Fourier recycling

The use of the Harker sections is made easier when a few heavy atoms are present in the unit cell their Harker maxima can be recognized and used to locate the heavy atoms. If they have a sufficiently high atomic number, they can be used as a good initial model to which one can apply the so-called Method of Fourier Recycling, to obtain the light atom positions and then to recover the complete structure. 

Figure 8.7 Flow diagram of the Method of Fourier Recycling for single crystal data.

H is now possible to solve rather large crystal structures, including small proteins with more than 1000 non-hydrogen atoms, by real/reciprocal space Fourier recycling methods [95] - [99]. These are very lenghtly procedures, and a powerful PC may require four weeks or more without breaks. These major problems usually involve measuring synchrotron data. 

The feasibility of diffuse reflectance NIR, Fourier transform mid-IR and FT-Raman spectroscopy in combination with multivariate data analysis for in/ on-line compositional analysis of binary polymer blends found in household and industrial recyclates has been reported [121, 122]. In addition, a thorough chemometric analysis of the Raman spectral data was performed. 

The multiple-quantum (MQ)/MAS NMR is one of the 2D NMR methods, which is capable of averaging out the second-order quadrupolar interaction in nuclei with spin > 1/2 such as H, "B, O, etc. The "B MQ/ MAS NMR measurements on boron as contained in silyl-carborane hybrid Si-based polymer networks considered here. The molded samples are cut into small pieces to insert them into a 4-mm NMR rotor and spun at 12 kHz in a MAS probe. The observation frequency of the "B nucleus (spin number I = 3/2 and isotope natural abundance = 80.42%) is 96.3 MHz. Excitation of both the echo (—3Q) and anti echo (+3Q) coherences is achieved by using a three-pulse sequence with a zero quantum filter (z-filter). The widths of the first, second, and third pulses are 3.0 4.1 ps, 1.1-1.6 ps, and 19-28 ps, respectively. The z-filter is 20 ps. The recycle delay time is 6-15 s and the data point of FI (vertical) axis is 64 and for each the number of scans is 144. Then, the total measurement time is 15-38 h. The phase cycling used in this experiment consists of 12 phases. Boron phosphate (BPO4 3 = 0 ppm) is used as an external standard for "B. The chemical shift value of BPO4 is —3.60 ppm from BF3 O(C2H5)2 which is used as a standard reference in " B NMR in the liquid state. The transmitter frequency of " B is set on peak of BPO4 for a trustworthy chemical shift after Fourier transform." " ... 

A variety of pulse sequence programs were employed. A conventional cross polarization, single contact program was used to obtain spectra of Intact sediments. Contact times were varied from 200-3000 psec with a three sec recycle time. For dephaslng delay experiments, a 50 psec delay was Inserted prior to data collection. This delay consisted of two 25 ysec Intervals separated by a 10 psec, 180° refocusing pulse. Data was collected In 2K of memory, exponentially multiplied with 50 Hz of line broadening, and expanded to 8 K prior to Fourier transformation. All spectra are the result of 5000 accumulations. 

All activity measurements were conducted in an in-situ infrared reactor cell placed in the sample compartment of a DIGILAB 15C Fourier Transform Infrared (FTIR) Spectrometer. The reactor, described in detail elsewhere [11], consisted of two aluminum flanges with CaF2 IR transparent windows, a gas inlet and outlet, and two foil fast response thermocouples which were placed in direct contat with the catalyst. The reactor temperature was maintained constant by external heaters controlled by a temperature programmed controller. A Teflon coated recycle pump permitted to maintain near isothermal conditions and improve the mixing in the reactor. The reactor and associated lines were tested for activity at the highest temperature used, and it was found to have negligible activity. 

Several techniques have been developed to rapidly identify additives in plastics as part of an overall plastics recycling operation. Some techniques such as Fourier transform infrared (FTIR) can combine resin identification with information of the presence or absence of additives such as flame retardants or talc fillers [49, 62, 65]. The sliding spark technique developed at the University of Duisburg in Germany can identify a range of heavy metals along with the type of resin [68, 69]. 

The manual sorting method is labor intensive and requires operators to monitor an assembly line and sort out clear plastic bottles (PET) from the milk containers (HDPE) and colored plastic containers (LDPE, PP, PVC). The automated method can employ one of several analytical techniques, including X-ray fluorescence, mass spectroscopy, Fourier Transform Near Infrared (FT-NIR) spectroscopy, Fourier Transform Medium Infrared (FTIR) spectroscopy, or tribo-electric analysis, on the recycled plastic materials. The state of Rhode Island has a single stream process to sort out the recycled materials with optical sorting technology. The recycled materials include cardboard, paper, glass, metal, and plastics (Rhode Island 2013). 

In the Master s dissertation entitled Effect of natural and accelerated ageing on the properties of PET/PC (80/20) blend , recycled polyethylene terephthalate (rPET) was blended with PC (80/20 wt/wt), and then submitted to natural ageing in the city of Rio de Janeiro [17]. For comparison purposes, we also monitored the accelerated ageing of the blend in an appropriate chamber under the same conditions, 2,000 h of exposure were performed. The Fourier-Transform infrared spectroscopy revealed the tendency of the PET and PC carbonyl indices to decrease upon an increase in... 

Virgin and recycled polyethylene terephthalate (PET) was blended with polyether-imide (PEI) in proportions between 0 and 50 percent PEI content and samples were examined by differential scaiming calorimetry and Fourier transform infrared spectroscopy. All blends were completely miscible, as indicated by a single glass transition temperature which is dependent on blend composition. Crystallisation rates of PET were retarded strongly at 20 percent PEI content and above, but degree of crystallinity was easily determined from a linear correlation between a structural parameter measured spectroscopically and enthalpy of fusion. Trans conformer activation energy measurement confirmed the effects of PEI content on crystallisation of PET. 9 refs. 

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