Cristobalite as a pigment substitute and as a composition enhancing mineral, compositions containing the same, and articles and coatings prepared with such compositions
A cristobalite includes: a d50 particle size selected within a range of from 1 μm to 15 μm; an L color coordinate of greater than 96; a color coordinate of less than 1; and a b color coordinate of 1 or less, in which the cristobalite is a powder. Also provided are compositions containing the cristobalite, coatings formed with compositions, and methods of preparing cristobalite.
1 . A cristobalite comprising:
a d 50 particle size selected within a range of from 1 μm to 15 μm;
an L color coordinate of greater than 96;
an a color coordinate of less than 1; and
a b color coordinate of 1 or less,
wherein the cristobalite is a powder,
wherein the cristobalite comprises a silica density within a range of from 2.2 to 2.3 g/cm 3 and a cristobalite fraction determined by x-ray diffraction is greater than 75%.
2 . The cristobalite of claim 1 , wherein the d 50 particle size is selected within a range of from 2 μm to 10 μm.
3 . The cristobalite of claim 1 , wherein the d 50 particle size is selected within a range of from 5 μm to 15 μm.
4 . The cristobalite of claim 1 , wherein the L color coordinate is greater than 98.
5 . The cristobalite of claim 1 , wherein the a color coordinate is less than 0.5.
6 . The cristobalite of claim 1 , wherein the b color coordinate is 0.7 or less.
7 . The cristobalite of claim 1 , wherein the cristobalite also has a loose bulk density of about 40.0 lbm/ft 3 and a tap bulk density of about 70 lbm/ft 3 at a d 50 particle size of 15 μm, or a loose bulk density of about 20.0 lbm/ft 3 and a tap bulk density of about 40 lbm/ft 3 at a d 50 particle size of 2 μm.
8 . The cristobalite of claim 1 , further comprising a coating applied over at least a portion of a surface of the cristobalite.
9 . The cristobalite of claim 8 , wherein the coating comprises a silane.
10 . A composition comprising the cristobalite according to claim 1 , wherein the cristobalite is incorporated into the composition as a pigment and/or as a composition enhancing mineral.
11 . The composition of claim 10 , wherein the cristobalite is incorporated into the composition as a pigment, and wherein the composition is substantially free of additional pigments other than the cristobalite.
12 . The composition of claim 10 , wherein the cristobalite is incorporated into the composition as a pigment, and wherein the composition further comprises at least a second pigment.
13 . The composition of claim 12 , wherein the cristobalite comprises at least 20 weight %, based on the total weight of pigments in the composition.
14 . The composition of claim 10 , further comprising a binder resin.
15 . The composition of claim 14 , wherein the composition comprises less binder resin than a composition formed with the same materials except for the cristobalite.
16 . An article formed with a composition for providing a colored appearance, wherein the composition comprises the composition of claim 10 .
17 . The article of claim 16 , wherein the article is a countertop, plastic, paper, or cementitious article.
18 . A coating formed with a composition for providing a colored appearance, wherein the composition comprises the composition according to claim 10 .
19 . A method of preparing cristobalite, the method comprising:
(a) mixing a whole grain silica and a fluxing agent to form a first mixture;
(b) processing the mixture through a reaction apparatus at a temperature within a range from 1000° C. to 1200° C. for a time period within a range of 0.5 to 2 hours to obtain cristobalite;
(c) filtering the cristobalite through a mesh screen to remove granules larger than 10 to 30 mesh; and
(d) grinding unfiltered cristobalite to a powdered cristobalite comprising a d 50 particle size within a range of from 1 μm to 15 μm, and wherein the powdered cristobalite comprises a silica density within a range of from 2.2 to 2.3 g/cm 3 and a cristobalite fraction determined by x-ray diffraction is greater than 75%.
20 . The method of claim 19 , wherein the whole grain silica comprises 0.3 weight % or less of a total amount of either iron oxide or titanium dioxide, based on the total weight of the whole grain silica itself.
21 . The method of claim 19 , wherein the whole grain silica has a d 50 particle size within a range of 30 to 270 mesh.
22 . The method of claim 19 , wherein the whole grain silica has a d 50 particle size within a range of 40 to 50 mesh.
23 . The method of claim 19 , wherein the first mixture comprises 0.3 weight % or less of the fluxing agent, based on the total combined weight of the whole grain silica and the fluxing agent.
24 . The method of claim 19 , wherein a pH of the powdered cristobalite is within a range of 8 to 10.
25 . A cristobalite comprising:
a d 50 particle size selected within a range of from 1 μm to 15 μm;
an L color coordinate of greater than 96;
an a color coordinate of less than 1; and
a b color coordinate of 1 or less,
wherein the cristobalite is a powder, and
wherein the cristobalite has a loose bulk density of about 40.0 lbm/ft 3 and a tap bulk density of about 70 lbm/ft 3 at a d 50 particle size of 15 μm, or a loose bulk density of about 20.0 lbm/ft 3 and a tap bulk density of about 40 lbm/ft 3 at a d 50 particle size of 2 μm.