Magnesia Contents Research Articles

A study of 11th–15th centuries AD glass beads from Mambrui, Kenya: An archaeological and chemical approach

Twenty-three 11th–15th centuries AD glass beads collected from the archaeological site of Mambrui in Kenya were analysed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results show that all of the glass samples are soda-alumina-silica glass. They belong to the mineral soda- alumina (m-Na-Al) glass type, characterised by high alumina and relatively low calcium and magnesia contents, that was widely distributed in eastern and southern Africa and southeast Asia in the 5th century BCE – 19th century CE. They were made with a mineral alkali flux called reh and sand. Comparison with contemporary m-Na-Al glass beads from Africa and southeast Asia shows that all of the Mambrui glass beads share similar characteristics to m-Na-Al 6 glass. This new glass type was recently identified by Dussubieux and Wood (2020) and is characterised by elevated levels of U (avg. 60 ppm) and Cs (~1.5 ppm). It is commonly found in eastern African sites such as Manda and Gede in Kenya. The lead isotope results suggest that the Mambrui glass beads might have been coloured using lead sources from four different sources including ores from India and northern Thailand.

The treatment of Basic Oxygen Furnace (BOF) slag with concentrated solar energy

Basic Oxygen Furnace (BOF) slag is one of the sub-products generated in the steelmaking process. This waste is characterized by its free lime and free magnesia contents that limit its application in construction. Moreover, the iron content in BOF slag of 14–30 wt% is a quantity which is problematic in the manufacture of cements. On the other hand, BOF slag is a source of available iron in the steelmaking industry. Concentrated solar energy offers a great potential in high temperature applications, so we used it to treat BOF slag. In this way, the slag was treated to stabilize it combining the free lime and free magnesia to give other phases (silicates, aluminates, and complex oxides), but also to transform iron into a magnetic phase that could be recovered through magnetic methods. The results demonstrate that the free lime and free magnesia reacted with silicates, aluminates, and ferrites to form stable phases which are not hydrated in the presence of water. Due to this, the treated BOF slag might find application in the construction industry. Furthermore, the iron was transformed into magnetite/maghemite, i.e. phases with magnetic properties.

The wet high intensity magnetic separation of magnesite ore waste

The wet high intensity magnetic separation of magnesite ore waste stocked in an open pit of a magnesite mine was investigated in this paper. The received sample was subjected to physical, chemical, thermal and phase characterizations. The magnesite ore waste sample contained 77.69 % MgCO3 and a considerable amount of Fe2O3 (3.14 %). The unwanted silica and iron impurities were removed and a high-grade magnesite was experimentally obtained. Results have shown that a high-grade magnesite was obtained after subjecting the non-magnetic portion of the processed sample twice at 1.8 T. It was possible to increase the magnesite content up to 91.03 % while reducing the iron content to 0.32 % by using magnetic separation. After the calcination process at 1000?C, the sample showed mass loss on ignition of 52 % and contained 85.39 % MgO with 0.32 % Fe2O3. The final product can be used in chemical and metallurgical applications where high magnesia contents are required. The experimental results provide useful information on wet magnetic separation of magnesite wastes.

Preparation and in vitro investigation on bioactivity of magnesia-contained bioactive glasses

Mg plays an important role in the human skeletal system as it stimulates the bone formation and reduces bone resorption. Magnesium has been substituted into SiO2–Na2O–CaO–P2O5 bioactive glass. In the present work, the bioactive glasses were designed to enhance bioactivity. Bioactivity of these glasses was assessed by the immersion of the samples in simulated body fluid (SBF) for different time periods. The formation of hydroxy carbonate apatite (HCA) layer was confirmed by scanning electron microscopy, X-ray diffractometry, and FTIR spectrometry which had shown the HCA layer formation and growth. The formation of HCA layer was found to increase on the surface of the SBF immersed bioactive glasses with increasing magnesia contents in the glass. In vitro cell culture investigations such as viability, proliferation, and cell attachment were studied using human osteosarcoma U2-OS cell lines. The in vitro results of new magnesium containing bioactive glasses had shown improved bioactivity as well as better biocompatibility.

Simultaneous Evaluation of Magnesia and Silica Contents’ Effect on in-vitro Bioactivity of Novel Bioglasses in the SiO2-CaO-MgO System

ABSTRACTIn this study, bioglasses in SiO2-CaO-MgO system were synthesized through sol-gel method and the effect of silica and magnesia contents on in-vitro bioactivity of the bioglasses were investigated. XRD patterns showed an amorphous structure after heat treatment at 600°C for 2 h for all glasses and also indicated that after immersion in SBF, apatite particles precipitated on glass surfaces and the rate of apatite formation decreased with increasing Mg/Ca ratio. On the other hand, the apatite formation rate was enhanced with increasing the silica content. Furthermore, magnesia contents increased the compressive strength of the samples. According to SEM, higher Mg/Ca ratio led to increase in particle size of the precipitated apatite. MTT assay showed that cell proliferation was inhibited with increasing Mg/Ca ratio, however, silica contents stimulated the osteoblast proliferation.

Microstructure, in vitro bioactivity and degradability of various magnesia-containing wollastonite

Wollastonite (CaSiO3) ceramics with various magnesia contents (0, 5, 10, 15 and 20mol%) were successfully prepared by sintering sol–gel derived precursors. The effects of MgO content on microstructure, in vitro bioactivity and degradability of wollastonite were reported. The ceramics are composed of β-CaSiO3. When adding 5mol% MgO, the new phase of Ca3Mg(SiO4)2 forms. With increasing MgO content, CaMgSi2O6 and Ca2MgSi2O7 form. All ceramics possess apatite formation ability in simulated body fluid. The TEM results indicated that the ceramic structure is polycrystal. MgO decreases the total pore volume of wollastonite and the degradation rate is decreased gradually with increasing MgO content.

New Data on the Soda Flux Used in the Production of Iznik Glazes and Byzantine Glasses

Previous research has shown that Iznik glazes are characterized by low potash and magnesia contents. It was therefore suggested that the flux used was either a purified plant ash or some unidentified mineral source of soda. More recently, as a result of the detection of small, but significant, amounts of boron and lithium in Byzantine glasses from western Turkey, which also exhibit low potash and magnesia contents, it has been suggested that the source of the flux used was a soda-rich evaporite associated in some way with the extensive borax deposits in the region. LA–ICP–MS has been used to establish that Iznik glazes also contain similarly small amounts of boron and lithium. The Na/K, Na/Mg, Na/Ca and Na/B ratios for these Iznik glazes are shown to be comparable to the equivalent ratios calculated from published data for waters from a range of Na–HCO3 type hot springs in western Turkey, with the closest match being to the hot springs around Afyon-Gazligol, which is consistent with documentary evidence. It is therefore proposed that the soda-rich salts produced by evaporating water from these springs to dryness would have provided the flux required for the production of Iznik glazes and high-boron Byzantine glasses.

A new karren feature: hummocky karren

Karren are small-scale landforms on karst surfaces and many types have been described so far. Here we present an apparently new feature which was found on the Hochschwab karst massive in the Northern Calcareous Alps of Austria. So far only few outcrops each having less than 1 m² within a very restricted area have been found. Morphometric analysis reveals that the karren consist of a randomly distributed, dispersed assemblage of small hummocks and depressions in between. The mean distance between neighbouring hummocks is 4 to 5 cm and the mean height is 0.85 cm. Longitudinal sections are gently sinuous. The occurrences are delimited by thin soil cover with grassy vegetation. The karst features continue below that vegetation cover. Therefore, it is clear that the karren have formed subcutaneously. Corroded fissures where water could infiltrate into the epikarst are absent. The bedrock lithology is Middle Triassic limestone of the Wetterstein Formation in lagoonal facies. Geological structures do not govern the feature. The surface is not a bedding plane and small joints and fractures do not govern the arrangement of the hummocks. Thin section analysis regarding rock texture and dolomite components show that there is no compositional difference between hummocks and depressions. Geochemical analyses show that the limestone is very pure with a very low content of Magnesia. Slightly higher Magnesia contents at the hummock surfaces are significant. The data obtained so far only indicate that some dissolution mechanism but not any rock property governs the irregular array. As there exist no descriptions of comparable features in literature, the name “hummocky karren” is suggested for that type of karren landform.

Effect of magnesia on structure, degradability and in vitro bioactivity of CaO–MgO–P 2O 5–SiO 2 system ceramics

CaO–MgO–P 2O 5–SiO 2 system ceramics with various magnesia contents (0, 5, 10 and 20 mol%) were successfully prepared by sintering the sol–gel-derived powder compacts. The ceramic degradation was evaluated through the weight loss in the tris-(hydroxymethyl)-aminomethane and hydrochloric acid (Tris–HCl) buffer solution, and their ability to form apatite was determined by soaking in simulated body fluid (SBF). Results indicated that the ceramics structure was greatly influenced by magnesia contents. New crystal phases of Ca 2MgSi 2O 7 and SiO 2 were formed when magnesia was added and with an increase of magnesia concentration the phase of Ca 2MgSi 2O 7 increased with a simultaneous decline of β-CaSiO 3. In addition, studies showed that magnesia played an important role in affecting the degradability and apatite forming ability of CaO–MgO–P 2O 5–SiO 2 system ceramics. It is observed that with increasing magnesia concentration, the ceramic degradability gradually decreased and the formation of apatite on samples was delayed.

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr2O3 contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al2O3 content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites ( 3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO2 contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).

Making foundry and conversion pig irons on slags with high alumina and magnesia contents in large furnaces

Making foundry and conversion pig irons on slags with high alumina and magnesia contents in large furnaces

Vanadium interactions with treated silica aluminas

Poisoning of fluid cracking catalysts by vanadium, nickel, iron and copper can decrease the selectivity and overall activity of such catalysts. Silica alumina is often used as a matrix to disperse the active zeolite component, to crack large hydrocarbons at initial stages of reaction and for stability of the fluid cracking catalyst. Vanadium poisons are particularly bothersome due to zeolite destruction by vanadium. This paper explores the interaction of vanadium with various silica aluminas including those with rare earth and magnesia contents. The effects of calcination and steaming were also determined. Spectroscopic techniques such as luminescence, diffuse reflectance, electron paramagnetic resonance, X-ray photoelectron spectroscopy and secondary ion mass spectrometry methods were used to study the oxidation state, chemical composition, and number and type of vanadium species in these materials. The results show that vanadium moves into the particle interior when magnesium or rare earth oxides are present. This is responsible for the decreased mobility of vanadium even during steaming conditions and results in higher catalytic selectivity for catalysts containing these materials.

Passive and Active Oxidation of Hot-Pressed Silicon Nitride Materials with Two Magnesia Contents

Hot-pressed Si3N4 materials containing 1 and 5 wt% MgO were oxidized for 1000 h at 1000°, 1100°, and 1200°C in helium at 0.4 to 0.8 Pa total oxidants. Transition from passive to active oxidation occurred between 1000° and 1100° C, in agreement with published theoretical calculations for pure Si3N4. The amounts of both passive and active oxidation were greater for the material containing 5 wt% MgO. Specimen surfaces were porous and oxide–free under active oxidation conditions but contained porous oxide at transition.

Interactions of Refractories and Reactor Materials with Sodium

As part of a program at Argonne National Laboratory (ANL) to investigate the compatibility of high-temperature sodium with materials being considered for core retention systems in liquid-metal fast breeder reactors, various commercial refractories and samples of reactor control materials were exposed to static sodium at 850°C for 5 h. The refractories tested were samples of magnesia, alumina, zirconia, mixed ceramic oxides, and graphite; the reactor control materials were boron carbide and tantalum. Samples of graphite, zirconia, and the refractories with high alumina or magnesia contents, but with low silica and chromic oxide contents, were found to be compatible with high-temperature sodium. Sample compatibility with sodium decreased with an increase in the silica content of the sample. Samples with large silica content failed completely. These results are in good agreement with results of other experiments, performed at ANL and at the Westinghouse Advanced Reactors Division, in which these materials were exposed to boiling sodium.

MINERAL AND CHEMICAL COMPOSITIONS OF THE SECONDARY SHIRASU

The so-called “Secondary Shirasu (lacustrine or marine sediments of pyroclastics)” is distributed in separate forms and in small scale, and occurs in association with the socalled “Shirasu or Primary Shirasu (pyroclastic flow deposits)” which is widely distributed over southern Kyushu. Mineral and chemical compositions, and optics of constitutent minerals of the Secondary Shirasu, which was derived from the Aira Shirasu, have been studied, and are compared with those of the Primary Shirasu, i. e. the Aira Shirasu which came from the Aira volcanic caldera. Mineral and chemical compositions show that the Secondary Shirasu is characterized by lower content of mafic minerals and by higher silica and lower ferrous iron oxide and magnesia contents than the Primary Shirasu. The differences in chemical composition are consistent with those in mineral composition between the Secondary and Primary Shirasu. The nature of the Secondary Shirasu is reffected in these differences.

Resistance of rice plant to the Imochi disease (rice blast disease) in relation to its silica and magnesia contents.

Resistance of rice plant to the Imochi disease (rice blast disease) in relation to its silica and magnesia contents.