Paramagnetic Meissner Effect

The explanation for the paramagnetic Meissner effect (PME) in high-temperature superconductors (HTSC) and niobium disks, distinct from previous discussions, is proposed. It is based on the impurity mechanism of high-temperature superconductivity and the general localization approach to the superconductivity problem. Turns of the local magnetic moments of the two-level systems are considered to be the cause of this effect in HTSC. The estimations of the magnetic moment magnitude and the magnetic moment concentration are given. In niobium disks, this effect is also explained by turns of the local magnetic moments, but of another nature. The role of the layered structure is demonstrated. It is shown that the proposed models can explain all available experimental facts. The connection between this effect and the electric field effect in HTSC is discussed.     

Paramagnetic Meissner Effect

The explanation for the paramagnetic Meissner effect (PME) in high-temperature superconductors (HTSC) and niobium disks, distinct from previous discussions, is proposed. It is based on the impurity mechanism of high-temperature superconductivity and the general localization approach to the superconductivity problem. Turns of the local magnetic moments of the two-level systems are considered to be the cause of this effect in HTSC. The estimations of the magnetic moment magnitude and the magnetic moment concentration are given. In niobium disks, this effect is also explained by turns of the local magnetic moments, but of another nature. The role of the layered structure is demonstrated. It is shown that the proposed models can explain all available experimental facts. The connection between this effect and the electric field effect in HTSC is discussed.     

Extraction kinetics of heavy metal-containing sludge

In order to remove and recover copper, zinc, cadmium, and chromium from the wastewater treatment sludge generated by an electroplating process, the heavy metal extraction kinetics was studied in a batch reactor using two different extraction agents (nitric and citric acid) at constant agitation speed (150 rpm) and solid to liquid ratio (10 g/L), but varying acid concentrations (0.02-0.10 N), temperatures (25-85 degrees C in nitric acid solution, 25-95 degrees C in citric acid solution), and sludge particle sizes. The shrinking-core model and empirical kinetic model were adopted to analyze the experimental data. Although both models could fit the experimental kinetic data well, the obtained parameters of the shrinking-core model did not show reasonable trends varying with the experimental variables while the empirical model parameters showed significant trends. The experimental and modeling results showed that the metal extraction rates increased with acid concentration, temperature, but decreased with increasing particle size. Nitric acid was found to be more effective than citric acid to extract the heavy metals from the sludge. The extraction activation energies obtained in this study suggested that both a physical diffusion process and a chemical reaction process might play important roles in the overall extraction process.     

Paramagnetic silica-coated gold nanoparticles

Water soluble gold nanoparticles, obtained by the reduction of the gold (III) chloride with sodium borohydride in the presence of citric acid or thioctic acid, were covered with a paramagnetic silica layer using the Stober method, yielding a hybrid metallic-inorganic nanomaterial (gold nanoparticles, with an average size of 5 nm, embedded into silica nanoparticles, with an average size of 100 nm). The paramagnetic silica layer was formed by copolymerization of a paramagnetic silica precursor (derived from 3-aminopropyltrimethoxysilane) with tetramethyorthosilicate. The paramagnetic silica precursor was obtained by coupling 3-aminopropyltrimethoxysilane with 3-carboxy-proxyl free radical. TEM pictures show that each silica nanoparticle of about 100 nm in size embedded about 10 gold nanoparticles. These hybrid nanoparticles are quite stable and exhibit the expected paramagnetic characteristics, as seen by electron paramagnetic resonance. The accessibility of methanol through the silica layer was also studied. Depending on the capping ligands of the gold nanoparticles (citric or thioctic acid), different silica networks are formed, as seen by the mobility of the spin-label inside the silica layer. The EPR spectra showed that the paramagnetic silica layer is very robust and the mobility of the spin-probe inside the silica layer is very little affected by methanol. However, if spin-labeled thioctic acid protected gold nanoparticles were used in the material synthesis, the mobility of the spins attached to the gold surface is quite high in the presence of methanol, while the spins embedded into the silica layer remains immobilized.     

Thermal and mechanical properties of metal-containing polypyromellitimides

Polyimides have useful mechanical properties over wide temperature ranges and extensive applications due to their radiation resistance, hydrolytic and thermo-oxidative stability and very high electrical resistivity. We have now developed some metal-containing polyimide systems. Mechanical properties were determined; the tensile strength values for all metal-containing films are much higher than the value for the polymer alone. Received: 25 August 2000 / Reviewed and accepted: 28 August 2000     

Preparation and characterizations of soluble regularly alternating polyazomethines from oligothienylenes

The preparation and characterization of oligothienylene dialdehydes and related soluble copolymers in which thenylenic segments regularly alternate with phenylenic portions linked by azomethine moieties is presented. The polymer series with three, six and eight thienylenic residues showed interesting evidences of electronic confinement in low-gap segments (thienylenic). Self-assembled structures of oligomers can be obtained either by evaporation in high vacuum or by a proper thermal treatment of spin coated films, depending on the molecule length. Polymers prepared by different synthetic routes show different thermal and structural properties as a function of the ratio of two possible isomers at imino linkage. The order degree also influences the optical properties in fact luminescence data are strictly related to the percentage of the two isomers.     

Shape memory polyurethane containing mesogenic moiety

The mechanical and thermal properties, in particular the shape memory effect, of TPUs synthesized from diol-terminated poly(caprolactone) (PCL diol), 4,4-diphenylmethane diisocyanate (MDI), and mesogenic chain extenders, 4,4-bis-(2-hydroxyethoxy)biphenyl (BEBP) or 4,4-bis-(6-hydroxyhexoxy)biphenyl (BHBP) were examined and compared with results for PCL diol/MDI/1,4-butanediol (BD) based TPUs in a previous study. Some results related to the rigid structure of BEBP or BHBP were observed in the thermomechanical properties. Shape fixity was related to the crystallization of the PCL phase.     

Stress-strain state of a three-layer metal-containing polymeric rod

We consider a three-layer metal-containing polymeric rod subjected to thermal and mechanical loads taking into account the physical nonlinearity and rheonomic properties of the materials of the layers. For this rod, we obtain an exact solution of the problem of the theory of elasticity. For the solution of the problem of thermoviscoelastoplasticity, we apply the method of “elastic” solutions and present the results of its numerical realization. Belorussian State Transport University, Gomel, Belorussia. Translated from Problemy Prochnosti, No. 3, pp. 114–123, May–June, 1998.     

Paramagnetic Attraction of Impurity-Helium Solids

A small permanent magnet was used to attract impurity-helium solid samples composed of hydrogen, deuterium, and nitrogen radicals. The magnetic field gradient was sufficiently strong to lift each of the impurity-helium solids while submerged in superfluid helium, but only strong enough to lift one of four samples through the liquid surface. This suggests ranges of local atomic radical concentrations that partially agree with previous ESR measurements. The attractive paramagnetic force is strong enough to be useful as a trap for the formation of a pure hydrogen impurity-helium solid, for use in radical concentration measurements and for sorting and moving impurity-helium solids.     

Paramagnetic Effect in Nano-opal-lead Structure

We report magnetic studies of the paramagnetic effect observed in the superconducting nano-structured opal-lead system. Positive magnetization is clearly observed when the sample is cooled in field. The paramagnetic effect is strongly dependent on the applied field and the cooling rate. The results suggest that the paramagnetic moment is due to flux trapping and the competition between the positive and negative moments due to the temperature dependence of the penetration depth.     

Study on microwave absorption properties of metal-containing foam glass

Materials with the properties of electromagnetic (EM) wave absorption are attractive topics. In this work, we report that EM wave absorption composites, consisting of foam glass, zinc and zinc oxide, were prepared by sintering mixture of foam glass raw material and zinc powder. Microwave reflection loss of composite was calculated based on the permittivity in the range of 8.2-12.4 GHz. The results show that zinc-containing foam glass absorbs efficiently microwaves. The sample with zinc filler to foam glass mass ratio of 3/18 had a reflection loss below −10 dB in the range of 11.3-12.4 GHz, and the minimum reflectivity was −15.6 dB at both 12.0 and 12.4 GHz. Microwave absorption performances of specimens can be controlled by changing the ratio between zinc powder and foam glass mass. The detailed mechanism of the control was investigated through X-ray diffraction (XRD) analysis and scanning electrical microscopy (SEM) observations.     

The role of RHA-blended cement in stabilizing metal-containing wastes

Time to final setting, strength development and leachability of heavy metals from the solidified wastes using reactive rice husk ash (rRHA)-blended cement as solidification binder were investigated. The rRHA was prepared by firing at 650 °C for 1 h. Synthetic metal hydroxides and plating sludge were solidified using cement blended with 0, 10, 20 and 30 wt.% rRHA. Experimental results showed that synthetic Zn(OH)₂ and the plating sludge caused rapid setting for cement paste but prolong the final setting for rRHA-blended cements. The rate of strength development was also decreased during the first 14 days of curing. However, these interfering effects were reduced when cement was blended with 10 wt.% rRHA. In addition, the plating sludge could be loaded at 30 wt.% to the cement blended with 10 wt.% rRHA and gave both the 28-day strength and metal concentration in TCLP leachates that meet the regulatory limits for landfilling.     

螺旋碳纤维的顺磁响应

采用化学气相沉积法制备了螺旋碳纤维,通过XRD、EDX和SEM对样品进行了表征和分析,采用研磨方法考察了螺旋结构的破坏情况,并对比了研磨前后样品的低温磁性。结果表明,在有效去除催化剂的情况下,螺旋形貌被破坏以后,碳纤维的抗磁性信号增强。基于单电子受缚于螺旋线的物理模型对实验结果进行分析和讨论,认为螺旋形貌具有顺磁响应,并阐释了其产生机理。     

Paramagnetic microspheres with core–shell-ed structures

Paramagnetic microspheres with core–shell-ed structures were successfully synthesized by electroless plating technique. The surface morphology and core–shell-ed structures of the paramagnetic microspheres were examined by scanning electron microscopy as well as optical microscopy. Under magnetic fields, the core–shell-ed microspheres self-assembled into ordered structures (chains, columns, or three-dimensional ordered structures) because of magnetic dipole–dipole interaction, having potential applications in optics.