Thermal characteristics and corrosion behaviour of Mg–xZn alloys for biomedical applications

The thermal parameters of Mg–xZn cast alloys with 0·5–9 wt% Zn were evaluated by using computer aided cooling curve thermal analysis (CA–CCTA), whereas the corrosion behaviour was investigated by potentiodynamic polarization and immersion tests. Thermal analysis results revealed that the dendrite coherency temperature (T _DCP ) decreased from 642·2 to 600 °C with the addition of Zn from 0·5 to 9 wt%. The liquid fraction at coherency point ( ${f}_{ L}^{ DCP}$ ) increased by 72% when Zn was increased up to 9 wt%. MgZn intermetallic phase was observed in samples with <3 wt% Zn. At higher percentages of Zn, the Mg ₅₁Zn ₂₀ intermetallic phase was also detected in addition to α-Mg and MgZn by first derivative cooling curves under non-equilibrium solidification. All these phases were observed along the grain boundary when Zn was rejected from the solid/liquid interface and enriched in the triple conjunction of grain boundary. The grain size decreased from 185·2 to 71·5 μm when Zn content was increased. The addition of Zn content had a significant effect on the corrosion rate and the corresponding mechanisms. The corrosion rate decreased from 2·1 to 1·81 mmpy as Zn content increased from 0·5 to 3 wt%; afterwards, however, this value increased with further increase of Zn. Mg–3Zn also had the lowest degradation rate and highest corrosion resistance which can be fully utilized for biodegradable orthopedic applications.     

MELTING CHARACTERISTIC AND SOLID FAT CONTENT OF MILK FAT AND PALM STEARIN BLENDS BEFORE AND AFTER ENZYMATIC INTERESTERIFICATION

Melting characteristics and solid fat content of anhydrous milk fat (AMF), soft palm oil stearin (SPOs), hard palm oil stearin (HPOs) and their blends were studied by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy, respectively. Solid fat contents (SFC) determined by NMR were used to construct isosolid diagrams; these indicated the presence of an eutectic effect along the binary blends of AMF:SPOs which only could be observed at 5 and 10C. The effect was reduced after interesterification by sn-1,3-specific lipase. The modification also reduced the number of the distinct DSC melting peaks, demonstrating a better miscibility among the blended fats. A substantial decrease in DSC melting enthalpy of interesterified blends was found to be parallel to a decrease in SFC that was observed at 25–40C. Fatty acid composition showed that improved functionality of AMF may be due to an enrichment in long-chain saturated fatty acids contributed both by SPOs and HPOs.     

Poisoning effect of bismuth on modification behaviour of strontium in LM25 alloy

Nucleation and growth, temperature measurements and microstructure observations of silicon phase are presented for strontium modified Al–7%Si (LM25) cast alloy treated with bismuth. The results show that addition of bismuth in strontium modified alloys may have a poisoning effect resulting in lost modification of the silicon phase. With increasing Bi/Sr ratio, thermal analysis measurements showed that the eutectic growth temperature increased remarkably to 573°C and recalescence decreased to 0·2°C and the morphology of silicon displayed the same flake-like structure as in the unmodified alloys. Microstructural observation showed that a minimum Bi/Sr ratio of 1·2 which is equivalent to a Sr/Bi ratio of 0·43 is required for effective strontium modification and neutralization of the poisoning effect of bismuth.     

CHEMICAL AND PHYSICAL PROPERTIES OF PLASTIC FAT PRODUCTS SOLD IN MALAYSIA

Five domestic and four imported Malaysian plastic fat products and their separated high melting point triacylglycerols (HMG) were analyzed for their chemical and physical characteristics. Chemical characteristics consisted of fatty acid (FA) and triacylglycerol (by TG carbon number) composition. Physical characteristics encompassed dropping and softening points, solid fat content, polymorphic crystal habit and DSC melting and crystallization patterns. β crystal habit was related to high levels of 16 or 18 carbon fatty acids in the HMG and high levels of TG48 or TG54 which are β tending. Domestic products contained very low levels of trans fatty acids; they were blends of natural fats such as palm oil, palm kernel and milk fat. Levels of the individual fats in the blends were estimated by means of FA and TG composition analyses. The content of solid fat, determined by the AOCS method, was much lower than that obtained by the IUPAC method. Texture at 23C of products, as determined by penetrometer test of the original materials, was similar for all products.     

Bi和Sr改性Al-7Si-0.4Mg合金显微组织的影响(英文)

研究单独添加Bi和联合添加Bi与Sr在不同凝固条件下对Al-7Si-0.4Mg合金中共晶硅结构的影响。结果表明:添加Bi对共晶硅有细化作用,其细化能力随着Bi质量分数(在<0.5%范围内)的增加而增强。当Bi添加到Sr改性的合金中时,为了得到充分的共晶硅改性,较高的Sr/Bi质量比(至少0.45)是必要的。     

涂层厚度对消失模铸Al-Si-Cu合金铸件的影响(英文)

对Al-Si-Cu合金进行消失模铸造,研究涂层厚度对Al-Si-Cu合金铸件缺陷、孔隙率和共晶硅间距的影响。结果表明,提高涂层浆料黏度和延长浸渍时间对铸件的完整性和显微组织有影响。薄的涂层有利于模腔充填性能的改善、显微组织的细化和低孔隙度高质量铸件的获得。     

THE EFFECT OF DIFFERENT TYPES OF STIRRER AND FRACTIONATION TEMPERATURES DURING FRACTIONATION ON THE YIELD, CHARACTERISTICS AND QUALITY OF OLEINS

Refined, bleached and deodorized (RED) palm oil was fractionated by dry fractionation using two different types of stirrer at 3 fractionation temperatures to produce palm olein (POo). Statistical analysis by SAS showed significant differences (P < 0.05) between fractionation temperatures of 15C and 21C, and no significant differences between two types of stirrer on product yield. Iodine value showed significant differences between fractionation temperatures of 15C and 18C, and 15C and 21C but no significant difference was observed between the two types of stirrers. Analysis showed that palm olein fractionated at lower temperature contained less saturated fatty acids, more unsaturated fatty acids and lower solid fat than oleins fractionated at higher temperatures.