تحضير مركبات عضوية جديدة ذات صفات بلورية سائلة == Preparing of New Organic Compounds With Liquid Crystalline Properties
Author name:
محمود عبد الستار يحيى القزاز
Supervisor name:
ابتسام خليفة جاسم
General topic:
Chemistry
Specific topic:
Physical Chemistry
Degree:
Master
University:
University of Baghdad - College Of Science - Chemistry Department
Language:
English
University location:
Baghdad
First pages:
25T1473 - p.pdf
Abstract:
يهدف هذا العمل لدراسة امكانية طلاء سطوح بعض المعادن مثل الفولاذ المقاوم للصدا 316، الحديد الكربوني، النحاس، الالمنيوم والزنك، بالمواد النانوية لتحسين مقاومة التاكل وذلك باستخدام اثنين من التقنيات، الاولى بواسطة الطلاء بالالياف النانوية لمادة متعدد الانيلي | This work aims to study the possibility of coating the surfaces of some metals such as stainless steel 316, carbon steel, copper, aluminum, zinc, with nanomaterials to improve the corrosion resistance using two techniques, first by coating with polyaniline nanofiber using electropolymerization of aniline monomer and the second technique by TiO2 nanoparticles via sol - gel process starting from titanium isopropoxide. The work focused on getting thin and homogeneous layer to cover the entire surface of the metal and protect it from corrosion in artificial seawater solution (3.5% NaCl) at 293, 303, 313, and 323 K.Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), Energy dispersive x - ray (EDX), x - ray photoelectronic spectroscopy (XPS), and x - ray diffraction (XRD) were used to diagnose and describe the structure and morphology of the layers that cover the surface of the metals under investigation, and finally the corrosion parameters ;corrosion potential (Ecorr), corrosion current (Icorr), protection efficiency (PE%), polarization resistance (Rp) and the effect of temperature on the inhibition efficiency in the absence and presence of polyaniline (PANI) or TiO2 coating at temperature ranging from 293 to 323 K were obtained and expressed as; Ea , ?H*, ?S*, and ?G* of all samples were estimated from Tafel plots using potentiostatic technique.The SEM and AFM images of PANI films reflect nanofibers (diameter from 50 to 70 nm); the thicknesses were measured by special AFM scans. They showed values between )700 to 1564 nm(, which may be attributed to the differences in oxidation - reduction potentials of the metals. The XRD patterns of the deposited PANI showed duplicate broad scattering peaks around 2? of 20? and 25?.The AFM images of TiO2 nanoparticles deposited on specimens revealed that the layer was extremely smooth, the particles are small spherical and the average diameter between 26 and 38 nm.The shifts in Ecorr of the uncoated with comparison of the PANI or TiO2 coated samples were small for; S.S316, C.S, Cu, Al, and Zn which means that the anodic and cathodic reactions affected by the same extent.The Rp of the PANI and TiO2 coated substrate was always more than the uncoated ones that attributed to the weak conductivity of PANI and the semiconducting properties of the Titania. All coated metals with PANI or TiO2 exhibited good degree of corrosion protectiveness. For PANI the PE ranged between 56 and 92 % and the best results was achieved for Zn metal this may attributed to the high corrosion values of the bared Zn, while TiO2 coating showed PE at the range of 68 and 93% and the best was for Al metal. The protection efficiencies showed small changes by increasing the temperature but for TiO2 in some cases the PE somehow increased with increasing the temperature. The data showed that the thermodynamic activation functions (Ea and ?H*) of the corrosion of the coated samples are higher than those of the uncoated ones indicating more energy barrier. The entropy of activation ?S* for the uncoated and coated samples are always negative ,this indicates that the activated complex in the rate determining step represents an association rather than a dissociation step, the measured ?G* values takes positive values and showed almost small change with increasing temperature, indicating that the activated complex was not stable and the probability of its formation decreased somehow with rise in temperature and the ?G* values for coated samples reveal that in the activated corrosion complex becomes less stable as compared to the uncoated specimens.Single cyclic potentiostatic tests conducted at 293 K to follow up the pitting probabilities of each metal in seawater before and after coating. The I - V plots indicated that only SS316 and Aluminium specimens suffer from pitting corrosion and the two types of coating reduces the pitting area of the hysterias loop with pushing the pitting potentials for more positive values
