Papers by Keyword: Calcium Pyrophosphate

Abstract: β-Tricalcium phosphate (β-TCP) ceramics are of interest for bone requirements implants due to resoption behavior. The mechanical properties of β-TCP, however, are not yet sufficient to allow load bearing application of implants. The aim of this work was to investigate the effect of Mg²⁺ substitution on the strength sintered TCP. Due to promotion of a liquid phase at 1200°C, Calcium pyrophosphate (CPP-C₂P₂O₇) was used to improve the sintering of the samples. The introduction of CPP was promoted by use of a Ca/P molar ratio of 1.45. The powders were synthesized using a mixture of Ca (OH)₂ suspension and diluted H₃PO₄ with addition of MgO and calcined at 750 °C, 900 °C and 1050 °C. The cold isostatic pressing compacts were sintered at 1200 °C and 1300 °C, respectively.It was shown that a small Mg content (1.5 mol%) increased both compressive strength and fractional density of the TCP material sintered at 1200 °C from 132 ± 39 MPa at 92.1 % of fractional density to 193 ± 29 MPa at 94.5 % of theoretical density. Higher amounts of Mg inhibited the grain growth provoking a increase of the boundary mobility activation energy. Abnormal grain growth (AGG) was observed after sintering at 1300°C, as result CPP - liquid phase formation. Increase of Mg content promoted AGG, due to inhibition of grain growth during normal grain growth resulting in a increase of the residual elastic energy of the system.

Abstract: The paper concerns the problem of exploitative composite materials with solid lubrication additions. The goal of the present investigation was to research the composite materials based on 316L stainless steel powders with the addition of calcium pyrophosphate (Ca2P2O7). The diffusion processes of main elements during sintering were analyzed. The influence of volume fraction of additions on structure of composites and their tribological properties were examined. Tribological tests were performed by a special tribometer, which allowed to realize research during the periodically variable motion with low velocity and variable values of pressure. The structure of materials was observed with scanning electron microscope (SEM). The intensive diffusion of main alloying elements brought the segregation of components and appearance of new phases. Changes in the microstructure, particularly the solution of phosphorus in austenite and attendance of phosphides and oxides insertions, had an effect on mechanical properties of materials. The microhardness, yield strength values as well as wear resistance increased considerably with the rise of modifier addition.

Abstract: The purpose of this study is to compare the osseointegration of calcium pyrophosphate(CPP) coated screws with uncoated screws. CPP coating was prepared and coated by dipping method. CPP coated and uncoated screws were inserted into the mongrel dogs. The insertion torques, radiographs, histology, histomorphometric analysis, and extraction torques were evaluated at 2, 4, and 8 weeks after surgery. The insertion torque was not different between CPP coated and uncoated screws. The extraction torques of CPP coated screws at 2, 4, and 8 weeks(5.45±2.05, 7.62±1.51 and 6.60±2.80 cNM) were significantly higher than their insertion torques(2.74±1.13, 2.98±0.70, and 2.18±1.34 cNM)(p<0.0001, <0.0001 and 0.0005 respectively) and significantly higher than the extraction torques of uncoated screws(1.14±0.470, 2.57±1.36, and 3.18 ±0.499 cNM). The percentages of direct bone-screw contact of CPP coated screws were statistically higher than those of uncoated screws at 2, 4, and 8 weeks. These results suggest that CPP coating may improve the clinical results by allowing early motion exercises and early weight bearing.

Abstract: b-tricalcium phosphate(TCP, Ca3(PO4)2) ceramics are preferred as a bioceramics because of its chemical stability and reasonable degradation rate in vivo, but it is difficult to obtain b-TCP ceramics with high compressive strength at lower temperature than that of phase transition to a-TCP. In this study, the sintering behavior of TCP, Ca2P2O7-doped TCP, and CaCO3-doped TCP in the range of 2wt%~5wt% were investigated respectively. Phase transition of pure TCP took place between 1100°C to 1150°C, and pure b-TCP ceramics could achieve a compressive strength of only 3MPa. However, calcium pyrophosphate (CPP, Ca2P2O7) additive prevented the transformation of b-TCP to a-TCP, but the second phase of CPP was observed in the resultant ceramics. Phase transition of TCP ceramics by addition of both CPP and calcium carbonate (CC, CaCO3) took place between 1200°C to 1250°C and the resultant TCP ceramics had few impurity of CPP. By adding CPP and CC to TCP, final ceramics with compressive strength over 12MPa could be obtained when sintered at 1200°C for 2hrs.