Thermo-physcial Properties and Characterization of TiO2 based Nanouid Blended with Moringa Oleifera Oil

: Nanoparticle TiO 2 was synthesized by the co-precipitate method and was dispersed in palm oil blended with Moringa oleifera seed oil (Enriched palm oil-EPO). Structural and compositional analysis of TiO 2 nanoparticles was carried out using SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction) and FTIR analysis (Fourier Transform Infrared Spectroscopy). Using the analytical method, particle dimension, crystallite size by Debye Scherrer’s equation and vibrational energy of the molecule was investigated. Palm oil was blended with synthesised Moring oil to enhance its oxidative stability. TiO 2 nanoparticles were dispersed at different volume fraction in EPO to analyse the temperature dependent physical properties. Bio-degradable lubricant nature of TiO 2 based nanofluid was investigated by the variation of viscosity and density with tempera ture (30 to 60˚C). The amphiphilic properties of fatty acids in blended oils can contribute better lubrication compared to mineral oils. Experimented viscosity and density values with temperature was fitted to a non-linear equations, and was pragmatic that quadratic equation exhibits a best fit R 2 > 0.999. Theoretical value of the viscosity was predicted using Einstein, Batchelor, and Wang mathematical model and was compared with the experimental value. Brownian motion of the particle in the oil was studied through the diffusion constant, diffusion time, and Brownian velocity. The present study could be used to synthesis nanofluid with desired volume fraction, viscosities and densities, so as work as a suitable bio degradable lubricant in many industrial applications.


Introduction:
Researchers, for the past two decades are working on biodegradable lubricant and coolant as nanoparticle based nanofluid are observed to be a vital substitute for petroleum based mineral oils [1]. Mineral and synthetic oils add environmental pollution to the earth. Hence, there is a need of an extensive biodegradable, non-toxic, renewable lubricants, hydraulic fluids, and coolants with high viscosity, high density, and low volatility an eco-friendly liquid [1,2]. Nanoparticles owe high surface to volume ratio; hence, when it is dispersed in a biodegradable and affordable vegetable oils the thermo-physical characteristics of the nanofluid properties would be enhanced [3]. Anyhow, there are some limitations in vegetable such as bad odour on oil degradation, discolouration of metal (green colour in copper), limitations in viscosity, temperature, etc. These limitations were reduced by the addition of nanoparticles as the particle plays the role of antioxidants in oil [4,5,6].
The ultimate work of a nanofluid can be elucidated as a coolant-to remove the unwanted heat energy, lubricant-to reducing friction between machines, and enhancing its efficiency by safeguarding the tool life. Hence, employing inventive and eco-friendly cooling-lubricant is necessary to develop the function and life span of machines [5,6,7]. Moreover, as most of the worldwide lubricants are petroleum-based that produce deleterious effects on the environment by increasing pollution, toxicity, a higher cost for disposal, and non-biodegradability [7].
Mineral oils are not only biodegradable, but also they do not produce any carcinogens effect on human skin due to repeated usage also the suspended nanoparticles in vegetable oil makes it more stable to increase the heat transfer efficiency of nanofluids [7,8]. The average particle size has to be reduced to investigate the variation of viscosity at different volume fractions, so that nanoparticle-based nanofluid can be used to entrain into the tribocontact.
Vegetable oils, because of their durable interfaces with the machinery and lubricating surface it could be used as an anti-wear and friction modernizers. Their hydrophobic and hydrophilic composites due to the presence of long chain fatty acids, it could form a flexible film between the lubricant surfaces [5,6,9]. To understand their effective variability in lubricating properties, studies on variation of viscosity and density at different volume fraction are vivacious to know the agglomeration of the particles in vegetable oils. To design a bio-lubricant that can enhance the life span of the machinery parts, nanoparticles have to be dispersed in a biodegradable oil to enhance the lubricating performance even with its micro-droplets [6,9,10]. The dynamic Brownian motion of nanoparticles suspended in vegetable oil makes nanofluids more stable compared to micro-fluids, as the heat transfer efficiency of the nanofluids would become high [10,11,12]. Sujith et al., (2019), in their research work, added Al2O3 to coconut oil and investigated the thermal, lubricating properties, and viscosity at different concentrations [13]. Xiaoming et al. 2020, for better lubrication vegetable oils, were used to spray the tool/ workpiece interface to attain an environmentally friendly turning [1]. Sina Nabati Shoghl et al, (2016) investigated the physical properties of multiwall carbon nanotubes dispersed into the water as nanofluid [14]. Şenol et al (2019), have investigated an eco-friendly lubricant at 4 different concentrations for the machining cutting conditions: surface roughness, cutting temperature, cutting force, tool wear, and tool life [7].
As viscosity and density of vegetable oils decreases with increase in temperature, it is highly used in a heat exchanger, piping, and pumping; hence, in the present work TiO2 nanoparticles was synthesized and characterized using morphological studies such as SEM (Scanning Electron Microscope), XRD (X-ray diffraction), and FTIR (Fourier Transform Infrared) spectrum. To develop a bio-lubricant, a nanoparticle of TiO2 was added to enriched palm oil (Palm oil + Moringa Oleifera seed oil) -EPO at different volume ratios, and its tribological behaviour using the parameter viscosity, and density was studied. Moringa oleifera seed oil contains 18 out of 20 amino acids and also contains antioxidants like flavonoids, polyphenols, stigmasterol, sitosterol, α, β, γ and δ tocopherols, and ascorbic acid [15].To

Materials and Methods:
Titanium nitride, hydroperoxide, hydrochloric acid, ammonia, and other chemicals were purchased in Sigma Aldrich. Moringa oleifera seeds were bought from Periyakulam, Tamilnadu, India, and the oil was prepared using hexane extract [15]. Palm oil was purchased from a government store, Thanjavur, Tamilnadu, India.

Preparation of TiO2 nanoparticles:
TiO2 nanoparticles was synthesized using a chemical co-precipitate method as shown in the flowchart of figure 1. Since previous researches have studied the antimicrobial and antifungal activities of TiO2 [16], usage of the nanoparticles in nanofluid can exhibit the behaviour as an enhanced lubricant.

Preparation of base fluid EP:
Palm oil constitutes 50-60% of saturated fatty acids. The unsaturated fatty acids 36-47% are prone to oxidation and produce unwanted degraded products. To increase the oxidative stability of the oil, Moringa oleifera seed extract which has high potent antioxidants (rare combination of zeatin, quercetin, β -sitosterol, sigma sitosterol, enriched tocopherol, caffeoylquinic acid, and kaempferol) [15] was added to palm oil (EPO) to form 154 ml (PO 150+ MO 4ml)

Preparation of nanofluid:
Nanoparticles were added with base liquids at different volume ratios and dispersed using a sonicator continuously. To create a long-time durable nanofluid, the nanoparticles were . After that, for 3 hours a magnetic stirrer was operated on it. Then, the prepared suspension was controlled to a 1-hour ultrasonic processor (20 kHz, 400 W) to cut down the likely clump of nanoparticles and produce a nanofluid with excellent diffusion. No surfactants was added as it may induce chemical contamination. Sample base fluid is taken as S1, which is a mixture of PO (150ml) + MO (4ml). S2 is a nanofluid in which TiO2 is dispersed in the base fluid with the =0.2, S3-=0.4, & S4-=0.6.

Measurement
Tribology nature of the nanofluid at different volume ratios along with the base fluid was determined using (1) density with ASTM standard method D891-09, (2) Viscosity with ASTM 445 was investigated precisely [4].

Morphological studies:
The synthesised nanoparticle was characterised using a scanning electron microscope (SEM), the nano-dimension of the particles ranges between 61 to 90nm. Figure 2 illustrates the study using SEM, where (a) illustrates the magnification of 10m, and (b) illustrates the magnification to 500nm. Figure 3 illustrates the aggregation of TiO2 in 163nm with a standard deviation of particle size 28nm. The titanium dioxide (TiO2) nanoparticles, synthesized by the co-precipitate method were subjected to the XRD method (PANalytical-PW 340/60 X'pert PRO X-ray diffractometer) for the structural confirmations [5]. Figure 4 shows the crystal structure and arrangement of the atoms that were studied using X-Ray Diffraction analysis.
Using the software CMPR, the maximum intensities of dominant peaks were found and they were compared with the previous pattern. On observing both the patterns of 2θ value, there was   Figure 6 illustrates the variation of viscosities of base fluid, and nanofluids ( = 0.2 -0.6), with temperature from 30˚ to 60˚C and was experimental that the viscosity decreases with increase in temperature. The viscosity of S2 increased by 0.03%, S3 by 0.08%, and S4 by 0.12% from the base fluid (S1). Hence, it was observed that variation of viscosity varies with temperature and volume fraction of nanoparticles. This investigation of viscosity related to volume fraction and its prediction is very important for any desired application in the industry. Viscosity of the vegetable oil is modified by the addition of nanoparticles to withstand high pressure and enhance the anti-friction properties in machinery [9,16,17]. Due to the vivacious properties such as antifungal and antimicrobial properties of TiO2, it precludes the fungal activities formed in nanofluid on hydrolysis [14].    To determine the theoretical values of the nanofluid at different volume fraction, Table 3 illustrates the calculated values of the viscosity using the above three models. The and Brinkman equations for a CuO nanoparticles dispersed in the mixture of glycol and water [22]. Similar work was done by Nabeel and Hemalatha (2013) for a nanofluid ZnO dispersed in coconut oil [10]. Amin and Farzad (2019), have studied the viscosities of ZnO and MgO in oil predicted the viscosities using above models. But the prediction of viscosities between 30 to 60˚C was carried out in this present work [17].  [12,23]. Agglomeration or dispersion of particle in the nanofluid, particle-particle interaction, and particle-liquid interface study could be determined using Stokes-Einstein's  Table 4 illustrates the diffusion constant increases with temperature but decreases with volume fraction. It was experimental that the value of D increases with increase in temperature as given in equation (10)  All the above parameter (D, D  , and VB) were related with each other as it depends on the motion of the particle in the liquid and could be calculated between the experiential temperatures. It was observed the % of increase or decrease were almost same as it is related with the same factor, temperature and viscosity. Table 5 illustrates the fitting of variation of density with temperature in same non-linear empirical equations (used to predict viscosity) and observed that again the second order quadratic logarithmic equation was highly correlated with good R 2 > 0.999 value. This equation could be used to predict density of nanofluid in the experiential volume fraction and temperature.

Conclusion:
Nanosized TiO2 was synthesised by means of chemical co-precipitate method, and nanofluid was prepared by dispersing the particle in the modified palm oil. Viscosity and density of the nanofluids at different volume fraction and temperature were determined.
Viscosity of the fluid decreases with increase in temperature and the data was fitted in empirical equations for the validity. Theoretical model equations were studied to predict viscosity at different volume fraction to extend the application of the present work. The experiential data was used to predict density at different temperature and viscosity was experimented and the data was fitted in empirical equations for statistical analysis. Brownian motion of particle in liquid was determined using diffusion constant, diffusion time, and diffusion velocity that infers the lubricating and heat transfer efficiency of the liquid.

Acknowledgments
The authors gratefully acknowledge Vice Chancellor of SASTRA Deemed University, for the constant encouragement to carry out the research work in the University Laboratory. We also thank Pondicherry University for helping us to measure the electrical properties at different frequencies and temperatures.

Conflict of Interest:
The manuscript is our own original work, and does not duplicate any other previously published work, including our own previously published work. The Research work is not funded by any agency. The authors and co-authors have no conflict of interest and agreed for submission to the journal.

Funding
This research did not receive any specific grant from funding agencies in public, commercial, or not-for-profit sectors.   Variation of viscosity with temperature and volume fraction