Pyroclastic rocks or pyroclastics are sedimentary clastic rocks composed or of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic. Associated with unsieved volcanic activity—such as Plinian or krakatoan eruption styles, or phreatomagmatic eruptions—pyroclastic deposits are formed from airborne ash and bombs or blocks ejected from the volcano itself, mixed in with shattered country rock. Pyroclastic rocks may be a range of clast sizes, from the largest agglomerates, to fine ashes and tuffs. Pyroclasts of different sizes are classified as volcanic bombs and volcanic ash. Ash is considered to be pyroclastic. One of the most spectacular forms of pyroclastic deposit are the ignimbrites, deposits formed by the high-temperature gas-and-ash mix of a pyroclastic flow event. Three modes of transport can be distinguished: pyroclastic flow, pyroclastic surge, pyroclastic fall. During Plinian eruptions and ash are formed when silicic magma is fragmented in the volcanic conduit, because of decompression and the growth of bubbles.
Pyroclasts are entrained in a buoyant eruption plume which can rise several kilometers into the air and cause aviation hazards. Particles falling from the eruption clouds form layers on the ground. Pyroclastic density currents, which are referred to as "flows" or "surges" depending on particle concentration and the level turbulence, are sometimes called glowing avalanches; the deposits of pumice-rich pyroclastic flows can be called ignimbrites. A pyroclastic eruption entails spitting or "fountaining" lava, where the lava will be thrown into the air along with ash, pyroclastic materials, other volcanic byproducts. Hawaiian eruptions such as those at Kīlauea can eject clots of magma suspended into gas; the magma clots. Pyroclastic deposits consist of pyroclasts. Pyroclastic rocks are pyroclastic deposits. Silicon dioxide Hyaloclastite – A volcaniclastic accumulation or breccia Peperite – Sedimentary rock that contains fragments of younger igneous material Scoria – Dark vesicular volcanic rock
In digestion, a bolus is a ball-like mixture of food and saliva that forms in the mouth during the process of chewing. It has the same color as the food being eaten, the saliva gives it an alkaline pH. Under normal circumstances, the bolus is swallowed, travels down the esophagus to the stomach for digestion. Once the bolus reaches the stomach, it mixes with gastric juices and becomes chyme, which travels through the intestines for further digestion and absorption, eventual discharge as feces. Chyme Chyle
Paper is a thin material produced by pressing together moist fibres of cellulose pulp derived from wood, rags or grasses, drying them into flexible sheets. It is a versatile material with many uses, including writing, packaging, decorating, a number of industrial and construction processes. Papers are essential in non-legal documentation; the pulp papermaking process is said to have been developed in China during the early 2nd century CE as early as the year 105 CE, by the Han court eunuch Cai Lun, although the earliest archaeological fragments of paper derive from the 2nd century BCE in China. The modern pulp and paper industry is global, with China leading its production and the United States right behind it; the oldest known archaeological fragments of the immediate precursor to modern paper date to the 2nd century BCE in China. The pulp paper-making process is ascribed to a 2nd-century CE Han court eunuch. In the 13th century, the knowledge and uses of paper spread from China through the Middle East to medieval Europe, where the first water powered paper mills were built.
Because paper was introduced to the West through the city of Baghdad, it was first called bagdatikos. In the 19th century, industrialization reduced the cost of manufacturing paper. In 1844, the Canadian inventor Charles Fenerty and the German F. G. Keller independently developed processes for pulping wood fibres. Before the industrialisation of paper production the most common fibre source was recycled fibres from used textiles, called rags; the rags were from hemp and cotton. A process for removing printing inks from recycled paper was invented by German jurist Justus Claproth in 1774. Today this method is called deinking, it was not until the introduction of wood pulp in 1843 that paper production was not dependent on recycled materials from ragpickers. The word "paper" is etymologically derived from Latin papyrus, which comes from the Greek πάπυρος, the word for the Cyperus papyrus plant. Papyrus is a thick, paper-like material produced from the pith of the Cyperus papyrus plant, used in ancient Egypt and other Mediterranean cultures for writing before the introduction of paper into the Middle East and Europe.
Although the word paper is etymologically derived from papyrus, the two are produced differently and the development of the first is distinct from the development of the second. Papyrus is a lamination of natural plant fibres, while paper is manufactured from fibres whose properties have been changed by maceration. To make pulp from wood, a chemical pulping process separates lignin from cellulose fibres; this is accomplished by dissolving lignin in a cooking liquor, so that it may be washed from the cellulose. Paper made from chemical pulps are known as wood-free papers–not to be confused with tree-free paper; the pulp can be bleached to produce white paper, but this consumes 5% of the fibres. There are three main chemical pulping processes: the sulfite process dates back to the 1840s and it was the dominant method extent before the second world war; the kraft process, invented in the 1870s and first used in the 1890s, is now the most practiced strategy, one of its advantages is the chemical reaction with lignin, that produces heat, which can be used to run a generator.
Most pulping operations using the kraft process are net contributors to the electricity grid or use the electricity to run an adjacent paper mill. Another advantage is that this process reuses all inorganic chemical reagents. Soda pulping is another specialty process used to pulp straws and hardwoods with high silicate content. There are two major mechanical pulps: groundwood pulp. In the TMP process, wood is chipped and fed into steam heated refiners, where the chips are squeezed and converted to fibres between two steel discs. In the groundwood process, debarked logs are fed into grinders where they are pressed against rotating stones to be made into fibres. Mechanical pulping does not remove the lignin, so the yield is high, >95%, however it causes the paper thus produced to turn yellow and become brittle over time. Mechanical pulps have rather short fibres. Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than the chemical kind. Paper recycling processes can use mechanically produced pulp.
Most recycled paper contains a proportion of virgin fibre for the sake of quality. There are three main classifications of recycled fibre:. Mill broke or internal mill waste – This incorporates any substandard or grade-change paper made within the paper mill itself, which goes back into the manufacturing system to be re-pulped back into paper; such out-of-specification paper is not sold and is therefore not classified as genuine reclaimed recycled fibre, however most paper mills have been reusing their own waste fibre for many years, long before recycling became popular. Preconsumer waste – This is offcut and processing waste, such as guillotine trims and envelope blank waste.
A ceramic is a solid material comprising an inorganic compound of metal, non-metal or metalloid atoms held in ionic and covalent bonds. Common examples are earthenware and brick; the crystallinity of ceramic materials ranges from oriented to semi-crystalline and completely amorphous. Most fired ceramics are either vitrified or semi-vitrified as is the case with earthenware and porcelain. Varying crystallinity and electron composition in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators. With such a large range of possible options for the composition/structure of a ceramic, the breadth of the subject is vast, identifiable attributes are difficult to specify for the group as a whole. General properties such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance and low ductility are the norm, with known exceptions to each of these rules. Many composites, such as fiberglass and carbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family.
The earliest ceramics made by humans were pottery objects or figurines made from clay, either by itself or mixed with other materials like silica and sintered in fire. Ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates. Ceramics now include domestic and building products, as well as a wide range of ceramic art. In the 20th century, new ceramic materials were developed for use in advanced ceramic engineering, such as in semiconductors; the word "ceramic" comes from the Greek word κεραμικός, "of pottery" or "for pottery", from κέραμος, "potter's clay, pottery". The earliest known mention of the root "ceram-" is the Mycenaean Greek ke-ra-me-we, "workers of ceramics", written in Linear B syllabic script; the word "ceramic" may be used as an adjective to describe a material, product or process, or it may be used as a noun, either singular, or, more as the plural noun "ceramics".
A ceramic material is an inorganic, non-metallic crystalline oxide, nitride or carbide material. Some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, strong in compression, weak in shearing and tension, they withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics can withstand high temperatures, ranging from 1,000 °C to 1,600 °C. Glass is not considered a ceramic because of its amorphous character. However, glassmaking involves several steps of the ceramic process, its mechanical properties are similar to ceramic materials. Traditional ceramic raw materials include clay minerals such as kaolinite, whereas more recent materials include aluminium oxide, more known as alumina; the modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued for their abrasion resistance and hence find use in applications such as the wear plates of crushing equipment in mining operations.
Advanced ceramics are used in the medicine, electronics industries and body armor. Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories – either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, sintering to form a solid body. Ceramic forming techniques include shaping by hand, slip casting, tape casting, injection molding, dry pressing, other variations. Noncrystalline ceramics, being glass, tend to be formed from melts; the glass is shaped when either molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing into a mold. If heat treatments cause this glass to become crystalline, the resulting material is known as a glass-ceramic used as cook-tops and as a glass composite material for nuclear waste disposal; the physical properties of any ceramic substance are a direct result of its crystalline structure and chemical composition.
Solid-state chemistry reveals the fundamental connection between microstructure and properties such as localized density variations, grain size distribution, type of porosity and second-phase content, which can all be correlated with ceramic properties such as mechanical strength σ by the Hall-Petch equation, toughness, dielectric constant, the optical properties exhibited by transparent materials. Ceramography is the art and science of preparation and evaluation of ceramic microstructures. Evaluation and characterization of ceramic microstructures is implemented on similar spatial scales to that used in the emerging field of nanotechnology: from tens of angstroms to tens of micrometers; this is somewhere between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, micro-