BRUCITE AS A SOURCE OF MAGNESIUM OXIDE IN GLASS COMPOSITIONS

Abstract

Glass fibers suitable for textile and reinforcements are described. The glass fibers have compositions that include SiO.sub.2, CaO, Al.sub.2O.sub.3, and MgO. A significant amount of the MgO is derived from the mineral brucite. In some instances, the compositions are essentially free of fluorine, sulfate, and titania. These glass fiber compositions typically have broad or large values for delta T (i.e., the difference between the log 3 or forming temperaturethe temperature at which the glass has a viscosity of approximately 1,000 poiseand the liquidus temperature).

Claims

1. Continuous glass fiber having a composition essentially free of boron and consisting essentially of 59.0 to 62.0 weight percent SiO.sub.2, 20.0 to 24.0 weight percent CaO, 12.0 to 15.0 weight percent Al.sub.2O.sub.3, 1.0 to 4.0 weight percent MgO, 0.0 to 0.5 weight percent F.sub.2, 0.1 to 2.0 weight percent Na.sub.2O, 0.0 to 0.9 weight percent TiO.sub.2, 0.0 to 0.5 weight percent Fe.sub.2O.sub.3, 0.0 to 2.0 weight percent K.sub.2O, and 0.0 to 0.5 weight percent SO.sub.3, wherein the composition has (i) a viscosity of 1000 poise at a forming temperature of from 2100 F. (1149 C.) to 2500 F. (1371 C.) and (ii) a liquidus temperature at least 100 F. (38 C.) below the forming temperature; and wherein at least a portion of the MgO is derived from brucite.

2. Continuous glass fiber according to claim 1, wherein the MgO content is 2.0 to 3.5 weight percent.

3. Continuous glass fiber according to claim 1, wherein the SiO.sub.2 content is 59.0 to 61.0 weight percent, the CaO content is 21.5 to 22.5 weight percent, the Al.sub.2O.sub.3 content is 12.7 to 14.0 weight percent, the MgO content is 2.5 to 3.3 weight percent, the total content of Na.sub.2+K.sub.2O is 0.1 to 2.0 weight percent, the TiO.sub.2 content is 0.0 to 0.6 weight percent, the forming temperature is from 2200 F. (1204 C.) to 2400 F. (1316 C.), and the difference between the forming temperature and the liquidus temperature is at least 125 F. (52 C.).

4. Continuous glass fiber according to claim 3, wherein the SiO.sub.2 content is 59.5 to 60.5 weight percent, the CaO content is 21.7 to 22.3 weight percent, the Al.sub.2O.sub.3 content is 13.0 to 13.5 weight percent, the MgO content is 2.7 to 3.3 weight percent, and the total content of Na.sub.2+K.sub.2O is 0.5 to 1.0 weight percent.

5. Continuous glass fiber according to claim 3, wherein the SiO.sub.2 content is 60.1 weight percent, the CaO content is 22.1 weight percent, the Al.sub.2O.sub.3 content is 13.2 weight percent, the MgO content is 3.0 weight percent, and the total content of Na.sub.2+K.sub.2O is 0.8 weight percent.

6. Continuous glass fiber according to claim 1, wherein the TiO.sub.2 content is not more than 0.6 weight percent.

7. Continuous glass fiber according to claim 6, wherein the TiO.sub.2 content is 0.00 to 0.04 weight percent.

8. Continuous glass fiber according to claim 7, wherein the F.sub.2 content is 0.00 to 0.04 weight percent.

9. Continuous glass fiber according to claim 1, wherein the composition is essentially free of TiO.sub.2.

10. Continuous glass fiber according to claim 1, wherein the composition is essentially free of F.sub.2.

11. Continuous glass fiber according to claim 1, wherein the composition is essentially free of SO.sub.3.

12. Continuous glass fiber according to claim 1, wherein the SO.sub.3, F.sub.2, and TiO.sub.2 contents are each no more than 0.05 weight percent.

13. Continuous glass fiber according to claim 1, wherein the difference between the forming temperature and the liquidus temperature is at least 150 F. (66 C.).

14. Continuous glass fiber according to claim 1, wherein the SiO.sub.2 content is 60.2 weight percent, the CaO content is 22.0 weight percent, the Al.sub.2O.sub.3 content is 13.2 weight percent, the MgO content is 3.0 weight percent, the total content of Na.sub.2+K.sub.2O is 0.8 weight percent, the forming temperature is from 2200 F. (1204 C.) to 2400 F. (1316 C.), and the difference between the forming temperature and the liquidus temperature is at least 125 F. (52 C.).

15. Continuous glass fiber according to claim 1, wherein the SiO.sub.2 content is about 60.1 weight percent, the CaO content is about 22.1 weight percent, the 3 content is about 13.2 weight percent, the MgO content is about 3.0 weight percent, the K.sub.2O content is about 0.2 weight percent, the Na.sub.2O content is about 0.6 weight percent, the Fe.sub.2O.sub.3 content is about 0.2 weight percent, the total content of SO.sub.3 and F.sub.2 content is about 0.1 weight percent, the TiO.sub.2 content is about 0.5 weight percent, the forming temperature is from about 2300 F. (1204 C.) to about 2400 F. (1316 C.), and the difference between the forming temperature and the liquidus temperature is at least about 150 F. (52 C.).

16. Continuous glass fiber according to claim 1, wherein at least 50% of the MgO in the composition is derived from brucite.

17. Continuous glass fiber according to claim 1, wherein at least 70% of the MgO in the composition is derived from brucite.

18. Continuous glass fiber according to claim 1, wherein at least 99% of the MgO in the composition is derived from brucite.

Description

DETAILED DESCRIPTION

[0021] The glass fiber compositions of the invention include magnesium oxide (MgO) that is derived from a source other than dolomite, such as brucite. In some exemplary embodiments, the glass compositions are essentially free of boron. By essentially free, we mean that the composition contains at most only a trace quantity of the specified component, e.g., from impurities in the raw materials. In some exemplary embodiments, the glass fibers are also essentially fluorine-free. In some exemplary embodiments, the glass fibers are also essentially titania-free.

[0022] In general, fibers according to the invention may be prepared as follows. The components, which may be obtained from suitable ingredients or raw materials (e.g., sand for SiO.sub.2, burnt lime for CaO, brucite for MgO) and may optionally contain trace quantities of other components, are mixed or blended in a conventional manner in the appropriate quantities to give the desired weight percentages of the final composition. The mixed batch is then melted in a furnace or melter, and the resulting molten glass is passed along a forehearth and into fiber-forming bushings located along the bottom of the forehearth. The molten glass is pulled or drawn through holes or orifices in the bottom or tip plate of the bushing to form glass fibers. The streams of molten glass flowing through the bushing orifies are attenuated to filaments by winding a strand of the filaments on a forming tube mounted on a rotatable collet of a winding machine. The fibers may be further processed in a conventional manner suitable for the intended application.

[0023] The temperatures of the glass at the furnace, forehearth, and bushing are selected to appropriately adjust the viscosity of the glass. The operating temperatures may be maintained using suitable means, such as control devices. Preferably, the temperature at the front end of the melter is automatically controlled to help avoid devitrification.

[0024] The use of sulfate in the furnace operation may help avoid seeding or bubbling problems in the glass. When producing large-scale melts, we have found it important to add carbon to the batch to control foam levels in the furnace. Preferably the sulfate-to-carbon ratio (SO.sub.3/C) in the batch is from about 0.6 to about 1.7, in contrast with E glass, which typically runs best at an SO.sub.3/C=3.0 to 10.0. The sulfate-to-carbon ratio is preferably controlled in the furnace to keep the foam at a manageable level and thereby allow heat to penetrate into the glass from the gas burners. It should be understood, however, that the compositions are preferably essentially free of sulfate, since this, like carbon, is almost completely or practically entirely eliminated from the glass during melting.

[0025] Furthermore, the addition of a small amount of alkali may help improve the melting rate of the batch. For example, about 0.70 weight percent Na.sub.2O may be added to facilitate melting.

[0026] The forehearth design should be such that throughout the forehearth the glass is kept above the liquidus temperature. The forehearth should be constructed to provide for even heating of the glass to avoid cold spots causing devitrification.

[0027] The glass compositions can be readily fiberized in any suitable manner, including using known bushing technology. See U.S. Pat. Nos. 5,055,119; 4,846,865; and 5,312,470, the disclosures of which are incorporated by reference herein. Through such bushing technology, the fibers may be formed at higher temperatures with smaller differences between the forming and liquidus temperatures. In general, the bushing should be structured to provide long life and resist sagging, which is dependent on the pressure of the glass on the tip plate and the temperature. For example, the bushing can be made of a stiff alloy composition, such as one containing about 22-25% rhodium and platinum. The stiffness of the tip plate may be enhanced through the use of structural or mechanical reinforcements, such as T-gussets. The bushing screen should have high corrosion resistance, which may be accomplished, e.g., by constructing the plate screen from platinum.

[0028] The discussion above regarding parameters and equipment is provided to illustrate a process for making the inventive glass fibers. It should be understood that the artisan may suitably modify or optimize the process parameters and equipment in light of the specific glass fibers being made and conventional design considerations.

[0029] The general inventive concepts will now be illustrated through the following exemplary embodiments.

Example I

[0030] Four production samples of reinforcement glass fibers were produced with an average glass composition analyzed as consisting essentially of, by weight: 60.01% SiO.sub.2; 22.13% CaO; 12.99% Al.sub.2O.sub.3; 3.11% MgO; 0.04% F.sub.2; 0.63% Na.sub.2 O; 0.55% TiO.sub.2; 0.25% Fe.sub.2O.sub.3; 0.14% K.sub.2O; and 0.02% SO.sub.3. On average, the forming temperature for a viscosity of 1,000 poise (log 3) was 2,298 F. (1,259 C.), the liquidus temperature was 2,146 F. (1,174 C.), and the forming-liquidus temperature difference (delta T) was 135 F. (57 C.).

Example II

[0031] Using a laboratory melter, glass fibers were produced from reagents providing the following batch composition, with percentages being by weight: 60.08% SiO.sub.2; 22.07% CaO; 13.21% Al.sub.2 O.sub.3; 3.01% MgO; 0.16% K.sub.2O; 0.23% Fe.sub.2O.sub.3; 0.05% SO.sub.3; 0.06% F.sub.2; 0.52% TiO.sub.2; and 0.60% Na.sub.2O. The resulting glass had the following temperature properties: log 3=2309 F. (1265 C.); liquidus=2156 F. (1180 C.); and delta T=153 F. (67 C.).

Examples III-VIII

[0032] In a manner analogous to that described in Example II, glass fibers were prepared from the batch compositions (with percentages being by weight) shown in the table below.

TABLE-US-00004 Example No.: III IV V VI VII VIII % SiO.sub.2: 59.45 61.05 59.05 59.05 59.45 59.96 % CaO: 22.69 22.29 24.29 22.29 22.69 22.18 % Al.sub.2O.sub.3: 13.48 13.08 13.08 15.08 13.48 13.19 % MgO: 3.23 2.83 2.83 2.83 3.23 3.07 % K.sub.2O 0.63 0.23 0.23 0.23 0.23 0.25 % Fe.sub.2O.sub.3: 0.36 0.36 0.36 0.36 0.36 0.28 % SO.sub.3: 0.05 0.05 0.05 0.05 0.05 0.05 % F.sub.2: 0.04 0.04 0.04 0.04 0.04 0.09 % TiO.sub.2: 0.04 0.04 0.04 0.04 0.04 0.37 % Na.sub.2O: 0.03 0.03 0.03 0.03 0.43 0.55 Log 3: 2308 F. 2334 F. 2279 F. 2353 F. 2298 F. 2310 F. (1264 C.) (1279 C.) (1248 C.) (1289 C.) (1259 C.) (1266 C.) Liquidus: 2180 F. 2161 F. 2136 F. 2227 F. 2171 F. 2181 F. (1193 C.) (1183 C.) (1169 C.) (1219 C.) (1188 C.) (1194 C.) Delta T: 128 F. 173 F. 143 F. 127 F. 127 F. 129 F. (53 C.) (78 C.) (62 C.) (53 C.) (53 C.) (54 C.)

Example IX

[0033] Glass fibers were prepared having the following composition with essentially zero fluorine, sulfate, and titania levels: 61.00% SiO.sub.2; 22.24% CaO; 12.00% Al.sub.2O.sub.3; 3.25% MgO; 0.52% K.sub.2O; 0.30% Fe.sub.2O.sub.3; 0.00% SO.sub.3; 0.00% F.sub.2; 0.00% TiO.sub.2; and 0.69% Na.sub.2O. The glass had the following temperature characteristics: log 3=2304 F. (1262 C.); liquidus=2203 F. (1206 C.); and delta T=101 F. (38 C.).

[0034] As is understood in the art, the above exemplary compositions do not always total precisely 100% of the listed components due to statistical conventions (e.g., rounding and averaging). Of course, the actual amounts of all components, including any impurities, in a specific composition always total to 100%.

[0035] Furthermore, it should be understood that where small quantities of components are specified in the compositions, e.g., quantities on the order of about 0.05 weight percent or less, those components may be present in the form of trace impurities present in the raw materials, rather than intentionally added. Moreover, components may be added to the batch composition, e.g., to facilitate processing, that are later eliminated, resulting in a glass composition that is essentially free of such components. Thus, for instance, although minute quantities of components such as fluorine and sulfate have been listed in various examples, the resulting glass composition may be essentially free of such components, e.g., they may be merely trace impurities in the raw materials for the silica, calcium oxide, alumina, and magnesia components in commercial practice of the invention or they may be processing aids that are essentially removed during manufacture. As apparent from the above examples, glass fiber compositions of the invention have advantageous properties, such as low viscosities and wide (high) delta T values. Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention.

[0036] Notwithstanding the specific examples of glass compositions provided herein, the general inventive concepts are not intended to be limited to these specific examples but instead are applicable to any fiberizable glass compositions having an MgO content. The MgO content of the glass compositions is primarily derived from a raw material other than dolomite. In some exemplary embodiments, at least 50% of the MgO in the glass composition is derived from brucite. In some exemplary embodiments, at least 70% of the MgO in the glass composition is derived from brucite. In some exemplary embodiments, substantially all of the MgO in the glass composition is obtained from brucite.

[0037] In some exemplary embodiments, the glass composition has an elevated level of MgO, such as greater than 4 weight percent. In some exemplary embodiments, the weight percent of the MgO in the glass composition ranges from 4 to 10. In some exemplary embodiments, the weight percent of the MgO in the glass composition ranges from 4 to 8.