RU2144906C1 - Inorganic fiber and method of preparation thereof - Google Patents

Abstract

FIELD: manufacture of inorganic fibers, soluble in physiological liquids. SUBSTANCE: described are inorganic fibers preparatory semiproducts of which have shrinkage of 3.5% or less when exposed at 126 C for 24 hours. Fibers have composition comprising SrO, Al₂O₃ and which is sufficient fiber-forming additive to form fibers, but not sufficient to increase shrinkage to more that 3.5 %. Fibers have preferable shrinkage of 3.5% or less when exposed for 24 hours and comprise, wt.%: SrO, 53.2-57.6; Al₂O₃, 30.4-40.1%; SiO₂, 5.06-10.1%. EFFECT: reduced shrinkage of the semiproduct. 18 cl, 3 tbl

Description

 The invention relates to artificial fibers of inorganic oxide. The invention also relates to products prepared from such fibers.

 Inorganic fibrous materials are well known and widely used for many purposes (for example, as thermal insulation or acoustic insulation in bulk, in the form of mats or cover, in the form of vacuum-formed forms, in the form of cardboard and paper formed in vacuum, and in the form of ropes, yarn or textile; as a reinforcing fiber for building materials, as a component of brake pads for vehicles). In most of these applications, the properties due to which inorganic fibrous materials are used require resistance to heat and often resistance to aggressive chemical environment.

 Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material, one of the forms of which is believed to be involved in respiratory disease.

 It is still unclear what is the causal mechanism that links some types of asbestos to the disease, but some researchers believe that this mechanism is mechanical and related to particle size. Asbestos with a critical particle size can penetrate into cells in the body and thus, through prolonged and repeated damage to the cell, have an adverse effect on health. Whether this mechanism is true or not, but regulatory authorities have required that any inorganic fiber product having a respiratory fraction be classified as unhealthy, regardless of whether there is any evidence to support such a classification. Unfortunately, for many applications that use inorganic fibers, there are no real substitutes.

 Thus, there is a need for inorganic fibers that will present the least possible danger (if any) and for which there are objective reasons to consider them safe.

 One direction in research was proposed, namely, that inorganic fibers would be made that were sufficiently soluble in physiological fluids so that their residence time in the human body was short; in this case, the damage would not have occurred or at least been minimized. Since the danger of an asbestos-related disease seems to depend very much on the duration of exposure with it, this idea seems reasonable. Asbestos is extremely insoluble.

 Since the intercellular fluid in nature is a saline (physiological) solution, the importance of dissolving fibers in saline has long been recognized. If the fibers are soluble in physiological saline, provided that the dissolved components are not toxic, the fibers should be safer than fibers that are insoluble. The shorter the fiber dwell time in the body, the less damage it can cause.

Such fibers are given as examples in earlier International Patent Applications of the applicant WO93 / 15028 and WO94 / 15883, which describe saline-soluble fibers used at temperatures of 1000 ^° C. and 1260 ^° C., respectively.

Another area of research suggests that hydratable fibers, which lose their fibrous nature in body fluids, may present a different path to “safe” fibers when the shape and size of the fibers are the cause of the damage. This route is described in European Patent Applications N 0586797 and N 0585547, the purpose of which is to provide compositions not containing silicon dioxide and which describe two compositions of calcium aluminate (one containing 50/50 wt.% Alumina / soda lime, and the other containing 63 / 30 wt.% Alumina / calcined lime with additives of 5% CaSO ₄ and 2% of other oxides). Such fibers hydrate easily with the loss of their fibrous nature. Asbestos is not hydrated and, apparently, retains its fibrous structure in body fluids effectively for an unlimited time.

It has been found that strontium aluminate compositions do not appear to form fibers when the products are from the melt, while such compositions including additives such as silicon dioxide do form fibers during melt blasting. Apparently, such fibers are hydrated like fibers of calcium aluminate and, in addition, exhibit potential for high temperature use. Formed in vacuum preforms (shapes) of some of these fibers exhibit shrinkage of 3.5% or less when exposed at 1260 ^o C for 24 hours; some show shrinkage of 3.5% or less when exposed at 1400 ^° C. for 24 hours and some even show shrinkage of 3.5% or less when exposed at 1500 ^° C. for 24 hours. Such fibers provide hydratable high temperature fibers useful in the above products.

Accordingly, this invention provides an inorganic fiber whose vacuum cast preform (shape) has a shrink of 3.5% or less when exposed at 1260 ^° C. for 24 hours, a fiber containing SrO, Al ₂ O ₃ and a sufficient amount of fiber forming additives for fiber formation, but insufficient (not so large) to increase shrinkage above 3.5%.

Preferably, the fiber-forming additive contains SiO ₂ and the constituents SrO, Al ₂ O ₃ and SiO ₂ comprise at least 90 wt.% (More preferably at least 95 wt.%) Of the fiber composition.

 The scope of this invention is clearly defined in the attached claims with reference to the following description.

 In the following discussion, in cases where saline-soluble fiber is mentioned, it should be understood that it is a fiber having a total solubility of more than 10 ppm (ppm) in saline when measured as described below, and preferably having higher solubility.

 The experimental results are described below with reference to tables 1, 2 and 3.

 Table 1 shows a number of compositions that have been melted and purged by conventional methods. Those compositions that are indicated as & did not form fibers to the desired degree, but formed a spherical powder. For each of these compositions shows the analyzed composition in wt. % (obtained using x-ray fluorescence analysis). If the number "<0.05" is given, it means that the corresponding component could not be detected.

Due to the nature of X-ray fluorescence measurements (which are sensitive to the environment), the total amount of material detected by this analysis can reach 100% or exceed 100%, and in this patent application (including in the description, claims and abstract) these numbers are not were normalized to 100%. However, for each composition, the total amount of the analyzed material is indicated and it can be seen that the deviation from 100% is small. In a column called "Relative wt.%", Wt. % SrO, Al ₂ O ₃ and SiO ₂ relative to the sum of these components. Unless the context otherwise indicates, any percentages indicated in this application are percentages obtained by X-ray fluorescence analysis, and not absolute percentages.

 Table 2 shows (in the same order as in Table 1) the shrinkage and solubility data for fiber-forming compositions. Solubility is expressed as parts per million in solution, as measured by the method described below.

All of the above compositions and including line A of Tables 1 and 2 inclusively contain 2.76 wt.% Or less SiO ₂ . It can be seen that most of these compositions did not form fibers. Some of these fibers include Na ₂ O in amounts of 2.46 wt.% Or more to promote fiber formation, but exhibit poor shrinkage characteristics at temperatures above 1000 ^o C (i.e., have a shrinkage of more than 3.5% when measured temperature).

One fiber (SA5 (2.5% K ₂ O / SiO ₂ )) containing 1.96% K ₂ O and 2.69% SiO ₂ has acceptable shrinkage at 1260 ^o C.

Thus, it can be seen that “pure” strontium aluminates do not form fibers, while by adding fiber-forming additives, for example SiO ₂ and Na ₂ O, fibers can be formed. The shrinkage characteristics of the obtained fibers depend on the additives used.

The fibers shown below line A and above and including line B have an SrO content of less than 35 wt.% And have poor shrinkage characteristics. The fibers shown below line B have an SrO content of more than 35 wt.% And, if measured, exhibit acceptable shrinkage at 1260 ^° C.

The fiber of line C contains 2.52 wt.% CaO and this, apparently, is detrimental to the performance at 1400 ^° C. The fibers shown below line D and above and on line E have an Al ₂ O ₃ content _of more than 48.8 wt. %, which, apparently, adversely affects the characteristics of the fibers at 1400 ^o C. The fiber below the line E has a SiO ₂ content _of 14.9 wt.%, which, apparently, is bad for the characteristics at 1400 ^o C (see below for the indicator at 1500 ^o C).

A further limited range of compositions (shown in bold in a column of 1400 ^° C.) tends to acceptable shrink at 1400 ^° C. These compositions lie below line C and above and on line D of Tables 1 and 2. Two fibers indicated in this range, which do not meet the shrinkage requirement of 3.5%, may simply be incorrect results.

Fibers lying below the C line and above the D line and on the D line were selected for relative wt.% SrO (as defined above), and it can be seen that compositions with a relative wt.% SrO greater than 53.7%, and less than 59.6% tend to have acceptable shrinkage at 1500 ^° C. A fiber in this region that does not have acceptable shrinkage at 1500 ^° C. is a fiber with a high SiO ₂ content (12.2 wt.% SiO ₂ ), which confirms the adverse effect of too high a content of SiO ₂ mentioned above.

Two fibers (SA5a and SA5aII) exhibit acceptable shrinkage at 1550 ^o C.

 In addition, it can be seen that some of these fibers exhibit very high solubilities and, thus, can provide usable difficult to process (stable) fibers that will dissolve in body fluids.

 All fibers showed hydration when introduced into aqueous fluids. Indeed, they tended to have some hydration in the formation of preforms that were used to test shrinkage. After 24 hours of solubility tests in physiological fluids, hydration was very pronounced. Hydration takes the form of visible dissolution and reprecipitation of crystals on the surface of the fibers, which leads to the loss of their fibrous nature.

 For some of the compositions, a dispersing and wetting agent (Troy EX 516-2 (Trade markof Troy Chemical Corporation)), which is a mixture of nonionic surfactants and chemically modified fatty acids, was used in the manufacture of the vacuum test preforms for testing. This was an attempt to reduce the exposure time with water and, consequently, the degree of hydration. From Table 3 it can be seen (Table 3 shows the same type of information as Table 2) that compositions that used a dispersant (indicated as "troy") tended to shrink more than an identical composition without a dispersant. It is assumed that this may be due to a partial hydration “closure” of the fibers together, so that any single fiber should have a shrinkage against stretching the supporting fibers along its length: such stretching can lead to thinning of the fiber rather than longitudinal shrinkage. In the case of using a dispersing agent, the fibers are free to shrink along their length.

 The following describes in detail methods for measuring shrinkage and solubility.

Shrinkage was measured using the proposed ISO standard ISO / TC33 / SC2 / N220 (equivalent to British Standard BS 1920, part 6.1986) with some modifications, taking into account the small size of the samples. The method in brief contains the manufacture of vacuum cast pre-blanks using 75 g of fiber per 500 cubic meters. cm 0.2% starch solution, in the device 120x65 mm. Platinum pins (approximately 0.5 mm in diameter) were placed separately at 4 corners in the form of a rectangle 100x45 mm. The longest lengths (L1 and L2) and diagonals (L3 and L4) were measured with an accuracy of 1 5 μm using a mobile microscope. Samples were placed in an oven and brought to a temperature 50 ^° C below the test temperature at a speed of 300 ^° C / h and at a speed of 120 ^° C / h for the last 50 ^° C to the test temperature and left for 24 hours. Shrinkage values are given as the average of 4 measurements.

 It should be noted that although this is a standard method for measuring fiber shrinkage, it has its inherent variability in that the final density of the preform can vary depending on the casting conditions. In addition, it should be noted that the fiber material will typically have a higher shrinkage than a preform made from the same fiber. Therefore, the figure of 3.5% mentioned in this application should be interpreted as a higher shrinkage in the final fabric of this fiber.

 Solubility was measured according to the following method.

 The fiber was first cut using a 10 mesh sieve. and the spherical powder was removed by hand sieving also through a 10 mesh sieve.

 The device for testing the solubility contained a vibration thermostatic water bath and the test solution had the composition shown in table. 4.

 The above substances were diluted to 1 liter with distilled water to form a saline solution similar to saline.

0.500 g, equal to 0.003 g of chopped fiber, was weighed into a plastic centrifuge tube and 25 ml (cm ³ ) of the above saline solution was added. The fiber and brine were shaken thoroughly and introduced into a vibration thermostatic water bath maintained at body temperature (37 ^° C ± 1 ^° C).

 The vibrator speed was set at 20 rpm.

 After 24 hours, the centrifuge tube was removed, the pop-up liquid was decanted and the liquid was passed through a filter (0.45 micron cellulose filter paper membrane [type WCN from Whatman Labsales Limited]) into a clear plastic bottle. Then the liquid was analyzed in one of two ways. The first method used was atomic absorption using a Thermo Jarrell Ash Smith - Hiefje II machine.

The working conditions were the same as those established in the earlier International Patent Applications of the applicant WO93,15028 and WO 94/15883. For SrO, the operating conditions were as follows:
WAVE LENGTH, (nm) 460.7
BAND WIDTH, 0
CURRENT, (mA) 12
FLAME, lean fuel
Strontium was measured relative to a standard solution for atomic absorption (Aldrich 970 μm / ml). Three standards were prepared to which 0.1% KCl was added (Sr [ppm] 9.7, 3.9 and 1.9). Usually, dilutions of 10 and 20 times were prepared to measure the Sr level in the sample. Then, SrO was calculated as 1.183xSr.

 All stock solutions were stored in plastic bottles.

 In the second method used (which, as was shown, gave results consistent with the results of the first method), the element concentrations were determined using inductively coupled plasma - atomic emission spectroscopy in accordance with the known method.

The above described allowed us to discuss the resistance to shrinkage of preforms exposed at 1260 ^° C. for 24 hours. This is the maximum temperature of fiber use. In practice, fibers are characterized by a maximum continuous temperature and a higher maximum exposure temperature. Typically, in industry, when selecting a fiber for use at a given temperature, a fiber is selected having a higher continuous use temperature than the temperature nominally required for the intended use. This is to ensure that any accidental increase in temperature does not damage the fibers. The difference between 100-150 ^o C. is quite common.

Applicants have not yet determined how many other oxides or other impurities will affect the characteristics of the fibers described above, and the appended claims allow, if the fiber-forming additive is SiO ₂ , up to 10 wt.% Materials other than SrO, Al ₂ O ₃ and SiO ₂ , although this should not be construed as limiting.

 Although the above description refers to the manufacture of fibers by blasting from a melt, this invention is not limited to blasting, but also covers drawing and other methods (technologies) in which the fibers are formed from the melt, and also includes fibers made in any other way.

Claims (15)

1. Inorganic fiber containing SrO and Al ₂ O ₃ , characterized in that the vacuum prefabricated fiber has a shrink of 3.5% or less when exposed at 1260 ^o C for 24 hours and the fiber has a composition of strontium aluminate, including SrO, Al ₂ O ₃ and a fiber-forming additive sufficient to form a fiber, but not so large as to increase shrinkage above 3.5% and when SiO _{2 is} present, the amount of SiO _{2 is} less than 14.9 wt.%. 2. The inorganic fiber according to claim 1, characterized in that the fiber-forming additive contains SiO ₂ and the components SrO, Al ₂ O ₃ and SiO ₂ comprise at least 90 wt.% Of the composition of the fiber. 3. The inorganic fiber according to claim 2, characterized in that the components of SrO, Al ₂ O ₃ and SiO ₂ comprise at least 95 wt.% The composition of the fiber.  4. Inorganic fiber according to any preceding paragraph, characterized in that it contains 35 wt.% Or more SrO. 5. Inorganic fiber according to any preceding paragraph, characterized in that it contains SrO 41.2 - 63.8 wt.% And Al ₂ O ₃ 29.9 - 53.1 wt.%. 6. The inorganic fiber according to claim 5, characterized in that it contains more than 2.76 wt.% SiO ₂ . 7. Inorganic fiber according to any one of the preceding paragraphs, characterized in that the vacuum preform has a shrinkage of 3.5% or less when held at 1400 ^o C for 24 hours 8. The inorganic fiber according to claim 7, characterized in that the amount of Al ₂ O ₃ is 48.8 wt.% Or less. 9. Inorganic fiber according to any one of the preceding paragraphs, characterized in that the vacuum preform has a shrink of 3.5% or less when holding at 1500 ^o C for 24 hours 10. The inorganic fiber according to claim 9, characterized in that the mass% SrO relative to the total amount of SrO plus Al ₂ O ₃ plus SiO ₂ is in the range from more than 53.7 wt.% To less than 59.6 wt.%. 11. Inorganic fiber according to claim 10, characterized in that it contains, by weight. %:
SrO - 53.2 - 57.6
Al ₂ O ₃ - 30.4 - 40.1
SiO ₂ - 5.06 - 10.1
12. Inorganic fiber according to any one of the preceding paragraphs, characterized in that it contains Na ₂ O in an amount of less than 2.46 wt.%. 13. Inorganic fiber according to any one of the preceding paragraphs, characterized in that the vacuum preform has a shrinkage of 3.5% or less when holding at 1550 ^o C for 24 hours 14. The inorganic fiber according to item 13, characterized in that it contains, by weight. %:
SrO - 53.2 - 54.9
Al ₂ O ₃ - 39.9 - 40.1
SiO ₂ - 5.06 - 5.34
15. Inorganic fiber according to any preceding paragraph, characterized in that it is soluble in saline fiber.  16. Inorganic fiber according to any preceding paragraph, characterized in that it is a hydratable saline-soluble fiber. 17. A method of producing fibers from a melt, characterized in that the melt contains predominantly SrO and Al ₂ O ₃ , to which minor amounts of SiO ₂ are added to form the fibers.

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