Study of Catalytic Filters for Soot Particulate Removal from Exhaust Gases

Two ceramic supports (sintered and foam) were employed for the preparation of catalytic filters for soot removal at diesel exhausts. Laboratory tests showed that while the foam filter is appropriate for small size and low engine backpressure, the sintered filter is more suitable for achieving high filtration efficiency. Tests carried out at the exhaust of a diesel engine showed that the catalytic filter can be continuously regenerated at operating conditions typical of diesel exhaust.     

Manufacturing of nano mullite-silicon carbide filters by in situ reaction bonding

In the present study, the effect of silica nanoparticles on the formation of nano-mullite phase for use in the manufacture of silicon carbide based ceramic foam filters has been investigated. Polyurethane foam filters were impregnated with nanosilica particles by slip casting. In this method, the effect of different percentages of nanosilica particles in the slurry on compressive strength, density and porosity of ceramic foam filters was investigated. The effect of silica nanoparticles on viscosity of slurry was studied using rheometric test. So, sample S₁₅ was selected to proceed. For thermal treatment of ceramic foams, different sintering temperatures were investigated and the best temperature was reported at 1250 °C. Compressive strength results showed that with increasing nano-silica content, CCS increased. XRD results from the samples showed that the nano-mullite phase was formed at 1250 °C along with silicon carbide and alumina phases. Scanning electron microscope images (SEM) showed that the mullite phase was formed in nano-dimensions in ceramic foam bodies. The formation of mullite phase in the microstructure of the filters is one of the factors of strengthening and increased refractory characteristics. EDS analysis by the scanning electron microscopy of the filter which passed ductile iron melt showed that cast iron inclusions and impurities were mostly consisted from FeO, MnO, SiO₂, Al₂O₃, MgO and CO, which were trapped inside the ceramic filter.     

Expansion of polystyrene using water as the blowing agent

Heating of polystyrene beads containing pentane isomers as the blowing agent traditionally produces polystyrene foam. Undesirable emissions of the blowing agent and its high flammability are the complications of this process. A new process for the production of expandable polystyrene has been developed, using water as the blowing agent. Water is trapped inside the polystyrene matrix through the use of starch that is introduced as a separate phase during the suspension polymerization. The problems created by the incompatibility of starch with the organic phase can be partially overcome by “compatibilization” with maleic anhydride. The type of starch can influence the foam morphology of the pre‐expanded beads, while the density is changed only in the range of the experimental error. The density of the pre‐expanded beads is influenced by the blowing technique used (hot air or high frequency electric field). The use of these different blowing techniques does not influence significantly the foam morphology.     

泡沫陶瓷过滤器的研究现状和发展趋势

本文阐述了国内外铸造用泡沫陶瓷过滤器的材料成分、生产工艺和结构特点 ,着重介绍了它们的技术性能及其在液态铸造合金过滤净化中的应用效果 ,同时探讨了铸造用泡沫陶瓷过滤器在新世纪的市场前景和发展趋势。     

铸造用泡沫陶瓷过滤器的生产工艺

本文详细介绍了泡沫陶瓷过滤器的生产工艺,并简单介绍了其过滤机理。对海绵加工、浆料调节及产品烧结等生产工序分别作了阐述,并提出了生产过滤器的技术要求和铸造使用过程中的注意事项。     

Theory of design of foam ceramic filters for cleaning molten metals

A new method of theoretical design of foam ceramic filters (FCF) for cleaning liquid metals is suggested. The method is based on the solution of an optimization problem involving the criterion of the operational capacity of the FCF that reflects the interrelation between the physicomechanical properties of the filter, the system of technological constraints in its production, and the target function that expresses the basic economical criterion, i.e., the cost of the FCF. Mathematical models of the process of filtration of liquid metals and the structure of the FCF are considered. The method is illustrated by solutions of optimization problems for specific production lines.     

Towards a new generation of environmentally-friendly ceramic foam filters: contribution of graphene nanoadditives in calcium aluminate-rich coatings

In this contribution, the widely used non-ecological production process of ceramic foam filters was modified into an environmentally friendly procedure, in which no hazardous materials are involved. Firstly, a large number of carbon-bonded ceramic foam filters were prepared by this approach. In the next step, a thin coating consisting of graphene-doped, carbon-bonded calcium aluminate was applied over these filters. Reference samples as well as coated samples were analyzed in detail with a focus on the phase composition, microstructural analysis, and mechanical as well as thermal properties. The results confirmed that the application of the developed coating improved the cold crushing strength of the ceramic foam filters. In addition, by application of graphene nanoadditives, it is also possible to vary the surface microroughness which will subsequently enable improved efficiency of inclusions elimination from metal melts during the filtration process.     

Additive manufactured polyamide foams with periodic grid as templates for the production of functional coated carbon-bonded alumina foam filters

For the industrial production of metal melt filters, the replica technique is established since several decades. The polyurethane foams used as templates show a rather random structure with several defects which are transferred into the final filter structure after the replication. In order to generate filters with periodic structure and low amount of defects, a periodic foam model was used and open cell foams were produced by selective laser sintering of aged polyamide 12 (PA12). The PA12 foams were then used as sacrificial templates for the replica technique in the production route of Al₂O₃-C filters with functional coatings based on a cold sprayed Al₂O₃-C coating or a flame sprayed coating based on Al₂O₃. The differences in geometry between the computer-generated model foam, the sacrificial PA12 foam, the foam after carbonization, and the additional functionalized filters with the cold and hot coating were analyzed by computed tomography. Based on CT-data isosurfaces of the foams were generated to virtualize and distinguish the differences. Preliminary mechanical tests showed a higher cold crushing strength for the filters coated via flame-spray technique than the cold coating.     

Processing of composite polystyrene foam with a honeycomb structure

Composite polystyrene foam with a honeycomb‐like barrier structure was processed from an expandable aqueous suspension. Optical observations confirmed the formation of such a unique structure that encapsulates each expanded polystyrene microsphere in the resulting foam. The suspension viscosity was found to highly influence the foam morphology. Results from mechanical tests showed that the existence of the barrier structure can considerably improve the mechanical performance of the composite foam. Fire retardation tests demonstrated that the barrier structure can effectively stop the fire path into the foam, suppress toxic smoke generation, and maintain structural integrity, leading to improved fire resistance in comparison with the neat polystyrene foam. POLYM. ENG. SCI., 55:1494–1503, 2015. © 2015 Society of Plastics Engineers     

Simultaneous Filtration and Catalytic Oxidation of Carbonaceous Particulates

Two catalytic filters prepared by the deposition of Cu–V–K–Cl catalyst on different ceramic supports, foam and sintered aluminosilicate monolith, were employed for the removal of soot from the exhaust of a gas-oil burner. The foam filter was more suitable than the sintered filter for this application allowing better soot–catalyst contact, lower gas pressure drop and easier spontaneous filter regeneration.     

The 3D-Printed building and performance of Al2O3 ceramic filters with gradient hole density structures

Ceramic filters with gradient hole density structures will be an attractive candidate for high-temperature alloy melt filtration because it combines good mechanical properties with filtration requirements. This paper focuses on the structural design, mechanical properties and printed forming mechanism of the new pattern Al₂O₃ filters with gradient hole density structures (Al₂O₃-GHDS). Al₂O₃-GHDS filters were designed based on a topologically optimized lattice and then fabricated by stereolithography (SLA) printing technology using our developed Al₂O₃ paste system. It was found that GHDS filters exhibited the resultant performances combining wide hole sizes and excellent structural stability, and their compressive strength, energy absorption value and bending strength were 4.7 MPa, 77.7 kJ/m³ and 6.7 MPa, respectively, which far exceeded the mechanical properties of the traditional ceramic foam filters. The thermal shock resistance of GHDS filters can reach 2.2 MPa, which was nearly five times the traditional ceramic foam filters. The GHDS ceramic filter finally can exhibit the hole diameter largely ranging from 0.76 mm to 5.35 mm, which covered the hole sizes from 10ppi to 40ppi uniform hole density structure (UHDS). Furthermore, the inner holes of our built GHDS ceramic filters also had the good connectivity without plugging phenomena.     

Microwave Regenerated Catalytic Foam: A More Effective Way for PM Reduction

In this work the effect of microwave irradiation on the regeneration of soot-loaded uncatalytic and catalytic ceramic foam filters was studied for two different catalytic filter formulations. Combining dielectric permittivity and catalytic activity of the foam filter components with microwave absorbing properties of soot allowed a more effective filter regeneration. Moreover, iron based catalysts, typically not active towards soot oxidation in case of electrical heating, showed a significant activity in the presence of microwave.     

Mechanical and physical characterization of Al2O3–C foam filters produced by distinct processing routes: The importance of the ceramic strut morphology

In this work the influence of the production route and filter dimensions on the mechanical properties of carbon-bonded alumina foam filters was investigated. Features like cold crushing strength and fracture behavior were analyzed and used to compare them. Microfocus computer tomography (μCT) was applied to characterize the geometry of the filters, providing a deep correlation with their fracture behavior. Furthermore, computer-generated filter geometries were used as reference. The results indicated that the centrifugation process is better suited for the production of carbon-bonded alumina filters, and is even more effective when the foam dimensions are increased in the range of those analyzed in this research. Finite element simulations showed the influence of the relative density and strut tapering on the cold crushing strength of filters, providing a correlation between filter structure and its failure mechanism. The attained results provided further insights towards the production of inclusions-free metal parts.     

Innovative carbon-bonded filters based on a new environmental-friendly binder system for steel melt filtration

New carbon-bonded alumina filters for steel melt filtration were developed. The carbonaceous matrix was based on a new, environmental friendly binder system based on lactose and tannin. The filter preparation was analogous to the production of conventional foam filters according to the Schwartzwalder process. The processing as well as the rheology of the slurries was investigated. An addition of n-Si increased the carbon yield and the cold crushing strength (CCS) of the samples. Higher values of CCS were obtained after coating of the filters with alumina. The material was characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The applicability of these new filters was assessed in impingement tests with a steel melt, in which three out of four recipes survived the thermal shock.     

Stability of catalytic foam diesel-soot filters based on Cs2O, MoO3, and Cs2SO4 molten-salt catalysts

The durability of catalytic alumina and zirconia-toughened mullite ceramic foam diesel-soot filters was tested by exposing them to severe, artificial exhaust conditions. The catalytic performance, composition, and mechanical strength were constantly monitored. It was concluded that the mechanical strength of the catalytic filters may be reduced by an interaction of the catalyst with certain compounds of ceramic filters. In practice, it should be possible to minimize the effect by carefully controlling the composition of the ceramic filter. For instance, the presence of phosphorous in alumina-based filters support should be avoided. The stability of the current catalyst phases, based on Cs₂O, MoO₃, and Cs₂SO₄, is too low for application. Due to partial evaporation, emission of catalyst compounds into the environment is likely and when that happens significant deactivation of the catalytic phase is unavoidable. The catalyst was also found to be soluble in water, which might be disastrous in the case of condensation occurring in the exhaust pipe.     

Investigation of mechanical and thermo-mechanical strength of ceramic foam filters (CFFs)

During aluminium production, the molten metal will always contain varying amounts of impurities, e.g., non-metallic inclusions, and for high-quality products removing such inclusions is essential. This can be achieved by filtration using ceramic foam filters (CFFs). However, these filters are highly brittle materials subjected to strong mechanical and thermo-mechanical stresses during transport and operation, which occasionally leads to failure of the filter material. In the present study, the compression strength of five different Al₂O₃-based CFFs was measured at room temperature and elevated temperature (compressed at 730 °C), as well as while submerged in molten aluminium with varying melt compositions (pure aluminium and an aluminium-magnesium alloy). The compression strengths at room temperature were established to be in the range of 1.19–2.09 MPa depending on the filter type tested. In the case of the CFFs compressed at elevated temperature, a reduction in compression strength in the range of 9.2–58.6% was established to exist depending on filter type and heating duration, except in three of the filter/duration-combinations tested. Compression of CFF samples submerged in molten aluminium led to an even further reduction in compression strength in the range of 42.6–69.4% depending on filter type and duration of exposure. With an exposure time of only 5 min, no difference in compression strength was observed between the two aluminium melts.     

Producing Ceramic Foams with Hollow Spheres

Ceramic foams have a large potential for many applications and can be produced in several ways. In the past, many have attempted to manufacture ceramic foams that combined sufficient strength and controlled microstructure. This study proposes a new two-step processing route to fulfill these requirements. First, sacrificial cores are coated with ceramic powder slurry and packed in a die. Second, the cores are connected together using another ceramic slurry coating. After they are burned out and sintered, ceramic foam structures can be obtained that have a density <10% of theoretical density. By varying the size and shape of the initial cores, ceramic foams with tailor-made microstructures can be easily produced.     

锆刚玉—莫来石泡沫陶瓷过滤器的研究及应用

以氧化铝粉和锆英石粉为原料，通过反应烧结制成了锆刚玉－莫来石泡沫陶瓷过滤器，研究了锆英石对抗弯强放抗热震性的影响，对球墨铸铁和铸钢的过滤试验结果表明，过滤后的夹杂物减少，冲击韧性明显提高。     

Validation of an experimental-numerical approach for the high temperature behaviour of open-cell ceramic foams

Open-cell ceramic foams are used as filters in casting processes of molten metal to reduce the amount of non-metallic inclusions. These filters are exposed to high temperatures and loadings, sometimes for a longer time. Therefore, the dimensional stability has to be considered, which suffers from inelastic deformations, in particular creep deformations.A recent work of the authors describes the creep deformation behaviour of such foam structures using an experimental-numerical approach based on bulk material creep tests. Now, the results of this prediction are validated by creep curves of real foam samples. This comparison shows a good accordance for the considered parameters (load, temperature, time, and creep phase).Moreover, the influences of different structural parameters on the elastic foam stiffness and foam creep resistance are investigated. The relative foam density has the greatest impact, followed by uniaxial pore stretching in one direction and strut shape, whereas polydispersity has only a very small effect.     

Authentication of Particulate Air Samples by Aerosol

A method was developed for the protection of aerosol filters against tampering that can be applied to any particulate sampler. In this method, tagged particles are dispersed into the sampled aerosol volume by liquid atomization to guarantee homogeneous distribution of the tag and deposition into the filter matrix. The tagged aerosols are collected insitu, together with the sampled dust particles. The tag can be measured in different ways. This feature can be used for self protection of the method. The authentication of the individual filters is preserved through the lifetime of the filter sample. Long-term field tests of the equipment indicate reliable performance.