Water vapour is commonly found on the surface of untreated metals and will either hydrogen bond to the surfaces or form metal hydroxides.20 In standard conditions their abundance will be in the range of submonolayer—monolayer coverage. Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, Reactions of isocyanates with (a) alcohol, (b) water, (c) amine, (d) isocyanate, (e) carbodiimide and (f) the structure of pMDI, The Ta4f spectrum of the metallic substrate shows tantalum is mainly present in the (V) state with small amounts of (IV) and (I) oxidation states present. Working off-campus? The global market for diisocyanates in the year 2000 was 4.4 million tonnes, of which 61.3% was methylene diphenyl diisocyanate (MDI), 34.1% was toluene diisocyanate (TDI), 3.4% was the total for hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), and 1.2% was the total for various others. By careful fitting of the N1s region contributions relating to interfacial bonding have been established. The Ta4p3/2 (V) component is separate enough from the rest of the components to still have confidence in its BE and FWHM when fitting the higher BE side of the component. Positively charged organic CN or NOx species have BE greater than 402 eV. Circled fragments indicate each repeat unit of MDI and the lower mass amine reaction products. pMDI is a part of the mixture separated during the synthesis of MDI; therefore, oligomers and other reactants will be present. Any queries (other than missing content) should be directed to the corresponding author for the article. The presence of the (IV) and (II) oxidation states could have formed during the UV‐ozone cleaning procedure, promoting the formation of suboxides on the surface. 6.U.S. The BE and FWHM of the (IV) and (II) components were set relative to this (V) component and results from the substrate analysis. CO, CO and C(O)O components were all constrained to full width at half maximum (FWHM) of 1.55 eV and CC/H to 1.50 eV. The decreased overlayer thickness can be accounted for by the cross‐linked network formed during curing as all the shorter chain oligomeric molecules will bind into one large network on the surface. 1998. The Ta4p3/2 components have only been added to illustrate the peak fitting procedure. The C1s spectrum of Ta‐01 (Figure S5) is indicative of pMDI strongly resembling the spectra of the high concentration Ta‐03 sample. Analysis of the high‐resolution ToF‐SIMS data shows the normalised peak area for the NH4+ fragment in Ta‐01/02 to be an order of magnitude larger than Ta‐03/04 (Table 5). The high‐resolution C1s and O1s spectra are indicative of pMDI with the isocyanate component clearly visible at 288.9 and 531.4 eV for the C1s and O1s spectra, respectively. The synthesis of MDI starts with the condensation of aniline with formaldehyde as shown in Figure 2.6 for the ortho adducts. Clayton J. Bevas, Department of Mechanical Engineering Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK. For this, the substrate was characterised with XPS and ToF‐SIMS. Carbodiimide components were observed in the XPS analysis of all samples, and their concentrations were accounted for by the chemical reaction of carbodiimide formation. Please check your email for instructions on resetting your password. The other sample was air‐dried for 3 h horizontally (average room temperature was 18°C). %PDF-1.6 %���� Spectra were obtained in constant analyser energy (CAE) mode with pass energies of 200 and 50 eV and a step size of 0.4 and 0.1 eV for survey and high‐resolution spectra, respectively. The BE and FWHM of the Ta4p3/2 (V) component were readily defined from high BE side of the spectrum.