The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τc, complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τc compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τB, adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements. 相似文献
The reductive benzylation of aromatic and aliphatic aldehydes with benzylic halides is reported using a nickel/zinc catalyst system. In addition to benzylic halides, the first report on the addition of benzylic triflates, acetates, tosylates and tritylates to aldehydes is also presented. By this new method a range of alcohols was synthesized efficiently from aldehydes and benzylic substrates at room temperature in moderate to high yields. The mild reaction conditions and good functional group tolerance make this nickel‐catalyzed process synthetically useful for the synthesis of diverse benzylic alcohols.
Dense conductive ceramic composites of MgAl2O4 and MoSi2 were processed using combustion synthesis under‐load methodology. The starting reactants were blends of MoO3, SiO2, MgO, and Al powders. The study revealed that to obtain dense composite with homogeneous microstructure, 30 wt. % of MoSi2, 18.5 μm Al average particle size, and 175 MPa load are required. The produced dense composite was found to have a low apparent porosity (<1.0 vol. %), moderate density 4.61 g/cm3, and low electrical resistivity 0.3 Ωcm. The dense composite exhibited excellent thermodynamic stability between its phases at 1400°C in open atmosphere. 相似文献
Dy_2O_3 is a rare earth oxide having a number of advanced applications in various fields including protective or antireflective coatings, Main objective of this novel research work is to check the effect of Cr and Cu addition on different properties of Dy_2O_3 and achievement of antireflective thin films with enhanced abso rption. Thin films of these materials we re deposited using DC magnetron with reactive cosputtering. XRD studies reveals the crystalline nature of thin films having Dy_2O_3(222) reflection in all samples with Cr_2O_3(116) and CuO(111) reflections in Cr and Cu containing compositions. Field emission scanning electron microscopy demonstrates the homogeneous deposition of thin films with uniform shape, size and distribution of grains. Refractive index, extinction coefficient and absorption coefficient significantly increase while optical reflectance decreases with Cr and Cu mediation corroborating an improved antireflective mechanism. The imaginary part of dielectric constant is found to increase slightly with low tangent loss for Cr containing composition co nsidered favorable for energy storage applications. 相似文献
ABSTRACT: BACKGROUND: Coffee and tea consumption was hypothesized to interact with variants of vitamin D-receptor polymorphisms, but limited evidence exists. Here we determine for the first time whether increased coffee and tea consumption affects circulating levels of 25-hydroxyvitamin D in a cohort of Saudi adolescents. METHODS: A total of 330 randomly selected Saudi adolescents were included. Anthropometrics were recorded and fasting blood samples were analyzed for routine analysis of fasting glucose, lipid levels, calcium, albumin and phosphorous. Frequency of coffee and tea intake was noted. 25-hydroxyvitamin D levels were measured using enzyme-linked immunosorbent assays. RESULTS: Improved lipid profiles were observed in both boys and girls, as demonstrated by increased levels of HDL-cholesterol, even after controlling for age and BMI, among those consuming 9--12 cups of coffee/week. Vitamin D levels were significantly highest among those consuming 9--12 cups of tea/week in all subjects (p-value 0.009) independent of age, gender, BMI, physical activity and sun exposure. CONCLUSION: This study suggests a link between tea consumption and vitamin D levels in a cohort of Saudi adolescents, independent of age, BMI, gender, physical activity and sun exposure. These findings should be confirmed prospectively. 相似文献
The structure effect on corrosion inhibition of two amines and their derivatives is the main object of this article. The first amine was 1,8-diaminooctane and its ethoxylated (50 e.o.) 1,8-diaminooctane and propoxylated (50 p.o.) 1,8-diaminooctane. The second amine is the tetraethylenepentamine and its ethoxylated (50 e.o.) and propoxylated (50 p.o.) derivatives. The investigations were carried out by open circuit potential, potentiodynamic polarization, electrochemical impedance, quantum calculations and SEM measurements. The data obtained for the first amine showed the minimum inhibition efficiency (65.5%), meanwhile the maximum inhibition efficiency was 78.9% for its propoxylated derivative. On the other hand the maximium inhibition efficiency was 91% for the second propoxylated amine. The electronic properties; HOMO and LUMO energy levels, energy gap, dipole moment, polarizability, log P, total energy, charge densities, area/molecule and hydration energy have been calculated. The inhibition efficiency was calculated theoretically using the electronic parameters. From the obtained results, there is a significant difference between the inhibition efficiency of the electronic and the inhibition efficiency experimentally. The results were discussed on the light of the chemical structure of the used inhibitors. In general, the inhibition efficiency is affected by the shape and structure of the molecule. 相似文献