U.S. patent application number 11/152783 was filed with the patent office on 2005-12-29 for aluminum and zirconium oxynitride abrasive grains.
This patent application is currently assigned to PEM Abrasifs-Refractaires. Invention is credited to Bourlier, Florent, Peillon, Florence.
Application Number | 20050284029 11/152783 |
Document ID | / |
Family ID | 32406380 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050284029 |
Kind Code |
A1 |
Bourlier, Florent ; et
al. |
December 29, 2005 |
Aluminum and zirconium oxynitride abrasive grains
Abstract
Corundum-zirconia abrasive grains containing more than 50 wt %
of an alumina-zirconia eutectic mixture. The grains contain 0.3 to
3% nitrogen, and more than 75% of the zirconia crystals are cubic
in shape. The abrasive grains are of particular use for making
grinding wheels, abrasive fabrics and papers, polishing compounds
and sprayed abrasives.
Inventors: |
Bourlier, Florent;
(Issy-Les-Moulineaux, FR) ; Peillon, Florence;
(Pourrieres, FR) |
Correspondence
Address: |
DENNISON, SCHULTZ, DOUGHERTY & MACDONALD
1727 KING STREET
SUITE 105
ALEXANDRIA
VA
22314
US
|
Assignee: |
PEM Abrasifs-Refractaires
|
Family ID: |
32406380 |
Appl. No.: |
11/152783 |
Filed: |
June 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11152783 |
Jun 15, 2005 |
|
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PCT/FR03/03787 |
Dec 18, 2003 |
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Current U.S.
Class: |
51/307 ;
51/309 |
Current CPC
Class: |
C04B 2235/402 20130101;
C04B 2235/46 20130101; C04B 2235/762 20130101; C04B 35/581
20130101; C04B 2235/76 20130101; C04B 2235/3865 20130101; C04B
2235/668 20130101; C09K 3/1418 20130101; C09K 3/1427 20130101; C04B
2235/3217 20130101; C04B 2235/80 20130101; C04B 2235/3244 20130101;
C04B 35/653 20130101; C04B 2235/3869 20130101; C04B 2235/3886
20130101; C04B 2235/96 20130101; C04B 35/119 20130101 |
Class at
Publication: |
051/307 ;
051/309 |
International
Class: |
B24D 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2002 |
FR |
02/16498 |
Claims
What is claimed is:
1. Abrasive grains containing more than 50% of a eutectic
alumina--zirconia mixture by weight, containing more than 0.3% of
nitrogen, wherein less than 25% of the zirconia crystals are in
monoclinic form
2. Abrasive grains according to claim 1 containing from 0.3% to 3%
of nitrogen, preferably from 0.3% to 1% of nitrogen.
3. Abrasive grains according to claim 1 wherein more than 75% of
the zirconia crystals are in tetragonal or in cubic form.
4. Abrasive grains according to claim 1 wherein more than 75% of
the zirconia crystals are in cubic form.
5. Abrasive grains according to claim 1, wherein most of the
nitrogen is in zirconium nitride form.
6. Abrasive grains according to claim 1, wherein the content of
metallic aluminum is less than 0.1% by weight and the content of
free aluminum nitride AlN is less than 0.1%.
7. Abrasive grains according to claim 6, wherein the content of
metallic aluminum is less than 0.01% and the content of free
aluminum nitride AlN is less than 0.01%.
8. Abrasive grains according to claim 5, wherein more than 90% of
the nitrogen not combined in the form of zirconium nitride is
combined in the form of aluminum oxynitride.
9. Abrasive grains according to claim 1, wherein the total contents
of zirconium and aluminum in the form of oxides, nitrides and
oxynitrides expressed in the form of equivalent contents of oxides,
are between 21 and 44% for ZrO.sub.2 and between 57 and 80% for
Al.sub.2O.sub.3.
10. Abrasive grains according to claim 1, characterised in that
they have a Knoop hardness equal to or greater than 19 GPa and a
tenacity equal to or greater than 2.3 MPa.sup.1/2.
11. Abrasive grains according to claim 1, having a Knoop hardness
equal to or greater than 20 GPa and a tenacity equal to or greater
than 2.7 MPa.m.sup.1/2.
12. Process of manufacturing abrasive grains according to claim 1,
by melting in an electric arc furnace with a load composed of
alumina and baddeleyite, characterised in that a nitride material
is added to this load composed of aluminum nitride and/or one or
several aluminum oxynitrides.
13. Process according to claim 12, wherein the nitride material is
prepared by nitriding of a load composed of an alumina and aluminum
powder mixture.
14. Process according to claim 12, wherein the nitride and/or the
aluminum oxynitrides react with zirconium during melting to form
zirconium nitride.
15. Process according to claim 12, wherein the mass melted in the
electric furnace is cast and solidified quickly.
16. Process according to claim 15, in which the fast solidification
of the molten mass is obtained by pouring it on a cold support,
wherein the mass of the cold support is equal to at least twice the
mass of the molten mass, and wherein its temperature before casting
is between 50.degree. C. and 350.degree. C.
17. Process for preparation of abrasive grains according to claim
1, including the preparation of a mixture of aluminum nitride AlN
and/or oxynitride Al.sub.XO.sub.YN.sub.Z, alumina and zirconia
powders, the reactive sintering of this mixture at a temperature
between 1500.degree. C. and 1600.degree. C., and fast cooling of
the sintered grains between 1100.degree. C. and ambient
temperature.
18. Process according to claim 17, comprising a final washing of
the grains with a solution with a pH between 2 and 7.
19. Grinding wheels designed for grinding metals and metallic
alloys or for precision grinding containing abrasive grains
according to claim 1.
20. Abrasive fabrics and papers designed for polishing containing
abrasive grains according to claim 1.
21. Polishing paste containing abrasive grains according to claim
1.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to the domain of abrasive grains, and
particularly agglomerated grains intended for grinding wheels,
grains applied to fabric and paper type supports, and grains used
for spraying or contained in a polishing paste.
[0002] Description of Related Art
[0003] Alumina-zirconia based electromolten abrasives have been
known for more than forty years and in particular have been
described in several patents by the Norton company. Patent U.S.
Pat. No. 3,181,939, filed in 1962, describes alumina-zirconia type
electromolten abrasives with ZrO.sub.2 content between 10 and 60%,
and a microstructure comprising an alumina-zirconia eutectic and
zirconia and .alpha. alumina crystals. Patent U.S. Pat. No.
3,891,408 filed in 1971 relates to alumina-zirconia type
electromolten abrasives with ZrO.sub.2 content of between 35 and
50%. Patent U.S. Pat. No. 3,993,119 published in 1976 describes a
molten abrasive oxides casting machine capable of vigorously
quenching the molten mass. Patent U.S. Pat. No. 4,457,767, 1984,
protects alumina-zirconia type electromolten abrasives with a
content of yttrium oxide Y.sub.2O.sub.3 between 0.1 and 2%.
[0004] More recently, the 3M Innovative Properties Company has
deposited patent applications:
[0005] WO 02/08143 that claims an electromolten abrasive grain
characterised by a fraction of at least 20% by volume, composed of
a eutectic mixture formed between firstly ZrO.sub.2 and secondly at
least two other constituents, including Al.sub.2O.sub.3 and/or
defined compounds of the Al.sub.2O.sub.3, Y.sub.2O.sub.3 type.
[0006] WO 02/08146 that claims an electromolten abrasive grain with
eutectic composition in which eutectic is formed between firstly
ZrO.sub.2 and secondly at least two constituents including
Al.sub.2O.sub.3 and/or defined compounds of the Al.sub.2O.sub.3--
rare earth oxides type.
[0007] The common point between these patent applications is that
the abrasive grains always contain either yttrium oxide or at least
one rare earth oxide, in one manner or another.
[0008] The Inorganic Chemistry Treaty by Paul Pascal, Masson, 1962,
already described that ZrO.sub.2 had three allotropic varieties.
The monoclinical form stable at low temperature is transformed into
quadratic zirconia at about 1100.degree. C., and then into cubic
zirconia. The cubic form is metastable at ambient temperature and
it can be obtained by quenching; some elements, without any further
precision, stabilise the cubic form.
[0009] The patents mentioned above always indicate that the product
is prepared by casting the molten product followed by vigorous
quenching, a process that tends to stabilise the metastable cubic
form; however, experience shows that the efficiency of this
quenching is fairly limited, which is the reason for the interest
in patent U.S. Pat. No. 4,457,767 that divulges that yttrium oxide
stabilises the cubic phase of ZrO.sub.2. Patent application WO
02/08146 suggests that other stabilising elements exist in the
group of rare earth metals.
[0010] Furthermore, patent EP 0 509 940 issued by the applicant
describes a wide range of electromolten products for abrasive or
refractory applications, composed of one or several oxynitrides of
metallic elements in the list containing aluminum and zirconium;
but there is no example of the case that mentions aluminum and
zirconium oxynitrides nor double aluminum and zirconium
oxynitrides.
SUMMARY OF THE INVENTION
[0011] The purpose of the invention is to provide abrasive grains
to be applied onto fabric or paper supports or agglomerated in
grinding wheels, or sprayed or contained in a polishing paste, and
that have a better tenacity and machining performances than
corundum--zirconia abrasives according to prior art with an
equivalent content of zirconia.
[0012] The subject of the invention is corundum--zirconia abrasive
grains containing more than 50% of a eutectic alumina--zirconia
mixture, characterised in that they contain more than 0.3% of
nitrogen, preferably from 0.3% to 3% of nitrogen, and more
preferably from 0.3 to 1% of nitrogen, and in that less than 25% of
the zirconia crystals are in monoclinic form. According to the
invention, more than 75% of the zirconia crystals are in tetragonal
or cubic form. Preferably, more than 75% of the zirconia crystals
are in cubic form
[0013] The content of metallic aluminum is less than 0.1% and
preferably 0.01%, and the content of aluminum nitride is less than
0.1% and preferably less than 0.01%.
[0014] Another purpose of the invention is a process for
manufacturing this type of abrasive grains by melting in an
electric arc furnace with a load composed of alumina and
baddeleyite, by adding a nitride material to this load composed of
aluminum nitride and/or one or several aluminum oxynitrides.
[0015] Another purpose is a process for preparation of abrasive
grains including the preparation of a mixture of aluminum nitride
and/or oxynitride Al.sub.XO.sub.YN.sub.Z, alumina and zirconia
powders, the reactive sintering of this mixture at a temperature
between 1500.degree. C. and 1600.degree. C., and fast cooling of
the sintered grains between 1100.degree. C. and ambient
temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Within the very wide range of abrasive compositions
described in patent EP 0509940, the applicant has demonstrated that
products based on aluminum and zirconium oxynitrides have better
performances than products according to prior art of the
corundum--zirconia type or the aluminum oxynitride type such as
AlON.
[0017] Products according to the invention contain oxides, nitrides
and oxynitrides of aluminum and zirconium, and it is not always
easy to measure the content of each of these compounds. However, it
is easy to measure the elementary contents of aluminum, zirconium
and nitrogen. This is why the "equivalent content" concept is used
by arbitrarily considering the product as being a mixture of
Al.sub.2O.sub.3, ZrO.sub.2 and AlN. The equivalent content of AlN
is the content for which all the nitrogen would be in AlN form, the
equivalent content of ZrO.sub.2 is the content for which all the
zirconium would be in ZrO.sub.2 form, and the equivalent content of
Al.sub.2O.sub.3 is the content for which aluminum would be in
Al.sub.2O.sub.3 form, except aluminum corresponding to the
equivalent content of AlN. Another advantage of this concept of
equivalent content is that the product can be compared with
corundum--zirconia abrasives according to prior art.
[0018] Products according to the invention are of the
corundum--zirconia type with an equivalent content of ZrO.sub.2
between 21 and 44%, an equivalent content of Al.sub.2O.sub.3
between 57 and 80% and a nitrogen content between 0.3 and 3%, and
preferably between 0.3 and 1%. For more than 50% of their weight,
their structure consists of a eutectic mixture of .alpha. alumina
and zirconia crystals. More than 75% of the zirconia crystals are
in cubic form, the remainder being in monoclinical form. Nitrogen
is present essentially in the form of zirconium nitride, more than
90% of the remainder being in the form of aluminum oxynitride.
[0019] It has been experimentally observed that the presence of
zirconium nitride in the product is accompanied by a large increase
in the relative proportion of the cubic form in the zirconia
contained. Zirconium nitride is a perfectly stable product in
contact with the water and acids, which is not the case for
aluminum nitride, which makes it an excellent stabilising
agent.
[0020] These products may be obtained by melting in an electric arc
furnace with a load composed of alumina, zirconia, for example in
the form of baddeleyite, and a nitride compound based on aluminum
nitride and/or oxynitride. The aluminum nitride and/or oxynitride
react with the zirconia during melting to form zirconium
nitride.
[0021] The molten mass is cast and solidified quickly by any means
known to those skilled in the art to cause efficient quenching;
during these tests, the applicant used the technique described in
patent U.S. Pat. No. 3,993,119, but using fixed casting equipment
considering the size of the tests. Casting is done on a cold
support, with a mass equal to at least twice the mass of the molten
mass, and at a temperature of between 50.degree. C. and 350.degree.
C. before casting.
[0022] If a product prepared by direct nitriding according to
patent EP 0494129 issued by the applicant and containing aluminum
nitride and oxynitride is used as the nitride compound, a product
is obtained in which the content of free aluminum nitride is small,
and typically less than 0.1%. Furthermore, this content can be
reduced to less than 0.01% by slight acid etching, with final
washing of the grains by a solution with a pH between 2 and 7,
without reducing the mechanical strength of the material. The same
is true for metallic aluminum.
[0023] Abrasive grains according to the invention can also be
prepared by reactive sintering starting from a mixture of alumina,
zirconia, and aluminum nitride and/or oxynitride powders.
[0024] Sintering is done at a temperature between 1500 and
1600.degree. C., followed by fast cooling of the grains starting
from 1100.degree. C.
[0025] Exceptional mechanical properties are obtained using
abrasive grains according to the invention, and particularly a
Knoop hardness greater than or equal to 19 GPa, or even 20 GPa, and
between 19 and 21 GPa, a tenacity of at least 2.3 MPa.m.sup.1/2,
very often more than 2.7 MPa.m.sup.1/2, and performances in the
machining test equal to 70% more than is obtained with a
conventional corundum--zirconia abrasive with the same content of
zirconia.
EXAMPLES
[0026] Analysis and Test Methods
[0027] The nitrogen content was measured on 5 mg samples weighed to
the nearest 0.1 mg, by combustion in a LECO TC 436 gas analyser,
and analysis by thermal conductivity of the gas obtained. The
result indicated on each sample is the average of five
measurements.
Example 1
[0028] 2500 kg of powder Bayer alumina with a size grading of less
than 100 .mu.m was mixed with 1000 kg of powder aluminum with a
size grading of less than 1.2 mm. This mixture was placed in a
sealed furnace, vacuum degassed and then heated under a nitrogen
pressure of 1 atm.
[0029] Nitriding began at about 700.degree. C., and the nitrogen
pressure was maintained to facilitate the increase in the
temperature of the load. The exothermal reaction resulted in a
temperature of about 1750.degree. C. at the end of the
operation.
[0030] After cooling, and at the end of the operation, the mass of
porous, homogenous and mechanically unsound aluminum oxynitride
recovered was 4010 kg.
[0031] The operation was repeated three times and finally a batch
of 16 100 kg of product was obtained and was ground to a size
grading of less than 10 mm, and then sampled and analysed; the
result of the analysis gave an equivalent AlN content equal to
35.6%.
Example 2
[0032] 400 kg of a mixture composed of 30 kg of the product
obtained in example No. 1, 100 kg of baddeleyite with 95% of
ZrO.sub.2 and 270 kg of Bayer alumina, was prepared.
[0033] This load was melted in a 100 kW melting arc furnace; the
molten mass was cast on an ingot mould composed of 12 vertical cast
iron plates (0.8 m.times.0.8 m.times.0.05 m) separated by 0.025 m.
The cast mass was 390 kg; the product analysis was:
1 Equivalent AlN content: 2.3% Zr content expressed in ZrO.sub.2:
23.6% Al content expressed in Al.sub.2O.sub.3: 73.7%
[0034] An examination of the product structure demonstrated the
existence of two majority phases:
[0035] .alpha. alumina and cubic zirconia, and two minority phases:
zirconium nitride and monoclinical zirconia. The chemical analysis
also gave a free AlN content of 0.07% in the product.
[0036] The hardness and tenacity measurements are shown in Table 1,
which also shows the results for similar product:
2 TABLE 1 Knoop Vickers hardness hardness Tenacity Product in 19.9
GPa 18.9 GPa 2.8 MPa .multidot. m.sup.1/2 example 2 Corundum - 18.7
GPa 17.9 GPa 2.1 MPa .multidot. m.sup.1/2 Zirconia with 25%
ZrO.sub.2 according to prior art White corundum 20.3 GPa 20 GPa 2.0
MPa .multidot. m.sup.1/2
[0037] It can be seen that the grains according to the invention
are slightly harder and with higher tenacity than grains of
corundum--zirconium with the same zirconia content.
Example 3
[0038] A batch of F80 abrasive grains (according to the FEPA
standard) was prepared starting from the product prepared in
Example 2 and tested in grinding according to the following
procedure:
[0039] A single layer of grains is fixed on the side part of a 160
mm diameter metallic drum using an acrylic thermosetting resin. The
grinding test consists of attacking an 18-8 stainless steel bar
with section 12 mm.times.12 mm pushed perpendicular with a force of
85 Newtons, in contact with the side face of the drum driven at
6000 rpm. The duration of the operation is three times one
minute.
[0040] The mass of the stainless steel bar is tested after one
minute, two minutes and three minutes to evaluate the weight loss.
The steel mass removed expressed in grams per minute are shown in
Table 2, which also shows the results of this test obtained with
other products using F80 grains.
3 TABLE 2 Mass removed minute by minute Product Supplier 1 2 3
Corundum The applicant 11.0 7.5 6.8 zirconia with 25% ZrO.sub.2
Corundum Competitive 10.8 7.9 7.7 zirconia with product 25%
ZrO.sub.2 Product in The applicant 19.6 16.5 14.9 example 2
[0041] It can be seen that the grains according to the invention
have significantly better abrasive performances than
corundum--zirconia grains with the same zirconia content.
* * * * *