石蜡/LDPE/OMMT/石墨复合相变储能材料的制备及性能

以石蜡为相变材料,低密度聚乙烯(LDPE)为支撑材料,有机蒙脱土(OMMT)为载体材料,石墨为填料,采用加热共熔法制备石蜡/LDPE/OMMT/石墨复合相变储能材料。采用扫描显微镜(SEM)、红外光谱仪(FTIR)、热重分析仪(TGA)、差示扫描量热仪(DSC)、广角X射线衍射仪(WAXD)、导热系数测定仪等对复合相变材料进行结构表征与性能测试。结果表明:当石蜡质量分数为50%,OMMT质量分数为15%,石墨质量分数为4%时,石蜡包覆良好,相变温度为57.45℃,相变潜热为92.95 J/g。该复合相变材料结构稳定、密封性能优异、热稳定性好和导热率高,应用前景广阔。     

80#石蜡/膨胀石墨定形复合相变材料的特性表征与分析

以80^#石蜡为相变材料,利用不同粒径膨胀石墨的多孔隙结构,以多层吸附、模压法压制方式制备了80^#石蜡/膨胀石墨定形复合相变材料。通过循环融冻实验分析了80^#石蜡的热稳定性和循环稳定性,滴定滤纸渗漏实验确定了不同组分复合相变材料的渗漏率。采用差示扫描量热仪(DSC)、扫描电子显微镜（SEM）、Hot Disk热常数分析仪等仪器对所制备复合相变材料的相变潜热、多孔基吸附结构、热导率、渗漏率等特性进行了分析。结果表明：当膨胀石墨的添加质量分数达到整体组分的8%时,复合定形相变材料的相变温度为80.86℃（吸热）和76.08℃（放热）,相变潜热为130.12kJ/kg,且渗漏率小于0.3%。制备的复合定形相变材料具有形状稳定、渗漏率低、蓄热密度高的特点,且具有较长的使用寿命。     

石蜡/膨胀石墨定形相变材料的性能

以石蜡为相变材料,利用膨胀石墨多孔网络结构,通过物理吸附法制备出石蜡/膨胀石墨复合相变材料,并通过模压法制成定形相变材料板块。采用差示扫描量热分析仪(DSC)、扫描电子显微镜(SEM)、偏光显微镜(POM)和Hot Disk 热常数分析仪等对复合相变材料进行了结构和性能的表征与测量,建立了冷/热循环实验系统以分析材料的蓄/放热性能等。结果表明:石蜡质量分数为80%的定形相变材料相变温度为27.27℃,相变焓为156.6 kJ·kg^-1。制备的定形相变材料具有相变过程形状稳定、热导率高、储热密度大等特点,并具有良好的稳定性和较长的使用寿命。     

HDPE/石蜡/活性炭三元相变储能材料的制备及热性能研究

以高密度聚乙烯(HDPE)、石蜡为相变主材料,活性炭为吸附载体材料,采用熔融共混法制备了HDPE/石蜡/活性炭三元相变储能材料,并分别利用真空烘箱和差示扫描量热仪(DSC)对该相变储能材料的宏观相变转换温度和热性能进行了表征。结果表明:随着HDPE/石蜡/活性炭相变储能材料中石蜡含量的增加(HDPE的含量相应减少),活性炭对石蜡的吸附能力相对降低;HDPE/石蜡/活性炭相变材料中,HDPE的实际焓值高于其理论焓值。     

PE-LD/石蜡复合相变储能材料的制备及性能研究

以固体石蜡、低密度聚乙烯(PE-LD)为原料,乙烯基三乙氧基硅烷改性的膨胀石墨/硅藻土为填料,过氧化二异丙苯(DCP)为交联剂,制备复合相变储能材料。研究了石蜡含量及改性后硅藻土/膨胀石墨用量对复合材料热稳定性及导热性的影响,探讨了DCP含量对复合相变材料微观结构、力学性能的影响。结果表明,当石蜡含量为60%(质量分数,下同)时,热稳定性良好,相变潜热和相变温度更合适;膨胀石墨及硅藻土的加入对复合相变材料热稳定性均有提升,且无机填料含量为4.6%时达到最大值,膨胀石墨对复合材料热稳定性改良效果强于硅藻土;膨胀石墨的加入对复合相变材料导热性能有所提升,当膨胀石墨含量为4.6%时,热导率为对比样的384.38%;DCP的加入使复合相变材料的力学性能有所增强,且含量在3%时综合性能良好。     

高密度聚乙烯/石墨/碳纤维导热复合材料性能的研究

采用高密度聚乙烯(HDPE)、石墨、碳纤维制备高导热、高强度的复合材料。通过SEM照片考察高密度聚乙烯/石墨/碳纤维复合体系的微观结构;研究石墨及碳纤维的加入是否可以形成导热通道以及随着石墨的添加量的提高,复合材料的导热性能及其力学性能的变化。结果表明:当石墨的质量分数为60%,碳纤维的质量分数为5%时,复合材料的导热系数达到7.938 W/(m.K),是纯HDPE的20倍。     

CS改性WF/HDPE复合材料性能研究

通过单因素方差试验方法,研究了壳聚糖(CS)用量对木粉(WF)/高密度聚乙烯(HDPE)复合材料界面相容性、力学性能、吸水性能和抑菌性能的影响,并采用傅里叶变换红外光谱仪(FTIR)和扫描电子显微镜(SEM)对复合材料的微观结构进行了表征。结果表明:CS能够改善WF/HDPE复合材料的界面相容性、力学性能,并赋予复合材料一定的抑菌性能。添加CS质量分数为6%时,WF/HDPE复合材料的综合性能最佳。     

聚乙烯/石蜡相变储能材料的渗出性能

以石蜡作为相变介质,以含有石墨的高密度聚乙烯(HDPE)为载体基质,通过熔融共混的方法制备出HDPE/石蜡相变储能材料,研究了加入了硅藻土和活性炭的HDPE/石蜡相变储能材料发生相变后,固体石蜡的渗出程度。通过SEM分析,背散射电镜放大到4 500倍后,可以看到硅藻土在HDPE基体中的附着镶嵌,放大2 200倍后,得到活性炭在HDPE基体中整齐排布的图像。扩散-渗出圈法测试结果表明:50%的石蜡含量是HDPE对石蜡的大包覆量;硅藻土和活性炭都能增强固体石蜡这种相变介质在发生相变后的渗出稳定性。     

多孔SiC陶瓷/石蜡复合相变材料定型封装及热性能研究

以微米级SiC粉为原料,采用冷冻干燥工艺制备具有连贯层状孔结构的SiC陶瓷。以多孔SiC陶瓷为基体,石蜡为相变芯材,通过真空浸渍法制备多孔SiC陶瓷/石蜡复合相变材料,研究了石蜡在层状多孔SiC陶瓷内的浸渗行为及复合材料的储热性能。结果表明,层片状多孔SiC陶瓷的显微形貌对石蜡的浸渗过程及储热性能有明显影响。当石蜡负载量为21.7%(质量分数)时,复合相变材料熔融温度为59.6 ℃,凝固温度为53.9 ℃,相变潜热为28.4 J/g,室温下的热导率为2.4 W·(m·K)^-1。复合相变材料吸热峰和放热峰强度随着石蜡负载量减少而降低,当温度为200 ℃时,多孔SiC陶瓷/石蜡复合相变材料失重为5%(质量分数),表明材料具有良好的热稳定性。复合相变材料在100 ℃热处理30 min后陶瓷基体未发生形变,经100次热循环后具有稳定的相变潜热和良好的定型能力。     

碳纳米管/石蜡复合相变储能材料的导热性能研究

以多壁碳纳米管为填料,采用两步法制备了不同质量分数(0.1%~1.0%)的CNTs/石蜡复合相变材料。采用HotDisk热分析仪测试了CNTs/石蜡复合相变材料在不同纳米颗粒质量分数、温度和粒径下的导热系数。研究表明,CNTs/石蜡复合相变材料的固、液态导热系数随CNTs颗粒质量分数的增加而大幅度提高,在25℃时,质量分数为0.5%的复合相变材料的导热系数提高了13.2%,体现了良好的强化导热效果。复合相变材料的导热系数对温度的依赖性不强,但在55℃时,复合相变材料的导热系数在固-液相变过程时出现了较大程度的增长。此外,复合相变材料的导热系数随CNTs颗粒粒径的增加而降低,25℃时,质量分数为0.1%的复合相变材料中,添加10 nm的碳纳米管后其导热系数提高了7.8%,添加100 nm的碳纳米管后其导热系数提高了2.2%。     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Synthesis and Characterization of Ti0.33Ta0.33Nb0.33C and Ti0.33Ta0.33Nb0.33CxN1-x Whiskers

Ta_0.33Ti_0.33Nb_0.33C and Ta_0.33Ti_0.33Nb_0.33C _x N_{1− x} whiskers were synthesized via a carbothermal vapor-liquid-solid growth mechanism in the temperature range 900°-1450°C in Ar or N₂. The optimum temperature was 1250°C. Whiskers were obtained in a yield of 70-90 vol%. The whiskers were 0.5–1 µm in diameter and 10–30 µm in length. The starting materials that produced the highest whisker yield were: TiO₂, Ta₂O₅, Nb₂O₅, C, Ni, and NaCl. C was added to reduce the oxides, and Ni to catalyze whisker growth. NaCl was used as a source of Cl for vapor-phase transportation of Ta and Nb oxochlorides and Ti chlorides to the catalyst. The catalyst metal was recycled several times during the synthesis and was transported as NiCl₂( g ) according to thermodynamic calculations. The rate of formation and the chemical composition of the whiskers depended on the synthesis temperature, the choice of catalyst, and the atmosphere. At low temperatures, the whiskers were enriched in Nb and Ta, whereas the Ti content increased with increased synthesis temperature.