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HEATPROOF RIGID HEAT-INSULATED WARES ON THE BASE OF BASALT FIBER

1Indyra Mavljutova , 1 Grigorij Jakovlev , 2Jadvyga Keriene

1Izhevsk State Technical University, Studencheskaya St. 7 , Izhevsk, 426069, Russia. E-mail: gyakov@istu.ru

2Vilnius Gediminas Technical University, Saulėtekio ave. 11, LT-10223 Vilnius, Lithuania. E-mail: jadvyga.keriene@vgtu.lt

Abstract. In the market of building materials production of mineral wool hoard is presented particularly by the wares, made of glass fiber or slag wool with use of organic binding, which don’t meet modern requirements on eco-logical and fire safety. Therefore an actual problem is creation heat-insulated rigid and semi fixed plates with the op-erational properties, allowing to use them in industrial and civil building without causing damage to human health and environment, also capable to work at temperatures to 700 ºC and at the same time not to be exposed to thermal destruction. Low heat-resistance of known heat-insulated wares is explained by use of polymeric pitches as a binding component, which collapse at high temperature. In this work for heat-resistance increase were used salt solutions, ca-pable to provide the physical coherence of the fibers which is strengthened by chemical cooperation of used salts with a surface of mineral fibers. To prevent a corrosion of fibers was used the basalt ultra thin fiber which was impreg-nated with a solution of water-soluble salt on the basis of aluminum sulfate. Wares produced on the basis of a basalt fiber simultaneously were exposed to treatment by waterproof mixture on a silicone basis that allowed to give them water resistance. Received heat-insulated material can be used for manufacture of rigid and semi fixed products of in-creased strength, low heat conductivity and high durability.

Keywords: basalt fiber, aluminum sulfate, binding, heat-insulated material, “Hydrotex”, microstructure.

1. Introduction

At present all over the world there is a tendency to increase the production of heat insulators made of basalt fiber. This is determined by the growing number of heat and energy saving objects and by their better technical and economic characteristics comparing with those of other heat insulators.

Until recently heat insulation materials made of glass fiber and mineral slag wool were in high demand, but these materials have some drawbacks. First of all, this is glass dust emission at mechanical failure of heat insula-tion, prickliness of these fibers, low operating tempera-ture (under 400 °С), presence of a binder which gradually evaporates toxic gases (Keriene 2002). These materials are far from the necessary ecological cleanness. The life-time of the listed heat insulation materials is limited and they disintegrate in 10–15 years

The basalt mineral wool is an inorganic product, ob-tained by means of centrifuging the melt of basalt with dolomite under the form of delicate elastic fiber agglom-erations with open structure. Adding a binder (phenol formaldehyde thermal rigid), more products with differ-

ent form and different density are obtained surfaces (Сентяков and Тимофеев 2003).

Basalt heat insulation is heat and sound insulator made of natural raw materials. (Gaidučis et al. 2009). The main distinctive feature of basalt heat insulator is its low thermal conductivity based on low heat transferring by the atmospheric air, which forms heat insulating structure of the material together with fibrous basalt base. Such qualities allow to insulate both external and internal structural units.

Due to their excellent physical-chemical perfor-mances, the basalt mineral wool products are used for all types of heat insulating and sound reduction between -50 °C and 700 °C and 1000 °C (they keep their heat insu-lating capacity at best values up to 700 °C and up to 1000 °C at moderate values).

In the market of building materials production of mineral wool hoard is presented particularly by the wares, made of glass fiber or slag wool with use of organic bind-ing, which don’t meet modern requirements on ecological and fire safety (Буянтуев et al. 2007, Гусев et al. 2005). Therefore an actual problem is creation heat-insulated rigid and semi fixed plates with the operational proper-

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ties, allowing to use them in industrial and civil building without causing damage to human health and environ-ment, also capable to work at temperatures to 700 ºC and at the same time not to be exposed to thermal destruction (Keriene 2002).

The analysis of examined literature found that im-proving of thermal insulation properties of mineral wool slabs of increased rigidity on the basis of basalt fibers may be due to the use of another binding. Bindings with the ability to operate at higher temperatures than current thermal insulation materials are of greater interest (Du-brovskii1 and Makhova 2004). Traditionally used poly-mer-based binding destructs at high temperature, that’s why an operating temperature of product is reduced to 200–240 °С. To increase the heat resistance of mineral wool wares in the work water-soluble salt of aluminum sulfate used as a binder.

2. Materials and research methodologies

Using of basalt fibers as base material makes it pos-sible to obtain ecologically clean products which have increased operating ability, with high thermal perform-ance (Лашманов 2003). But there is a problem to obtain rigid goods because of low penetrating power of the ba-salt fiber canvas impregnated with bindings. For compo-sition preparation was used basalt fiber 16,4 micrometer in diameter. Was used basalt fiber from the field in Kon-dapoga (Republic of Karelia). Basalt has a composition with 45–55 % Si02, 2–6 % in total alkali oxides, 0.5–2 % Ti02, 5–13 % FeO, 5–12 % MgO, 10 % CaO and 14 % or more of A1203 (Lonnroth and Yue, 2009).

Form of binding and the way of its inclusion into the fiber is an important factor, determining the quality of fibrous materials.

Below are the investigation of physical and technical properties and structure of the mineral wool slabs of in-creased rigidity on the basis of basalt fibers, using water-soluble salts of aluminum sulfate as the binding. Alumi-num sulfate have an ability to dissolve in water and in the solution to cover the surface of basalt fibers with the formation of both adhesive and cohesive ties, providing the production of mineral wool slabs of increased rigidity.

Wares produced on the basis of a basalt fiber simul-taneously were exposed to treatment by waterproof mix-ture on a silicone basis that allowed to give them water resistance.

Microstructure analysis was carried out under an op-tical microscope company Leica DM 4000B and Digital Microscope “Dino-Lite”.

X-ray analysis in the study of source materials and tumors in the structure of consolidated compositions was carried out on general-purpose diffractometer DRON-3. In the subsequent data were processed manually using the graphical editor "Grapher".

Differential thermal analysis of basalt fibers bided by aluminum sulfate performed on thermal analyzer Diamond TG/DTA. Rate of rise in temperature was 10 °C per minute.

3. Result of research

From sources (Дубовый et al. 2005) it is known that aluminum sulfate in contact with the surface of basalt fibers forms chemical bonds, which determine the in-creased cohesion and provide creation of rigid mineral wool frame in heat insulation product.

In Figs 1 and 2 are shown the microstructures of ba-salt fibers before and after the inclusion of aluminum sulfate. It is evident that before the inclusion of aluminum sulfate fibers do not have a clutch with each other (Fig 1), and after the inclusion of the salt solution at the intersec-tion of fibers observed it’s wrapping by aluminum sulfate hydrate, which connects fibers (Fig 2). Obviously, at the dissolution of aluminum sulfate in water happens hy-drolysis of this salt with the formation of basic salts, alu-minum sulfate hydrate and free acid ions). Available in a solution of free sulfate anions SO4

2- act upon the surface of basalt fibers, forming sulfates of alkaline earth metals (calcium and magnesium) on the surface. It should be noted that since the process of interaction happens at room temperature, the formed compounds are found only on the surface layer of the fiber.

Fig 1. Microstructure of basalt fibers under an optical microscope before the inclusion of aluminum sulfate at 200-fold increase.

Fig 2. Microstructure of basalt fibers under an optical microscope after the inclusion of 25% solution of aluminum sulfate at 600-fold increase

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Chemical interactions does not confirmed by Х-ray phase analysis, carried out on the diffractometer DRON-3 (Figs 3, 4).

Fig 3. X-ray diffraction pattern of basalt fiber

The result of X-ray diffraction analysis of the basalt

fiber shows that fiber is represented an amorphous phase ("rump" in the 2θ = 16 – 38 °), and also shows, that in it is small amount of crystalline quartz. X-ray spectrum of basalt fiber with aluminum sulfate include an amorphous structure of basalt fiber and aluminum sulfate hydrate Al2(SO4)3·17H2O (4.48 Ǻ) (Лебединский and Шевчук 1971). The absence of reflections of calcium sulfate and magnesium sulfate in the X-ray spectrum confirm that the interaction with the sulfate ions is on the fiber surface and the number of compounds is not enough for reliable re-cording of the X-ray diffractometer.

Differential thermal analysis of basalt fibers bided by aluminum sulfate, shows presence of crystalline hy-drated water in aluminum sulfate, which is proved by endothermic effect (Fig 5) (Сахы et al. 2006). As the result of the first effect partly dehydrated Al2(SO4)3·17H2O at 120 °С turns into crystallohydrate with 5.5 water molecules. As a result of the second endo-thermic effect at 260 °С it turns into a barren salt Al2(SO4)3 (Горшков et al. 1994). As a result of endo-thermic effect at 800 °С aluminum sulfate Al2(SO4)3 is turned into aluminum oxide Al2O3.

Formed aluminum sulfate hydrate is soluble, that’s why to increase water resistance at preparing rigid prod-uct was added hydrophobic substance on the basis of organic silicon compound called “Hydrotex”.

Fig 4. X-ray diffraction pattern of basalt fibers with the addition of aluminum sulfate

Fig 5. DTA-TG diagrams of basalt fiber with the addition of aluminum sulfate

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This is an effective substance for surface treatment of building materials and construction to prevent water saturation, the appearance of efflorescence and fungi. It does not change the appearance and natural texture of material.

On Figs 6–9 we can see efficiency of hydrophobic additions. Without adding “Hydrotex” new formed alu-minum sulfate hydrate Al2(SO4)3·17H2O is unstable be-cause it have developed fibrous structure (Figs 6, 7), which is highly soluble in contact with water. When you add “Hydrotex” (Figs 8, 9) the surface of fibers, coated with new formations and secured by organic silicon com-pound, has a distinct membrane. This membrane prevents the dissolution of soluble binder compounds, it increases the water-proof products based on basalt fiber.

Fig 6. Microstructure of basalt fiber under an optical microscope with 600-fold increase after the inclusion of the concentrate solution of aluminum sulfate at the intersections of fiber

Fig 7. Microstructure of basalt fiber under an optical microscope with 600-fold increase after the inclusion of the concentrate solution of aluminum sulfate of a single fiber

A sample was tested on the thermal conductivity,

and its characteristics are given in Table 1. Thermal conductivity of the tested sample was

0.051 W/(m·K). It is higher than thermal conductivity of mineral wool slabs mark WJP – 200 (GOST 22950-95 – Mineral wool slabs of higher rigidity on synthetic bond) by 11%. But at the same time, the density of the tested

products higher by 86 %. This fact allow to say, that the relative thermal conductivity of products lower than at mineral wool mark WJP – 200.

Fig 8. Microstructure of basalt fiber under an optical microscope with 600-fold increase after the inclusion of the concentrate solution of aluminum sulfate with add-ing of “Hydrotex” before beginning of crystallization

Fig 9. Microstructure of basalt fiber under an optical microscope with 600-fold increase after the inclusion of the concentrate solution of aluminum sulfate with adding of “Hydrotex” after beginning of crystalliza-tion

Table 1. Characteristics of the sample, tested on the thermal conductivity

Name of index Units Significance Size of the sample mm 100×100×14 Mass of the sample g 58.7 Density of the sample kg/m3 419.3 Thermal conductivity W/(m·K) 0.051

Therefore, in further experiments when a mark will

reach the density of D200, evidently attainment of ther-mal conductivity will be lower than at the plate WJP – 200.

Conclusions

In this work for heat-resistance increase were used salt solutions, capable to provide the physical coherence

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of the fibers which is strengthened by chemical coopera-tion of used salts with a surface of mineral fibers.

It was empirically established that the strength of such composites can be increased by adding aluminum sulfate to a mineral-fiber mass, but the mechanism of this reinforcement is still incompletely clear. It is obvious that knowledge of this mechanism will offer new possibilities in the development of methods for controlled and auto-mated production of composites based on mineral fibers.

To prevent a corrosion of fibers was used the basalt ultra thin fiber which was impregnated with a solution of water-soluble salt on the basis of aluminum sulfate.

Received heat-insulated material can be used for manufacture of rigid and semi fixed products of increased strength, low heat conductivity and high durability.

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