National University of Science and Technology "MISIS"

L. V. Myakisheva, Senior Research Officer, phone: (495) 638-46–90

O. P. Chernova, Assistant Professor
V. S. Panov, Professor
V. Yu. Lopatin, Assistant Professor

This investigation is devoted to estimation of physical-chemical characteristics of fine-grained gadolinium hydroxide powders which can be used as alloying additives of new generation introduced in small amount into UO₂-based nuclear fuel. Gadolinium hydroxide was precipitated from maximum diluted hydrochloric solutions at permanent stirring and pH ~ 6. The powder grain-size dependence on precipitator concentration is studied. It was established that most fine-grain powders (with equiaxial and spherical particles of 0,5 to 5 μm) are obtained using 5 to 10% solution of ammonium hydrate, whereas increasing of NH₃·H₂O concentration up to 25% leads basically to precipitation of large particles and agglomerates of amorphous (according to X-rays diffraction method) Gd(OH)₃ up to 80 μm. Using X-rays and gravimetric analysis the conditions are determined for amorphous Gd(OH)₃ formation and its stabilization by transformation to monohydrate of gadolinium metahydroxide which forms crystalline gadolinium oxide during two-stage dehydration accompanied by formation of Gd(OOH) line structure and final compound Gd₂O₃. Chromatic effect for gadolinium hydroxide powders — color changing from white to pink-violet as a result of variation in precipitation condition and thermal treatment (drying) — is confirmed.

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