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Continuous Mineral Fibers

#A-1067


Use of the Armenian Rocks in Manufacturing of Continuous Mineral Fibers

Tech Area / Field

  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
3 Approved without Funding

Registration date
13.08.2003

Leading Institute
NPF "Stone & Silicates", Armenia, Yerevan

Collaborators

  • Rheinisch-Westfalische Technische Hochschule / Institut fuer Gesteinshuttenkunde, Germany, Aachen\nUniversity of Aveiro, Portugal, Aveiro\nGeosciences Management Institute, Inc., USA, NV, Boulder City\nTaiyo Yuden Co., Ltd, Japan, Gunma-Gun\nUniversita' Degli Studi di Modena / Dipartimento di Chimica, Italy, Modena\nArgonne National Laboratory (ANL), USA, IL, Argonne\nPennsylvania State University / Materials Research Institute, USA, PA, University Park\nAalborg University / Department of Production, Denmark, Aalborg\nGeorgia Institute of Technology / School of Polymer, Textile & Fiber Engineering, USA, GA, Atlanta\nUniversity of Trento / Department of Materials Engineering and Industrial Technologies, Italy, Trento

Project summary

The purpose of the Project is to investigate rocks of Armenia for their further application in manufacture of continuous mineral fibers (CMF).

Continuous glass fibers are widely applied in various fields of industry and, first of all, they are used as reinforcing component in manufacture of polymer composite materials such as glass plastics.

Owing to the rapid growth of the glass fiber industry supply of raw materials fails to cover the growing demand. This is true, in particular, for standard alumoborosilicate E-glass production due to the lack of boric acid and alum. This is why a search for new and more available sources of raw materials and the ways of their application in manufacture becomes a necessity and with this respect rocks proved to be the ones.

Meanwhile, certain technical complications, conservatism of the continuous fiber industry as well as particularly strict requirements to the properties of the melt have continually limited and restrained application of rocks as single-component raw materials in fiber manufacture. Thus, there existed an opinion that a range of viscosity of a melt had to be 102,2-102,6 Pa-s at Т = 1240-1250 °С; the temperature of upper limit of crystallization - not more than 1150 °С; diameter of elementary fibers that provides sufficient durability and ability for textile processing - not more than 5-7 mcm. Properties of rocks melts do not satisfy these requirements: the temperature of higher limit of crystallization lies within the range 1200-1250 °С; at the same time higher temperature (1320-1360 °С) is required to reach necessary working viscosity.

However, an existing belief that fiber durability depends to large extend on its diameter has changed recently. As investigations revealed, durability of fibers first of all depends on the conditions of processing, in particular, on increased temperature and speed of cooling of mould zone (low inclination of a melt to crystallization is taken for granted). Practically no correlation between durability of fibers and their diameter was observed when processing was conducted at certain optimal conditions.

As it follows from various publications, at certain conditions of high-temperature processing and optimal speed of cooling, fibers of durability 5-6 GPa can be manufactured from magnesium-alumosilicate and calcium-aluminate glasses, which do not contain SiO2 and have high inclination to crystallization. This indicates that potential reserves of durability of fibers of various chemical composition and structure, including those manufactured from rocks, are great and that high temperature regimes of moulding should not prevent manufacturers from their Industrial mastering. In general, information on application of rocks in manufacture of continuous fibers is scarce. There are a few references about manufacture of basalt continuous fibers and goods manufactured on their base and they concern Russia, the Ukraine and the experimental-industrial plant in Armenia. The latter has a capacity of 35 ton per year and was constructed in 1990-1991 under the order of the military industry complex of the USSR. Our group represents the plant and participated in its construction and start up. We have developed and manufactured experimental lots of basalt rowing fabric and basalt linen, which are analogues to glass fabrics and glass linen.

Moreover, our laboratory studies revealed that it is possible to widen the raw material range for manufacture of continuous fibers by application of rocks other than basalt. We would like to mention that Armenia disposes abound source of tuffs, volcanic scoria and perlites. Reserves of basalts, andezites, andezito-datsites, etc., are tremendous here.

As a criterion for assessment of applicability of rocks for continuous fiber manufacture we suggest to use (МеO + MeI2O)/(Al2O3 + Fe2O3) ratio, where Me – Ca, Mg; MeI – Na, K and [O]/[Si + 0,75Al + 0,75 Fe] is the coefficient of anions structure (CAS). The ratio (МеO + MeI2O)/(Al2O3 + Fe2O3) must be і1 so as all Аl3+ and Fe3+ ions were in tetrahedral surrounding within the glass structure. We have found that this condition is actual for rocks and the given above ratio for basalts and ores close to them makes 1.2-1.5, for tuffs – 1.02-1.19, for volcanic scoria – 1.48. These values indicate to the high level of space packing up of anionic frame of rock melt and the ability to transfer into the glass state. On the other hand, specification of the composition and anionic structure of the melt by means of the CAS provides a very convenient tool for a search for new recipes of non-crystallizing melts capable of overcooling and glass forming. Investigations show that melts with CAS = 2.2-2.4 have viscosity not more than 5 Pa-s at 1500 °С. They fuse well and form homogenous glasses during slow cooling. For basalts and ores close to them CAS = 2.14-2.19, and for volcanic scoria CAS = 2.26-2.29. To compare with, in alumoborosilicate glass, which is widely used in manufacture of continuous fibers, CAS = 2.32 and the ratio of the sum of modifiers to the sum of oxides of «conditional» glass-formers is equal 2.8. Comparison of the indices for E-glass and for the glass made from rocks suggests that the latter can be used for manufacture of fibers. This suggestion is in full agreement with the results of our resent studies, which for the first time went to prove that it is possible to manufacture continuous fibers from the rocks different from basalts.

A well-established by our group fact that volcanic scoria, andezito-dacites as well as perlites with improved composition can be applied as single-component raw material in the production of continuous mineral fibers provides wide prospective for material science, in particular, in the field of development of new fiber materials. Thus, we should point out some certain advantages of application of these materials compared to that of basalt rocks. Ordinary basalts are rather refractory full-crystalline ores as a rule. At the same time a substantial part of andezito-dacites mass is made up of volcanic glass; in tuffs, perlites and volcanic scoria glass content reaches up to 90-95% and, therefore, energy consumption at melt-making based on them is considerably lower. Besides, melts of volcanic scoria, in particular, have lower upper margin of crystallization. This allows for fibers forming at relatively low temperatures (compared to basalts) and diminishes the tear and wear of very expensive equipment of fiber moulding unit.

Particularity of chemical compound as well as relatively high temperature regime of moulding of continuous fibers made from volcanic scoria, andezito-dacites and others allow for predicting creation of a new generation of fibers with higher exploiting parameters. We are currently aiming at obtaining of fibers with alkali resistance not lower than 90% (estimated at three hours’ boiling in 2 mol/l NaOH solution), stretching durability 2.2-2.5 GPa, stretching elasticity module of 90 GPa, with the diameter of elementary fibers varying between 9-16 mcm and with longer expiry term when exploiting at 500-550 °С.

We have determined that rock melts have rather high indices of surface stretching (s). It is possible to decrease the latter and simultaneously regulate the viscosity of the melt (h) within a wide range 5-100 Pa-s by introducing mineralizing additives. This also allows for keeping up with the demanded value of the ratio h/s, or otherwise preserving the fiber forming ability at the demanded level, and implies that the developed compositions and the conditions of fiber forming should produce fibers that are capable of lixiviation in acids, of forming high silica fibers containing 95-97% SiO2 and are close to the fibers made from quartz glass with respect to their heat-protection, dielectric properties and chemical stability. Fibers with the designed volume mass of 100-120 kg/m3 will have heat conduction coefficient of approximately 0.078-0.080 W/(m-K) at 250 °C and 0.120-0.80 W/(m-K) at 450 °С with the upper limit of application of 1200 °С. Owing to these characteristics they can be used in heat-protection compositions, manufacture of heat blow restraining screen, heat resistance insulation and aggressive media filtration. Besides, owing to the particularity of the manufacturing technology silica fibers have porous structure, which allows for their application in production of highly heat-resistant sorbents.

Let’s consider the economy aspect of rocks application in manufacture of continuous fibers.

Experience of our experts, Project participants, in manufacture of continuous basalt fibers on the experimental plant suggests that manufacture of fibers based on rocks compared to that of E-glass is economically more feasible. We can claim that the cost of production based on rocks will decrease for 30-35%. Here we give some data to substantiate our opinion:

– As distinct from glass batch, demanding high temperatures (1550 °C and higher) for glass melting, rocks present physical-chemical system where silicate formation processes are completed and glass-forming process should be considered as a result of melting (1180-1380 °С). The temperature 1450 °C is sufficient for the melt degassing and for homogenization stage.

– Continuous glass fibers are traditionally manufactured in two stages: the first stage is making semi-fabricate (glass balls) and the second stage is melting of the latter; the technology of fiber manufacture from rocks is a single-stage process, which allows for cutting consumption of thermal energy for about 50%.

– One ton of batch for manufacture of glass fibers costs about 250-260 US $, while the raw material for production of continuous fiber based on rocks is the waste of stone-mining and stone-processing and the cost is only determined by transportation expenses.

We would also like to mention another advantage of application of rocks for continuous fiber manufacture. On the one hand, materials such as boric acid, soda, sodium sulfate, and spar used in glass butch are rather expensive. On the other hand, due to their volatility, cost of losses of those materials during the process of glass making are huge and at the same time the environment is being contaminated. The process of rock melting, on the contrary, is not accompanied by any pollution and the losses of the volatile components are minimal.

The purpose of the Project.

The goal of the Project is to widen the raw material range for production of continuous mineral fiber and to develop a new generation of fiber materials used in construction, filtration, heat- and sound protection area. It is proposed that rocks will be used as monobatch (single component raw) or with sub-batching (correction of composition). The problems that should be solved are the following:


– Investigate the glass forming process and conduct a study of physical-chemical properties of glasses based on natural raw materials;
– Evaluate suitability of rocks of Armenia for manufacture of continuous mineral fibers;
– Determine the optimal conditions for moulding of continuous fibers based on rocks with a complex of designed properties;
– Develop the compositions and processing terms to manufacture fibers capable of lixiviation in acid solutions and of forming high silica fibers;
– Work out laboratory samples of fibers and study their physical-chemical and physical-mechanical properties;
– Re-orient the highly qualified scientific staff from military to peace area and support peace-oriented researches and development;
– Integration of scientists into the international scientific community;
– Establish a new way of work directed to support and assist national and international technical and economical progress.

The staff of scientists of SI&P CJSC «Stone and Silicates» possesses an immense scientific and practical experience in the field of research and development (R&D) as well as in manufacture of continuous fibers and meets all requirements for solution of the problems listed in the present Project. The Project is open for cooperation with research organizations and private experts from the USA, countries of European Community, Japan, and Korea.


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