Non-Contact Electromagnetic Control Methods of the Specific Conductivity Powders Materials , Solid Inorganic and Polymer Film
Specific conductivity is one of the defining parameters of the powdered materials, solid inorga nic nd polymer film. These properties can characterize not only ph ysical parameters as it but also materials purity, components uniform distribution, etc. Test the specific conductivity for material s characterization can be use in chemical industry du ing materials synthesis. Specific conductivity of materials is es pecially important also for energy storage industry (battery, supercapacitor, fuel cell) where some electrodes an d electrolyte materials with a low conductivity are used. Well known contact methods for testing the conductivity of powdered materials, solid or polyme r plasticized film, (for example battery electrolyte) have severa l disadvantages connected with the direct contact b etween the test probe and the material surface. Information about c nductivity includes additional resistance between probe and materials surface. This error depends significantly on the contact pressure and area of contact betwee n probe and materials, as well as the operating range of materi al conductivity and its plasticity in the case poly mer film. In a number of cases, (powders or thin films of a few te ns of microns) this parameter is practically non -measurable due to the impossibility to attach the electrodes to material. The goal of current is to develop an effecti ve non-destructive non-contact methods and devices for test conductivity powdered and thin film materials. Method’s background. It is known a number of devices for non-cont act conductivity measurement in conducting material s – metals and their alloys by electromagnetic eddy-current method [1,2]. However, neither a sensor design, nor their operation frequency ranges are unacceptable for work with rel atively low-conducting materials. Low conductivity of materials stipulates the work necessary to get the appreciabl e reacting of sensor to tens and hundreds of MHz. I n this case, use of the classic methods becomes problematic due of t uning away from the influence of clearance changes between the sensor end and the material surface based on th e phase conversions. It is connected with the incr easing amplitude-phase error, parasitic incursions in the c annels of phase indicator, etc. The method sensitivity depends on the frequen cy of eddy magnetic field of probing material by it s specific conductivity Z ad=48×10 ωRW℮βφ(ξ,β), where ω= 2πf –circular frequency; Rradius of eddy-current se nsor; Wa number of turns; α=2h/R, where hvalue of the clearance between working surface of edd y-current sensor and the surface of the control led material; β= R√ωσμ0 – generalized parameter, σspecific conductivity of material; μ0=4π×10 Гн/m; ξ=2d/R, where d – thickness of powder (film) layer; φ=(ξ,β) – special function . For determination of specific conductivity by non-contact non-destructive control method we have obtained: special mathematical dependence conformably to t he resonance method, allowing to calculate specifi c conductivity by the indirect measured parameters. special designs of applied and straight through parametric converters have been developed. This method enables tuning out from the influ ence of the change of clearance and skewing of eddy -current converters relative to the surface of the measured object. Modulus of the specialized microprocessor w ith the analogue channel of data input is the core of the a pparatus solution of the method. Conductivity test powdered material. Common contact measurements of the powdered ma terials conductivity, in the main give the informat ion about the value of contact resistance between grains. The ir results depend significantly on the powdered mat eri l density, electrical properties of powder grain surface and a re characterized by the essential errors running up to 20-30% and more. This error depends significantly on the amoun t f grains contacting with the area of measuring e lectrode at each measurement The contact measurements fail to d etermine powdered materials conductivity as the ele ctrical resistance of the grains chain to the current that flows in succession through them is mainly determin ed by the contact resistances in places the grains contact ea ch other, while these resistances substantially exc eed their inner resistances. This is explained by two reasons. First, the c ontacting grains, when the powder is of minor densi ty (within the operating range of the powder densities being used for electrode coats of the chemical power sources) obtained by vibration compacting, have relatively small areas o f contact there among. Second, the surface resistan ce of the powder grains is as a rule substantially higher of the volume resistance. This is explained by a lower concentration of free charge carriers on the surface of the grain s nd by their lower mobility, by forming, due to t he chemical interaction with the atmosphere, of various types o f insulating films, surface layers, inclusions, etc . The authors of the paper have developed the ma in principles of electromagnetic eddy-current metho d measurement of the conductivity of material grain o f on-metal powders and concentration of grains (ox ides, sulphides, different modifications of graphite, spi nel, etc) at the different bulk densities of powder s. Developed method could be transformed from stationary conditi ons materials test after synthesis to conditions ac tive test during material synthesis. Conductivity test solid inorganic and polymer plast icized film. Solid inorganic and polymer solid or plastici zed film materiel often use as electrolyte energy s torage like lithium battery, supercapacitor, fuel cell. Serviceability of chemical power sources is determined to a great extent by the properties of their solid or polymer electrolytes. Among these properties, ionic conductivity is of pa rticular significance. For use of the non-contact electromagnetic met hod for testing conductivity of solid electrolytes several serious problems must be addressed. The surface of the samp les is some times quite small making it difficult t o use differential measurements. The introduced impedance of the induction coil within the meter wave length range (corresponding to the operating frequency range of the eddy-current conductance measurements of polyme r electrolytes) is subject to the influence of the di lectric losses of the polymer. Hence, the conducti vity being measured depends on the frequency even in case wher the conductivity of the polymer electrolyte is re lat d to the movement of the free charge carriers and is frequen cy-independent. Electromagnetic methods with the combined sen sor and electromagnetic capacitance methods develop ed by authors of this paper will allow generation of vali d results for the measurement of specific electrica l conductivity of solid inorganic or polymer electrolytes. Depending o electrolyte conductivity, it is preferred to use th combined sensor or capacitance non-destructive non-contact m ethod. In the case electromagnetic methods with combi ned sensors the measurement is achieved by means of integral probe for non-contact electrical conductivity deter mination in polymer electrolytic films. The method consists of placing the film on a flat dielectric substrate, ex citation of an eddy-current magnetic field by means of an inductance coil at a series of discrete frequencies, and measu ring its impedance at these frequencies while the o perating end face of the coil is located on the film surface and o the substrate. In the case of the non-contact capacitance me asur ment method of ionic conductivity in solid ele ctrolytes a complex methods based on the use of converters with a harmonically variable electric field is used. Co ntact areas of the same shape and surface area are applied to the opposite faces of a sample located on the same axis . Measurement of the frequency characteristic of the sample activ e resistance between the contact electrodes is then carried out, along with investigation of the characteristic freq u ncy gradient for the active resistance of the sam ple.
Measurement of Complex Electrical Conductivity of Metallic Powders in a Sealed Tube
We studied the method of complex-electrical-conductivity measurement for powders placed in a sealed tube at microwave and millimeter-wave frequencies, using a cavity perturbation technique. We applied this technique to a molecular superconductor K3C60, whose electrical conduction is well known in single crystals, and reproduced the metallic conductivity with the magnitude of 0.5–1.2 mΩcm at 20 K which is in good agreement with the data for single crystals. From this result, it was found that the cavity perturbation technique works well for the conductivity measurement of anaerobic powders, with respect to metallic materials.
Metal-insulator transition in ammoniated K3C60.
Magnetic susceptibility, electron spin resonance, and 13 C nuclear-magnetic-resonance data on NH 3 K 3 C 60 reveal that NH 3 K 3 C 60 is a narrow-band metal with a transition to an insulating ground state at 40 K. This transition suppresses the superconductivity that is expected to occur at around 30 K according to a simple empirical relation between T c and the cell volume in alkali-metal-doped C 60 superconductors.