GB2237014A - Producing articles from filtering ceramic foam - Google Patents
Producing articles from filtering ceramic foam Download PDFInfo
- Publication number
- GB2237014A GB2237014A GB8923263A GB8923263A GB2237014A GB 2237014 A GB2237014 A GB 2237014A GB 8923263 A GB8923263 A GB 8923263A GB 8923263 A GB8923263 A GB 8923263A GB 2237014 A GB2237014 A GB 2237014A
- Authority
- GB
- United Kingdom
- Prior art keywords
- foam
- ceramic
- filters
- temperature
- alumina
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/06—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances
- C04B38/0615—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances the burned-out substance being a monolitic element having approximately the same dimensions as the final article, e.g. a porous polyurethane sheet or a prepreg obtained by bonding together resin particles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/14—Other self-supporting filtering material ; Other filtering material
- B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
- B01D39/2068—Other inorganic materials, e.g. ceramics
- B01D39/2093—Ceramic foam
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
- C04B2111/00793—Uses not provided for elsewhere in C04B2111/00 as filters or diaphragms
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
- C04B2111/0081—Uses not provided for elsewhere in C04B2111/00 as catalysts or catalyst carriers
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Filtering Materials (AREA)
Abstract
Ceramic foam articles useful as filters or catalyst carriers are produced by impregnating polyurethane foam with an alumina-containing ceramic slip containing an aluminophosphate binder, the latter incorporating 0.2 to 5% of a water-soluble compound of potassium. The impregnated product is then dried and roasted.
Description
p d' i I- PROCESS FOR PRODUCING ARTICLES FROM FILTERING CERAMIC FOAM The
present invention relates to the production of ceramics and, more particularly, to processes for making articles from a highly permeable refractory ceramic foam 5 having-a thridimensional reticulated structure.
The process according to the present invention can be useful in various fields of art, including the production of heat-resistant foam filters for refining of ferrous and non-ferrous metals, catalyst carriers, filters for purifi- cation of air and lining materials.
In the practical metallurgy for the removal of nonmetal inclusions widely employed are ceramic-foam filters distinguished by their high efficiency, good economic parameters and convenience in operation.
Known in the art are processes for the production of a ceramic foam with a three-dimensional reticulated structure, wherein a blank of an organic flexible foam of a predetermined size is preliminarily compressed and immersed into a suspension of a refractory material, wherein it res- tores its form by absorbing a certain amount of ceramic particles The excessive amount of the ceramic slip is re moved by compression. Then the blank is dried and calcined, When requiredg the blank isrepeatedly impregnated with the suspension, again dried and.calainede These processes have the following disadvantages: a low mechanical strength of the resulting articles, a comp licated double impregnation procedure, increased power con sumption.
1 Also known in the art is a process, wherein ceramic- foam filters are obtained by impregnation of an organic - 2 foam; the ceramic suspension incorporates 20 to 75% of an inert filler (zircon, alumina and-the like), as well as 20 to 75% of a binding component lowering the calcination temperature. The binding agents can be exemplified in this case by calcium.. aluminate, orthophosphoric acid or liquid glass.
However. the articles produced by this process have an an insufficient mechanical strength. heat-resistance and a chemical resistance to a corroding effect of molten me- talz.
Known in the art are processes for the production of ceramic-foam filters with a satisfactory mechanical strength by way of a secondary impregnation of roasted articles with suspensions incorporating sols of oxides of oxides of aluminium, zirconium or hydroxides thereof. However. such process is rather complicated and expensive and does not result in an increased heatresistance of filters.
Known in the art are processes for the production of a filtering ceramic foam based on alumina with a binder of alum-Inophosphates by way of:impregnating a polyurethane foam therewith. followed by drying and roasting, wherein the slip composition incorporates ceramic fibres for the purpose of improving the mechanical strength, However. these processes, while slightly reducing the permeability of the ceramic foam and making the procedure more complicated. do not enable any essential improvement of the heat-resistance and chemical resistance of the re- sulting ceramic articles.
-11 Known in the art is a process for the production of ceramic-foam filters comprising preparation of an aqueous solution of athixotropic slip of a particular viscosityg impregnation of an organic foam therewith, the removal of the excessive suspension by compression of the saturated foam by 50-90%. followed by drying and roasting at 6, temperature ranging from 1,100 to 1,400OCe The advisable composition incorporates: as the -base alumina and aluminophosphates, as additives - argillaceous minerals and C 2 0 3 In this process use is made of relatively economically efficient raw materials such as alumina and phosphates making it possible to obtain an inexpensive ceramic-foam material therefrom at low roasting temperatures which material is suitable for filtration of non-ferrous metals.
However, this process has rather serious disadvantages residing in that the resulting articles have an insufficient mechanical strength and low heat-resistance, whereby their exploitation characteristics are substantially impaired.
Due to the fact that sharp temperature drops result in deterioration of filtersp there is excluded the possibilit,r of using them without heating upon casting of both ferrous and non-ferrous metals, thus complicating the production process and making it more expensive, forcing to resort to different formulations and procedures for the production of filters for different applications thereof.
The main reason lowering the quality of a corundum ceramic foam with a binder of aluminophosphates resides in that the latter during the roasting at a temperature above 1 1,100-1,2000C substantially fully recrystallize into the modification of cristobalite which produces a detrimental effect on the mechanical strength and especially heat-resistance of the roasted material. Additives of argillace- ous materials or colloidal silica slightly improve the phase composition of a ceramic foam, but do not radically solve the problem of quality improvement, since the share of the heat-resistant tridymite modification retained with their aid is not high and above 1,200-1,250C it is trans- formed into the cristobalite modification.
Another dsadvantage of the prior art compositions incorporating corundum and aluminophosphates is a contradiction residing in that foam filters roasted at a temperature of less than 1,2500C have minimal satisfactory mecha- nical strength and heat-resistance, but insufficient resistance in metals at a temperature above 1,OOOOC, whereas after roasting at a temperature of 1,300'C and over a satisfactory chemical resistance, but insufficient mechanical strength characteristics and especially heat-resistance which is explained by the above-given data on the phase composition of such ceramics.
It is an object of the present invention to overcome the above-mentioned disadvantages.
The present invention is directed to the provision of a process for the manufacture of articles from a filtering ceramic foam with a biAder from aluminophosphates which would have a phase composition ensuring an increased mecha nical strength and a n improved heat-resistance.
This object is accomplished by that in a process for the production of articles from a filtering ceramic foam comprising impregnation of a polyurethane foam with an alumina-containing dross with an aluminophosphate binders drying androasting of the prefabricated product,, in accordance with the present invention, depending on the content of phosphates in the dross. 0.2 to 5% of water-soluble compounds containing a potassium ion dissociating in an aqueous medium are introduced thereinto and the roasting is effected with an isothermal residence for at least 5 minutes to 1.400'C.
The process according to the present invention makes it possible to improve the mechanical strength and resis tance to thermal shocks of the ceramic foam, while retain ing its high chemical resistance.
The present invention resides in that the binding aluminophosphates are intentionally crystallized by means of a mineralizator into modifications of tridymite posses sing essential advantages over the cristobalite form as regards its mechanical strength and heat-resistance.
It is known that upon roasting of aluminophosphate compositions with a high content of alumina mainly synthe sized are aluminium orthophosphates-in modifications of cristobalite, tridymite, berlinite and in an amorphous state, At a roasting temperature of, depending on the cera- mic composition. above 1.100-1,2000C all the above-mentioned forms in known compositions substantially fully pass into phosphooristobalite having the lowest mechanical strength and heat resistance, It has been found in the course of experiments that if a water-soluble potassium salt is introduced into aluminophosphate systems dispersed in an aqueous medium, the TU- ion of potassium after dissociation provides a strong neralizing effect on the phase composition of the material enabling the production of a corundum ceramic on an.aluminophosphate binder in the form of tridymite at a substantially total absence of the cristobalite modifications. It is especially important that the resulting optimal phase composition is retained up to a temperatur of 1,400'C thus making it possible to attain during roasting at such temperatures a maximum chemical resistance of filters without losing their heat-resistance and mechanical strength as it is the ca se in roasting of known compositions at a tempera- ture above l200-1q2500C.
For a better understanding of the present invention, some specific examples illustrating its particular embodiments are given hereinbelow by way of illustration.
Example 1
A ceramic slip is prepared which consists of 47% of alumina. 13% of 0r2 0 3' 1.5% of bentonite. 2.5% of china clay and 36% of an aluminophosphate binder of a 50% concen tration. The slip is divided into two portions and into one of them 1% of potassium chloride is Introduced. The thus.
obtained slips are used for Impregnation of blanks of an open-pore polyurethane foam with the size of 200x200x50 mm which are then dried and roasted at the temperature of 1,35000 at the heating rate of 5000/h and with the resid.
ence time-of 2 hours at the temperature of 2501% for 1 - 7 20 minutes at 8500C and for 3 hours at the temperature of 1,300'C. The properties of the thus-obtained samples are shown in Table 1 hereinbelow.
Table 1
Properties Characteristics of samples made from compositions with potassiwithout addium ion addi- tive tive Porosity, % 88 88 Ultimate compression strength, MPA 1.9 0.9 Heat-resistance after broken after thermal change: the 1-st - 800OC-air over 5 cycle The ready made ceramic-foam filters were tested for casting of an aluminium alloy incorporating 6% of magnesium without a preliminary heating of the ceramics and upon the supply of the metal from below. The filters produced by the novel process withstood the test successfully, whereas those produced without the addition of potassium salts were broken Example 2
Blanks of an elastic polyurethane foam with the same diameter of pores aftd with the size of 100x100x23 mm are impregnated with a S.lip of the following composition:
alumina - 69.80115. aluminochromophosphate binder of a 40% concentration 30%, potash (X2C03 0.21a; a simular com position but without potash is also used for impregnation.
The prefabricate is dried and roasted at the temperature of 1.400'C at the heating rate of 150'C/h and with the residence time as follows: within the range of from 250 to 300'C - 2 hours. at 850-900C - 45 minutes. at 1.400'C 5- - 5 minutes. The ultimate compression strength for the samples with the addition of potash was 1.6 to 2.3 MPa, that for the samples without potash was within the range of from 0.7 to 1.1 MPa.
Through the resulting ceramic-foam filters. without any preliminary heating thereof. 50 kg of iron were passed at the temperature of 1.380'C and refractory steel at the temperature of 1,500'C. The articles with the additive of potash have shown good results as regards their resistance and filtration. whereas the samples without potash were broken.
Example 3
A ceramic slip is prepared which has the following composition: alumina 58%. bentonite - 1%. chine clay - 3%. aluminoborophosphate binder - 38%. the latter has the concentration of 45%. Into the half amount of the mixture 5% of potassium oxalate are introduced. Prom the resulting compositions two-layer ceramic-foam filters have been made with the size of 400x200x500 mm. The number of pores per mm of the length in the first layer is 16. on the second - 28. The filters are roasted at the temperature of 1P3001c with the retidence time: at 250-300OG--- 5 hours. at 850 90000 - 2 hours, at 1.3000 - 4 hours.
The ultimate compression strength for the samples with the addition of the salt of potassium is 1.4 to 240 MPa.
that for the samples without the additive - 0.7-1.1 MPa, The porosity of both &oups of articles is 87%. A comparative analysis of heat-resistance is effected in the following manner, The ceramic-foam filters heated to the tem- peratureof 3000C are placed into a casting device, where- after an aluminium alloy at the temperature of 750'C is passed therethroughe The articles produced by the process according to the present invention have withstood the test. whereas those produced from the known composition juve been broken at the bonding plane.
It should be noted that the process according to the present invention is also applicable to the cases where in addition to alumina the compositions incorporate other ref- ractory materials such as zircon, mullite, zirconium dio- xide. titanium dioxide. cordierite and the like, and where the article.%_-after roasting incorporate aluminium ortho phosphate. These cases. for reasons of similarity, are not described in the present specification.
The above-given examples quite clearly illustrate the advantages of the novel proceis in increasing the mechani cal strength and heat-resistance of ceramic-foam articles.
It should be also noted that the roasting of ceramic fpam at a temperature within the range of from 19300 to 19400'G increases the chemical resistance of articles which after the heat- treatment at a temperature of from 1.200 to 1.250'C is substantially smaller. thus limiting the range of appli. cations of the resulting filters,- - 10 The process according to the present invention makes it possible to produce, from inexpensive raw materials and without complication of the procedure, ceramic-foam filters for all-Purpose applications suitable for filtr- ation of large quantities of non-ferrous metals and special solders, as well as for the production of filtering aids in casting of alloys into moulds, including ferrous metals, at a melt temperature of up to 1,500C.
A great advantage of the present invention resides in an increased heat-resistance of the ceramic foam, which in some cases makes it possible to carry out the refining process without any preliminary heating of the filters. An especially noticeable gain in quality is attained in the manufacture of multi-layer ceramic-foam filters with different pore size along the height of the article.
- Therefore, the use of the process according to the present invention makes it possible to use the same procedure for ceramic-foam filters of various applications, thus essentially lowering the production costs and impro- ving its efficiency.
c 1 %
Claims (2)
1. A process for producing articles from a filtering ceramic foam comprising impregnation of a polyurethane foam with an alumina-containing slip based on an aluminaphosphate binder and, depending on the content of phosphates in the slip. the latter incorporates 0.2 to 5% of watersoluble compounds containing potassium ion dissociating in an aqueous medium, drying and roasting of the prefabricate which is effected with isothermal residence for at least 5 minutes at a temperature of up to 19400'C.
2. A process according to the foregoing Claim 1,, substantially as described in the Specification and Examples hereinbefore.
Published 1991 atIbe Patent Office.State House. 66/71 High Holhorn. London WClR47P. Further copies may be obtained froyn Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8923263A GB2237014A (en) | 1989-10-16 | 1989-10-16 | Producing articles from filtering ceramic foam |
| DE19893934496 DE3934496A1 (en) | 1989-10-16 | 1989-10-16 | METHOD FOR PRODUCING FILTER FOAM CERAMIC PRODUCTS |
| HU538289A HUT58262A (en) | 1989-10-16 | 1989-10-20 | Process for producing foam-ceramic filters |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8923263A GB2237014A (en) | 1989-10-16 | 1989-10-16 | Producing articles from filtering ceramic foam |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8923263D0 GB8923263D0 (en) | 1989-12-06 |
| GB2237014A true GB2237014A (en) | 1991-04-24 |
Family
ID=10664649
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8923263A Withdrawn GB2237014A (en) | 1989-10-16 | 1989-10-16 | Producing articles from filtering ceramic foam |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE3934496A1 (en) |
| GB (1) | GB2237014A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2260538A (en) * | 1991-10-15 | 1993-04-21 | Peter Gant | Porous ceramics |
| US5998317A (en) * | 1996-11-21 | 1999-12-07 | Basf Aktiengesellschaft | Open-celled porous sintered products and their production |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5976454A (en) * | 1996-04-01 | 1999-11-02 | Basf Aktiengesellschaft | Process for producing open-celled, inorganic sintered foam products |
| DE19619986A1 (en) | 1996-05-17 | 1997-11-20 | Basf Ag | Process for stabilizing sintered foam and for producing open-cell sintered foam parts |
| DE19648329C2 (en) * | 1996-11-22 | 1998-10-22 | Herbert Wittekind | Process for the production of a ceramic mixing vessel and mixing vessel |
| GB0115204D0 (en) * | 2001-06-21 | 2001-08-15 | Zellwerk Gmbh | Ceramic materials, method for their production and use thereof |
-
1989
- 1989-10-16 GB GB8923263A patent/GB2237014A/en not_active Withdrawn
- 1989-10-16 DE DE19893934496 patent/DE3934496A1/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2260538A (en) * | 1991-10-15 | 1993-04-21 | Peter Gant | Porous ceramics |
| GB2260538B (en) * | 1991-10-15 | 1995-08-16 | Peter Gant | Ceramic block for liquid retention |
| US5998317A (en) * | 1996-11-21 | 1999-12-07 | Basf Aktiengesellschaft | Open-celled porous sintered products and their production |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8923263D0 (en) | 1989-12-06 |
| DE3934496A1 (en) | 1991-04-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |