Carbonate matrix treatments

It is suggested that a detailed examination of the effect of heat-treatment temperature on the gas reactivity of the carbons studied by Walker and Baumbach 143) might show a series of reactivity maxima which correspond to temperatures at which different catalytic impurities first begin to show significant solid state diffusion and reaction with the carbon matrix followed at higher temperatures by their complete volatilization from the sample. The advent of significant diffusion and reaction of the impurity with the carbon could result in a subseiiuent increase in gas reactivity. Complete volatilization of the impurity from the sample could result in a subsequent decrease in gas reactivity. 

New high-surface-area zirconia-carbon composites were prepared by a sol-gel method followed by a high-temperature treatment in inert gas.420 The samples proved to be very active and selective in the aromatization of Cg+ alkanes (n-hexane and n-octane). From n-octane, as main products, only ethylbenzene and o-xylene were formed. The catalysts have low acidity due to significant dehydration of the zirconia surface, and high surface area since the carbon matrix prevents sintering of the Zr02 particles. 

Oxygen is the main heteroatom in the carbon matrix, and the occurrence of functional groups, such as carboxyl, carbonyl, phenols, ends, lactones, and quinones, has been suggested [176,181], These surface groups can be produced during the activation procedure and can as well be introduced subsequent to preparation by an oxidation treatment [178] (see Figure 2.32). 

Carbon fiber reinforced ceramic composites also find some important applications. Carbon is an excellent high temperature material when used in an inert or nonoxidizing atmosphere. In carbon fiber reinforced ceramics, the matrix may be carbon or some other glass or ceramic. Unlike other nonoxide ceramics, carbon powder is nonsinterable. Thus, the carbon matrix is generally obtained from pitch or phenolic resins. Heat treatment decomposes the pitch or phenolic to carbon. Many pores are formed during this conversion from a hydrocarbon to carbon. Thus, a dense and strong pore-free carbon/carbon composite is not easy to fabricate. 

Polyamic Acid-KOH-Polyimide Interactions. Table I shows C Is and K 2p data that demonstrates the effects of KOH and KOH-acetic acid (0.5% by volume) treatments on PI5878 polyamic acid surfaces. For the non-treated surface, C Is chemical shifts of 4.23 eV, 3.34 eV and 1.02 eV reflect acid, amide and "partially oxidized" bonding types. Treatment with KOH produced two effects (a) incorporation of potassium into the carbon matrix,... 

The introduction of sulfur functionalities to a carbon surface is usually done by heating carbons in the presence of elemental sulfur [183] or other sulfur-containing compounds, such as hydrogen sulfide [122,123], In this way, up to 10% of sulfur can be fixed to the carbon matrix. The temperature of heat treatment varies from 476 to 1273 K. The most common sulfur reactions on the carbon surface are addition to the carbon active sites, substitution of oxygen, and reaction with metals, leading to formation of sulfides. Moreover, a significant amount of CS2 can be deposited on the surface. Generally, it was proposed that at temperatures below 873 K, addition of H2S to the active sites of carbons... 

Hydrogen treatment at high temperatures has also been used for the removal of oxygen complexes. In this case, no carbon-hydrogen bonds are formed during the treatment in feet, a ftaction of the combined hydrogen is also eliminated from the carbon matrix during tliis process [95, 96]. 

Investigation of industrial potential for con- 77 3 version of cornstarch into D-glucose in a fluidized-bed immobilized enzyme reactor Investigation of effects of pre-treatments on 774 the structure and subsequent behaviour of the active carbon matrix as a support material for enzyme immobilization... 

Boron nitride derived from the borazine oligomer has been successfully used to replace the carbonaceous matrix in carbon fiber/carbon matrix composites (C/C) [15,18]. The carbon fiber/boron nitride matrix composites (C/BN) exhibit improved oxidation resistance over the C/C. Excellent mechanical strength and toughness have also been observed in the C/BN. As shown in Figure 2.16, both the flexural strength and modulus of pitch carbon fiber/BN specimens actually increase with extended heat treatment [18]. 

---