Supplementary Information
Characterisation of Fresh FA and MCA-FA
S1.1 Morphological study
The morphologies and surface texture of the fresh FA and MCA-FA were determined using FESEM images. From Fig. S1(a) it was observed that fresh FA particles have smooth surfaces with spherical shape possessing a wide range of particle sizes. The furnace temperature and the rate of cooling of the flue gases at thermal power station determine the morphology of the FA. The inorganic and organic constituents present in the coal oxidize at very high operating temperatures in the furnace. These disintegrate resulting in a wide range of particle sizes with different morphologies of FA. It can also be seen that smaller particles are adhering to the large solid spheres; due to the insufficient time during the cooling process of FA. FESEM image of MCA-FA (Fig. S1(b)) shows particles with irregular shape and rough surface. The impact and shear forces exerted during the high energy ball milling destroys the surface structure of the FA into clusters of irregular shaped particles [1, 2].
Fig. S1 FESEM images of (a) fresh FA, (b) MCA-FA, (c-d) TEM micrographs of MCA-FA, and (e) SAED pattern of MCA-FA
The TEM images of MCA-FA at lower and higher magnifications are shown in Fig. S1(c–d). The particles are of irregular shape due to the repeated fracturing by the compression, shear and impact forces acting on FA particles during the milling process. This rough surface and irregularity in shape of MCA-FA is expected to provide a better mechanical interlocking with the polymer chains, which inturn, would enhance the mechanical properties of the resultant composites [3]. The SAED pattern of MCA-FA shown in Fig. S1(e) indicates that even after 48 h of milling the MCA-FA has retained its polycrystalline nature. The individual crystals are randomly distributed and oriented within the rings of constant radius [4].
S1.2 XRD results
XRD patterns of the fresh FA and MCA-FA are shown in Fig. S2. The major constituents of the fresh FA are quartz, mullite, iron oxide and calcium oxide (Fig. S2), as revealed by X’pert high score software.
Fig. S2 XRD patterns of fresh FA and MCA-FA
X-ray diffraction was used for determining the mean crystallite size in fresh FA and MCA-FA. According to Scherrer’s formula (Eq. S1) the average crystallite size, t, is:
Where λ is the wavelength of the X-rays in nanometers (nm), B is the FWHM of the diffraction peak, θ is the diffraction angle and K is a constant normally taken either as 0.9 or 1 for usual crystals. [5, 6]
The crystalline structure of the FA is damaged due to the high stresses exerted by miiling media, which resulted in formation of amorphous segments in the diffraction peaks at 2θ vaules in the range of 24-28°. The low intensity peaks of oxides of CaO, Fe2O3, SiO2 and 3Al2O3.2SiO2 observed in the fresh FA were diminished after 48 h of milling. The crystallite size of maximun intense peak of the quartz phase present in the fresh FA at 2θ values of 26.5° was 28 nm, which got reduced to 7.7 nm after mechano-chemical activation. This signifies that during high energy milling process the impact and shear force induced on the FA particles damages the crystalline structure causing the fragmentation of crystallites.
S1.3 Particle size and specific surface area
Table S1 DLS results showing particle sizes of fresh FA, sieved FA and MCA-FA
Samples / D10 / D50 / D90Fresh FA / 23.2 μm / 36.5 μm / 58.4 μm
Sieved FA (-170# + 200#) / 43.2 μm / 79.4 μm / 99.9 μm
MCA-FA / 220 nm / 329 nm / 955 nm
The average particle size of fresh FA D50 (median size) was 36.5 μm obtained from DLS result. This implies that the size of 50% volume of the particles is greater than 36.5 μm and that of the remaining ones is less than 36.5 μm. The particle size at D10, D50 and D90 of fresh FA, sieved FA and MCA-FA are shown in Table S1. It was observed that after 48 h of mechano-chemical activation the particle size of sieved FA (D50) has decreased from 79.4 μm to 329 nm. The tremendous stress energy exerted by vigorous milling for 48 h on FA particles resulted in 8.73 m2g-1 of specific surface area. The reduction in the particle size and increased surface area may be due to the process parameters such as dispersing medium and surfactant. The medium, ethyl acetate has a viscosity of 0.42 cP and surface tension of 23.75 mNm-1 [7] resulted in better dispersion of FA particles and the surfactant triton X-100 provides a repulsive force between the particles and reduce the agglomeration.
S1.4 Contact angle measurements
The contact angle measurements made by distilled water on fresh FA and MCA-FA pellets are shown in Fig. S3 (a-b). Initially the fresh FA pellet made an angle of 28.62°, which drastically fell down to 5.3° in 0.9 sec. This implies that the fresh FA is easily wetable by water droplet, which spread rapidly over the pellet surface. The MCA-FA made a contact angle of 17.30° that slowly decreased to 1.58° after 72 sec; this implies that the surfactant molecules form a coating on MCA-FA. It is due to the formation of micelles that disentangles agglomerates by steric repulsive forces among MCA-FA particles.
Fig. S3 Static contact angle measurements of fresh FA and MCA-FA pellets with water
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