Inclusion of octahedron-shaped ZnFe2O4 nanoparticles in combination with carbon dots into carbonyl iron based magnetorheological suspension as additive

Journal of Alloys and Compounds 737 (2018) 536e548

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Inclusion of octahedron-shaped ZnFe2O4 nanoparticles in combination with carbon dots into carbonyl iron based magnetorheological suspension as additive Abdollah Hajalilou a, *, Ebrahim Abouzari-Lotf b, c, Vahid Abbasi-Chianeh d, Taha Roodbar Shojaei e, Ehsan Rezaie a a

Faculty of Mechanical Engineering, Department of Materials Engineering, University of Tabriz, Tabriz, Iran Advanced Materials Research Group, Center of Hydrogen Energy, Universiti Teknologi Malaysia, 54100, Kuala Lumpur, Malaysia Department of Chemical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Malaysia d Faculty of Mining and Materials Engineering, Urmia University of Technology, Urmia, Iran e Department of Mechanical Engineering of Agricultural Machinery, Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 25 September 2017 Received in revised form 12 November 2017 Accepted 7 December 2017 Available online 13 December 2017

Octahedron-shaped nanoparticles of ZnFe2O4 and functionalized superparamagnetic nanoparticles of carbon (CNP) were synthesized and used as additives to prepare carbonyl-iron magnetorheological (CIMR) fluids with improved shear stress and sedimentation rate. Single phase spinel ZnFe2O4 nanoparticles with cubic structure was prepared with hydrothermal route. Appearance of two absorption bands correspond to T-band at
471.77 and O-band at 556.19 cm1 in FTIR spectra confirmed spinel phase formation. HRTEM micrographs indicated the average size of 12 nm and range of 5e15 nm for octahedron-shaped particles. Heating the as-synthesized ZnFe2O4 nanoparticles at 650  C resulted in the lattice fringes with strong spotty ring in SAED patterns, indicating the good crystallinity of the assynthesized nanopowders. Such heated nanoparticles showed an increase in the saturation magnetization from
21e52 emu/g and decrease in the coercivity from 80 to 35 Oe in the VSM analysis. Additionally, HRTEM image of the superparamagnetic nanoparticles of carbon (CNP) exhibited irregular shaped particles with the average size of 5 nm. Raman revealed the presence of D and G bands associated with the vibration of sp2-bonded carbon and the presence of defects. As prepared CNPs and heatedZnFe2O4 nanopowder were introduced into the CI-MR suspension as additives. The rheological characteristics of the samples were investigated by employing various magnetic field strengths and temperatures. It was shown that the inclusion of nanoparticles in the free space of micron-sized CI particles results in strengthened chain-like structure formation as the yield shear stress of CI-based MR suspension with 1 vol% (CNPs-ZnFe2O4) additive is increased up to
12% at 500 mT at 25  C. On the other hand, the sedimentation rate becomes slower up to
18% due to the increment of friction force in the presence of nanoparticles additive. © 2017 Elsevier B.V. All rights reserved.

Keywords: Magnetic materials Nanoparticles MR fluid Carbonyl iron Sedimentation Additives

1. Introduction Magnetorheological (MR) fluids are normally composed of micron-sized soft magnetic particles such as carbonyl iron (CI) suspended in aqueous carrier or nonmagnetic fluids such as silicon oil, hydrocarbon oil, etc. Their rheological characteristics of yield

* Corresponding author. E-mail address: [email protected] (A. Hajalilou). https://doi.org/10.1016/j.jallcom.2017.12.071 0925-8388/© 2017 Elsevier B.V. All rights reserved.

stress and shear viscosity are strongly dependent on various factors including MR fluid's constituent, applied magnetic field and preparation conditions [1e3]. The fluid normally represents Newtonian behavior once there is no externally applied field [4]. It simply means that the MR fluid behaves like a normal liquid that can easily flow in the absence of applied magnetic field. However, a unique phase transition from a liquid-like to a solid-like state would occur within milliseconds in the presence of a magnetic field [1e3]. This is due to the alignment of the magnetic particles in the direction of an applied magnetic field and subsequent formation of a robust

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

chain-like structure with their adjacent particles. This phenomenon happens through the polarization of magnetic particles in MR suspension due to the dipole-dipole interactions of the magnetic particles with their adjacent particles, which results in alteration of MR fluid from fluid to solid state [1]. Therefore, a force named as yield stress is required to make the fluid re-flow again, and this action, which is considerably fast and reversible, provides several potential engineering applications. The dynamic yield stress of MR fluid maybe fitted in terms of various rheological models such as the Bingham plastic, HerschelBulkley Model, Bi-viscose and Herschel-Bulkley with pre-yield viscosity [1]. Among them, the Bingham plastic is widely employed to describe the MR effect. The mathematical state of this model is given in equation (1). Accordingly, the dynamic yield stress value is evaluated trough the shear stress as a function of the shear rate at constant magnetic field strengths [1].

t ¼ ty þ hg_ ; forjtj  ty g_ ¼ 0; forjtj < ty

(1)

Here, g_ refers to the shear rate, h designates the shear viscosity, ty donates the yield stress in terms of magnetic field, and t is the shear stress [1]. Indeed, this model represents a non-vanishing yield stress of the material, which is considered as a stress where the fluid transmits from a solid to liquid-like state at zero shear rates. The minimum dynamic yield stress is needed for the fluid to flow. Otherwise, when t falls below ty, a solid structure is formed [1]. Besides the strength of an externally applied magnetic field, the MR effects are usually influenced through the state of magnetic particles such as shape, type and size as well as the carrier fluid type and surfactant [1]. Therefore, a wide range of engineering applications are expected by optimum control of the variables [1]. Most MR suspensions are made by employing micron-sized carbonyl iron (CI) particles in a base carrier medium [1e5]. This is due to the relatively favorable low coercivity (Hc) and high saturation magnetization (Ms) of the CI particles compared to other soft magnetic compounds [3,5,6]. On the other side, their higher density in compared to a continuous medium (
7.87 g/cm3 [6]) results in their noticeable sedimentation through the suspension during long period of application time and restricts the MR fluids applications. Generally, three main techniques of introducing nanoparticles additive into MR suspension [1e6], polymer coating on magnetic particles [6,7] and bi-dispersing of nano and micron-sized particles [8] have been proposed and undertaken to overcome this limitation. Although coating process remarkably reduced the CI particles density, it was found to be a complicated process to control the states of coated particles as the coating thickness is dependent on the several factors such as temperature, the reactive agent molar ratio, etc. [6,7]. Similarly, even though the bi-disperse causes a remarkable reduction in the particles settling in MR suspension, it is difficult to compensate for the resulting enhancement in off-state viscosity and the decline in yield stress [9,10]. On the other hand, introducing additives into MR suspensions can be considered as a simple and practical method of improving stability [1e5]. Finding proper additive for specific application is critical for MR fluids since additives have various influences on the MR properties. For example, the redispersibility of the MR fluids is enhanced by oleic acid additive, but the sedimentation of particles was inevitable. On the other hand, adding silica nanoparticles can mitigate particle settling under quiescent conditions, but makes redispersion extremely difficult [11]. So far, various nanoparticles of soft magnetic species such as Ni-Zn ferrite [3], CI [2], Fe3O4 [5,12], and/or binary mixture of Ni-Zn ferrite as well as magnetite nanoparticles additive [5] are introduced into the CI-based MR suspensions as

537

additive. Indeed, these additives can be introduced into to the magnetic suspension either as stabilizer or surfactants to vary the initial viscosity of the MR suspensions. This gives rise to the stable suspension formation and its lubrication enhancement, which results in the reduction of the magnetic particles sedimentation [13]. In addition, these additives materials may have an antiabrasion/erosion and anti-friction role in some diverse applications. Thixotropic agent compounds and oleic acid are example of these materials [1]. For example, high viscosity materials, e.g., thixotropic materials are introduced into magnetorheological fluid to improve stability of particles against sedimentation in the MR fluid. Furthermore, iron oleate or iron naphthalate are introduced into suspension as dispersants, while metallic soaps like sodium stearate and/or lithium stearate are introduced as thixotropic additives. In fact, they are used to hinder thickening of the MR suspension after several cycles of use as well as the interparticle friction and the particles sedimentation [14]. It has been stated that the thixotropic agents would make a network of particles, which forms a weak structure at low shear rates, resulting in the reduction of the magnetic particles sedimentation [15]. Investigation the influence of submicron organoclays additives on the CI-based MR fluid indicated that the addition of up to 1 wt% would improve stability and redistribution of the suspension [16]. An improvement in the MR suspension stability was observed by introducing of organoclay without considerable alteration in MR effect [17]. Furthermore, the CI particles were exposed to argon and octafluorocyclobutane plasma to form fluorine bonds on the CI particles surface [18]. It was found that the MR suspension including surface fluorinated CI exhibits an improved stability in compared to the pristine CI-based MR suspension. This phenomenon is associated with the attractive force of a fluorine bond on the CI particles surface as well as of a methyl group that exists in the carrier fluid. In other work, Jung and Choi [12] studied the influence of octahedral-shaped Fe3O4 nanoparticles additive on CI-based MR suspension. The best MR effect was obtained for 10% vol Fe3O4 nanoparticles. Both the stability and the shear stress of MR suspension improved. Similar results of improved sedimentation stability, low zero field viscosity and high shear yield stress was reported by Liu et al. [19] upon introduction a certain amount of Fe3O4 nanoparticles (i.e. 4 and 6 wt%). Besides foregoing-mentioned characteristics on MR effect, the preparation route of nanoparticles has shown various influences on MR effects [20]. Thus, in this study, carbon nanoparticles (CNPs) were synthesized from used-tissues (waste) and ZnFe2O4 nanoparticles from their nitrate salts via hydrothermal route. Indeed, combination of these nanoparticles, for the first time, to the best of our knowledge, was introduced into CI-based MR suspension as additive. Also, it was expected that addition of these nanoparticles is prevailing due to the prevention effect against the mutual contacts of magnetic particles, which results in an improvement on the rheological effects in the case of hard baking. These effects were undertaken under an applied magnetic field via rotational tests. Sedimentation stability of the MR fluids was also investigated. 2. Experiments To synthesize ZnFe2O4 nanoparticles, 0.35 g of Zn(NO3)2$6H2O (99%, Sigma-Aldrich) and 1.8 g of Fe(NO3)3$9(H2O) (99.99%, Sigma-Aldrich) in a molar ratio of 1:2 were used as starting materials without further purification. The mixed salts were dissolved in 100 mL distilled water and its pH adjusted at 12 using 5 Molar NaOH. Then, the prepared solution was transferred in Teflon-sealed autoclave and heated at 180  C for 12 h. Thereafter, the synthesized nanoparticles were collected using a magnet and washed several times with distilled water to remove NaOH. The resultant ZnFe2O4

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nanoparticles were dried in oven at 50  C for 20 h. Finally, the assynthesized ZnFe2O4 nanopowders were heated in a carbolite furnace at 650  C for 2 h in air atmosphere. To synthesize CNPs, used facial tissues were washed three times with distilled water and dried in an oven at 38  C for 120 min. After burning the dried samples in air atmosphere, the achieved ash was dispersed in 50 mL distilled water. Then, 3.34 mL of HNO3 (SigmaAldrich) was introduced into the suspension and stirred for 30 min. The suspension was sonicated (HWASHIN power sonic 420, 60 Hz) for 60 min, and filtered through a filter paper (Filtres Fioroni, France). Subsequently, it was centrifuged at 12000 rpm for 14 min to obtain a transparent solution. The structural and phase formation of the samples were taken into account through X-ray diffraction analysis (XRD) (Philips, PW 3710) with a Cu Ka radiation of l ¼ 0.154 nm. The average crystallite size and lattice strain were computed using Williamson-Hall method as follows [21]:

bcosq ¼

0:9l þ 2hsinq d

(2)

where d is the average crystallite size, h is the lattice strain, b is full width of pea k at half intensity (rad) or the full width at half maximum (FWHM) from High Score software, q is position of peak in the pattern (rad), l the wavelength of X-ray (nm). The morphological changes of the samples were evaluated via field emission scanning electron microscopy (FeSEM) using an FEI NOVA NanoSEM 230 machine and high-resolution transmission electron microscopy (HRTEM) using a JEOL JEM TEM (Tokyo Japan). The HRTEM images were taken by preparation of dispersed powders in 95% acetone. Indeed, 0.1 mg of the powders dispersed in 25 mL of acetone and sonificated for 25 min. Then, one drop of the suspension was placed on copper TEM grids. The magnetic behavior of the samples was measured via a vibrating sample magnetometer (VSM) (Malek Ashtar, Iran) with 10 kOe at room temperature. For sample preparation, 0.025 g of powder, for each sample, was placed between transparent tapes and punched in order to obtain the MeH hysteresis loops and evaluate the saturation magnetization (Ms) and the coercivity (Hc). Thermogravimetric analyses (TG) of the samples were carried out on a Mettler thermobalance TG-50 in a Mettler TA-4000 System. The experimental conditions were adjusted for almost 20 mg powders at heating temperature up to 800  C with rate of 10  C/min under argon atmosphere. Differential scanning calorimetry (DSC)

analysis was performed using STARe SW 9.20 apparatus in the heating temperature of up to 800  C in argon atmosphere by holding constant heating rate at 10  C/min. The absorption band and optical characteristics of the samples were evaluated via Fourier transform Infrared transmission spectra (FT-IR) using the Jasco-680-plus spectrophotometer (Tokyo, Japan) in the rage of 400e4000 cm1 and Uevisible spectrophotometer (UV 2401pc). The FT-IR analyses of the samples was carried out by mixing synthesized powder with KBr powder reference and the UV analyses was measured by dispersing synthesized powder in distilled water solution. To evaluate the MR effect of the samples, two types of MR suspensions were prepared: (1) without additive; 30 vol% CI þ 63.5 vol % Polyalphaolefin (PAO) oil þ 6.5 vol% oleic acid (OC) and (2) with additives; 30 vol% magnetic particles (99 vol% CI þ 1 vol% CNPsZnFe4O4) þ 63.5 vol% PAO oil þ 6.5 vol% OC. The prepared samples were mechanically stirred for 10 min to ensure complete dispersion of aggregates. An MCR 302 Anton-Paar-provided rheometer was employed to evaluate the samples' rheological behavior in rotational state. The externally applied magnetic field was in the range of 0e500 mT, with 100 increments, in the perpendicular direction to the flow.

3. Results and discussion 3.1. Synthesis of CNPs The CNPs were synthesized and functionalized by carbonization of the cellulose, hemicellulose, and lignin of waste facial tissue to make the core followed by addition of functionalized groups on the surface of core. Their HRTEM image exhibited almost spherical shaped particles with the average size of 5 nm (Fig. 1a). The corresponding FeSEM image is also shown in inset of Fig. 1b. The particles distribution is roughly homogeneous with spherical shapes, which confirms the HRTEM results. The XRD pattern revealed a broad peak of carbon particles correspond to (002) plane at diffraction angle (2q) about of 19.50 in the range of 0e70 (Fig. 1b). As shown in Fig. 2a, CNPs showed characteristic IR absorption bands of CeN stretching vibrations at 1388 cm1, CeO stretching at 1078, 1132 and 1724 cm1, CeC at 1637 cm1, CeH at 2904 and 2927 cm1 and OeH at 3459 cm1. Indeed, the presence of hydroxyl, carbonyl or carboxylic acid groups on the CNPs surface was indicative of the oxidizing effect of HNO3 on some of the surface

Fig. 1. The CNPs (a) HRTEM image and (b) XRD pattern.

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

539

Fig. 2. The CNPs (a) FT-IR and (b) Raman spectra.

carbon atoms converting them into carboxylic groups during the HNO3 treatment step. Besides, Raman study revealed the presence of D and G bands emerged at 1356 and 1595 cm1 (Fig. 2b), which are associated with the vibration of sp2-bonded carbon and the presence of defects, respectively [22]. The defect sites are ascribed to the presence of sp3 carbons, oxygen, and nitrogen [22]. The G band corresponds to the E2g mode of the graphite and is attributed to the vibration of sp2-bonded carbon atoms in a two-dimensional hexagonal lattice. 3.2. The hydrothermal synthesis of ZnFe2O4 nanoparticles

a ¼ dðhklÞ

(3)

1.4

*

y = 0.5185x + 0.6511 R² = 0.0184

(b)

1

βCosθ

(ii)

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h2 þ k2 þ l2

where d is the lattice spacing of any (hkl) plan. The value of lattice constant of as-synthesized ZnFe2O4 (about 0.8394 nm) is lower than that of the bulk one (about 0.8447 nm) according to the JCPDS (00-022- 1012) file for ZnFe2O4. It has been stated that both the size and shape of particles affect the lattice constant, where the discrepancy in particle shape is taken into account by a shape factor [23]. Furthermore, the lattice constant would decline by several nanometers once the particle size decreases [23]. The lattice constant of the as-synthesized ZnFe2O4 increased by the heating process, and its value is almost closed to bulk one; about 0.8451 nm. This suggests that as-synthesized ZnFe2O4 presents a mixed spinel

1.2

* (533)

* (422)(511) * * (440)

ZnFe2O4

*

(220)

Intensity (a. u.)

*

(a)

(311) * (222) * (440)

Fig. 3a shows the XRD patterns of the synthesized-ZnFe2O4 nanoparticles, indicating single phase spinel ferrite formation. The samples diffraction peaks perfectly matched with a spinel structure (JCPDS card no. 73-1963) without any traces from other impurity phases. The most intense reflections are observed at 2q values of 31.28 , 35.67, 37.24 , 44.311, 53.67, 57.22 , 62.73 and 74.25 , which are assigned to (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3), respectively. The broadening of the crystalline diffraction peaks in the synthesized sample is due to the crystallite size refinement and internal strain accumulation [1,4,21]. In order to increase the phase crystallinity and also reduce the internal lattice strain, the synthesized powders were heated in a furnace at 650  C for 12 h in air atmosphere. The corresponding XRD pattern

to this sample is shown in Fig. 3a as well. No new phase was observed in the heated samples. Intensifying the XRD pattern's peaks indicates the phase crystallinity and crystallite growth in the ZnFe2O4 nanopowders. The average crystallite size and lattice strain of the samples were computed in terms of Williamson-Hall method [21] and their results are shown in Fig. 3b. It indicates that the average crystallite size grew from
12 nm (as-synthesized ZnFe2O4) to
26 nm (as-synthesized-heated ZnFe2O4 at 650  C), while the lattice strain decreased from 1.153% to 0.651%, accordingly. The lattice constant (a) of the samples was calculated using equation (3):

y = -0.743x + 1.1533 R² = 0.2533

0.8 0.6 0.4

As-synthesized ZnFe2O4 Heated ZnFe2O4 Linear (As-synthesized ZnFe2O4) Linear (Heated ZnFe2O4)

(i) 0.2 0 20

40

2θ(˚)

60

80

0

0.2

0.4

0.6

0.8

2Sinθ

Fig. 3. (a) XRD pattern of the ZnFe2O4 samples; (i) as-synthesized and (ii) heated sample, and (b) Williamson-Hall approaches for ZnFe2O4 samples based on their XRD patterns.

540

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

mode, in spite that it has a normal mode in the bulk form. In other words, the Zn2þ ions would migrate from the tetrahedral site to the octahedral site once the size of particles reduces. Indeed, in bulk mode, Zn2þ ions occupy the tetrahedral sites due to the great power of ligands. On the other hand, since the ionic radius of zinc is 0.74 Å and the ionic radius of iron is 0.68 Å, they have tendency to migrate to the greater positions (octahedral sites), which results in random distribution of cations in ZnFe2O4 structure. A thermal analysis and the mechanism of phase formation were studied through TGA and DSC. In TG, ZnFe2O4 phase formation is observed with total weight loss of
90% in three different stages, as shown in Fig. 4. A slight weight loss of about 8.5% in the range below
180  C is associated with the moisture elimination from the powders. A rapid mass loss (about 70%) was observed in the range of
180-495  C, which matches with the appearance of an exothermic peak occurred at
290  C in the DSC curve. This suggests the release of H2O, CO2 and N2 from the combustion of the nitrates and organic impurities. An observation intense exothermic peak in the range of
400-500  C in the DSC curve is more likely attributed to the decomposition of precursor into ZnFe2O4 nanoparticles [24,25]. No further mass loss and stable thermal effect after 550  C in both the TGA and DSC curves indicate the formation of ZnFe2O4 nanoparticles. The nanocrystalline structure of the as-synthesized ZnFe2O4 and heated-ZnFe2O4 powder is also confirmed by HRTEM microphotographs. Their corresponding HRTEM bright field microphotograph and the corresponding selected area electron diffraction (SAED) are shown in Fig. 5. The microphotographs reveal that the particles are nearly in octahedron shape and in non-agglomerated state with uniform sizes (Fig. 5a and b). Fig. 5a1 and b1 demonstrate the crystal structure of ZnFe2O4 with the average lattice spacing of
2.5114 nm for the as-synthesized sample. This value increased to
2.9878 nm upon heating the sample. The lattice fringes of the microphotograph correspond to a group of atomic planes within powder particles, which designate a nanocrystalline structure of the ZnFe2O4 samples, supported by well-pronounced diffraction rings. The particles size obtained from the HRTEM microphotographs ranges between 5 and 15 nm for the as-synthesized sample and between 8 and 40 nm for the heated sample, which are relatively consistent with the value estimated by the analysis of the X-ray diffraction data. Microphotographs 5a2 and b2 indicate that each particle is composed of a large number of nanosized crystals. It would worth to mention that spots in the SAED pattern are diffraction from a single crystal, and one can identify the zone axis for these patterns. Rings are due to multiple crystals. From the HRTEM image of the heated sample, the lattice fringes with strong spotty ring patterns clearly indicate the enhanced crystallinity of

EXo

100 TGA

8.5%

DSC

80

Weight Loss (%)

Heat Flow (mW/mg-1)

90

70

81.5%

60 50 40 30 20 10 0 0

100

200

300

400

500

600

700

800

Temperature (˚C) Fig. 4. DSC-TG curves of the as-synthesized ZnFe2O4 nanopowders.

the nanoparticles in comparison with the as-synthesize ZnFe2O4 sample. The two main absorption bands, the high frequency band nl around 650-550 cm1, (which is assigned T-band and belongs to Zn-O) and the low frequency band n2 around 525-400 cm1, (which is assigned O-band and belongs to Fe-O), arise from tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice, respectively [23,26]. In fact, the absorption band n1 1 is due to the stretching vibration of the tetrahedral metal-oxygen bond, and the absorption band n2 is arising from the metal-oxygen vibrations in octahedral sites [27]. According to this explanation, the observed absorption peaks at
471.77 and 556.19 cm1 in FTIR spectra confirm the spinel phase ZnFe2O4 formation (Fig. 6a). The FTIR spectrum of the heated-ZnFe2O4 sample suggests a dependency of absorption bands on the heating condition. In other words, the absorption bands shifted to 467.61 cm1 in T-band and 564.96 cm1 in O-band in the heated sample. Shifting T-band to lower wavelength is associated with the release of lattice strain and of the particle growth in the heated sample [26]. This phenomenon is also responsible for the reduced peaks intensity. Bulk ZnFe2O4 has a normal spinel structure with Zn2þ ions in the A-site and Fe3þ ions in the B-sites [28]. On the other hand, the cations in nanostructured ferrites would occupy lattice sites by a certain degree against their preference in micron grain bulk materials and this inversion degree is dependent on the particle size [29]. Shifting O-band to higher wavelength in the heated sample confirms this phenomenon. In other words, Znþ2 with greater ionic radius of 0.84 Å replaces with Fe3þ ion (0.64  A) in Bsites and push them into A-site, which results in shifting of wave number to higher value. Interestingly, appearing a peak at
666.88 cm1 in the heated ZnFe2O4 nanopowders may be associated with this effect as well. This is further confirmed by the XRD pattern of this sample that the (hkl) plane corresponds to (222) emerged after the heating process in the as-synthesized ZnFe2O4 nanopowders. Other observed peaks in the FTIR spectra of both the samples in the range of
1000e4000 cm1 are associated with hydrocarbon impurities and absorbed moisture, which are explained in Refs. [23,26]. For example, the strong peak at around 3425 cm1 is associated with OH group, which is assigned to surface OH group of ZnFe2O4 nanoparticles and implying the absorption of large amount of water. The UVeVisible absorption spectra of the ZnFe2O4 samples were recorded in the wavelength range of 200e800 nm and shown in Fig. 6b. The spectrum exhibits the absorption peak of assynthesized ZnFe2O4 at ~285 nm and the shift to ~302 nm upon heating. The energy band gap is obtained by extrapolating the linear portion of the plots of (ahnÞ2 against hn to the energy axis (inset of Fig. 6b) by employing Tauc's relationship (i.e. ahv ¼ Aðhy  Eg Þ1=2 [30], herein, Eg is the energy band gap,hn is the photon energy, A is a constant and a is the absorption coefficient expressed by the following equation:

a ¼ 2:303



Ab t

 (4)

where t is the thickness of the cuvette and Ab is the absorbance. The estimated band gap (Eg) of the as-synthesized and heated ZnFe2O4 samples was found to be ~4.35 and ~4.11 eV, respectively. A large augmentation was observed in the band gap energy of the as-synthesized ZnFe2O4 (4.35 eV) in comparison with its bulk one (1.9 eV). It implies a large variation in the optical characteristics of the octahedron-shaped ZnFe2O4 nanoparticles. Increasing in the band gap energy is the evidence of the nanocrystalline nature of the material (crystallite size of
12 nm). This suggests that the energy

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

541

Fig. 5. HRTEM microphotograph and SAED pattern of a ZnFe2O4 samples, left column is the as-synthesized and right column is the heated sample.

(b) 5

heated ZnFe2O4

-CH2-antisymmetric stretching 2924 cm-1

-CH2- antisymmetric stretching 1095 cm-1 H2O antisymmetric stretching 1650 cm-1 T− band

Water symmetric stretching 3456 cm-1

568 cm-1

orbsorbance (a. u.)

As-synthesized ZnFe2O4

Transmittance (%)

(a)

4 Heated ZnFe2O4

3 As-synthesized ZnFe2O4

2 1

O− band

513 cm-1 0 200

3400

2400

Wavenumbers (cm-1)

1400

400

300

400

500

600

700

800

Wavelength (nm)

Fig. 6. (a) FT-IR spectra, and (b) Optical absorption spectrum of ZnFe2O4 nanoparticles before and after heating at 650  C.

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

band gap increase, as ZnFe2O4 particles size reduces to the nanosized scale. 3.3. Evaluation of magnetic and rheological characteristics Fig. 7a shows a room temperature M-H hysteresis curves of the synthesized CNPs, as-synthesized ZnFe2O4, heated ZnFe2O4 and CI. The CNPs sample's curve indicates that the nanoparticles are not saturated even at applied field of 10 kOe. The magnetization (M) values are asymmetrical;
0.004 emu/g on positive and
0.007 emu/g on negative side. Furthermore, the Hc is negligible, indicating superparamagnetic behavior of the synthesized-CNPs [31]. A weak ordered magnetization observed for the as-synthesized ZnFe2O4 sample suggests paramagnetic with small superparamagnetic behavior. The lower Ms value of about 21 emu/g and higher Hc of about 80 Oe correspond to the particles with small size could be associated with the surface distortion of particles owing to the interaction of transition metal ions (Zn2þ) with oxygen atoms in the spinel lattice, which results in the net magnetic moment reduction in the particle. This phenomenon is particularly prominent for the ultrafine particles because of possessing a large surface to volume ratio. On the other hand, once the sample is exposed to the heat at 650  C, it showed ferrimagnetic behavior; Ms
52 emu/ g and Hc
35 Oe. Since there is an inverse relationship between Hc and grain size for multi-domain grains [31,32], it is expected that the nanometer-sized grains of ferrites exhibit a much higher coercivity in comparison to the micron-sized grains. In other words, Hc would decrease with grain growth as a result of the heating process. This is due to the fact that the larger grains possess greater domain walls, and hence, an increase is achieved in the wall movement contribution to magnetization and demagnetization, which requires less energy than domain rotation. Therefore, the smaller grains are expected to have a higher Hc [32]. On the other hand, dependency of Ms value with temperature can be described as [31]:

  3T Ms ¼ 8:1661 exp 1000

(5)

where T is the heating temperature. It suggests that by exposing the as-synthesized ZnFe2O4 sample to heating, the Ms would increase. Indeed, by increasing the heating temperature, the grain growth occurs and results in reduced volume fraction of grain boundaries, which act as barrier to domain wall motion. Furthermore, the

M (emu/g)

(a)

fgb ¼ 1  ðd  tÞ3 =d3

m ¼ 4pm0 R3 bH

(7)

200

150

150

100

100

50

50

0

-10000

0 -50 -100 -150 -200

H (Oe)

10000

Heated ZnFe2O4

(6)

where parameter of t is the effective grain boundary thickness, which comprises 2 to 3 atomic layers and d is the average grain diameter [33]. Here, interplanar spacing for the (311) set of planes is considered to estimate the “t” value. Accordingly, the fgb declines from
22.54% at room temperature to
1.85% at 650  C. Higher Ms value of about 195.48 emu/g for CI is due to its ferromagnetic micron-sized particles; making it a superior choice for MR particulate material. Besides the measurement of the magnetic behaviors of isolated particles, the static magnetic characteristics of MR suspensions evaluated by M-H hysteresis curves are also imperative. Theoretical models for MR suspensions and devices need magnetization as an input. These magnetic behaviors would also assist in forecasting the MR response dependency on the applied current in the device. Fig. 7b shows the M-H curves of pristine CI-based MR and CNPsZnFe2O4-CI-based MR suspensions. The Ms value of CI-MR suspension reduces (about 9%) as compared to isolate CI particles. This is more probably due to non-magnetic MR suspension affects on the CI magnetic behaviors and declines the total Ms value of the sample. On the other hand, higher value of Ms around 189.38 emu/g for the additive-CI-based suspension compared to CI-based MR suspension suggests better rheological effects in the presence of additive nanoparticles. The magnetic dipole moment induced in magnetic particles within the MR suspension at very low magnetic fields would be calculated as [34].

(b)

200

-200 -20

induced lattice strain during the synthesize process declined as well as remained precursors from the synthesized state diffused into the spinel ferrite lattice structure by the heating process. Indeed, since the grain boundaries and surface of grain have higher energy compared to volume (or lattice) of grain, they play a key role in the determination of their magnetic behavior so that the groundstate magnetic configuration of the atoms placed in the surface or interface regions differs from those corresponding to bulk materials [31]. In polycrystalline nanostructured materials, the grain boundaries volume fraction (fgb ) is obtained through the following equation:

M (emu/g)

542

0 -10000

0

10000

-50

CNPs

-100

Additive-CI-based MR suspenstion

As-synthesized ZnFe2O4 CIP

-150

CI-based MR suspension

-200

H (Oe)

Fig. 7. M-H hysteresis curves of (a) synthesized samples, and (b) MR suspensions.

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

b¼

mp  mf mp þ 2mf

543

(8)

where mf and mp are the relative permeabilities of the fluid and particles, respectively and R is the particle radius. On the other hand, the magnitude of the moments becomes independent of the field at higher fields, where the magnetization of the particles reaches saturation state [35]. In this case,

m¼

4 pm R3 Ms 3 0

(9)

where m0 Ms is the bulk magnetic solid saturation magnetization, which is equal to the saturation magnetization of MR fluid, m0 Mf. Thus, the m0 Ms through the magnetic particles volume fraction ð∅Þ, yields:

m0 Mf ¼ ∅m0 Ms

(10)

 and Ginder stated static magnetic characteristics of two Phule types of MR suspensions using a custom-built magnetic hysteresis graph. The m0 Mf value for the 36 vol% Fe-based MR suspension yielded 0.75 T and for the 35 vol% ferrite-based MR suspension recorded at ~0.14 T. The bulk saturation magnetization of Fe is 2.1 T and for ferrite is 0.4 T [36]. To calculate the magnetic dipole-dipole interaction energy, it was assumed that each soft magnetic particle behaves as a magnetic dipole moment with a dipole moment (M) in the absence of a magnetic field,

4  a 3 M ¼ m0 Mr p 3 3

(11)

where a is the particles average diameter, m0 is the vacuum magnetic permeability and is equal to 4p  107 Wb/Ampere-m, m0 Mr is the remnant magnetization of the material. The interaction energy between two magnetic particles is given by

Vm ¼

pM2 4pm0 R3

(12)

where R is the distance between the two spherical particles center and p is the two particles alignment, which ranges from 2 to 2 and is given as

p ¼ 3 cos 2∅  1

(13)

where ∅ is the angle between the central radius vector (R) between the particles and the magnetic moment of the particle. Once ∅ becomes equal to zero and p ¼ 2, the magnetic particles would align. It was assumed that the particles in 0.30 vol fraction in an MR suspension to be packed in simple cubic (SC) configuration in order to estimate the interparticle distance in an MR suspension. For SC configuration, center to center distance (R) is obtained ~1.1624a and the interfacial distance between the particles (h) to be ~0.16245a. eq. (12) becomes

Vm ¼

pðm0 Mr Þ2 a3 72m0

(14)

The magnetic interaction energy was then normalized to kBT ¼ 4.115 1021 J at 25  C (see Fig. 8). Fig. 9 exhibits shear stress versus shear rate for the MR suspensions under various magnetic field strengths. Both pristine CIbased MR and 1 vol% (CNPs-ZnFe2O4)-CI-based MR suspensions represented almost Newtonian characteristic in the absence of the

Fig. 8. Schematic representation of magnetic particles atoms configuration in simple cubic (SC) structure.

magnetic field. A negligible shear stress observed in both samples, but the CNPs-ZnFe2O4-CI suspension represented a much higher shear stress than that of the pristine CI-based MR suspension in the absence of applied magnetic field. This is more probably associated with the remnant magnetization of magnetic particles [1e3]. This indicates that the additive nanoparticles improve the MR effect of suspension even in the absence of externally magnetic field. On the other hand, both curves exhibited a non-zero yield stress at an almost zero shear rate in the presence of an applied magnetic field. This indicates a Bingham plastic characteristic of the suspensions; suggesting the stable chain-like structure formation through the magnetized particles [3,37]. Bingham model means that a minimum yield stress is needed to let the fluid flow [38]. The shear stress increases with the enhancement in the magnetic field strengths for the entire shear rate region for both the suspensions. The yield stresses were evaluated by extrapolating the shear stress curve at a zero shear rate [1,39]. The values found to be
43 kPa for the pristine CI MR fluid and
50 kPa for 1 vol% magnetic additive suspension at 500 mT, which is a relatively highvalue in comparison with the ER fluids and could be considered for commercial applications. The reason could be due to enhancement occurred in the interaction strength among the CI particles by introducing 1 vol% nanoparticles additive [3]. Yield stresses of the CI-based MR suspension is lower than that of the additive-CI based MR suspension for all the externally applied magnetic field strengths; showing a same trend of yield stress. The stresses are proportional to H under an induction period lower than 26 kA/m [40], and afterward the stresses are rapidly augmented with the relationship of H [40,41]. In the high-magnetic field strengths range, there is a trend for the slope of stress in terms of the field to start to drop. Because this change of slope in terms of applied magnetic fields at low H was not found to be due to the CI particles magnetization. These traits could be thought the chainlike structures formation under magnetic fields. Thus, for magnetic field strengths smaller than 26 kA/m, the magnetization given within the CI particles is insufficient to create fully developed structures. Measuring viscosity versus shear rate under various magnetic field strengths (Fig. 9aa and bb) indicates an enhancement for both

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(a)

(b) 500

OFF; Addive+CI

100 mT

200 mT

300 mT

400 mT

500 mT

10

1

OFF; CI 200 mT

100 mT 300 mT

400 mT

500 mT

Shear Stress (Pa)

Shear Stress (Pa)

100

50

0.1

5 5

Shear rate (1/s)

OFF-CI 100 mT 200 mT 300 mT 400 mT 500 mT

(d) 1.00E+09 Viscosity (Pa.s)

50

1.00E+08 1.00E+07 1.00E+06 1.00E+05 1.00E+04 1.00E+03

H direction

1.00E+02

0.5

50

OFF, addive-CI 100 mT 200 mT 300 mT 400 mT 500 mT

1.00E+08 1.00E+07 1.00E+06 1.00E+05 1.00E+04

H direction

1.00E+03 1.00E+02

1.00E+01

1.00E+01

1.00E+00

1.00E+00 0.1

5

Shear rate (1/s)

(c)1.00E+09

Viscosity (Pa.s)

0.5

10

Shear rate (1/s)

1000

0.1

1

10

100

1000

Shear rate (1/s)

Fig. 9. Shear stress curves vs. shear rate (on a log-log scale) for (a) CI-based and (b) 1 vol% (CNPs-ZnFe2O4)-CI MR suspensions; their corresponding viscosity vs. shear rate are shown in (c) and (d), respectively.

the MR fluids with the increase in magnetic field strengths. This suggests a shear thinning behavior of the suspensions under each magnetic field strength, even before the application of a magnetic field due to the high volume fraction of the magnetic particles. In shear flow, the suspended magnetic particles would rotate and arrange in the shear direction, thereby the viscosity reduce. Under a magnetic field, the connected particles segments or particle chains are deformed, aligned, and finally broken as the shear rate is increased, resulting a decrease in viscosity. The inset in Fig. 3c and d represents a particle chain-like structure formation of the magnetic particles under the stimulus of a magnet. The particles are aligned along the direction of the long axis due to the easy magnetization. Appling different magnetic field strengths indicated that the MR suspensions represent the magneto-viscous effect for both the samples. The fluid viscosity becomes greater by enhancing the strength of applied magnetic field; representing shear thinning behavior. This simply means that the shear stress increases much faster at a lower shear rate and then alters slowly at a high shear rate. This more probably due to the fact that disordered arrangement of particles gives rise to the augmentation of flow resistance at lower shear rate, while particles initiate to arrange their orientation along the direction of shear at higher shear rate, which results reduction in viscosity [42]. It could be mention that the

magnetically induced chain clusters sustain their consistencies at low shear rate due to dominant magnetic interactions, while these structures would break down and fluids initiate to flow at high shear rate [43]. In addition, even though the flow curves of the MR suspensions apparently look following the Bingham model, it was attempted to fit the data using other models such as the Casson model, which is the most commonly used empirical model in describing the flow curve of shear stress versus shear rate, as given in eq. (15) [44] and has been employed on various MR fluids [45]. 1=2 _ 1=2 t1=2 ¼ t1=2 0 h∞ g

(15)

where h∞ is the suspension viscosity at infinite shear rate and t0 is the yield stress from the Casson model. Fig. 10 represents that the Casson equation of t1=2 in terms of g_ 1=2 fits the experimental data for the MR suspensions at low magnetic fields. The curves also obviously exhibit that a finite yield stress value exists for the MR suspension and at zero magnetic field the intercept associated with yield stress is close to zero, i.e., almost the Newtonian fluid behavior. Moreover, the curve's slope is attributed to the shear viscosity at infinite shear rate. To further study the MR effect of the suspensions, HerschelBulkley (H-B) model, a generalized model of a non-Newtonian suspension fluid, was employed to evaluate the shear yield stress

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

545

Fig. 10. Casson equation fitting of t1=2 in terms of g_ 1=2 of the (a) additive-CI based, and (b) CI-based MR suspensions.

value as follows [1,46,47]:

t ¼ ty þkg_ n

(16)

Yield stress (Pa)

where t is the shear stress, ty is the shear yield stress in the presence and absence of applied magnetic field, g_ is the shear rate, n is the shear thinning exponent and k is the consistency index. The term kg_ indicates the shear thinning behavior of the suspensions under the magnetic field. The n indicates the degree to which a material is shear thickening (n > 1) or shear thinning (n < 1). Fig. 11 shows the shear yield stress values in terms of magnetic field strength by fitting the H-B model to the experimental curves. The value of n is lower than 1, indicating that the rheological characteristics for both suspensions are shear thinning. Furthermore, the shear yield stress increases with increase of the applied magnetic field strengths. In other words, as the magnetic field intensity is greater, a larger shear stress is required to break the column-like structures for the fluid to start to flow [47]. This can be associated with the stronger pull force among magnetic particles in the presence of applied magnetic field. Comparing the H-B model for the MR suspensions indicates that, however, both the CI-based and additive-CI-based MR suspensions behaved like a non-Newtonian in the presence of applied magnetic fields. The CI-based MR fluid curve is fitted more properly by eq. (16). Dependency of the maximum yield (t0 ) in the examined temperature (T) at various magnetic field strengths (H) is exhibited in Fig. 12. It is evident that the t0 declines from
50 to 39 kPa upon

60000

CI suspension

50000

Additive-CI suspension

40000

Linear (CI suspension)

pffiffiffiffi  H

t0 aHn tanh

where n is the equation exponent [52]. On the other hand, considering the Arrhenius relation for explanation the viscosity (h) and T dependency, indicates that t0 is not only dependent upon the applied magnetic field strengths (H), but also the temperature (T) as follows;



h ¼ Aexp

 Ea RT

(18)

where Ea is the activation energy, R is the universal gas constant and A is the equation constant. This equation relates the h to T exponentially like t0 f H1.3 exp(0.005T) as the concept of t0 is similar to h [53]. In the other words, the Arrhenius equation relates viscosity and flow to the activation energy, which is similar to the concept of the ‘yield stress.’ Herein, it is assumed that the yield stress of MR suspensions is correlated to temperature as part of an exponent. From the definition of the static yield stress, the proportionality equation is given as

t0 ak :Ba :

Linear (Additive-CI suspension)

In terms of the Arrhenius equation and the dipole model [54,55], a new yield stress model is suggested as:

t0 ak :Ba :elT

10000 0 0

(17)

Linear (CI suspension) 30000 20000

elevating the temperature from 25 to 75  C in the additive-CI-based MR suspension at 500 mT. A similar trend was observed for the pristine CI-based MR suspension; reducing from 43 kPa at 25  C to 14 kPa at 75  C. This suggests that t0 would decline with the increase in T. Similar results were reported elsewhere [48,49]. Furthermore, the influences of T on the t0 becomes less once the T increases. At a constant temperature, there is a relationship between the t0 and H [50,51], e.g. as follows:

100

200

300

400

500

Magnetic field strength (mT) Fig. 11. Shear yield stress vs. applied magnetic field strengths for the MR suspensions.

(19)

(20)

where T is the absolute temperature and K, a, and l are constants and are found from continuous shear mode tests. By exploring this equation and considering the role of H it can be written as

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A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

(a)

0 mT 300 mT

100 mT 400 mT

200 mT 500 mT

(b)

--- Exponentially fited

40000 35000 30000 25000 20000 15000 10000 5000 0 20

40

60

60000

Maximum Yield Stress, Pa

Maximum Yield Stress, Pa

45000

0 mT

100 mT

200 mT

300 mT

400 mT

500 mT

--- Exponentially fited

50000 40000 30000 20000 10000 0

80

20

Temperature,˚C

40

60

80

Temperature,˚C

Fig. 12. Maximum yield stress as a function of temperature at various magnetic field strengths for (a) CI-based and (b) additive-CI-based MR suspensions.

pffiffiffiffi  H expðbtÞ

t0 aHn tanh

(21)

where a and b are the equation constants. Their values are obtained by fitting the data of Fig. 12 for the t0 . In this case, the main equation is given as

t0 a65:25  H1:41

pffiffiffiffi    tanh H exp  5:38  103 T

(22)

This suggests more dependency of t0 on H in comparison with T. It also indicates that the t0 decreases as the temperature increases [50e53]. This is more probably due to the fact that as the T increases, the gel structure of the suspension becomes weaker and consequently the fluid resistance against movement declines. CI particles have density of around 7.85 g/cm3, while carrier fluids usually have density of around 1 g/cm3. Thus, a density mismatch between magnetic CI particles and base carrier fluid results in the magnetic particles to settle down by passing time in a MR suspension. In this case, CI particles would lose or alter the filed-dependent MR effect [5,47]. Several methods have been suggested to measure the sedimentation ratio (R) [1]. In this study, R was measured by putting the MR suspension in a vertical

cylindrical container at room temperature. Then, the following equation was used to estimate its value;

R¼

Dh h

(23)

where h is the initial volume of the suspension fluids and Dh is the volume of the turbid fluids (particles settled). The results are shown in Fig. 13. The dispersion stability of the MR suspensions revealed that the pristine CI-based MR suspension settles more faster (due to density mismatch between CI and fluid) than that of the MR suspension with additives for the same duration of time. Indeed, the nanosized particles fill the free space of the micron-sized CI particles and result in improved dispersion stability. The improved stability may be understood through both the use of additive materials with lower mass densities and particle geometries such as elongated cylinders that form percolated networks and increased the friction force due to nanoparticle additives. Since the friction force becomes greater as the surface area of particles increases in the presence of the additive nanoparticles, an opposing force-friction of the fluid-contributing to hinder particles sedimentation [5,47]. Indeed, anisotropic nanoparticles of carbon and ZnFe2O4, which have a large surface area in compared to the

Fig. 13. (a) Sedimentation ratio vs. time, and (b) simulation of particle settling vs time.

A. Hajalilou et al. / Journal of Alloys and Compounds 737 (2018) 536e548

micron-size CI particles, results in higher friction force formation in MR suspensions that prevents the CI particles sedimentation. It has also been stated that the anisotropic particles play a role of steric repulsion which leads to the improvement of fluid stability [56]. Furthermore, the much better long-term stability of the additive-CI based MR suspension compared to CI-based MR suspension is associated with the lower density of particles because of the actions of composite components [57]. Particles settling vs. time is simulated and shown in Fig. 13b. It reveals that the particles sediment at four stages. In the initial stage, coalescence of particles occurs during settling (large particles with high velocities overtake small particles with low velocities). Furthermore, collision frequency is proportional to solids concentration as well as level of turbulence (but too high intensity will promote break-up). Moreover, the cumulative number of collisions increases with time in this stage. In the second stage, in comparison with the first stage, overflow rate is significant and fractional removal is a function of overflow rate and residence time. It can conclude that the longer residence times and deeper tanks promote coalescence, so that particle agglomerates have higher settling velocities. In stage three, underflow densities are typically 50e65% solids. Also, safety factors should be applied to reduce effect of uncertainties regarding flocculent settling velocities. In the final stage, the particles almost become stable with time. As a general idea, shortage of redispersibility of most MR fluids is however associated with several factors. The magnetic particles' remanent magnetization and van der Waals interactions play vital roles. With regards the first phenomenon, the magnetic contribution of the interparticle potential energy should be considered, in the second effect, van der Waals energy between the magnetic particles should be computed. Indeed, in order to consider the magnetic interactions and van der Waals, the following equation is given:

 VVDW ¼

A212 6

 

# " #!  " l2 þ 4l 2 2 þ þ In l2 þ 4l ðl þ 2Þ2 ðl þ 2Þ2

(24)

where a is the particle diameter, l is equal to 2h/a, where h donates the interfacial distance. For simplicity, it was assumed that the effective Hamaker constant for an MR suspensions (A212) to be 1016 J. This equation indicates that the magnetic interactions inducing from remnant magnetization are strong with regard to the distance and their effect on the agglomeration of magnetic particles employed in MR suspensions or a cake-like formation is expected to be occurring, which is quite important. Furthermore, the longrange magnetic interactions and the short range van der Waals interactions, which are induced from the remnant magnetization, can play a key role on the stability and redispersibility of the MR suspensions. The calculations of these interaction energies, which are additive in nature, suggest that enhancement in the average interparticle distance can be resulted in the MR suspensions with improved redispersibility. Although diluting the MR suspension enhances the interparticle distance, it also declines the MR suspension's strength. Inclusion of the coated or modified-surface of magnetic particles, which provide electrosteric or steric repulsion, into MR suspension would be a more practical way to enhance the stability and redispersibility concurrent with holding the MR suspension strength at highest possible values [6].

4. Conclusion Octahedron-shaped particles of ZnFe2O4 nanoparticles with the average crystallite size of
12 nm were synthesized via hydrothermal route. Then, the 650C-heated powders were combined with carbon nanoparticles with the average diameter of 5 nm,

547

which synthesized from the used and waste tissue, and adjusted as additive for CI-based suspension. The sample with nanoparticle additives represented relatively higher yield characteristics and higher shear stress in the entire range of shear rates. This signifies a robust chain-like structure formation due to orientation of both the CI and nanoparticle additives in the magnetic field direction. From the field-dependent rheological test, it was found that the yield shear stress (t0 ) of the additive-CI-based MR suspension is increasing up to 12% in compared with the origin CI-based MR suspension. Furthermore, t0 increased with the increase in the strengths of magnetic field (H), while its value decreased as the operated temperature (T) enhanced. More dependency of t0 on H in comparison with T was found. Sedimentation behavior of the suspensions significantly improves upon the inclusion of ZnFe2O4 and CNPs nanoparticles into CI-based suspension. More explicitly, the sedimentation rate becomes slower up to
18% in the additive-CIbased suspension due to the increment of friction force in octahedron-shaped particles of ZnFe2O4 and spherical-shaped CPs. The improved rheological performance of the MR fluids enables them to be used in for applications in mechanical systems that require the active control of vibrations or the transmission of torque. Acknowledgement Acknowledging a financial support from the Iranian Nano Research Center. References [1] A. Hajalilou, S.A. Mazlan, H. Lavvafi, K. Shameli, Field Responsive Fluids as Smart Materials, Springer, 2016. [2] B.J. Park, K.H. Song, H.J. Choi, Mater. Lett. 63 (2009) 1350e1352. [3] A. Hajalilou, S.A. Mazlan, S.T. Shila, Mater. Lett. 181 (2016) 196e199. [4] Y.B. Yang, G. Chen, L. Li, W.H. Li, Int. J. Mod. Phys. B 20 (2006) 579e592. [5] A. Hajalilou, S.A. Mazlan, S.T. Shilan, E. Abouzari-Lotf, Colloid Polym. Sci. 295 (9) (2017) 1499e1510. [6] A. Hajalilou, A. Kianvash, K. Shameli, H. Lavvafi, Appl. Phys. Lett. 110 (26) (2017), 261902. [7] B.J. Park, M.S. Kim, H.J. Choi, Mater. Lett. 63 (24) (2009) 2178e2180. [8] K. Shah, J.S. Oh, S.B. Choi, R.V. Upadhyay, J. Appl. Phys. 114 (21) (2013), 213904. [9] A. Chaudhuri, N.M. Wereley, R. Radhakrishnan, S.B. Choi, J. Intell. Mater. Syst. Struct. 17 (2006) 261. [10] A. Chaudhuri, N.M. Wereley, S. Kotha, R. Radhakrishnan, T.S. Sudarshan, J. Magn. Magn. Mater. 293 (2005) 206. pez-Lo pez, A. Zugaldia, F. Gonz n, J. Rheol. 50 [11] M.T. Lo alez-Caballero, J.D.G. Dura (2006) 543e560. [12] H.S. Jung, H.J. Choi, J. Appl. Phys. 117 (2015), 17E708, https://doi.org/10.1063/ 1.4915099. [13] M. Kciuk, R. Turczyn, J. Achiev Mater. Manuf. Eng. 18 (2006) 127e130. [14] A.G. Olabi, A. Grunwald, Mater. Des. 28 (10) (2007) 2658e2664. [15] S.W. Charles, in: Stefan Odenbach (Ed.), The Preparation of Magnetic Fluids, vol. 594, LNP, 2002, pp. 3e18. [16] M.J. Hato, H.J. Choi, H.H. Sim, B.O. Park, S.S. Raya, Colloids Surf. A Physicochem. Eng. Asp. 377 (2011) 103e109. [17] S.T. Lim, H.J. Choi, M.S. Jhon, IEEE Trans. Magn. 41 (10) (2005) 3745e3747. [18] M. Sedlacik, V. Pavlinek, M. Lehocky, A. Mracek, O. Grulichc, P. Svrcinovad, P. Filip, A. Vesele, Colloids Surf. A Physicochem. Eng. Asp. 387 (2011) 99e103. [19] X. Liu, L. Wang, H. Lu, D. Wang, Q. Chen, Z. Wang, Mater. Manuf. Process. 30 (2) (2015) 204e209. [20] A. Hajalilou, S.A. Mazlan, M. Abbasi, H. Lavvafi, RSC Adv. 6 (92) (2016) 89510e89522. [21] A. Hajalilou, M. Hashim, M. Nahavandi, I. Ismail, Adv. Powder Technol. 25 (1) (2014) 423e429. [22] L. Cao, M.J. Meziani, S. Sahu, Y.P. Sun, Acc. Chem. Res. 46 (2013) 171e180. [23] A. Hajalilou, M. Hashim, R. Ebrahimi-Kahrizsangi, N. Sarami, Ceram. Int. 40 (4) (2014) 5881e5887. [24] J.L. Wang, Y.Q. Li, Y.J. Byon, S.G. Mei, G.L. Zhang, Powder Technol. 235 (2013) 303e306. [25] L. Liu, A. Han, M. Ye, W. Feng, Sol. Energy 113 (2015) 48e56. [26] A. Hajalilou, M. Hashim, R. Ebrahimi-Kahrizsangi, H.M. Kamari, J. Therm. Anal. Calorim. 119 (2) (2015) 995e1000. [27] M.C. Chhantbar, U.N. Trivedi, P.V. Tanna, H.J. Shah, H.H. Joshi, K.B. Modi, Indian J. Phys. 78 (2004) 321.

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