DESIGN OF THE CONTACT POTENTIALS DIFFERENCE PROBES

The contact potential difference probes distinguished by great variety and produced mostly in the laboratory for specific experimental applications. As a rule, they consist of commercially available instrumentation, and have a number of disadvantages: large dimensions, complexity and high cost, small sensitivity, operating speed, noiseproof, etc. The purpose of this paper is to describe the basic approaches to design of the small dimension, complete contact potential difference probes, providing high sensitivity, operating speed, and noise immunity. In this paper the contact potential difference probe, which is a electrometer with dynamic capacitor plate at about 0.1–5 mm2 . These probes are could be used in scanning systems, such as a Scanning Kelvin Probe, as well as for controlling system of manufacturing processes, e.g. under friction. The design of such contact potential difference probes conducted using modern electronic components, unique circuitry and design solutions described in detail at paper. The electromechanical modulator applied for mechanical vibrations of the reference sample. To provide a high amplitude and phase stability the upgraded generator with Wien bridge was used instead traditional oscillation sensor. The preamplifier made on the base of modern operational amplifiers with femtoampere current input. The power of the preamplifier designed with «floating ground». It allows keeping the relation constant potential to the probe components when changing over a wide range the compensation voltage. The phase detector-integrator based on the electronic antiphase switches with the modulation frequency of the contact potential difference and the integrator. Fullwave phase detection would greatly increase the sensitivity of the probe. In addition, the application of the phase detection allows suppressing noise and crosstalk at frequencies different from the modulation frequency. The preamplifier and the reference sample mounted on a flexible printed circuit board and the edge mechanically connected with a vibrator. Modulator, phase detector-integrator, and other electronic components placed on a separate board. This design contributes to reduce the influence of electromagnetic interference and noise as well as removing microphonic effects, etc

Light-Reflecting coatings on the basis of polymeric powder compositions and micro spheric reflectors

Tailored compositions and the structure of light-reflecting coatings with the use of thermosetting polymeric powder compositions and micro-spheric reflectors on the basis of inorganic glass are developed. In order to get light-reflecting coatings with the preset complex of optical and physical-chemical figures we developed technological process. The technological process of powder compositions application and coating formation is carried out with the help of the specialized equipment complex. We defined the basic optical properties of the coatings and optimum operating parameters of their derivation. We developed optico-physical model of multilayer filled coating structure considering the optical and other characteristics of the components which form the coating. © IDOSI Publications, 2014

Sound-absorbing polyurethane foam for the auto industry

© 2017, Allerton Press, Inc.Ambient noise harms the human organism: it produces high levels of the stress hormones, disrupts the operation of the nervous system, provokes cardiovascular damage, and impairs hearing. In the creation of new noise-reducing materials, the goal is to increase porosity without loss of structural strength. With greater porosity and reduced thickness, acoustic insulation will be lighter, which is better for use in automobiles. In addition, the dynamic characteristics are improved, and vehicle assembly is simplified

КОМПЕНСАЦИЯ ПОГРЕШНОСТЕЙ ИЗМЕРЕНИЯ ЭЛЕКТРИЧЕСКОГО ПОТЕНЦИАЛА ПРИ УМЕНЬШЕНИИ РАЗМЕРОВ ЗОНДА КЕЛЬВИНА

The study is based on results of modeling of measurement circuit containing vibrating-plate capacitor using a complex-harmonic analysis technique. Low value of normalized frequency of small-sized scanning Kelvin probe leads to high distortion factor of probe’s measurement signal that in turn leads to high measurement errors. The way to lower measurement errors is to register measurement signal on its second harmonic and to control the probe-to-sample gap by monitoring the ratio between the second and the first harmonics’ amplitudes.Представлены результаты моделирования измерительной цепи, содержащей динамический конденсатор, методом комплексно-гармонического анализа. Из-за малого значения нормированной частоты вибрации измерительный сигнал зонда Кельвина с чувствительным элементом малых размеров характеризуется значительными гармоническими искажениями, приводящими к резкому увеличению погрешности измерений. Уменьшение погрешностей может быть обеспечено за счет регистрации сигнала на его второй гармонике и контроля величины зазора зонд-образец на основе измерений отношения амплитуд первой и второй гармоники сигнала.

Prediction of elastic modulus for polymer composites

© Research India Publications.Elasticity of the composites was analyzed as inhomogeneous systems and their predictive estimation was provided using relevant models by Eshelby, nonlinear patterns of elastic de-formation of bodies with rigid inclusions (Einstein, Guth-Smallwood, Eilersvan Dijck, Kerner, Mooney, Halpin-Tsai, Nielsen, Ishai equations). With the Shklovsky-De Gennes model the topological model was obtained in order to deter-mine the fractal dimension of particulate filled polymer composites. The critical concentration of particulate filler in polymer composites was updated (percolation threshold υ=0, 15) to reveal a structural transition from isolated clusters to a skeleton lattice which consists of dispersed particles and polymer film matrix. Using the percolation theory a value of critical exponent t3 (universal exponent for state of structural topology of particulate filled polymer system) was found and defined. The universal critical exponent t3=1, 58 was found, it determines a skeleton of fractal percolation cluster from fractal point of view, and it was revealed to have a pivotal effect on increasing the elasticity of composite materials. The pre-diction mathematical models (polynomial, exponential, etc.) were obtained for dynamic modulus and impact resistance of epoxy, polyether, epoxy-polyurethane composites according to the concentration of different hardeners. The optimum concentrations of matrix components (hardeners, modifiers) which provide high elasticity and impact resistance of the polymer matrices under study were defined. Based on the Kelvin-Voigt model a new structural mechanical model of particulate filled polymer composites was developed. It reflects the strain condition of matrix-mass, matrix-film and percolation lattice which consists of dispersed particles. With the Verhult’s method the prediction models were obtained to describe the change in dynamic modulus according to volume content of reinforcing fillers. A two-component modifying agent was developed for epoxy-polyurethane composite materials with higher stress-strain properties. It consists of poly-ether and polyisocyanate in a ratio of 1 to 1. The formulas of effective filled epoxy, polyether and epoxy-polyurethane composites were specified

CONTROL OF METAL SURFACES MACHINED IN ACCORDANCE WITH THE DIAMOND NANOMACHINING TECHNOLOGY BASED ON THE ELECTRON WORK FUNCTION

Dimensional machining technology is based on the use of integrated geometric parameters of machined surfaces. Technological impact of a pick results in oxidation processes and changes in physic-chemical parameters of surface. Control of only geometric parameters is insufficient to describe characteristics of machining and formation of ultra-smooth surfaces. The electron work function is therefore used. The aim of the work was to study electrophysical states of optic surfaces of non-ferrous metals and alloys in relation to geometric and physic-chemical parameters according to the distribution of the electron work function over the surface. We conducted the study on experimental metal samples made of copper and aluminum alloy, machined in accordance with the diamond nanomachining technology. The diamond nanomachining technology would be capable of ensuring the roughness of non-ferrous metals and alloys machined at the level of Ra ≤ 0,005 µm. Modernized Kelvin probe was used as the registration technique of the changes of the electron work function over the surface. Dependence between the electron work function value, as well as its alteration and the physicchemical and geometric parameters of a surface has been determined. It has been shown that the diamond nanomachining technology makes it possible to obtain electro-physically uniform optical surfaces on copper and aluminum alloy with the minimal range of the distribution of the electric potential over the surface

АНАЛИЗ МЕТОДА ИЗМЕРЕНИЯ ПОВЕРХНОСТНОГО ПОТЕНЦИАЛА ДИЭЛЕКТРИКОВ ПО СХЕМЕ ТОКОВОЙ КОМПЕНСАЦИИ

The comparative analysis of time-varying probe methods of measurement of a surface potential is held. Regarding contactless measurement of dielectrics' surface potential in a wide range of meanings, a current feedback scheme is found to be optimal. Advantages of this scheme are high spatial resolution, a wide measuring range and an independence of output signal on a probe-to-surface gap in a certain range of gap meanings. Metrological characteristics of the scheme are analyzed resulting in a mathematical expression for a normalized methodical measurement error.Проведен сравнительный анализ динамических зондовых методов измерения поверхностного потенциала. Показано, что для бесконтактных измерений поверхностного потенциала диэлектриков в широком диапазоне значений оптимальным является использование схемы с токовой компенсацией. Преимуществами данной схемы являются высокое пространственное разрешение, широкий диапазон измерений поверхностного потенциала, независимость измерительного сигнала от расстояния между зондом и исследуемой поверхностью в пределах определенного диапазона расстояний. Проанализированы метрологические характеристики предлагаемой схемы и получена расчетная формула для определения предела приведенной методической погрешности измерения

ДИАГНОСТИКА ЛОКАЛЬНЫХ ИЗМЕНЕНИЙ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ ПО РАБОТЕ ВЫХОДА ЭЛЕКТРОНА

The paper describes the electronic work function measurements by the contact potential difference technique, and experimental demonstration of the possibility of these methods application for the stress-strain state of the surface layer of the metals and alloys. The techniques end examples of their application of localization of plastic deformation studies using the Kelvin probe are developed and present. The study topology of work function the deformed surface possible to determine the type of deformation and dynamics ofРассмотрены вопросы измерения работы выхода электрона по контактной разности потенциалов и экспериментально обоснована возможность применения этих методов для оценки напряженно-деформированного состояния поверхностных слоев металлов и сплавов. Разработаны методики и приведены примеры их применения для исследования локализации пластической деформации с применением зонда Кельвина. Показано, что исследование топологии работы выхода электрона деформируемой поверхности позволяет определять вид деформации, изучать динамику дефектов на поверхности, выявлять потенциальные очаги разрушения на локальных участках поверхности.

МЕТОДЫ ИЗМЕРЕНИЙ РАБОТЫ ВЫХОДА ЭЛЕКТРОНА ДЛЯ КОНТРОЛЯ СОСТОЯНИЯ ПОВЕРХНОСТЕЙ В ПРОЦЕССЕ ТРЕНИЯ

The paper describes the electronic work function measurements by the contact potential difference technique, and experimental demonstration of the possibility of their application for the monitoring of the friction surface. The techniques of tribological studies using contact potential difference probes are developed. Examples of measurements work function during friction for the bronze and steel samples are present. The study work function directly in the process of friction possible to determine the modes of friction and dynamics of defects on the surface friction, identify spots of destruction on local microroughnesses.Рассмотрены вопросы измерения работы выхода электрона по контактной разности потенциалов; экспериментально обоснована возможность их применения для оценки и контроля состояния поверхности трения. Разработаны методики и приведены примеры их применения для определения работы выхода электрона при трибологических исследований с применением зонда Кельвина. Показано, что исследование работы выхода электрона непосредственно в процессе трения позволяет определить режимы трения, изучать динамику дефектов на поверхности трения, выявлять очаги разрушения на локальных микронеровностях