WAXS patterns

Inl y Casting Waxes. The three types of inlay casting waxes, ie, types A, B, and C, are used to produce wax patterns for the lost wax casting process in the production of cast gold inlays, crowns, and bridges. Some inlay wax is also used to produce patterns for acryflc restorations. 

Beat-Cured Restm. For optimum comfort and to impede further loss of chewing efficiency, close adaptation of the denture base to contiguous oral tissues is required, which necessitates custom-made appHances. Nearly all dentures are made of acryHc resins. A wax pattern is used to form a custom denture base in which the denture teeth are embedded. A plaster or dental-stone investment spHt mold of this wax denture base and teeth is prepared. The wax portion is removed and the surface of the resulting mold cavity is painted with a separating medium, usually an aqueous solution of alginate, to aid in the removal of the cured acryHc from the plaster mold. 

This process is used to produce intricate, thin-section parts with great dimensional accuracy, fine detail, and very smooth surfaces. All ferrous and nonferrous alloys can be cast in investment molds. Investment casting begins with expendable wax patterns that are assembled into clusters, then coated with a series of successively coarser ceramic slurries. The assembly is then fired in a furnace to dry and harden the ceramic shell and to melt out the wax, leaving a cavity into which molten metal is poured to form the casting. 

Casting by the lost wax method entails initially creating a core of clay covered with a layer of beeswax, and modeling the outer layer of the wax in the exact pattern of the desired cast. Once the wax pattern is made, the sequence of operations listed below is generally followed (Feinberg 1983 Ammen 1979) ... 

A mold is made from a refractory material to surround the wax pattern. 

Spinning a crystal during measurement of WAXS patterns is an old method that turns any scattering pattern into a fiber pattern. The rotational axis becomes the principal axis. Thereafter isotropization of the scattering data is simplified because the mathematical treatment can resort to fiber symmetry of the measured data. In the literature the method is addressed as the rotating-crystal method or oscillating-crystal method. 

If the orientation is uniaxial (i.e., fiber symmetrical), the strong peaks of polymer materials are, in general, found in specific regions of the pattern. The strong WAXS peaks are found close to the equator7 of the WAXS pattern. Thus it is good practice to let an offset WAXS detector monitor the equator region. 

Titania films prepared by the methods described above are, however, just partially crystalline. Although WAXS patterns indicate formation of anatase crystals of ca. 10-12nm in size (Fig. 9.3a), the electron microscopy study demonstrates that the elongated crystals are actually embedded into an amorphous mesoporous matrix (Fig. 9.3c). The degree of crystallinity for such films usually does not exceed 60% attempts to increase it by calcination at higher temperatures cause uncontrolled crystal growth, which leads to collapse of mesoporos-ity and a drastic decrease in the surface area (Fig. 9.3d). 

Morphological characteristics of LDH, MMT and their modified forms (OLDH and OMMT) have been discussed with respect to their WAXS patterns [23] (Fig. 24). The 20-values along the -axis can be converted to layer spacing values... 

The WAXS patterns of two nanocomposites at different LDH concentrations are shown in Fig. 55. The similarity of these patterns between the two systems is that the first three Bragg s reflections of LDH-C10 can be detected in both. This means that the LDH particles are not fully exfoliated in any of the matrices. 

Fig. 55 WAXS patterns of the EPDM-LDH nanocomposites (a) and XNBRLDH nanocomposites (b) (the number at the end of sample designation EL and XL indicates the amount of LDH-C10 in phr) [104]...

The conclusions made from the WAXS patterns of the nanocomposites could be further established by analyzing the micrographs of these materials. The micrographs for both the systems containing 7.5 phr of LDH-C10 are shown in Fig. 56. It is clear that in these nanocomposites, LDH-C10 particles were dispersed... 

Short range order in liquid-like systems as well as long range order in crystalline domains are reflected in WAXS-patterns very dearly. Some examples of calculated X-ray patterns from PTFE (Phase I), a smectic LC-phase and even a PE melt, show that our model covers a wide range of macromolecular structures running the whole scale from crystalline systems over mesophases up to polymer melts. The range of intra- and intermolecular order can be estimated fairly well with the help of density correlation functions. 

On the other hand, WAXS measurements of PE melt clearly indicate a range of intermolecular distance correlations of about 25 A [3]. Together with the relatively high density of polymer melts, the fact that the first interchain halo in WAXS patterns of oriented amorphous polymers tends to lie in the equatorial direction and the relatively high WAXS intensity of the interchain halo support the idea of parallel chain segments on the short range scale. 

The autocorrelation function (Fig. 2) shows clearly that a representative chain segment embracing about 5-7 CH2-units should be sufficiently long to describe the intramolecular interference modulation in the WAXS-pattern of a PE-melt completely up to distances of approx. 30 A. 

The structure factor of the model short range order regions and the experimental WAXS pattern are shown in Fig. 21. The strong Guinier scattering at... 

The correct calculation of WAXS patterns of Condis phases and smectic LC phases would provide us additional information, because in some of these systems, intramolecular torsions and rotations occur which do not affect the lateral chain packing. We chose the high-temperature phase of PTFE (phase I) and a SE-phase of a LC main-chain polyester as model systems. 

The effects of this transition on the WAXS pattern have been investigated in detail by Clark and Muus [27,28]. The local rotation of chain segments around the helix axis smears out the hkl-reflections along the layer lines leaving only the equatorial hkO-reflections and the intramolecular helix reflections near the meridian (Fig. 22). 

The WAXS pattern can be calculated in a quantitative way when we arrange 10 x 12 PTFE stems of length 40 A (two monomers) on a two-dimensional hexagonal lattice with a = 5.66 A (Fig. 24). Therefore, the lateral size of these Condis-crystals is at least 60 A. 

With our model we are in a good position to discuss the LC-main chain polymem in a smectic phase. It must be seen as a typical feature that only one single very strong interference appears. A representative WAXS-pattern of a smectic LC-polyester (Fig. 25, Fig. 26) is shown in Fig. 27. 

We conclude that the existence of side chain smectic LC-polymers is basically dependent on the length of the spacer. This length must be sufficiently large to allow rotation of segments in the mesogenic units as well as to allow a perfect separation of these units from the incompatible spacer-chain-complex. This hypothesis is qualitatively justified by finding analogous characteristics of WAXS-patterns as shown in this paper. 

Fig. 5.7 Representative WAXS patterns for PE-containing diblocks. Data for a PE-PEE diblock with Mn = 44 kg mol = 0.75 (Ryan el al. 1995). Top, 100 °C bottom, 140 °C.

The relative degree of crystallinity can also be estimated from the WAXS pattern from the ratio of the integrated intensity of the crystal peak to that of the total amorphous and crystalline scattering (Balta-Calleja and Vonk 1989). For PE, the amorphous scattering below the (110) peak (Fig. 5.7) is relatively insensitive to the degree of crystallinity, so the integrated area of the (110) reflection compared to the broad amorphous halo is directly proportional to XPE. However, the absolute degree of crystallinity cannot be determined in this way (Ryan et al. 1995). 

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