Introduction

The Arvida Research and Development Centre (ARDC) produces, certifies and distributes standard samples of aluminum and its alloys for use as certified reference materials (CRM).

These standards are designed for use with direct reading optical emission spectrometers for spark emission analysis.

ARDC has produced these standards since 1949, primarily to analyze aluminum alloys produced by the Rio Tinto Alcan group.

Intent of Use

Rio Tinto Alcan Certified Reference Material (CRM) for the spectrochemical analysis of aluminum and its alloys is produced by a direct chill, continuous cast method.

The cast billets measure generally 70 mm in diameter and up to 3 m in length. They are subsequently scalped and sliced, producing about 300 to 600 disks per cast.

Each finished disk measures 57 mm in diameter by 25 mm thick.  The disk is permanently stamped or labeled with:

• The Rio Tinto Alcan logo

• The reference material name

• A unique identifier indicating the source billet and the disk position within the billet.

Some older standards may also have individually certified concentration values stamped on their back.

The Rio Tinto Alcan CRMs are specifically prepared and certified for the spectrochemical analysis of metallic aluminum and its alloys.

To minimize any residual effects of macro and microstructure on the spectral response, the CRMs should be analyzed by Optical Emission Spectrometric method, on the annular band at a distance of 10 mm from the edge of the sample, as specified in the Rio Tinto Alcan Method of analysis 1304 or ASTM E1251.

Nomenclature

Rio Tinto Alcan reference material names take the form AAAA SSS, where “AAAA” is generally the identification of the alloy using the Aluminum Association nomenclature and “SSS” identifies the particular cast (series) with the exception of special CRMs (examples: the boron standards).

The series identification is two-letters, in the sequence from “AA” to “ZZ”, with an optional single letter prefix indicating the category of standard.

ARDC produces five basic types of drift RM and OES CRMs:

• High purity standards use HP as the alloy identification followed by the two-letter series identification, for example HP FK.  HP standards are samples of aluminum with very high purity, >99.999%.  They are used during the standardization of the instrument to fix the bottom of the analytical curve for alloying elements.

• Blank standards use the alloy identification with a “C” prefix to the two-letter series identification, for example 3104 CAP.  Blank standards are aluminum alloy standards fabricated from high purity aluminum, so therefore have trace element concentrations < 1 ppm.  They are used during the standardization to fix the bottom of the analytical curve generally for minor and trace elements to compensate for matrix effects of the alloying elements.

• Working standards use the alloy identification followed by the two-letter series identification, for example 3104 AR.  They are also known as TOP standards and are generally certified for 24 or more alloying and trace elements.

• Boron standards are aluminum samples containing only three elements used for boron analysis. They are certified for boron, silicon, and iron.  Example: 1S CAM.

• Drift samples use the alloy identification with a “D” prefix to the two-letter series identification, for example 3104 DAS.  They are aluminum alloy samples with a low concentration of trace elements.

Drift samples are very homogeneous but are not certified. They are used to determine whether the measuring instrument has drifted enough to require standardization.

Method of Analysis

Methods of analysis used for certification vary from classical wet chemistry to modern instrumental techniques. They include:

• Photometric method

• Atomic Absorption Spectrometry (AAS)

• Inductively Coupled Plasma- Atomic Emission Spectrometry and Mass Spectrometry (ICP/AES and ICP/ MS )

• Optical Emission Spectrometry (OES)

• Glow Discharge Mass Spectrometry (GDMS).

Values below 0.5 ppm are indicated by “L” within the catalogue, uncertified values used for alloy identification are indicated by “N” within the catalogue.

Traceability

The traceability of the certified values is ensured by the comparative use of other internationally recognized certified reference materials produced by NIST, and other suppliers of OES CRMs.

Assignment of Uncertainty

The certified values listed are the mean values from several analyses, using at least two methods performed by two different analysts when possible.  Generally, values from an external laboratory are also included in the certification process.

Each analytical measurement has the uncertainty reported with a 95% level of confidence. The uncertainty reported for the certified value includes the standard deviation of the homogeneity within the billet (for elements not certified individually).

Individual Certification

All billets are tested for cast homogeneity using OES.  When indicated by the homogeneity test, each disk is assigned an individual certified value.

Homogeneity testing reveals that some elements are not always uniformly distributed, usually because of the loss (burn off) of light elements (e.g. Li, Na, Ca, Mg) during casting.  In these cases, each disk is assigned an individual value as determined from the homogeneity test.

The uncertainty reported for individually certified elements is on the individual value and does not include any variation due to billet homogeneity.

Individually certified elements are indicated by an “i” on the global certificate and in the catalogue.

Certificate of Analysis

There are two formats of certificate of analysis.

• A global certificate of analysis indicates the certified values with the uncertainties and the elements individually certified.

• Individual certificates are generated for standards with individually certified elements.  The certificate for each disc reports its certified composition, including the individual values.

• For blank, boron and HP standards, only the global certificate is provided; these CRMs do not contain individually certified elements.

Period of Validity

The Rio Tinto Alcan certification is valid within the stated uncertainty for the lifetime of the CRM when used for the intended methods of analysis.

A certification revision may be required when an improved method of analysis becomes available.

Signatures

The original unmodified certificate provided by RioTinto Alcan is valid without signature (refer to ISO Guide 31) as long as it includes, in the heading of the certificate, the name of the organization, the full address, the telephone and fax numbers, and the name of the person responsible for the information appearing on the certificate.

Accreditation Testing

The Arvida Research and Development Centre analytical laboratory is accredited ISO 17025 and is audited biannually by the Standard Council of Canada.  The laboratory prides itself in maintaining its high standards in performing the methods of analysis referred to above.  The original certification date is August 8th, 1989.

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