温度对碳纤维/乙烯基酯树脂导电复合材料电性能的影响

以乙烯基酯树脂作为基体,用不同质量分数的短切碳纤维制备了导电复合材料,研究了材料的电阻率与温度和伏安特性的影响。结果表明:导电复合材料的PTC转变温度随碳纤维质量分数的增加而升高;复合材料的升温曲线和降温曲线不能重合,随着碳纤维质量分数的增加,回滞环的面积变小;在0～23 V的电压范围内,复合材料的电流-电压关系在低温下符合欧姆定律,随着温度升高,材料的电流-电压关系偏离欧姆定律。     

聚乳酸/乙烯-醋酸乙烯酯共聚物/碳酸钙复合材料的性能研究

采用熔融共混法制备了聚乳酸/乙烯-醋酸乙烯酯共聚物/碳酸钙（PLA/EVA/CaCO3）复合材料,利用差示扫描量热仪、X射线衍射仪、偏光显微镜、扫描电子显微镜、力学性能测试和热变形温度测试等手段,研究了EVA和CaCO3对复合材料的结晶性能、断面形貌、力学性能和耐热性能的影响。结果表明,EVA 具有增韧作用,但降低了复合材料的强度和耐热性;而CaCO3可以提高复合材料的强度、韧性、结晶性能和耐热性能;CaCO3与EVA的加入对PLA有协同增韧作用,且不改变PLA的晶型;当PLA/EVA=90/10,加入10 %（质量分数,下同）的CaCO3时,复合材料有最佳的综合性能。     

树脂基复合材料在雷达结构中的应用

本文介绍了树脂基复合材料的性能和成型工艺特点及其结构件的设计方法；阐述了树脂基复合材料在雷达结构中的应用；分析了目前树脂基复合材料在雷达结构中应用存在的问题，并给出了一些建议。     

不饱和聚酯酰胺树脂/聚磷酸钙纤维复合材料及性能研究

通过熔融缩聚法合成出一种低成本的不饱和聚酯酰胺树脂并表征了其性能,以此为基体,以聚磷酸钙纤维(CPPF)为增强体,引入20 %的交联剂乙酸乙烯酯、0.1%~0.3%的引发剂过氧化苯甲酰和0.1%~0.3%的促进剂N,N-二甲基苯胺室温交联后在195℃下深度交联成可完全降解不饱和聚酯酰胺树脂/CPPF复合材料,并研究了其力学和降解性能。结果表明, 随着CPPF含量的增加, 不饱和聚酯酰胺树脂/CPPF复合材料的力学性能尤其是冲击强度有大幅度的提高,但当CPPF含量超过60 %（质量分数,下同）时,复合材料的力学性能出现下降的趋势;复合材料在模拟体液环境中降解7周后,降解介质的pH和Ca2+浓度保持一个恒定值,降解3个月后含30 %和50 %CPPF的复合材料的弯曲强度分别能保持143、148 MPa。     

Stepwise Conversion of Methane over Supported Metal-Boron Amorphous Alloy Catalysts

The stepwise conversion of CH₄ to higher hydrocarbons over HMCM-22 zeolite supported metal-boron amorphous alloy catalysts has been investigated, including: (1) the influence of metals (Co, Ni, Pt, Rh and Ru) of the catalysts on the reaction; (2) the promotional effect of V on the catalytic behavior of the catalysts; (3) the influence of hydrogenation pressure and CH₄ decomposition temperature; and (4) the nature of carbon species. It is found that the yield of C⁺ ₂ hydrocarbons is strongly dependent on the metals. Good yields of C⁺ ₂ hydrocarbon are reached only on the supported NiB and CoB catalysts. The probability of C--C chain growth is increased by V promotion without seriously affecting the activities of CH₄ decomposition and hydrogenation. The ease of carbon removal via hydrogenation is strongly affected by the CH₄ decomposition temperature. Increasing hydrogenation temperature has a negative effect on the yield of C⁺ ₂ hydrocarbons. XPS measurements show that a carbide(-like) carbon species is active and selective for hydrogenation to produce higher hydrocarbons. Its activity/selectivity is greatly reduced at high CH₄ decomposition temperatures, mainly due to transition of the reactive carbidic to unreactive graphitic form. Graphite/filamental carbons were found to be formed at high CH₄ decomposition temperature.     

普钙产品转化率的数值计算方法

对影响普钙产品转化率的各种因素进行了分析,利用MATLAB 软件包得到了转化率的计算公式,提出了确定未分解磷矿的比例和由倍半氧化物引起的有效磷退化幅度的方法,为生产系统的预测和调整提供了一种途径。     

非晶聚酯树脂的合成研究

以对苯二甲酸（PTA）和乙二醇（MEG）为原料，以Sb2O3为催化剂，通过共聚改性制备了非结晶性聚酯，通过在合成过程中加入辅助催化剂ZnAc2制得高特性粘度的非结晶性聚酯。共聚改性有使酯化速度减慢的趋势，但对缩聚反应时间的影响不显著。     

超分散剂对聚丙烯复合材料性能的影响

以丙烯酸甲酯,二亚乙基三胺及硬脂酸等为原料,合成超支化分散剂(HBPL),采用傅立叶红外光谱(FT-IR)对其结构进行表征。结果表明:经HBPL改性后,聚丙烯/CaCO3复合材料的界面相容性得到很大的提高,冲击强度、弯曲强度分别比未经分散剂改性粉体的复合材料提高了50.2%和8.8%,复合材料的结晶形态基本保持不变,并采用扫描电镜(SEM)观察复合材料的冲击断面形貌。     

树脂含量对碳布/环氧复合材料力学性能的影响

主要研究了不同树脂含量下，碳布／环氧复合材料的径向拉伸和纬向压缩性能，并初步探讨了树脂含量对复合材料拉伸、压缩性能的影响机理。试验结果表明：树脂含量对复合材料力学性能的影响较大，当树脂质量含量在42％－45％之间时，拉伸、压缩性能较好。     

乙烯基酯树脂固化条件及其复合材料的研究

研究了过氧化二苯甲酰(BPO)、过氧化二异丙苯(DCP)、过氧化苯甲酸叔丁酯(TBPB)3种固化剂对乙烯基酯树脂固化工艺的影响,并根据固化工艺制备出树脂浇铸体及其碳纤维复合材料。采用差示扫描量热(DSC)法研究了不同树脂固化体系的反应放热特性,采用扫描电镜(SEM)分析了浇注体的断面的表面形态。并对浇注体及复合材料进行了力学性能测试和热稳定性表征,结果表明制得的复合材料具有优良的力学性能和热稳定性。     

Properties of Injection Molded Composites Containing Corn Fiber and Poly(Vinyl Alcohol)

Composites based on natural polymers alone are extremely sensitive to moisture and their mechanical properties deteriorate upon the absorption of water, limiting their usefulness in practical applications. Ongoing research cooperation between USDA and the University of Pisa, Italy, has yielded several composites based on poly(vinyl alcohol) (PVA) and corn fibers (CF). In this study, variable amounts of CF and PVA were processed in the presence of both dry and liquid plasticizers, glycerol and pentaerythritol. Cornstarch was introduced in the formulation to reduce the cost and to further increase the composition of natural components in the composites. Composites made with as low as 30% PVA were injection molded into tensile bars and evaluated. The addition of starch moderately reduced the tensile properties of the composites, lowering the elongation (∼600% to 400%) and increasing Young's modulus (∼36 MPa to ∼100 MPa) while the ultimate tensile strength remained constant at about 8 MPa. Composites prepared from CF and PVA showed little change in their mechanical properties even after conditioning them at various relative humidities, or after soaking in water. Composites tested after storage for one year, at 50% relative humidity and 23°C, exhibited mechanical properties similar to those of freshly prepared composites. *Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standards of the product and the use of the name USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Degree of Conversion and BisGMA,TEGDMA, UDMA Elution from Flowable Bulk Fill Composites

The degree of conversion (DC) and the released bisphenol A diglycidyl ether dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) monomers of bulk-fill composites compared to that of conventional flowable ones were assessed using micro-Raman spectroscopy and high performance liquid chromatography (HPLC). Four millimeter-thick samples were prepared from SureFil SDR Flow (SDR), X-tra Base (XB), Filtek Bulk Fill (FBF) and two and four millimeter samples from Filtek Ultimate Flow (FUF). They were measured with micro-Raman spectroscopy to determine the DC% of the top and the bottom surfaces. The amount of released monomers in 75% ethanol extraction media was measured with HPLC. The differences between the top and bottom DC% were significant for each material. The mean DC values were in the following order for the bottom surfaces: SDR_4mm_20s > FUF_2mm_20s > XB_4mm_20s > FBF_4mm_20s > XB_4mm_10s > FBF_4mm_10s > FUF_4mm_20s. The highest rate in the amount of released BisGMA and TEGDMA was found from the 4 mm-thick conventional flowable FUF. Among bulk-fills, FBF showed a twenty times higher amount of eluted UDMA and twice more BisGMA; meanwhile, SDR released a significantly higher amount of TEGDMA. SDR bulk-fill showed significantly higher DC%; meanwhile XB, FBF did not reach the same level DC, as that of the 2 mm-thick conventional composite at the bottom surface. Conventional flowable composites showed a higher rate of monomer elution compared to the bulk-fills, except FBF, which showed a high amount of UDMA release.     

Molecular Dynamics Simulations of Amorphous Si–C–N Ceramics: Composition Dependence of the Atomic Structure

We have performed classical molecular dynamics simulations of amorphous Si–C–N materials. The dependence of the local order and of the microstructure on the chemical composition was investigated. Our simulations show that for a stoichiometric nitrogen/silicon ratio equal to or higher than 4/3, the amorphous ceramic separates into different amorphous domains, namely C-rich, SiN-rich, and SiC-rich phases. Below this ratio, the material is composed of mixed structures, homogeneously spread within the material. For a very particular composition range, we found that carbon atoms crystallize into monoatomic graphitic layers surrounding the SiN-rich domains.     

钛酸钾晶须及硫酸钙晶须改性环氧树脂

应用硅烷及钛酸酯等偶联剂对钛酸钾晶须及硫酸钙晶须进行表面处理，考察晶须对环氧树脂力学性能、工艺性等的影响。研究表明，钛酸钾晶须经硅烷偶联剂处理后，能很好地改善复合材料的性能，硅烷的表面处理效果较钛酸酯的好。钛酸钾晶须添加到环氧树脂中后，材料的弯曲强度随晶须含量增大逐渐增大，在晶须含量为8％时达到最大值，之后性能稍有下降；材料的弯曲模量随晶须添加量的增加逐渐增大，冲击强度稍有降低。体系中添加硫酸钙晶须后，材料的性能也得到一定程度的提高。硫酸钙晶须对环氧树脂工艺性的影响较钛酸钾晶须小。SEM表明，晶须经合适的偶联剂表面改性后，与树脂基体的界面粘接得到有效改善。     

Effect of Composition on Properties of Alumina/Titanium Silicon Carbide Composites

In the present study, the room-temperature properties of Al₂O₃-Ti₃SiC₂ composites with different Ti₃SiC₂ contents are determined. The composites are prepared by attrition milling Al₂O₃ and Ti₃SiC₂ mixture powders followed by spark plasma sintering (SPS) under vacuum. From a closer examination of the dependencies of the electrical conductivity on compositions in this system, we determined the percolation threshold at which an interconnected network of electrically conductive phase arises. Since the hardness of Ti₃SiC₂ is lower than that of Al₂O₃, the Vickers hardness decreased with the increasing of Ti₃SiC₂ content while the fracture toughness and the strength increased. The maximum strength (673 MPa) and the maximum toughness (9.3 MPa·m^1/2) were reached in the pure Ti₃SiC₂ material.     

表面化学改性碳酸钙晶须对环氧树脂杂化材料的结构性能影响

利用硅烷偶联剂对碳酸钙晶须表面进行化学改性,研究了表面改性对环氧树脂/碳酸钙晶须复合材料的结构与性能的影响。研究结果表明,表面化学改性能够增加环氧树脂与碳酸钙晶须的相容性,增强碳酸钙晶须与环氧树脂之间的相互作用,改善碳酸钙晶须在环氧树脂中的分散。碳酸钙晶须与环氧树脂之间的界面相互作用是复合材料能够大幅度提高冲击强度的主要原因。     

Effect of magnesium content on bioactivity of near invert phosphate-based glasses

A series of phosphate glasses 40P₂O₅-(40−x)CaO-xMgO-(20−y)Na₂O-yTiO₂ (where 0 ≤ x ≤ 24 and y = 0 or 1) with varying MgO contents were investigated for their in vitro calcium phosphate (CaP) formation. Thermal analysis of these glass compositions was conducted and a significant decrease in glass transition temperature from 448°C to 430°C was seen with reducing MgO content from 24 to 8 mol%. Degradation studies were performed in phosphate buffered saline (PBS) at 37°C, where the 8 mol% MgO glass showed the highest mass loss of around 3.4% after 28 days of immersion. Cation release studies were conducted via ion chromatography, using ultrapure water at 37°C as the degradation medium. The highest release of Ca²⁺ and Na⁺ ions was observed with the 8 mol% MgO glass. In vitro CaP formation studies were conducted using glass discs immersed in simulated body fluid (SBF) at 37°C for up to 28 days. The amorphous phase and chemical composition of deposited CaP layers on the glass discs were confirmed via X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) analysis, respectively. CaP layers with Ca/P ratio 0.8-1.1 were found to be deposited on the lower MgO content (8 to 2 mol%) glass surface after 28 days of SBF study.     

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.     

不同络合剂对电沉积磷酸钙涂层作用的比较

研究了在电沉积磷酸钙陶瓷涂层溶液中三种络合剂丙酸、柠檬酸及磷酸对磷酸钙涂层质量电量比、组成、结构及形貌的影响,通过SEM、XRD观测、分析,结果显示:在含有丙酸、柠檬酸及磷酸不同的络合剂溶液中,电沉积得到涂层组成分别为CaHPO4·nH2O;CaHPO4·nH2O,Ca3(PO4)2·nH2O;Ca3(PO4)2·nH2O,Ca10(PO4)6(OH)2。而且涂层质量电量比、结构、形貌也存在较大的差别。     

氟化铵与硫酸钙制备氟化钙的试验研究

研究了以氟化铵和硫酸钙为原料,生产氟化钙联产硫酸铵的工艺,通过正交试验研究了反应最优条件,确定了最佳反应条件:氟化铵与硫酸钙物质的量为1.15∶1,反应时间为2.5 h,搅拌速度为100 r/min,氟化铵质量分数度为10%,反应温度为80℃。