Ömer Sahin

Effect of surface charge distribution on the crystal growth of sodium perborate tetrahydrate

Growth and dissolution rates of sodium perborate crystals have been measured in a flow-type single-crystal cell. Sodium perborate grows dendritically at any level of supersaturation and shows growth and dissolution rate dispersion. Both the growth and dissolution rates of sodium perborate were found to be controlled by surface charge distribution which is represented by applied voltages in an electrostatic separator. It was determined that high surface charge dominates the crystal growth rate when compared with low surface charge under identical conditions. The results obtained showed that the formation of dendritic structure is not a function of supersaturation but a function of surface charge. The rate of dissolution of a crystal with a high surface charge is greater than that with a low surface charge.

Effect of Electrical Field and Temperature on the Crystal Growth Rates of Boric Acid

Growth rates of boric acid have been measured both in the absence and in the presence of electrical field at 1.00 DC voltage as a function of supersaturation in a laboratory-scale fluidized bed crystallizer at the temperature range of 20 °C to 52 °C. The values of overall rate coefficient (K G ), diffusion rate coefficient (k d ), reaction rate constant (k r ) and reaction order (r) were determined by trail and error method at different temperatures. In the absence of electrical field increasing the temperature causes to increase the values of K G k c k r and r. Activation energies are also determined for K G , k and k d separately. The effect of electrical field on the crystallization steps were determined by similar route. It was observed that electrical field caused to decrease the values of kinetic parameters (K G , k d , k r and r) by increasing temperature.

Production of high bulk density anhydrous borax in fluidized bed granulator

Abstract Production of anhydrous borax from borax pentahydrate was investigated in a fluidized bed calcinator. Single step calcination gives a puffed product with very low density. In order to obtain high bulk density product dehydration should be carried out at least in two stages. The most important step dominating the final bulk density is the first step. Dehydration of borax pentahydrate up to around 80% Na2B4O7 content at temperatures lower than 393 K in the first step gives high bulk density anhydrous borax at the final stage. After this critical point, thermal shock imposed on the particle has only slight effect on the final bulk density value and anhydrous borax with a bulk density higher than 0.6 g cm−3 may easily be obtained at temperatures less than 800 K.