Properties of pore structure of thin-layer external plasters under ageing in simulated environment

The basic and commonly used four types of thin-layer facade plasters on cement and silicate binders were subjected to 400 cycles of accelerated ageing in the simulate chamber. The main attention was focused on the character of pore structure evolution during of ageing process. To reach this objective, examinations of the microstructure by the mercury intrusion method and total porosity by the densitometry method were carried out in time per 100 cycles. During the study, the main emphasis was put on the open porosity and changes of dimensional groups of pores. On the ground of the hysteresis of the mercury pressure by mercury intrusion porosimetry testing, the presence of pores with capillary entrance was suggested. In view of this, the cylindrical and spherical model of porous structure has been defined. The contribution of capillary and spherical pores vary in time together with properties such as: average pore radius, length of cylindrical pores and their tortuosity. The changes of these values confirm that atmospherical ageing influences plasters’ binders in two zones. It appears on the one hand by the decrease of total porosity, length and diameter of capillaries but on the other hand by the increase of open porosity and the decrease of pores’ tortuosity. It indicates the tightening character of the inside pore structure of the examined plasters and at the same time it gives diverse effect in its external zone.     

Synthesis of Ternary Titanium Aluminum Carbides Using Self-Propagating High-Temperature Synthesis Technique

Different ternary carbide phases, namely Ti₃AlC₂, Ti₃AlC, and Ti₂AlC, were successfully synthesized in a self-sustaining regime. Direct reactions among elemental powders of titanium, aluminum, and carbon are strongly exothermic, and the resulting reaction products consist of binary carbides and they are partially molten. The use of TiAl, instead of elemental titanium and aluminum, significantly reduces the combustion temperature. As a result, ternary titanium aluminum carbide phases are formed. In addition, the combustion-synthesized products are not sintered and easy to deagglomerate. Reaction conditions and X-ray diffraction patterns of different ternary phases formed in a self-sustaining regime are presented.     

DOMAIN OF INFLUENCE IN THERMOELASTICITY WITH ONE RELAXATION TIME

A domain-of-influence theorem for an initial-boundary-value problem of thermoelasticity with one relaxation time, proposed by Lord and Schulman, is established. The theorem asserts that for a finite time t > 0 a pair (<φ, ), in which φ and are the thermoelastic potential and temperature, respectively, generates no thermoelastic disturbances outside a bounded domain D_t.     

Hydroprocesssing of light gas oil — rape oil mixtures

Two series of experiments of hydroprocessing of light gas oil - rape oil mixtures were carried out. The reactor feed was composed of raw material: first series — 10 wt.% rape oil and 90 wt.% of diesel oil; second series — 20 wt.% rape oil and 80 wt.% of diesel oil.     

Wideband Low‐Reflection Transmission Lines for Bare Chip on Multilayer PCB

The pad pitch of modern radio frequency integrated circuits is in the order of few tens of micrometers. Connecting a large number of high‐speed I/Os to the outside world with good signal fidelity at low cost is an extremely challenging task. To cope with this requirement, we need reflection‐free transmission lines from an on‐chip pad to on‐board SMA connectors. Such a transmission line is very hard to design due to the difference in on‐chip and on‐board feature size and the requirement for extremely large bandwidth. In this paper, we propose the use of narrow tracks close to chip and wide tracks away from the chip. This narrow‐to‐wide transition in width results in impedance discontinuity. A step change in substrate thickness is utilized to cancel the effect of the width discontinuity, thus achieving a reflection‐free microstrip. To verify the concept, several microstrips were designed on multilayer FR4 PCB without any additional manufacturing steps. The TDR measurements reveal that the impedance variation is less than 3 Ω for a 50 Ω microstrip and S11 better than –9 dB for the frequency range 1 GHz to 6 GHz when the width changes from 165 µm to 940 µm, and substrate thickness changes from 100 µm to 500 µm.     

Effect of the diffusion phenomena in the catalyst grain on the selectivity of a system of parallel-consecutive reactions involved in the process of n-heptane dehydrocyclization

Analytical relations were derived for analyzing the selectivity of consecutive-parallel reactions occurring under conditions of the reforming process. With these relations it is also possible to determine how the shape of the catalyst grain, as well as the kinetic and diffusion phenomena that govern the process, affects the efficiency of the desired final products.     

Analysis of emptiness (lacunarity) as a measure of the degree of space filling and of the internal structure of a set

The study presents a comparative evaluation of emptiness (lacunarity) in model structures with different types of inhomogeneity of dispersed particle distributions. The research on emptiness (lacunarity) as a measure of the degree of space filling and, at the same time, of the internal characterization of a set has been based on the optimal covering and gliding-box methods.     

Synthesis and surface activity of nonionic surfactants containing fluorocarbon hydrophobes

Nonionic surfactants having polydisperse polyoxyethylene chains and highly fluorinated hydrophobes were synthesized via a complex reaction route and their adsorption at water/air interfaces studied. They exhibit high surface activity and decrease both effectively and efficiently the surface tension of their aqueous solutions. The effect of the length of the polyoxyethylene chain upon surfactant surface activity is relatively low. Lower values of surface tension, below 30 mN m^?1, are obtained for surfactants having a low degree of ethoxylation. Surfactants having two terminal highly fluorinated hydrophobes are less surface active than analogues with one terminal hydrophobe.