RU2416577C2 - Modifying alkali-earth silicate fibre - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing fire resistant alkali-earth silicate fibre from molten mass involves using an alkali metal as a predetermined component to improve mechanical properties of the fibre compared to fibre in which no alkali metal is used. The fibre contains M₂O, in which M denotes an alkali metal and in which either 65% < SiO₂, 13.5% < CaO < 27.5%, 72% < SiO₂ + ZrO₂ + B₂O₃ + 5P₂O₅, M₂O > 0.5%, or 75% < SiO₂, 13.8% < CaO < 27.8%, 75% < SiO₂ + ZrO₂ + B₂O₃ + 5P₂O₅ and M₂O > 0.2%.

EFFECT: improved mechanical and thermal properties of the fibre.

12 cl, 9 dwg, 6 tbl

Description

The present invention relates to alkaline earth silicate fibers.

Inorganic fibrous materials are well known and widely used for various purposes (for example, as heat or sound insulation in bulk, in the form of a mat or in the form of a cloth, in the form of vacuum-formed forms, vacuum-formed plates and paper, as well as ropes, yarn or textiles; as a reinforcing fiber for building materials; as a component of brake pads for vehicles). In most of these applications, those properties due to which inorganic fibrous materials are used require heat resistance and often resistance to aggressive chemical environments.

Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material, one of the forms of which is the main cause of respiratory diseases.

It is still not clear what is the mechanism by which some types of asbestos cause the development of such diseases, but some researchers believe that this mechanism is associated with mechanical properties and particle size. Critical sized asbestos particles can pierce cells in the body and, thus, with prolonged and regular damage to cells, have a detrimental effect on health. Regardless of whether the mechanism of action of asbestos is such or not, regulatory authorities pointed out the need to classify as hazardous any product with inorganic fibers that contains a respiratory fraction, regardless of whether there is any evidence to support such a classification. Unfortunately, there are no real substitutes for such inorganic fibers for use in many fields.

Therefore, there remains a need for inorganic fibers, which will have the least possible danger (if any) and for which there will be objective reasons to consider them safe.

In accordance with one direction of the study, it was suggested that if inorganic fibers were made that were sufficiently soluble in physiological fluids so that their residence time in the human body was short, then damage would not be caused, or at least it will be reduced to a minimum. Since, as it turned out, the risk of a disease associated with asbestos exposure is very much dependent on the duration of exposure, this idea seemed quite reasonable. Asbestos is highly insoluble.

Since intercellular fluid is saline in nature, the importance of fiber solubility in saline has been established for a long time. If the fibers are soluble in physiological saline, then, provided that the dissolved components are not toxic, such fibers should be safer than fibers that do not have such solubility. Alkaline-earth silicate fibers have been proposed as soluble in saline, non-metallic, amorphous, inorganic oxides of refractory fibrous materials. The invention, in particular, relates to vitreous alkaline earth silicate fibers with silica as their main component.

International patent application WO87 / 05007 discloses fibers including magnesium oxide, silicon dioxide (silica), calcium oxide and less than 10% alumina, which are soluble in saline. The solubilities of the fibers disclosed there were presented based on parts per million of silicon (extracted from a silicon-containing fiber material) present in the saline solution after aging for 5 hours. WO87 / 05007 states that pure materials should be used and an upper limit of 2% by weight of the total content of all impurities that might be present is given. Alkali metals were not mentioned in said patent application.

International patent application WO89 / 12032 discloses other fibers that are soluble in saline and discusses some of the components that may be present in such fibers. Said application discloses the addition of Na ₂ O in amounts ranging from 0.28 to 6.84 wt.%, But there is no indication that the presence of Na ₂ O had any effect.

European Patent Application No. 0399320 discloses glass fibers having high physiological solubility and containing 10-20 mol% Na ₂ O and 0-5 mol% K ₂ O. Although these fibers have been shown to be physiologically soluble, their maximum temperature application has not been given.

Other patent descriptions disclosing the choice of fibers for their solubility in saline include, for example, European 0412878 and 0459897, French 2662687 and 2662688, PCT WO86 / 04807, WO90 / 02713, WO92 / 09536, WO93 / 22251, WO94 / 15883, WO97 / 16386 and U.S. 5,250,488.

The refractoriness of the fibers disclosed in these various prior art documents varies widely, and in the case of such alkaline earth silicate materials, this property is critically dependent on composition.

As a rule, it is relatively easy to obtain alkaline earth silicate fibers that work well at low temperatures since additives for the low-temperature application can be added, such as boron oxide, to ensure good fiber formation and to vary the amounts of components to provide the desired material properties. However, when it is necessary to increase the refractoriness of alkaline earth silicate fibers, it is necessary to reduce the amount of added additives, since usually (although with exceptions), the more components are present, the lower the refractoriness.

WO93 / 15028 discloses fibers comprising, as main components, CaO, MgO, SiO ₂ and, optionally, ZrO ₂ . Such fibers are commonly known as Calcium Magnesium Silicate (CMS) or Calcium Magnesium Zirconia Silicate (CMZS) fibers. WO93 / 15028 requires that the compositions used be substantially free of alkali metal oxides. It has been shown that for materials suitable for use as insulation at 1000 ° C., amounts up to 0.65 wt.% Are acceptable. In addition, WO93 / 15028 shows the need for low levels of Al ₂ O ₃ (<3.97%).

WO94 / 15883 discloses a number of such fibers useful as refractory insulation at temperatures up to 1260 ° C or more. As in WO93 / 15028, this patent application emphasizes that the alkali metal oxide content should be kept low, but it is indicated that some alkaline earth silicate fibers could be tolerant to higher levels of alkali metal oxide than some others. However, it has been suggested that levels of Na ₂ O of 0.3% and 0.4% by weight cause increased shrinkage of materials when used as insulation at 1260 ° C. The paper also emphasized the importance of maintaining a low level of alumina.

WO97 / 16386 discloses fibers useful as refractory insulation at temperatures up to 1260 ° C or more. These fibers include MgO, SiO ₂ and, optionally, ZrO ₂ as main components. It is indicated that, in such fibers, alkali metal oxides are essentially not required, in addition to trace amounts (present, at the most, in hundredths of a percent based on alkali metal oxide). Fibers have a common composition

SiO ₂ 65-86% MgO 14-35%

moreover, these components MgO and SiO ₂ constitute at least 82.5% by weight of the fiber, and the rest are said components and viscosity modifiers. Such magnesium silicate fibers may include minor amounts of other alkaline earth metals. This document also emphasizes the importance of maintaining a low level of alumina.

WO2003 / 059835 discloses some calcium silicate fibers, some of which exhibit a low ability to react with aluminosilicate bricks, namely:

65% <SiO ₂ <86%

MgO <10%

14% <CaO <28%

Al ₂ O ₃ <2%

ZrO ₂ <3%

B ₂ O ₃ <5%

P ₂ O ₅ <5%

72% <SiO ₂ + ZrO ₂ + B ₂ O ₃ + 5 · P ₂ O ₅

95% <SiO ₂ + CaO + MgO + Al ₂ O ₃ + ZrO ₂ + B ₂ O ₃ + P ₂ O ₅ .

The patent application also discloses the use of La ₂ O ₃ or other lanthanoid additives to improve the strength of fibers and webs made from these fibers. The indicated patent application does not disclose the levels of alkali metal oxides, but in the fibers intended for use as insulation at temperatures up to 1260 ° C or more, amounts are disclosed in the range of ~ 0.5 wt.%. WO2003 / 060016 claims a low-shrink, high temperature-resistant inorganic fiber with a temperature of application up to at least 1330 ° C, which retains mechanical integrity after exposure to the temperature of the application and which is short-lived in physiological fluids, including the product of fiber formation from more than 71.25 to about 85 weight percent silica, from 0 to about 20 weight percent magnesium oxide, from about 5 to about 28.75 weight percent calcium oxide, and from 0 to an example but 5 weight percent zirconia and, optionally, a viscosity modifier in an amount effective to impart fiber formation to the product.

EP 1323687 claims the composition of a bio-soluble ceramic fiber for high temperature insulation material, including 75-80 wt.% SiO ₂ , 13-25 wt.% CaO, 1-8 wt.% MgO, 0.5-3 wt.% ZrO ₂ and 0-0.5 wt.% Al ₂ O ₃ , and the content of (ZrO ₂ + Al ₂ O ₃ ) is 0.5-3 wt.%, And the content of (CaO + MgO) is 15-26 wt.% .

The term “alkaline earth silicate fibers” was defined in the Chemical Abstract Service Registry [Registry Number 436083-99-7]:

“ Chemicals produced in the form of fibers. This category covers substances obtained by blowing or drawing a molten mixture of alkaline earth metal oxides, silicon dioxide and other minor / trace oxides. It melts around 1500 ° C (2732 ° F). It mainly consists of silicon dioxide (50-82 wt.%), Calcium oxide and magnesium oxide (18-43 wt.%), Alumina, titanium dioxide and zirconia (<6% wt.) And trace oxides . "

This definition reflects the European Health and Safety regulations, which establish the requirements for special labeling of silicate fibers containing less than 18% alkaline earth metal oxides.

However, as clearly shown in connection with WO2003 / 059835, WO2003 / 060016 and EP 1323687, the silica content in alkaline earth silicate fibers increases with the need for higher application temperatures, and this leads to a decrease in alkaline earth metal contents.

The present invention is applicable not only to alkaline earth silicate fibers corresponding to this narrow value as defined in Chemical Abstracts, but also to alkaline earth silicate fibers with lower levels of alkaline earth metal oxides.

Accordingly, in the present description, alkaline earth silicate fibers should be considered as materials comprising predominantly silicon dioxide and alkaline earth metal oxides and containing less than 10 wt.% Alumina [as described in WO87 / 05007, where such fibers are first described], preferably in which the amount of oxide aluminum, zirconia and titanium dioxide is less than 6 wt.% [as indicated in the definition of Chemical Abstracts]. For regulatory reasons, preferred materials contain more than 18% alkaline earth metal oxides.

In the prior art it is shown that in the case of refractory alkaline earth silicate fibers, alkali metals are considered as impurities that can only be admissible at low levels of content, but which adversely affect refractoriness at higher levels of content.

The applicant has found that, contrary to traditional concepts in the field of refractory alkaline earth silicate fibers, the addition of small amounts of alkali metals within a narrow range improves the mechanical quality of the obtained fibers (especially the strength of the fibers) without a noticeable decrease in the fire resistance of these fibers.

Accordingly, the present invention provides a method for manufacturing refractory alkaline earth silicate fibers from a melt, comprising adding an alkali metal as a deliberate melt component to improve the mechanical and / or thermal properties of the fiber compared to an alkali-free fiber.

Preferably, the amount of alkali metal (M) expressed as M ₂ O oxide is more than 0.2 mol%, and preferably is in the range from 0.2 mol% to 2.5 mol%, more preferably from 0 , 25 mol.% Up to 2 mol.%.

The term “alkali-free fiber” means a fiber in which all other components are present in the same proportions, but in which there is no alkali metal.

The alkali metal is preferably present in an amount sufficient to increase the tensile strength of the web made using this fiber by> 50% relative to the tensile strength of the web, free from alkali metal, and less than the amount that will lead to the measured by the method described below, shrinkage of more than 3.5% in a vacuum-cast preform of these fibers when exposed to a temperature of 1250 ° C for 24 hours.

It will be understood that the alkali metal can be added either as an additive to the melt (preferably in the form of an oxide), or by using suitable amounts of materials containing the alkali metal as a component or impurity as a melt ingredients or as an additive and as a component or impurities. The invention consists in ensuring that the melt possesses the desired amount of alkali metal to achieve the beneficial effects of the invention.

The invention can be applied to all of the aforementioned alkaline earth silicate compositions of the prior art.

The scope and additional features of the invention will become apparent from the claims in light of the following illustrative description and when referring to the drawings, in which:

Figure 1 is a graph showing the ratio of tensile strength / density depending on the temperature of the melt flow, determined during the production test of a number of fibers with different Na ₂ O content;

Figure 2 is a graph showing the maximum, average and minimum values of the ratio of tensile strength / density depending on the content of Na ₂ O for the same fibers;

Figure 3 is a graph with experimentally determined viscosity / temperature curves for a number of formulations;

Figure 4 is a graph showing the content of kings depending on the content of Na ₂ O for the fibers of Figure 1;

Figure 5 is a graph of the content of kings on the content of Na ₂ O of some alkaline earth silicate fibers;

6 is a graph of linear shrinkage values for alkaline earth silicate fibers of various compositions in comparison with known refractory ceramic fibers (CRF);

Fig.7 is a graph of the effect on the strength of the canvas adding sodium to a number of alkaline earth silicate fibers;

Fig. 8 compares micrographs showing various fibers after exposure to a series of temperatures;

Fig.9 is a graph comparing the measured thermal conductivity for a number of fibers.

The inventors made a fiber web using an experimental production line at their factory in Brombourought, England. The fiber was produced through the formation of a melt, followed by allowing the melt to spontaneously drain onto a pair of spinning machines (in accordance with the traditional method).

The main melt had the following nominal composition in mass percent:

SiO ₂ 73.5 Cao 25 La ₂ o ₃ 1,5

while the other components formed impurities, and sodium oxide was added in the indicated amounts.

The temperature of the melt flow was controlled using two color pyrometers.

The fibers obtained at the exit of the spinning machines were passed onto a conveyor and then sewn (punched) with needles to obtain a web in the traditional way.

The thickness, density, and tensile strength of the webs were measured in the case of fibers obtained using a number of different conditions.

The canvas was obtained in order to determine the effect on the quality of the fibers of the temperature of the flow of violence, since it was believed that it affects the quality of the fiber.

The inventors also decided to add alkali metal oxides in order to equalize the viscosity-temperature curve of the melt, since this was considered an important factor in the production of fiber, as explained below.

The results of these tests are presented in table 1 and shown graphically in figures 1 and 2. Table 1 for all compositions presents the temperature of the melt flow, web thickness, web density, tensile strength and tensile strength divided by density. [The tensile strength divided by density was calculated to eliminate differences associated with different amounts of material in the canvas]. In addition, for the selected compositions, the shrinkage of the preformed workpiece was measured at 1150 ° C and 1250 ° C in the same manner as in WO2003 / 059835.

The first thing that deserves attention is that the tensile strengths of the canvases showed strong inconstancy. This is due to the fact that the production of the canvas differs in many variable parameters, among which:

- the composition of the melt;

- melt temperature;

- temperature of the melt stream;

- the content of kings (melt that has hardened in the form of drops, not fibers)

- fiber diameter;

- fiber length;

- conditions for needle piercing;

- thermal background after hardening.

Obtaining different fibers on the same line and significantly changing only the temperature of the melt flow and composition (each of these parameters will affect the content of kings, fiber diameter and fiber length), it was supposed to reduce such inconstancy. However, since the web is a combined mass of individual fibers, a statistical difference in aggregate properties such as tensile strength is inevitable.

As can be seen from the results presented in Fig. 1, the change in strength with a change in the temperature of the melt flow is relatively small, but this is not surprising, since the selected temperature range of the melt flow was chosen to cover only areas previously established as effective.

However, it can be seen that with an increasing increase in the content of Na ₂ O, the strength tends to increase. Figure 2 shows the maximum, minimum and average strength values established for a number of compositions, while it can be seen that the strength of the fabric shows a strong positive correlation with the content of Na ₂ O. On the contrary, almost no effect on the shrinkage of the fibers.

Fibers with a nominal zero Na ₂ O content, of course, contained insignificant trace amounts of Na ₂ O (the average measured content was 0.038%, the maximum was 0.11%). Extrapolation in the direction of decreasing the content of Na ₂ O to zero gives an average ratio of tensile strength / density of 0.0675 kPa [kg / m ³ ]. The average ratio of tensile strength / density with the addition of 0.3% Na ₂ O is 0.1426. The increase in web strength exceeds 100%, and it is expected that smaller additions (e.g. 0.25 mol%) will exceed the 50% improvement.

Based on the results obtained and in order to determine the upper limit of the alkali metal oxide content, which would be acceptable, the inventors made several types of additional alkaline earth silicate fibers using an experimental setup in which a melt of the corresponding composition was obtained, passed through an 8-16 mm hole and blown to obtain fiber in a known manner. (The size of the outlet changed according to the viscosity of the melt - such regulation should be determined experimentally in accordance with the equipment and composition used). The shrinkage of fiber preforms at 1150 ° C and 1250 ° C was measured in the same manner as in WO2003 / 059835. For some samples, the overall solubility of the main glass components in ppm was also determined. (ppm) in physiological saline after a 24-hour statistical test.

The results of these studies are presented in Table 2. The fibers shown in the table on the left were tested to determine the effect of adding approximately equimolar amounts of alkali metal additive to calcium silicate fiber containing La ₂ O ₃ (as in WO2003 / 059835), while how the fibers shown in the table on the right were tested to assess the effect of varying the amount of Na ₂ O in such a fiber. The results obtained show, although these are not conclusive conclusions, that the shrinkage in the case of these fibers with Na ₂ O and K ₂ O was no worse and even better than that of the fibers free of Na ₂ O, while Li ₂ O has an unfavorable effect on shrinkage.

However, the latter conclusion seems unreliable because it was determined when lithium was added in the form of lithium tetraborate, and the introduction of boron could have a significant effect. Unless proven otherwise, the inventors have suggested that all alkali metals can be used in the invention, but the absolute amount of alkali metal can vary from metal to metal and from fiber to fiber. Solubility indices demonstrate that when alkali metal oxide is added, the total solubility is slightly increased.

table 2 Sample PAT STD 01 PAT Na ₂ O 02 PAT Li ₂ O 03 PAT K ₂ O 04 BG-X-04-0305 BG-X-04-0277 BG-X-04-0279 Component Na ₂ O 0.26 0.95 0.12 0.24 0.6 0.72 1.14 MgO 0.38 0.39 0.36 0.36 0.35 0.38 0.36 Al ₂ O ₃ 0.6 0.64 0.56 0.62 0.38 0.02 0 SiO ₂ 72.58 72.47 72.43 72.40 73.26 73.58 73.76 K ₂ O 0.08 0.08 0,07 1.05 0,07 0.08 0.08 CaO 24.05 23.27 23.62 22.67 22.82 23.52 23.22 TiO ₂ 0.1 0.10 0.11 0.15 0.1 0.1 0.1 Fe ₂ O ₃ 0.16 0.19 0.21 0.23 0.16 0.18 0.18 La ₂ O ₃ (estimated) 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Li ₂ O 0.34 * % linear shrinkage 850 ° C / 24 h 0.38 0.21 0.22 1150 ° C /
24 h 1.05 0.88 1,58 0.63 0.47 0.36 0.59 1250 ° C /
24 h 1,08 1,08 1.71 0.79 0.48 0.69 0.84 % shrink thickness 850 ° C / 24 h 0.42 0.71 1.31 1150 ° C /
24 h 0.93 0.71 1.44 1250 ° C /
24 h 0.91 0.72 6.43 Solubility under static conditions 24 h (ppm) 191 202 200 on

As can be seen from the results presented on the right side of Table 2, only a ~ 1% higher silica content has a significant effect on shrinkage, leading to a significant reduction in shrinkage. It turned out that for these fibers, the addition of sodium oxide in all the amounts tested did not affect the linear shrinkage at 850 ° C / 24 h, however, it affected, albeit slightly, the shrinkage in thickness. At 1150 ° C / 24 h, there is a slight increase in both linear shrinkage and thickness shrinkage, but at 1250 ° C / 24 h, the shrinkage in thickness, although still acceptable, increases more significantly with more sodium oxide added. Moreover, all of these indicators are acceptable for certain applications, while in other applications, the addition of Na ₂ O in the largest amount tested may not be acceptable.

The improvement in shrinkage at higher levels of silicon dioxide led the inventors to consider materials containing even higher amounts of silicon dioxide, and the results are presented in table 3.

Table 3 Sample PAT Na ₂ O 05 PAT Na ₂ O 06 PAT Na ₂ O 07 PAT Na ₂ O 08 PAT Na ₂ O 09 PAT Na ₂ O 10 Component Na ₂ O 0.5 0.5 0.5 0.5 0.5 1,1 MgO 0.4 0.3 0.3 0.4 0.3 0.4 Al ₂ O ₃ 0.6 0.5 0.6 0.8 0.6 0.8 SiO ₂ 73.9 74.3 74.5 75,2 76.3 77.7 K ₂ O 0.1 0.1 0.1 0.1 0.1 0.1 Cao 23.6 22.9 22.6 22.0 21,4 19.3 TiO ₂ 0.1 0.1 0.1 0.1 0.1 0.1 Fe ₂ O ₃ 0.2 0.2 0.2 0.2 0.2 0.2 La ₂ o ₃ 1.3 1.3 1.3 1.3 1.3 1.3 % linear shrinkage 1150 ° C /
24 h 0.54 0.8 0.61 0.56 0.65 0.58 1250 ° C /
24 h 1,1 1,07 on 0.84 0.86 on Solubility under static conditions 24 h (ppm) 199 208 165 194 245 107

The presented results show low shrinkage and reasonably high solubility over the entire interval. It turned out that the addition of alkali metal oxide can increase the amount of silicon dioxide that can be added to obtain a treatable alkaline earth silicate fiber, possibly with acceptable solubility. This is very important, since usually an increase in the content of silicon dioxide allows the use of alkaline earth silicate fibers at higher temperatures.

Figure 6 presents the shrinkage at various temperatures of preformed blanks from a number of alkaline earth silicate fibers. The designation “SW613” refers to lanthanum-containing materials of a composition similar to those shown in table 3, with varying silica contents according to the indicated, but without adding any alkali metal. [Silica and calcium oxide make up most of this material, and lanthanum oxide is present in an amount of about 1.3%]. About 2 wt.% MgO was added to the fiber of one of these species. Shrinkage values for traditional aluminosilicate fiber (RCF) and magnesium silicate fiber (“MgO silicate”) are also presented.

It can be seen that all SW613 fibers have less shrinkage than that of RCF fibers and MgO silicate fibers, up to 1350 ° C, but then exceed. However, with increasing silicon dioxide content, there is a gradual increase in refractoriness. For SW613 fiber containing 77% and 79% SiO ₂ , the shrinkage remains below the shrinkage of the RCF fiber and MgO silicate fiber, up to 1400 ° C, and it is expected that at higher silica contents it could still improve. On the contrary, it can also be seen that the addition of 2% MgO to SW613 formulations has an adverse effect on shrinkage. High silica alkaline earth silicate fibers are difficult to manufacture, and the addition of alkali metals to such compositions should improve the quality of such fibers and simplify their production process.

Having identified the results described above, the applicants conducted tests on the manufacture of canvas on the production line in order to confirm the initially obtained results on shrinkage. Used the main composition containing:

SiO ₂ 72.5-74 wt.% CaO 24-26.5 wt.% MgO 0.4-0.8 wt.% Al ₂ O ₂ <0.3 wt.% La ₂ o ₃ 1.2-1.5 wt.%,

to which various amounts of Na ₂ O were added. A web with a density of 128 kg / m ³ and a thickness of ~ 25 mm was made. The results presented in Fig.7, showed a significant increase in the strength of the canvas with the addition of Na ₂ O.

These results relate to compositions containing La ₂ O ₃ as one of the components, but similar effects of alkali metal additions were found in the case of alkaline earth silicate fibers not containing La ₂ O ₃ as one of the components.

The inventors also investigated the properties of other alkaline earth silicate fibers containing mainly magnesium (magnesium silicate fibers) as the alkaline earth component, and the results are shown in Table 4.

The results presented in this table show that, while Na ₂ O and K ₂ O have, respectively, a small or large negative effect on shrinkage, Li ₂ O is unlikely to have any effect on shrinkage at all. However, this does not imply the absence of any influence whatsoever, and the inventors found that while fibers with Na ₂ O and K ₂ O were similar to fibers without such additives (coarse), the fiber with the addition of Li ₂ O was significantly more thin and better quality. At lower amounts of Na ₂ O and K ₂ O still lead to shrinkage, which is acceptable in most applications.

Table 4 Sample 04 MgO 01 04 MgO 02 04 MgO 03 04 MgO 04 Component Na ₂ O 0,0 0.5 0,0 0,0 MgO 20,0 19.1 19.6 18.3 Al ₂ O ₃ 1.7 2.0 1.8 1.7 SiO ₂ 77.6 77.5 77.8 78,2 K ₂ O 0,0 0,0 0,0 0,0 CaO 0.5 0.5 0.6 0.5 TiO ₂ 0.1 0.1 0.1 0.1 Fe ₂ O ₃ 0.5 0.5 0.5 0.5 Li ₂ O 0.3 % linear shrinkage 1150 ° C / 24 h 2,53 3.53 2,34 5.59 1250 ° C / 24 h 2.16 3.57 2,3 9.94 Solubility in static conditions for 24 hours (ppm) 297 on 331 on

The purpose of adding an alkali metal is to attempt to change the viscosity-temperature curve for alkaline earth silicate materials so as to provide a more useful operating range for these silicate materials. Figure 3 graphically presents the experimental curves of viscosity-temperature for:

• Sodium glass with a high content of sodium oxide having approximately the following composition in wt.%:

SiO ₂ 68 Na ₂ O 13,4 Cao 7.94 B ₂ O ₃ 4.74 MgO 2,8 Al ₂ O ₃ 2.66 Fe ₂ O ₃ 1.17 TiO ₂ 0.09 ZrO ₂ 0.08 Cr ₂ O ₃ 0.06

• alkaline earth silicate melt having approximately the following composition:

Cao 29th MgO 6% SiO ₂ 64.5 + others up to 100%

• the same alkaline-earth silicate melt, comprising respectively 1 wt.% Na ₂ O and 2 wt.% Na ₂ O as an additive.

The viscosity-temperature graph for high sodium sodium glass is a smooth line with increasing values with decreasing temperature.

For a well-known alkaline-earth silicate melt (SW), the viscosity is lower and then increases steeply at a critical temperature (this is shown in the graph as a slope, but this is an artifact of the graphing process, in reality it represents a much more drastic change).

The addition of Na ₂ O to this melt shifts this increase to lower temperatures.

This extends the working range of the melt in such a way that it becomes less dependent on temperature, and therefore, the range of acceptable conditions for the process of forming the fiber from the melt expands. Although the temperature of the melt flow is of great importance, the melt is rapidly cooled during the process of forming the fiber, so a wider range of production properties of the composition leads to an improvement in the process of forming the fiber. The addition of alkali metal oxides can also help stabilize the melt flow, so for a given set of conditions there is an amount that reduces the content of kings.

In addition, it has been suggested that, in small amounts, alkali metal oxides serve to suppress phase separation in alkaline earth silicate fibers.

Since alkaline earth silicate systems have a two-fluid region in their phase diagrams, the applicants have suggested that the addition of alkali metal oxides can move the melts outside the two-fluid region to a single-phase region.

Such an addition also has an effect on reducing the temperature of the melt flow, which may contribute to stability.

The effectiveness of these measures is also shown by the number of kings present in the finished material. In the process of forming the fiber, the melt droplets quickly accelerate (when they break away from the spinning wheel or are blown away by a gas stream) and form long “tails” that become fibers.

However, that part of the droplets that did not form fibers remains in the finished material in the form of particles, known in the industry as “kings”. Kings usually degrade the thermal properties of the insulation formed from such fibers, and therefore in industry they tend to reduce the number of kings.

Applicants found that the addition of small amounts of alkali metal to the melt has an effect on reducing the number of kings, and this is shown in Figure 4 for lanthanum-containing materials according to table 1, where it can be seen that the content of kings was reduced from ~ 51% to ~ 48% .

Similar effects apply to implant-free materials. Table 5 presents the analyzed compositions of some alkaline earth silicate fibers (with lower maximum application temperatures), made in accordance with the compositions according to WO93 / 15028, which were obtained by drawing from the melt at a flow temperature of 1380-1420 ° C using a pair of spinning dies cars.

Figure 5 presents the experimentally established content of the kings with the boundaries of permissible errors, showing the standard deviation from the mean. You can see that in the range from 0.35 to 1.5 wt.% Na ₂ O there is a statistically significant improvement in the content of kings, which is the result of this addition. In particular, a reduction in the content of kings by 3% with a content of sodium oxide of 0.35 wt.% Is significant.

Since there was no adverse effect on shrinkage at such levels of content (and in fact there is even a slight improvement), it can be seen that the addition of alkali metal oxides is useful in the preparation of such materials.

Table 5 Sample 04-C43-1 04C56-7 04C46-5 04C47-2 04C51-6 04C50-8 04C49-6 Component Na ₂ O 0.11 0.35 0.66 1.01 1.47 2.03 2.46 MgO 4.78 5.90 5.18 5.47 5.71 5.76 6.20 Al ₂ O ₃ 1,07 0.40 0.35 0.27 0.30 0.36 0.30 SiO ₂ 65.1 65.16 65.07 64.96 65.91 66.15 65.24 P ₂ O ₅ 0 0.00 0.00 0.00 0.00 0.00 0.00 K ₂ O 0.08 0.08 0.08 0,07 0,07 0,07 0,07 CaO 28.92 27.84 28.47 28.12 26.25 25.36 24.79 TiO ₂ 0.02 0.02 0,03 0.01 0.02 0,03 0.02 Cr ₂ O ₃ 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Mn ₃ O ₄ 0,03 0,03 0,03 0,03 0,03 0,03 0,03

Fe ₂ O ₃ 0.2 0.19 0.19 0.18 0.18 0.18 0.18 Zno 0 0.00 0.00 0.00 0.00 0.01 0.00 Sro 0.01 0.01 0.01 0.01 0.01 0.01 0.01 ZrO ₂ 0 0.00 0.00 0.00 0.00 0.00 0.00 Bao 0 0.00 0.00 0.00 0.00 0.00 0.00 HfO ₂ 0 0.00 0.00 0.00 0.00 0.00 0.00 Pbo on on on on on on on Sno ₂ on on on on on on on CuO on on on on on on on % linear shrinkage 1000 ° C /
24 h 1.42 1.33 1,54 4.18 1100 ° C /
24 h 1.39 1.20 1.77 4.85

The addition of alkali metal should take place in such quantities that it does not have an excessive adverse effect on other properties of the fiber (for example, shrinkage), but for different applications, the amount that is "excessive" will be different.

The fibers can be used for thermal insulation and can either form an insulation component (for example, with other fibers and / or fillers and / or binders), or can form the entire insulation. Fibers can be formed into insulation in the form of a cloth.

Although the initial study was primarily related to the addition of Na ₂ O to alkaline earth silicate fibers, applicants found that when Na ₂ O was used as an additive to fibers with a high calcium and low magnesium content, it tended to promote crystallization ( and, as a consequence, the powderiness of the fibers) after exposure to temperatures of ~ 1000 ° C. This can be seen in Fig. 8, on which the fibers a) -e) had the main compositions falling into the region:

SiO ₂ 72-75 wt.% CaO 22-26.5 wt.% MgO 0.4-1 wt.% Al ₂ O ₂ <0.3 wt.% La ₂ o ₃ 1.2-1.5 wt.%

The results show the effect on the appearance of the surfaces of the fibers a), b) and c) after exposure to a temperature of 1050 ° C for 24 hours on fibers containing increasing amounts of Na ₂ O (respectively, from ~ 0 to 0.5 wt.% And up to 1 , 06 wt.%). The results show that the fiber in which Na ₂ O is absent has a smooth appearance, which indicates a small crystallization, while an increase in the content of Na ₂ O leads to an increase in surface roughness, which indicates crystallization.

Conversely, d) and e) fibers showed that at 1100 ° C, a fiber containing ~ 0.5 wt.% K ₂ O is slightly different from a fiber free from K ₂ O, and begins to show a slight surface roughness only at 1150 ° C.

Table 6 presents the values of the thermal conductivity of paintings with an approximate density of 96 kg · m ^-3 , formed from fibers, the main ingredients of which are given there. The values of the specific thermal conductivity of these paintings are also presented in Fig.9. From the above data it can be seen that the addition of Na ₂ O and K ₂ O seems to lead to lower thermal conductivity of the paintings, which indicates an improvement in their insulating ability.

Table 6 Ca silicate cloth Mg silicate cloth Ca silicate with the addition of K ₂ O Ca silicate with the addition of Na ₂ O Na ₂ O 0.22 0 0 1.06 MgO 0.4 19.13 0.74 0.96 Al ₂ O ₃ 0.79 1,58 0.15 0.13 SiO ₂ 73.94 79.08 74.7 72.1 K ₂ O 0.06 0 0.75 0 CaO 22.69 0.25 22.3 24.5 TiO ₂ 0 0.06 0 0 Fe ₂ O ₃ 0.16 0.38 0.04 0 La ₂ o ₃ 2.07 on 1.36 1.26 Temperature (° C) Thermal conductivity (W · m ^-1 · K ^-1 ) 200 0.06 0.06 400 0.12 0.11 600 0.35 0.35 0.21 0.2 800 0.59 0.57 0.33 0.34 1000 0.9 0.85 0.49 0.52 1200 1.3 1,2 0.67 0.75

Thus, the applicants have identified additional benefits of using alkali metal oxides as additives to the material of alkaline earth silicate paintings, and a particular advantage when using potassium. In particular, for facilitating removal of sodium by crystallization of at least 75 mol.% Of an alkali metal is preferably potassium. More preferably at least 90%, even more preferably at least 95%, and even more preferably at least 99% of the alkali metal is potassium.

To test the combined effect of La ₂ O ₃ and K ₂ O on the properties of the fibers, some fibers were formed into canvases and tested for shrinkage at different temperatures [24-hour exposure at a specific temperature].

It was found that La ₂ O ₃ could be reduced in content and replaced with K ₂ O without significant deterioration of the shrinkage properties of materials, but this led to the onset of crystallization at lower temperatures than in the case of La ₂ O ₃ -containing materials. However, the partial replacement of La ₂ O ₃ with alumina alleviates this problem. Table 7 shows a number of tested materials, the temperature at which crystallization began, and the temperature at which the crystals reached a size of ~ 1 μm. All materials had a basic composition with approximately 73.1-74.4 wt.% SiO ₂ and 24.6-25.3 wt.% CaO, while the content of all other ingredients was less than 3% in total.

Structure The beginning of crystallization, ° C Crystal enlargement to ~ 1 mm, ° С CaO-SiO ₂ -La ₂ O ₃ (1.3%) 1100 1200 CaO-SiO ₂ -K ₂ O (0.75%) 1000 1100 CaO-SiO ₂ -K ₂ O (0.75%) - La ₂ O ₃ (1.3%) 1050 1150 CaO-SiO ₂ -K ₂ O (0.75%) - La ₂ O ₃ (1.3%) 1050 1150 CaO-SiO ₂ -K ₂ O (0.8%) - La ₂ O ₃ (0.4%) 1050 1200 CaO-SiO ₂ -K ₂ O (0.6%) - La ₂ O ₃ (0.15%) - Al ₂ O ₃ (0.94%) 1100 1200

Accordingly, in the preferred range of compositions include:

72% <SiO ₂ <79%

MgO <10%

13.8% <CaO <27.8%

Al ₂ O ₃ <2%

ZrO ₂ <3%

B ₂ O ₃ <5%

P ₂ O ₅ <5%

95% <SiO ₂ + CaO + MgO + Al ₂ O ₃ + ZrO ₂ + B ₂ O ₃ + P ₂ O ₅

M ₂ O> 0.2% and <1.5%,

where M is an alkali metal, at least 90 mol.% of which is potassium.

More preferably, the total content of SiO ₂ plus CaO> 95%, and in the preferred preferred range of compositions include

72% <SiO ₂ <75%

MgO <2.5%

24% <CaO <26%

0.5% <Al ₂ O ₃ <1.5%

ZrO ₂ <1%

B ₂ O ₃ <1%

P ₂ O ₅ <1%

M ₂ O> 0.2% and <1.5%,

where M is an alkali metal, at least 90 mol.% of which is potassium.

A particularly preferred range is:

SiO ₂ 74 ± 2%

MgO <1%

CaO 25 ± 2%

K ₂ O 1 ± 0.5%

Al ₂ O ₃ <1.5%

98% <SiO ₂ + CaO + MgO + Al ₂ O ₃ + K ₂ O.

And the preferred ranges described above may additionally include R ₂ O ₃ <0.5 wt.%, Where R is selected from the group Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y or mixtures thereof.

In the course of additional tests, another region of fiber compositions was established that gave good results. These fibers had the composition:

SiO = 67.8-70%

CaO = 27.2-29%

MgO = 1-1.8%

Al ₂ O ₃ = <0.25%

La ₂ O ₃ = 0.81-1.08%

K ₂ O = 0.47-0.63.

These fibers had high strength (80-105 kPa for the web with a thickness of ~ 25 mm and a density of ~ 128 kg / m ³ ) and a low content of kings (total content of ~ 41%).

The described fibers can also be used in other applications where alkaline earth silicate fibers are currently used (for example, as components of friction materials).

Claims (12)

1. Refractory alkaline earth silicate fibers obtained from a melt and containing an alkali metal, in which at least 75 mol.% Of the alkali metal is potassium, and the fibers have a composition, wt.%:
SiO ₂ <86
MgO <10
Al ₂ O ₃ <2
ZrO ₂ <3
B ₂ O ₃ <5
P ₂ O ₅ <5
95 <SiO ₂ + CaO + MgO + Al ₂ O ₃ + ZrO ₂ + B ₂ O ₃ + P ₂ O ₅
and contain M ₂ O, in which M is an alkali metal, and in which either
65 <SiO ₂
13.5 <CaO <27.5
72 <SiO ₂ + ZrO ₂ + B ₂ O ₃ + 5P ₂ O ₅ and
M ₂ O> 0.5, or
75 <SiO ₂
13.8 <CaO <27.8
75 <SiO ₂ + ZrO ₂ + B ₂ O ₃ + 5P ₂ O ₅ and
M ₂ O> 0.2. 2. The fibers according to claim 1, in which SiO ₂ > 75 wt.%. 3. The fibers according to claim 1, in which the amount of MgO is less than 2 wt.%. 4. The fibers according to claim 1, in which M ₂ About <1.5 wt.%. 5. The fibers according to claim 1, in which
97.5 wt.% <SiO ₂ + CaO + MgO + Al ₂ O ₃ + ZrO ₂ + B ₂ O ₃ + P ₂ O ₅ + M ₂ O. 6. The fibers of claim 1, further comprising
0.1 wt.% <R ₂ O ₃ <4 wt.%,
where R is selected from the group Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, or mixtures thereof. 7. Fibers according to any one of claims 1 to 6, in which at least 90 mol.% Alkali metal is potassium. 8. The fiber according to claim 7, in which at least 95 mol.% Alkali metal is potassium. 9. The fibers of claim 8, wherein at least 99 mol% of the alkali metal is potassium. 10. The fibers according to claim 1, having a composition, wt.%:
SiO ₂ 74 ± 2
MgO <1
CaO 25 ± 2
K ₂ O 1 ± 0.5
Al ₂ O ₃ <1.5
98 <SiO ₂ + CaO + MgO + Al ₂ O ₃ + K ₂ O. 11. Thermal insulation containing fibers according to any one of claims 1 to 10. 12. Thermal insulation according to claim 11 in the form of a web.

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