麝香体系结晶分离研究

研究了根据酮麝香、1,3-二甲基-2,4-二硝基-5-叔丁基苯晶体生长速度的不同,从对二者均达到饱和的溶液中分离得到1,3-二甲基-2,4-二硝基-5-叔丁基苯晶体的过程,计算了晶体生长速度并进行了实验验证。     

Crystallographic Texture Development in Bismuth Sodium Titanate Prepared by Reactive-Templated Grain Growth Method

Bi_0.5Na_0.5TiO₃ (BNT) and 0.94Bi_0.5Na_0.5TiO₃·0.06BaTiO₃ (BNT–BT) bulk ceramics with extensive 〈100〉 texture were prepared by the reactive-templated grain growth method, using platelike Bi₄Ti₃O₁₂ (BIT) particles as templates for BNT. Calcined compacts were composed of matrix grains with random orientation and 〈100〉-oriented grains transformed from aligned BIT particles, and the texture developed by the growth of oriented grains during sintering. Ceramics with extensive texture were obtained by using the starting mixture containing the maximum concentration of platelike BIT to form the maximum volume fraction of oriented grains.     

Influence of the cross‐sectional shape on the structure and properties of polyester fibers

The effects of the fiber cross‐sectional shape on the structure and properties of polyester fibers were investigated. Fully drawn yarn (FDY) polyester fibers (167 dtex and 48 filaments) were produced under the same spinning conditions used in a spinning plant. The only difference between the fibers was their cross‐sectional shapes. Four different cross‐sectional shapes were chosen for the experimental work: round, hollow‐round, trilobal, and hollow‐trilobal. The crystallinity and values of the maximum stress, maximum strain, modulus, yield stress, shrinkage in boiling water, and unevenness of the fibers were determined. The difference in the cross‐sectional shapes influenced the modulus, maximum strain, yield stress, and shrinkage in boiling water. No effects on the crystallinity and maximum stress were observed. The results suggested that the hollow fibers had higher amorphous orientation than the full fibers. The hollow‐round fiber had the highest unevenness value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2615–2621, 2007     

Role of heat transfer and thermal conductivity in the crystallization behavior of polypropylene‐containing additives: A phenomenological model

The thermal conductivity of a filler and the thermal conductivity of a composite made from that filler influence the heat‐transfer process during melt processing. The heat‐transfer process from the melt to the mold wall becomes an important factor in developing the skin–core morphology. These aspects were examined in this study. The thermal conductivity of polypropylene–filler composites was estimated with a standard model for various fillers such as calcium carbonate, talc, silica, wollastonite, mica, and carbon fibers. The rate of cooling under given conditions, including the melting temperature, mold wall temperature, mass of the composite, and filler content, was estimated with standard heat‐transfer equations. The time to attain the crystallization temperature for polypropylene was evaluated with a regression method with differential temperature steps. The crystallization curves were experimentally determined for the different fillers, and from them, the induction period for the onset of crystallization was estimated. These observations were correlated with the expected trends from the aforementioned formalism. The excellent fit of the curves showed that in all these cases, the thermal conductivity of the filler and composite played a dominant role in controlling the onset of the crystallization process. However, the nucleation effects became important in the later stages after the crystallization temperature was attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2994–2999, 2003     

Band Gap Modification of Diamond Photonic Crystals by Changing the Volume Fraction of the Dielectric Lattice

Photonic crystals with a diamond structure of epoxy lattices in which TiO₂-based ceramic particles are dispersed were fabricated by stereolithography. The periodicity of the lattice was designed to reflect electromagnetic waves in the gigahertz range. The volume fraction (β) of the dielectric lattice medium was modified from 14% to 33% by changing the rod diameter of the lattice. The photonic band gap was observed along Γ-L 〈111〉, Γ-X 〈100〉, and Γ-K 〈110〉 directions and the complete photonic band gap was formed at over β= 20%. The width of the forbidden gap increased gradually when the β increased over 14%, and reached 2.4 GHz at β= 33%. These results agreed with the band calculation using the plane wave expansion method.     

0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3的析晶行为及助溶剂法生长

研究了0.91Pb(znl/3Nb2/3)O3-0.09PbTiO3(PZNT91/9,摩尔分数)在不同组分和配比熔盐中的析晶行为及其对晶体生长的影响。发现B2O3,PbF2等助溶剂不利于钙钛矿相的析出;而BaTiO3-PbO复合体系虽然能够促进钙钛矿相析出,但晶体析出量很少;只有适当比例的。PbO助溶剂比较适合于生长具有铁电性的钙钛矿相PZNT91/9单晶。助溶剂法生长的工艺参数为:溶质与PbO助溶剂的摩尔比为l:l,泡料温度1 150-1 200℃,泡料时间10 h,晶体生长时降温速度0.8-2℃/h,当温度降到900℃时停止生长,以50℃/h快速冷却至室温。所得晶体为琥珀色,最大尺寸达φ30 mm×15 mm,其压电系数和机电偶合系数分别为2000 pc/N和0.92。     

垂直管内弹状气泡上升中壁面传递的实验研究

垂直管内弹状流壁面传递是诸多工业应用中需研究的重要问题之一。今用极限扩散电流技术,对弹状气泡上升时瞬时壁面剪应力和传质系数进行了测定,结果显示:当基于表观气速的Froude数FrG < 0.74时,壁面剪应力随弹状气泡和液塞的到来呈现方向相反的交替变化,壁面传质系数亦相应变化;而当FrG > 0.74时,剪应力方向一直向下,说明液膜向下流动,且弹状气泡和液塞的到来对壁面传质系数的影响很小。这说明下落液膜射流穿透了液塞段,控制了整个壁面传递过程。研究还对下落液膜区、尾迹区及液塞段的不同传递特征及机理进行了分析, 并结合气泡塔熔融结晶器中弹状气泡上升时的传热,对结晶操作条件的合理选择进行了讨论。     

氧化钕填充尼龙6的结晶行为

利用示差扫描量热仪（ＤＳＣ）研究了氧化钕（Ｎｄ２Ｏ３）对尼龙６（ＰＡ６）等温结晶行为的影响。结果表明，Ｎｄ２Ｏ３在ＰＡ６体系中起到了异相成核作用，提高了ＰＡ６的晶体增长速率。     

Miscibility of oligomeric poly(dimethyl siloxanes) with long-chain unbranched alkanes: 2. Unsymmetrical cloud point curves

Previously obtained cloud point curves for mixtures of oligomeric poly(dimethyl siloxanes) (weight fraction W₁) with oligomeric polyethylenes have been supplemented by the use of samples of higher molecular weight. Initial flat regions at low-medium W₁ as well as a slight shoulder at extremely high W₁ are now considered to be due to crystallization, since the temperatures at which they occur are the melting points of the oligoethylenes. The actual cloud point curves were of an unsymmetrical dome shape, the form of which could not be simulated by using a concentration-independent interaction parameter g in the Flory-Huggins equation. However, spinodals calculated by assuming a quadratic dependence of g on composition were of the same shape as the experimental cloud point curves. The critical compositions calculated on this basis were also close to the experimental ones.     

Crystallization of poly(3‐hydroxybutyrate) by exfoliated graphite nanoplatelets

Poly(3‐hydroxybutyrate) (PHB) has been shown to be efficiently nucleated by exfoliated graphite nanoplatelets (xGnP). The nucleating effect of xGnP was investigated using differential scanning calorimetry, optical microscopy and atomic force microscopy. Nonisothermal crystallization of PHB from the melt required lower activation energies for PHB containing 1 wt % and 3 wt % xGnP (?214 and ?102 kJ/mol respectively) than for pure PHB (?60 kJ/mol). A kinetic study of the PHB/xGnP crystallization employing a modified form of the Avrami equation revealed that the presence of xGnP increased the PHB crystallization temperature, as well as the crystallization rates, and generated smaller and more numerous spherulites. Optical microscopy and atomic force microscopy confirmed the incorporation of xGnP into the lamellar structure of the PHB spherulites and provided insight into the influence of xGnP on spherulite size and lamellae thickness. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007