Relative crystallinity

Addition of H3B.THF to 1,5-cyclooctadiene gives a mixture of 9-borabicyclo[4.2.1]nonane and 9-borabicyclo[3.3.1]nonane. On heating, the [4.2.1] system isomerizes to the thermodynamically more stable [3.3.1] compound which is known as 9-BBN (Equation B1.12). As 9-BBN is crystalline, relatively stable to air and heat, and is available from commercial sources, this dialkylborane is a popular hydroborating agent. 

Calcium aluminate cements harden rapidly as soon as the massive precipitation of hydrates begins. This may be attributed to the fact that, unlike those of Portland cement, the major hydration products are crystalline. Relatively high proportions of water are taken up in the hydration reactions, the theoretical w/c ratios needed for complete hydration of CA being 1.14, 0.63 and 0.46 for the formation of CAHj, CjAHg -F AHj and CjAH -F 2AHj, respectively. For this reason, and also because of the rapid heat... 

H. F. Leach As mentioned briefly in the paper, the catalysts were examined by x-ray diffraction, and for all the samples used there was no apparent loss of crystallinity relative to the parent NaX. The catalysts were also characterized by measurement of surface area the value for NaX was 870 m gram" and for all the other zeolites lay within the range 840-900 m gram" We considered that these results indicated that very little decomposition of the zeolite to amorphous silica or silica-alumina occurred. 

Fig. 6.6.5. Pulse sequences for measuring proton and fluorine relaxation times selectively for different domains in a semicrystalline polymer, (a) The Torchia method as modified for Tf. (b) Sequence for Tfp. (c) (See next page) Pre-CP proton spin inversion for T . (d) (See next page) Pre-CP proton spin-locking for T . For (c) acquisitions from the two component sequences add (upper sequence) and subtract (lower sequence) to give a Freeman-Hill type of measurement. For measurement of Tf by sequence 5(d) the time t is varied. However, when this sequence is used to discriminate in favour of crystalline (relatively rigid) domains, it is fixed at a value between those of Tf for the crystalline and rigid domains. [CT = contact time SL = spin-lock time DD = high-power (dipolar) decoupling ACQ = acquisition.]...

Diffusion of solvent in the polymeric material may induce swelling causing changes in its internal structure if there are heterogeneities which induce stresses between more or less swollen areas. These areas may be amorphous (relatively accessible) or crystalline (relatively inaccessible). This swelling can also occitr when the kinetics of diffusion of the solvent create concentration gradients. 

Crystallinity Relative rigidity Softening temp, Tensile strength... 

PLA 15 wt%/v HMW PCL, XRD peaks of PLA PCL occur at diffraction angles of 2 = 20.11° and 23.2°, which correspond to the crystal planes (101) and (200), respectively. As indicated from Table 4.1, a higher degree of crystallinity (Xc) is presented for PLA 15wt%/v HMW PCL as opposed to PLA 15wt%/v LMW PCL, which is ascribed to HMW PCL with moderate crystallinity relative to amorphous-phase-dominant PLA with low crystallinity. 

CgH,3BrN202. A soil-acting herbicide. White crystalline solid, m.p. 158-159" C. It is a non-selective inhibitor of photosynthesis used for weed control In citrus and cane fruit plantations. It is relatively non-toxic to animal life. 

The relative intensity of a certain LEED diffraction spot is 0.25 at 300 K and 0.050 at 570 K using 390-eV electrons. Calculate the Debye temperature of the crystalline surface (in this case of Ru metal). 

One class of large molecules that was investigated relatively early was liquid crystals [37, 38], and in particular the group 4-n-alkyl-4 -cyanbiphenyl (mCB). These molecules fonu a highly crystalline surface adlayer, and STM images clearly show the characteristic shape of the molecule (figure B 1.19.8). 

The C-C linkage in tire polymeric [60]fullerene composite is highly unstable and, in turn, tire reversible [2+2] phototransfonnation leads to an almost quantitative recovery of tire crystalline fullerene. In contrast tire similarly conducted illumination of [70]fullerene films results in an irreversible and randomly occurring photodimerization. The important aspect which underlines tire markedly different reactivity of tire [60]fullerene polymer material relative to, for example, tire analogous [36]fullerene composites, is tire reversible transfomration of tire fomrer back to the initial fee phase. 

Order and dense packing are relative in tire context of tliese systems and depend on tire point of view. Usually tire tenn order is used in connection witli translational symmetry in molecular stmctures, i.e. in a two-dimensional monolayer witli a crystal stmcture. Dense packing in organic layers is connected witli tire density of crystalline polyetliylene. 

Many different approaches have been suggested as possible approaches to this problem, from the 1960s onwards [Verwer and Leusen 1998]. What is obvious from all of these ellorts is that this is an extremely difficult problem. Both thermodynamics and kinetics can be important in determining which crystalline form is obtained under a certain se1 of experimental conditions. Kinetic effects are particularly difficult to take into accouni and so are usually ignored. A proper treatment of the thermodynamic factors would lequire one to deal with the relative free energies of the different possible polymorphs... 

Crystalline silicon has a metallic luster and grayish color. Silicon is a relatively inert element, but it is attacked by halogens and dilute alkali. Most acids, except hydrofluoric, do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared, from 1.3 to 6.y... 

The metal has a silvery appearance and takes on a yellow tarnish when slightly oxidized. It is chemically reactive. A relatively large piece of plutonium is warm to the touch because of the energy given off in alpha decay. Larger pieces will produce enough heat to boil water. The metal readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or perchloric acid. The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cms. 

Nitronium salts are colourless, crystalline and very hygroscopic nitronium perchlorate and sulphate are unstable and liable to spontaneous decomposition, whereas nitronium tetrafluoroborate and other complex fluoro-salts are relatively stable. 

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