Tetsuji Chohji

Morphology control of brushite prepared by aqueous solution synthesis

Abstract Dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O), also known as brushite, is one of the important bioceramics due to not only diseases factors such as kidney stone and plaque formation but also purpose as fluoride insolubilization material. It is used medicinally to supply calcium, and is of interest for its unique properties in biological and pathological mineralization. It is important to control the crystal morphology of brushite since its chemical reactivity depends strongly on its surface properties; thus, its morphology is a key issue for its applications as a functional material or precursor for other bioceramics. Here, we report the effects of the initial pH and the Ca and phosphate ion concentrations on the morphology of DCPD particles during aqueous solution synthesis. Crystal morphologies were analyzed by scanning electron microscopy and X-ray diffraction. The morphology phase diagram of DCPD crystallization revealed that increasing the initial pH and/or ion concentration transformed DCPD morphology from petal-like into plate-like structures.

Effect of Anions on Morphology Control of Brushite Particles

Brushite (DCPD, CaHPO4·2H2O) crystals are of great significance in a range of fields including biology, medicine, chemistry, and materials science. One important issue is the control of their morphology; when the crystal growth conditions are changed, the morphology and surface crystal conditions also change. The chemical reaction behavior depends strongly on the surface condition of the particles. Here, we report the effect of coexisting anions on the morphology control of DCPD particles. We synthesized the particles through a liquid-phase reaction by mixing a starting solution of ammonium dihydrogen phosphate (NH4H2PO4) and calcium salts. Calcium nitrate (Ca (NO3)2) and calcium acetate (Ca (CH3COO)2) were used as the calcium sources to clarify the pH dependence of the morphology. We mixed the solutions with the same pH values and agitated them, and observed the products by scanning electron microscopy (SEM) and X-ray diffraction (XRD); the DCPD morphology varies from petal-like to parallelogram structures depending on the initial pH value of the solution and the combination of the starting mixture. The effect of the acetic acid anion is to increase the driving force for the generation of DCPD crystal nuclei.

Effect of Hydroxyapatite on Reaction of Dicalcium Phosphate Dihydrate DCPD) and Fluoride Ion

DCPD, dicalcium phosphate dihydrate (CaHPO4•2H2O) reacts with fluoride ion in an aqueous solution, and forms fluorapatite (FAp, Ca10(PO4)6F2). In previous study, we have found that DCPD does not react with fluoride ion directly, but show few hours of induction period by reaction with fluoride. In this study, effect of hydroxyapatite (HA, Ca10(PO4)6(OH)2) on the reactivity of DCPD with fluoride ion was investigated. By mixing HA with DCPD, it was appeared that the induction period of the reaction was shortened. Morphology of the obtained FAp was similar to HA paricles. We carried on coating of HA on the DCPD particle by soaking DCPD in simulated body fluid (SBF, Kokubo Solution). By coating HA on DCPD particles, particle morphology of the obtained FAp was consistency to the DCPD particles. These results suggest that the shape and particle size of FAp after reaction of DCPD is controllable by DCPD particle as template, and coating with HA.

Chemical prosperity of various chemical gypsums from viewpoint of particle morphology

Dissolution rate of various chemical gypsums in the water was investigated by using batch experiment. The rate of the dissolution of the gypsum had good agreement for explanation of dissolution of plate particle. The rate constants of the experimental formula were different with particle morphology of the gypsums. When morphology of the particle was sheet-liked, the dissolution rate was 10 timed large than it of block-shaped particle. From result of observation of dissolution phenomena of the in the water, it was find that dissolution of the gypsum was preceded on long axis. From these results, particle morphology is seems to be important parameter for using chemical gypsums.

Kinetic analysis of CO2 recovery from flue gas by an ecotechnological system

Kinetic analysis of Ca 2+ desorption due to the displacement of Ca 2+ from cation exchange resin by H + which is generated by bubbling CO 2 to the resin containing water at room temperature has been studied. Ca 2+ was rapidly displaced by H + at room temperature. This indicates that cation exchange resin or soil which acts as cation exchange resin may be good material for CO 2 recovery from flue gases.