extra notes for selected topics `

浏览上一个主题 浏览下一个主题 向下

extra notes for selected topics `

帖子 由 Giraffe 于 周二 七月 28, 2009 7:16 am

Synthetic inorganic pigments

Synthetic inorganic pigments are mineral compounds created through chemical manufacturing rather than by grinding and washing clays or minerals taken directly from the earth. The techniques for producing these substances on an industrial scale were developed after 1800, *** them the first modern synthetic pigments of importance to artists.
Nearly all synthetic inorganic pigments were discovered or identified in the grand European flowering of inorganic chemistry that occurred in the century after 1750, when European industries sponsored intensive mineralogical and metallurgical research, and early chemists isolated and identified many new metallic elements — cadmium, cobalt, chromium, zinc, manganese, magnesium, and so on. (These new puzzle pieces helped John Dalton to formulate modern atomic theory in around 1805.) Several synthetic inorganic pigments still used today, including iron blue,Cobalt Green,Cobalt blue and Zinc Oxide, were discovered prior to 1800.
These manufactured pigment compounds generally have excellent chemical purity and color consistency, and are cheaper to buy and available in larger quantities than natural inorganic pigments. With very few exceptions, all inorganic pigments used in artists' paints today are industrially manufactured. (Some dry powder natural inorganic pigments are available from specialty pigment retailers.)
As an artist, your primary concern is to understand the generic attributes of these pigments across different manufacturers and different pigment hues (chemical or crystal variations) — that is, to see paints as Physical Substances rather than as Colours. For example, the violet and blue Ultramarines are typically granulating and moderately transparent; the many lemon yellow to deep red Cadmiums are all powdery, permanent, opaque and quite staining; compounds made with mercury are poisonous and fugitive. The historical information can also help you to understand the rapid expansion in artists' pigments that occurred in Europe between the 18th and 19th centuries
The following table presents the average pigment attributes for the most important synthetic organic pigments, based on all paint ratings in the Guide to Watercolor pigments.


由Giraffe于周二 七月 28, 2009 7:17 am进行了最后一次编辑,总共编辑了1次

Giraffe
校长
校长

帖子数 : 542
学分 1018
来自 : johor
注册日期 : 09-07-22
年龄 : 24

查阅用户资料 http://thestudents.forumotion.com

返回页首 向下

回复: extra notes for selected topics `

帖子 由 Giraffe 于 周二 七月 28, 2009 7:17 am

Inorganic Components of the Agricultural Ecosystem


Soil is the primary medium in which biological activity and chemical reactions occur. It is a three-phase system consisting of solid, liquid, and gas. Approximately 50 percent of the volume in a typical agricultural soil is solid material classified chemically as either organic or inorganic compounds. Organic materials usually constitute 1 to 5 percent of the weight of the solid phase. The remainder of the soil volume is pore space that is either filled with gases such as CO2 and O2, or water.

Su***ce area and charge characteristics of the inorganic portion of the solid phase control chemical reactivity. Soil particles are classified based on their size, with sand-sized particles having diameters of 2 to 0.05 millimeters (0.08 to 0.002 inches) and silt-sized particles from 0.05 to 0.002 millimeters (0.002 to 0.00008 inches). Clay-sized materials of less than 0.002 millimeters (0.00008 inches) in diameter have the largest su***ce area per unit weight, reaching as much as 800 meters (2,625 feet) squared per gram. Because of large su***ce areas, clay-sized materials greatly influence the sorption
of chemicals such as fertilizers and pesticides and play a major role in catalyzing reactions.

Crystalline layer silicates or phyllosilicates present in the clay-sized fraction are especially important because they function as ion exchangers. Most phyllosilicates have a net negative charge and thus attract cations. This cation exchange capacity (CEC) controls whether plant nutrients, pesticides, and other charged molecules are retained in soil or if they are transported out of the soil system. In contrast, aluminum and iron oxides also present in the clay-sized fraction typically possess a net positive charge or an anion
exchange capacity (AEC). Soils in temperate regions are dominated most often by solid phase materials that impart a net CEC, whereas soils in tropical regions often contain oxides that contribute substantial AEC.

Giraffe
校长
校长

帖子数 : 542
学分 1018
来自 : johor
注册日期 : 09-07-22
年龄 : 24

查阅用户资料 http://thestudents.forumotion.com

返回页首 向下

回复: extra notes for selected topics `

帖子 由 Giraffe 于 周二 七月 28, 2009 7:17 am

Green chemistry and organic chemistry

As we all know, organic chemistry in particular organic synthetic chemistry is developing a more complete discipline. In the history of human civilization, improve its quality of life of mankind made a huge contribution. However, it is undeniable that the "traditional" methods of chemical synthesis and established according to the "tradition" of the chemical industry, on the whole of mankind's survival of the ecological environment caused serious pollution and destruction. The past to solve the problem is the primary means of governance, production, or even shut down, people for controlling environmental pollution spend a lot of manpower, material and financial resources. The early 1990s, chemists made with the traditional "pollution treatment" different "green chemistry" concept, that is, how to decrease from the source, or even eliminate the pollution generated. Through research and improve the chemical process and the corresponding technology, and fundamentally reduce and eliminate by-products or waste generated, to achieve the protection and improvement of the environment. "Green chemistry" of the goal and requirements of any chemical activities, including the use of chemical raw materials, chemical and chemical process and the final grain production, human health and the environment should be friendly. Thus, the results of research on green chemistry to solve environmental problems is of fundamental significance. For the environment and the sustainable development of chemical production also has important significance. More than 10 years ago, on the concept of green chemistry, objectives, principles and basic research fields, and so has to move clearly, the initial formation of a multidisciplinary pay * the new field of study. Specifically, the basic principles of green chemistry can include the following: a) to prevent the pollution generated superior to the pollution control; 2) atom economy; 3) as long as possible, should try to use the toxic chemical synthesis on the line: 4) more secure chemical crystal design should be able to retain their effectiveness, but lower toxicity; 5) should do everything possible to avoid the use of auxiliary materials (such as solvents, separation etc.), such as when a drug-free; 6) should be considered To energy consumption on the environment and economic impact, and should be minimal use of energy; 7) should be renewable raw materials, rather than be depleted; Cool to avoid unnecessary derivative of the steps 9) catalytic reagents ( Have the best possible optional) is better than equivalent of the reagent, 10) chemical products after the completion of its mission and should not be Residues in the environment, and should be able to sound degradation of the material: 11) analysis methods must be further developed to The formation of harmful substances in the former to carry out immediate and on-line tracking and control: 12) in the chemical conversion process, the chosen material and substances should be able to form as much as possible to reduce the possibility of a chemical accident.

Giraffe
校长
校长

帖子数 : 542
学分 1018
来自 : johor
注册日期 : 09-07-22
年龄 : 24

查阅用户资料 http://thestudents.forumotion.com

返回页首 向下

回复: extra notes for selected topics `

帖子 由 Giraffe 于 周二 七月 28, 2009 7:18 am

Physical and Chemical Properties of the noble gases

The noble gases, also known as rare or inert gases, form Group 18 of the Periodic Table, embedded between the alkali metals and the halogens. The elements helium, neon, argon, krypton, xenon, and radon are the members of this group.

The chemical inertness of the noble gases is based on their electronic structure. Each element has a completely filled valence shell. In fact their inertness helped to develop the key idea of a stable octet.

The atomic sizes of the noble gas elements increase from top to bottom in the Periodic Table, and the amount of energy needed to remove an electron from their outermost shell, the ionization energy, decreases in the same order. Within each period, however, the noble gases have the largest ionization energies, reflecting their chemical inertness. Based on increasing atomic size, the electron clouds of the spherical, nonpolar, atoms become increasingly polarizable, leading to stronger interactions among the atoms (van der Waals forces). Thus, the formation of solids and liquids is more easily attained for the heavier elements, as reflected in their higher melting points and BOILING POINTs. As their name implies, all members of the family are gases at room temperature and can, with the exception of helium, be liquefied at atmospheric pressure.

Giraffe
校长
校长

帖子数 : 542
学分 1018
来自 : johor
注册日期 : 09-07-22
年龄 : 24

查阅用户资料 http://thestudents.forumotion.com

返回页首 向下

回复: extra notes for selected topics `

帖子 由 Giraffe 于 周二 七月 28, 2009 7:19 am

fertilizer

A fertilizer is a plant nutrient added to a soil to increase its yield. Plants need nutrients to grow and produce fruits and vegetables. Two categories of nutrients have been identified in fertilization: macronutrients and micronutrients. There are only six macronutrients and they are required in large amounts by plants: nitrogen, phosphorus, potassium, sulfur, magnesium, and calcium. However, a larger number of micronutrients are required but in trace amounts: iron, manganese, boron, zinc, copper, molybdenum, chlorine, cobalt, nickel, sodium, and silicon. Eliminate any of these elements, and plants will display abnormal growth and deficiency, or they may not reproduce.
The most popular fertilizers contain the three major nutrients: nitrogen, phosphorus, and potassium, and they are therefore referred to as NPK fertilizers. To illustrate their importance in any economy, in 2000, the world consumption of the total fertilizer nutrient (N + P2O5 + K2O) was 140 million tons, representing 52 million tons for developed countries and 88 million tons for developing countries.
Nitrogen forms part of proteins, hormones, chlorophyll, vitamins, and enzymes, and promotes stem and leaf growth. Too much nitrogen can delay fruiting, while a deficiency of it can reduce yields and induce yellowing of leaves and stunted growth. Nitrogen fertilizers are applied in organic and/or inorganic forms. Organic nitrogen fertilizers are farmyard manure, guano (excreta and remains of seabirds), dried blood, hoof, and horn. However, organic nitrogen sources must undergo microbial processes that produce nitrate nitrogen.
Inorganic nitrogen sources are directly available to plants and include the following: sodium nitrate, calcium nitrate, ammonium sulfate, ammonium nitrate, urea, calcium cyanamide, and ammonia. In addition, atmospheric nitrogen may be used as a source of plant nitrogen by the process called "nitrogen fixation." Legumes and a few other plants, in association with cyanobacteria (microscopic aquatic bacteria, for example, Anabaena azollae), convert nitrogen to biologically useful ammonia. This process occurs in small growths on the roots called "nodules." Ammonia is subsequently available for many biological molecules, such as amino acids, proteins, vitamins, and nucleic acids.
Phosphorus plays an important role in seed germination, photosynthesis, protein formation, overall growth and metabolism, and flower and fruit formation. Phosphorus deficiency induces purple stems and leaves, poor flowering and fruiting. Low soil pH (<4) ties up phosphates by favoring the formation of insoluble aluminum and iron phosphates. Phosphorus fertilizers come from different sources: bones, rock phosphate, superphosphate (a mixture of calcium dihydrogen phosphate and calcium sulfate), nitrophosphate, ammonium phosphate, basic slag (by-product in steel manufacture), etc.
Potassium contributes to the formation of sugars, carbohydrates, proteins and to cell division; adjusts water balance; enhances the flavor, color, and oil content of fruits; and is very important for leafy crops. Potassium deficiency produces a spotted, curled, or burned appearance to leaves and lowers crop yields. Potassium fertilizers are applied in the following forms: potassium chloride, potassium sulfate, potassium nitrate, and wood ash.
Other macronutrients are supplied as part of NPK fertilizers. First, sulfur is available from the sulfate of fertilizers. It contributes to the formation of amino acids, proteins, and enzymes, and is essential to chlorophyll. It also affects flavor in many vegetables. Second, magnesium is naturally present in the soil and is generally associated with potassium sulfate and calcium phosphate, used as NPK. It is a critical part of chlorophyll, and contributes to the functioning of enzymes for carbohydrates, fruit and nut formation, and the germination of seeds. Magnesium deficiency induces yellowing between the veins of older leaves, and leaves droop (hang down) as a result. Finally, calcium is also present in the soil and is available from calcium phosphate and nitrate, and lime. It activates enzymes, contributes to the structural part of cell walls, and influences water movement, cell growth, and division.
Micronutrients are not specifically applied to soil since they are naturally found in soils. However, there are some extreme cases where they must be supplied. For example, animal disorders have been linked to a lack of trace amounts of elements, not necessary for plant growth but essential for some species of animals. In some parts of Great Britain, for example, sheep and cattle suffered from "pining disease" that resulted in severe weight loss and general debilitation. The disease was found to result from a shortage of cobalt in the herbage. It has also been established that selenium deficiencies in some soils cause muscular dystrophy, while selenium excesses induce selenium toxicity in livestock.

Giraffe
校长
校长

帖子数 : 542
学分 1018
来自 : johor
注册日期 : 09-07-22
年龄 : 24

查阅用户资料 http://thestudents.forumotion.com

返回页首 向下

浏览上一个主题 浏览下一个主题 返回页首


 
您在这个论坛的权限:
不能在这个论坛回复主题