Scanning Electrical Microscope Research Articles

Properties of Si<sub>3</sub>N<sub>4</sub> Based Nanocomposites Prepared by Pressureless Sintering Method

Si3N4 based nanocomposites were prepared with nano-sized amorphous SiO2 and Si3N4 powders by pressureless sintering method. The microstructures, phase composition, mechanical and dielectric properties of the nanocomposites were investigated. The scanning electrical microscope (SEM) photographs reveal that the grains are big and elongated. The X-ray diffraction (XRD) analysis shows that the main crystalline phase in the composites is Si2N2O formed during the sintering process. More β-Si3N4 phases were retained in the nanocomposites with the increase amount of the amorphous Si3N4 powders and no phase of SiO2 were observed. The densities and the strength of the nanocomposites decreased with the increase of amorphous SiO2 content. Despite low density, the flexural strengths of the composites reaches 220MPa and the ceramic has excellent dielectric properties with dielectric constant as low as 3.2-4.7 and dielectric loss in the range 2.6-3.9×10-3.

Microstructure Effect of Injection Molded Nanoparticle/Polymer Composites on their Resistivity

Although the progress has been achieved in conductive Nanoparticle/Polymer Composites(NPC), but there are many problems to be solved before their commercial application in a large scale, especially on their processing technology. The barriers include the dispersion of nanoparticle, the effect of nanoparticle concentration and interface on the overall properties of materials. In order to improve the application of NPC, the microstructural effect of injection molded NPC on its resistivity was investigated to build the relationship between the processing conditions and the properties in this paper. Composites used in the experiment were carbon black(CB)/polypropylene(PP). The microstructures of the injection molded parts at different positions were investigated with Scanning Electrical Microscope, and corresponsive properties were tested. The results showed that the distribution of CB nanoparticles changed with the injection pressure and had significant effect on the conductivity of the part. With the increase of injection pressure CB particles strongly oriented towards the flow direction of the polymer and thickness of oriented layer increased, which improve conductivity of the composites. The results also showed that crystallization was enhanced because of existence of nanoparticles, which should have increased the mechanical properties of the composite and decreased its resistivity because of the interfacial action between CB particles and polymer matrix.

The potential pozzolanic activity of glass and red-clay ceramic waste as cement mortars components

The objective of this experimental study was to examine the possibility of reusing ceramic materials waste from container glass, bricks and tiles of red-clay ceramic industry in Portugal as partial cement replacement in mortar and concrete. The different types of waste were finely ground to specific sizes (0–45μm, 45–75μm and 75–150μm) and its pozzolanic activity was determined. The reduction of glass and ceramic waste particle size was accomplished in the laboratory by crushing and grinding using a ball jar mill. After gridding, the fine waste materials were characterized by the determination of density, Blaine fineness and particle morphology using scanning electrical microscope. The compressive strength activity index, at 7, 28 and 90days, was determined in mortars produced with each finely grounded waste ceramics and different percentages of partial cement replacement. Standard ASTM accelerated mortar bar tests and a modified test carried on in 40×40×160mm size mortar specimens were performed to investigate the potential expansion caused by the alkali–silica reaction of finely grounded waste glass as partially cement replacement.The results obtained confirm the pozzolanic activity of the grounded waste, collected in the central region of Portugal, making feasible their incorporation as cement mortars and concrete components.

Pretreatment of contaminated raw water by a novel double-layer biological aerated filter for drinking water treatment

Abstract Polluted source water presents a challenge for the conventional water treatment process. Biological pretreatment would be helpful if feasible. To our knowledge, few literatures were reported about the pretreatment of polluted source water by biological aerated filter. A novel double-layer biological aerated filter (DLBAF) was devised using floating media (polyethylene) and sunken media (clinoptilolite) as the under layer and the upper layer media, respectively. The results indicated that DLBAF was efficient for ammonium, TOC and UV254 removal, with an average removal rate of 80.87%, 24.62%, 20.74%, respectively. Particle counts with sizes of 2∼15 μm presented a removal rate above 55%, although the sizes distribution had not been altered. Microorganisms on the surface of the media were observed by scanning electrical microscope (SEM), and it indicated that there were different bio-film structures in the under and the upper media. The novel DLBAF got a simultaneous removal of organic matter and amm...

Electrical Treeing Breakdown Properties for Polyimide Nanocomposite Film in Inverter-Fed Motors

The failure of magnet wires used in inter-turn insulation of inverter-fed motor winding is the main cause which leads to the motor insulation breakdown. This paper conducted electrical tree breakdown experiments on magnet wire insulating film (FCR 100) used in the inter-turn insulation of JD117 inverter-fed motor and meanwhile combining with energy spectrum analysis and scanning electrical microscope (SEM), by which type and content of elements, breakdown main body and electrical tree channel could be clearly observed, the corresponding failure mechanisms were analyzed. The experiment results reveal that all the breakdown main bodies are located at the pointedness and insulation joint of magnet wires, of which dielectric strength is relatively lower; they are the insulation “weak point”, which should be paid enough attention and strengthened at the manufacturing period. The electrical tree breakdown time is quite long and the life span of magnet wire is 11 hours. The electrical breakdown strength of envelope is very low when containing metal impurity. It is also found that the aluminum occupies the highest content tested by energy spectrum analysis.

Pretreatment of contaminated raw water by a novel double-layer biological aerated filter for drinking water treatment

Abstract Polluted source water presents a challenge for the conventional water treatment process. Biological pretreatment would be helpful if feasible. To our knowledge, few literatures were reported about the pretreatment of polluted source water by biological aerated filter. A novel double-layer biological aerated filter (DLBAF) was devised using floating media (polyethylene) and sunken media (clinoptilolite) as the under layer and the upper layer media, respectively. The results indicated that DLBAF was efficient for ammonium, TOC and UV254 removal, with an average removal rate of 80.87%, 24.62%, 20.74%, respectively. Particle counts with sizes of 2∼15 μm presented a removal rate above 55%, although the sizes distribution had not been altered. Microorganisms on the surface of the media were observed by scanning electrical microscope (SEM), and it indicated that there were different bio-film structures in the under and the upper media. The novel DLBAF got a simultaneous removal of organic matter and ammonium, and had a great potential for pretreatment of polluted drinking water resources.

Processing Effect of Injection Molded Nanoparticle/Polymer Composites on their Resistivity

In order to improve the application of nano-particles/polymer composite, we investigated the relationship between microstructures and electrical properties on injection molded composites made from carbon black(CB) particles mixed with polypropylene(PP). Standard tensile specimens were injected under different processing conditions, after which, the specimens were cut off along the surface to observe the microstructures at different positions of the moldings. The microstructures were observed with Scanning Electrical Microscope(SEM), and electrical properties were measured by using a two-terminal standard resistor under DC condition at room temperature. The results showed that CB nano-particles may form the best conductive path under the higher packing pressure combined higher injection pressure. If packing pressure is low, the resistivities at the skin zone loaded by high injection pressure are smaller than low injection pressure, but the resistivities increase at the sub-skin zone. We found that the sub-skin zone is a high resistivity district which would expand with higher injection pressure matched lower packing pressure. Contrast to the injection molded polymer whose microstructural orientation is stronger at the sub-skin zones, injection molded CB particles/polymer composites develop strong oriented microstructures at the core zones in stead of the skin or sub-skin zones due to CB particles’ migration.

The Influences of Anticipated Heat Treatment on the Electroless Nickel Plating on Magnesium Alloys

In this paper, effects of anticipated heat treatment on the electroless nickel plating coated on magnesium alloys AZ91D were investigated by using heat treatments of solution (T4) and solution + aging (T6) before electroless nickel plating. The influence of anticipated heat treatment on the structure, composition and anti-corrosion property of electroless coating were studied by using Scanning Electrical Microscope (SEM), EDS and Corrodkote corrosion test. It is shown that compared with the as-casted magnesium alloys and samples treated with T4, the deposition rate of Ni, the P contained in the coating and the anti-corrosion property of samples treated with T6 are the highest for the given system studied, and T6 treatment can promote the anti-corrosion property of the coating effectively.

Mechanical behaviors of Al 2O 3 nanoparticles reinforced polyetheretherketone

In order to improve the mechanical properties of Polyetheretherketone (PEEK), nanometer Al 2O 3 particles were used as fillers. The effect of size and content of Al 2O 3 particles, various coupling agents and dispersing methods on the mechanical properties were all studied. The reinforced PEEK filled with 15 nm and 5 wt.% Al 2O 3 particles possessed higher tensile, flexural and impact performance than that filled with 90 nm and 10 wt.% Al 2O 3 particles possessed. Especially, the impact strength of the PEEK filled with titanate treated nanometer Al 2O 3 particles was about eight times that of neat PEEK. Furthermore, the higher tensile, flexural, compression and impact strength of PEEK filled with nanometer Al 2O 3 particles than that of PEEK filled with nanometer SiO 2 particles were presented. In addition, through the analysis of fractographs for tensile specimens by scanning electrical microscope (SEM), the relativity between mechanical characteristics and fracture mechanism were discussed.

Properties of hot-pressed of SiC/Si 3N 4 nanocomposites

SiC/Si 3N 4 nanocomposites were prepared with carbon black and α-Si 3N 4 powders by hot-pressed method. The microstructure, phase composition, dielectric and mechanical properties of the nanocomposites were investigated. The relative densities of SiC/Si 3N 4 nanocomposites decreased from 99 to 86% when the carbon black content increased from 0 to 10 wt%. The X-ray diffraction (XRD) analysis shows that there are SiC crystals formed during the sintering process in the samples with carbon black. The main crystalline phase in the pure Si 3N 4 ceramic is β-Si 3N 4. The scanning electrical microscope (SEM) photographs reveal that the Si 3N 4 grains in Si 3N 4 ceramic are big and elongated. But the transformation of α-Si 3N 4 to β-Si 3N 4 is impeded in the samples with carbon black. More α-Si 3N 4 were retained in the nanocomposites with the increase of the carbon black content. The Si 3N 4 grains in samples with carbon black are small and particulate. The reason is that the incorporation of carbon black increases the viscosity of sintering liquid and prevents the transformation of α-Si 3N 4 to β-Si 3N 4 and the growth of Si 3N 4 grain. The strength of the nanocomposites is degraded due to the addition of the carbon black. The real and imaginary parts of the permittivity and dielectric loss of the SiC/Si 3N 4 nanocomposites all increase with the increase of carbon black content.

ULTRA-PRECISION GRINDING OF BK7 OPTICAL GLASS USING COARSE-GRAINED ELECTROPLATED DIAMOND WHEEL

A novel conditioning technique is developed to precisely and effectively condition the 151μm grain-sized nickel electroplated monolayer coarse- grained diamond grinding wheel in aiming to realize ductile grinding of brittle materials. During the conditioning process, a copper bonded diamond grinding wheel (91μm grain size) dressed by ELID (electrolytic in-process dressing) is applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system are used to in-situ monitor the modified wheel surface status. Ultimately the coarse-grained diamond wheel is conditioned to achieve an ideal state in terms of less than 2μm run-out error, top-flattened diamond grains and constant wheel envelop profile. Then the well- conditioned 151μm wheel is applied to conduct taper grinding and contour grinding tests, the ground surface and sub-surface integrity are measured by WLI (white light interferometer), AFM (atomic force microscope) and SEM (scanning electrical microscope) respectively. The experimental results indicate that the well-conditioned 151μm grain-sized diamond wheel is able to realize ductile grinding of BK7 with nano-scale surface roughness, as well as the almost damage free sub-surface integrity. The results also show the promising prospect of the conditioning technique and coarse-grained diamond wheels to be applied in machining the hard-machine-materials and the other brittle materials such as ceramic and silicon carbide, etc.

Optical limiting effects of multi-walled carbon nanotubes suspension and silica xerogel composite

Nanostructured composite of multi-walled carbon nanotubes (MWNTs) doped silica xerogel matrix was prepared by sol–gel technique. The successful encapsulation of MWNTs was checked by linear transmittance spectra and scanning electrical microscope images which show that MWNTs were well dispersed in the matrix. The optical limiting responses of MWNTs suspension and xerogel composite were observed at both 532 and 1064 nm with nanosecond laser pulses and shown to be good optical limiters. The optical limiting properties of MWNTs are maintained or even improved after being introduced into solid state matrix. The implying mechanism of nonlinear absorption other than the presently accepted nonlinear scattering is proposed and discussed.

Supercondcuting properties in MgB2/Fe wires prepared by PIT method

The MgB2 formation was analyzed physically and chemically and the MgB2/Fe wires were fabricated by powder in tube (PIT) technology. The microstructure of MgB2 in wires was studied by the scanning electrical microscope (SEM), which shows a good connection of grains and the size of MgB2 grain is 1–3 μm. The results ofJc measured by the standard four probes method show thatJc value reaches 6.1×104 A/cm2 at 20 K in self field.

New metal organic deposition method using trifluoroacetate for fabrication on YBCO thick film on metal tape

A new method to prepare high purifying trifluoroacetate (TFA) coating solution according to the mechanism of neutralization reaction between the hydroxid of Y, Ba, Cu and TFA is reported. High-quality YBa 2Cu 3O 7− x (YBCO) thick films on texture Ni tapes with NiO buffer layer have been successfully fabricated by the coating solution. The effect of heat treatment process including firing process and atmosphere on the microstructure and properties of YBCO films were studied by X-ray diffraction and scanning electrical microscope. The results show that coating solution can decrease the microcracks in film by appropriate heat treatment process and the grain size of YBCO approach to nanometer level.

Depletion of Fe and Cr within precipitates during Zircaloy-4 oxidation

Analyses of the oxide layers which were formed in a static autoclave of 400 °C steam after the heat-treatment to coarsen the precipitates were performed with the optical microscope, scanning electrical microscope (SEM), transmission electron microscope, electron probe micro-analyzer (EPMA), synchrotron X-ray diffractometer (XRD), and secondary ion mass spectroscope (SIMS), paying attention to the oxidation of Fe and Cr within Zr(Fe,Cr) 2 precipitates in Zircaloy-4. The oxide analyses were concentrated on the oxidized samples in the regime of pre- and post-transition. It could be confirmed from the SEM observation of the interfacial oxide that the Zr matrix was oxidized earlier than the precipitates. During the oxidation process, the unoxidized precipitates were incorporated in the interfacial oxide, and then the precipitates were oxidized gradually in the oxide layer. From EPMA, synchrotron XRD and SIMS analyses, the alloying elements such as Fe and Cr within precipitates exhibited differences in oxidation rate. It was found that the Fe depletion from precipitates in the initial stage stabilized the tetragonal ZrO 2 phase of the surrounding oxide and when the oxidation time increased, the depletion of Fe and Cr initiated the phase transformation of the oxide crystal structure from tetragonal ZrO 2 to monoclinic ZrO 2. All Fe within precipitates were depleted in the preference to Cr. It is thought that the overall corrosion rate of Zircaloy-4 can be governed mostly by the oxidation of Zr(Fe,Cr) 2 precipitates, and the oxidation rate of Fe was much faster than that of Cr in precipitates.

Interfacial activity of a novel family of polymeric surfactants

A novel series of polymeric surfactants based on carboxy methyl cellulose and alkyl poly(etheroxy) acrylate were synthesized by ultrasonic irradiation. These polymeric surfactants have exhibit excellent surface activity due to their unique structure. The influences of salt, alcohol and alkali on the interfacial activity of these polymeric surfactants were studied by interfacial tensiometery, dynamic laser scattering (DLS), UV spectroscope and environmental scanning electrical microscope (ESEM). The surface tension and interfacial tension (IFT) properties change little with NaCl added. The formed micelles shrink, their size becomes smaller. Alcohols cause the IFT to decrease a little because a small amount of free chains present in solution. Under the influence of added alkali, the IFT of the polymeric surfactants, in aqueous solution, decreases so much that sometimes it is less than 10 −2 mN/m. Using data from the equivalent alkane scan, one cannot draw the conclusion that the action of alkali with the acidic components in crude oil leads to the ultra-low IFT. The analyses by UV, DLS and ESEM show that the micelles formed by polymeric surfactants could be disaggregated or destroyed sharply by the action of alkali. So the size of micelles decreases greatly and the number of free chains increases. That more polymeric surfactants molecules move to the interface of oil/water and rearrange at the interface of oil/water is believed to be the main reason of the ultra-low IFT (10 −3 mN/m) that is obtained.

Development and characterization of poly(trimethylene terephthalate)‐based bicomponent meltblown nonwovens

AbstractPoly(trimethylene terephthalate) (PTT)‐based mono and bico meltblown webs have been produced by using a Reicofil® Bi‐Component Meltblown Line at TANDEC, located at the University of Tennessee, Knoxville, TN. Thermal and flow properties of PTT were first examined by DSC (differential scanning calorimetry) and with a Melt Indexer for an effective experimental design through the Surface Response Methodology (SRM). The processability of meltblowing in a wide range of operating windows was extensively investigated. Melt temperature, melt throughput, air temperature, airflow rate, and DCD (distance of collector to die) were considered as primary process control variables. The produced webs were characterized for fiber diameter, bulk density, air permeability, hydrostatic head, tensile properties, and heat shrinkage. Non‐round and curly or twisted fibers were observed in the bico PP/PTT webs by SEM (scanning electrical microscope). The PTT grade studied is quite suitable for the meltblown process. The PTT/PP‐based bico webs showed enhanced barrier properties and heat resistance. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1280–1287, 2002

Investigations of local electrical surface characteristics by dynamical scanning force microscopy

A technique is presented that allows to obtain information about sample surface topography and local electrical surface properties simultaneously. A scanning electrical force microscope is used for that purpose which is based on an atomic force microscope (AFM) working in the dynamical mode. Different information channels contained in the cantilever excitation spectrum are separated by a lock-in technique. The physical content of the technique is discussed in detail and the influence of surface topography on the non-topographic imaging is demonstrated. Finally, the real advantages of cross-sectional sample preparation (as known from electron microscopy) for this kind of scanning probe microscopy with respect to various applications is presented.

Detecting electrical forces in noncontact atomic force microscopy

A scanning electrical force microscope (SEFM) is presented, for which the mechanical cantilever modulation frequency is close to the mechanical resonance, whereas the fundamental of an electrical modulation far below the mechanical resonance is used for Kelvin feedback and the second harmonic of the electrical modulation is used for detecting the derivative of the capacitance with respect to the tip-sample spacing. The operation of the microscope is demonstrated for a test sample with structured chromium electrodes on a glass substrate. The imaging of surface potential distributions as well as of local capacitances is discussed. For gold films on silicon, variations in capacitance caused by variations of the tip-sample geometry show the sensitivity of the method.