气割渣和等离子切割渣有什么不同，属于什么化学成分？

气割焰一般是氧、乙炔，而等离子切割主要是压缩空气、等离子弧，所以形成的熔渣与参与的气体成分不同而不同。另外还与被切割的材料成分有关。氧、乙炔的气割渣主要是四氧化三铁、三氧化二铁，而等离子切割渣除了有氧，还有氮等其它成分。更详细、更准确的需要光谱分析可以得出。

等离子体

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等离子灯

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等离子灯

等离子体（等离子态，电浆，英文：Plasma）是一种电离的气体，由于存在电离出来的自由电子和带电离子，等离子体具有很高的电导率，与电磁场存在极强的耦合作用。等离子态在宇宙中广泛存在，常被看作物质的第四态（有人也称之为“超气态”）。等离子体由克鲁克斯在1879年发现，“Plasma”这个词，由朗廖尔在1928年最早采用。

目录

[隐藏]

o 21 电离

o

o 23 速率分布

3 参见

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常见的等离子体

等离子体是存在最广泛的一种物态，目前观测到的宇宙物质中，99%都是等离子体。

人造的等离子体

o 荧光灯，霓虹灯灯管中的电离气体

o 核聚变实验中的高温电离气体

o 电焊时产生的高温电弧

地球上的等离子体

o 火焰（上部的高温部分）

o 闪电

o 大气层中的电离层

o 极光

宇宙空间中的等离子体

o 恒星

o 太阳风

o 行星际物质

o 恒星际物质

o 星云

其它等离子体

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等离子体的性质

等离子态常被称为“超气态”，它和气体有很多相似之处，比如：没有确定形状和体积，具有流动性，但等离子也有很多独特的性质。

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电离

等离子体和普通气体的最大区别是它是一种电离气体。由于存在带负电的自由电子和带正电的离子，有很高的电导率，和电磁场的耦合作用也极强：带电粒子可以同电场耦合，带电粒子流可以和磁场耦合。描述等离子体要用到电动力学，并因此发展起来一门叫做磁流体动力学的理论。

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组成粒子

和一般气体不同的是，等离子体包含两到三种不同组成粒子：自由电子，带正电的离子和未电离的原子。这使得我们针对不同的组分定义不同的温度：电子温度和离子温度。轻度电离的等离子体，离子温度一般远低于电子温度，称之为“低温等离子体”。高度电离的等离子体，离子温度和电子温度都很高，称为“高温等离子体”。

相比于一般气体，等离子体组成粒子间的相互作用也大很多。

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速率分布

一般气体的速率分布满足麦克斯韦分布，但等离子体由于与电场的耦合，可能偏离麦克斯韦分布。

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参见

等离子体物理学

取自"http://zhwikipediaorg/wiki/%E7%AD%89%E7%A6%BB%E5%AD%90%E4%BD%93"

Category: 等离子体物理学

Plasma (physics)

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This article is about plasma in the sense of an ionized gas For other uses of the term, such as blood plasma, see plasma (disambiguation)

A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation

Enlarge

A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation

In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter "Ionized" in this case means that at least one electron has been removed from a significant fraction of the molecules The free electric charges make the plasma electrically conductive so that it couples strongly to electromagnetic fields This fourth state of matter was first identified by Sir William Crookes in 1879 and dubbed "plasma" by Irving Langmuir in 1928, because it reminded him of a blood plasma Ref

Contents

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1 Common plasmas

2 Characteristics

o 21 Plasma scaling

o 22 Temperatures

o 23 Densities

o 24 Potentials

3 In contrast to the gas phase

4 Complex plasma phenomena

5 Ultracold Plasmas

6 Mathematical descriptions

o 61 Fluid

o 62 Kinetic

o 63 Particle-in-cell

7 Fundamental plasma parameters

o 71 Frequencies

o 72 Lengths

o 73 Velocities

o 74 Dimensionless

o 75 Miscellaneous

8 Fields of active research

9 See also

10 External links

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Common plasmas

A solar coronal mass ejection blasts plasma throughout the Solar System http://antwrpgsfcnasagov/apod/ap020516html Ref & Credit

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A solar coronal mass ejection blasts plasma throughout the Solar System http://antwrpgsfcnasagov/apod/ap020516html Ref & Credit

Plasmas are the most common phase of matter The entire visible universe outside the Solar System is plasma, since all we can see are stars Since the space between the stars is filled with a plasma, although a very sparse one (see interstellar- and intergalactic medium), essentially the entire volume of the universe is plasma In the Solar System, the planet Jupiter accounts for most of the non-plasma, only about 01% of the mass and 10-15 of the volume within the orbit of Pluto Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of a plasma (see dusty plasmas)

Commonly encountered forms of plasma include:

Artificially produced

o Inside fluorescent lamps (low energy lighting), neon signs

o Rocket exhaust

o The area in front of a spacecraft's heat shield during reentry into the atmosphere

o Fusion energy research

o The electric arc in an arc lamp or an arc welder

o Plasma ball (sometimes called a plasma sphere or plasma globe)

Earth plasmas

o Flames (ie fire)

o Lightning

o The ionosphere

o The polar aurorae

Space and astrophysical

o The Sun and other stars (which are plasmas heated by nuclear fusion)

o The solar wind

o The Interplanetary medium (the space between the planets)

o The Interstellar medium (the space between star systems)

o The Intergalactic medium (the space between galaxies)

o The Io-Jupiter flux-tube

o Accretion disks

o Interstellar nebulae

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Characteristics

The term plasma is generally reserved for a system of charged particles large enough to behave as one Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (ie respond to magnetic fields and be highly electrically conductive)

In technical terms, the typical characteristics of a plasma are:

1 Debye screening lengths that are short compared to the physical size of the plasma

2 Large number of particles within a sphere with a radius of the Debye length

3 Mean time between collisions usually is long when compared to the period of plasma oscillations

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Plasma scaling

Plasmas and their characteristics exist over a wide range of scales (ie they are scaleable over many orders of magnitude) The following chart deals only with conventional atomic plasmas and not other exotic phenomena, such as, quark gluon plasmas:

Typical plasma scaling ranges: orders of magnitude (OOM)

Characteristic Terrestrial plasmas Cosmic plasmas

Size

in metres (m) 10-6 m (lab plasmas) to:

102 m (lightning) (~8 OOM) 10-6 m (spacecraft sheath) to

1025 m (intergalactic nebula) (~31 OOM)

Lifetime

in seconds (s) 10-12 s (laser-produced plasma) to:

107 s (fluorescent lights) (~19 OOM) 101 s (solar flares) to:

1017 s (intergalactic plasma) (~17 OOM)

Density

in particles per

cubic metre 107 to:

1021 (inertial confinement plasma) 1030 (stellar core) to:

100 (ie, 1) (intergalactic medium)

Temperature

in kelvins (K) ~0 K (Crystalline non-neutral plasma[2]) to:

108 K (magnetic fusion plasma) 102 K (aurora) to:

107 K (Solar core)

Magnetic fields

in teslas (T) 10-4 T (Lab plasma) to:

103 T (pulsed-power plasma) 10-12 T (intergalactic medium) to:

107 T (Solar core)

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Temperatures

The central electrode of a plasma lamp, showing a glowing blue plasma streaming upwards The colors are a result of the radiative recombination of electrons and ions and the relaxation of electrons in excited states back to lower energy states These processes emit light in a spectrum characteristic of the gas being excited

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The central electrode of a plasma lamp, showing a glowing blue plasma streaming upwards The colors are a result of the radiative recombination of electrons and ions and the relaxation of electrons in excited states back to lower energy states These processes emit light in a spectrum characteristic of the gas being excited

The defining characteristic of a plasma is ionization Although ionization can be caused by UV radiation, energetic particles, or strong electric fields, (processes that tend to result in a non-Maxwellian electron distribution function), it is more commonly caused by heating the electrons in such a way that they are close to thermal equilibrium so the electron temperature is relatively well-defined Because the large mass of the ions relative to the electrons hinders energy transfer, it is possible for the ion temperature to be very different from (usually lower than) the electron temperature

The degree of ionization is determined by the electron temperature relative to the ionization energy (and more weakly by the density) in accordance with the Saha equation If only a small fraction of the gas molecules are ionized (for example 1%), then the plasma is said to be a cold plasma, even though the electron temperature is typically several thousand degrees The ion temperature in a cold plasma is often near the ambient temperature Because the plasmas utilized in plasma technology are typically cold, they are sometimes called technological plasmas They are often created by using a very high electric field to accelerate electrons, which then ionize the atoms The electric field is either capacitively or inductively coupled into the gas by means of a plasma source, eg microwaves Common applications of cold plasmas include plasma-enhanced chemical vapor deposition, plasma ion doping, and reactive ion etching

A hot plasma, on the other hand, is nearly fully ionized This is what would commonly be known as the "fourth-state of matter" The Sun is an example of a hot plasma The electrons and ions are more likely to have equal temperatures in a hot plasma, but there can still be significant differences

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Densities

Next to the temperature, which is of fundamental importance for the very existence of a plasma, the most important property is the density The word "plasma density" by itself usually refers to the electron density, that is, the number of free electrons per unit volume The ion density is related to this by the average charge state \langle Z\rangle of the ions through n_e=\langle Z\rangle n_i (See quasineutrality below) The third important quantity is the density of neutrals n0 In a hot plasma this is small, but may still determine important physics The degree of ionization is ni / (n0 + ni)

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Potentials

Lightning is an example of plasma present at Earth's surface Typically, lightning discharges 30 thousand amps, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays [1] Plasma temperatures in lightning can approach 28,000 kelvins and electron densities may exceed 1024/m3

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Lightning is an example of plasma present at Earth's surface Typically, lightning discharges 30 thousand amps, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays [1] Plasma temperatures in lightning can approach 28,000 kelvins and electron densities may exceed 1024/m3

Since plasmas are very good conductors, electric potentials play an important role The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the plasma potential or the space potential If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to the development of a Debye sheath Due to the good electrical conductivity, the electric fields in plasmas tend to be very small, although where double layers are formed, the potential drop can be large enough to accelerate ions to relativistic velocities and produce synchrotron radiation such as x-rays and gamma rays This results in the important concept of quasineutrality, which says that, on the one hand, it is a very good approximation to assume that the density of negative charges is equal to the density of positive charges (n_e=\langle Z\rangle n_i), but that, on the other hand, electric fields can be assumed to exist as needed for the physics at hand

The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density A common example is to assume that the electrons satisfy the Boltzmann relation, n_e \propto e^{e\Phi/k_BT_e} Differentiating this relation provides a means to calculate the electric field from the density: \vec{E} = (k_BT_e/e)(\nabla n_e/n_e)

It is, of course, possible to produce a plasma that is not quasineutral An electron beam, for example, has only negative charges The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive electrostatic force

In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie greater than the Debye length) But the existence of charged particles causes the plasma to generate and be affected by magnetic fields This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object that separates charge over a few tens of Debye lengths The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics

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In contrast to the gas phase

Plasma is often called the fourth state of matter It is distinct from the three lower-energy phases of matter; solid, liquid, and gas, although it is closely related to the gas phase in that it also has no definite form or volume There is still some disagreement as to whether a plasma is a distinct state of matter or simply a type of gas Most physicists consider a plasma to be more than a gas because of a number of distinct properties including the following:

Property Gas Plasma

Electrical Conductivity Very low

Very high

1 For many purposes the electric field in a plasma may be treated as zero, although when current flows the voltage drop, though small, is finite, and density gradients are usually associated with an electric field according to the Boltzmann relation

2 The possibility of currents couples the plasma strongly to magnetic fields, which are responsible for a large variety of structures such as filaments, sheets, and jets

3 Collective phenomena are common because the electric and magnetic forces are both long-range and potentially many orders of magnitude stronger than gravitational forces

Independently acting species One Two or three

Electrons, ions, and neutrals can be distinguished by the sign of their charge so that they behave independently in many circumstances, having different velocities or even different temperatures, leading to new types of waves and instabilities, among other things

Velocity distribution Maxwellian May be non-Maxwellian

Whereas collisional interactions always lead to a Maxwellian velocity distribution, electric fields influence the particle velocities differently The velocity dependence of the Coulomb collision cross section can amplify these differences, resulting in phenomena like two-temperature distributions and run-away electrons

Interactions Binary

Two-particle collisions are the rule, three-body collisions extremely rare Collective

Each particle interacts simultaneously with many others These collective interactions are about ten times more important than binary collisions

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Complex plasma phenomena

Tycho's Supernova remnant, a huge ball of expanding plasma Langmuir coined the name plasma because of its similarity to blood plasma, and Hannes Alfvén noted its cellular nature Note also the filamentary blue outer shell of X-ray emitting high-speed electrons

Enlarge

Tycho's Supernova remnant, a huge ball of expanding plasma Langmuir coined the name plasma because of its similarity to blood plasma, and Hannes Alfvén noted its cellular nature Note also the filamentary blue outer shell of X-ray emitting high-speed electrons

Plasma may exhibit complex behaviour And just as plasma properties scale over many orders of magnitude (see table above), so do these complex features Many of these features were first studied in the laboratory, and in more recent years, have been applied to, and recognised throughout the universe Some of these features include:

Filamentation, the striations or "stringy things" seen in a "plasma ball", the aurora, lightning, and nebulae They are caused by larger current densities, and are also called magnetic ropes or plasma cables

Double layers, localised charge separation regions that have a large potential difference across the layer, and a vanishing electric field on either side Double layers are found between adjacent plasmas regions with different physical characteristics, and can accelerate ions and produce synchrotron radiation (such as x-rays and gamma rays)

Birkeland currents, a magnetic-field-aligned electric current, first observed in the Earth's aurora, and also found in plasma filaments

Circuits Birkeland currents imply electric circuits, that follow Kirchhoff's circuit laws Circuits have a resistance and inductance, and the behaviour of the plasma depends on the entire circuit Such circuits also store inductive energy, and should the circuit be disrupted, for example, by a plasma instability, the inductive energy will be released in the plasma

Cellular structure Plasma double layers may separate regions with different properties such as magnetization, density, and temperature, resulting in cell-like regions Examples include the magnetosphere, heliosphere, and heliospheric current sheet

Critical ionization velocity in which the relative velocity between an ionized plasma and a neutral gas, may cause further ionization of the gas, resulting in a greater influence of electomagnetic forces

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Ultracold Plasmas

It is also possible to create ultracold plasmas, by using lasers to trap and cool neutral atoms to temperatures of 1 mK or lower Another laser then ionizes the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion

The key point about ultracold plasmas is that by manipulating the atoms with lasers, the kinetic energy of the liberated electrons can be controlled Using standard pulsed lasers, the electron energy can be made to correspond to a temperature of as low as 01 K ­ a limit set by the frequency bandwidth of the laser pulse The ions, however, retain the millikelvin temperatures of the neutral atoms This type of non-equilibrium ultracold plasma evolves rapidly, and many fundamental questions about its behaviour remain unanswered Experiments conducted so far have revealed surprising dynamics and recombination behaviour that are pushing the limits of our knowledge of plasma physics

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Mathematical descriptions

Plasmas may be usefully described with various levels of detail However the plasma itself is described, if electric or magnetic fields are present, then Maxwell's equations will be needed to describe them The coupling of the description of a conductive fluid to electromagnetic fields is known generally as magnetohydrodynamics, or simply MHD

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Fluid

The simplest possibility is to treat the plasma as a single fluid governed by the Navier Stokes Equations A more general description is the two-fluid picture, where the ions and electrons are considered to be distinct

[edit]

Kinetic

For some cases the fluid description is not sufficient Kinetic models inc

等离子指在电离过程频繁发生的条件下，电子和阳离子的浓度达到一定数值，从而形成的一种物质状态，其物理性质与固态、液态和气态不同。

1、概念

当电离过程频繁发生，使电子和阳离子的浓度达到一定的数值时，物质的状态也就起了根本的变化，它的性质也变得与气体完全不同。为区别于固体、液体和气体这三种状态，我们称物质的这种状态为物质的第四态，又起名叫等离子态。

2、特点

等离子态下的物质具有类似于气态的性质，比如良好的流动性和扩散性。但是，由于等离子体的基本组成粒子是离子和电子，因此它也具有许多区别于气态的性质，比如良好的导电性、导热性。特别的，根据科学计算，等离子体的比热容与温度成正比，高温下等离子体的比热容往往是气体的数百倍。

3、用途

等离子体的用途非常广泛。从我们的日常生活到工业、农业、环保、军事、医学、宇航、能源、天体等方面，它都有非常重要的应用价值。

在工业上的应用有等离子切割机，等离子切割配合不同的工作气体可以切割各种氧气切割难以切割的金属，尤其是对于有色金属（不锈钢、铝、铜、钛、镍）切割效果更佳；其主要优点在于切割厚度不大的金属的时候，等离子切割速度快，尤其在切割普通碳素钢薄板时，速度可达氧切割法的5~6倍、切割面光洁、热变形小、几乎没有热影响区。

等离子体的应用如下：

1、等离子体冶炼：用于冶炼用普通方法难于冶炼的材料，例如高熔点的锆（Zr）、钛（Ti）、钽（Ta）、铌（Nb）、钒（V）、钨（W）等金属；还用于简化工艺过程，例如直接从ZrCl、MoS、TaO和TiCl中分别获得Zr、Mo、Ta和Ti。

用等离子体熔化快速固化法可开发硬的高熔点粉末，如碳化钨-钴、Mo-Co、Mo-Ti-Zr-C等粉末，等离子体冶炼的优点是产品成分及微结构的一致性好，可免除容器材料的污染。

2、等离子体喷涂：许多设备的部件应能耐磨耐腐蚀、抗高温，为此需要在其表面喷涂一层具有特殊性能的材料。

用等离子体沉积快速固化法可将特种材料粉末喷入热等离子体中熔化，并喷涂到基体（部件）上，使之迅速冷却、固化，形成接近网状结构的表层，这可大大提高喷涂质量。

3、等离子体焊接：可用以焊接钢、合金钢；铝、铜、钛等及其合金。特点是焊缝平整，可以再加工，没有氧化物杂质，焊接速度快。用于切割钢、铝及其合金，切割厚度大。