氢氧化镁与七水硫酸镁水热法合成碱式硫酸镁晶须

为了获得高品质的碱式硫酸镁晶须，采用氢氧化镁和七水硫酸镁为原料，通过水热法合成碱式硫酸镁晶须。考察了七水硫酸镁与氢氧化镁的物质的量比、水热时间、搅拌转速、七水硫酸镁的添加量及水热温度等条件因素对晶须生长的影响，利用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、选区电子衍射（SAED）及傅里叶红外光谱（FT-IR）等对晶须产品进行了分析。结果表明：优化的工艺参数为七水硫酸镁与氢氧化镁物质的量比为3∶1、水热时间为2 h、搅拌转速为400 r/min、七水硫酸镁添加量为4.93 g、水热温度为180℃、80 mL水作为反应介质；在优化条件下合成的产品主要为纤维状晶须，晶须的直径为300～500 nm、长度为80～100μm，其长径比大于160。工艺参数的优化可有效提高碱式硫酸镁晶须的分散性和长径比。     

高性能无机阻燃、增强纤维——镁盐晶须在塑料改性和涂料工业中的应用

晶须（新型纤维）和纳米材料是二十一世纪材料科学和材料产业最重要的二大类尖端产品。镁盐晶须是继钛酸钾晶须后的第二代晶须产品，在世界上也只有少数国家可以生产，镁盐晶须以其晶体结构无缺陷的纤维增强效果。耐老化性能，耐温性能到国内几家著名生产改性塑料的大公司的认可和使用，本文着重介绍新型高性能补强材料-镁盐晶须在塑料改性和涂料等行业中的应用。     

以活性氧化镁和氯化镁为原料合成氧化镁晶须

探讨了一种合成氧化镁晶须的新的工艺方法。首先以活性氧化镁和氯化镁为原料合成了前驱体碱式氯化镁晶须，接着将碱式氯化镁焙烧成氧化镁晶须。分别用X射线衍射仪（XRD）、扫描电镜（SEM）、热重分析仪（TGA）和化学分析，分析了中间体碱式氯化镁和产品氧化镁晶须的成分、形貌和热化学行为。探讨了各个工艺条件对产物的影响，探索出最佳的工艺条件：活性氧化镁与氯化镁的物质的量比在0．08左右，氯化镁溶液的浓度为3mol／L，反应温度40～50℃，陈化时间在48-72h，陈化温度50℃。在此条件下制得了形貌良好的前驱物碱式氯化镁晶须。将碱式氯化镁晶须焙烧，控制升温速率在2—5℃／min，采取分段升温方式升温至600℃，即可制得氧化镁晶须。制得的晶须长度在100μm左右，直径约0．5μm。     

碳酸钙晶须制备及其对聚丙烯的改性

研究了碳酸钙（CaCO3）晶须的制备方法，探索了以氯化镁（MgCl2）为促进剂时CaCO3晶须生长的影响因素，试验得到了制备CaCO3晶须的最佳条件。采用红外光谱、拉曼光谱等对CaCO3晶须结构进行了性能和结构表征，发现所制备的产物中晶须含量达97％（质量分数），长径比（L／D）为20～30。探讨了所制晶须对聚丙烯（PP）材料改性的效果，结果表明，晶须改性PP的力学性能、流动性明显优于普通重质CaCO3填充PP的。与纯PP相比，在填充量15％（质量分数）的情况下，CaCO3晶须改性的PP，其拉伸断裂强度提高35．7％，弯曲模量提高117％，冲击强度提高31．5％，熔体流动速率基本不下降。     

硅钙镁晶须增强RPUF复合材料的制备与性能研究

研究了硅钙镁（SCM）晶须在硬质聚氨酯泡沫塑料（RPUF）基体中的分散状况及SCM晶须用量对SCM晶须／RPUF复合材料的力学性能、表皮结构和尺寸稳定性的影响。结果表明：SCM晶须在RPUF基体中具有较好的分散性；随着SCM晶须用量的增加，复合材料的压缩性能逐渐提高，直至晶须用量超过60g／100g聚醚后，复合材料的压缩性能开始下降；复合材料的冲击强度随着SCM晶须用量的增加明显下降；复合材料的表皮随晶须用量的增加越来越致密；在一定用量范围内，SCM晶须可改善复合材料的尺寸稳定性。     

四针状氧化锌晶须的制备

用锌粉氧化的方法，通过控制反应器内的气相过饱和度，可以获得不同尺度的四针状氧化锌晶须（T－ZnOW)。合成出的ZnO的晶须纯度高，晶体结构完整，晶须尺度可控（针长为10-60μm，根部尺寸约为1-6μm）。晶须的生长机理为气－固（VS）机理。     

磷石膏制备硫酸钙晶须的条件研究

磷石膏是湿法制备磷酸过程中产生的固体废渣,既会对环境产生污染,又会造成资源浪费。为提高废料磷石膏的综合利用价值,研究了以磷石膏原料制备硫酸钙晶须,考察了原料预处理、料浆浓度、晶型助长剂和pH对硫酸钙晶须产率和形貌的影响。用扫描电镜（SEM）、图像颗粒分析显微镜和X射线衍射（XRD）对产品进行观察和检测。结果表明, 通过原料的预处理,可得到最佳反应条件：料浆质量分数为2%、采用硫酸镁为晶型助长剂、pH为3。在此条件下,晶须产率可达36.4%,平均长径比可达60,产品为半水硫酸钙晶须。     

硅钙镁晶须填充聚丙烯复合材料的性能研究

在啮合同向双螺杆挤出机中制备了聚丙烯（PP）/硅钙镁（SCM）晶须复合材料,研究了硅烷偶联剂用量、SCM晶须含量对复合材料力学性能以及熔体流动性能的影响。实验结果表明,当硅烷偶联剂用量占晶须的2 ％（质量分数,下同）时,PP与SCM晶须的配比为80/20（质量比,下同）时,PP/SCM晶须复合材料的拉伸强度、弯曲强度和冲击强度等综合力学性能最佳。     

混合脂肪酸钠辅助制备硫酸钙晶须

硫酸钙晶须应用范围广、综合性能优异、性价比高,具有良好的应用前景。以氯化钙为主要原料,添加油酸钠、硬脂酸钠以及油酸钠与硬脂酸钠的混合物作为改性剂,采用常压酸化法制备了长径比高、疏水性能好的硫酸钙晶须。探究了氯化钙浓度、反应时间、反应温度、油酸钠和硬脂酸钠及其混合物的用量等因素对制备的硫酸钙晶须长径比及疏水性的影响,确定了最佳制备条件。采用扫描电镜（SEM）、接触角测量仪、X射线衍射仪（XRD）、红外光谱（FT-IR）及Zeta电位分析等对产品进行了表征。通过实验得到制备硫酸钙晶须的最佳工艺条件：氯化钙溶液质量浓度为0.11 g/mL时,添加与氯化钙等物质的量的浓硫酸4.8 mL,加入4%油酸钠和6%硬脂酸钠混合物（以质量分数计）作为改性剂,在140 ℃油浴锅中加热搅拌1 h。在此工艺条件下,制备的硫酸钙晶须长径比为32~106,接触角可达120.2°。XRD结果表明,所得硫酸钙晶须为半水硫酸钙晶须和二水硫酸钙晶须的混合物。红外光谱和Zeta电位分析表明,油酸钠和硬脂酸钠以化学吸附的形式吸附在晶须表面。当加入油酸钠和硬脂酸钠混合物时,油酸钠和硬脂酸钠共吸附于晶须表面,使得晶须表面吸附的脂肪酸更多,晶须疏水性更强。     

针状（晶须）纳米碳酸钙

纳米碳酸钙是一种新型超细功能材料，是最廉价的纳米跚陛剂，广泛应用于橡胶、塑料、涂料、胶粘剂、造纸、油墨、医疗等领域，还有许多用途有待开发，因此已成为当前纳米材料领域竞相研究和开发的热点。我国已可生产五、六个型号的纳米碳酸钙产品，但高档纳米碳酸钙产品尚需进口。河北科技大学（石家庄）率先在工业化装置上制备出稳定的方解石型针状（晶须）纳米碳酸钙高档产品。     

Effect of Vapor—Liquid—Solid and Vapor—solid Silicon Carbide Whiskers on the Effective Thermal Diffusivity/Conductivity of Silicon Nitride Matrix Composites

A study was conducted of the relative effect of vapor—liquid—solid (VLS) and vapor—solid (VS) SiC whiskers on the effective thermal diffusivity and conductivity of pressed-densified silicon nitride. It was found that VLS whiskers cause an increase in the thermal diffusivity/conductivity, whereas the opposite effect was found for the VS-SiC whiskers. Comparison with composite theory suggests that the VS-SiC whiskers have a thermal conductivity as low as 25 to 30 W/(m·K). In contrast the VLS-SiC whiskers appear to have a value for the thermal conductivity of at least about 100 W/(m·K) to as high as 250 W/(m·K). These large differences in thermal conductivity for these two types of SiC whiskers are attributed to the much larger density of structural defects in the VS-SiC whiskers, which act as phonon scatterers, thereby lowering the thermal conductivity.     

SiC_w/莫来石和SiC_w/Y-TZP/莫来石复合材料的力学性能与显微结构

以莫来石为基体,SiC晶须(SiC_w)和Y-TZP(Y_2O_3稳定的四方ZrO_2多晶)为两种补强剂,采用热压烧结工艺,制备SIC_w/莫来石和SIC_w/Y-TZP/英来石复合材料。研究了复合材料的力学性能与显微结构,并对强化增韧机制进行了分析。结果表明,SiC晶须补强莫来石,可以改善其强度和断裂韧性。若SiC晶须和Y-TZP共同补强英来石,则可以进一步提高其强度和断裂韧性。晶须引起裂纹偏转,晶须拔出以及由ZrO_2相变引起的微裂纹增韧是该复合材料的主要增韧机制。SiC晶须和Y-TZP两种补强剂的共同作用,对莫来石强度和断裂韧性的提高具有叠加或协同效应。     

Colloidal Processing of SiC Whisker Composites

In the present study, the dispersion processing and the characterization of the dispersity of SiC whiskers for reinforced ceramic-based composites were studied. Two kinds of methods were used to determine the dispersity of SiC whiskers. First, the sedimentation density was employed to directly characterize the dispersity of the SiC whiskers. The other is an indirect characterization. The dispersity and the distribution of the SiC whisker in a ceramic matrix were analyzed and characterized indirectly with SEM observation and the determination of the relative density. By means of the colloidal processing of the whiskers in which electrostatic and steric interaction were used to counteract the attractive forces between whiskers, four dispersion processing routes were used to mix the SiC whisker into the Al₂O₃ powder. The sedimentation results indicated that, with aluminum alkoxide as a dispersant, SiC whiskers were completely deflocculated and the sedimentation density increased twofold from 8.5% to 24% of theoretical density, and both the homogeneous distribution of SiC whiskers and densification of the 30 vol% SiC whisker-reinforced Al₂O₃ (AS) were achieved by hot pressing. The relative density of the AS composites was more than 99.7%. SEM observation showed no agglomeration of SiC whiskers.     

Silicon Carbide Whiskers: Preparation and High Dielectric Permittivity

Silicon Carbide whiskers have been synthesized using silica sol and activated carbon as reagents via microwave heating without the presence of any of the catalysts, such as Fe, Ni, and Al etc.. The synthesized whiskers were separated and concentrated from the as‐synthesized products using the gravity concentration process. The dielectric properties of the concentrated SiC whiskers were investigated in the frequency range 2–18 GHz. The results indicate that the SiC whiskers exhibit higher dielectric permittivity and loss tangent than those of SiC powders, respectively, due to the high density of stacking faults formed in the SiC whiskers prepared by microwave heating.     

The Manipulation and Alignment of Silicon Carbide Whiskers for Gallium Nitride Epitaxial Growth

As a substrate candidate for low‐cost III‐nitride thin film growth, 3C–SiC whiskers are employed and manipulated in this work. The alignment of the whiskers is achieved on a patterned 3M Vikuiti^? Brightness Enhancement Film surface. The degree of whisker alignment using this approach is higher than the whiskers lined up by extrusion methods according to X‐ray diffraction (XRD) analysis. The aligned whiskers are transferred from the 3M film and embedded into an alumina matrix by tape casting. A self‐regulating sintering technique for SiC whiskers is used to protect the whiskers from being oxidized in air during sintering at 1600°C. The aligned whiskers are rigidly embedded in the alumina matrix as shown in scanning electron microscopy (SEM) images and energy‐dispersive X‐ray spectrometry energy mapping images. GaN thin films grown by a low‐cost sputtering process on Alumina/SiC as well as Si and SiC as reference materials are characterized by XRD and SEM.     

Toughening of Silicon Nitride Matrix Composites by the Addition of Both Silicon Carbide Whiskers and Silicon Carbide Particles

Si₃N₄ matrix composites reinforced by SiC whiskers, SiC particles, or both were fabricated using the hot-pressing technique. The mechanical properties of the composites containing various amounts of these SiC reinforcing materials and different sizes of SiC particles were investigated. Fracture toughness of the composites was significantly improved by introducing SiC whiskers and particles together, compared with that obtained by adding SiC whiskers or SiC particles alone. On increasing the size of the added SiC particles, the fracture toughness of the composites reinforced by both whiskers and particles was increased. Their fracture toughness also showed a strong dependence on the amount of SiC particles (average size 40 μm) and was a maximum at the particle content of 10 vol%. The maximum fracture toughness of these composites was 10.5 MPa·m^1/2 and the flexural strength was 550 MPa after addition of 20 vol% of SiC whiskers and 10 vol% of SiC particles having an average particle size of 40 μm. These mechanical properties were almost constant from room temperature to temperatures around 1000°C. Fracture surface observations revealed that the reinforcing mechanisms acting in these composites were crack deflection and crack branching by SiC particles and pullout of SiC whiskers.     

Investigation of Anelastic Creep Recovery in SiC Whisker-Reinforced Alumina Composites

Anelastic strain recovery has been studied in SiC whisker-reinforced alumina composites following tensile creep. The magnitude of the recovered strains were ∼10⁻³ with 20 vol% SiC whiskers upon unloading from 74 MPa at 1673 K, while no such behavior was observed with 10 vol% SiC whiskers. A strain recovery mechanism based on Hertzian contact deformation within a percolating whisker (or particle) network is suggested, which appears to be consistent with the experimental observations. Two models (for whiskers and particles) have been developed which seem to predict the magnitude of recoverable strain reasonably well.     

Synthesis of SiC Whiskers from Silicon Nitride in Argon Atmosphere

SiC whiskers were synthesized by carbothermal reduction of silicon nitride. α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron oxide as catalyst. The synthesized SiC whiskers were characterized by XRD and SEM. The results showed that the synthesizing temperature should be above 1 716 K; the decomposition of Si3N4 was the limited step in the synthesis of SiC whiskers; and catalyst not only offered the liquid condition, bu...     

Effect of SiC nanoparticles on in-situ synthesis of SiC whiskers in corundum–mullite–SiC composites obtained by carbothermal reduction

Corundum–mullite–SiC composites were synthesised using a carbothermal reduction method. The effects of SiC nanoparticles and sintering temperatures on the phase transformation of the composites and the synthesis of SiC whiskers were studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Results indicated that corundum, mullite, and SiC whiskers were produced as final products at 1600–1650 °C. SiC whiskers were formed through the vapor–solid mechanism. The added SiC nanoparticles worked as nucleating agents to facilitate the carbothermal reduction of aluminosilicates and formation of SiC whiskers. The sample with the added SiC nanoparticles exhibited a high yield of β-SiC of 17.1%. Furthermore, the SiC nanoparticles decreased the formation temperature of SiC whiskers from the original 1600 °C to 1500 °C, and the porosity of the composites was increased from 56.7% to 64.7% by increasing the partial pressure of SiO gas. This study provides an insight into the more efficient synthesis of composites with SiC whiskers through the carbothermal reduction of aluminosilicates.     

Nitridation of Silicon Containing MgO and CeO2 Powders and SiC Whiskers

Processing and nitridation of MgO/CeO₂-doped silicon containing SiC whiskers was studied. The reaction time was dramatically reduced by incorporating MgO/CeO₂ dopants and SiC whiskers in silicon powders prior to nitridation. The decomposition of SiC whiskers depends on the nitriding temperature, sintering aids, and whisker surface composition.