Method for making soot filters.

p0001The invention relates to a process for the manufacture of porous fiber mats of wound or loose, to a felt or wadding-like structure matched fibers, which are brought into contact with a connecting means the fibers.

p0002From DE-OS 27 50 960, the use of such fiber mats as particle filters for diesel exhaust is known. The existing fiber felt of loose fibers is surrounded for these purposes of supporting bodies and downstream additionally provided with woven fiber mats to prevent the gas stream also blows the loose fibers. It can in this case not prevent the fibers are entrained in the gas flow, are deposited before the nonwoven mat and even penetrate into the pores of the mat.

p0003It has been shown that fiber mats, in particular as filters have good characteristics, namely that can be distinguished in high particle retention capacity to over 90%. However, the durability of the material and the durability thereof porosity proves to be unsatisfactory.

p0004Therefore, efforts to integrate with appropriate measures the fibers to form a strong and durable body.

p0005From US-3,826,076 a method of the initially mentioned type is known in which the fibers compacted and solidified with a silicate binder. However, the silicate binder forms lumps and pulls the fibers themselves. The result of this is that the fibers are bonded to each other along a certain length of fiber and therefore no reproducible pore size can be achieved, as FIG. 3 shows.

p0006Another attempt to stabilize the fibers is known from DE-OS 21 55 507, after which the mat of agglomerated fibrous elements are produced, which have a bristled circumference and form between them a number of interstices. This should not lead to a dense clogging the gaps compressing the fiber pad. The particle storage capacity is greatly reduced in this embodiment due to the agglomeration.

p0007also entail wound from continuous fibers fiber mats the risk of undermining the porosity by slipping the relatively loosely wound fibers.

p0008The invention has for its object to provide a method of the type mentioned, the fiber mats are produced with a reproducible porosity.

p0009The object is achieved by the measures indicated in claim. 1

p0010Here, the fibers are not separately coated as single fibers, but within the fiber mat, so that the coating material not only surrounds the individual fibers, but also the cross points of fibers which are closer to each other, bridges. This has the consequence that the fibers are bonded at their intersections with each other by the coating material, while the voids between the fibers remain as voids even after the coating.

p0011The loose fibers are anchored in this way within the fiber body in a simple manner so that it can no longer be compressed, for example, when used as an exhaust gas filter by the exhaust gas flow or blown out of the felt. The effectiveness of working as a depth filter filter of loose fibers, which is determined by the size and distribution of fiber distances and spaces, is preserved in this manner even under operating load.

p0012The inventive process also has the advantage that the fibers obtained by the coating material has a rough surface, for example by crystallization of the coating material whereby the active surface of the soot or particulate matter deposition is increased.

p0013By the method according to the invention also the mechanical stability of the fiber mat is increased.

p0014The fiber mats are made of suitable for the respective application materials. You may be fibers of only one material or different materials for each one mat can be used. Also, it is possible to obtain a homogeneous or a heterogeneous dimensions (length, diameter) to select the fibers.

p0015The application of the connecting fibers layer can be accomplished by depositing the selected for the respective application material from the gas phase (CVD).

p0016This method is well suited as the first order, consisting of loose or loose fibers matt structure is largely preserved during the coating process.

p0017The coating process according to a further embodiment of the invention in stages, ie with one or more interruptions, whereby each new nucleation caused. This is for applications, such. As in filters, advantageous because the layer is given a highly structured and very rough surface.

p0018However, it is possible to obtain a coating by another method, for. example, impregnating with a solution, precipitation of a solid and subsequent firing to achieve or by deposition of amorphous products from the liquid phase by the sol-gel method (Journal of Non-cristallin -Solids 63, (1984) 237-241, Holland).

p0019The invention extends to a characterized in claim 7 particulate filter.

p0020The invention will now be described with reference to embodiments. Show it:<ul><li>Fig. 1 is a fiber mat,</li><li>Fig. 2 shows a detail from Fig. 1,</li><li>Fig. 3 is a photomicrograph of a fiber mat prepared according to known methods and</li><li>Fig. 4 - 6 micrographs of prepared according to the invention fiber mats.</li></ul>

p0021From loose fibers (10) (Fig. 1) is a porous felt or cotton-like fiber mat (11) is formed in which the fibers (10) with one another and thereby to a certain extent are intertwined. Based on a large-mesh support (12), the mat (11) is subjected to a known coating method.

p0022In the CVD method, the mat (11) is contacted with the carrier (12) in a reaction furnace in an atmosphere containing the coating material at an elevated temperature. After a coating time of a few minutes to several hours, an individual fibers (10) be coated layer (14) can be achieved by a few micrometers. Nodes or cross points (15) of fibers in which the fiber spacing (16) maximum is twice the layer thickness, are thereby bridged by the coating material (17), so that the fibers at such locations (15) are connected to each other, as in the . shown greatly enlarged detail of FIG 2 and in the micrographs (Fig. 4 - 6) is clearly shown.

p0023The micrographs show the formation of crystals or irregular deposits on the fibers. This gives the fibers (14) has a rough surface, which favors an improved Abhäsion particular of very small particles, such as soot or ash particles when the fiber mat is to be used as a filter.

p0024The mounting of Fig. 3 shows a fiber mat treated by a known method. The fibers are bonded or glued together along the same. It is different in patients treated according to the invention, fiber mats, as the recordings 4 show up. 6 The coated with a coating fibers are bonded together only at their crossing points. The shoot 4 to 6 show the sequence after the results of in Examples 2, 3 and 12 produced fiber mats.

p0025The fiber mat (11) may be coated by soaking or wetting the fibers (10) in a mass, in which the coating material is in colloidal suspension. The solid particles consist of the fibers and coat them. The excess liquid (sol) is then aspirated. The impregnated fiber material is dried and fired so that the deposited solids are sintered with the fibers.

p0026In the same way, the coatings are performed for wound of continuous fibers fiber mats. Porous, wound fiber mats are wound in alternate cross plies loosely, thereby incorporate pore-forming passageways. Again, the compound of the fibers takes place only at the crossing points.

p0027Regardless of the coating method and on the design of the fiber mat remains a porous body (11) whose porosity is determined by the packing density of the fibers (10) as a final product. The shaping of the final filter body can be effected both before coating and after coating.

p0028After the procedure produced fiber mats according to the invention such. B. with catalytically active materials can be treated readily be coated. The type and duration of the coating depends on the selected fiber mat having a density and the desired porosity from. These are determined empirically in general. The examples described below of manufacturing processes of fiber mats according to the invention give evidence.

Example 1:

p0029<ul><li>a) Al₂0₃-fiber wool and alternatively Al₂0₃-fiber mat with an average fiber diameter of 3 microns was dissolved using machine combs mechanically spread out on a belt and needled to form a manageable fibrous web having substantially a random fiber orientation has been achieved. The nonwoven fabric had a bulk density below 0.1 gcm⁻³, which is in the use of the filter as an exhaust gas particulate filter of importance to create a very low back pressure. The nonwoven fabric was finally brought by mounting in a heat-resistant wire mesh into the desired shape.</li><li>b) The nonwoven fabric thus prepared was then coated by the CVD method with Al₂0₃. The deposition of Al₂0₃ inside the fiber braid was made by reacting AlCl₃ with CO₂ and H₂. The deposition was carried out as follows.</li></ul>

p0030At a temperature of 850 ° C and a process gas pressure of 6 kPa, a deposition gas of 6.0 mol% AlCl₃, 7,8 passed mol% CO₂ and the balance H₂ through the fiber material. The total deposition time was 12h. The deposition has been interrupted twice, in each case at the new beginning to bring about the formation of new Al₂O₃ nuclei and thus to effect a finely crystalline growth. This infiltration of the Al₂O₃ Al₂O₃ fibers have been completely coated with a fine crystalline Al₂0₃ layer of about 1 .mu.m thickness and thereby joined at the points of contact established with neighboring fibers. In this way resulted in a dimensionally stable, highly porous, ceramic structures.

Example 2:

p0031<ul><li>a) a product made according to Example 1a nonwoven was used and coated by the CVD process as follows.</li><li>b) At a temperature of 950 ° C and a pressure of 6 kPa, the impregnation of the fibers with a gas composition of 6.0 mol% AlCl₃ was made 7.8 mol% CO₂ and residual H₂. The duration of deposition was Al₂0₃-6h in this case. These process data in a more structured surface of the fixed fused together Al₂0₃ fibers was achieved, a photomicrograph thereof is shown in Fig. 4.</li></ul>

Example 3:

p0032<ul><li>a) as Example 2a.</li><li>b) at a temperature of 1,050 ° C and a pressure of 100 kPa, a gas having a composition of 2.7 mol% AlCl₃, 3.5 mol% CO₂ and H₂ residue was used for the deposition of Al₂0₃ in the submitted fiber braid. Thus, after a deposition time of 4 h, a solid compound of Al₂0₃ fibers was achieved by grown in the form of a pronounced crystalline surface-rich layer Al₂0₃ (see Fig. 5).</li></ul>

p0033In another experiment with the same physical conditions, and the same gas composition but over a period of 12h and four times with interruption of the process gas supply, a solid compound of the fiber nodes has been achieved by an order of about 4 microns Al₂0₃. Thus, a highly porous but mechanically resilient ceramic body was obtained.

Example 4:

p0034<ul><li>a) fiber wool of mullite (Al₆Si₂0₁₃) having an average fiber diameter of 3 microns was suspended by stirring with a high-speed stirrer in a mixture of water and 20% by volume of polyethylene glycol. In order to avoid the formation of air bubbles during intensive stirring, and thus damage the fiber, the preparation of the suspension was performed in an evacuated vessel.</li></ul>

p0035The fiber suspension was poured in a double walled, tubular suction filter and subjected to a pressure filtration. In this manner, a fiber mesh was obtained from randomly-oriented fibers having tubular geometry, wherein the remaining at the fiber surfaces polyethylene glycol caused sufficient for handling cohesion. As in Example 1, the semi-finished fiber was combined in a heat-resistant wire mesh in tubular form and freed by thermal treatment from adhering polyethylene glycol.<ul><li>b) Such a semi-finished product was impregnated by the so-called sol-gel method in the manner described below and solidified by targeted heat treatment. 10 mol Tetramethyloxysilan, Si (0CH₃) ₄ (TMOS) were dissolved in 5 l of isopropanol. To this solution was added 30 mol of aluminum tri-secondary butoxide, Al (0-secC₄H₉) ₃ admixed. The resulting solution was added 1l 96% ethyl alcohol, C₂H₅0H with heating and stirring. The first occurred in the admixture of C₂H₅0H haze has disappeared slowly. It has emerged a clear Hydroxidsol. In this sol, the fiber pieces were immersed to the point of saturation. Thereafter, the main amount of the sol was sucked from the fiber body. The adhesive remaining on the fibers rest were let dry in air to give the fibers a Trockengelüberzug has formed. Thereafter, the impregnated fiber were fired in the air convection oven stepwise with each 2-hour hold time at 70, 200, 400 and 900 ° C to 1,100 ° C. After 4 hours of reaction at 1,100 ° C is an adherent coating of substantially pure mullite has formed on the fibers, whereby these were connected at the intersections firmly together. The structure of the produced by the sol-gel process mullite coating was finely crystalline and surface-rich.</li></ul>

Example 5:

p0036From matt shaped processed, cut staple fiber with the composition 62% Al₂0₃, 24% Si0₂, 14% B₂0₃ and glassy amorphous structure disc-shaped bodies were prepared. The first loose fibers of about 3 mm in length and about 12 microns in diameter, were joined by the following method firmly together so that a stable and durable structure with high porosity was.

p0037A part of the disk-shaped fibrous body was infiltrated in a CVD reactor for 6 hours at a temperature of 800 ° C with a gas composition of 8 mol% BCl₃ and 9 mol% NH₃, balance H₂, at a total pressure of 10 kPa. It has specialized in the fibers of boron nitride (BN) deposited in a layer thickness of about 2 microns. Subsequently, the deposition retort was flushed with N₂ from the process gas. Meanwhile, the temperature was raised to 1100 ° C. After reaching this temperature N₂ has been replaced with air and passed through the 2H-impregnated BN fiber discs. This oxidation treatment a Boroxidfilm has formed on the BN, which has caused a solid sintering the linked by the BN fibers.

Example 6:

p0038As an alternative to Example 5, the impregnation with BN 3h at 1100 ° C with 4 mol% and 5 mol% NH₃ BBr₃ carried out in H₂ at 5 kPa total pressure and the oxidation treatment at the same temperature has been connected.

Example 7:

p0039The same output fiber material as in Example 5 was impregnated in a further series of experiments by the sol-gel process, wherein the compound has been targeted to a first loose fibers with a fiber material in its composition to the blended material.

p0040To a solution of 0.7 mol Tetraethyloxysilon (TEOS) and 0.7 mol TMOS in 3l I C₃H₇0H were intensive stirring 4.4 mol Al (0-sec.C₄H₉) ₃ added. To this mixture was added to 2L of a solution of 0.35 mol / l B (0CH₃) ₃ in i-C₃H₇0H also with stirring and warming. the disk shaped preformed and rimmed in wire mesh fiber mat was immersed in the resulting clear sol. After complete impregnation it was removed from the immersion bath, drain on room air and finally sucked. Here a gel has formed on the fibers. The excess material was aspirated. After drying in air at ambient temperature, the impregnated fiber body in air were gradually heated to 900 ° C, with each two hour hold times at 70, 200 and 600 ° C. After 2 hours at 900 ° C was cooled. the coating material has been bonded to the surface of the fibers by this heat treatment. The fiber coating had a glassy-amorphous crystal structure, however, a highly structured morphology. The fibers were tied together tightly by the coating at the intersections.

Example 8:

p0041<ul><li>a) From silicon carbide filaments with a diameter of about 12 microns have been produced by winding a multi-ring thread eye on perforated pipes with wire mesh support fiber tubes. The fibers were stacked crosswise. It has therefore been taken that the fibers together were just so strong that during the further handling slippage could be prevented. The still slightly resilient, fiber-wound tubes were solidified by impregnation with mullite (Al₆Si₂0₁₃) by the CVD method. The method for impregnation of SiC fiber with the oxide-ceramic material based on those described in Examples 1 - 3 described procedures for Al₂0₃ deposition, wherein the deposition of the mixed oxide used by suitable admixing of silicon tetrachloride (SiCl₄) to the Al₂0₃ deposition gas phase was achieved from AlCl₃, C0₂ and H₂. With respect to the mullite was always uses slightly less than stoichiometric amounts of SiCl₄ to avoid the occurrence of free Si0₂.</li><li>b) a gas selected with the following composition for the deposition. 6.0 mol% AlCl₃; 1.8 mol% SiCl₄; 12.8 mol% C0₂; Rest H₂. The process data are consistent with from Example 1b. Subsequently, a thermal after-treatment at 1000 ° C, 3h, carried out in the forced air oven to complete the Mullitphasenbildung. It was a fine crystalline coating of mullite obtained on SiC fibers with heavily textured surface that held together the fibers laid.</li></ul>

Example 9:

p0042<ul><li>a) as Example 8a.</li><li>b) As Example 8b but with 6h deposition time at 980 ° C. Under these conditions a somewhat coarser, uniform Mullitüberzug on the SiC fibers was formed, which also resulted in a stabilized form body through the connection of the fibers.</li></ul>

Example 10:

p0043<ul><li>a) As Example 8a.</li><li>b) As example 8b, but with 5.4 mol% AlCl₃; 1.6 mol% SiCl₄; 10.5 mol% CO₂; Rest H₂; Total pressure of 100 kPa; Deposition temperature 1050 ° C and deposition time 4h. It has been accomplished on the SiC fibers, a crystalline, surface-rich layer of mullite, which led to a stable cohesion of the fiber wound body.</li></ul>

Example 11:

p0044From matt shaped processed, cut Al₂0₃ staple fiber having a fiber diameter of about 20 microns disc-shaped bodies were prepared. The first non-entangled fibers having an average length of about 6 mm were fixed by coating over the gas phase with titanium dioxide (TiO₂) of fiber crossing points to each other, whereby solid dimensionally stable and highly porous fiber body has also been made in this case. The impregnation of the fiber structure with Ti0₂ was at a temperature of 800 ° C with a reactive gas phase of the composition 10 mol% TiCl₄; 22 mol% C0₂; Residual H₂ and performed at a gas pressure of 10 kPa. The deposition time was 5h. The fibers were after deposition with a 3 - plated 5 micron thick layer of Ti0₂ that showed only weakly pronounced peaks at a radiographic fine structure determination and thus was present in practically amorphous form.

p0045Fiber mats made according to the invention can be after-treated if necessary. For example, they can be used as a catalyst carrier and are subjected to an appropriate post-treatment. The following examples relate to the post-coating with catalytically active materials for the production of catalytic converters in particular diesel exhaust gas catalysts.

Example 12:

p0046According to the examples 1-3 stabilized fiber mats vapor deposition with copper and vanadium can also be impregnated with chemical.

p0047For this acetylacetonates were (N₂ Ar and alternative) led by Cu and V in an inert gas through the fiber body, which were heated to temperatures between 300 and 600 ° C. The acetylacetonates have been applied in concentrations of 0.1 to 2 mol% in an inert gas. The formation of oxides by pyrolysis of metal acetylacetonates was promoted by addition of small amounts of water vapor (partial pressure of 10 Pa to 1 kPa).

p0048With the thus-treated fiber bodies (FIG. 6) tests were carried out in the diesel engine exhaust gas again. Here, a high catalytic efficiency of these filters has shown which has allowed for the given exhaust gas temperatures a substantial erosion of the soot particles with the adhering hydrocarbon radicals. For the high efficiency of the catalyst-coated fiber filter passes next to the catalytic acceleration of the oxidation reaction by Kupfervanadate, which have formed from the resulting from the cleavage of the acetylacetonates oxides of copper and vanadium in a subsequent reaction, the large surface area of ​​the fibrous structure is additionally increased by the impregnated Al₂0₃ and its effect as an active intermediate layer ( "wash coat") a significant role. It became apparent to extend the operating time of the filter to the non recoated filters.

Example 13:

p0049For coating a solution prepared according to Example 4 stabilized fiber mat with an oxidation catalyst which Tränkungsmethode was chosen. In a dilute alcoholic solution of europium-tri-ethoxide and cobalt nitrate (0.01 mol / l in i-C₃H₇0H) the solidified fiber bodies were dipped, drained and dried in air. They were then heated slowly in air circulating oven at 600 ° C, 2h maintained at this temperature and then heated for 0.5 h at 900 ° C. This resulted in a coating with the composition EuCo0₃, fine in shape, submicroscopic in the Al₆Si₂O₁₃ structure embedded agglomerates crystals.

p0050When emissions test an effect comparable to the under Examples 1 was - test filters described 3 and 12 scored. Again, the efficiency due to the combination of the properties of the solidified fiber composite structure and the catalyst properties.

Example 14:

p0051In an additional series of tests, the composition of the catalytic coating has been changed, at constant production method of the fiber filter according to Example 4. The mixed oxides SmCo0₃, EuCr0₃, EuMn0₃, CeCo0₃, CeCr0₃, CeMn0₃ and SmFe0₃ were impregnated into the fiber composite structure. They also have in principle been found suitable to catalyze the oxidation of soot.

p0052The solidified with BN and B₂0₃ according to Examples 5 or 6 fiber body were coated for later use as a diesel exhaust particulate filter with oxidation catalysts. As active interlayer Ti0₂ has been used. In carrying out the coating two alternative ways (Examples 15 and 16) have been taken.

Example 15:

p0053A portion of the fiber body has been initially only with the Ti0₂ interlayer, as described below, impregnated and coated thereon in a separate process the catalyst.

p0054To a solution of 2 mol / l tetraethyl titanate, Ti (0C₂H₅) ₄, in i-C₃H₇0H was (96%) in the ratio I C₃H₇0H ethanol: C₂H₅0H = 10: 1 was added and vigorously stirred. In this mixture, the fiber pieces were immersed to drain air and sucked it. After drying in air at ambient temperature, the impregnated fiber body in air were gradually heated to 900 ° C with in each case two hour hold times at 70, 200 and 600 ° C. After 2 hours at 900 ° C was cooled. It was achieved by this treatment a stable, adherent and high-surface intermediate layer of Ti0₂.

p0055The provided with the amorphous Ti0₂ intermediate layer fiber body said catalysts in Example 13 were applied using the method described therein.

Example 16:

p0056The Ti described in Example 15 (0C₂H₅) ₄ stock solution were added per 0.02 mol / l Mn (N0₃) ₂ and Co (N0₃) ₃. The subsequent procedure was the same as in Example 15 for the preparation of Ti0₂ interlayer. This a well-adhering catalytically active coating was obtained, in which the catalyst is integrated into the carrier layer. It should be next to the Ti0₂ various mixed oxide phases have formed, but which could not be identified because of the amorphous nature of the coating.

p0057Both of Example 15 and the filter coatings prepared according to Example 16 recorded adjacent to the catalytic activity with respect to the soot and HC oxidation by particular chemical stability under the conditions of the filter insert.

Example 17:

p0058As a catalyst carrier, a fiber mat prepared according to Example 7 was used. The preparation of a catalytic coating following the same principles as in Examples 15, 16, that is, it was (a) at a portion of the fiber body is first applied a separate intermediate layer and then only the actual catalyst and (b) in a second part of the intermediate layer material and the catalytic material impregnated together in one process step.<ul><li>a) The solidified fiber bodies were ethylate with a 0.1 molar solution of titanium (IV), Ti (0C₂H₅) ₄ and cerium (IV) isopropylate, Ce (i-0C₃H₇) ₄ soaked in isopropanol, the immediately previously 10 wt.% ammonikalisches ethanol has been added. The excess Ti / Ce sol was drained and the moist fiber body 1h leave to air dry. Thereafter, the fiber bodies were heat treated according to Example 15th The provided with the intermediate layer of a finely dispersed mixture of Ti0₂ and Ce0₂ fiber fittings were in a further process step with a 0.01 molar aqueous solution of copper (II) - hexanoate and Ni (II), Cu (C₅H₁₁C0₂) ₂ and Ni ( C₅H₁₁C0₂) ₂ soaked, the weight immediately before the impregnation. 1% 0.01 molar ammonia water was added. The impregnation solution with the fiber bodies was on 60 - heated to 70 ° C.</li></ul>

p0059After reaching this temperature, the fiber body of the impregnation solution were removed, drain and in an oven slowly over 4 hours, heated to 500 ° C and 2 hours left at this temperature. This gave a highly dispersed on the Ti0₂ / Ce0₂ interlayer adherent coating of Cu0 and Ni 0.

p0060In use tests on a diesel engine has been found that these fiber products have a very good effect as a particulate filter and a catalyst for the soot combustion due to the aforementioned specific properties.<ul><li>b) The second part of the solidified with Al₂0₃ / Si0₂ / B₂0₃ fiber moldings was Cu with a solution of 0.1 mol / l Ti (0C₂H₅) ₄, 0.1 mol / l Ce (i-0C₃H₇) ₄, 0.005 mol / l (C₅H₁₁C0₂) ₂ and 0.005 mol / l Ni (C₅H₁₁C0₂) ₂ soaked in i-C₃H₇0H after the solution immediately above 10 wt.% 0.01 molar ammonia water had been added. Once removed from the colloidal solution was allowed to drain and then aspirated. The freed from excess sol fiber body remained lying 12h to gel on the fibers at the room air. They were then in an air convection oven gradually heated to 800 ° C and 2-hour hold time at 70, 180 and 400 ° C. The holding time at the final temperature was 3h. The impregnated fiber bodies were furnace cooled to room temperature.</li></ul>

p0061Also this treatment resulted in a coating having the desired properties and the fiber filters, a variant with which the given 17a similar effect, as experiments have shown to exhaust filtration.

Example 18:

p0062The fiber molded article produced according to Examples 8 to 10 were as provided in the previous examples with a catalytic coating on the Mullitzwischenschichten before they were tested on the engine exhaust gas test rig for their effectiveness to particle filtration.

p0063For this purpose, the fiber bodies were in a colloidally disperse solution of 2 mol / l titanium oxide hydrate which have 0.1 mol / l MnCl₂ additionally contained, soaked, then dried and finally calcined at 500 ° C in H₂ current. There is a layer of (Ti, Mn) 0₂ mixed oxide was thereby obtained. With the thus provided fiber filter body has a high filtration and Rußabbrandwirksamkeit when used in diesel engine exhaust gas could be achieved.

Example 19:

p0064A fiber mat prepared according to Example 11 was subsequently coated with a catalyst for the soot and hydrocarbon oxidation. It has been found that could be brought because of the linking of the fibers deposited thereon Ti0₂ the catalyst directly without an intermediate layer thereon. For this purpose, an argon carrier gas stream which passed 1 mole% Molybdenum, Mo (C0) ₆, and 0.5 mol% dimanganese decacarbonyl, Mn₂ (C0) ₁₀ through the fiber structure at a temperature of 500 ° C. By half-hour was depositing a deep blue-black, adherent coating of a non-stoichiometric molybdenum, Mo0_3-x and manganese oxide formed in a highly dispersed form. When filtration test, a high efficiency in terms of particle removal and the carbon and hydrocarbon combustion showed. As a further feature of this fiber filter version a very low back pressure structure was found.