|
|
The study of the different percentage performance of nanoparticles on the properties of epoxy resin
Hudec, Jiří ; Neděla, Vilém ; Polsterová, H.
This paper deals with the study of impact of different percentage filling of nanoparticles on the electrical properties of epoxy resin, which has very good mechanical and electrical properties. The sample is the blended mixture which is evacuated, subjected to ultrasound and then cured. It is expected that the formation of lumps should be minimised due to the influence of microwaves. Nanoparticles should be equally distributed in epoxide volume for this case. Unfortunately, this assumption was not proven. The mixture contains an epoxy resin CY228, hardener HY918, softener DY045 and accelerator DY062. Nanoparticles of alumina (Al2O3), sulfur dioxide (SiO2), titanium dioxide (TiO2) and tungsten oxide (WO3) from Sigma Aldrich Company were used as a filler. There were made samples for each filler with 0.25, 0.5, 1, 2 weight percent for our experiment and were determined values of the dissipation factor tg.delta., permittivity .epsilon.r and resistivity .rho.v by measuring.
|
|
|
Using environmental scanning electron microscopy (ESEM) as a non-invasive method to studying fixed parasites
Mašová, Šárka ; Neděla, Vilém ; Tihlaříková, Eva
Scanning electron microscopy (SEM) is popular and for taxonomy of parasites very important and not substituted method in many times. However sometimes taxonomists have only one specimen and cannot use classical SEM, because their sample (poor conductor) have to be fixed, dehydrated and coated before it can be observed. This method condemns samples for destroying and do not allow other using of it, e.g. for molecular study or depositing as type material in museum. Moreover, the specimen preparation is often long and slow. Environmental scanning electron microscopy (ESEM) brings two main advantages: elimination of speed of sample preparation and non-invasivity.
|
|
|
The Study of Ice Impurities Using the Environmental Scanning Electron Microscopy at Higher Pressures and Temperatures
Neděla, Vilém ; Runštuk, Jiří ; Klán, P. ; Heger, D.
Natural ice and snow accumulate and concentrate significant amounts of impurities that can be stored or chemically transformed, and eventually released to the environment. The location of impurities and their interactions with the water molecules of ice have not yet been sufficiently clarified. The aim of this work is to observe an uranyl-salt brine layer on the ice surface using a back scattered electron detection and the ice surface morphology using a secondary electron detection under equilibrium conditions in a specimen chamber of environmental scanning electron microscope (ESEM). Our specially modified ESEM AQUASEM II equipped with the YAG:Ce3+ backscattered electron detector, an ionization detector of secondary electrons, a special hydration system and a Peltier cooled stage was used. The pressures between 400-700 Pa, 50% water-vapor saturation, and the temperatures above 250 K were utilized in our experiments. At these conditions, the phenomena of etching and subsequent stripping of impurities are largely suppressed.
|
guest ::
