Fillers, active amorphous

Fluid cracking catalysts manufactured prior to 1960 were amorphous mixtures of silica and alumina, combined in such a manner that the mixture could be spray dried into a roughly spherical shape about 70 microns in diameter. Today s cracking catalyst in addition contains an inert filler and zeolite the principle active ingredient 0. today s cracking catalysts. 

The first reactor-type thermoplastic polyolefin (R-TPO) was LLDPE/PP [Yamazaki and Eujimaki, 1970, 1972]. The three-component R-TPO s (PE with PP and EPR) soon followed [Strametz et al, 1975]. PE was also polymerized in the presence of active catalyst and an olefinic copolymer [Morita and Kashiwa, 1981]. Blending amorphous co-polyolefins with crystalline PO s (HDPE, LLDPE, PP), and a filler resulted in moldable blends, characterized by excellent sets of properties [Davis and Valaitis, 1993, 1994]. Blends of polycycloolefin (PCO) with a block copolymer (both polymerized in metallocene catalyzed process) and PE, were reported to show outstanding properties, viz. strength, modulus, heat resistance and toughness [Epple and Brekner, 1994]. 

Fig.l shows the XRD patterns of the residues of powder mixtures pyrolyzed at different temperatures. It can be found from these curves that at 1200°C, there is no obvious diffraction peaks except a broad peak for (3-SiC with very low intensity, the diffraction peaks of boron also disappeared. There are some small diffraction peaks of B4C when pyrolysed at 1300°C. Above 1400°C the intensities of diffraction peaks for (3-SiC increased and the peak for h-BN at 26° also appears. When the samples are heat-treated at high temperatures, several reactions may occur. At temperatures below 800°C, PCS will decompose to some hydrocarbons and solid residues. When the temperature increases to temperatures above 1000°C, the solid residues will gradually convert into amorphous SiC plus excessive carbon., then at temperatures above 1200°C, active filler (boron) will react with hydrocarbons and carbon to form B4C. At temperatures above 1300°C, the formed B4C and the unreacted boron will react with protective gas (N2) to form h-BN. When the temperature reaches 1400°C, SiOC phase in the materials begin to decompose into SiO and CO,... 

Silica fume. Silica fume (SF) is a waste product of manufacturing ferro-sihcon alloys. It consists of an extremely fine powder of amorphous silica. Average particle diameter is about 100 times smaller than that of Portland cement and the specific surface area is enormous 13000-30000 m /kg compared to 300-400 m /kg for common Portland cements. Silica fume shows an elevated pozzolanic activity and is also a very effective filler. For these reasons, addition of silica fume to Portland cement may lead to a very low porosity of the cement paste, increasing the strength and lowering the permeability. It is usually added in the proportion of 5 to 10 % and it is combined with the use of a superplasticizer in order to maintain adequate workability of the fresh concrete. 

The addition of the filler into a polysiloxane matrix will also influence the porosity of the resulting material. Differences in permeabihty between porous and amorphous sihcone membranes have been determined [73]. The authors concluded that the trcuisport of gcises through porous rubber membranes is primarily due to capihary flow-through pores, whereas the transport of gcises through amorphous rubber films is attributed to activated diffusion, hi facf structural analysis of a PMDS-sihca mixture by small-angle neutron... 

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