Properties of Aluminosilicate Glasses Prepared by Red Mud with Various [Al2O3]/[CaO] Mass Ratios

By introducing other oxide materials（SiO_2, Al_2O_3, CaO） into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe_2O_3-5.7CaO-18.2Al_2O_3-50SiO_2-5.9Na_2O-3TiO_2 system glasses, [Al_2O_3]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al_2O_3 when [Al_2O_3]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al_2O_3]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite（γ-Fe_2O_3） will increase which provides the possibility for production of black glass-ceramic further.

Influence of Al_(2)O_(3)/SiO_(2) Ratio on the Structure and Properties of Na^(+)/K^(+)Ion Exchange Na_(2)O-MgO-Al_(2)O_(3)-SiO_(2) Glasses

In this work,the structure,viscosity and ion-exchange process of Na_(2)O-MgO-Al_(2)O_(3)-SiO_(2) glasses with different Al_(2)O_(3)/SiO_(2) molar ratios were investigated.The results showed that,with increasing Al_(2)O_(3)/SiO_(2) ratio,the simple structural units Q_(1) and Q_(2) transformed into highly aggregated structural units Q_(3) and Q_(4),indicating the increase of polymerization degree of glass network.Meanwhile,the coefficient of thermal expansion decreased from 9.23×10^(-6)℃^(-1) to 8.88×10^(-6)℃^(-1).The characteristic temperatures such as melting,forming,softening and glass transition temperatures increased with the increase of Al_(2)O_(3)/SiO_(2) ratio,while the glasses working temperature range became narrow.The increasing Al_(2)O_(3)/SiO_(2) ratio and prolonging ion-exchange time enhanced the surface compressive stress(CS)and depth of stress layer(DOL).However,the increase of ion exchange temperature increased the DOL and decreased the CS affected by stress relaxation.There was a good linear relationship between stress relaxation and surface compressive stress.Chemical strengthening significantly improved the hardness of glasses,which reached the maximum value of(622.1±10)MPa for sample with Al_(2)O_(3)/SiO_(2) ratio of 0.27 after heat treated at 410℃for 2 h.

Effect of Fe_(2)O_(3)on the Structure,Physical Properties and Crystallization of CaO-Al_(2)O_(3)-SiO_(2)Glass

The calcium aluminosilicate-based glasses(CaO-Al_(2)O_(3)-SiO_(2),CAS)with different Fe_(2)O_(3)content(0.10wt%,0.50wt%,0.90wt%,and 1.30wt%)were prepared by traditional melt-quenching method.The glass network structure,thermal and mechanical properties,and crystallization behavior changes were investigated by nuclear magnetic resonance spectrometer,Fourier-transform infrared spectro-photometer,X-ray diffractometer,differential scanning calorimetry and field emission scanning electron microscope measurements.The change of Q^(n)in glass structures reveals the glass network connectivity decreases due to the increasing content of Fe_(2)O_(3)addition,resulting in the increasing of non-bridging number in glass structure.The glass densities slightly rise from 2.644 to 2.681 g/cm^(3),while Vickers’s hardness increases at first,from 6.469 to 6.901 GPa,then slightly drops to 6.745 GPa,with Fe_(2)O_(3)content increase.There is almost no thermal expansion coefficient change from different Fe_(2)O_(3)content.The glass transmittance in visible range gradually decreases with higher Fe_(2)O_(3)content,resulting from the strong absorption of Fe^(2+)and Fe^(3+)ions.The calculated activation energy from thermal analysis results first decreases from 282.70 to 231.18 kJ/mol,and then increases to 244.02 kJ/mol,with the Fe_(2)O_(3)content increasing from 0.10wt%to 1.30wt%.Meanwhile,the maximum Avrami constant of 2.33 means the CAS glasses exhibit two-dimensional crystallization.All of the CAS glass-ceramics samples contain main crystal phase of anorthite,the microstructure appears lamellar and columnar crystals.

The Effect of ZnO on the Physicochemical and Mechanical Properties of Aluminosilicate Dental Cements

In this study,the effect of the addition of various amounts of ZnO(0,1,2,and 3 wt.%)to aluminosilicate bioactive glass(BGs)network(SiO_(2)-Al_(2)O_(3)-P_(2)O_(5)-CaF_(2)-CaO-K_(2)O-Na_(2)O)on the mechanical properties of the fabricated glass ionomer cement(GIC)samples was studied.The GIC samples were fabricated by mixing the synthesized aluminosilicate BGs with Riva-self cure liquid.The synthesized aluminosilicate glass was characterized using differential thermal analysis(DTA),X-Ray diffraction(XRD),Fourier-transform infrared spectroscopy(FTIR),and scanning electron microscopy(SEM).Besides,the mechanical properties of GICs were evaluated using Vickers microhardness and Diametral tensile strength(DTS)test.According to DTA analysis,the glass transition temperature(Tg)of aluminosilicate BGs was decreased from 575 to 525°C.According to the results,the aluminosilicate BGs with an amorphous state(~90%)and the grain size of 36μm were synthesized.Doping of the ZnO to glass network up to 3 wt.%could increase the amorphous phase up to 95%and decrease the grain size of the particles up to 28μm.The microhardness and DTS of the GIC samples containing the aluminosilicate BGs were about 677 Hv and 8.5 MPa,respectively.Doping of ZnO to the glass network increased the mentioned values up to 816 Hv and 12.1 MPa,respectively.

Effect of ZnO,La_(2)O_(3),and YF_(3)on Crystallization and Rehological Behavior of Y_(2)O_(3)-Al_(2)O_(3)-SiO_(2)Glass

The effect of substitution La_(2)O_(3)and YF_(3)as network modifiers respectively for Y_(2)O_(3),and ZnO as intermediate oxide for Al_(2)O_(3)on crystallization and viscous behavior of Y_(2)O_(3)-Al_(2)O_(3)-SiO_(2)glass was studied.La_(2)O_(3)and YF_(3)substitution for Y_(2)O_(3)decreases the melting temperature of studied glass from 1402 to 1346 and 1379℃,and the activation energy of viscous flow decreases from 340 to 250 and 265 kJ/mol.Meanwhile,ZnO substitution for Al_(2)O_(3)decreases the melting temperature to 1379℃while increases the activation energy of viscous flow to 542 kJ/mol,due to their different role in glass structure.Substitution ZnO for Al_(2)O_(3)refines and homogenizes the crystals size and lowers crystallinity because the nucleation and crystal growth are depressed by higher activation energy of crystallization and change of crystallization mechanism from bulk crystallization to surface crystallization.Replacement of Y_(2)O_(3)by La_(2)O_(3)and YF_(3)respectively also decreases the crystallinity of Y_(2)O_(3)-Al_(2)O_(3)-SiO_(2)glass ceramic due to competitive and hindering effect on the rearranged atoms,structural units and groups required by precipitated two crystals.Besides,y-Y2Si2O7,precipitation of Y4.67(SiO4)3O,ZnAl_(2)O_(4),and Y3Si3O10F were observed respectively due to incorporation of La_(2)O_(3),ZnO,and YF_(3).

Transformation of inherent and extraneous minerals in feed coals of commercial power stations and their density-separated fractions

The main objective of this work is to relate the coalescence of inherent minerals and the fragmentation of extraneous minerals to the slagging propensities of South African pulverised feed coals during combustion.By incorporating the behaviour of inherent mineral matter or extraneous mineral matter in these coals under combustion conditions into ash-deposition prediction methods,the heterogeneous nature of the ash properties,which were disregarded in previous conventional ash deposition predictions,is considered in the study.The mode of occurrence of mineral matter in feed coals plays a crucial role in the formation of high-temperature mineral phases under combustion conditions.The float and sink fractions of the three different coals evaluated in this distinctive alternative approach provide different chemical and mineralogical properties of the derived ashes when subjected to elevated temperatures under oxidising conditions.Formation of significant concentrations of high-temperature minerals(such as mullite and cristobalite)is mainly due to the transformation reactions of extraneous kaolinite and quartz which are not associated with the extraneous fluxing minerals at elevated temperatures.However,the formation of anorthite at elevated temperatures can be attributed to the interaction of either inherent or extraneous fluxing minerals(namely calcite,dolomite,pyrite,and siderite)that are associated with either inherent or extraneous kaolinite in the coal samples under the oxidising condition.Furthermore,the anorthite,mullite,and calcium/magnesium/iron/aluminosilicate and silica glasses in ashes are formed either via crystallisation during the cooling of the hightemperature molten solution or via the solid state reactions.These high-temperature minerals and their glasses present in ashes can therefore be used as the indicators of the slagging propensity of coals.The implementation of results from this unique case study,will be of great significance to other industrial combustion processes to minimise or control ash deposition,slagging,and equipment erosion problems by either blending the density-separated fractions of coals or coals from different mines based on the chemical and mineralogical properties to prepare suitable feed coals.Furthermore,this unique alternative approach can be followed to further evaluate other feed coals in the global power stations during combustion.