Darvan 821A Research Articles

Porous Bioceramics use Albumin as a Pore-Forming Material

Porous bioceramics have been used in biomedical field, especially for bone implant. To generate pores in bioceramics, pore creating substances are added into the process of making ceramic bodies. The purpose of this study is to make porous bioceramics with tri calcium phosphate (TCP) raw material using albumin with variation in the amount of albumin in the raw material and drying temperature on the physical and chemical properties of TCP. Raw material slurry was made by mixing 7 g of TCP, 2 g of starch and 1.5 g of Darvan 821A with 5 g, 7 g and 9 g of albumin in a beaker glass while stirring at a rate of 150 rpm for 3 hours. The slurry was poured into a mold and heated in an oven at 180°C, 200°C and 220°C for 1 hour. Subsequently the sample was burned at 600˚C for 1 hour, following with sintering at 1.100°C for 2 hours. Bioceramic porosity is greater by increasing the amount of albumin and drying temperature, while the compressive strength decreases. Obtained TCP porosity is in the ranges of 68% -78% and compressive strength 0.14-1.4 MPa.

Additive manufacturing of complexly shaped SiC with high density via extrusion-based technique – Effects of slurry thixotropic behavior and 3D printing parameters

Additive manufacturing of dense SiC parts was achieved via an extrusion-based process followed by electrical-field assisted pressure-less sintering. The aim of this research was to study the effect of the rheological behavior of SiC slurry on the printing process and quality, as well as the influence of 3D printing parameters on the dimensions of the extruded filament, which are directly related to the printing precision and quality. Different solid contents and dispersant- Darvan 821A concentrations were studied to optimize the viscosity, thixotropy and sedimentation rate of the slurry. The optimal slurry was composed of 77.5 wt% SiC, Y2O3 and Al2O3 powders, 0.25 wt% dispersant and 0.01 wt% defoamer. The printing parameters studied included extrusion pressure, nozzle size, layer height and printing speed; the one that had the most prominent effect on filament width and height was indicated as layer height. The nozzle inner diameter of 1.04 mm, speed of 350 mm/min, layer height of 0.7 mm and extrusion air pressure of 0.31 MPa were the optimal printing parameters. Furthermore, the relationship between the printing parameters and the filament dimensions was successfully predicted by using machine learning and grey system theory. Finally, the relative density of the printed SiC parts sintered at 1900 oC reached 94.7±1.5%.

Preparation of Hydroxyapatite Scaffold using Luffa Cylindrica Sponge as Template

Hydroxyapatite (HA) scaffold has been widely applied in the biomedical field especially for bone implants. The purpose of this research is to determine the influence of dispersant addition and stirring time on HA scaffold which formed using gambas sponges as a template. HA slurry was made by mixing 10 grams of HA, 12 grams of aquadest, 0,2; 0,25; 0,3 grams of Darvan 821A and 1 gram of sago. The slurry was impregnated into Luffa cylindrica sponges. The sample then dried at 110oC for 3 hours. The green bodies were burned at 600oC for 1 hour and followed by sintering at 1250oC for 1 hour. The results showed that the addition of dispersant and increasing of stirring time lead to smaller porosity and shrinkage. In addition 0,2; 0,25; and 0,3 grams dispersant, the resulting porosity in the range of 63,85-70,78%; 58,74-70,35%; and 53,42-69,66%. Shrinkage 39,43-53,71%; 27,75-50,68%; and 13,61-41,25%. Compressive strength 0,61-1,05 MPa; 2,88-3,81MPa; and 0,52-2,96 MPa. The macroporous and microporous average pore sized was 50 µm dan 5 µm.

Response Surface Methodology Study on Macroporous Hydroxyapatite Prepared by Protein Foaming-Consolidation Method

Macroporous hydroxyapatite have been used in biomedical application especially for bone graft. The objective of this research was to study the effect of yolk addition, rate of sintering temperature rise, and rate of stirring on the physical, chemical and mechanical properties of porous hydroxyapatite prepared using protein foaming-starch consolidation method. The slurry was made by mixing the hydroxyapatite and starch powder with Darvan 821A and yolk in a beaker glass. The slurry was stirred mechanically at rate of 150 rpm for 3 hours and it poured in cylindrical mold. Subsequently the slurry was heated in air oven at 180°C for 1 hour. The dried green bodies were burn out at 600°C ended by sintering at 1250°C. The porous hydroxyapatite with average pore size in the range of 13.7-17.9 μm, porosity of 59.3-63.6 % and compressive strength of 5.17-8.2 MPa was obtained. The calculation result of response surface methodology shows that p-value < 0.05 and lack of fit > 0.05. The most effecting factor significantly was hydroxyapatite addition that followed by mixing rate and temperature rising rate of sintering. Optimum condition hydroxyapatite addition of 22 gr, mixing rate of 150 rpm and temperature rising rate of sintering of 2.8°C/minutes with the optimum value of response for pore size by 17.665 μm, porosity by 63.475% and compressive strength 5.17 MPa.

Synthesis and incorporation of rod-like nano-hydroxyapatite into type I collagen matrix: A hybrid formulation for 3D printing of bone scaffolds

Over the recent years, nanometric hydroxyapatite (HA) has gained interest as constituent of hybrid systems for bone scaffold fabrication, due to its biomimicry and biocompatibility. In this study, rod-like nano-HA particles were introduced in a type I collagen matrix to create a composite mimicking the bone composition. HA nano-rods (40−60 nm × 20 nm) were synthesised by hydrothermal method involving the use of an ammonium-based dispersing agent (Darvan 821-A) and fully characterised. The homogeneous dispersion of HA nanoparticles throughout the final hybrid formulation was achieved through their suspension in a collagen solution in presence of Darvan 821-A. The resulting homogeneous collagen/nano-HA suspension proved to be suitable for extrusion printing applications, showing shear thinning and sol-gel transition upon simil-physiological conditions. Furthermore, mesh-like structures were printed in a gelatine-supporting bath by means of a commercial bioprinter further demonstrating the potential of the designed hybrid system for the fabrication of 3D bone-like scaffolds.

Influence of dispersing agents on microstructure-related properties of slip cast cordierite ceramics

Abstract This study aims to reveal the effects of the concentrations of solids and dispersing agents on the rheological properties of the suspensions prepared from multicomponent cordierite precursor powder system and on the final properties of the cordierite bodies consolidated by slip casting. For this purpose, the suspensions having solid loadings of 40, 45, and 50 wt% were prepared. In these suspensions, Darvan 821A and Dolapix CE-64 were used as dispersants. The dispersant-induced changes in the properties of both casting suspensions and their slip-cast bodies were characterised. The results indicate that Dolapix CE-64 had less impact on reducing the shear stress values compared to the Darvan series, and thus Darvan 821A rendered suspensions with lower shear stress values than observed with Dolapix CE-64. Both dispersants also caused distinct effects on the crystallinity, secondary phase formation, and porosity, as well as on the physico-mechanical properties. Dolapix CE-64 provided good physico-mechanical properties, which may be attributed to the formation of clustered and interlocked mullite crystals within the cordierite glass matrix. Furthermore, the results revealed that Darvan 821A confers higher thermal conductivities to the cordierite ceramics, while Dolapix CE-64 favours the sintered density and enhances the dielectric constant and dielectric loss tangent values. Consequently, it was found that the slip-cast bodies prepared from the suspensions dispersed with the different type of dispersants exhibit different microstructure-related properties.

Effect of dispersant on the rheological properties of gelcast fused silica ceramics

Fused silica ceramics with high flexural strength, low porosity, low dielectric constant and loss tangent were fabricated by gelcasting, a near-net shape fabrication technique. Fused silica suspensions with solid loading as high as 73 vol.% with low viscosity has been prepared using various dispersants in acidic and alkaline regions/medium. Commercially available Darvan 821A, Darvan C-N, Dolapix A88 and Dolapix CE64 were used as dispersants. Investigations were carried out to determine the suitable dispersant and effects of dispersant percentage, pH value, zeta potential, and solid loading on the rheological properties of the suspension. Darvan 821A showed better results in the suspension of fused silica particles in aqueous gelcast system. At 1250°C the flexural strength of fused silica bodies is as high as 52.3 MPa, and the dielectric constant and loss tangent (1 MHz) were as low as 3.25 and 1 X L52M0-3 for solid loading of 70 vol.% respectively. Such properties are highly desirable for ceramic radomes used in lower range missiles.

Room-temperature injection molding of aqueous alumina-polyvinylpyrrolidone suspensions

Abstract Room-temperature injection molding, a novel, environmentally benign ceramic processing method, produced dense, near-net shape alumina rings by utilizing unique flow properties of aqueous, highly loaded (>50 vol.%) ceramic suspensions with ≤5 vol.% polyvinylpyrrolidone (PVP) dispersed using Darvan 821A. The rheological behavior of suspensions along with microstructural and mechanical properties of resulting specimens were evaluated by varying PVP content to determine the optimal composition for forming. Parallel-plate rheometry revealed that suspensions containing ≤5 vol.% PVP were yield pseudoplastic at room temperature, which facilitated processing without heating or complex chemical reactions. Alumina rings with high green densities (>60% true density (TD)) were machined before binder removal, and increasing PVP content was observed to enhance green machinability. After binder burnout and sintering, bulk densities were ∼98%TD with

Aqueous dispersion of red clay-based ceramic powder with the addition of starch

The optimum dispersion and rheological properties of red clay-based ceramic suspension loaded with unary and binary starch were investigated in aqueous medium. The aqueous ceramic suspension was prepared consisting of red clay, quartz, feldspar, and distilled water. Using a polyelectrolyte dispersant (Darvan 821A), the ternary ceramic powder was initially optimized to give the smallest average particle size at 0.8 wt. (%) dispersant dosage as supported by sedimentation test. This resulted into an optimum high solid loading of 55 wt. (%). The addition of either unary or binary starches to the optimized ceramic slurry increased the viscosity but maintained an acceptable fluidity. The mechanism of such viscosity increase was found to be due to an adsorption of starch granules onto ceramic surfaces causing tolerable agglomeration. Correspondingly, the rheological evaluations showed that the flow behaviors of all starch-loaded ceramic slurries can be described using Herschel-Bulkley model. The parameters from this model indicated that all ceramic slurries loaded with starch are shear thinning that is required for direct casting process.

Porous Media of LZSA Glass-Ceramic for Burner Applications

A LZSA (Li2O-ZrO2-SiO2-Al2O3) glass-ceramic porous media produced by the replication method has been studied for relatively low temperature applications. Different suspensions have been tested, and appropriated parameters to obtain good impregnation and green strength were determined. The structures after the sintering process (975 °C for 120 min) were evaluated by scanning electron microscopy and showed a good reproducibility for the best tested suspensions (70.0 wt.% LZSA, 3.5 wt.% bentonite as binder and 1.5 wt.% Darvan 821A as dispersant) Strut and geometric densities were determined so that glass-ceramic foams with porosity of about 91% were obtained.

Preparation of high solid loading titania suspension in gelcasting using modified boiling rice extract (MBRE) as binder

Preparation of high solid loading homogeneous titania suspension using modified boiling rice extract (BRE) as consolidator (network-former)/binder for gelcasting application has been investigated. To achieve in situ consolidation forming of TiO 2 ceramic, the gel network formed by swelling and gelatinization of the modified BRE (MBRE) with 2-hydroxyethylmethacrylate was studied. The dispersion behaviour of the titania powder and rheology of the suspension under the influence of binder content, dispersant (Darvan 821A) concentration and pH of the dispersing media have been discussed. The present process of gel casting deals with 50–80 weight% solid loading of titania particles with MBRE (2–10 weight% to that of total solid loading) in presence of dispersant (ammonium salt of polyacrylic acid [(C 4H 5O 2–NH 4 +) n]). The influence of BRE concentration and solid particle loading on rheological properties of aqueous titania suspensions has been analyzed under steady and oscillatory shear conditions. Thermogravimetry (TG) and differential thermal analysis (DTA) on gelcast green body has been evaluated and analyzed. The characterization of green and sintered body has been done with respect to density, porosity and microstructure.

Aqueous Tape Casting Using Organic Binder: A Case Study with YSZ

Aqueous tape casting of yttria stabilized zirconia (YSZ) having very wide particle size range was investigated using bio‐polymer, gelatin as binder and glycerol as plasticizer. Best dispersion of YSZ powder was obtained by using an anionic polyelectrolyte DARVAN 821A at pH 7.5. Gelling properties of gelatin, plasticized with water and glycerol have been studied by dynamic shear measurements. Decreasing concentration of gelatin significantly decreases the gelling temperature of it. With the addition of optimum amount of binder and plasticizer, it has been possible to prepare stable YSZ suspension of 45–50 wt% solid loading that exhibited the desired shear‐thinning behavior. Green tapes with good flexibility (strain to failure: 12%–24%) and strength (2–3 MPa) with total organics content of 10–14 wt% were obtained. After removal of organics, the tapes were sintered at 1550°C for 3 h. The sintered density of the tapes thus obtained was about 99% of the theoretical density. The grain size of the sintered tape was fairly large (10–20 μm); but the surface of the sintered tape (thickness: 100 μm) did not show any visible porosity.

The synthesis and characterization of nanophase hydroxyapatite using a novel dispersant‐aided precipitation method

The synthesis of nanophase hydroxyapatite (nHA) is of importance in the field of biomaterials and bone tissue engineering. The bioactive and osteoconductive properties of nHA are of much benefit to a wide range of biomedical applications such as producing bone tissue engineered constructs, coating medical implants, or as a carrier for plasmid DNA in gene delivery. This study aimed to develop a novel low-temperature dispersant-aided precipitation reaction to produce nHA particles (<100 nm), which are regarded as being preferable to micron-sized agglomerates of nHA. The variables investigated and optimized include the reaction pH, the rate of reactant mixing, use of sonication, order of addition, and concentration of the primary reactants, in addition, the effect of using poly(vinyl alcohol) (PVA) surfactant and Darvan 821A® dispersing agent during the reaction was also examined. It was found that by fine-tuning the synthesis parameters and incorporating the dispersing agent, monodisperse, phase-pure nano-sized particles under 100 nm were attained, suitable for clinical applications in bone regeneration.

Comparison of Two Different Commercially Available Polyacrylate Dispersants for Gelcasting Alumina Slurries

Rheological behaviour of gelcast alumina slurries, prepared using different amounts of two commercially available dispersants, Darvan 821A and M-20C having difference in molecular weight, were studied. The optimum dispersant amount for each of the dispersants was determined in terms of attainment of minimum in the viscosity. The optimal amount of dispersant required was different for the two dispersants owing to the difference in molecular weight. The lowest viscosity value was found to be a little higher for M-20C based slurries, which could be attributed to the lesser electrosteric repulsion with M-20C as compared to that of Darvan. The differences in power law index value ‘n’ and also the thixotropy were directly correlated with the molecular weight of the dispersants.

Texture Development in KSr&lt;sub&gt;2&lt;/sub&gt;Nb&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;15&lt;/sub&gt; Ceramics Fabricated by Reactive Templated Grain Growth

Texture Development in KSr&lt;sub&gt;2&lt;/sub&gt;Nb&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;15&lt;/sub&gt; Ceramics Fabricated by Reactive Templated Grain Growth

SrBi2Ta2O9 ferroelectric thick films prepared by electrophoretic deposition using aqueous suspension

SrBi2Ta2O9 ferroelectric thick films were prepared by electrophoretic deposition (EPD). For that, ceramic powders were prepared by chemical method in order to obtain compounds with chemical homogeneity. The polymeric precursor method was used for the synthesis of the SrBi2Ta2O9 powder. The crystallographic structure of the powder was examined by X-ray diffraction, and the surface area was determined by single point BET adsorption. The 0.03 vol.% suspension was formed by dispersing the powder in water using two different polymers as dispersants: an ester polyphosphate (C213) and an ammonium polyacrilate (Darvan 821-A). It was investigated the influence of the different dispersants in the surface properties of the powder by zeta potential measurements. The films were deposited on platinum-coated alumina and Pt/Ti/SiO2/Si substrates by a 4 mA constant current, for 10 min, using two parallel electrodes placed at a separation distance of 3 mm in the suspension. Several cycles of deposition-drying of the deposit were carried out until reaching the desired thickness. After thermal treatment at temperatures ranging from 700 to 1000 °C, the films were characterized by X-ray diffraction and scanning electron microscopy for the microstructure observation.

The use of poly (N-isopropylacrylamide) microgels as a multi-functional processing aid for aqueous alumina suspensions

Two temperature sensitive microgels of poly (N-isopropylacrylamide) were prepared, one anionic in nature and the other cationic. The microgels were concentrated by centrifugation and the rheological properties of the microgels measured as a function of temperature. The anionic microgel showed a transition from an elastic gel like structure to a liquid like structure at 32°C, whilst the cationic microgel demonstrated the same transition, but at a slightly higher temperature of 34°C. Both systems were completely reversible. A sub micron sized alumina powder was then mixed into the microgels using an anionic dispersant, (Darvan 821A ) to stabilise the powder. The powder was added until the system was just reversible. The aim was to see which microgel behaved as the best processing aid for the alumina particles, in terms of dispersion, gelation and adhesion after drying. The resulting mixtures were freeze dried, sintered and investigated by electron microscopy. The best microgel / alumina system was the one with similarly charged particles, i.e. the anionic microgel, whereas the system containing the oppositely charged cationic microgel particles flocculated, as would be expected from simple electrostatic theory. The presence of the inorganic particles caused the sharp transition from elastic gel to viscous fluid to broaden and the systems to behave viscoelastically over the whole temperature range. Sintered products made from the two systems were remarkably different. With the cationic microgel the resulting structures crumbled, but with the anionic microgel robust structures were obtained. Hence it is feasible to use similarly charged microgels as processing aids for ceramics as long as both particles are not oppositely charged.

Experimental methods for measuring the optimum amount of dispersant for seven Sumitomo alumina powders

Seven Sumitomo alumina powders of different surface areas and particle size distributions were studied with a view to determining the optimum amount of dispersant (Darvan 821A) required to stabilise aqueous suspensions prepared from the powders. Three different techniques were used; sedimentation, particle sizing and acoustophoresis. Acoustophoresis proved to be the most accurate and quickest way of establishing the optimum amount. It was also shown that the optimum amount of dispersant (0.59mg/m2/) required to stabilise the different sized alumina powders was independent of thepowder surface area/size. Sedimentation results demonstrated that the larger particles acted like hard spheres with thin double layers and gave a smaller relative sediment height than the small particles under the same conditions, i.e. volume fraction and electrolyte strength. This was because the small particles acted as soft spheres with thick double layers that resulted in the particles keeping far apart from one another and hence giving a larger sediment volume.