The invention relates to a tubular composite body, like a tubular composite ceramic body, which can be used for example as a filter, in particular a MIEC-ceramic filter.

Background of the Invention

US patent No. 7,935,254 discloses a device for the thermolysis or thermal decomposition of water at temperatures exceeding 2000°C. However, at such temperatures, the filters have proven to be weak in mechanical strength. The production of such filters is done in a classic way by utilization of molds or by extrusion, which takes weeks and has a high rate of defects.

Summary of the Invention

The main goal of the invention is to provide tubular composite bodies which have a better mechanical strength and can be produced in a faster and easier way.

To this effect, the inventor has developed a tubular composite body, which is a tubular composite body comprising a cylinder net made from threads and embedded in a hardened material. The particularity of such a tubular composite body is that the threads are made of silicon carbide (SiC) and the hardened material is a mixed ionic-electronic conducting (MIEC) ceramic material.

Such a tubular composite body can be used as a filter, in particular in a device for splitting water into hydrogen and oxygen by thermolysis. Such a filter has shown to have a better mechanical resistance and particularly to be less brittle than the conventional ceramic filters.

Other features and advantages of the invention will now be described in detail in the following description, which refers to the appended figure 1 that schematically shows a device for cooling a hot tubular body.

Detailed description of the invention

The tubular composite body of the invention contains a perforated cylinder. This perforated cylinder may be made of a solid rigid material, like a metal, a metal alloy or a ceramic material.

It may have the form of a net, for instance a cylinder net made from a ceramic material thread, like silicon carbide (SiC). For example, the cylinder net may have a diameter of 20 mm and the SiC threads a diameter of 0.25-0.5 mm. The size of the meshes may be 30-50 mm.

The perforations (or meshes) in the cylinder make it possible during the fabrication for the hardening paste to cross the perforations, so that the hardening paste on the internal side of the cylinder wall be materially bonded to the hardening paste on the external side of the cylinder wall. That continuity of matter will make the perforated cylinder firmly embedded in the tubular composite body, preferably in the middle, once the hardening paste turns into a hardened material.

The thermal expansion coefficient of the perforated cylinder preferably is the same or substantially the same as the thermal expansion coefficient of the hardened material in order to reduce the risks of cracking or fissuring when the temperature varies.

The hardening paste preferably is a ceramic paste so that the hardened material is a ceramic material.

The tubular composite body of the invention is preferably made in the following device.

Such a device first comprises a hollow cylindrical platform intended to be arranged vertically, on which a perforated cylinder, having a diameter greater than the internal diameter of the cylindrical platform and smaller than the external diameter of the cylindrical platform, is positioned also vertically on the upper end of the cylindrical platform.

Then an internal cylinder of the device, having an external diameter which is about the same as the internal diameter of the cylindrical platform, is introduced into the cylindrical platform, until its upper end is at the same level than the upper end of the cylindrical platform, near the bottom of the perforated cylinder.

An external cylinder of the device, having an internal diameter which is the same of the external diameter of the cylindrical platform, is positioned around the cylindrical platform, until its upper end is at the same level than the upper end of the cylindrical platform, near the bottom of the perforated cylinder.

An internal nozzle of a 3D printer of the device is then positioned near the bottom of the perforated cylinder, adjacent to its inside wall and above the cylindrical platform.

An external nozzle of the 3D printer is positioned near the bottom of the perforated cylinder adjacent to its outside wall and above the cylindrical platform. A hardening paste is then applied through the nozzles while appropriate means of the device rotate the internal nozzle along a first circle and the external nozzle along a second circle greater than the first circle. The hardening paste starts to fill the space between the internal and the external cylinders, which are removably fixed to a movable structure of the device, to which the nozzles are also fixed. The device also comprises means which move the movable structure upwards in a direction parallel to the axis of the cylindrical platform, and guiding means which guide the external and internal cylinders when they move upwards with the movable structure and the nozzles.

The perforated cylinder may be fixed to the cylindrical platform of from the top with a bar, in order to avoid any risk that it moves upwards with the internal and external cylinders.

The guiding means may be a fixed metal plate with a hole for the external cylinder and a disk disposed horizontally within the internal cylinder and fixed to the cylindrical platform or from the top with a bar. In this manner, the external cylinder can move upwards while remaining surrounded by the fixed metal plate and the internal cylinder can also move upwards around the fixed disk.

When the nozzles reach the top of the perforated cylinder, the internal and external cylinders are freed from the movable structure but they remain maintained by the guiding means.

The movable structure with the means for moving the structure upwards and the nozzles is then moved away.

The hardening paste is allowed to solidify, usually for 2-3 hours, depending on the time the plasticizer used in the ceramic paste needs to set.

Afterwards, the internal and external cylinders are freed from the guiding means and removed.

A hollow tubular composite body is then obtained on the top of the cylindrical platform.

The external cylinder preferably has a longitudinal slot along its entire axial length which allows it to be removed more easily and which additionally allows its external diameter to be adjusted and so that the thickness of the tubular composite body is adjustable.

The tubular composite body may for example have an outside diameter of 20 mm and an inside diameter of 16 min. Since at this stage the tubular composite body is a so- called "green body", it must be heated in order first to dry it and then to become sintered.

The sintering is preferably carried out in a device and with a process described in the European Patent Application filed by the Applicant on March 23 ^rd , 2021 under filing number EP 21315049.3 and with the title "DEVICE AND PROCESS FOR TRANSFORMING A MATERIAL".

After the sintering, the tubular composite body is allowed to slowly cool in a cooling device. The cooling of a ceramic body, a composite body or a ceramic composite body is an extremely delicate step where a high percentage of reject is usually observed.

The failures are in most cases related to convection (of the air) as well as conductivity (of the matter) factors. This is why a device for cooling the hot tubular body is shown on Figure 1 and its components and operation are explained as follows.

A hot tubular body 5 is introduced into an elongated insulated cooling chamber 4. Air is introduced via an air inlet 3, made to flow in the hot tubular body in a direction from one end of the insulated cooling chamber 4 to the other by pumping means 8 and then exits via air outlet 6.

The hot tubular body is rotated by rotating means 7, for example at a speed of 60 revolutions/min. In addition, means 9 for cooling the air outside of the hot tubular body 5 are provided. The temperature of the air outside of the hot tubular body 5 is measured by measuring means 10 like a thermocouple.

The air outside of the hot tubular body 5 is then cooled on the basis at least of the measured temperature.

Means are provided to move the hot tubular body from one side of the insulated chamber 4 to the other.

The pumping means 8 and the means 9 are preferably controlled by controlling means, for example a computer with an appropriate program.

The means 9 may comprise a pipe surrounding the hot tubular body in which a refrigerating liquid like water or a brine flows.

The controlling means are preferably able to regulate the temperature of the refrigerating liquid and preferably also its flow.

The controlling means also controls the movement of the hot tubular body from one side of the insulated cooling chamber 4 to the other. The controlling means, preferably a computer program, controls, on the basis of the measured temperature of the air outside of the hot tubular body:

- the flow of air through the hot tubular body 5,

- the cooling of the air outside of the hot tubular body 5 and

- the movement of the tubular body from one side of the insulated chamber 4 to the other and

- optionally the rotation means 7.

The computer may allow the hot tubular body to move only when the temperature of the outside air the tubular body reaches a determined level. The insulated cooling chamber 4 is preferably sufficient long to cool several tubular bodies at the same time, for example with an axial length of 7.2 - 8 m.

Several means 9 are preferably provided, each having substantially the length i of a tubular body.

The controlling means then preferably control each means 9 individually.

A preliminary step is preferably provided, wherein the conductivity of a sample of the tubular body is measured as a function of temperature. The data are then fed to the computer of the controlling means, where the computer program calculates the thermal energy and consequently the temperature of the liquid refrigerant as well as its flow rate to be supplied to the means 9 in order to have a precise control of the cooling of the tubular body. This avoids crack of fissures and reduces the reject rate of the tubular body.

The device may be controlled so that the temperature of the tubular body drops from the entry temperature, usually about 2200°C, to an outgoing temperature of about 50°C.

The above devices and methods are particularly useful with a ceramic paste which is a mixed ionic-electronic conducting (MIEC) ceramic paste and a perforated cylinder which is a net cylinder of SiC threads having the same thermal expansion coefficient as the MIEC ceramic paste once sintered. The tubular composite body dried, sintered and cooled may then be used as a ceramic MIEC filter.

This is what the inventor made in the following example.

Example

A 600 mm long filter tube essentially of MIEC ceramic with an outside diameter of 40 mm and an inside diameter of 38 mm and having in the middle a SiC net with meshes of 50 mm obtained by weaving a SiC thread of a thickness of 0.25 mm was made as a green body in about 30 minutes. After a drying at about 800°C was done equally in the whole wall mass in about 20 minutes, without allowing the filter tube to cool, the latter was sintered at about 2200°C during about 30 minutes. Then the filter tube was slowly cooled in the device of Fig. 1. It was subsequently subjected to X-ray diffraction (XRD) and scanning electron microscopy (SEM) measures and to a BET analysis. The oxygen filtering extraction capacity was then determined.

A final fully satisfactory product with no crack or fissure was obtained in 4 days whereas the conventional method of making ceramic MIEC filters usually takes 4 weeks or even more.

Use of the tubular composite body of the invention The tubular composite body of the invention may advantageously be used in a device for splitting water into hydrogen and oxygen by thermolysis, like that disclosed in the above US patent No. 7,935,254.

It is most preferably used in the device and process as described in European patent application filed by the Applicant on 4 ^th February 2021 under filing number EP 21315016.2 or in a heating unit as described in European patent application filed by the Applicant on 5 ^th February 2021 under filing number EP 21315017.0

In both cases the tubular composite body is advantageously used as a filter, particularly an oxygen filter.