Sea Water Magnesia Research Articles

Raw materials for manufacturing of Superior quality MgO-C bricks

In SAIL Plant, Magnesia carbon (MgO-C) bricks are used as lining material for Metallurgical Vessels like Steel ladles as well as Basic Oxygen Furnaces (BOF). MgO-C bricks are the most suitable refractory in these conditions for slag line as they possess superior slag penetration resistance and excellent thermal shock resistance at elevated temperature. In Iron & Steel Industry, manufacturing processes has changed significantly due to the rising demand of quality steel in the market. Furnace capacities have increased & technological parameters have changed. Plants have been modernized with addition of secondary steel making facilities to meet the stringent quality requirement of newer grades of steel.Refractories in steel ladle are subjected to severe operating conditions like high temperature (1670-1700°C) tapping of liquid steel from BOF, thermal shock, abrasion with molten metal due to stirring during gas purging, localized heating in slag zone due to arcing, corrosion with slag, thermo mechanical stress etc. Hence, use of superior quality refractory material with evenly distributed impurities is essential to get an end product of very high corrosion and spalling resistance and high thermo-mechanical properties. Easier application technique is also required for higher lining life with less down time. Various qualities of magnesia carbon refractories are used in different zones of steel ladles & BOF. Magnesia carbon refractories are essentially constitute of two highly refractory components i.e. magnesia and graphite.Sea water magnesia is mainly used in SAIL as the main raw material for manufacturing of magnesia carbon bricks. Fused magnesia has also been tried by partially mixing with sea water magnesia. Although MgO content in magnesia is important up to a certain level, but the type of impurities and their relative proportions plays vital role in achieving good performance. Besides chemical purity, bulk density and crystal size are considered to be very important properties of magnesia for application in BOF and steel ladles. Beside magnesia, graphite of both indigenous and import sources were used in different occasions. Purity of graphite has been reported to have great influence on slag corrosion resistance and hot properties of magnesia carbon bricks. Particle size distribution of graphite influences porosity and thermal shock resistance properties of magnesia carbon bricks.This paper deals with the properties of different raw materials for making of superior quality MgO-C bricks for improved performance in Metallurgical vessels of SAIL plants.

海水マグネシアによるマグネシア・セメントの研究 (第1報)

海水マグネシアによるマグネシア・セメントの研究 (第1報)

Comparative study for physical properties and corrosion mechanism of synthetic and in situ MgAl2O4 spinel formation zero cement refractory castables

Magnesium aluminate spinel (MgAl2O4) is an excellent castable refractory product due to its high temperature thermal, chemical and mechanical properties. Alumina spinel castables are produced by addition of synthetic spinel or in situ spinel formation during the firing process. In the first part of the experimental studies, alumina rich MgAl2O4 spinel castable was produced using a solid state reaction technique. Tabular alumina and sea water magnesia (<100 μm) were used as starting raw materials. In the second part of the experimental studies, commercial synthetic spinel added castables were produced. In order to compare experimental results, both parts of the experimental study involved compositions with the same proportions of MgO. α-500 hydratable alumina was used as binder. Castables were sintered at 1500 and 1600°C. Water absorption, apparent porosity, bulk density and cold crushing strength values were considered and the optimum sintering temperature, proportions of synthetic spinel and sea water magnesia were determined. The XRD patterns confirm the phase formation of MgAl2O4. Moreover, the physical properties of the castables were supported by this XRD analysis. Scanning electron microscopy investigations of the fired samples were carried out to compare the effect of synthetic spinel addition and in situ phase formation on the physical properties of the castables. The mechanism of slag penetration to two types of zero cement castables for steel ladles was examined and the penetration layer chemically analysed by energy dispersive X-ray analysis studies.

Effect of Magnesia Addition on Physical Properties and Slag Attack Resistance of Ultra-Low Cement Castables (ULC)

In this study, tabular alumina and seawater magnesia were used to synthesize in situ Al2O3-MgO spinel castables. Secar® 71 cement was used as a binder. In order to produce in situ formation of Al2O3-MgO spinel castables, the effect of MgO content on refractory properties was investigated by adding to the mixture at the proportions of 3, 4, 5, 6, 7 wt%. Using 5 wt% content of MgO decreased the bulk density of castables to 3.03 g/cm3 and increased the porosity to about 17.43%. In situ spinel formation in samples led to the expansion in its lattice as well as an increase in the porosity. On the other hand, 5 wt% MgO had a positive effect on Cold Crushing Strength (CCS) of the castable. SEM investigations of fired samples were carried out to compare the effect of MgO addition and in situ phase formation on the physico-mechanical properties of castables. The effect of MgO content on the mechanism of slag penetration of ultra-low cement castables (ULC) for steel ladles was examined and the penetration layer was chemically analyzed.

Effect of Magnesia Addition on Physical Properties and Slag Attack Resistance of Ultra-Low Cement Castables (ULC)

In this study, tabular alumina and seawater magnesia were used to synthesize in situ Al2O3-MgO spinel castables. Secar® 71 cement was used as a binder. In order to produce in situ formation of Al2O3-MgO spinel castables, the effect of MgO content on refractory properties was investigated by adding to the mixture at the proportions of 3, 4, 5, 6, 7 wt%. Using 5 wt% content of MgO decreased the bulk density of castables to 3.03 g/cm3 and increased the porosity to about 17.43%. In situ spinel formation in samples led to the expansion in its lattice as well as an increase in the porosity. On the other hand, 5 wt% MgO had a positive effect on Cold Crushing Strength (CCS) of the castable. SEM investigations of fired samples were carried out to compare the effect of MgO addition and in situ phase formation on the physico-mechanical properties of castables. The effect of MgO content on the mechanism of slag penetration of ultra-low cement castables (ULC) for steel ladles was examined and the penetration layer was chemically analyzed.

Effect of in situ spinel seeding on synthesis of MgO-rich MgAl2O4 composite

MgO-rich MgAl2O4 spinel was prepared by adopting solid-state reaction of commercially available sintered seawater magnesia and α-alumina. Starting materials were mixed in weight ratio (Al2O3: MgO) of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, where the developed MgAl2O4 spinel crystal seed in calcined powder varied (5–50%) with respect to addition of MgO content and temperature. Around 70% spinellisation could be noticed in Al2O3: MgO (1:1) batch through double stage sintering. Densification and grain size of the sintered specimen was found to be greatly dependent on initial calcination temperature and content of primary spinel seed. The diametrical compressive strength of sintered specimen was ∼115 MPa for highest amount of spinel content. The hardness of MgO-rich spinel composite was varied with spinel addition.

Preparation of MgO–MgAl2O4 composite for refractory application

Solid-state reaction was adopted to prepare MgO-rich MgAl 2 O 4 spinel from commercially available sintered seawater magnesia and α-alumina. The starting materials were mixed in weight ratio (Al 2 O 3 :MgO) of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4. Calcination led to the development of MgAl 2 O 4 spinel crystal seed, which was varied (5–50%) with respect to MgO content and temperature. Spinellisation of 70 vol.% was observed for equal weight proportionate calcined powder, when calcined at 1000 °C for 2 h and subsequent sintered at 1600 °C for 4 h. The initial calcination temperature and hence the primary spinel seed content was found to influence the densification and microstructure of sintered specimen. Finally attempts were made to correlate the effect of spinel seed content on the crystallization behavior and microstructure.

The production of hydrotalcite from magnesite ore as non-toxic heat stabiliser for polyvinyl chloride

In recent years polyvinyl chloride (PVC) processors had to submit to worldwide pressure to convert to environmentally friendly stabilisers such as hydrotalcite (HT), since most of the heat stabilisers currently in use contain heavy metals such as lead, cadmium or barium – these being highly toxic. The presently used HT production process is, however, very expensive as it involves the recovering of magnesium from seawater magnesia. The purpose of this study was to prove that it is indeed possible to produce cost effective and non-toxic HT from an alternative source. During this study the costing and heat stabilising ability of the hydrotalcite produced from magnesite was compared to that of commercially available heat stabilisers. The effect of the pre-mixing process, as well as the influence of particle size distribution was also investigated. A cost comparative and stabilising efficiency study indicated the cost effectiveness of HT produced from magnesite ore, in comparison with other commercially available stabilisers. The use of HT as produced from magnesite ore would indeed assist in the worldwide changeover to environmentally friendly stabilisers.

Reaction sintering of different spinel compositions in the presence of Y 2O 3

Reaction sintering of spinels (MgO–Al 2O 3 molar ratio 1:1 and 2:1) was done in the temperature range of 1550–1650 °C using sintered sea water magnesia and commercial alumina as the starting materials and Y 2O 3 as additive up to 4 wt.%. An attrition mill was used for the reduction of particle size. Dilatometric study was done to evaluate the effect of additive on reaction and sintering. Sintered products were characterized in terms of densification, phase analysis, hot strength, microstructure and energy-dispersive X-ray analysis (EDAX) studies. Y 2O 3 was found to be beneficial for both the compositions.

Effect of alumina reactivity on the densification of reaction sintered nonstoichiometric spinels

Densification of two different nonstoichiometric spinels (Al 2O 3 content 66 wt.% and 90 wt.%) was studied by using the reaction sintering technique. Sintered sea water magnesia and commercial alumina were used as starting materials. Reactivity of alumina was changed by calcinations between 800 and 1600 °C. Sintering for all the batches was carried out in the temperature range of 1600 and 1700 °C. Sintered products were characterized by bulk density, phase analysis and microstructure. Alumina calcined at 1200 °C was found to be optimum for densification of non-stoichiometric spinels.

Microstructural characterization of magnesias derived from different sources and their influence on the structure of ceramic films formed on a 3% silicon steel surface

A study on the influence of the type of magnesium oxide on the structure of the ceramic coating and consequently on the magnetic properties of a 3% Si steel was carried out. Decarburized samples coming from industrial equipment were coated with magnesia slurries and submitted to final annealing at 1200°C for 15 hours under H2 atmosphere. We used magnesia synthesized from magnesium chloride and dolomite. The magnesia samples were characterized using granulometry measurements, scanning electron microscopy (SEM), nitrogen adsorption-desorption analyses, helium pycnometry, thermal analyses (TG and DTA), reactivity tests and calcination mass loss. The magnesia sintered from brine has the highest density, surface area and porosity. The rheological behavior of magnesia slurries, the magnetic properties of the steel and the ceramic film structure were correlated with the type of magnesia used. The slurry made with MgO from dolomite has the highest viscosity and the slurry made with oxide from brine the smallest one. Brine magnesia films are darker, thicker and rougher and sea water magnesia films are light gray, thinner and smoother.

Reduction of silica from complex calcite ore for use in seawater magnesia production

The amenability of a calcite-bearing ore to the reduction of silica to below 0.2% by physical beneficiation was studied. The objective was to use the ore as a raw material for seawater magnesia production. The ore contains complex gangue minerals such as diopside, forsterite, phlogopite, clinohumite, graphite and quartz. These contribute to around 25% acid insolubles with 6% SiO2. Reverse-flotation studies using various cationic collectors with tannin as a depressant indicated the possibility of reducing the acid insolubles to around 5%. Direct flotation of calcite with anionic sodium oleate in the presence of sodium silicate and lactic acid as a depressant indicated the possibility of reducing the acid insolubles to below 3% and the SiO2 to from 0.2% to 0.3%. Lactic acid was found to be an effective depressant of the complex gangue minerals in the ore.

The break point in the pressure-density curve of magnesia prepared by the sea water magnesia process

Uniaxial compacting behaviour of MgO powders calcined at a temperature between 900 and 1200°C in air was investigated; the break point which appeared in the pressure-density curve of MgO powder was effective in elucidating the agglomeration state in the powder. The packing density of MgO powder as a function of calcination temperature was measured before and after milling operations. The plots of relative density versus logarithmic pressure also exhibited a break point indicating the pressure at which the contact points in porous agglomerates began to be destroyed. The agglomerate strength of MgO powders calcined at low and high temperatures (900 and 1200°C) only were measured. The microstructural differences between agglomerates in MgO powder and the surface of a compressed powder (applied pressure 150 MPa) were examined by scanning electron microscopy.

A New Large Crystal Sintermagnesia: Production, Properties, Performance

The development of new basic refractory raw material is a complex process, one that requires careful consideration of many technological, economic, market and commercial factors. This paper reviews the issues considered and the approach adopted by the sea-water magnesia manufacturer, Premier Periclase Limited, Drogheda, Ireland, in the development of a new synthetic large crystal sintermagnesia.Because of the heavy dependence on magnesia usage in steel- making, key technical and market developments in that industry over the past 10–15 years were examined. This, combined with a study of basic refractories development and their wear mechanisms in steel plant applications enabled the formulation of a sound product strategy. Finally, the development programme from initial prototype material preparation and testing to plant selection and product launch in late 1990 is described.

Magnesium Aluminate Hydrate as a Chemical Bond of Magnesia Refractories—Part III: Thermomechanical Properties

The present paper is the third of a series of papers on a new chemical bond on magnesia refractories. Results of the compressive creep testing of the chemically bonded samples at elevated temperature up to 1500°C, prepared from sea-water magnesia (Japan) and natural magnesite (Salem, India), cured at 110°C for 24 hrs, have been presented in this part. Samples prepared with the bond (0.25 wt%) evaluated by creep experiments with a compressive load of 3 kg.cm−2 up to 1500°C for 30 hrs showed a maximum strain rate of 0.2% per hour without failure. This makes it an acceptable chemical bond of the future for magnesia refractories. The deformation mechanism suggested a diffusion controlled Nabarro-Herring creep, while a grain-boundary diffusion process might also be a possibility.

Men and magnesia

The unusual title does not indicate an interest in Pharmaceuticals-just an overwhelming conviction that success in research, development, and, particularly, application depends as much on men as on the materials or new techniques tested. The hypothesis will be illustrated by case histories with which the lecturer has been closely associated and where the human factors can be identified without any recourse to statistical methods. These range from the true density of pure magnesia to the origins of the sea water magnesia process.

Distribution of Boron in Magnesia Clinker

The distribution of boron contained in small quantities in sea-water and natural magnesia clinkers was determined by α-particle tracks that resulted from 10B(n, α)7Li reaction. Cellulose nitrate film was pressed onto the polished surface of specimens which had been moistened with amyl acetate, then the specimens were irradiated in thermal neutron flux to 1014n/cm2. After the irradiation, the α-track image was developed in the film by etching the film surface. Comparing with α-track analysis, electron probe microanalysis was made on the same position of the same specimen.As for the sea-water magnesia containing 0.26wt% B2O3 and having the CaO/SiO2 ratio of 0.46, it was found that boron existed around periclase grains together with calcium in a form of matrix. As for the specimens having the C/S ratio of more than 2.5, boron was also distributed at grain boundary, but it was not confirmed owing to background whether boron existed in periclase grain.

Use of Kuzin dolomites in the production of seawater magnesia

Use of Kuzin dolomites in the production of seawater magnesia

Producing synthetic ceramic magnesia ? Alumina spinel for roof refractories

Laboratory and technological studies to obtain magnesia spinel from raw materials of different qualities showed that, as regards the degree of activity, the magnesia constituents can be arranged in the following decreasing order: chemically pure magnesia → metallurgical magnesite → seawater magnesia. The use of technical alumina as the aluminous constituent is preferable to corundum. The minimum degree of sintering occurs in specimens of spinel having a stoichiometric composition. The sintering is improved with an increase both in the excess periclase and in the excess alumina over the stoichiometric ratio. A positive influence on the spinel formation and degree of crystallization is exerted by small (up to 5%) additions of chromite. The industrial significance of small (up to 2%) additions of TiO2, B2O3, and V2O5 for the synthesis of spinels is not established. Thus, the spinel used as the batch constituent for making high quality magnesite spinel refractories should contain excess periclase and small quantities of chromite.

Periclase ? Spinel refractories from seawater magnesia and beneficiated chromite

Periclase ? Spinel refractories from seawater magnesia and beneficiated chromite