熔煉，煅燒和石墨化之簡(jiǎn)介

日期：2018-03-25 點(diǎn)擊次數(shù)：2090

熔煉，煅燒和石墨化之簡(jiǎn)介

2018-03-25 石墨盟

【TiangongKaiwu Tripod casting】

哈嘍，小編尼克向諸位問好！歡迎光顧石墨化之友！今天就讓我們一起探尋與冶煉相關(guān)的事吧！本期我們主要致力于熔煉，煅燒和石墨化等的區(qū)別，后期我們會(huì)逐漸轉(zhuǎn)向石墨化技術(shù)探討和研究。期待各位的繼續(xù)關(guān)注，您的關(guān)注和訂閱是小編*大的動(dòng)力！

說到熔煉，我們*先聽到的或許就是我國(guó)古代的“天工開物”了。“熔煉，是將金屬材料及其它輔助材料投入加熱爐溶化并調(diào)質(zhì)，爐料在高溫（1300～1600K）爐內(nèi)物料發(fā)生一定的物理、化學(xué)變化，產(chǎn)出粗金屬或金屬富集物和爐渣的火法冶金過程。爐料除精礦、焙砂、燒結(jié)礦等外，有時(shí)還需添加為使?fàn)t料易于熔融的熔劑，以及為進(jìn)行某種反應(yīng)而加入還原劑。此外，為提供必須的溫度，往往需加入燃料燃燒，并送入空氣或富氧空氣。粗金屬或金屬富集物由于與熔融爐渣互溶度很小和密度差分為兩層而得以分離。富集物有锍、黃渣等，它們尚須經(jīng)過吹煉或其他方法處理才能得到金屬。”——來自百度百科

【Cowles furnace】

Smelting is a process of applying heat to ore in order to melt out a base metal. It is a form of extractivemetallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducingagent todecompose the ore, driving off other elements as gases or slag and leaving the metal base behind.The reducing agent is commonly a source of carbon, such as coke—or, in earlier times, charcoal.

The carbon (or carbon monoxide derived from it)removes oxygen from the ore, leaving the elementalmetal. The carbon thus oxidizes in two stages, producing firstcarbonmonoxide andthen carbon dioxide. As most ores are impure, it isoften necessary to use flux, such as limestone, to remove the accompanying rockgangue as slag. Plants for the electrolytic reduction of aluminium are also generally referred to as aluminiumsmelters. Laborersworking in the smelting industry have reported respiratory illnesses inhibitingtheir ability to perform the physical tasks demanded by their jobs. Smeltinginvolves more than just melting the metal out of its ore. Most ores are thechemical compound of the metal and other elements, such as oxygen (as an oxide), sulfur (as a sulfide), or carbon and oxygen together (asa carbonate). To extract the metal, workersmust make these compounds undergo a chemical reaction. Smelting thereforeconsists of using suitablereducingsubstances that combine with those oxidizing elements to free the metal.

【Phosphate Smelting Furnace】

煅燒(calcining)是指緩和了物質(zhì)分子結(jié)構(gòu)的內(nèi)在張力，從而使之能夠適應(yīng)在塑形過程中不斷增強(qiáng)的力量，并于完工時(shí)更加結(jié)實(shí)。玻璃在窯中吹制后，借由在窯中煅燒及慢慢冷卻，可使其強(qiáng)度和硬度增高。金屬的延展性更大，因此它可以適于如錘打、扭轉(zhuǎn)和彎曲等處理方式。由于這些操作均會(huì)增加金屬堅(jiān)固性能，因此為了達(dá)到好的效果，有時(shí)就必須重復(fù)煅燒。有些材料如玻璃和鋼，煅燒后的冷卻要徐徐進(jìn)行，而在其他如銅或黃銅煅燒后就需急速冷卻。

【Lime Shaft】

而我們后期會(huì)討論無煙煤(Anthracites)煅燒獲取煤質(zhì)增碳劑的相關(guān)研究。煅煤增碳劑的生產(chǎn)設(shè)施與石灰窯的原理類似，如上圖所示。無煙煤因?yàn)槠鋬r(jià)格低廉，含碳量高，結(jié)構(gòu)致密，被用作多種炭素材料的原料。但是作為炭素材料原料，無煙煤在使用之前必須先要經(jīng)過煅燒，去除其中的揮發(fā)分，并使其電阻率降低，導(dǎo)熱率和真密度提高。在工業(yè)獲取無煙煤增碳劑中，無煙煤的煅燒通常是采取兩種方法完成。一種的在1300℃左右的罐式爐或回轉(zhuǎn)窯中進(jìn)行煅燒的氣煅煤，另一種是在平均溫度1700℃左右的電煅爐中煅燒的電煅煤。

【原煤的工業(yè)分析】

【氣煤和電煅煤的性能指標(biāo)】

【無煙煤中的顯微結(jié)構(gòu)類型】

Calcination also refers to as calcining. The IUPAC defines it as 'heating to hightemperatures in air or oxygen'. However, calcination is also used to mean athermaltreatmentprocess in the absence or limited supply of air or oxygen applied to ores and other solid materials to bringabout a thermaldecomposition. A calciner is a steel cylinder that rotates inside a heated furnace andperforms indirect high-temperature processing (550–1150 °C, or1000–2100 °F) within a controlled atmosphere.

The process of calcination derives its name fromthe Latin calcinare (to burn lime) due to its most commonapplication, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide, in order to create cement. The product of calcination isusually referred to in general as "calcine", regardless of the actualminerals undergoing thermal treatment. Calcination is carried out infurnaces or reactors (sometimes referred toas kilns or calciners) of various designsincluding shaftfurnaces, rotarykilns, multiplehearth furnaces, andfluidizedbed reactors.

Examplesof calcination processes include the following:

?      decomposition of carbonate minerals, as in the calcination of limestoneto drive off carbondioxide;

?      decomposition of hydrated minerals, as in the calcination of bauxite andgypsum, to remove crystalline water as water vapor;

?      decomposition of volatile matter contained in raw petroleum coke;

?      heat treatment to effect phase transformations, as in conversion ofanatase to rutile or devitrification of glass materials

?      removal of ammoniumions in the synthesis of zeolites.

Calcination reactions usually take place at orabove the thermal decomposition temperature (for decomposition andvolatilization reactions) or the transition temperature (for phasetransitions). This temperature is usually defined as the temperature at whichthe standard Gibbs freeenergy for aparticular calcination reaction is equal to zero. For example, in limestonecalcination, a decomposition process, the chemical reaction is CaCO₃→ CaO + CO₂(g)The standard Gibbs free energy of reaction is approximated as ΔG°_r= 177,100 ? 158 T (J/mol). The standard free energy ofreaction is 0 in this case when the temperature, T, is equal to 1121 K,or 848 °C.

碳的微觀結(jié)構(gòu)示意圖：1易石墨化碳 2難石墨化碳 3介于之間

石墨化是把焙燒制品置于石墨化爐內(nèi)保護(hù)介質(zhì)中加熱到高溫，使六角碳原子平面網(wǎng)格從二維空間的無序重疊轉(zhuǎn)變?yōu)?span style=";padding: 0px;max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;color: black">三維空間的有序重疊，且具有石墨結(jié)構(gòu)的高溫?zé)崽幚磉^程。

Some applications, such as graphite electrodes forthe electric arc furnace require a higher thermal and electrical conductivitythan that of baked carbon materials. These synthetic graphites normally followa production process similar to that of baked carbon (forming, impregnation,rebaking) but require an additional process step, that of graphitization wheretemperatures of around 3000°C are achieved.

The final step in graphite manufacture is aconversion of baked carbon to graphite, called graphitizing, i.e. heat-treatingthe material at temperatures in the region of 2600 °C to 3300 °C. During thegraphitizing process, the more or less pre-ordered carbon (turbostratic carbon)is converted into a three-dimensionally ordered graphite structure. Depending onthe raw materials and the processing parameters, various degrees of convergenceto the ideal structure of a graphite single crystal are achieved.

Since graphitization increases the lattice orderand produces smaller layer distances, it simultaneously leads to a considerablegrowth of ordered domains. However, the degree of order that can be reacheddepends largely on the crystalline pre-order of the solid used. These reducedlattice layer distances are macroscopically noted as a contraction in volume. Thisgraphitization-shrinkage is approximately 3 to 5%. Due to this shrinkage,density of the graphite increases.

In general, the graphitization process includes thestages as given below:

?Amorphousor baked carbon is converted to electro graphite by a thermal treatment atapproximately 3000°C.

?Essentiallyany amorphous carbon material can be graphitized. The potential crystallitegrowth and ordering are latent within the baked carbon structure.

?Underthe influence of temperature the crystallites grow and rearrange in an orderedpattern of stacked parallel planes. This transformation is accompanied by achange in the physical properties of the material.

?Thegreater the degree of crystallite growth during heating up, the better thegraphitability (graphitization degree), which effects the final resistivityachieved.

?Thereis a variation among different needle cokes concerning the graphitability.

?Thegraphitization degree depends on the structure of the basic material(graphitability) and the applied graphitization temperature. It is determinedby x-ray measurements.

The graphitizing process is also accompanied by apurification of the material treated, normally reducing the content ofimpurities to considerably less than 1000ppm. For many applications, this purityis insufficient, so that a thermal purification at higher temperatures up to3100°C with longer residence times is carried out to reduce the impurities to aconcentration of less than 200ppm. If still lower ash values are required, athermo-chemical purification is necessary.

Even after graphitization at around 3000°C mostgraphites contain small amounts of metallic impurities. If the ash values inthe material have to be below 200ppm, thermal purification is applied. Byadding gaseous halogens or halogen compounds, all hetero-atoms forming stablecarbides are transferred into volatile halogen compounds and thus removed. Bymeans of this procedure, impurities may be lowered to less than 1ppm.

石油焦一般在1700℃就開始石墨化，而瀝青焦則要在2000℃左右才能進(jìn)入石墨化的轉(zhuǎn)化階段。（信息來源：石墨化之友）

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