Sieve diffraction pattern

Zeolites. In heterogeneous catalysis porosity is nearly always of essential importance. In most cases porous materials are synthesized using the above de.scribed sol-gel techniques resulting in so-called amorphous catalysts. Porosity is introduced in the agglomeration process in which the sol is transformed into a gel. From X-ray Diffraction patterns it is clear that the material shows only weak broad lines, characteristic of non-crystalline materials. Silica and alumina are typical examples. Zeolites are an exception they are crystalline materials but nevertheless exhibit high (micro) porosity. Zeolites belong to the class of molecular sieves, which are porous solids with pores of molecular dimensions, i.e., typically the pore diameter ranges from 0.3 to 10 nm. Examples of molecular sieves are carbons, oxides and zeolites. 

TUD-1 is an amorphous material. Unlike crystalhne stractnres, it has no characteristic x-ray diffraction pattern. Figure 41.1 illustrates the pore diameter of TUD-1 in comparison to some major molecular sieves - ZSM-5, Zeohte Y, and MCM-41. It is important to note that the pore diameter of TUD-1 can be varied from about 40A to 250 A. 

A complete particle-size analysis can require the use of various analysis technologies. A microscopic examination may be performed before the sieve analysis, which in turn can be followed by a sedimentation analysis or the recording and the evaluation of a diffraction pattern. 

There is no systematic nomenclature developed for molecular sieve materials. The discoverer of a synthehc species based on a characteristic X-ray powder diffraction pattern and chemical composihon typicaUy assigns trivial symbols. The early syn-thehc materials discovered by Milton, Breck and coworkers at Uruon Carbide used the modem Lahn alphabet, for example, zeoHtes A, B, X, Y, L. The use of the Greek alphabet was inihated by Mobil and Union Carbide with the zeoHtes alpha, beta, omega. Many of the synthetic zeoHtes which have the structural topology of mineral zeoHte species were assigned the name of the mineral, for example, syn-thehc mordenite, chabazite, erionite and offretite.The molecular sieve Hterature is replete with acronyms ZSM-5, -11, ZK-4 (Mobil), EU-1, FU-1, NU-1 (ICI), LZ-210, AlPO, SAPO, MeAPO, etc. (Union Carbide, UOP) and ECR-1 (Exxon). The one pubHcaHon on nomenclature by lUPAC in 1979 is Hmited to the then-known zeoHte-type materials [3]. 

Silicates comprise more than 95% by weight of the earth s crust and mantle, and are widely used in glasses, ceramics, sieves, catalysts, and electronic devices. Crystals of silicates are often hard, and may show considerable extinction in their diffraction pattern, which means not only that small samples must be used, but also that ambient temperatures may be adequate for charge density studies.2... 

The X-ray powder diffraction patterns of the parent materials showed the hexagonal structure characteristic for MCM-41 and SBA-15, and the cubic structure for MCM-48, respectively. All the patterns matched well with the reported patterns, confirming the successful synthesis of the mesoporous molecular sieves. The intensity of the reflection did not change essentially upon loading the carrier with the organometallic complexes, nor after a catalytic cycle, showing that the mesoporous structures were not affected by incorporation of the catalyst. 

Mineral matter was a Deis ter table concentrate from Robena mine coal. It contained 68% pyrite and less than 4% organic material. The remainder was largely clay. In one case, a handpicked sample taken from a pyrite nodule found in a Pittsburgh seam coal was used. The microcrystals were crushed and sieved to 325 x 400 mesh. X-ray diffraction analysis indicated the only major component was pyrite, with a trace of marcasite also present. After heating in tetralin at 450°C for 15 min., the X-ray diffraction patterns of the recovered microcrystals indicated conversion was complete to pyrrhotite 1C. The coal was hvB, Homestead Mine, Kentucky, ground to pass 200 mesh. Ash and pyrite contents were 16.8% and 4.9%, respectively. The asphaltene was a homogenized mixture of samples isolated from liquid products derived from Pittsburgh seam, hvA coal. Its ash content was <0.1%( ). 

Crystalline material is gronnd into eqniaxial, randomly oriented grains of abont 50 pm. Appropriate sieves can be nsed. The thin layer of crystals is spread onto a glass microscope slide or a holder specially designed for the particnlar x-ray diffraction setup. If there is preferred rather than random orientation of the grains, the diffraction pattern will be distorted. 

The textiuai characteristics of the samples as a function of heating temperature and duration are listed in Table 1. From these data, it appears that the increase of heating temperature fevours the formation of large pore mesoporous molecular sieves. Too long heating at higher temperature, 100°C for exan le, will however lead to the destruction of the conqx>imds. Their X-ray diffraction pattern will not show any... 

Finally, the chemical stability of the catalysts employed in this study was tested by means of XRD and EDXS analyses. The examination of fresh and used catalysts shows that during the reaction course metal ions are slowly leached into the aqueous solution, which can be attributed either to the temperature of operation or the presence of complexing carboxylic acids and benzoquinones in the liquid-phase. Contrary to the results obtained in continuous-flow fixed-bed reactors [8, 9], the extent of catalyst dissolution in the slurry reactor was considerable. This is probably due to the higher accumulation of benzoquinones which are known to form stable complexes with metal ions. Examination of the X-ray powder diffraction patterns of the molecular sieves before and after the liquid-phase phenol oxidation... 

Figure 8. X-ray powder diffraction patterns of molecular sieves before and after liquid-phase phenol oxidation performed in a semibatch slurry reactor at 403 K.

For SAPO-11 type materials it was observed (29) that the as synthesized SYN (with di-n propylamine template) the calcined (CAL), hydrated (WAT) and cyclohexane (CYC) saturated samples exhibit different XRD patterns as shown in fig.5. As for other molecular sieves it was important to determine if silicon was incorporated into the AIPO4 framework or not and subsequently if basic or acidic properties were induced depending if Si " was substituting Al or P ", respectively. The X-ray diffraction pattern analysis allowed us to show that A1 and P atoms are strictly alternate and that the material crystallizes in the non centro symmetric Ima2 space group with a = 1.867 (2), b= 1.3373 (2) and c = 0.84220 (9) nm (33). The channels along c axis are elliptical and are occupied by the di-n propylamine molecules. Disordered domains were also evidenced presumably... 

Diffraction Pattern of Undamaged Sieve Cloth (Spatial Filter)... 

Figure 3.6. Optical methods can be used to discover damaged apeitures in a sieving surface [22, 23, 24]. a) Diffraction pattern of an undamaged sieve mesh, b) Optical spatial filtering system used to detect sieve damage, c) Photogtaph of a damaged electroformed sieve surface, d) Spatially filtered image of the damaged sieve of (c).

Recent applications of the dynamic diffraction experimental techniques were mostly in the areas of temperature-induced dehydration processes in natural zeolites, hydrothermal crystallization of aluminosilicate and aluminophosphate microporous materials, thermal decomposition of layer silicate minerals, high-temperature synthesis of advanced ceramics, and hydrothermal ion-exchange and conversion processes in synthetic molecular sieves. The time-resolved powder diffraction patterns relative to the isothermal nucleation and growth process of zeoUte-A by the hydrothermal treatment of activated metakaollnite is shown in Figure 6. 

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