BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in further detail in the following with the aid of exemplary embodiments, showing in:
FIG. 1 A differential thermo-analysis (differential scanning calorimetry DSC) of expanded perlite in air. The heating rate was 20 K/min while the exothermic sintering process started at approximately 700° C.
FIG. 2 A differential thermo-analysis (DSC) of a mixture of expanded perlite in air and sodium carbonate, in a weight ratio of 1:1. The heating rate was 20 K/min while the endothermic peak of approximately 850° C. was near the melting temperature of the carbonate (852° C.).
FIG. 3 Image of a hardened, dimensionally stable perlite material, produced with the method according to the invention.
FIG. 4 Magnified images showing pores in the tempered product of expanded perlite and sodium carbonate in the mm range. Scale: 1000 μm and 500 μm.
FIG. 5 Images obtained with the ESEM (environmental scanning electron microscope) of the porous structure of the tempered product, composed of expanding perlite and sodium carbonate, in a multi-modal distribution in the μm range. The right image shows the sodium zeolites that bloomed during the cooling down period and function to control the moisture.
FIG. 6 The isothermal sorption behavior of a sample comprising expanded perlite and sodium carbonate, obtained through the dynamic steam sorption method (DVS).
DETAILED DESCRIPTION OF THE INVENTION
In a first embodiment, 2 g of expanded perlite and 2 g of sodium carbonate Na2CO3 are mixed together in a weight ratio of 1:1. The mixture is then tempered for 15 minutes at about 800° C. inside a cylindrical crucible in a chamber furnace. Depending on the quantity used, the duration of the tempering process is about 10 to 20 minutes. A dimensionally stable cylinder (FIG. 3) with pores in the micrometer range (FIG. 4) is thus obtained, in which sodium zeolite blooms (FIG. 5). Deviations by up to ±5 percent from the starting weight ratio are not important for the final result.
In a second embodiment, 2 g of natural perlite are mixed with 2 g of sodium carbonate Na2CO3 in a 1:1 weight ratio and tempered in a chamber furnace at about 850° C. for 20 minutes. Depending on the quantity used, the duration of the tempering process is about 15 to 30 minutes.
The DSC graph (differential scanning calorimetry) in FIG. 1 shows that expanded perlite begins to sinter at approximately 700° C., while sodium carbonate Na2CO3 has a melting point of 852° C. A DSC analysis of a mixture of Na2CO3 and expanded perlite, in a weight ratio of 1:1, shows that the mixture begins to melt at approximately 800° C. and that the endothermic melting peak practically coincides with that of the Na2CO3 (852° C.). Sodium zeolite, which can control moisture, is precipitated out during the cooling period. Since the moisture is controlled by the sodium zeolites and not the glass, the heat-insulating capacity is not reduced by the moisture which may be present.
Owing to the lowering of the melting point, the mixture of expanded perlite and Na2CO3 begins to melt at a temperature of about 800° C. during the tempering, wherein two glass components with different sodium contents are formed in the process. An EDS analysis showed that the original perlite material was melted on and that two mixed melts with different sodium contents formed. During the melting on, CO2 is released in part, which results in the formation of pores in the range of a few μm to several mm because of the relatively high viscosity of the silicate glass.
The formed body produced according to the invention has an approximate density of 0.5 g/cm3, while its material density is approximately 2.1 g/cm3. The resistance to pressure of this material is higher than 1500 kN/m2. ESEM images (FIG. 5) show that the sodium zeolites, which bloom on the surface of the material, are known for their good moisture adsorption and desorption. If the formed body is placed in water, the sodium zeolites are leached out after only 5 minutes. The heat-insulating material itself remains undamaged, even after three weeks in water.
The isothermal sorption behavior of a sample made of expanded perlite and sodium carbonate was tested with the dynamic steam sorption method (DVS, Differential Vapor Sorption). After equilibrium was established at 0% humidity, the humidity was incrementally increased. FIG. 6 illustrates measurements taken between −40 and 98% air humidity for three cycles. Here, H (%) represents the humidity as a percentage, and Δm (%) represents the increase or decrease, respectively, of the mass relative to the dried sample, for which Δm (%)=0%.
FIG. 6 depicts an increase in weight by 200% relative to the total weight of the sample (insulating material) because of water adsorption. Desorption occurs virtually without hysteresis, and the water is completely re-released. The zeolites on the surface of the glass, as shown in FIG. 5, for example, are responsible for this sorption behavior. Although a small proportion of about 14% remains bound in the zeolite structure following the first cycle, it has no detrimental effect on the sorption behavior of subsequent cycles.
The invention has been disclosed in conjunction with various exemplary embodiments thereof, and a number of modifications and variations have been discussed. Other modifications and variations will readily suggest themselves to persons of ordinary skill in the art. The invention is intended to embrace these and all other modifications and variations that fall within the spirit and broad scope of the appended claims.
Patent Application
20070281146
