Fracture Toughness of Spray-Dried Powder Compacts

The strengths and fracture toughness values were measured for alumina powder compacts containing two different binder systems. Diametral compression was used to measure both the tensile strength and the fracture toughness (through-thickness notch). This methodology was very useful in linking processing parameters, such as binder choice and compaction stress, to the quality of the green bodies. Observations of the compact structure before and after fracture showed that the binders segregated to the region between the spray-dried granules. The presence of the excess binder in this region was linked to both the failure mode and the creation of secondary cracks.     

Direct Evidence for Low-Density Regions in Compacted Spray-Dried Powders

Pore structure in a ceramic green body was directly observed with a novel characterization tool to examine the detrimental effect of a binder on the microstructure of ceramics for powder compaction processing. The binder segregated on the surface of granules and formed a low-density region at the boundaries of granules in the compact after binder removal. A network of pores with round shapes was produced in the sintering process from the low-density region. This paper also explains a new characterization technique, confocal laser scanning fluorescent microscopy.     

Direct Observation of Internal Structure in Spray-Dried Alumina Granules

The internal structure of spray-dried alumina granules was characterized by optical microscopy by immersing them in a liquid having a refractive index close to that of alumina. This method provides a unique technique for the detailed analysis of the internal structure of spray-dried granules.     

氮化硅陶瓷粉料造粒的研究进展

氮化硅陶瓷具有高强度、高硬度、良好的断裂韧性等优异力学性能,并具有独特的自润滑性能,而日益受到重视.氮化硅陶瓷粉料是制备氮化硅陶瓷的关键原料,粉料的处理方式是影响陶瓷性能的关键步骤.本文介绍了目前较为常见的氮化硅陶瓷粉料的处理方法,并对各处理工艺的优缺点进行了分析,重点阐述了喷雾造粒工艺及其目前研究进展.最后分析了目前氮化硅粉料处理方法存在的问题,并对氮化硅粉料处理方法的发展提出了展望.     

Effect of Externally Applied Plasticizer on Compaction Behavior of Spray-Dried Powders

The effects of an externally applied plasticizer on compaction behavior and green microstructure quality of spray-dried powders was investigated. The plasticizer was applied to the external surfaces of already spray-dried powders by spraying it on tumbling spray-dried granules. The apparent yield point of the spray-dried powder was reduced when the plasticizer was added. Microstructures of compacts made from these granules (with and without the externally applied plasticizer) were compared at different compaction pressures. Better knitting across granule interfaces and fewer defects were obtained for the granules with the externally applied plasticizer.     

Control of Composition and Structure in Laminated Silicon Nitride/Boron Nitride Composites

Based on a biomimetic design, Si₃N₄/BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si₃N₄ matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si₃N₄ or Al₂O₃. The results showed that the addition of SiC whiskers in the Si₃N₄ matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m^1/2), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al₂O₃ or 10 wt% Si₃N₄ to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si₃N₄/BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si₃N₄/BN composites were present as the first-level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull-out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers.     

Atomic Resolution Transmission Electron Microscopy of the Intergranular Structure of a Y2O3-Containing Silicon Nitride Ceramic

High-resolution transmission electron microscopy (HRTEM) employing focus-variation phase-reconstruction methods is used to image the atomic structure of grain boundaries in a silicon nitride ceramic at subangstrom resolution. Complementary energy-dispersive X-ray emission spectroscopy experiments revealed the presence of yttrium ions segregated to the 0.5–0.7-nm thin amorphous boundary layers that separate individual grains. Our objective here is probing if yttrium ions attach to the prismatic planes of the Si₃N₄ at the interface toward the amorphous layer, using Scherzer and phase-reconstruction imaging, as well as image simulation. Crystal structure images of grain boundaries in thin sample (<100 Å) areas do not reveal the attachment of yttrium at these positions, although lattice images from thicker areas do suggest the presence of yttrium at these sites. It is concluded that most of the yttrium atoms are located in the amorphous phase and only a few atoms may attach to the terminating prism plane. In this case, the line concentrations of such yttrium in the latter location are estimated to be at most one yttrium atom every 17 Å.     

红外辅助冷冻干燥装置摔制系统的研发

真空泠冻干燥产品质量优异,广受青睐,但其干燥速率慢、耗能较大,制约其在普通产品干燥的推广应用。本文基于红外辅助加热和搁板传导的结合,提高对物料加热的有效性。并研发了红外辅助冷冻干燥装置的控制系统,以实现对物料冻结和加热的可控性和用户友好操作。     

Density Gradients and Sintered Dimensional Tolerance in Compacts Formed from Spray-Dried Alumina

This study proves that initial density gradients have lasting detrimental effects on final dimensional tolerances. X-ray computed tomography has been used to quantify changes in density following sintering; associated dimensional changes have been monitored using a laser micrometer. Nonuniformities present in the green state are still present at an overall relative density of ∼73%; in fact, these nonuniformities are exaggerated. Major losses of dimensional tolerance are triggered by the initial density gradients.     

Following the drying of spray paints using space and time contrast of dynamic speckle

The short drying times of spray paints are of great benefit in some applications, and this property allows for painting over almost-immediately. However, this fast-drying process precludes following it using conventional techniques. In a previous article, we used the dynamic speckle to follow the drying process of solvent-based and water-based paints with relatively long drying times, and recently we developed alternative speckle contrast methods to characterize faster processes. This article presents the application of these methods using dynamic speckle techniques to study the drying of a spray paint. Activity image display is also included.     

Infrared Spectroscopic Method for Determination of Thermal Properties of Fluorophosphate Glasses

Fluorophosphate glasses of the Ba(PO₃)₂–MgF₂–CaF₂–AlF₃ system exhibit anomalous behavior, in regard to the glass-transition temperature ( T _g) and the coefficient of thermal expansion (α_CTE), at a fluoride concentration of ∼36 mol%. A similar trend in the infrared band absorption coefficient (α_IR) at 2170 cm⁻¹ of the overtone of 2ν_ss(OPO) and/or a combination of ν_as(OPO)+ν_as(POP) fundamental vibrations of PO₄ tetrahedra also has been observed, relative to changes in the glass composition. Statistical analyses have shown that the T _g and α_CTE values are correlated with α_IR at 2170 cm⁻¹ by linear equations. The thermal properties of some of the glasses have been calculated using these equations, to test their validity and utility. The experimental property values of the glasses present a very good fit of data within a 95% confidence interval of the calculated mean values.     

Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried Powders

The role of internal lubricants in the closure of large intergranular pores during dry-pressing was investigated. Alumina was spray-dried with and without an internal lubricant to yield granules with similar characteristics other than lubricant effects. Green and sintered microstructures were evaluated at different compaction pressures. The defects were quantified by evaluating the fracture surface of ∼90% dense sintered compacts. The samples that contained an internal lubricant had higher green densities and fewer defects at comparable compaction pressures. The internal lubricant did not cause any significant reduction in green strength or increase in springback.     

Crystallization of Amorphous Components in Spray-Dried Powders

Spray-dried powders are typically produced as amorphous particles. Long storage of the particles tends to crystallize the powders, a reaction affected by moisture, time, and temperature. This work has examined partial crystallization from amorphous spray-dried powders by moisture sorption. Powders of citrus fiber with hibiscus extract, maltodextrin, coffee, tea, skim milk, and sucrose were produced with a laboratory-scale spray dryer. The powders were exposed to ambient temperature and various relative humidities, with weight measurements recorded over time. It has been found that, in different materials, the amorphous to crystalline state change is observed at varying rates depending on the relative humidities and molecular weights. This observation may be associated with all amorphous spray-dried materials.     

食品和农产品干燥的一种有效方法-红外加热法

农业和食品行业需要能源高效和环境友好的干燥技术,最近红外加热干燥的应用得到广泛研究。作为现代干燥技术的另一种选择,红外干燥具有加热均匀、干燥速率高、干燥时间短、节约能源、产品品质和安全性高等引人注目的优点。研究表明。将红外方法可以减少干燥时间并且节能。与热可以对果蔬实现同步漂烫和干燥,干燥和热风干燥相结合能够有效的减少干燥时间。所开发的红外冷冻相继干燥常规的空气干燥或冷冻干燥相比,更适合于生产高品质的酥脆果蔬片。红外加对稻谷进行同步干燥和杀虫。本文将综述红外加热技术的最新研究和进展。     

Physical and Functional Properties of Blackberry Freeze- and Spray-Dried Powders

The aim of the present work was to develop two products from blackberry juice by freeze and spray drying with potential use as food colorants or healthy ingredients. A characterization of the physical and functional properties of the powdered juices was done. Maltodextrin or a mixture of trehalose and maltodextrin were assessed as carrier matrices. Freeze-dried, maltodextrin-containing powders presented the best retention of bioactive compounds and antiradical activity; however, they showed a narrow relative humidity range for storage in the glassy state. Spray-dried powders showed better physical properties, bearing higher glass transition temperature and lower molecular mobility than freeze-dried formulations.     

Crystallization of Amorphous Components in Spray-Dried Powders

Spray-dried powders are typically produced as amorphous particles. Long storage of the particles tends to crystallize the powders, a reaction affected by moisture, time, and temperature. This work has examined partial crystallization from amorphous spray-dried powders by moisture sorption. Powders of citrus fiber with hibiscus extract, maltodextrin, coffee, tea, skim milk, and sucrose were produced with a laboratory-scale spray dryer. The powders were exposed to ambient temperature and various relative humidities, with weight measurements recorded over time. It has been found that, in different materials, the amorphous to crystalline state change is observed at varying rates depending on the relative humidities and molecular weights. This observation may be associated with all amorphous spray-dried materials.     

Molecular Dynamics Study of Atomic Structure and Diffusion Behavior in Amorphous Silicon Nitride Containing Boron

We have performed molecular dynamics simulations of amorphous Si₃N₄ containing boron (Si-B-N). We have examined short-range atomic arrangements and self-diffusion constants of amorphous Si-B-N systems with various boron contents. Our simulations show that boron atoms are threefold coordinated by nitrogen atoms and that nitrogen atoms are bonded to both silicon and boron atoms in the amorphous network of Si-B-N. Also, the self-diffusion constant of nitrogen in Si-B-N is much decreased compared with that in amorphous Si₃N₄. This suggests that boron is important in decreasing the mobility of atoms in amorphous Si-B-N, which may explain the improved thermal stability of amorphous Si-B-N relative to amorphous Si₃N₄ observed experimentally.     

Application of Intermediate-Wave Infrared Drying in Preparation of Mushroom Chewing Tablets

Two drying methods, namely intermediate-wave infrared drying (IWIR) and hot-air drying (HA), were compared in preparation of mushroom chewing tablets (MCT). It was observed that IWIR enhanced the drying rate and shortened the time required for MCT. IWIR technology was better than HA in preserving thermal-sensitive materials by thermo gravimetric analysis. In addition, IWIR had a significant effect on the flavor of the samples, which would be used for retaining flavor ingredients and be conducive to the processing of the product. The results indicated that IWIR may have the potential to be developed as a new drying process in the food industry.     

Grinding Temperature Measurements in Magnesia-Partially-Stabilized Zirconia Using Infrared Spectrometry

Results of temperature measurements by analysis of the thermal emission spectra generated during grinding and subsequently transmitted through partially stabilized zirconia workpieces are presented. Portions of emitted visible and near-infrared spectra were collected with spectrometers. Source temperatures were determined by fitting the scaled spectrometer output spectra to blackbody curves. Simulations showed that the effective temperatures determined by this method will be strongly biased toward hot-spot (flash) temperatures, which are expected to occur at the grinding grit–workpiece interface. Hot-spot temperatures on the order of 3000 K were obtained for grinding with both SiC and diamond wheels. These high temperatures modify the grinding process and the phase content of grinding chips.     

支持向量机算法用于甲壳素红外干燥建模

在红外干燥条件下,对甲壳素的干燥特性进行了研究,采用支持向量机对不同温度下的干燥速率建立模型。该模型能较好地预测各干燥阶段的干燥速率及含水量,确定合理的干燥工艺以便调控干燥环境,达到高效低耗的目的。