May 2016 Archives

Analyzing the harmful substances content is a requirement for products in order to pass the criteria defined in WEEE and RoHS Directive. From this volume, we will be introducing you instrumental analysis methods, including the fluorescent X-ray analysis, which is a popular method of simplified analysis, as well as the official methods of analysis, including the atomic absorption and ICP emission spectrometric analysis. Now, let's start with the fluorescent X-ray analysis.

(1) Measurement principle

Atoms comprising a substance have their unique core electron level. Emitting X-ray, γ-ray, or electron beam to this atom generates the X-ray with characteristics unique to that atom (so called "characteristic X-ray"). This X-ray is called fluorescent X-ray. The energy (wavelength) is known to correspond with difference of atom's core electron level, which is equal to the characteristic energy transferred between the atom shells.
The fluorescent X-ray analysis analyzes the type and volume of atoms present in a substance by using this fluorescent X-ray. The qualitative analysis identifies the type of atoms while the quantitative analysis measures the contained amount.

(2) Characteristics

(1) Qualitative analysis

This method can identify impurity elements attached to or mixed into compounds, mixtures, and reagents and can easily perform analyses of elements such as rare-earth elements that are difficult for normal analyses.

(2) Quantitative analysis

In addition to the ratio by weight or molar ratio of the element, this method can measure coating thickness of plating and the weight of a trace substance.

(3) No use of reference sample

This analysis used to require a reference sample. However, adopting the fundamental parameter (FP) method has eliminated the need for reference samples in the analysis. The improvement of data processing abilities by PC and its lowered cost have made the integration of atom-specific energy database and FP method programs easier than ever. Therefore, if you know the composition information of a sample, it is possible to calculate the X-ray strength by inputting FP (physical constant or fundamental constant) along with the measurement conditions into the logical formula based on the generation principle of fluorescent X-ray. This calculation result can be used for identifying elements and analyzing the amount.

(4) No pretreatment required

Usual analytical methods require pretreatment processes, such as dissolving a sample into acid. However, with the fluorescent X-ray analysis, you can analyze samples in the solid state without performing such pretreatment process.

The European Union (EU) member states have long been interested in resolving environmental problems and promoting the movements of regulating harmful substances contained in telecommunication equipment and computer products. Accordingly, they issued the Directive on the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment (RoHS Directive, in short).

This law became effective in July 2006. Since then, only the products that have passed the criteria of this directive are allowed for export. The corporations were trying hard to keep up with the new enforcement. [Table 1] shows the restricted substances and their concentration level permitted. Now, let's take a look at each item.

[Table 1] Restricted substances and maximum permitted concentration defined in RoHS Directive

Use of cadmium has been banned for electroplating. However, cadmium has been used as a stabilizer for plastics.

A slight amount of hexavalent chromium is present in the chromate film as a result of using the treatment liquid containing this material during the chromate treatment after applying zinc plating on steel screws, chassis, and metallic parts. Hexavalent chromium was also used for chemical conversion coating applied to aluminum alloy and magnesium alloy in order to improve anticorrosion properties. Currently, trivalent chromium is an alternative chemical for hexavalent chromium. However, the ultimate goal is to eliminate chromium in the products regardless of what type of ionic form it is.

Mercury is never used for surface treatment processes. However, because some of the batteries contain mercury, they are the restriction target of this directive.

The lead regulation mainly targets the lead content in tin-lead alloy solder used for attaching parts to printed circuit boards or tin-lead alloy solder plating applied to soldered areas. In addition to this, the lead content was also found as pigments in coating films and plastic materials.

The use of lead in solder itself or solder plating has become obsolete. Instead, using tin-silver or tin-copper alloy solder and ternary/quaternary alloy seems to be common nowadays.

PBBs and PBDEs are added to the plastic materials that make up printed circuit boards and used as flame retardants.

In recent years, more and more corporations are asked from their clients to present the analysis result of product content concerning these restricted substances. If you perform an official analysis (concentration measurement by dissolving a certain weight of sample into "agua regia" - a mixture of nitric acid and hydrochloric acid and diluting it with pure water) in the units of ppm, it requires tremendous cost and time. Therefore, the atomic absorption analysis or ICP emission spectrometric analysis will be selected for heavy metal products. For organic materials such as PBB, the gas chromatography mass spectrometry will be adopted.

The effective analysis method in terms of the time and cost is to perform a simplified analysis to check for an existence of the restricted substances first. Then, perform the official analysis only when such content was found. The fluorescent X-ray analysis is a common method of the simplified analysis.

(1) Description of the law

In addition to complying with the effluent standards defined by laws and regulations for water discharged from factories and plants, it is also important for them to implement soil management practices for their factory site. It is imperative for the management to implement countermeasures for preventing soil and groundwater contamination caused by harmful substances leaked to or soaked into the factory ground.
In the past, old factory site developed into a common area or a residential area turned out to be contaminated with heavy metals or organic compounds such as trichloroethylene, which posed danger to the residents.
To prevent such problems, the Soil Contamination Countermeasures Act was established, which went into effect on February 15, 2003. The purpose of this law is to mandate the plants and factories involving the use of harmful substances in their processes including surface treatments to perform a pollution survey when they sell the business or reuse the land for new construction. If the soil is contaminated, the land is subject to soil purification.
The harmful substances designated by this law are as follows:

Category I Specified Toxic Substances

11 types of volatile organic compounds (such as Trichloroethylene)

Category II Specified Toxic Substances

Nine types of heavy metals including lead and its compounds

Category III Specified Toxic Substances

Five types of agrichemical substances including Simazine

(2) Standards for heavy metals

The soil elution amount and content are the two reference values used for evaluating the degree of soil contamination caused by heavy metals. [Table 1] shows these reference values.

[Table 1] Reference values of soil elution amount and its content

(1) Soil Leachate Standard

The Soil Leachate Standard was established in consideration of health risks caused by ingesting groundwater containing harmful heavy metals eluted into it through rainwater and waterways. The concentration is calculated by using a soil sample of certain weight and measuring the amount of harmful substances dissolved into pure water.

(2) Soil Concentration Standard

The Soil Concentration Standard was established in consideration of health risks caused by a high concentration of harmful substances in the soil containing heavy metals when people inhale the soil particles by accident or the soil contacts the skin after it had spread into atmosphere.

Water quality standards of water discharged from plants and factories are referred to as "effluent standards" in legal terms. The effluent standards define the maximum allowable values of restricted substances in units of the concentration level (mg/L). [Table 1] is an example of items related to surface treatment processes that are regulated by the effluent standards.

[Table 1] Example of effluent standards 1)

Restricted substances Water Pollution Control Act Sewerage Act Sewerage Ordinance of Tokyo Metropolitan Government Tokyo Metropolitan Ordinance on Environmental Preservation Cyanogen mg/L 1 1 1 1 Hexavalent chromium mg/L 0.5 0.5 0.5 0.5 Cadmium mg/L 0.1 0.1 0.1 0.1 Lead mg/L 0.1 0.1 0.1 0.1 Arsenic mg/L 0.1 0.5 0.5 0.1 Total mercury mg/L 0.005 0.005 0.005 0.005 Alkyl mercury mg/L Not Detected 2) Not Detected Not Detected Not Detected Organic phosphorus mg/L 1 1 1 1 Trichloro- ethylene mg/L 0.3 0.3 0.3 0.3 Tetrachloro- ethylene mg/L 0.1 0.1 0.1 0.1 Boron and its compounds mg/L 10 10 10 10 Fluorine and its compounds mg/L 8 8 8 8 pH - 5.8〜8.6 5〜9 5〜9 5.8〜8.6 Temp ℃ 45 45 45 40 Total chromium mg/L 2 2 2 2 Copper mg/L 3 3 3 3 Zinc mg/L 5 5 5 5 Soluble iron mg/L 10 10 10 10 Soluble Mn mg/L 10 10 10 10 Phenol mg/L 5 5 5 5 Mineral oil mg/L 5 5 5 5 Nitrogen mg/L 120 240 120 120 Phosphorus mg/L 16 32 16 16 BOD mg/L 300 600 600 25 SS mg/L 300 600 300 50 Restricted substances Water Pollution Control Act Sewerage Act Sewerage Ordinance of Tokyo Metropolitan Government Tokyo Metropolitan Ordinance on Environmental Preservation

As we have seen here, the surface treatment plants must fully comply with various regulations for discharging water from the plants. In order to do so, they must implement measures, such as adopting a process of converting toxic substances into non-toxic substances, etc.