表面活性物质在陶瓷中的应用

本文介绍了表面活性物质对陶瓷物料的助磨,瘠性料浆的悬浮和泥团的增塑作用并简要论述了其机理。     

海藻酸钠稳定Al2O3—ZrSiO4注浆料的研究

本文以海藻酸钠(SA)为分散剂制备Al_2O_3—ZrSiO_4料浆.通过对悬浮体PH值、SA加入量与粘度和Zeta电位关系的研究,确定了最佳工艺条件,制得浇注性能良好,固相浓度为68wt%的浆料,并通过注浆成型获得性能良好结构均匀的氧化铝—莫来石—氧化锆复合烧结体.     

瘠性陶瓷原料挤塑成型及其烧结性能研究

着重研究了有机—无机塑化剂对瘠性陶瓷原料挤塑成型及烧结性能的影响。实验发现 ,通过适当的塑化剂组合可以较好的实现瘠性料的挤塑成型 ,解决塑化剂及矿化剂加入量不当所产生的剧烈的烧结收缩 ,使挤塑成型制品的烧结收缩率小于 1～ 2 % ,确保了挤塑成型制品尺寸的稳定性     

有机添加剂在陶瓷瘠性料浆中的应用研究

本文根据特陶泥浆、全熔块釉浆等系统的解凝实验结果,对有机添加剂在陶瓷瘠性料浆的选择、应用进行了讨论,并对其作用机理进了理论探讨。     

合成Si_3N_4-SiC材料的浆料调制

通过对外加剂和瘠性料浆料性能的相关性试验,确定了完整的生产工艺及其控制参数,调制出生产不同氮化硅结合碳化硅产品的浆料。     

整体式催化剂制备过程中料浆流动特性测定及其对催化剂机械性能的影响

利用浇注压制成型制备了SO_2氧化反应的整体式催化剂,研究了成型过程中不同处理方法和不同的配方对浇注料浆流动性质的影响规律,测定了催化剂料浆在不同处理条件下的塑限、液限、流动度等参数,讨论了浆料流动性质与成型后的催化剂机械强度之间的关系。结果表明通过对催化剂硅藻土载体的酸洗处理、调节催化剂活性组分浆料pH值、对浆料进行捏合处理、适当添加润滑剂等措施,可以有效提高浆料的流动性、降低浆料在相同流动性情况下的含水量,利用该浆料浇注压制成型的催化剂裂纹少、机械强度高。     

ZrO_2基陶瓷注凝成型料浆流变性的研究

陶瓷料浆流变性能是注凝成型工艺的关键,料浆流变性要求高固含量,低粘度。实验通过在ZrO2表面包覆A l2O3,形成ZrO2-A l2O3复相陶瓷料浆。根据静电位阻稳定理论,通过调节pH值和分散剂的加入量,可得到满足成型要求的高固含量,低粘度的料浆。结果表明,在pH值为10左右,分散剂加入量为粉料质量的3%时,料浆固相体积分数可以达到40%。同时表明了A l2O3对ZrO2颗粒表面有改性作用,提高了悬浮体的稳定性。     

水基SiC料浆的分散稳定机制及喷雾造粒

以去离子水为液体介质,引入有机添加剂,配制水基SiC悬浮料浆,研究了水基料浆的分散稳定机制及其喷雾造粒行为,分析了有机添加剂和固相含量对料浆流变性能、造粒粉粒径分布及成型性能的影响机制.结果表明:当料浆pH≥10时,水基碳化硅料浆的分散性和稳定性较好,料浆具有剪切稀化的非Newton体特性:当加入0.2%(质量分数,下同)四甲基氢氧化铵、2.0%聚乙烯醇和1.0%聚乙二醇时,料浆黏度较小:固相含量为50%水基料浆喷雾造粒后,造粒粉的流动性、填充性能及成型性能明显提高,但球状造粒粉需要在一定成型压力下才能完全破碎.     

提拉浸渍用氧化铝陶瓷平板膜料浆的制备工艺研究

陶瓷平板膜具有过滤精度高、化学稳定性好、价格适宜、使用寿命长等优点,可有效解决当前有机类膜材料可靠性差、寿命短,运行成本高等问题,在膜法水处理领域,具有广阔的应用前景。但是国内在陶瓷平板膜的制备、应用等方面的研究较少,面向产业化、工程化方面的研究开发工作极为匮乏,导致陶瓷平板膜的品控较差。而料浆的性能是决定陶瓷膜最终成型质量的重要因素,但是国内对于此项工作的研究报道较少。本工作以高纯α-Al_2O_3和高纯硅溶胶为主要原料,研究了陶瓷膜规模化制备过程中浆料湿法球磨时间、分散剂种类及加入量、pH值对陶瓷膜料浆性能的影响作用。结果表明:分离膜浆料湿法球磨6h,选用聚丙烯酸钠为分散剂且外加量为3.5wt%,浆料pH值为9时,浆料分散性能、悬浮性能最优。     

超细ZrO2—CaO水系料浆的分散与稳定性研究

本文对瘠性的、超细的ZrO2-CaO水系料浆的表面特性和分散途径进行了分析。并以开发、选择新型分散剂为重要内容，对该系统的分散与稳定进行较系统的实验研究和机理探讨。     

Egg-yolk lipid fractionation and lecithin characterization

Egg-yolk lecithin has phospholipid (PL) classes and a FA composition that differ from soybean lecithin and may have unique functional properties. The purposes of this research were to develop an effective method for extracting a sufficient amount to lecithin from fresh egg yolks and to evaluate its functional properties. Ethanol was used to dehydrate and partially extract the PL, after which hexane was used to extract the total lipids. A phase separation of the combined extracts resulted in neutral and polar lipid fractions. An acetone precipitation of PL from the final polar lipid fraction was necessary to remove the residual neutral lipids, especially cholesterol. The purity of PL in the lecithin product was 95%. Surface tension reduction, emulsion stability, and oxidative stability studies were conducted to characterize the functional properties of egg-yolk lecithin. Egg-yolk lecithin and soy lecithin had similar surface activities, as evaluated by the surface tension reduction in an aqueous system and the critical micelle concentration. Soybean lecithin created a more stable emulsion than egg-yolk lecithin. However, egg-yolk lecithin was more oxidatively stable than soybean lecithin.     

A review of lecithin chemistry and glandless cottonseed as a potential commercial source

Industrial lecithin can be fractionated as phospholipids and glycolipids after neutral lipids and protein-containing contaminants are removed. The polar lipids are very reactive and are difficult to extract and purify from oilseeds. Their purity and special properties can be improved by a number of methods including solvent fractionation, hydrogenation, sulfonation, and ethoxylation. Studies are determining the role of the polar lipids of lecithin in (a) the synthesis of triglycerides in maturing seeds, (b) the structure of biological membranes, and (c) the molecular basis of the functionality of food ingredients. Lecithin, having both polar and nonpolar groups, has high surface activity and is reactive with both oil and protein, making it an excellent emulsifying agent in food systems; lecithin also slows autoxidation and enzyme hydrolysis of fats. Cottonseed lecithin is low in linolenic acid, prevents flavor deterioration of soybean oil and can be used to stabilize sunflower oil against color change during high temperature use. Gossypol binds to lecithin in oil from glanded cottonseed economically negating it as a commercial source of this product. New cultivars producing glandless, or gossypol-free cottonseed, may have potential as commercial sources of edible lecithin.     

Relationship between mechanical properties of and crack progogation in epoxy resin adhesives

Crack propagation in a series of amine-cured epoxy resin adhesives in both the bulk material and adhesive joints has been studied as a function of the formulation of the resins and the conditions of testing using a linear elastic fracture mechanics approach. In both cases propagation was found to take place in either a stick—slip (unstable) or a continuous (stable) manner; the particular type of propagation depending upon the amount and type of hardener used and the temperature and rate of testing. A constant crack opening displacement (δ) has been shown to be a unique failure criterion for continuous propagation with δ having approximately the same value in both bulk material and joints. However δ was found to increase in the stick—slip mode of propagation. These crack propagation characteristics have been related to the compressive yield behaviour of each material as determined by uniaxial compression tests performed on the epoxy resins. Possible mechanisms of crack propagation have also been discussed.     

Hydrophobic interactions in the purification of soybean lecithin

Phospholipids have a nonpolar fatty acyl chain and a polar head group, which give them unique physicochemical behavior. They form micellar structures with glycerides, as in the hydration of lecithin, where mixed bilayers of phospholipids and glycerides are formed. In hydrated lecithin, the 70:30 phospholipid/glyceride composition shows the maximum interaction energy and corresponds to the most stable mixed layer. During purification of commercial soybean lecithin (CSL) with acetone, it was observed that the triglyceride extraction curves corresponded to an exponential function shared by the acetone and phospholipid phases. During CSL purification, a fraction of the triglycerides was dissolved, and the rest remained attached to the phospholipids, thus making total separation by simple contact with the solvent impossible. The behavior of these glyceride-phospholipid systems is controlled by such factors as Van der Waals forces, configurational entropy, and alterations in the structure of the adjacent water, similar to the hydrophobic interactions that exist between proteins and lipid chains in biological membranes. In this study, equilibrium plots for the phospholipid/triglyceride/acetone system were obtained and provided evidence of hydrophobic interaction.     

卵磷脂改善泥浆性能的研究

研究了卵磷脂改善泥浆性能的作用。通过在一定含水量的泥浆中，比较加入卵磷脂前与加入卵磷脂后的泥浆性能，以及比较加入不同系列型号的卵磷脂问的泥浆性能，得到卵磷脂对泥浆性能的影响，从而优化出改善泥料性能的卵磷脂的种类与用量。     

Couette grain flow experiments: The effects of the coefficient of restitution, global solid fraction, and materials

Granular flows are complex flows of solid granular material which are being studied in several industries. However, it has been a challenge to understand them because of their non-linear and multiphase behavior. The present experimental work investigates granular flows undergoing shear, by specifically studying the interaction between rough surfaces and granular flows when the global solid fraction and the material comprising the rough shearing surface are varied. A two-dimensional annular shear cell, with a stationary outer ring and inner driving wheel, and digital particle tracking velocimetry (DPTV) technique were used to obtain local granular flow properties such as velocity, local solid fraction, granular temperature, and slip. A customized particle drop test apparatus was built to experimentally determine the coefficient of restitution (COR) between the granular and surface materials using high-speed photography. Results showed that wheel surface materials that produce higher COR values exhibit higher velocity and granular temperature values near the wheel, and lower slip velocities. The local solid fraction appears inversely related to the COR values. The global solid fraction seemed to correspond with velocity and granular temperature, while displaying an inverse relationship to slip. Results also showed an initial decrease in the kinetic energy of the flow as the global solid fraction increased, due to the formation of a distinct contact region. This was followed by a rise in kinetic energy as the global solid fraction continued to increase, based on the increase of particles present in the kinetic region of the flow.     

Stability of Oil-in-Water Emulsions with Sunflower (Helianthus annuus L.) and Chia (Salvia hispanica L.) By-Products

Emulsifiers and stabilizers play an important role in emulsion stability. Optical characterization and droplet size distribution of oil‐in‐water emulsions formulated with different types and concentrations of modified sunflower lecithin [phosphatidylcholine (PC) enriched lecithin and deoiled sunflower lecithin], with or without chia mucilage (0.75 % wt/wt), have been evaluated as a function of storage time at 4 ± 1 °C. Emulsions with PC‐enriched lecithin (without chia mucilage) exhibited the highest stability at the different concentrations because of the high PC/phosphatidylethanolamine ratio in comparison to Control lecithin. The addition of 0.75 % wt/wt mucilage contributed to obtain stable emulsions for all type and concentrations of emulsifiers studied, mainly with PC‐enriched lecithin due to the reduction of the mobility of oil particles by the formation of a tridimensional network.     

Lecithins in oil-continuous emulsions. Fat crystal wetting and interfacial tension

Lecithin is a powerful emulsifier widely used in foods, feeds and pharmaceuticals. Several analytical methods have been proposed to characterize lecithins, but they are often inadequate to determine the industrial functionality. The purpose of this study was to find a relationship between the interfacial properties of lecithins (adsorption to oil/water and fat crystal/oil/water interfaces), phospholipid composition and functionality. Results show that all lecithins adsorb to fat crystals at the triglyceride oil/water interface, making their surface more polar (observed as an increase in the contact angle measured through the oil at the interface: fat crystal/oil/water). This adsorption process is quick (less than five minutes) for relatively polar lecithins, such as soybean phosphatidylcholine (PC), and results in highly polar surfaces (contact angle ∼180°). Less polar lecithins give slow adsorption (some hours) and less polar crystals (contact angle ≤90°). The adsorption of different lecithins to the oil/water interface, observed as a decrease in interfacial tension, follows the adsorption pattern to the fat crystals. We found a relation between high-fat crystal polarity and poor lecithin functionality in margarine (margarines spatters during frying), and also between high-fat crystal polarity and a high polar to nonpolar phospholipids [Σ(PI + PA + LPC)/ΣPE; PI, phosphatidylinositol; PA, phosphatidic acid; LPC, lysoPC, PE, phosphatidylethanolamine] ratio in lecithin. The correlations might bevia aggregation properties of lecithin in the oil. We found also that monoolein shifted the adsorption kinetics of lecithin (soybean PC) to fat crystals and the hydrophilicity of adsorbed layers probably due to formation of mixed aggregates between monoolein and soybean PC.     

Molding Silicon Carbide Articles by Freezing Aqueous Slip

Molding silicon carbide articles by freezing aqueous slip is considered. The freezing conditions are determined. The slip composition is selected. Firing in a nitrogen-hydrogen medium at 1850°C made it possible to obtain samples whose properties are typical of this material.