Thermal Expansion of Uranium Pyrophosphate and of Ceramic Bodies in the System UO 2 –UP 2 O 7

During an investigation of methods of predicting the thermal expansion of pure, single‐phase ceramics, uranium pyrophosphate (UP 2 O 7 ) was synthesized and the thermal‐expansion properties were measured by the X‐ray diffraction and dilatometer methods. The basis for the selection of UP 2 O 7 is discussed. Cubic UP 2 O 7 expands with increasing temperature up to 400°C. Above this temperature the material contracts so that the specimen returns to the room‐temperature length at about 1000°C. Intermediate phases in the system UO 2 –UP 2 O 7 were prepared and the thermal‐expansion properties were measured. Ceramic bodies in the system UO 2 –UP 2 O 7 were prepared. The thermal‐expansion properties of these bodies are discussed in relation to the properties of the individual phases.