Title of Invention

A PROCESS FOR MAKING INSITU SPINEL FORMING HIGH ALUMINA CASTABLE COMPOSITIONS

Abstract

A process for making insitu spinel forming high alumina castables, comprising: a. Adding fine powder ingredients in the following order and in the indicated proportion: i. Sea Water Magnesia-Fused or sintered (5-7 part by weight); ii. Calcined Micro fine Alumina (11-13 part by weight); iii. Calcined Super fine Alumina (3-4 part by weight); iv. Sintered Alumina fines (6-7 part by weight); b. Mixing the same thoroughly and mixing is continued while adding the following one by one in the given order and in the indicated proportion: i. Micro fine silica (0-1 part by weight); ii. Sodium hexa meta phosphate (0.1-0.2 part by weight); iii. Citric acid (0.02-0.05 part by weight); iv. White fused Alumina fines (8-12 part by weight) and Alumina grains(56-62 part by weight); v. High Alumina Cement(2-3 part by weight); c. Preparing a thorough blend to obtain a final storable insitu spinel forming high alumina castable product.

Full Text

FIELD OF INVENTION: The present invention relates to the process of making a class of high alumina refractory castables in which spinel is formed insitu during service at high temperature. The invention is in particular related to development of a new class of refractory products with very good corrosion resistance to steel making slag and thermal shock resistance in addition to other superior physical and thermo- mechanical properties. The invented class of materials are to substitute spinel added high alumina castables for use in working lining, well Block, nozzle, purging plug of Ladle Furnaces and other critical areas of steel making processes in a cost effective manner. Spinel structure is such that within its unit cell considerable octahedral and tetrahedra! rites remain vacant. Therefore it can form a solid solution with varying amount of Al203, MgO and other oxides. Due to this characteristic, spinel can be made to have either excess MgO or Al203 in the form of solid solution. Also spinel traps the rapidly diffusing species such as oxides of iron and manganese from the slag within its crystal structure forming complex spinel, i.e. (Mg,Mn,Fe)o.(Fe,AI)2O3. Further the lime of slag reacts with alumina of alumina- rich spinel forming highly refractory Ca0.6AI2O3. Depletion of MnO, FeO and CaO makes the slag richer in silica and hence more viscous. This increase in viscosity of slag reduces its ability to penetrate inside the castable lining. As a result slag corrosion resistance of high alumina castable containing spinel rich in alumina is improved, which is one of the main criteria of steel ladle refractories. Another contribution of spinel addition in high alumina castable is in the improvement of thermal shock resistance of the later owing to its lower thermal expansion co-efficient and modulus of elasticity. In conventional spinel based high alumina castables preformed spinel is added to achieve the above advantages of spinel in order to improve performance of the high alumina refractory lining. However, the above characteristics of spinel can be further improved if the spinel is formed in situ in the refractory during service. The insitu formed spinel is very fine and is more effective in trapping FeO and MnO of slag and thereby further improves corrosion resistance of high alumina castables. The objective of the present invention was to develop a process for making alumina-magnesia based high alumina castables wherein spinel is formed in situ during service at high temperature. This has been achieved by incorporating magnesia in the matrix of the castable instead of adding preformed spinel. The added magnesia reacts with the alumina present in the castable matrix at high temperature during service and fcrms insitu-spinel. From laboratory study it was established that presence of silica in the matrix of castable accelerates insitu spinel formation at the service temperature. Sillica forms liquid phase in combination with Al203, CaO (from added cement) and MgO present in the castable matrix at high temperature and, this liquid phase facilitates in accelerating insitu spinel formation. Therefore silica has been incorporated in the castable matrix to maximise spinel formation within a short period at high temperature. But since too much of liquid formation at high temperature deteriorates the refractoriness under load (RUL) of a refractory, so silica addition was carefully controlled along with the cement content of the castable. Further presence of magnesia fines in high alumina castables impairs its rhelogical characteristics (i.e., consistency upon mixing with water, subsequent working duration of the mix and flow under vibration during placement), which were taken care by optimising the amount of fines in added magnesia and incorporating an additive. This invention involved development of a process for making tailor made insitu spinel forming high alumina castable compositions. The invented castable compositions were arrived at after extensive laboratory work and trials on different formulations and, subsequent optimisation with respect to properties and batch compositions. The laboratory work and trials carried out comprised of following studies on high alumina castables: Study on the matrix of such castables to find the effect of different ingredients and temperature on spinel formation and alumina content of spinel formed. Rheological behaviour of such high alumina castables in presence of magnesia fine particles, green and fired strength, permanent linear change (PLC) after heating to high temperature, apparent porosity after firing, refractoriness under load (RUL (a). 2 kg/cm" ). spinel formation and alumina content of the spinel formed by XRD analysis, thermal shock resistance by water quenching from 1200°C and slag resistance by Induction Furnace Slag Corrosion Test at 1650-1700°C for 5 hours using synthetic slag. The invented castable compositions comprised of sintered/fused alumina grains, calcined and sintered alumina fines, sea water magnesia, micro fine silica, high alumina cement and additives to achieve the desired properties. Chemical Composition The chemical composition of the total mix can be varied to achieve specific end properties depending upon area/condition of applications. The broad range is given in Annexure I. During manufacturing stage or during subsequent storage no chemical reaction takes place between various ingredients of the compositions. Whatever reactions/changes do occur, those are during application and service at high temperature only. Results of Trials Conducted Extensive Laboratory work/trials have been conducted during development stage of the process for the invented castables and, the final outcome of Laboratory scale trials are summarised in Annexure-I. These, arc the properties achieved for this invented castables as obtained on samples made after mixing with specified amount ot water following standard procedures of sample making by vibro-casting and after drying and firing at different temperatures. Properties of conventional high Alumina spinel added castables as reported in literature are given in Annexure-II. Process of Manufacturing: According an aspect of the present invention, fine powder ingredients are first added in a specific sequence and intimately mixed in suitable mixer. Coarse ingredients are then added in the mixer and the whole mass is mixed thoroughly. After mixing is over the castable thus obtained is inspected, packed in waterproof bags and stored in a dry place. According to a preferred aspect of the present invention directed to a process for making insitu spinel forming high alumina castables, comprising: a. Adding fine powder ingredients in the following order and in the indicated proportion: i) Sea Water Magnesia-Fused or sintered (5-7 part by weight); ii) Calcined Micro fine Alumina (11-13 part by weight); iii) Calcined Super fine Alumina (3-4 part by weight); iv) Sintered Alumina fines (6-7 part by weight); b. Mixing the same thoroughly and mixing is continued while adding the following one by one in the given order and in the indicated proportion: i) Micro silica (0-1 part by weight); ii) Sodium hexa meta phosphate (0.1-0.2 part by weight); iii) Citric acid (0.02-0.05 part by weight); iv) White fused Alumina fines (8-12 part by weight) and Alumina grains(56-62 part by weight); v) High Alumina Cement(2-3 part by weight); c. preparing a thorough blend to obtain a final storable insitu spinel forming high alumina castable product. A further aspect of the process for making in situ spinel formed high Alumina coated surfaces comprising mixing the in-situ spinel with 5.5-6% water, involving vibro-casting followed by curing, air drying, drying and preheating (up to at least 1000°C) as per schedules normally followed for low moisture castables and thereafter the lining or the prefabricated shape made out of this castable is ready for actual service where service temperature is about 1700°C. According to another aspect of the present invention, unlike the conventional process using pre-formed spinel added while making the high alumina castables, the invented castables of the present process do not use any pre-formed spinel and instead magnesia is added which reacts at high temperature during service with the fine alumina present and forms insitu spinel. This insitu formed spinel is more effective than pre-formed spinel in improving resistance of the castable lining from slag attack. Further as preformed spinel is a very high cost raw material as compared to magnesia and alumina, so cost of the invented castable is substantially less than that of pre-formed spinel added castables. Batch composition of invented castables, details of different components and manufacturing process flow chart are given in Annexure -III, IV and V. Potential areas of application: -Working lining of steel ladle in bottom and metal zones; -Teeming well block of Steel ladles; -Porous plug and its seating block for steel ladles; -Any other working lining that comes in contact with steel and high FeO and MgO containing slag at high temperature; The features of the invention as claimed to be novel are comprising the formulations and process for controlled formation of alumina rich insitu spinel in high alumina castable with following characteristics: • Controlled expansion on exposure to high temperature; • Excellent resistance to steel making slag; • Excellent thermal shock resistance; • Moderate liquid formation at high temperature; • High refractoriness under load (RUL). We claim: 1. A process for making insitu spinel forming high alumina castables, comprising: a. Adding fine powder ingredients in the following order and in the indicated proportion: i. Sea Water Magnesia-Fused or sintered (5-7 part by weight); ii. Calcined Micro fine Alumina (11-13 part by weight); iii. Calcined Super fine Alumina (3-4 part by weight); iv. Sintered Alumina fines (6-7 part by weight); b. Mixing the same thoroughly and mixing is continued while adding the following one by one in the given order and in the indicated proportion: i. Micro fine silica (0-1 part by weight); ii. Sodium hexa meta phosphate (0.1-0.2 part by weight); iii. Citric acid (0.02-0.05 part by weight); iv. White fused Alumina fines (8-12 part by weight) and Alumina grains(56-62 part by weight); v. High Alumina Cement(2-3 part by weight); c. Preparing a thorough blend to obtain a final storable insitu spinel forming high alumina castable product. 2. A process as claimed in claim 1, wherein, the preferred grain sizes of the various ingredients are as follows: 3. A process as claimed in claims 1 and 2, wherein the Al2O3 content of the various alumna sources are as follows: i) Sintered Alumina grains and fines (SAG and SAF): Al2O3-99.0% min. ii) Fused Alumina grains and fines (FAG and FAF): 4. A process as claimed in claims 1 to 3, wherein, the Sodium hexa meta phosphate(SHMP) has a minimum 60% P2O5. 5. A process as claimed in claims 1 to 4, wherein, the Citric acid (CA) has a minimum of 99.5% C6H8O7,H20. 6. A process as claimed in claims 1 to 5, wherein, the Micro silica has a minimum of 97% Silica. 7. A process as claimed in claims 1 to 6, which will produce insitu spinel forming high Alumina Castable with the following characteristics developed during service at high temperature (about 1600°C). i) Controlled expansion, ii) Spinel rich in Alumina, iii) Excellent resistance to steel making slag, iv) Excellent thermal shock resistance, v) Moderate liquid phase formation; 8. A process as claimed in claims 1 to 7, wherein, the properties of the insitu spinel forming high alumina castable is as given in Table 1. 9. A process of making in situ spinel formed high Alumina castable lining, which comprises: a. first preparing insitu spinel forming high Alumina Castable composition as claimed in claims 1 to 8 and thereafter: b. mixing with 5.5-6% water, c. making the lining by vibro-casting after placing the water mixed castable, d. followed by curing, air drying, drying and preheating (upto at least 1000°C) as per schedule normally followed for low moisture castables. e. the lining obtained is capable for use at service temperature of up to about 1700°C. 10. A process for making insitu spinel forming high Alumina castable lining compositions substantially as herein described with reference to the examples. A process for making insitu spinel forming high alumina castables, comprising: a. Adding fine powder ingredients in the following order and in the indicated proportion: i. Sea Water Magnesia-Fused or sintered (5-7 part by weight); ii. Calcined Micro fine Alumina (11-13 part by weight); iii. Calcined Super fine Alumina (3-4 part by weight); iv. Sintered Alumina fines (6-7 part by weight); b. Mixing the same thoroughly and mixing is continued while adding the following one by one in the given order and in the indicated proportion: i. Micro fine silica (0-1 part by weight); ii. Sodium hexa meta phosphate (0.1-0.2 part by weight); iii. Citric acid (0.02-0.05 part by weight); iv. White fused Alumina fines (8-12 part by weight) and Alumina grains(56-62 part by weight); v. High Alumina Cement(2-3 part by weight); c. Preparing a thorough blend to obtain a final storable insitu spinel forming high alumina castable product.

Documents:

558-CAL-2002-CORRESPONDENCE.pdf

558-CAL-2002-FORM 27.pdf

558-cal-2002-granted-abstract.pdf

558-cal-2002-granted-claims.pdf

558-cal-2002-granted-correspondence.pdf

558-cal-2002-granted-description (complete).pdf

558-cal-2002-granted-examination report.pdf

558-cal-2002-granted-form 1.pdf

558-cal-2002-granted-form 13.pdf

558-cal-2002-granted-form 18.pdf

558-cal-2002-granted-form 2.pdf

558-cal-2002-granted-form 3.pdf

558-cal-2002-granted-gpa.pdf

558-cal-2002-granted-pa.pdf

558-cal-2002-granted-reply to examination report.pdf

558-cal-2002-granted-specification.pdf