GB2064370A - Coating of particles - Google Patents
Coating of particles Download PDFInfo
- Publication number
- GB2064370A GB2064370A GB8035481A GB8035481A GB2064370A GB 2064370 A GB2064370 A GB 2064370A GB 8035481 A GB8035481 A GB 8035481A GB 8035481 A GB8035481 A GB 8035481A GB 2064370 A GB2064370 A GB 2064370A
- Authority
- GB
- United Kingdom
- Prior art keywords
- particles
- metallic
- coating
- ceramic material
- coat
- 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.)
- Granted
Links
- 238000000576 coating method Methods 0.000 title claims abstract description 32
- 239000002245 particle Substances 0.000 title claims abstract description 32
- 239000011248 coating agent Substances 0.000 title claims abstract description 29
- 239000013528 metallic particle Substances 0.000 claims abstract description 21
- 239000000843 powder Substances 0.000 claims abstract description 19
- 239000000919 ceramic Substances 0.000 claims abstract description 11
- 239000000725 suspension Substances 0.000 claims abstract description 6
- 238000010304 firing Methods 0.000 claims abstract description 4
- 238000000034 method Methods 0.000 claims description 18
- 229910010293 ceramic material Inorganic materials 0.000 claims description 16
- 229910000519 Ferrosilicon Inorganic materials 0.000 claims description 9
- 229910000616 Ferromanganese Inorganic materials 0.000 claims description 4
- DALUDRGQOYMVLD-UHFFFAOYSA-N iron manganese Chemical compound [Mn].[Fe] DALUDRGQOYMVLD-UHFFFAOYSA-N 0.000 claims description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 239000011651 chromium Substances 0.000 claims description 2
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 abstract description 4
- 229910021502 aluminium hydroxide Inorganic materials 0.000 abstract description 4
- 229910001593 boehmite Inorganic materials 0.000 abstract description 4
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 abstract description 4
- 238000001035 drying Methods 0.000 abstract description 2
- 239000002054 inoculum Substances 0.000 abstract description 2
- 238000005524 ceramic coating Methods 0.000 abstract 1
- 229910001679 gibbsite Inorganic materials 0.000 abstract 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- 239000000155 melt Substances 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000005054 agglomeration Methods 0.000 description 3
- 230000002776 aggregation Effects 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 3
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000013067 intermediate product Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 239000011856 silicon-based particle Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- MXRIRQGCELJRSN-UHFFFAOYSA-N O.O.O.[Al] Chemical compound O.O.O.[Al] MXRIRQGCELJRSN-UHFFFAOYSA-N 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 239000000404 calcium aluminium silicate Substances 0.000 description 1
- 235000012215 calcium aluminium silicate Nutrition 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 description 1
- 239000007888 film coating Substances 0.000 description 1
- 238000009501 film coating Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000013341 scale-up Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000009974 thixotropic effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910052845 zircon Inorganic materials 0.000 description 1
- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0006—Adding metallic additives
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/08—Manufacture of cast-iron
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Paints Or Removers (AREA)
Abstract
The invention relates to the coating of particles for use, for example, as inoculants in the metallurgical field. A fluidised bed of metallic-particles (e.g. Fe/Si, Fe/Mn of size range 50 mu m to 3000 mu m or higher) is contacted with a wash-coat comprising a suspension of a non-dispersible ceramic powder in a sol (e.g. a suspension of Al(OH)3 powder in a boehmite sol). Subsequent controlled drying and firing produces a ceramic coating on the particles which has good adhesion and thermal stability and whose thickness and density can readily be controlled.
Description
SPECIFICATION
Coating of particles
This invention relates to a method of coating metallic-particles with a ceramic material.
There is a requirement in the metallurgical field for coated metallic-particles in sizes in the range, for example, from 50 ,um to 600 ym. Such particles are required, for example, as inoculants for addition to a melt where the coating protects the particles from a too rapid dissolution into the melt. The coating must therefore be of sufficient coherence, density and thermal stability to inhibit or delay dissolution into the melt. We have now devised a method of coating metallic-particles which give a product which meets these criteria and which may also be suitable for other applications where such a coating is required.
The present invention provides a method of coating metallic-particles with a ceramic material which comprises generating a fluidised bed of the metallic-particles; contacting the metallicparticles in the bed with a wash-coat comprising a suspension of a non-dispersible ceramic powder in a sol of colloidal-particles convertible to the ceramic material thereby to coat the metallicparticles with the ceramic-particles and the colloidal-particles; and subsequently firing to produce a coating of the ceramic material.
We have found that this method enables coatings of controlled density, thickness and adhesion to be produced in an operation which has potential for scale-up. Moreover, the method may enable coated particles to be produced in batches with insignificant agglomeration of the particles and produces coatings which are resistant to thermal shock.
We attribute the success of our method to the use of the above wash-coat in combination with the use of a fluidised bed technique. Thus, if a sol lacking the non-dispersible powder were used, the large volume change on drying and firing would give rise to a poorly adherent and mechanically weak coating. The colloidal-particles in the sol interact with non-dispersible powder to produce a coating of controlled integrity in a way which would be impossible if, say, a pure solution were used together with the non-dispersible powder.
The use of a fluidised bed technique, in addition to providing operational advantages, inhibits agglomeration of particles and enables coatings of even thickness to be applied. This is because the wash-coat dries almost instantaneously when it touches the particles and because static interparticle contact is minimised in a fluidised bed.
The method of the invention may be applied to any metallic-particles on which it is desired to provide a coating. The metal may, for example, be a metal suitable for use as a melt additive such as ferrosilicon, ferromanganese and chromium. The particle size may be within a wide range, for example, from 50 ym to 5 mm provided, of course, that a fluidised bed of the metallic particles can be generated. We are, however, most interested in the size range from 50 Mm to 600 Mm since this represents a preferred size range for certain melt additive applications.
The ceramic material is most preferably a ceramic oxide such as- alumina, silica, titania, zirconia, ceria or chromia or may be a mixture of ceramic oxides. In such cases the wash-coat used comprises a suspension of non-dispersible ceramic oxide powder in a sol of colloidal-particles convertible to the ceramic oxide. The ceramic material may also be a compound oxide such as zircon or may be a mixture of a ceramic oxide with another ceramic material. In an example of the latter case, the wash coat used may comprise a suspension of a non-dispersible ceramic material powder, e.g. a cement such as calcium aluminium silicate, in a sol of colloidal-particles convertible to a ceramic oxide such as alumina. Suitable powders in the wash coats are commercially available ceramic oxide powders, specific examples of which are given hereinafter.The particle size of the powder is one of the factors controlling the thickness of the coating in that a coarser powder produces a thicker, less dense coating than a finer powder. If it is desired to increase the packing density of the coating, the powder in the wash-coat may be constituted by particles having two or more different particle sizes, for example 5 lm and 0.5 m.
Examples of sols which may be used are a boehmite sol as described in U.K. Patent
Specification No. 1,174,648, an alumina sol as described in West German OLS No. 2 647 701, a ceria sol as described in International Patent
Application Publication No. WO/79/00248, a titania sol as described in U.K. Patent
Specification No. 1,412,937 and a silica sol believed to be made by hydrolysis of sodium silicate and sold commercially by Monsanto under the trade name of 'Syton'.
We generally prefer that the wash-coat contains a high proportion of powder since such wash-coats exhibit thixotropic as opposed to dilatant properties and are therefore more suitable for coating purposes. By "high" we mean greater than 80% by weight of the total ceramic material content of the wash-coat, i.e. the weight of the non-dispersible powder plus the weight of the colloidal particles. It is possible, however, to use wash-coats having a lower proportion of powder though we have generally found that the more dilute wash-coats are less stable with regard to their settling properties.
The metallic-particles may be contacted with the wash-coat by spraying the wash-coat into a fluidised bed of the metallic-particles, e.g. in a commercially available fluidised bed coating apparatus. An example of such a coating apparatus is manufactured by Aeromatic AG of
Switzerland and, using a laboratory scale version of such an apparatus, we have been able to coat batches of ferro-silicon and ferro-manganese in the batch range from T to 5 Kg. When coating finer particles, we prefer to spray downwardly into the fluidised bed. However, when heavy, coarse particles are to be sprayed a strong fluidising air flow is required and we prefer to spray upwardly into the bed.
The invention will now be particularly described, by way of example only, as follows.
EXAMPLE 1
Preparation of wash-coat
A water-dispersible boehmite (39 g) prepared as described in U.K. Patent Specification No.
1,174,648 was added slowly to water (1 I) with stirring and stirred for at least a further 30 minutes to give a boehmite sol. Commercially available non-dispersible aluminium hydroxide (Martifin, ex
Croxton 9 Garry Ltd; 390 g, particle size 80% < 0.5 ssm) was added slowly to the sol with stirring and the pH adjusted to that before addition of the non-dispersible aluminium hydroxide by addition of nitric acid (7 M). The resulting wash coat was stirred for a further 1 hour and allowed to stand for 24 hours at room temperature. The pH was again adjusted, if necessary, to that before addition of the non-dispersible aluminium hydroxide by addition of nitric acid (7 M). The final pH was 3.5.
Coating of particles
A fluidised bed film coating apparatus supplied by Aeromatic AG of Switzerland was loaded with ferro-silicon (2 Kg; particle size > 500 jam).
Heated air was passed up through the ferro-silicon to generate a fluidised bed thereof. The wash-coat prepared as above was sprayed upwardly into the fluidised bed so that the fluidised ferro-silicon particles were coated with a thin spray of the wash-coat which was dried almost instantaneously. Ideally, the rate of coating should be such that there is always insufficient liquid present to cause the ferro-silicon particles to agglomerate. The intermediate coated product was studied and found to have a thick coating (50 jam) which had adhered well and had only slight crazing.
The above product was then fired at 10000C for 1 hour to give the final coated particles. The resulting coating was found to have very good adhesion with some cracks.
EXAMPLE 2
The procedure of Example 1 was repeated but using ferro-manganese (particle size 150 ssm) instead of ferro-silicon. The intermediate product was found to be somewhat similar in respect of the coating to that obtained from the ferro-silicon with the exception that some particle agglomeration was exhibited. The coating in the final product was similar to that of the intermediate product; there was good adhesion with some crazing.
Other examples of non-dispersible commercially available oxides which may be used in the practice of our invention are: Kestel '600' amorphous silica, Linde B alumina, calcined RP ceria, though this list should not in any way be considered exhaustive.
Claims (8)
1. A method of coating metallic-particles with a ceramic material which comprises generating a fluidised bed of metallic-particles; contacting the metallic-particles in the bed with a wash-coat comprising a suspension of a non-dispersible ceramic powder in a sol of colloidal-particles convertible to the ceramic material thereby to coat the metallic-particles with the ceramic-particles and the colloidal-particles; and subsequently firing to produce a coating of the ceramic material.
2. A method according to claim 1 wherein the metallic-particles are of ferrosilicon, ferromanganese or chromium.
3. A method according to either of the preceding claims wherein the metallic-particles have a particle-size within the range of 50 jam to
5 mm.
4. A method according to claim 3 wherein the
metallic-particles have a particle size within the
range of 50 jam to 600 jam.
5. A method according to any of the preceding
claims wherein the ceramic material is a ceramic oxide.
6. A method according to any of the preceding
claims wherein the wash-coat contains greater than 80% by weight of the non-dispersible powder
based on the total ceramic material content thereof.
7. A method of coating metallic-particles with a
ceramic material substantially as described herein
with reference to either of the examples.
8. Metallic-particles coated with a ceramic
material by a method according to any of the
preceding claims.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8035481A GB2064370B (en) | 1979-12-05 | 1980-11-05 | Coating of particles |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7942058 | 1979-12-05 | ||
| GB8035481A GB2064370B (en) | 1979-12-05 | 1980-11-05 | Coating of particles |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2064370A true GB2064370A (en) | 1981-06-17 |
| GB2064370B GB2064370B (en) | 1983-09-01 |
Family
ID=26273800
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8035481A Expired GB2064370B (en) | 1979-12-05 | 1980-11-05 | Coating of particles |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2064370B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6773521B2 (en) * | 1996-03-15 | 2004-08-10 | Kemp Development Corporation | Apparatus and process for treating a particulate material within a rotating retort |
| WO2014147342A1 (en) * | 2013-03-19 | 2014-09-25 | Ferropem | Inoculant with surface particles |
-
1980
- 1980-11-05 GB GB8035481A patent/GB2064370B/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6773521B2 (en) * | 1996-03-15 | 2004-08-10 | Kemp Development Corporation | Apparatus and process for treating a particulate material within a rotating retort |
| WO2014147342A1 (en) * | 2013-03-19 | 2014-09-25 | Ferropem | Inoculant with surface particles |
| FR3003577A1 (en) * | 2013-03-19 | 2014-09-26 | Ferropem | INOCULANT WITH SURFACE PARTICLES |
| US20160047008A1 (en) * | 2013-03-19 | 2016-02-18 | Ferropem | Inoculant with surface particles |
| US10351920B2 (en) * | 2013-03-19 | 2019-07-16 | Perropem | Inoculant with surface particles |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2064370B (en) | 1983-09-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 746 | Register noted 'licences of right' (sect. 46/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |