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Does the chromium in stainless steel contain 'chrome 6' (Cr6+ ) and is this a potential health hazard
      
标题:在不锈钢中存在的铬是否包含六价铬(Cr6+),是否对人体有潜在的危害?



Valency states of chromium

铬的价态
      
The valency (oxidation state) of chromium metal as an alloying constituent of stainless steels is 0 (zero).

当铬元素以不锈钢合金存在的时候,铬的价态(即氧化状态)是0(zero)。

Chromium atoms are present in stainless steels in 'substitutional' lattice positions, replacing iron atoms. This is the same as other 'large' atoms from elements such nickel. The atoms are held together in the lattice structure by the 'metallic bond'. This involves the sharing of electrons between atoms with no loss or gain of electrons from atom to atom. The valency state is therefore taken as 0 (zero).

铬的原子是以一种“替代式的”晶格位置,代替铁原子存在于不锈钢之中。这和不锈钢中的其它大量元素的原子的状态一样,比如镍。这些个原子通过“金属键”以晶格结构结合在一起。这使得原子之间的电子共享而原子相互间并没有得到或者失去电子。这样的价态被称作为0(zero)。

The chromium in solid stainless steels should not be regarded as a health hazard.

因此,在固态不锈钢合金中的铬不应被当作健康的危害因素。

In contrast ionic bonding in compounds, such as sodium chloride (common salt), involves the exchange of electrons between atoms and hence valency states of 1, 2, 3 etc depending on how many electrons the element has lost or gained. It is compounds involving chromium 'ions' with a valency state of 6 (which includes chromates) that have been identified as a cause for health concerns. This valency state is also referred to as 'chromium 6', 'hexavalent chromium' or 'Cr6+'

对比化合物中的离子键结合,比如氯化钠(即盐),它的原子间存在电子交换,它的元素得到或者失去了不同数量的电子因而产生了1,2,3等不同的价态。如果有种化合物使得铬离子形成了6这个价态(其中包括铬酸盐)那么这种化合物是对体有害的。这个价态也被称为“6价铬”、“六价铬”或“Cr6+”。

Release of chromium if stainless steels corrodes      

不锈钢受到腐蚀时析出的铬

If stainless steels are subject to corrosion metal ions are released from the alloy into the surrounding environment. Under these conditions, chromium ions are usually in the trivalent state (Cr3+), which like the chromium in the un-corroded steel, is not be a health hazard. There is one very specific example where corrosion may produce very small quantities of hexavalent chromium at ambient temperature. This is where some strong oxidisers with a pH of 10-14 are in prolonged contact with stainless steel and cause corrosion over time.

一旦不锈钢受到腐蚀,金属离子就会被从合金中释放到周围环境。这时候析出的铬离子往往是三价铬(Cr3+),它跟未腐蚀的金属中的铬一样对人体是无害的。但是有一个很特殊的情况使得不锈钢在室温下受到腐蚀时会产生极少量的六价铬,那就是让不锈钢和一些PH值在10-14的强氧化剂长时间接触并受到腐蚀的时候。

Chromium in stainless steel welding fumes

 不锈钢焊接烟尘中的铬

Fumes from welding stainless steels may contain hexavalent chromium ions, depending on the process and any fluxes used.

在焊接不锈钢产生烟尘中可能包含六价的铬离子,这取决于焊接过程和使用的焊剂。

This is described in more detail, separately; fume associated with welding stainless steel

更详细的描述在另一篇文章:fume associated with welding stainless steel

Efficient local exhaust ventilation systems should normally be suitable for maintaining exposure limits below the 0.05 mg/m3 limit for hexavalent chromium ions.

焊接时应具备良好的通风排气系统使得六价铬离子的接触限值低于0.05 mg/m3这个限值。

Fume associated with welding and cutting stainless steels

标题:焊接和切割不锈钢时的烟尘

Fume associated with welding stainless steel      

焊接不锈钢时的烟尘
      
Fume is generated by arc welding processes used for welding stainless steels, both the flux-shielded processes (manual metal arc and flux cored arc) and the gas-shielded processes (tungsten inert gas and metal inert/active gas). Plasma arc cutting also produces fume.

选择电弧焊对不锈钢进行焊接时,不管是在焊剂保护焊(包括手工金属电弧焊和药芯焊丝电弧焊)或是在气体保护焊(包括钨极惰性气体保护焊和金属极惰性/活性气体保护焊)下焊接都会产生烟尘。使用等离子弧进行切割的时候同样会产生烟尘。

Fume can be defined as the airborne particles and gases arising during welding or cutting by vaporisation and reaction. Flux-shielded processes form particles of complex composition. Ozone is created by the action of ultraviolet radiation on the atmosphere in the gas-shielded processes. The tungsten inert gas process produces little particulate fume but the metal inert/active gas processes generate both particles and ozone.

随着焊接或者切割时的气化反应所产生的烟尘,可以分为空气微粒和气体。焊剂保护焊过程中会生成复合物微粒。而在气体保护焊过程中造成的紫外线会在周围的空气中制造出臭氧。钨极惰性气体保护焊过程中会产生少量的微粒烟尘,但是在金属极惰性/活性气体保护焊过程中会同时产生微粒烟尘和臭氧。

There have been concerns that fume from welding of stainless steels, particularly the particles containing hexavalent chromium formed in flux-shielded processes, is a cause of cancer. Extensive studies over a long period have not supported this view but have nevertheless shown that there is a slight excess of lung cancer among all welders, whether of mild steel or alloy steels. It is therefore sensible to take action to limit contact with welding fume by process selection and/or engineering controls, such as ventilation and extraction. Local fume extraction is more effective than general ventilation. While personal protective equipment such as an air-fed helmet may also safeguard the wearer, it should only be considered for situations such as confined spaces, if only because ancillary workers are otherwise left unprotected.
   
有人担心,不锈钢焊接时产生的烟尘,尤其是焊剂保护焊产生的微粒含有六价铬,是癌症的一个诱因。长期的研究表明这个观点并不成立,但是却又有证据显示不锈钢焊工在所有的焊工中,不论是碳钢焊工还是合金钢焊工之中得肺癌的机率稍微有点偏高。因此,采取合理的焊接工艺或者流程控制来减少对焊接烟尘的接触是明智的选择,比如采取通风和排烟系统。采用局部排烟系统比一般通风方式更有效。虽然个人防护用品比如一个空气头盔也可能会保护好穿戴者,但它只适合在密闭空间的情形下使用,否则相关的辅助工人就会失去保护。

There is a statutory requirement to control exposure to welding fume, expressed as a general exposure limit for welding fume and OES (occupational exposure standards) and MEL (maximum exposure limits), for individual elements, as specified by the Health and Safety Executive. Sampling to determine exposure is expensive and should only be considered when control measures have been taken and a residual risk has been identified. There are also methods of calculating exposure levels from consumable manufacturers' data.

已经有一些相关的法规来控制人与焊接烟尘的接触,比如由健康和安全执行机构针对个别元素制定了焊接烟尘的一般接触限值、OES(职业接触标准)和MEL(最大接触限值)。以抽样的方式确定接触值成本很高,而且只能在有完备的测量方法并且剩余量明确的情况下才被考虑。也有从制造商的数据中计算接触等级的方法。

A typical safety data sheet relating to stainless steel can be downloaded from here.

还有一篇来自美国劳工部网站的文章提到在工业生产中几种受到六价铬危害的情况

■Welding and other types of "hot work" on stainless steel and other metals that contain chromium     

对不锈钢和其它含铬的材料进行焊接等高温作业   

■Use of pigments, spray paints and coatings      

使用颜料,喷漆和镀膜涂层时
        
■Operating chrome plating baths       

镀铬浴操作时