Influence of structure of iron nanoparticles in aggregates on their magnetic properties

Zero-valent iron nanoparticles rapidly aggregate. One of the reasons is magnetic forces among the nanoparticles. Magnetic field around particles is caused by composition of the particles. Their core is formed from zero-valent iron, and shell is a layer of magnetite. The magnetic forces contribute to attractive forces among the nanoparticles and that leads to increasing of aggregation of the nanoparticles. This effect is undesirable for decreasing of remediation properties of iron particles and limited transport possibilities. The aggregation of iron nanoparticles was established for consequent processes: Brownian motion, sedimentation, velocity gradient of fluid around particles and electrostatic forces. In our previous work, an introduction of influence of magnetic forces among particles on the aggregation was presented. These forces have significant impact on the rate of aggregation. In this article, a numerical computation of magnetic forces between an aggregate and a nanoparticle and between two aggregates is shown. It is done for random position of nanoparticles in an aggregate and random or arranged directions of magnetic polarizations and for structured aggregates with arranged vectors of polarizations. Statistical computation by Monte Carlo is done, and range of dominant area of magnetic forces around particles is assessed. © 2011 Rosická and Šembera

Influence of structure of iron nanoparticles in aggregates on their magnetic properties

Zero-valent iron nanoparticles rapidly aggregate. One of the reasons is magnetic forces among the nanoparticles. Magnetic field around particles is caused by composition of the particles. Their core is formed from zero-valent iron, and shell is a layer of magnetite. The magnetic forces contribute to attractive forces among the nanoparticles and that leads to increasing of aggregation of the nanoparticles. This effect is undesirable for decreasing of remediation properties of iron particles and limited transport possibilities. The aggregation of iron nanoparticles was established for consequent processes: Brownian motion, sedimentation, velocity gradient of fluid around particles and electrostatic forces. In our previous work, an introduction of influence of magnetic forces among particles on the aggregation was presented. These forces have significant impact on the rate of aggregation. In this article, a numerical computation of magnetic forces between an aggregate and a nanoparticle and between two aggregates is shown. It is done for random position of nanoparticles in an aggregate and random or arranged directions of magnetic polarizations and for structured aggregates with arranged vectors of polarizations. Statistical computation by Monte Carlo is done, and range of dominant area of magnetic forces around particles is assessed

Changes in the nanoparticle aggregation rate due to the additional effect of electrostatic and magnetic forces on mass transport coefficients

The need may arise to be able to simulate the migration of groundwater nanoparticles through the ground. Transportation velocities of nanoparticles are different from that of water and depend on many processes that occur during migration. Unstable nanoparticles, such as zero-valent iron nanoparticles, are especially slowed down by aggregation between them. The aggregation occurs when attracting forces outweigh repulsive forces between the particles. In the case of iron nanoparticles that are used for remediation, magnetic forces between particles contribute to attractive forces and nanoparticles aggregate rapidly. This paper describes the addition of attractive magnetic forces and repulsive electrostatic forces between particles (by 'particle', we mean both single nanoparticles and created aggregates) into a basic model of aggregation which is commonly used. This model is created on the basis of the flow of particles in the proximity of observed particles that gives the rate of aggregation of the observed particle. By using a limit distance that has been described in our previous work, the flow of particles around one particle is observed in larger spacing between the particles. Attractive magnetic forces between particles draw the particles into closer proximity and result in aggregation. This model fits more closely with rapid aggregation which occurs between magnetic nanoparticles.Ministry of Education of the Czech Republic of the Technical University in Liberec [7822]; Ministry of Education of the Czech Republic [FR-TI1/456]; Ministry of Industry and Trad

Thermal expansion of piezoelectric PZT ceramics

katedra: KFY; přílohy: 1 CD; rozsah: 54 s.The purpose of thesis is the study of the thermal expansion of piezoelectric PZT ceramics. The work is dealing about basic elektromechanical property of piezoelectric material, as a piezoelectricity, ferroelectricity and pyroelectricity. Description of a PZT ceramic follows, including description of thermal expansion and its coefficients. Thermal expansion of PZT ceramics is measured by laser interferometry. The small prism shape samples were studied. Laser interferometer HP Agilent and Michelson interferometer were modifieded for them. Samples are measured in broad range of temperatures. A temperature stabilized chamber was adapted for this measurement. Short-circuited samples of hard ceramics (APC 880, APC 840) and soft ceramics (APC 850, APC856) were applied. Components of thermal expansion tensor were specified from measured values.Cílem bakalářské práce je studium teplotní roztažnosti piezoelektrické PZT keramiky. Práce se nejprve zaobírá základními elektromechanickými vlastnostmi piezoelektrických látek jako je piezoelektřina, feroelektřina a pyroelektřina. Dále následuje popis PZT keramiky a jejích vlastností, včetně popisu teplotní roztažnosti a jejích koeficientů. Teplotní roztažnost PZT keramiky se měří pomocí laserové interferometrie. Zkoumají se vzorky tvaru kvádru malých rozměrů, pro které byly upraveny laserový interferometr HP Agilent a Michelsonův interferometr. Vzorky se proměřují v širokém rozsahu teplot. Proto byla uzpůsobena teplotně stabilizovaná komůrka. K měření byly použity zkratované vzorky tvrdé keramiky (APC 880, APC 840) a měkké keramiky (APC 850, APC856). Z naměřených hodnot byly určeny složky tenzoru teplotní roztažnosti

Assessment of Influence of Magnetic Forces on Aggregation of Zero-valent Iron Nanoparticles

Aggregation of zero-valent nanoparticles in groundwater is influenced by several physical phenomena. The article shortly introduces preceding works in modeling of aggregation of small particles including influence of sedimentation, velocity profile of water, heat fluctuations, and surface electric charge. A brief description of inclusion of magnetic forces into the model of aggregation follows. Rate of influence of the magnetic forces on the aggregation depends on the magnitude of magnetization of the particles, radius of nanoparticles, size of the aggregates, and their concentration in the solution. Presented results show that the magnetic forces have significant influence on aggregation especially of the smallest iron particles.Ministry of Education [FR-TI1/456]; Ministry of Industry and Trad