Black composites, alumina

Compositions of high-alumina cement containing quartz or glass, calcium carbonate, microsilica, carbon black, iron oxide red mud or screened fly ash, and styrene-butadiene latex have been described [141,1803,1804]. 

Cortinas et al. [89] eliminated colloidal suspended material (pitch) from kraft black liquors and partly recycled the liquor to the digester to reduce the consumption of chemicals. The colloidal pitch is formed by wood extractives. In particular, compounds such as waxes, sterols, and sterol esters that do not form soluble salts or dissolve during cooking form colloidal particles. The concentrated liquors (14%-15% solids) were filtered at high temperature using a 0.2 xm alumina membrane (USF Shumacher, Crailsheim, Germany). The pitch was almost completely retained (>99.9%), but the flux was sensitive to the black liquor composition and sometimes decreased to less than 100 L/(m h). 

However, the powders prepared as calcination temperatures at 1300°C and at 1400°C were composite particles with black particles incorporated into the white particles (Figs 2 and 3). EDX revealed that the white particles were alumina and the black particles were zirconia. This demonstrated that when the powders were calcinated at 1300X or 1400 C, the zirconia became incorporated with the alumina to form composite particles. 

Figure 2.TEM micrograph of Ce-TZP/Al203 mixture calcined at 1300 °C. A TEM micrograph showed composite particles with black particles (zireonia) incorporated into the white alumina particles.

But PVC forms many composite materials with particulate and fibrous fillers. Cellulose fiber and newsprint recycled fiber are two common examples of fibrous materials. The list of powders is longer, including talc, mica, clay, wood flour, carbon black, glass beads, hydrotalcite, alumina trihydrate, polypyrrole, and various nano-materials including nano-calcium carbonates. 

The effects of composite formation are not only restricted to the improvement of mechanical properties, such as toughness, tensile strength, and many other, but also include, improvement of thermal and electric conductivities (carbon black, pol yrrole), reduction of water migration (platelet fillers such as talc and mica), improvement fire resistance (alumina trihydrate), improvement of quality (wood-like feel with wood filler), and decorative value. 

Specific fillers may be added to add or enhance specific properties in magnetic materials. Alumina, antimony trioxide or magnesium carbonate may be added to improve the flame retardant properties of the composite. The addition of lead oxide or carbide lead is suggested for improve resistance to nuclear radiation. To improve thermal conductivity, alumina, aluminium powder or silicates can be added. Silica, talc, mica or kaolin are indicated to increase the electrical resistance. The inclusion of metal powders, metal oxides or silicates are suggested to thermal absorption improvement. To increase the tensile strength in NR-based materials, carbon black in general, fibres or polymeric materials may be added. 

The earliest HTCC structures were produced using 92% alumina [17]. Today, this composition remains a "workhorse" material. As shown in Table 6.1, there is a variety of AI2O3 formulations in commercial production. Manufacturers tend to maintain some secrecy as to the specific ingredients however, in addition to purity, the color of alumina ceramics is a distinguishing characteristic. Kyocera s "black" ceramic (90%) is actually a deep-red composition resulting from the inclusion of a small amount of Cr203. Other additives (W, Mo, and Ti) have also been included in HTCC to darken the ceramic. This opacification has no functional benefit although it eliminates the visibility of subsurface metallization. Ceramic vendors introduced this... 

The four combinations above can be observed in an equilibrium, however in practice the ceramic part may appear black and the conductor part may appear reddish brown. If a glass/alumina composite using glass... 

Organic-ceramic composites may use an epoxy as the matrix and glass or ceramic powder as the filler. A common example is the fiberglass-reinforced epoxy used as a printed circuit laminate. An epoxy substrate filled with alumina and carbon black has also been developed. By weight, the composition is 10.8 percent epoxy resin, 89 percent alumina, and 0.2 percent carbon black. This material has a thermal conductivity of 3.0 to 4.0 W/(m K), compared to both glass-epoxy printed circuit material [0.2 W/(m K)] and glass-alumina low temperature cofired substrates [2.5 W/(m K)]. The TCE (17 ppm/°C) is substantially below that... 

Moreover, similar alumina/ SiC composite was also prepared by substituting the raw carbon powder from the carbon black fine powder to mixed fullerene powder (nanomix. Frontier Carbon, Ltd., Japan). The composite was expected to include smaller SiC nanometer sized particles than ASI8NP. Also the alumina/ SiC composite is abbreviated as ASI8NPF in this paper. 

Using nanometer-sized carbon black and mixed fullerene as raw carbon powder, the present authors succeeded to fabricate alumina composites containing nanometer-sized SiC particles whose particle sizes are 20-50 nm and less than 10 nm, respectively. The self-healing behaviors of the prepared composites were investigated at several temperatures. 

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