Method for producing continuous basalt fibre

The proposed inventions pertain to technology of continuous inorganic fibres manufacturing, preferably, by way of drawing from melted minerals. Such continuous inorganic fibres may be used in production of heat-resistant threads, rovings, cut fibres, fabrics, composition materials and products based on such materials.

Production of fibrous materials based on mineral, glass and other fibres is intensively developing in CIS and other countries. Nevertheless, the production volume increase is restrained by growing technical demands to such materials and also by the deficit of raw materials.

Meeting the increasing needs in fibrous materials is predetermined by drastic increase of their quality. With a view to the above, in CIS prevailing production type is production of basalt fibres and materials based on such fibres with rocks (basalt, gabbro-diabases, porphyrites, etc.) used as one-component raw material.

Using basalt fibres as a raw material enables production of materials replacing asbestos, metal, wood, etc.

The most similar to the proposed composition in terms of a number of essential features is the composition for production of continuous basalt fibre containing the mixture of silicon (SiO₂), aluminium (Al₂O₃), titan (TiO₂), iron (Fe₂O₃ and FeO), calcium (CaO), magnesium (MgO), manganese (MnO) oxides and also admixtures (RF Patent <patcit id="pcit0001" dnum="WO02118300A"><text>No. 02118300</text></patcit>, IPC 6 C03B 37/02, 1998). Average elements of the initial composition are presented in Table 1. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="11"><colspec colnum="1" colname="col1" colwidth="20mm" /><colspec colnum="2" colname="col2" colwidth="13mm" /><colspec colnum="3" colname="col3" colwidth="13mm" /><colspec colnum="4" colname="col4" colwidth="15mm" /><colspec colnum="5" colname="col5" colwidth="15mm" /><colspec colnum="6" colname="col6" colwidth="13mm" /><colspec colnum="7" colname="col7" colwidth="13mm" /><colspec colnum="8" colname="col8" colwidth="13mm" /><colspec colnum="9" colname="col9" colwidth="13mm" /><colspec colnum="10" colname="col10" colwidth="15mm" /><colspec colnum="11" colname="col11" colwidth="13mm" /><thead><row><entry morerows="1" align="center" valign="top">Comp. No.</entry><entry namest="col2" nameend="col11" align="center" valign="top">Average elements of the initial composition</entry></row><row><entry align="center" valign="top">Na</entry><entry align="center" valign="top">Mg</entry><entry align="center" valign="top">Al</entry><entry align="center" valign="top">Si</entry><entry align="center" valign="top">K</entry><entry align="center" valign="top">Ca</entry><entry align="center" valign="top">Ti</entry><entry align="center" valign="top">Mn</entry><entry align="center" valign="top">Fe</entry><entry align="center" valign="top">P</entry></row></thead><tbody><row><entry align="center">1</entry><entry align="char" char=".">6.325</entry><entry align="char" char="." charoff="14">1.970</entry><entry align="char" char="." charoff="25">17.833</entry><entry align="char" char="." charoff="25">55.903</entry><entry align="char" char="." charoff="14">4.558</entry><entry align="char" char="." charoff="14">4.672</entry><entry align="char" char="." charoff="14">1.582</entry><entry align="char" char="." charoff="14">0.160</entry><entry align="char" char="." charoff="25">6.997</entry><entry align="char" char="." charoff="14">0.000</entry></row><row><entry align="center">2</entry><entry align="char" char=".">5.083</entry><entry align="char" char="." charoff="14">7.932</entry><entry align="char" char="." charoff="25">14.127</entry><entry align="char" char="." charoff="25">46.154</entry><entry align="char" char="." charoff="14">2.320</entry><entry align="char" char="." charoff="14">4.697</entry><entry align="char" char="." charoff="14">1.343</entry><entry align="char" char="." charoff="14">0.396</entry><entry align="char" char="." charoff="25">16.461</entry><entry align="char" char="." charoff="14">1.512</entry></row><row><entry align="center">3</entry><entry align="char" char=".">5.877</entry><entry align="char" char="." charoff="14">2.773</entry><entry align="char" char="." charoff="25">17.493</entry><entry align="char" char="." charoff="25">53.716</entry><entry align="char" char="." charoff="14">3.923</entry><entry align="char" char="." charoff="14">4.867</entry><entry align="char" char="." charoff="14">1.299</entry><entry align="char" char="." charoff="14">0.098</entry><entry align="char" char="." charoff="25">8.276</entry><entry align="char" char="." charoff="14">1.680</entry></row><row><entry align="center">4</entry><entry align="char" char=".">4.357</entry><entry align="char" char="." charoff="14">3.187</entry><entry align="char" char="." charoff="25">17.660</entry><entry align="char" char="." charoff="25">52.501</entry><entry align="char" char="." charoff="14">3.927</entry><entry align="char" char="." charoff="14">5.515</entry><entry align="char" char="." charoff="14">1.701</entry><entry align="char" char="." charoff="14">0.155</entry><entry align="char" char="." charoff="25">8.541</entry><entry align="char" char="." charoff="14">1.953</entry></row><row><entry align="center">5</entry><entry align="char" char=".">4.404</entry><entry align="char" char="." charoff="14">3.470</entry><entry align="char" char="." charoff="25">15.324</entry><entry align="char" char="." charoff="25">51.606</entry><entry align="char" char="." charoff="14">2.810</entry><entry align="char" char="." charoff="14">7.681</entry><entry align="char" char="." charoff="14">1.852</entry><entry align="char" char="." charoff="14">0.185</entry><entry align="char" char="." charoff="25">9.223</entry><entry align="char" char="." charoff="14">2.944</entry></row></tbody></tgroup></table></tables>

The drawback of the described composition is insufficient strength of continuous fibres produced. This is due to high upper limit of crystallization of the composition (1245 to 1290°C), which prevents stable process of continuous basalt fibre formation.

In terms of a number of essential features, the closest method to the proposed one is the method of continuous basalt fibres production comprising operations of the crushed composition loading into the melting furnace, melting, melt homogenization, subsequent stabilization of the melt in the melting furnace feeder, drawing, lubrication and winding the fibre onto the reel (RF <patcit id="pcit0002" dnum="WO02118300A"><text>Patent No. 02118300</text></patcit>, IPC 6 C03B 37/02, 1998).

The drawback of the described method is insufficient strength and chemical stability of continuous fibres produced in this way, which is due to narrow temperature range of fibres forming. Difference between fibre forming temperature and upper crystallization limit is 70 to 100°C on the average, which causes instability of continuous fibre drawing due to primary crystallization occurring is such temperature range. Such primary crystallization causes thread breakages. As seen from the practice, the temperature of forming should be at least 110°C above upper crystallization limit.

The proposed inventions aim at providing the means for obtaining stronger and chemically more stable fibres by way of creating the conditions for decreasing the number of defects on the fibre surfaces.

This objective is attained by the proposed composition for production of continuous basalt fibre containing the mixture of silicon (SiO₂), aluminium (Al₂O₃), titan (TiO₂), iron (Fe₂O₃ and FeO), calcium (CaO), magnesium (MgO), manganese (MnO) oxides and admixtures and also, <i>according to the present invention,</i> this composition further contains potassium (K₂O), sodium (Na₂O), barium (BaO) oxides with the following components ratio (in mass %): <tables id="tabl0002" num="0002"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="22mm" /><colspec colnum="2" colname="col2" colwidth="24mm" /><tbody><row><entry>Al₂O₃</entry><entry>15.90 - 18.10</entry></row><row><entry>TiO₂</entry><entry>0.75 - 1.20</entry></row><row><entry>Fe₂O₃+FeO</entry><entry>7.51 - 9.53</entry></row><row><entry>CaO</entry><entry>6.41 - 8.95</entry></row><row><entry>MgO</entry><entry>2.50 - 6.40</entry></row><row><entry>K₂O</entry><entry>1.60 - 2.72</entry></row><row><entry>Na₂O</entry><entry>3.30 - 4.10</entry></row><row><entry>P₂O₅</entry><entry>0.23 - 0.50</entry></row><row><entry>SO₃</entry><entry>0.02-0.15</entry></row><row><entry>MnO</entry><entry>0.12 - 0.21</entry></row><row><entry>BaO</entry><entry>0.05 - 0.19</entry></row><row><entry>admixtures,</entry><entry>up to 1.00</entry></row><row><entry>SiO₂</entry><entry>the rest</entry></row></tbody></tgroup></table></tables>

The objective is also attained by the proposed method, which, like the known method of continuous basalt fibres production, comprises operations of the crushed composition loading into the melting furnace, melting, melt homogenization, subsequent stabilization of the melt in the melting furnace feeder, drawing, lubrication and winding the fibre onto the reel, and, <i>according to the invention,</i> the composition is held in alkaline solution during 15 to 20 minutes, then washed by running water during 20 to 30 minutes and loaded into the melting furnace after such washing.

The feature of the proposed method is the use of sodium hydroxide (NaOH) and potassium hydroxide (KOH) solution with (0.1...0.5) N concentration as the alkaline solution.

The invention idea is in creation of conditions for obtaining melt with pH 5...7. This is because our experiments show that such melt pH ensures producing of homogenous chemical composition. Acidic melt components react with alkaline components and give chemically neutral melt. Gas microbubbles do not appear in such relatively neutral melt during cooling, unlike conventional rock melts. Thus, the number of surface defects on the fibres produced is much less, therefore, diameter of elementary fibres may be smaller without compromising the strength. Adding alkali metals oxides to the known composition of the furnace charge in the above amount promotes producing of chemically neutral melt composition. Thus, with K₂O and Na₂O in amount over 4.1 mass % and less than 1.6 mass % the melt acidity is changed causing chemical reactions in the melt and microbubbles generation. BaO presence in the melt in amount of 0.05 to 0.19 mass % as well as other admixtures presence increases melt diathermancy, thus forming interval becomes larger and conditions of fibre forming are improved, surface defects become less, and conditions for compressed surface layer are created, while such compressed layer prevents stretching forces appearance under bending loads. The latter is attained by changing the composition of the surface layer by way of substituting alkali ions with a big radius by ions having smaller radius and vice-versa. The oxides listed among the admixtures are present in the composition of the fibre being strengthened for ion exchange purposes. In addition, for example, presence of zinc oxide (ZnO) in the proposed composition as an admixture results in formation of acid resistant solid solution together with aluminium oxide (Al₂O₃). Acid resistance is also improved by phosphorus oxides and other admixtures, i.e. oxides of the elements of the III and V groups in Mendeleev's Periodic Table of the Elements. By experimental way the authors have found that the substances with structures similar to precipitates structures are formed on the fibres obtained. This is occurring in case of treating the furnace charge of the proposed composition by alkaline solution prior to its loading to the melting furnace. Such structures essentially increase the fibres surface strength.

Also, by way of experiments, the authors have found the processing mode parameters for the proposed composition, beginning from its loading to the melting furnace until continuous basalt fibres production. Thus, in case of holding the proposed composition (furnace charge) in alkaline solution for less than 15 minutes, the effect of the proposed method is not practically visible. Holding the furnace charge in alkaline solution for more than 20 minutes is not justified economically.

Furnace charge is washed in the running water during 20 to 30 minutes, because this time is enough to remove the alkaline solution which otherwise may cause corrosion of the melting furnace walls.

The proposed composition contains the following admixtures (mass %): <tables id="tabl0003" num="0003"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="41mm" /><colspec colnum="2" colname="col2" colwidth="28mm" /><tbody><row><entry>Cr₂O₃</entry><entry>0.010 - 0.0315</entry></row><row><entry>Co₂O₃</entry><entry>0.0005 - 0.0047</entry></row><row><entry>NiO</entry><entry>0.0079 - 0.0091</entry></row><row><entry>CuO</entry><entry>0.0065 - 0.0087</entry></row><row><entry>ZnO</entry><entry>0.0083 - 0.0159</entry></row><row><entry>Ga₂O₃</entry><entry>0.0029 - 0.0051</entry></row><row><entry>Rb₂O</entry><entry>0.0049 - 0.0095</entry></row><row><entry>SrO</entry><entry>0.0585 - 0.0923</entry></row><row><entry>ZrO₂</entry><entry>0.0127 - 0.0173</entry></row><row><entry>Nb₂O₅</entry><entry>0.0011 - 0.0019</entry></row><row><entry>V₂O₅</entry><entry>0.029 - 0.043,</entry></row><row><entry>F-containing compounds</entry><entry>0.06 - 0.11</entry></row><row><entry>Cl-containing compounds</entry><entry>0.0270 - 0.0520,</entry></row></tbody></tgroup></table></tables> their amount practically has no effect on the quantity of structures similar to precipitates appearing on the fibre surfaces.

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) solutions have approximately the same chemical characteristics. But the furnace charge material structure is not homogenous. Thus, some of its elements react more actively with sodium hydroxide (NaOH), while others react more actively with potassium hydroxide (KOH). The amounts of sodium hydroxide (NaOH) and potassium hydroxide (KOH) in solution are approximately the same. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) solution concentration is (0.1...0.5)N. Using more concentrated solutions is not economically justified.

Implementation of the proposed inventions results in producing of the stronger continuous basalt fibre. The continuous fibres so obtained also possess higher heat and acid resistance.

The method is realized as follows.

The above composition, ground to dispersion level of 1.0...5.0 mm, was charged into a tank filled with sodium hydroxide (NaOH) and potassium hydroxide (KOH) solution with concentration 0.5 N and the temperature +20°...+60°C. Such ground composition was held in the solution during 15 to 20 minutes under continuous agitation. Then the solution was poured out and the ground charge was washed by running water during 30 minutes. The charge was then dried by air forced through the charge. Treated and dried charge was loaded into the melting furnace with temperature set at 1400-2000°C. Melt was produced from the charge. This melt was left to stay for some time for homogenization. Homogenized melt was fed to fibre forming zone, which is a feeder and spinnerets. The temperature in the forming zone was maintained at the level exceeding crystallization temperature of the melt produced. The melt came out of the spinnerets in the form of drops forming cones, which separated from the spinnerets after some increase in mass and formed the fibres. Fibres drawing was performed without stops and delays. To prevent mutual friction and adhesion of the fibres, they were lubricated on the roller lubricating unit. Continuous fibre forming was stable.

Table 2 shows that the upper crystallization limit (T_ucl) was lower for the proposed composition compared to the prototype, while fibre forming interval was larger.

Also, experimental evaluation of chemical resistance of the fibres produced using hydrochloric acid (HCl) solution proved that these fibres possess higher acid resistance than the fibres produced according to prototype method.

The continuous fibres chemical resistance to acid and alkali solutions was determined by measuring the mass loss from the 5000 sq.cm surface after 3 hours of boiling (Table 3). <tables id="tabl0004" num="0004"><table frame="all"><title>Table 2</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="54mm" /><colspec colnum="2" colname="col2" colwidth="56mm" /><colspec colnum="3" colname="col3" colwidth="56mm" /><thead><row><entry morerows="1" align="center" valign="middle">Melt and fibres technological properties</entry><entry namest="col2" nameend="col3" align="center" valign="middle">Composition of fibre</entry></row><row><entry align="center" valign="middle">produced according to the proposed method</entry><entry align="center" valign="middle">produced according to the prototype method</entry></row></thead><tbody><row><entry valign="middle">Upper crystallization limit temperature, T_ucl, °C</entry><entry align="center" valign="middle">1210 - 1230</entry><entry align="center" valign="middle">1240 - 1290</entry></row><row><entry valign="middle">Forming temperature interval, °C</entry><entry align="center" valign="middle">1320 - 1430</entry><entry align="center" valign="middle">1350 - 1430</entry></row><row><entry valign="middle">Elementary fibre average diameter, µm</entry><entry align="center" valign="middle">7 ± 2</entry><entry align="center" valign="middle">8.5</entry></row><row><entry valign="middle">Tensile strength, MPa</entry><entry align="center" valign="middle">2250 - 3200</entry><entry align="center" valign="middle">2240 - 3110</entry></row></tbody></tgroup></table></tables><tables id="tabl0005" num="0005"><table frame="all"><title>Table 3</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="31mm" /><colspec colnum="2" colname="col2" colwidth="67mm" /><colspec colnum="3" colname="col3" colwidth="68mm" /><thead><row><entry align="center" valign="middle">Medium</entry><entry align="center" valign="middle">Resistance of fibres produced from the proposed composition, %</entry><entry align="center" valign="middle">Resistance of fibres produced from the prototype composition, %</entry></row></thead><tbody><row><entry>2N HCL solution</entry><entry align="char" char=".">97.1</entry><entry align="char" char=".">91.0</entry></row><row><entry>2N NaOH solution</entry><entry align="char" char=".">98.2</entry><entry align="char" char=".">96.8</entry></row><row><entry>Ca(OH)₂</entry><entry align="char" char=".">99.7</entry><entry align="center">-----</entry></row></tbody></tgroup></table></tables>

Table 3 shows that continuous fibres produced from the proposed composition and by the proposed method possess high resistance to both acids and saturated alkaline solution (Ca(OH)₂). Therefore they may be widely used, for example, in filter materials, composite reinforcing fillers, etc. resistant to aggressive media.

Information sources:

<ul id="ul0001" list-style="none" compact="compact"><li>1. <patcit id="pcit0003" dnum="RU2018491C1"><text>RU 2018491 C1</text></patcit>, 28.02.79</li><li>2. <patcit id="pcit0004" dnum="SU649670A"><text>SU 649670 A</text></patcit>, 03.03.79</li></ul>