Nanoscience and nanotechnology has become the buzzword in recent years since its inception in 1990’s. It literally means any technology performed in the nanoscale down to molecular level. Nanotechnology encompasses the production and application of physical, chemical and biological systems at scales ranging from individual atoms or molecules to submicron level as well as integration of the resulting nano structure to larger systems . Nanomaterial is defined as the materials with the microstructure having at least one dimension in nanometer range. It has appeal of miniaturization; also it imparts enhanced electronic, magnetic, optical and chemical properties to a level that cannot be achieved by conventional materials. The key characteristics of nanomaterials are its small size, narrow size distribution, low levels of agglomeration and high dispersability .
A variety of ways have been reported to synthesize nano level materials such as plasma arcing, chemical vapor deposition, electro deposition, sol–gel synthesis, high intensity ball milling etc . Among these methods high energy milling has advantages of being simple, relatively inexpensive to produce, applicable to any class of materials and can be easily scaled up to large quantities . In this mechanical treatment, powder particles are subjected to a severe plastic deformation due to the repetitive compressive loads arising from the impacts between the balls and the powder. The high concentration of defects and the continuous interfaces renewal, associated with the milling-induced enhanced atomic mobility, promote different phenomena depending on the materials being milled [5–7]. This produces novel crystalline and amorphous materials with crystallite sizes at the nanometer scale.
Coal-burning power plants that consume pulverized solid fuels produce large amounts of fly ash. These are the finely divided mineral residue resulting from the combustion of ground or powdered coal in electric power generating plant. The fly ash consists of inorganic, incombustible matter present in the coal that has been fused during combustion into a glassy, amorphous structure. This material is solidified while suspended in the exhaust gases and is collected by particulate emission control devices, such as electrostatic precipitators or filter fabric bag houses. Fly ash, often called pulverized fuel ash, is the largest produced industrial waste in the world, mainly due to the global reliance on the coal-fired power plants . Since the particles solidify while suspended in the exhaust gases, fly ash particles are mostly spherical in shape and range in size from 0.5 μm to 100 μm. They consist mostly of mullite(3Al2O3 · 2SiO2), quartz (SiO2), aluminium oxide (Al2O3), hematite (Fe2O3), lime(CaO) and gypsum(CaSO4 · 2H2O). As a result it possesses various physical, chemical and mineralogical properties, depending on the mineralogical composition of the used coal and on the combustion technology .
About 75% of India’s energy supply is coal based and shall be so for the next few decades. There are about 82 utility thermal power stations to produce approximately 110 million tonnes of fly ash per annum in the Country . Nearly 38% of the fly ash waste is utilized in the Country at present , in various fields including landfills, cement making and concrete product making such as bricks, blocks and tiles, in road making, in filling of the mines. Attempts have been made earlier to utilize this fly ash waste in the polymer industry in making polymeric composites where fly ash is being used as inorganic particulate filler without much breakthrough. The utilization of fly ash is determined by their properties such as fineness, specific surface area, particle shape, hardness, freeze-thaw resistance, etc. Many investigations have been carried out towards the effective utilization of fly ash and with understanding of potential environmental and health impacts associated with its disposal by land filling.
In this paper an attempt has been made to modify the fly ash by transforming the micro sized fly ash into nanostructured fly ash using high energy ball mill. The smooth, glassy and inert surface of the fly ash can be altered to a rough and more reactive by this technique. The nano structured fly ash thus obtained may be characterized using sophisticated analytical techniques. Thus, nano level mineral filler can be used as reinforcing filler in making polymer composites, in particular rubber based composites.