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Summary Due to growing environmental concerns and the need to use less energy-intensive building products, alternatives and improvements to Portland cement (PC) are being actively researched worldwide. Use of supplementary materials is now a common practice where PC is the predominant component of inorganic building products. This study aims to investigate the potential of magnesia (MgO), derived from a naturally occurring raw material magnesite, as a supplementary material. Results from mortar samples prepared with 10 and 20% replacements of ordinary Portland cement (OPC) by MgO are presented. DTA-TG was used to study and characterise the hydration behaviour of MgO in OPC environment after 3, 7, 14, 28, 56 and 90 days of moist curing. Microstructural and compressive strength determinations providing additional information on the influence of hydrated phases are also reported.
Abstract
The reactivity of MgO obtained from calcination of magnesium carbonate at different temperatures has been investigated by means of hydration in a constant relative humidity environment at 40°C for periods up to 24 days. Natural magnesite and AR grade basic MgCO3 calcined in the range of 500–1000°C was characterised in terms of surface area, crystallite size, morphology, and hydration rate. It was found that the hydration rate is dependent on the surface area and crystallite size where temperature was the main variable affecting them. The most reactive MgO was produced at the lowest calcination temperature with the highest surface area and the smallest crystallite size. The basic MgO specimens showed higher degree of hydration compared to the natural MgO specimens due to the smaller surface area and larger crystallite size. The low MgO content of the starting natural magnesite is also attributable to the lower reactivity. This preliminary study serves as a mean to investigate potential utilisation of reactive MgO as a supplementary cementitious material in eco-friendly cements.
temperature at 10 °C min −1 , sample mass approximately 4 mg, sample pan 30 μl aluminum pan with a hole, and purge gas nitrogen [ 2 ]. Milk of magnesia (MoM) is a suspension of magnesium hydroxide Mg(OH) 2 in water. It is widely used as an antacid to
magnesia and the calcinations temperature in terms of specific surface area, pore volume is shown in Table 1 . The BET surface area and the pore volume value of the samples calcined at 550 °C increases from 76.5 to 138.3 m 2 /g and from 0.208 to 0.339 cc g
density and apparent porosity, and also on the volume shrinkage of the prepared porous structures. 2 Experimental work 2.1 Materials Ceramic oxides like monoclinic zirconia, alumina, and magnesia were chosen in this research as biomedical substances
Abstract
Tin oxide was supported on alumina, titania, magnesia and silica, treated with hydrogen at different temperatures and characterized by Mössbauer spectroscopy and X-ray diffraction. For the samples calcined at 773 K, tin is present as SnO2 on alumina, magnesia and silica, but it occupies Ti sites on titania. After hydrogen treatment at high temperatures, tin is reduced from Sn(IV) to Sn(II) on alumina and titania, from Sn(IV) to Sn(0) on silica, but practically not reduced on magnesia. These results show the different degree of interaction between tin and the supporting material.
Abstract
Several ppm of sodium can be determined in aluminum, alumina and magnesia samples by INAA in which fast neutron interferences are corrected by irradiating the samples in various locations of the thermal column different in fast to thermal neutron flux ratio. A simple INAA using thermal column is effective for sodium determination in geochemical standard reference samples of peridotite and dolomite containing considerable amount of magnesia as one of the matrix elements.
The sanctuary of Apollon mentioned in the letter of Gadata is not to be sought in Magnesia on Meander but in the town of Tralleis/Tralles. Tralleis was located in the territory of the satrapy Caria whose capital was Magnesia in the age of Dareios. Therefore it is understandable that it was the satrap of Caria who must remedy the abuse which hurted the interests of the priest of Apollon. The inscription containing the letter of Gadata can be a later copy of a Greek original text because its language and orthography has some characterics of the prehellenistic age. This inscription could be seen by Xenophon who probably here has got the idee of naming Gadatas one of the eunuchs in his Oikonomika. Plutarch informs us that the memory of the Persian wars was living in Magnesia in the age of Hadrian, too. It seems that the Roman emperor has visited Tralleis personally.
TG, DTG and DTA curves of magnesite are dependent on procedural variables, especially sample mass, heating rate and partial pressure of carbon dioxide, in a similar manner to those of calcite [1], although the magnitude of the effect is less for magnesite. The first stage of the decomposition of dolomite varies with increasing partial pressure of carbon dioxide in an anomalous manner and hence the effects of these procedural variables (except heating rate) are not similar to those observed for magnesite and calcite. The second stage of the decomposition of dolomite is, however, strongly dependent on these procedural variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesia. A 1∶1 molar mixture of magnesite and calcite also behaves as would be predicted from the behaviour of the single carbonates but differently from that of dolomite.
Abstract
A bibliometric study based on worldwide scientific and technical publications on refractory materials used in iron and steelmaking processes during 1980–87, has been carried out. Six bibliographic databases were searched and from them 2464 references were retrieved. The highest percentage of published documents were journal articles (60%), followed by patents (33%). The core journals areOgneupory (USSR) andTaikabutsu (Japan). The USSR was by far the most productive country, both in number of published papers and in number of journal titles devoted to the subject. In The Soviet Union research work is mainly carried out in universities and institutes of the Academy of Sciences. On the other hand, Japan is the most productive country in patent registered, and research work is carried out there either in private refractory companies or in steelmaking enterprises. The trend in worldwide research points towards shaped refractories, particularly based in high alumina, magnesia, zircon carbides and mixtures containing oxides and carbon, which are largely used in converters, transport ladles and continuous casting processes.
