AL-Butoksit'in Sol-Jel yöntemi ile modifikasyonu ve oluşan ürünün kaplamada kullanılması

Abstract

Geliştirilen ve yeni bulunan her bileşik teknik ve endüstriyel ilerlemelerde önemli rol oynamaktadır. Son yıllarda, tüm sanayi dallarında yeni özelliklere sahip maddelerin sentezlenmesi ile ilgili çalışmalar hızla artmaktadır. Cam, seramik, anorganik-organik polimerler özel yöntemlerle üretildiklerinde termal ve mekanik etkilere karşı dayanıklı ürünler elde edilmekte ve bunlar metallerin ve organik polimerlerin yerini almaktadır. Bu tür bileşiklerin sentezlenmesinde, metal alkoksitler ve bunların kontrollü bir şekilde hazırlanan hidroliz ve kondensasyon ürünleri kullanılmakta ve bu malzemeler son yıllarda hızlı bir şekilde gelişen sol- jel yöntemi ile sentezlenmektedir. Bu çalışmada, hidrolize karşı çok kararsız olan alüminyum butoksitin kararlılığını arttırmak, anorganik ve organik polimerleşmeye imkan sağlayarak yeni özelliklere sahip metal anorganik-organik bileşikleri sentezleyerek kaplama özelliklerini incelemek için metakrilik asit ve akrilik asit seçilmiştir. Bu amaçla Al(OsBu)3 a) Metakrilik asit ve akrilik asit ile kompleksleştirilip, hidroliz ve polimerize edilerek reaksiyonlar incelenmiştir, b) Kompleks üründen hazırlanan solün kaplama özelliklerini belirlemek için örnek plakalar üzerinde kaplama testleri yapılmıştır, c) Kompleks üründen hazırlanan sol kısmen hidroliz edilen TEOS ile reaksiyona sokularak elde edilen çözeltiden kaplamalar yapılmış ve teste tabi tutulmuştur.

In recent years together with the developments of technology and industry, the properties of materials like metal, plastic, glass and ceramic have become insufficient to reply to many demands. Corrosion of metals in many environments, the easy breakage of glass and ceramics, deformation of plastics at high temperatures have been started the work of synthesizing new materials with improved properties. The first example of such materials are silicons. The idea of modifying the two dimensional network of RgSiO in order to obtain a firm and rigid tri dimensional structure gave rise to the work of synthesizing organically modified ceramics (ormocers) and organic- inorganic polymers. Ceramic oxide materials (Si02,TiO^Zr02;Al203 etc.) can be reacted with organic groups (-CH3(-C3H7(-CH=CH^-C(CH3) = CH2 etc.) to synthesize organic- inorganic polymers and ormocers by the so called sol-gel process which enables the conjunction of the heat sensitive organic group with the inorganic network. Sol-gel process involves the use of liguid solutions as mixtures of raw materials. Since mixing is with low viscosity liquids, homogenization can be achieved at a molecular level in a short time. The use of synthetic materials rather then minerals quarantees high purity since the reactants are so well mixed in the solutions. They are likely to be equally well-mixed at the molecular level when the gel is formed. Thus on heating the gel, chemical reaction will be easy and requires lower temperatures. Lower reaction temperatures would lower vaporization losses and minimize reactions with containers and the ambient atmosphere. Lower Reaction temperatures would also suppress phase- vii transformations at higher temperatures and thus permit the formation of glasses and ceramics which cannot normally be prepared. The use of solutions permit the fabrication of thin films and fibers. Controlled heating of the porous gel can give porous ceramics and porous non-crystaline solids whith ultrafine pores. Impregnation of the pores with organic and inorganic materials result in unique composites. Modification of the structure of metal-organic precursors such that organic groups remaining after gelation can yield unique new polimers. Although many examples of applications of the sol- gel process have been described, proven succesfull applications are few. Sol-gel process is ideal for the fabrication of composites by dispersing a filler in the form of powders or fibers in a gelling solution. The resultant solid gel then becomes a porous composite. Porous gels have been impregnated with organic polymers such as PMMA to give transparent colorless, dense composites with unique mechanical and optical properties. Oxide gels, after heat treatment can still retain a great deal of porosity and such gels can be used as membranes and filters. The sol-gel process is particularly advantageous for the formation of thin oxide coatings. Complex shapes can be coated by dipcoating easily and small quantities of raw materials result in low cost products. Despite large shrinkages during drying, thin coatings apparently do not crack if surface preparations are adequate as the gel film would shrink in the thickness direction rather than laterally. The sol-gel process has been suggested as an alternative to conventional methods such as sputtering, chemical vapor deposition and plasma spray for applying thin ceramic coatings. The process is suprisingly simple. A solution containing the desired alkoxide is prepared with a solvent and water. It is applied to a substrate by spinning, dipping and draining. via Sol-gel process involves the use of molecular precursors, mainly metal alkoxides, from which a solid network is obtained through a hydrolysis-condensation reaction. Metal alkoxides can be represented by the general formula M(OR)n where "M" is a metal with valency Mn" and "R" is an alkyl group. These are generally very reactive compounds which may be due to the presence of electronegative alkoxy groups making the metal atoms higly prone to nucleophilic attack. One of the characteristics of metal alkoxides is their solubility in organic solvents and volatility except the methoxides. Another marked characteristic of metal alkoxides is their extreme susceptibility to hydrolysis by atmospheric moisture and these therefore require careful handling. Hydrolysis is the main step in the transformation of metal alkoxides to oxides. From this point of view, the facility with which these alkoxides undergo hydrolysis is the most important factor for their succesful use as precursors in the sol-gel process. The rate of hydrolysis is also crucial in sol-gel processing. In order to control the reaction rates and to obtain a clear sol for the metal alkoxide systems chelating ligands such as glycols, organic acids and dicarbonyl ligands have been used. After forming a complex with a chelating ligand, the complex formed between metal and chelating agent is less prone to hydrolysis. The steps in the sol-gel process are the hydrolysis-condensation of the precursor, gellation, drying, calcination or sintering. Hydrolysis rate is the most important step effecting the sol and gel properties. It is difficult to differentiate between the hydrolysis and condensation reactions which tend to occur simultaneously. Gellation is the formation of colloidal or polymeric gel starting from different precursors. The gellation process is influenced by many variables such as ix Table 1: Examples of sol-gel coatings Single oxide Si02, Ti02, V205, Zr02, Al^, ln203 Various transition metal oxides Ru02, Rh02, Th02 Binary oxides Si02 - Ge02,Si02 - Ti02,Si02 - Aİ203 Si02 - Zr02, Cd - Sn04, Sn02 - Sb203" Ba - Ti03,Ce02 - Ti02,Fe203 - Si02 Mult i component coatings Pt - Si02, Pd - Si02, Pt - ALp3 Si02 - Ti02 - ALP3, Si02 - Zr02 - Ti02 Si02 - Ti02 - Zr02 - A1203 Fep3 - P205 - Si02 Coatings are characterized by hardness test adhesion test, taber test, humidity test, UV test, cyclic thermal test and chemicals test. Sol-gel coatings have not been characterized in the published literature. No information is given on micrographs of the cross section, adhesion and cyclic thermal effects, on the substrate sol-gel coated system. In this work, Al(OsBu)3 which is a very unstable compound was chemically modified for a better control of the hydrolysis-condensation process to obtain organic and inorganic polimerization in order to synthesize products with new properties that can be used for coating. For this purpose methacrylic and acrylic acids were chosen as the chelating ligands. The modification of Al(03Bu)3 was investigated by using 1H and 13C NMR, FTIR and DTA/TG. The sol prepared from the modified alkoxides was coated on to substrates and tested for coating characteristics. The tests applied to the substrates were humidity test, hardness test, UV resistance, coating thickness and optical transmission test. The experimental section of this work was composed of two sections. XI 1) The investigation of complexation, hydrolysis- condensation and polimerization reactions of Al(OaBu)3 modified with methacrylic acid and acrylic acid. 2) Using the modified Al(08Bu)3 for coating PMMA, Al and Steel substrates and characterization of the coating. The complexation reaction of Al(OsBu)3 with methacrylic acid and acrylic acid in 1:2 ratio was followed by FTIR and NMR spectrophotometers. The complexed product was hydrolized with 1 mole of water and investigated by FTIR and NMR. The presence of OH groups attached to Al were detected at 3433 cm-1 by FTIR. After the hydrolysis reactions of metal alkoxides, alcohol condensation may occur between hydoxyl and alkoxide groups, to produce M-O-M bonds. The chelating bonds in the A2/MA alkoxide complexes, due to IT -overlapping, are expected to be more resistant then the alkoxide bonds to hydolysis and condensation. The polimerized product of modified Al(03Bu)3 was inspected by FTIR and DTA/TG. It was observed that the intensity of the bond at 1650 cm-1 due to C=C of the chelating agents was lower in the polymerized product than in the complex product. The DTA/TG studies on the polymerized product showed a weight loss of 84.7 % starting from 120 ° C up to 660° C. The exothermic and endothermic peaks relate to the loss of water and decomposition of organic components in the product. In the second section of this work, modified Al(OsBu)3 was applied on PMMA, Al and Steel subsrates. After heat treatment at 100° C the coating characteristics were determined. SEM was used to investigate the coating made on glass through fructure surface. Thickness, hardness measurements, humidity and UV resistance tests were carried on coatings applied on different subsrates. The optical transmittance of the coatings applied on PMMA were measured.