WO2008087047A1

WO2008087047A1 - Method for producing glass vacuum hollow spheres, vacuum hollow spheres and use thereof

Info

Publication number: WO2008087047A1
Application number: PCT/EP2008/000422
Authority: WO
Inventors: Manfred Krauss; Bernhard Durschang; Dietmar Hietel; Robert Fessler; Norbert Siedow; Michael Heil; Ulrich Heinemann; Volker Drach; Hans-Peter Ebert
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2007-01-19
Filing date: 2008-01-21
Publication date: 2008-07-24
Also published as: DE102007002904A1

Abstract

The invention relates to the development of a novel and economical method for producing vacuum spheres based on vacuumised glass hollow spheres (vacuum hollow spheres or vacuum spheres), vacuum hollow spheres and to the use thereof. During said method, the addition of suitable additives initiates the formation of gases which inflate the glass sphere in the cooling phase and which, during solidification, resublimate inside the sphere to form a solid matter. The resublimation/condensation process is based on controlled chemical reactions of the formed gases amongst themselves and/or with glass components. The gases deposit themselves as a solid matter in the inside of the glass sphere or on the inner walls (e.g. carbon compounds, sulphur compounds, halogen compounds such as carbonates, sulfates, chlorides). This allows three types of novel isolation materials (bulk material, insulation board and sprayed rendering) to be developed. The application techniques of said insulating materials are also suitable for facades and wooden houses.

Description

Process for the production of hollow glass spheres made of glass, hollow hollow spheres and their use

The present invention relates to the development of a new and cost-effective production process for vacuum pellets, based on hollow glass spheres (hollow vacuum spheres or vacuum pellets), vacuum hollow spheres, and their use.

Conventional glassmaking can cause glass defects, such as bubbles in the glass. At high temperatures, they re-form when a gas component, which is physically or chemically dissolved in the melt, shows considerable supersaturation (refining) or gases are liberated by chemical reaction (blowing). The internal bladder pressure can be reduced by the effect of surface tension

Pi = σ / 2r pi Overpressure inside the bubble σ Surface tension r Bubble radius become high [J. Backhausen, E. Muysenberg, and J. Ullrich: The iraportance of understanding the basic quality issues for improving the technology in glass melting. Int. Glass J., Vol. 2003, Issue 23, Jan. 2004, 31-36].

The bubbles may contain gases (often air, Ar, H ₂ O, O ₂ , N ₂ , SO ₂ , CO ₂ ), but also H ₂ S, HF, HCl) or evacuated. Partial deposits are also observed in the interior of the bladder [H. Jebsen-Marwedel: Glass-technical manufacturing defects. Springer-Verlag Berlin Göttingen, Heidelberg, 166]. Bubble contents that condense at room temperature are NaCl, sulfur, Na ₂ SO ₄ , sulfides, carbon, and others. Bubbles formed by such condensed matter are gas-free at room temperature and are referred to as vacuoles or vacuum bubbles. CO ₂ diffuses into / out of the melt until equilibrium is established.

During the melting process, the composition of the bubble content may change. The various gases are present in different concentrations in the bubble and in the surrounding furnace atmosphere. Therefore, diffusion processes begin to approximate the gas composition of the gas bubble and the furnace atmosphere. This diffusion process leads to a change in bubble size (Schäffer, HA: General Technology of Glass, Institute of Materials Science, Chair III, Glass and Ceramics, Erlangen, 1995, p. The gases have different diffusion coefficients, solubilities and permeabilities (Table 1). Table 1

Comparison of the diffusion coefficients, solubilities and permeabilities of gases

Since the bubbles constantly change their gas composition during the melting process, it is difficult to conclude from the gas composition in the final product on the original composition and thus the bubble cause. The glasses contain dissolved gases.

Under reducing conditions, for example, nitrogen can be dissolved in the silicate glass melt. The chemical solubility is greater by a factor of 10 ³ to 10 ⁴ than the physical solubility.

Various types of glass beads are known in the art.

a) Massive glass balls, glass beads

The production of massive small glass spheres (eg Ballotini production, gel route, Potters Ballotini ™ Scotchlite ™ glass beads, www.pottersbeads.com/markests/cleaning.asp) and expanded glass, eg from Dennert-Poraver (expanded glass and expanded glass granules Den- nert-Poraver GmbH, www.poraver.de) has been known for a long time. Using the Ballotini process, glass microbeads with a diameter of approximately 0.025 to 2 mm are produced. They are used eg for light reflectors in traffic signs. The glass spheres can be produced by different methods.

a) by heating glass bodies (semolina or flour) in the suspended state (gas stream or soot bed) by blowing into a hot exhaust gas stream, b) by trickling in a heated shaft, wherein from the vorgesiebten fractionated glass powder irregularly shaped grains by melting the balls c) blowing a jet of compressed air into a molten glass thread, producing short glass filaments which melt under the action of temperature and form spheres as a result of the surface tension; d) mixing glass granules with boron nitride and heating in ovens, e ) Placing the glass melt on a sputtering element, eg a rapidly rotating disc provided with blades (ball diameter up to 20 microns).

b) Non-evacuated, gas-filled hollow glass spheres

The preparation of gas-filled hollow microspheres (e.g., 3M ™ Scotchlite ™ Glass Bubbles, www.rpcompany.com/info/briefs/bases.pdf) and hollow microspheres of silica glass (US 4,336,338) are prior art.

Hollow glass microspheres filled with air or other gases are used as fillers for synthetic resins, plastics, adhesives, protective coatings, paint ben, artificial marble, Leichtbaufüllstoffe and Fugenfüller used. They usually consist of low-alkali Borosi- licatglas with high chemical resistance. Hollow glass spheres are not flammable, gas-tight and resistant to water. Their diameter is between 15 and 120 μm, the thermal conductivity of a bed between 0.06 and 0.2 W / mK.

Hollow glass balls are produced by a multi-stage process. First soda-borosilicate glass is prepared and ground to a fine powder. Subsequently, the Hohlglaskugelbildung takes place in a high-temperature heat transfer process. As the temperature increases, the viscosity of the glass drops decreases in such a way that the surface tension leads to the formation of glass beads. The high temperature causes the outgassing of an added propellant. The resulting gas pressure is the cause of the growth of the glass particles from small massive to larger hollow spheres. The internal pressure of the again cooled balls is about one third of the atmospheric pressure. Hollow ceramic microparticles in which reduced pressure or vacuum prevails are used for insulating materials [JP 2003335588], but are hitherto only suitable for a few applications (e.g., ceramic tanks, ceramic lavatories, metallic water valves) due to their weight, limited ceramic compositions and low elasticity. Hollow bodies of glass or resins coated with metals or glass, in which

Vacuum of about 10 mbar are used for thermal high-tech insulation [JP 11199347].

For flat solar collectors, elongated cylindrical or spherical microballoons have been developed [WO 80/00438]. They can contain a vacuum and have a thin metal coating (5 to 500 nm) inside. The diameters range from 200 to 10,000 μm and the wall thicknesses from 0.1 to 1000 μm. The production takes place via an elaborate blowing process in which a thin film of molten glass is stretched over the opening of a coaxial tuyere. The tuyere is provided with an inner nozzle to supply the flowing gas with positive pressure to the inside of the liquid film. An external cross-flow creates a pulsating or fluctuating pressure field with periodic vibrations that acts on the microballoon and aids in both formation and detachment from the orifice. To detach the beads, a centrifuge can also be used. The flowing gas used is metal vapor (eg zinc vapor), which is deposited as a metal film on the inner wall of the hollow microbead.

c) Partially evacuated hollow spheres

The research shows that in the early 1990s there were activities in the USA to develop, manufacture and market insulation materials and coatings based on partially evacuated hollow glass microspheres

[Thermal insulating material and method of manufacturing same, US patents 5,500,287 and 5,501,871].

d) evacuated hollow glass spheres

The production of evacuated glass microspheres by leakage of residual gas from the gas-filled beads at sufficiently high temperatures has been described (US 5,713,974, US 5,501,871). The evacuated microspheres consist of glass or polymers with an IR-reflecting layer (sphere diameter 5 to 5,000 μm). The manufacturing process is two-stage and leads to partially evacuated glass beads, as a residual gas content does not diffuse through the glass wall even in a vacuum. In US Pat. No. 4,303,433, the production of evacuated glass beads is explained by means of a centrifuge. The molten glass is passed as a liquid film through a nozzle through which metal vapor is blown. Due to the centrifugal force, gas-filled drops are thrown outward and contracted into balls. By depositing a thin metal film inside the hollow sphere, vacuum is formed.

By blowing individual hollow spheres of glass and plastic by using a nozzle, hollow spheres are produced in the publications US Pat. No. 4,303,732 and US Pat. No. 3,607,169. Above the opening of a coaxial nozzle, a liquid glass film spans, which is inflated by a flowing gas with overpressure to hollow micro glass beads and then quenched. Additives in the blowing gas are metal particles and organometallic compounds. These become gaseous at high temperatures and lead to precipitation or film formation on the inner wall of the spheres (diameter: 500 to 6000 μm, wall thickness 0.5 to 400 μm) at decreasing temperatures, e.g. Formation of a zinc film, and so to the vacuum inside.

All of the processes described in the prior art require separate operations and thus a process management, which is associated with a considerable effort. In addition, the nozzle devices used in the prior art have a high susceptibility to interference. Proceeding from this, it is an object of the present invention to provide a process for the production of hollow vacuum spheres, which allows the simplest possible process control. It is a further object of the present invention to provide vacuum hollow spheres which have improved insulating properties.

These objects are achieved on the one hand by the method with the features of claim 1 and by the hollow vacuum balls with the features of claim 27. With the claims 37 to 42 uses of vacuum hollow spheres are called. The respective dependent claims represent advantageous embodiments.

According to the invention, a method is provided for producing hollow glass spheres made of glass, which is characterized by the following steps:

a) introduction of a material containing glass powder into an oven having at least one heating module, b) blowing of reaction and / or carrier gas into the oven, c) melting of the material in the oven, d) formation of hollow spheres by swelling by means of temperature increase, and Solidification of the hollow spheres by cooling with binding and / or condensation of the expanding gas.

The method according to the invention therefore requires complicated apparatuses, as known from the prior art (for example, coaxial nozzles). Devices) and the associated disadvantages lapsed. Thus, economic benefits can be achieved.

The glass as a shell material combines the advantages of high diffusion-tightness and pressure stability with low raw material costs.

In the production of hollow glass spheres, surprisingly evacuated spheres form, analogously to the formation of vacuoles in the molten glass. Deposits are observed inside the hollow spheres.

In the process, it proves to be advantageous if the furnace is vertically aligned. In this case, the glass powder-containing material is blown from below into the oven and the finished product (i.e., the glass beads) after step e) preferably removed from the oven by suction. The furnace is also flowed through by the reaction and / or carrier gas, preferably in the vertical direction, ie from bottom to top.

In particular, there are advantages when a flow gradient is generated in the furnace. A flow gradient is understood according to the invention to mean a course which is not uniform with respect to the magnitude and / or direction of the flow of the reaction and / or carrier gas within the furnace.

An advantageous variant for generating a positive flow gradient of the reaction and / or carrier gas provides that the furnace is substantially tubular and the flow gradient by cross-sectional taper of the tube in the flow direction (tapering of the circular cross-section) and / or is created by introducing a from bottom to top of diameter increasing, substantially conical body (taper of the ring cross-section). A positive flow gradient is understood to mean that the flow rate of the reaction and / or carrier gas increases in the flow direction of the furnace. The increase of the flow velocity thus takes place by reducing the tube diameter of the quasi-tubular opening, be it by an example tapered taper of the furnace itself and / or by introducing a body into the furnace, the average increases in the flow direction. Preferably, the body is arranged concentrically in the oven and is, for example, as a bar o.Ä. educated.

An alternative, but equally advantageous variant provides for the generation of a negative flow gradient of the reaction and / or carrier gas. In this case, the flow gradient in the substantially tubular furnace is produced by cross-sectional widening of the pipe in the flow direction (widening of the circular cross-section) and / or by introducing a substantially conical body decreasing in diameter in the flow direction (widening of the annular cross-section). A negative flow gradient is understood to mean that the flow rate of the reaction and / or carrier gas decreases in the flow direction of the furnace. Accordingly, the flow velocity is reduced by widening the tube diameter of the quasi-tubular furnace, be it by a conically widening of the furnace itself, for example, and / or by introducing a body into the furnace whose average decreases in the flow direction. Preferably, the body is while concentrically arranged in the oven and is for example a rod or similar. educated.

Preferably, the flow rate and / or the flow gradient of the reaction and / or carrier gas through the furnace is adjusted so that a transport of the glass powder-containing material is ensured in the flow direction through the furnace. This possibility can be achieved in a variety of ways that reveal the advantages of this procedure:

On the one hand, the flow gradient can be adjusted so that, on the one hand, depending on size and specific weight of the glass powder forming glass particles, the air resistance in the lower part of the furnace is greater than gravity, so that the glass particles are transported into the oven, the speed However, the reaction and / or carrier gas in a higher part of the furnace but decreases such that the air resistance force no longer overcomes the gravity in the top of the heating tube, so that the particles come into a limbo.

Likewise, an advantageous continuous operation of such a vertical furnace and thereby a continuous process control is possible. In this case, the flow rate and / or the flow gradient of the reaction and / or carrier gas in the furnace is set so that the glass particles are in a floating state at the level of the at least one zone in which the heating module is located. The heating within the heating zone leads to the swelling of the glass particles, with an increase in the diameter of the glass particles towards hollow spheres. This is accompanied by an increase in that air resistance, as a result, these blown glass beads are transported upwards out of the at least one heating zone and then cooled.

However, this also opens up a further advantageous possibility for carrying out the method according to the invention, wherein a performance in batch mode is made possible. The flow velocity and / or the flow gradient of the

Reactive and / or carrier gas initially adjusted so that the glass particles are in the amount of a zone in limbo, in which there is at least one heating module. The particles are kept within the heating zone until they are melted and inflated. This is followed by a brief increase in the volume flow of the reaction and / or carrier gas in order to reliably transport the expanded glass beads upwards out of the heating zone and thus to cool them.

The starting material in the process according to the invention is preferably glass powder selected from the group consisting of recycled glass, soda-lime silicate glass (grade purity, impurities, grain size glass powder, glass flour), borosilicate glass and / or mixtures thereof. In their selection, glasses with a high gas content are preferred, which means both physically and chemically dissolved glass or already contained gas bubbles.

In this case, the glass powder used preferably contains glass particles having an average particle diameter d _{50 of} the glass particles between 1 and 1000 μm, preferably between 2 and 200 μm, particularly preferably between 2 and 200 μm. see 5 and 50 microns. It is advantageous if the glass powder is obtained before step a) by grinding and / or sieving.

It is advantageous if the introduction of the glass powder-containing material into the oven by blowing and / or sucking takes place.

Furthermore, it is preferred if the material containing the glass powder contains at least one further additive and / or blowing agent selected from the group consisting of SiO ₂ , B ₂ O ₃ , 2 CaO "3 B ₂ O ₃ " 5 H ₂ O, H ₃ BO _3, Na ₂ B ₄ O ₇ '10 H ₂ O (borax), 2 CaO ^■ 3 ^■ B ₂ O ₃ 5 H ₂ O (CoIe- manit), P ₂ O _5, H ₃ PO ₄ (phosphoric acid), Ca ₃ (PO ₄ J ₂ , AlPO ₄ , Ba (PO ₃ ) ₂ , Ca (PO ₃ J ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , ZrSiO ₃ , (HPO ₃ ) _X ( Metaphosphoric acid), (NaPO ₃ J _x (Madrell's salt), (KPO ₃ ) _X (Kurrol's salt), Na ₃ (P ₃ O ₉ ) (trimetaphosphate), Na ₂ CO ₃ , Na ₂ CO ₃ ^■ NaHCO ₃ ^■ 2H ₂ O, Na ₂ SO _4, Na ₂ SO ₄ '10 H ₂ O, NaOH (aq, sodium hydroxide), NaOH, NaCl, NaNO _3, Na ₂ SiO _4, Na ₂ SiF _6, K ₂ CO ₃ , KNO ₃ , KI, Li ₂ CO ₃ , CaCO ₃ , CaCO ₃ ^• MgCO ₃ (dolomite), CaSO ₄ , Ca (NO ₃ J ₂ , Ca (NO ₃ J ₂ ^• 4 H ₂ O, CaF, MgCO ₃ , MgO, BaSO ₄ , BaS, Ba (NO ₃ ) ₂ , ZnS, NH ₄ Cl, BN, BC, SiC, organometallic compounds of Al, Zn, Ag, Cu, Ni, Sn , Au, Mg, Ca, Na, Cs and / or mixtures thereof. In particular, the oxides of Mg, Al, Si, Ti and Zr prevent the sticking of the evacuated hollow spheres. In part, these compounds also form as solid precipitates in the hollow spheres.

The at least one additive can be used for glass powder in any weight ratio, it is advantageous, however, if the at least one additive with respect to the glass powder between 0.1 and 30 wt .-%, preferably between 0.1 and 10 wt .-%, more preferably between 0.1 and 5 wt .-% is added.

The reaction and / or carrier gas in step b) is preferably a gas selected from the group consisting of CO ₂ , O ₂ , H ₂ , NH ₃ , HF, HCl, SO ₂ , metal vapor, steam and / or mixtures from this, used.

The steps a) and b) are preferably carried out simultaneously.

It is likewise advantageous if, in step c), a temperature between 300 and 1500 ^° C., preferably between 500 and 1300 ^° C., is set in the oven having at least one heating module.

The oven preferably has three heating modules, and it is furthermore advantageous if different temperatures prevail in the respective heating modules. In particular, the temperatures in the heating modules are adjusted so that the temperatures in the second heating module are higher than in the first and in the third lower than in the second. For example, a favorable temperature distribution is given when the temperature in the first heating module between 600 ⁰ C and 1000 ⁰ C, in the second heating module between 1100 ⁰ C and 1500 ⁰ C and in the third heating module between 700 ⁰ C and 1100 ⁰ C, without the To limit the invention to this exemplary indication.

To solidify the hollow glass spheres, it proves to be advantageous if, in step e), the temperature of the glass spheres is successively lowered to room temperature. According to the invention it is irrelevant how fast the cooling takes place. Surprisingly, it has been found that the vacuum formation in step e) takes place only below a temperature of 600 ^° C., preferably below 500 ^° C. Thus, the glass matrix is already sufficiently viscous again and thus stable enough to withstand the resulting negative pressure inside. As a result, there is no deformation or even destruction of the hollow spheres.

After the removal of the glass spheres, preference is given to classifying the glass spheres according to their size and / or classifying them with regard to the nominal density of the glass spheres by combining weight and size classification (for example aerodynamic classification).

The process can be carried out both as a batch process and as a continuous process, the continuous variant offering economic advantages.

According to the invention, hollow hollow spheres containing glass are also provided whose gas pressure in the interior is at most 1 mbar, preferably at most 0.2 mbar, particularly preferably at most 0.1 mbar.

By the invention thus very low internal pressures are achieved in the hollow glass spheres, which can not be achieved by the mere effect of cooling.

The glass materials are preferably selected from the group consisting of recycled glass, soda lime silicate glass, borosilicate glass and / or mixtures thereof. The hollow vacuum spheres may in principle be of any size, but it is advantageous if the mean diameter d _{50 is} between 1 and 1000 μm, preferably between 5 and 500 μm, particularly preferably between 10 and 200 μm.

In a further embodiment, the wall thickness of the hollow vacuum spheres is between 0.1 and 25 μm, preferably between 0.2 and 10 μm, particularly preferably between 1 and 5 μm.

It is advantageous if the cavity enclosed by the wall is between 10 and 98% by volume, preferably between 90 and 98% by volume, of the total volume of the hollow vacuum ball.

Furthermore, the hollow vacuum spheres are characterized by the advantageous properties that they have a pressure stability against external pressures of at least 5 bar, preferably of at least 15 bar. The pressures can be exerted mechanically, pneumatically or hydraulically on the balls. Decisive is that it does not cause any damage or destruction of the balls.

Likewise, the lower density of the vacuum spheres proves to be particularly advantageous, in particular between 50 and 300 kg / m ³ , preferably between 50 and 200 kg / m ³ , more preferably between 70 and 100 kg / m ³ . The density is defined as the ball weight per sphere volume. As a result, the excellent insulation properties can be achieved while maintaining low weight.

Another advantageous feature of the vacuum hollow balls is their extremely low thermal conductivity It is preferably at most 0.05 W / mK, preferably at most 0.03 W / mK, particularly preferably at most 0.02 W / mK, and is incorporated in a bed of the vacuum spheres of the invention or of a material into which the vacuum spheres according to the invention are determined.

Furthermore, it is advantageous if the hollow vacuum spheres are coated. The coating can be applied after the manufacturing process and in particular contain metals. The coating is used in particular to fix the balls against each other, to increase their durability and / or resistance to external influences.

Advantageously, the vacuum hollow spheres described here can be produced by the method according to the invention mentioned in detail.

According to the invention, uses of hollow vacuum spheres are also indicated. In particular, the hollow vacuum spheres are suitable for the production of composite materials (wherein the hollow spheres can be sintered or embedded in a matrix) or Dämmmateria- materials.

The vacuum hollow glass spheres are used to develop novel insulating materials which, while retaining the principle-based advantages of the vacuum idea (significant improvement of the insulating effect and / or reduction of the required layer thickness), overcome the disadvantages in terms of fabricability and vulnerability. These materials must consist of small evacuated cells. Compared to classic insulating materials, the materials produced on the basis of the hollow glass spheres are characterized by a clear reduced thermal conductivity (factor 2 - 3). Thus, either the insulation effect can be improved or the wall thickness can be significantly reduced. Compared with the vacuum insulation panels developed in recent years, which have an even better insulating effect, the new materials have considerable advantages in terms of manufacturability and vulnerability. The problem of unwanted thermal bridges, which occurs again and again in practical use, can be effectively combated with them. In addition, glass has as shell material of the vacuum beads excellent properties in terms of diffusion-tightness and pressure stability at the same time low raw material costs. Overall, this results in a significant competitive advantage in the various links in the value chain (base material, insulation materials, application technology).

With densest ball packing results for micro hollow glass spheres with a pressure stability of 15 to 20 bar, a density of 100 to 120 kg / m ³ . With comparable wall thickness, vacuum spheres have nearly equal densities. Depending on the insulation material (bulk material, insulation board, spray plaster), the vacuum spheres can be embedded in a carrier matrix. If the carrier matrix has typical insulating material properties, a total density results clearly below 150 kg / m ³ . The investigations carried out show that for such a system, compared to traditional insulating materials with thermal conductivities of about 0.03 to

0.05 W / mK an improvement by a factor of 2 to 3 to less than 0.020 W / mK is possible. The idea of thermal insulation with vacuum spheres in bulk materials and insulation boards is therefore very promising. For spray plaster, it is to be expected that the thermal conductivity will be significantly lower than that of standard plaster. will be. A "thermal barrier plaster" is comparatively easy to apply and consistent, thus avoiding construction-related thermal bridges and, together with the advantages outlined above other vacuum solutions, results in enormous technical innovation potential for the three mentioned insulating materials.

Looking at the total reduction in CO ₂ emissions achieved (15% between 1990 and 1998 alone), climate protection in Germany appears to be making progress. However, this reduction is essentially due to the sharp decline in industry and energy in the new federal states. An essential energy and C0 ₂ savings of about 140 million tonnes of CO ₂ per year have the approximately 23 million units of old buildings. In order to exploit this potential and achieve the medium-term climate protection targets in accordance with the Kyoto Protocol, considerable efforts are required - especially with regard to thermal insulation.

In the last 10 years, evacuated, highly efficient thermal insulation in the form of flat vacuum insulation panels has also been developed into marketable products for applications in the construction sector. These insulating elements consist of a pressure-bearing filling core and a sufficiently gastight envelope. However, the enormous potential for improvement compared to conventional insulation (factor 5 to 10) can only be realized if the complete insulation layer is not broken. In practice, however, joints, for example, can not be avoided. Even an air gap in the millimeter range is a non-negligible thermal bridge compared to the high-insulating panels. Will even the shell of a panel Pierce a site, the heat transfer increases for the whole panel on the value of the non-evacuated material.

To clarify the process steps and reactions taking place in the method according to the invention, an overview of the production process of the hollow glass vacuum spheres is given with the following exemplary embodiment, wherein reference is also made to FIG. However, the specific conditions and values mentioned here are merely exemplary in nature and should not be understood to limit the invention to this embodiment.

embodiment

The starting glass powder 1 is blown after grinding (d ₅₀ - value 10-90 microns) and classifying a weighing and dosing unit 2 in the reaction chamber of the furnace 3 from below and sucked off at the opposite side by applying a negative pressure.

In the furnace 3 occurs during the melting of the starting glass powder 1 at high temperatures (about 600 ⁰ C to 800 ⁰ C) for evaporation of individual components of the hot glass surface, using, for example, those mentioned in Table 2 chemical reactions and substances are involved. In this case, a fusion takes place to larger glass parts. At the same time, reaction and / or carrier gases are injected

(CO ₂ , O ₂ , H ₂ , NH ₃ , HF, HCl, SO ₂ , metal vapor); Air is excluded since N ₂ and Ar are inert to the air and do not react with vaporized glass components or the hot glass surface inside the ball, thus preventing the formation of vacuum. Water vapor can only be used to a limited extent, as it uses glass not completely react to solid, water-containing substances. Likewise, components are added which decompose or sublime at defined temperatures.

This results in a floating distribution of the molten glass particles / blowing agents and / or additives (carbonates, oxides, ammonium, halogen, carbon, sulfur, boron, phosphorus, metal compounds) in the reaction chamber (about 700 to 1200 ⁰ C, few s).

Table 2

Condensation and decomposition temperatures of selected substances

The furnace consists of three separate heating modules 6, 7, 8, which are individually controlled by a furnace controller 9. The monitoring of the temperature takes place in each case by a thermocouple 10. The gases and vapors from the surrounding atmosphere (carrier, reaction gas) and from the glass as a function of temperature and pressure released gases (H ₂ , O ₂ , CO ₂ , SO ₂ , HF, H ₂ O, HCl, NH ₃ ) are enclosed by the molten, viscous glass material, enclosed by individual glass grains in the sintering together, collected during the melting process between the glass particles and are trapped or diffused into the glass depending on temperature and pressure. Due to surface tension, glass spheres form. The enclosed gases combine to form a cavity until the internal pressure is equal to the external pressure.

By diffusion of gases into the interior of the sphere and expansion of the gases, the glass spheres expand due to an increase in temperature (900 to 1300 ^° C.). In the process, glass components evaporate from the hot glass surface of the balls.

Depending on the material parameters, the vapor condenses or resorbs inside the hollow sphere at a given pressure (condensation, resublimation temperature), i. it changes from the gaseous to the liquid or solid state of matter. This can e.g. by reaction of the gases with each other and / or with components of the hot glass surface, the resublimation / condensation of solid components inside the sphere leads to vacuum formation.

Important here is the choice of the appropriate temperature-time-pressure program; which must meet the following criteria:

a) The temperature must be high enough to cause it to swell the glass ball, to the desired condensation reactions and thus to the formation of vacuum inside (with sufficiently small wall thickness of the

Balls) comes.

b) viscosity of the glass must increase at the same time suitably.

Surprisingly, the vacuum formation takes place only at a Temperature (500-700 ⁰ C to room temperature) at which the glass envelope of the ball is already so strong that the external air / gas pressure does not cause the ball to collapse (log η 3-12.3 dPas).

As a result of gravity, heavy solid balls fall downwards in the furnace 3 out of the reaction space (FIG. 1).

Subsequently, the vacuum hollow glass balls are sucked off and classified on the screening machine 5 according to the ball size.

Suitable glass compositions, blowing agents, gases, condensation reactions, temperature-time intervals, heating rates and pressure ratios (process chemistry, thermodynamics, kinetics) were determined.

In the pressure and temperature conditions where sublimation occurs, there is no liquid state of matter. Substances with a relatively high vapor pressure when heated reach the atmospheric pressure at a temperature below their melting point. It is not reached when heated, and these substances go directly into the gaseous state, they sublimate.

The sublimation curve of the phase diagram is given by the phase boundary line between solid and gas below the triple point at which liquid and solid have the same vapor pressure. The temperature at which the vapor pressure of the solid is equal to the external pressure is called the sublimation temperature. If the pressure is reduced, the sublimation point may shift below the melting point even for substances that melt under normal pressure. The phase transformation in the opposite direction to the sublimation is called resublimation (also called desublimation, solidification, deposition). The vapors condense directly into crystals, bypassing the liquid phase. For pure substances the re-sublimation point is identical to the sublimation point. For mixtures, as they occur inside the hollow glass sphere, both can differ and therefore also influence the direction of the phase transformation.

If a sublimation temperature exists at normal pressure, this is referred to as normal sublimation temperature (data without additional sublimation pressure). Otherwise, the sublimation temperature and pressure must be taken into account. Each fabric absorbs sublimation heat of sublimation, which is equal to the sum of melting and evaporation heat and is released again in the resublimation.

Particularly strong evaporation from the glass surface occurs when the temperature increases in alkali borosilicate glasses (alkali metalaborates), lead glasses (lead oxides) and fluorine opaque glasses (fluorides of Si). At high temperatures and reducing conditions, SiO (silica glass melt) evaporates.

Although alkali metal oxides, alkaline earth oxides, SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ show comparatively lower tendency to evaporate than lead, fluorine compounds and metaborates.

However, it also occurs in the case of alkali metals, alkaline earth oxides and B ₂ O ₃ , in particular when it comes to reactions with water vapor, for example to metaboric acid or to the reaction of the alkalis with the hydroxide. Boric acid losses due to water vapor increase by 3% with borax by 1 to 2% for crystalline boric acid.

The evaporation and decomposition of the boric acid begins at 600 ⁰ C and leads via metaboric acid to the boron oxide.

2 H ₃ BO ₃ → 2 HBO ₂ + 2 H ₂ O → B ₂ O ₃ + H ₂ O

The water vapor liberated during the thermal decomposition reacts very rapidly with the less volatile metaboric acid to form H ₃ BO ₃ vapor. A renewed Borverdampfung takes place only above 1000 ⁰ C. In the presence of Na ₂ CO ₃ or K ₂ CO ₃ , these processes are superimposed by formation of a carbonate-boric acid melt. It is to be expected with the formation of a glassy sodium borate in the temperature range> 300 ⁰ C with the beginning of CO ₂ elimination.

In the case of boron-containing glasses, Na ₂ O- and SO ₂ -containing gases influence the condensation of liquid Na ₂ SO ₄ by boron. The condensation temperature of sodium sulfate may be up to 200 K lower than in corresponding boron-free gases. In the condensate B ₂ O _{3 is} dissolved. Borates can condense in SO ₂ -free or -low gases.

Many fluorides have high vapor pressure and can sublime / resublimate (see Table 3). This means that glass components or fluorine-containing additives easily evaporate from fluorine-containing glasses. Table 3

Sublimation / resublimation temperatures of selected substances

The negative influence of the water content in the gas is shown by the formula:

H ₂ O + 2 F ^" -» 2 HF + O ^{2 '}

Fluorides react with water to form a gas, which should be avoided in the hollow sphere, otherwise there will be insufficient evacuation inside.

This also applies to water vapor in the ball inside, which, also partially condensed to water, depending on temperature and pressure prevents the formation of a sufficiently high vacuum.

Evaporation of alkalis from the hot glass surface increases in the following series:

Li ₂ O - Na ₂ O - K ₂ O

The condensation of the vaporized substances can often lead to corrosion and blockage in conventional glass tanks in the lower furnace. In the hollow glass spheres, the condensation and desublimation by variation of temperature, pressure, residence time in the oven,

Glass composition, blowing and reaction gases and the addition of substances which, at certain temperatures, decompose or sublimate defined.

It is assumed that Na ₂ O and K ₂ O dissociate before evaporation into Na or K and oxygen

(Schäffer, H. A .: General Technology of Glass, Institute of Materials Science, Chair III, Glass and Ceramics, Erlangen, 1995).

Na ₂ O _^ → 2 Na + MO ₂

K ₂ O ₁ → 2 K + MO ₂

Li ₂ O, fluorides and alkali borates evaporate without decomposition.

The intermediates formed alkali react with oxygen present to the oxides.

4 Na + O ₂ → 2 Na ₂ O

The leads in the hollow glass spheres to the reduction of the existing oxygen.

From the vapors emitted condenses in the presence of SO ₂ (formed by decomposition of sulfur-containing substances) liquid sodium sulfate.

2 Na + SO ₂ + O _{2 *} - → Na ₂ SO ₄

Under local reducing conditions, sodium sulfide may form.

2 Na + SO ₂ <- → Na ₂ S + O ₂

This can react with sodium sulfate. 3 Na ₂ SO ₄ + Na ₂ S -> 4 Na ₂ O + 4 SO ₂

A higher chlorine content increases the sodium content of the melt, while a higher sulfur content lowers the sodium content.

Potassium behaves similarly, but condenses at lower temperature.

In the presence of CO ₂ (carrier, reaction gas and decomposition of carbonates) this can react with the vaporized / dissociated / sublimated components.

2 Na + CO ₂ + HO ₂ → Na ₂ CO ₃ Na ₂ O + CO ₂ → Na ₂ CO ₃

NaCl + NH ₃ + CO ₂ + H ₂ O - NH ₄ Cl + NaHCO ₃

Present water also reacts.

2 Na + H ₂ O + O ₂ → 2 NaOH Na ₂ O + H ₂ O → 2 NaOH

Na ₂ O + CO ₂ + 10 H ₂ O → Na ₂ CO ₃ '10 H ₂ O Na ₂ O + 2 CO ₂ + H ₂ O → 2 NaHCO ₃

Solid state reactions

The carbonates condensed within the sphere can react with each other.

Na ₂ CO ₃ + MgCO ₃ → Na ₂ Mg (CO ₃ ) ₂ > 300 ⁰ C Na ₂ O + CaCO ₃ - _* Na ₂ Ca (CO ₃ J ₂ > 500 ⁰ C

Na ₂ Ca (CO-J) ₂ + 2 SiO ₂ → Na ₂ SiO ₃ + CaSiO ₃ + CO ₂ 600-800 ⁰ C Na ₂ CO ₃ + SiO ₂ → Na ₂ SiO ₃ + CO ₂ 700-850 ⁰ C

2 CaCO ₃ + SiO ₂ → Ca ₂ SiO ₄ + CO 2 _2> 600 ⁰ C

It can lead to the formation of carbonic melts.

The system Na ₂ Ca (CO ₃ ) ₂ - Na ₂ CO ₃ has a eutectic at 740 ^° C., so that a melt with a eutectic composition forms at this temperature.

As the temperature increases further, the pure components, double carbonates, soda and potash also melt.

Na ₂ Ca (CO ₃ ) ₂ 820 ⁰ C

Na ₂ CO ₃ 850 ⁰ C

K ₂ CO ₃ 890 ⁰ C

This is prevented by suitable temperature-time pressure guidance of the manufacturing process (see embodiments).

Thermal decomposition / sublimation of aggregates

In the temperature range around 900 ⁰ C, the carbonates decompose and CO ₂ is released.

CaCO ₃ → CaO + CO ₂ _CO 2 p 1 bar, 910 ⁰ C.

Na ₂ Ca (CO ₃ ) ₂ → CaO + Na ₂ O + 2 CO ₂ P _CO 2 1 bar, 960 ⁰ C 2 NaHCO ₃ → Na ₂ CO ₃ + CO ₂ + H ₂ O MgCO ₃ → MgO + CO ₂ P _CO 2 1 bar, 540 ^° C.

Na ₂ SO ₄ → Na ₂ O + SO ₃ → Na ₂ O + SO ₂ + XO ₂ > 1300 ^° C.

Na ₂ SO ₄ + C → Na ₂ O + SO ₂ + CO> 900 ^° C.

The vacuum is formed at temperatures of 600 ⁰ C to room temperature, at which the glass envelope of the ball is already so strong that the external air / gas pressure does not lead to collapse of the hollow sphere (log η 3- 12, 3 dPas).

The production process of the vacuum hollow glass balls runs between the viscosity fixing points

10 ³ Pa s Flow Point 10 ⁶ ' ⁶ Pa s Littleton Temperature (Softening Point) 10 ¹² - 10 ¹² ' ³ Pa s Transformation Range (T ₉ )

of the respective glass.

Claims

claims

1. A process for the preparation of hollow glass spheres of glass, characterized by the following steps: a) introducing a material containing glass powder in at least one heating module having furnace, b) blowing reaction and / or carrier gas into the furnace, c) melting the material in Furnace, d) formation of hollow spheres by swelling by means of temperature increase, and e) solidification of the hollow spheres by cooling with binding and / or condensation of the expanding gas.

2. The method according to claim 1, characterized in that the furnace is vertically aligned.

3. The method according to the preceding claim, characterized in that the furnace is loaded from below with the containing material and the hollow balls are removed following step e) at the upper end of the furnace.

4. Method according to the preceding claim, characterized in that the removal of the hollow balls is effected by suction.

5. The method according to any one of the preceding claims, characterized in that the furnace is flowed through with the reaction and / or carrier gas, preferably from bottom to top.

6. The method according to any one of the preceding claims, characterized in that in the furnace, a flow gradient is generated.

7. The method according to the preceding claim, characterized in that the furnace is formed substantially tubular and a positive flow gradient by cross-sectional tapering of the tube in the flow direction and / or by introducing a diameter increasing in the flow direction, substantially conical

Body is generated.

8. The method according to claim 6, characterized in that the furnace is substantially tubular and a negative Strömungsgra- serves by cross-sectional expansion of the tube in

Flow direction and / or by introducing a decreasing in the flow direction diameter, substantially conical body is generated.

9. The method according to any one of the preceding claims, characterized in that a flow rate and / or a flow gradient of the reaction and / or carrier gas is adjusted by the furnace so that a transport of the glass powder-containing material is ensured in the flow direction through the furnace.

10. The method according to any one of the preceding claims, characterized in that a glass powder selected from the group consisting of recycle glass, soda-lime-silicate glass, borosilicate glass glass powders and / or mixtures thereof is used.

11. The method according to any one of the preceding claims, characterized in that the glass powder contains glasses with a high gas content.

12. The method according to any one of the preceding Ansprü- che, characterized in that a glass powder having an average diameter d _{50 of} the glass particles between 1 and 1000 microns, preferably between 2 and 200 microns, more preferably between 5 and 50 microns is used.

13. The method according to any one of the preceding claims, characterized in that the glass powder is obtained prior to step a) by grinding and / or sieving.

14. The method according to any one of the preceding claims, characterized in that the introduction of the glass powder-containing material in the O-fen by blowing and / or sucking takes place.

15. The method according to any one of the preceding claims, characterized in that the glass powder-containing material at least one further

Additive and / or blowing agent selected from the group consisting of SiO ₂ , B ₂ O ₃ , 2 CaO "3 B ₂ O ₃ '5 H ₂ O, H ₃ BO ₃ , Na ₂ B ₄ O ₇ ^■ 10 H ₂ O ( Borax), 2 CaO ^• 3 B ₂ O ₃ '5 H ₂ O (colemanite), P ₂ O ₅ , H ₃ PO ₄ (phosphoric acid), Ca ₃ (PO ₄ ) ₂ , AlPO ₄ , Ba (PO ₃ J ₂ , Ca (PO ₃ J ₂ ,

Al ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , ZrSiO ₃ , (HPO ₃ ) _x (metaphoric acid), (NaPO ₃ ) _x (Madrell's salt), (KPO ₃ ) _X (Kurrol ''s salt), Na ₃ (P ₃ O ₉₎ (trimethylsilyl taphosphat), Na ₂ CO _3, Na ₂ CO ₃ ^• NaHCO ₃ ^■ 2H ₂ O, Na ₂ SO _4, Na ₂ SO ₄ ^• 10 H ₂ O , NaOH (aqueous, sodium hydroxide), NaOH, NaCl, NaNO ₃ , Na ₂ SiO ₄ , Na ₂ SiF ₆ , K ₂ CO ₃ , KNO ₃ , KI, Li ₂ CO ₃ , CaCO ₃ , CaCO ₃ ^• MgCO ₃ (dolomite ), CaSO _4, Ca (NO ₃₎ _2, Ca (NO ₃₎ ₂ 4 ^■ H ₂ O, CaF, MgCO _3, MgO, BaSO ₄ , BaS, Ba (NO ₃ ) _{2 /} ZnS, NH ₄ Cl, BN, BC, SiC, organometallic compounds of Al, Zn, Ag, Cu, Ni, Sn, Au, Mg, Ca, Na, Cs and / or mixtures thereof.

16. The method according to the preceding claim, characterized in that the at least one additive with respect to the glass powder between 0.1 and 30 wt .-%, preferably between 0.1 and 10 wt .-%, particularly preferably between 0.1 and 5 wt .-% is added.

17. The method according to any one of the preceding claims, characterized in that in step b) a reaction and / or carrier gas selected from the group consisting of CO ₂ , O ₂ , H ₂ , NH ₃ , HF, HCl, SO ₂ , metal vapor , Steam and / or mixtures thereof, is blown.

18. The method according to any one of the preceding claims, that step a) and step b) are carried out simultaneously.

19. The method according to any one of the preceding claims, characterized in that in step c) in the at least one heating module having a furnace temperature between 300 and 1500 ⁰ C, preferably between 500 and 1300 ⁰ C is set.

20. The method according to any one of the preceding claims, characterized in that the furnace has three heating modules.

21. The method according to the preceding claim, characterized in that prevail in the respective heating modules different temperatures.

22. The method according to any one of claims 20 or 21, characterized in that the temperatures in the second heating module are higher than in the first and in the third lower than in the second.

23. The method according to any one of the preceding claims, characterized in that in step e), the temperature of the glass beads is successively lowered to room temperature.

24. The method according to any one of the preceding Ansprü- surface, characterized in that the vacuum formation in step e) only below a temperature of 600 ⁰ C, preferably below 500 ⁰ C takes place.

25. The method according to any one of the preceding claims, characterized in that subsequent to step e) a classification of the glass beads according to their size and / or a classification with respect to the nominal density of the glass beads by combining weight and size classification (eg aerodynamic classification) takes place ,

26. The method according to any one of the preceding claims, characterized in that it is carried out as a continuous process or in batch mode.

27. Vacuum hollow spheres containing glass whose gas pressure in the interior is at most 1 mbar, preferably at most 0.2 mbar, particularly preferably at most 0.1 mbar.

28. Vacuum hollow spheres according to claim 27, characterized in that the glass materials are selected from the group consisting of recycled ling glass, soda lime silicate glass, borosilicate glass and / or mixtures thereof.

29. Vacuum hollow spheres according to one of claims 27 to

28, characterized in that the average diameter d ₅₀ between 1 to 1000 microns, preferably between 5 and 500 microns, more preferably between 10 and 200 microns.

30. Vacuum hollow spheres according to one of claims 27 to

29, characterized in that the wall thickness between 0.1 and 25 microns, preferably between 0.2 and 10 microns, more preferably between 1 and 5 microns.

31. Vacuum hollow spheres according to one of claims 27 to

30, characterized in that the wall enclosed by the cavity between 10 and

98 vol .-%, preferably between 90 and 98 vol .-% of the total volume of the hollow vacuum ball is.

32. Vacuum hollow spheres according to one of claims 27 to

31, characterized in that they have a pressure stability of at least 5 bar, preferably of at least 15 bar.

33. Vacuum hollow spheres according to one of claims 27 to

32, characterized by a density between 50 and 300 kg / m ³ , preferably between 50 and 200 kg / m ³ , particularly preferably between 70 and 100 kg / m ³ .

34. Vacuum hollow spheres according to one of claims 27 to

33, characterized by a thermal conductivity of a bed of hollow vacuum spheres or a material in which the hollow hollow spheres are incorporated, of a maximum of 0.05 W / mK, preferably at most 0.03 W / mK, more preferably at most 0.02 W / mK.

35. Vacuum hollow spheres according to one of claims 27 to

34, characterized in that the vacuum hollow balls are coated.

36. Vacuum hollow spheres according to one of claims 27 to

35, producible according to a method according to one of claims 1 to 26.

37. Use of hollow vacuum spheres according to one of claims 27 to 36 for the production of a composite material.

38. Use according to claim 37, characterized in that the vacuum hollow spheres are sintered.

39. Use according to claim 37, characterized in that the hollow hollow spheres are embedded in a carrier matrix.

40. Use according to the preceding claim, characterized in that the carrier matrix is selected from the group consisting of inorganic and / or organic binders, plastics, inorganic building materials, plasters, Lehmen and / or mixtures thereof.

41. Use of hollow vacuum spheres according to one of claims 27 to 36 as an insulating material.

42. Use according to the preceding claim, characterized in that the insulating material is applied as bulk material, injection molding, thermal insulation plaster, insulation boards and / or insulation panels.