FR2696444A1 - Binder for ceramic masses. - Google Patents

Abstract

This binder has the following characteristics: it is composed of at least one refractory oxide and it has a particle size curve which is connected in a substantially continuous manner to the end concerning the fine particle size, of the particle size curve of the ceramic mass and then covers , together with the ceramic mass, a particle size spectrum between 0 and the maximum grain size of the ceramic mass, of at least 98% by weight.

Description

BINDER FOR CERAMIC MASSES

  The invention relates to a binder for ceramic masses

  based on refractory oxides.

  Various types of binders are known for the preparation of

  This includes, for example, sulphates, phosphates, cements,

  soluble glass, alumina and / or

  In the latter, we generally aim at

  to obtain a "carbon bond"; we speak in part

  of a "carbon structure" which is formed during the

pyrolysis process.

  In other cases, it is more or less

  the use of which involves, inter alia,

following problems:

  Under the effect of temperature, binders vaporize

  more or less early, so that in the structure of the mass, respectively of the shaped part manufactured from it, is formed a corresponding porosity, which is often undesirable Thus, a high porosity leads, as a rule, also to a decrease in resistance to

filtration and corrosion.

  The other problem is that binders

  known frequently decrease undesirably the resistance

  fire resistance of the corresponding mass (of the shaped part).

  The object of the invention is therefore to propose a binder for ceramic masses based on refractory oxides, which, after

  addition to a ceramic mass and, where appropriate, after

  parts, provides good green strength and good heat resistance of the product The last properties mentioned above and specific to the application, such as the resistance to filtration, the resistance to

  corrosion, etc., must be obtained to the extent

sible or even improved.

  Regarding the solution of this problem, we started from the following consideration: -the refractory ceramic masses

  conventional techniques as used in the art are

  granular matrix with a granular

  largely continuous metric The term "largely continuous" signifies that there is no significant gap between the grains From the point of view of the manufacturing technique, however, it is necessary that starting from very large grains it does not obtain a continuous grain size curve down to "O".

  Moreover, the characteristic grain size curve ends at a certain distance from the "0 value"; as a rule, at about 10 to 10 m. That is, typically 96 to 98% by weight of the ceramic mass is within the aforementioned lower or upper limits of particle size, while the remainder is partially composed of impurities and partially grains of larger or smaller size. This being considered, the invention starts from the consideration

  the binder must be connected, as far as

  its composition, to the granulometric curve of the ceramic mass, to continue it continuously "downwards", as far as possible until "O" In this case, the binder can and must also be composed of refractory oxides, so that a purely ceramic bond is not established

  of cooking and that any combustion of the thermal components

volatile is prevented.

  The binder portion which is, for example, between 2 and 15% by weight of the total mass may be prepared in an entirely different process, to obtain the particle size fractions.

desired fine.

  The refractory oxides of the binder can then be obtained

  as reoxidized vaporization products, during the fu-

  reducing the chromium aluminum supports or

  magnesium, in electric arc furnaces.

  Therefore, the invention relates to a binder for masses

  of refractory oxides, the granular structure

  metric mass according to a wide granulometric curve

  continuously, and having the following characteristics: the binder is composed of at least a refractory oxide and the binder has a gramulometric curve which connects substantially continuously to the end concerning the

  fine particle size, the grain size curve of the mas-

  is ceramic and then covers, together with the ceramic mass, a particle size spectrum between 0 and the maximum grain size of the ceramic mass, at least

98% by weight.

  In the ideal case, a granulometric curve is obtained

  continues from "O" up to a maximum particle size, the range of the lower binder size and the granular range.

  Upper Jometry being covered by the ceramic mass. A value of 100% by weight then constitutes, in this measure, a "theoretical" value, because impurities exist as a rule, and a limited grarnulometry of a technical nature in the fine particle size range.

  (eg less than 0.1 μm), for technological reasons.

  According to an advantageous embodiment, the aim is then

  at a value greater than 99% by weight in the range of the granulometric spectrum cited.

  In this sense, it is important for, the mode of action of the

  According to the invention, it covers the granulometric range.

  below the refractory oxides of the ceramic mass.

  ramic, so to fill the "corners" in the mass with

  refractory oxides In this way, one obtains a

  filling of the structure, almost optimal, both

  for 'resistance believed that also on the cooked product.

  Since the binder is also composed of refractory oxides

  the problem of shrinkage processes during drying or in the pyrolysis process is

  ceramics The binder does not contain any

  volatile constituent "or at least no volatile constituent

table.

  It is also intentionally given up to the content of SiO 2 which is most often contained in amorphous form in the known binders. The disadvantage of this binder containing SiO 2 is its adverse influence on the heat resistance and the resistance to hot corrosion of the ceramic products thus produced.

  The fraction of Si 02 leads indeed to the realization of

  its mullitic and / or vitreous in the product From

  phase system A 1203-Si 02, we can see that we can compute

  with the appearance of a first melting at approximately 1595 Celsius, while for example pure A 1203 -as for example in the form of refractory oxide used in a binder

  according to the invention then melts, little above 2000 Celsius.

  Thanks to the configuration according to the invention of the binder, it is possible to dispense with the additives that are phosphates or alkalis

  as binders in the classical sense, which have an adverse effect

  The additives containing phosphates or alkalis, if any, are contained only in the sense of forming a dispersing agent.

  and thus also in a significantly smaller amount of addition.

dre.

  Expressed otherwise: because the binder preferably contains

  the same refractory oxide as that of the ceramic mass

  that this favorite binder has the properties of resistance and

  erosion, as well as the barrier effect

  trations of the products thus formed.

  The refractory oxides used in the binder must

  as far as possible to have densities close to density

  pure, so that they are practically not subject to any

  The "separation granulometry" between the

  ceramic mass and the binder is determined according to the case

  this separation granulometry is usually

is about 10 to 30 inches.

  Correspondingly to an embodiment, se-

  where 95% by weight of the binder is present with a fraction of

  In the case of a separation particle size of, for example, 30 μm, this means that 95% by weight of the binder is in a particle size fraction 4 Him. As explained above, the binder must have a granulometric fraction chosen so that it continuously extends the particle size curve of the corresponding ceramic mass in the fine particle size range. The granulometric curve of the binder can then also follow a course. It is particularly preferred to have a binder with one or more of the following refractory oxides: AI 203, Cr 203,

  Zr 02, Mg O. The refractory oxides of the binder may be identical to those of the refractory ceramic mass It is totally possible

  it is possible to prepare a ceramic mass containing, for example, 99% by weight of A 1203 and the binder of which is also composed

  almost exclusively (with some impurities) of

from A 1203.

  The use of different oxides for the formation of mixed crystals, for example of the type A 1203-Cr 203, is however

  also within the scope of the invention In the case of

  cited, the melting point increases with the content of Cr 203.

  According to other characteristics of the invention: the fractions of refractory oxide form themselves and / or with the refractory oxides of the ceramic mass,

spinel.

  one or more of the refractory oxides mentioned is

  in the form of colloidal solution or gel.

  the particles of the refractory oxide components have been

  previously individualized using a dispersing agent

  health. the refractory oxide component is in a mixture

homogeneous with a dispersing agent.

  The behavior of the binder can be optimized by the fact that these particles are dispersed beforehand or added to the

  ceramic mass together with a dispersing agent.

  A prior dispersion can be carried out for example as follows:

  A dry mixture composed of a microm

  oxidizing agent and a dispersing agent powder to form a mixed aggregate, such that, for example,

  0.6% of phosphate-based dispersant to micromé

  and mix for 5 mm.

  It is possible to indicate as dispersing agent added to the binder for example sodium tripolyphosphate. The binder can then be

  be prepared as a mixture added to the mass of the

  refractory ceramic and the total mass may be pre-

trimmed with added water.

  Depending on the field of application, the binder may also have a content of flocculating agent (preferably from 0.01 to 1.0% by weight relative to the binder), selected from substances acting at a time after which the dispersion of the

  In this sense the particles are especially suitable.

  stanzas supplying calcium ions, contained in salts

  calcium, or other earthy alkaline salts.

  Finally, the invention also provides for the addition of so-called conditioning agents, which exert

  influence on the binding behavior of the

  attach to them link accelerators and delays in

  Depending on the application case, for example, bonding agents are used to delay the bonding. For example, carbonic acids, such as citric acid, may be used. Additives, such as cellulose derivatives, which are influence on the water repetition capacity, the viscosity

  and the possibility of treatment of the binder, to satisfy des-

  design the specific application case.

  Range limits of such dispersing agents, flocculating agent and conditioning agent are indicated below.

  calculated each time with respect to the total mass of the binder.

  dispersing agent: 0.01% to 2.0% flocculating agent: 0.01% to 2.0% conditioning agent: 0.01% to 2.0%

  the total content of the additives must not exceed 6%.

  The invention is explained below in more detail with the aid of an exemplary embodiment. We have a mass of alumina of a particle size

  maximum of 3 mm. The granulometric spectrum of the ceramic mass

  The refractory strength is as follows: 3.0 to 1.2 mm 30% by weight 1.2 to 0.163 mm 48% by weight 0.063 to 0.005 mm 14% by weight <0.005 mm 8% by weight% by weight now 5% by weight of a binder

  according to the invention, itself also composed of a half

  alumina crumble, of which 98% by weight is

  in a particle size fraction (at 0.005 mm.

  The attached figure shows that the grain size cut

  the binder is connected almost continuously to the

  be granulometric of the ceramic mass and extends it into the finest particle size fractions

(close to 0).

  The benefits that can be obtained through the use of

  binder according to the invention are explained in detail below.

above.

Claims (13)

  1 Binder for ceramic masses based on refractory oxides   the granular structure of the mass according to a cur-   The binder is composed of at least one refractile oxide and 1.2 It has a granulometric curve which is connected   substantially continuously at the relevant end   the fine granulometry of the particle size curve   that ceramic mass and covers then, conjoin   with the ceramic mass, a granulometric spectrum   between O and the maximum grain size of   the ceramic mass, at least 98% by weight.   Binder according to Claim 1, characterized in that the granulometric fraction of the binder is chosen such that the   binder covers with the mass a particle size spectrum   taken between O and the maximum grain size of the ceramic mass at least 99% by weight.   Binder according to claim 1 or 2, characterized in that it comprises a proportion exceeding 95% by weight of a   particle size fraction smaller than the particle size   that of separation vis-à-vis the ceramic mass.   Binder according to claim 3, characterized in that it comprises a proportion exceeding 95% by weight of fraction granulometric (30 Wm.   Binder according to one of Claims 1 to 4, characterized   in that the granulometric curve follows a curve of Fuller.   Binder according to one of Claims 1 to 5, characterized   in that it contains mainly one or more of the oxides   refractories: A 1203, Cr 203, Zr O 2, Mg 0.   Binder according to any one of claims 1 to 6,   characterized in that the refractory oxide (s) corre-   responde (nt) to that or those of the ceramic mass.   Binder according to any one of Claims 1 to 7, characterized in that the refractory oxide fractions form   themselves and / or with the refractory oxides of the ceramic mass, spinel. Binder according to any one of claims 1 to 8,   characterized in that one or more of the refractory oxides   res cited is in the form of a colloidal solution dale or gel.   Binder according to one of Claims 1 to 9,   characterized in that the particles of the refractory oxide components have been previously individualized using a dispersing agent.   Binder according to one of Claims 1 to 9,   characterized in that the refractory oxide component is   in homogeneous mixture with a dispersing agent.   Binder according to Claim 11, characterized in that   the dispersing agent is composed of phosphates.   Binder according to any one of claims 1 to   12, characterized in that the refractory oxide component holds a flocculant.   Binder according to Claim 13, characterized in that the flocculating agent is composed of calcium salt or other alkaline earth salts.   Binder according to any one of claims 1 to   14, characterized in that the refractory oxide component contains an additive influencing the binding behavior (conditioning agent).   Binder according to Claim 15, characterized in that the additive is composed of cellulose and / or acid derivatives Carbonic.   Binder according to any one of claims 11 to   16, characterized in that the dispersing agent, the flocculating agent   and / or the conditioning agent is present each in a maximum amount of 2.0% by weight, together in a total maximum of 6.0% by weight, based on the whole of the binding agent.