Silicone rubber composites filled with FeSiAl alloys and multi-walled carbon nanotubes(MWCNT)/graphite have been prepared for the first time by a coating process.The complex permittivity and permeability of the composites were measured with a vector network analyzer in a 1-4 GHz frequency range,and the DC electric conductivity was measured by a standard four-point contact method.These parameters were then used to calculate the reflection loss(RL) and shielding effectiveness(SE) of the composites.The results showed that the added MWCNT increased the permittivity and permeability of composites in the L-band,while the added graphite increased only the permittivity.The variation lies in the interactions between two carbonous absorbents.Addition of 1 wt% MWCNT enhanced the RL in the L-band(minimum 5.7 dB at 1 mm,7.3 dB at 1.5 mm),while the addition of graphite did not.Addition of MWCNT as well as graphite reinforced the shielding property of the composites(maximum SE 13.3 dB at 1 mm,18.3 dB at 1.5 mm) owing to the increase of conductivity.The addition of these carbonous materials could hold the promise of enforcing the absorption and shielding property of the absorbers.
Diatom frustules,considered as novel bio-functional materials,display a diversity of patterns and unique micro-and nanostructures which may be useful in many areas of application.Existing devices directly use the original structure of the biosilica frustules,limiting their function and structural scale.Current research into the shapes,materials and structural properties of frustules are considered;a series of frustule processing methods including structure processing,material modification,bonding and assembly techniques are reviewed and discussed.The aim is to improve the function of diatom frustules allowing them to meet the design requirements of different types of micro devices.In addition,the importance of the comprehensive use of diatom processing methods in device research is discussed using biosensors and solar cells as examples,and the potential of bio-manufacturing technology based on diatom frustules is examined.
The bio-limited forming technology, a new technology organically integrating microbiology, manufacturing science and materials science, is used in the manufacturing of magnetic or conductive microstructures of different standard shapes. This paper explores the feasibility of magnetizing microorganism with thermal decomposition method. The principle of thermal decomposition of iron pentacarbonyl has been adopted to investigate the cells of Spirulina (a type of nature micro-helical microorganism) coated with pure iron. Further analysis have been conducted on the observations results of hollow micro-helical magnetic particles form, components and the phase structure obtained by using various tools including optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray detector (EDX), transmission electron microscopy (TEM), and X-ray diffraction analysis (XRD). Results showed that Spirulina cells could be coated with iron particles after the completion of thermal decomposition process, with well-kept shape of natural helixes and consistent components of different sampling points on the surface layer and thickness of layer. After the heat treatment at 700°C, the type of the surface iron layer formed was α-Fe. The paper also investigates the kinetics of the cell magnetization technology by thermal decomposition.
Spirulina platensis were chosen as templates to produce microscopic helical soft-core magnetic particles by way of depositing ferromagnetic alloy onto their surface using electroplating technique,and the process of electroplating ferromagnetic alloy onto microorganism cells was studied.The morphology and appearance of the coated Spirulina platensis were analyzed with optical microscopy and scanning electron microscopy,respectively,and the ingredients and phase structure of the alloy coating were analyzed with energy dispersive X-ray detector(EDX) and X-ray diffractive analysis(XRD),respectively.The result showed that the particles were successfully coated with uniform metal coating and their initial helical shape was perfectly replicated.The coating was NiFe alloy,and its phase structure was face-centered cubic structure.The magnetic properties of the coated particles were tested with vibrating sample magnetometer(VSM),and the result showed that the particles were ferro-magnetic,which means the magnetic electroplating of the microorganism cells was successfully achieved.The electrochemical reaction mechanism of the magnetic plating process was also analyzed;the result showed that the deposition of NiFe on the microorganism cells was anomalous codeposition,and that Fe2+ ion was preferential deposited when magnetic stirring was applied.
