Ceramic paste mixtures

Hypothetical ceramic paste mixtures are generated from clays and tempers of known concentrations by calculating elemental concentrations according to... 

Heated Mineral Mixtures Related to Ancient Ceramic Pastes... 

Several studies of the effects of heating on pure clays have been reported in archaeological literature, but very little systematic work has been done on the effects of admixed mineral impurities upon the clays that constitute ceramic paste. The purpose of this chapter is to study the controlled firing of four measured mixtures of the clays, kaolinite and montmorillonite, with the common carbonates, calcite and dolomite. 

This study is concerned with four different mixtures, including kaolinite and calcite (kc) kaolinite and dolomite (kd) montmorillonite and calcite (me) and montmorillonite and dolomite (md). All the mixtures, by weight, were 95% clay and 5% carbonate mineral. The minerals were first ground to a fine powder and thoroughly mixed by hand before heating in a muffle furnace (temperature controlled to within 20 °C). Each mixture was heated for 1 h, air quenched at room temperature, and analyzed by X-ray diffraction. X-ray films were made in cameras of 11.46-cm diameter with filtered copper radiation and exposure times of 6 h. Several wet mixtures that simulated ceramic paste before firing were heated and studied in like manner, but they showed no differences from the dry mixtures. 

The mineral phases observed in this study are summarized in Table II. For each phase, the mixtures that yielded them and their observed temperature stability ranges are given. When these phases are encountered in X-ray diffraction studies of ceramic pastes, it should be possible to determine the maximum temperature at which the ceramic was heated, providing it did not exceed 1100 °C and contained a mixture close to the clay-carbonate... 

Originally for the extrusion of ceramic bricks and tiles, clay and water were used to endow ceramic particle mixtures with sufficient plastic behavior to permit practical shaping of the ceratnic bodies. High performance ceramics, however, often require the elimination of clay from extrusion formulations because the chemistry of the clay is incompatible with that of the desired ceramic materials. Therefore organic materials are frequently used in ceramic extrusion to provide plastic flow. Not only plastic behavior is important for the extrusion of ceramic bodies. There are many other characteristics which can be tailored by the suitable addition of organics in a ceramic extrusion paste, or feedstock. 

Clay was supplied by a clay quarry located in Bailen, Jaen (Spain) and was obtained by mixing three types of raw clay in equal parts red, yellow and black clay. Clay was crushed and ground to yield a powder with a particle size suitable to pass through a 150 pm sieve. The waste, olive wastewater and olive oil wastewater were supplied by a local olive oil extraction plant and used directly without any prior pretreatment. The ceramic paste for the extrusion was prepared by adding fresh water (FW) or residue resulting from olive oil extraction (OW or OOW) to the clay in a mixer. The amoimt of added water in the mixer depends on clay plasticity and on its consistency while performing the extrusion. In the present work 22 wt % of FW, OW or OOW was added to the clay. The same value as used at industrial scale for this kind of clay mixture. Extrusion was carried out in a laboratory Venco extruder. Extruded test pieces were dried at room temperature for about 24 h, and then heated in an oven at 110 °C until constant weight for at least 24 h. 

Metal powder—glass powder—binder mixtures are used to apply conductive (or resistive) coatings to ceramics or metals, especially for printed circuits and electronics parts on ceramic substrates, such as multichip modules. Multiple layers of aluminum nitride [24304-00-5] AIN, or aluminay ceramic are fused with copper sheet and other metals in powdered form. The mixtures are appHed as a paste, paint, or slurry, then fired to fuse the metal and glass to the surface while burning off the binder. Copper, palladium, gold, silver, and many alloys are commonly used. 

Slip-casting of technical ceramics has been steadily introduced over the past 60 years or so, and now it is standard practice to cast alumina crucibles and large tubes. The process has been successfully extended to include silica, beryllia, magnesia, zirconia, silicon (to make the preforms for reaction-bonded silicon nitride articles) and mixtures of silicon carbide and carbon (to make the preforms for a variety of self-bonded silicon carbide articles). Many metallics and intermetallics, including tungsten, molybdenum, chromium, WC, ZrC and MoSi2, have also been successfully slip-cast. 

Pyrometric cones (Figure 1.1) have been in common use over the past century in the manufacture of ceramic ware. They are a series of fired mixtures of ceramic materials pointing 8° from vertical, which droop after exposure to elevated temperatures for a period of time. The manufacturer [4] provides a series of sixty-four cone numbers ranging from 022 (deformation at 576°C at a heating rate of l°C/min) to 42 (over 1800°C).3 By placing a series of cones near the firing ware in a kiln, the operator can determine when firing of the ware is complete, even when the furnace temperature is only loosely controlled. The refractories industry has made cone shapes out... 

In ceramics, the term plastic mass or paste denotes an easily workable mixture which keeps its shape after forming. Up to a certain stress, such a mixture behaves as a solid and exhibits approximately elastic behaviour. It is irreversibly deformed only beyond a critical stress called the yield point. Beyond the yield point its behaviour can be characterized by the respective deformation rate from which the so-called plastic viscosity can be determined. The rheological behaviour involved is essentially of the... 

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