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…
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…
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-…
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…
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…
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,…
The Meissner effect is an expulsion of a magnetic field from a superconductor during its transition to the superconducting state. T he German physicists Walther Meissner and Robert Ochsenfeld discovered the phenomenon in 1933 by measuring the magnetic field distribution outsidesuperconducting tin and lead samples. The interior of a bulk superconductor cannot be penetrated by a weak magnetic field, a phenomenon known as the Meissner effect. When the applied magnetic field becomes too large, superconductivity breaks down. Superconductors can be divided into two types according to how thisbreakdown occurs. In type-I superconductors, superconductivity is abruptly destroyed via a first order phase transition when the strength of the applied field rises above a critical value Hc. Type-II superconductor is characterized by the formation of magnetic vortices in an applied magnetic field. This occurs above a certain critical field strength Hc1. The vortex density increases with increasing field strength. At a higher critical field Hc2, superconductivity is completely destroyed.
Superconductivity is the ability of certain materials to conduct electrical current with no resistance and extremely low losses. This ability to carry large amounts of current can be applied to electric power devices such as motors and generators, and to electricity transmission in power lines. For example, superconductors can carry as much as 100 times the amount of electricity of ordinary copper or aluminum wires of the same size. Scientists had been intrigued with the concept of superconductivity since its discovery in the early 1900s, but the extreme low temperatures the phenomenon required was a barrier to practical and low-cost applications. This all changed in 1986, when a new class of ceramic superconductors was discovered that "superconducted" at higher temperatures. The science of high-temperature superconductivity (HTS) was born, and along with it came the prospect for an elegant technology that promises to "supercharge" the way energy is generated, delivered, and used.
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.
