Birendra Kumar Mohapatra

Structural and Microstructural Properties of Fused ZrO2-Mullites

Silimanite and zircon rich sea beach sand is taken with alumina powder for the synthesis of fused zirconia mullite (MUZ) composites by extended arc thermal plasma reactor. The bulk density value of fused MUZ (∼3.79 g/cm3) is well comparable to the density value of commercial available MUZ (∼3.6 gm/cm3). The electron probe microstructure analysis predicts that alumina is rich in mullite grains, whereas the grain boundary region is rich with zirconia. A small percentage of zirconia is also present in the intragrain region, which reveals that mullite compound is surrounded by well-structured and compacted zirconia. The X-ray photoelectron spectrum reveals the presence of mullite phase along with crystalline Si in the composites.

Correlation between properties of zirconia mullite and Y2O3 stabilised zirconia mullite derived by various processing techniques

Abstract Abstract Zirconia mullite (MUZ) and Y2O3–MUZ composites were synthesised by plasma melting, plasma sintering and conventional sintering techniques. Mixtures of tetragonal and cubic phases have been observed in all the processed Y2O3–MUZ composites. This observation infers that though the available temperature in plasma sintered and conventionally sintered MUZ specimens is not sufficient for the transformation of monoclinic to cubic zirconia, the addition of Y2O3 favours this transformation and also stabilises the cubic zirconia phase at room temperature. The optical absorption studies completely reflect the improvement in optical band gap of Y2O3–MUZ composites to prove it as a suitable candidate for refractory applications. The bulk density, hardness and higher crystalline nature of plasma sintered composites indicate that better quality of products can be synthesised by direct current extended arc thermal plasma heating technique within a short duration of time.

Detrital iron-ore deposits in the Iron Ore Group of rocks, northern Orissa, eastern India

Detrital iron deposits (DID) are located adjacent to the Precambrian bedded iron deposit (BID) of Joda near the eastern limb of the horseshoe-shaped synclinorium, in the Bonai–Keonjhar belt of Orissa. The detrital ores overlie the Dhanjori Group sandstone as two isolated orebodies (Chamakpur and Inganjharan) near the eastern and western banks of the Baitarani River, respectively. The DID occur as pebble/cobble conglomerates containing iron-rich clasts cemented by goethite. Mineralogy, chemistry and lamination of these clasts are similar to that found in the nearby BID ores. Enrichment of trace and rare-earth elements in the DID relative to the BID is attributed to their concentration during the precipitation of cementing material. The detrital iron orebodies formed when Proterozoic weathering processes eroded pre-existing BID outcrops located on the Joda Ranges, and the resulting detritus accumulated in the paleochannels. In situ dissolution in association with abundant organic material produced Fe-saturated groundwater, which re-precipitated as goethite within the aggraded channel to cement the detritals. Growth of microplaty hematite in the goethite matrix suggests some level of subsequent burial metamorphism.

Chemical Composition and Ultrastructure of Shells of Unfertilized Eggs of Olive Ridley Turtles, Lepidochelys olivacea

Abstract: Unfertilized eggs of Lepidochelys olivacea were examined for elemental composition and structure of the eggshell and mineral contents of the yolk-albumen fraction. Calcium was the major inorganic component both in the eggshell and egg contents. Other elements were present in traces. Scanning electron microscopic study revealed that the eggshell had two layers: an outer calcareous matrix in its aragonite morph and a membrane layer with fibres. The calcareous layer was made up of loosely and irregularly arranged 10–40 µm wide nodular shell units. The shell thickness was 125 to 150 µm. The membrane fibres were less dense, less netted than their normal counterparts and of variable thickness. The composition and structure of unfertilized eggshell were more or less similar to those reported for their normal counterparts except for the arrangement of fibres in the membrane layer.

Recovery of sillimanite from beach sand of Chhatrapur, Orissa, India and its thermal treatment for refractory application

Beach sands of Chhatrapur, Orissa, India comprise about 18% of heavy minerals, mixed with light minerals like quartz and feldspar. Sillimanite, which has refractory applications, accounts for 8% of these heavy minerals. Sillimanite was separated from garnet, monazite, zircon, rutile, ilmenite, magnetite, hematite and pseudo-rutile by combination of spiral, Wet High-Intensity Magnetic Separation (WHIMS) and flotation techniques. The cleaned sillimanite concentrate was then mixed with pure alumina powder in different proportions and treated in an indigenously developed plasma reactor for preparation of mullite refractory material. Out of the three products obtained, sillimanite alumina powder in the ratio of 75 : 25 was found to have the necessary physical and compositional properties suitable for refractory applications.

Optical and Micro-Raman Characterization of Fused Mullite Prepared from Beach Sand Sillimanite

Plasma-fused mullite compounds were prepared from beach sand sillimanite with varying sillimanite and alumina ratio (60:40 = MU1, 65:35 = MU2, and 75:25 = MU3) within five minutes of thermal plasma treatment. The X-ray diffraction (XRD) and micro-Raman studies indicate the presence of corundum phase in MU1 and MU2 compounds, whereas no signature of corundum phase is evident in MU3. This observation confirms that sillimanite and alumina taken in the ratio 75:25 (MU3) are exactly in the appropriate proportion for the complete conversion of mullite. The bulk density is higher in fused MU3 as compared to other two compositions. The optical band gap measured using UV-Visible spectrophotometer for this composition is found to be 3.37 eV.

Synergetic Surface and Chemical Durability Study of the Aesthetically Enhanced Natural Quartz by Heat Treatment

The change in surface behavior of natural quartz stone before and after heat treatment with metal oxides such as: cobalt oxide (Co3O4) and copper oxide (Cu2O) under vacuum and open atmosphere has been investigated. The surface feature, bulk density and hardness value of quartz changed after heat treatment, converting to a high value product. Difference in crystallinity of quartz, pre- and post-heat treatment was obtained through X-ray diffraction (XRD) study. The electron probe microanalysis results clearly explicated the diffusion of metal ion in quartz matrix exposed under vacuum atmosphere but as coating on the surface under open atmosphere. The structural transformation of quartz after heat treatment has been observed from the XRD data and well corroborated with the nanoindentation results. Durability of such quartz to chemical hazardous environment was observed. Thus, this communication demonstrates the change in physical and chemical characteristics of natural quartz stone after heat treatment under different atmosphere.

Mineralogy, petrography and micro-chemical characteristics of enclaves of mylonitic BIFs within Sukinda ultramafic complex, Odisha

Elongated NE-SW trending bodies of iron-rich rock are exposed adjacent to pyroxenite dyke within Sukinda ultramafic complex, Odisha. Field study followed by optical and electron microscopy, XRD and EPMA investigation reveal the rocks to be fine grained, weathered, limonitised; containing quartz, magnetite, hematite/martite and goethite. The rock has suffered from deformation during intrusion of chromiferous magma. It rarely shows banding/lamination, but largely exhibits mylonitic fabric, resulting from magmatic intrusion. The stronger deformation is evident from sub-grain formation, deformed mineral grains; often with orientation, stretching (boudinage) and shortening (folding); presence of porphyroclasts, pull-apart structure, undulose extinction, dynamic recrystallisation etc. From the microstructure and mineral abundance, the rock is designated as “Mylonitic Magentite Quartzite” (MMQ).Enrichment of some elements like Ni, Mg, Cr in the magnetite phase of MMQ is attributed to solid state diffusion of these elements from chromiferous mafic magma during thermal metamorphism. This is determined from electron probe microanalysis of iron-rich phase in MMQ, which is found to contain 88-90 wt% of FeO(t) with ~1%, NiO, ~1%, MgO and 0.1% Cr2O3 having around 3 mole% of trevorite; 4-6% of magnesioferrite; 0.15-0.3% of chromite; 86-87% of magnetite and 3-4% of wustite. Considering presence of wustite as temperature indicator, the temperature of magma envisaged to be around 950-1100°C.In a later period, the MMQ has undergone oxidation and lateritisation owing to its prolonged exposure. During this process, new minerals like hematite and goethite substituted magnetite, resulting leaching of iron (FeO: 62-68%) and magnesium (MgO: 0.1-0.35) and enrichment of chromium (Cr2O3:4-7%) and nickel (NiO: 1.6-2.3%). The silica (SiO2: 4-5%), alumina (Al2O3:~1%) are contributed by kaolinite, formed during lateritisation.The field and laboratory studies confirm these iron-rich exposures to be enclaves of BIFs, banded magnetite quartzite (BMQ) in particular, within the Sukinda chromiferous ultramafic complex. Micro-structural features and microchemical composition of iron minerals in these exposures are interpreted as the influence of forceful ultramafic intrusion into the existing BMQ and effect of thermal metamorphism followed by oxidation, weathering/lateritisation.

Shirozulite, a Brittle Mn-mica in Manganese Formation of Gangpur Group, Eastern India

Shirozulite, ideally KMn3(AlSi3)O10(OH)2, is recorded for the first time in metamorphosed manganese formation of Gangpur group in eastern India. It is associated with spessartine, jacobsite, calcite, rhodochrosite and muscovite which seemingly formed by the reaction of muscovite with rhodochrosite. In-situ chemical composition shows some variation in Mn-content from the original shirozulite reported from Japan. Powder X-Ray diffraction studies reveal the unit cell parameters of shirozulite in the triclinic system as a=5.14±0.02Å, b=9.21±0.01Å, c=10.17±0.13Å, β=94.14±0.31° and cell volume in Å3 = 487.22.

A Comparative Study of CaO-MUZ Composites Elaboration by Plasma Melting and Sintering Techniques

CaO doped zirconia mullite (CaO-MUZ) samples were synthesized through plasma melting, plasma sintering, and conventional sintering using plasma reactor and high temperature furnace as the heating sources. The compositional ratio (wt) of silimanite, alumina, and zircon were taken as 47:38:15, and 4 wt% of CaO was added to the above compositional ratio for the synthesis of CaO-MUZ. A mixture of tetragonal and cubic zirconia phases have been observed in all the processed CaO-MUZ composites. This observation infers that though the available temperature in plasma sintered and conventionally sintered MUZ specimens is not sufficient for the transformation of monoclinic zirconia to cubic zirconia, the addition of CaO favors this transformation. The arrangement of close compacted small and large crystal grains in conventionally sintered specimen increases the bulk density, while the hardness remains lower in comparison to the plasma-sintered CaO-MUZ. The optical bandgap measurements predict that the CaO-MUZ composites can be used as suitable refractory materials for ceramic industrial applications. We report the suitability of heating sources and the impact of melting and sintering techniques on the structural, microstructural, mechanical, and optical properties of CaO-MUZ, so that one can choose appropriate synthesis techniques to achieve the desired product at the industrial scale.