Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-11-13
2004-05-04
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S693000, C106S801000
Reexamination Certificate
active
06730159
ABSTRACT:
The present invention relates to a clinker-type hydraulic binder obtained by burning comprising a magnesia spinel mineralogical phase and at least one calcium aluminate mineralogical phase, with a lime content of less than 15% of the binder by dry weight. It also relates to the use and a method of making such a binder.
Ladle steel metallurgy has developed these last years up to become a key point in the steel-manufacturing process. A ladle is a real chemical reactor with internal temperatures adapted to reach 1700° C. and being able to contain up to 300 tonnes of melted material. Conventionally used refractory concretes (first shaped, and then more and more monolithic) in steel ladles are not satisfactory any more and the performances thereof in such a field have to be improved.
In particular, the steel ladles contain wear linings in contact with steel and slag and more particularly exposed to slag infiltration and corrosion. Such wear linings should be able to best resist such aggressions.
More particularly there is an interest for monolithic concretes with low lime content (lower than 2.5% by dry weight in concrete) so-called LCC concretes (Low Cement Concrete), and with very low lime content (lower than 1% by dry weight in concrete) so-called ULCC concretes (Ultra Low Cement Concrete). The low lime content of such concretes is advantageous for obtaining a high refractoriness required for applications with steel ladles.
The Applicant has described in publication UNITECR'97, vol. III, pp. 1347-1354 (1997) of N. Blunt, C. Revais and M. Vialle entitled “Additives in calcium aluminate cement containing castables”, a study over castable monolithic refractory concrete types based on a blend of aluminous cement and magnesian spinel, particularly with a low lime content. The magnesian spinel and calcium aluminates contained in the aluminous cement have therein functions of refractory component et hydraulic component.
The concretes being described in such a publication bring out difficulties to reach a satisfactory rheology and an easy implementation.
Other solutions have been proposed to make refractory concretes through a clinker based on magnesian spinel and calcium aluminates.
Thus, Patent FR-1,575,633 discloses an aluminous refractory cement produced from a blend of 30 to 50% dolomite and 50 to 70% calcined alumina by burning up to clinkerization or melting.
FR-2,043,678 is an addition certificate application attached to FR-1,575,633, which described an aluminous refractory cement based on magnesian spinel and calcium aluminates obtained from a blend of dolomite and calcined bauxite or calcined alumina, lime and magnesia, through burning up to clinkerization or melting.
Japanese Patent Application JP-8-198649 is per se relative to a composition of refractory cement or concrete based on a calcium aluminate material prepared from lime, alumina and magnesia, through melting and/or calcination.
The compositions of the three above-mentioned last documents have the inconvenient that they are not sufficiently well adapted for refractory applications in steel ladles, particularly for producing LCC or ULCC concretes able to resist slag infiltration in steel ladles and resulting corrosion.
The invention relates to a clinker-type hydraulic binder obtained by burning particularly adapted for producing steel ladles and having a very high resistance to slag infiltration and corrosion compared particularly to the known binders.
The binder according to the invention allows to produce refractory monolithic concretes LCC or ULCC based on magnesian spinel, making possible an implementation with very satisfactory reactivity (setting time) and rheology (fluidity, castability).
The invention also relates to the use of such a binder for making a refractory concrete.
It has also as an object a process for making such a binder, making possible an easy implementation from currently available raw materials and advantageously at a low burning temperature (lower than 1800° C.).
Other advantages associated with the binder according to the invention, besides the refractoriness and the resistance to slag infiltration and corrosion, include the following ones:
cancellation of the 12CaO.7Al
2
O
3
(so indicated C
12
A
7
), except possibly in a strongly underburnt clinker and only on a temporary basis, such phase being able to bring about stiffening difficulties in concrete formulations;
binder microstructure being advantageous for the milling thereof so as to reach high granular fineness, so improving the corrosion resistance;
very low content in free residual magnesia, i.e. non combined in magnesian spinel, so as to be able to prevent the generation of cracks due to free magnesia in brucite during the implementation step for the refractory concrete produced from the binder.
Thus, an object of the invention is a clinker-type hydraulic binder obtained through burning comprising:
a magnesian spinel mineralogical phase, and
at least a calcium aluminate mineralogical phase with a lime content of less than 15% of the binder by dry weight.
According to the invention, the magnesian spinel comprises between 68% and 81% of the binder by dry weight.
Surprisingly such high proportions of the magnesian spinel allow to obtain the above-mentioned advantages, in particular good corrosion resistance properties.
By contrast, the known clinker-type binders comprising magnesian spinel and calcium aluminates and with a lime content of less than 15% have substantially lower magnesian spinel contents. In particular, FR-1,575,633 and FR-2,043,678 disclose proportions comprised between 25 and 45% magnesian spinel.
JP-8-198649 relates as per se to a binder with a lime content comprised between 15% and 30%, thus inappropriate for making LCC or ULCC concretes.
The term “clinker-type binder” means not only the proper clinker, thus the product before milling, but also the clinker being milled.
Such a clinker may be produced either at high temperature (higher than 1800°C.) by melting, for example in an electric oven, or advantageously through calcination (sintering) at low temperature (lower than 1800° C.).
Preferably, the binder is used for making concrete to which it gives magnesian spinel fine particles. The concrete formulation is then advantageously supplemented by fine reactive aluminas and by large magnesia spinel, as well as other granulates.
The high proportion of magnesian spinel in the binder allows to supply the total fine spinel of the concrete while preventing the problems encountered with a direct mixture of aluminous cement and magnesian spinel, as in UNITECR'97 above-mentioned. Moreover, the so-made concrete may have a low or very low lime content.
Preferably, the calcium aluminates are all under crystallized form.
More precisely, it is advantageous that the calcium aluminates should be essentially made of CA and CA
2
, with CA being CaO and A being Al
2
O
3
.
Such a binder composition, with a pattern MA—CA—CA
2
(with M═MgO), leads to such a surprising and advantageously consequence that the presence of C
12
A
7
is prevented, such a phase being adapted to lead to a stiffening cement.
Advantageously the calcium aluminates CA and CA
2
comprise between 19% and 32% of the binder by dry weight. More particularly it is strongly interesting the binder should comprise by dry weight of the binder:
71±2% MA (magnesian spinel)
18±2% CA, and
11±2% CA
2
.
Such a composition is in thermodynamic equilibrium in the CaO—MgO—Al
2
O
3
system, so that C
12
A
7
cannot be present in this combination, except possibly in a strongly underburnt clinker and on a temporary basis.
In an alternative embodiment, the calcium aluminates are present under an amorphous form, particularly under a vitreous form.
Preferably, the binder is quasi-free from free residual MgO at least as it can be observed on X-ray diffraction spectrum for the binder.
Practically the X-ray diffraction technique allows to insure that the free magnesia is present in a lower proportion than 0.5% of the binder by dry weight.
Thus, the magnesia p
Falaschi Jean-Pierre
Fryda Hervé
Letourneux Jean-Pierre
Parr Christopher
Touzo Bruno
Lafarge Aluminates
Marcantoni Paul
Young & Thompson
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