Manufacturing of a ceramic groove part based on additive and subtractive technologies

Ceramic stereolithography Three-Dimensional (SL-3D) printing has a unique advantage in forming ceramic parts with complex shapes. However, because of the effects of the slicing layer thickness, laser spot diameter, and curing inhomogeneity, its manufacturing dimensional accuracy still lags far behind traditional processing methods. In this study, a manufacturing process based on additive and subtractive technologies was used to prepare ceramic groove parts. The manufacturing process of ceramic groove parts is composed of SL-3D printing, debinding, micro-milling, and sintering processes. In order to improve the dimensional accuracy of ceramic groove parts, a model based on shrinkage compensation and micro-milling was proposed. The dimensional change pattern in the curing phase was modelled and a shrinkage compensation method was established to control the dimensional accuracy of the finished parts. A method to characterize the micro-chipping on machined edges of the workpiece was investigated by applying a micro-milling cutter to process the 3D-printed part pre-sintered at 1150 °C. The effectiveness of the proposed dimensional accuracy control method was verified by the case study of a ZrO₂ ceramic part.     

Preparation of low-shrinkage and high-performance alumina ceramics via incorporation of pre-sintered alumina powder based on Isobam gelcasting

Mechanically robust alumina ceramics with low shrinkage were successfully prepared via gelcasting using Isobam as the gelling agent and pre-sintered alumina powder as the raw material for the first time. The influence of amount of pre-sintered alumina powder and powder's pre-sintering temperature on the viscosity of suspension and mechanical properties of low-shrinkage alumina ceramics were systematically investigated. The results showed that low-shrinkage alumina ceramics with flexural strength of 294.5?±?33.0?MPa, linear shrinkage of 7.79% and relative density of 91.5% can be obtained with the addition of 60?wt% alumina powder pre-sintered at 1600?°C. This convenient and facile approach is promising to fabricate low-shrinkage alumina ceramics with large sizes, high dimensional accuracy and complex shapes.     

双分散反相悬浮聚合制备吸水微球方法及装置

针对反相悬浮聚合存在热力学不稳定、分散剂难于清洗及难以实现工业化生产的缺点,基于落球法测黏度原理,建立了先后采用机械搅拌分散和自然沉降分散的反相悬浮聚合制备微球的方法,并设计了制备装置。该方法依靠搅拌速度及水相与油相体积比确定球径,然后在不采用分散剂的条件下,利用自然动力使微球边沉降边反应,有效避免微球粘连结块;制备装置结构简单,可实现连续生产,反应釜体高度需大于2 m以保证足够的反应时间,釜体材质为非极性材料以防止微球吸附釜壁。聚丙烯酰胺微球制备实验表明,制备工艺易于操作,微球不存在粘连,分散介质可重复使用,且无污染,便于工业化生产。     

Multiscale 2D/3D microshaping and property tuning of polymer-derived SiCN ceramics

Polymer-derived ceramics exhibit excellent properties and are compatible with many shaping techniques due to their liquid precursors. We present a fast and pressureless process for the fabrication of SiCN. Using varied amounts of the filler divinyl benzene, defect-free monolithic disc samples are obtained at high yields. Their electrical conductivity is adjustable across 10 orders of magnitude, flexural strength is improved up to 1.7 GPa, and cytocompatibility is demonstrated. This processing route is applied to a new multiscale microshaping method combining the advantages of two-photon polymerization and casting. The parts’ general shape is defined by KOH-etched silicon molds whereas individual freeform microfeatures like a 3D QR code are implemented through sacrificial 2PP photoresin microstructures added to the mold. The green body is pyrolyzed directly in the mold, whereby the photoresin decomposes and the ceramic part with the submicrometer resolution features imprinted releases itself from the mold undamaged due to ～30% shrinkage.     

3D printing of open-porous cellular ceramics with high specific strength

We present a novel processing route for manufacturing highly open porous, hierarchically structured ceramics via direct ink writing. We manufactured cellular samples with overall porosities up to 88% that exhibit fully open-porous struts with porosities between 45 and 60% and pore sizes x_50,3 < 6 μm using capillary suspension based inks. An innovative processing strategy enabled manufacturing crack-free, undeformed cellular ceramic samples.We printed hexagonal honeycomb structures that showed exceptionally high specific strength under compression load and significantly enlarged the strength-density range that was covered by sintered capillary suspensions, so far. Without loss of mechanical strength the density of ceramic parts was decreased by about a factor of 2–3. Strength of in-plane and out-of-plane loaded hexagonal honeycomb structures varies according to common scaling laws for cellular structures. The honeycombs are mechanically more efficient than bulk specimens from capillary suspensions, since they show a distinctly lower sensitivity of strength on density.     

DRYING OF FINE CERAMICS

The drying mechanism of shaped ceramics is reviewed and some methods for eliminating defects produced by drying are discussed in this report. The types of defects depend upon the shaping method, shape, properties of the raw materials, drying process and other items. Most defects of dried ceramics are produced during the initial or middle drying stage when large shrinkage of the ceramic body occurs. These defects may be successfully eliminated by heating the body from the inside. Self-deformation caused by weight is also a serious defect. The near net shaping of fine ceramics to reduce machining requires uniform body shrinkage and hence, highly controlled drying. Examples of electric current drying, dielectric drying, and dewaxing are also shown in this report.     

Effect of micro-lamellar talc on dimensional accuracy and stability in injection molding of PLA/PBSA blends

The present work is aimed at developing innovative solutions to enhance mechanical and physical properties of Poly(Lactic) Acid (PLA) blends, specifically designed for melt processing applications. Attention is drawn on dimensional accuracy and stability of PLA-based components manufactured by injection molding. PLA belongs to the class of bioplastic materials, entirely relying on renewable resources. It is a semi-crystalline linear aliphatic polyester, highly prone to recrystallize in harsh temperature conditions that can arise during transportation or storage of injection-molded components. Recrystallization is known to cause shrinkage of polymeric materials and, consequently, a marked warpage of components produced from them, causing scraps or parts that do not conform to the functional requirements. In this context, the experimental investigation deals with the effect of increasing amounts of micro-lamellar talc in PLA and Poly(butylene) Succinate Co-Adipate (PBSA) blends. In particular, the role of talc aliquot on dimensional accuracy and stability of injection-molded coffee capsules manufactured by PLA/PBSA blends is studied, with emphasis on the key role of recrystallization. For that purpose, commercial grade PLA and PBSA are compounded with micro-lamellar talc and several processing additives by a twin screw co-rotating extruder. The resulting compound is reprocessed to form coffee capsules by injection molding. Characterization tests include Differential Scanning Calorimetry (DSC), Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) spectroscopy and Field Emission Gun Scanning Electron Microscopy (FEG – SEM). Measurements of the characteristic dimensions of the molded components reveals the effect of increasing amounts of talc in PLA/PBSA blends on dimensional accuracy and stability properties of coffee capsules. Brewing tests allowed to identify the formulations that can ensure the utmost geometrical accuracy of the coffee capsules and their suitability for brewing in instant coffee machine. Based on experimental evidences, lowest shrinkage and improved stability are found on components manufactured by polymeric blends that involve the highest amount of talc.     

CONDUCTIVE DRIlNG CHARACTERISTICS OF GELATINIZED RICE STARCH

ABSTRACT

The drying mechanism of shaped ceramics is reviewed and some methods for eliminating defects produced by drying are discussed in this report. The types of defects depend upon the shaping method, shape, properties of the raw materials, drying process and other items. Most defects of dried ceramics are produced during the initial or middle drying stage when large shrinkage of the ceramic body occurs. These defects may be successfully eliminated by heating the body from the inside. Self-deformation caused by weight is also a serious defect. The near net shaping of fine ceramics to reduce machining requires uniform body shrinkage and hence, highly controlled drying. Examples of electric current drying, dielectric drying, and dewaxing are also shown in this report.     

Ceramic Capillary Suspensions: Novel Processing Route for Macroporous Ceramic Materials

We introduce a novel method to produce macroporous ceramics by capillary suspensions. Adding a small amount (~1 vol%) of an immiscible secondary phase to a low concentration (~20 vol%) suspension can increase the yield stress by several orders of magnitude. This drastic change in flow behavior is induced by the creation of a sample‐spanning particle network in the suspension controlled by capillary forces. This strong network may persist even if the primary bulk phase is removed. Accordingly, capillary suspensions can be used as a precursor for manufacturing porous materials. Here, we focus on the specific features of this universal, low‐cost processing route for porous ceramics. An Al₂O₃ model system is used to demonstrate how to adjust porosity and pore size. With this system, we were able to achieve open porosities higher than 60% with an average pore size below 10 μm.     

Die katalytische Herstellung von Zuckeralkoholen und deren Verwendung

Catalytic production of sugar alcohols (polyols) and their application . The article surveys the numerous applications of the principal sugar alcohols sorbitol and xylitol and their world production in 1978. Nowadays, the industrial production of sugar alcohols is almost exclusively by catalytic hydrogenation of the corresponding sugars; thus sorbitol is manufactured by hydrogenation of D-glucose, xylitol by hydrogenation of xylose, and mannitol by hydrogenation of invert sugar or fructose. Some 80% of the world production of sugar alcohols are manufactured in batch suspension processes using Raney nickel catalysts. Apart from the Atlas Powder continuous suspension process employing nickel-carrier catalysts, continuous processes have recently been developed which use Raney nickel and prove more economical owing to the lower catalyst costs. Trickling processes with fixed catalyst continue to play a minor role. Available production capacity based on batch suspension processes can be expanded by process optimization and new catalyst developments. A newly developed special Raney nickel catalyst reduces the specific catalyst consumption by about 50%.     

Colloidal Processing of Zirconium Diboride Ultra‐High Temperature Ceramics

Colloidal processing of the Ultra‐High Temperature Ceramic (UHTC) zirconium diboride (ZrB₂) to develop near?net‐shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB₂ suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex‐shaped components that can be densified at lower sintering temperatures without pressure.     

Cure shrinkage characterization of an epoxy resin system by two in situ measurement methods

Dimensional accuracy of composites manufacturing is a major issue for part producers, especially when tight tolerances are required. One of the main causes of dimensional variations is the resin volumetric changes during the cure. In this article, volumetric cure shrinkage of a one part epoxy system was characterized using two different methods. First, a modified rheology method was used to measure the volumetric cure shrinkage after the gel point. Second, a gravimetric method measured the shrinkage over the entire cure. A linear relationship between the volumetric cure shrinkage and the degree‐of‐cure was deduced from the results and the resin cure kinetic models. Results show a good agreement between the two techniques. POLYM. COMPOS., 31:1603–1610, 2010. © 2009 Society of Plastics Engineers     

Stereolithography process: Influence of the rheology of silica suspensions and of the medium on polymerization kinetics – Cured depth and width

UV laser stereolithography is a rather new shaping technique that makes it possible the fabrication of complex 3D ceramic structures with a high dimensional accuracy. The green part is built through layer by layer photopolymerization of a light sensitive suspension.Polymerization is thus a critical step to control in this shaping technique. Photopolymerization, with the initiation, propagation and termination reactions, involves the mobility of reactive species and is then sensible to the rheology of the media. This study investigated the influence of the rheology of suspensions of silica particles in an acrylate oligomer and of the intergranular curable organic phase on the UV polymerization. In this respect, the effects of the powder concentration, the state of dispersion and of the dilution of the reactive oligomer on polymerization, are measured.In addition, the influence of the powder loading on the cure depth and cure width, which are respectively pertinent indicators of the reactivity of the suspension and of the dimensional accuracy of the green part, is evaluated.     

New challenges in polymer foaming: A review of extrusion processes assisted by supercritical carbon dioxide

It is well known that supercritical carbon dioxide (sc-CO₂) is soluble in molten polymers and acts as a plasticizer. The dissolution of sc-CO₂ leads to a decrease in the viscosity of the liquid polymer, the melting point and the glass transition temperature. These properties have been used in several particle generation processes such as PGSS (particles from gas saturated solutions).It is therefore highly likely that extrusion processes would benefit from the use of sc-CO₂ since the rationale of the extrusion processes is to formulate, texture and shape molten polymers by forcing them through a die. Combining these two technologies, extrusion and supercritical fluids, could open up new applications in extrusion.The main advantage of introducing sc-CO₂ in the barrel of an extruder is its function as a plasticizer, which allows the processing of molecules which would otherwise be too fragile to withstand the mechanical stresses and the operating temperatures of a standard extrusion process. In addition, the dissolved CO₂ acts as a foaming agent during expansion through the die. It is therefore possible to control pore generation and growth by controlling the operating conditions.This review focuses on experimental work carried out using continuous extrusion. A continuous process is more economically favourable than batch foaming processes because it is easier to control, has a higher throughput and is very versatile in the properties and shapes of the products obtained.The coupling of extrusion and supercritical CO₂ technologies has already broadened the range of application of extrusion processes. The first applications were developed for the agro-food industry 20 years ago. However, most thermoplastics could potentially be submitted to sc-CO₂-assisted extrusion, opening new challenging opportunities, particularly in the field of pharmaceutical applications.This coupled technology is however still very new and further developments of both experimental and modelling studies will be necessary to gain better theoretical understanding and technical expertise prior to industrial use, especially in the pharmaceutical field.     

Production and properties of highly porous zircon materials

Conclusions We proposed, using zircon as an example, the principle of forming pores of two types — cellular and capillary — for obtaining highly porous (up to 90%) ceramics. It consists of a combination of the foam method and the introduction of removeable foamed polystyrene. At the stage of forming and drying the system is distinguished by a high volume constancy, uniformity of properties, and the possibility of carrying out rapid drying.On the basis of a zircon suspension as the bond and crushed zircon foamed ceramics as the filler we obtained a highly porous ceramic concrete with a porosity of 50–70% and a compressive strength of 12–24 MPa.A marked influence on the properties of the resulting materials is exerted by the microcracks formed as a result of the removal of the expanded polystyrene (PPS) in the foamed ceramic, and the presence of uncompensated shrinkage in the ceramic concrete. With an increase in the value of the uncompensated shrinkage from 0 to 7%, the thermal-shock resistance of the ceramic concretes is increased 1.3 times and the thermal conductivity is reduced by a factor of 1.25.Translated from Ogneupory, No. 7, pp. 20–25, July, 1984.     

Effect of thermal treatment on structure and properties of polyester tire cords

Polyester and nylon are the mostly used reinforcing textile fibers in many industrial rubber applications. Now‐a‐days body ply of a passenger car radial is mostly made up of polyester fiber. Because of its thermoplastic nature, it undergoes some kind of thermal shrinkage during processing and vulcanization, which lead to many problems related to shape, dimension, and dimensional stability. To avoid this, polyester is subjected to thermal treatment at higher temperature. Hence, thermomechanical properties of polyester tire cords become very important. During the thermal treatment, there is not only change in shrinkage, shrinkage force, and mechanical properties but also it affects structural and morphological properties. In this work, the changes in thermomechanical properties due to heat setting have been correlated to structural and morphological changes like crystallinity, crystal size, orientation, crystal perfection, etc. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The influence of shaping and firing technology on ceramic properties of calcareous and non-calcareous illitic–chloritic clays

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage's indexes than the calcareous ones. In any case, the Maage's durability factor is higher in extruded samples.     

Diameter and morphology dependence on experimental conditions of carbon nanotube arrays grown by spray pyrolysis

A systematic study on the controlled growth of large areas of aligned multi-wall carbon nanotube arrays, from ferrocene-benzene precursor, and of nanotube junctions from ferrocene-thiophene precursor, without hydrogen addition, using an injection CVD method easy to scale up for industrial production is reported.A detailed study is presented of how the synthesis parameters such as growth temperature, active solution flow rate, catalyst concentration or sulfur addition can control the properties and morphology of the grown nanotube mat. Nanotube junctions with considerable yield can be grown with our method by adding sulfur to the synthesis process. The sulfur addition also results in growth of carbon nanocones (CNC) in the lower temperature regime of the furnace. Observation of single-wall carbon nanotubes in our STM investigations provides further indication that under properly chosen conditions SWCNTs can be grown with similar continuous processes.