We discuss the characterization of radiation sensitive organic pigment particles by TEM, as well as retrieval of internal microstructure of polymer composite particles used in xerographic toners by electron tomography and by slice-and-view in dual beam (FIB/SEM) instrument.Printing is a multibillion dollar industry that relies on high-quality marking materials to deliver excellent print quality, speed and value to consumers. New innovations in marking materials require an understanding of the attributes and microstructure of dye or pigments used as colorant. Since the color properties of organic pigments are mainly determined by the choice of chromogen molecule as well as pigment size and morphology , then electron microscopy provides a suitable means to investigate the physical structure and microstructure of pigments and other components that are located within toner particles. As both toners and pigment particles are 'soft' organic materials that are highly sensitive to electron beam irradiation, it is necessary to optimize microscopy to maximize information per unit irradiation dose.We studied commercially available quinacridone-type pigments, such as 2,9-dimethylquinacridone pigment known as Pigment Red 122 (PR 122). We estimated the loss of long range order from loss of intensity in diffraction ring corresponding to 0.3 nm lattice spacings in the pigment crystallites. At room temperature we have obtained characteristic dose D C = (0.35±0.05) C/cm 2 . All imaging experiments were performed at less than ½ D C . The dose D C corresponds to the cross section for carbon 1s carbon excitation within a factor of two, suggesting that the primary damage mechanism is due to core loss excitation of carbon . When the samples were observed at T = 90 K, the characteristic dose increased by about factor of 2.4. At T = 90 K, lattice fringes with spacings down to 0.32 nm were observed in the sample. All experiments were conducted at 200 keV incident electron energy. Fig. 1 shows a typical thickness map obtained at a magnification sufficient to observe 1.6 nm lattice fringes (the presence and spacing of lattice fringes was confirmed in zero-loss filtered images). Fig. 2 depicts the relationship between the pigment particle external morphology and the crystal lattice planes. Fig. 3 shows a diffraction pattern of the PR 122. The spacings correspond to alpha, beta or gamma structure of 2,9-dimethylquinacridone. The pigment particle shape in 3D was determined from the thickness maps. The distribution of particle sized for PR122 was obtained by examining dimensions of individual particles in the plane perpendicular to the incident electron beam, while the third size dimension of the particle was obtained from thickness mapping by energy-filtering TEM. We have found that the PR122 particles were tetragonal with a long axis L = (190 ± 30) nm while the other two dimensions were found to be W =T = (28 ± 8) nm, an aspect ratio of approximately 7. HRTEM images similar to Fig. 1 revealed that the 1.6 nm spacing of the molecules is...
Zeolite supported noble metal catalysts provide simultaneously both hydrogenation active sites and acid sites for hydrocracking reaction, which have been widely used in petroleum hydroprocessing processes. The size, location and distribution of the metal particles, as well as the pore structure and crystallinity of the zeolite support are the key factors affecting the activity and selectivity of the catalyst. To enhance the activity and durability of the catalyst, it is of great importance to obtain highly dispersed noble metal clusters within zeolite support. It is of particular importance to introduce small metal particles into the confines of the zeolite micropores. While the conventional ion exchange method works only for inserting metal ion precursors into larger pore zeolite such as zeolite Y, it is difficult to add metal precursors into the cavity of zeolite A due to the small pore size of NaA. So far, much effort has been devoted to introducing Pt into zeolite A by adding a platinum precursor to the synthesis mixture containing both Al and Si source [1,2]. Although preliminary results of chemisorption and shape-selective catalytic test have indicated that the platinum clusters located inside the larger cavity (α cage) of zeolite A [1,3-5], the direct information on the location and distribution of Pt particles, and the microstructure of zeolite support after loading is still in shortage. Transmission electron microscopy (TEM) can provide insight into the structure (atomic/nanoscopic) , crystallography and chemical composition of solid catalysts. Our SEM and Xray diffraction (XRD) study has shown that both morphology and crystallinity of the synthesized zeolite changed when a platinum precursor was incorporated into the initial synthesis mixture (see Fig. 1) . Here, we present the experimental results of the Pt nanoparticles and the microstructure of the aforementioned samples in TEM (JEOL 2200FS). To obtain ultrathin sections (~40 nm) of the zeolite catalysts, samples were first embedded in epoxy resin, and then microtomed and collected onto a carbon coated Cu-grid. Figure 2 presents the high angle annular dark field (HAADF) STEM image for the high Pt loaded sample, showing that very small (less than 2 nm) Pt particles are evenly distributed within the support. The diffraction rings can be attributed to Face Centered Cubic (FCC) platinum, and no obvious reflections from zeolite were observed. Figure 3 shows the STEM image taken from 0.69 wt% Pt loaded sample. Selected area electron diffraction (SAED) patterns recorded from different particles indicate that the large particles (μm scale in Fig. 1) are crystalline while the smaller ones with rough surfaces (see inset of Fig. 1b) are amorphous. The sharp diffraction rings originate from Pt. Electron Energy Loss Spectra (EELS) were also taken for local structural and chemical analysis. Figure 4 shows a comparison of EELS spectra of O-K edge between NaA and high Pt loaded sample after background subtraction and Fourier-ratio deconvolution . The dramatic...
scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
334 Leonard St
Brooklyn, NY 11211
Copyright © 2023 scite Inc. All rights reserved.
Made with 💙 for researchers