GB/T 31931-2015 English PDF (GBT31931-2015)

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GB/T 31931-2015: Zinc or zinc alloy coating on steel sheets or strips -- Determination of hexavalent chromium content. 1, 5-Diphenylcarbohydrazide (diphenylcarbazide) spectrophotometric method
GB/T 31931-2015
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.080.01
H 11
Zinc or Zinc Alloy Coating on Steel Sheets or Strips –
Determination of Hexavalent Chromium Content – 1,5-
Diphenylcarbohydrazide (Diphenylcarbazide)
Spectrophotometric Method
ISSUED ON. SEPTEMBER 11, 2015
IMPLEMENTED ON. JUNE 1, 2016
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Principle ... 5
4 Reagents and Materials ... 5
5 Apparatus ... 6
6 Sample Preparation ... 6
7 Test Procedures ... 6
8 Allowable Difference ... 8
9 Test Report ... 9
Foreword
This Standard was drafted as per the rules specified in GB/T 1.1-2009.
This Standard was proposed by China Iron and Steel Association.
This Standard shall be under the jurisdiction of National Technical Committee for
Standardization of Steel (SAC/TC 183).
Drafting organizations of this Standard. Anshan Iron and Steel Group Corporation,
SGS-CSTC Standards Technical Services (Shanghai) Co., Ltd., Central Iron Steel
Research Institute, and China Metallurgical Information and Standardization Institute.
Chief drafting staffs of this Standard. Chen Yiqing, Li Feng, Zhong Bin, Wang Yiling,
Han Xiaodong, Wang Haidan, Hou Yanxia, Liao Xiaoquan, and Chen Zibin.
Zinc or Zinc Alloy Coating on Steel Sheets or Strips –
Determination of Hexavalent Chromium Content – 1,5-
Diphenylcarbohydrazide (Diphenylcarbazide)
Spectrophotometric Method
Warning. personnel using this Standard shall have practical experience working
in the formal laboratory. This Standard doesn’t address all the possible safety
issues. The users shall assume the responsibility to take appropriate safety and
health measures, and ensure the compliance with the relevant national
regulations.
1 Scope
This Standard specifies using Diphenylcarbazide Spectrophotometric Method to
determine the hexavalent chromium content.
This Standard is applicable to the zinc and zinc alloy coating on steel sheets or strips,
thereof including the determination of hexavalent chromium content on the pure zinc,
zinc-iron alloy, zinc-aluminum and aluminum-zinc alloy coating surfaces. The
measuring range is 2µg/g~100µg/g or 0.020µg/cm2~10µg/cm2.
2 Normative References
The following documents are essential to the application of this document. For the
dated documents, only the versions with the dates indicated are applicable to this
document; for the undated documents, only the latest version (including all the
amendments) are applicable to this document.
GB/T 1839 Test Method for Gravimetric Determination of the Mass per Unit Area
of Galvanized Coatings on Steel Products
GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods
GB/T 7729 Chemical Analysis of Metallurgical Products - General Rule for
Spectrophotometric Methods
7.7.1 The hexavalent chromium content per unit area shall be expressed in µg/cm2;
the results shall retain two decimals, and be calculated as per Formula (1).
... (1)
Where.
W1 – Hexavalent chromium content per unit area (indicating single- or double-
surface), in µg/cm2;
G - Hexavalent chromium amount found on the calibration curve, in µg;
V – Total volume of the test solution, in mL;
V1 – Volume of sub-specimen solution, in mL;
A – Specimen single-surface area, in cm2.
7.7.2 Take the coating mass as the base, the hexavalent chromium content is
expressed in µg/g; the result shall retain two decimals, and be calculated as per
Formula (2).
... (2)
Where.
W2 – Hexavalent chromium content per unit area coating (indicating single-
or double-surface), in µg/cm2;
W1 – Hexavalent chromium content per unit area (indicating single- or double-
surface), in µg/cm2;
W3 – Coating mass per unit area (indicating single- or double-surface), in
g/m2.
8 Allowable Difference
The relative allowable difference between the two analytical results of the same
sample shall be no greater than the provision stipulated in Table 3.