Starch Consolidation Casting Research Articles

Porosity and pore morphology characteristics of zirconia-alumina bioceramics

AbstractManufacturing ceramic green structures using starch consolidation casting is an established process that is simple, non-hazard, and low-cost. In this study, starch consolidation casting is used to prepare ceramics based on submicron monoclinic zirconia with additions of alumina and magnesia. Scanning electron microscopy results indicate that the size of pores decreased and the morphological irregularity increased when the tapioca starch content increased. The sample with 30 wt.% tapioca starch in a 55 wt.% slurry concentration had the highest estimated apparent porosity (around 56%), whereas the sample with 10 wt.% in a 68 wt.% suspension concentration had the lowest (about 35%).

Porous alumina‐based ceramics with very low thermal conductivity prepared by the starch consolidation route

AbstractAlumina‐based porous ceramics were fabricated via the starch consolidation casting route, using titanium oxide as a sintering additive. Alumina‐titania‐starch slurries with starch contents of 2.5, 5, 7.5, and 10 wt% relative to the alumina‐titania system were prepared. Titania was added to the slurries in proportions of 0, 1, 3, and 5 wt%, relative to alumina. The effects of starch and titania contents in the green bodies on the linear and volumetric shrinkage, as well as the total and open porosities of the sintered alumina product, were investigated. The effect of titania addition on mechanical, electrical, and thermal properties of the obtained porous alumina ceramics was studied. Microstructure and pores morphology were characterized by SEM. The alumina‐based ceramics obtained had external porosities that varied between 54 and 76 vol%. Thermal conductivities as low as 0.06–0.1 W/m.K were achieved and the volume electrical resistivity ranged from 3.6 to 600 GΩ·m, while compressive strengths up to 2.8 MPa for a titania ratio of 1 wt% were attained.

Starch consolidation casting of porous alumina and functional gradient porosity development

Starch consolidation casting (SCC) technique was successfully employed to produce both porous alumina and graded porous alumina ceramics. The solid content in the alumina suspension was maintained at 40 vol.%, with potato starch varying from 5 to 15%. Structures of the porous alumina (monolithic) samples obtained by SCC and uniaxial pressing were compared. In addition, the influence of the SCC consolidation temperature and the starch content were evaluated in the monolithic samples, while the consolidation temperature and the number of layers numbers were evaluated in the graded samples. The lower SCC consolidation temperature resulted in lower linear shrinkage and a slight increase in total porosity due to the increased pore size. The compressive strength values for the monolithic samples ranged from 60 to 200MPa, which can be considered high when compared to previous works. The graded samples exhibited porosity variations across layers and interfaces were free of cracks and imperfections. Linear shrinkage was the same for the adopted consolidation temperature and the porosity was slightly higher for the 3-layer samples. They achieved strength of 60MPa with fracture mode parallel to the applied load.

Temperature dependence of Young’s modulus and the occurrence of an elastic anomaly in porous alumina-mullite composites prepared by starch consolidation casting

The temperature dependence of Young’s modulus has been measured by impulse excitation up to 1400 °C (heating and cooling) for alumina-mullite composites with 40–60 wt% alumina prepared by starch consolidation casting, after firing at 1570 °C, resulting in materials with high porosities (43–57 %). Using previously determined temperature master curves, both analytical predictions and numerical computations on computer-generated microstructures are compared with experimental data, resulting in excellent agreement for the alumina-mullite composites. Apart from the overall decrease of Young’s modulus during heating, an elastic anomaly starting at around 950 °C and cumulating at around 1050 °C is observed in all cases during heating (but not during cooling), and is shown to be stronger with increasing alumina content and porosity. The results are discussed in terms of a “glass phase hypothesis” and a “phase transition hypothesis”, although neither of them provides a satisfactory explanation of the observed phenomenon.

Ceramic Thermal Insulator Based on Diatomite Obtained by Starch Consolidation Casting.

Researchers are continuously seeking to develop new materials to protect against inclement weather and thus optimize energy efficiency in housing. This research aimed to determine the influence of corn starch percentage on the physicomechanical and microstructural properties of a diatomite-based porous ceramic. The starch consolidation casting technique was applied to fabricate a diatomite-based thermal insulating ceramic with hierarchical porosity. Diatomite mixtures with 0%, 10%, 20%, 30%, and 40% starch were consolidated. The results show that starch content significantly influences apparent porosity, and this, in turn, influences several parameters, such as thermal conductivity, diametral compressive strength, microstructure, and water absorption of diatomite-based ceramics. The porous ceramic processed by the starch consolidation casting method corresponding to the mixture of diatomite with 30% starch obtained the best properties, with a thermal conductivity of 0.0984 W/m·K, an apparent porosity of 57.88%, a water absorption of 58.45%, and a diametral compressive strength of 35.18 kg/cm2 (3.45 MPa). Our results reveal that the diatomite-based ceramic thermal insulator obtained by starch consolidation is effective for use on roofs to improve thermal comfort in dwellings located in cold regions.

Structure and properties of ZrO2-Al2O3-MgO porous ceramic for biomedical applications

Starch consolidation casting (SCC), which involves pouring starch-containing slurries into an impermeable mould, is a flexible, easy, not harmful, not expensive, and firmly established method for manufacturing ceramic green structures. The procedure depends on the fact that the starch granules, when heated to about 80 °C, start to swell and absorb the water from the ceramic slurries. Following sintering, the starch granules have been completely destroyed by burning, resulting in the formation of porous-structured ceramics. In the current study, porous zirconia-alumina–magnesia (77.5 wt% ZrO2, 2.5 wt% MgO, and 20 wt% Al2O3) ceramic composites have been produced using starch consolidation casting method at different suspension concentration (60, 65, and 70 wt%). Potato or tapioca starches with varying quantities (10, 20, and 30 wt% related to the solid ceramics) were used as a pore and body forming agents. The sintered microstructures were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, the research activity investigates how the apparent density and apparent porosity of the porous ceramic structure that has been produced are affected by the addition of different proportions of starches in different suspension concentrations. The XRD result after sintering reveals monoclinic zirconia, indicating that the tetragonal phase of zirconia is not stabilized by MgO and returns to monoclinic upon cooling. Magnesia does not act as a stabilizer for zirconia, but it is combined with alumina to produce a spinel structure. Maximum apparent porosity value of around 73% were demonstrated for porous-structured ceramics made with (30 wt%) potato starch and (60 wt%) suspension concentration. The SEM analysis of porous-structured ceramics revealed the presence of pore fills in the shape of miniature sintered ceramic shells within the pores. These shells form throughout the drying and burn-out processes, when the starch granules undergo a process that causes them to shrink. For nominal starch quantities of approximately 10 wt%, starch swelling is noticeable, and the pores left behind by sintering are bigger than the starch granules. Swelling is limited for greater amounts of starch by the amount of available space and/or water, and the matrix shrinkage that occurs during sintering more than compensates for the swelling impact, resulting in ceramic pores much smaller than the initial starch granule size. SEM and high-pressure mercury porosimetry results indicated that the prepared porous-structured ceramics have a bimodal pore structure. The maximum compressive strength at around 15.87 MPa for a sample containing 10 wt% tapioca starch and 70 wt% suspension concentration. Compressive strength drastically reduced when starch content increased from 10 to 30 wt% and suspension concentration reduced from 70 to 60 wt%.

Starch Consolidation Casting Method for Preparation Of ZrO2–Al2O3–MgO Porous Structure

The starch consolidation casting (SCC) method was used for the preparation of porous structure ceramic based on partially stabilized ZrO2 with other oxides such as MgO and Al2O3 with the addition of tapioca and potato starch as a binder and pore-forming agents. For casting purpose, three impermeable plastic moulds were designed and manufactured with different sizes and shapes depending on the shape and size of the required samples. The method is based on the fact that after being heated to about 80°C, starch may swell and absorb water from aqueous ceramic solutions. The process's simplicity, the ability to create complicated shapes using different moulds, and the inexpensive cost of the necessary processing tools and materials are its main benefits.

Linear Shrinkage, Strength and Porosity of Alumina-Based Ceramic Foam with Corn Starch as Pore Former

In this study, ceramic foams were produced using starch consolidation casting method. This research focused on the preparation of alumina-based ceramic foam by using corn starch as a pore-forming agent. Preparation of alumina based ceramic foam is studied to observe the effect of the addition of corn starch on its physical, mechanical and morphological properties. The composition of the suspension used included 64–58 wt.% alumina, 55 wt.% deionised water and other materials, such as silica and polyethylene glycol (PEG), were used as additive and dispersing agent respectively. Corn starch was added at 4, 6, 8 and 10 wt.%. The samples were preheated for gelation and coagulation processes, then dried and sintered at 1250 °C for 2 h. The ceramic foam gave a linear shrinkage from 1.07% to 3.39%. The obtained flexural strength was between 0.594 and 1.996 MPa. The average total porosity ranged from 54.05% to 70.70%. This study found that the suitable amount of corn starch in alumina foam is 4 wt.% because the resulting porosity values and flexural strength are appropriate for ceramic foams.

Preparation of porous Al2O3 ceramics by starch consolidation casting method

AbstractPorous alumina ceramics were fabricated by starch consolidation casting using corn starch as a curing agent while their microstructure, mechanical properties, pore size distribution, and corrosion resistance were examined. Results showed that the porous alumina ceramics with the flexural strength of about 44.31MPa, apparent porosity of about 47.67% and pore size distribution in the range of 1‐4 μm could be obtained with 3wt% SiO2 and 3wt% MgO additives. Corrosion resistance results showed mass losses: hot H2SO4 solution and NaOH solution for 10 hours were 0.77% and 2.19%, which showed that these porous alumina ceramics may offer better corrosion resistance in acidic conditions.

Cordierite thermal insulation materials reinforced by aluminosilicate fiber/mullite whiskers hierarchical structure

AbstractCordierite thermal insulation materials were prepared via a starch consolidation casting (SCC) technique, using kyanite, MgO and SiO2 as raw materials. Aluminosilicate ceramic fiber were used as the substrate for in situ synthesized mullite whiskers. The mullite whiskers grew in situ on the surface of the aluminosilicate ceramic fiber via AlF3 and were interspersed among the cordierite crystalline. The as‐prepared cordierite materials reinforced by the aluminosilicate ceramic fiber/mullite whiskers hierarchical structure had a relatively high cold modulus strength and cold compression strength. Moreover, the thermal conductivity of the materials was as low as 0.329 W/(m K) (RT‐1000°C). We propose a growing mechanism of mullite whiskers on the surface of the aluminosilicate ceramic fiber.

Porous cordierite-based ceramics processed by starch consolidation casting – Microstructure and high-temperature mechanical behavior

Porous cordierite-based ceramics with different microstructural features and mechanical behavior were formed by starch consolidation casting (SCC) using native potato and corn starches and sintered at 1275, 1300 and 1330°C. The composition and microstructure of the ceramic materials were investigated via quantitative phase analysis using X-ray diffraction (with Rietveld refinement), the Archimedes method, mercury porosimetry, scanning electron microscopy and optical microscopy with stereology-based image analysis. The mechanical behavior of samples was evaluated by diametral compression tests at room temperature, 1000 and 1100°C. The type of starch used and the sintering temperatures were the main factors determining the characteristics of the developed porous microstructures. Materials prepared with corn starch achieved the lowest porosity and the lowest values of mean chord length, mean pore distance and pore throat size. Because of these features, these materials thus presented, in general, higher values of apparent Young's modulus, elastic limit and mechanical strength than those prepared with potato starch. Despite the presence of a silicate glassy phase, both porous materials, mainly those prepared with corn starch, still enhanced the basic mechanical properties at high temperature, in particular, the mechanical strength and the apparent Young's modulus due to the special combination of the porous microstructure features.

Macroporous mullite materials prepared by novel shaping strategies based on starch thermogelation for thermal insulation

AbstractA rigorous microstructural analysis of porous mullite materials developed using novel shaping strategies based on the starch consolidation casting, and their thermal properties in relation to the processing and starch type were accomplished in view of their use as thermal insulators. In order to characterize the size and morphology of pore, basic size and 2D shape factors, and global 3D stereological parameters were determined using microscopy techniques. Results indicated that the porosity volume, pore connectivity degree, and mean free path were the determining factors of the lowest heat transfer by conduction registered in materials prepared with cassava starch. This material is the best candidate to be used in thermal insulation.

Porous Ceramics Obtained by Slip/Starch Casting Consolidation Method (SSCC)

Slip/starch casting consolidation (SSCC) is a technique for obtaining porous ceramics, which joins the forming process by starch consolidation with the slip casting method. In this work, a slip which contains ceramic powders, starch and dispersant, is poured into a porous mold and is taken to an oven so that the gelling process occurs. After sintering, it is noticed that the ceramics show different characteristics from the ones obtained exclusively by slip casting or by starch consolidation. Alumina ceramics were produced by using the three methods presented in this work. The ceramics were characterized by apparent porosity, mechanical resistance and scanning electron microscopy. The ceramics produced by SSCC presented the highest mechanical resistance value (289 MPa), while the ones produced by starch consolidation and slip casting presented values of 126 MPa and 191 MPa, respectively.

Preparation of Porous Forsterite Ceramic Using Waste Silica Fumes by the Starch Consolidation Method

The fabrication of porous forsterite samples through starch consolidation casting (SCC), utilizing waste silica fume and calcined magnesia has been performed. Three different forsterite contents of solid loading (56.5, 52 and 48 mass-%) were prepared, calculated in a stoichiometric ratio based on utilizing highly pure calcined magnesia and waste silica fume. In addition, corn starch was used as the source of pore forming that was added to the colloidal suspensions then gelatinized in water at elevated temperature (80°C) followed by pressing and firing at 1400, 1450 and 1500°C/2 h). The effect of corn starch content versus the fired temperatures on the physical properties, linear shrinkage, apparent pore size distribution, phase variation, microstuctural evolution and electrical resistivity as well as the cold crushing strength on the fired ceramics was investigated. Results showed that open porosity ranged from 45.5 to 80.5% and compressive strength ranging from 38.1 to 20.2 MPa was obtained depending on starch content in precursor suspensions and firing temperatures, to develop porous forsterite ceramics having varied thermal and electrical applications.

Preparation of porous Al2TiO5-Mullite ceramic by starch consolidation casting and its corrosion resistance characterization

Stabilized Al2TiO5 (AT)-mullite (M) porous ceramics were fabricated by starch consolidation casting using corn starch as curing agent and their microstructure, mechanical properties, pore size distribution and corrosion resistance were examined. Results showed that AT-M porous ceramic with the flexural strength of 11.5MPa, apparent porosity of about 54.7% and pore size distribution in the range of 1–15µm could be obtained with 10wt% corn starch addition. Corrosion resistance results showed mass losses in hot H2SO4 solution and NaOH solution for 10h to decreased from 1.03% to 0.36% and 4.39–2% when the calcination temperature increased from 1400°C to 1450°C, which proved these AT-M porous ceramics to possess an excellent corrosion resistance in acidic condition when calcined at 1450°C.

Processing of porous mullite ceramics using novel routes by starch consolidation casting

Abstract In this article, the development and characterization of porous mullite bodies prepared using two novel forming routes with native starches were studied with the aim of developing bodies without deformation and with homogeneous porous microstructures. Mullite–starch suspensions specific for each route were prepared by mixing and characterized by measuring viscosity. Mullite green bodies were fabricated by heating the suspensions in metallic molds and by burning out the starch, while final porous materials were obtained by sintering at different temperatures. Bodies obtained before and after the burning-out process, and sintered disks, were characterized with porosity measurements and microstructural analysis by SEM. The phases generated after the sintering process were determined by XRD, and pore size distributions were studied by Hg-porosimetry. The obtained results showed that the use of both routes allowed the shaping of homogeneous mullite bodies without causing cracks or deformations and the consequent development of controlled porous mullite microstructures.

Porous Mullite Ceramics Formed by Direct Consolidation Using Native and Granular Cold‐Water‐Soluble Starches

In this article, the processing and microstructures of porous mullite bodies prepared by modifying the conventional route of the starch consolidation casting method were studied. The proposed route, called the “soluble route”, involves the use of native starches (i.e., potato, cassava, and corn starches) and a synthesized granular cold‐water‐soluble (GCWS) starch. Stable aqueous mullite‐starch suspensions (0.25 starch volume fraction of 40 vol% total solids) were prepared by mixing. The total starch content was a mixture of ungelatinized native starch and GCWS starch with a 1:10 ratio of GCWS starch to total starch. Steady‐state shear flow properties of the suspensions were analyzed by measuring viscosity. The addition of CGWS starch increased the starting suspension viscosity and thus prevented the particle segregation. Porous mullite bodies were obtained by heating (80°C, 2 h) the suspensions in metallic molds and by drying (40°C, 24 h) and sintering (1650°C, 2 h) the green disks after burning out the starch (650°C, 2 h). Green bodies obtained before and after the burning‐out process, and the sintered disks were characterized with density and porosity measurements (Archimedes method) and microstructural analysis by scanning electron microscopy. The phases generated after the sintering process were determined by X‐ray diffraction analysis, and pore size distributions were studied by Hg‐porosimetry. The obtained results showed that the use of the GCWS starch made the shaping of homogeneous mullite bodies without cracks or deformations possible along with the development of controlled porous microstructures.

Microstructural comparison of porous oxide ceramics from the system Al2O3–ZrO2 prepared with starch as a pore-forming agent

Abstract In this paper we show examples of microstructures of porous oxide ceramics prepared by traditional slip casting (TSC) and starch consolidation casting (SCC) and present results obtained using different microstructural characterization techniques; Archimedes method (open and total porosity), shrinkage measurement, mercury intrusion porosimetry (pore size distribution) and microscopic methods – optical microscopy with microscopic image analysis (pore size distribution) and scanning electron microscopy (detailed investigation of the local microstructure). In particular, microstructures are compared for porous ceramics from the system Al 2 O 3 –ZrO 2 prepared with rice and corn starch. It is shown that maximum values of the total porosity of porous ceramics prepared with starch as a pore-forming agent were approx. 50%. A major finding by using SEM with respect to starch-produced porous ceramics is the existence of pore fillings in the form of small sintered ceramic shell inside the pores, as a result of starch granule shrinkage during the drying and burn-out steps.

Preparation and characterization of porous alumina ceramics through starch consolidation casting technique

This work aims at studying the influence of thermal treatment on the microstructure, resistivity and technological properties of porous alumina ceramics prepared via starch consolidation casting (SCC) technique. Colloidal suspensions were prepared with three different contents of alumina solid loading (55, 60 and 65mass%) and corn starch (3, 8 and 13mass%). The sintered samples at 1400, 1500, 1600 and 1700°C, show open porosity between 46 and 64%, depending on the starch content in the precursor suspensions and sintering temperature. The pore structures were analyzed by SEM. The effect of corn starch content on the apparent porosity, pore size distribution, linear shrinkage and electrical resistivity as well as cold crushing strength of the sintered porous alumina ceramics was also measured. These porous alumina ceramics are promising porous ceramic materials for using in a wide range of thermal, electrical and bioceramics applications as well as filters/membranes and gas burners, due to their excellent combination properties.

Process control and optimized preparation of porous alumina ceramics by starch consolidation casting

This work concerns details of porosity and pore size control in starch consolidation casting of alumina ceramics using corn starch. In particular, the influence of the solids loading (68–78 wt.% alumina in suspensions with nominal starch contents of 20–50 vol.%) on the porosity, bulk density and shrinkage of alumina ceramics is studied. The results indicate a linear decrease of the linear shrinkage and the bulk density (and a corresponding increase in porosity) as the alumina concentration increases, with slopes that are independent of the starch content. The pore size is characterized via microscopic image analysis, the pore throat size via mercury porosimetry. Relations between the volumetric shrinkage, porosity and the volume fractions of starch and water in the suspensions are discussed, and a new concept, called “affine limit porosity” is proposed to explain the apparently paradoxical finding that the porosity increases with increasing alumina content in the suspension.