Solution combustion synthesis of lithium orthosilicate as the tritium breeder: Effects of microwave power and fuel-to-oxidizer ratio on phase, microstructure and sintering

Abstract Lithium orthosilicate (Li4SiO4) is regarded as a candidate solid tritium breeding material for the fusion reactors, but the phase control and densification for this ceramic are difficult. Microwave-induced solution combustion synthesis (MSCS) offers an efficient and flexible route for preparing the tritium breeders in a single step. The combustion process can be effectively controlled by the microwave power output and the fuel-to-oxidizer ratio (φ), which can be taken advantage of for the phase control of the product. The results show that the combustion temperature increases linearly with the increase of the φ value, and the Li4SiO4 becomes the main product when the φ value is higher than 0.75. Lithium metasilicate (Li2SiO3) is detected in minimum quantities in the products, and its content can be reduced when the microwave power output is 1100 W, which can be further removed by calcination at 873 K for 2 hours. The thermal analysis results show that the redox reaction between the LiNO3 and citric acid provides the heat for the combustion. The ceramic body can be sintered to 84 % of the theoretical density at a low temperature of 1073 K, and the relative density is close to 96 % with high purity at the sintering temperature of 1373 K.