Producing Polydicyclopentadiene from Lower-Grade Dicyclopentadiene

Russian Engineering Research - Polymer samples based on polydicyclopentadiene produced from Russian dicyclopentadiene are investigated by thermogravimetric analysis and differential scanning...     

Thermal Properties of (Zr,TM)B2 Solid Solutions with TM = Hf,Nb, W,Ti, and Y

The thermal properties were investigated for hot‐pressed zirconium diboride—transition‐metal boride solid solutions. The transition‐metal additives included hafnium, niobium, tungsten, titanium, and yttrium. The nominal additions were equivalent to 3 at.% of each metal with respect to zirconium. Powders were hot‐pressed to nearly full density at 2150°C using 0.5 wt% carbon as a sintering aid. Thermal diffusivity was measured using the laser flash method. Thermal conductivity was calculated from the thermal diffusivity results using temperature‐dependent values for density and heat capacity. At 25°C, the thermal conductivity ranged from 88 to 34 W·(m·K)^?1 for specimens with various additives. Electrical resistivity measurements and the Wiedemann–Franz law were used to calculate the electron contribution of the thermal conductivity and revealed that thermal conductivity was dominated by the electron contribution. The decrease in thermal conductivity correlated with a decrease in unit cell volume, indicating that lattice strain may affect both phonon and electron transport in ZrB₂.     

Thermal Expansion of Alkaline‐Doped Lanthanum Ferrite Near the Néel Temperature

The thermal expansion and magnetic behaviors of divalent, alkaline‐doped lanthanum ferrites (La_0.9M_0.1FeO₃, M=Ca, Sr, Ba) were assessed using a combination of dilatometry, magnetometry, time‐of‐flight neutron diffraction, and high‐temperature X‐ray diffraction. Néel temperatures were determined through vibrating sample magnetometry and correlated well with changes in thermal expansion behavior observed during both dilatometry and X‐ray diffraction. The Néel temperatures observed for pure, Ca‐doped, Sr‐doped, and Ba‐doped lanthanum ferrites were 471°C, 351°C, 465°C, and 466°C, respectively. The effect of divalent substitutions on the magnetic behavior are attributed to charge compensation mechanisms and structural changes in the material.     

Improved electro-assisted removal of phosphates and nitrates using mesoporous carbon aerogels with controlled porosity

Three-activated carbon aerogels were synthesized by CO₂ activation of the materials prepared by the polycondensation of resorcinol and formaldehyde mixtures followed by supercritical drying. The obtained carbon aerogels were characterized and used as electrode materials for the electrosorption of sodium phosphate and nitrate. X-ray diffraction and Raman spectroscopy showed the dependence of the structural ordering of the aerogels with the resorcinol/catalyst ratio and the extent of activation. The electrosorption capacitance evaluated by cyclic voltammetry revealed large values for the activated samples containing a large contribution of mesopores, regardless the electrolyte salt. Due to an adequate combination of chemical and porous features, the desalting capacity of the activated carbon aerogel electrodes exceeded that of the as-prepared materials. The evaluation of the kinetic properties by chronocoulometric relaxation and impedance spectroscopy showed a decrease of time constant and resistances for highly mesoporous activated samples. A high deionization capacity and fast electrode discharge was detected for the deionization of sodium nitrate on the highly mesoporous activated aerogel. Data also showed the efficient electrosorption of ionic species on consecutive charge/discharge cycles, confirming the stability of the aerogel electrodes at the high applied potentials.     

Drying dynamics of polymers films by an interferometric technique

We analyze a simple laser reflectivity measurement as a tool to monitor the drying kinetics of transparent polymer films. The reflectivity signal of a laser beam at normal incidence shows oscillations due to interference arising from multiple reflection of the laser light within the drying film. We develop a model to interpret the reflectivity curves in terms of time evolving refractive indices at the top and bottom of the film. We present results of the drying kinetics of transparent alkyd films on a glass substrate of high refractive index. Data shows a clear hallmark indicating the evolution of the crosslinking process. From the reflectivity curves, the time evolution of the refractive indices at the top and bottom is obtained. Assuming a linear-gradient of the refractive index along the depth of the film the average refractive index and consequently the film thickness as a function of time are estimated. Clear features in the time evolution of the refractive indices and thickness, correlate well with qualitative “dust”, “touch” and “fingerprint” drying times. Additionally, we present some preliminary results for water based latex binders, where scattering of light is present, showing that this simple optical technique could be extended for studying latex film formation.     

Tuning of dielectric and ferroelectric properties in single phase BiFeO3 ceramics with controlled Fe/Fe ratio

Single phase multiferroic BiFeO₃ (BFO) ceramics were synthesized with controllable amount of Fe²⁺ and oxygen vacancies in a very wide concentration range. Double ferroelectric hysteresis loops are observed in fresh BFO ceramics at room temperature without any aging processes. Detailed study shows that this is due to the defect dipoles which have preferential orientations antiparallel to the direction of spontaneous polarization, providing a driving force for domain back-switching. The dielectric constant of BFO could be enormously enhanced by 100 times by increasing the Fe²⁺ content, employing a polaronic relaxation process.     

Long-Term Spinal Ventral Root Reimplantation,but not Bone Marrow Mononuclear Cell Treatment,Positively Influences Ultrastructural Synapse Recovery and Motor Axonal Regrowth

We recently proposed a new surgical approach to treat ventral root avulsion, resulting in motoneuron protection. The present work combined such a surgical approach with bone marrow mononuclear cells (MC) therapy. Therefore, MC were added to the site of reimplantation. Female Lewis rats (seven weeks old) were subjected to unilateral ventral root avulsion (VRA) at L4, L5 and L6 levels and divided into the following groups (n = 5 for each group): Avulsion, sealant reimplanted roots and sealant reimplanted roots plus MC. After four weeks and 12 weeks post-surgery, the lumbar intumescences were processed by transmission electron microscopy, to analyze synaptic inputs to the repaired α motoneurons. Also, the ipsi and contralateral sciatic nerves were processed for axon counting and morphometry. The ultrastructural results indicated a significant preservation of inhibitory pre-synaptic boutons in the groups repaired with sealant alone and associated with MC therapy. Moreover, the average number of axons was higher in treated groups when compared to avulsion only. Complementary to the fiber counting, the morphometric analysis of axonal diameter and “g” ratio demonstrated that root reimplantation improved the motor component recovery. In conclusion, the data herein demonstrate that root reimplantation at the lesion site may be considered a therapeutic approach, following proximal lesions in the interface of central nervous system (CNS) and peripheral nervous system (PNS), and that MC therapy does not further improve the regenerative recovery, up to 12 weeks post lesion.     

Influence of Waste Glass Powder as an Aluminosilicate Precursor in Synthesizing Ternary Blended Alkali-Activated Binder

Silicon - The formation of alkali-activated binders from industrial end products and landfill materials attracts considerable interest in construction technology since it diminishes the waste...