Dolapix CE64 Research Articles

Formation features of MgO–Y2O3 nanocomposite of complex shape through aqueous slip casting using glycine-nitrate nanopowder

A homogeneous MgO–Y2O3 (50:50 vol%) nanocomposite semispherical green bodies with diameter up to 90 mm and relative green density of 46 % were successfully fabricated by the slip casting using nanopowder, synthesized by the glycine-nitrate method. To advance the rheological properties of MgO–Y2O3 aqueous suspensions, the effect of Dolapix CE64 and NH4PAA as dispersants was examined by viscosity measurements, sedimentation tests. A stable MgO–Y2O3 slurry showing near-Newtonian behavior was prepared with 30 wt% solid loading and 2 wt% of Dolapix CE64. Finally, sinterability of MgO–Y2O3 composite nanopowder was studied by vacuum sintering method for the first time. MgO–Y2O3 nanocomposite of complex shape vacuum-sintered at 1300 °C demonstrate optical transmittance of 45 % at the wavelength of 5.3 μm, and the average grain size of MgO and Y2O3 components of 355 nm and 342 nm, respectively.

A new method for judging and predicting the stability of ceramic suspensions by rheological tests

In preparing stable ceramic suspensions, the interactions of particles and polymer chains should be emphatically considered, which depends on DLVO stabilization theory. However, DLVO stabilization theory are qualitative and lack quantitative methods for judging and predicting stability. The present study introduced a new method for directly judging and predicting suspension stability based on rheological tests and established a correlation between measured data and the state of ceramic suspensions. Among rheological properties, the dominance of the storage modulus G' is more conducive to the realization of steric stabilization, whereas the loss modulus G" exerts a more significant influence in bridging and depletion flocculation states. The stability of suspensions with a given particle size can be judged and predicted by comparing the value of tan δ (the ratio of G" and G') under identical measurement conditions. Lower values of tan δ indicate better stability of the ceramic suspensions. The new method has been verified by experiments of classical alumina suspensions. The results indicate that the alumina suspensions with 14, 17, 20, and 23 vol% of solid particles exhibit optimal stability when combined with PVA concentrations of 3.5, 3.0, 2.5, and 2.0 wt%. Meanwhile, this combination leads to the minimum values of tan δ within the linear viscoelastic region (0.71, 0.45, 0.33, and 0.31, respectively). The universality of the method has been further demonstrated in zirconia suspensions dispersed with Dolapix CE64 dispersant. The application of this method has demonstrated its significance in judging and predicting the stability of ceramic suspensions.

Evaluation of the methacrylamide/ N’N,-methylenebisacrylamide gel binder system for gel-casting of titanium powder

Gel-casting, a near-net-shape manufacturing technique developed for ceramic powder processing, is investigated to produce titanium parts. In this study, the MAM/MBAM gel-binder system is used to develop a suitable slurry formulation and gel-casting procedure for commercially pure titanium powder. The polymeric binder system was evaluated by altering process parameters to produce a stable slurry of uniformly dispersed titanium powder that resists particle settling. Stable slurry formulations are gel-cast into rectangular bars to evaluate the green properties. The suitability of the binder system was studied by evaluating the gelation time and settling behaviour of the slurry for three dispersants at concentrations up to 0.6 wt% of the titanium powder, a range of MAM:MBAM ratios from 3:1 to 15:1 and monomer concentrations from 17 to 40 wt% of the premix solution. The green density and strength were evaluated for bars that were gel-cast from slurries with 37 vol% solids loading, 0.6 wt% Dolapix CE64 dispersant, a MAM:MBAM ratio of 3:1 and a monomer concentration of 23, 29 and 37 wt% in the premix solution. The 37 wt% monomer concentration gel-cast titanium bar produced the highest green density, 2.50 g/cm3 (55% relative density), with density gradients varying less than 4% from this average within the green part. This formulation also produced the highest green strength of 8.92 MPa.

Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria‐stabilized zirconia sediments

AbstractIn the present work, particle arrangement and their packing in the sediment layer of zirconia suspension were studied. To evaluate the particle settling, aqueous suspensions of zirconia nanoparticles were prepared in different dispersion states. In one state, Dolapix CE64 was used as a dispersant to provide electrosteric mechanism. In another state, pH of the suspension was adjusted at 4 to provide electrostatic mechanism. The other state was the combination of dispersant and pH adjustment which resulted in the most stable suspension. First of all, the stability of all dispersion states was evaluated by zeta potential, sediment volume (SV) and height, viscosity, and packing density (PD). Then, the sediment layers of all suspensions were characterized. Incorporation of electrostatic mechanism was resulted in a main decrease in viscosity with high surface charges, while electrosteric mechanism caused lower sedimentation of particles. Fall velocities of particles/agglomerates were estimated, and the influences of dispersion states on the particles fall velocities were characterized. The microstructural observation revealed homogeneous packing of particles in the sediment layer of the stable suspension demonstrating the proper dispersion of particles. Dolapix CE64 and pH adjustment resulted in a uniform arrangement of particles without agglomeration and spherical and regular granules with a uniform shape.

Processing study of gel-cast tubular porous NiO/SDC composite materials from gel-combustion synthesized nanopowder

In the present research, NiO–SDC (Samarium doped Ceria) nanopowder was synthesized through sol–gel combustion method using citric acid as a reducing agent (fuel) and metal nitrates as an oxidant. The characteristics of the synthesized powder were thoroughly analyzed by DTA/TG, XRD, BET and FESEM/EDX. Tubular gel-casted porous specimens of NiO–SDC (50:50 wt%) composite materials were produced after stabilizing suspensions of composite powder in an aqueous environment by addition of 3 wt% dispersant and 2.5 wt% agar as the gel builder. The effect of Dolapix CE64 as a dispersant, agar as a gel-builder and the amount of solid loadings on the processing and properties of porous ceramics was investigated. Viscosity measurements, zeta potentials of suspensions with and without dispersant and sedimentation measurement were used to determine the optimum dispersant concentration and solid concentration needed to prepare a stable slurry. The phase composition and microstructure of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Moreover, the distribution and porosity of the samples were determined through mercury porosimetry method. Results confirmed that stable NiO–SDC slurries with high solid loading (60 %) were achieved with Dolapix CE64, which also met the requirements to reach porous tubular samples with up to 60% porosity.

Development of free binder zirconia-based pastes for the production of dental pieces by robocasting

The current work aims to develop high solid load zirconia pastes without organic binder additives, for the robocasting of dental structures. The effect of the amount of Dolapix CE64 dispersant on the stabilisation of zirconia aqueous suspensions was first tested. The determined optimal amount of dispersant was then used to produce pastes with zirconia concentration in the 80−90 wt% range. Pastes were further studied regarding rheological behaviour and printability. The most printable were used to produce parallelepiped blocks by robocasting; slip casting samples were also produced for comparison. Density, surface roughness, porosity, hardness and toughness of both types of samples were assessed after sintering. Finally, a model molar tooth was produced by robocasting and sintered. The most encouraging robocasting results were obtained using a paste with 0.5 wt% Dolapix CE64 and 88 wt% zirconia. The produced samples displayed 97.1 % of theoretical density, Vickers hardness of 1485 ± 32 and fracture toughness of 4.11 ± 0.09 MPa.m1/2 after sintering. Similar values were obtained for slip casting parts. A model molar tooth with adequate surface finishing was successfully obtained using the described processing parameters, together with a brushing treatment carried out in the green state. Attained results show that it is possible to build zirconia prosthetic dental structures with adequate morphological and mechanical properties by robocasting of binder free pastes. This opens an opportunity window for the cost-effective and environmentally friendly customized production of prosthetic dental structures by additive manufacturing.

Slip-casting process of MgO–Y2O3 nanocomposite: Investigation of powder synthesis method

In this paper, yttria-magnesia composite nano-powders with a chloride and nitrate-acetate precursors were synthesized using the sol-gel method. The green body of MgO–Y2O3 nanocomposite was fabricated by the slip-casting method and the rheological properties were improved by adding Dolapix CE64 to the slurries as a dispersant agent. The Y2O3–MgO nanocomposite slurry with a solid loading of 60 wt% and the pH of 12 was obtained using 1 wt% Dolapix CE64.The X-ray diffraction (XRD), Field Emission Scanning Microscope (FESEM) and Brunaure-Emmett-Teller (BET) tests were used.Various slip/slurry characterization techniques such as sedimentation, viscosity measurements and porosimetry were used to optimize the slip casting parameters. The relative densities of the green and sintered body (1400 °C/2 h) were 50% and 86%, respectively. The FESEM results of the sintered yttria-magnesia composite with the chloride precursors showed the more uniform distribution of MgO and Y2O3 phases than the nitrate precursors.

Preparation of zirconia granules with a low molecular weight dispersant

In the present work, different conditions, such as PVA content as a high molecular weight polymer, Dolapix CE64 level with a lower molecular weight and pH adjusted by HCl, were investigated for the preparation of the yttria-stabilized zirconia (YSZ) granules from nanosized YSZ particles. It was found that the suspension prepared at pH = 4 and with 0.1 wt.% Dolapix CE64 has a reasonable value of viscosity for spray drying. The morphology of granules and their cross-sections were characterized through microstructural observation. The flowability of the prepared granules and the Hausner ratio were also evaluated. The results indicated that the addition of only 0.1 wt.% of PVA binder and the use of Dolapix can produce the YSZ granules with good flowability. Replacement of PAA by Dolapix has the benefits of achieving uniform granules with a dense shell layer, decreasing the amount of binder and accelerating the feeding rate of suspensions. The mechanism of the solid and hollow granule formation by a low molecular weight dispersant was suggested.

Dispersion Study of Zirconia Nano-Powders Using Dolapix CE64 and M65 Dispersant to Develop UF Membrane over Novel Clay-Alumina Based Ceramic Support for Water Treatment

ABSTRACTDispersion of zirconia powder in aqueous suspension using suitable dispersant for coating application was studied. Zeta potential experiments were conducted in search of stable suspensions. Sedimentation tests were carried out in both acidic and basic pH range, i.e. from 2 to 11. Zirconia slurry as coating material was used for coating on clay-alumina tubular ceramic support. The slurry was composed of zirconia nano powder, water, dispersant and organic binder. Z irconia nano powders were characterized by XRD, surface area by multipoint BET and TEM. The effect of dispersant concentration on zeta potential of zirconia suspension and effect of pH, sedimentation rate and rheology (viscosity) of zirconia suspension were studied. The coated tubes were air dried and sintered in furnace at 700°C for 2 h. The prepared UF membrane was subjected to characterization in terms of permeability, FESEM, molecular weight cut off, etc. The UF membrane was used for separation of two types of water – effluent A (kitchen sink wastewater) and effluent B (surface water of a lake). The membrane was effective to remove the pathogenic organisms, organic load in terms of BOD, COD, etc. The treated water may be reused in agriculture or industrial purposes.

The effects of ball milling time on the rheological, optical, and microstructural properties of YAG transparent ceramics

AbstractStable slurries dispersed mixture of commercial Al2O3 and Y2O3 powders, ammonium poly meta acrylate (Dolapix CE64) as the dispersant, and tetraethyl orthosilicate (TEOS) as the sintering aid were prepared by ball milling process. The effects of the milling time on the fabrication of transparent polycrystalline yttrium aluminum garnet (YAG) ceramics were investigated by slip casting and vacuum sintering. The results showed that the best milling time for the deagglomeration of the powder mixture was 16 hours and the slurry prepared during this time showed a near‐Newtonian behavior due to the better deagglomeration and lower viscosity. X‐ray patterns also showed that all samples were pure YAG phase. The results also revealed that the sample prepared by 16 hours ball milling time suspensions exhibited higher relative green and final density, as well as the maximum transmittance at 1064 nm (≈ 77%). These samples had a more uniform microstructure too.

Optimization of slip casting parameters for spark plasma sintering of transparent MgAl2O4 /Si3N4 nanocomposite

This paper aims at optimizing the slip casting process as a pre-processing step for the preparation of spark plasma sintered MgAl2O4-xSi3N4 (0 < x < 5 wt%) transparent nanocomposites. In this research, different amounts of Si3N4 nanoparticles (1,3, and 5 wt%) were added to the slurries of spinel to prepare transparent MgAl2O4-xSi3N4 (0 < x < 5 wt%) nanocomposites. The green bodies were prepared from slurries with 60 wt% solid loading and 1 wt% Dolapix CE64 as a dispersant. Slurries were jar milled before slip casting to make sure that powders were homogeneously mixed. Slurries were then cast in a mold, made of alumina. Rheological characteristics of slurries, containing Si3N4 nanoparticles, were thoroughly investigated. The results of viscometry showed that any increase in the Si3N4 content of the slurry is associated with an increase in the viscosity. Bulk spinel-3wt% Si3N4 nanocomposite was prepared by spark plasma sintering (SPS) at 1550 °C under pressure of 85 MPa for 20 min. Field emission scanning electron microscope (FESEM), X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and UV–Visible spectrometer were used to study the structure and optical properties of prepared composites. XRD patterns of sintered spinel-based nanocomposite showed great stability of spinel phase during sintering. Results also showed that the consolidated sample shows a maximum transmission of 70% and 60% in the wavelength of near-IR and mid-IR, respectively.

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.

Influence of TEOS and MgO addition on slurry rheological, optical, and microstructure properties of YAG transparent ceramic

Stable dispersed slurries were prepared from a mixture of commercial Al2O3 and Y2O3 powders by the ball milling process. Ammonium poly meta acrylate (Dolapix CE64) as the dispersant and different amounts of tetraethyl orthosilicate (TEOS)+0.1 wt% MgO as the sintering aids were added to the slurries. The effects of TEOS and MgO addition on the fabrication of transparent polycrystalline YAG ceramics were investigated by slip casting and vacuum sintering. The results showed that almost all slurries containing TEOS and TEOS + MgO had a near-Newtonian behavior, but the slurry containing only MgO had shear thickening with a thixotropic behavior. Also, by increasing the amounts of TEOS, due to the creation of steric repulsion, the viscosity was decreased. In comparison, TEOS + MgO slurries had lower viscosity than the TEOS ones. This was due to both the release of more ethanol and MgO action as a dispersant agent among the particles of yttria and alumina. All samples were pure YAG phase. The maximum transmittance at 1064 nm (≈83%) was obtained for the sample of 0.5 wt% TEOS+0.1 wt% MgO. A nearly pore-free microstructure with high relative final density (99.99%), a narrow grain size distribution (2.5–7.5 μm), with the average grain size of 4.5 μm, was achieved in this sample.

Influence of solid loading on the rheological, porosity distribution, optical and the microstructural properties of YAG transparent ceramic

Stable aqueous dispersed mixture of commercial Al2O3 and Y2O3 nano powders was prepared by ball mill. Ammonium poly meta acrylate (Dolapix CE64) and tetraethyl orthosilicate (TEOS) were added as dispersant and sintering aid, respectively. The effects of slurry solid loading on the fabrication of transparent polycrystalline YAG ceramics by slip casting method were investigated. The rheological properties of slurries with different solid loading (64, 70 and 76 wt%) were studied by measuring the viscosity and shear stress as a function of shear rate. The effect of solid loadings on the porosity distribution was examined. The specimens were vacuum-sintered at 1715 °C for 10 h. Slips with 64 and 70 wt% solid loading behaved as near-Newtonian and as non-Newtonian with thixotropic behavior at 76 wt% solid loading. The relative densities of the green bodies increased from 58.0 ± 0.6% (SD = 0.424) to 64.0 ± 0.3% (SD = 0.228) by increasing the solid loading from 64 wt% to 70 wt% and then decreased to 63.0 ± 0.2% (SD = 0.141) at 76 wt% solid loading. The results showed that the suitable solid loading for fabricating transparent YAG ceramics is 70 wt%. This sample had the narrowest pore size distribution (4–100 nm), homogenized surface fracture of green body, dense microstructure (99.990 ± 0.005% final relative density, SD = 0.003) and the average grain size of 6 µm. It had the highest in-line transmittance, which was approximately 77% at 1064 nm.

Laser-synthesized Y2O3:Eu3+ nanophosphors and their stabilization in water suspensions

Europium doped yttrium oxide nanophosphors (Y2O3 doped with 5% Eu3+), which consists of spherical single-phase monoclinic particles with an average size of 17 nm, was prepared by laser synthesis. While the monoclinic material has a low efficiency of only 19% of a μm-sized commercial Y2O3:Eu product, the cubic phase after calcination at 900 °C achieves 68% despite the remaining hydroxo-groups at the surface and still small crystallite size (56 nm). An ethanolammonium salt of citric acid (Dolapix CE64) was used as a dispersant in water suspension. To estimate the stability of the dispersed phase, the electrokinetic potential and agglomerate sizes were measured as a function of pH. With this dispersant, a 30 wt% nanopowder water suspension, showing a Newtonian viscosity of about 6 mPa × s, was obtained. Maximum content of the nanopowder of about 60 wt% can be accomplished in the slurry, still fluid enough to be used to cast a highly uniform and dense ceramic green body to sinter nanostructured Y2O3:Eu3+ phosphors ceramics.

Low temperature fabrication and characterization of Si-O-C cured alumina toughened zirconia (ATZ)

Ceramics such as zirconia and alumina have witnessed wide research and engineering interest owing to their high specific strength, fracture toughness, elasticity, hardness and wear resistance. In this study, yttriastabilised zirconia (YSZ) reinforced alumina (Al2O3)were synthesized by gel casting and infiltrated with polymer derived ceramic (PDC) resin. The composite denoted as ATZ were characterized by means of SEM-based microstructural studies, X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FT-IR) studies. Microstructural characterization, composition profiles, XRD and FT-IR results reveal the formation of strong interfacial bonding of Al2O3 microstructures within YSZ matrix. This suggests the effectiveness of dispersant used; Dolapix CE64 and the possibility of enhanced mechanical properties for the composite.

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.

Direct Probing of Dispersion Quality of ZrO2 Nanoparticles Coated by Polyelectrolyte at Different Concentrated Suspensions.

This study reports useful application of the electrokinetic sonic amplitude (ESA) technique in combination with rheometry and electron microscopy techniques for direct probing the stability of low and high-concentrated zirconia (ZrO2) nanosuspensions in the presence of an alkali-free anionic polyelectrolyte dispersant Dolapix CE64. A comparative study of the electrokinetic characteristics and the rheological behavior of concentrated ZrO2 nanosuspensions has been done. Good agreement was obtained from relationship between the electrokinetic characteristics (zeta potential, ESA signal), viscosity, and its pH dependence for each concentrated ZrO2 nanosuspension with different dispersant concentration in the range of 0.9–1.5 mass%. A nanoscale colloidal hypothesis is proposed to illustrate that the addition of different amounts of dispersant influences on both the stability and the electrokinetic and rheological properties of concentrated ZrO2 nanosuspensions. It is found that an optimum amount of 1.4 mass% dispersant at the inherent pH (>9.2) can be attached fully onto the nanoparticles with sufficient electrosteric dispersion effects, suitable for casting applications. Supplementary scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) analyses followed by colorization effect were taken to verify the visible interaction between dispersant and nanoparticles surfaces. SEM and HR-TEM images proved the existence of visible coverage of dispersant on the surface of individual nanoparticles and showed that thin polyelectrolyte layers were physically bound onto the particles’ surfaces. This study will be of interest to materials scientists and engineers who are dealing with dispersion technology, nanoparticle surface treatments, functionalization, characterization, and application of bio/nanoparticle suspensions at various concentrations using different types of polymers.

Preparation of spherical calcium phosphate granulates suitable for the biofunctionalization of active brazed titanium alloy coatings.

Titanium-based alloys can be actively brazed onto bio-inert ceramics and potentially be used as biocompatible coatings. To further improve their bioactivity in vivo, introduction of calcium phosphate (CaP)-based granulates onto their surface layer is possible. For this, mechanically stable CaP-based granulates need to be able to withstand the demand of the brazing process. In this study, spherical granulates, made of a calcium phosphate composite composed primarily of β-tricalcium phosphate and hydroxyapatite, a bioactive glass, and a mixture of the previous two, were manufactured by spray drying. The influence of organic additives (Dolapix CE64, trisodium citrate) and solids content (30-80 wt%) in the slurry on the physical characteristics of granulates was investigated. X-ray diffraction, Brunauer, Emmett, Teller specific surface area standard method, scanning electron microscopy, granulate size analysis, and single granule strength were performed. Our results showed that trisodium citrate permitted the production of granulates with regular morphology, high density, and increased failure stress values. The strong granules also withstood the brazing process. These results show that CaP bioactive agents can be generated and be integrated during the demanding metallurgical processes, allowing for one-step bioactivation of metal brazes.

Effect of aqueous graphite dispersion on alumina-zircon suspension

The effect of two dispersants (Glydol N1055 and kx9009) on high solids content graphite suspensions were characterized by rheological behavior, sedimentation test and zeta potential. Only the Glydol N1055 dispersant was effective for the wettability of graphite, and kx9009 dispersant being superior to Glydol for graphite suspension as a result of a greater zeta potential and lower viscosity or sedimentation behavior. Alumina-zircon-graphite suspensions were prepared using alumina and zircon powders and graphite dispersion. These suspensions had shear-thinning behavior and could be dispersed using the Dolapix CE-64 dispersant (0.5 wt.%) as well as Glydol (4 wt.%) and kx9009 (0.3 wt.%). Graphite dispersions displayed no sedimentation when alumina-zircon powders and Dolapix were added.