Manoel Ribeiro da Silva

Preparation of composite materials containing iron in a cross-linked resin host based on styrene and divinylbenzene

Iron composite materials based on styrene/divinylbenzene network hosts were produced using aqueous suspension polymerization. The effects of different kinds of porogen agent, toluene, toluene/n-heptane mixture or a toluene solution of polyphenyleneoxide on the bulk density, swelling in toluene and ferromagnetic properties of these materials were evaluated. The specific area and average porous diameter of network resins were characterized by BET and BJH methods, while the iron content was determined by atomic absorption spectrometry. The morphology of the composites was studied by both optical microscopy and scanning electron microscopy with energy dispersive X-ray analysis. All the spherical beads, irrespective of their sizes, have agglomerated iron particles located only on their surface. The particles have exhibited ferromagnetic behavior, with a coercivity of 328.69 Oe. The porogen agents used affect the iron particle distribution on the bead surfaces.

A Study of the Initiator Concentration's Effect on Styrene- Divinylbenzene Polymerization with Iron Particles

This paper describes the preparation of magnetic copolymer obtained from suspension polymerization of styrene (Sty) and divinylbenzene (DVB) in the presence of iron particles treated and not treated with oleic acid. The magnetic copolymers were characterized according to their morphology, particle size distribution and magnetic properties. The results show that incorporation of iron particles significantly changed the particles’ morphology. All samples presented higher saturation magnetization than the values reported in the literature and the particle size distribution was more monodisperse when the polymerization was conducted with 5%wt of benzoyl peroxide (BPO).

Magnetic and Electrical Properties of MnxCu1-xFe2O4 Ferrite

In the present work, mixed manganese-copper ferrite of composition MnxCu1-xFe2O4 (within x=0.40, 0.42, 0.44, 0.46, 0.48 and 0.50) have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization. MnxCu1-xFe2O4 ferrite samples were prepared by uniaxial pressing from the oxide mixture, synthesized at 1000°C during 45 hours and finally heated to 1200°C by 5h, at room atmosphere. The X-ray diffractograms show that the samples with different compositions were formed by compact structure spinel with cubic cell. The saturated magnetization of the MnxCu1-xFe2O4 ferrites increased with x up to 0.46, which presented the smallest coercitive field. All samples showed hysteresis characteristic of soft magnetic materials. This electrical behavior is compatible with an insulator. The results were analyzed in the framework of grain/barrier model.

Síntese e caracterização de copolímeros à base de metacrilato de metila e divinilbenzeno com propriedades magnéticas

In this work, copolymers based on methyl methacrylate and divinylbenzene containing iron with magnetic properties were produced using the suspension polymerization method. An investigation was performed of the effect from the concentration of iron added to the polymerization, the MMA/DVB molar ratio in the copolymer formation, type of suspension agent and stirring speed on the synthesis of the copolymers. The copolymers morphology, thermal stability, contents of embedded iron, particle size distribution, magnetic properties, surface area, volume and pore size were evaluated. Polymeric microspheres with magnetic properties were successfully obtained. These materials showed good control of the spherical shape and agglomeration of iron particles under the surface of the microsphere. The analysis of magnetic properties pointed to materials with no hysteresis loops, thus being close to a material with superparamagnetic properties with saturation magnetization between 8.0 and 13.0 emu.g-1.

Tensile properties of duplex UNS S32205 and lean duplex UNS S32304 steels and the influence of short duration 475 ºC aging

Duplex stainless steels are high strength and corrosion resistant steels extensively used in the petrochemical and chemical industries. The aging at 475 °C for long periods of time provokes embrittlement and deterioration of corrosion resistance. However, short duration aging at 475 °C may be used as heat treatment to improve mechanical resistance with small decrease in the other properties. In this work the flow stress curves of lean duplex UNS S32304 and duplex UNS S32205 steels were modeled with Hollomon’s equation and work hardening exponents (n) were determined. The analyses were conducted in specimens annealed and heat treated at 475 °C for short periods of time. The aging at 475 °C for 4 hours, 8 hours and 12 hours promoted significant hardening with small decrease of ductility. The work hardening exponents of both steels were compared, being higher in the duplex steel than in the lean duplex grade.

Magnetic properties and retained austenite quantification in SAE 4340 steel

Magnetic properties (coercive force and saturation magnetization) of SAE 4340 steel, heat treated in different ways, were measured in a Vibrating Sample Magnetometer. Four soaking temperatures were investigated: 860°C, 960°C, 1060°C and 1160°C. The oil-quenched samples were tempered at different temperatures between the range of 200°C and 650°C. The increase of the soaking temperature promotes the decrease of the saturation magnetization, which is mainly due to the retained austenite in the steel. This austenite transforms into bainite during tempering between 200°C and 300°C. The saturation magnetization measurements were used to quantify the amount of retained austenite in the different samples. The coercive force of the steel varied from 115.0 Oe (9151.7 A/m) to 133.0 Oe (10584.1 A/m), depending on the heat treatment condition.

Analysis of networks based on styrene and divinylbenzene containing iron anchored using variable pressure scanning electron microscopy

There is great demand for the development of composite materials containing small metal or metal oxides particles, owing to their variable properties and wide application. However, microscopic evaluation of these materials using high‐vacuum scanning electron microscopy is difficult because the samples must undergo a series of preparation steps to reach a high image quality and to avoid becoming shrunk inside the microscope vacuum chamber. Thus, in this study, we used variable pressure scanning electron microscopy to evaluate the morphology and iron distribution on the surface of magnetic microspheres based on poly(styrene‐co‐divinylbenzene). These materials were obtained by suspension copolymerization of styrene and divinylbenzene in the presence of fine iron particles. Energy‐dispersive X‐rays were also used to analyse distribution of the iron particles. The results indicate that, under the conditions used, magnetic microspheres with a relatively narrow size distribution were formed. Moreover, the micrographs show that agglomerated iron particles appeared only on the microsphere surface.

Síntese e caracterização de copolímeros reticulados à base de estireno, divinilbenzeno e metacrilato de metila com propriedades magnéticas

In this work, copolymers based on styrene (STY), divinylbenzene (DVB) and methyl methacrylate (MMA) with magnetic properties were synthesized using the suspension polymerization technique. The copolymers were characterized according to morphology, iron content incorporated, bulk density, particle size distribution and magnetic properties. The effect of MMA content on the characteristics of polymeric particles was investigated. Generally, copolymers without MMA presented the biggest iron content incorporated and the best morphologic control. When the temperature was decreased from 80 oC to 70 oC and the stirring speed was reduced from 480 rpm to 360 rpm the iron content in the polymeric particles increased.

AFM Characterization of Composite Materials Containing Iron in a Resin Host Based on Styrene and Divinylbenzene

The development of composite materials containing small metal or metal oxides particles has attracted a great deal of attention for their interesting chemical, physical and magnetic properties, providing their use for several technological applications. However, it is necessary that a complete evaluation of the morphological features of these composite be performed and correlated to the above mentioned properties. Therefore, the aim of this work was to use VP-SEM and AFM to investigate the morphology and the phase difference of composite materials based on styrene (STY) and divinylbenzene (DVB), containing iron particles. MFM analysis was also carried out to verify the magnetic properties of surface iron particles.

Síntese e caracterização do ferroespinélio Ni0,7Zn0,3Fe2O4: avaliação de desempenho na esterificação metílica e etílica

O ferroespinelio Ni0,7Zn0,3Fe2O4 foi sintetizado por reacao de combustao e seu desempenho catalitico na reacao de esterificacao metilica e etilica do oleo de soja foi investigado. As amostras foram caracterizadas por difracao de raios X, analise de refinamento, espectroscopia de fluorescencia de raios X por energia dispersiva, espectroscopia no infravermelho com transformada de Fourier, analise textural, microscopia eletronica de varredura, densidade por picnometria de helio, analise granulometrica, analise termogravimetrica, medidas magneticas e testes cataliticos. A sintese foi eficiente obtendo o ferroespinelio com fase unica Ni0,7Zn0,3Fe2O4, com tamanho de cristalito de 20 nm, elevada area superficial (86 m2/g) e magnetizacao de saturacao de 18 emu/g. O ferroespinelio possibilitou atividade catalitica promissora em ambas as condicoes reacionais estudadas, sendo mais ativo na conversao do oleo de soja em biodiesel na esterificacao metilica apresentando conversao media de 93,9±2,8%.