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T.V. Vakalova,N.P. Sergeev,V.E. Maksimova,P.G. Rusinov,D.I. Balamygin 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.106 No.-
The processes of obtaining a new type of ceramic proppants with high physical and mechanical propertiesbased on serpentinite rocks, which were not previously used for this purpose are investigated. Toincrease the strength of ceramic materials, methods of improving the sintering of magnesia-silicateceramics with a forsterite crystalline phase are considered. It was found that the activation of the sinteringprocess is provided by the transformation of hard-to-sinter forsterite into enstatite. This is possible byadding of siliceous raw materials with different reactivity (quartz sand, marshalite, gaize and diatomite)to the pre-calcined serpentinite. The use of diatomite and gaize additives in an amount of 20–30% insteadof quartz sand allows to reduce the firing temperature by 50–70 C (from 1300–1350 C to 1280 C–1250 C) and ensure the mechanical strength of pressed specimens up to 440 MPa. This made it possibleto develop compositions and technological parameters for obtaining magnesia-silicate proppants witha bulk density of 1.58–1.62 g/cm3 at a firing temperature of 1250–1300 C, capable of withstandingbreaking pressure up to 52 MPa.
A.L. Solovjov,L.V. Omelchenko,R.V. Vovk,O.V. Dobrovolskiy,S.N. Kamchatnaya,D.M. Sergeev 한국물리학회 2016 Current Applied Physics Vol.16 No.9
The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity s0(T) and the pseudogap D*(T) in optimally doped YBa2Cu3O7d single crystals (Tc x 91.1 K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of dlnD*/dP z 0.32, which is only a factor of 1.12 smaller than in slightly doped single crystals, is revealed for the first time. This implies a somewhat more moderate increase of the coupling strength in optimally doped cuprates with increasing pressure. Simultaneously, the ratio 2D*(Tc)/kBTc z 5 at P ¼ 0 GPa, which is typical for high-temperature superconductors with strong coupling, increases by 16% with increasing pressure. At the same time, the pressure effect on Tc is minor: dTc/dP z þ0.73 K GPa1, whereas dlnr/dP z (17 ± 0.2)% GPa1 is comparable with that in lightly doped YBCO single crystals. This suggests that the mechanisms of the pressure effect on r(T) and Tc are noticeably different. Independently of pressure, near Tc, s0(T) is well described by the Aslamazov-Larkin (3D-AL) and 2D Hikami- Larkin fluctuation theories, exhibiting a 3De2D crossover with increasing temperature. However, the temperature interval Tc < T < T01, in which s0(T) obeys the classical fluctuation theories, is exceptionally narrow (z1.16 K). Nevertheless, a peculiarity at the temperature T01, up to which the wave function phase stiffness in the superconductor is maintained, is clearly observed in the dependence D*(T). Below T01 a fast growth of D*(T) is revealed for the first time. It can be associated with a sudden increase of the superfluid density, ns, that is the density of fluctuating Cooper pairs (short-range phase correlations) forming in the sample when T approaches Tc.
I. V. Zotova,N. S. Ginzburg,A. S. Sergeev,M. I. Yalandin,A. G. Reutova,M. R. Ulmaskulov,A. K. Sharypov,S. A. Shunailov 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61
The first experiments on observation of amplification of ultrashort microwave superradiance (SR) pulses under propagating along quasistationary electron beams were performed. For this purpose experimental set-up based on two high current accelerators RADAN synchronized with accuracy 100-300 ps was build up. The first accelerator was used to drive the 37 GHz generator of superradiance pulses with duration ~300 ps based on relativistic BWO. The second accelerator with current up to 1.2 kA and electron energy ~300 keV drives the amplification section in the form of dielectric loaded waveguide. According to theoretical analysis amplification of electromagnetic pulses (minimum in 4 times on power) was accompanied by significant shortening of SR pulse duration fewer than 100 ps.