Control of structurization processes in wood-cement systems at fixed pH

The paper presents a study of structurization processes in the wood-cement systemmixed with the buffer solutions and the improvement of service properties of products produced therefrom. Infrared spectroscopy, X-ray phase analysis, and pH measurements show that structurization processes in wood-cement systems depend on the acidity of aqueous solution, the behavior of hydration, neutralization, and polycondensation reactions with the formation of polymer products including those with cement grout components and functional groups of wood. It is shown that phosphate buffer solutions used for mixing wood-cement compositions improve their strength properties and reduce water absorption. The optimum acidity of the buffered medium for service properties of the wood-cement systemis pH = 4.8

Creation of functional solid-state composites based on black peat

The paper presents investigations of composite materials based on black peats of Barabinskoe and Taganskoe deposits of the Tomsk region and carboxymethyl cellulose, both modified with iron (Ш) and copper (II) chloride solutions. In order to improve hydrophobic properties of compositions, optimum salt concentrations are detected. Water sorption and desorption isotherms are obtained for modified specimens. It is suggested to employ synthesized solid-state compositions as insulators in the capacity of both humidity controller and indoor-contaminant absorber

Structural-energy states of water and aqueous solutions under external influence

The surface state of alkaline-earth metals and magnesium oxides obtained by means of commercial and laboratory ways has been studied in this paper. A complex of methods has been used for identification, determination of a phase composition and morphology of the samples. The high basic character of surface centres has been shown with the help of pH-metry and adsorption of indicators methods. Acid-basic parameters (pHt, pHiis, etc.) can be used for the estimation of a general acid-basic state of metal oxides samples surface and for the supposition about different nature and strength of acid-basic centres as well as for the initial control in the process of acid basic properties of solid oxides surface properties evaluation

Hydrophobic composition based on mixed-molecular weight polyethylene

The paper presents investigations of compositions based on low and high molecular weight polyethylene so as to synthesize a hydrophobic composition for moisture protection of timber. X-ray phase analysis and measurements of the tear-off force of hydrophobic coating needed to apply to the timber surface and the limiting wetting angle are carried out to detect the hydrophobic, adhesive, electrophysical, and physicochemical properties of compositions. Kinetic dependencies are given for moisture absorption of timber specimens. It is shown that the preliminary formation of the texture by the surface patterning or its treatment with low-temperature plasma with the following protective coating results in the improvement of hydrophobic properties of the suggested compositions. These compositions can be used in the capacity of water repellents to protect building materials from moisture including restoration works

Optical pump–terahertz probe study of HR GaAs:Cr and SI GaAs:El2 structures with long charge carrier lifetimes

The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of surface and volume Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that, in most cases for HR GaAs:Cr and SI GaAs:EL2, Auger recombination mechanisms make the largest contribution to the recombination rate of nonequilibrium charge carriers at injection levels above ~(0.5–3)·1018 cm−3, typical of pump–probe experiments. At a lower photogenerated charge carrier concentration, the SRH recombination prevails. The derived charge carrier lifetimes, due to the SRH recombination, are approximately 1.5 and 25 ns in HR GaAs:Cr and SI GaAs:EL2, respectively. These values are closer to but still lower than the values determined by photoluminescence decay or charge collection efficiency measurements at low injection levels. The obtained results indicate the importance of a proper experimental data analysis when applying terahertz time-resolved spectroscopy to the determination of charge carrier lifetimes in semiconductor crystals intended for the fabrication of devices working at lower injection levels than those at measurements by the optical pump–terahertz probe technique. It was found that the charge carrier lifetime in HR GaAs:Cr is lower than that in SI GaAs:EL2 at injection levels > 1016 cm−3.В ст. ошибочно: Irina A. Kolesnikov

Water-repellent coatings for surface and 3D wood processing

The paper presents the results of research in organic chemical compositions for hydrophobic protection of wood with the use of surface and three-dimensional coating techniques of impregnation and chemical compositions. Water absorption indicators, angles of contact on the surface of treated samples are detected herein. Kinetic equation of the moisture diffusion transition in capillary-porous structure of wood is suggested

Electrical relaxation and transport properties of ZnGeP2 and 4H-SiC crystals measured with terahertz spectroscopy

Terahertz photoconductivity and charge carrier recombination dynamics at two-photon (ZnGeP2) and three-photon (4H-SiC) excitation were studied. Thermally annealed, high-energy electron-irradiated and Sc-doped ZnGeP2 crystals were tested. The terahertz charge carrier mobilities were extracted from both the differential terahertz transmission at a specified photoexcitation condition and the Drude–Smith fitting of the photoconductivity spectra. The determined terahertz charge carrier mobility values are ~453 cm2/V·s for 4H-SiC and ~37 cm2/V·s for ZnGeP2 crystals. The charge carrier lifetimes and the сontributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of bulk and surface Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that ZnGeP2 possesses short charge carrier lifetimes (a~0.01 ps−1, b~6·10−19 cm3·ps−1 and c~7·10−40 cm6·ps−1) compared with 4H-SiC (a~0.001 ps−1, b~3·10−18 cm3·ps−1 and c~2·10−36 cm6·ps−1), i.e., τ~100 ps and τ~1 ns at the limit of relatively low injection, when the contribution from Auger and interband radiative recombination is small. The thermal annealing of as-grown ZnGeP2 crystals and the electron irradiation reduced the charge carrier lifetime, while their doping with 0.01 mass % of Sc increased the charger carrier lifetime and reduced mobility. It was found that the dark terahertz complex conductivity of the measured crystals is not fitted by the Drude–Smith model with reasonable parameters, while their terahertz photoconductivity can be fitted with acceptable accuracy

MODIFICATION OF NON-AUTOCLAVED FOAM CONCRETE WITH PEAT ADDITIVE TMT600

The authors have studied the effect of a thermally modified additive based on peat TMT600 on the properties and structure of foam concrete of non-autoclave hardening and proposed a model of a fragment of the structure of the gas–solid–liquid interface and a model for the formation of a porous structure of foam concrete of non-autoclave hardening. The paper reveals the mechanism of the role of the foaming agent in formation of the porous structure of foam concrete. Tomography methods have shown that the real structure of foam concrete corresponds to the proposed models, as well as the achievement of a uniform distribution of pores by volume. It was established that in hydration after the dissolution of tobermorite and ettringite, the cement particles are recharged, and, consequently, the electrokinetic potential changes from positive to negative values. The mass transfer of particles is carried out not only by diffusion, but also by convection during foam formation. The accelerated movement of particles can also be carried out due to the electrostatic interaction of charges both on the surface of the foam and the peat additive. The geometry of the structural cells of the foam has the form of polygons, consisting mainly of hexagons and pentagons. As a result of the ongoing processes, a complex hierarchical structure is formed, in which the Plateau–Gibbs channels in the foam are calmed (clogged), forming a stronger skeleton, and after cement hydration, due to the recharging of the surface of the latter, an interpore partition of increased strength is eventually formed with a simultaneous uniform distribution of pores in foam concrete structure. The developed wall material has not only high strength, frost resistance, but also increased thermal insulation properties. The foam concrete obtained with the use of the TMT600 additive fully meets the seven fundamental criteria of the modern concept of building materials science, such as: technological availability and efficiency, energy and resource saving, environmental safety and natural compatibility, economic feasibility, ethical acceptability of practical application, aesthetic expressiveness and social orientation

Terahertz generation by optical rectification of 780 nm laser pulses in pure and Sc-doped ZnGeP2 crystals

Terahertz wave generation through the optical rectification of 780 nm femtosecond laser pulses in ZnGeP2 crystals has been studied. All of the possible interactions of types I and II were analyzed by modeling and experimentally. We demonstrate the possibility of broadband “low-frequency” terahertz generation by an ee–e interaction (with two pumping waves and a generated terahertz wave; all of these had extraordinary polarization in the crystal) and “high-frequency” terahertz generation by an oe–e interaction. The arising possibility of achieving the narrowing of the terahertz generation bandwidth at the oe–e interaction using thicker ZnGeP2 crystals is experimentally confirmed. It has been found that the thermal annealing of as-grown ZnGeP2 crystals and their doping with a 0.01 mass % of Sc reduces the absorption in the “anomalous absorption” region (λ = 0.62–3 μm). The terahertz generation by the oo–e interaction in (110) ZnGeP2:Sc and the as-grown ZnGeP2 crystals of equal thicknesses was compared. It has been found that ZnGeP2:Sc is more efficient for 780 nm femtosecond laser pulses optical rectification