Microstructural evolution of potassium titanate whiskers during the synthesis by the calcination and slow-cooling method

K₂Ti₆O₁₃ whisker was synthesized by the calcination and slow-cooling method, and the microstructural evolution of whiskers, and the relations between the phase and the layer structure, were investigated. The amount of K₂O in the starting powder mixture played a key role in forming a layer structure, which can be obtained by addition of excess K₂O. During calcination, rod-like K₂Ti₆O₁₃ particles with a layer structure were formed by reactions between K₂O and TiO₂. During slow-cooling, the K₂O-rich liquid phase reacted with K₂Ti₆O₁₃ layers near the boundary and k₂Ti₄O₉ whiskers were produced by the splitting of layers within rod-like k₂T₆O₁₃ particles. k₂Ti₄O₉ whiskers were reformed into k₂T₆O₁₃ whiskers by treatment in boiling water and reheating. The synthesized k₂T₆O₁₃ whiskers had a clean surface and a length exceeding 100 m.     

Study on the formation and growth of potassium titanate whiskers

In this paper, K₂Ti₂O₅ single crystals, K₂Ti₄O₉ whiskers and K₂Ti₆O₁₃ whiskers are synthesized form the anatase-K₂CO₃ starting materials by the heating calcination and the corresponding morphologic and structural evolution of products are observed. After dissolving non-crystalline hydrosoluble products contained in sinters, the morphologic difference between the original sinter and the whiskers in it shows the sinter microstructure. The further analysis to crystal components in sinters and to the phase diagram proves that K₂Ti₄O₉ whiskers are firstly formed in K₂Ti₂O₅ crystals and there only exists the phase transformation from K₂Ti₄O₉ whiskers with layered crystal structure to~K₂Ti₆O₁₃ whiskers with tunnel crystal structure. The K₂O-rich liquid melt generated from K₂Ti₂O₅ crystals (/and K₂Ti₄O₉ whiskers) coats on the surface of K₂Ti₄O₉ whiskers (/and K₂Ti₆O₁₃ whiskers), which makes the sinters taking on the layer-by-layer structure (/and the bunch structure). The formation and growth of whiskers is dictated by the K₂O-rich non-crystalline hydrosoluble melt generated in phase transformations from solid to liquid-solid and its split effect induced by the orientation melting. A generalized liquid melt inducing mechanistic model explaining the formation and growth of potassium titanate whiskers was proposed.     

Effects of sintering temperature of whisker preform on the microstructures and tensile properties of Bi(OH)3-coated Al18B4O33 whisker-reinforced aluminum matrix composites

A alumina borate whisker with Bi(OH)₃ coating was prepared by a chemical method. The coated whiskers were sintered at various temperatures. The coated whisker-reinforced pure aluminum matrix composite was fabricated by squeeze casting method. The microstructures of the coated whiskers and coated composites with the different sintering temperature of whisker preform were studied, and the tensile properties of the coated composites at room temperature were also investigated. It can be found that the microstructures of coatings on the whisker surfaces and at the interface in the coated composites are strongly dependent on the sintering temperature of whisker preform. The ultimate tensile strength and elongation to fracture of the coated composites increased with the increasing of sintering temperature of the whisker preform.     

Effect of sintering additives on the behaviour of SiC whisker-reinforced Si3N4 composites

The effects of sintering additives on the microstructural development, whisker stability, oxidation resistance and room-temperature mechanical properties of the SiC whisker-reinforced Si₃N₄ matrix composites were investigated. Seven different combinations of Y₂O₃ and Al₂O₃ were used as sintering additives. The composites containing 20 vol % SiC whiskers were densified by hot pressing. The microstructure of the resulting composites was characterized using X-ray diffraction, scanning and transmission electron microscopy. Oxidation testing of the composite at 1400 °C was conducted to investigate the relationship between matrix compositions and oxidation resistance. The flexural strength, fracture toughness and crack propagation patterns were also characterized and correlated with the microstructural features.     

Rheology,fiber distribution and mechanical properties of calcium carbonate (CaCO3) whisker reinforced cement mortar

Calcium carbonate (CaCO₃) whiskers are a new kind of microfiber used in cementitious composites and have proved to provide excellent effect on strengthening and toughening. In order to further improve the mechanical properties of CaCO₃ whisker-reinforced cementitious composites, rheological properties of fresh mixtures and the CaCO₃ whisker distribution in the hardened matrix were investigated. The yield stress and plastic viscosity increased with an increasing content of CaCO₃ whisker and a decreasing water-cement ratio. Also, the rheological properties were affected by the distribution of CaCO₃ whisker in the matrix. The largest increments in flexural and compressive strength were 27.59% and 12.60% for the mortars with CaCO₃ whisker contents of 2.0% and 1.5%, respectively. The properties responsible for the mechanical response were explained in terms of the effects of CaCO₃ whisker reinforcement, the distribution of CaCO₃ whiskers, and the porosity as well as pore size distribution.     

不同偶联剂改性PTW对PP/GF复合材料性能的影响

目的研究六钛酸钾晶须表面改性对聚丙烯复合材料的力学性能影响,以探索最佳表面改性手段。方法分别采用硅烷偶联剂KH550、KH570、正十二烷基三甲氧基硅烷,钛酸酯偶联剂NDE311、改性六钛酸钾晶须(PTW),然后将改性过的六钛酸钾晶须、玻璃纤维、聚丙烯通过熔融共混制得聚PP/GF/PTW复合材料。结果比较六钛酸钾晶须经不同偶联剂改性前后对聚丙烯/玻璃纤维复合材料性能的影响,发现改性过的六钛酸钾晶须可改善复合材料的力学性能。比较不同偶联剂改性六钛酸钾晶须对聚丙烯/玻璃纤维复合材料性能的影响,发现经KH550偶联剂处理后,与未改性相比,复合材料的弯曲性能提高了58.63%,拉伸性能提高了16.07%,冲击性能提高了63.1%。结论六钛酸钾晶须经KH550偶联剂处理后,复合材料的综合性能最好。     

Splitting behavior and structural transformation process of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> whiskers under hydrothermal conditions

The splitting behavior and structural transformation process of K₂Ti₆O₁₃ whiskers in various hydrothermal solutions were investigated by the X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. TiO₂ (B) particle aggregates and rutile twinned crystals were produced respectively in diluted and concentrated HCl solutions via “dissolution-precipitation” mechanism, while no changes were observed in deionized water. In contrary to the chemical inertia of K₂Ti₆O₁₃ whiskers in KOH solution, trititanate nanowires were synthesized by splitting the bulk K₂Ti₆O₁₃ whiskers in NaOH solution. The driving force for the formation of nanowires originated from the intrinsic strain induced by the phase transition from K₂Ti₆O₁₃ with a tunnel structure to layered trititanate. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

钛酸钾晶须填充新型PPESK的性能及形态研究

采用填料对含二氮杂萘结构的聚醚砜酮(PPESK)进行填充改性,能够快捷有效的提高其性能,为此采溶液共沉析的方法制备了含二氮杂萘结构的聚芳醚砜酮/钛酸钾晶须(PPESK/Whisker)复合材料.使用不同比例的钛酸酯偶联剂进行晶须表面处理,研究了晶须表面处理和晶须含量对PPESK复合材料机械性能的影响;考察了复合材料的热性能,并用扫描电镜观察了复合材料的形貌.结果表明,钛酸钾晶须作为填充材料,使得复合材料机械性能得到明显改善;对晶须进行适当的表面处理后,晶须与PPESK基体的相容得到改善.     

填充剂表面改性对硫化胶疲劳性能的影响

研究了 13种白炭黑表面改性剂对 NR/BR硫化胶疲劳性能的影响 ,分析了偶联剂改性白炭黑填充硫化胶疲劳过程中微观结构的变化及其对疲劳性能的影响。发现 :不同硅烷类偶联剂对胶料初期性能的影响为 :NDZ2 0 1>NDZ311>NDZ4 0 1>NDZ311W;不同表面活性剂对胶料疲劳性能影响为 ABS>T4 0>ATAC。硫化胶疲劳过程中的“自愈合”能力是影响疲劳性能的重要因素     

Slurry processing for fabrication of SiC whisker-reinforced Si3N4 composites

In order to solve the major problems of processing whisker-reinforced ceramic composites, such as agglomeration of whiskers, correlation between pH and viscosity has been carefully investigated in a mixed slurry of whiskers and matrix powder. SiC whiskers and Si₃N₄ powder were dispersed homogeneously by controlling pH in aqueous suspension, and the state was successfully fixed by a sudden change of pH to make the slurry more viscous. The slurry was then filtrated rapidly and dried. The strength of hot pressed composites obtained by this procedure was scarcely lowered, with increased whisker loading in the range 0–30 wt% and fracture toughness increased more than 75%.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

钛酸钾晶须水热合成多形体TiO2及结构演变

从不同种类的钛酸钾晶须(K2Ti6O13,K2Ti4O9和K2Ti8O17)出发,通过水热条件下转晶得到了多形体TiO2晶粒,其中K2Ti6.O13晶须通过酸性条件下水热反应得到形貌规整的孪晶金红石TiO2.并借助XRI)、SEM和TEM等手段,考察了水热反应过程中的晶体结构演变,证明了前驱物中的弱结合晶面是发生晶体结构转变的关键因素,K2Ti6O13.通过{100}和{201-}晶面上的原子重排,生成孪晶金红石型TiO2.     

Microstructure and mechanical properties of SiC Whisker reinforced ZrO2–Y2O3 composites

Abstract

The mechanical properties of 20 vol.-%SiC whisker reinforced ZrO₂?V₂O₃ composites containing 2 and 6 mol.-% Y₂O₃ were measured at room temperature and the fracture surface was examined. The results indicate that the mechanical behaviour of the composites is strongly influenced by the Y₂O₃ content. The magnitude of the enhancement of the toughness in composites containing 2 mol.-% Y₂O₃ compared with unreinforced ZrO₂?Y₂O₃ matrix is larger than that for the composites containing 6 mol.-% Y₂O₃. Crack propagation modes were characterised by crack deflection, whisker bridging, and whisker pullout. High resolution electron microscopic observations show that in composites containing 2 mol.-% Y₂O₃ the whiskers are directly bonded to the matrix. However, in composites containing 6 mol.-% Y₂O₃ there is always a thick amorphous layer at the interface, indicating that the high Y₂O₃ content has promoted the formation of interfacial amorphous layers. These interfacial amorphous layers strengthen the interfacial bonding, resulting in a composite with a low fracture toughness.

MST/2043     

Microscopic examination of the interface region in AC8A/Al18B4O33w composites reinforced with as-received and artificial nitrided Al18B4O33 whiskers

Aimed to control the interfacial reaction in Al₁₈B₄O₃₃/Al composites, the artificial nitridation process is proposed based on thermodynamic calculations, which leads to a 50-nm thick artificial nitrided coating surrounding a Al₁₈B₄O₃₃ whisker. Aluminum (AC8A) matrix composites reinforced with different Al₁₈B₄O₃₃ whiskers were processed and Al₁₈B₄O₃₃ whiskers were used in their as-received form and after artificial nitridation. The interface region between the aluminum matrix and Al₁₈B₄O₃₃ was charactered using transmission electron microscopy. Results show that extensive reaction takes place during the incorporation process between the as-received Al₁₈B₄O₃₃ whiskers and the aluminum matrix and Mg in the base alloy forms MgAl₂O₄ spinel phases. Such interfacial reaction is enhanced after T6 heat treatment. In the case of artificially nitrided Al₁₈B₄O₃₃ whiskers, even though the artificial nitrided coating surrounds the Al₁₈B₄O₃₃ whisker, it can react with the AC8A alloy to produce MgAl₂O₄, but the degree of the interfacial reaction is reduced. The interfacial reaction only consumes the artificial nitrided coating instead of the reinforcement whiskers and the integrity of the whisker is preserved.     

晶须增强增韧聚合物基复合材料机理研究进展

简介了晶须增强增韧聚合物基复合材料研究的现状;并较全面地介绍了各种增强增韧机理,主要包括:裂纹桥接、裂纹偏转、拔出效应等机理。晶须增强增韧聚合物基复合材料主要表现在:(1)晶须导致基体局部应力状态改变;(2)晶须对基体结晶行为产生影响。文中还简要介绍了在实验过程中影响聚合物基晶须复合材料性能的几个重要的因素,如与界面相关的一系列因素和晶须在基体中含量、晶须在基体中的分散程度、晶须长径比以及在基体中的排列方向等。     

团簇对粉末热挤压铝基复合材料力学性能的影响

为明确晶须团簇行为对材料力学性能的影响,采用粉末热挤压法制备了硼酸镁晶须增强铝基复合材料,对不同含量的晶须增强铝基复合材料进行了力学性能测试,并基于载荷传递模式提出相应的模型对材料强度进行预测.结果表明:随着硼酸镁晶须含量的增加,团簇加剧;当晶须体积分数大于10%时,材料力学性能降低;提出的模型考虑了团簇因素,成功预测了复合材料的实验强度.     

Processing of pressureless-sintered SiC whisker-reinforced Al2O3 composites

Silicon carbide whisker-reinforced Al₂O₃ Composites were prepared using a processing scheme in which the constituents were dispersed in nonaqueous media, then colloid-pressed and pressureless-sintered under an inert atmosphere. Novel oligomeric and polymeric dispersants were used to sterically stabilize the SiC whiskers in the presence of the Al₂O₃ powder. The sintering studies indicated that in the absence of a suitable sintering aid, the whiskers significantly inhibited densification of the Al₂O₃ matrix. Doped composites containing yttrium isopmpoxide as a sintering aid were pressureless-sintered to final densities 95% of theoretical.     

Mechanical properties of Al2O3 and Al2O3 + ZrO2 ceramics reinforced by SiC whiskers

The effect of the SiC whisker content on the mechanical properties of Al₂O₃ and Al₂O₃ + 20 vol% ZrO₂ (2 mol% Y₂O₃) ceramic composites has been investigated. It is shown that the strength and fracture toughness of the composites are increased by the addition of 0–30 vol% SiC whiskers with only one exception that 30 vol% SiC whisker leads to a decrease in the flexure strength. The addition of 20 vol% ZrO₂ (2 mol% Y₂O₃) significantly improves the mechanical properties of the Al₂O₃ + SiC whisker (SiC_w) composites and the t-m phase transformation of ZrO₂ is enhanced by the residual stresses caused by the thermal incompatibility between the SiC_w and the matrix. The toughening effect of both SiC whiskers and the t-m phase transformation of ZrO₂ (2 mol% Y₂O₃) is shown to be additive, but the addition of ZrO₂ decreases the strengthening effect of the SiC whiskers.     

Synthesis of K2Ti4O9 whiskers

Potassium tetratitanate (K₂Ti₄O₉) whiskers were synthesized by the calcination and slow-cooling method. Powder X-ray diffraction (XRD) analysis and differential thermal analysis (DTA) were used to study the formation of K₂Ti₄O₉. In the slow-cooling calcination process, the control of cooling rate was crucial to growth of K₂Ti₄O₉ whiskers. The characterization of the whiskers was carried out by means of scanning electron microscope (SEM).     

Quantitative determination of the stability of SiC whisker in reaction-bonded/hot-pressed Si3N4 composites by X-ray diffraction

A method was developed for the quantitative determination of weight fractions of the phases in SiC whisker-reinforced reaction-bonded Si₃N₄ composites using X-ray diffraction. Composites with different amounts of sintering additives and whiskers were fabricated using reaction bonding followed by hot pressing. The amount of whiskers remaining in each composite after each processing stage was determined. In order to study the degradation mechanism, the microstructural development after each processing step was examined using scanning and transmission electron microscopy. Finally, the effect of sintering additives on the microstructural development and whisker stability was also investigated.