Material Science

Common plastics and their typical uses

Polyethylene (PE) wide range of uses, very inexpensive Polypropylene (PP) food containers, appliances Polystyrene (PS) packaging foam, food containers, disposable cups, plates and cutlery Polyethylene terephthalate (PETE) beverage containers Polyamide (PA) (Nylon) fibers, toothbrush bristles, fishing line Polyester (PES) fibres, textiles Polyvinyl chloride (PVC) plumbing pipes, flooring, shower curtains, erotic clothing Polycarbonate (PC)…

September 14, 2021 · Jacob

Material Science

Types of Polymers/plastics

Thermosetting plastics (thermosets) are polymer materials that cure, through the addition of energy, to a stronger form. The energy may be in the form of heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation. Thermoset materials are usually liquid, powder, or malleable prior to curing, and designed to be molded into their final form, or used as adhesives. The curing process transforms the resin into a plastic or rubber by a cross-linking process. Energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated…

September 14, 2021 · Jacob

Material Science

Applications and Processing of Polymers/ Plastics

Plastic covers a range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or economics. There are few natural polymers generally considered to be “plastics”. Plastics can be formed into objects or films or fibers. Their name is derived from the fact that many are malleable, having the property of plasticity. Plastic can be classified in many ways but most commonly by their polymer backbone (polyvinyl chloride, polyethylene, acrylic, silicone, urethane, etc.). Other classifications include thermoplastic vs. thermoset, elastomer, engineering plastic, addition or condensation, and Glass transition temperature or Tg. A lot of plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures at which the degree of cross-linking is substantially reduced). Plastics are polymers: long chains of atoms bonded to one another. These chains are made up of many repeating molecular units, or “monomers”. The vast majority of plastics are composed of…

September 14, 2021 · Jacob

Material Science

Fabrication and processing of ceramics

Ceramic Synthesis Our expertise and capabilities in synthesizing ceramics are based onchemical solution techniques. Chemical solution or sol-gel approaches have beendeveloped to fabricate powders, films, and porous bodies. Materials of interest range from silica to complex, multicomponent electronic ceramics. The complexity inherent in fabricating materials with structured nanoporosity or complex chemistries requires a fundamental understanding of these chemical solution approaches. Fabrication of unique precursors for complex oxides is being done with novel metal alkoxide chemistry to produce powders and thin-film materials with carefully controlled properties. Our ability to synthesize materials with complex structures, chemistries, or both, is at the heart of numerous research and development efforts at Sandia. Ceramic Processing Sandia’s fabrication of ceramic components and devices is based on a strong ceramic-processing capability. We recently have demonstrated the ability to characterize and model the powder- compaction process in detail, and to address and control density gradients in powder compacts that cause shape distortion and differential shrinkage. Proprietary 3D, finite-element code packing and compaction models, and process-control tools are now available to improve the production of ceramic components. Sandia…

September 14, 2021 · Jacob

Material Science

Portland Cement

Portland cement is a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other compounds, to which gypsum is added in the final grinding process to regulate the setting time of the concrete. Some of the raw materials used to manufacture cement are limestone, shells, and chalk or marl, combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore. Lime and silica make up approximately 85 percent of the mass The term “Portland” in Portland cement originated in 1824 when an English mason obtained a patent for his product, which he named Portland Cement. This was because his cement blend produced concrete that resembled the color of the natural limestone quarried on the Isle of Portland in the English Channel. Different types of Portland cement are manufactured to meet different physical and chemical requirements for specific purposes. Common…

September 14, 2021 · Jacob

Material Science

Types and applications of ceramics

Ceramics offer a high temperature range. However, ceramics are not very strong. To compensate for their lack of strength ceramics are usually combined with some other material to form a ceramic composite. 1) Glasses and glass ceramics- The glasses are a familiar group of ceramics; containers, windows, lenses and fiberglass represent typical applications. The properties of standard vitrified products are insufficient for architectural applications and structural building components, insulation or other specialized applications. Yet there is an effective way to improve these properties without major alterations to the process itself – the introduction of a controlled crystallization process through a subsequent heat treatment, i.e. by forming a glass-ceramic. Production of Glass-Ceramics Glass-ceramic articles may be produced by three routes: • The heat treatment of solid glass (the traditional route) • The controlled cooling of a molten glass, known as the petrurgic method • The sintering and crystallisation of glass powders. In the latter case, the powders are densified at relatively low temperatures by exploiting a viscous flow sintering mechanism. After densification, the material is subjected to a crystallisation heat- treatment to obtain the required glass-ceramic microstructure. Alternatively, both densification and crystallisation may take place during…

September 14, 2021 · Jacob

Material Science

Ceramics (Applications and Processing)

Ceramics encompass such a vast array of materials that a concise definition is almost impossible. However, one workable definition is: Ceramics can be defined as inorganic, nonmetallic materials. They are typically crystalline in nature and are compounds formed between metallic and nonmetallic elements such as aluminum and oxygen (alumina-Al2O3), calcium and oxygen (calcia – CaO), and silicon and nitrogen (silicon nitride-Si3N4). Ceramics is a refractory, inorganic, and nonmetallic material. Ceramics can be divided into two classes: traditional and advanced. Traditional ceramics include clay products, silicate glass and cement; while advanced ceramics consist of carbides (SiC), pure oxides (Al2O3), nitrides (Si3N4), non-silicate glasses and many others. Ceramics offer many advantages compared to other materials. They are harder and stiffer than steel; more heat and corrosion resistant than metals or polymers; less dense than most metals and their alloys; and their raw materials are both plentiful and inexpensive. Ceramic materials display a wide range of properties which facilitate their use in many different product areas. In general, most ceramics are: – hard, – wear-resistant, – brittle, – refractory,…

September 14, 2021 · Jacob

Material Science

Conduction in Ionic Materials

In ionic materials, the band gap is too large for thermal electron promotion. Cation vacancies allow ionic motion in the direction of an applied electric field, this is referred to as ionic conduction. High temperatures produce more vacancies and higher ionic conductivity. At low temperatures, electrical conduction in insulators is usually along the surface, due to the deposition of moisture that contains impurity ions.

September 14, 2021 · Jacob

Material Science

Semiconductor Devices

A semiconductor diode is made by the intimate junction of a p-type and an n-typesemiconductor (an n-p junction). Unlike a metal, the intensity of the electrical current that passes through the material depends on the polarity of the applied voltage. If the positive side of abattery is connected to the p-side, a situation called forward bias, a large amount of current can flow since holes and electrons are pushed into the junction region, where they recombine (annihilate). If the polarity of the voltage is flipped, the diode operates under reverse bias. Holes andelectrons are removed from the region of the junction, which therefore becomes depleted of carriers and behaves like an insulator. For this reason, the current is very small under reverse bias. The asymmetric current-voltage characteristics of diodes is used to convert alternating current into direct current. This is called rectification. A p-n-p junction transistor contains two diodes back-to-back. The central region is very thin and is called the base. A small voltage applied to the base has a large effect on the current passing through the transistor, and this can be used to amplify electrical signals (Fig. 19.22). Anothercommon device is the MOSFET transistor where a gate serves the function of the base in a junction transistor. Control of the current through the transistor is by means of the electric field induced by the gate, which is isolated electrically by an oxide layer.

September 14, 2021 · Jacob

Material Science

Electrical Resistivity of Metals

The resistivity then depends on collisions. Quantum mechanics tells us that electrons behave like waves. One of the effects of this is that electrons do not scatter from a perfect lattice. They scatter by defects, which can be: – atoms displaced by lattice vibrations – vacancies and interstitials – dislocations, grain boundaries – impurities One can express the total resistivity ρtot by the Matthiessen rule, as a sum of resistivities due to thermal vibrations, impurities and dislocations. Fig. 19.8 illustrates how the resistivity increases with temperature, with deformation, and with alloying..

September 14, 2021 · Jacob