Patent Application
20140237896
The novel technology relates generally to the field of ceramic materials and, specifically, to a foamed glass substrate system having including hydrophilic pore walls for water storage and root propagation.
Hydroponics is the science of growing plants in a nutrient solution with the mechanical support of an inert medium. Hydroponics is an old art, and a variety of inert media are known as suitable for the germination, rooting and growth of plants. Such substrates include peat, vermiculite, perlite, fly ash, pumice, rock wool, glass wool, organic and inorganic fibers, polymers such as polyurethane, polystyrene, polyethylene, and the like. These substrates have been used for true hydroponics or in quasi-hydroponic environments such as in admixtures with soil. Typically, the inert medium is either in the form of a contained loose particulate, such as sand, or as a rigid and self-supporting structure that can support growth of the plant. The rigid structure has some notable advantages over the loose particulates, in particular the ability to stand alone without a requisite container. However, the loose particulate media tend to offer better pathways for water and gasses to be delivered to and from the root systems.
One problem common to hydroponic gardening is under/overwatering. Some media offer limited porosity and/or limited means for circulating water into and out of pores. As a result, vegetation growing hydroponically is often underwatered. Conversely, hydroponic techniques lend themselves to the provision of excessive water to the plant root system, often in response to the underwatering that is occurring. Overwatering can result in chlorosis, retarded growth, pallor, and, eventually death. In such situations, the water around the roots becomes stagnant and gasses dissolved therein are only urged to and from the roots through diffusion. Moreover, vital gasses quickly become depleted and waste gasses saturated in the water proximate the roots, exacerbating the situation. Thus, it is desired to reduce the stagnant water around the roots by circulating the water.
Most of the substrates currently known are solids with limited porosity. Some known substrates have attempted to add or increase the porosity of the substrate in order to better provide for gas exchange to the roots. One such substrate has been produced in the form of a sponge-like or foraminous foamed polymer body with conduits 1-5 millimeter in nominal diameter, spaced about 1-8 mm apart and extending throughout the substrate. The conduits drain water from the substrate and provide reservoirs of oxygen for the plant roots and at the same time allow substrate to hold some water that may then be available to the roots. The porosity of this substrate ranges from between 6 and 53 percent. Soil or the like is deposited on top of the substrate and a seed, cutting or small plant is placed in the soil. With the substrate under the soil layer, over-watering induced problems are prevented, as excess water drains from the substrate, filling the conduits with air and oxygen will be readily available to the roots.
Another issue with known substrates is pH control. Natural substrates tend to include soluble mineral residue that dissolves at uncontrolled rates, shifting water pH. Man-made substrates likewise may include materials that dissolve over time and at nonlinear rates, shifting pH as they do. Changes in pH can have a drastic and deleterious effects on plant growth.
While useful in hydroponic and soil amendment applications, the above substrates are still hampered by a lower than optimal porosity, limited wicking capacity, low capacity for water infiltration and retention, and uncontrolled pH arising from mineral dissolution. Thus, there remains a need for a highly porous substrate for supporting plant growth. There also remains a need for improves the aeration of soil and allows for better water filtration and irrigation. The present novel technology addresses these needs.
The present novel technology relates to a foamed glass material system for supporting plant growth, and the method for making the same. One object of the present novel technology is to provide an improved foamed glass plant support substrate material. Related objects and advantages of the present novel technology will be apparent from the following description.
For the purposes of promoting an understanding of the principles of the novel technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates.
Foamed glass, like most ceramics, is naturally hydrophobic. As hydrophobic surfaces are not conducive to wetting and impede capillary action, treatment is typically done to make the pore walls 17 hydrophyllic. In one embodiment, the pore walls 17 are coated to form a plurality of microcracks 19 therein. The microcracks 19 supply increased surface area to support wicking. Alternately, or in addition, an agent may be added to further amend the surface properties to make the foamed glass more hydrophilic. Such an agent may be a large divalent cation contributor, such as ZnO, BaO, SrO or the like. The hydrophilic agent is typically added in small amounts, typically less than 1.5 weight percent and more typically in amounts of about 0.1 weight percent.
The combination is mixed 26, and the resulting dry mixture 27 may then be placed into a mold 28, pressed into a green body and fired without the use of a mold, or, more typically, arrayed into rows 31 of powder mixture 27 for firing and foaming. Typically, whether placed 29 into the mold 28 or not, the mixture 27 is typically arrayed in the form of several rows 31, such as in mounds or piles of mixture typically having a natural angle of repose of about 15 to 50 degrees, although even greater angles to the horizontal can be achieved by compressing the dry mixture 27. This arraying of the rows 31 allows increased control, equilibration and optimization of the heating of the powder 27 during firing, reducing hot and cold spots in the furnace as the powder 27 is heated. This combing of the powder 27 into typically rows 31 of triangular cross-sections allows heat to be reflected and redirected to keep heating of the rows generally constant.
The mold 28, if used, is typically a refractory material, such as a steel or ceramic, and is more typically made in the shape of a frustum so as to facilitate easy release of the final foamed glass substrate 10. Typically, the inside surfaces of the mold 28 are coated with a soft refractory release agent to further facilitate separation of the foam glass substrate 10 from the mold 28. In a continuous process, the powder 27 is typically supported by a fiberglass mesh fleece or the like to prevent fines from spilling as the powder 27 is moved via conveyor through a tunnel kiln; the fleece is burned away as the powder 27 sinters.
The so-loaded mold 28 is heated 30 in a furnace by either a batch or continuous foaming process. More typically, the mixture 27 is then heated 30 in order to first dry 32, the sinter 34, fuse 36, soften 38, and foam 40 the mixture 27 and thereby produce a foamed glass substrate 10 having a desired density, pore size and hardness. As the powdered mixture 27 is heated to above the softening point of glass (approximately 1050 degrees Fahrenheit) the mixture 27 begins to soften 38, sinter 34, and shrink. The division of the powdered mixture 27 into rows or mounds allows the glass to absorb heat more rapidly and to therefore foam faster by reducing the ability of the foaming glass to insulate itself. At approximately 1025 degrees Fahrenheit, the calcium carbonate, if calcium carbonate has been used as the foaming agent 22, begins to react with some of the silicon dioxide in the glass 20 to produce calcium silicate and evolved carbon dioxide. Carbon dioxide is also evolved by decomposition of any remaining calcium carbonate once the mixture reaches about 1540 degrees Fahrenheit, above which calcium carbonate breaks down into calcium oxide and carbon dioxide gas. Once the temperature of the mixture 27 reaches about 1450 degrees Fahrenheit, the glass mixture 27 will have softened sufficiently for the released carbon dioxide to expand and escape through the softened, viscous glass; this escape of carbon dioxide through the softened glass mass is primarily responsible for the formation of cells and pores therein. The mixture 27 in the mold 28 is held for a period of time at a peak foaming temperature of, for example, between about 1275 and about 1700 degrees Fahrenheit, more typically between about 1450 and about 1600 degrees Fahrenheit, or even higher, depending on the properties that are desired. By adjusting the firing temperatures and times, the density and hardness as well as other properties of the resultant substrate 10 may be closely controlled.
As the mixture 27 reaches foaming temperatures, each mass of foaming 40 glass, originating from one of the discrete rows or mounds, expands until it comes into contact and fuses with its neighbors. The fused mass of foaming glass then expands to conform to the shape of the walls of the mold 28, filling all of the corners. The shapes and sizes of the initial mounds of mixture are determined with the anticipation that the foaming 40 mixture 27 exactly fills the mold 28. After the glass is foamed 40 to the desired density and pore structure, the temperature of the furnace is rapidly reduced to halt foaming 40 of the glass. When the exterior of the foamed glass in the mold has rigidified sufficiently, the resultant body 10 of foamed glass is removed from the mold 28 and is typically then air quenched to thermally shock the glass to produce a crazed microstructure 19. Once cooled, any skin or crust is typically cut off of the foamed glass substrate 10, which may then be cut or otherwise formed into a variety of desired shapes. Pore size can be carefully controlled within the range of about 5 mm to about 0.5 mm, more typically within the range of between about 2.0 mm and 0.2 mm, and is typically controlled such that the interconnected or open porosity may readily accommodate a typical plant root 135 (see
The substrate 10 may be either provided as a machined polyhedral shape 10 or, more typically, as a continuous sheet that may be impacted and/or crushed to yield aggregate or pebbles 50 (typically sized to be less than 1 inch in diameter). The crushed substrate material 50 may be used to retain water and increase air volume in given soil combinations. The polyhedrally shaped substrate bodies 10 are typically sized and shaped as growing media for seeds and immature plants, such as for use in soil or hydroponic systems 140 (see
Crushed foam bodies 50 may be rapidly made by an alternate method. Using soda-lime glass frit or powder as the glass component 22, the processing is similar to that described above but without the annealing step. The alternate method employs the same foaming temperature ranges as related above. The batch material 27 consists of up to 8 percent by mass limestone, magnesite, or other applicable foaming agent 22, usually less than 2 percent by mass dicalcium phosphate 24, with the balance being a borosilicate, silicate, borate or phosphate glass frit 22. The batch 27 is then placed in a typically shallow mold 28, more typically having a configuration of less than 2″ batch for every square yard of mold surface. The mold 28 is typically then heated to approximately 250° C. above the dilatometric softening point for soda-lime glass (or the equivalent viscosity for other glass compositions) and allowed to foam. The mold 28 is held at the foaming temperature for less than 30 minutes and then pan quenched, i.e. substantially no annealing is allowed to occur
This method typically yields a material 10 of density less than 0.25 g/cc, and more typically as low as about 0.03 g/cc. This material 10 is then crushed into pebbles 50, with a corresponding lower bulk density as per the above-described method. Material made by this alternate method has similar chemical properties as described above, can accommodate an even larger nutrient content, but has substantially lower strength.
Still another alternate method of preparing foamed glass substrate material 10 is as follows. A batch 27 is prepared as discussed above and pressed into small (typically less than 5 mm diameter) pellets. The pellets are rapidly heated, such as by passage through a flame source, passage through a rotary furnace, or the like. Typically, the pellets are heated to about 1500 degrees Fahrenheit, such as to cause the pellet to expand as a foam particulate without the need for a mold. This material yields the weakest, but least dense foam particles. The typical density may be as low as 0.02 g/cc or as high as 0.2 g/cc, or higher.
The foamed glass substrate 10, either in polyhedral body form or crushed product form, may serve as a root system support and an aeration and/or water retention aid. The material 10 typically enjoys a void fraction of at least about 80 percent. The substrate 10 is typically mechanically mixed with as little as 15% by volume soil or soil mixture and this new mixture will still generate solution chemistry dominated by soil.
The polyhedral product 10 typically functions as a supporting substrate for both soil based and hydroponic applications. The polyhedral substrate 10 may be tailored to be compatible with mildly acidic, neutral, or mildly alkaline solution pH. The pore network 15 is compatible with root propagation through the material 10. The pore network typically has surface adhesion or adsorption properties such that chemical additives 51, such as plant growth nutrients, herbicides, pesticides or combinations thereof, may be physically adsorbed thereonto for later release. Typically, these additives are added in small amounts, such as a few weight percent (0.5 1, 2, 5, or the like) of the substrate product 10.
The foamed glass substrate 10 typically has a porosity in the range of between about sixty-five and about eighty-five percent. Air holding capacity is typically between about forty and about fifty-five percent. Water holding capacity typically ranges from between about twenty and about thirty-five percent.
Porosity is measured during the production process using a parometer testing protocol. Bulk density and pH are also measured during production, with the results providing active feedback for a control loop.
The pore size is typically between about 0.2 mm and about 2.0 mm in diameter, with a relatively tight pore size distribution. The finished substrate 10 is typically processed through a series of conveyors and crushing equipment to yield a desired size spread of pellets 50.
The precursor glass material is typically recycled or post-consumer waste glass, such as plate, window and/or bottle glass. The glass is ground or milled to a fine mesh profile of minus 107 microns. A typical sieve analysis of the precursor glass is given as Table 1, and a compositional analysis of the glass is given as Table 2.
A plant growth support substrate 10 having a pore network 15 and pH control agent 24 embedded therein is produced from a precursor batch of about 1.25 weight percent calcium carbonate, about 1.25 weight percent dicalcium phosphate anhydrous, about 0.2 weight percent iron oxide colorant, and about 97 weight percent recycled post-consumer glass ground or milled to minus 107 microns, are mixed together. The resulting mixture 27 is placed into a stainless steel mold 28 having inside dimensions of 4.25 inches by 4 inches by 8.25 inches. The mold 28 is covered with a one-half inch stainless steel plate. The mold 28 with the mixture 27 therein is fired 30 in a tunnel kiln having a plurality of zones with a travel rate of about 10 inches per minute and a residence time in each zone of about 9 minutes. The first zone typically has a temperature of about between about 200 and about 500 degrees Fahrenheit, more typically between about 400 and about 450 degrees Fahrenheit, and still more typically about 225 degrees Fahrenheit, wherein drying 32 of the mixture 27 is accomplished. Zones 2-4 have temperatures increasing from about 1300 to about 1500 degrees Fahrenheit, and sintering 34 is accomplished therein. Foaming 40 occurs primarily in zones 4 and 5, with zone 5 having a temperature of about 1580 degrees Fahrenheit. In zone 6, temperature about 1570, foaming 40 is finalized and the resultant soft foamed body 42 is cured 44. In the final zone, cooling begins as the temperature is decreased to about 1400 degrees Fahrenheit. Upon exiting the tunnel kiln, the foamed body 42 is air quenched 46 to produce the desired crazed microstructure 19. The cooled block of foamed glass 10 is removed from the mold 28, and the outer layer of crust is removed (such as with a band saw) to expose the open porosity. The substrate 10 is further cooled and quenched until it is approximately at room temperature. The resulting block typically has a density of about fourteen pounds per cubic foot and a pore size distribution ranging from about 0.5 to 2 mm. The resulting block has open, interconnected pore cells.
While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.
