Magnesia Clinker Research Articles

Fused dolomite-magnesia co-clinker for fired dolomite refractories

In this work a new method of obtaining doloma-magnesia co-clinker, which involves fusing a mixture of dolomite decarbonate and caustic magnesia, has been presented. Fused dolomite clinker and fused doloma-magnesia co-clinker have been prepared from high purity raw materials. The properties of a fired material obtained from such co-clinker were compared with a product obtained from fused dolomite clinker without any addition of MgO and with a product enriched with magnesium oxide in the traditional way – by substituting the finest grain fractions with magnesia clinker. It has been proved that it is possible to obtain a fired doloma-magnesia material based on fused doloma-magnesia co-clinker characterized by high chemical purity as well as high resistance to corrosion, hydration and thermal shocks.

Influence of zirconia addition on the properties of magnesia refractories

This paper concerns basic refractories used, among others, in the cement industry. Zirconium oxide was added to modify the properties of an MgO refractory. These MgO–ZrO2 materials can replace magnesia-chromite refractory ceramics in accordance with current environmental policy guidelines and can improve the properties, such as thermal shock resistance, of a typical magnesia refractory. In the experiments, commercially available magnesia clinker and monoclinic zirconia were used. The effect of particle size and amount of zirconium oxide content were determined in the prepared ceramic masses. The addition of zirconia was at a level of from 0 to 8wt% in green compacts. After the firing cycle at 1660°C the ceramic properties were measured, such as linear shrinkage, open porosity, apparent density, cold crushing strength, gas permeability and thermal shock resistance (water cycles). For selected materials, resistance to corrosion by two different corrosive agents was determined. The research results show that the addition of zirconia improved the refractories' properties. The cold crushing strength of samples with 2wt% of added ZrO2 reached maximum values. The obtained ceramics were also characterised by good dimensional stability (firing shrinkage less than 1%), high cold crushing strength (50–75MPa) and uncommonly high values of thermal shock resistance (8–10 water cycles). The addition of ZrO2 also clearly increased the materials’ corrosion resistance against a cement-like and glass-like agent.

EVALUATION OF MAGNESIA CLINKER EXTRACTED FROM DOLOMITE ROCKS

The present study examines the possibility of using locally available raw material for the production of magnesia clinker. The basic raw material is magnesia, which was extracted from dolomite rocks. The suitability of magnesia for the production of magnesia clinker depends on its sintering tendency; 3–8% Fe2O3 has been added to raw magnesia in order to increase the sintering rate of the magnesia. Specimens of each mix were fired at 1400, 1450, 1550, 1600, and 1650°C in order to produce magnesite clinker (dead-burned magnesia). The produced magnesite clinker has been investigated in order to determine the optimum firing temperature and optimum content of Fe2O3 addition. The results obtained during the present work indicated that the firing temperature at 1550°C and Fe2O3 content of 8% produced the best results.

Formation Mechanism of Mg(OH)<sub>2</sub> Prepared by Hydration of Magnesia Clinker in Magnesium Salt Solution (Part 1)

Mg(OH)2 particles of hexagonal plate and prism are prepared by hydration of magnesia clinker in magnesium salt solution. The hydration mechanism of magnesia was investigated by measuring reaction rates and SEM observations. The hydration rate was proportional to the surface area of MgO particles, suggesting that the reaction proceeds by the dissolution of MgO particles followed by the precipitation of Mg(OH)2 and that the dissolution was rate-controlling. In Mg(CH3COO)2 system, the reaction was divided roughly into two stages. The rate of the first stage was about half that of the second stage. MgO surface was covered with dense Mg(OH)2 layer during the first stage. At the second stage, however, Mg(OH)2 layer peeled off from MgO surface. These results suggested that the rate-controlling mechanism in the dissolution of MgO was diffusion through the product layer of Mg(OH)2 at the first stage, and surface reaction at the second stage. In MgCl2 system, the rate remained constant only in a short period and decreased gradually with reaction time. Mg(OH)2 films on MgO were observed as in Mg(CH3COO)2 system, though it did not peel off completely. Hence, this product layer prevented MgO from dissolution and limited the rate in MgCl2 system.

Reaction of Magnesium Oxide with Acetic Acid

Fused magnesia and magnesia clinker which were pulverized to such a fineness as shown in Table 1, were proven to react rather readily with glacial acetic acid at a temperature from 20° to 65°C. When the fractions of magnesia reacted were followed at each constant temperature by determining magnesium acetate formed in the reaction mixture which was soluble in methanol, the reactions proceeded after Jander's rate-equation except later reaction-stage as shown in Fig. 1 with an apparent activation energy of 21.8kcal/mol, though any diffusion layer didn't be observed around magnesia grains under microscope. In a semi-adiabatic condition, the temperature of the mixture should rise owing to the heat of reaction, resulting in acceleration of the rate of reaction more and more to cause the mixture to boil. These situations were examined at an initial temperature from 30° to 60°C. The results were shown in Fig. 3 in comparison with those obtained by numerical calculation using the rate data at constant temperatures and heat contents of the matters concerning to the reaction system.

Chelatometric titration of calcium and magnesium in the presence of a large amount of magnesium

A chelatometric titration method was recommended to the determination of calcium and magnesium in the coexistence of a large amount of the latter. The outline of the procedure is as follows: Three aliquots of the sample solution are taken. A preliminary titration of calcium in the first aliquot is made with ethylene glycol bis (2-aminoethyl ether)-N, N, N', N'-tetraacetic acid (EGTA) at about pH 13 using either 2-hydroxy-1-(2'-hydroxy-4'-sulfo-1'-naphthylazo)-3naphthoic acid (NN) or Calcichrome as an indicator. The volume of EGTA consumed in the above titration and further 0.5 ml are added to the second aliquot of the solution and then a precise direct determination of magnesium is carried out by means of the titration with ethylenediaminetetraacetic acid (EDTA) at pH 9.510.0 using Eriochrome Black T (EBT) as an indicator. In the third aliquot the sum of calcium and magnesium is titrated with EDTA at pH 9.510.0 using EBT as an indicator. The accurate value of calcium is calculated from the difference between the second and the third titration.According to this method calcium and magnesium in the samples containing a large amount of magnesium such as magnesia clinker, dolomite, dolomitic limestone, etc. are determined with satisfactory precision.

Studies on the Interaction Between Fe<sub>2</sub>O<sub>3</sub> and MgO and It's Effect on the Sintering of MgO

The tablets consisting of chemically purest Mg(OH)2 and 0-1.5wt. per cent Fe2O3 were fired at 1000°-1550°C to examine the appearance after the firing as well as the microstructure.The firing shrinkage and the bulk density began to increase markedly from 1000° to 1200°C (Figs. 1-4). At 1200°C the coloured regions, which had developed by the diffusion of iron from Fe2O3 grains, began to spread abruptly with the remarkable growth of periclase crystals. From the results mentioned above, it may be inferred that the sintering of Mg(OH)2 occurs in two successive stages; (1) up to 1200°C the periclase crystals formed by the decomposition of Mg(OH)2 come into intimate contact each other showing the remarkable shrinkage of the specimens, and (2) in the second stage during which the growth of periclase crystals takes place with the rapid diffusion of iron from Fe2O3 through the contact points between periclase grains.The mechanism of the reaction of Fe2O3 and MgO examined by poralization microscope and X-ray diffraction may be interpreted clearly with the aid of the phase diagram of the binary system MgO and Fe2O3 (B. Phillips, S. Somiya, and A. Muan, J. Am. Ceram. Soc., 44, 169 (1961)).The reaction is a kind of the counter diffusion processes. MgO diffuses into Fe2O3 grains to form magnesioferrite. With the elevation of temperature, Fe3O4 content of the magnesioferrite becomes higher until it changes to very dark colour. On the other hand, Fe2O3 is reduced into ferrous state which duffuses into MgO to form a solid solution, magnesiowüstite. With increasing temperature the content of ferrous iron increases up to the saturation limit with a result that the further introduction of iron oxide to the periclase phase gives rise to the formation of magnesioferrite.The acicular hematite crystals are exsoluted from the magnesioferrite during cooling, which distribute between the grains of magnesioferrite, as the solid solution limit of Fe3O4 decreases with decreasing temperature. Also magnesioferrite is exsoluted from magnesiowüstite and spread throughout the periclase phase, as the solid solution limit of FeO in periclase decreases grately with decreasing temperature.The results of the experiments mentioned above suggest that the following conditions should be held in order to maintain the higher FeO content of magnesia clinker: (1) In order to enlarge the area of the solid solution limits of FeO in periclase, and of Fe3O4 in magnesioferrite, it is desirable that the firing temperature is kept as high as possible. (2) To maintain the conditions in higher temperature the clinkers should be cooled quickly. (3) To accelerate the reactions between Fe2O3 and MgO the grain size should be reduced as far as possible. In practice the refractories can not be cooled rapid enough to prevent the exsolution of FeO. If we consider only this phenomenon, it seems to be inferred that the magnesia clinker mineralized with Fe2O3 is not suitable for the fired refractories, and if the clinker mineralized with Fe2O3 is used, unburned refractories seem to be prefered rather than the fired ones.From the experimental results concerning the relation between the firing shrinkage and Fe2O3 contents, it is suggested that only a small amount of Fe2O3 would be sufficient for the mineralizer of magnesia clinker.During the heating up the growth of periclase grains proceeds gradually together with the diffusion of iron from Fe2O3 grains. Pores between the periclase grains, and perhaps the oxygen releases by the reduction of

A Radioisotope Study of the Corrosion Resistance of the Dunite Refractories to Molten Slag

Radioisotope techniques were used for the study of the corrosion resistance of the four kinds of sintered dunite refractory materials.The crushed powder of electrically fused dunite (see Table 1) were mixed with or without dolomite, limestone, or magnesia clinker (see Table 2 and 4), shaped into a crucible-like form by pressing, sintered at SK 27-32. The steel-making lime slag added with a small amount of R. I. 45Ca in the form of 45Ca(NO3)2 was melted in the crucible at 1610°C for about 1 hr. The penetration of 45Ca into the inner fine structure of the crucible was examined by autoradiography.The results obtained were as follows:1) Autoradiography has given an informative picture of the actual penetration of the slag into the fine structure of refractories, with good resolution, which is unobtainable with an ordinary microscope.2) The penetration of 45Ca has been found to be fairly slight for the refractory material added with magnesia clinker, while extremely deep for those added with lime stone or dolomite, compared with for the material consisting of only fused dunite.

冶金用充填層の圧損と熱伝達について

The pressure loss and heat-transfer in the packed column were studied at elevated temperatures. In spite of many investigations most of their results were based on comparatively low temperature experiments relating chemical industries.The authors found that their results were hardly available for elevated temperature fluid (more than 300°C mean temperature) and obtained experimental formulas available for the fluid of 300°C, 450°C and room temperature. Air was used as the flowing fluid and magnesia clinker as packed material. The authors' formulas were led from the results of dimensional analysis and could apply 40-500 Reynolds number. Heat-transfer in the packed column at elevated temperaby use tures was analysed of Kuzuoka's equation that had already reported.

Effect of Mineralizer on Dolomite Clinker from Coarse Granule

The authors studied on manufacture of dolomite clinker from dolomite coarse granule for refractory use. The results obtained are as follows;1) The rate of slaking of dolmite clinker was retarded by mineralizer containing Fe2O3 and TiO2, but not by SiO2.2) TiO2 and MnO have good effect in promoting anti-slaking property as submineralizer of Fe2O3.3) Dolomite clinker was coated with mixtures of Fe2O3 and magnesite have greater anti-slaking property than it coated with Fe2O3 only.4) Clinker added Fe2O3 is protected from slaking with one layer consists of composition Fe2O3/MgO≥1, but high magnesia clinker is protected with double layer; one layer consists of MgO obserbed a little of Fe2O3 and another composition Fe2O3/MgO≥1

Studies on Manufacturing Processes and Compositions of Sea Water Magnesia, (IV)

In continuing previous studies (Reports Part I-III by one of the present authors Shoichiro NAGAI and his collaborators, this Journal, 59, 456 (1951), 60, 540 (1952), 62, 248 (1954), the present authors reported the results of further continued studies on the preparation and chemical compositions of magnesium hydroxide by reacting diluted bittern solution to lime containing solution obtained from slaked lime, quick lime or calcined dolomite. Various kinds of reacting conditions between these two kinds of solutions were fully experimented and discussed by comparing the results of analyses of lime content and other impurities in the precipitated magnesium hydroxide, and its calcined magnesia or magnesia clinker, precipitating velocity, and volume or density of the precipitate Mg(OH)2.The products of these experiments, magnesium hydroxide, calcined magnesia or magnesia clinker, are already in some parts studied and are also being now further studied on their utilization methods to make (a) magnesia-chromite basic refractories, (b) magnesia cement (magnesium oxychloride cement), (c) magnesia gypsum or magnesia-dolomite plasters, etc., which results are already reported in some parts in the separate studies (Studies on Magnesia Cement from Sea Water Magnesia (Report I and II): Bulletin of the Society of Salt Science, Japan, 5, 251 (1951), 6, 6 (1952); Studies on Chrome-Magnesia Refractories by using Sea Water Magnesia (Report I-III): this Journal, 60, 60 and 422 (1952) 61, 152 (1953); Studies on Special Magnesia Cement by using Sea Water Magnesia (Report I): this Journal, 61, 266 (1953), etc., and will be further reported in the near future as continued reports of the above cited papers.

Studies on Chromite-Magnesia Refractories by using Sea-Water Magnesia, (IV)

In continuing the previous studies (This Journal, 60 No. 668, p. 60-65 and No. 676, p. 422-425 (1952); 61 No. 682, p. 152-154 (1953)), the present authors reported in the present paper, the results of further studies on the chromite-magnesia refractories by using chromite ore and special sea-water magnesia clinker obtained by dead burning special magnesium hydroxide contained a few percents of ferric oxide, which was specially obtained from dilute bittern solution by settling with slaked dolomite slurry from calcined dolomite with 3-5% limonite powder.Among many comparative testings, the best result was obtained as one of the example, having, the following phisical properties and chemical compositions: True density: 3.86, Aparent density: 3.83, Volume density: 2.90, Perosity: 24.1%, Water absorption: 8.3%, Compressive strength: 420kg/cm2, SiO2: about 8%, Al2O3: about 12%, Fe2O3: about 15%, CaO: about 3%, MgO: about 32% and Cr2O3: about 32%. But these contents of SiO2, Al2O3 and Fe2O3 are a little too large owing to the low grade of chromite ore, and the content of CaO is a little too large owing to the high lime content of sea-water magnesia clinker.

Studies on Manufacturing Processes and Compositions of Sea Water Magnesia, (II)

In continuing previous studies (Reports Part I-III by one of the present authors Shoichiro NAGAI and his collaborators, this Journal, 59, 456 (1951), 60, 540 (1952), 62, 248 (1954), the present authors reported the results of further continued studies on the preparation and chemical compositions of magnesium hydroxide by reacting diluted bittern solution to lime containing solution obtained from slaked lime, quick lime or calcined dolomite. Various kinds of reacting conditions between these two kinds of solutions were fully experimented and discussed by comparing the results of analyses of lime content and other impurities in the precipitated magnesium hydroxide, and its calcined magnesia or magnesia clinker, precipitating velocity, and volume or density of the precipitate Mg(OH)2.The products of these experiments, magnesium hydroxide, calcined magnesia or magnesia clinker, are already in some parts studied and are also being now further studied on their utilization methods to make (a) magnesia-chromite basic refractories, (b) magnesia cement (magnesium oxychloride cement), (c) magnesia gypsum or magnesia-dolomite plasters, etc., which results are already reported in some parts in the separate studies (Studies on Magnesia Cement from Sea Water Magnesia (Report I and II): Bulletin of the Society of Salt Science, Japan, 5, 251 (1951), 6, 6 (1952); Studies on Chrome-Magnesia Refractories by using Sea Water Magnesia (Report I-III): this Journal, 60, 60 and 422 (1952) 61, 152 (1953); Studies on Special Magnesia Cement by using Sea Water Magnesia (Report I): this Journal, 61, 266 (1953), etc., and will be further reported in the near future as continued reports of the above cited papers.

Studies on Chromite-Magnesia Refractories by using Sea Water Magnesia, (II)

In continuing the previous studies (This Journal, 60 No. 668, p. 60-65 and No. 676, p. 422-425 (1952); 61 No. 682, p. 152-154 (1953)), the present authors reported in the present paper, the results of further studies on the chromite-magnesia refractories by using chromite ore and special sea-water magnesia clinker obtained by dead burning special magnesium hydroxide contained a few percents of ferric oxide, which was specially obtained from dilute bittern solution by settling with slaked dolomite slurry from calcined dolomite with 3-5% limonite powder.Among many comparative testings, the best result was obtained as one of the example, having, the following phisical properties and chemical compositions: True density: 3.86, Aparent density: 3.83, Volume density: 2.90, Perosity: 24.1%, Water absorption: 8.3%, Compressive strength: 420kg/cm2, SiO2: about 8%, Al2O3: about 12%, Fe2O3: about 15%, CaO: about 3%, MgO: about 32% and Cr2O3: about 32%. But these contents of SiO2, Al2O3 and Fe2O3 are a little too large owing to the low grade of chromite ore, and the content of CaO is a little too large owing to the high lime content of sea-water magnesia clinker.

The Effects of CaO and SiO<sub>2</sub> on the produced Compound and the microstructure of magnesia clinker (I)

The Effects of CaO and SiO<sub>2</sub> on the produced Compound and the microstructure of magnesia clinker (I)