Fired ceramics

Deteriora.tlon. Ceramic objects are fragile, and mechanical damages through breakage and abrasions are the most likely source of destmction. Low fired ceramics can suffer through the rehydration of the body material this process results ia a complete loss of mechanical streagth. The preseace of soluble salts ia porous ceramic bodies has the same disastrous results as ia stoae (136). 

The most significant commercial product is barium titanate, BaTiO, used to produce the ceramic capacitors found in almost all electronic products. As electronic circuitry has been rniniaturized, demand has increased for capacitors that can store a high amount of charge in a relatively small volume. This demand led to the development of highly efficient multilayer ceramic capacitors. In these devices, several layers of ceramic, from 25—50 ]lni in thickness, are separated by even thinner layers of electrode metal. Each layer must be dense, free of pin-holes and flaws, and ideally consist of several uniform grains of fired ceramic. Manufacturers are trying to reduce the layer thickness to 10—12 ]lni. Conventionally prepared ceramic powders cannot meet the rigorous demands of these appHcations, therefore an emphasis has been placed on production of advanced powders by hydrothermal synthesis and other methods. 

Filtered-Particle Inspection. Solids containing extensive inteiconnected porosity, eg, sintered metallic or fired ceramic bodies formed of particles that ate typically of 0.15-mm (100-mesh) screen size, are not inspectable by normal Hquid penetrant methods. The preferred test medium consists of a suspension of dyed soHd particles, which may be contained in a Hquid vehicle dyed with a different color. Test indications can form wherever suspensions can enter cracks and other discontinuities open to the surface and be absorbed in porous material along interior crack walls. The soHd particles that form test indications ate removed by filtration along the line of the crack at the surface where they form color or fluorescent indications visible under near-ultraviolet light (1,3). 

Bulk ceramics are produced conventionally by the sintering of powders. The strength, toughness, thermal stability, and dielectric properties of the fired ceramic depend strongly on the size and uniformity of the precursor powder and on the chemical properties of the powder smface. 

Fired ceramic spheroids have been described for use as a well proppant [1051], Each spheroid has a core made from raw materials comprising mineral particulates, silicium carbide, and a binder. The mixture includes a mineral with chemically bound water or sulfur, which blows the mixture during firing. Therefore the core has a number of closed air cells. Each spheroid has an outer shell surrounding the core, comprising a metal oxide selected from aluminum oxide and magnesium oxide. The fired ceramic spheroids have a fired density less than 2.2 g/cm. ... 

Pricing as well as reliability considerations have led to an almost exclusive use of Si-based (i.e. Si and SOI) micro machined devices. Packaging and assembly has focused on ceramics (A1203, AIN, Low Temperature Co-fired Ceramics LTCC), Printed Circuit Board (PCB-) and Surface Mount Device (SMD-) technology and multichip modules (MCM s). 

The theory behind chemical provenancing of ceramics is extremely simple -perhaps to the point of being naive. It is assumed that the chemical composition of the fired ceramic is indicative of the chemical composition of the principal raw material - clay. It has always been acknowledged that the transformation of raw clay into fired pottery is potentially a complex process, which might involve a number of factors, all of which could influence the final composition of the product. These include ... 

The discovery of the working properties of clays must have resulted in one of humankind s first expressions of representational art, roughly contemporaneous with the discovery of the colouring properties of natural pigments and their use in cave art. The additional discovery that the result of the manipulation of this art form could be rendered permanent by the use of fire must indeed have been a source of wonder. The earliest fired ceramic so far known is a small moulded figurine from Dolni Vestonice in what was Czechoslovakia, dated to approximately 26000 years BP (Vandiver et al., 1989). By approximately 10000 years ago, simple utilitarian vessels were being produced in the Near and Far East. 

One profitable line of enquiry has been the application of the concept of CEC, familiar in the study of clays, but only sporadically applied to fired ceramics (e.g., Hedges and McLellan, 1976). This is an experimental measure of the proportion of exchangeable cations held by the clay (or ceramic), and may... 

For these and other reasons, it has become commonplace to compare fired ceramic material with fired ceramic material assumed to be representative of a particular production centre. Material of assumed provenance can be used, but, for preference, kiln wasters are often used as comparative material. These are vessels that have failed in the firing for some reason, and... 

LIGA lithographie, galvanoformung, abformtechnik LTCC low-temperature co-fired ceramics MEMS microelectromechanical systems... 

LTCC low-temperature co-fired ceramic (an aluminum borosilicate) Luminol 5-amino-2,3-dihydro- 1,4-phthalazinedione... 

Over the past two decades MLC technology has been progressively developed for advanced packaging, especially by main frame computer manufacturers, and it is increasingly exploited for microwave communications. Especially significant is the emergence of low temperature co-fired ceramic (LTCC) technology. 

TFML interconnections can be fabricated on a variety of substrates, including ceramics, metals, or silicon wafers. An approach proposed by Honeywell (8), which uses a multilayer co-fired ceramic substrate, is illustrated in Figure 1. The co-fired ceramic substrate is 50-100 mm square, with internal metal layers for power and ground distribution and pins brazed to the bottom for connection to a PWB. Metallized strips on the bottom of the substrate contact the PWB to conduct heat away from the package. A metal seal ring around the perimeter of the substrate permits hermetic sealing to provide mechanical and environmental protection for the chips and interconnections. 

In-plant impregnation of low-fired ceramic products. Low-fired ceramic products such as roof tiles, facing tiles and unglazed floor tiles are made water repellent by immersing them in dilute silicone masonry water repellents thereby preventing efflorescence and imparting water repellency (Wacker-Chemie, 1982). Prefabricated concrete components, plaster of paris and aerated concrete can also be treated in this way. 

The ability to control temperature in a furnace or oven as exemplified by the appearance of high-fired ceramics and glasswork was also evidenced in the flourishing trade and production of metals that began in... 

The fired ceramic body is a mixture of two phases mullite and silica. Mullite, a rare mineral in nature, takes the form of needlelike crystals that interpenetrate and confer strength on the ceramic. When the temperature is above 1470°C, the silica phase forms as minute grains of cristobalite, one of the several crystalline forms of Si02. 

If chemically pure kaolinite is fired, the finished ceramic object is white. Such purified clay minerals are the raw material for fine china. As they occur in nature, clays contain impurities, such as transition-metal oxides, that affect the color of both the unfired clay and the fired ceramic object if they are not removed. The colors of the metal oxides arise from their absorption of light at visible wavelengths, as explained by crystal field theory (see Section 8.5). Common colors for ceramics are yellow or greenish yellow, brown, and red. Bricks are red when the clay used to make them has high iron content. 

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