几种增稠剂对三水醋酸钠晶析现象的影响研究

晶析现象是三水醋酸钠作为相变材料在实际应用中存在的一个很大的问题。在太阳能跨季储热过程中,我们能利用三水醋酸钠的过冷现象,长期稳定的将太阳能储存起来,但是相变材料晶析的问题依然需要解决。本文选用几种增稠剂并对添加这些增稠剂后的三水醋酸钠混合材料的晶析状况、激发温度变化和相变潜热能力的变化进行实验研究,确定了一种较好的增稠剂来减少晶析现象的发生。     

三水合醋酸钠纳米成核剂的性能研究

三水合醋酸钠是一种具有较高的储能密度和热导率的储热相变材料,但是在凝固过程中的过冷和相分离现象限制了它的应用,需要寻求有效的成核剂和增稠剂来克服过冷和相分离的问题。本文实验分析了几种纳米材料（AIN、Si₃N₄、ZrB₂、SiO₂、BC₄、SiB₆）的成核效果,结果表明质量分数5%或4%的Si₃N₄、10%ZrB₂、5%AlN在自然分散下就能够消除三水合醋酸钠过冷度,质量分数2%的SiO₂在熔化的三水合醋酸钠中经磁力搅拌和超声分散后能够消除其过冷度。结合纳米材料的粒度分析结果,表明粒度分布在几十纳米到300纳米左右的纳米材料有较好的成核效果。     

醋酸钠水溶液过冷特性探究

过冷在相变储能中是个不容忽视的问题,通常是使用添加剂来减小或者消除过冷。我们只是改变溶液的浓度,在过冷存在的前提下,使溶液达到更低的结晶温度,以便能将夏天的能量存储到冬天使用,达到跨季储能的目的。实验发现,浓度55%-60.3%范围的醋酸钠溶液可以基本达到这一要求;液面高度对结晶温度没有明显影响,可以根据需要选取液面高度;增加冷却速率能降低结晶温度。     

深过冷Ag-Cu-Ge三元共晶合金的相组成与凝固特征

在Ag_38.5Cu_33.4Ge_28.1三元共晶合金的深过冷实验中，获得的最大过冷度为175 K(0.22T_E). XRD分析表明，不同过冷条件下其共晶组织均由(Ag),(Ge)和η(Cu₃Ge)三相组成. 在小过冷条件下，三个共晶相协同生长，凝固组织粗大.随着过冷度的增大，共晶组织明显细化，(Ge)相与其他两相分离，以初生相方式生长，而(Ag)相与η相始终呈二相层片共晶方式共生生长. 当过冷度超过80 K时，初生相(Ge)由小过冷时的块状转变为具有小面相特征的枝晶方式生长. 部分小面相(Ge)枝晶出现规则的花状，花瓣数介于5—8之间，并且过冷度越大(Ge)相越容易分瓣. 花状(Ge)枝晶的晶体表面为{111}晶面簇，择优生长方向为〈100〉晶向族. 关键词： 三元共晶 晶体形核 深过冷 快速凝固     

相场晶体法模拟过冷熔体中的晶体生长

利用相场晶体(phase-field crystal)模型,采用有限差分法,模拟了过冷熔体中晶体生长过程,研究了不同相区、不同过冷度对晶体生长过程的影响.结果表明,在共存区中,随着演化的进行,晶体生长被抑制,液-晶边界层逐渐变厚;在单相区中,随着过冷度的增大,晶态区面积显著增加,液-晶边界层逐渐变薄.晶体生长速度和过冷度成近似线性的关系. 关键词： 相场晶体 自由能函数 过冷熔体 晶体生长     

水过冷流动沸腾传热关联式研究

水过冷流动沸腾传热计算在核能、热动力、以及电子设备冷却等领域有着广泛应用。现有过冷流动沸腾传热关联式对水的误差较大,不能适应工程应用的需要。本文系统总结了过冷流动沸腾传热关联式,收集了1412组水的过冷流动沸腾传热实验数据,用此对16个现有过冷流动沸腾传热关联式进行了评价分析。对流动沸腾传热建模方法进行了大量研究,在提高模型精度方面获得突破。提出了水过冷流动沸腾传热的新关联式,其误差MAD只有11.3%,50.8%的数据点的误差在士10%以内。而最好的现有公式的MAD为38.3%,只有19.7%的数据点的误差在±10%以内。     

超声对水的过冷现象影响研究

水的过冷受到诸多因素的影响。本文对800 kHz超声波作用下的水的过冷度进行了实验研究,发现超声波能够大幅度降低水的过冷度。超声的这种作用与由空化导致的压力波动有关。     

纳米氧化锆水悬浮液的稳定性

通过黏度、表面张力、密度及粒度测试等手段研究了球磨剂、球磨时间、pH值、添加剂等因素对纳米氧化锆水悬浮液稳定性的影响。结果表明:球磨时间2h,球磨剂与氧化锆质量比为3.5%,添加剂可用乙二醇,悬浮液pH值为10.0,氧化锆粒径小于15nm时,纳米氧化锆水悬浮液可稳定30天。     

火龙果果皮色素的提取及稳定性

采用不同比例的水与乙醇混合液作为提取剂、不同的超声波提取时间、不同的火龙果果皮重量,研究了火龙果果皮色素的提取条件。其提取液最大吸收波长在538nm处,长时间放置后色素被氧化,其氧化产物最大吸收波长在390nm处。还研究了火龙果果皮色素与食品添加剂共存的情况。     

液态五元Zr57Cu20Al10Ni8Ti5合金的微观结构演变与非晶形成机制

利用电磁悬浮无容器处理技术实现了液态五元Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅合金的深过冷与快速凝固,同时通过分子动力学模拟计算揭示了非晶形成的微观机制.实验发现,凝固组织具有明显的核-壳结构特征,核区为非晶相,壳区主要由ZrCu, Zr₂Cu和Zr₈Cu₅晶体相组成.非晶体积分数随合金过冷度的升高逐渐增大,当达到实验最大过冷度300 K (0.26T_L)时,非晶体积分数增至81.3%.由此导出完全非晶凝固所需临界过冷度为334 K. TEM分析显示,过冷度增大并接近临界过冷度时,合金凝固组织中晶体相主要为Zr₈Cu₅相,而ZrCu和Zr₂Cu相的生长被抑制.在达到临界过冷度后,过冷液相的凝固路径由Zr₈Cu₅结晶生长转变为非晶凝固.此外,合金的晶体壳中存在少量的晶间非晶相,而非晶核中...     

Effect of Metallic Salts of Phenylmalonic Acid on the Crystallization of Poly(L-lactide)

The effect of the metallic salts of phenylmalonic acid (PMA), as novel nucleating agents, on the melt and crystallization behaviors, spherulitic morphologies, and crystal structures of poly(L-lactide) (PLLA) was studied by means of differential scanning calorimetry, polarized light microscopy, and wide angle X-ray diffraction (WAXD). The results showed that calcium and cadmium salts of PMA are good nucleating agents for PLLA. Lithium, sodium, magnesium, strontium, and zinc salts of PMA are moderate nucleating agents, barium and aluminum salts of PMA are weak nucleating agents, while potassium phenylmalonate is not a nucleating agent for PLLA. The presence of nucleating agents significantly increased the number and decreased the size of the spherulites, but the crystal structures of the nucleated PLLA samples were not changed.     

醇类低温保护剂水溶液过冷和水合性质研究

利用差示扫描量热仪研究了乙二醇、丙三醇、1,3丙二醇、1,3丁二醇和2,3丁二醇水溶液的过冷行为和水合性质,得出了这些性质与线性多元醇溶液浓度的关系.研究发现,在低浓度过冷度与浓度之间没有明显关系;而在中高浓度则具有相似的变化规律,即随着溶液浓度增大而增大.各低温保护剂在水合性质上所表现出的差异性,体现了保护剂的官能团(羟基、甲基)所起到的重要作用.     

Effect of Metallic Salts of Malonic Acid on the Formation of β Crystalline Form in Isotactic Polypropylene

The effects of malonic acid and the lithium, sodium, potassium, zinc, magnesium, calcium, strontium, and barium salts of malonic acid on the formation of β crystalline form in isotactic polypropylene at the crystallization temperatures 120 and 130°C have been investigated. It was found that malonic acid and the lithium, sodium, and potassium salts of malonic acid inhibit the formation of β crystalline form in polypropylene. Zinc malonate has a limited positive effect on the formation of β crystalline form, while magnesium, calcium, strontium, and barium salts are β nucleating agents, in descending order. The decreased β nucleation abilities of the alkaline earth metallic salts of malonic acid are attributed to the increasing atomic radii of the combined metals and decreasing crystallization temperatures.     

Surfactant-assisted organic reactions in water. Effect of ultrasound on condensation reactions between active methylene compounds and arylaldehydes

A series of quaternary ammonium salts has been tested as phase transfer agents to promote condensation reactions in an aqueous solution of sodium hydroxide in the absence of any organic solvent. Methyltrioctylammonium chloride (Aliquat 336) emerges as the most efficient catalyst. Sonication of the reaction media has a poor but positive kinetic effect.     

Comparison of Nucleation Effects of Organic Phosphorous and Sorbitol Derivative Nucleating Agents in Isotactic Polypropylene

Organic phosphorous and sorbitol derivatives are two types of very effective nucleating agents for isotactic polypropylene (iPP). The effects of two kinds of organic phosphorous nucleating agents, Irgastab NA-11 and ADK NA-21, and two kinds of sorbitol derivatives, Irgaclear DM and Millad 3988, on mechanical properties and crystallization behaviors of iPP are compared in this paper. The organic phosphorous nucleating agents had better effects on mechanical properties of iPP than sorbitol derivatives, whereas the latter had better effects on transparency of iPP than the former. At the same time, the organic phosphorous nucleating agents and sorbitol derivatives had similar effects on the crystallization peak temperature (Tc) of iPP. When the concentration of nucleating agents was 0.2 wt%, compared to those of virgin iPP, the tensile strength and flexural modulus of iPP nucleated with Irgastab NA-11 and ADK NA-21 were increased by 19.35% and 17.67%, and 29.48% and 24.84%, and the haze value was decreased by 43.58% and 44.01%, respectively. On the other hand, the tensile strength and flexural modulus of iPP nucleated with Irgaclear DM and Millad 3988 were increased by 7.03% and 7.46%, and 7.20% and 11.96%, and the haze value was decreased by 51.03% and 52.23%, respectively. When the cooling rate was 10°C /min, the Tc of iPP nucleated with these four nucleating agents was increased from 118.74°C of virgin iPP to about 130°C. Meanwhile, the morphology study showed that addition of both organic phosphorous and sorbitol derivative type nucleating agents could decrease the spherulite size of iPP significantly and that sorbitol derivatives have greater effects.     

聚丙烯中电树枝生长机理研究

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一.聚丙烯(PP)是典型半结晶聚合物,其复杂的非均匀聚集态结构影响电树枝的生长.本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验,通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响.以相界面自由能的热驱动作用以及放电雪崩理论为基础,对电树枝生长的热力学和动力学机理进行分析,阐明电场分布对电树枝生长的重要作用.根据半结晶材料的结晶相和非晶相的物理性能,建立材料内部电场分布计算模型,模拟针-板电极条件下聚合物材料内部的局域电场分布情况,分析了电树枝通道的动力学生长特征,探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用.     

Long-term retention of ice-nucleating active Pseudomonas fluorescens by overwintering colorado potato beetles

Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.     

Structural and physical aspects of the formation of salt crystals from solutions

The peculiarities of the crystallization of about 100 solutions of different salts have been experimentally studied. A correlation is established between the maximum attainable supercooling temperature of the solution and the structure of the crystals formed. It is found that the highest supercoolings are characteristic of solutions of acentric crystals.     

Nucleating Efficiency of Organic Phosphates in Polypropylene

Organic phosphates used as nucleating agents can remarkably promote the stiffness and crystallization rate of polypropylene homopolymer and ethylene–propylene copolymer. In this article, the nucleating activity of 2,2′-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid and its derivatives for isotactic polypropylene (iPP) were investigated with a differential scanning calorimeter (DSC) and polarized light microscope (PLM), and their influence on mechanical properties of polypropylene was also studied. The results showed that the sodium salt (NA7) and the glyceride ester (NA8) of the organic phosphoric acid were of high nucleating efficiency. If 0.4 wt% of NA7 or NA8 was added to PP, the crystallization peak temperature of PP was raised 15°C or 11°C, respectively, the amount of crystallinity was increased by 3 to 6%, and the crystallization rate was enhanced significantly. The nucleating activity is thermally stable when the mixture of iPP and a nucleating agent was melted and crystallized repeatedly in the DSC. The nucleating agents mentioned above could increase the modulus of the polymer by 20 to about 30% and could increase the flexural strength by 10 to about 20%. However, a number of other organic phosphates tested have little nucleating effect.