Synthesis of Mg_2B_2O_5 whiskers via coprecipitation and sintering process

Mg2B2O5 whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl2-6H2O, H3BO3, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calo- rimetry （TG-DSC）, X-ray diffraction （XRD）, and scanning electron microcopy （SEM）. It is found that the products synthesized at 832℃ are monoclinic Mg2B205 whiskers with a diameter of 200-400 nm and a length of 50-80 μm. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） analyses show that the whiskers obtained at 832℃ are single crystalline and grow along with the [010] direction. The growth mechanism of Mg2B2O5 whiskers was also presented.

EFFECTS OF HEAT TREATMENT ON THE THERMAL EXPANSION BEHAVIOR OF SiC WHISKER REINFORCED ALUMINUM COMPOSITE

The thermal expansion behaviors of commercially-available SiC whisker reinforced pure aluminum composites subjected to different heat treatments were studied. The results indicated that the thermal expansion behaviors were greatly affected by heat treatment. To explain the results, the microstructures and thermal mismatch stresses in the matrix of the composite were examined by the transmission electron microscope and X-ray diffraction, respectively. The results show that the dislocation density and thermal mismatch stresses in the matrix of the composites water-quenched from 600°C are much higher than those of the composite slowly cooled from 600°C. The analysis suggests that the coefficients of thermal expansion (CTE) are closely related to the change of thermal mismatch stresses and the yield strength of the matrix of the composite. The comparison of the coefficients of thermal expansion between experiments and calculations suggests that the temperature behaviors of CTE of SiC/Al composite agree better with those of Kerner's model within lower temperature range.

纳米纤维对钢纤维-UHPC基体界面黏结性能的影响

研究了钢纤维(SF)埋置深度(5、10、15、20 mm)、碳纳米管(CNTs)掺量(0.1%、0.2%、0.3%、0.4%)、碳酸钙晶须(CAS)掺量(1%、2%、3%、4%)对SF-UHPC基体界面黏结性能的影响,并进行了微观机理分析。结果表明:随着SF埋置深度的增加,拉拔峰值荷载和SF-UHPC基体的拉拔能均呈增大趋势,但界面黏结强度呈降低趋势;CNTs的掺入虽降低了SF-UHPC基体的拉拔能,但适量CNTs可提升拉拔峰值荷载和SF-UHPC基体的界面黏结强度;掺入适量CAS可显著改善SF-UHPC基体的界面黏结性能;相较于CNTs,CAS对SF-UHPC基体界面黏结性能改善效果相对更好。

Micro-structure Parameter Optimization Design of Short-fiber/whisker Reinforced Composite

The influence on the stiffness modulus of composites exerted by the volume fraction of reinforcers, aspect ratio, the modulus ratio of the whisker to the matrix, the effect of reinforcers orientation and heat treatment state is discussed, the quantificational relations between microstructure parameters of the short-fiber/whisker reinforced metal matrix composite and its macro mechanical properties are built, and an optimal design method of micro-structure parameters about original isotropy and singularity tropism distribution of the whisker reinforced metal matrix composite is developed. Typical optimal design examples concerning the micro-structure parameter of this kind of material are presented.

盐酸溶解磷石膏重结晶制备石膏晶须

以工业磷石膏为原料,使用盐酸对其进行溶解,探索了单因素试验条件(盐酸浓度、液固比、反应温度、反应时间)对磷石膏溶解率的影响,得到了磷石膏最佳溶解条件:盐酸浓度4 mol/L、液固比20 mL/g、反应温度80℃、反应时间20 min,在此条件下溶解率为86.12%;探究了控温速率对石膏晶须析出率、产物组分、结晶程度和微观显微形貌的影响规律,结果表明:降温速率差异对石膏晶须析出程度几乎没有影响;4种降温速率(0.40、0.30、0.27、0.20℃/min)下的产物均为二水硫酸钙;石膏晶须的特征衍射峰均较尖锐,形成的晶粒较大,结晶程度较高;随着降温速率的减小,石膏晶须的长径比不断增大、形貌更加均匀。研究成果为工业磷石膏的高值高效利用提供了新思路。

硅烷偶联剂对低含量碱式硫酸镁晶须/聚丙烯复合材料的结晶行为及力学性能的影响

选用十六烷基、氨基、环氧基3种不同硅烷偶联剂,先对碱式硫酸镁晶须(MOSw)进行表面处理,再与聚丙烯(PP)熔融共混改性,结合偶联剂的处理、加工工艺、树脂协同复配等技术,制备了低MOSw含量(质量分数仅为3%)的MOSw/PP复合材料,利用场发射扫描电镜、红外光谱、差示扫描量热仪等分析测试手段,探讨了3种硅烷偶联剂对MOSw红外光谱和微观形貌的影响以及对MOSw/PP复合材料的结晶行为、力学性能的影响,并分析了其变化规律及机理。结果表明,3种硅烷偶联剂中,十六烷基硅烷由于—C16H33基团的碳链最长、极性小,对MOSw的分散效果最好,环氧基硅烷次之,氨基硅烷最差;MOSw的加入对PP的结晶起到了阻碍的作用,硅烷偶联剂改性后提高了MOSw的分散性,进一步阻碍了PP的结晶,添加十六烷基硅烷改性晶须的复合材料的结晶度最低,仅为39.3%,与纯PP的结晶度相比下降了14.4%,并且添加十六烷基硅烷、环氧基硅烷改性的MOSw,加快了复合材料结晶速度;经十六烷基硅烷改性的MOSw与PP的结合力最好,基于3%质量分数的MOSw制备的复合材料的性能得到了大幅度的提升,密度仅0.963 g/cm^(3),与纯PP的力学性能相比,弯曲模量提高了116%,达到了2323 MPa,拉伸强度提高了7.8%,缺口冲击强度提高了2.5%,性能好、密度低,可用于制备轻量化的产品。

Preparation, Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.

Growth Habit of the Basic Oxysulfate Magnesium Whisker

The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-（OH）_4]^（2-） and HSO_4^-.[Mg-（OH）_4]^（2-） is the favorable growth unit and whisker growth is in the direction of the [Mg-（OH）_4]^（2-） combination.A plurality of [Mg-（OH）_4]^（2-） s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4^- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.

Synthesis of Calcium Chloroborate Whiskers Via Sedimentation and Sintering Process

Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca2B5O9Cl. SEM and TEM results show that the Ca2B5O9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.

Effects of PSMA and experimental conditions on the morphologies of BaCO_3 whiskers

BaCO3 whiskers exhibiting different morphologies were fabricated by a simple precipitation reaction of barium chloride with sodium carbonate in the absence and presence of poly-（styrene-alt-maleic acid） （PSMA） as a crystal growth modifier at room temperature. The as-prepared products were characterized by scanning electron microscopy （SEM）,transmission electron microscopy （TEM）,and X-ray diffraction （XRD）. The influences of experimental parameters on the size and morphology of BaCO3 whiskers were investigated and discussed. It was found that the as-prepared BaCO3 whiskers are single crystals with diameter ranging from 100 to 300?nm,and grow along the crystallographic a-axis or [100] direction. BaCO3 whiskers with different morphologies,such as branching and dendritic structure,can be obtained depending on the experimental conditions. With increasing PSMA concentration,the diameter of BaCO3 whiskers decreases.

Effects of PSMA and experimental conditions on the morphologies of BaCO_3 whiskers

BaCO3 whiskers exhibiting different morphologies were fabricated by a simple precipitation reaction of barium ch/oride with sodium carbonate in the absence and presence of poly-（styrene-alt-maleic acid） （PSMA） as a crystal growth modifier at room temperature. The as-prepared products were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and X-ray diffraction （XRD）. The influences of experimental parameters on the size and morphology of BaCO3 whiskers were investigated and discussed. It was found that the as-prepared BaCO3 whiskers are single crystals with diameter ranging from 100 to 300 run, and grow along the crystallographic a-axis or [100] direction. BaCO3 whiskers with different morphologies, such as branching and dendritic structure, can be obtained depending on the experimental conditions. With increasing PSMA concentration, the diameter of BaCO3 whiskers decreases.

高密度聚乙烯/硅烷偶联剂改性硫酸钙晶须复合材料的制备与性能

以γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH570)改性的硫酸钙晶须(CSW)为高密度聚乙烯(HDPE)的填料,采用熔融共混法制备了HDPE/CSW复合材料。通过SEM、XRD、TG、DSC表征了KH570改性的CSW对复合材料HDPE/CSW的性能影响。结果表明,改性CSW质量分数为20%时,HDPE/CSW的拉伸和弯曲强度比纯HDPE分别增加9.28%和33.04%,且易产生异相结晶,提升了HDPE/CSW复合材料的耐热性和结晶度。纯HDPE的热降解反应活化能为244.11 k J/mol,改性CSW质量分数为50%时,HDPE/CSW复合材料的热降解反应活化能降到236.99 kJ/mol,表明CSW提升了HDPE/CSW复合材料的热降解反应速率,扩展了复合材料的使用范围。

凝胶注模-固相反应法制备硼酸铝多孔陶瓷

为了提高硼酸铝基陶瓷的强度和隔热性能,以Al_(2)O_(3)纳米粉和B_(2)O_(3)微粉为主要原料,采用叔丁醇基凝胶注模结合原位固相反应工艺制备硼酸铝多孔陶瓷,研究了Al、B物质的量比(分别为9∶2、9∶4和9∶6)、热处理温度(分别为1000、1200和1400℃)对硼酸铝多孔陶瓷性能的影响。结果表明:1)由于B_(2)O_(3)在高温下易挥发,过量的B_(2)O_(3)有利于硼酸铝晶须的生成;但过量太多会使生成的硼酸铝晶须过于粗大,导致试样致密度过高。2)热处理温度过低,硼酸铝晶须发育较差,试样致密度较低;而热处理温度过高,晶须之间会发生烧结致密化。3)当Al、B物质的量比为9∶4,热处理温度为1200℃时,硼酸铝晶须长径比较大,并相互交织形成三维网络结构;所得多孔陶瓷具有较小的体积密度(0.67 g·cm^(-3))、较低的热导率(室温下0.141 W·m^(-1)·K^(-1))和较高的常温耐压强度(6.23 MPa)。

纤维状石墨晶体材料:石墨晶须、石墨晶锥和石墨多面体晶体

纤维状石墨晶体材料因其独特的外观结构、高度的石墨微晶规整性、极高的机械性能和导电性能、复杂的生长机理、丰富多样的制备方法和潜在的应用前景而极具吸引力。然而,与气相生长炭纤维(VGCFs)和碳纳米管(CNTs)不同的石墨晶须、石墨晶锥和石墨多面体晶体(GPCs)尚未得到广泛研究和总结。本文综述了石墨晶须、石墨晶锥和石墨多面体晶体的不同制备方法、特殊的拉曼光谱以及在机理方面的最新研究成果,还对其未来应用领域进行了预测。关于它们自身的性质,如光学、电学、磁学等,还需要系统和深入地研究。这些具有新颖独特外观结构的炭材料有望成为继碳纳米管之后的一种新型潜在的功能性石墨晶体材料。

Mg^(2+) 对半水硫酸钙晶须结晶习性的影响

本文以磷石膏为原料蒸压制备半水硫酸钙晶须,采用数字显微镜、X射线衍射(XRD)和X射线光电子能谱(XPS)等微观测试方法对Mg^(2+)作用下的半水硫酸钙晶须微观形貌、组成及晶面发育情况等进行试验研究,运用分子动力学技术模拟计算Mg^(2+)在半水硫酸钙晶体晶面的相互作用能和径向分布函数,两者结合探讨Mg^(2+)对半水硫酸钙晶体不同晶面结晶习性的影响。结果表明,Mg^(2+)和半水硫酸钙晶体不同晶面的相互作用能从小到大顺序为:ΔE_((200))<ΔE_((002))<ΔE_((400))<ΔE_((020))<ΔE_((204))即Mg^(2+)主要吸附在半水硫酸钙晶体的(200)、(002)、(400)晶面上。Mg^(2+)与SO^(2-)_(4)间的作用距离小于Ca^(2+)与SO^(2-)_(4)间的作用距离,Mg与S之间产生了明显的电子效应,且电子效应随硫酸镁掺量的增加而增强,XRD衍射峰位置随硫酸镁掺量的增多向右偏移变得更加明显,说明有少量的Mg^(2+)嵌入半水硫酸钙晶格。在硫酸镁掺量0.15%(质量分数,下同)时,优先促进晶体c轴方向的生长,使半水硫酸钙晶须呈细长针状,平均长度为47.29μm,平均长径比为36.07;在硫酸镁掺量为0.30%时,抑制晶体沿c轴和径向的生长,使半水硫酸钙晶须呈细短针状,平均长度为39.72μm,平均长径比为28.91。

玉米须水晶梨复合保健饮料的研制

以玉米须、水晶梨为主要原料研制复合保健饮料,并采用单因素试验及正交试验优化玉米须水晶梨复合保健饮料的工艺配方。结果表明,玉米须水晶梨复合保健饮料的最佳工艺配方为:玉米须与水晶梨提取液的质量比2∶7,黄原胶添加量0.03%,柠檬酸添加量0.045%,木糖醇添加量6%,蜂蜜添加量0.02%。在此条件下,玉米须水晶梨复合保健饮料清新可口、酸甜适口、风味协调、色泽均匀。

三水碳酸镁晶体形貌的调控研究

采用共沉淀法,用工业级卤水和纯碱制备棒状三水碳酸镁晶须。在一定反应时间和一定进料方式下探究晶体形貌的影响因素,得到最适宜条件为:反应温度35℃,卤水浓度1.5 mol/L,陈化时间60 min。在该条件下制备出的MgCO_(3)·3H_(2)O产品表面光滑,晶体发育完整,长度达到30μm。同时探究了40℃下小颗粒悬浮物和添加剂对MgCO_(3)·3H_(2)O产品形貌的影响,发现在40℃下小颗粒沉淀物对产品形貌有一定影响,但影响程度不大,而添加剂在40℃下则可以促进MgCO_(3)·3H_(2)O的晶体形成。

四针状ZnOw的微波吸收及微波-热转换特性研究

用四针状ＺｎＯｗ为吸波剂主要成份制备了一种轻质高效吸波涂料，并对其在Ｋｕ波段的吸收特性作了初步研究。结果表明，在１３．５～１７．５ＧＨｚ的Ｋｕ波段，上述材料雷达波反射率均达到－１０～－２０ｄＢ。进一步的研究表明，涂层的吸波效果与ＺｎＯｗ针状体的长径比有关，在１３．５０～１７．５０ＧＨｚ的频率范围内，控制ＺｎＯｗ针状体平均长径比为３０～５０，可获得最佳效果。 ＺｎＯｗ微波－热转换的初步研究发现，ＺｎＯｗ及其复合材料具有优异的微波－热转换性能，当ＺｎＯｗ针状体长径比为４０～６０的情况下，表观比重为０．１５～０．１８ｇ／ｃｍ３，可以达到最佳发热效率。

SiCW/AZ91镁基复合材料及AZ91镁合金的高温变形行为

利用Gleeble1500对SiCW/AZ91复合材料和AZ91镁合金在温度为423～723K、应变速率为0.002～0.25s1、最大应变量为60%的条件下进行高温压缩变形行为的研究。测试了其真应力应变曲线,观察了变形后的显微组织。结果表明:晶须的转动和折断导致复合材料的应变软化现象较合金明显;复合材料和合金的应变速率敏感指数(m)和表观激活能(Q)均随温度的升高而增大;晶须的加入细化了晶粒,使复合材料的m值比合金高;同时晶须的加入也限制了位错交滑移和晶界的迁移,因此复合材料的Q值比合金高;压缩变形过程中,合金和复合材料发生了动态回复和动态再结晶。

化学气相反应法制备SiC涂层

采用化学气相反应法,以3种不同工艺在C/C复合材料表面制备了SiC涂层,并检测了其抗氧化性能。以工业用Si和辅助剂SiO2为原料,在高温、惰性环境中反应产生SiO蒸气,将其引入反应室与C/C复合材料在不同温度下进行气相反应,在试样表面生成一层致密的SiC涂层。X射线衍射分析表明:涂层是由βSiC组成。从试样截面的扫描电镜可知:不同工艺制得的SiC涂层界面过渡带颗粒的微观形貌各异。经最优工艺制备的涂层过渡带很窄,有βSiC纳米晶须生成,且其抗氧化性能最佳。