Carbon self-supported

Specimens on grids are an alternative to self-supporting disks. Specimens in the form of small particles may be supported on a thin film (e.g. an amorphous carbon film) before being placed on the grid. Thin slices of the material may be produced by an instrument known as an ultramicrotome. The principal advantage of the technique is that it leaves the chemistry unchanged, and it may be employed to create uniform thin films of multiphase material. The instrument operates by moving... 

For dry reforming, carbon formation is very likely, especially when carried out in a membrane reactor [24]. For this application noble metals are used, which are intrinsically less prone to carbon formation because, unlike nickel, they do not dissolve carbon. Irusta et al. [24] have shown above-equilibrium methane conversion in a reactor equipped with a self-supported Pd-Ag tube. Small amounts of coke were formed on their Rh/La203/Si02 catalyst, but this is reported not to have any effect on activity. 

Las but not least, sample preparation is also an important issue. If we want to examine nanocrystalline powder samples. The grain size must be just a few nanometers, the layer, formed by these nanocrystals must be as thin as possible (to minimize dynamic difiraction), continuous and self-supporting. In many cases not all these requirements are fulfilled simultaneously. The nanocrystalline material to be studied is frequently present on a thin supporting carbon layer. In such cases peak decomposition can not yield an acceptable fit unless the presence of the amorphous material (in the form of a few diffuse rings) is taken explicitly into account in the model to be fitted. The size of the background is also affected by scattering in such a carbon support. 

This work is about the development of a new porous composite material [18] which consists of a silica network intercrossed with a carbon network of high activity, being both networks independent and self supported. This new composite was obtained by the sol-gel method, it has an open pore size distribution curve characterized by a big sharpened zone near the 1000 A diameter, and it possess a high thermal stability. 

The SC-155 material calcined in oxidizing atmosphere at 1000 "C and until constant weight produced a self supported porous silica network (the carbon was burnt out) which was called S-155 this silica structure maintained the same shape and volume as the original composite. On the other hand, the SC-155 treated with 20 % HF aqueous solution until the elimination of Si02 produced a self supported carbon network called C-155, and this carbon structure maintained the same shape and volume as the original composite. 

It was mentioned that when a piece of SC-155 was calcined at 1000 "C in oxidizing atmosphere, the obtained product was a white porous amorphous silica material with the same shape and external volume as the starting one, and when a piece of the same material was submitted to acid attack by 20 % HF aqueous solution, a self supported carbon network was obtained, also with the same shape and external volume as the original These experiences show that the silica network and carbon network are self supported structures and independent one from the other. 

Currently, several forms of infrared spectroscopy are in general use, as illustrated in Figure 8.4. The most common form of the technique is transmission infrared spectroscopy, in which the sample consists typically of 10 to 100 mg of catalyst, pressed into a self-supporting disk of approximately 1 cm2 and a few tenths of a millimeter thickness. Transmission infrared spectroscopy can be applied if the bulk of the catalyst absorbs weakly. This is usually the case with typical oxide supports for wavenumbers above about 1000 cm-1, whereas carbon-supported catalysts cannot be measured in transmission mode. Another condition is that the support particles are smaller than the wavelength of the infrared radiation, otherwise scattering losses become important. 

Foamed carbon has 600 times the thermal insulation capacity of the same weight of firebrick and is therefore used as a self-supporting thermal insulation material in furnaces or in fire-retarding sandwich-constructions. Foamed carbon cores are used in foundry technology, because they are easily produced and can be easily removed by combustion from inaccessible cavities. Furthermore foamed carbon is utilized as a filter material for the filtration of corrosive materials, as sintered plugs in gas inlets, as an electrode material and as a catalyst support. 

A coral reef may be considered as a self-supporting system, but with considerable interzonal transfer. The major site of metabolic activity is the reef flat, and probably the upper reaches of the seaward slope. The reef flat is a net consumer requiring an input of organic carbon. This gain is probably obtained from the algal pavement and the upper slope, which are seaward of the reef flat. 

Recently activated carbons such as activated carbon fibers (ACFs) and superhigh surface area carbons have been developed. New activated carbons have more uniform micropore size distribution and greater surface area than traditional activated carbons. The carbon membranes for gas separation have been also developed lately[8]. The activation of the polyamide film leads to self-supported activated carbon film whose surface area is larger than 1100 m /g [9]. Thus various kinds of carbon adsorbents have been developed to find new applications. Scientific studies on activated carbon have been increasing according to development of these new carbon adsorbents with a special relevance to energy and environmental demands. In particular, controll of an adsorptive ability of activated carbon is requisite for new application. Consequently, basic principles for control of the micropore filling mechanism of activated carbons are shown here. 

O2 adsorption infrared studies were performed using self-supported oxide wafers ( 50 mg). In order to eliminate surface pollutants, mainly carbonates, all... 

The PS layer formed on a Si substrate is the most frequently used as a PS host. Sometimes, partial or complete modification of the PS layer (by annealing, oxidation, carbonization, etc.) is performed prior to pore filling or coating process [2]. Multi-layered PS structures (with different porosity) [8], self-supported PS films [9], and PS grains (PS layer separated from Si substrate and divided onto grains) [10] are used as well. 

FTIR spectroscopy (BRUKER IFS 110) study of the adsorption of carbon dioxide on the solids was used to determine the free alumina surface area. More precisely, the adsorption of CO2 onto hydroxyl groups of the alumina produced characteristic bands of hydrogenocarbonate species [6,7], The optical density of the band at 1235 cm l, (5 C-O-H bending mode), after taking into accoimt the bands displayed by ceria, was measured and used to determine the free alumina surface. From this method and by comparison with total BET surface area, a ceria surface has been estimated. Ceria-aluminas, alumina and ceria were used as self supported wafers (0.01 to 0.03 g/cm ) they were thermally treated up to 673 K, under oxygen and then under high vacuum, in situ, before adsorption of CO2 at room temperature. Then, the catalysts were evacuated at 295, 373, 473 and 573 K, for 1 h. IR spectra were recorded at room temperature, after CO2 adsorption and after each desorption temperature. 

Self-supported Carbon Nanotubes through Constraint Synthesis... 

Fig. 7.4 (A) Optical micrograph showing the improvement on the apparent density of the carbon nanotubes synthesized without and under constraint. The total weight of each sample was 7g. (B) Examples of the macroscopic size of the self-supported carbon nanotubes obtained by varying the diameter of the reactor.

Fig. 7.5 Optical micrographs illustrating the isotropic shrinkage of the cylinder of self-supported multi-walled carbon nanotubes after wetting with water and slow drying in air at room temperature.

Other Ordered Mesoporous Silicas as Hard Template Other mesoporous silicas including MCM-41, HMS, MSU-1, MSU-H, SBA-1, SBA-7, SBA-12 and SBA-16 have also been explored as hard templates to fabricate mesoporous carbons. Mesoporous silica MCM-41, which has hexagonally ordered cylindrical one-dimensional pores, was found to be unsuitable as a template for mesoporous carbon as its use yielded disordered high surface area microporous carbon. This is due to the absence of complementary micropores within the MCM-41 silica walls. However, Tian et al. have successfully produced self-supported, ordered, ultrathin carbon nanowire arrays by employing the mesoporous silica MCM-41 as template.The carbon nanowire arrays exhibit high surface areas up to 1400 m g , large pore volumes of 1.1 cm g and uniform mesopore size of ca 2.2 nm. 

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