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We investigate the structural and transport properties of Mn doped hematite ( alpha -Fe sub(2O) sub(3)). The X-ray diffraction pattern identifies the single-phase and corundum (Al sub(2O) sub(3)) ...type structure of the polycrystalline samples Fe sub(2-) sub(x)Mn sub(xO) sub(3) (x = 0, 0.01, 0.10 and 0.50). The resistivity curve shows a Morin transition (T sub(M) in hematite ( alpha -Fe) sub(2)O sub(3) at about 262 K. As the Mn-content increases in the solid solution of hematite ( alpha -Fe) sub(2)O sub(3), the number of pairs of (Fesuper2+, Fesuper3+) and (Mnsuper2+, Mnsuper3+) in the solid solution increases which changes the conductivity of the solid solution. The Mn doping influences the Morin transition and T) sub(M) shifts towards lower temperatures on enhanced doping. For higher doping, T sub(M is further suppressed significantly. The Raman measurements of alpha -Fe) sub(2)O sub(3 samples shows seven Raman active modes at A) sub(1) sub(g(1) inline image 225 cmsuper-1, E) sub(g)(1) inline image 249 cmsuper-1, E sub(g(2) inline image 292 cmsuper-1, E) sub(g)(3) inline image 297 cmsuper-1, E sub(g(4) inline image 409 cmsuper-1, E) sub(g)(5) inline image 496 cmsuper-1, and A sub(1) sub(g)(2) inline image 609 cmsuper-1. Moessbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields clearly show the presence of ferric (Fesuper3+) state and strong magnetic ordering in all samples. Fe sub(2-) sub(x)Mn sub(xO) sub(4) hematites are in single phase and possess corundum type structure. Resistivity data shows Morin transition for parent -Fe sub(2O) sub(3) observed at T sub(M 262 K. Mn doping influences Morin transition and T) sub(M) shifts towards lower temperatures. Seven Raman active modes are identified for Mnsuper2+ doped Fe sub(2-) sub(x)Mn sub(xO) sub(4) hematites. Room temperature Moessbauer spectrum confirms +3 oxidation state of Fe as ferric.
In present work, the novel Al2O3‐C ceramic filter fabricated by using microporous corundum‐spinel powder instead of dense Al2O3 powder and reinforced by SiC whiskers is proposed. The effects of Si ...powder content (0, 3, 6, and 9 wt. %) on the microstructures and mechanical properties of the filters were studied. After replacing the α‐Al2O3 micro‐powder with microporous corundum‐spinel powder, the in situ spinel whiskers were formed inside the filter skeleton under the reducing atmosphere. The rough surface structure of the microporous powder increased the interface contact area with the small‐sized carbon particles, resulting in a compact interface bonding in the filter skeleton and a higher cold compressive strength of the filter. When the Si powder content increased to 6–9 wt. %, the in‐situ SiC whiskers were formed not only between the microporous powder, but also inside the pores near the surface of it by vapor‐solid reaction mechanism in the filter skeleton. The SiC whiskers synergized with the microporous powder to form a more compact interface structure, thus remarkably enhancing their cold compressive strength and thermal shock resistance. Overall, the mechanical properties of the filters were significantly improved by the addition of 9 wt. % Si powder. The filter skeleton had an apparent porosity of 36.2% and a bulk density of 1.93 g/cm3. The filter also exhibited a high cold compressive strength of 1.59 MPa and a superior thermal shock resistance. It has the potential for better purification efficiency on molten steel in the future due to a rougher skeleton surface structure compared to existing Al2O3‐C filters.
The occurrence of 1-2 cm in diameter, anhedral xenocrystals of red corundum (ruby) in a dacitic lava- flow from central Mexico -in the state of Hidalgo- has been recorded. Geochemically, this dacite ...nearly resembles adakitic rock (SiO2=63.73 66.64 wt %), with low alumina contents (Al2O3=14.38 14.93 wt %), sodium (Na2O=3.29 3.57wt %) and titanium (TiO2=0.55 0.60 wt %), slightly peraluminous (A/ CNK=1.04 1.17) and moderately potassic (K2O=1.90-2.04 wt %; K2O/Na2O=0.53-0.62), with rare earth spectra enriched in light-rare earth elements (La/Yb)N=9.71 10.98. The origin of the dacite is linked to the early geological evolution of the eastern sector of the Trans-Mexican Volcanic Belt (TMVB) during the Miocene, and its provenance could be a melt of a basaltic and pelitic-sediments slab and magmatic differentiation that generated adakitic magma. The gem-type corundum could have resulted after the addition of refractory products disaggregated from the Precambrian basement, carried, and transported to the surface by ascending magma.
The following article presents the current state of knowledge about technologies connected with microcrystalline sintered corundum against the backdrop of present abrasive products and the ...contemporary grains market. The complementary presentation of issues related to the microcrystalline sintered corundum abrasive grains, which constitute an important group of abrasives used in modern grinding technology, was given. The most important stages in the development of sintered corundum grains production technology, from the 1960s to current developments (nanocrystalline sintered corundum) in this field, were presented in chronological order. The production technology, properties, working conditions, wear phenomena and most important areas of application of such abrasive grains were described. Particular attention was paid to the wear phenomena of microcrystalline sintered corundum abrasive grains occurring during the grinding process. The collection of phenomena affecting the extension of the life of these types of grain in comparison with the white fused alumina grains were described. Moreover, forecasts concerning the development of abrasive grains of micro- and nanocrystalline sintered corundum were presented.
The ultra-high performance steel fiber reinforced concrete (UHP-SFRC) with the corundum coarse aggregate (UHP-CASFRC) was prepared under common curing temperature and pressure procedures. The static ...tests on UHP-CASFRC were conducted, including the uniaxial compression, direct tensile and four points bending tests. Totally 16 shots of reduce-scaled projectile penetration tests on UHP-CASFRC and 2 comparative shots on HSC targets were conducted. The influences of the strength (hardness), size and volumetric ratio of coarse aggregate, incident velocity of the projectile (510–850 m/s) as well as the repeated strikes on the depth of penetration (DOP), area and volume of the impact crater, as well as the structural integrity and mass loss of the projectile were discussed.
By comparisons with the previous conducted basalt aggregated UHP-SFRC (UHP-BASFRC), the superior projectile impact resistance of UHP-CASFRC targets was verified. Within the discussed parametric variation ranges, it derived that: (i) Enlarging the size of the coarse aggregates can help reducing the DOP, impact crater area and volume, the harder coarse aggregate can decreasing the DOP by aggravating the mass abrasions of the projectile. The influences of coarse aggregate hardness on impact crater area and volume mainly depends on its surface roughness; (ii) When the sizes of the coarse aggregates were less than the projectile shank diameter (d), the harder coarse aggregates only aggravates the mass abrasions of the projectile, while the structural integrity of projectile could be maintained; (iii) For UHP-CASFRC target, the structural destruction of the projectile occurred when the coarse aggregates sizes increasing larger than d. From a structure protective point of view, the corundum sizes ≥1.5d is suggested; (iv) The hardness of the coarse aggregate is the most influential factor on the mass abrasion of the projectile, and the previously proposed engineering models for mass abrasions of the ogive-nosed projectile high-speed penetrating into concrete target are further validated.
•UHP-CASFRC was prepared under common curing temperature and pressure procedures.•Influences of coarse aggregates on static strengths and projectile impact resistance were experimentally studied.•UHP-CASFRC was validated having superior projectile impact resistance than UHP-BASFRC and HSC.•UHP-CASFRC with the corundum sizes ≥1.5d was suggested for the constructions of protective structures.•Mass loss and DOP of the ogive-nosed projectile penetrating into UHP-CASFRC target were analyzed.
The aim of the work is to review publications on a narrow circle of composites, namely corundum graphene. Quite a lot of research has been devoted to this composite to conduct generalizations and ...identify patterns.
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