Introduction Nowadays, a large number of inorganic natural or syn- thesized materials have the incremented use in order to supply the demands of high modern nanotechnology. Among such classes of compounds those materials containing phosphates are characterized to have homo- geneous properties with the advantage in forming many minerals and also biocompounds [1]. This versa- tility comes from the fact that the tetrahedral phosphate monomer units with great reactivity can condense as oligomers and polymers by forming open or close chains by inclosing a great variety of gel, crystalline or vitreous solids, in addition to microorganism constitu- ents [2]. The anhydrous calcium phosphate can be ob- tained from the dehydration of brushita [3], hydro- thermal synthesis [4] and obtaining through shelf-life of other phosphates at room temperature [5]. A promi- nence feature associated to phosphate is the enormous application in medicine and industry, which is focused to biological participation. Some phosphate derivates are potentially used as catalysts in heterogeneous catal- ysis. Depending on the nature of the cations linked to phosphate anion, they can exhibit acidic behaviour (Al 3+ ,B 3+ ), basic (alkaline and alkaline earth metals) or redox properties (transition cations) [6]. An interesting procedure for obtaining bifunctional catalysts based on the partial substitution of original cations such as Na + , Li + and (NH 4 ) + by transition ions, e.g. copper in a phos- phate with of Nasicon type or substitution of calcium by Co 2+ and Ni 2+ in tricalcium phosphate [6]. In this di- rection, a mixed phosphate composed of calcium and nickel with general formula Ca 3–x Ni x (PO 4 ) 2 (0≤x≤0.275) was used as catalyst for butene to butadienes [7] dehydrogenation. Phosphates contain- ing calcium, sodium and copper in different composi- tions as Ca 10–5x Cu x (PO 4 ) 7 (0≤x≤1) and Ca 10–x/2 Na x Cu 0.5 (PO 4 ) 7 (0≤x≤ 1) with the same struc- ture of tricalcium phosphate β-Ca 3 (PO 4 ) 2 was applied to catalyze the dehydrogenation of 2-butanol [8]. The aim of this investigation is the synthesis and thermal characterization of six calcium copper phos- phates with general formula of Ca 1–x Cu x (HPO 4 ), where x varied from 0.05 to 0.5 by exploring also the stabilities of the new solids at several pH conditions. Experimental Materials Chemicals Ammonium phosphate (NH 4 ) 2 HPO 4 , calcium chlo- ride CaCl 2 ·2H 2 O and copper nitrate hexahydrate Cu(NO 3 ) 2 ·6H 2 O were used without previous purifica- tion. Besides, deionized water was used in the prepa- rations. Synthesis of phosphates This mixed phosphates were synthesized by precipita- tion method [9], mixing three aqueous solutions of 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2006 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 87 (2007) 3, 775–778 SYNTHESIS AND THERMAL CHARACTERIZATION OF COPPER AND CALCIUM MIXED PHOSPHATES E. C. da Silva Filho 1 , Oberto G. da Silva 2 , Maria G. da Fonseca 2* , Luiza N. H. Arakaki 2 and C. Airoldi 3 1 Química, Universidade Federal do Piauí, 64900-000 Bom Jesus, Piauí, Brazil 2 Departamento de Química, CCEN, Universidade Federal da Paraíba, 58059-900 Jo ±o Pessoa, Paraíba, Brazil 3 Instituto de Química, Universidade Estadual de Campinas, Caixa Postal 6154, 13084-971 Campinas, S ±o Paulo, Brazil A series of compounds with composition of Ca 1–x Cu x HPO 4 , where x varied from 0.05 to 0.5 were synthesized by precipitation method. The compounds were characterized by elemental analysis, X-ray diffraction, infrared spectroscopy, scanning electron mi- croscopy, and thermogravimetry. The chemical stabilities of solids were investigated at several pH. Elemental analysis of copper, calcium and phosphorus are in agreement with the proposed composition. The formation of lamellar phosphates was evidenced. The stability of the set of compounds was better for samples with high copper content. Keywords: calcium phosphate, copper phosphate, thermogravimetry * Author for correspondence: mgardennia@quimica.ufpb.br