Carbon replicas

Fig 1. Electron micrograph of a platinum/carbon replica prepared by the fast-freeze, deep-etch, rotary-shadow replica technique printed in reverse contrast. Cell walls of onion parenchyma have an elaborate structure with many thin fibres bridging between thicker cellulosic microfibrils. Scale bar represents 200nm. 

Franklin and Bradley, by means of electron microscopy of carbon replicas, reported that the spores of a majority of species of Bacillus and Clostridium are readily distinguished by surface patterns. The surfaces may be smooth or ribbed, with the ribs usually longitudinal. 

Nitrogen-containing carbon replicas of SBA-15 and MLV prepared from pyrrole as carbon precursor... 

In the present work, a different technique (pyrrole polimerisation and carbonisation) has been applied to prepare nitrogen-containing carbons from mesoporous materials. The influence of iron present in the matrix skeletons, introduced by impregnating the matrices with FeCl3, on the properties of the carbon replicas has been evaluated. 

The parent siliceous materials of the SBA-15 and MLV types were synthesised after typical procedures [2], The carbon replicas were prepared via polymerisation, catalysed by ferric chloride, of pyrrole introduced into the mesopores of matrices [3]. The products were characterised by the nitrogen adsorption, TEM, and thermal analysis (DTG, DTA). The nitrogen content in carbons was determined using elemental analysis, XPS, and EDX, while the Si and Fe contents, with XPS. The replicas of SBA-15 and MLV-0.75 are denoted as CMK-3Nx and OCM-.Nx, respectively, were x refers to the number of g of FeCl3 per 1 g of silica used for preparations. 

As reported earlier [1], the X-ray diffraction patterns of both the pure and nitrogen-containing CMK-3 indicate similar, well-ordered structures. On the other hand, the carbon replicas of onion-like materials show lack of an ordered system of mesopores [2]. 

Figure 1. N2 adsorption (filled) and desorption (open symbols) isotherms for a) pure and Fe-modified SBA-15 and their N-doped carbon replicas b) pure and Fe-modified MLV-0.75 and their N-doped replicas (for clarity, the relevant isotherms are shifted up by 200 or 600 cm3g 1). Pore size distributions calculated from the desorption isotherms with the modified BJH method for c) pure and Fe-modified SBA-15 and CMK-3 carbons d) pure and Fe-modified MLV-0.75 and OCM carbons.

The nitrogen-containing carbon replicas of MLV-0.75 exhibit a poorer structure ordering as compared to the carbons obtained from sucrose. It is in contrast to the CMK-3 samples as replicas of SBA-15. The OCM carbons contain up to 6.5% N whereas CMK-3, up to 5%. Probably, the removal of nitrogen during carbonisation proceeds from hexagonal structures easier than from onion-like ones. In the OCM samples, the amount of the used FeCh determines their structure ordering. 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

Most research on the structure of skeletal catalysts has focused on nickel and involved methods such as x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), electron diffraction, Auger spectroscopy, and x-ray photoelectron spectroscopy (XPS), in addition to pore size and surface area measurements. Direct imaging of skeletal catalyst structures was not possible for a long while, and so was inferred from indirect methods such as carbon replicas of surfaces [54], The problem is that the materials are often pyrophoric and require storage under water. On drying, they oxidize rapidly and can generate sufficient heat to cause ignition. 

Fig. 7.2 (a) TEM micrograph of the carbon replica obtain by a 100 % pore filling of SBA-15 template (b)TEM micrograph of the carbon replica obtained after a 25% pore filling of SBA-15 template. 

In a related approach, these same porous alumina membranes serve as a mask through which O2 plasmas are used to etch underlying carbon films. This etching process produces honeycomb carbon structures that are positive replicas of the alumina-membrane mask. This process has successfully produced honeycomb structures of both diamond and graphitic carbon, with pore sizes in the carbon replica around 70 nm. 

Figure 5. Electron micrograph of the W preshadowed carbon replica of the surface of an unannealed Loeb-Sourirafan-type cellulose acetate membrane (XI40,-000)...

Fig. 1.3.2 TEM image of a carbon replica of monodispersed Co304 particles obtained on aging for 4 h at I00°C in 10-2 mol dm-3 Co(ll) acetate solutions in air. (From Ref. 1.)...

Fig. 2.1.13 Transmission electron micrograph of carbon replica of natural opal. (From Ref. 82.)...

Fig. 5.1.3 TEM images (a) basic iron sulfate particles prepared by aging a 0.088 mol din-3 Fe2(S04)3 at 98°C in an oven for 3 h (b) carbon replica of the same particles as described in (a) (c) basic iron sulfate particles prepared by aging a solution of 0.18 mol dm-3 in Fe(N03)3 and 0.53 mol dm-3 in Na2S04 in oil bath heated from room temperature to 80°C at a constant rate of 1.5°C min-1 and aged at 80pC for 1.5 h (d) carbon replica of the same panicles as in (c), but aged for 2 h at 80°C. (From Ref. 9.)...

Fig. 2. Using the carbon replica technique, this is an electron micrograph of cubic silver bromide grains in which the comers have been slightly rounded due to the presence of a silver complexing agent. (Photo by Dr. Donald h Black, Eastman Kodak Company)...

In TEM, thin sections of samples are embedded in epoxy resins or, alternatively, platinum-carbon replicas of the samples are produced in order to the avoid release of vapor or gases. 

Nano-materials in lithium ion battery electrode design, presentation of a plasma-assisted method to create a carbon replica of an alumina template membrane... 

Association Structures. The onset of micellization was observed using light-scattering data and confirmed by electron microscopy of carbon replicas from freeze fracturing of samples frozen to — 150°C. The light-scattering unit was a Sophica Photo Gonia Diffusometer, Model... 

Ghadially EN, Lock CJL, Lalonde JMA, Ghadially R. Platinosomes produced in synovial membrane by platinum coordination complexes. Virchows Arch., B, Cell Pathol. 1981 35 123-131. Beretta GL, Righetti SC, Lombardi L, Zunino F, Perego P. Electron microscopy analysis of early localization of cisplatin in ovarian carcinoma cells. Ultrastruct. Pathol. 2002 26 331-334. Ruben GC. Ultrathin (Inm) vertically shadowed platinum-carbon replicas for imaging individual molecules in freeze-etched biological DNA and material science metal and plastic specimens. J. Electron. Microsc. Tech. 1989 13 335-354. 

Figure 6. Electron micrographs (preshadowed carbon replicas) showing the morphologies of AgBr crystals obtained from double-jet precipitation in bone gelatin at the indicated bromide concentration...

Figure 15. TEM of cellulose micr ibrils (Mi) and macrofibrils (Ma) uMhin the secondary fiber wall of balsam fir direct carbon replica.

Figure 17, TEM of randomly arranged microfibrils in the fiber primary wall (PW) of balsam fir direct carbon replica.

Figure 24. TEM of warty layer in softwood (A) and hardwood (B) fibers direct carbon replicas. (A) Lumen surface of fiber in balsam fir. Note the amorphous substance masking the S3. (Reproduced with permission from Ref. 20. Copyright 1974, Society of Wood Science and Technology.) (B) Lumen surface of a warty fiber in sycamore. The slits shown here are pit apertures. (Reproduced with permission from Ref 23. Copyright 1974,...

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