Dielectric Specimens Research Articles

Irradiation and mechanical testing of ITER relevant magnet insulation

In the scope of ITER Engineering Design Activities (EDA) the European Home Team performs an irradiation test program on industrially fabricated specimens of magnet insulation. At the unique test facility available at the research reactor of the Technical University of Munich, the shear compression test samples were irradiated at 5 K and tested without warming up. The samples, provided by Japanese, US and European industry, were fabricated using different types of epoxy resin, but the same boron-free glass fabrics inter-leafed with Kapton foil. The results are presented and assessed. The Munich test facility is no longer available. A complementary test program carried out at the research reactor of the Atomic Institute in Vienna will form the basis of future irradiation work. It is focused on the assessment of intrinsic material parameters and takes advantage of a new fatigue testing machine allowing operation at 77 K. Links to the Munich program were made by irradiating identical samples in both reactors (at 5 K in Munich and at ambient temperature in Vienna). Special sample geometry was developed and scaled versus standards for tensile and inter-laminar shear testing under cyclic load. Results on the static and dynamic properties are presented.

Clustering equilibrium and deactivation kinetics in arsenic doped silicon

The equilibrium between clusters and dopant in solution was studied on silicon on insulator specimens uniformly doped with As at concentrations CAs from 1 to 7.6×1020 cm−3. The values of the carrier density n* after equilibration at 700, 800, and 900 °C are reported. With increasing dopant concentration n* rapidly saturates to the limiting value of the carrier density ne, thus simulating a precipitation process. It is shown that the values of n* at different temperatures and dopant concentrations can be calculated by an equation derived in the Appendix by using a simple cluster model. The deactivation was analyzed by isothermal annealing of the specimens at temperatures in the range 550–800 °C. At high temperature the kinetics accurately complies with the rate equation −dn/dt=A{exp[−(E−αn)/kT]−(n0−n)/(n0−n*)exp[−(E−αn*)/kT]} which is the one reported in [D. Nobili, S. Solmi, M. Merli, and J. Shao, J. Electrochem. Soc. 146, 4246 (1999)] complemented by the second term on the right to account for the declustering process. Deviations leading to rates lower than predicted by the above equation are presented by the most heavily doped compositions after partial deactivation at temperatures ⩽ 700 °C. The analysis of this phenomenon puts into evidence that clustering presents a limiting rate which only depends on temperature and carrier density, and is insensitive to As concentration.

Nuclear qualification of PVC insulated cables

Cables insulated with eleven different PVC compounds representing fire-retardant, non-fire retardant, 60, 75 and 90/spl deg/C temperature ratings were evaluated. The specimens were subjected to accelerated thermal, radiation, and sequential radiation and thermal exposure simulating 15, 20, 30 and 40 yr in-service environments in Ontario Power Generation Nuclear Plants. The radiation level was limited to 12 to 30 Mrad. Two sets of samples were evaluated. The first contained 15 cm insulation specimens in tubular form with the conductors removed. The material performance of the insulations was assessed using the 15 cm specimens during the various stages of aging exposures by conventional elongation measurement. The second set was made from 4.3 m single or twisted pair of cable samples (unjacketed) wound on mandrels. The cable samples were sequentially irradiated and thermally aged and subjected to an additional 5 Mrad accident radiation exposure, followed by a simulated loss of coolant accident (LOCA). Similarly thermal only aged specimens with 2 Mrad of background radiation representing powerhouse environment were subjected to a main steam line break (MSLB) steam test. During the steam tests, samples were energized and their insulation resistance (IR) values were continuously monitored using an on-line setup and periodically with a megohm meter at 500 V/sub dc/. The results from the insulation samples were compared with the electrical performance of the cable samples wound on mandrels that had been subjected to the LOCA/MSLB steam test. The test results indicate that elongation values were not a good indicator of electrical performance of PVC insulated cables subjected to radiation and thermal environment. With remaining elongation values ranging from 50 to 150% absolute, four out of eleven compounds performed poorly electrically during the steam test. All thermal only aged specimens functioned satisfactorily. In addition, two additional compounds rated for 60/spl deg/C applications were investigated and functioned unsatisfactorily despite high elongation values. It was found that specific additives were responsible for poor electrical behavior. During radiation exposure ionic salts were formed as a result of break down of PVC and of some plasticizers. Upon thermal aging or later in the steam test these ionic compounds migrated to the conductor surface. Then, under high temperature and pressure steam conditions, the salts were dissolved and created an electrical leakage path. Similarly, in thermal only aged specimens, breakdown products of specific plasticizers caused poor electrical behavior.

Reduction of PD in a void by additives of azobenzoic compound in HDPE insulating material

In order to reduce partial discharges (PD) in a void within an organic insulator, the material of the inner wall of the void was modified by additives, i.e. four types of azobenzo materials: azobenzene, p-nitro-azobenzene, p-amino-azobenzene and nitrobenzene-azo-resorcinol. The voids in the insulator specimens have a cylindrical configuration with a diameter of 1 mm diameter and a height of 100 /spl mu/m. The materials of the top and bottom surfaces of the cylindrical void are high-density polyethylene (HDPE) with additive, prepared by the solution casting method. The specimen was placed between plane electrodes. It was found that the PD for the specimen with additive was reduced to as low as /spl sim/20% of that for the specimen without additive when the applied voltage was near the PD inception. The reduction of PD in the voids was observed for all four kinds of additives. The effective additive concentration was between 0.05 and 0.5% wt. The mechanisms for the reduction in PD were discussed, focusing on two factors: prevention against secondary electron emission from the void wall due to the excitation of the additive, and prevention of electron detachment from the void wall due to the charge traps by the additive, which may play significant roles in the reduction of the PD in the voids.

Image contrast of charged insulator specimen in the scanning electron microscope

Image contrast of charged insulator specimen in the scanning electron microscope

A Technique for Obtaining Thermal Resistance of the Dielectric-Substrate Contact under High-Intensity Irradiation

Heating of dielectric materials is investigated under irradiation of specimens by periodically pulsed ion-beams. The solution to the equation of thermal conductivity yields constrained variations of the specimen's temperature around its average value, with the repetition rate being that of the radiation-pulse frequency. Initially, the average variation-period temperature is found to grow, while after saturation it approaches a quasi-stationary value controlled entirely by the thermal resistance of the specimen-substrate contact under the same irradiation conditions. A method for the time-averaged dielectric temperature under saturation is proposed. Using this method, an express-technique for calculating thermal resistance of the dielectric-substrate contact is offered. It is based on periodically pulsed heating of the dielectric specimen by a moderate-density ion beam and precision measurements of the its average temperature. The error of the express technique is evaluated and so is its applicability range. A hypothesis is put forward that proceeding form this new method for thermal resistance one may determine the energy lost in ion sputtering.

X-Ray Microanalysis of Insulators in the ESEM

Abstract We have investigated the affect of accelerating voltage (E0), pressure (P), GSED bias (VGSED), field line geometry and specimen conductivity on the landing energy of the primary beam in an XL30 ESEM. The landing energy of the primary beam can be measured by using the Duane-Hunt cut-off energy, EDH, in EDS X-ray spectra. We present experimental evidence that the landing energy of the primary beam can be significantly altered when analyzing insulators in an ESEM. Shifts in EDH result from electric fields produced by the presence of positive ions in the ESEM chamber and electrons trapped in the bulk. No shift in EDH was observed with conductive specimens at all E0 and P. Changes in the landing energy of the primary beam can significantly effect the relative intensity of characteristic peaks in EDS spectra measured in the ESEM (Figure 1). The magnitude and sign of the shift in EDH is determined by E0 and P for a specific insulator specimen and stage geometry.

Clustering Equilibrium and Deactivation Kinetics in As doped Si

AbstractClustering equilibrium was studied on silicon on insulator specimens uniformly doped with As at concentrations CAs up to 7.6 × 1020 cm−3. Values of the carrier density n* after equilibration at 700, 800 and 900°C are reported. It is shown that both the concentration and the temperature dependence of n* can be accurately simulated by a simple cluster model detailed in the Appendix. The analysis of the clustering kinetics of these compositions was performed at temperatures in the range 550 to 800°C. It is found that at 800°C the kinetics accurately complies with the rate equation:-dn/ dt = A{exp[-(E-αn)/kT] - (n0- n)/( n0- n*) exp[-(E-αn*)/kT]which is the one reported in Ref.[14] complemented by the second term on the right to account for the declustering process. Deviations leading to rates lower than predicted by the above equation are observed by annealing at lower temperatures. The dependence of this phenomenon on composition and temperature is reported.

In situ Performance of Expanded Molded Polystyrene in the Exterior Basement Insulation Systems (EIBS)

Several different Exterior Basement Insulation Systems (EIBS) were built and instrumented as part of the basement consortium2 research project. These EIBS specimens were instrumented prior to back filling with soil, and their in situ thermal performance was monitored over two years. Soil temperatures and moisture content were monitored concurrently. Weather data were recorded on a daily basis. Through analysis of the measured surface temperature records, the presence of water was detected at the outer surface during various periods of heavy rain and major thaws throughout the two-year period. During these periods, the surface of the concrete showed no evidence of water penetration through the insulation layer over most of the height of the basement wall. Since the test setup involved different thermal insulating materials placed next to each other, the presence of lateral heat flow was inevitable. Both 2-D and 3-D models were used to quantify the lateral heat flow across the edges of different in sulating materials. The measured spatial and temporal temperature profiles were used as boundary conditions. The thermal performance of each insulation specimen was found to remain sta ble over the two-year period and was not significantly affected by episodes of wa ter movement at the exterior face of the specimens. The thermal resistance of

Beam Induced Composition Modifications During Electron Beam Microanalysis

The most common cause of composition modification to a specimen during electron probe microanalysis is the field induced migration of light elements. This is an indirect effect which occurs in response to the long range electric fields that form when dielectric specimens suffer charge imbalance. The result is that the ions are redistributed within the sample according to their respective mobilities and the affect is enhanced rather than eliminated when the sample is coated. The ions typically move radially outward in thin samples because of the excess production of secondary electrons from the specimen surfaces, Cazaux(1986)and downwards in conventional SEM samples when the field is due primarily to the deposition of electrons within the bulk of the specimenField induced migration is responsible for most of the elemental signal variations observed during the microanalysis of silicate glasses containing sodium or potassium ions.

Effect of neutron radiation on the dielectric, mechanical and thermal properties of ceramics for rf transmission windows

The behavior of electrically insulating ceramics was investigated before and after exposure to neutron radiation. Mechanical, thermal and dielectric specimens were studied after exposure to a fast neutron dose of 0.1 displacements per atom (dpa) at Oak Ridge National Laboratory (ORNL). Four materials were compared to alumina: polycrystalline spinel, aluminum nitride, sialon and silicon nitride. Mechanical bend tests were performed before and after irradiation. Thermal diffusivity was measured using a room temperature laser flash technique. Dielectric loss factor was measured at 105 MHz with a special high resolution resonance cavity. The materials exhibited a significant degradation of thermal diffusivity and an increase in dielectric loss tangent. The flexural strength and physical dimensions were not significantly affected by the 0.1 dpa level of neutron radiation. The aluminum nitride and S silicon nitride showed superior rf window performance over the sialon and the alumina. The results are compared to radiation studies on similar materials.

Space-charge distribution in XLPE by TSM, using the inverse matrix technique

TSM (Thermal Step Method) is a nondestructive technique to determine space charge distribution in thin and thick dielectric specimens. Although the experimental procedure is simple, the numerical techniques required for analyzing the data are complex and time consuming. Fourier analysis is commonly employed to analyze the TSM data. This paper proposes the use of the inverse matrix technique to simplify the analysis of the signals acquired by TSM. Numerical simulation by the inverse matrix technique is compared with the Fourier analysis technique. Corona charged as well as DC poled XLPE specimens are tested to confirm the validity of the inverse matrix technique. It is shown that this technique gives better results and requires less computing time than other techniques usually employed for the TSM.

Development of a Capacitor Probe to Detect Subsurface Deterioration in Concrete

ABSTRACTPortland cement concrete (PCC) structures deteriorate with age and need to be maintained or replaced. Early detection of deterioration in PCC (e.g., alkali-silica reaction, freeze/thaw damage, or chloride presence) can lead to significant reductions in maintenance costs. However, it is often too late to perform low-cost preventative maintenance by the time deterioration becomes evident. By developing techniques that would enable civil engineers to evaluate PCC structures and detect deterioration at early stages (without causing further damage), optimization of life-cycle costs of the constructed facility and minimization of disturbance to the facility users can be achieved.Nondestructive evaluation (NDE) methods are potentially one of the most useful techniques ever developed for assessing constructed facilities. They are noninvasive and can be performed rapidly. Portland cement concrete can be nondestructively evaluated by electrically characterizing its complex dielectric constant. The real part of the dielectric constant depicts the velocity of electromagnetic waves in PCC. The imaginary part, termed the “loss factor,” describes the conductivity of PCC and the attenuation of electromagnetic waves.Dielectric properties of PCC have been investigated in a laboratory setting using a parallel plate capacitor operating in the frequency range of 0.1 to 40.1MIHz. This capacitor set-up consists of two horizontal-parallel plates with an adjustable separation for insertion of a dielectric specimen (PCC). While useful in research, this approach is not practical for field implementation. A new capacitor probe has been developed which consists of two plates, located within the same horizontal plane, for placement upon the specimen to be tested. Preliminary results show that this technique is feasible and results are promising; further testing and evaluation is currently underway.

Observation of subcellular nanostructure of single neurons with an illumination mode photon scanning tunneling microscope

We report about the observation of microtubules lying underneath the cell membrane of neural process in neurons with a resolution as high as that of an electron microscope by an illumination mode photon scanning tunneling microscope. Nanoapertures used in our observations were fabricated by means of selective chemical etching and metal coating of an optical fiber. The narrowest observed tube has got an average diameter of 26 nm. Comparing this with its nominal value of 25 nm, the difference which is considered as a measure of resolution (δ) is 1 nm implying a resolution comparable to that of an electron microscope in imaging dielectric specimens. This was possible due to the presence of a boundary between the glass and the metal coating and also due to the use of an aperture of almost the same size as that of the microtubule that enhances the detection.

Image contrast of dielectric specimens in transmission mode near‐field scanning optical microscopy: imaging properties and tip artefacts

SUMMARYNear‐field scanning optical microscopy (NSOM) is a scanned probe technique utilizing a subwavelength‐sized light source for high‐resolution imaging of surfaces. Although NSOM has the potential to exploit and extend the experimental utility of the modern light microscope, the interpretation of image contrast is not straightforward. In near‐field microscopy the illumination intensity of the source (probe) is not a constant value, rather it is a function of the probe–sample electronic environment. A number of dielectric specimens have been studied by NSOM to elucidate the contrast role of specimen type, topography and crystallinity; a summary of metallic specimen observations is presented for comparative purposes. Near‐field image contrast is found to be a result of lateral changes in optical density and edge scattering for specimens with little sample topography. For surfaces with considerable topography the contributions of topographic (Z) axis contrast to lateral (X,Y) changes in optical density have been characterized. Selected near‐field probes have also been shown to exhibit a variety of unusual contrast artefacts. Thorough study of polarization contrast, optical edge (scattering) contrast, as well as molecular orientation in crystalline specimens, can be used to distinguish lateral contrast from topographic components. In a few cases Fourier filtering can be successfully applied to separate the topographic and lateral contrast components.

Measurement of low losses in dielectric materials in the millimeter and submillimeter bands

It is shown that by using beam-guiding methods to measure the transmission and reflection coefficients of dielectric specimens one can increase the accuracy with which the losses in the materials are determined compared with the usual free-space and waveguide methods.

Calibration of a Heat Flow Meter Apparatus

A series of calibration measurements was done on a 600 mm × 600 mm heat flow meter apparatus. Several specimens of medium density glass fiber in sulation and expanded polystyrene insulation were used as transfer standards. The thickness of these transfer standards varied from 25 to 160 mm. The mean tempera ture varied from 0 to 40°C and the temperature difference across the insulation spec imens varied from 10 to 40 K. Measurements included cases in which the ambient temperature of the test assembly was either maintained within 1 K of the mean tem perature, or those with only edge insulation, and an enclosure for the whole test assembly in order to reduce the edge heat losses. A total of 91 sets of measurements were made. Each set of measurements included two sub-sets, one for the warmer(hot) plate and the other for the colder(cold) plate and each sub-set included a heat flow transducer output and the temperatures on either side of the transducer assembly. For 90 out of the 91 sets of measurements, the steady state heat flux across the specimen was correlated, with a standard deviation of 2%, to a simple linear rela tion between the average transducer output and the average of the surface tempera tures of the two transducer assemblies.

Measurement of specimen charging in scanning electron microscopy with a kelvin probe

AbstractA vibrating Kelvin probe in form of a platinum wire loop is used to measure the surface potential Us on electron‐irradiated free‐floating metal and insulator specimens as a function of electron energy E. This allows an accurate measurement of the critical electron energy E2 for no charging. At energies below E2, the positive charging increases with decreasing energy to Us=2–5 eV at E=0.5 keV and switching off the collector bias of the Everhart‐Thornley detector. A two‐to threefold increase of Us is observed when the bias is switched on. For E > E2, the strong increase of a negative surface potential can be measured. Insulating films free‐supported on a conductive substrate show a steep decrease to small positive and negative Us when the film thickness becomes lower than the electron range at a critical energy E3 > E2. At insulating specimen the temporal decrease of charging can be measured when the electron beam is switched off.

E‐Beam SNMS: A complementary surface analysis technique

AbstractSputtered neutral mass spectrometry (SNMS) with ionization by low‐energy electron beam offers several analytical advantages that complement the capabilities of the major surface analysis techniques: XPS, AES and SIMS. These include easy operation on insulator specimens, reduced influence of topography or sample tilt, low spread of elemental relative sensitivity factors (RSFs) across the periodic table, near‐constant RSFs in different matrices and hence quantification from 100% down to trace concentrations, ppm detection limits, microprobe operation for depth profiling and submicron imaging and depth resolutions as for SIMS (≥1 nm). In addition to these analytical performances, the equipment shares much in common with quadrupole SIMS facilities and, as with that technique, is easily integrated into multitechnique instruments.This paper compares performances of SNMS and SIMS on the same samples and presents some imaging and useful yield data from a close‐coupled ionizer, which is a new development on the 410 SIMSLAB. Comparisons are also made between, SIMS, SNMS and AES.

Moisture Diffusivity of Cellulose Insulation

Test specimens of blown cellulose insulation were placed in contact with water to initiate an isothermal moisture intake process in which liquid water was allowed to enter freely against gravity into the specimens. The transient moisture distribution in the specimens was determined using the gamma-ray attenuation method over a period of 10 days. The results indicate that, as with most porous systems, the specimens first establish a characteristic water retention curve and then undergo a unique secondary moisture transport process. This paper presents the experimental data from the investigation. The data were used to derive information on the moisture diffusivity of cellulose insulation, in relation to the secondary mois ture transport process undergone by the test specimens.