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Calcite                    : CaCO3 Refractive Index         : 1.66-1.74 Specific Gravity         : 2.71 Mohs Hardness          : 3 Aragonite              : CaCO3 Refractive Index        : 1.68-1.69 Specific Gravity        : 2.95 Mohs Hardness         : 3.5-4 The mineral calcite is the major or sole constituent of most commercial calcium carbonate products. These include natural limestone, marble, and chalk, plus most precipitated calcium carbonate. Aragonite is a metastable polymorph of calcite that typically has an acicular crystal shape. Natural aragonite products are less common, but precipitated varieties are available. Many calcium carb...

Barite                  : BaSO4 Refractive Index   : 1.64-1.65 Specific Gravity   : 4.5 Mohs Hardness    : 3-3.5 The commercial significance of barite is related almost entirely to its high specific gravity. Most processed barite (90%) is used as a weighting agent in well drillling fluids. Its physical and chemical properties assume more importance for its filler applications and for its use as a source of barium. Common mineral impurities in barite ores are quartz, carbonate minerals, sulfide minerals, and clay. Processing of barite depends upon ore purity and the nature of associated minerals. Drilling grades often require only crushing, grinding, screening, and milling. An intermediate washing step may be employed to achieve required minimal specific gravity and BaSO4 content. Applications requiring high brightness and high chemical or mineralogical purity may necessitate flotation, bleaching with sulf...

Chrysotile            : Mg3Si2O5(OH)4 Refractive Index   : 1.53-1.56 Specific Gravity   : 2.5-2.6 Mohs Hardness    : 2.5-4 Asbestos is a generic term applied to six minerals that occur in nature as strong, flexible, heat-resistant fibers. Nearly all (>98%) commercial asbestos is the mineral chrysotile. Chrysotile is differentiated from the other five asbestos minerals by its tubular serpentine rather than ribbon-like amphibole structure, its generally greater fiber flexibility and strength, its lower heat resistance, its greater surface area and positive surface charge, its lower refractive index, and its greater susceptibility to decomposition by strong acids. Of the ampibole asbestos minerals, only two − amosite, a magnesium iron silicate, and crocidolite, a sodium iron silicate − are produced in commercial quantities.   The other three − anthophyllite asbestos, tremolite asbestos, and actinolite asbestos − are rare asb...

Pyrophyllite − If the kaolin structure is bound through shared oxygens to a layer of silica rings on its alumina side, the pyrophyllite structure of Figure 9 results.  Pyrophyllite Because both faces of a pyrophyllite platelet are composed of silica oxygens, interlaminar bonding is by relatively weak van der Waals forces. Pure pyrophyllite is therefore soft with talc-like slipperiness, because its laminae will slide past each other or separate fairly easily.

Kaolinite − When a layer of silica rings is joined to a layer of alumina octahedra through shared oxygens, as shown in Figure 8, the mineral kaolinite is formed. Kaolinite is the sole or dominant constituent of what is known as kaolin clay or simply kaolin. Kaolinite Kaolin may be considered the prototypical phyllosilicate in that its sheet structure results in platy or flake-shaped particles that occur as overlapping, separable layers. Because an individual kaolin particle has an oxygen surface on one side and an hydroxyl surface on the other, it is strongly hydrogen bonded to the laminae above and below it. These particles stack together in such a way that under magnification they look like sheaves of paper and are often called “books”. It is difficult to delaminate kaolin books into individual platelets, although this is done commercially. Compared to the silica, feldspar, and chain silicate structures, kaolin, and phyllosilicates in general, are relatively soft and lo...

Among the industrial minerals high terahedra density and consequent hardness are also found in chain silicates. Wollastonite is characterized by the repeating, twisted, three-tetrahedra unit depicted in Figure 5. Wollastonite   The chains formed by these silica tetrahedra are connected by calcium in octahedral coordination. Because of this chain structure wollastonite can occur as acicular crystals, in some cases of  macroscopic dimensions. This acicular particle shape is important in certain uses as a functional mineral filler.

Similar dense-packed tetrahedra characterize the crystal framework of feldspar minerals, as depicted in Figure 4. Feldspar   This figure shows a single layer viewed perpendicular to its plane. The framework is extended by rotating each successive layer 90 degree. Feldspars usually have one of every four Si4+ substituted with Al3+. The resulting charge imbalance is compensated by sodium, and/or potassium ions. Some feldspars have half their silicon replaced by aluminum with calcium balancing the framework charge. Feldspars are nearly as hard as quartz and are exploited for their chemistry in glassmaking and ceramics, since the aluminum content improves chemical and physical stability while its alkali content provides fluxing action.

The fundamental structural unit of industrial silicate minerals is the silica tetrahedron. Quartz is just a densely packed arrangement of these tetrahedra, as depicted in Figure 3.  Quartz Extended in three dimensions, this structure provides the characteristic hardness and inertness of quartz. The different forms of crystalline silica − most commonly quartz, cristobalite, and tridymite − differ mainly in the relative orientation of adjacent tetrahedra and the shape of voids created within a given plane.

                                             ELECTRICITY AND WATER ARE A DEADLY COMBINATION Underwater welder Underwater welders are specialised engineers who perform repairs on submerged structures like bridge supports and offshore oil rigs. Their work involves a unique and deadly cocktail of hazards, including electric shocks, drowning, hypothermia, explosions, marine life attacks and the bends.   During wet welding, technologies like protective rubberised dry suits and insulated electrodes reduce the risk of electrocution. A second option – dry welding – involves building a sealed enclosure around the work site, pumping it full of pressurised air, and working within it as if on dry land. However, this is not without its own risks; if concentrated pockets of oxygen an...

Tips on Storing Teflon Stopcock-Equipped Glassware Tips on Storing Teflon Stopcock-Equipped Glassware Since the thermal expansion of Teflon® is significantly different from that of glass, special techniques are required when an apparatus is to be used in a cold room (0-5ºC). The Teflon® plug will contract more than the glass barrel on cooling. Thus, the stopcock will give a good tight seal at room temperature, but eventually will leak when stored in a cold room. Conversely, the stopcock can be tightened in the cold room to give a tight seal, but on warming to room temperature, the Teflon® expands, freezing the stopcock.  The best solution to the above problem is to retighten the stopcock in the cold room after the apparatus has cooled for about 15 minutes. Thereafter, open and close the stopcock only in the cold room. Do not attempt to turn the stopcock after it has warmed to room temperature. Teflon® will cold flow slowly with time. Therefore, unattended long-...

Description and Characteristics Boric Acid Gel is a cross-linked polymer insoluble in water and all organic solvents. It is prepared by the cross-linking copolymerization of dihydroxyborylanilino- substituted methacrylic acid with 1,4-butanediol dimethacrylate. The gel is swollen in distilled water, then activated with 0.5N HCl. It is then washed to neutral pH and vacuum-dried. Thus, the gel is supplied "activated," as a nearly free-flowing granulate. Boric Acid Gel Appearance                                    : nearly dry, off-white granules Boron content                                 : 1.4% (dry) Packing volume    ...

SUGAR MILL ROLLER GROOVING     The three rolls of a conventional mill are arranged in a triangle so that the fiber is squeezed twice between the top roll and the feed roll and the top roll and the discharge roll. The rolls have cast iron, grooved shells mounted on steel shafts. Fiber passing between the top and feed roll is conducted over a turner plate to the discharge roll. The rolls are pinion driven from the top roll which is driven at a speed of 3 to 6 rpm by a gear reduction system. The feed and discharge rolls are fixed, while the top roll is free to move up and down by means of a hydraulic pressure system. Cane is moved between mills by means of intermediate conveyors. They are generally rake or drag-slat type, which carry the fiber to a fixed chute leading to the next mill. 1)       Circumferential Grooves a)       Cutting grooves around the roll gives a corrugated surface of increased are...

Description Mechanical seals are designed to prevent leakage between a rotating shaft and its housing under conditions of extreme pressure, shaft speed and temperature. Mechanical seals can be single acting or double acting. Single (acting) mechanical seals have one sealing gap. The lubrication film required by the sliding seal faces is provided by the medium to be sealed. The lubrication film required by the seal faces in double (acting) mechanical seals is provided by a higher pressure buffer medium (sealant liquid) that is compatible with the pumped product. The sealant liquid is at a higher-pressure so that any leakage across the seal faces will be the sealant liquid into the pumped product. This buffer serves to separate the product and the atmosphere. Design Choices for Mechanical Seals Seal design choices include pusher, metal bellows, and elastomeric bellows.   A pusher mechanical seal utilizes a dynamic secondary seal or o-ring that is r esponsi...