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Zhou Y.,South China Normal University | Shen K.,Jewelry Institute of Guangzhou Panyu Polytechnic | Zeng Q.,South China Normal University
Refractories and Industrial Ceramics | Year: 2014

Cristobalite SiO2 can be obtained from fused silica ceramic wastes formed at factories that make polycrystalline silicon, where fused silica is converted to cristobalite during the production of polycrystalline ingots. High-purity cristobalite powder is obtained by grinding these wastes. A study was made of the coefficient of linear thermal expansion of molds which are composed of cristobalite with a gypsum binder and are used to make jewelry. It was established that the thermal expansion which takes place during the transition to the cristobalite phase can effectively compensate for the shrinkage which the gypsum undergoes in the temperature range from 200 to 400°C. Experiments involving the casting of a copper alloy showed that the use of cristobalite can improve the thermal performance of molds employed in the production of jewelry. © 2014 Springer Science+Business Media New York.


Yuan J.-P.,Jewelry Institute of Guangzhou Panyu Polytechnic | Li W.,Jinan University | Wang C.,Jewelry Institute of Guangzhou Panyu Polytechnic | Ma C.-Y.,Jewelry Institute of Guangzhou Panyu Polytechnic | And 2 more authors.
Journal of Iron and Steel Research International | Year: 2015

Nickel-containing stainless steels have been widely applied in watch and jewelry production, and their responses to the Nickel Directive become a universal concern in the industry. The nickel release rates and corrosion behaviors of types 316L, 304, 303 and 201 stainless steels under the conditions of solid solution and mirror polishing were studied by artificial sweat soaking and electrochemical methods. The results show that the weekly nickel release rates in artificial sweat do not strictly correspond to the nickel contents, which present a descending order as 303 stainless steel of 2. 06 μg/cm2, 201 stainless steel of 1. 51 μg/cm2 304 stainless steel of 0. 08 μg/cm2 and 316L stainless steel of 0. 02 μg/cm2. Both the nickel release rates of type 303 and 201 stainless steels significantly exceed the threshold values regulated in EN1811: 2011; therefore, they should be avoided to be used as watch and jewelry materials owing to the risk of nickel sensitization. The nickel release rates of 316L and 304 stainless steels meet the requirements of the standard. Sulfide inclusions in stainless steel become the sources of pitting and exacerbate the damage of the passivation membrane, which is the significant cause to enhance the nickel release rates. © 2015 Central Iron and Steel Research Institute.


Yuan J.P.,Jinan University | Yuan J.P.,Jewelry Institute of Guangzhou Panyu Polytechnic | Li W.,Jinan University | Wang C.,Jewelry Institute of Guangzhou Panyu Polytechnic
Materials Science and Engineering C | Year: 2013

316L stainless steel is widely used for fashion jewelry but it can carry a large number of bacteria and cause the potential risk of infection since it has no antimicrobial ability. In this paper, La is used as an alloying addition. The antibacterial capability, corrosion resistance and processability of the La-modified 316L are investigated by microscopic observation, thin-film adhering quantitative bacteriostasis, electrochemical measurement and mechanical test. The investigations reveal that the La-containing 316L exhibits the Hormesis effect against Staphylococcus aureus ATCC 25923 and Escherichia coli DH5α, 0.05 wt.% La stimulates their growth, as La increases, the modified 316L exhibits the improved antibacterial effect. The more amount of La is added, the better antibacterial ability is achieved, and 0.42 wt.% La shows excellent antibacterial efficacy. No more than 0.11 wt.% La addition improves slightly the corrosion resistance in artificial sweat and has no observable impact on the processability of 316L, while a larger La content degrades them. Therefore, the addition of La alone in 316L is difficult to obtain the optimal combination of corrosion resistance, antibacterial capability and processability. In spite of that, 0.15 wt.% La around is inferred to be the trade-off for the best overall performance. © 2012 Elsevier B.V.


Yuan J.-P.,Jinan University | Yuan J.-P.,Jewelry Institute of Guangzhou Panyu Polytechnic | Li W.,Jinan University | Liu W.-M.,Jewelry Institute of Guangzhou Panyu Polytechnic
Rare Metals | Year: 2013

Nickel is widely used as a bleaching element in white gold alloys, but it is a potential allergen. In this paper, a popular 18 KW gold alloy, often called "safe nickel," was chosen as the experimental material; its nickel release rates under six different processing conditions were evaluated according to the EN1811 standard. The results reveal that both the surface processing method and heat treatment technology significantly affect the nickel release rate. A coarse surface releases more nickel ions than a smooth surface. The sample normalized at 700 C in the single region has a lower nickel release rate than the one treated at 550 C in the two-phase phase region, while high temperature normalizing at 800 C will accelerate it. All the measured nickel release rates of the experimental material under various processing conditions exceed the permitted threshold value in the Nickel Directive, which indicates that there exists the potential risk of nickel-induced allergy when it is used to make jewelries, especially for piercing types. © 2013 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg.


Yuan J.,Jinan University | Yuan J.,Jewelry Institute of Guangzhou Panyu Polytechnic | Li W.,Jinan University | Shen K.,Jewelry Institute of Guangzhou Panyu Polytechnic
China Foundry | Year: 2012

316L stainless steel is widely used for fashion jewelry, but it can carry a large number of bacteria and bring the risk of infection since the steel has no antimicrobial performance. In this paper, the effects of Ce on the antibacterial property, corrosion resistance and processability of 316L were studied by microscopic observation, thinfilm adhering quantitative bacteriostasis, and electrochemical and mechanical tests. The results show that a trace of Ce can distribute uniformly in the matrix of 316L and slightly improve its corrosion resistance in artificial sweat. With an increase in Ce content, the Ce is prone to form clustering, which degrades the corrosion resistance and the processability. The Ce-containing 316L exhibits Hormesis effect against S. aureus. A small Ce addition stimulates the growth of S. aureus. As the Ce content increases, the modified 316L exhibits an improved antibacterial efficacy. The more Ce is added, the better antibacterial capability is achieved. Overall, if the 316L is modified with Ce alone, it is difficult to obtain the optimal combination of corrosion resistance, antibacterial performance and processability. In spite of that, 0.15 wt.%-0.20 wt.% Ce around is inferred to be the best trade-off.

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