Two conventional ceramic fillers: aluminum oxide and silicon carbide and two industrial wastes: flyash and cement by-pass dust (CBPD) are chosen to be used as particulate fillers in pre-determined proportions in various composites prepared for this investigation. While, Al2O3 and SiC have conventionally been used in many composite applications, the wastes flyash and cement by-pass dust (CBPD) can be considered as non-conventional materials for use as fillers in polymer composites. Here the fillers taken in this study are in the range of 80-100 µm.
Alumina is an inorganic material that has the potential to be used as filler in various polymer matrices. Aluminium oxide (Al2O3) commonly referred to as alumina, can exist in several crystalline phases which all revert to the most stable hexagonal alpha phase at elevated temperatures. This is the phase of particular interest for structural applications. Alumina is the most cost effective and widely used material in the family of engineering ceramics. It is hard, wear-resistant, has excellent dielectric properties, resistance to strong acid and alkali attack at elevated temperatures, high strength and stiffness. With an excellent combination of properties and a reasonable price, it is no surprise that fine grain technical grade alumina has a very wide range of applications.
Similarly, silicon carbide (SiC) is another ceramic material that too has the potential to be used as filler in various polymer matrices. It is an excellent abrasive and has been produced and made into grinding wheels and other abrasive products for over one hundred years. It is the only chemical compound of carbon and silicon. It was
originally produced by a high temperature electro-chemical reaction of sand and carbon. Today the material has been developed into a high quality technical grade ceramic with very good mechanical properties. It is used in abrasives, refractories, ceramics, and numerous high-performance applications. The material can also be made an electrical conductor and has applications in resistance heating, flame igniters and electronic components. Structural and wear applications are constantly developing. Silicon carbide is composed of tetrahedra of carbon and silicon atoms with strong bonds in the crystal lattice. This produces a very hard and strong material. It is not attacked by any acids or alkalis or molten salts up to 800°C. The high thermal conductivity coupled with low thermal expansion and high strength gives this material exceptional thermal shock resistant qualities. Silicon carbide has low density of about 3.1 gm/cc, low thermal expansion, high elastic modulus, high strength, high thermal conductivity, high hardness, excellent thermal shock resistance and superior chemical inertness.
The fly ash used here is of cenosphere type and has been collected from the Captive Power Plant of National Aluminium Co. (NALCO) located at Angul in India. Fly ash is a finely divided powder generated in huge quantities during power generation in coal based power plants. It is essentially a mixture of ceramic materials such as: SiO2, Fe2O3, Al2O3 and TiO2 etc.
Cement by-pass dust (CBPD) is a by-product of cement manufacturing. It is a fine powdery material similar in appearance to Portland cement. It is generated during the calcining process in the kiln. As the raw materials are heated in the kiln, dust particles are produced and then carried out with the exhaust gases at the upper end of the kiln. These gases are cooled and the accompanying dust particles are captured by efficient dust collection systems. Lime (CaO) constitutes about 40% of CBPD composition. Other compounds include SiO2, Al2O3, Fe2O3, K2O, Na2O, Cl–, etc. The chemical compositions/formulae and physical properties such as density and hardness of these particulate fillers are given in Table 3.1.
The composites prepared for this study are designated as A1, B1, C1, C2, C3, C4, C5, C6, C7, C8 and C9 respectively. The detailed compositions along with the designation are presented in Table 3.2.
Table 3.1. Chemical compositions and Physical properties of filler materials
Source: * Thermal spray coating of red mud on metals, Ph.D thesis, N.I.T.Rourkela, India (2005) ** Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview,
Resources, Conservation and Recycling 48 (2006) 315–338.
Table 3.2. Designation and detailed compositions of the composites
3.2 Composite fabrication
Cross plied E-glass fibers are reinforced in unsaturated isophthalic polyester resin in three different weight proportions (30wt%, 40wt% and 50wt%) to prepare the composites A1(Polyester +30wt% glass fiber), B1 (Polyester +40wt% glass fiber) and C1(Polyester +50wt% glass fiber) respectively. Each ply of glass-fiber is of dimension 200 × 170 mm2. No particulate filler is used in these composites. The composite slabs are made by conventional hand-lay-up technique followed by light compression moulding technique. A stainless steel mould having dimensions of 210 × 180 × 20 mm3 is used. A releasing agent (Silicon spray) is used to facilitate easy removal of the composite from the mould after curing. The curing of the polyester resin was done by incorporation of 2% cobalt nephthalate (as accelerator)
Filler Composition/Chemical formula Mean hardness
(Hv)
Density (gm/cm3)
Flyash* SiO2 (48.3%),Al2O3 (20.2%) Fe2O3 (6.4%),TiO2 (1.9%) 725 3.15 Alumina Al2O3 1175 3.89 Silicon Carbide SiC 2800 3.22 CBPD** CaO (40.5%), SiO2 (14.5% ), K2O (4.66%) Al2O3(4.10%), Fe2O3 (2%), 695 2.40 Designation Composition
A1 Polyester +30wt% glass fiber B1 Polyester +40wt% glass fiber C1 Polyester +50wt% glass fiber
C2 Polyester +50wt% glass fiber + 10wt% flyash C3 Polyester +50wt% glass fiber +20wt% flyash C4 Polyester +50wt% glass fiber +10wt% Alumina C5 Polyester +50wt% glass fiber +20wt% Alumina C6 Polyester +50wt% glass fiber +10wt% SiC C7 Polyester +50wt% glass fiber +20wt% SiC C8 Polyester +50wt% glass fiber +10wt% CBPD C9 Polyester +50wt% glass fiber +20wt% CBPD
mixed thoroughly in the polyester resin and then 2% methyl-ethyl-ketone-peroxide (MEKP) as hardener prior to reinforcement. The mix is stirred manually to disperse the fibres in the matrix. Care is taken to ensure a uniform sample since fibres have a tendency to clump and tangle together when mixed. The cast of each composite was cured under light pressure of 0.0156 MPa for 24 h before it removed from the mould. Then this cast is post cured in the air for another 24 h after removing out of the mould. Specimens of suitable dimension are cut using a diamond cutter for physical characterization and mechanical testing. Utmost care has been taken to maintain uniformity and homogeneity of the composite although reproducibility is somewhat difficult in hand-lay up techniques.
The other composite samples C2-C9 with particulate fillers of fixed weight percentage are fabricated by the same technique. The fillers are mixed thoroughly in the polyester resin before the glass fiber mats (50 wt%) are reinforced in the matrix body. Composites C2 and C3 contain flyash particles in 10 wt% and 20wt% proportions respectively. Similarly C4 and C5, C6 and C7, C8 and C9 are the composites containing alumina, silicon carbide and cement by-pass dust fillers respectively along with 50wt% of glass fibers in them.
3.3 Mechanical characterization
Micro-hardness
Micro-hardness measurement is done using a Leitz micro-hardness tester. A diamond indenter, in the form of a right pyramid with a square base and an angle 1360 between opposite faces, is forced into the material under a load F. The two diagonals X and Y of the indentation left on the surface of the material after removal of the load are measured and their arithmetic mean L is calculated. In the present study, the load considered F = 24.54N and Vickers hardness number is calculated using the following equation.
0.1889 2 L F HV = (3.1) and 2 Y X L= +
where, F is the applied load (N), L is the diagonal of square impression (mm), X is the horizontal length (mm) and Y is the vertical length (mm).