Organic Burnout Research Articles

A challenge to the sintering of nanocrystalline metals: Organic burnout and oxide reduction compete with powder consolidation

In nanocrystalline materials atomic transport is enhanced by diffusion along grain boundaries and triple junctions, aggressively accelerating sintering kinetics to the point that the onset of consolidation can precede organic debinding reactions at low temperature. What is more, nanocrystalline metals typically have (or at one time had) more surface area, and thus a greater degree of native oxide that can react with organics upon sintering. In this paper, we explore the sintering behavior of high-energy ball-milled nanocrystalline Ni-10Fe powder, quantitatively evaluating the interference of densification with the process of organic removal. Early sintering leads to trapping of evolved gas and substantial swelling of a nominally sintering compact. Volatilizing process additives remain trapped until very high temperatures, causing microstructural degradation through creep foaming. Finally, in an alloy system with more than one native oxide phase, there are shown to be multiple oxide reduction events that can renew gas evolution to very high temperatures. After quantitatively evaluating these mechanisms in the Ni-10Fe powder specifically, we also generalize their consideration to a range of nanocrystalline metals, to provide guidance for development of powder processing routes for those materials.

Direct ink writing of dense alumina ceramics prepared by rapid sintering

Direct ink writing, as one kind of 3D printing technology, can produce alumina ceramics with complex shapes that are difficult to be obtained by conventional technology. However, how to quickly and efficiently produce dense and high-strength alumina ceramics by directing ink writing remains a challenge. In this work, a simple formulation of alumina inks containing trace amounts of organic additives (including 0.54 wt% dispersants and 0.9 wt% binders) was applied to prepare dense ceramics with various complex structures. The dispersants activate alumina particles through electrostatic repulsion and spatial site resistance effects, which can help alumina inks with a high mass fraction show the excellent printability. In addition, sintering aids significantly promote densification of alumina ceramics and reduce sintering temperature by introducing lattice defects and forming liquid phases. Due to the trace organics in the green bodies and low sintering temperature, a rapid temperature rise and organic burnout can be adopted to shorten debinding and sintering time and improve productivity. This work provides a new additive manufacturing idea for simple and efficient preparation of dense alumina ceramics with high mechanical properties and complex structures.

A Challenge to the Sintering of Nanocrystalline Metals: Organic Burnout and Oxide Reduction Compete with Powder Consolidation

A Challenge to the Sintering of Nanocrystalline Metals: Organic Burnout and Oxide Reduction Compete with Powder Consolidation

Up-Cycling of LCD Glass by Additive Manufacturing of Porous Translucent Glass Scaffolds

Additive manufacturing technologies, compared to conventional shaping methods, offer great opportunities in design versatility, for the manufacturing of highly porous ceramic components. However, the application to glass powders, later subjected to viscous flow sintering, involves significant challenges, especially in shape retention and in the achievement of a substantial degree of translucency in the final products. The present paper disclosed the potential of glass recovered from liquid crystal displays (LCD) for the manufacturing of highly porous scaffolds by direct ink writing and masked stereolithography of fine powders mixed with suitable organic additives, and sintered at 950 °C, for 1–1.5 h, in air. The specific glass, featuring a relatively high transition temperature (Tg~700 °C), allowed for the complete burn-out of organics before viscous flow sintering could take place; in addition, translucency was favored by the successful removal of porosity in the struts and by the resistance of the used glass to crystallization.

Ceramic decals – predesigned thick-film sensors for variable surfaces

Manufacturing of ceramic multilayer applications by deposition techniques like screen printing, dispensing, or aerosol jet printing is state of the art today. However, in an industrial environment it is a complex challenge to integrate all equipment for precise paste handling and screen print of the microstructures in an existing production line. Moreover, big sized devices or items with a curved surface cannot be handled with standard screen print equipment. To overcome these limitations, a decal technology was investigated. The functional layers are stacked on non-adhesive paper by screen print, fulfilling all demands on precision in line/space ratio and layer thickness. Afterwards, a polymer varnish is printed on top of the stack, which allows to transfer the high precision thick film assembly to nearly any application surface including non-planar surfaces. Since the layers are co-fired, the sintering behavior of the materials has to be regulated. The top layer needs to remain porous until the organic burn-out and the sintering of the bottom layer is complete. Ways to obtain thick film metallization and isolation pastes which have satisfying firing behavior are examined, and the excellent functional properties are discussed. The performance of the developed thick film decals is demonstrated on the example of an alarm sensor on tempered safety glass for windows.

Influence of Fe3O4 nanoparticles on pseudocapacitive behavior of the charge storage process

Nano-crystalline Fe3O4 powders were added to form manganese oxide/iron oxide composite film electrode in order to combine the excellent capacitance characteristics of manganese oxide and iron oxide. Due to the addition of Fe3O4, the crack film formation increases the contact area of electrolyte and electrode and the surface and electronic conductivity of pseudo-capacitors increased. The specific capacitance value can be enhanced by adding iron oxide. The surface of the composite film with Fe3O4 added had small holes due to the burnout of organics, and the network of nano-powders formed uniform and fine pores at 300°C annealing. The EXAFS results to the XRD results, the peaks shift due to the formation of Mn3O4 and Mn2O3 between 250 and 350°C. The best results in this study were 316.1F/g obtained at 1at.% of manganese oxide/iron oxide composite film electrode after 300°C annealing. The 1at.% manganese oxide/iron oxide composite film electrode after 1000cycles, the highest specific capacitance value was 85.8%. The results showed that manganese oxide/iron oxide composite film electrode have good cycle stability of capacitance.

Lightweight bricks manufactured from water treatment sludge and rice husks

Novel lightweight bricks have been produced by sintering mixes of dried water treatment sludge and rice husk. Samples containing up to 20 wt.% rice husk have been fired using a heating schedule that allowed effective organic burn-out. Rice husk addition increased the porosity of sintered samples and higher sintering temperatures increased compressive strengths. Materials containing 15 wt.% rice husk that were sintered at 1100 °C produced low bulk density and relatively high strength materials that were compliant with relevant Taiwan standards for use as lightweight bricks.

Manganese oxide films prepared by sol–gel process for supercapacitor application

In this study, manganese oxide electrodes with promising pseudo-capacitive behavior were prepared by sol–gel process using manganese acetate as the precursor. Effects of post-heat treatment on material characteristics and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, synchrotron X-ray absorption spectroscopy (XAS), and cycling voltammetry (CV). Experimental results showed that manganese oxide films prepared by sol–gel technique exhibited Mn 2O 3 and Mn 3O 4 phases after heat treating at a temperature higher than 300 °C. Meanwhile, a porous manganese oxide coating was observed due to the burnout of organics. The specific capacitance of the manganese oxide electrodes was 53.2, 230.5, 185.6, and 189.9 F/g after heat treating at 250, 300, 350, and 400 °C, respectively. After three hundred charging–discharging cycles, the specific capacitance of the manganese oxide electrodes heat treated at 300 °C decreased to 78.6% of its maximum. Synchrotron XAS examination revealed that manganese oxide electrodes exhibited the same trend where the trivalent manganese was transited into tetravalent manganese after cyclic voltammetry tests.

Nano-aluminum-phosphate via a polymerized organic–inorganic complex route

Abstract Nano-aluminum-phosphate (AlPO4) powder has been synthesized by an ethylene glycol (EG), polymerization, complexation route. The AlPO4 powder has a particle size ≤10 nm via TEM. The differential thermal analysis (DTA) and the thermo-gravimetric analysis (TGA) show complete burn-out of organics is achieved ≤680 °C and crystallization initiates ≤500 °C. X-ray diffraction (XRD) shows crystallization is well developed by 700 °C. Scanning electron microscopy shows a fine grain size with fused edges indicating partial sintering of the powder at 900 °C.

High Quality Microwave Zr0.8Sn0.2TiO4 Dielectric Thin Film Prepared by Sol–Gel Method

High-quality zirconium tin titanate (Zr0.8Sn0.2TiO4, ZST) thin films are deposited along the (100) plane on a p-type Si substrate by the sol–gel method. The effects of two different heat treatment temperatures, 250 and 450°C, for organic burn-out between each spin coating on the crystal structure, morphology, roughness and thickness of the films are investigated. X-ray diffraction confirms a pronounced preferred orientation in thinner films and a polycrystalline structure in thicker films. Microstructure analyses by scanning electronic microscopy (SEM) and atomic force microscopy (AFM) prove that a high-quality ZST film approximately 75 nm thick with a smooth surface (surface roughness of 4 nm) is obtained under suitable processing conditions.

Lead magnesium niobate–lead titanate fibres by a modified sol–gel method

Lead magnesium niobate–lead titanate (PMN–PT) ceramic fibres with the nominal composition of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 have been fabricated by a modified sol–gel method. Due to the difficulty of dissolving the magnesium component, the mixed oxide method was used together with the traditional sol–gel method. To obtain crack-free fibres, pyrolysis was carried out at a very slow heating rate under specific atmosphere to control the organic burnout. The thermal and microstructural properties were investigated using thermogravimetric analysis, scanning electron microscopy and X-ray diffraction. The optimum sintering temperature is 1200 °C and yields a fibre with a final diameter of around 100 μm. A single PMN–PT fibre has been poled and its electrical properties were measured. The properties of the fibre are found to be better than that of a ceramic disc.

Investigation of interactions between co-fired LTCC components

In spite of many advantages it offers for micro-electronic packaging, the low temperature co-fired ceramic (LTCC) technology has yet certain issues to be solved. Physical and chemical reactions, for instance, within and between the passive electronic components (thick film conductors, resistors—TFR) and the LTCC tapes (green sheets) during processing are one of the major challenges of this technology. This study aims to better understand and control the nature of such interactions, which have a direct effect on properties. The work is conducted on PTC (positive temperature coefficient) resistors, which are screen printed on (co-fired) and in (buried) LTCC sheets and fired at various temperatures. The final properties such as temperature coefficient of resistance (TCR) and sheet resistance are evaluated in terms of processing parameters using scanning electron microscopy (SEM), dilatometry and electro dispersive X-ray (EDXS) analysis as characterization tools. The results show that the TFR properties of buried samples deviate more strongly from the expected values compared to those of co-fired ones. It is primarily related to the destroyed conductor and resistor lines, which is closely related to the entrapped gases in buried structures as a result of organic burnout of printed inks.

Burnout of the organic vehicle in an electrically conductive thick-film paste

The burnout of the organic vehicle in a silver-particle, glass-free, electrically conductive, thick-film paste during firing in air was studied. For a vehicle consisting of ethyl cellulose dissolved in ether, burnout primarily involves the thermal decomposition of ethyl cellulose. The presence of ether with dissolved ethyl cellulose facilitates the burnout of ethyl cellulose. Excessive ethyl cellulose hinders the burnout. A high heating rate results in more residue after burnout. By interrupting the heating at 160°C for 15 min, the residue after subsequent burnout is diminished probably because of reduced temporal overlap of the processes of organic burnout and silver particle necking. By interrupting the heating at either 300°C or 385°C for 30 min, the temperature required for complete burnout is reduced. The addition of silver particles facilitates drying at room temperature and burnout upon heating.

Thermal processing of multilayer PLZT actuators

Cofired multilayer actuators (MLAs) can suffer from reliability problems due to internal cracking, resulting from imperfections formed during binder extraction or sintering. Thermal processing methodology was developed to optimize manufacturing output of defect-free multilayer actuators. Rate-controlled thermogravimetry (RCT), in which furnace power is adjusted to maintain a constant specimen weight loss rates, was used for organic binder burnout in MLAs. The effectiveness of the various thermal schedules in eliminating MLA damage was determined through image analysis of depth profiles, ground perpendicular to the layers. The damage resulting from RCT schedules were compared to those produced using conventional temperature-controlled thermogravimetry (TCT). Specimens heat-treated with mass loss rates of 0.003 to 0.03 wt%/min showed fewer microstructural defects than all evaluated TCT schedules. Under RCT, furnace power was adjusted to mitigate the effects of rapid burnout of the multicomponent binder, which surged at specific temperature ranges. The effect of introducing a modified atmosphere of MLAs was also investigated using thermogravimetry in conjunction with mass spectrometry.

Burnout of Organic Components of Glass Ceramic Composite Tapes: Thermoanalytical investigations

Glass ceramic composite tapes are composed of inorganic raw materials (borosilicate glasses and inert fillers) and organic additives (polymer binder, plasticizer, dispergent, residues of solvent from the tape casting process). Burnout of organics in air is a complex process of vaporization, depolymerization and oxidation. Conditions of this process can be simulated by thermal analysis of plasticizer, various binders and binder/plasticizer mixtures with alumina, prepared by impregnation of alumina powder with corresponding solutions and subsequent drying. This allows a quantitative interpretation of the results of burnout of tapes.

Binder extraction from green multilayer ceramics using a weight loss rate-controlled thermogravimetric analyzer

A weight loss rate-controlled organic extraction furnace was built and demonstrated using a multilayer green ceramic. Multirate weight loss schedules as well as automated atmosphere control and detection were demonstrated. The low thermal mass furnace showed good tracking with 300 °C heating and cooling rates. This furnace, coupled with appropriate PID control constants, facilitated feedback control which could extract organics rapidly without self-ignition to uncontrolled combustion. Controlled organic burnout was demonstrated at weight loss rates up to 0.5%/min in air. Damage-free multilayers were observed using a burnout rate requiring 150 min for extraction, rather than the days commonly associated with this task when using conventional furnaces.

Oxide Laminates with High Strength and Work-of-Fracture

ABSTRACTSix types of oxide laminates consisting of combinations of xenotime (YPO4) with zirconia (ZrO2), monazite (LaPO4) with ZrO2, and aluminum orthophosphate (AlPO4) with alumina (Al2O3) were studied. They were fabricated by repeatedly stacking two or three kinds of tape-cast layers, lamination, organic burnout and consolidation by hot-pressing. Two of the YPO4-containing ZrO2 laminates were stacked in a YPO4/yttria-stabilized ZrO2 (Y-ZrO2)/30 vol% Y-ZrO2-70 vol% Al2O3(YZ3-A7)/Y-ZrO2 sequence and in a YPO4/Y-ZrO2 sequence. High strength (∼360 MPa) and apparent work-of-fracture (WOF = ∼ 8.2 kJ/m2) were measured in the first laminate. This oxide laminate demonstrates high damage-tolerance without loss of strength. Both properties were comparable with those of non-oxide laminates. There was an approximately 200-fold increase in WOF, as compared with pure Al2O3. A toughening mechanism by means of the residual, interlaminar shear stress-enhanced, interface delamination is proposed for these good results. Two of the LaP04-containing ZrO2 laminates were fabricated in a LaPO4/70 vol% doped ZrO2-30 vol% Al2O3 stacking sequence and in a LaPO4/Y-ZrO2 sequence. Another two of the AlPO4-containing Al2O3 laminates are fabricated in an AlPO4/Al2O3 and in a (50 vol% AlPO4-50 vol% Al2O3)/Al2O3 stacking sequence. The fracture behavior of these multilayered laminates was also studied. The different results among the three kinds of laminates are discussed.

Rate-controlled organic burnout of multilayer green ceramics

Rate-controlled thermogravimetry was used for organic burnout in multilayer PZT ceramics. A proportional-derivative control algorithm operating on specimen weight adjusted the furnace power to maintain a specified rate of weight loss. Specimens heat-treated with mass loss rates of 0.01 to 0.001 mg min −1 showed no microstructural defects resulting from organic removal.

Chemical Synthesis and Characterization of Calcium Aluminate Powders

The Pechini process was used to produce high‐purity, monocalcium aluminate (CaAl2O4) powders at temperatures as low as 900°C. Absorption spectrometry and BET measurements revealed particles with sizes ranging from submicrometer to 100 μm, with specific surface areas as high as 10 m2/g. Auger electron spectrometry (AES) was used to study the progressive elimination of surface carbon from the organic burnout as a function of temperature. The growth kinetics of calcium aluminate crystallites from a polymeric precursor were studied during calcination as a function of temperature, using transmission electron microscopy (TEM). At the early stages of crystallization, the activation energy for crystallite growth was found to be 118 kJ/mol. This is substantially less than the 356 kJ/mol previously reported. A growth kinetic exponent of n = 1.68 was determined for the amorphous‐to‐crystalline transformation in the temperature range 700° to 850°C. These values were consistent with growth by short‐range diffusion.

Spherical lead zirconate titanate emulsion powder from water-soluble inorganic precursors via plasma burning

Coprecipitation of metal hydroxides inside water-in-oil (W/O)-emulsion droplets leads to spherical gel-particles. Stoichiometric Nd-doped lead zirconate titanate (PZT) ceramic powders are prepared from the water-soluble inorganic precursors Pb(NO3)2, ZrO(NO3)2, TiO(NO3)2, and the dopant Nd(NO3)3. The injection of gaseous NH3 into the emulsion provides the coprecipitation of the corresponding hydroxides. The spray-dried powder consists of surfactant-covered spheres containing portions on HN4NO3. Thermal decomposition of NH4NO3 during calcination may destruct the gel spheres. Therefore, NH4NO3 was removed by sublimation during plasma burning and simultaneously the oxidation of the organic compounds was accelerated. Surprisingly, plasma burning (< 180°C) results in a PZT-phase with small amounts of unreacted PbO. SEM-micrographs show discrete narrow-distributed spheres without destructions caused by NH4NO3 decomposition or by organic burnout.