火焰原子吸收光谱法测定合质银中金含量

通常采用火法试金的方法来测定金的含量,但合质银中银是主含量,金的含量很低,火法试金法测定低含量金的分析准确性有待商榷。本文描述了用火焰原子吸收光谱法测定合质银样品中少量的金含量的实验,结果准确,操作步骤简便。

Ag_3PO_4/Ag_2CO_3 p–n heterojunction composites with enhanced photocatalytic activity under visible light

Formation of a p–n heterojunction rather than p-type or n-type semiconductors can enhance the separation of photogenerated electrons and holes and increase the quantum efficiency of photocatalytic reactions owing to the difference of the electric potential in the inner electric field near the junction,pointing from n toward p. n-Ag3PO4/p-Ag2CO3 p–n heterojunction composites are prepared through a facile coprecipitation process. The obtained Ag3PO4/Ag2CO3 p–n heterojunctions exhibit excellent photocatalytic performance in the removal of rhodamine B（RhB） compared with Ag3PO4 and Ag2CO3. The 40%-Ag3PO4/Ag2CO3 composite photocatalyst（40 mol% Ag3PO4 and 60 mol% Ag2CO3） exhibits the best photocatalytic activity under visible light,demonstrating the ability to completely degrade RhB within 15 min. Transient photovoltage characterization and an active species trapping experiment further indicate that the formation of a p–n heterojunction structure can greatly enhance the separation efficiency of photogenerated carriers and produce more free h＋active species,which is the predominant contributor for RhB removal.

Modeling of whole process of ageing precipitation and strengthening in Al-Cu-Mg-Ag alloys with high Cu-to-Mg mass ratio

A physically based numerical model to predict the microstructure evolution and yield strength of high Cu-to-Mg mass ratio Al-Cu-Mg-Ag alloys during the whole ageing process was developed.A thermodynamically-based precipitation model,employing the classical nucleation and growth theories,was adapted to deal with the precipitation kinetics (evolution of radius and volume fraction of precipitates for Ω phase) of aged Al-Cu-Mg-Ag alloys.The model gives an estimation of the precipitation kinetics (evolution of radius and density of precipitates for both θ' and Ω phases) of the alloy.The strengthening model based on Orowan mechanism was deduced.The microstructural development and strength predictions of the model are generally in good agreement with the experimental data.

Effect of Hydrogen Reduction of Silver Ions on the Performance and Structure of New Solid Polymer Electrolyte PEI/Pebax2533/AgBF4 Composite Membranes

In this paper, the effect of hydrogen reduction of silver ions on the performance and structure of new solid polymer electrolyte polyetherimide （PEI）/Pebax2533 （Polynylonl2/tetramethylene oxide block copolymer, PA12-PTMO）/AgBF4 composite membranes is investigated. For PEI/Pebax2533/AgBF4 composite membranesprepared with dillerent AgBF4 concentration, the permeances of propylene and ethylene increase with the increase of AgBF4 concentration due to the carrier-facilitated transport, resulting in a high selectivity. But for propyl- ene/propane mixture, the mixed-gas selectivity is lower than its ideal selectivity. The hydrogen reduction strongly influences the membrane performance, which causes the decrease of propylene permeance and the increase of pro-pane permeance. With the increase of hydrogen reduction time, the membranes show a clearly color change from white to brown, yielding a great selectivity loss. The data of X-ray diffraction and FT-IR prove that silver ions are reduced to Ago after hydrogen reduction, and aggregated on the surface of PEI/Pebax2533/AgBF4 composite mem- branes.

Crystallographic Characterization of the Novel Inorganic-organic Hybrid Coordinated Polymer: [(C_(22)H_(50)N_2)(Ag_2I_4)]_n

A novel coordinated polymer [(C22H50N2)(Ag2I4)]n([C22H50N2]2+ = N,N?-1,2- ethylence-bis(N,N?-dimethyl octane ammonium) (EDO)) was synthesized by the reaction of AgI and EDO at room temperature with pH = 6.8, and structurally characterized by means of X-ray single- crystal diffraction. It crystallizes in triclinic, space group P1 with a = 9.6080(1), b = 12.7643(2), c = 7.2157(8) ? a = 100.835(8), ?= 91.030(3), ? = 91.297(9)o, (C21.50H48.50Ag2I4N2), Mr = 1058.46, V = 868.71(19) 3, Z = 1, Dc = 2.023g/cm3, F(000) = 497.5, ?MoKa) = 4.692 mm-1, the final R = 0.0623 and wR = 0.1949 for 2641 observed reflections with I > 2s(I). The title compound consists of cations ([C22H50N2]2+) and anion chain (Ag2I42-)∞ which are combined by static attracting forces in the crystal to form the so-called organic-inorganic hybrid material.

Enhancement effect of terbium complex luminescence by binding to silver nanoparticles in the solution

The luminescent properties of terbium complex (terbium citrate) by binding to silver nanopartilces in the solution have been reported in this paper.The enhanced luminescence of the complex containing silver nanoparticles was observed at a limited particle concentration region.The nanoparticle concentration dependence of the luminescent intensity was regarded as the result of a delicate balance between an enhancing and a quenching effect of the silver nanoparticles.Furthermore,silver nanoparticles also affected the asymmetric ratio (AS) value of terbium luminescence.We discuss the luminescent properties of the terbium complex in terms of the local electromagnetic field,refractive index,and the ligand field around terbium ion.

The Impact of Corporate Governance on Banks Performance and Loan Quality： Evidence From Italian Cooperative Banks

In the banking system, a context characterized by growing instability and by the speed of evolution of business dynamics, the system of corporate governance plays a key role, both for large banks and for banks with a smaller size. The paper aims to investigate the influence of corporate governance of the banks that operate in the cooperative credit system on performance and quality of loans, over the years 2010-2011-2012. In order to achieve this aim, the following research hypotheses have been formulated： There is a statistically significant relationship between the size and the structure of the board and banks Performance operating in the cooperative credit system; there is a statistically significant relationship between the size and structure of the board and the credit quality of banks operating in the cooperative credit system. The analysis is conducted on a sample composed of 48 Italian banks, divided into 24 cooperative banks and 24 popular banks. The sample is made up of banks from all over Italy and very different in terms of dimension. For the sample construction, data relative to governance of banks were collected from the balance sheets in the period from June to August 2014. Financial-economic data were collected from the Financial Statements and from Bankscope database. The methodology of analysis is based on multivariate OLS （ordinary least squares） regression models. The main results refer to the presence of significant relationships between board dimension and the quality of loans and among the number of committees and performance and the quality of loans. The presence of a significant and negative relationship between the board dimension and the ratio of impaired loans to gross loans indicates the possibility that enlargement of board dimension allows a better quality of loans. The presence of a positive relationship between the number of committees and the ratio of impaired loans to gross loans signals the possibility that a greater number of committees can produce a worse quality of loans. The presence of a negative relationship between the number of committees and bank performance suggests to limit and manage the complexity of governance in banks operating in the cooperative credit system.