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Coulometry at an imposed, constant current in the electrochemical cell. Direct coulometry at controlled current is usually carried out in convective mass transfer mode. The end-point of the electrolysis, at which the current is stopped, must be determined either from the inflection point in the E–t curve or by using visual or objective end-point indi- cation, similar to volumetric methods. The total electric charge is calculated as the product of the constant current and time of electrolysis or can be measured directly using a coulometer. The advantage of this method is that the electric charge consumed during the electrode reaction is directly proportional to the electrolysis time. Care must be taken to avoid the potential region where another electrode reaction may occur. (en) +
In principle, the end point at which I = 0, i.e. when the concentration of species under study becomes zero, can be reached only at infinite time. However, in practice, the electrolysis is stopped when the current has decayed to a few percent of the initial value and the charge passed at infinite time is calculated from a plot of charge Q(t) against time t. For a simple system under diffusion control Qt= Q∞[1 − exp(−DAt/Vδ)], where Q∞ = limt→∞Q(t) is the total charge passed at infinite time, D is the diffusion coefficient of the electroactive species, A the electrode area, δ the diffusion layer thickness, and V the volume of the solution. (en) +, Coulometry at a preselected constant potential of the working electrode. Direct coulometry at controlled potential is usually carried out in convective mass trans- fer mode using a large surface working electrode. Reference and auxiliary electrodes are placed in separate compartments. The total electric charge is obtained by integration of the I–t curve or can be measured directly using a coulometer. (en) +
Method of determining the internal resistance of an electrochemical cell by applying a low current followed by higher current within a short period, and then record the changes of battery voltage and current. (en) +
Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. In the scope of DLS, temporal fluctuations are usually analyzed using the intensity or photon auto-correlation function (also known as photon correlation spectroscopy - PCS or quasi-elastic light scattering - QELS). (en) +
Dynamic mechanical analysis (abbreviated DMA) is a characterisation technique where a sinusoidal stress is applied and the strain in the material is measured, allowing one to determine the complex modulus. The temperature of the sample or the frequency of the stress are often varied, leading to variations in the complex modulus; this approach can be used to locate the glass transition temperature[1] of the material, as well as to identify transitions corresponding to other molecular motions. (en) +
Dynamic Mechanical Analysis (DMA) is a material characterization technique where a small deformation is applied to a sample in a cyclic manner. This allows measurement of the materials response to stress, temperature, frequency or time. The term is also used to refer to the analyzer that performs the test. (en) +
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a characterisation method used in electrochemistry (en) +
Electrochemical measurement method of the complex impedance of an electrochemical system as a function of the frequency of a small amplitude (normally 5 to 10 mV) sinusoidal voltage perturbation superimposed on a fixed value of applied potential or on the open circuit potential. Impedimetric sensors are based on measurement of a concentration-dependent parameter taken from analysis of the respective electrochemical impedance spectra, or from the impedance magnitudes at a chosen fixed frequency. The sinusoidal current response lags behind the sinusoidal voltage perturbation by a phase angle φ. Resistances (e.g. to charge transfer) give a response in phase with the voltage perturbation; capacitances (e.g. double layer) give a response 90° out of phase; combinations of resistances and capacitances give phase angles between 0 and 90°. Plots of the out of phase vs. the in phase component of the impedance for all the frequencies tested are called complex plane (or Nyquist) plots. Plots of the phase angle and the magnitude of the impedance vs. the logarithm of perturbation frequency are called Bode diagrams. Complex plane plots are the more commonly used for electrochemical sensors. (en) +
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Measurement principle in which the complex electric impedance of a system is measured, usually as a function of a small amplitude sinusoidal electrode potential. (en) +
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Electrogravimetry using an electrochemical quartz crystal microbalance. The change of mass is, for rigid deposits, linearly proportional to the change of the reso- nance frequency of the quartz crystal, according to the Sauerbrey equation. For non- rigid deposits, corrections must be made. (en) +
Method of electroanalytical chemistry used to separate by electrolyse ions of a substance and to derive the amount of this substance from the increase in mass of an electrode. (en) +, method of electroanalytical chemistry used to separate by electrolyse ions of a substance and to derive the amount of this substance from the increase in mass of an electrode. (en) +
Electron backscatter diffraction (EBSD) is a scanning electron microscopy (SEM) technique used to study the crystallographic structure of materials. EBSD is carried out in a scanning electron microscope equipped with an EBSD detector comprising at least a phosphorescent screen, a compact lens and a low-light camera. In this configuration, the SEM incident beam hits the tilted sample. As backscattered electrons leave the sample, they interact with the crystal's periodic atomic lattice planes and diffract according to Bragg's law at various scattering angles before reaching the phosphor screen forming Kikuchi patterns (EBSPs). EBSD spatial resolution depends on many factors, including the nature of the material under study and the sample preparation. Thus, EBSPs can be indexed to provide information about the material's grain structure, grain orientation, and phase at the micro-scale. EBSD is applied for impurities and defect studies, plastic deformation, and statistical analysis for average misorientation, grain size, and crystallographic texture. EBSD can also be combined with energy-dispersive X-ray spectroscopy (EDS), cathodoluminescence (CL), and wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery. (en) +
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The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the sample. (en) +
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Electron probe microanalysis (EPMA) is used for quantitative analysis of the elemental composition of solid specimens at a micrometer scale. The method uses bombardment of the specimen by keV electrons to excite characteristic X-rays from the sample, which are then detected by using wavelength-dispersive (WD) spectrometers. (en) +
Ellipsometry is an optical technique that uses polarised light to probe the dielectric properties of a sample (optical system). The common application of ellipsometry is the analysis of thin films. Through the analysis of the state of polarisation of the light that is reflected from the sample, ellipsometry yields information on the layers that are thinner than the wavelength of the light itself, down to a single atomic layer or less. Depending on what is already known about the sample, the technique can probe a range of properties including layer thickness, morphology, and chemical composition. (en) +
An analytical technique used for the elemental analysis or chemical characterization of a sample. (en) +
The environmental scanning electron microscope (ESEM) is a scanning electron microscope (SEM) that allows for the option of collecting electron micrographs of specimens that are wet, uncoated, or both by allowing for a gaseous environment in the specimen chamber. (en) +
Extended X-ray absorption fine structure (EXAFS), along with X-ray absorption near edge structure (XANES), is a subset of X-ray absorption spectroscopy (XAS). Like other absorption spectroscopies, XAS techniques follow Beer's law. The X-ray absorption coefficient of a material as a function of energy is obtained by directing X-rays of a narrow energy range at a sample, while recording the incident and transmitted x-ray intensity, as the incident x-ray energy is incremented. When the incident x-ray energy matches the binding energy of an electron of an atom within the sample, the number of x-rays absorbed by the sample increases dramatically, causing a drop in the transmitted x-ray intensity. This results in an absorption edge. Every element has a set of unique absorption edges corresponding to different binding energies of its electrons, giving XAS element selectivity. XAS spectra are most often collected at synchrotrons because of the high intensity of synchrotron X-ray sources allow the concentration of the absorbing element to reach as low as a few parts per million. Absorption would be undetectable if the source is too weak. Because X-rays are highly penetrating, XAS samples can be gases, solids or liquids. (en) +
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Fatigue testing is a specialised form of mechanical testing that is performed by applying cyclic loading to a coupon or structure. These tests are used either to generate fatigue life and crack growth data, identify critical locations or demonstrate the safety of a structure that may be susceptible to fatigue. (en) +