Potassium whisker

Small single crystals, such as those of potassium titanatc, are being used at an annual rate of over 10,000 tons for the reinforcement of nylon and other thermoplastics. These composites are replacing die-cast metals in many applications. Another microfiber, sodium hydroxycarbonate (Dawsonite), also improves the physical properties and flame resistance of many polymers. Many other single crystals, called whiskers, such as alumina, chromia, and boron carbide, have been used for making high-performance composites. 

Finally, there are potassium titanate fibers that are produced by heating titanium dioxide and potassium carbonate in a furnace to produce whisker-like short fibers, about 0.5 xm in diameter and 50 xm or more in length. Potassium... 

More than 100 different materials have to date been produced as whiskers and characterized. However, only SiC- (50 to 100 t, 1996) and potassium titanate whiskers (ca. 5000 t) have achieved commercial importance. Important properties of whiskers are summarized in Table 5.2-18. 

Silicon carbide whiskers are generally manufaclured by a metal-catalyzed process, in which carbon and silicon are condensed from the gas phase. Another jtroccss utilizes rice husks decomposed at 500°C. At temperatures of 1800°C the carbon/Si02-mixture formed is converted into a-SiC. Potassium titanate whiskers are synthesized from potassium molybdate, potassium carbonate and litanium dioxide at temperatures above 1200°C. 

Aluminium titanate (tielite, Al2Ti05) has excellent thermal shock resistance but poor mechanical strength which can, however, be improved by reinforcing with whiskers of a related phase such as potassium hollandite (K2Al2Ti60i6). Such composites can be formed by thermal decomposition of sol-gel precursors, reaction sintering of the two phases or by thermal treatment of an appropriate glass-ceramic material. Al MS NMR has been used to study the co-formation of these two phases during thermal treatment, and indicates that hollandite crystallises as whiskers within the tielite matrix (Kohn and Jansen 1998). 

Potassium titanate whiskers were found to improve the tribological properties of NAO friction materials. These soft, synthetic refractory materials stabilize friction level, reduce pad wear, noise, fade, thermal conductivity, control porosity, and provide thermal reinforcement. Fibrous potassium titanates are being replaced by platelet and powder versions because of health concerns associated with respirable fibers. 

The growth mechanism appears to be the same, irrespective of the hydrocarbon. However, the resulting morphology depends not only on the metal and particle size but also on the type of hydrocarbon and the reaction temperature. The importance of step sites on the catalyst surface for the nudeation of carbon was recently confirmed by in situ investigations employing high resolution transmission electron microscopy the results indicate the segregation of carbon when the formation of whiskers takes place at specific sites on the nickel surface. The addition of potassium to the nickel catalyst leads to an increase in the induction period (t ) for CH4 decomposition, which... 

Tjong, S. C. and Meng, Y. Z. 1999. Microstructural and mechanical characteristics of compatibilized polypropylene hybrid composites containing potassium titanate whisker and liquid crystalline copolyester. Polymer 40 7275-7281. 

Chen, S., Wang, Q., Wang, T., Pei, X. Preparation, damping and thermal properties of potassium tltanate whiskers filled castor oil-based polyurethane/epoxy Interpenetrating polymer network composites. Mater. Des. 32, 803-807 (2011)... 

Well dispersed potassium titanate whiskers can serve as partially heterogeneous nucleating agents in PEEK resin to promote its crystallization, which is beneficial in increasing the mechanical and tribological properties of PEEK. ... 

Carbon fibres Potassium titanate Silicon carbide whiskers Other inorganic crystalline fibres... 

Crocidolite or potassium octatitanate whisker instilled intratracheally into male Wistar rats (2 mg in saline) peaked levels of IL-la mRNA in alveolar macrophages at 1 month thereafter (Tsuda et al. 1997). 

Four weeks after intratracheal instillation of 2 mg of respirable potassium titanate whiskers into male Wistar rats RNA extracted from LPS stimulated alveolar macrophages expression of IL-la was increased (Tsuda et al. 1996,1997). The expression of IL-la mRNA was by fibres was greatest in potassium octatitanate whisker > UICC crocidolite > UICC chrysotile > refractory ceramic fibre-instilled rat alveolar macrophages. The levels of IL-la and TNF-a mRNA in alveolar macrophages (expressed in their ratio to P-actin) peaked at 1 month and 3 days after exposure to octatitanate, respectively. 

Another approach for inhibition of carbon formation is to retard the full dissociation of the hydrocarbon into adsorbed carbon atoms. The presence of potassium on a nickel catalyst results in a significant increase in the induction period for nucleation of carbon whiskers (refer to Figure 5.6). It means that potassium works as promoter also without the presence of water. 

Huai-Yuan Wang, Xiao-Hua Lu, Yi-Jun Shi, and Xin Feng. "Tribological behavior of polyfether ether ketone) composites filled with potassium tita-nate whiskers sliding in different media." Journal ofAppliedPolymer Science, pp. 1935-1941,2010. 

Jiazhen Lu, Xiaohua Lu. Elastic interlayer toughening of potassium titanate whiskers-nylon66 composites and their fractal research. 

Potassium titanate whiskers can be used as thermal insulation material, electrical insulating material, catalyst carriers, filtration material, friction material, and so on based on their special performances. In addition, they are applied as... 

Higher tensile strength than potassium titanate whiskers... 

The self-assembly method has attracted much attention because it can form monomolecular films on the surface of many matrixes, such as silicon oxide and titanium oxide. Considering potassium titanate whiskers as an example, the similar surface structure (Ti-O) between potassium titanate whiskers and titanium oxide means there is some comparability between them. 

Wang et al. surface modified potassium titanate whiskers (PTW) using the self-assembly of octadecyl trichloro silane (OTS). The process is as follows. Add 0.5 mL of OTS to the suspension liquid of whiskers (10 g) and heptane (200 ml) with stirring and continue stirring for 20 minutes after the whiskers are evenly dispersed in the solution. Then the mixture is filtered and washed several times to remove dissociative OTS and dried in a vacuum. 

As shown in Table 3.16, the whiskers modified with OTS have lower surface energy, lower polar component, and better hydrophobic and lipophilic properties than untreated whiskers. The dispersive component ratio of potassium titanate whiskers modified with OTS to OTS molecules is much closer to the dispersion value of the -CH2- group rather than the -CH3-group, which indicates that the whisker surface modified with... 

Table 3.16 Surface Energy, Dispersive, and Polar Components of Unmodified/Modified Potassium Titanate Whiskers...

Table 3.17 shows the adsorption work and interfacial tension of potassium titanate whiskers before and after modification with OTS with water and benzene. After modification with OTS, the adsorption work of modified whiskers to oil is lower than to water, and the interfacial tension of whiskers to water increases while that to oil is close to zero. These prove that whiskers treated with OTS have more typical hydrophobicity and lipophilicity. 

Table 3.17 Adsorptive Work and Interfacial Tension of Potassium Titanate Whiskers before and after Modification with Water...

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