Improving the properties of M type strontium hexaferrite (SrO.6Fe2O3) magnet synthesized using local raw materials by substitution compounds

The history of magnetism is coeval with the history of science. The magnet's ability to attract ferrous object from a distance has drawn much attention of human being. Weak permanent magnets are quite widespread in nature in the form of lodestones – rocks rich in magnetite, Fe3O4 – which were magnetized by huge electric currents caused by lightning strikes. First known ancient magnetic device is a device called the 'South Pointer', which has a lodestone carved in the shape of a Chinese spoon as centrepiece. Used for geomancy in China at the beginning of our era, the spoon turns on the base to align its handle with the Earth's magnetic field. The evidence of its application can be seen in the grid-like street plans of certain Chinese towns, where the axes of quarters built at different times are misaligned because of the secular variation of the direction of the horizontal component of the Earth's magnetic field. A propitious discovery, attributed to Zheng Gongliang in 1064, was that iron could acquire a thermoremanent magnetization when quenched from red heat. Steel needles thus magnetized in the Earth's field were the first artificial permanent magnets. They aligned themselves with the field when floated or suitably suspended. A short step led to the invention of the navigational compass, which was described by Shen Kua around 1088. Reinvented in Europe a century later, the compass enabled the great voyages of discovery, including the European discovery of America by Christopher Columbus in 1492 and the earlier Chinese discovery of Africa by admiral Cheng Hou in 1433. When we come to the Middle Ages, virtues and superstitions had accreted to the lodestone like iron fillings. Some were associated with its name. People dreamt of perpetual motion and magnetic levitation. The first European text on magnetism by Petrus Peregrinus describes a perpetuum mobile. Perpetual motion was not to be, except perhaps in the never-ending dance of electrons in atomic orbitals with quantized angular momentum, but purely passive magnetic levation was eventually achieved at the end of the twentieth century. Magnetic research in the seventeenth and eighteenth centuries was mostly the domain of the military, particularly the British Navy. An important civilian advance, promoted by the Swiss polymath Daniel Bernoulli, was the invention in 1743 of the horseshoe magnet. This was to become magnetism's most enduring archetype. The horseshoe is an ingenious solution to the problem of making reasonably compact magnet which will not destroy itself in its own demagnetizing field. It has remained the icon of magnetism up to the present day. Usually red, and marked with 'North' and 'South' poles, horseshoe magnets still feature in primary school science books all over the world, despite the fact that these horseshoed have been quite obsolete for the past 50 years. A technical landmark in the early nineteenth century was William Sturgeon's invention of the iron-cored electromagnet in 1824. The horseshoe-shaped core was temporarily magnetized by the magnetic field produced by the current flowing in the windings. Electromagnets proved more effective than weak permanent magnets then available for excitation of electric motors and generators. Recent decades have witnessed an immense expansion of magnetic applications. The science developed over a century, mostly in Europe, was ripe for exploitation throughout the industrialized world. Advances in permanent magnetism, magnetic recording and high frequency materials underpin much of the progress that has been made with computers, telecommunication equipment and consumer goods that benefit most people on Earth. Permanent magnets have come back to replace electromagnets in a billion tiny motors manufactured every year. Magnetic recording sustains the information revolution and the Internet. There have been seminal advances in earth science, medical imaging and the theory of phase transitions that can be laid at the door of magnetism. The third millennium sees us at the threshold of the spin electronics age. Conventional electronics has ignored the spin of the electron. The essential practical characteristic of any ferromagnetic material is the irreversible nonlinear response of magnetization M to an imposed magnetic field H. This response is epitomized by the hysteresis loop. The applied field must be comparable in magnitude to the magnetization in order to trace a hysteresis loop. Hard magnetic materials have broad, square M (H) loops. They are suitable for permanent magnets because, once magnetized by applying a field H ≥ Ms sufficient to saturate the magnetization, they remain in a magnetized state when the field is removed. The hysteresis loop is central to technical magnetism; physicists endeavor to explain it, material scientists aim to improve it and engineers work to exploit it. The loop combines information on an intrinsic magnetic property, the spontaneous magnetization Ms which exists within a domain of a ferromagnet, and two extrinsic properties, the remanence Mr and coercivity Hc, which depend on a host of extraneous factors including the sample shape, surface roughness, microscopic defects and thermal history, as well as the rate at which the field is swept in order to trace the loop. Aim of this study is to determine the effects of various factors on M type strontium hexaferrite magnets. Scale, as the iron oxide source and commercial strontium carbonate, as the strontium source, were used for synthesis as starting materials. Also, LaCl3 and Co2O3 were used for La and Co sources as substitution compounds. The strontium hexaferrite was synthesized by conventional ceramic process. First of all, non-magnetic contaminations were removed from the scale using magnetic separation. Then, in order to improve the effectiveness of milling, the scale was subjected to heat treatment, at 1050 oC for 8 hours. After that, the heat treated scale was first ball milled and then milled using attritor. Following milling process, batches of different strontium carbonate – scale ratios (1/5; 1/5,5; 1/6) were prepared. Then, prepared batches were calcined at 1200 oC for 24 hours. The reaction occurs during calcination is as follows: SrCO3 + 6Fe2O3 → SrFe12O19 + CO2 Calcined strontium hexaferrite was again ball milled and milled using attritor, consecutively. Obtained strontium hexaferrite powders were pressed into pellets. 0.5 wt% SiO2 and 0.5 wt% CaCO3 were added to some part of the calcination product, then sintered. After shaping, the pellets were sintered at 1200 oC for 4 hours. Finally, sintered samples were magnetized. During the study, some analyses were also carried out. The chemical composition of the scales, which are used as raw material, were determined by chemical analysis. It's found out that two different scales contain different amount of impurities. After XRD analysis of the calcined strontium hexaferrites with two different scales as raw material, the results showed that while strontium hexaferrite (SrFe12O19) phase ratio is around 88-90 % for the sample with higher impurity containing scale, it is approximately 100 % for the sample with lower impurity containing scale. Considering this results, scale with lower impurity content was used for the rest of the study. After shaping the strontium hexaferrite powders using press, samples were sintered and then magnetized. Following magnetization, magnetic property analyses were carried out using permeagraph. The best results obtained from samples are remanence (Br) of 231 mT and maximum energy product [(BH)max] of 8,2 kJ/m2.