Electrochemical Study and Application on Shikonin at Poly（diallyldimethylammonium chloride） Functionalized Graphene Sheets Modified Glass Carbon Electrode

The electrochemical behaviors of shikonin at a poly（diallyldimethylammonium chloride） functionalized graphene sheets modified glass carbon electrode（PDDA-GS/GCE） have been investigated. Shikonin could exhibit a pair of well-defined redox peaks at the PDDA-GS/GCE located at 0.681 V（Epa） and 0.662 V（Epc）[vs. saturated calo- mel electrode（SCE）] in 0.1 mol/L phosphate buffer solution（pH=2.0） with a peak-to-peak separation of about 20 mV, revealing a fast electron-transfer process. Moreover, the current response was remarkably increased at PDDA- GS/GCE compared with that at the bare GCE. The electrochemical behaviors of shikonin at the modified electrode were investigated. And the results indicate that the reaction involves the transfer of two electrons, accompanied by two protons and the electrochemical process is a diffusional-controlled electrode process. The electrochemical para- meters of shikonin at the modified electrode, the electron-transfer coefficient（a）, the electron-transfer number（n） and the electrode reaction rate constant（ks） were calculated to be as 0.53, 2.18 and 3.6 s^-1, respectively. Under the optimal conditions, the peak current of differential pulse voltammetry（DPV） increased linearly with the shikonin concentra- tion in a range from 9A72×10^-8 mol/L to 3,789×10^-6 mol/L with a detection limit of 3,157× 10^-8 mol/L. The linear regression equation was Ip=O.7366c＋0.7855（R=0.9978; lp： 10-7 A, c： 10-8 mol/L）. In addition, the modified glass carbon electrode also exhibited good stability, selectivity and acceptable reproducibility that could be used for the sensitive, simple and rapid determination of shikonin in real samples. Therefore, the present work offers a new way to broaden the analytical application of graphene in pharmaceutical analysis.

Production of the Modified Liquid Glass in the Processing of Kaolinitic Clay

Production of modified liquid glass and quartz materials from kaolinite clay of Alekseev deposit of Kazakhstan was studied. The sodium liquid glass processed by kaolinite clay, with chemical composition (g/dm3): SiO2-350;Na2O-155;Al2O3-2.1;Fe2O3- 0.3, silicate module-2.33 and density-1.49 g/cm3 has been used. The sodium liquid glass complies with the Russian Interstate standard 13078-81 for sodium liquid glass.10 samples of modified liquid glass were synthesized by introducing modifiers in an amount of 4% by weight of the solution into the liquid glass. Hard quartz material produced by using synthesized modified liquid glass was obtained. It has been established that the obtained modified liquid glass from kaolinite clay can improve the strength of the quartz material for 1.6 - 3.12 times higher than the initial liquid glass. Using liquid glass modifier to the inorganic sodium nitrate (NaNO3) increases the strength 3.12 times.

Abnormal IR Spectra of CO Adsorbed on the Surface of Glass Carbon Electrode Modified with Polypyrrole Film with Platinum Microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Modification of inorganic binder used for sand core-making in foundry practice

With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide,sodium hexametaphosphate and white sugar were applied as the modifiers of water glass.The optimum proportion of the modifiers was determined through the combination of single factor test and orthogonal test.The optimum proportion of water glass,potassium hydroxide,sodium hexametaphosphate and white sugar is 1000:40:5:5(wt.).In terms of weight,modified binder and micro silicon powders accounted for 2%and 0.6%of sand,respectively.The sand core was hardened by going through a warm core box process,in which the temperature of core box was 150°C,and the compressed hot air was blown at 120°C for 40 s under a pressure of 0.2 MPa.As for the sand core bonded with modified water glass,the tensile strength is 2.46 MPa at room temperature(σ0)and 2.49 MPa at 25°C and 40%RH for 24 h(σ24),which are 2 times more than that with unmodified binder.The bonded strengths of sand core are increased as a result of the reaction between-OH groups from addition of potassium hydroxide and SiO2 particles widely distributed in the sand core.Comparing with the sand core bonded with unmodified water glass,the high temperature residual tensile strength(σr)of sand core bonded with modified water glass under 600°C for 5 min,is sharply reduced from 0.20 MPa to 0.01 MPa.By the comparison with unmodified water glass,the dynamic viscosity of the modified water glass and the flowability of molding sand using modified water glass are increased from 74 mPa·s and 2.15 g to 80 mPa·s and 2.21 g,respectively.As revealed by FT-IR analysis,new groups including PO3-,PO43-,and Si-O-C appear in the molecular structure of modified water glass,which are beneficial to the collapsibility of sand core.

Strong upconversion luminescence in Er^(3+)/Yb^(3+)-doped halide modified tellurite glass

Upconversion luminescence of Er3+/Yb3+-doped halide tellurite glass is investigated experimentally upon 976-nm excitation. Three intense emissions centered at 525, 545 and 655 nm owing to the transitions 2H11/2-4I15/2, 4S3/2 -4I15/2 and 4F9/2-4I15/2, respectively, are observed when pumping power is as low as 20 mW. The upconversion mechanisms and power dependent intensities are discussed. The high-populated 4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes.

Effect of glass network modifier R_2O(R=Li, Na and K) on upconversion luminescence in Er^(3+)/Yb^(3+) co-doped NaYF_4 oxyfluoride glass-ceramics

The effect of glass network modifier R2O （R=Li, Na, K） on upconversion luminescence in Er3＋/yb3＋ co-doped NaYF4 oxyfluoride glass-ceramics was investigated. NaYF4 nanocrystals with different sizes were studied under glass network modifier alkali mental oxide. The nanocrystals size in NaYF4 of Li2O modified samples was 11 nm, whereas in the Na20 and K2O modified sample, the crystal size was 25 and 43 nm, respectively. It was found that red, yellow and green upconversions were observed in SAL, SAN, SAK glass ceramics. The reported results would deepen the understanding of size effects on the lanthanide upcon- version in nanocrystals.