الفهرس 
Nucleation and crystal growthOnly 14 pages are availabe for public view
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Abstract
The mechanism of crystallization of COM crystals at conditions simulating to artificial urine was studied:
The present work consists of three chapters:
Chapter I (Introduction):
It includes, general introduction, nucleation, crystal growth, crystal dissolution and reaction mechanism. Inhibition and effect of additives are also discussed. It also contains, literature survey on crystal growth and dissolution of COM crystals.
Chapter II (Experimental):
It includes the preparation of solutions, preparation of seed crystals and techniques of methods used in this study. Also, it includes the types of analysis used to elucidate the structure of prepared crystals as XRD, FTIR, SEM, SSA and EDX
Chapter III (Results and discussion):
This chapter includes three main sections A,B,C:
A) Studying the crystallization of COM in absence of an additives:
The crystallization of COM crystals was carried out at different supersaturation (ɣ = 0.3 - 0.8) . Under experimental conditions at t= 37o C , I = 0.3 mol dm-3 , pH = 5.5 , ɣ = 0.4 , and the reaction experiment initiated using 0.01 g of seed crystals used to intiate the crystallization of COM in each experiment. Constant composition method was also used. The order of crystallization of COM crystals at experimental conditions was
" ~ "
2 , which suggests surface – controlled mechanism. The un effect of fluid dynamics on the rates of crystallization of COM crystals and the lower value of Ea (was 0.144 KJ/mol), supported the surface – controlled mechanism. The rates of crystallization of COM crystals were decreased by increasing the values of ionic strength of the medium. Increasing the values of pH of the medium till pH = 8 and decreasing after this value was found.
B) Studying the mechanism of crystallization of COM crystals in presence of some organic additives:
Using some amino phosphonates (A1,A2,A3,A4,A5) as additives in crystallization of prepared COM crystals at the same experimental conditions was studied. It was found that concentration as low as 10-6 mol dm-3decreased the crystallization of COM crystals, by, 95.7%, 87.7%, 76.9%, 71.4% and 71%, in the presence of (A1,A2,A3,A4,A5) respectively. from these results, the order of increase of inhibition was :
A1>A2>A3>A4>A5
The molecules of the additives adsorbed on the active sites on the surface of COM crystals blocking them and decreased their numbers.
The validity of application of Langmuir – isotherm, supported the surface –controlled mechanism and good inhibitory effect of these additives.
The values of ΔG, KL and Kads in the presence of(A1,A2,A3,A4,A5) supported the order of inhibition of crystallization of COM crystals at the experimental conditions (A1,A2,A3,A4,A5) and supported the adsorption of the molecules of the additive on the surface of seed crystals and that these additives were good inhibitor.
These substances inhibited the crystallization process of COM
crystals and the order increase of inhibition of them were: A1>A2>A3>A4>A5
The values of KL of these inhibitors were: (12.5 x 105 , 11 x 105 ,7 x 105 ,4.167 x 105 and1.714 x 105 ) J/mol in case of the presence of (A1,A2,A3,A4 and A5) respectively. The values of ΔG in the presence of these additives were `( -40.4, -40.0, -39.0,-38.5,-38.2) kJ/mol-1 respectively.
The values of ΔG and KL in the presence of these additives supported the order of inhibition of them as mentioned previously.
The % of total area covered by A1 on the surface of COM crystals was 12.5 %, indicating the low numbers of active sites and confirming the surface – controlled mechanism and the adsorption of additive on the active sites of the surface of COM crystals of the rate determining step.
The values of Qdiff for kink and terrace in the presence of A1, indicated that the molecules of A1 adsorbed on both kink and terrace sites but nearly favourite the kink sites.
The rates of crystallization of COM crystals were also studied in the presence of 10-7 mol.dm-3A1 it was found that :
1- The rates of crystallization of COM crystals in the presence of A1 was increased by increasing pH values of medium.
2- At constant values of experimental conditions and varying the values of temperature, the activation energy (Ea) equal 4.0578 kJ/mol was found to have small value .
3- The rates of crystallization of COM crystals increase with increasing the values of the ionic strength of the medium.
The low value of ΔS in the presence of A1 equal 31.96 J/mol/k indicated the adsorption of molecules of A1 on the active sites of COM crystals.