Effect of average degree of polymerization of vitreous sodium phosphate on the strength of magnesite bodies

Pirogov, Yu. A.; Babkina, L. A.; Kuz'menkov, M. I.; Pechkovskii, V. V.; Cherches, G. Kh.

doi:10.1007/bf01285739

Refractories

1973

DOI: 10.1007/bf01285739

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Effect of average degree of polymerization of vitreous sodium phosphate on the strength of magnesite bodies

Yu. A. Pirogov

L. A. Babkina

M. I. Kuz'menkov

et al.

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Cited by 5 publications

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“…With the use as a binder of sodium polyphosphate with n equal to 4-6, 15-17, and 20-25 the specimens with (NAP03) n with n = 20-25 possess the greatest strength, which agrees with the earlier obtained results [2,3]. This is the result of the better wettability of the magnesite grains by the solution with a broader mo!ecular-mass distribution.…”

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confidence: 91%

Unfired periclase plates for steel teeming ladle slide gates

Mezentsev¹,

Bibaev²

1987

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The method of production of fired periclase plates for slide gates has a number of significant disadvantages, the primary of which is increased firing scrap.The expenditures of manual labor in loading and unloading the charge on furnace cars are high and the fuel consumption for firing of the plates (1600~ is significant.Because of their low heat resistance fired plates crack even after teeming of a single heat and become unsuitable for teeming of a second heat.The high thermal conductivity of fired periclase plates limits the decrease in their material consumption as the result of possible overheating and warping of the metal gates.To eliminate these disadvantages a method for unfired periclase plates with a phosphate binder has been developed [i]. Densely sintered magnesite powder of the 3-0.063-mm fraction is used as the granular filler.Sodium polyphosphate (NAP03) n to GOST 20-291-80 with a degree of polymerization of n = 20-25 produced by S. Ordzhonikidze Perm Chemical Plant is used as the phosphate binder. According to the data of [2] polyphosphates with n = 21-24 provide the maximum strength of magnesite mixtures.The P205 content in the polyphosphate is 60-65%.* Powdered lignosulfonate (mash concentrate) to Technical Specification 81-04-225-79 is used as the organic plasticizer and inhibitor reducing the rate,of interaction of the polyphosphate with MgO and CaO in the stage of preparation of the mixture and the hardening green compact in pressing.To increase the strength of the freshly pressed compact, causticmagnesite powder is also added.The sodium polyphosphate is used in the form of an aqueous solution with a density of 1.50-1.55 g/cm 3. The sodium polyphosphate is dissolved in cold water according to the reaction 2NAP03 + H20 + NaH2PO~, which is accompanied by the liberation of heat.In batch solution of sodium polyphosphate with n = 21 in cold water the solution heats to a temperature of ~ot more than 35~ which does not lead to loss by it of the necessary properties, while in solution of polyphosphate with n = 4-6 the so_lution temperature increases to 52~ The solution prepared from sodium polyphosphate with n = 21 produced by Perm Chemical Plant remains transparent and does not lo_se its binder properties during long storage while a solution of sodium polyphosphate with n = 4-6 produced by Uvarovo Chemical Plant even after two or three days of storage changes to an opaque colloidal highly viscous mass not suitable for use as a binder.During storage of the sodium polyphosphate solution its pH and viscosity change (Table i). A solution with a density of 1.60 g/cm 3 possesses high viscosity and is poorly distributed in the mixture.The most suitable is a solution with a density of 1.50 g/cm 3.With the use as a binder of sodium polyphosphate with n equal to 4-6, 15-17, and 20-25 the specimens with (NAP03) n with n = 20-25 possess the greatest strength, which agrees with the earlier obtained results [2,3]. This is the result of the better wettability of the magnesite grains by the solution with a broader ...

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supporting

confidence: 91%

Unfired periclase plates for steel teeming ladle slide gates

Mezentsev¹,

Bibaev²

1987

Refractories

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“…Figure la shows the generally accepted structure of the phosphate-anion entering the composition of the molecules of orthophosphoric acid. Each PO, 3-ion is capable of forming three bonds.Commercial-grade sodium polyphosphate is a linear polymer having a chainlike structure and consists of a mixture of different polyphosphates having an average polymerization index n in the 8-12 range [5]. Its structure is shown in Fig.…”

mentioning

confidence: 99%

“…Commercial-grade sodium polyphosphate is a linear polymer having a chainlike structure and consists of a mixture of different polyphosphates having an average polymerization index n in the 8-12 range [5]. Its structure is shown in Fig.…”

mentioning

confidence: 99%

“…Based on a comparative study of the content of the mole fractions of the oxides and their recalculation (conversion) into the mole fractions of the compounds, one determines the phase composition in terms of mole, weight, and volume fractions (%), the theoretical density D of the material, its heat capacity Cp and refractoriness, the shrinkage of the material AV during the firing process, the magnesia modulus, and the iron modulus. The quality of the raw materials is evaluated taking the practical aspects with respect to their purity (with respect to the content of the oxide impurities) [5] into account. The minimum quantity of the periclase powder (additive) required for obtaining the refractories is calculated.…”

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confidence: 99%

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Effect of the structure of the phosphorus-containing anion in the phosphate binder on the inhibition of thermal oxidation of graphite powders

Pirogov¹,

Pustovar²,

Dovgopol³

et al. 1990

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At the present time, carbonaceous ramming bodies are being widely used for lining the metallurgical units working under reducing atmospheres. The bodies of the high-alumina and corundum compositions can contain orthophosphoric acid as a binder and the bodies of the periclase composition can contain commercial-grade sodium polyphosphate binder [1][2][3].The inhibiting effect of the phosphate binders on the thermal oxidation of the graphite powders introduced into the ramming bodies was demonstrated recently [4]. This paper establishes the relationship between the inhibiting effect and the structure of the phosphorus-containing anion of the binder. Figure la shows the generally accepted structure of the phosphate-anion entering the composition of the molecules of orthophosphoric acid. Each PO, 3-ion is capable of forming three bonds.Commercial-grade sodium polyphosphate is a linear polymer having a chainlike structure and consists of a mixture of different polyphosphates having an average polymerization index n in the 8-12 range [5]. Its structure is shown in Fig. lb. Sodium polyphosphate consists of PO43-tetrahedra that are mutually bonded oxygen atoms. Each phosphorus atom in the chain consumes one sodium atom. Besides this, a sodium atom is present at each end of the chain. In aqueous solutions, the end (terminal) groups dissociate to form two Na + ions and a chain-anion that is capable of establishing two bonds.

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“…The x-ray phase analysis of the specimens was carried out from diffraction diagrams recorded on a , Polyphosphates with p = 21-24 give magnesite compositions maximum strength [6].…”

mentioning

confidence: 99%

Composition of the phosphate bond in unfired magnesite refractories

et al. 1978

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The processes in the interaction of magnesium oxide with the sodium polyphosphates used as binder in the production of unfired magnesia refractories have been the subject of earlier research [1][2][3][4][5]. According to Lyon et al. [1 ], magnesium oxide (96-98% MgO) reacts with sodium polyphosphates to give a bond which consists of mono-and disubstitution products of magnesium orthophosphates. The magnesium phosphates undergo condensation over the temperature range 260-1200"C. This results in the formation of an amorphous phosphate glass with the general formula [Mg(POs)2]x. Further heating results in the partial crystaIlization of the glass to the form Mgs(PO4) 2. It has been established that in the interaction of periclase with (NaPO3)21-24, an increase in the temperature causes the content of orthophosphates and poIyphosphates with a mean degree of polymerization p below 20 in the phosphate bond to increase and the proportion of pyrophosphates and cyclic phosphates to decrease [2]. When using fired natural magnesites, the phase composition of the phosphate bond varies with the CaO and 5202 content of the starting material.According to Venable and Treffner [3], in mixes of MgO, CaO, and sodium polyphosphate the principal phase giving unfired refractories strength is sodium calcium phosphate Na20.2CaO 9 P205 which forms over the temperature range 800-1500~In addition to that compound, calcium silicophosphate 7CaO 9 25202 . P205 forms at temperatures above 1250~ in the presence of 5202. Over the temperature range 1500-1700~ the sodium is volatilized out of the Na20.2CaO. P205 which results in the formation of calcium orthophosphate Ca3 (Po4)2. Dibello and Pradel [4] carried out a high-temperature phase analysis of a composition of magnesite powder containing 93% MgO and 2% CaO with 10% added sodium polyphosphate and found that firing at 1190~ resulted in the formation of a mixed calcium-magnesium orthophosphate Ca3Mg 3 (PO4) 4 in the composition. According to Khoroshavin et al. [5], any CaO in a mix containing metallurgical magnesite and added (NaPO~) 6 reacts with the sodium poiyphosphate at 120-150~ to give a cryptocrystalline aqueous sodium calcium pyrophosphate Na2CaP207 .pH20 which at 300-360~ is dehydrated and crystallized and at 500-800~ interacts with the MgO to give a mixed orthophosphate Na2CaMg(POr 2 (bryan[re).The foregoing data provide evidence that the mechanism of the formation of the phosphate bond in unfired magnesia refractories is complex and has not been adequately investigated. In this article the results are reported of an investigation by x-ray, mass-spectrometric, petrographic, and chemical analyses and paper chromatography of the composition of the products of the interaction of a powder of sintered magnesite with sodium polyphosphate with ~ = 21-24 after heat treatments at various temperatures.* The powder of sintered magnesite of particle size below 1.0 mm including 32% finer than 0.088 mm contained 90.82% MgO, 2.83% CaO, and 2.32% 5202. A petrographic analysis showed that the powder ...

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Effect of average degree of polymerization of vitreous sodium phosphate on the strength of magnesite bodies

Cited by 5 publications

References 2 publications

Unfired periclase plates for steel teeming ladle slide gates

Unfired periclase plates for steel teeming ladle slide gates

Effect of the structure of the phosphorus-containing anion in the phosphate binder on the inhibition of thermal oxidation of graphite powders

Composition of the phosphate bond in unfired magnesite refractories

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