M. C. Paputa Peck

Characterization of phosphorus-poisoned automotive exhaust catalysts

Abstract Oil-derived contaminants on light-off catalysts from high mileage taxis were characterized by a variety of physical and chemical methods. The contaminants (mostly phosphates) deposit in a strong axial gradient from the front to the back of the monolithic catalyst channels. Two major forms of phosphorus contamination were observed: (1) an overlayer of Zn, Ca, and Mg phosphates, and (2) aluminum phosphate within the washcoat. The data also suggest the formation of cerium(III) phosphate. Laboratory catalytic reaction measurements on core samples from the taxi catalysts confirm a strong deactivating effect due to the phosphorus contamination. The activity improves dramatically after removing phosphorus via an oxalic acid wash.

Photo-stabilization and photo-degradation in organic coatings containing a hindered amine light stabilizer: Part IV—Photo-initiation rates and photo-oxidation rates in unstabilized coatings

Abstract The chemistries and rates of photo-oxidation have been studied in a series of acrylic melamine coatings as a function of exposure condition. Electron spin resonance (ESR) spectroscopy has been used to determine the photo-initiation rate (PIR) of free radicals using a nitroxide doping technique. Infrared spectroscopy has been used to follow changes in the relative concentrations of different functional groups. In particular, the rate of carbonyl group formation has been measured. This rate has been found to be proportional to the square root of the photo-initiation rate, confirming that the formation of carbonyl species in these coatings is a free radical induced photo-oxidation process. Infrared spectroscopic measurements of carbonyl formation can be used to evaluate the effectiveness of free-radical scavengers such as hindered amine light stabilizers in retarding photo-oxidation in polymer coatings.

The characterization of polymer surfaces by photoacoustic fourier transform infrared spectroscopy

Abstract Weathered surfaces of intact polymer films on standard test substrates have been characterized with photoacoustic detection Fourier transform infrared spectroscopy with minimum sample preparation. Vibrational spectra were obtained from the surface of fully formulated and pigmented paint samples aged in Florida testing, and in QUV and carbon arc accelerated weathering environments. Single- and two-component polyester urethane resin films on polybutyleneterephthalate-polycarbonate-rubber substrate were examined to a depth of approximately 8–12 μm. The samples were analyzed for differences in chemical changes occurring during natural and accelerated testing. Spectra for these samples were compared with those obtained by attenuated total reflection (ATR) infrared spectroscopy, which requires time-consuming sample preparation. Photoacoustic detection infrared is applicable for heavily pigmented and opaque samples which are difficult to examine by conventional transmission or reflection techniques. The essence of photoacoustic detection in a Fourier transform infrared experiment is discussed.

Photoacoustic Detection of Rapid-Scan Fourier Transform Infrared Spectra from Low-Surface-Area Solid Samples

We have demonstrated that the PAS cell volume, and the state of the background material as well as the interferometer mirror velocity and the cell gas composition, must be controlled when one is recording spectra of solid samples. An optically thick, totally absorbing material with a volume matching that of the sample is needed in order to properly normalize spectra of solid samples. With the proper detection bandwidth, mirror speeds of up to 0.181 cm/s can be used with helium as a transfer medium, for the cell specified. The improvement attained at high frequency by using helium can be as much as 10-fold over that obtained with air. The Helmholtz design of the cell produces a resonance at 1.4 kHz with air and 2.65 kHz with helium. These resonances are also affected by the volume and composition of the gas in the sample chamber. Thus, it is essential to select an appropriate background sample for the purpose of normalizing spectra.

Infrared Photoacoustic Spectroscopy of Carbon Black Filled Rubber: Concentration Limits for Samples and Background

Infrared spectroscopy studies of the cure chemistry, state of cure, and surface bloom on rubber materials have always been limited by the presence of carbon black in samples. One of the modern methods for recording infrared spectra of solid samples is photoacoustic detection Fourier transform spectroscopy. It has been demonstrated in the past that surface-segregated species can be identified with this technique, but the results are complicated by the presence of carbon black, which limits the optical depth. As for the study of bulk chemistry, photoacoustic detection does not require that the sample be infrared transparent, and the method can be used with samples containing as much as a 15 wt % carbon. At loadings higher than 30 wt %, the material becomes a total absorber and can be used to record an instrument background spectrum.

An infrared spectroscopic study of polyethylene terephthalate degradation in polyester fiber/nitrile rubber composites

Abstract Fourier transform infrared spectroscopy (FT-IR) was used to study the degradation mechanism of polyethylene terephthalate (PET) fibers in rubber composites. The mechanisms of chemical failure were postulated by comparing the FT-IR spectra of samples obtained from in-service use and under laboratory conditions. Amines from the rubber diffused into the fiber causing uniform degradation (aminolysis). Aminolysis was the predominant mechanism of polyester decomposition. Hydrolysis, known to occur primarily at the surface of the PET fiber, was apparently not appreciable.

Wear control in a lubricated contact through externally applied Electric Current

It has been reported earlier that when an electric current is externally applied between two sliding surfaces in a lubricated contact, an electrochemical cell is produced with the lubricant acting as an electrolyte and two sliding surfaces acting as electrodes. In this paper, the effect of an externally applied direct current on friction and wear of a sliding steel pair lubricated by engine oils has been investigated using a ball on disk machine. The current was passed through the contact by connecting the ball and disk specimens to a current source. It has been observed that the magnitude and the direction of current can significantly alter wear of sliding surfaces but does not greatly impact friction coefficients. The wear of the cathode surface decreased while that of the anode surface increased compared to the condition when no current passed through the contact. It was also observed that wear on anode and cathode surfaces was influenced by lubricant chemistry. The wear reduction on cathode surface is believed to be related to the modification of elemental composition of lubricant derived surface films due to the passage of an electric current.

The Infrared Analysis of Polyethylene Terephthalate Fibers and of Their Strength as Related to Sample Preparation and to Particle Size

An explanation is presented for the broadening of intense spectral features observed in the infrared spectra of polyethylene terephthalate fibers prepared as KBr pellets. Since band broadening occurs in the spectra of stronger, undegraded fiber, it is proposed that, the stronger the fiber, the more the difficulty one has in pulverizing the sample. Larger particles result from undegraded polyester, which lead to broader bands for intense features. The local sample pathlength in the region of the large particles is greater than that for small particles, which can be more homogeneously mixed. Fiber samples can also be presented to an infrared microscope either “as is” or flattened. Striking differences exist between spectra for flattened and round fibers that were otherwise similar.