Kinetic study of the polymeric binder burnout in green low temperature co-fired ceramic tapes

The binder decomposition and burnout process of a commercial low temperature co-fired ceramic (LTCC) tape and an alumina tape which is used as a sacrificial tape for the constrained sintering process of the LTCC-tape was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 550 °C at different heating rates (from 1.5 to 10 K min⁻¹) in air. TG revealed a multistage degradation behaviour of the binder system for both tapes, but the temperature range of the different degradation stages varied. The activation energy of decomposition was determined by the Flynn–Wall isoconversional method and the Coats–Redfern method.     

Diol—Based Sol–Gel as a Novel Binder for Barium Titanate Ceramics

The relative merits of using a diol-based sol–gel precursor as a binder in the fabrication of barium titanate ceramics made by die-pressing a mixed oxide starting powder have been investigated. The characteristics of powder compacts were compared to samples prepared using a conventional PVB organic binder. The green strength of pellets with the PVB binder was higher than for samples containing the gel, but strength after binder burnout from gel samples was double that of pellets made with PVB. The gel led to improvements in densification during sintering, but these were most noticeable at low sintering temperatures and at intermediate stages of densification. After sintering for 2 h at 1150C, the gel-containing samples reached 75% of theoretical density, some 5% more than for the organic polymer binder. Sintering at 1300C for 2 h, gave a sintered density of ~96% of theoretical density using the gel additive, which was only 2% higher than for the conventional PVB binder system. The decomposition characteristics of the gel were investigated by TGA, FTIR and GC-MS techniques.     

Thermal analysis of starch for realizing embedded channel in low temperature co-fired ceramic

The rapidly developing biotechnology, automotive industry, chemical and environmental fields have increasing needs for analytical systems with desires such as smaller sizes, lower sample volumes. Reduction in size results in further requirements in functionalities such as multi-sensor devices with low cost. These microsystems usually contain three-dimensional structures. In the fabrication of microfluidic devices ensuring a well-shaped channel is a challenge. During firing of the low temperature co-fired ceramic (LTCC) substrate, these embedded structures tend to deform and sag because the green glass–ceramic material is very weak. Starch was used as sacrificial volume material (SVM) to support the embedded structures of the LTCC during lamination and sintering. As a consequence of burnout, the increased fraction of evolving gases from SVM requires an adequate adaptation of the firing process to control starch degradation and provide a residue-free burnout. Using thermal analysis techniques and describing degradation kinetics of SVM, a new heating profile is demonstrated which insures complete starch burnout without damaging the LTCC structures.     

Thermogravimetric study of yttrium isopropoxide and dispersant burnout in aluminum nitride ceramic processing

Yttrium isopropoxide, an yttrium oxide precursor, is sometimes used as a sintering aid for producing aluminum nitride ceramics. In the present work, this sintering aid was used with isopropanol as the solvent and polyethyleneimine as the dispersing agent. After initial ball milling and drying steps, the burnout behaviour of samples taken from isostatically pressed pellets was studied by thermal analysis in nitrogen and air. In addition to the milled and pressed pellets, each component was also analyzed separately. Complete conversion to yttrium oxide, with no residual carbon, would be a desirable property of this system. However, during the preparation of the aluminum nitride pellet, there was only partial yttrium isopropoxide decomposition. The nitrogen burnout residue contained carbon formed from the yttrium isopropoxide and dispersant overlapping thermal decomposition, mostly from an intermediary decomposition stage of the former that occurs between 300 and 550°C. The residual carbon content and the previous yttrium isopropoxide decomposition were estimated by thermogravimetry.     

A Sol-Gel Precursor as a Powder Binder for PZT Ceramic Fabrication

A lead zirconate titanate (PZT) precursor sol was prepared by a diol sol-gel route and used as a binder for assisting the uniaxial die pressing of PZT powders. The powders, of composition Pb(Zr_0.52Ti_0.48) O₃, were prepared by a two step mixed oxide route using lead carbonate, zirconia and titania starting powders. The densification characteristics of the powders, which were not milled after the final calcination step, were compared to samples prepared using PVA as a conventional binder. Improved sintering behaviour was observed for the novel sol-gel binder system. For example, using a sol concentration, equivalent to 7 wt% of PZT derived from the binder, pellets of 95% theoretical density were obtained after firing at 1150°C for 4 h, whereas for the same firing conditions, samples blended with PVA resulted in a density of only 78% theoretical.     

Nanoporous morphology of alumina films prepared by sol–gel dip coating method on alumina substrate

Nanoporous crack free alumina thin films were fabricated in two phases gamma (??) and alpha (??) by sol?Cgel dip coating method. The thickness of the mesoporous films was increased with binder by varying its concentration, and with increasing the number of coating. The porosity, pore size, surface area and phase were controlled by sintering temperature. Interconnected pore structure of 8?C15?nm diameter were successfully prepared by repeating the deposition several times. FESEM, BET, AFM and XRD techniques were employed for the microstructural characterization.     

Production of doped ZnO powders for varistor applications using sol-gel techniques

The electrical behaviour of ZnO varistors is controlled by the characteristics of the ceramic microstructure which depends strongly on the properties of the initial powder. This paper describes a study of the effect of different chemical methods to synthesise doped ZnO powders. The ceramic powders were synthesised by the following routes: a) classical mixing of oxides (for comparison purposes), b) aqueous solution of inorganic salts and c) hydrolysis and polycondensation of metalorganic compounds in an organic solvent. The physicochemical characteristics of these powders were evaluated using a scanning electron microscope and thermoanalytical instrumentation. Standard spray drying technology was used to pelletise the powders to obtain an agglomerated powder suitable for uniaxial pressing. The discs were sintered in an electric furnace under air atmosphere using several temperature programmes. The ceramic microstructure was characterised using SEM and X-ray diffraction. The effects of powder processing route on sintering and microstructural development are discussed. Powders prepared by the metalorganic route exhibited somewhat lower sintering temperatures than conventional powders. However, the rate of sintering was slower for metalorganic and aqueous solution powders. These observations were related to powder morphology. The ZnO–Bi₂O₃–CoO system exhibited the best varistor characteristics as it was expected, whereas the binary systems supported much lower voltages at low currents than ternary systems.     

A novel programmed shrinkage dilatometer for optimized sintering of powder ceramics

A fast-firing shrinkage rate controlled dilatometer was developed as a tool for optimizing sintering of powder compacts. The instrument described in this work features an infrared imaging radiation furnace and a low thermal mass dilatometer assembly which allowed controlled heating and cooling rates of up to 500°C min^?1. Shrinkage control was accomplished using a computer interfaced PID control algorithm. Adjustments were made to hardware and software which reduced specimen creep under dilatometer pushrod load, eliminated non-uniform pushrod expansion, fostered reproducible specimen temperature determination, accounted for thermal expansion during sintering, and generated instantaneous termination of sintering at the specified end of RCS. Tests performed on ZnO samples demonstrated very rapid thermal response and excellent shrinkage control.     

Quantitative Mass Spectrometry of Decarburisation and Denitridation of Cemented Carbonitrides During Sintering

 Quantitative quadrupole mass spectrometry of (Ti, W)C-based cemented carbonitrides was carried out in order to monitor the evolution of the gas species as a function of time and temperature during vacuum sintering. Solid standards and gas mixtures as well as precise flow control were employed for calibration. Upon integration of the outgassing rates the carbon and nitrogen evolutions and mass losses during sintering of raw hardmetal powder mixtures (WC, TiC,…) and cemented carbonitrides could be quantified. Outgassing occurs in the range of temperatures 490–1480 °C. Nitrogen outgassing of (Ti, W)(C, N) was greater than that of Ti(C, N) due to the presence of W which increases the nitrogen activity in the solid causing a higher nitrogen equilibrium pressure. TiN showed a CO (0.2 wt%) and N₂ (0.5 wt%) weight loss only in the presence of the binder phase. For powder mixtures, it was observed that the amount of CO, CO₂ and N₂ liberated during vacuum sintering increased with the addition of cobalt in comparison with the same powders without binder phase. Nitrogen containing cermet alloys showed a greater loss of carbon than (Ti, W)C-based hardmetals. A careful control of carbon content by doping seems to be necessary in such alloys to avoid η-phase formation. Received July 7, 2000. Revision December 4, 2000.     

Fabrication of magnesium bentonite hollow fibre ceramic membrane for oil-water separation

In this study, low-cost magnesium bentonite (MB) was used for the fabrication of bentonite hollow fibre (BHF) membrane with high pure water flux. MB powder was initially characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size distribution (PSD) analyser, Brunnauer -Emmett- Teller (BET) method, and field emission scanning electron microscope (FESEM). The BHF membrane obtained was then fabricated through dope suspension mixing, phase inversion and sintering process. The dope suspension was prepared by mixing MB, dispersant, polymer binder, and solvent using a planetary ball mill. While the spinning process was carried out at the extrusion rate of 8 mL/min, a fluid bore rate of 10 mL/min and air gap of 5 cm, and this was followed by sintering operation at 950 °C, 1000 °C, 1050 °C, and 1100 °C. The resulting BHF membrane was characterized by scanning electron microscopy (SEM) and XRD; the porosity test, water flux and oil rejection were also examined. The SEM surface morphology of BHF at sintering temperature of 950 °C showed spongy-like and nested macrovoids structure; the porosity was 49.09% with a mean pore size of 3.9 µm. The performance test on the bentonite-based hollow fibre membrane showed that the membrane prepared at 20 wt% and sintering temperature of 1000 °C, which induced high and stable permeate water flux and oil rejection of BHFC membrane were 544 L/m² h and 97%, respectively. The results have shown that the presence of magnesium in bentonite can enhance and promote the needed support material for the fabrication of hollow fibre ceramic membrane.     

Polymer melting and polymer powder sintering by thermal analysis

Sintering of polymeric powders is a peculiar characteristic of many processing technologies, including rotational moulding and selective laser sintering (SLS). During polymer sintering, viscosity reduction in the melt state promotes densification of polymer powders, through a double stage mechanism, involving powder coalescence and bubble removal. In particular, sintering of semi-crystalline polymers is strongly influenced by the melting behaviour. Nevertheless, melting itself in absence of pressure is not necessarily accompanied by powder sintering, unless low viscosities are achieved. In this work, the melting and sintering behaviour of recycled high density polyethylene (rHDPE) have been analysed through differential scanning calorimetry (DSC) and Thermomechanical Analysis (TMA). Efficient models capable of describing the melting temperature distribution and rate of sintering of rHDPE powders have been developed, highlighting the inherent differences between the two distinct processes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sinterability enhancement in semicokes obtained by controlled pyrolysis of a petroleum residue

Self-sintering semicokes were prepared by pyrolysis of an aromatic petroleum residue at 460–480 °C and pressures of 0.1–1.0 MPa. The evolution of gases and thermoplasticity from resultant semicokes were monitored by TGA and TMA, respectively. Sintering behaviour of the semicokes is extremely sensitive to pyrolysis conditions which determine contents of volatile matter and binder phase. Semicokes produced at 1.0 MPa have high volatile contents with excessive plasticity. Changes of temperature and soak time, used to reduce volatile matter contents induce reductions to the plasticity and sintering. A lower pyrolysis pressure has a similar effect. Although the operational window is narrow, heat-treated compacts (2500 °C) can be made with high density (1.9 g cm⁻³) and bending strengths >75 MPa. Using high-temperature pyrolysis (460 °C) with a post-treatment at 350–400 °C eliminates light components, without decreasing sintering properties. Compacts from these powders also exhibit high density (1.9 g cm⁻³) with higher bending strengths >90 MPa, comparable or superior to mesocarbon microbeads (MCMB) obtained from the same precursor.     

Preparation and characterization of inorganic hollow fiber membranes

Inorganic hollow fiber membranes were prepared by spinning a polymer solution containing suspended aluminum oxide (Al₂O₃) powders to a hollow fiber precursor, which is then sintered at elevated temperatures. In spinning these hollow fiber precursors, polyethersulfone (PESf), N-methyl-2-pyrrolidone (NMP), and polyvinyl pyrrolidone (PVP) were used as a polymer binder, a solvent, and an additive, respectively. The inorganic hollow fiber membranes prepared were characterized using scanning electron microscope (SEM), gas permeation techniques Coulter porometer, and gravimetric analysis. Some primary factors affecting the structure and performance of the membranes such as the sintering temperature and the ratio of the aluminum oxide to the PESf polymer binder were studied extensively. The prepared inorganic membranes show an asymmetric structure, which is similar to the conventional polymeric membranes prepared from the same phase-inversion technique. The inorganic hollow fiber membrane with a higher porosity and better mechanical strength could be prepared by blending the spinning solution with a smaller amount of aluminum oxide powder.     

Melt pelletization of a hygroscopic drug in a high shear mixer. Part 3. Effects of binder variation

Melt pelletization experiments with sodium valproate as a hygroscopic drug were performed in a laboratory scale high shear mixer. In the current part, the effect of altering the binder liquid properties (using different binders, varying the temperature, or adding highly dispersed silicon dioxide to the molten binder) on the pellet size, size distribution and the growth rate was studied. Three meltable binders, namely glycerol monostearate (GMS), hydrated castor oil (HCO), and polyethylene glycol (PEG), were included in the study. Two series of experiments with GMS or HCO showed a higher granule growth rate with decreasing binder viscosity. Also, increases in the granule growth rate were observed for all meltable binders tested, when the binder amount and the impeller speed were increased. Factorial designs with all three binders were performed under the same conditions. In these experiments, no correlation existed between the granule growth rate and the viscosity of the different binders. The different granule growth rate, however, was mainly attributed to the different solubility of sodium valproate in the binder liquid used. Higher solubility increased the volume of the binder liquid and, accordingly, the granule growth rate. Taking the amount of dissolved drug into account, the granule growth rates of GMS and PEG were comparable. However, HCO displayed a lower granule growth rate, which might be related to its low adhesion tension. During melt pelletization in a high shear mixer the solubility of the drug in the molten binder strongly influences the pelletization process.     

High-temperature dilatometer with pyrometer measuring system and rate-controlled sintering capability

An optical pyrometer is used to measure and, in conjunction with temperature programmer and controller, control the temperature of the NETSZSCH Dilatometer DIL 402 E/7 up to 2400°C. This instrument is thus suitable to investigate sintering of technical ceramic materials such as SSiC and ZrO₂. Measurements carried out on these materials containing organic additives show that the sintering range of SSiC starts at 1800°C—although its final density is not reached at 2400°C at a heating rate of 20 deg·min^?1—and that the densification of ZrO₂ occurs between 1000° and 1800°C. Using rate controlled sintering (RCS) the sintering process can be extended on a time scale, but the same densities are obtained at the same temperatures when comparing the measurements with and without RCS.     

Electrochemical Processing of Reaction-bonded Ceramic Composite Coatings

Ceramic matrix composite coatings are currently of much interest for application in high-temperature and highly corrosive environments. Formation of ceramic coatings by electrochemical processing is a relatively new mean^[1-2]. It presents several advantages over alternative coating techniques, the thickness and morphology of the deposit can be controlled by the electrochemical parameters, relatively uniform deposits are obtainable on complex shapes, the deposition rate is higher than that using most other methods and the equipment required is of low cost Recently we developed a novel fabrication technique for the production of ceramic/ceramic and ceramic/metal composite coatings by electrochemical processing^[3]. The technique combined two electrochemical deposition methods, electrophoretic deposition (EPD) and electrolytic deposition (ELD), which can produce uniform composite layers of closely controlled thickness on both metallic and ceramic substrates at ambient temperature with inexpensive equipment. However, the main problem associated with electrochemical processing is the difficulty in sintering of the coatings. First, high temperature is required for sintering of the coatings. Secondly, the volume shrinkage of the coatings during sintering leads to the formation of cracks in coatings bonded to metal substrates. So a reaction forming technique, reaction bonding process, also has been developed to produce near net-shape ceramic coatings, which overcome problems caused by the shrinkage of ceramics during sintering.     

Effects of Sintering Temperature and Press Pressure on the Microstructure and Electrochemical Behaviour of the Ag2O/GO Nanocomposite

The purpose of this study was to evaluate the effects of press pressure and sintering temperature on the microstructure and electrochemical performance of silver oxide-graphene oxide composite as a novel electrode produced by the powder metallurgy (PM) route. Scanning electron microscopy method used to investigate the microstructure of electrodes and energy dispersive X-ray spectroscopy analysis method was used for point analysis. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to research the effects of sintering temperature and press pressure on the electrochemical behaviour in the 1.4 wt % KOH solution and electrical discharge test was used for evaluate the ultimate electrical capacity of silver oxide-zinc batteries with electrolyte of the 1.4 wt % KOH solution.

     

Thermal and electrical properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> synthesized by soft chemistry route

The non-isothermal sintering process of cerium dioxide containing gadolinium sesquioxide powders within a wide range of specific surface area was investigated by dilatometry. Linear shrinkage data of powder compacts were recorded under several constant rates of heating. Dilatometry data were analyzed by two methodologies enabling to preview the relative density for any temperature/time profile, and determination of the apparent activation energy for sintering. Correlation of dilatometry results with microstructure evolution was also carried out. Remarkable differences in sintering powders with different specific surface areas were found. The apparent activation energy for sintering increases with decreasing specific surface area and, in most cases, it does not change significantly in the approximately 70–85% range of relative density.     

Ignition of highly reactive metal particles

It was shown that, with increasing reaction rate constant above a certain limit, the bulk ignition mechanism changes to a surface mechanism. In this case, surface layers of a particle undergo local heating and a reaction front forms and propagates into the particle. The time of the frontal burnout of the particle is shorter than the time of its bulk burnout, during which the temperature field relaxes instantaneously.     

Selected thermoanalytical methods and their applications from medicine to construction

There are many thermoanalytical techniques but only several of them such as thermogravimetric analysis (TG), high resolution thermogravimetric analysis (Hi-Res™ TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), calorimetry, differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), evolved gas analysis (EGA), transient thermal analysis (TTA) and thermal conductivity (k) have selected to be discussed in this paper. Simultaneous thermal analysis (STA) is ideal for investigating issues such as the glass transition of modified glasses, binder burnout, dehydration of ceramic materials or decomposition behaviour of inorganic building materials, also with gas analysis. Selected applications of various thermoanalytical techniques from medicine to construction have also been discussed in this paper.