MATERIAL PREPARATION
5.3. MATERIAL PREPARATION
It is known that basaltic rocks are available in abundance in nature, i.e. on the earth’s crust. Many years ago, the magmatologists of France were interested to work with the materials scientists like us to explore how the magmas were fast-cooled to a ‘glassy’ or ‘crystalline’ state onto the earth’s crust. The idea was to know about the ‘history’ of our planet’s creation through the creation of such materials available in nature. Since, this basaltic rocks contain a large amount of iron oxide, it must have some kind of magnetic property and it is definitely possible to extract some useful information on our planet through magnetization measurements on such materials. By this brief account, the readers would appre- ciate the importance of such materials in magmatology or, geology. However, no attempt is made here in this book to go towards this interesting subject, since we are mainly concerned with nano materials.
MAGNETIC PROPERTIES
181 In India, basaltic rocks are found in the Deccan range of mountains, and the Deccan basalts also
contain a large amount of iron oxides in order to justify experimental work on magnetization. The geologists can obviously talk more on this subject and can identify other basalts, which are available in India and which are also useful for various interesting studies. For the present work, the basaltic rocks were taken from the famous Holyoke Basalt Flow at Westfield in the state of Massachusetts (USA). Its
chemical composition is : 52.0% SiO 2 , 14.1% Al 2 O 3 , 12.8% Fe 2 O 3 , 9.3% CaO, 6.4% MgO, 3.2 Na 2 O, 1.2% K 2 O, 1% Ti 2 O (wt.%).
The entire raw material processing and consequent glass fabrication were done at Corning Glass Works (USA) [1]. The basaltic rocks were crushed and ground to a fine powder, and then it was melted 'twice' to bring homogeneity in a large platinum crucible at 1500°C for 16 hours. After casting large plates of glass, they were annealed at 525°C. First of all, a dilatometric experiment was carried out at a
heating rate of 3°C/min. From ΔL/L 0 vs. T plot, the glass transition temperature (T g ) was estimated to be 635°C. The glasses were cut into small square (1 cm × 1cm) pieces and heat-treated at 600, 650, 700, 800 and 900°C respectively for 8 hours (5 samples) so that crystallization and other studies could be performed. There were mainly six samples including the as-annealed glass, which is called a ‘blank glass’.
5.3.1. Nano Particles and X-ray Data
On all the above six samples, the X-ray diffraction measurements were carried out, which is based on the intensity of diffracted beam [I( θ)] at different angles of diffraction (2θ) following Bragg’s diffraction Law : n λ = 2d sin θ, where λ is the wavelength of CuK α radiation, and d is the inter-atomic distance. It was observed that there is no crystalline peak in the ‘blank glass’, 600 and 650 samples. The
peaks due to “magnetite” (Fe 3 O 4 ) having an inverse spinel structure appeared for the 700 sample. The strongest peak was at d-spacing of 2.50 Å.
For the 800 and 900 samples, there were peaks due to magnetite and also due to pyroxene (CaMgSi 2 O 6 ) giving the strongest peak at d-spacing of 2.97 Å plus some other minor phases. However, the 'Transmission Electron Microscopy (TEM) showed that magnetite was present in the 650 sample also and obviously for 700 sample, while the last two samples contained a mixture of phases. From the X-ray data, no quantitative estimate of the amount of magnetite or pyroxene was made. However, from the well-known Scherrer equation, the particle sizes of magnetite were estimated from the respective magnetite peaks at 2.50 Å for 650, 700, 800 and 900 samples, which were found to be 4.5 nm, 5.5 nm,
6.4 nm and 7.0 nm respectively. A detailed study of ‘Small Angle Neutron Scattering’ (SANS) showed for the 700 sample that the particle size should be of the similar order as that found by X-ray data [2]. From these data, it can be said that the particles size distribution is quite narrow within the domain of this study.