Influence des additions sur le frittage de phosphate naturel

Abstract

In this present work and in the first part the studied of the reaction-sintering between fluorapatite and alumina using natural phosphate and boehmite is investigated. The addition of alumina, resulting from the boehmite transitions, to the fluorapatite (FAp) has been carried out to obtain various composites based on FAp, yeelemite, mayenite, grossite (CA2), hibonite (CA6) and β-TCP. Several samples were prepared by varying the boehmite (AlOOH) amount to obtain six compositions which contain after sintering: 5, 10, 15, 20, 25 and 30 wt% of Al2O3. After ball-milling for 5 h, all compositions were sintered in the air for 2 h at different temperatures ranging from 1000 to 1500 ◦C. The micro hardness and densification of the sintered body showed a marked improvement by increasing the alumina content and sintering temperature, so the preparation of low cost composites based on fluorapatite, yeelimite and grossite from natural phosphate and alumina are feasible. In the second part, the addition of ZnO to natural phosphate generates a significant change in the mineralogical composition, where the formation of new phases has been observed; zinc phosphate, titra-calcium phosphate (TTCP), tricalcium phosphate (β-TCP) and oxyapatite. In addition, the addition of a large amount of ZnO caused the destabilization of Fluorapatite simultaneously with the precipitation of an additional amount of calcium phosphate. Above 1200°C, the densification and the mechanical properties are hindered by the allotropic transformations of the TCP phase. The effect of ZnO addition on the mechanical properties of Fap was studied. While the strength of the FAp ZnO composite reaches a maximum value (43 MPa) in the case of the sample which contains 10% of ZnO.