Performance whiskers

This new sandwich structure effectively reduces and even prevents whisker formation, as shown in Table 1.2, because less stress is induced due to the much lower diffusion of both Cu and Sn. This innovative process fulfills the requirements of several currently implemented OEM whisker-reduction specifications. The product was introduced in 2004 with some high volume PCB manufacturers. The PCB manufacturers choosing to apply Ormecon immersion tin technologies can easily change between the standard immersion tin product Ormecon CSN FF and the high-performance, whisker-reducing immersion tin product Ormecon CSN FF-W. The difference between two such products is only the predip step. 

Composite powders, i.e., powder particles that are built up of alternating layers of different materials or particles with surfaces of a material other than the one of the interior are occasionally necessary as components in composites. Powder particles with modified surfaces can easily be made by means of CVD in a fluidized bed, which is of considerable interest because the nature of the interface between component phases in composites determines their performance. Whiskers and fibers... 

Figure 1.5 High performance whisker reinforcements compared to other materials...

High Strength Titanium Boride Whiskers, Japanese New Materials High Performance Ceramics (Jan. 1989)... 

Whipple s rules, 20 138 Whisker reinforcement, 5 554, 555, 654 performance in ceramic—matrix composites, 5 572-575 physical properties, 5 557t synthesis, 5 642-643 and toughening, 5 622 Whiskers, silicon carbide, 22 533-534 White... 

The graph shown in Figure 6.7 plots the strength versus the modulus of some typical fibres. Note the very special performance of the whiskers (single-crystal fibres). 

The main advantage of as-described heterocycUc single-source precursors compared to Lewis acid-base adducts is, that these don t tend to give MSb whiskers. Unfortunately, their volatility is much lower and the MOCVD process has to be performed under high-vacuum conditions (10 -10 mbar). In addition, the precursor has to be heated up to 130 °C in order to ensure a reasonable precursor hux rate. 

Whiskers can be incorporated into the metallic matrix using a number of compositeprocessing techniques. Melt infiltration is a common technique used for the production of SiC whisker-aluminum matrix MMCs. In one version of the infiltration technique, the whiskers are blended with binders to form a thick slurry, which is poured into a cavity and vacuum-molded to form a pre-impregnation body, or pre-preg, of the desired shape. The cured slurry is then fired at elevated temperature to remove moisture and binders. After firing, the preform consists of a partially bonded collection of interlocked whiskers that have a very open structure that is ideal for molten metal penetration. The whisker preform is heated to promote easy metal flow, or infiltration, which is usually performed at low pressures. The infiltration process can be done in air, but is usually performed in vacuum. 

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. 

Another graphical description of the data is used when comparing the results of several trials is the box plot (also called box-and-whisker plot). A box represents the range of the middle 50% of the data, and whiskers extend to the maximum and minimum values. A line is drawn at the median value. A glance a this plot allows one to assess the symmetry and spread of the data. Figure 5.4 is a box plot for the carbonate data of figure 5.2. Specific plots, such as Youden two-sample plots for method performance studies, are discussed below. 

SiC whisker-reinforced glass matrix composites were fabricated at the same process viscosity of the matrices and were well consolidated. All the composites were 30 wt% whiskers (No. 1) composites. The properties of these composites are given in Table 3.19. A comparison of the 1723 matrix composite and the 7052 composite shows that the latter is much weaker and has a lower modulus. Comparing the 7052 and 7740 systems, the 7740 composites are weaker still. A comparison of the 0080 and 1723 systems again shows a lower performance for the 0080 composite. 

Table 3.20 Comparison of whisker performance in code 1723 glass matrix composites10...

Studies have also shown that, since the amount of reinforcement added affects all mechanical and thermal properties, there is an optimum volume fraction of particle or whisker reinforcement that should be added to the matrix material to ensure superior resistance to thermal shock (Becher, 1981 Jia etal., 1996 Sbaizero and Pezzotti, 2003 Pettersson and Johnson, 2003). The shape of the reinforcement also plays an important role in determining behaviour under thermal shock. Sbaizero and Pezzotti (2003) showed that the use of coarse and elongated particles resulted in better CMC performance compared with the use of fine-grained particles. 

The behaviour of particle- and whisker-reinforced CMCs can be adequately described by using and adapting the models and methodology developed for monolithic ceramics. By contrast, analysis and modelling of the performance... 

Tatsumi K, Zaghib K, Abe H, Higuchi S, Ohsaki T, Sawada Y. A modification in the preparation process of a carbon whisker for the anode performance of lithium rechargeable batteries. J Power Sources 1995 54 425-427. 

Alternative approaches using box and whisker plots, pie charts and different types of visualizations of density functions are discussed in Ibrekk Morgan (1987) and Morgan Henrion (1990). Each has advantages for specific tasks, but the performance of a display depends upon the information that a subject is trying to extract (central tendency or variation). 

The most important polymeric matrices are linear and cross-linked polyesters, epoxy resins and linear and cross-linked polyimides the most important reinforcements are high-performance polymeric fibres and filaments (for polymeric composites), filaments of refractory metals and inorganic materials (E-glass, A12C>3, B, BN, SiC and Carbon) and whiskers (fibrillar single crystals of A1203, B4C, WC, SiC and C, exclusively for reinforcement of metals). 

SiC whiskers are known to vary in their physical and chemical characteristics from manufacturer to manufacturer and in some cases from batch to batch. While the differences can be quite minor, they can make major impacts in the performance of ceramic matrix composites both at room and elevated temperature. 

K. Xia and T. G. Langdon, The Mechanical Properties at High Temperatures of SiC Whisker-Reinforced Alumina, in High Temperature/High Performance Composites, Materials Research Society Symposium Proceedings, Vol. 120, eds. F. D. Lemkey, S. G. Fishman, A. G. Evans, and J. R. Strife, Materials Research Society, Pittsburgh, PA, 1988, pp. 265-271. 

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