Mechanical and thermal properties of hot pressed neodymium-substituted britholite Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 Damien Bre ´giroux a,b , Fabienne Audubert b , Eric Champion a , Didier Bernache-Assollant a, * a Science des Proce ´de ´s Ce ´ramiques et des Traitements de Surfaces, UMR CNRS 6638, 123 Avenue Albert Thomas, 87060 Limoges Cedex, France b CEA Cadarache, DEN/DED/SEP/LCC, 13108 Saint Paul Lez Durance, France Received 21 November 2002; accepted 17 January 2003 Abstract Neodymium-substituted britholite, a phosphate – silicate apatite Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 , is considered as a potential host matrix for specific immobilization of radionuclides. Complementary investigations have been carried out to complete the database concerning this compound. The aim was to establish mechanical and thermal properties of dense britholite. Hot pressing was used to nearly fully densify the material. Low values of mechanical properties were found: 0.75 MPa m 1/2 for the fracture toughness and 95 MPa for the flexural strength. The Young’s modulus and the Poisson’s ratio were 108 GPa and 0.30, respectively. The specific and the thermal conductivity at 298 K were Cp = 0.75 J g  1 K  1 and k =1.15 W m  1 K  1 . The average coefficient of thermal expansion in the 20 – 1000 jC temperature range was a = 21  10  6 K  1 . D 2003 Elsevier Science B.V. All rights reserved. Keywords: Ceramics; Britholites; Mechanical properties; Elastic properties; Thermal properties 1. Introduction One of the fields of research conducted in the framework of the French law of 30 December 1991 concerning the management of long-lived and high- activity radioactive waste consists in separating the radionuclides to perform their specific immobilization. Thus, it is necessary to optimize adapted host matrices for long-live radionuclides [1,2]. Several types of matrices have been investigated: glasses, ceramics and composites [3–5]. Geological observations have led scientists to study apatite minerals as nuclear waste matrices [6]. Studies of natural apatites from the fossil nuclear reactor of Oklo (Gabon) showed that these compounds can support a very high dose of external and internal alpha irradiation. They can also incorpo- rate a large amount of actinides, rare-earth elements and halogens [7]. Neodymium-substituted britholite, a phosphate–silicate apatite Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 , is considered as a potential host matrix for the specific immobilization of actinides (americium, curium and neptunium). Neodymium is used to simulate the triva- lent actinides because of its similar chemical properties. The optimal formula Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 allows the 0167-577X/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(03)00120-4 * Corresponding author. Tel.: +33-5-55-45-73-70; fax: +33-5- 55-45-75-86. E-mail address: bernache@unilim.fr (D. Bernache-Assollant). www.elsevier.com/locate/matlet Materials Letters 57 (2003) 3526 – 3531