultrasonication to ensure even distribution. To enhance the properties of epoxy composites by reinforcing them with CeAlO₃ nanoparticles. The epoxy matrix selected was Araldite epoxy resin XIN-100 IN and Araldite hardener XIN-900 IN. Then, a thorough analysis of the materials, focusing on their morphology, elemental composition, phase identification, and thermal characteristics was done. SEM images indicated that, at higher concentrations, CeAlO₃ nanoparticles exhibited porosity but tended to aggregate. Specifically, samples containing 0.5 wt.% CeAlO₃ displayed agglomerated spherical particles. EDX analysis validated the existence of Ce, Al, and O elements in the CeAlO₃ nanoparticles. X-ray Diffraction (XRD) patterns validated the formation of the CeAlO₃ phase, with distinct peaks at around 28.9° in samples impregnated with CeAlO₃ nanofillers. Fourier Transform Infrared (FTIR) spectra displayed a unique peak at 2937 and 2918 cm⁻¹, indicating OH stretching vibrations. In CeAlO₃-impregnated epoxy polymer composites, the intensity of the CeAlO₃ stretching vibration peak correlated directly with the CeAlO₃ concentration, increasing from 0.5 to 2.5 wt.%. Thermogravimetric Analysis (TGA) revealed that pristine CeAlO₃ showed minimal mass loss of 8.63 % at 200 °C. Adding 0.5 wt.% of CeAlO₃ increased the onset temperature of degradation. CeAlO₃-impregnated epoxy polymer composites (ranging from 0.5 to 2.5 wt.%) retained between 89–93 % of their mass at 200 °C, indicating improved thermal stability. However, a higher concentration of CeAlO₃ led to a reduction in the onset temperature for degradation. This study highlights the potential of incorporating a small quantity of CeAlO₃ nanoparticles to create advanced polymer composites with multiple scales. It provides the opportunity to combine nano- and micro-scale particles within fibre-reinforced polymer matrices, offering enhanced properties and capabilities for various applications. The luminescence spectra of both CeAlO₃ nanoparticles and CeAlO₃ polymer composites displayed peaks falling within the 400–800 nm range. A phenomenon known as peak shifting, where the peak location transitions towards longer wavelengths with an increase in excitation wavelength, was observed. The peak shift is due to nanoparticles re-absorbing photons, leading to a redshift in the photoluminescence peak. Mechanical testing revealed that the tensile strength reached its maximum at 0.5wt.% CeAlO₃ filler loading. Tensile modulus increased with an increase in filler loading. Initially, compressive strength saw an increment, but it gradually declined as the filler concentration increased. On the other hand, the compressive modulus of the epoxy composites showed a linear increase with the concentration of nanoparticles in the matrix. The optimal combination for both tensile strength and compressive strength was observed in the epoxy-0.5 wt.% CeAlO₃ composite improved over the original epoxy. The highest values for tensile modulus and compressive modulus were noted in a nanocomposite with epoxy-2.5wt.% CeAlO₃ compared to other filler loading and pristine epoxy.

Acknowledgments

The authors acknowledge the Centre for Advanced Materials Technology of M. S. Ramaiah Institute of Technology, Bangalore, Karnataka, India for the necessary characterisation facilities used in this study. SEM-EDX characterisation was performed at BMS College of Engineering, Bangalore, Karnataka, India.

Disclosure statement

No potential conflict of interest was reported by the author(s).