Different Degrees Of Crystallinity Research Articles

Genesis of Clay Mineral Assemblages and Micropaleoclimatic Implications in the Tertiary Powder River Basin, Wyoming: ABSTRACT

An x-ray diffraction (XRD) study was undertaken on the clay mineralogy of the early Tertiary coal-bearing sequences of the Powder River basin. The vertical and lateral distribution of alternating fluvial conglomerates, sandstones, mudstones, shales, coals, and paleosols reveals a transition from alluvial fans along the basin margin to an alluvial plain and peat bogs basinward. Samples included unweathered shales and mudstones from a borehole and a variety of corresponding surface outcrop samples of Cambrian to Eocene age. Samples older than Tertiary were collected along the basin margin specifically to determine the potential source of parent material during Tertiary sedimentation. XRD analyses were performed on the <2-{mu}m fraction prepared as oriented aggregates. To investigate the materials in their natural state, no chemical pre-treatments the authors applied before the analysis. A series of specific post-treatments, consisting of catonic saturation (Li+, K+), a solution with polyalcohols, heating, acid attack and hydrazine saturation was selectively applied. These post-treatments permit a good discrimination between the mimetic clay minerals such as smectite and illite-smectite mixed layers that constitute the bulk of the clay fraction in the Tertiary rocks. When analyzed only using routine XRD, these swelling minerals are apparently uniformly distributed in the fluvial sedimentary rocksmore » and are better interpreted as a single smectitic population. However, the post-treatments clearly differentiate both qualitatively and quantitatively this smectitic stock. Other clays include illite and kaolinite, which have different degrees of crystallinity, and minor interstratified clays (i.e., illite-chlorite, chlorite-smectite). The clay minerals in pre-Tertiary (and pedogenic) materials are different from those in the Tertiary rocks.« less

The effect of heat setting on the elastic and viscoelastic properties of nylon-6 films

Abstract The elastic and viscoelastic properties of nylon-6 films with different structural forms and different degrees of crystallinity, obtained by heat setting nylon-6 films at various temperatures, without constraint, have been investigated. The elastic modulus increases with increasing degree of crystallinity. The values of the transverse elastic moduli for completely amorphous and completely crystalline samples have been calculated on the basis of these results. The measurements of dynamic mechanical properties were carried out at two different frequencies, viz., 11 Hz and 110 Hz, over a range of temperature from room temperature to 150°C under ambient conditions of humidity. It is observed that the moisture content increases whereas the glass transition temperature decreases with increasing temperature of pretreatment. The activation energy of the α transition has also been calculated.

Nature of the protonic species and the gel—crystal transition in hydrated zirconium phosphate

Various samples of hydrated zirconium hydrogen phosphate Zr(HPO 4) 2· nH 2O have been prepared using different methods. The three main types of the phosphate, corresponding to a powdered gel, a transparent monolithic gel and crystals, have different degrees of crystallinity, water content and conductivity. The phosphates were studied using differential scanning calorimetry, thermogravimetry, X-ray diffraction and infrared and Raman spectroscopy. The results allow the composition of this compound, the nature of the protonic species and the correlation between structural features and the conductivity mechanism, to be established.

A comparison between the magnetic quenching of positronium in atactic polypropylene and that in isotactic polypropylene

The properties of Ps-like systems in atactic and isotactic polypropylene were investigated by lifetime measurements and by magnetic quenching experiments. The magnetic quenching results are markedly different: in atactic polypropylene they indicate the formation of an electron-positron bound system, 'swollen' in comparison with a Ps atom in free space. The magnetic quenching for isotactic polypropylene is anomalously high at low fields and seems to suggest the existence of two Ps-like centres, related to regions with different degrees of crystallinity.

Carbon-13 Nuclear Magnetic Resonance of 3,4/cis-1,4-polyisoprenes Prepared with Fe(acac)3-Al(i-Bu)3Catalyst

Abstract 3,4/cis-1,4-Polyisoprenes were prepared with Fe(acac)3-Al(i-Bu)3 catalyst. These polymers are of interest because of their higher 3,4 content and different degree of crystallinity. The 13 C-NMR spectra of these polymers were much more complex than those previously reported and were assigned using slightly modified empirical parameters based on Gronski et al. In order to further clarify the assignments, hydrogenation of the polymers was carried out, and the 13 C-NMR spectra of the hydrogenated polymers were partially assigned. Based on these assignments, it was found that the existence of long sequences of vinyl monomer units might be a favorable factor for the formation of partially crystallized polymer. Finally, the 13C-spin relaxation times T 1, as well as their temperature dependence, were also measured in chloroform-d 1 solvent at 50 MHz, and the Arrhenius activation energy was estimated.

Saccharification of cellulose samples by acid hydrolysis.

Heterogeneous hydrolysis of three cellulose species, Cotton linter (C), NBSP (P) and Regenerated cellulose (R) having a different degree of crystallinity, and homogeneous hydrolysis of P sample were carried out using sulfuric acid. The following results were obtained.The rate of hydrolysis was greater in such a sample with a low crystallinity, and it was in the order of C<P<R sample. When hydrolyzed with 3N H2SO4 at 100°C, _??_, _??_and Polydispersity (PD) initially decreased rapidly and then became constant. The leveling off values of _??_, _??_and PD were about 700, 200, and 3.5, respectively (C, P sample). The corresponding values for R sample were about 50, 40 and 1.2. In case of homogeneous system of P sample after 30min hydrolysis, _??_, _??_and PD were about 140, 80 and 1.8, respectively. _??_and _??_decreased further with hydrolysis time.The yield of sugar was very low in the heterogeneous system, but high in the homogeneous system (attained about 100% at 23°C for 7hr). In case of the homogeneous hydrolysis of P sample (72% H2SO4, 23°C, 7hr), the yields of glucose, cellobiose and cellotriose were 40.1, 16.8 and 10.0%, respectively. Furthermore, when P sample was hydrolyzed with 72% H2SO4 at 23°C for 5hr (primary), diluted to 1% and hydrolyzed again at 60°C for lhr (secondary), the yields of glucose, cellobiose and cellotriose increased to 45.7, 32.7 and 14.1%, respectively.

A study of the electrical conductivity of amorphous-crystalline selenium mixtures

A series of compressed powder samples of a double-phase selenium mixture were prepared with various fractional volumes of amorphous (a) and crystalline (c) phases. The direct current properties of the samples were measured and are discussed. The activation energy was found to decrease from 1.8 eV (for the 90% amorphous-10% crystalline sample) to 0.67 eV (for the 100% crystalline sample). For the same range of fractional volumes, the conductivity σ m of the mixture at room temperatures was found to increase from 5.5 × 10 −13 Ω −1 cm −1 to 5.25 × 10 −7 Ω −1 cm −1 ,and the pre-exponential factor σ 0 increased from 5×10 −4 Ω −1 cm −1 to 2.75 Ω −1 cm −1 . An empirical formula to fit the measured conductivity data over the entire range of the double-phase mixture is proposed. This formula was also tested for massive selenium samples of different degrees of crystallinity (defined from X-ray measurements) and very satisfactory results were obtained.

Kinetic aspects of kaolinite acid dissolution: II. Mineral after mechanochemical treatment

The kinetics and mechanism of acid dissolution of two kaolinites with different degrees of crystallinity were studied. These minerals were obtained through mechanochemical treatment of a well crystallized kaolinite. The parameters obtained through a nucleation and growth model (rate constant, pre-exponential factor and apparent activation energy) are analyzed. The reaction rates are strongly dependent on the concentration of superficial defects created through the mechanochemical treatment. Cation-exchange capacity is used as a representative parameter to describe the observed increase in reaction rates.

Determination of cellulose accessibility by differential scanning calorimetry

AbstractThe thermal behavior of various cellulose samples with different degrees of crystallinity as measured by X‐ray diffraction techniques was studied with a differential scanning calorimeter (DSC). The broad endothermic peak which appears between 110 and 160°C is due to loss of absorbed (bound) water. Since a direct relationship was observed between the area of this peak and the crystallinity of the sample, a new procedure for estimating cellulose accessibility (which is related to crystallinity) was proposed and developed. DSC curves obtained on cellulose samples preconditioned at certain constant relative humidities were used to determine sample accessibilities by the proposed method. The accessibility values obtained by DSC showed excellent agreement with crystallinity values determined by more traditional techniques. Completely amorphous cellulose was obtained by anhydrous deacetylation of cellulose triacetate and was used as the standard amorphous cellulose material.

Effect of the degree of crystallinity on the friction and wear of poly(ethylene terephthalate) under water lubrication

By means of a pin-on-disk type of wear-testing apparatus, coefficients of friction and wear depths of various poly(ethylene terephthalate) (PET) specimens with different degrees of crystallinity were measured at sliding speeds of 0.01 and 0.1 m s −1 under a constant load of 10 N with water lubrication. The coefficients of friction with lubrication were lower than those for unlubricated conditions and there was little dependence on the degree of crystallinity. However, the wear rates with lubrication were higher than those obtained under dry conditions and decreased with increasing degree of crystallinity, in contrast with the unlubricated wear rates. These results are discussed on the basis of the plasticization of worn polymer surfaces by water. The worn surfaces and frictional tracks were observed by optical and electron microscopy. The frictional tracks for low crystallinity PET were smooth with many fine scratches and characteristic of transfer wear. For high crystallinity, frictional tracks were somewhat different from those for low crystallinity PET.

A comparative study of the crystallinity degree of pet by DTA, X-ray diffraction and iodine sorption techniques

PET fibres, with different degrees of crystallinity induced by different thermal treatments have been investigated by DTA, X-ray diffraction and iodine sorption techniques and the results have been compared with the mechanical properties of the yarns spun from these fibres. Values for the degree of crystallinity have been plotted vs. temperature at which thermal treatment was carried out and the curves obtained have been compared with graphs of mechanical properties vs. temperature. Good agreement of the results from the three different methods was obtained.

Thermal Neutron Scattering Kernel for Polyethylene of Various Degrees of Crystallinity

AbstractA thermal neutron inelastic scattering kernel for polyethylene (PE) of any degree of crystallinity based on a recently proposed dynamic model is suggested. The dynamic model takes proper account of the anisotropic linear chain structure of PE that gives rise to an acoustic phonon frequency distribution function, which is quite different from the usual Debye type, and that has been successful in explaining the observed temperature variation of the specific heat of PE of different degrees of crystallinity. The expressions for zero-phonon and one-phonon neutron scattering cross sections are derived by making use of the frequency distribution function. The kernel incorporates the contribution of two-phonon acoustic modes and also that of optical modes. The kernel has been used to calculate the total scattering cross sections of thermal neutrons from crystalline and noncrystalline PE, including amorphous PE. The calculated values of total scattering cross sections are in reasonable agreement with the e...

Main features of polypropylene crystallization from the quenched state

AbstractThe structure formation during transition from the quenched into the crystalline state has been studied for isotactic polypropylene by wide‐angle X‐ray scattering. Based on the temperature dependence of the shape of the curve of amorphous scattering the composition of samples with different degrees of crystallinity and different content of paracrystalline form was determined quantitatively. By means of IR spectroscopy it was shown that stretching of quenched polypropylene leads to the freezing of the conformational array in macromolecules. This freezing hinders the transition into the crystalline state upon heating.

Intrinsic birefringence of nylon 6

Different values are reported in the literature for the intrinsic birefringence of the crystalline (Δn) and the amorphous (Δn) phases in nylon 6. Mostly, these values have either been determined by extrapolation (and then it is assumed that Δn = Δn) or calculated theoretically. In this study, intrinsic birefringence values Δn and Δn for nylon 6 were determined using the Samuels two-phase model which correlates sonic modulus with structural parameters. Three series of fiber samples were used: (1) isotropic samples of different degrees of crystallinity for estimation of E and E moduli at two temperatures. The following modulus values were obtained: 1.62 × 109 and 6.66 × 109 N/m2 for 28.5°C, and 1.81 × 109 and 6.71 × 109 N/m2 for −20°C; (2) anisotropic, amorphous fiber samples for estimation of Δn = 0.076 and E = 1.63 × 109 N/m2 at 28.5°C; (3) semicrystalline samples of various draw ratios for estimations of Δn = 0.089 and Δn = 0.078. All measurements were carried out with carefully dried samples to avoid erroneous results caused by moisture.

The effect of noncrystallinity on the α→ε transition of Fe85B14Si1 alloy

The electrical resistance behavior under pressure of an Fe85B14Si1 alloy in the as-cast amorphous condition and in three different annealed states with different degrees of crystallinity was studied. We found that in the as-cast amorphous sample there is no measurable resistance-jump with application of pressure up to about 300 kbar. Subsequent annealing of the amorphous sample for different lengths of time results in the reappearance of the resistance-jump with different amplitudes.

Dynamics of noncrystalline polyethylene

AbstractAn anisotropic dispersive continuum model for the collective modes of polyethylene of any degree of crystallinity is suggested. The model successfully explains the experimental results for specific heat of polyethylene of 100%, 84.1%, 74.5%, 45.9%, and 0% crystallinity in the temperature range 2.5–60 K, where the specific heat of amorphous polyethylene is markedly different from that of crystalline polyethylene. The variation of specific heat with degree of crystallinity can be obtained by varying only one parameter θ1 (characterizing the low energy cubic modes), keeping the other two parameters (characterizing the transverse and longitudinal chain modes) constant. Thus, in going from the crystalline to the amorphous state, it is essentially the interchain binding which is affected, the chain modes being left undisturbed. Using the calculated values of specific heat for varying degrees of crystallinity, the variation of θ1 with the crystallinity is reported. Observed high‐temperature specific heats for crystalline and amorphous polyethylene up to 300 K are also explained using additional optical modes. The anisotropic Mössbauer elastic scattering fraction (MESF) for polyethylene of different degrees of crystallinity in the temperature range 0–425 K is obtained. For a given degree of crystallinity there is marked anisotropy in MESF which increases with increase in temperature. For a given direction, longitudinal or transverse, there is a large difference between the MESF of 0% and 100% crystalline polyethylene, which also increases with the increase in temperature. It is quite possible that the MESF experiment may prove to be more sensitive than the usual method for the determination of degree of crystallinity.

Infra red and electron spin resonance studies of clays representative of the sedimentary evolution of the Basin of Autun

AbstractThree samples have been selected to represent the sedimentary variations of the Basin of Autun. IR and ESR techniques have been used to study the sheet composition of the different kinds of clays. The kaolinites are fire clays with two different degrees of crystallinity. The illites have a muscovite origin and belong to the 1 M polytype with mainly tetrahedral Al3+ and Fe3+ substitutions but also with some octahedral Fe3+ substitutions. The dioctahedral phyllosilicates contain mostly divalent and trivalent octahedral substitutions.

Electrochromism and local order in amorphous WO3

WO3 films prepared under different conditions (evaporation, reactive sputtering and spraying of aqueous solutions of metatungstic acid) differ by orders of magnitude in their electrochromic sensitivity. Diffuse X-ray studies show the evaporated and sputtered films to be amorphous and to consists of a disordered network of corner sharing WO6 octahedra. Sprayed films have different degrees of crystallinity depending on spraying conditions. From differential scanning calorimetry we conclude that the crystal water present in most films strongly affects the local order of the corner sharing octahedra. We find that crystal water not only provides a high ionic conductivity which is conditional for a fast electrochromic reaction but also stabilises electrocatalytically active surface sites for fast hydrogen or Li exchange with the adjacent electrolyte.

Effect of the structure and chemical composition of polymers on the concentration and type of motion of excess charge carriers, formed by exposure to ionizing radiation

A crystal counter was used to determine values of ʌμτ (ʌ is the radiation yield of charge carriers, μ, microscopic mobility; τ, life time of the quasi-free charge carrier) for PE with different degrees of crystallinity and PMMA. Relations between ʌμτ and temperature were also examined for PE. It was established that the degree of crystallinity and temperature have a slight effect on the value of ʌμτ. On transition from PE to PMMA the value of ʌμτ decreases by one order of magnitude. It was shown using PS that molecular weight M υ has a slight effect on radiation electrical conductivity σ r while increasing it from 10 5 to 10 7. A correlation was derived between the variation of material density (as a result of pre-treatment and compression) and the variation of the value of σ r.

On the mechanism of ion exchange in zirconium phosphates—XIV The effect of crystallinity on NH 4+/H + exchange of α-zirconium phosphate

The ion exchange behavior of zirconium phosphates possessing different degrees of crystallinity was examined for the NH 4 +/H + system. In the most crystalline exchangers ammonium ion is initially taken into solid-solution without phase change. This initial uptake is followed by conversion of the solid solution to a fully exchanged ammonium ion phase Zr(NH 4PO 4) 2·H 2O. The composition range of the solid solution increases with decreasing crystallinity until, in the amorphous exchanger it covers the entire range of ammonium ion uptake. The exchange process is reversible for the amorphous exchanger with K = 7·4 × 10 −5. However, with the more crystalline exchangers a half-exchanged phase, Zr(NH 4)H(PO 4) 2·0·33H 2O, is obtained when H + replaces NH 4 +. These results differ significantly from other published data.