Particulate Coatings for Infrared Based Detection and Protective Coatings for Reduced Oxidation of Steel at High Temperatures

Despite the rich information content provided by infrared spectroscopy, this analytical tool is rarely found in analytical labs devoted to the identification and quantification of toxic compounds in water. This is primarily due to the opacity of water in the infrared spectral region. One aim of the work presented in this thesis is to develop sampling methods that circumvent this limitation thus enabling infrared spectroscopic based methods for detection of soluble analytes in water. In our methods, we converted the analytes: phosphate, arsenate, and Strong Acid Dissociables cyanide (SADs-CN) in water into solids, capture them onto an IR transparent membrane, and record their IR spectrum. To capture phosphate and arsenate from solution, an excess amount of AgNO3 was added producing Ag3PO4 and Ag3AsO4 that give unique IR bands at 960 cm-1 and 785 cm-1, respectively. A quantification limit of 6 ppb and 9 ppb was obtained for phosphate and arsenate, respectively. Similarly, to detect and quantify SADs-CN ([Fe(CN)6]3-, [Co(CN)6]3-, and [Au(CN)2]-), cetyltrimethylethylammonium bromide (CTAB) was added to capture SADs-CN, producing unique bands for [Fe(CN)6]3-, [Co(CN)6]3-, and [Au(CN)2]- at 2115, 2123, and 2145 cm-1 which in turn, enabled both speciation and quantification of each cyano species. A quantification limit of 20 ppb CN was achieved [Fe(CN)6]3- and [Co(CN)6]3-, whereas 100 ppb CN for [Au(CN)2]-. Solutions specific to gold mining areas were evaluated by precipitating free CN- and [Au(CN)2]- matrices using AgNO3. IR spectra recorded for these matrices show an additional band at 2187 cm-1 corresponding to a new species formed upon reaction between AgCN and [Au(CN)2]- , which was identified as AgAu(CN)3. In the second project, we developed a Layer-by-Layer (LBL) method to create highly oriented kaolin films on glass, silicon, and steel using alternating cationic and anionic kaolin suspensions. Cationic and anionic kaolin were prepared by dropwise addition of dilute suspension of kaolin to concentrated solutions of cationic and anionic polymers, respectively. SEM, IR, and XRD analyses confirmed kaolin platelets aligned parallel to the substrates, demonstrating controlled deposition. Kaolin coatings reduced oxidation on 440 steel by 73% at 1000 ℃. We applied CeO2 or SiO2 topcoats on kaolin to improves its adhesion under cyclic conditions. SiO2 and CeO2 reduced oxidation by 96% and 66%, respectively, after one cycle at 1000 ℃. However, delamination occurred for SiO2 but not for CeO2 under thermal cycling due to a mismatch in the coefficient of thermal expansion between SiO2 and the 440 steel.