Needl-like materials

Inorganic whiskers, a kind of single crystal fibrous or needle-like material that appeared in recent years, are used to reinforce thermosetting resin, thermoplastic resin, rubber, metal, and ceramics through filling and to prepare advanced engineering plastic, composite materials, adhesive, sealant, and paint. The excellent performances of inorganic whiskers have led to their wide application as composite materials- ... 

Besides the expected glassy carbon structure, the resulting product often contained considerable amounts of needle-like material that was determined to have a three-dimensional graphitic structure. The graphitic whiskers resulting from the experiments were usually a few microns long and about 1 (tm thick. Electron diffraction and transmission electron microscopy (TEM) revealed the twinned structure of the whiskers. The angle between the layers was measured to be about 135°. 

The polycrystaliine 2W(a)-TaS2 should be free-flowing and in the form of black platelets. Any gold-colored material indicates the presence of the 1T phase and results from improper annealing. Further, the presence of a fibrous or needle-like material indicates incomplete reaction of the tantalum. This fibrous material is most likely TaSj, which decomposes above 650°. ... 

When sublimed, anthraquinone forms a pale yeUow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286°C and boils at 379°—381°C. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubiUty in alcohol or benzene and is best recrystallized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the it spectmm, the double aUyflc ketone absorbs at 5.95 p.m (1681 cm ), and the aromatic double bond absorbs at 6.25 p.m (1600 cm ) and 6.30 pm (1587 cm ). 

Accelerated aging and crystal transformation rates have also been traced to high residual moisture content. Ando et al. studied the effect of moisture content on the crystallization of anhydrous theophylline in tablets [9]. Their results also indicate that anhydrous materials convert to hydrates at high levels of relative humidity. In addition, if hygroscopic materials (e.g., polyethylene glycol 6000) are also contained in the formulation, needle-like crystals form at the tablet surface and significantly reduce the release rate of the theophylline. 

Fig. 17. Confocal fluorescence imaging of [Zn(ATSM)] in IGROV cells (100 pM, where Q1 — Q2 = Me, M = Zn(II), R1 = R3 = H and R2 = R4 = Me, /ex = 488 nm, DMEM with 1% DMSO). Brightfield image shows formation of needle-like crystalline material on the cell plate (N.B. Small crystallites may be endocytosed by the cells rather than passively diffuse through the cell membrane).

Physical state White solid with needle-like crystals. Produced by chlorination of molten phenol. Technical-grade material is dark gray to brown... 

An important consideration of reactions in which a new solid phase appears is the number, source and location of nucleation sites and the form of the new phase. A needle-like new phase can result in a marked apparent expansion of the material leading to particle disintegration in packed beds. 

The nature and relevance of colloids is one of the main current research topics (Birdi, 2002). They are an important class of materials, intermediate between bulk and molecularly dispersed systems. Colloid particles may be spherical but, in some cases, one dimension can be much larger than the other two (as in a needle-like shape). The size of particles also determines whether they can be seen by the naked eye. Colloids are not visible to the naked eye or under an ordinary optical microscope. The scattering of light can be suitably used to see such colloidal particles (such as dust particles, etc.). Their size then may range from 1() 4 to 1() 7 cm. The units used are as follows ... 

Wollastonite is a form of calcium silicate (CaSiOj). It is a relatively hard (Moh hardness 4.8) white material with needle-like particles. The specific gravity is... 

Further, it may often be desired to identify poorly formed crystals such as needle-like crystals without definite faces, or skeletal growths, or even completely irregular fragments. This can only be achieved by measuring some properties of the crystal material itself, properties which are independent of the shape of the crystals. Of such properties, by far the most important and the most convenient for measurement are the optical properties, especially the refractive indices. An elemen-... 

Large, needle-like grains, or large, needle-like grains in a fine matrix Fine grained or ass// ss or ass materials Fine grained/needle-like grains... 

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