Stabilisation of the materials

Reference materials find their utility because the analyst can use them when he wants. Therefore, they must be stable. CRMs have a guaranteed — certified — content of a substance the producer must guarantee the stability of this substance and of the matrix. RMs for intralaboratory and interlaboratory studies must also be stable. As already mentioned above, stabilisation of the material must be done in such a way that it does not affect the representativeness of the material. In the food/feed control field, as well as in the 

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Finally, as shown in Figure 4.7, stabilisation of the material may be necessary at various stages of the procedure. The best choice will depend on the type of material, size of batch and equipment available. 

Stability remains a difficult aspect of the production of CRMs, in particular matrix materials for environmental monitoring. Feasibility studies devoted to the stabilisation of the material must be conducted before any production starts. New materials, such as fresh materials, required by analysts increase the problem of... 

The effect of carbon on the corrosion of stainless steels in liquid sodium depends upon the test conditions and the composition of the steels . Stabilised stainless steels tend to pick up carbon from sodium, leading to a degree of carburisation which corresponds to the carbon activity in the liquid metal. Conversely, unstabilised stainless steels suffer slight decarburisation when exposed to very pure sodium. The decarburisation may promote corrosion in the surface region of the material and, under creep rupture conditions, can lead to cavity formation at the grain boundaries and decreased strength. 

It is a well-known fact that specific plastic materials like flexible PVC, Polyurethane or Silicone may be easily attacked by microorganisms leading to discoloration or mechanical failures.14 This susceptibility to microbial attack is mainly attributed to the plasticiser content of the material as well as other ingredients such as stabiliser or antioxidants.5,6 The predominant organisms on the surface of those plastics are fungi and actinomycetes and it is said that by the action of their extracellular enzymes other organisms such as bacteria may be able to grow on the material.7... 

The energy required to effect such a process decreases as t rises the process is also facilitated by increasing solvation, and consequent stabilisation, of the developing ion pair compared with the starting material. That such effects, particularly solvation, are of prime importance is borne out by the fact that SN1 type reactions are extremely uncommon in the gas phase. 

Radical attack on methylbenzene (toluene, 60) results in preferential hydrogen abstraction by Cl leading to overall substitution in the CH3 group, rather than addition to the nucleus. This reflects the greater stability of the first formed (delocalised) benzyl radical, PhCH2 (61), rather than the hexadienyl radical (62), in which the aromatic stabilisation of the starting material has been lost ... 

Annex II lists all those materials and components that are exempt from 4(2) (a). Eor example lead as an element (i.e. steel upto 0.35% lead by weight, aluminium, copper), lead compounds in components (i.e. batteries, petrol tank coatings, vibration dampers, stabilisers in protective paint), hexavalent chromium (used as coating on various key vehicle components) and mercury (as can be found in bulbs and instrument panel displays). As ruled in 4(2) (b), the Commission shall regularly amend Annex II, i.e. review all substances that are currently exempt from 4(2) (a). If the use of any of the materials or compounds listed in Annex II can be avoided, those substances will be deleted from this Annex. 

This behavior is not yet fully understood. So far, most of the material development has been performed in companies, indicating that the market for microwave dielectrics has been grown tremendously over the last years (as an example, each commercial satellite receiver contains a small microwave ceramic disk as frequency stabilising element for the local microwave... 

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