The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB 2 matrix of high-pressuresynthesized-materials (2 GPa) which can influence pining: higher borides (MgB 12 ) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on j c
The DTA and TG study in air of Ti2Al (C1-xNx) and Ti3AlC2 synthesized under Ar 0.1 MPa pressure and densified in thermobaric conditions at 2 GPa, 1400 °C, for 1 h showed that the increase of the amount of TiC layers in Ti-Al-C MAX phases structures leads to the increase of their stability against oxidation: 321 MAX phase Ti3AlC2 are more stable than Ti2AlC and Ti2Al (C1-xNx) solid solutions both before and after thermobaric treatment. The oxide film formed on the surface of the highly dense (ρ=4.27 g/cm3, porosity 1 %) material based on nanolaminated MAX phase Ti3AlC2 (89 % Ti3AlC2, 6 % TiC, 5 % Al2O3) manufactured by hot pressing (at 30 MPa) made the material highly resistant in air at high temperatures: after 1000 hours of exposition at 600 °C it demonstrated a higher resistance to oxidation than chromium ferrite steels (Crofer GPU and JDA types). Due to the surface oxidation self-healing of defects took place. Besides, the Ti3AlC2 material demonstrated resistance against high-temperature creep and after being kept in H2 at 600 °C for 3h its bending strength reduced by 5 % only. At room temperature the Ti3AlC2 bulk exhibited microhardness Hμ = 4.6 GPa (at 5 N), hardness HV50 = 630 (at 50 N ) and HRA = 70 (at 600 N), Young modulus was 140 ± 29 GPa, bending strength =500 MPa, compression strength 700 MPa, and fracture toughness K1C=10.2 MPa·m0.5.
The Ti3AlC2-, (Ti,Nb)3AlC2-and Ti2AlC-based materials turned out to be more resistant than Crofer JDA steel in oxidizing atmosphere as 1000 h long tests at 600• C have shown. But the amounts of oxygen absorbed by the materials during testing were different. The Ti2AlC-based material demonstrated the lowest oxygen uptake, (Ti,Nb)3AlC2-based absorbed a somewhat higher amount and the highest amount was absorbed by Ti3AlC2-based material. Scanning electron microscopy and the Auger study witnessed that amounts of oxygen in the MAX phases before the exposure in air were as well different: the approximate stoichiometries of the matrix phases of materials were Ti3.1−3.2AlC2−2.2, Ti1.9−4Nb0.06−0.1AlC1.6−2.2O0.1−1.2 and Ti2.3−3.6AlC1−1.9O0.2−0.6, respectively. The higher amount of oxygen present in the MAX phase structures may be the reason for higher resistance to oxidation during long-term heating in air at elevated temperature. The studied materials demonstrated high stabilities in hydrogen atmosphere as well. The bending strength of the Ti3AlC2-and (Ti,Nb)3AlC2-based materials after keeping at 600• C in air and hydrogen increased by 10-15%, but the highest absolute value of bending strength before and after being kept in air and hydrogen demonstrated the Ti2AlC-based material (about 590 MPa).
The study of high pressure (2 GPa) synthesized MgB 2 -based materials allows us to conclude that higher borides (with near MgB 12 stoichiometry) and oxygen-enriched Mg-B-O inclusions can be pinning centers in nanostructural magnesium diboride matrix (with average grain sizes of 15-37 nm). It has been established that additions of Ti or SiC as well as manufacturing temperature can affect the size, amount and distribution of these inclusions in the material structure and thus, influence critical current density. The superconducting behavior of materials with near MgB 12 stoichiometry of matrix is discussed.
PURPOSE. To evaluate the effectiveness of surgical treatment of secondary glaucoma and to present the clinical features of the postoperative period in a patient with Sturge-Weber syndrome (SWS). METHODS. A patient with SWS, choroidal hemangioma and secondary glaucoma was examined and treated (Ahmed valve implantation) at the S.N. Fedorov National Medical Research Center "MNTK "Eye Microsurgery" in Moscow. RESULTS. Hypotension, a decrease in anterior chamber depth, serous choroidal detachment were observed on the first day after surgery on the left eye. Posterior scleral trepanation and injection of viscoelastic into the anterior chamber was performed. On the next day, IOP normalization and complete choroidal attachment were achieved, but macular detachment of neuroepithelium occurred and was successfully treated with injections of glucocorticosteroids. After one month, the retina and choroid were attached, IOP was 16 mm Hg in the left eye without hypotensive drops, visual acuity was 1.0 in both eyes. CONCLUSION. Implantation of the Ahmed valve can be used in the treatment of secondary glaucoma in patients with SWS in order to reduce the IOP and minimize the risks of complications.
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