Abstract: Ulexite (Na2O.2CaO.5B2O3.16H2O) is boron mineral
that is found in large quantities in the Turkey and world. In this
study, the dissolution of this mineral in the disodium hydrogen
phosphate solutions has been studied. Temperature, concentration,
stirring speed, solid liquid ratio and particle size were selected as
parameters. The experimental results were successfully correlated by
linear regression using Statistica program. Dissolution curves were
evaluated shrinking core models for solid-fluid systems. It was
observed that increase in the reaction temperature and decrease in the
solid/liquid ratio causes an increase the dissolution rate of ulexite.
The activation energy was found to be 63.4 kJ/mol. The leaching of
ulexite was controlled by chemical reaction.
Abstract: Calcium phosphate cement (CPC) is one of the most
attractive bioceramics due to its moldable and shape ability to fill
complicated bony cavities or small dental defect positions. In this
study, CPC was produced by using mixture of tetracalcium phosphate
(TTCP, Ca4O(PO4)2) and dicalcium phosphate anhydrous (DCPA,
CaHPO4) in equimolar ratio (1/1) with aqueous solutions of acetic
acid (C2H4O2) and disodium hydrogen phosphate dehydrate
(Na2HPO4.2H2O) in combination with sodium alginate in order to
improve theirs moldable characteristic. The concentration of the
aqueous solutions and sodium alginate were varied to investigate the
effect of different aqueous solutions and alginate on properties of the
cements. The cement paste was prepared by mixing cement powder
(P) with aqueous solution (L) in a P/L ratio of 1.0g/0.35ml. X-ray
diffraction (XRD) was used to analyses phase formation of the
cements. Setting time and compressive strength of the set CPCs were
measured using the Gilmore apparatus and Universal testing
machine, respectively.
The results showed that CPCs could be produced by using both
basic (Na2HPO4.2H2O) and acidic (C2H4O2) solutions. XRD results
show the precipitation of hydroxyapatite in all cement samples. No
change in phase formation among cements using difference
concentrations of Na2HPO4.2H2O solutions. With increasing
concentration of acidic solutions, samples obtained less
hydroxyapatite with a high dicalcium phosphate dehydrate leaded to
a shorter setting time. Samples with sodium alginate exhibited higher
crystallization of hydroxyapatite than that of without alginate as a
result of shorten setting time in a basic solution but a longer setting
time in an acidic solution. The stronger cement was attained from
samples using the acidic solution with sodium alginate; however the
strength was lower than that of using the basic solution.