GB2233643A - Glass fiber high in tensile strength - Google Patents

Abstract

The invention provides a high strength glass fiber formed of a glass composition essentially consisting of 52-56 wt% of SiO2, 28-32 wt% of Al2O3, 9-12 wt% of a combination of CaO and MgO and 4-7 wt% of at least one of Y2O3, La2O3 and CeO2. The glass composition may optionally contain up to 1.5 wt% of ZrO2 and/or up to 1 wt% of a clarifying agent. This glass composition is meltable at a temperature below about 1650 DEG C, and the glass can easily be fiberized by a conventional spinning method at a temperature below 1500 DEG C. The tensile strength of the obtained glass fiber reaches or exceeds 450 kg/mm<2>.

Description

GLASS FIBER HIGH IN TENSILE STRENGTH This invention relates to a high strength glass fiber formed of a glass composition containing at least one selected rare earth element oxide.

Glass fibers are widely used as reinforcing components of composite materials. A borosilicate glass composition known as E glass has long been used for producing glass fibers, especially continuous fibers.

A fiber of E glass has a tensile strength of about 2 280 kg/mm , and glass fibers of such strength serve as reinforcing materials for producing composite materials for general purposes. However, for use in some composite materials to be formed into power-transmitting belts or the like to which high tension is applied continuously or intermittently and abruptly, fibers of E glass are insufficient in tensile strength.

Judging from molecular binding energies in oxide glasses, it is presumable that the possible maximum for the tensile strength of a glass fiber exceeds 500 kg/mm2.

This is a good reason for making efforts to develop practically formable glass fibers which are close to 500 kg/mm2in tensile strength.

As an advantageous substitute for E glass, British patent specification No. 1,209,244 shows a fiberizable glass composition consisting of 50-68 wt% of SiO2, 1232 wt% of Awl 203 and 14-20 wt% of CaO and/or MgO.

Furthermore, French patent specification No. 1,435,073 shows a fiberizable glass composition consisting of 50-65 wt% of SiO2, 20-30 wt% of At203, 5-20 wt% of MgO and 2-10 wt% of CaO. These glass compositions are higher in tensile strength than E glass, but the tensile strength of a fiber of either of these glass compositions is still lower than 450 kg/mm2.

It is an object of the present invention to porovide a glass fiber which has a tensile strength of 2 450 kg/mm or higher and is formed of a glass composition that can be melted and easily fiberized at industrially favorable temperatures, i.e. meltable at a temperature below about 1650 C and fiberizable at a temperature below about 15000C.

According to the invention there is provided a glass fiber formed of a glass composition consisting essentially of 52-56 wt% of Si02, 28-32 wt% of A1203, 9-12 wt% of an alkaline earth metal oxide component which is a combination of CaO and MgO, 4-7 wt% of at least one rare earth element oxide selected from Y203, La203 and CeO2, 0-1.5 wt% of Zero2, and 0-1 wt% of an auxiliary component selected from CaF2, As203, Sb203 and Cay06.

The invention can be embodied in either continuous glass fibers or discontinuous glass fibers (glass wool).

Continuous glass fibers according to the invention can be gathered together into strands, and the strands can be combined into yarns by conventional techniques.

A glass fiber according to the invention is very high in tensile strength. In the form of a filament the tensile strength of the glass fiber at room temperature reaches or exceeds 450 kg/mm2. Besides, this glass fiber is excellent in chemical resistance. Therefore, glass fibers according to the invention are very suitable as reinforcing materials for various kinds of composite materials, and the glass fibers in the composite materials exhibit good durability even when the composite materials are used in such a manner that high tensile force acts on the glass fibers as in the cases of timing belts and other power-transmitting belts.

A glass composition employed in the present invention can be melted at a temperature not higher than 16500C, and the glass can be fiberized by a conventional technique at a temperature lower than 15000C.

As a fiberizable glass the present invention employs a glass composition containing at least one rare earth element oxide as defined above. In the glass composition the proportions of the ingredients are strictly specified mainly for the following reasons.

The glass composition contains 52-56 wt% of SiO2 as the principal material of the glass. Although Si02 is relatively high in melting point and difficult to fiberize, a combination of SiO2, Al203, CaO and MgO in appropriate proportions is fairly low in liquidus temperature and can easily be melted. If the amount of SiO2 is less than 52 wt% the glass composition is unsatisfactory in formability or fiberizability and relatively high in liquidus temperature. If the amount of SiO2 is more than 56 wt% the glass can hardly provide glass fibers sufficiently high in tensile strength, and the liquidus temperature is not always low enough.

The glass composition contains 28-32 wt% of Awl 203 which has the effect of lowering the liquidus temperature and easing melting of the composition. If the amount of Awl 203 is less than 28 wt% the expected effect is insufficient, and it is difficult to obtain a glass fiber sufficiently high in tensile strength. If the amount of A1203 is more than 32 wt% the glass composition is not easy to fiberize.

The glass composition includes CaO and Mug0, and the total amount of CaO and MgO must be 9-12 wt%. If the total of CaO and MgO is less than 9 wt% the glass composition is relatively high in liquidus temperature and is not always good in meltability. If the total of CaO and MgO is more than 12 wt% it is difficult to obtain a glass fiber high in tensile strength and good in other properties. Although the propotion of MgO to CaO is not strictly specified, it is favorable for lowering of the liquidus temperature and easing of fiberization to use nearly equal amounts of MgO and CaO. That is, preferably the proportion of MgO to CaO is from 40:60 to 60:40 by weight.

The glass composition contains at least one of Y203, La203 and CeO2 for the purpose of enhancing the tensile strength of the obtained glass fiber without significantly raising the liquidus temperature. The amount of this component (in total in the case of using more than one of the three kinds of rare earth element oxides) must be 4-7 wt%. If the amount of the rare earth element oxide(s) is less than 4 wt% the expected effect is insufficient. If the amount of the rare earth element oxide(s) exceeds 7 wt% the glass composition becomes relatively high in liquidus temperature and inferior in meltability. Y203 is slightly better than La203 or CeO2 in the effect of enhancing the tensile strength of the obtained glass fiber.

The inclusion of any of Y203, La203 and CeO2 is effective also for enhancement of chemical resistance of the obtained glass fiber.

The glass composition may optionally contain up to 1.5 wt% of ZrO2 for further enhancing chemical resistance and tensile strength of the obtained glass fibers. However, if the amount of ZrO2 exceeds 1.5 wt% the glass composition becomes inferior in meltability and fiberizability.

Also optionally the glass composition may contain up to 1 wt% of CaF2, As2O3, Sb203 and/or CaSO4 as an auxiliary component which serves mainly as a clarifying agent.

As to almost inevitable impurities such as Na20, K2O, Fe203 and/or Mono,, it is desirable that the content of each of such impurities in the glass composition is not more than 0.5 wt%.

In preparing a desired glass composition it is possible to use a silica sand on the market as the raw material of SiO2. Instead of alumina it is possible to use another aluminum compound such as, for example, aluminum hydroxide as the source of Al203, and instead of calcia and magnesia it is possible to use, for example, calcium carbonate and magnesium carbonate.

A glass fiber according to the invention can be produced by using conventional methods and apparatus.

First a batch of the ingredients of a predetermined glass composition is melted, for example, in a crucible or a tank furnace. The melting of the batch to obtain a uniform melt of glass can be accomplished by maintaining the batch at a temperature not higher than 1650 C for a period of time not longer than 4 hr. Then the molten glass is cooled to solidify, and the glass is introduced into a spinning furnace. The glass can easily be melted and fiberized at a temperature lower than 15000C.

EXAMPLES 1-5 The glass compositions shown in the following table were formulated in Examples 1 to 5, respectively. In each example a batch of ingredients for the prescribed glass composition was put into a platinum crucible and melted in an electric furnace. As shown in the table the melting was accomplished by maintaining the batch of ingredients at a predetermined temperature ranging from 1600 to 1650 0C for a predetermined length of time ranging from 3 to 4 hr. The molten glass was taken out of the furnace and cooled to solidify. Using a small sample of the solidified glass the liquidus temperature of the glass was measured in a temperature gradient furnace by the usual method.

In every example the glass prepared by the above method was put into a spinning furnace made of a platinum-rhodium alloy. The glass was melted and maintained at a suitable temperature which was determined with reference to the liquidus temperature and ranged from 1460 to 14900C as shown in the table, and the molten glass was passed through a spinning nozzle with an orifice about 1.7 mm in diameter and drawn into a continuous fiber having a diameter of about 9 Xm. The tensile strength of the glass fiber was measured at room temperature.

As shown in the table, in every example the glass could be fiberized at a temperature lower than 15000C, and the tensile strength of the obtained glass fiber was 450 kg/mm2 or higher.

COMPARATIVE EXAMPLES 1-5 As shown in the table, five kinds of glass compositions not in accordance with the invention were formulated as Comparative Examples 1 to 5, respectively.

In these comparative examples both the melting of a batch of ingredients and the fiberization of the obtained glass were carried by the same operations as in Examples 1-5, though the melting and spinning temperatures were varied according to the need.

Glass Composition (wt%) Melting Liquidus Spinning Tensile Temp. -Time Temp. Temp. Strength SiO2 Al2O3 MgO CaO Y2O3 La2O3 CeO2 ( C - hr) ( C) ( C) (kg/mm2) Example 1 52.0 32.0 5.0 7.0 4.0 - - 1600 - 3 1430 1460 460 Example 2 56.0 28.0 5.0 4.0 - - 7.0 1650 - 3 1460 1480 470 Example 3 55.0 29.0 5.0 4.0 7.0 - - 1650 - 4 1480 1490 480 Example 4 55.0 29.0 6.0 6.0 2.0 - 2.0 1600 - 3 1450 1460 450 Example 5 55.0 29.0 5.5 4.5 2.0 2.0 2.0 1600 - 3 1430 1460 460 Comp. Ex. 1 65.0 25.0 10.0 - - - - 1680 - 4 1480 1500 440 Comp. Ex. 2 60.0 25.0 6.0 9.0 - - - 1550 - 3 1300 1350 410 Comp. Ex. 3 50.0 34.0 10.0 6.0 - - - 1600 - 3 1450 1470 430 Comp. Ex. 4 55.0 29.0 - 6.0 10.0 - - > 1700 - - Comp.Ex. 5 55.0 29.0 7.5 6.5 2.0 - - 1550 - 3 1310 1350 440 In Comparative Example 1 using a glass composition not containing CaO and any rare earth element oxide the melting of the ingredients had to be carried out at a temperature above 1650 C, and the molten glass was relatively high in viscosity so that the spinning temperature had to be raised to 1500 C. In this case the tensile strength of the obtained glass fiber did not reach 450 kg/mm2.

In Comparative Examples 2 and 3 the glass compositions did not contain any rare earth metal oxide either, though CaO was included. In these cases there was little problem as to meltability and fiberizability of the glass compositions, but the obtained glass fibers were insufficient in tensile strength.

In Comparative Example 4 the glass composition contained an excessively large amount of F203 and did not contain MgO. In this case it was impossible to completely melt a batch of the ingredients at a temperature not higher than 17000C.

In Comparative Example 5 the glass composition included all of the essential components specified in this invention, but the amount of the rare earth element oxide component was too small whereas the total amount of MgO and CaO was too large. In this case the tensile strength of the obtained glass fiber did not reach 450 kg/mm2.

Claims (5)

1. A glass fiber formed of a glass composition consisting essentially of 52-56 wt% of SiO2, 28-32 wt% of Al203, 9-12 wt% of an alkaline earth metal oxide component which is a combination of CaO and MgO, 4-7 wt% of at least one rare earth element oxide selected from Y203, La203 and CeO2, 0-1.5 wt% of ZrO2 and 0-1 wt% of an auxiliary component selected from CaF2, As203, Sb2O3 and CaSO

2. A glass fiber according to Claim 1, wherein the proportion of MgO to CaO in the glass composition is in the range from 40:60 to 60:40 by weight.

3. A glass fiber according to Claim 1, having tensile strength of 450 kg/mm2 or higher at room temperature.

4. A glass fiber substantially as hereinbefore described in any of Examples 1 to

5.