Study of Breakage Tendencies of Palm Kernel, Coconut and Periwinkle Shells using Ball-Milling Process

Abstract

(TEM) and X-Ray Diffractometer (XRD). 5kg each of palm kernel, coconut and periwinkle shells were rinsed and dried at 6 hours per day for four weeks at 120˚C using Shel lab oven to eliminate moisture and subsequently crushed into pieces at Federal Industrial Institute of Research Oshodi (FIIRO) with the aid of Broyeur Clero Hammer Crusher, model 000T (No. 13634) and pulverised into powder with the use of disc grinder. Part of agricultural waste powders obtained was sorted into different particle sizes using set of sieves (650-45 μm) vibrated with a sine shaker for 1 hour. The powders retained below the 45 μm sized sieve, were used as the feed powders for the synthesis of nanoparticles. The remaining powders each of PKS, CNS and PS were placed in different known weight crucibles, sealed, reweighed and fired to 1100oC using electric furnace. This process is called carbonization. The carbonization temperature used is in line with literature (Bello et al., 2017a, Bello et al., 2016, Abiko et al., 2010). Each of the powder samples was held at this temperature for 1 hour after which the furnace was switched off and the powders were left in the furnace to cool to room temperature. Crucibles were reweighed and the carbonized samples were graded using the same set of sieves vibrated for the same time as explained in the case of uncarbonized samples. Samples of carbonized powders retained below 45 μm sized sieve, were selected for nanoparticle synthesis. Ball-milling of each powder sample was carried out for 74 hours at 10 charge ratios and 195 revolutions per minute (rpm) using balls of the same size ranges (5-70 mm). A tightly packed Flender Himmel electric motor powered tumbler ball mill, model A50A2043 was used. Each milled sample was analysed using XRD and TEM. Figure 1 shows the photo macrographs of agricultural wastes used in this study before and after milling. III RESULTS AND DISCUSSION Figures 2-7 reveal the TEM images, size distribution and elemental compositions of uncarbonized and carbonized agricultural waste particles obtained after 74 hours milling at 10 charge ratios. Fine particles of PKS are seen in Figure 2 forming globular networks of different sizes. The globules are attributed to coalescence of numerous fine particles due to milling ball impacts. Size determination using Gwyddion software indicates that size of PKS particles varies between 1.4 and 160.2 nm. Energy dispersive X-ray spectroscopic analysis reveals that PKS contains both metals and non-metals. Oxygen (O), calcium (Ca), Carbon (C) and Copper (Cu) have higher peaks while others are the minor elements. Most of these elements represent mineral contents such as silicate, and oxides of the PKS as indicated by X-ray diffractogram in Figure 8. Carbon (C) may represent amorphous organic compounds present in the PKS as revealed by broad peaks in Figure 8. This observation is analogous to that of (Edmund et al., 2014). Similarly, sizes of uncarbonised CNS and PS particles vary between 0 and 191 nm and 0 and 148 nm, respectively. CNS has C, Cu and O as major elements as indicated by EDX in Figure 3. This agrees with XRD in Figure 9 showing C8 with the highest peak. Other elements such as Cu, Si and Mg exist as silicates which are mineral components of the CNS. Bello et al., (2015) reported synthesis of CNS nanoparticles through ball milling for a period range from 16 to 70 hours. Average size of their CNS nanoparticles at 70 hours is 56.03 nm. Findings from XRD study on CNS by (Bello et al., 2015a) have revealed CNS structures which are like observation in this present study. Also, sizes of PS particles fall between 0 and 148 nm. Energy dispersive X-ray spectroscopic analysis indicates Ca as a major element of PS as shown in Figure 4. This element (Ca) exists as carbonate as shown by XRD in Figure 10. A change in properties was observed after carbonization of the agricultural wastes as shown in Figures 5-7. Image of carbonized PKS particles in Figure 5 appears more fused together than what is observed in Figure 2 of uncarbonized PKS particles. Sizes of carbonised PKS particles fall between 0 and 160 nm. Carbon peak in Figure 5 is much higher than that in Figure 2. This can be attributed to distillation of the volatile components which has led to an increase in C counts. An increase in C content is compensated by reduction in the counts of the elements such as O. Similar observation was made in case of carbonized CNS and PS particles. This finding is in line with literature (Adebisi et al., 2017b, Bello et al., 2106, Bello et al., 2015a, Bello et al., 2015b). Moreover, XRD peaks in Figure 8 show Mg2O4Si, Al2.7CaCu0.83, Al0.56Mg0.44. These compounds represent mineral components of PKS and agree with findings from XRD in Figure 2. Presence of intermetallic compounds including Al2.7CaCu0.83, Al0.56Mg0.44 is attributed to unavoidable chemical reaction between phases of uncarbonised PKS during ball milling process. Similar chemical reaction was disclosed in literature during refinement of CNS through ball-milling process (Bello et al., Figure 1: Natural fillers: uncarbonized (a) palm kernel (b) coconut (c) periwinkle shells; carbonized (d) palm kernel (e) coconut shell; (f) palm kernel (g) coconut shell and (h) periwinkle shell particles.