何謂碳黑Soot すす?www.tool-tool.com

Bewise Inc. Reference source from the internet.

炭黑是一種黑色粉末狀的。

炭黑是由平均直徑為2~3nm的球狀或鏈狀粒子聚積而成的,內部是含有直徑3~500nm的微結晶結構,可以和各種反 應。炭黑的為 1.8~1.9,顆粒狀炭黑的堆比重為0.35~0.4,粉末狀炭黑的堆比重為 0.04~0.08。

在 800℃以上的高溫下,用數的時間進行,就得到了炭黑。以和餾 分為原料,在爐中進行部分燃燒,得到爐炭黑。另外根據原料和製法的不同有槽法、法、 熱裂解法、燈法等,其用途也不相同。

炭黑主要作為增強劑使用,用於汽車的製造。其他還用作(、、用),用 導電劑,載體、超硬質材 料。全球炭黑約有70%用於輪胎的製造,20%用在其他橡膠,其餘不到10%則用於塑料添加劑、染料、印刷油墨等工業。

Soot (pronounced ) is a general term that refers to impure particles resulting from the incomplete combustion of a . It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as , charred wood, petroleum coke, etc. that may become airborne during and which are more properly identified as cokes or chars. The gas-phase soots contain (PAHs). The PAHs in soot are known and probable human . They are classified as a "known human carcinogen" by the International Agency for Research on Cancer (IARC).

Soot, as an airborne contaminant in the environment has many different sources but they are all the result of some form of pyrolysis. They include soot from internal combustion engines, power plant boilers, hog-fuel boilers, ship boilers, central steam heat boilers, waste incineration, local field burning, house fires, forest fires, fireplaces, furnaces, etc. These exterior sources also contribute to the indoor environment sources such as smoking of plant matter, cooking, oil lamps, candles, quartz/halogen bulbs with settled dust, fireplaces, defective furnaces, etc. Soot in very low concentrations is capable of darkening surfaces or making particle agglomerates, such as those from ventilation systems, appear black. Soot is the primary cause of “ghosting”, the discoloration of walls and ceilings or walls and flooring where they meet. It is generally responsible for the discoloration of the walls above baseboard electric heating units.

The formation of soot depends strongly on the fuel composition. The rank ordering of sooting tendency of fuel components is: naphthalenes > benzenes > aliphatics. However, the order of sooting tendencies of the aliphatics (alkanes, alkenes, alkynes) varies dramatically depending on the flame type. The difference between the sooting tendencies of aliphatics and aromatics is thought to result mainly from the different routes of formation. Aliphatics appear to first form acetylene and polyacetylenes; aromatics can form soot both by this route and also by a more direct pathway involving ring condensation or polymerization reactions building on the existing aromatic structure .

Description

The production of soot in a flame is a complex process consisting of several chemical reactions taking place in series. In the fuel-pyrolysis zone of the flame, typically clear or blue, the fuel molecules are broken down into various fragments, including carbon-ring structures, (C2H2), the radical C3H3 (and higher order), as well as monatomic and diatomic hydrogen. As the combustion process continues the radicals quickly combine into new structures, giving off heat. These precursors polymerize into larger "pre-soot" chains then gather into formations of hydrogen-rich spheres in the soot-inception zone. In the soot-growth zone these spheres give up their hydrogen gas through diffusion, resulting in solids consisting of several of the formerly liquid spheres stuck together into larger chains. It is this portion of the flame that has the bright yellow color. Hydrogen-rich examples then further oxidize, releasing more heat. In perfect combustion the soot would break down into almost pure CO2 and H2O; it is only in incomplete combustion that the soot is able to form and escape the flame.

Soot normally forms at about 140 °C, forming an excellent of colors in the yellow to red spectrum. The typical yellow color of a candle flame or wood fire is produced primarily by the hot soot forming inside.

The energy being radiated from the soot is an important contributor to the ongoing combustion process, cooling the flame above the soot-growth zone and feeding energy back into the fuel-pyrolysis zone. In "pool fires" of open liquid fuel this process can feed as much as 50% of the flame's energy back into the liquid fuel below, which vaporizes it and keeps the reaction going; it would otherwise burn much more slowly. The same release of energy is responsible for quickly cooling the flame above the soot-growth region, limiting its further combustion into lighter molecules, and explaining why these fires release so much soot. A canonical example is the , which released massive amounts of soot and covered the skies over a large portion of the London area.

The separation of flame into zones of different chemical reactions is due to forcing the hot reactants upward. In or convection no longer occurs, and such flames tend to become more blue and more efficient, producing much less soot. Experiments by reveal that in microgravity allow more soot to be completely oxidized than in conditions on Earth, because of a series of mechanisms that differ from those in normal gravity conditions.

Role in global warming

Soot is found worldwide, but its presence and impact are particularly strong in Asia.

One of the most complex effects on albedo is from (BC) particles. All are capable of scattering incoming radiation back to space, BC is no exception. A portion of incoming is scattered back to space by BC particles. A study done by Conant et.al (2003) determined the single albedo (ω) of a black carbon particle at 500 nm wavelength and 80% relative humidity to be 0.226. The low single scattering albedo (ω) demonstrates the strong absorption properties of BC particles. While a portion of incoming radiation is scattered back to space, a larger portion of the incoming solar radiation is absorbed by BC containing particles in the air. The absorbed fraction of results in surface cooling because the solar radiation that would have reached the Earth is absorbed in the atmosphere. Although surface warming is seen under these conditions, atmospheric warming is also observed because the incoming radiation is trapped in the atmosphere.

There are two primary sources that contribute to BC emission on the global scale: fossil fuel emissions and biomass burning. The AR-4 published by the in 2007 suggests the raditaive forcing from these two combined sources is +0.44 ± 0.13 Wm-2. Carbonaceuos aerosol emissions inventories are currently (as reported by the IPCC) claiming that 34-38% of emissions is generated from biomass burning, the remainder from fossil fuel burning.

BC also has an indirect effect on climate change as it relates to the albedo effects of snow, ice, and land use changes. There is potential for BC particles to decrease the albedo of snow and also affect the rate of snowmelt. Hansen and Nazarenko (2004) reported a radiative forcing value of +0.15 Wm-2 in AR-4 with respect to changes in snow and ice albedo; however, this estimate has high uncertainty levels. (Forster, et al., 2007)

Hazards

Soot is in the general category of airborne matter, and as such is considered hazardous to the lungs and general health when the particles are less than five micrometres in diameter, as such particles are not filtered out by the upper respiratory tract.[] Smoke from , while composed mostly of carbon soot, is considered especially dangerous owing to both its particulate size and the many other chemical compounds present.[]

Soot can stain clothing and can possibly cause illness if inhaled. Breathing common urban air pollution (containing soot) is much deadlier than previously thought, according to a major study and an editorial published in on February 1, 2007.

Diesel (DE) gas is a major contributor to combustion derived particulate matter air pollution. In several human experimental studies using a well validated exposure chamber setup DE has been linked to acute vascular dysfunction and increased thrombus formation. This serves as a plausible mechanistic link between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality.

すす(煤)は、がを起こして生じるの 微粒子や、のな どに溜まるきめの細かいの ことである。

概ね過去の生活様式となったが、室内のにやを使用したり、にやを 使うことで、すすが室内に溜まるのが日常であった。今でもこうした照明を用いるやで は、すすが発生している。また、燃焼に伴う煙中の微粒子だけに限らず、室内に溜まる細かな粒子状の汚れを指してすすと呼ぶことがある。

す すの実体は詳しくは解明されていない。すすは物質としては黒鉛に近いが薄膜状にならず、微細な粒子が多数寄り集まって構成されているのが判っている。

生 成機構

燃焼によって生じるすすは、燃料の熱分解過程で酸素が不足していたことを物語っており、燃焼ガス中で油滴や微粉炭中の残炭分が 重合して未燃のまま排出される。すすが多くが炭素原子から構成されていることが判っており、他にも1-3%程の水素を含み、また、燃料の純度が劣る場合に は灰分を多く含む。

すすの生成機構の最初の分子レベルでの初期状態に関して、主に3つの説が存在する。

  1. 多環 芳香族炭化水素(Polynuclear aromatic hydrocarbon, PAH)を経由して生成される
  2. を経由して生成される
  3. C3H3+やCHO+の ような炭化水素イオンを経由 して生成される

当初は電荷を帯びた巨大分子だったものが電気的に引き合うことで凝縮し、ごく微 細な液体状や固体状となった粒子同士が衝突と合体を繰り返しながら、脱水素反応を起こして数nm-数十nm程度の固体の球状粒子に成長してゆく。球状粒子 の状態で酸化されることもある。この球状粒子は電荷によって数珠繋ぎになり、やがてぶどうの房状に集まって数十nm-数百nm程度の大きさの凝集体を作り 上げる。この凝集体は、互いの煙路や排気経路付近に堆積することでさらに大きな粒子の煤煙となる[

燃焼への寄 与

ボイラーなどで火炎の中に一時的に生じるすすは、熱線を放つことで燃焼へ寄与している。燃焼時にOH、CH、C2と いった ラジカルが放つの波長は青色や紫外線領域の狭いバンドで発光するものが多く加熱としてはあまり有効でないが、高温の固体であるすすが放つ赤外線領域の連続 スペクトルでの放射光が周囲の燃料を輻射により加熱することで燃焼を助ける働きをしている。このような炎を輝炎と呼び、す すをまったく生じない不輝炎と比べると強力な赤外線を放射する

 

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