Determination of gold bar purity remains one of the most challenging tasks in gold industry. Currently, the existing instruments have a limitation to determine the purity, which in turn have produced inaccurate gold purity measurement. For example, X-ray fluorescence (XRF) technique has a limitation to penetrate the gold bar and XRF was only used to determine the surface purity. Therefore, an improved non-destructive method and precise technique has been developed to determine the gold purity. Gold density measurement can verify the purity of the gold and in this study, the density of gold bar was calculated using a custom made hydrostatic weighing system (HWS). Several measurements of density were carried out for gold bar and tungsten bar. Using HWS, the density of gold bar and tungsten bar were 19.268 g/ml and 19.206 g/ml respectively. The expanded uncertainty was also evaluated and the value was 0.006 g/ml. The new developed HWS method was also verified with existing density measurement instruments where the same density results has been obtained but the existing instruments have produced bigger uncertainty of 0.2 g/ml. Thus, this study demonstrates that the developed HWS is appropriate to be used to measure the density of gold bar accurately. Furthermore, the new developed system of HWS have shown better measurement with smaller uncertainty and hence the improvement in gold bar purity measurement.
AbstrakPenentuan ketulenan jongkong emas dengan kaedah ujian tanpa musnah adalah perkara yang paling mencabar dalam industri emas terutama jika jongkong emas dipalsukan dengan cara meletakkan tungsten di dalamnya. Instrumen yang sedia ada mempunyai keterbatasan untuk menentukan ketulenan jongkong emas dan sukar untuk mengesan tungsten di dalamnya kerana tungsten mempunyai ketumpatan yang hampir sama dengan emas. Kajian ini mengemukakan keterbatasan instrumen kaedah ujian tanpa musnah seperti densimeter, alat timbangan, sinar-x pendarfluor dan ultrasonik. Dalam kajian ini menemui kesukaran untuk mengenal pasti emas palsu menggunakan instrumen kaedah ujian tanpa musnah seperti ultrasonik dan x-ray fluorescence (XRF) kerana instrumen ini mempunyai batasan. Setakat ini tiada lagi kajian yang berkaitan pemalsuan jongkong emas kerana harganya yang mahal untuk dijadikan sebagai sampel kajian. Masalah jongkong emas palsu dapat diselesaikan jika ketepatan instrumen yang digunakan untuk mengukur ketumpatan dapat ditingkatkan lagi sehingga 0.01 g/ml. Ini kerana perbezaan antara ketumpatan emas dan tungsten adalah 0.05 g/ml. Pemalsuan emas dengan mencampurkan tungsten akan dapat dikesan jika ada instrumen yang mempunyai ketepatan sekurang-kurangnya 0.01 g/ml. Manakala instrumen lain seperti XRF digunakan untuk mengesahkan ketulenan emas di bahagian permukaan sahaja. Oleh itu, bagi pengujian yang lebih menyeluruh masalah jongkong emas palsu ini perlu diselesaikan dengan menggabungkan kedua-dua kaedah ini. Abstract Determination of the gold bar purity by non-destructive method remains one of the most challenging in gold industry especially when the tungsten is inside the gold bar. The existing instruments have limitations in their accuracy to determine the purity of gold when tungsten also inside the gold bar since both tungsten and gold have almost similar densities. This study presents the limitations of the non-destructive test method instruments such as densimeter, weighing balance, x-ray fluorescence (XRF) and ultrasonic in determining the purity of gold. In this study found the difficulty in identifying counterfeit gold using non-destructive test method instruments such as ultrasonic and XRF due to some limitations. So far, there are no studies related to the counterfeiting of gold bars due to its expensive price to be used as a study sample. The problem of counterfeit gold bars can be solved if the accuracy of the instrument used to measure the density can be further increased up to 0.01 g/ml. This is because the difference between the density of gold and tungsten is 0.05 g/ml. Gold counterfeiting by mixing tungsten will be detectable if there is an instrument that has an accuracy of at least 0.01 g/ml. While other instruments such as XRF will be used to verify the purity of gold on the surface only. Therefore, for more thorough testing the problem of fake gold ingots needs to be solved by combining these two methods.
Main text This report describes the APMP key comparison on the hydrometer calibrations, APMP.M.D-K4. This comparison is an APMP regional key comparison of CIPM key comparison CCM.D-K4. Three hydrometers in the density range from 640 kg m-3 and 1 320 kg m-3 were used as travelling standards. Each hydrometer has a nominal density range of 20 kg m-3 with a scale division of 0.2 kg m-3. Eleven laboratories participated in this comparison. All laboratories except NMISA are from APMP. NMISA from AFRIMETS is also an APMP associate member. Each participant reported the results of hydrometer calibration using Cuckow's method. The reference temperature for the hydrometer calibration was 20 °C and the surface tension of the reference liquid was given in the protocol for this comparison. KRISS and NMIJ acted as pilot and coordinating laboratories. The measurement was performed between July 2008 and April 2010. The report from participants was completed in February 2012. The results of this comparison were linked to CCM.D-K4 through the results of KRISS, NMIJ, and NMIA. NPLI, SNSU-BSN, and NMISA withdrew their results while preparing Draft A report of this comparison. The results of two participants, MSL and NIM, were inconsistent. However, because it has been more than 10 years since the measurements were completed, it is difficult to determine that the results reflect the current measurement capabilities of the two participants. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
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