Synthesis and Characterisation of Carbon Nanotubes Prepared Using Pulsed Laser Ablation Deposition Technique

Carbon nanotubes (CNTs) has been the focus of a virtual storm research, both to better understand its unique properties and to harness its potential in commercial applications such as hydrogen storage, atomic force microscopy probe, microelectronic transistor, electrical field emitter of flat panel display. There are two main premises in this research project; the first premise was to synthesis the CNTs via Pulsed Laser Ablation Deposition (PLAD) technique, and the second premise was to study the effect of Fe2O3 as catalyst on the magnetic properties of the deposited materials. This work reports the formation of carbon web-like nano structure synthesized in a T-shape stainless steel chamber. ND:YAG laser with 532nm wavelength and 10.24 W power was used to ablate the target of graphite and catalyst. Fe2O3 and NiO were mixed separately as the catalyst with graphite (carbon) to form the target. The vacuum level was kept at 5 mtorr with argon gas flowing from bottom of the chamber. The soot that was deposited on the glass substrate was then characterized using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), EDX and Vibrating Sample Magnetometer (VSM). The SEM images confirm a web-like structure formed after the ablation. The graphite target that was ablated with laser does not form web-like structure. However, when NiO or Fe2O3 were introduced as the oxide catalysts, the web-like structure was formed successfully. The TEM pictures proved the web-like structure is the carbon nanotubes. Magnetic characterization via VSM was conducted after the CNTs structure was confirmed. From the magnetic characterization, we found that CNTs behaves as non-magnetic material due to the absence of the hysteresis curve. When it was filled with Fe2O3, the magnetic properties enhanced tremendously. It was also concluded that these Fe2O3 nano particles magnetic materials were trapped in the tubes. The CNTs acted as nano-wires and were able to induce the magnetization of the magnetic particles

Effects of sintering temperature on grain growth and the complex permeability of Co0.2Ni0.3Zn0.5Fe2O4 material prepared using mechanically alloyed nanoparticles.

Nanoparticle-sized Co0.2Ni0.3Zn0.5Fe2O4 was prepared using mechanical alloying and sintering. The starting raw materials were milled in air and subsequently sintered at various temperatures from 600 to 1300 °C. The effects of sintering temperature on physical, magnetic and electrical characteristics were studied. The complex permittivity and permeability were investigated in the frequency range 10 MHz to 1.0 GHz. The results show that single phase Co0.2Ni0.3Zn0.5Fe2O4 could not be formed during milling alone and therefore requires sintering. The crystallization of the ferrite sample increases with increasing sintering temperature; which decrease the porosity and increase the density, crystallite size and the shrinkage of the material. The maximum magnetization value of 83.1 emu/g was obtained for a sample sintered at 1200 °C, while both the retentivity and the coercivity decrease with increasing the sintering temperature. The permeability values vary with both the sintering temperature and the frequency and the absolute value of the permeability decreased after the natural resonance frequency. The real part of the permittivity was constant within the measured frequency, while the loss tangent values decreased gradually with increasing frequency

Evolution of Magnetic Properties in Ferrites: Trends of Single- Sample and Multi-Sample Sintering

Microstructure of magnetic materials greatly influences the performance of magnetic properties, and sintering has been used as an agent to tailor the microstructure of these magnetic materials especially ferrites. Nanostructured ferrites prepared by high-energy milling method are often inherently unstable owing to their small constituent sizes, non-equilibrium cation distribution, disordered spin configuration, and high chemical activity. Therefore, sintering of the milled ferrites recrystallizes the nanostructure and causes its transition from an excited metastable (activated) state into the low-energy crystalline state. A better understanding of the response of nanoscale ferrites with changes in temperature is crucial not only for basic science (the development of an atomistic and microscopic theory of the mechanochemical processes) but also because of the technological high-temperature applications in catalysis, ferrofluids and information storage. This chapter discusses on two different sintering schemes, which are a commonly applied multi-sample sintering and a rarely adopted single-sample sintering. Experimental results of single-sample and multi-sample sintering of NiZn ferrites and yttrium iron garnet (YIG) were highlighted, and their microstructural consequences on the magnetic properties were also discussed

Sintering Processing of Complex Magnetic Ceramic Oxides: A Comparison Between Sintering of Bottom-Up Approach Synthesis and Mechanochemical Process of Top-Down Approach Synthesis

Sintering is a common synthesis method for the fabrication of ceramics. The widespread use of sintering for the production of complex ceramic oxide especially ferrites has led to a variety of investigations on the subject. Top-down approach synthesis like mechanochemical process has recently been suggested as a promising synthesis method for replacing bottom-up approach synthesis methods like sintering, questioning its necessity for thermal treatment at high temperature. Understanding of sintering mechanism is crucial in order to optimize and enhance the advantages of sintering, which cannot be replaced by other techniques. In general, ferrites with particular set of behaviors require a particular set of microstructural properties influenced by the sintering steps. The main objective of this chapter is to understand how the increase of sintering temperature affects the microstructural evolution, in order to develop a fundamental science understanding for the mechanism of sintering. In the second part of this chapter, presentation of experimental results on sintering of mechanically activated Ni0.5Zn0.5Fe2O4 nanoparticles and its effect on microstructural, magnetic, and optical properties was reported. Lastly, a comparative study between sintering (bottom-up approach) and mechanochemical (top-down approach) process is presented

Sintering temperature dependence of evolving morphologies and magnetic properties of Ni0.5Zn0.5Fe2O4 synthesized via mechanical alloying

We report on an investigation to unravel morphological and magnetic-property dependence on sintering temperature for samples of Ni0.5Zn0.5Fe2O4 synthesized via mechanical alloying. The samples were sintered at various sintering temperatures from 800 °C to 1000 °C. The morphology of the samples was studied by means of scanning electron microscopy (SEM); hysteresis and permeability measurement were carried out using a BH hysteresisgraph system and an impedance analyzer, respectively. The morphological studies show a microstructural evolution with the increase of sintering temperature. The relationship between ordered magnetism and the microstructure of the samples show that the important grain-size threshold for the appearance of significant ordered magnetism (mainly ferromagnetism) is about ≥0.3 μm. We found that two factors sensitively influenced the samples content of ordered magnetism, their ferrite-phase crystallinity degree and the number of grains above the critical grain size

Microwave sintering of Ni-Cr doped strontium hexaferrite synthesized via sol-gel method

The magnetic behavior of Strontium hexaferrite ceramics with nominal composition SrFe12-2xNixCrxO19 (where x = 0.2, 0.4, 0.6, 0.8) samples are reported in this paper. Four samples were synthesized by the sol-gel method. The XRD analysis confirms the single phase and various parameters such as lattice constants (a and c), are calculated from the XRD data. Magnetic properties, such as specific saturation magnetization (Ms) and coercivity (Hc) are calculated from the hysteresis loops. Values of coercivity are found to increase up to the substitution level of x = 0.0-0.2 and then decreases continuously while that of saturation magnetization decrease continuously with increase in Ni-Cr concentration. The results show that microwave sintering requires about 75% less processing time than required by conventional method and still provides better magnetic properties

Hydrocarbon sources for the carbon nanotubes production by chemical vapour deposition: a review

The synthesis of carbon nanotubes (CNTs) using a chemical vapour deposition (CVD) method requires the use of hydrocarbon as the carbon precursor. Among the commonly used hydrocarbons are methane and acetylene, which are both light gas-phase substances. Besides that, other carbon-rich sources, such as carbon monoxide and coal, have also been reportedly used. Nowadays, researches have also been conducted into utilising heavier hydrocarbons and petrochemical products for the production of CNTs, such as kerosene and diesel oil. Therefore, this article reviews the different kind of hydrocarbon sources for CNTs production using a CVD method. The method is used for it allows the decomposition of the carbon-rich source with the aid of a catalyst at a temperature in the range 600-1200°C. This synthesis technique gives an advantage as a high yield and high-quality CNTs can be produced at a relatively low cost process. As compared to other processes for CNTs production such as arc discharge and laser ablation, they may produce high quality CNTs but has a disadvantage for use as large scale synthesis routes

Influence of Zn-Nb on the magnetic properties of barium hexaferrite

In the present study, BaFe12-2x Zn x Nb x O19 (x=0. 2, 0.4, 0.6 and 0.8) hexaferrites were prepared by the sol-gel technique and subsequent thermal treatment. The crystal structure, grain size, and magnetic properties were studied by means of X-ray diffraction (XRD), high-resolution scanning electron microscope (HR-SEM) and vibrating sample magnetometer (VSM). The X-ray diffraction analysis showed that the barium hexaferrite with small substitutions still maintained a hexagonal magneto-plumbite phase. It was found that the mean size of the grains increased with increasing substitution. The saturation magnetization increased slightly with increasing x, which was attributed to different preferential site occupation of Zn-Nb at low and high concentration ranges. The coercivity decreased with increasing x. Structural and magnetic characterizations of these ferrites provide significant information about their reactive physical properties

Conductivity analysis of Bi4Ti3O12 ferroelectric ceramic: a comprehensive study from the dynamic aspects of hopping conduction

Objectives: We focus solely on a comprehensive conductivity analysis of Bi4Ti3O12 ceramic, in a bid to bring seminal ideas for dielectric components, in particular frequency and temperature ranges. Methods/Statistical Analysis: The synthesis of Bi4Ti3O12 ceramic is based on a mechanical activation method. The following sintering at 1273 K ascertains the Bi4Ti3O12 appears to be of single phase crystallizes in orthorhombic form, whose conductivity is determined from the dielectric function in the context of Kramers-Kronig relation on which of this is measured in the frequency domain at varying temperatures. The evaluation of conductivity data is mainly in terms of activation energy. Findings: We find that the separately discussed dc and ac conductivities in similar manner are best isolated into two distinct temperature regions. Charge transport by hopping to the target localized states is the relevant conduction mechanism in bringing insights into the dynamic responses. Variable range and small polaron hopping models associated with the adiabatic small polaron are the decent choices, each of which explaining the dc conductions in these temperature regions. The former involves distant hops, whereas the latter denotes as nearest-neighbour hopping. The percolation treatments applied in the dc conductivity yield promising results if different percolation expressions are used. The correlation between dc and ac conductions for each temperature is irrefutably made through the Barton-Nakajima-Namikawa fitting. In frequency dependence ac regions, the thermally activated hopping carriers are transported in a correlated to a random manner between preferred sites. Performing a Summerfield ac scaling in these temperature regions leads to different scenarios in view of time-temperature superposition principle. Applications/Improvements: Further experiments are encouraged to support the hopping conduction mechanisms from another aspect in order to prompt the use as energy storage function in the electromagnetic application

Preparation and magnetic properties of Ni-Cr doped strontium hexaferrite

The Ni-Cr-substituted M-type Strontium Hexaferrite such as SrFe12-2xNixCrxO19, with x =0.2, 0.4, 0.6, 0.8 mol% has been successfully prepared by the sol-gel process. The ferrites were systematically investigated by using powder X-Ray diffractometer (XRD), High Resolution Scanning Electron Microscope (HR-SEM) and Vibrating Sample Magnetometer (VSM). The XRD analysis confirms the single phase and lattice constants (a and c), have been calculated from the XRD data using powderX software. The lattice parameter was found to increase with increasing nickel-chromium concentration. Values of coercivity are found to increase up to the substitution level of x = 0.0-0.2 and then decrease slightly while that of saturation decrease continuously with increase in Ni-Cr concentration