Abrasive particles, abrasive articles, and methods of making...

Details Abrasive particles, abrasive articles, and methods of making... Abrasive particles, abrasive articles, and methods of making...

2003-04-17

2004-10-12

Marcheschi, Michael (Department: 1755)

Abrasive tool making process, material, or composition

With inorganic material

C051S309000, C051S295000, C051S298000, C051S293000, C451S028000

Reexamination Certificate

active

06802878

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to abrasive particles and methods of making the same. The abrasive particles can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
BACKGROUND
In the early 1980's a new and substantially improved type of alumina abrasive particles, commonly referred to as “sol gel” or “sol gel-derived” abrasive particles, was commercialized. This new type of alpha alumina abrasive particle had a microstructure made up of very fine alpha alumina crystallites. The grinding performance of the new abrasive particle on metal, as measured, for example, by life of abrasive products made with the particles was dramatically longer than such products made from conventional, fused alumina abrasive particles.
In general, sol gel abrasive particles are typically made by preparing a dispersion or sol comprising water, alumina monohydrate (boehmite), and optionally peptizing agent (e.g., an acid such as nitric acid), gelling the dispersion, drying the gelled dispersion, crushing the dried dispersion into particles, calcining the particles to remove volatiles, and sintering the calcined particles at a temperature below the melting point of alumina Frequently, the dispersion also includes one or more oxide modifiers (e.g., CeO
2
, Cr
2
O
3
, CoO, Dy
2
O
3
, Er
2
O
3
, Eu
2
O
3
, Fe
2
O
3
, Gd
2
O
3
, HfO
2
, La
2
O
3
, Li
2
O, MgO, MnO, Na
2
O, Nd
2
O
3
, NiO, Pr
2
O
3
, Sm
2
O
3
, SiO
2
, SnO
2
, TiO
2
, Y
2
O
3
, Yb
2
O
3
, ZnO, and ZrO
2
), nucleating agents (e.g., &agr;-Al
2
O
3
, &agr;-Cr
2
O
3
, and &agr;-Fe
2
O
3
) and/or precursors thereof. Such additions are typically made to alter or otherwise modify the physical properties and/or microstructure of the sintered abrasive particles. In addition, or alternatively, such oxide modifiers, nucleating agents, and/or precursors thereof may be impregnated into the dried or calcined material (typically calcined particles).
Certain preferred alpha alumina-based abrasive particles are highly dense (i.e., greater than 95% of theoretical) and have a fine (e.g., submicrometer), uniform alpha alumina microstructure. Further, some preferred alpha alumina-based abrasive particles include oxide modifiers, as discussed above, which may, in some cases also include submicrometer oxides other than alpha alumina, wherein the latter may or may not be submicrometer. The grain size of the alpha alumina and other oxides, the oxide phases present in the abrasive particles, as well as the physical properties (e.g., density, hardness, and toughness) or characteristics may depend, for example, on the particular composition and/or process (including sintering time and temperature) used to make the abrasive particles. For example, longer sintering times and higher temperatures tend to provide higher density abrasive particles. However, longer sintering times and higher temperatures also tend to undesirably increase grain growth.
Sol-gel-derived alpha alumina-based sintered abrasive particles have been used in a wide variety of abrasive products (e.g., bonded abrasives, coated abrasives, and abrasive brushes) and abrading applications, including both low and high pressure grinding applications.
Even though there are a variety of abrasive particles known, including a number of sol-gel-derived abrasive particles, the abrasive industry continues to desire additional abrasive particles which may offer a performance advantage(s) in one or more applications.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a sintered alpha alumina-based abrasive particle comprising alpha alumina (in some embodiments, 55 to 97, or even 55 to 93 percent by weight), and, by weight, Gd
2
O
3
in a range from 1 to 15 percent (in some embodiments, 2 to 8 percent), and ZnO in a range from 0.2 to 8 percent (in some embodiments, 1 to 5 percent), based on the total metal oxide content of the abrasive particle, and a Gd
2
O
3
to ZnO molar ratio in a range from 2:1 to 1:5 (in some embodiments, in a range from 1:2 to 1:4, or even 1:2 to 1:3), wherein less than 0.05 (in some embodiments, less than 0.025, or even less than 0.01) volume percent of the alpha alumina present in the sintered alpha alumina-based abrasive particle was nucleated with a nucleating agent (i.e., material having the same or approximately the same crystalline structure as alpha alumina, or otherwise behaving as alpha alumina) itself (e.g., alpha alumina seeds, alpha Fe
2
O
3
seeds, or alpha Cr
2
O
3
seeds) or a precursor thereof; other nucleating agents may include Ti
2
O
3
(having a trigonal crystal structure), MnO
2
(having a rhombic crystal structure), Li
2
O (having a cubic crystal structure), and titanates (e.g., magnesium titanate and nickel titanate).
In another aspect, the present invention provides a method for making sintered alpha alumina-based abrasive particles according to the present invention, the method comprising:
preparing a dispersion by combining components comprising liquid medium, peptizing agent, boehmite, a Gd
2
O
3
source (e.g., a gadolinium salt), and a ZnO source (e.g., a zinc salt);
converting the dispersion to particulate alpha alumina-based abrasive particle precursor material; and
sintering the particulate alpha alumina-based abrasive particle precursor material to provide the sintered alpha alumina-based abrasive particles.
In another aspect, the present invention provides a method for making sintered alpha alumina-based abrasive particles according to the present invention, the method comprising:
preparing a dispersion by combining components comprising liquid medium, peptizing agent and boehmite;
converting the dispersion to particulate alpha alumina-based abrasive particle precursor material;
calcining the particulate alpha alumina-based abrasive particle precursor material to provide first calcined alpha alumina-based abrasive particle precursor particles;
impregnating the first calcined particles with an impregnation composition comprising liquid medium to provide impregnated alpha alumina-based abrasive particle precursor particles;
calcining the impregnated alpha alumina-based abrasive particle precursor particles to provide second calcined alpha alumina-based abrasive particle precursor particles; and
sintering the second calcined particles to provide the sintered alpha alumina-based abrasive particles, wherein at least one of the dispersion or the impregnation composition comprise a Gd
2
O
3
source (e.g., gadolinium salt) and a ZnO source (e.g., a zinc salt).
In this application:
“Boehmite” refers to alpha alumina monohydrate and boehmite commonly referred to in the art as “pseudo” boehmite (i.e., Al
2
O
3
.xH
2
O, wherein x=1 to 2).
“Alpha alumina-based abrasive particle precursor,” “Abrasive particle precursor” or “unsintered abrasive particle” refers to a dried alumina-based dispersion (i.e., “dried abrasive particle precursor”) or a calcined alumina-based dispersion (i.e., “calcined abrasive particle precursor”), typically in the form of particles, that has a density of less than 80% (typically less than 60%) of theoretical, and is capable of being sintered or impregnated with an impregnation composition and then sintered to provide sintered alpha alumina-based abrasive particle.
“Sintered alpha alumina-based abrasive particle” as used herein refers to an alpha abrasive particle that has been sintered to a density of at least 85% (preferably, at least 90% and more preferably, at least 95%) of theoretical, and contains, on a theoretical oxide basis, at least 60) by weight Al
2
O
3
.
“Dispersion” or “sol” refers to a solid-in-liquid two-phase system wherein one phase comprises finely divided particles (in the colloidal size range) distributed throughout a liquid. A “stable dispersion” or “stable sol” refer to a dispersion or sol from which the solids do not appear by visual inspection to begin to gel, separate, or settle upon standing undisturbed for about 2 hours.
“Impregnation composition” refers to a solution or dispersion of a li

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