Binder Burn Research Articles

Material-extrusion based additive manufacturing of BaTiO3 ceramics: from filament production to sintered properties

Material extrusion (MEX) of thermoplastic filaments represents one of the most widely adopted additive manufacturing (AM) technologies. Unlike vat photopolymerization and powder-bed fusion methods that require high energy sources such as UV light and lasers, this fabrication method can be adapted for the fabrication of ceramics by using ceramic loaded filaments as feedstock, yet still employing relatively cheap equipment meant for polymeric materials with little adaptation of the process parameters; this potentially enables a broader diffusion of AM ceramic components. In this work, composite filaments with various weight fractions (60 – 80 wt%) of BaTiO3 were fabricated and characterized by electron microscopy, compressive mechanical testing, rheometry and thermogravimetric analysis to ensure a smooth and reliable printing process. After optimizing the printing parameters, the dense and porous printed samples were carefully debinded and sintered to obtain dense (∼ 92 %) and defect-free ceramic bodies. The sintered samples were characterized for phase development, microstructure, and pore size distribution. Careful observations reveal a particular range of pore size (0.1 – 5 µm), which originates from the binder burn out process. The dielectric and ferroelectric properties of the fabricated samples were in good agreement with those reported in previous literature. This work provides a foundation for rapid prototyping of functional electro ceramics into reliable products with desired functional properties.

Preparation and Characterization of 3D Printed Porous 45S5 Bioglass Bioceramic for Bone Tissue Engineering Application.

Three-dimensional (3D) printing technology provides advanced technical support for designing personalized bone tissue engineering scaffold. In this study, two porous diffusing models, namely, average and layered perforated cylindrical scaffolds, were designed for bone tissue engineering scaffold. The designed models were fabricated by liquid crystal display mask stereolithography printing. Structural design and finite element mechanical analysis were conducted. 45S5 bioglass was selected as the raw material for preparing the printing inks for bone tissue engineering scaffolds. By adjusting the viscosity and temperature of the slurry, the maximum proportion of 45S5 bioglass (40 wt%) was added into the photosensitive resin for preparing 3D printing slurry. Our results indicated that an optimized sintering condition includes the debinding rate (0.5°C/min), and temperature raising rate (5°C/min) and sintering temperature (1100°C) were proposed to sinter 45S5 bioceramic scaffolds. The amorphous 45S5 bioglass showed good crystallization after sintering, and the scaffold porous structure showed good integrity. Micropores were observed in the struts which interconnected with each other. Moreover, the porosities were tested as 57% and 45% with a uniform pore distribution. The shrinkage rate was about 10% during sintering process due to binder burning and crystallization shrinkage. The compressive strength of the sintered scaffold was 0.71 ± 0.048 MPa and 2.13 ± 0.054 MPa, respectively, which are consistent with the finite element mechanical analysis simulation results. In conclusion, the layered perforated 45S5 bioglass scaffold shows good mechanical properties and porosity, indicating that it could be a promising candidate for bone tissue engineering.

Processing of Alumina Honeycomb Catalyst Substrates and Studies on Methyl Cellulose Binder Burn Out Kinetics

Processing of Alumina Honeycomb Catalyst Substrates and Studies on Methyl Cellulose Binder Burn Out Kinetics

Combustion mechanism of nitro ester binders with nitramines

The combustion of binary compositions of nitramines (HMX, RDX, Bi-HMX, and CL-20) with two nitro ester binders, one of which is characterized by gas-phase combustion, and the other by the burning-rate controlling reaction in the condensed phase, was studied in the pressure range 2–15 MPa. It is shown that in compositions with the binder characterized by gas-phase combustion, HMX in concentrations up to 50% acts as an inert additive. Depending on the size and concentration of HMX particles, three types of combustion of the mixtures can be identified: combustion along the binder layers, combustion as a single system, and the model of combustion with a coolant. At higher nitramine concentrations, combustion control passes to nitramine, and the burning-rate controlling reaction occurs in the liquid phase of nitramine. For Bi-HMX and CL-20 nitramines, which are less stable and more fast burning than HMX and in a mixture with a binder characterized by gas-phase combustion, only two combustion models are observed: the model with fast burning additives or combustion as a single unit. In compositions of the nitramines RDX and HMX with a binder burning by the c-phase mechanism, the combustion model with fast burning additives is applicable only in a narrow range of conditions. The compositions mostly burn only as a single unit, and the addition of nitramine increases the burning rate of nitro ester by transferring heat from the overlying zone to the condensed phase.

Water-based tape-casting of SOFC composite 3YSZ/8YSZ electrolytes and ionic conductivity of their pellets

Abstract Electrolyte supports for SOFC applications were obtained by water-based tape-casting. Slurries of commercial 3YSZ and 8YSZ and mixtures with a mass ratio of 25/75 and 75/25, respectively, were prepared. A commercial acrylic polymer binder with dispersive properties was used. The drying conditions for obtaining crack-free green tapes were studied. Crack formation during drying was greatly affected by the carrier speed at a fixed temperature. Thermal analysis was performed on the green tapes to study the binder burn out properties. Weight loss of the green tapes occurred until 400 °C and a pre-heating step was therefore included in the sintering program. The microstructure of the green and sintered tapes were investigated by SEM. Fully densified tapes were obtained after sintering at 1450 °C. The ionic conductivity of pressed pellets were characterized by impedance spectroscopy in the temperature range of 200–1000 °C. Phase and crystal structure of pressed pellets were analyzed by XRD. The crystallinity varied from a majority of monoclinic structure (pure 3YSZ) to a majority of tetragonal structure with increasing the 8YSZ content. A cubic single phase structure was obtained by further increasing the 8YSZ content. It was shown that the ionic conductivity of the composite samples were modified with respect to the pure materials. At high temperatures the pure cubic structure gave rise to high conductivity. At low temperatures the conductivity was affected by the grain boundary resistance which was the lowest for the pure 3YSZ, the highest for the pure 8YSZ and decreased as a function of increasing 8YSZ content.

Effects of CaO–B2O3 Glass on Sintering and Microwave Properties of Cordierite Ceramics for Low-Temperature Cofired Ceramics

The densification behavior and dielectric properties of cordierite ceramics adding three different proportions of CaO–B2O3 glass were investigated. The cordierite ceramics were prepared from the waste of porous ceramics. Their crystalline phases, densification parameters, dielectric properties, and microstructure were addressed. The densities of all samples firstly increased and then decreased. The crystalline phase of samples was cordierite. It was considered that CaO–B2O3 glass and cordierite ceramic did not react in the process of sintering. With 10, 15, 20 wt % CaO–B2O3 glass added, the maximal densities of samples were 2.46, 2.42, and 2.33 g/cm3, respectively, obtained at 1060, 1000, and 940 °C. The materials had a low dielectric constant and a low dielectric loss [ε≈5, tan δ≈(2–3)×10-3, at about 10 GHz]. The sample, with 15 wt % CaO–B2O3 glass added, sintered at 1020 °C (binder burning temperature at 500 °C, with a heating rate of 3 °C/min) had better properties (ε=5.14, tan δ=2.23×10-3 at 10.328 GHz).

Fabrication of PMN0.65-PT0.35 Tubes for Transducer Applications by High Temperature Extrusion

The piezoelectric tubes with optimum inner to outer radius ratio were theoretically shown to have zero radial and large axial displacement, which is useful for transducer application. In an effort to fabricate such tubes, the powder processing, tube fabrication and characterization was carried out. PMN 0.65 -PT 0.35 precursor powders were prepared by modified solid-state method and added with 0.15 wt% Mn. Mn addition increased the d 33 coefficient from 530 to 650 pC/N after sintering. Low-density polyethylene based binder was developed for these Mn added powders to fabricate ceramic discs and tubes. The tubes with different inner to outer diameter ratio were fabricated by high temperature extrusion. The samples were subjected to optimized binder burn out cycle and sintered at 1150°C to achieve 92% theoretical density ceramics. The sintered pellets, despite being processed with 50 vol% of binder, showed high piezoelectric coefficients. Preliminary characterization of the tubes indicates high longitudinal displacement.

The use of yttrium (III) isopropoxide to improve thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics

Instead of Y2O3 powders, yittrium isopropoxide (YIP) was used as a sintering additive to sinter high thermal conductivity polycrystalline aluminum nitride (AlN). The reasons for using sintering additive in sol-gel form are due to the fact that the particle sizes are uniform in the nano scale and also they promote a better coating of AlN grains, being more effective during sintering process. The binder burn out was carried in two different atmospheres, N2 (N2 BBO) and air (air BBO). The thermal conductivity of dense polycrystalline aluminum nitride samples with the addition of Y2O3 (YIP formulation) ranging from 1.0 to 10.0 wt% with N2 BBO and air BBO was measured by the laser-flash technique. The results of measured thermal conductivity exhibited higher values than those reported for samples of same yttria formulation (Y2O3 powder) and sintered conditions.

Aqueous tape casting processing of low dielectric constant cordierite-based glass-ceramics—selection of binder

In this paper, four different binders were investigated in the process of aqueous tape casting of cordierite-based glass-ceramics and their effects on the rheological behaviour of the suspensions and on the microstructures of the green tapes were compared. Meanwhile, a good compatibility between the dispersant and binder was found to be a predominant factor to obtain an optimised cordierite glass-ceramic tape. The microstructure of the green tape was observed by SEM and the weight loss during binder burn out process was determined by DTA/TG. The dielectric constant and dielectric loss of the sintered tapes (at 1150 °C for 2 h) was also measured.

Fabrication of Continuously Porous Alumina Body by Fibrous Monolithic and Sintering Process

A continuously porous alumina sintered body was successfully fabricated using by the fibrous monolithic process, in which carbon and flour were used as a pore forming agent. An equation was driven for anticipating the microstructural change during extrusion as a function of the extrusion ratio, and it was identified that the resultant microstructure obtained from using the fibrous monolithic process agreed well with the calculated size using the equation. The third passed and sintered alumina body includes continuous pores of about 42.5 μm in diameter at an intended direction, while the second one consists of 228 μm. Fine pores were also found to form along the alumina surfaces with 0.1-10 μm in diameter. There was no shape change during binder burning out and sintering processes.

Dielectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3/polyurethane 0-3 composites

In recent years, lead-based relaxor materials have been much researched for diverse applications. These include devices such as ferroelectric random access memory (FeRAM) [1], multilayer ceramic capacitor (MLCC) [2], ultrasonic transducer [3], and display devices [4] due to their high dielectric constant [5]. Composite piezoelectric materials are an especially useful choice for transducers such as medical ultrasound devices. These composites show voltage charge constant g33values that lead to the increased sensitivity. Moreover, the matching efficiency of acoustic impedance also improves due to the low density and the low velocity of composite material [6]. This paper considers the dielectric properties of Pb(Mg1/3Nb2/3)O3PbTiO3/polyurethane 0–3 composites not yet reported, showing the dependence of those properties. A 0–3 connectivity, a three dimensionally connected polymer matrix filled with discrete loaded piezoelectric ceramic particles, was considered. Historically, various connectivity patterns of PZT (lead zirconate titanate)-polymer composites have been studied to improve the piezoelectric properties of PZT ceramics [7, 8]. J. T. Wang et al. reports the composites have been studied using rigid epoxy with Pb(Mg1/3Nb2/3)O3PbTiO3 (PMN-PT) [9]. In contrast, J. Su et al. [10] states that polyurethane rubber produces 0.85% strain when an electric field of 7 MV/m is applied to a 0.1 mm thick sample. Moreover, a polyurethane composite, rather than epoxy composite, decreases stress inside the piezoelectric materials [11]. Therefore, piezoelectric composites with 0–3 connectivity were fabricated from PMN-PT powders and polyurethane rubber. These composites were investigated for dielectric properties with variations in active particle and PMN-PT/polyurethane interfacing. For the study, PMN-PT calcined powders were used as PMN-38 purchased from TRS Ceramics, Inc., PA, USA. The powders were pressed to form a disk of 25 mm × 1 mm under 100 MPa pressure. Following binder burn out at 500 ◦C, the pellets were then sintered at 1100 ◦C and 1150 ◦C for 2 h with the heating rate 50 ◦C/h and natural cooling in the furnace. Excess PbO (10 wt%) and PbZrO3 were added as PMN-PT source powders. The pellets were put on the platinum foil in a closed alumina crucible, and an oxygen atmosphere was employed for sintering. The sintered disks were crushed to powder with a mortar and pestle. The prepared powders were obtained by first sieving with

Binder burnout-material-process interaction during sintering of MnZn-ferrites

The binder burnout process step for MnZn-ferrite materials has been investigated in order to explain the origin of the binder burnout cracks that occur during the sintering of MnZn-ferrites. The binder burnout reaction extends to temperature regions where oxidation of the ferrite material (i.e. Mn 2+≧Mn 3+≧Mn 4+) occurs simultaneously. Under such conditions, the oxidation of the binder is favoured relative to that of the ferrite until the binder burn out oxidation has been completed. As a consequence, the ferrite oxidation occurs at higher temperatures and at higher reaction rates. The associated material shrinkage rates are therefore also increased, enhancing defect formation and eventual crack development within the products. When ferrite products of large dimensions are considered, the developed temperature gradients across the body provide a position dependency of these reactions, which results in the development of high stresses and ultimately in product cracking.

Improved Compaction in Multilayer Capacitor Fabrication

The most common defects found in multi-layer ceramic capacitors are derived from residual porosity formed when solvents and binders are released from a ceramic green body. Without a well-controlled compaction technique, defects between sheets in the stacked body are often present, leading to lamination problems. This paper suggests alternative approaches, using compaction applied before and/or after the process of binder burnout with the intention of reducing the number of stacking-generated defects and the volume of voids formed after binder burn-out. Barium titanate tapes and stacked multilayer electroded discs have been investigated and characterised by microstructural examination and density measurement. The resulting properties are described, and the behaviour of the multi-layers discussed in terms of the microstructure and processing procedures. It is shown that the porosity content of sintered samples compacted at 300MPa is approximately half that of samples compacted at 30MPa when both are sintered at 1300°C for 2h. A further improvement of densification can be achieved by a postcompaction treatment after binder burn out.

99/02201 Shrinkage, weight loss and crack prevention during binder burn out of components produced by fused deposition of ceramics (FDC): Bhargava, P. et al. Solid Freeform Fabr. Symp. Proc., 1997, 395–402

99/02201 Shrinkage, weight loss and crack prevention during binder burn out of components produced by fused deposition of ceramics (FDC): Bhargava, P. et al. Solid Freeform Fabr. Symp. Proc., 1997, 395–402

Gelation forming of ceramic compacts using agarose

AbstractThe development of a cast forming process for ceramics based on agarose gelation is described and the properties of green and sintered bodies are presented. For this process, a warm alumina slurry containing more than 50 vol.-% solids loading and ∼1 wt-% agarose binder (Al2O3 basis) is cast into a relatively cold, non-porous mould, resulting in a tough green body formed by gelation (37°C) of the agarose molecules. The green compacts show uniform density distribution, with precise dimensions and very smooth surfaces. After drying, they can be sintered directly without special binder burn out procedures. Complex ceramic parts with thick and thin cross-sections can be formed. The process is illustrated for the preparation of a turbine rotor component.

Optimization of firing parameters for ceramic wares by thermal analysis

Aesthetic and utilitarian properties of traditional ceramic wares as well as engineering properties of modern advanced ceramics are attained by maintaining an optimum temperature-time-atmosphere relationship, called firing schedule, in the kiln. The contribution of modern thermal analysis (TA) techniques such as TG/DTG, TG/EGA, TG/MS, DTA, DSC, TDA, etc. in 1) optimizing production steps by raw material quality control, by studying binder burn out, product densification, 2) in simulating appropriate preheating, firing and cooling schedules as well as 3) in developing shorter firing cycles has been extensively reported in recent literature. The paper will first discuss theoretical curves and energy required for ceramic firing and present from the literature selected examples of applications of thermal analysis in ceramic technology.

Effects of Calcination on Life Time of BaTiO3-based Multilayer Ceramic Chip Capacitors with Nickel Electrodes.

The studies on calcination have illustrated clear influence on the life time of multilayer ceramic chip capacitors with Ni electrodes by means of highly accelerated life test. Regarding the life time of the capacitors, the experimen tal results showed remarkable evidence of (1) effects of suitable amount of Fe and Mn additives, (2) homogeneous calcination with maintaining A/B≈a1.01 nonstoichiometry of ABO3 perovskite structure, and (3) high temperature calcination after completion of binder burn out. By computer aided microstructural analysis, the distribution of constituent and impurity ele ments of the capacitors were found to be dependent on calcination tempera ture. The change of the lattice constant of ABO3 at high temperatures and thermal behavior of ABO3 are also discussed.

Processing of Extruded BPSCCO Superconductor-PMMA Composite for Sintering and Texture Development

Bi-based superconducting shapes were fabricated by extrusion of ceramic-polymer mixture involving a solgel derived superconductor and in situ polymerized polymethylmethacrylate as binder. The powder was intimately mixed with methylmethacrylate monomer and polymerized in the presence of other organic additives such as butylbenzyl phthalate, phosphate ester and benzoyl peroxide. The viscous mass was then extruded to wires 3mm in diameter and 25mm in length. They were heat-treated at controlled rates for binder burn out and sintering at 840°C for 20h. Zone melting refining was carried out on the sintered samples in a three-zone furnace at a controlled speed of 30mm per hour for introducing texture. The surface morphology of starting powder and microstructure of fractured surface of sintered and textured wires are presented and compared.

Binder burn out of tape cast ceramics by microwave energy

Microwave power was used to burn out binder from tape-casted barium strontium titanate ceramics. Compared with conventional methods of binder burn out, microwave heating offers some distinctive advantages. The binder burn out process was completed using microwave power at lower temperature and less time. By characterizing the dielectric properties of the tapes at different stages of microwave heating, a better understanding of microwave and conventional binder burn out mechanisms is realized.