First-order Phase Transition Magnetocaloric Effect Materials And Thermomagnetic Power Generation

Thermomagnetic power generation is a new power generation technology, which converts heat energy directly to electrical energy by using first-order phase transition materials. This thesis are organized as follows:(1) The preparation, structure, magnetic properties and thermomagnetic generation properties in Mn1.2Feo.8P0.4Sio.6 compounds were studied. (2) The phase transition and magnetocaloric effect in Mn1.3Fe0.7PxSi1-x compounds were studied. (3) A simple demonstration device for thermomagnetic generator was designed and built.(1) The high energy ball-milling technique and solid-state reaction method were used for the preparation of Mn1.3Fe0.7PxSi1-x(x=0.45,0.46, 0.50,0.55). The phase transition and magnetocaloric effect in this system were studied by varying the P/Si ratio. Magnetic measurements show that the Curie temperature of the compounds decreases by adding P concentration. The maximal magnetic entropy change of compounds is determined to be 9.3 J/kgK,8.0 J/kgK,6.4 J/kgK and 11.3 J/kgK for x 0.45,0.46,0.50,0.55 in 1.5T, respectively. The thermal hysteresis of compounds reduces gradually with increasing Si concentration,2 K,2 K, 5 K, and 10 K, respectively. The existence of thermal hysteresis indicates that the phase transition of these compounds is of first order. The giant magnetocaloric effect in these compounds is due to first-order phase transition.(2) A demonstration device of thermomagnetic generator was designed and built up. This device has the advantages as follows:â‘ The frame of design is relatively simple. The device consists of the electromagnet, induction coil and water heater (heat source). We made the solenoid-type induction coils of 1000,1500,2000 and 2710 turns.â‘¡ By comparing with existing power generation techniques, this generator converts heat energy to electrical energy directly in the absence of mechanical transmission links.â‘¢The most significant feature of this kind of generator is that it takes advantage of the first-order phase transition materials to generate electricity. Very broad Curie temperature range was observed in these compounds, consequently, this generator could generate the electricity by using excess heat.(3) The thermomagnetic generation properties in Mn1.2Feo.7Po.4Sio.6 were studied. On the basic of the work of Mn1.3Fe0.7PxSi1-x compound, Mn1.2Feo.7P0.4Sio.6 compound with Tc=337 K has been further explored. The XRD pattern shows that the compounds crystallize in the Fe2P-type hexagonal structure (space group p-62m) with a minor amount of Mn5Si3 as second phase. The magnetic measurements show that the first-order phase transition from ferromagnetic state to paramagnetic state was observed in Mn1.2 Fe0.7P0.4Sio.6 compound, characterized by a sharp change of the magnetization. The maximal magnetic entropy change of the compound in the magnetic field change of 0-1.5 T is 11.3 J/kgK, which is three times larger than that of metal Gd. According to this feature, we have designed a demonstration device of the thermomagnetic generator and successfully observed the current produced by the phase transition induced by heating.The thermomagnetic power generation properties of Mn1.2Feo.7Po.4Sio.6 compound is given for three operating conditions using the materials with different weights, the coils with different turns and the magnetic field with different magnitude. First, the generation properties of compound with the weight of 10 g,20 g,30 g,40 g and 50 g were tested in the magnetic field 533 mT. The results show that the current increases with increasing the material weight. Second, the materials with same weights (10 g) were put into solenoid-type induction coils to test their generation power. The results indicate that the induced current increases with increasing turns of induction coil. Thirdly, the generation properties of compound with same weight of 50 g were tested in the magnetic field 465 mT,497 mT and 535 mT. The experiment results show that the induced current increases slightly with the increasing magnetic field.Finally, the thermomagnetic generation properties of Mn1.2Feo.8Po.4Sio.6 compound and Mn1.1Feo.9Po.4Sio.6 compound were compared in same condition. The Curie temperature of Mn1.1Feo.9P0.4Si0.6 is 360 K. The XRD pattern shows that the compounds crystallize in the Fe2P-type hexagonal structure (space group p-62m) with a minor amount of Mn5Si3 as the second phase. The magnetic measurements show that the first-order phase transition from ferromagnetic state to paramagnetic state was observed in this compound, characterized by a sharp change of the magnetization. The maximal magnetic entropy change of the compound in the magnetic field change of 0-1.5 T is 9.8 J/kgK. The thermomagnetic generation properties of Mn1.2Feo.8Po.4Sio.6 are better than that of Mn1.1Feo.9Po.4Sio.6.