Crystal standard

TABLE 19. Typical C—F bond distances (in pm) in crystals, standard deviations a and number of observations n in various substructures... 

Low raw sugars (sugars with purities below that of refined sugar) and white centrifugal wash water are added to the thick juice in the melters to make standard liquor from which white sugar is crystallized. Standard liquor is usually filtered with diatomaceous earth before going to the vacuum pan. 

The crystal standard of (7r-cp)2Ti(NCO)2 has been determined and confirms that, in the solid state, the cyanate group is here N-bonded it was only in the last stages of the analysis that the 0-bonded alternative could be finally eliminated (i). Hexa-iV-cyanato complexes of ytterbium, erbium, and neodymium have been reported as quaternary onium salts (16) and reference made to the series of tetraethylammonium salts of [Ln(NCO)0] (Ln = Eu-Yb) (22) these results extend Table XLII. The ESR spectra of series of complexes CuL2(NCO)2 (L = an, or substituted an) have been interpreted to show Cu— N(CO)—Cu bridges with no indication of any Cu-0 interactions (19). The ESCA spectra of [M(NCO)4] (M = Mn, Co, Zn) have been recorded (12). 

Infrared measurements were recorded on a Perkin-Elmer Model 580B Spectrophotometer. Absorption data were obtained on NaCl crystals. Standard instrument conditions were used and a computer driven data station was used to assist in analyzing the spectra. 

Conical cooling crystallizer with settling zone according to Howard, vibrated crystallizer to prevent build-up of solid on the heating elements, fluidized-bed crystallizer system Krystal with cooling, evaporation or vacuum crystallization, DP-crystallizer system Escher-Wyss-Tsukishima, evaporation crystallizer with carrier gas by Robinson, vortex crystallizer Standard-MESSO. 

Menczel and Leslie (1990, 1993) and Menczel (1994, 1997) found three liquid crystal standards suitable for cooling calibration of DSCs ... 

The use of these standards was advantegous, because they had several liquid crystalline transitions well separated from each other. Unfortunately, these standards are no longer available. But ASTM issued a standard procedlure for cooling calibration (E2069-06), and they now recommend the following three liquid crystal standards ... 

Figure 2.16. Heating and cooling DSC curves of an E. Merck iiquid crystal standard CE-8 [(+)-(4-(2 -methylbutyl)phenyl-4 -n-octylbiphenyl-4-carboxylate] recorded on a Perkin-Elmer DSC7. Heating rate is 5°C/min, cooling rate is 5°C/min. In order of increasing temperature, the transitions are to Sf, Sf to S, Sa to Ch, and Ch to isotropic. [From Menczel and Leslie (1993), reproduced with permission of Springer-Verlag.]...

This paper has described in very general terms the unique problems encountered in the determination of the molecular packing in polymeric crystals. Standard crystallographic procedures lose their utility when dealing with such problems, and additional information, such as stereochemical constraints and packing energies, should be brought to bear in the problem. Finally, a method of structural refinement which is especially suited to polymeric structures should be employed in place of classical least squares methods. A subsequent paper will deal with the application of these principles and techniques to the determination of the crystal structures of several crystalline polyethers. 

Figure 11.5 shows the ACRT sequence that was also used for these high-x crystals. Standard bi-directional rotation is still employed with rapid accelera-tion/deceleration (in 1-2 s). From considerations of the simple model [5] it was seen that maximum rotation rates for these 20-mm diameter crystals should be between 4 and 30rpm. Also for these crystals short mn and stop times (8 and 1 s, respectively) were used as for standard crystals. To maximize the Ekman stirring, i.e. increase the vertical and horizontal flow velocities (to values of >R/%e), we... 

The use of Cu and Pt standards allowed the measurement of the composition of the first and second atomic layers (Figure 3.3.25). At an incident angle of 55° to the surface, only the surface atoms were exposed to the incident ion beam and hence the surface atomic layer composition could be determined using the Cu and Pt single crystal standards for calibration. Then the geometry was altered to an incident direction of 34° to the surface, which exposes the first and second atomic layers to the incident beam. This then provides a combined composition of the first and second atomic layers however, as the concentration of the first atomic layer has already been determined, it is possible to extract the composition of the second atomic layer. It was concluded that the surface atomic layer was composed of 80%... 

Temperature and heat flow calibrations were performed upon heating at 10 K/min with indium (Tm = 156.6 °C) and a liquid crystal standard (+)-4-n-hexyloxyphenyl-4 -(2 -methylbutyl)-biphenyl-4-carboxylate [20] (CE-3 from T.M. Leslie, University of Alabama smectic to cholesteric transition at 78.8 °C). The temperature and heat flow are considered to be within 0.10 K and 0.20 J/g, respectively. The calibrations were checked at regular intervals during the DSC studies by performing check runs using CE-3 and indium. 

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