- Email: [email protected]
Effect of NiLaxFe2−xO4 nanoparticles on the thermal and coating properties of epoxy resin composites
Composites: Part B 51 (2013) 11–18
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Effect of NiLaxFe2xO4 nanoparticles on the thermal and coating properties of epoxy resin composites Abdullah M. Asiri a,b,⇑, Mahmoud A. Hussein a,c,⇑, Bahaa M. Abu-Zied a,b,c, Abou-Elhagag A. Hermas a,c a
Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia c Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt b
a r t i c l e
i n f o
Article history: Received 16 October 2012 Received in revised form 10 January 2013 Accepted 20 February 2013 Available online 5 March 2013 Keywords: A. Resins A. Metal–matrix composites (MMCs) A. Nano-structures B. Adhesion D. Thermal analysis
a b s t r a c t Epoxy resin has been modified with Ni–La–Fe–O nanoparticles in the form of NiLaxFe2xO4/epoxy nanocomposites to improve their coating properties. The new composites of different x composition (x = 0.00, 0.50, 1.00, 1.50 and 2.00) were synthesized in situ while epoxy resin was prepared by using a simple solution method with ultrasonic assistance. The new nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermogravemetric analysis (TGA) and scanning electron microscopy (SEM). The thermal degradation showed a more complicated behavior in the presence of Ni–Fe–La–O as shown by the presence of two maxima in the 300–475 °C temperature range. Reinforced composites with nanoparticles showed enhanced compressive coating properties. Ni–Fe formulations showed great promise to improve epoxy coating due to their higher barrier properties and ionic charge transfer resistance. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Composite materials have always been the hope of metallurgists to be able to produce structural materials possessing both great strength and extreme ductility. Great strength offers high load-carrying capacity. During the last 2 decades, composite materials became widely used due to their superior properties, such as low density and cost. Numerous applications have been allocated for these materials of automotive and aerospace industries such as bushes, seals, gears, cams, and shaft [1–3]. The increases in the use of the composite materials mean that it is necessary to know their behaviors under working conditions. Composite materials are being preferred more and more instead of steels and other metals because of their high strength at low specific weight. Nanoscale materials have attracted much attention recently due to many unusual properties predicted [4]. The development of nanoparticle reinforced polymer composites is presently seen as one of the most promising approaches in the field of future engineering applications. Nanocomposite materials consisted of organic polymeric matrix and inorganic nano-particles have a great deal of academic and industrial research activities due to their uniqueness of combining the organic and inorganic characteristics at the molec⇑ Corresponding authors at: Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia. Tel.: +966 26952305. E-mail addresses: [email protected] (A.M. Asiri), mahmoud.hussein74@yahoo. com (M.A. Hussein). 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2013.02.023
ular level, leading to the formation of nanocomposite materials with flexibility and the ability to form films [5]. These new materials have effectively enhanced properties such as thermal properties [6,7], mechanical properties [8,9], permeability properties [10], and corrosion protection properties [11] of polymers. Furthermore, this kind of new materials has received world-wide attention in the field of material science. This is due to the fact that the resultant materials may offer superior performance in terms of mechanical toughness for engineering resins, permeability and selectivity for gas/liquid separation, and photoconductivity for electronics [12–14]. If these inorganic particles possess functions such as magnetic susceptibility, electrical conductivity, catalytic activity, or electroactivity, it may be possible to form functional composites from them [15,16]. Epoxy resins are the most commonly used thermoset plastic in polymer matrix composites. Epoxy resins are a family of thermoset plastic materials which have good adhesion to other materials, good chemical and environmental resistance, good chemical and insulating properties. Epoxy resins of several families are now available ranging from viscous liquids to high-melting solids. Among them, the conventional epoxy resins manufactured from epichlorohydrin and bisphenol remain the major type used. In the past, thermosetting polymers such as epoxy resin, attracted many chemists, physicists, and material scientists devoting efforts to study their nanocomposites. Epoxy resins evoked intensive studies much in the preparation of nanocomposite materials lately due to their high tensile strength, and modulus, good adhesive properties, good chemical, and corrosion resistance, low shrinkage
12
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
in cure, and excellent dimensional stability. Up to date, many published literatures have study the effect of nanoparticles on the coating properties of epoxy resin [17–20]. At present, epoxy resins are widely used in various engineering and structural applications such as electrical industries, and commercial and military aircrafts industries. In order to improve their processing and product coating performances and to reduce cost, various fillers are introduced into the resins during processing [21]. More particularly it is known that, most of the ferrite particles specially the Ni-ferrites are hydrophilic and cannot be dispersed homogeneously in organic resins. Thus, the surface modification of ferrite powders with a coupling agent in epoxy resin formulations can offer superior performance, such as improved dispersibility, increased compatibility between the ferrites and epoxy resin and adhesion strength between the ferrite particles and polymer matrix because the coupling agent grafts onto the ferrite powder surface [22]. In this respect, Chen et al. [23] reported that, that the dispersion of Ni–Zn ferrite powders and the affinity of Ni–Zn ferrites and epoxy resin can be substantially enhanced by coating with a titanate coupling agent onto the ferrite powder surfaces. To the best of our knowledge, there is a lack of information concerning the use of lanthanum together with ferrite nanoparticles as filler for the epoxy resins. Therefore, we aimed to synthesize such formulations to study the effect of lanthanum ions on the thermal and coating properties for epoxy resin. In the present work, we aimed to synthesize and characterize NiLaxFe2xO4/epoxy nanocomposites. The formed nanocomposites are examined by Fourier transform infrared spectroscopy, thermogravimetry thermal analysis, X-ray diffraction analysis, and scanning electron microscopy. Furthermore, the effects of NiLaxFe2xO4/epoxy nanocomposite materials on the epoxy coating properties have been studied. Furthermore, composite materials are experimentally investigated under same loads of different x from nanoparticles.
2. Experimental 2.1. Materials Commercially available Epikote 1001 x-75% (2642) epoxy along with crayamid – 100% (2580) hardener epoxy were used as matrix material in fabrication of different compositions. For processing the mix ratio of 1:1 (by weight) and used without further purification. Chloroform (analytical grade) obtained from Merck, and also used without further purification as solvent in the composites preparation.
2.2. Preparation of nanocrystalline NiLaxFe2xO4 The reagents used in the materials preparation, Ni(NO3)26H2O, Fe(NO3)39H2O, La(NO3)36H2O, and urea were analytical grade chemicals and were used without further purification. Five mixtures having the general formula NiLaxFe2xO4 (x = 0.00, 0.50, 1.00, 1.50, and 2.00) were prepared using urea as a combustion fuel. The molar ratio of urea/nitrate was adjusted to be 1. Prior to the calcination, the appropriate amounts of the different materials were first dissolved in little added distilled water and mixed in a small porcelain crucible, then heated in an oven at 90 °C. Finally, after the solution was converted to a viscous gel it was calcined, for 1 h, in air at 500 °C, and then quenched to room temperature. Due to the exothermicity of the combustion reaction only small portions of the gels were calcined. Full detailed characterization for the desired nanocrystalline particles was presented in our previous study [24]. In this context, it is worth mentioning that the calculated particles size for the samples having x = 0.00, 0.50,
1.00, 1.50, and 2.00 were found to be 9.75, 6.26, 13.62, 18.39, and 14.29 nm, respectively [24]. 2.3. Preparation of nanocomposites The typical procedure to synthesize the NiLaxFe2xO4/epoxy resin nanocomposites was given as follows: epoxy matrix was prepared by adding 1:1 ratio (by weight) from Epikote 1001 and hardener epoxy dissolved in chloroform. While epoxy resin was prepared, nanocrystalline NiLaxFe2xO4 particles (5% weight) of different x (x = 0.00, 0.50, 1.00, 1.50 and 2.00) ratio were mixed and dispersed in the epoxy matrix and sonicated for 10 min. This was followed by solvent evaporation in Petri dishes for at least 24 h at room temperature and dried in the oven at 50 °C. 2.4. Preparation of coated steal samples NiLaxFe2xO4/epoxy composite as coating materials was studied by using stainless steal (ss)-coated samples. After dissolution in chloroform, the epoxy composites were cast drop wisely onto the ss plate with dimensions of 1 1 cm2 and the coating treated over night and then by drying in oven for 2 h at 50 °C. 3. Instrumentation 3.1. Fourier transform infrared spectroscopy FTIR spectra were performed by using smart part technique in the wavenumber range 4000–400 cm1 using Thermo-Nicolet6700 FTIR spectrophotometer. 3.2. X-ray diffraction analysis XRD patterns for the nanoparticles and composites were obtained in the 2h range from 4° to 80° with the aid of a Philips model PW 2103/00 diffractometer. The Philips generator, operated at 35 kV and 20 mA, provided a source of Cu Ka radiation. 3.3. Thermal analysis The TGA curve was recorded with a TA instrument apparatus model TGA-Q500 using a heating rate of 10 °C min1 in nitrogen atmosphere. The average masses of the samples were 5 mg. 3.4. Scanning electron microscopy The morphological properties of the new composites were analyzed by field-emission scanning electron microscope (FE-SEM) on a JEOL model JSM-7600F microscope. 3.5. Sorption of water Gravimetric method was used to determine the water sorption (WS) of the different epoxy coatings. The epoxy samples were immersed in 0.1 M NaCl solution for intervals of time. The WS of the epoxy sample is defined as
WS ¼ M t M o =Mo 100
ð1Þ
where Mo and Mt are the mass of the sample before and after immersion. 3.6. Impedance measurements Electrochemical impedance spectroscopy (EIS) was recorded using a potentiostat of type Auto lab PGSTAT30, coupled to a
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
computer equipped with FRA software. A three electrode arrangement was used, consisting of an Ag/AgCl reference electrode, a platinum counter electrode and the epoxy coated ss (exposed surface area 3 cm2 and 100 lm thickness layer) as working electrode and immersed in 0.1 M NaCl solution. EIS measurements were conducted potentiostatically at open circuit potential (Ecor) with 10 mV rms with frequency range 50 kHz to 0.1 Hz. 4. Results and discussion 4.1. Characterization study The FT-IR spectroscopic analysis of the epoxy resin and NiLaxFe2xO4/epoxy nanocomposites was scanned from 4000 to 400 cm1 as shown in Fig. 1. The spectra show the characteristic absorption bands for epoxy and NiLaxFe2xO4. The results are indicating that the epoxy was physically combined with nanoparticles additives. The FTIR spectra of the NiLaxFe2xO4/epoxy nanocomposites reveal the bands associated with pure epoxy and nanoparticle peaks. From the spectra l data for pure epoxy, we can observe band at 3059–3010 cm1 due to the valent CH vibrations of the epoxy ring (tCH), at 1235 cm1 for the valent CO vibrations of the epoxy ring (tCO), and at 918–810 cm1 for the bending CH vibrations of the epoxy ring (tCH). In addition to bands at 2921 cm1, at about 3037 cm1 are caused by the stretching vibration of the –CH2 functional group, the stretching CH vibration of the aromatic ring. All of these adsorption bands can also be observed in the spectra of the prepared composites. Furthermore, Fig. 1 shows the characteristic bands for different formulation of NiLaxFe2xO4 (x = 0.00–2.00) two prominent absorption bands (t1 and t2) at 600–430 cm1 due to ferrite form. t1 is attributed to stretching of tetrahedral metal ion and oxygen bonding, while t2 is due to vibrations of oxygen in the direction perpendicular to the axis joining the tetrahedral ion
13
and oxygen. These bands are common features of all the ferrites as reported in the literature [25]. This two bands is clearly decreased with increasing the percentage of La (x = 0.5, 1.00, 1.50 and 2.00) in the formulations. The morphological photographs of selected NiLaxFe2xO4/epoxy nanocomposites were examined by SEM micrographs x = 0.00 and x = 1.00 as shown in Figs. 2 and 3 respectively. Both samples show the same morphology. They consist of agglomerations of crystallites having similar shape. It is obvious that the nanoparticles are tightly embedded in the epoxy matrix with evidence of composite formation. This indicates good cohesion between the nanoparticles and matrix, which is very important to reach a strong interfacial adhesion. In addition, the micrograph shows a good distribution of nanoparticles within the polymer matrix. High compatibility between the nanoparticles and polymer matrix is observed. The XRD diffractograms of the nanocrystalline NiLaxFe2xO4/ epoxy composite gives a clear evident for the composites formation. Both NiLaxFe2xO4 and epoxy were able to be physically combined with each other through the composite formation. The data shows peaks characterizing both NiLaxFe2xO4 and epoxy. No other peaks attributable to the presence of impurities or other phases were detected. Fig. 4 depicts the wide-angle XRD patterns of pure epoxy resin and the nano-NiLaxFe2xO4/epoxy composites. The pattern for the neat epoxy resin exhibits two broad reflection peak occurred at 2h = 19.43° and 42.71° and a third small peak at 72.22°. The diffractograms for the different epoxy resin/nano-NiLaxFe2xO4 composites reveal the disappearance of the two broad reflections of neat epoxy resin. Inspection of the diffractogram for the composite with x = 0.00 reveals the presence of two phases; NiFe2O4 (JCPDS File no. 74-2081) as a major phase and Fe2O3 (JCPDS File no. 84-0311) as a minor one. For the end member of this series, i.e. epoxy resin/nanoNiLa2O4 composite, the relevant XRD pattern reveals that it composed of La2NiO4 (JCPDS File no. 80-1346) as a major phase together with trace amount of La2O2CO3 (JCPDS File no. 23-0322). Increasing the x-value from 0.00 to 2.00 is accompanied by a continuous decrease of the reflections due to NiFe2O4 and the development of the NiLa2O4 reflections. It was reported that, the crystallinities of the PEG/silica (MCM41 and SBA-15) and PEG/activated carbon (AC) composites, having PEG weight percentage of 80%, were much lower than that of pure PEG [26]. The XRD patterns for the PEG/silica composites having PEG weight percentage of 70% showed no crystallization peak due to PEG, whereas the PEG/AC reveals the persistence of the PEG reflections in its XRD pattern but with lower intensities. Accordingly, it was suggested that the influence of the silica stabilizer on the crystallinity of PEG is greater than that of the AC stabilizer [26]. Such stabilization was correlated with the polarity of silica, compared to the nonpolar nature of AC, which may enhance the interaction between polar PEG and silica [26]. Accordingly, it is plausible to suggest that the disappearance of the two broad reflections due to the epoxy resin in all nano-NiLaxFe2xO4 containing composites indicated the strong interaction between the epoxy resin and the nanocrystalline NiLaxFe2xO4 particles. 4.2. Thermal behavior
Fig. 1. FT-IR for pure epoxy and NiLaxFe2xO4/epoxy nanocomposites.
The crosslinking is an important factor that determines the thermal behavior of the resin. For the stoichiometric ratio 1:1 there is a crosslink at every amine–epoxy junction, i.e. all amine groups react with all epoxide groups [27,28]. In non-stoichiometric epoxy resin, the presence of an excess amine groups increased the number of un-reacted amine groups, thus influencing the thermal stability of the non-stoichiometric composite [27,28]. The mechanical tests for epoxy resin (diglycidylether of bisphenol ‘‘A’’, DGEBA) crosslinked with ethylenediamine (ETDA) revealed that, the
14
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 2. SEM micrographs for nanocrystalline NiLaxFe2xO4/epoxy composite x = 0.00.
Fig. 3. SEM micrographs for nanocrystalline NiLaxFe2xO4/epoxy composite x = 1.00.
Fig. 4. XRD patterns of neat epoxy resin (a) and the epoxy resin/nano-NiLaxFe2xO4 composites having x = 0.00 (b), 0.50 (c), 1.00 (d), 1.50 (e), and 2.00 (f).
highest breaking strength for the 1:1 epoxy–amine ratio without metallic filler [28]. Accordingly, in the preparation of our mixture we used the stoichiometric ratio. The thermal stability of the epoxy resin/nano-NiLaxFe2xO4 composites was examined by TGA at a heating rate of 10 °C/min under a nitrogen atmosphere (60 ml/min). Fig. 5a shows the obtained TGA curves. T5, T25, T50 (the temperatures of 5%, 25%, and 50% weight loss, respectively), and the solid residue left at 500 °C are the main criteria indicating the thermal stability of the composites. The higher these values are the higher is the thermal stability. These data are shown in Table 1. The temperature at which decomposition is maximum (Tmax) can be calculated from the DTG curves presented in Fig. 5b. A relatively short stage with 8–14% weight loss is happened at 30 and 225 °C, which is attributed to the breaking of un-reacted epoxy or other impurity traces apart from the cured resin [29] and water molecules [28,30]. The relative stability of pure epoxy resin as well as the epoxy resin-nanocomposites was compared by their initial decomposition temperature T5 as shown in Table 1. In the case of pure epoxy resin the decomposition starts at 128 °C. After the addition of NiLaxFe2xO4 to the epoxies, the T5 shifted towards lower temperatures. A rapid mass loss (a decrease of approximately 85%) of the neat epoxy resin can be seen from the TGA curves at the 250–500 °C temperature range. Such weight loss could be related to chain scission and resin decomposition, resulting in fragmentation of the resin into low molecular weight products [30,31]. For neat epoxy resin, decomposition starts at 340 °C and is completed at 475 °C in a single step degradation process (maximized at 423 °C,
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 5. TG (a) and DTG (b) curves of neat epoxy resin as well as its NiLaxFe2xO4 composites under nitrogen atmosphere.
Table 1 TGA data of nanocrystalline NiLaxFe2xO4 epoxy composite under nitrogen atmosphere. Sample
T5 (°C)
T25 (°C)
T50 (°C)
R500 (%)
Pure epoxy Epoxy–NiFe2O4 Epoxy–NiLa0.50Fe1.50O4 Epoxy–NiFeLaO4 Epoxy–NiLa1.50Fe0.50O4 Epoxy–NiLa2O4
128 122 104 115 94 95
372 362 351 351 360 361
407 394 386 392 397 397
0.90 13.53 8.59 6.31 8.55 10.04
Fig. 5b). It can be seen that the thermal stability of the neat epoxy resin, at such temperature range, is decreased considerably in the presence of Ni–La–Fe–O nanoparticles (Fig. 5a). Moreover, in the presence of Ni–Fe–La–O the thermal degradation showed a more complicated behavior as shown by the presence of two maxima in the 300–475 °C temperature range (Fig. 5b). The first one is maximized at 385, 378, 395, 396, and 397 °C whereas the second one is located at 421, 429, 428, 431, and 426 °C for the composites having x = 0.00, 0.50, 1.00, 1.50, and 2.00, respectively. In the open literature there are many interesting reports dealing with the role of inorganic additives in influencing the thermal
15
stability of epoxy resin composites. Lakshmi et al. [31] reported an enhancement effect of montmorillonite (MMT) clay in improving the thermal stability of expoxies composites. In agreement, Guo et al. [32] reported an improvement of the thermal stability of the cocamidopropyl betaine epoxy resin via the formation of epoxy nanocomposites with MMT-clay. This was attributed to the protection of epoxy polymer chains present between hard MMT-clay nanolayers that act as a barrier protecting from volatilizing the epoxy polymer matrix [31]. It was concluded that the existence of inorganic phases like, SiO2, Al2O3, and MgO that dominate in the nanocomposites causes such enhanced thermal stability [31]. More recently, Mustata et al. [33] reported slight thermal stability of composites decrease compared with diglycidyl ether of bisphenol A/p-aminobenzoic acid (DGEBA/p-ABA) sample, as a result of some possible modification in thermal degradation mechanism in the presence of calcium carbonate particles. On the other hand, transition metals oxides like ZnO [34], CuO [35], and TiO2 [36] and oxides structures like Ni–Zn ferrite [27] were reported to decrease the thermal stability of epoxy resin composites. Such destabilization was ascribed to their catalytic action. Thus it is plausible to suggest that the added Ni–La–Fe–O nanoparticles could serve as catalysts to degrade the epoxy matrix. The parameter R500 (Table 1) refers to the residue remaining at 500 °C. It is seen that even after complete degradation; char residue is around 1% for neat epoxy resin whereas higher values, 6.3–13.5%, are obtained for the different composites. The highest residue values were observed for the samples having x = 0.00 and 2.00, i.e. for the composites containing NiFe2O4 and La2NiO4 phases, whereas the lowest one was exhibited by the NiLaFeO4 containing composite. Such residue is due to the presence of thermally stable char together with NiLaxFe2xO4 phases. The increased rate of mass loss beyond 600 °C, Fig. 5a, illustrates the continued degradation of the char layer for all the Ni–Fe–La–O containing samples. In this context, char residue was obtained during the thermal decomposition of epoxy resins/nano-Al2O3 composites [37]. The char at 800 °C of the composites increased gradually with increasing nano-Al2O3 content [37]. In agreement, the char yield from the thermal decomposition of Ni–Zn ferrite epoxy composite increased with increasing the Ni–Zn ferrite from 2% to 8% [27]. Concurrently, Wu et al. [38] has reported the formation of a char with excellent thermal stability via the thermal decomposition of water resistance of epoxy/microencapsulated ammonium polyphosphate composite. 4.3. Water sorption, electrochemical impedance and coating measurements Fig. 6 shows the variation of WS of the epoxy samples with the immersion time. The WS of all epoxy samples increases with time, but, the pure epoxy has very large values of WS along immersion periods. A straight line could be obtained for the points after 10 min and has a slope 0.165 for the pure epoxy while 0.057 for the epoxy composite (x = 0). This indicated larger continuous absorption of water for the pure epoxy and the nanoparticle additives decrease effectively the WS of the epoxy. Presence of Ni–Fe nanoparticles in the epoxy suppressed sharply the sorption of water. But, introduce La to the nanoparticles improves slightly the suppression of WS. The Nyquist plot obtained from EIS measurements for the epoxy coated steel samples after 10 and 120 min immersion times in 0.1 M NaCl solution are shown in Figs. 7a and b. Fig. 7a shows the impedance of pure epoxy coating, it is dominated by the coating capacitance at high frequencies and coated resistance at the low frequency. The coating resistance decreased after longer immersion time indicating the sorption of water in the epoxy body. The absorption of water and movement of ion species in the epoxy
16
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 6. The variation of WS of the epoxy samples with the immersion time.
material increase the conductivity of this coated layer [39,40]. The impedance spectrum of the epoxy composite (x = 0) coating show (Fig. 7b) very larger coating resistance which indicate lower sorption of water in this type of coating. There is no any significant change in the coating resistance after 2 h immersion. Similar results were obtained for the other epoxy composites coatings. The impedance spectra are fitted well with the equivalent circuit as shown in Fig. 8. In this circuit, Rs is the solution resistance, Rc and Cc are coating resistance and coating capacitance, respectively. The capacitance element is fitted by constant phase element (CPE) to compensate for non-ideal capacitance. The values of Cc and Rc for the epoxy coating sample are recorded in Table 2. The epoxy composites exhibited very larger values of Rc and very low values of Cc at the initial immersion (5.44 103 kO and 2.23 109 F, respectively, for the epoxy composite, x = 0) in comparison with those of pure epoxy (92.4 kO and 1.47 105 F, respectively). The Rc and Cc values of the epoxy composite not significantly changed after 2 h immersion in chloride solution while it changed to 46.4 kO and 3.1 105 F, respectively, for the pure epoxy. This indicated that the epoxy composite coatings have good resistance for sorption of water and protection of steel corrosion. The impedance data of the La-containing epoxy composite coating is almost close to that of La-free epoxy composite coating. In agreement with
Fig. 7a. The impedance spectrum of pure epoxy coating.
Fig. 7b. The impedance spectrum of nanocrystalline NiLaxFe2xO4/epoxy composite coating (x = 0.00).
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
17
References
Fig. 8. The equivalent circuit.
Table 2 EIS parameters of different epoxy coatings after immersion in 0.1 M NaCl. Sample
Rc (O)
Cc(F), n
10 min
120 min
10 min
120 min
Pure epoxy
9.24 104
4.64 104
Epoxy–NiFe2O4
5.44 106
5.37 106
Epoxy–NiLa0.50Fe1.50O4 Epoxy–NiFeLaO4
2.0 107
5.6 106
8.3 106
8.4 106
Epoxy–NiLa1.50Fe0.50O4
8.8 108
4.3 108
1.47 105, 0.54 2.23 109, 0.59 2.0 1010, 0.89 2.41 1010, 0.88 2.24 1010, 0.89
3.1 105, 0.47 2.2 109, 0.58 1.58 1010, 0.81 2.2 1010, 0.89 3.9 1010, 0.89
the gravimetric method the insertion of La to the nanoparticle of Ni–Fe has slight improve in the resistance of the epoxy coating. It is concluded that the coating resistance of epoxy coatings containing Ni–Fe nanoparticles is larger than that of pure epoxy coating. This may be attributed to the higher barrier properties and ionic charge transfer resistance of Ni–Fe nanoparticles embedded in the epoxy coating layer.
5. Conclusions New nanocrystalline NiLaxFe2xO4/epoxy composites of different x have been synthesized in situ while epoxy resin is prepared using solution method with the help of ultrasonic assistance. FT-IR, SEM and XRD give good evidences for the composites formation. XRD data are indicating that the pure epoxy is physically combined with nanoparticle additives. The thermal degradation show a more complicated behavior in the presence of Ni–Fe–La–O as illustrated by the presence of two maxima in the 300–475 °C temperature range. The added Ni–La–Fe–O nanoparticles could serve as catalysts to degrade the epoxy matrix. The presence of Ni–Fe nanoparticles in the epoxy suppresses sharply the sorption of water. On the other hand, the insertion of La atoms into the nanoparticles improves slightly the suppression of water sorption. The coating resistance and thus corrosion protection of the epoxy nanocomposites is higher than that of pure epoxy. Acknowledgements The authors are grateful to the Center of Research Excellence in Corrosion CoRE-C at King Fahad University for Petroleum and Mineral (KFUPM) for providing financial support for this work Via Grant No. CR-7-2010. We also acknowledge the center of excellence for advanced materials Research (CEAMR) at King Abdulaziz University for providing Research facilities.
[1] El-Tayeb NSM, Yousif BF, Brevern, PV. On the measurements of interface temperature and friction coefficient of glass-fiberreinforced epoxy composite under dry sliding contact. In: Proceedings of the international conference on recent advances in mechanical and materials engineering, 30–31 May, 2005, Kuala Lumpur, Malaysia; 2005. p. 1006–113. [2] El-Tayeb NSM, Yousif BF. Wear and friction behaviour of CGRP and WGRP composites subjected to dry sliding. In: Proceedings of WTC2005 world tribology congress III September 12–16, 2005, Washington, DC, USA, Paper No. WTC 2005-63097. [3] Edwards KL. An overview of the technology of fiber-reinforced plastics for design purposes. Mater Des 1998;19:1–10. [4] Geim AK, Novoselov KS. The rise of graphene. Nat Mater 2007;6:183–91. [5] Zhang M, Gao G, Li CQ, Liu FQ. Titania-coated polystyrene hybrid microballs prepared with miniemulsion polymerization. Langmuir 2004;20:1420–4. [6] Lan T, Kaviratna PD, Pinnavaia TJ. On the nature of polyimide–clay hybrid composites. Chem Mater 1994;6:573–5. [7] Yao KJ, Song M, Hourston DJ, Luo DZ. Polymer/layered clay nanocomposites: 2 polyurethane nanocomposites. Polymer 2002;43:1017–20. [8] Yeh JM, Chen CL, Huang CC, Chang FC, Chen SC, Su PL, et al. Effect of organoclay on the thermal stability, mechanical strength, and surface wettability of injection-molded ABS–clay nanocomposite materials prepared by melt intercalation. J Appl Polym Sci 2006;99:1576–82. [9] Li C, Wilkes GL. Silicone/amine resin hybrid materials as abrasion resistant coatings. Chem Mater 2001;13:3663–8. [10] Yeh JM, Yu MY, Liou SJ. Dehydration of water–alcohol mixtures by vapor permeation through PVA/clay nanocomposite membrane. J Appl Polym Sci 2003;89:3632–8. [11] Yeh JM, Liou SJ, Lai CY, Wu PC. Enhancement of corrosion protection effect in polyaniline via the formation of polyaniline–clay nanocomposite materials. Chem Mater 2001;13:1131–6. [12] Peng GW, Qiu F, Ginzburg VV, Jasnow D, Balazs AC. Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures. Science 2000;288:1802–4. [13] Merkel TC, Freeman BD, Spontak RJ, He Z, Pinnau I, Meakin P, et al. Ultrapermeable, reverse-selective nanocomposite membranes. Science 2002;296:519–22. [14] Wang Y, Herron N. X-ray photoconductive nanocomposites. Science 1996;273:632–4. [15] Csetneki I, Kabai Faix M, Szilagyi A, Kovacs AL, Nemeth Z, Zrinyi M. Preparation of magnetic polystyrene latex via the miniemulsion polymerization technique. J Polym Sci Part A Polym Chem 2004;42:4802–8. [16] Taden A, Antonietti M, Heilig A, Landfester K. Inorganic films from three different phosphors via a liquid coating route from inverse miniemulsions. Chem Mater 2004;16:5081–7. [17] Shi X, Nguyen TA, Suo Z, Liu Y, Avci Recep. Effect of nanoparticles on the anticorrosion and mechanical properties of epoxy coating. Surf Coat Technol 2009;204:237–45. [18] Chen C, Khobaib M, Curliss D. Epoxy layered-silicate nanocomposites. Prog Org Coat 2003;47:376–83. [19] Ramezanzadeh B, Attar MM, Farzam M. A study on the anticorrosion performance of the epoxy–polyamide nanocomposites containing ZnO nanoparticles. Prog Org Coat 2011;72:410–22. [20] Olad A, Barati M, Behboudi S. Preparation of PANI/epoxy/Zn nanocomposite using Zn nanoparticles and epoxy resin as additives and investigation of its corrosion protection behavior on iron. Prog Org Coat 2012;74:221–7. [21] Huang ZM. Tensile strength of fibrous composites at elevated temperature. Mater Sci Technol 2000;16:81–93. [22] Hsiang HI, Tsai JY. Titanate coupling agent effects on nonaqueous Co2Z ferrite suspensions dispersion. J Mater Sci 2006;41:6339–46. [23] Chen W-Sh, Chang Y-L, Hsiang H-I, Hsu F-C, Yen F-S. Effects of titanate coupling agent on the dielectric properties of NiZn ferrite powders–epoxy resin coatings. Ceram Int 2011;37:2347–52. [24] Abu-Zied BM, Asiri AM. Urea based combustion process for the synthesis of nanocrystalline Ni–La–Fe–O catalysts. J Nanomater 2012;2012:1–7. [25] Shaikh AM, Jadhav SA, Watawe SC, Chougule BK. Infrared spectral studies of Zn-substituted Li–Mg ferrites. Mater Lett 2000;44:192. [26] Feng L, Zhao W, Zheng J, Frisco S, Song P, Li X. The shape-stabilized phase change materials composed of polyethylene glycol and various mesoporous matrices (AC, SBA-15 and MCM-41). Sol Energy Mater Sol Cells 2011;95:3550. [27] Boon MS, Serena Saw WP, Mariatti M. Magnetic, dielectric and thermal stability of Ni–Zn ferrite-epoxy composite thin films for electronic applications. J Magn Magn Mater 2012;324:755–60. [28] Brito Z, Sánchez G. Influence of metallic fillers on the thermal and mechanical behaviour in composites of epoxy matrix. Compos Struct 2000;48:79–81. [29] Park S-J, Jin F-L. Thermal stabilities and dynamic mechanical properties of sulfone-containing epoxy resin cured with anhydride. Polym Degrad Stab 2004;86:515–20. [30] Kandola BK, Biswas B, Price D, Horrocks AR. Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin. Polym Degrad Stab 2010;95:144–52. [31] Lakshmi MS, Narmadha B, Reddy BSR. Enhanced thermal stability and structural characteristics of different MMT-clay/epoxy-nanocomposite materials. Polym Degrad Stab 2008;93:201–13.
18
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
[32] Guo B, Jia D, Cai C. Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites. Eur Polym J 2004;40:1743–8. [33] Mustata F, Tudorachi N, Rosu D. Thermal behavior of some organic/inorganic composites based on epoxy resin and calcium carbonate obtained from conch shell of Rapana thomasiana. Compos B 2012;43:702–10. [34] Liufu SC, Xiao HM, Li YP. Thermal analysis and degradation mechanism of polyacrylate/ZnO nanocomposites. Polym Degrad Stab 2005;87:103–10. [35] Guo ZH, Liang XF, Pereira T, Scaffaro R, Hahn HT. CuO nanoparticles filled vinyl-ester resin nanocomposites: fabrication, characterization and property analysis. Compos Sci Technol 2007;67:2036–44. [36] Chiang PC, Whang WZ. The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films. Polymer 2003;44:2249–53.
[37] Jiang W, Jin F-L, Park S-J. Thermo-mechanical behaviors of epoxy resins reinforced with nano-Al2O3 particles. J Ind Eng Chem 2012;18:594–6. [38] Wu K, Zhang Y-K, Zhang K, Shen M-M, Hu Y. Effect of microencapsulation on thermal properties and flammability performance of epoxy composite. J Anal Appl Pyrol 2012;94:196–201. [39] Behzadnasab M, Mirabedini SM, Kabiri K, Jamali S. Corrosion performance of epoxy coatings containing silane treated ZrO2 nanoparticles on mild steel in 3.5% NaCl solution. Corros Sci 2011;53:89–98. [40] Niknahad M, Moradian S, Mirabedini SM. The adhesion properties and corrosion performance of differently pretreated epoxy coatings on an aluminum alloys. Coros Sci 2010;52:1348–57.
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Effect of NiLaxFe2xO4 nanoparticles on the thermal and coating properties of epoxy resin composites Abdullah M. Asiri a,b,⇑, Mahmoud A. Hussein a,c,⇑, Bahaa M. Abu-Zied a,b,c, Abou-Elhagag A. Hermas a,c a
Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia c Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt b
a r t i c l e
i n f o
Article history: Received 16 October 2012 Received in revised form 10 January 2013 Accepted 20 February 2013 Available online 5 March 2013 Keywords: A. Resins A. Metal–matrix composites (MMCs) A. Nano-structures B. Adhesion D. Thermal analysis
a b s t r a c t Epoxy resin has been modified with Ni–La–Fe–O nanoparticles in the form of NiLaxFe2xO4/epoxy nanocomposites to improve their coating properties. The new composites of different x composition (x = 0.00, 0.50, 1.00, 1.50 and 2.00) were synthesized in situ while epoxy resin was prepared by using a simple solution method with ultrasonic assistance. The new nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermogravemetric analysis (TGA) and scanning electron microscopy (SEM). The thermal degradation showed a more complicated behavior in the presence of Ni–Fe–La–O as shown by the presence of two maxima in the 300–475 °C temperature range. Reinforced composites with nanoparticles showed enhanced compressive coating properties. Ni–Fe formulations showed great promise to improve epoxy coating due to their higher barrier properties and ionic charge transfer resistance. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Composite materials have always been the hope of metallurgists to be able to produce structural materials possessing both great strength and extreme ductility. Great strength offers high load-carrying capacity. During the last 2 decades, composite materials became widely used due to their superior properties, such as low density and cost. Numerous applications have been allocated for these materials of automotive and aerospace industries such as bushes, seals, gears, cams, and shaft [1–3]. The increases in the use of the composite materials mean that it is necessary to know their behaviors under working conditions. Composite materials are being preferred more and more instead of steels and other metals because of their high strength at low specific weight. Nanoscale materials have attracted much attention recently due to many unusual properties predicted [4]. The development of nanoparticle reinforced polymer composites is presently seen as one of the most promising approaches in the field of future engineering applications. Nanocomposite materials consisted of organic polymeric matrix and inorganic nano-particles have a great deal of academic and industrial research activities due to their uniqueness of combining the organic and inorganic characteristics at the molec⇑ Corresponding authors at: Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia. Tel.: +966 26952305. E-mail addresses: [email protected] (A.M. Asiri), mahmoud.hussein74@yahoo. com (M.A. Hussein). 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2013.02.023
ular level, leading to the formation of nanocomposite materials with flexibility and the ability to form films [5]. These new materials have effectively enhanced properties such as thermal properties [6,7], mechanical properties [8,9], permeability properties [10], and corrosion protection properties [11] of polymers. Furthermore, this kind of new materials has received world-wide attention in the field of material science. This is due to the fact that the resultant materials may offer superior performance in terms of mechanical toughness for engineering resins, permeability and selectivity for gas/liquid separation, and photoconductivity for electronics [12–14]. If these inorganic particles possess functions such as magnetic susceptibility, electrical conductivity, catalytic activity, or electroactivity, it may be possible to form functional composites from them [15,16]. Epoxy resins are the most commonly used thermoset plastic in polymer matrix composites. Epoxy resins are a family of thermoset plastic materials which have good adhesion to other materials, good chemical and environmental resistance, good chemical and insulating properties. Epoxy resins of several families are now available ranging from viscous liquids to high-melting solids. Among them, the conventional epoxy resins manufactured from epichlorohydrin and bisphenol remain the major type used. In the past, thermosetting polymers such as epoxy resin, attracted many chemists, physicists, and material scientists devoting efforts to study their nanocomposites. Epoxy resins evoked intensive studies much in the preparation of nanocomposite materials lately due to their high tensile strength, and modulus, good adhesive properties, good chemical, and corrosion resistance, low shrinkage
12
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
in cure, and excellent dimensional stability. Up to date, many published literatures have study the effect of nanoparticles on the coating properties of epoxy resin [17–20]. At present, epoxy resins are widely used in various engineering and structural applications such as electrical industries, and commercial and military aircrafts industries. In order to improve their processing and product coating performances and to reduce cost, various fillers are introduced into the resins during processing [21]. More particularly it is known that, most of the ferrite particles specially the Ni-ferrites are hydrophilic and cannot be dispersed homogeneously in organic resins. Thus, the surface modification of ferrite powders with a coupling agent in epoxy resin formulations can offer superior performance, such as improved dispersibility, increased compatibility between the ferrites and epoxy resin and adhesion strength between the ferrite particles and polymer matrix because the coupling agent grafts onto the ferrite powder surface [22]. In this respect, Chen et al. [23] reported that, that the dispersion of Ni–Zn ferrite powders and the affinity of Ni–Zn ferrites and epoxy resin can be substantially enhanced by coating with a titanate coupling agent onto the ferrite powder surfaces. To the best of our knowledge, there is a lack of information concerning the use of lanthanum together with ferrite nanoparticles as filler for the epoxy resins. Therefore, we aimed to synthesize such formulations to study the effect of lanthanum ions on the thermal and coating properties for epoxy resin. In the present work, we aimed to synthesize and characterize NiLaxFe2xO4/epoxy nanocomposites. The formed nanocomposites are examined by Fourier transform infrared spectroscopy, thermogravimetry thermal analysis, X-ray diffraction analysis, and scanning electron microscopy. Furthermore, the effects of NiLaxFe2xO4/epoxy nanocomposite materials on the epoxy coating properties have been studied. Furthermore, composite materials are experimentally investigated under same loads of different x from nanoparticles.
2. Experimental 2.1. Materials Commercially available Epikote 1001 x-75% (2642) epoxy along with crayamid – 100% (2580) hardener epoxy were used as matrix material in fabrication of different compositions. For processing the mix ratio of 1:1 (by weight) and used without further purification. Chloroform (analytical grade) obtained from Merck, and also used without further purification as solvent in the composites preparation.
2.2. Preparation of nanocrystalline NiLaxFe2xO4 The reagents used in the materials preparation, Ni(NO3)26H2O, Fe(NO3)39H2O, La(NO3)36H2O, and urea were analytical grade chemicals and were used without further purification. Five mixtures having the general formula NiLaxFe2xO4 (x = 0.00, 0.50, 1.00, 1.50, and 2.00) were prepared using urea as a combustion fuel. The molar ratio of urea/nitrate was adjusted to be 1. Prior to the calcination, the appropriate amounts of the different materials were first dissolved in little added distilled water and mixed in a small porcelain crucible, then heated in an oven at 90 °C. Finally, after the solution was converted to a viscous gel it was calcined, for 1 h, in air at 500 °C, and then quenched to room temperature. Due to the exothermicity of the combustion reaction only small portions of the gels were calcined. Full detailed characterization for the desired nanocrystalline particles was presented in our previous study [24]. In this context, it is worth mentioning that the calculated particles size for the samples having x = 0.00, 0.50,
1.00, 1.50, and 2.00 were found to be 9.75, 6.26, 13.62, 18.39, and 14.29 nm, respectively [24]. 2.3. Preparation of nanocomposites The typical procedure to synthesize the NiLaxFe2xO4/epoxy resin nanocomposites was given as follows: epoxy matrix was prepared by adding 1:1 ratio (by weight) from Epikote 1001 and hardener epoxy dissolved in chloroform. While epoxy resin was prepared, nanocrystalline NiLaxFe2xO4 particles (5% weight) of different x (x = 0.00, 0.50, 1.00, 1.50 and 2.00) ratio were mixed and dispersed in the epoxy matrix and sonicated for 10 min. This was followed by solvent evaporation in Petri dishes for at least 24 h at room temperature and dried in the oven at 50 °C. 2.4. Preparation of coated steal samples NiLaxFe2xO4/epoxy composite as coating materials was studied by using stainless steal (ss)-coated samples. After dissolution in chloroform, the epoxy composites were cast drop wisely onto the ss plate with dimensions of 1 1 cm2 and the coating treated over night and then by drying in oven for 2 h at 50 °C. 3. Instrumentation 3.1. Fourier transform infrared spectroscopy FTIR spectra were performed by using smart part technique in the wavenumber range 4000–400 cm1 using Thermo-Nicolet6700 FTIR spectrophotometer. 3.2. X-ray diffraction analysis XRD patterns for the nanoparticles and composites were obtained in the 2h range from 4° to 80° with the aid of a Philips model PW 2103/00 diffractometer. The Philips generator, operated at 35 kV and 20 mA, provided a source of Cu Ka radiation. 3.3. Thermal analysis The TGA curve was recorded with a TA instrument apparatus model TGA-Q500 using a heating rate of 10 °C min1 in nitrogen atmosphere. The average masses of the samples were 5 mg. 3.4. Scanning electron microscopy The morphological properties of the new composites were analyzed by field-emission scanning electron microscope (FE-SEM) on a JEOL model JSM-7600F microscope. 3.5. Sorption of water Gravimetric method was used to determine the water sorption (WS) of the different epoxy coatings. The epoxy samples were immersed in 0.1 M NaCl solution for intervals of time. The WS of the epoxy sample is defined as
WS ¼ M t M o =Mo 100
ð1Þ
where Mo and Mt are the mass of the sample before and after immersion. 3.6. Impedance measurements Electrochemical impedance spectroscopy (EIS) was recorded using a potentiostat of type Auto lab PGSTAT30, coupled to a
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
computer equipped with FRA software. A three electrode arrangement was used, consisting of an Ag/AgCl reference electrode, a platinum counter electrode and the epoxy coated ss (exposed surface area 3 cm2 and 100 lm thickness layer) as working electrode and immersed in 0.1 M NaCl solution. EIS measurements were conducted potentiostatically at open circuit potential (Ecor) with 10 mV rms with frequency range 50 kHz to 0.1 Hz. 4. Results and discussion 4.1. Characterization study The FT-IR spectroscopic analysis of the epoxy resin and NiLaxFe2xO4/epoxy nanocomposites was scanned from 4000 to 400 cm1 as shown in Fig. 1. The spectra show the characteristic absorption bands for epoxy and NiLaxFe2xO4. The results are indicating that the epoxy was physically combined with nanoparticles additives. The FTIR spectra of the NiLaxFe2xO4/epoxy nanocomposites reveal the bands associated with pure epoxy and nanoparticle peaks. From the spectra l data for pure epoxy, we can observe band at 3059–3010 cm1 due to the valent CH vibrations of the epoxy ring (tCH), at 1235 cm1 for the valent CO vibrations of the epoxy ring (tCO), and at 918–810 cm1 for the bending CH vibrations of the epoxy ring (tCH). In addition to bands at 2921 cm1, at about 3037 cm1 are caused by the stretching vibration of the –CH2 functional group, the stretching CH vibration of the aromatic ring. All of these adsorption bands can also be observed in the spectra of the prepared composites. Furthermore, Fig. 1 shows the characteristic bands for different formulation of NiLaxFe2xO4 (x = 0.00–2.00) two prominent absorption bands (t1 and t2) at 600–430 cm1 due to ferrite form. t1 is attributed to stretching of tetrahedral metal ion and oxygen bonding, while t2 is due to vibrations of oxygen in the direction perpendicular to the axis joining the tetrahedral ion
13
and oxygen. These bands are common features of all the ferrites as reported in the literature [25]. This two bands is clearly decreased with increasing the percentage of La (x = 0.5, 1.00, 1.50 and 2.00) in the formulations. The morphological photographs of selected NiLaxFe2xO4/epoxy nanocomposites were examined by SEM micrographs x = 0.00 and x = 1.00 as shown in Figs. 2 and 3 respectively. Both samples show the same morphology. They consist of agglomerations of crystallites having similar shape. It is obvious that the nanoparticles are tightly embedded in the epoxy matrix with evidence of composite formation. This indicates good cohesion between the nanoparticles and matrix, which is very important to reach a strong interfacial adhesion. In addition, the micrograph shows a good distribution of nanoparticles within the polymer matrix. High compatibility between the nanoparticles and polymer matrix is observed. The XRD diffractograms of the nanocrystalline NiLaxFe2xO4/ epoxy composite gives a clear evident for the composites formation. Both NiLaxFe2xO4 and epoxy were able to be physically combined with each other through the composite formation. The data shows peaks characterizing both NiLaxFe2xO4 and epoxy. No other peaks attributable to the presence of impurities or other phases were detected. Fig. 4 depicts the wide-angle XRD patterns of pure epoxy resin and the nano-NiLaxFe2xO4/epoxy composites. The pattern for the neat epoxy resin exhibits two broad reflection peak occurred at 2h = 19.43° and 42.71° and a third small peak at 72.22°. The diffractograms for the different epoxy resin/nano-NiLaxFe2xO4 composites reveal the disappearance of the two broad reflections of neat epoxy resin. Inspection of the diffractogram for the composite with x = 0.00 reveals the presence of two phases; NiFe2O4 (JCPDS File no. 74-2081) as a major phase and Fe2O3 (JCPDS File no. 84-0311) as a minor one. For the end member of this series, i.e. epoxy resin/nanoNiLa2O4 composite, the relevant XRD pattern reveals that it composed of La2NiO4 (JCPDS File no. 80-1346) as a major phase together with trace amount of La2O2CO3 (JCPDS File no. 23-0322). Increasing the x-value from 0.00 to 2.00 is accompanied by a continuous decrease of the reflections due to NiFe2O4 and the development of the NiLa2O4 reflections. It was reported that, the crystallinities of the PEG/silica (MCM41 and SBA-15) and PEG/activated carbon (AC) composites, having PEG weight percentage of 80%, were much lower than that of pure PEG [26]. The XRD patterns for the PEG/silica composites having PEG weight percentage of 70% showed no crystallization peak due to PEG, whereas the PEG/AC reveals the persistence of the PEG reflections in its XRD pattern but with lower intensities. Accordingly, it was suggested that the influence of the silica stabilizer on the crystallinity of PEG is greater than that of the AC stabilizer [26]. Such stabilization was correlated with the polarity of silica, compared to the nonpolar nature of AC, which may enhance the interaction between polar PEG and silica [26]. Accordingly, it is plausible to suggest that the disappearance of the two broad reflections due to the epoxy resin in all nano-NiLaxFe2xO4 containing composites indicated the strong interaction between the epoxy resin and the nanocrystalline NiLaxFe2xO4 particles. 4.2. Thermal behavior
Fig. 1. FT-IR for pure epoxy and NiLaxFe2xO4/epoxy nanocomposites.
The crosslinking is an important factor that determines the thermal behavior of the resin. For the stoichiometric ratio 1:1 there is a crosslink at every amine–epoxy junction, i.e. all amine groups react with all epoxide groups [27,28]. In non-stoichiometric epoxy resin, the presence of an excess amine groups increased the number of un-reacted amine groups, thus influencing the thermal stability of the non-stoichiometric composite [27,28]. The mechanical tests for epoxy resin (diglycidylether of bisphenol ‘‘A’’, DGEBA) crosslinked with ethylenediamine (ETDA) revealed that, the
14
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 2. SEM micrographs for nanocrystalline NiLaxFe2xO4/epoxy composite x = 0.00.
Fig. 3. SEM micrographs for nanocrystalline NiLaxFe2xO4/epoxy composite x = 1.00.
Fig. 4. XRD patterns of neat epoxy resin (a) and the epoxy resin/nano-NiLaxFe2xO4 composites having x = 0.00 (b), 0.50 (c), 1.00 (d), 1.50 (e), and 2.00 (f).
highest breaking strength for the 1:1 epoxy–amine ratio without metallic filler [28]. Accordingly, in the preparation of our mixture we used the stoichiometric ratio. The thermal stability of the epoxy resin/nano-NiLaxFe2xO4 composites was examined by TGA at a heating rate of 10 °C/min under a nitrogen atmosphere (60 ml/min). Fig. 5a shows the obtained TGA curves. T5, T25, T50 (the temperatures of 5%, 25%, and 50% weight loss, respectively), and the solid residue left at 500 °C are the main criteria indicating the thermal stability of the composites. The higher these values are the higher is the thermal stability. These data are shown in Table 1. The temperature at which decomposition is maximum (Tmax) can be calculated from the DTG curves presented in Fig. 5b. A relatively short stage with 8–14% weight loss is happened at 30 and 225 °C, which is attributed to the breaking of un-reacted epoxy or other impurity traces apart from the cured resin [29] and water molecules [28,30]. The relative stability of pure epoxy resin as well as the epoxy resin-nanocomposites was compared by their initial decomposition temperature T5 as shown in Table 1. In the case of pure epoxy resin the decomposition starts at 128 °C. After the addition of NiLaxFe2xO4 to the epoxies, the T5 shifted towards lower temperatures. A rapid mass loss (a decrease of approximately 85%) of the neat epoxy resin can be seen from the TGA curves at the 250–500 °C temperature range. Such weight loss could be related to chain scission and resin decomposition, resulting in fragmentation of the resin into low molecular weight products [30,31]. For neat epoxy resin, decomposition starts at 340 °C and is completed at 475 °C in a single step degradation process (maximized at 423 °C,
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 5. TG (a) and DTG (b) curves of neat epoxy resin as well as its NiLaxFe2xO4 composites under nitrogen atmosphere.
Table 1 TGA data of nanocrystalline NiLaxFe2xO4 epoxy composite under nitrogen atmosphere. Sample
T5 (°C)
T25 (°C)
T50 (°C)
R500 (%)
Pure epoxy Epoxy–NiFe2O4 Epoxy–NiLa0.50Fe1.50O4 Epoxy–NiFeLaO4 Epoxy–NiLa1.50Fe0.50O4 Epoxy–NiLa2O4
128 122 104 115 94 95
372 362 351 351 360 361
407 394 386 392 397 397
0.90 13.53 8.59 6.31 8.55 10.04
Fig. 5b). It can be seen that the thermal stability of the neat epoxy resin, at such temperature range, is decreased considerably in the presence of Ni–La–Fe–O nanoparticles (Fig. 5a). Moreover, in the presence of Ni–Fe–La–O the thermal degradation showed a more complicated behavior as shown by the presence of two maxima in the 300–475 °C temperature range (Fig. 5b). The first one is maximized at 385, 378, 395, 396, and 397 °C whereas the second one is located at 421, 429, 428, 431, and 426 °C for the composites having x = 0.00, 0.50, 1.00, 1.50, and 2.00, respectively. In the open literature there are many interesting reports dealing with the role of inorganic additives in influencing the thermal
15
stability of epoxy resin composites. Lakshmi et al. [31] reported an enhancement effect of montmorillonite (MMT) clay in improving the thermal stability of expoxies composites. In agreement, Guo et al. [32] reported an improvement of the thermal stability of the cocamidopropyl betaine epoxy resin via the formation of epoxy nanocomposites with MMT-clay. This was attributed to the protection of epoxy polymer chains present between hard MMT-clay nanolayers that act as a barrier protecting from volatilizing the epoxy polymer matrix [31]. It was concluded that the existence of inorganic phases like, SiO2, Al2O3, and MgO that dominate in the nanocomposites causes such enhanced thermal stability [31]. More recently, Mustata et al. [33] reported slight thermal stability of composites decrease compared with diglycidyl ether of bisphenol A/p-aminobenzoic acid (DGEBA/p-ABA) sample, as a result of some possible modification in thermal degradation mechanism in the presence of calcium carbonate particles. On the other hand, transition metals oxides like ZnO [34], CuO [35], and TiO2 [36] and oxides structures like Ni–Zn ferrite [27] were reported to decrease the thermal stability of epoxy resin composites. Such destabilization was ascribed to their catalytic action. Thus it is plausible to suggest that the added Ni–La–Fe–O nanoparticles could serve as catalysts to degrade the epoxy matrix. The parameter R500 (Table 1) refers to the residue remaining at 500 °C. It is seen that even after complete degradation; char residue is around 1% for neat epoxy resin whereas higher values, 6.3–13.5%, are obtained for the different composites. The highest residue values were observed for the samples having x = 0.00 and 2.00, i.e. for the composites containing NiFe2O4 and La2NiO4 phases, whereas the lowest one was exhibited by the NiLaFeO4 containing composite. Such residue is due to the presence of thermally stable char together with NiLaxFe2xO4 phases. The increased rate of mass loss beyond 600 °C, Fig. 5a, illustrates the continued degradation of the char layer for all the Ni–Fe–La–O containing samples. In this context, char residue was obtained during the thermal decomposition of epoxy resins/nano-Al2O3 composites [37]. The char at 800 °C of the composites increased gradually with increasing nano-Al2O3 content [37]. In agreement, the char yield from the thermal decomposition of Ni–Zn ferrite epoxy composite increased with increasing the Ni–Zn ferrite from 2% to 8% [27]. Concurrently, Wu et al. [38] has reported the formation of a char with excellent thermal stability via the thermal decomposition of water resistance of epoxy/microencapsulated ammonium polyphosphate composite. 4.3. Water sorption, electrochemical impedance and coating measurements Fig. 6 shows the variation of WS of the epoxy samples with the immersion time. The WS of all epoxy samples increases with time, but, the pure epoxy has very large values of WS along immersion periods. A straight line could be obtained for the points after 10 min and has a slope 0.165 for the pure epoxy while 0.057 for the epoxy composite (x = 0). This indicated larger continuous absorption of water for the pure epoxy and the nanoparticle additives decrease effectively the WS of the epoxy. Presence of Ni–Fe nanoparticles in the epoxy suppressed sharply the sorption of water. But, introduce La to the nanoparticles improves slightly the suppression of WS. The Nyquist plot obtained from EIS measurements for the epoxy coated steel samples after 10 and 120 min immersion times in 0.1 M NaCl solution are shown in Figs. 7a and b. Fig. 7a shows the impedance of pure epoxy coating, it is dominated by the coating capacitance at high frequencies and coated resistance at the low frequency. The coating resistance decreased after longer immersion time indicating the sorption of water in the epoxy body. The absorption of water and movement of ion species in the epoxy
16
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
Fig. 6. The variation of WS of the epoxy samples with the immersion time.
material increase the conductivity of this coated layer [39,40]. The impedance spectrum of the epoxy composite (x = 0) coating show (Fig. 7b) very larger coating resistance which indicate lower sorption of water in this type of coating. There is no any significant change in the coating resistance after 2 h immersion. Similar results were obtained for the other epoxy composites coatings. The impedance spectra are fitted well with the equivalent circuit as shown in Fig. 8. In this circuit, Rs is the solution resistance, Rc and Cc are coating resistance and coating capacitance, respectively. The capacitance element is fitted by constant phase element (CPE) to compensate for non-ideal capacitance. The values of Cc and Rc for the epoxy coating sample are recorded in Table 2. The epoxy composites exhibited very larger values of Rc and very low values of Cc at the initial immersion (5.44 103 kO and 2.23 109 F, respectively, for the epoxy composite, x = 0) in comparison with those of pure epoxy (92.4 kO and 1.47 105 F, respectively). The Rc and Cc values of the epoxy composite not significantly changed after 2 h immersion in chloride solution while it changed to 46.4 kO and 3.1 105 F, respectively, for the pure epoxy. This indicated that the epoxy composite coatings have good resistance for sorption of water and protection of steel corrosion. The impedance data of the La-containing epoxy composite coating is almost close to that of La-free epoxy composite coating. In agreement with
Fig. 7a. The impedance spectrum of pure epoxy coating.
Fig. 7b. The impedance spectrum of nanocrystalline NiLaxFe2xO4/epoxy composite coating (x = 0.00).
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
17
References
Fig. 8. The equivalent circuit.
Table 2 EIS parameters of different epoxy coatings after immersion in 0.1 M NaCl. Sample
Rc (O)
Cc(F), n
10 min
120 min
10 min
120 min
Pure epoxy
9.24 104
4.64 104
Epoxy–NiFe2O4
5.44 106
5.37 106
Epoxy–NiLa0.50Fe1.50O4 Epoxy–NiFeLaO4
2.0 107
5.6 106
8.3 106
8.4 106
Epoxy–NiLa1.50Fe0.50O4
8.8 108
4.3 108
1.47 105, 0.54 2.23 109, 0.59 2.0 1010, 0.89 2.41 1010, 0.88 2.24 1010, 0.89
3.1 105, 0.47 2.2 109, 0.58 1.58 1010, 0.81 2.2 1010, 0.89 3.9 1010, 0.89
the gravimetric method the insertion of La to the nanoparticle of Ni–Fe has slight improve in the resistance of the epoxy coating. It is concluded that the coating resistance of epoxy coatings containing Ni–Fe nanoparticles is larger than that of pure epoxy coating. This may be attributed to the higher barrier properties and ionic charge transfer resistance of Ni–Fe nanoparticles embedded in the epoxy coating layer.
5. Conclusions New nanocrystalline NiLaxFe2xO4/epoxy composites of different x have been synthesized in situ while epoxy resin is prepared using solution method with the help of ultrasonic assistance. FT-IR, SEM and XRD give good evidences for the composites formation. XRD data are indicating that the pure epoxy is physically combined with nanoparticle additives. The thermal degradation show a more complicated behavior in the presence of Ni–Fe–La–O as illustrated by the presence of two maxima in the 300–475 °C temperature range. The added Ni–La–Fe–O nanoparticles could serve as catalysts to degrade the epoxy matrix. The presence of Ni–Fe nanoparticles in the epoxy suppresses sharply the sorption of water. On the other hand, the insertion of La atoms into the nanoparticles improves slightly the suppression of water sorption. The coating resistance and thus corrosion protection of the epoxy nanocomposites is higher than that of pure epoxy. Acknowledgements The authors are grateful to the Center of Research Excellence in Corrosion CoRE-C at King Fahad University for Petroleum and Mineral (KFUPM) for providing financial support for this work Via Grant No. CR-7-2010. We also acknowledge the center of excellence for advanced materials Research (CEAMR) at King Abdulaziz University for providing Research facilities.
[1] El-Tayeb NSM, Yousif BF, Brevern, PV. On the measurements of interface temperature and friction coefficient of glass-fiberreinforced epoxy composite under dry sliding contact. In: Proceedings of the international conference on recent advances in mechanical and materials engineering, 30–31 May, 2005, Kuala Lumpur, Malaysia; 2005. p. 1006–113. [2] El-Tayeb NSM, Yousif BF. Wear and friction behaviour of CGRP and WGRP composites subjected to dry sliding. In: Proceedings of WTC2005 world tribology congress III September 12–16, 2005, Washington, DC, USA, Paper No. WTC 2005-63097. [3] Edwards KL. An overview of the technology of fiber-reinforced plastics for design purposes. Mater Des 1998;19:1–10. [4] Geim AK, Novoselov KS. The rise of graphene. Nat Mater 2007;6:183–91. [5] Zhang M, Gao G, Li CQ, Liu FQ. Titania-coated polystyrene hybrid microballs prepared with miniemulsion polymerization. Langmuir 2004;20:1420–4. [6] Lan T, Kaviratna PD, Pinnavaia TJ. On the nature of polyimide–clay hybrid composites. Chem Mater 1994;6:573–5. [7] Yao KJ, Song M, Hourston DJ, Luo DZ. Polymer/layered clay nanocomposites: 2 polyurethane nanocomposites. Polymer 2002;43:1017–20. [8] Yeh JM, Chen CL, Huang CC, Chang FC, Chen SC, Su PL, et al. Effect of organoclay on the thermal stability, mechanical strength, and surface wettability of injection-molded ABS–clay nanocomposite materials prepared by melt intercalation. J Appl Polym Sci 2006;99:1576–82. [9] Li C, Wilkes GL. Silicone/amine resin hybrid materials as abrasion resistant coatings. Chem Mater 2001;13:3663–8. [10] Yeh JM, Yu MY, Liou SJ. Dehydration of water–alcohol mixtures by vapor permeation through PVA/clay nanocomposite membrane. J Appl Polym Sci 2003;89:3632–8. [11] Yeh JM, Liou SJ, Lai CY, Wu PC. Enhancement of corrosion protection effect in polyaniline via the formation of polyaniline–clay nanocomposite materials. Chem Mater 2001;13:1131–6. [12] Peng GW, Qiu F, Ginzburg VV, Jasnow D, Balazs AC. Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures. Science 2000;288:1802–4. [13] Merkel TC, Freeman BD, Spontak RJ, He Z, Pinnau I, Meakin P, et al. Ultrapermeable, reverse-selective nanocomposite membranes. Science 2002;296:519–22. [14] Wang Y, Herron N. X-ray photoconductive nanocomposites. Science 1996;273:632–4. [15] Csetneki I, Kabai Faix M, Szilagyi A, Kovacs AL, Nemeth Z, Zrinyi M. Preparation of magnetic polystyrene latex via the miniemulsion polymerization technique. J Polym Sci Part A Polym Chem 2004;42:4802–8. [16] Taden A, Antonietti M, Heilig A, Landfester K. Inorganic films from three different phosphors via a liquid coating route from inverse miniemulsions. Chem Mater 2004;16:5081–7. [17] Shi X, Nguyen TA, Suo Z, Liu Y, Avci Recep. Effect of nanoparticles on the anticorrosion and mechanical properties of epoxy coating. Surf Coat Technol 2009;204:237–45. [18] Chen C, Khobaib M, Curliss D. Epoxy layered-silicate nanocomposites. Prog Org Coat 2003;47:376–83. [19] Ramezanzadeh B, Attar MM, Farzam M. A study on the anticorrosion performance of the epoxy–polyamide nanocomposites containing ZnO nanoparticles. Prog Org Coat 2011;72:410–22. [20] Olad A, Barati M, Behboudi S. Preparation of PANI/epoxy/Zn nanocomposite using Zn nanoparticles and epoxy resin as additives and investigation of its corrosion protection behavior on iron. Prog Org Coat 2012;74:221–7. [21] Huang ZM. Tensile strength of fibrous composites at elevated temperature. Mater Sci Technol 2000;16:81–93. [22] Hsiang HI, Tsai JY. Titanate coupling agent effects on nonaqueous Co2Z ferrite suspensions dispersion. J Mater Sci 2006;41:6339–46. [23] Chen W-Sh, Chang Y-L, Hsiang H-I, Hsu F-C, Yen F-S. Effects of titanate coupling agent on the dielectric properties of NiZn ferrite powders–epoxy resin coatings. Ceram Int 2011;37:2347–52. [24] Abu-Zied BM, Asiri AM. Urea based combustion process for the synthesis of nanocrystalline Ni–La–Fe–O catalysts. J Nanomater 2012;2012:1–7. [25] Shaikh AM, Jadhav SA, Watawe SC, Chougule BK. Infrared spectral studies of Zn-substituted Li–Mg ferrites. Mater Lett 2000;44:192. [26] Feng L, Zhao W, Zheng J, Frisco S, Song P, Li X. The shape-stabilized phase change materials composed of polyethylene glycol and various mesoporous matrices (AC, SBA-15 and MCM-41). Sol Energy Mater Sol Cells 2011;95:3550. [27] Boon MS, Serena Saw WP, Mariatti M. Magnetic, dielectric and thermal stability of Ni–Zn ferrite-epoxy composite thin films for electronic applications. J Magn Magn Mater 2012;324:755–60. [28] Brito Z, Sánchez G. Influence of metallic fillers on the thermal and mechanical behaviour in composites of epoxy matrix. Compos Struct 2000;48:79–81. [29] Park S-J, Jin F-L. Thermal stabilities and dynamic mechanical properties of sulfone-containing epoxy resin cured with anhydride. Polym Degrad Stab 2004;86:515–20. [30] Kandola BK, Biswas B, Price D, Horrocks AR. Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin. Polym Degrad Stab 2010;95:144–52. [31] Lakshmi MS, Narmadha B, Reddy BSR. Enhanced thermal stability and structural characteristics of different MMT-clay/epoxy-nanocomposite materials. Polym Degrad Stab 2008;93:201–13.
18
A.M. Asiri et al. / Composites: Part B 51 (2013) 11–18
[32] Guo B, Jia D, Cai C. Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites. Eur Polym J 2004;40:1743–8. [33] Mustata F, Tudorachi N, Rosu D. Thermal behavior of some organic/inorganic composites based on epoxy resin and calcium carbonate obtained from conch shell of Rapana thomasiana. Compos B 2012;43:702–10. [34] Liufu SC, Xiao HM, Li YP. Thermal analysis and degradation mechanism of polyacrylate/ZnO nanocomposites. Polym Degrad Stab 2005;87:103–10. [35] Guo ZH, Liang XF, Pereira T, Scaffaro R, Hahn HT. CuO nanoparticles filled vinyl-ester resin nanocomposites: fabrication, characterization and property analysis. Compos Sci Technol 2007;67:2036–44. [36] Chiang PC, Whang WZ. The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films. Polymer 2003;44:2249–53.
[37] Jiang W, Jin F-L, Park S-J. Thermo-mechanical behaviors of epoxy resins reinforced with nano-Al2O3 particles. J Ind Eng Chem 2012;18:594–6. [38] Wu K, Zhang Y-K, Zhang K, Shen M-M, Hu Y. Effect of microencapsulation on thermal properties and flammability performance of epoxy composite. J Anal Appl Pyrol 2012;94:196–201. [39] Behzadnasab M, Mirabedini SM, Kabiri K, Jamali S. Corrosion performance of epoxy coatings containing silane treated ZrO2 nanoparticles on mild steel in 3.5% NaCl solution. Corros Sci 2011;53:89–98. [40] Niknahad M, Moradian S, Mirabedini SM. The adhesion properties and corrosion performance of differently pretreated epoxy coatings on an aluminum alloys. Coros Sci 2010;52:1348–57.