Thin (approximately 2 nm) and thick layers of polymeric MDI were deposited on tantalum; one set was cured at 200°C, the other dried at ambient temperature (20°C). Table 4 shows the N1s peak fitting values and surface concentrations for both low concentration samples. Evidence of formal bonding in the ToF‐SIMS analysis is currently inconclusive, and further analysis will reveal further information. The tantalum pentoxide reference material was analysed first to obtain reference spectra for the Ta4f and Ta4p3/2 regions of tantalum pentoxide (Figures S3 and S4). Acid–base interactions within pMDI have also been identified. Carbodiimides form from the reaction between two isocyanates. Two new components were identified in the N1s spectrum of Ta‐02, an amine and a nitride‐like peak (Figure 10). It is hoped that with such information, tantalum could become a viable alternative material for decreasing fouling rates in heat exchangers. Surfaces were analysed by X‐ray photoelectron spectroscopy (XPS) using a Thermo Scientific K‐Alpha+ system. The O1s spectra (Figures S6 and S8 for Ta‐01 and Ta‐02, respectively) shows similar characteristics to the high concentration Ta‐03 sample with an additional oxide component from the substrate. With this, Ta4p3/2 peaks can be reliably fitted over the Ta4p3/2 spectrum of the substrate with confidence, which will in turn inform the peak fitting of the N1s spectral region. 804 0 obj
Huntsman PU, Botlek Rotterdam, The Netherlands. If in a solution it may or may not burn depending on the nature of the material and/or the solvent. Their BE and FWHM were restrained to the values obtained from the pMDI analysis per their corresponding preparation conditions (air‐dry or 200°C cure). With the above interface chemistry of MDI established, this knowledge can be used as a guide for what we may expect to see with tantalum. 4,4'‐Methylene diphenyl isocyanate is produced in two grades of purity (Schauerte 1983): . A monochromated Al Kα X‐ray source was used with a 400‐μm radius spot and electron take off angle normal to the surface. 50%. At elevated temperatures, suboxides form between the tantalum metal and the pentoxide layer. �¯EoîÓ7Biõ*† İR˜84ftav�…ğrt¨'[L)} k hl"rí,>$ó’2L�Ğœúğ@×¤ç;Y3f. Characterising the pMDI surface is best achieved with the negative ToF‐SIMS spectra. A lower binding energy component at ca 396 eV on the air‐dried thin layer of pMDI is the result of a formal reaction between pMDI and tantalum yielding a nitride‐like species in the N1s spectrum. The XPS survey spectra of the high concentration samples (Ta‐03 and Ta‐04 for cured and air‐dried, respectively) show surfaces indicative of pMDI (Figure 4). The thicker layer of Ta‐01 (cured sample) gives confidence in the BE and FWHM of the N1s isocyanate component and was fitted first, constraining its FWHM to what was found in the corresponding analysis of pMDI. Working off-campus? This is to be expected with the thicker overlayer diminishing any signal from nitride‐like bonding interactions that may be present at the interface. The pattern observed in this ToF‐SIMS analysis confirms the conclusions drawn from the XPS analysis regarding acid–base interactions. 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. This reaction occurs spontaneously at temperatures above 180°C. CT = constant tail height = 0.00 (1 = tail height same as peak height; 0 = no constant tail). Analysis of the tantalum pentoxide reference material has provided a guide of the expected XPS BE and FWHM of Ta4f and Ta4p3/2 components and has informed the accurate peak fitting of the substrate.