FR2458522A1 - PROCESS FOR PRODUCING THERMO-INSULATING AND CURABLE FIBROUS BODIES, ESPECIALLY CERAMIC, CORRESPONDING PRODUCTS AND THEIR APPLICATION - Google Patents

Abstract

THE INVENTION CONCERNS A PROCESS FOR MANUFACTURING THERMO-INSULATING AND HARDENED FIBROUS BODIES, IN PARTICULAR CERAMICS, CORRESPONDING PRODUCTS AND THEIR APPLICATION. ACCORDING TO THIS PROCEDURE, THE FIBROUS BODIES, MOLDED IN ITSELF KNOWN, ARE IMPREGNATED WITH AN AQUEOUS ALUMINUM DIHYDROGENOPHOSPHATE SOLUTION, DRY, THERMAL TREATMENT AT A TEMPERATURE OF AT LEAST 400C AND , IF APPLICABLE, A COOKING. APPLICATION TO METALLURGICAL AND CHEMICAL INDUSTRIES.

Description

- 1 - Process for producing heat-insulating and hardened fibrous bodies,

  The present invention relates to a process for the manufacture of fibrous thermally insulating bodies, in particular ceramics, which are cured on the basis of

  if necessary using other binders.

  Ceramic heat-insulating fibrous bodies are known in refractory fibers and organic or inorganic binders, some of low mechanical strength and high compressibility, the others having high characteristics of strength, density and dimensional stability. Thus, the German patent application (second publication) 12 74 490 describes a furnace combustion chamber, made by forming a fibrous pulp with added binder, in which the concentration of the binder must decrease over the entire extent of the section of the wall. Suitable binders include:

  clays, alkali silicates, aluminum phosphate, silicon

  colloidal medium, in a proportion by weight of 5 to 35%, of

  preferably 10%. But the fibrous bodies thus obtained do not respond to

  to a sufficient extent to the requirements of heavy loads, because of their dense and hard face on the one hand, their

  opposite side soft and soft on the other hand.

  In the process according to German Patent Application 2732387, each mineral fiber plate, previously bonded by means of an organic plastic binder, must be hardened by impregnation with an aqueous suspension of clay. and a subsequent heat treatment. The process according to the German patent application (first publication) 16 46 696 provides the reinforcement of each thermal insulation

  fibrous layer by surface treatment and, in particular,

  that of the underlying layer by means of a silicate solution. Thermal insulation treated in this way is also intended as a channel coating for molten metals.

  liquids. According to the German patent application (second

  It is proposed to obtain molded bodies of heat-insulating refractory material of homogeneous structure, by means of microwave drying, molded bodies which are intended for example for the insulation of turbine casings. the

  coating of gas convectors and furnace cladding.

  Preferred compositions include mixtures of solutions of silicon dioxide and aluminum silicate fibers. But these fibrous thermo-insulating bodies already known

  have the disadvantage, at high temperatures, of not presenting

  sufficient characteristics of mechanical strength,

  resistance to corrosion and dimensional stability.

  The object of the present invention is to eliminate the disadvantages that hitherto exist for fibrous bodies, in particular ceramics, heat-insulating and hardened, and to design fibrous bodies.

  having high dimensional stability characteristics

  corrosion resistance, as well as chemical resistance

  î. 20 mic with hot and aggressive gases, especially acids, while keeping practically unchanged their apparent density

  and their thermal conductivity. Said aggressive gases contain

  examples of acid reaction components: SO 2,

  Cl, F, which attack and strongly corrode part of the

  ceramics, used in the manufacture of

fibrous body.

  The problem thus posed is solved by a process characterized in that the fibrous bodies, molded in a manner known per se, are impregnated with an aqueous solution of aluminum dihydrogenphosphate, dried, subjected to a heat treatment at a temperature of at least 4000C and, where appropriate,

cooking.

  Preferably used for impregnating fibrous bodies an aqueous solution of aluminum dihydrogenphosphate of 20 to 50 dan

  preferably from 30 to 40%. It has been found that such a concentration

  This treatment made it possible to obtain optimal curing characteristics together with the desired dimensional stability of the fibrous bodies obtained at high temperatures. At higher concentrations there is still the risk of a significant change in structure during the implementation of fibrous bodies. Thus, fibrous bodies based on aluminum silicate fibers containing 47% by weight of Al 2 O 3, after treatment for one hour with a solution of 40% aluminum dihydrogenphosphate and cooking at 1000 ° C. have not accused at the end

  4 hours, no withdrawal species,

  At 50% aluminum dihydrogenphosphate, a linear expansion of about 1% was observed. The fibrous bodies are preferably baked at a temperature of 800.degree. C. to 14000.degree. C., which gives them an even better dimensional stability. baking fibrous bodies after heat treatment is not essential in

  in all cases, because this cooking or high temperature treatment

  ture can only intervene during the first use of the fibrous bodies used, for example after packing a

furnace or reactor.

  It has been found even more advantageous in said manufacture of fibrous bodies to add sodium polyphosphate in a small proportion. According to an interesting embodiment,

  can add sodium polyphosphate in the solid state or

  under the aluminum dihydrogenphosphate solution, and this

  to do well in a proportion of 0 to 15% by weight,

  carried to the existing aluminum dihydrogen phosphate. According to another form which is also of interest, it is possible to

  also add sodium polyphosphate to the aqueous suspension

  fiber to form the fibrous bodies, and this in a proportion of 0 to 5% by weight, referred to these ceramic fibers used for said manufacture, in which case the polyphosphate is to be added to the 'state

solid, finely divided.

  In the manufacture or molding of fibrous bodies, known methods such as vibrating and pressing a mixture, wet-milling, ceramic fibers and binder or pouring a suitable suspension into a mold provided with a bottom sieve and suction of liquid. In this

  concerning the process of this latter form of

  tion, reference may be made to the German patent application

(second publication) 19 46 018.

  According to another equally advantageous embodiment of the invention, in the presence of another binder, the fibrous bodies which have not yet taken an aqueous solution of aluminum dihydrogenphosphate are thoroughly impregnated and the solution is then removed. in excess. Fibrous bodies of uniform structure are thus advantageously obtained, and the proportion of aluminum dihydrogenphosphate used can be reduced to a relatively low value.

  It is also possible, of course, to ensure that the

  The hardened and dried fibers are thoroughly impregnated with an aqueous solution of aluminum dihydrogenphosphate, the excess solution being then removed. The fibrous materials, in particular ceramics, used in the manufacture of the fibrous bodies, are known materials, especially materials. aluminum silicate, having in particular a high alumina content, of the order of 45

at 95% by weight.

  But the process according to the invention can also use other mineral fibers such as rockwool or glass fibers. These glass fibers are preferably used in the form of staple fibers, i.e.

  length of 1 to 5 mm, but it is also possible to use

  the so-called "triturated" fibers having a length of

  from 100 to 500 μm. The diameter of the fibers is in general of the order of 1 to 25 μm, in particular 2% to 8 μm. But of course it is possible to use other fibers as well

dimensional characteristics.

  In the manufacture of fibrous bodies according to the state of the art, it is already known to use binders which may be of inorganic or organic nature. As examples of inorganic binders, mention may be made of: clays, finely ground chamotte,

  bauxite, alumina or bentonite, and as an example of an organic binder

  the starch. But in the process according to the invention, it is not absolutely essential to use such binders, apart from aluminum dihydrogen phosphate acting as a binder, which is to say that it is simply possible to manufacture a fibrous body in the usual way, from fibers suspended in water,

  for example by means of a suction mold, and to treat

  the invention this fibrous body (before or after drying)

  by a solution of aluminum dihydrogenphosphate.

  Aluminum dihydrogenphosphate is understood to mean the compound Al (H 2 PO 4) 3 which exists commercially in the form of a 50% aqueous solution. Depending on the needs, this aqueous solution

  % may be more or less expanse of water.

  Since the fibers used in the manufacture of fibrous bodies are partially etched and corroded by phosphates and also by aluminum dihydrogen phosphate, the use of

  simultaneously with these fibers and the dihydrogen

  Aluminum phosphate was not immediately conceivable.

  But we were surprised to find that by the process according to the invention fibrous bodies were obtained which, while

  reinforcing, were such that their structure

  ture and their temperature limit of use remained

  changed. The fibrous bodies manufactured according to the invention can be in the usual forms, for example mats,

  plates, tubes or other molded elements.

  The fibrous bodies manufactured according to the process of the invention, because of their high resistance to corrosion and their

  good chemical resistance, are suitable in all

  This is particularly important for pipe coating for high velocity and / or high temperature circulating gases. The fibrous bodies can also be used as thermo-insulating materials, storing little heat, in furnaces,

  to form a layer facing the combustion space.

  By addition of sodium polyphosphate, the mechanical strength of the fibrous bodies can be further improved and adjusted to the requirements. The heat treatment to be provided, according to the method of the invention, at a temperature of at least 4000 ° C is set

  depending on the size and shape of the

  to make, usually for 0.5 to 4 hours,

  at 3 o'clock, the maximum value of the temperature

  being usually 6000C and better still 550C.

  The firing optionally of the fibrous bodies having undergone said heat treatment is also performed, depending on the

  size and shape of the fibrous body, for 0.5 to 4 hours.

  But, of course, it is also possible that the heat treatment and the baking overlap and that in particular in the case of small fibrous bodies, in which the equilibrium of the temperatures is rapidly reached, it is possible to use the same heat.

  happy to bring them to cooking temperatures, especially

  from 800 to 14000C, following their drying, so that heat treatment and cooking interpenetrate without discontinuity.

  During the impregnation of the fibrous

  with a solution of aluminum dihydrogenphosphate

  nium an adsorption of it is done inside the body

  fibrous, so that a certain proportion of dihydrogen

  Aluminum phosphate remains attached to the fibers. It constitutes a protective layer for the fibers. Depending on the concentration of the aluminum dihydrogenphosphate solution used and

  the diameter and length of the fibers, the proportion

  Phosphate remaining fixed on the fibers is more or less large. By varying the concentration of the phosphate solution used in the impregnation of the fibers, as well as the force of the suction applied to the impregnated fibrous body, it is possible, however, "on the basis of simple preliminary tests, to adjust the proportion of phosphate remaining attached to the fibers which can be determined chemically

  simple way, after finishing the fibrous body; it is usual

  indicated in the form of P205 content. The fibrous bodies manufactured according to the invention generally have a content

  in P205 from 5 to 38% by weight, preferably 10 to 32% by weight.

  It is proposed to explain now the invention with the help of

following examples.

Example 1

  In one operation, 30 kg of ceramic silicate fibers containing 52% by weight of Al 2 O 3 and 48% by weight of SiO 2 were mixed in 1800 liters of water as a main component accompanied by the usual impurities having a length of from 2 to 3. mm and a diameter of 2 to 3 μm, with 1.5 kg of starch and 2.2 kg of bentonite, at room temperature. From this suspension was molded into a suction mold of 500 x 1000 mm a mat of a thickness of 25 mmo After suction of the water was dried this mat at 120 C for 1 hour. After drying, a piece intended for

  serve as a comparison test.

  The remainder of the dried mat of 7 L was impregnated with a 33% by weight solution of aluminum dihydrogenphosphate at room temperature for 10 minutes and the excess solution was then sucked into the mat using a sieve as support, then the mat was dried again at about C and the two mats were finally subjected to a treatment

  thermal at 420 C for 2 hours.

  The mat according to the invention was subjected to analysis, after treatment with a solution of aluminum dihydrogenphosphate

  and heat treatment, a content of 27% by weight of P205.

  In the following table, the values of the characteristics

  characteristics on this mat with those of the comparison mat, which had not been treated by the solution of

aluminum dihydrogen phosphate.

BOARD

  next mat untreated mat the invention by a solution of

dihydrogen

  aluminum luster Bulk density (in g / cm3) 0.48 0.26 Resistance to cold bending (in N / mm2) 1, -0 0.3 Flexural strength after 4 hours of 1.0 0.06 cooking at 1000 C Removal after 24 hours

at 10000C - 0.75 - 1.83

at 12500C - 1.1 - 3.25

  From this table it can be seen that the fibrous body treated next

  the invention with a solution of aluminum dihydrogenphosphate

  nium had better characteristics than the test

comparison.

  In addition, it has been found that the gas permeability of the body

  fibrous according to the invention remained virtually unchanged.

Example 2

  The procedure described above was repeated, but using

  a fiber suspension containing only 30 kg of

  bres used in Example 1 in 1800 l of water. By operating as in Example 1, a fibrous body in the form of

  mat that was impregnated with 7 1 of the dihydrogen solution

  aluminum phosphate used in Example 1. After treatment

  at 4500C a very stable mat was obtained.

Example 3

  The procedure of Example 1 was repeated once more, but using ceramic fibers containing 95% by weight of Al 2 O 3 and 5% by weight of SiO 2, which had a diameter of 1 to 2> n and a length of from 1 to 2 mm. We got a mat

  having outstanding mechanical characteristics.

Example 4

  In this example, crushed fibers having a diameter of

  meter of 1 to 2 μm and a length of 200 to 300 Sm. We got

  a mat having a somewhat lower density and a

remarkable gas meableness.

Example 5

  Operating as in Example 2 was manufactured a mat in

- 1 0 _

  ceramic fibers containing 62% by weight of Al 2 O 3 and 38% by weight of SiO 2. The mat obtained was subjected to a heat treatment at 4400C for 2 hours and exhibited after cooking at 10000C for 2 hours a remarkable gas permeability Set good mechanical characteristics.

Example 6

  By operating as in Example 2, we started from a suspension

  35 kg of the fibers used in Example 2 in 1600 l of water.

  1.5 kg of starch and 0.75 kg of solid sodium polyphosphate, finely ground and then poured were added.

  immediately the fibrous suspension obtained on a sieve.

  After impregnation with a solution of aluminum dihydrogenphosphate and heat treatment at 4000 ° C., a fibrous mat-shaped body having a porosity of about

  not much lower but an increased mechanical resistance.

Example 7

  The procedure was as in Example 6, however adding 0.75 kg of sodium polyphosphate in the solid state, finely ground,

  not to the fibrous suspension but to the dihydro-

  aluminum genophosphate used in the impregnation.

  A mat of lesser porosity was obtained, but better adhesion of the elementary fibers to each other, that after firing of the mat at 950 ° C.

- 11 -

Claims (8)

  1. A process for producing thermally insulating fibrous bodies,   especially ceramics, hardened if necessary using   very binders, characterized by the fact that the fibrous bodies, molded in a manner known per se, are impregnated with an aqueous solution of aluminum dihydrogenphosphate, they are dried, they are subjected to a heat treatment at a temperature of at   minus 400 ° C and, if appropriate, cooking.   2. Method according to claim 1, characterized in that the fibrous bodies are impregnated with an aqueous solution of aluminum dihydrogenphosphate of 20 to 50%, preferably 30 to 40% o   3o Process according to any one of claims 1 and 2,   characterized by baking the fibrous bodies at a   temperature between 800 and 1400 C.   4b Process according to any one of claims 1 to 3,   characterized by the fact that the fibrous bodies are thoroughly impregnated   have not yet hardened with an aqueous solution of dihydro-   aluminum genophosphate and remove it immediately after the solution in excess.   5. Method according to any one of claims I to 3,   characterized in that the hardened and dried fibrous bodies are impregnated with an aqueous solution of aluminum dihydrogenphosphate and removed immediately after the excess solution.   6. Process according to any one of claims 1 to 5,   characterized in that a solution of aluminum dihydrogenphosphate is used for the impregnation of the fibrous bodies,   containing a small proportion of sodium polyphosphate. - 12 -   7. Process according to any one of claims 1 to 5,   characterized by subjecting the molded fibrous bodies to impregnation, in the preparation of which sodium polyphosphate.   Thermally insulating fibrous body, in particular ceramics, characterized   rised by the fact that it was manufactured by the process defined in Claims 1 to 7.   9. Application of fibrous body according to claim 8, to the thermal insulation of pipelines for gas circulating under   high pressure and temperature and / or high speed.   10. Application of fibrous body according to claim 8, to the coating of reaction spaces, in particular in the case of ovens in an acid atmosphere.   11. Application of fibrous body according to claim 8, as wear liners for containers, in particular for transport,   for molten metal liquids, in particular aluminum.