CA2767774A1 - Porous ceramic material having a macroporosity controlled by layering pore-forming agents - Google Patents

Abstract

Porous ceramic material comprising: a micro-structure comprising a material of crystalline xonotlite and / or tobermorite structure crystallized in the form of needles linked to each other so as to provide between them a pore diameter D95 greater than or equal to 0.4 μm and less than 5 µm and an average pore diameter D50 greater than or equal to 0.4 µm and less than 1.5 µm; preferably from 0.4 to 1 μm; and a macro structure constituted by a continuous or / and discontinuous stack of macro pores.

Description

Porous ceramic material having a controlled macroporosity by stacking porogens The present invention relates to a novel ceramic porous material, the process of this new material, the containers containing it, and that the use of containers for storing fluids such as gases and / or liquids.
It is known to use pressurized containers containing gases, such as than acetylene, dissolved in a solvent, such as acetone or DMF, in different applications, and in particular for carrying out welding, brazing and heating in combination with a bottle of oxygen;
These containers are usually filled with solid filling materials, intended to stabilize the gases they contain, which are thermodynamically unstable under the effect of pressure or / and temperature variations and therefore likely to break down during storage, transport and / or distribution.
These materials must have sufficient porosity to facilitate adsorption and release of the gases contained in the container. They must also be incombustible, inert to these gases and have good mechanical strength. These materials are conventionally constituted by porous silica-calcium ceramic masses, obtained by example from a homogeneous mixture in quicklime water or milk of lime and silica (especially in the form of quartz flour), as described in Documents WO-A-93/16011, WO-A-98/29682, EP-A-262031, to form a mash that is then subjected to a hydrothermal synthesis. Precisely, the mash is introduced in the container fill, under partial vacuum, which is then subjected to autoclaving in pressure and temperature, then baking in an oven to completely eliminate water and form a monolithic solid mass of composition Ca ,, SiyOzjw.H2O exhibiting structures crystalline type tobermorite and xonotlite, with a possible presence residual quartz.
Various additives may be added to these prior art blends for improve the dispersion of lime and silica and thus avoid formation structural inhomogeneities and the shrinkage phenomena observed during hardening of the mass porous. The filler materials obtained must indeed have porosity homogeneous without

2 empty spaces in which pockets of gas could accumulate and cause risks explosion.
EP-A-264550 further indicates that a porous mass containing at least minus 50%, or even at least 65%, or even at least 75% by weight of phase crystalline (relative to the weight of calcium silicate) makes it possible to satisfy the double requirement of resistance to compression and shrinkage at synthetic temperatures hydrothermal and cooking.
If the known porous masses are generally satisfactory in terms of their mechanical resistance, the fact remains that the filling times, restitution, Draining and filtration remain long.
Indeed, according to the operating conditions (temperature of use, flow working, quantity of gas contained in the bottle ...), they do not allow always to extract the gas that they contain continuously, at a high rate, for the duration necessary to certain applications, particularly welding, with a restitution rate of maximum gas, corresponding to the ratio of the amount of usable gas to the quantity of gas initially stored. However, it would be desirable to be able to satisfy a flow rate of 200 l / h continuously during 15 minutes and at a peak flow of 400 l / h for 4 minutes, for a rate of gas capacity greater than or equal to 50% at the start of the test (defined as the ratio of number of gas present at this time to the amount of gas initially charged in the container), the container having a diameter / length ratio of between 0.2 and 0.7, preferably between 0.35 and 0.5, for a minimum water capacity of one liter and preferably between 3 and 10 liters.
This deficiency is particularly related to the significant loss of load generated by the microstructure. This microstructure is constituted by a microporosity formed by the stack of sand-lime needles (porous distribution of the material in that case), mainly consisting of xonotlite and / or tobermorite and / or other types phases of type CSH (foshagitis, Riversideite ...). It is understood by CHS the ratio lime / water / silica.
The vacant space between the needles thus forms an open porosity that can vary from 60 to 95%. Such a microstructure is described in particular in the documents EP 1 887,275 and EP 1 886 982. The significant loss of load is due to the very small size pores (between

3 0.1 m and 1 m) and their very narrow volume distribution (such as almost monomodal).
It is understood by pore size the average stack generated by the points mainly xonotlite.
From there, a problem is to provide a porous material ceramic in which the pressure losses are limited so as to increase the gas diffusion and / or liquids within the porous material. This would allow for example restore more quickly the liquid or gaseous content of the volume while maintaining a coefficient of satisfactory security.
A solution of the invention is a ceramic porous material comprising:
a microstructure comprising a material of crystalline structure xonotlite and or tobermorite crystallized in the form of needles linked to each other way to spare between them a pore diameter D95 greater than or equal to 0.4 m and less than 5 m and one average pore diameter D50 greater than or equal to 0.4 m and less than 1.5 m;
preferentially from 0.4 to 1 m; and and a macrostructure consisting of a continuous stack and / or a discontinuous stack of macro pores.
The term "porous pores" with a diameter of between 10 and 2,000 m.
These Macro pores can be spherical, oval, sticks, ...
By microstructure is meant the microscopic structure of the material.
Macrostructure means the architecture of matter. Here this architecture in form of interconnected macro-pores or not allows the formation of paths preferential continuous or discontinuous for the diffusion of fluids within the microstructure.
Figure 1 shows on the left the only needle microstructure of a mass porous ceramic for storage of gas and / or liquid and right the combination microstructure - macrostructure (these are shaped pore stacks sticks).
By pore diameter D95 is meant a diameter at which 95% by volume of the pores have a diameter less than 5 m.
By mean pore diameter D 50 is meant a diameter at which 50% by volume of pores have a diameter less than 1.5 m.

4 Xonotlite is a calcium silicate of formula Ca6Si6O17 (OH) 2, which presents repetitive units consisting of three tetrahedra. Moreover, the tobermorite is also a calcium silicate, of the formula Ca5Si6 (O, OH) 18.5H2O, crystallized in the form of orthorhombic.
The mechanism of formation of xonotlite most generally accepted at from CaO and SiO 2 precursors in the CaO / SiO 2 molar ratio of approximately 1 with the water used as a solvent is the following:

CaO / SiO 2 / H 2 O - * Ca (OH) 2 / SiO 2 / H 2 O - * CSH Gel - * tobermorite - *
xonotlite The set of intermediate phases preferably represents from 0 to 10% and more preferably from 0 to 5% of the weight of the crystalline phase present in the porous material.
Calcium carbonate and silica each preferably represent less 3% of total weight of these final crystalline phases.
The use of a porous material in the form of a stack of needles entangled with each other allows the structure to present the qualities required for stabilize the solvent in which the gas and / or the liquid is dissolved and limit decomposition confining it to an infinity of microscopic spaces, thus ensuring security of containers and their regulatory compliance with normative tests, such as ISO 3807-1 standard.
Preferably the interconnected macroporides or not have a mean diameter superior at 10 m.
The porosity of the ceramic porous mass will be the consequence of the stacking of the porogens, and the continuity or not of the network will be the consequence of the interconnection of so-called pore-forming elements, this interconnection being a function of content volume and the form of so-called porogens. The advantage of this technique is to be able to vary the macrostructure of the porous mass as a function of the porogen (or mixture of porogens) used during the manufacture namely its rate in the mash departure (formulation) and its geometric form (s).
The shape and dimensions of the pores are directly related to the agents blowing initial. It is understood by initial pore-forming agent a natural carbon compound (starch, starch of potato, ...) or not (PMMA, polystyrene, ...). Continuous stacking and or discontinuous is a function of the initial rate of porogenic agent (s) in the starting formulation. he is commonly understood that if the content is less than 35% by report to volumes of solids interconnection will be discontinuous majority.
Beyond this value the macro structure will be considered continuous.

As the case may be, the porous material may have one or more of characteristics following:
the macrostructure consists of macro-pores of a given diameter between 10 gm and 10 mm, preferably between 10 gm and 2 mm;
the macro-pores have a geometric shape chosen from among the spheres, the platelets, cylinders, cubes or a combination of these forms;
said needles have a length ranging from 2 to 10 m, preferably from 2 to at 5 m, a width ranging from 0.0 to 0.25 gm and thickness less than 0.25 gm the material contains at least 70% by weight of crystalline phase, preferentially less 90%.
On the other hand the porous material may also comprise selected fibers among the synthetic carbon-based fibers, as described in particular in the US-A-3,454,362, the alkaline-resistant glass fibers, such as described especially in EP-A-26203 1, and mixtures thereof, without this list is limiting. These fibers are particularly useful as reinforcing materials, to improve the impact resistance of the porous material, and also allow to avoid problems cracking when drying the structure. These fibers can be used as is or after treatment of their surface.
The porous ceramic material may further in its process of elaboration (dough formulation) include dispersing agents or binders, such as derivatives of cellulose, in particular carboxymethylcellulose, hydroxypropylcellulose or ethylhydroxyethylcellulose, polyethers, such as polyethylene glycol, clays synthetic smectite, amorphous silica of specific surface advantageously between 150 and 300 m2 / g, and mixtures thereof, without this list being limiting.
The porous ceramic material may furthermore also contain compounds silico limestones, such as wolastonite (CaSiO3) serving nucleating agent (s)

6 (sowing operation) allowing a faster germination of crystals of tobermorite and / or xonotlite. The content of nucleating agent varies from 0.1 at 5% by mass compared to all solid precursors.
The porous ceramic material may further contain in its process development phosphoric acid (<1% of the total volume of the pâté containing lime, silica and water).
Preferably, the porous material contains fibers, in particular fibers of carbon and / or glass and / or cellulose. The amount of fiber is advantageously less than 55% by weight, relative to all the solid precursors implemented in the method of manufacturing the porous material. It is preferably between 3 and 20%
in weight.
The porous material according to the invention preferably has a resistance to compression greater than or equal to 15 kg / cm 2, ie 1.5 MPa, more preferably greater than 25 kg / m2, that is 2.5 MPa. The mechanical resistance to compression can be measured by sample a cube of 100 x 100 mm2 in the porous material and application on the face Superior of this one with a force in pressure while it is held against a metal plate horizontal. This force corresponds to the pressure from which the matter starts to get crack.
In this context, and to achieve the specific ceramic porous material described previously, the subject of the present invention is a method of manufacturing the porous material according to the invention, comprising the following steps:
a) a step of preparing a pasty mixture based on calcium oxide, silica and water in excess. This mixture may also contain glass fibers, compounds organic, nucleating agents and phosphoric acid, b) an introduction step, in the mixture prepared in step a), of a mixture of at least one pore-forming agent which can decompose thermally at temperatures between 150 and 600 C, c) a step of hydrothermal synthesis of the porous material around stacking blowing agents of step b), from the mixture resulting from step a) and including porogens of step b),

7 d) a step of drying the porous material resulting from step c), and e) a step of extracting porogens by combustion at a temperature less than 600 C.
Figure 2 illustrates the different steps of the manufacturing process according to the invention.
It is understood that this process may include steps other than those mentioned above, which may be preliminary steps, intermediaries or additional to these.
Depending on the case, the manufacturing method according to the invention may have a or many of the following features steps d) and e) are coupled;
porogens are polymeric;
the porogens are based on PVC, polymethyl methacrylate, polystyrene, polyurethane, polyethylene, vegetable fiber (starch, apple starch of earth, nuts coconut, ...), carbon or a mixture of these elements. Indeed, nature porogens must be polymer, carbon or natural.
Porogens can be of different shapes: beads, fibers, nodules, platelets.
The size of the porogen will be chosen according to the macroporosity that one wish get. In general, it will be between 10 gm and 2 mm.
The second step (step b)) consists in introducing a mixture of agent (s) porogen (s) carbon (s) preferentially polymeric and / or natural in the mixture of departure including silico-calcareous precursors (lime and silica). We hear by pore-forming agent set of small form elements (spherical, fiber or other) and size controlled. It is the stacking of a multitude of these elements that forms a macro structure that will be used as negative to obtain a macroporosity.
Once the mixture of porogens incorporated, we proceed to the third step (step c) which consists in subjecting the lime-silica mixture of step a) in which one introduced the porogens to a hydrothermal synthesis at a temperature between 170 C
and 300 C
approximately, preferably between 180 and 220 C, for a period of time, according to the volume of container to be filled, from 10h to 70h, for example close to 40h for a container volume in water equal to 6 liters.

8 The fourth step of the process (step d)) or drying step has the function no only to evacuate the residual water, but also to confer on the mass processed a structure predominantly crystalline. This operation is carried out in an oven traditional electric or gas (the same or not that used for the synthesis operation hydrothermal), at the atmospheric pressure.
The fifth step of the process (step e)) is to extract the porogens by combustion. Extraction leads to the formation of pores facilitating the diffusion of fluids liquid or gaseous within the microstructure. For this, we apply a temperature on the porous material that burns the carbonaceous pore elements. This temperature must stay below 600 C to avoid destroying the initial microstructure.
This step can be coupled with the drying step. Once the mixture of porogens has been removed, gets within of the porous ceramic material a continuous and / or discontinuous stack corresponding to the forms initial pore-forming agents. We then have a coupled porosity macro according to the invention with a microporosity, formed of a double porosity (micro and macro-pores).
Figure 3 shows on the left an overview of the porous material according to the invention and on the right a zoomed view of this same porous material. We can see on this figure the macrostructure formed by interconnected macro-pores. These macro-pores are from size between 0.1 and 0.2 mm.
Figure 4 shows 4 photographs showing more precisely the macro-interconnected pores. The photographs were taken by microscopy electronic on a FESEM Ultra Zeiss 55.
Figure 4 includes two photographs on the left (an overview and a view zoomed) showing the porous material according to the state of the art, i.e.
without macro interconnected pores, and on the right two photographs (a global view and a zoomed view) showing the porous material according to the invention, that is to say with macro pore interconnected.
In some areas of the cells, it is possible to observe small canals (5-10 m) formed by the degassing linked to the combustion of porogenic agents during of the stage of drying. These channels participate in the overall permeability of the material. The Figure 5 illustrates these degassing channels.

9 The invention also relates to a container containing a porous material such as previously described, which container is able to contain and distribute a fluid.
The container may be thermally insulated at its outer wall and able to contain and dispense a cryogenic fluid.
The container usually comprises a metal casing enclosing the material porous described above. The metal casing may consist of a material metal such as steel, for example a standard carbon steel P265NB
according to standard NF ENI 0120, the thickness of which makes it suitable to withstand at least the pressure proof of 60 bar (6 MPa), the normative regulatory value for the packaging of acetylene in the conditions described previously. The container is furthermore usually of form cylindrical and generally provided with closure means and a regulator pressure.
This container preferably has a diameter / length ratio of between 0.2 and 0.7 more preferably between 0.35 and 0.5, and a minimum water capacity of one liter.
Usually, such a container will be in the shape of a bottle.
The fluids stored in the packing structure according to the invention can to be gases or liquids.
As gases, mention may be made of pure compressed gases or mixtures thereof gas or liquid, such as hydrogen, gaseous hydrocarbons (alkanes, alkynes, alkenes), nitrogen and acetylene, and gases dissolved in a solvent such as acetylene and mixtures acetylene-ethylene or acetylene-ethylene-propylene dissolved in a solvent such that acetone or dimethylformamide (DMF).
As liquids, mention may in particular be made of organometallic precursors such as than Ga and In precursors, used in particular in electronics, as well as nitroglycerine. All the alcohols or mixtures of alcohol can also be mentioned.
In particular, the container according to the invention contains dissolved acetylene in DMF or acetone.
The container can, according to another possibility, be thermally insulated level of his outer wall and adapted to contain and distribute a cryogenic fluid such that: hydrogen, helium, oxygen, nitrogen or any other liquid gas.

Finally, the ceramic porous material according to the invention makes it possible to reduce the effects related to the loss of charge (long filling, restitution, emptying). In effect, the architecture (macrostructure) deployed allows gas and solvent to arrive more quickly within the porous mass and in a perfectly homogeneous way, while maintaining 5 the microstructure according to the state of the art.
For example, for the case of acetylene bottles dissolved in acetone or DMF, the flow is limited by the significant pressure loss of the material porous current (without micro channels). This has as consequences :
- When filling, increase the filling time: about 6 hours in

10 average for a bottle - When emptying, limit the flow of gas and the quantity of gas that can be returned of the bottle: for a bottle of 6 liters the flow is limited to 400 1 / h during about 40 minutes, and the amount of releasable gas is about 50% per draw.
The ceramic porous material according to the invention with a macroporosity controlled reduces these negative effects while maintaining a safety factor satisfactory.

Claims (14)

A ceramic porous material comprising:
a microstructure comprising a material of crystalline structure xonotlite and or tobermorite crystallized in the form of needles linked to each other way to spare between them a pore diameter D95 greater than or equal to 0.4 μm and less at 5 μm and one average pore diameter D50 greater than or equal to 0.4 μm and less than 1.5 microns;
preferentially from 0.4 to 1 μm; and and a macrostructure consisting of a continuous stack and / or a discontinuous stack of macro pores. 2. Porous material according to claim 1, characterized in that the macrostructure is constituted by macro-pores with a diameter of between 10 μm and 10 mm, preference between 10 μm and 2 mm. 3. Porous material according to one of claims 1 or 2, characterized in that that the macro-pores have a geometric shape chosen from spheres, platelets, cylinders, the cubes or a combination of these forms. 4. Porous material according to one of claims 1 to 3, characterized in that that said needles have a length ranging from 2 to 10 μm, preferably from 2 to 5 μm.
μm, a width of from 0.010 to 0.25 μm and a thickness of less than 0.25 μm 5. Porous material according to one of claims 1 to 4, characterized in that that said matter contains at least 70% by weight of crystalline phase, preferentially at less 90%. 6. A method of manufacturing a porous ceramic material according to one of any of Claims 1 to 5, characterized in that it comprises the following steps:

a) a step of preparing a pasty mixture based on calcium oxide, silica and water in excess, b) an introduction step, in the mixture prepared in step a), of a mixture of at least one pore-forming agent which can decompose thermally at temperatures between 150 and 600 ° C, c) a step of hydrothermal synthesis of the porous material around stacking blowing agents of step b), from the mixture resulting from step a) and including porogens of step b), d) a step of drying the porous material resulting from step c), and e) a step of extracting porogens by combustion at a temperature less than 600 ° C. 7. Manufacturing process according to claim 6, characterized in that the steps d) and e) are coupled. 8. Method according to one of claims 6 or 7, characterized in that the porogens are polymer. 9. Method according to one of claims 6 or 7, characterized in that the porogens are at base of PVC, polymethyl methacrylate, polystyrene, polyurethane, of polyethylene, vegetable fibers, carbon or a mixture of these elements. 10. Container containing a porous material as defined in one of any of 1 to 5, which container in the form of a bottle suitable for contain and distribute a liquid and / or gaseous fluid. Container according to claim 10, characterized in that it contains dissolved acetylene in a solvent, in particular DMF or acetone. Container according to claim 10, characterized in that said container is isolated thermally at its outer wall and able to contain and distribute a fluid cryogenic. 13. Use of a container according to claim 10 or 11, or a porous material according to one of claims 1 to 4 for storing acetylene. 14. Use of a container according to claim 10, or a material porous ceramic according to one of claims 1 to 5 for storing organic liquids.