Ceramic Foam Filters Research Articles

A new technology on continuous purification of galvanized zinc liquid through supergravity-induced filtration

The removing of suspended dross in galvanized zinc is the key point to obtain defect free coatings and inhibit the generation of solid wastes including surface and bottom dross which are detrimental to preserving environment. A supergravity technology was used to induce the galvanized zinc liquid to be purifying through ceramic foam filter (Al2O3 CFF). Al-Fe intermetallic were the dominant inclusions and precipitated in the galvanized zinc liquid as suspended dross. During the processing of purifying galvanized zinc liquid, inclusions were intercepted on the surface of Al2O3 CFF as residue by the way of being wrapped in oxide film, and some fine inclusions were captured in the filter. The removal ratio of Fe (RFe), loss percentage of Al (LAl) and the yield of zinc (YZn) respectively reached 76%, 63% and 96% at T = 450 °C and G= 50 through the Al2O3 CFF with pore size of 170 ppi and thickness of 20 mm. According to the exploratory experiment on the purification, a continuous purification was further performed for completing engineering scale purification of galvanized zinc liquid. RFe of 73% and LAl of 59% were obtained after the process of continuously purifying 8 kg molten galvanized zinc.

Filtration Efficiency in the Recycling Process of Particle-Reinforced Aluminum Alloys Using Different Filter Materials

In this study, filtration of aluminum alloy (Al) with different weight fractions of SiC particles (SiCp) was investigated. Therefore, three different filter materials of 20 pores per inch (ppi) ceramic foam filters (CFF) were tested. A special three-chamber furan mold was used for the casting trials to provide uniform filling and flow conditions for the filtration process. Samples from sections of the gating system, as well as from the filter, were analyzed by optical light microscopy to determine the amount, size, and distribution of SiCp. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) was used for obtaining the element distribution in the composite. The filtration efficiency increased by decreasing the weight fraction from 20 to 5% of SiCp and reached a significant particle reduction of over 90%. Investigations of CFFs with a weight fraction of 10% have shown a clogging effect and metal flow interruption through the 20 ppi filter. An oxide layer was detected around the respective SiCp in the EDS. Moreover, a strong accumulation effect was observed, indicated by a steadily flattening curve of the density functions after each additional remelting cycle of the same composite material.

Effect of Batch Dissimilarity on Permeability of Stacked Ceramic Foam Filters and Incompressible Fluid Flow: Experimental and Numerical Investigation

Ceramic foam filters (CFFs) are used to remove inclusions and/or solid particles from molten metal. In general, the molten metal poured on the top of a CFF should reach a certain height to form the pressure (metal head) required to prime the filter. For estimating the required metal head and obtaining the permeability coefficients of the CFFs, permeability experiments are essential. Recently, electromagnetic priming and filtration of molten aluminum with low and high grades of CFF, i.e., 30, 50 and 80 pore per inch (PPI) CFFs, have been introduced. Since then, there has been interest in exploring the possibility of obtaining further inclusion entrapment and aluminum refinement by using electromagnetic force to prime and filter with stacked CFFs. The successful execution of such trials requires a profound understanding concerning the permeability parameters of the stacked filters. Such data were deemed not to exist prior to this study. As a result, this study presents experimental findings of permeability measurements for stacks of three 30, three 50 and three 80 PPI commercial alumina CFFs from different industrial batches and compares the findings to numerically modelled data as well as previous research works. Both experimental and numerical findings showed a good agreement with previous results. The deviation between the experimentally and numerically obtained data lies in the range of 0.4 to 6.3%.

Catalytic O2-steam gasification of biomass over Fe2-xMnxO3 oxides supported on ceramic foam filters

In the present study, catalytic gasification of biomass was investigated by incorporation of a supported Fe2-xMnxO3 catalyst into the freeboard zone of a bubbling fluidized bed gasifier. The material was processed by combining incipient wetness impregnation with microwave-assisted firing methods. These catalysts were characterized by elemental, structural and microstructural analyses, and redox testing by thermogravimetry. Catalytic performance was assessed by comparison with blank tests and used to study the influence of the catalyst temperature, equivalence ratio and gas hourly space velocity on tar decomposition. The catalyst revealed higher activity in converting tar compounds with increasing temperature and equivalence ratio, while increasing the gas hourly space velocity showed a negative impact on catalyst performance. Under optimal operating conditions, the catalyst exhibited a significant impact on tar conversion (83 %) and gasification parameters, such as the gas yield (0.81 to 0.93 Nmdry,gas3∙kgdry,fuel-1), carbon conversion efficiency (55.3 to 65.1 %) and cold gas efficiency (50.7 to 61.6 %). Post-mortem analysis of the tested catalyst provided further information on redox changes and their dependence on temperature, which were co-related with catalytic performance. Elemental mapping showed traces of sulphur, which increased with temperature and did not correlate with the catalytic performance; this was interpreted by thermodynamic modelling, based on the wide redox stability range of divalent manganese oxide and its enhanced tolerance to hydrogen sulphide.

Preparation of Ceramic Foam Filters With a Lithium-Containing Surface

Hydrogen in aluminum causes the formation of detrimental hydrogen porosity in castings. In order to reduce the formation of hydrogen pores, an approach was targeted using lithium as target for hydrogen. This approach utilizes the affinity of lithium for hydrogen, whereby spodumene (a lithium aluminum silicate) and lithium aluminate were used as lithium providers. Within the scope of this study, the preparation of ceramic foam filters with a coating of lithium-containing raw materials (spodumene) was investigated. Those investigations revealed that the spodumene coating has a detrimental influence on the bending strength of the foams when a certain level of spodumene is exceeded. This observation might be explainable by the intrusion of the spodumene into the alumina matrix of the skeleton foam. Two wetting tests at different temperatures were conducted, verifying the significant influence of the temperature on the reaction between the spodumene and AlSi7Mg. Furthermore, test filters coated with raw materials exhibiting different amounts of lithium were conducted. The hydrogen pores were evaluated by light microscopy and computed tomography. The analyzed pore size distribution in the aluminum did not elucidate the proximate influence of the lithium-coating on the ceramic foam filter on the hydrogen porosity in the aluminum.

Reaction Sintering of MgAlON at 1500 °C from Al2O3, MgO and AlN and Its Wettability by AlSi7Mg

The aim of this study is the investigation of a technological synthesis of MgAlON, which is a prospective coating material on ceramic foam filters for the filtration of magnesium, aluminum, and other metal melts. Thermodynamic calculations are performed, and the synthesis is carried out at 1500 °C in nitrogen atmosphere using samples consisting of different fractions of Al2O3, MgO, and AlN as starting materials. The effect of the quantity of these components on the conversion degree of the educts is evaluated. Furthermore, the effect of the holding time at the synthesis temperature, as well as the composition points or regions showing the highest conversion degree, are determined. XRD analysis is performed to evaluate the phase fractions and lattice parameters of the spinel after the respective reaction, and the nitrogen content of selected samples is evaluated. Sessile drop tests using AlSi7Mg are performed at 950 °C on selected sintered samples, determining their wettability, and therefore, applicability of the material in light metal melt filtration.

Increasing the efficiency of refining and modification of aluminum alloys when using electromagnetic factors

Mechanical properties of aluminum alloys and their corrosion resistance are strongly influenced by the content of non-metallic inclusions and hydrogen dissolved in the melt, therefore, the improvement of technologies for refining aluminum alloys is important. The use of electromagnetic factors for this purpose has not yet been studied enough, but theoretical studies and experiments carried out show that this direction is promising. The paper presents the results of testing a new technology in which electromagnetic factors are used to enhance the efficiency of aluminum alloy refining from non-metallic inclusions and hydrogen. A melt flow was initiated through a ceramic foam filter by an electromagnetic pump, through which an electric current with a frequency of 50 Hz passes. At the same time, argon was introduced perpendicular to the flow direction at the crucible bottom. After refining, a modifier was introduced into the liquid metal bath and electromagnetic stirring was started. Metallographic studies of the sample cast from the refined metal have shown a significant quality increase. Cast mechanical properties increased accordingly. Tables 1, Figs 1, Refs 10.

Removal of Fe from molten Al by filtration in a centrifuge

A separation method induced by centrifugal force and combined with alumina ceramic foam filter (Al2O3 CFF) was proposed to remove Fe from molten aluminum. In exploratory the separation, the effect of Al2O3 CFF (pore size (P) and thickness (H)), temperature (T) and gravity coefficient (G) on the separation efficiencies were analyzed. The walls in Al2O3 CFF acting as nucleation sites promoted the formation of iron-rich phase which was either sticked on the wall or intercepted at other place in the inner Al2O3 CFF. Under the condition of P = 80 ppi, H= 35 mm, T = 700 °C and G= 10, the removal efficiency of Fe (RFe) and loss percentage of Si (LSi) were 75% and 58%, respectively. On the basis of exploratory experiment on the separation, a centrifugal separation apparatus combined with Al2O3 CFF was designed for continuously removing Fe element from molten aluminum on an engineering scale and the result obtained from the experiment treating 4 kg molten aluminum were 70% for RFe and 52% for LSi. Results indicate separation induced by centrifugal force and using Al2O3 CFF can be employed as a practical process.

Numerical Assessment of the Immersion Process of a Ceramic Foam Filter in a Steel Melt

Visualization of the melt immersion process at time step t = 1.2 s in the XSITE CAVE. The image shows the upper half of the filter in its original orientation. Entrapped gas bubbles are visualized as blue blobs on the surfaces of the filter and inside pores. Photo credit: Amjad Asad, article number 2100753, Institute of Mechanics and Fluid Dynamics, Henry Lehmann, Virtual Reality and Multimedia Group, TU Bergakademie Freiberg.

Effect of Inclusion and Filtration on Grain Refinement Efficiency of Aluminum Alloy

It is well known that the filtration efficiency of ceramic foam filters (CFF) on aluminum melt can be significantly reduced by the addition of grain refiner particles under a high inclusion load. Also, it is usually considered that the filtration process has little impact on grain refinement efficiency. In this work, the influence of inclusions and filtration on the grain refinement effect of AA 6060 alloy has been studied. This was done through TP-1 type solidification experiments where the aluminum melt prior to and after the filter during a pilot-scale filtration test was investigated. In the experiments, 80 PPi CFFs were used to filtrate aluminum melt with an ultra-high inclusion load and two addition levels of Al–3Ti–1B master alloys. It is found that both inclusions and filtration significantly reduce the grain refinement efficiency of the grain refiner master alloys. A detailed characterization of the used filters shows that the reduction of grain refinement efficiency is due to the strong adherence of TiB2 particles to the oxide films, which are blocked by the CFF during filtration. A grain size prediction model based on deterministic nucleation mechanisms and dendritic growth kinetics has been applied to calculate the solidification grain size and estimate the loss of effective grain refiner particles during filtration. It is shown that due to the strong adherence between TiB2 particles and oxide films in the melt, the high addition level of aluminum chips also has an influence on reducing the grain refinement efficiency of aluminum melt without filtration. The results of this study extended our understanding of the behavior and performance of inoculant particles in CFF and their interactions with the inclusions.

Ceramic foam filters for filtration refining of ferrous metals

Literature review of refractories used for the production of ceramic foam filters is carried out, on the basis of which ceramic foam filters are made from combination of three different compositions of refractory suspensions, the physical and mechanical properties of the obtained filters are studied. It is found that filters with the composition 85 % Al2O3 + 15 % ТiO2 and 85 % Al2O3 + 15 % ZrO2•SiO2 have higher strength properties in comparison with other samples.

Influence of the method of out-of-furnace melt treatment on hydrogen content in 5083 aluminum alloy

The work was carried out in laboratory conditions at the semicontinuous ingot casting installation (SICI) in the casting laboratory of the Siberian Federal University. The article presents the results of comparative studies of the dynamics of aluminum saturation with hydrogen over the entire hardware and technological scheme. The article gives a schematic diagram of the semicontinuous ingot-casting unit. Studies were carried out using a single- and two-stage aluminum melt filtration system with the use of ceramic foam filters with an alumosilicate binder bonded with stabilized borosilicate glass. The results of investigations of the ceramic foam filter heating temperature influence (less than 500 oC and higher than 500 oC) on hydrogen concentration in an aluminum alloy are presented. The hydrogen content studies have been carried out during complex passing of aluminum melt through a single- or two-stage filtration by a ceramic foam filter. The paper presents the results obtained by applying a degassing unit that operates on the principle of the molten metal inert gas blowing (argon). During the study, it was found that the average hydrogen concentration in an aluminum alloy before passing through a ceramic foam filter was 0.19 cm3/100 g Al, and that after passing through the filtration system with ceramic foam filters was 0.185 cm3/100 g Al. The paper shows that the ceramic foam filter heating degree does not affect the aluminum alloy saturation with hydrogen. In the course of the work, it was found that the most significant effect of reducing hydrogen concentration could be achieved by blowing aluminum with inert gas (argon) along with filtration by a ceramic foam filter (CFF), which was confirmed by a series of experiments. The research was carried out in the context a regional competition for the best projects of interdisciplinary fundamental scientific research conducted by the RFBR, the Government of the Krasnoyarsk Territory, the Regional Foundation and enterprises operating in the Krasnoyarsk Territory, as well as organizations participating in the Yenisey Siberia complex investment project (No. 20-48-242916).

Computer‐Aided Design of Metal Melt Filters: Geometric Modifications of Open‐Cell Foams, Effective Hydraulic Properties and Filtration Performance

The combination of additive manufacturing and replication technique enables the development of new ceramic foam filters (CFFs) for the filtration of metal melts based on computer‐generated templates. This article presents a numerical study on the sensitivity of filtration performance with respect to different geometric modifications, applied to an artificial monodisperse base structure. Three different geometric modifications are implemented, namely, elliptical elongation and flattening of the strut cross section with respect to the flow direction, additional finger‐like struts protruding into the pore cavity, and addition of deliberately closed windows. All modifications are implemented for overall porosities of 70–90%. The performance of the new structures is evaluated for continuous casting of aluminum by comparing the hydraulic tortuosity, the permeability, the Forchheimer coefficient, and the filtration coefficient, which are obtained from detailed pore‐scale simulations of the melt flow and inclusions transport using an Euler–Langrange approach. For the fast determination of the permeability coefficients, a novel and extremely simple model for the prediction of the Forchheimer coefficient is described. The investigation shows that geometric modifications to open‐cell foams potentially improve the filtration performance without significant decrease in filter porosity and can be considered as templates for the design of efficient CFFs.

The Influences of Grain Refiner, Inclusion Level, and Filter Grade on the Filtration Performance of Aluminum Melt

The addition of grain refiner particles in the aluminum melt is known to reduce the filtration efficiency of ceramic foam filter (CFF). In the present work, a systematic study on the influence of the addition level of Al-Ti-B master alloys and the inclusion level on the filtration performance of aluminum melt has been investigated by pilot-scale filtration tests using 50 PPi and 80 PPi filters. The inclusion level of the melt has been measured using both LiMCA and PoDFA. For 80 PPi CFF, the N20 inclusion (diameter larger than 20 μm) value in the post-filtrated melt does not increase when an ultra-high level of inclusions is introduced in the form of chips. For the melts with a low level of grain refiners (~ 0.5 kg/ton), the filtration performance of CFF is not affected by grain refiners, regardless of inclusion load. An addition of 2.0 kg/ton grain refiners reduces the filtration performance for melts with a high inclusion level, where post-filtration inclusions with the size of 15-20 µm were significantly increased. It is found, however, for the melts with an ultra-high inclusion load, the filtration performance of 80 PPi CFF is not affected by the grain refiner addition up to 2.0 kg/ton. The interactions between inclusions and grain refiner particles and the filtration mechanism have been studied by characterizing the spent filter and measuring the pressure drop during the filtration process. It is revealed that the strong adherence between oxide film with grain refiner particles dominates the grain refiner influence on the filtration performance of CFF. During the filtration process, oxide films have strong influences on the capturing of other inclusions such as oxide particles and TiB2 particles by the filter. A mechanism based on the interactions between oxide films and grain refiner particles is proposed to explain the CFF performance under the influence of grain refiner.

Numerical Assessment of the Immersion Process of a Ceramic Foam Filter in a Steel Melt

Herein, the immersion process of a ceramic foam filter in a steel melt is investigated by means of numerical simulations, which are mainly based on the volume of fluid approach. The geometry of the used filters is modeled using an artificially generated beam model, which is convolved with a Gaussian kernel. The modeling approach enables the generation of filter geometries with, e.g., pore density and strut thickness similar to real ceramic foam filters. The main scope of the article is to show the effect of the immersion velocity of the filter on the formation of gas bubbles inside the pore cavities of the ceramic filter. Moreover, the influence of the contact angle on the volume fraction of gas bubbles, which remain in the filter, is investigated. For better understanding, the numerical results are underlined using 3D visualization and virtual reality.

Numerical Investigation of the Combined Effect of Reactive Cleaning and Active Filtration on Inclusion Removal in an Induction Crucible Furnace

Herein, the combined influence of reactive cleaning and active filtration on inclusion removal is investigated using numerical simulations. Carbon‐bonded ceramic foam filters with active and reactive effect are inserted into the steel melt to remove nonmetallic inclusions. In case of reactive cleaning, carbon can dissolve from the filters into the melt. As a result, carbon reacts with oxygen on inclusion surface to form carbon monoxide bubbles. The filters can capture inclusions in terms of its active effect. A numerical model is developed in the open source library OpenFOAM to study the efficiency of the combined effect of filters. The results of the numerical simulations show that the flow field and the concentration of carbon are affected considerably by the position and the number of the used filters. Moreover, the results highlight the significant positive effect of reactive cleaning on the level of melt cleanliness despite the short time of the reactive phase of the filters. Moreover, it is apparent from the results that reactive cleaning dominates active filtration. The findings of the article prove the importance of reactive cleaning in the steel casting industry to enhance inclusion removal and improve steel quality.

Experimental investigation on the emission reduction potential of metal oxide-coated ceramic foam filters as substrates for diesel engines

Experimental investigation on the emission reduction potential of metal oxide-coated ceramic foam filters as substrates for diesel engines

Influencing the Hydrogen Porosity in Aluminum Casting by (Re)active Filter Materials

Nonmetallic inclusions and pores are the most common sources of aluminum casting defects. For this reason, great importance is attached to cleaning the aluminum melts, especially in secondary metallurgy. Herein, the results of several experiments in which innovative filter materials are tested with regard to their influence on hydrogen porosity in castings made of an AlCu4Ti alloy are presented. Reactive filter materials based on spodumene (LiAl(Si2O6)) are applied and compared with conventional ceramic foam filters made of alumina and new active carbon‐bonded alumina filters. It is found that spodumene has two different functions. On the one hand, the use of a spodumene‐containing filter material promotes the formation of gaseous hydrogen and, on the other hand, it can be assumed that some of the hydrogen is bound within the filter. Above phenomena are dependent on the reactivity of the filter coating. Therefore, spodumene in appropriate amounts can contribute to a reduction of porosity in the casting.

Fabrication of Cordierite Ceramic Foam Filter by Replication Method

Ceramic foam filter (CFF) is widely used to improve the quality of molten metal prior to casting. Cordierite is one of the most commonly used materials for making CFF. In this research, the fabrication of cordierite-based CFF by a replication method using a polyurethane template has been studied. Waterglass and polymethacrylic acid (PMAA) were used as defloculants to synthesize ceramic suspensions. CFF was made from kaolin, talc, alumina with a defloculant concentration of 0.3% which is sintered at a temperature of 1300 - 1350 oC. The experimental results showed that the porosity obtained for all CFF samples were above 70%. The best shape of CFF was obtained by using PMAA as defloculant. However, CFF did not reach the maximum strength yet so it is necessary to carry out further research on the CFF body composition.

Heavy metal ions and particulate pollutants can be effectively removed by a gravity-driven ceramic foam filter optimized by carbon nanotube implantation

It is of great significance to develop a new gravity-driven filter to remove water pollutants, but it is still challenging. Here, a novel and simple strategy is demonstrated to manufacture fly ash (FA) ceramic foams showing a three-dimensional interconnected porous structure, with multiwalled carbon nanotubes (MWCNTs) implanted by combining carbamate grafting and polydimethylsiloxane coating. The polydimethylsiloxane formed a physical coating on the carbamate group, generating an effective thermal insulating layer on the outer side of the entire MWCNT. The FA foam, which shows a sufficient adsorption capacity for Pb(II) (51.67 ± 1.17 mg g−1) and Cd(II) (30.12 ± 0.37 mg g−1) at pH = 5, T = 25 °C, has a 96.33%, 95.12%, 89.50% removal efficiency for Cd(II), Pb(II), and particulate pollutants, and exhibits excellent recycling performance. This paper provides new opportunities to fabricate gravity-driven filters with low energy consumption for wastewater treatment.