• Journal of the Korea Institute of Building Construction
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• v.14 no.1
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• pp.68-75
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• 2014

In order to increase the integrity of the wellbore which is used to prevent the leakage of supercritical $CO_2$, it is necessary to develop a concrete that is strongly resistant to carbonation. In an environment where the concentration of $CO_2$ is exceptionally high, $Ca^{2+}$ ion concentration in pore solution of Portland cement concrete will drop significantly due to the rapid consumption of calcium hydroxide, which decreases the stability of the calcium silicate hydrate. In this research, calcium phosphates were used to modify Portland cement system in order to produce hydroxyapatite, a hydration product that is strongly resistant to carbonation under such an environment. According to the experimental results, calcium phosphates reacted with Portland cement to form hydroxyapatite. The formation of hydroxyapatite was verified using X-ray diffraction analyses with selective extraction techniques. When using dicalcium phosphate dihydrate and tricalcium phosphate, the 28-day compressive strength was lower than that of plain cement paste. However, the specimen with monocalcium phosphate monohydrate showed equivalent strength to that of plain cement paste.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.3
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• pp.96-102
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• 2022

Hydroxyapatite (HAp) was synthesized from calcium hydroxide (Ca(OH)₂) reacting with phosphoric acid (H₃PO₄) in aqueous solution. HAp powders were synthesized from extremely high concentration of precursor solutions over 3 M of Ca(OH)₂ aqueous suspension using modified process parameters such as phosphoric acid (H₃PO₄) pouring rate, aging time and post ball milling process. Regardless of phosphoric acid pouring rate, the DCPD (dicalcium phosphate dihydrate) was formed at room temperature and when heated above 700℃, β-TCP (tricalcium phosphate) was synthesized and the amount reached its maximum at 900℃. When the synthesized powder was sintered at 1150℃, β-TCP, a high temperature impurity phase, remained. The single HAp phase without DCPD was obtained from post ball-milled precipitates followed by 3 day aging. For the ball-milled precipitates even without the aging process, the desired single HAp phase without β-TCP could be obtained by heat treatment above 500℃. The post ball milling process provided a convenient route for HAp synthesis.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.730-734
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• 2003

This research examined the effect, which it follows in particle size distribution change of CaHPO$_4$ㆍ2$H_{2}O$ (DCPD). We used two kinds of compositions; tetracalcium phosphate (TTCP)/dicalcium phosphate dihydrate (DCPD) composition and $\alpha$-tricalcium phosphate ($\alpha$-TCP)TTCP/DCPD composition. As the result, the mean particle size of the DCPD decreased, the setting tine shortened at all compositions. The reference powder (DR), which did not milling, showed about 2 times strength value compared with other milling sample. Especially, the compressive strength of 60 : 20 : 20 sample (DR(do$_{0.5}$)=12.08 $\mu\textrm{m}$) after curing 7 days in simulated body fluid solution was 40$\pm$0.5 MPa, which was the highest. This resulted from the packing density at $\alpha$-TCP/TTCP/DCPD combination.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.1
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• pp.73-82
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• 2009

Injectable calcium phosphate cement (CPC) has been used as bone substitute successfully due to good biocompatibility and osteoconductivity. One of the important mechanical characteristics of CPC is flowablility, which can be evaluated by measuring rheological parameters. However, there have been few studies that measured rheological properties of CPC. The purpose of this study was to evaluate the effects of temperature and concentrations of 2 kinds of setting solutions, hydroxyprophyl methylcellulose (HPMC) and polyacrylic acid (PAA), on rheological properties of CPC. The CPC used was dicalcium phosphate dihydrate (DCPD). Rheological properties of CPC paste were measured using rheometer. The effect of concentrations of each solution (2% and 1% HPMC and 35% and 17.5% PAA) was evaluated. The effect of temperature ($25^{\circ}C$ and $37^{\circ}C$) on the rheological properties of CPC was also investigated. The statistical analysis was carried out with Mann-whitney test with Bonferronis collection. CPC with both setting solutions showed shear thinning behavior. Higher concentrations of setting solution (2% HPMC and 35% PAA) produced significantly higher viscosity than lower concentrations of setting solution (1% HPMC and 17.5% PAA). CPC with HPMC showed significantly higher viscosity at $37^{\circ}C$ that at $25^{\circ}C$. CPC with PAA showed lower viscosity at $37^{\circ}C$ than at $25^{\circ}C$, although the difference was not statistically significant. The results showed that CPC with HPMC or PAA solutions are pseudoplastic and the concentrations of setting solutions and temperature may have an effect on the rheological properties of CPC paste. These results showed that the flowability of injectable CPC could be improved by use of increasing frequency of oscillation. In clinical practice, the use of ultrasonic vibration would be helpful in application of injectable CPC. CPC with HPMC could be more easily applicated at $25^{\circ}C$ than $37^{\circ}C$. The use of lower concentrations of HPMC and PAA solution would be beneficial in terms of flowability.

• Applied Biological Chemistry
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• v.18 no.3
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• pp.145-166
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• 1975

The calcium balance study was carried out to determine the availability of calcium in different sources for chicks and laying hens. The sources of calcium were calcium carbonate (CC), dicalcium phosphate-dihydrate (DCPH), and dicalcium phosphate-anhydride (DCPA) for chicks and calcium carbonate (CC) and oyster shell (OS) for laying hens. The radioisotope dilution method was employed to measure the endogenous excreta calcium during the period of balance study following preliminary feeding. A. Experimental results with chicks: No significant difference was found among feed consumption of chicks fed diets containing different sources of calcium. Body weight gain of chicks was dependent upon the source of calcium. The gain decreased in the order of DCPH, DCPA and CC (P<0.01). The feed conversion efficiency in chicks fed DCPH was better than those in chicks fed CC or DCPA. The average tibia ash contents for chicks fed different sources of calcium were similar. The DCPH was superior to CC or DCPA regarding the calcium content in tibia ash. There were no significant differences among the average calcium contents in plasma trichloracetic acid filtrate in chicks irrespective of calcium sources. The mean apparent retention of calcium by chicks fed DCPH, CC and DCPA were 65.9, 64.0 and 59.9% respectively. The calcium to phosphorus ratios in tibia ash and plasma trichloracetic acid filtrate for chicks fed different sources of calcium were similar. The chicks fed DCPH showed the partition of endogenous excreta calcium in total excreta calcium as 35.6% which was higher than 31.0 or 31.4% for chicks fed CC or DCPA. The endogenous excreta calcium per day per chick in group fed DCPH, DCPA or CC were 17.2, 16.1 and 14.6mg respectively. The true retained calcium per day per chick in group fed DCPH were 109.9 mg which was higher than those observed with CC or DCPA group (P<0.01). The true retention of calcium by the birds fed diets containing DCPH, CC or DCPA were 78.1, 75.1 or 72.6% respectively. B. Experimental results with laying hens: The feed consumption, egg production and feed converion efficiency of laying hens fed diets containing different sources of calcium were similar. Calcium concentration in plasma trichloracetic acid filtrate in laying birds fed CC was equivalent to the value obtained by feeding OS. The apparent calcium retention by laying birds fed CC was 61.6% and it was significantly more than that of hens fed OS of 51.6% (P<0.05). The partition of endogenous excreta calcium in total excreta calcium of laying hens fed CC was 23.5% and this was higher than that of birds fed OS of 15.6%. The laying hens fed CC showed 310 mg of endogenous excreta calcium per day per bird while birds fed OS showed 261mg. The true retention of calcium by layers fed CC was 70.7% against 59.2% for birds fed OS (P<0.05).