Investigation of a spinel-based refractory as a carrier for a steel melt temperature sensor

• Main Author: Berglund, Henrik
• Format: Others
• Language: English
• Published: Uppsala universitet, Mikrosystemteknik 2020
• Subjects: Natural Sciences; Naturvetenskap
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-402596

This master thesis work explored the possibility to measure the temperature in a steel melt for a longer time. A thermocouple was embedded in a ceramic material based on spinel (MgAl2O4), chosen as a sensor. The ceramic material was evaluated with regard to chemical corrosion from slag, thermal shock, and resistivity. Finally, a functional test in a steel melt was done in Sandvik’s experiment furnace. The corrosion study was made with two ceramic materials, one with a large amount of alumina and the other with a large amount of spinel. The materials were synthesised from different raw materials, which were mixed and sintered at 1000°C and 1650°C. This process led to four materials that were tested against two types of slags, at a temperature of 1600°C for 2 hours. One of the slag types had a large amount of calcium oxide (CaO) and the other a mixture of calcium oxide and added fluorspar (CaF2). The study shows that the spinel-rich material can withstand the corrosive slag better than an alumina-rich material. The thermal shock test was done with the two kinds of ceramic materials that were sintered at the higher temperature of 1650°C. The materials were subjected to a cold shock with a temperature difference of 1080°C which decreased the flexural strength with about 90%. The electrical resistivity test was tested by coating platina wireswith two types of electric insulating layers of a dielectric pasteor a type of cement. These two layers increased the resistance between two embedded wires inside the spinel-rich material at temperatures below 1000°C. The final results from the temperature measurements showed that continuous monitoring of the temperature in molten steel can be achieved by the design of a thermocouple embedded into the spinelmaterial, in shapes of cylindrical lances. Two, essentially identical, sensor lances were immersed 10 cm deep into molten steel, through the corrosive slag line, and measured the temperature in a steel melt around 1500°C. One of the sensors measured temperaturesof 1100-1300°C for 18 minutes, the other sensor measured temperatures around 1400°C for 9 minutes.