The influence of Cr2O3 and B2O3 on viscosities of CaO–SiO2–MgO–23.2 wt% Al2O3–TiO2‐based slags is studied by the rotating cylinder method in this work. Furthermore, the Raman spectra of the quenched slags are also investigated to obtain the structure information of slags with different Cr2O3 and B2O3 contents. From the viscosity experimental results, it is indicated that the viscosity increased with the addition of Cr2O3 and decreased with the addition of B2O3. The Raman spectra analyses reveal that Cr2O3 may exist as a network former and the polymerization degree of the slags increases with the rising content of Cr2O3. B2O3 also behaves as network formers in the present slag, which can increase the degree of polymerization and polymerize the network structure of the slags. The effect of network forming on visicosity is smaller than the effect of low melting point compound formations, which leads to the slag viscosity decrease with B2O3 addition.
The effects of TiO2 and FeO on the viscosities of CaO–MgO–Al2O3–SiO2–TiO2‐FeO slag are investigated by the rotating cylinder method. The structural characterization of the quenched samples are also studied by Fourier transform infra‐red and Raman spectroscopy. Experimental results show that viscosity decreases with increasing TiO2 or FeO, while keeping the basicity and contents of other components constant. Both, Fourier transform infra‐red and Raman spectroscopy results show that there are no significant change of the asymmetric stretching vibration bands for [AlO4] tetrahedra among the slags and there is no Q3 in the slags. It is concluded that both TiO2 and FeO in the slags behave as basic oxides, which break the silicate network in the slag and reduce the slag viscosity. The Raman spectroscopy results show that the Q2 in slag increases with increasing FeO and decreasing TiO2. The polymerization degree of silicates decreases with decreasing Ti–O–Si or Ti–O–Ti stretch vibration and increasing O–Ti–O or O–(Si, Ti)–O stretch vibration, which make the slag viscosity decrease.
This paper reviewed our research progress in respects of th intercalation law of acetylsalicylic acid (ASP) with magnesium aluminate layered double hydroxide (LDH), the drug release mechanism and the tablet preparation effect of LDH-ASP system. We also discussed the propositions about the composite assembly rules, slow-release mechanism, and dosage form processing of the layered double hydroxide drug delivery system. Intercalation way and drug structure should be taken into consideration in assembly LDH-drugs system. The characteristic parameter of the composite LDH-drug reflected finely their loading efficiency and correlated definitely with drug release property. It had been found that the release rate and extent of intercalated drug was closely linked to the retarding status of LDH interlayer, which was dependent on the exchange mole ratio of n(drug) with n[HnPO4(3-n)-]. In addition, the grafting reaction and phase transformation degree of LDH layer was hinged on the acidity of solution. The slow-release function of the LDH-drug system could be improved significantly by compositing with dextran (DET). A sustained-release skeleton tablet was producted with DET-LDH-ASP drug delivery system and hydrophilic gel material HPMC, which could effectively overcome the "first pass effect" and " burst release problem" of LDH-drug oral agents. The slow-release effect of LDH drug delivery system could be ulteriorly improved in systemic circulation environments, attributed to the triple control of HPMC-DET-LDH, DET-LDH-drugs three-level supramolecular assembly and the special circulation in vivo.
Key words: Layered double hydroxide, Supramolecular assembly, Release control, Slow controlled release drug delivery system
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