The availability of a high alumina, silica-free, fiber-free insulation with fine porosity will fulfill unmet needs for various industries. Ceramatec, Inc. (Salt Lake City, UT) inventors Akash Akash and G. Nair Balakrishnan divulge methods for manufacturing silica-free insulation materials and insulation for high temperature applications using novel nano-to-micro scale castable powder-based ceramics in U.S. Patent 7,628,951.
The silica-free ceramic components produced using the Ceramatec process offer (i) a fine porosity (from nano-to micro scale); (ii) a superior strength-to-weight ratio; and (iii) flexibility in designing multilayered features offering multifunctionality. Those qualities will increase the service lifetime of insulation and refractory components used in the solid oxide fuel cell, direct carbon fuel cell, furnace, metal melting, glass, chemical, paper/pulp, automobile, industrial heating, coal, and power generation industries. Further, the ceramic components made using Ceramatec’s method may have net-shape and/or net-size advantages with minimum post machining requirements.
Nano and micro ceramic insulation is produced by introducing very small-sized porosity in the fired ceramic in a controlled fashion, and production of multilayered, multifunctional ceramic components. Ceramatec methods also produce net-shape and/or net-size ceramic insulation components. Ceramatec nano-to-micro scale ceramics are applicable for high temperature applications as insulation or refractory components. The insulation can be designed for both load-bearing (structural) and non-load bearing applications.
In the solid oxide fuel cell industry, silica in the insulation surrounding the fuel cell is detrimental for the long-term performance of the solid oxide fuel cells (SOFC). Silica, in the presence of humidity and high temperatures converts into a gaseous form SiO, which may then react and adversely affect the fuel cell performance. Therefore, a silica-free, oxide-based insulation is desired for SOFC. Currently, there are only two alternative commercially-available products that meet the need for high alumina, silica-free insulation for solid oxide fuel cells. Both have significantly high cost. Thus, it is an advancement in the art to provide a lower cost high alumina insulation to fuel cell manufacturers.
In the furnace industry, fiber-based (non-load bearing) insulation is the most commonly used high temperature insulation. Alumina-fiber insulation is used in reducing environments or where there is high humidity and/or high temperature requirements. However, manufacture and use of high alumina fiber-based insulation is often associated with health concerns and high product cost. The Ceramatec process can produce alumina-based fiber-free insulation at a lower cost that competing processes. .
Most of the oxide based, silica-free, structural (load-bearing) insulation have a density of 2.5-3.0 g/cc and a flexural strength of less than <10 MPa (1450 psi). Further, the flexural strength of the insulation quickly degrades (sometimes by as much as 50%) when exposed to temperatures above 600.degree. C. i.e. they have poor hot strength.
In the solid oxide fuel cell industry, silica in the insulation surrounding the fuel cell is detrimental for the long-term performance of the solid oxide fuel cells (SOFC). Silica, in the presence of humidity and high temperatures converts into a gaseous form SiO, which may then react and adversely affect the fuel cell performance. Therefore, a silica-free, oxide-based insulation is desired for SOFC. Currently, there are only two alternative commercially-available products that meet the need for high alumina, silica-free insulation for solid oxide fuel cells. Both have significantly high cost. Thus, it is an advancement in the art to provide a lower cost high alumina insulation to fuel cell manufacturers.
In the furnace industry, fiber-based (non-load bearing) insulation is the most commonly used high temperature insulation. Alumina-fiber insulation is used in reducing environments or where there is high humidity and/or high temperature requirements. However, manufacture and use of high alumina fiber-based insulation is often associated with health concerns and high product cost. The Ceramatec process can produce alumina-based fiber-free insulation at a lower cost that competing processes. .
Most of the oxide based, silica-free, structural (load-bearing) insulation have a density of 2.5-3.0 g/cc and a flexural strength of less than <10 MPa (1450 psi). Further, the flexural strength of the insulation quickly degrades (sometimes by as much as 50%) when exposed to temperatures above 600.degree. C. i.e. they have poor hot strength.
Ceramatec’s silica-free insulation has a higher strength-to-weight ratio over conventional insulation products currently available in the market and also has good mechanical and thermo-chemical stability at the operating temperatures.
High strength-to-weight ratio ceramic components can be used in a wide range of applications due to their insulative properties. These applications can be in diesel particulate filters (DPF) as ceramic honeycomb structures, or diesel particulate filter frame materials, or DPF mount supports where lightweight and good strength are critical. Other applications can be ceramic hot gas filters, and supports or carriers for catalyst where tailored micro-porosity and strength is critical to their lifetime performance. The new alternative compositions are lightweight, possess good hot strength, and also provide flexibility in designing appropriate pore structures.
Ceramic components made using Ceramatec technology may have the following unique properties:
(i) mechanical 4-point bend strength of <1-150 MPa (<145-21,750 psi)--three to five times stronger than what is currently available in the form of structural, ceramic oxide-based insulation (with comparable fired densities);
(ii) Excellent erosion and wear resistance (higher strength is generally correlated with higher wear- and erosion-resistance);
(iii) high temperature capability (the maximum service temperature can be as high as 1650.degree. C.);
(iv) excellent hot modulus of rupture strength, i.e., it retains its mechanical strength at high temperatures);
(iv) longer lifetime/improved corrosion and chemical resistance (the ultrafine nano-, meso-, and micro-porosity will limit gas diffusion and molten metal/glass/black liquor/slag penetration into the ceramic insulation);
(v) good insulation and thermal shock properties (thermal conductivity can range from 0.2-5.0 W/mK (7.0-35.0 BTUin/hrft.sup.2F--depending on the fired density)--its superior thermal shock resistance (along with nanoporosity and high strength) is expected to offer increased lifetime and superior performance in harsh environments;
(vi) environmental and thermo-chemical stability (the material offers robust, stable performance in both oxidizing and reducing environments at high temperatures);
(vii) Process flexibility & product availability: the material can be made available in various forms--castable mixes or powder pressed forms. This process flexibility allows the material to be available in a wide range of densities (0.6-3.5 g/cc, or, 37-217 lbs/cu. ft.) to suit the end user's needs--a lower density material, due to its lower thermal mass, can result in potential energy savings. On the other hand, the higher density version can be a good candidate for products where high strength or low permeability to gases is desired);
(viii) design flexibility (functionally graded designs can be easily incorporated into the final products. For example, the porosity and chemical composition of the outer surface can be tailored to be different from that of inner bulk. Optionally, incorporating fibrous or particulate materials as mechanical reinforcements and infrared opacifants can also be achieved.
Lastly, while the product is a high alumina (>95%), reaction bonded ceramic, it can have a second phase (<90 vol. %) in the form of mullite, zirconia, magnesia, iron oxide, chrome oxide, spinel, aluminum silicate, silicon carbide (SiC), or if requested by the end user, silica-based too.
The material can be made available in a castable or a moldable form as a ceramic slip for conventional casting, of filter-pressing or as ceramic green feedstock for extrusion or injection molding. Thus the net-shaped and/or net-sized components can be formed in the green (pre-fired) stage. Such materials may provide low cost, one step processing, and under certain processing conditions may give net-shape or net-size components which will eliminate the need for post-machining processes. The proposed material system and method has also got a cost advantage over similar high alumina-based insulation available in the market.
The material can be made available in a castable or a moldable form as a ceramic slip for conventional casting, of filter-pressing or as ceramic green feedstock for extrusion or injection molding. Thus the net-shaped and/or net-sized components can be formed in the green (pre-fired) stage. Such materials may provide low cost, one step processing, and under certain processing conditions may give net-shape or net-size components which will eliminate the need for post-machining processes. The proposed material system and method has also got a cost advantage over similar high alumina-based insulation available in the market.
