Amorphous Silica

The diatomaceous earth (DE), collected from the Mariovo region in North Macedonia, was characterized and thermally modified. The material represents a sedimentary rock of biogenic origin, soft solid that can be easily disintegrated, with white to grayish color, with bulk density of 0.51-0.55 g/cm 3 , total porosity of 61-63%, and specific gravity of 2.25 g/cm 3. The chemical composition is as follows: SiO 2, 86.03; Al 2 O 3 , 3.01; Fe 2 O 3 , 2.89; MnO, 0.06; TiO 2, 0.20; CaO, 0.76; MgO, 0.28; K 2 O, 0.69; Na 2 O, 0.19; P 2 O 5 , 0.15; and loss of ignition, 5.66 (wt%). The mineralogy of the raw DE is characterized by the predominant presence of amorphous phase, followed by crystalline quartz, mus-covite, kaolinite, and feldspar. Significant changes in the opal phase are observed in the 1,000-1,200°C temperature region. At 1,100°C, the entire opal underwent solid-solid transition to cristobalite. Further ramp of the temperature (1,100-1,200°C) induced formation of mullite. Scanning electron microscopy (SEM) and transmission electron micro-scopy depict the presence of micro-and nanostructures with pores varying from 260 to 650 nm. SEM analysis further determined morphological changes in terms of the pore diameters shrinkage to 120-250 nm in comparison to the larger pores found in the initial material. The results from this investigation improve the understanding of mechanism of silica phase transition and the relevant phase alterations that took place in DE upon calcination temperatures from 500 to 1,200°C.

This paper investigates the properties of rice husk ash (RHA) produced by using a ferro-cement furnace. The effect of grinding on the particle size and the surface area was first investigated, then the XRD analysis was conducted to verify the presence of amorphous silica in the ash. Furthermore, the effect of RHA average particle size and percentage on concrete workability, fresh density, superplasticizer (SP) content and the compressive strength were also investigated. Although grinding RHA would reduce its average particle size (APS), it was not the main factor controlling the surface area and it is thus resulted from RHA's multilayered, angular and microporous surface. Incorporation of RHA in concrete increased water demand. RHA concrete gave excellent improvement in strength for 10% replacement (30.8% increment compared to the control mix), and up to 20% of cement could be valuably replaced with RHA without adversely affecting the strength. Increasing RHA fineness enhanced the strength of blended concrete compared to coarser RHA and control OPC mixtures. © 2010.

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The phase transformations of the amorphous SiO2 have a very important role in the application
of diatomite in the production of ceramic products. Therefore the phase transformations of diatomite are observed
with the use of DTA and TGA at temperatures up to 1100°C, and diatomite in powder state heated at temperature
1000–1200°C for a period of 1 and 2 hours. DTA and TGA analyzis show that during thermal treatment up to 1100°C
the diatomite remains in its amorphous phase. Roentgen-structural examinations of probes heated at 1000–1200°C for
a period of 1–2 hours show no presence of crystalline phases at 1100°C. XRD examinations of probes heated at
1200°C show presence of the crystalline phases cristobalite and quartz. The samples was heated at 1200°C for a period
of 2 hours, and was observed with an increase of the cristobalite content compared with quartz. SEM and TEM
examinations results of diatomite heated at 1200°C for a period of 2 hours show that the probes undergoes sintering
followed by reduced porosity.

The diatomaceous earth (DE), collected from the Mariovo region in North Macedonia, was characterized and thermally modified. The material represents a sedimentary rock of biogenic origin, soft solid that can be easily disintegrated, with white to grayish color, with bulk density of 0.51–0.55 g/cm3, total porosity of 61–63%, and specific gravity of 2.25 g/cm3. The chemical composition is as follows: SiO2, 86.03; Al2O3, 3.01; Fe2O3, 2.89; MnO, 0.06; TiO2, 0.20; CaO, 0.76; MgO, 0.28; K2O, 0.69; Na2O, 0.19; P2O5, 0.15; and loss of ignition, 5.66 (wt%). The mineralogy of the raw DE is characterized by the predominant presence of amorphous phase, followed by crystalline quartz, muscovite, kaolinite, and feldspar. Significant changes in the opal phase are observed in the 1,000–1,200°C temperature region. At 1,100°C, the entire opal underwent solid–solid transition to cristobalite. Further ramp of the temperature (1,100–1,200°C) induced formation of mullite. Scanning electron microscopy (SE...

Synthesis of sol-gel glass with incorporation of Na2O is extremely difficult, as such glasses have a great tendency to crystallize. Slow drying and aging over several days or weeks is usually required in sol-gel preparation procedures. This work reports a fast, novel route for the synthesis of bioglass powders in a considerably shortened period of 1 h. A comparative study of sol-gel derived glasses made by this novel route using rotary evaporator drying, and a conventional route using oven drying and aging, revealed that the two methods produce stabilized (devitrified) bio-glasses with virtually identical behavior and properties. Indeed, the rapidly dried powder exhibited slightly enhanced properties that should result in improved bioactivity. Fourier-transform infrared spectroscopy was used to understand the structures of the synthesized powders, and MAS-NMR was used to look at the degree of polymerization. This innovative, rapid route was successfully demonstrated to produce glass and devitrified glass nanopowders more than one hundred times quicker than the quickest reported standard drying methods.

A b s t r a c t: For the characterization of the natural amorphous SiO2 found in a new deposit in Republic of Macedonia, the following examinations were performed: physical-mechanical, chemical, mineralogical, SEM, IR and thermal examinations. Physical-mechanical analyses show that it is a white to grey colored rock, of low hardness, with a low volumetric mass and high porosity. Chemical analyses show that the material dominantly contains SiO2.
Mineralogical and XRD analyses show high percentage of isotropic amorphous mass content, with minimal contents
of submicroscopic cryptocrystalline mass. Thermal analyses show high thermal stability. Based on the conducted research
of the raw material from the new deposit, it can be concluded that it represents SiO2-diatomite of high quality,
useful for various purposes.

Two Zn-doped sol− gel glasses with the same ZnO content (5 wt%; 4% mol) but different overall composition have been synthesized and characterized, in comparison with a bioactive Zn-free reference glass. The role of ZnO in modifying the bioactivity of sol− gel ...

This paper investigates the properties of rice husk ash (RHA) produced by using a ferro-cement furnace. The effect of grinding on the particle size and the surface area was first investigated, then the XRD analysis was conducted to verify the presence of amorphous silica in the ash. Furthermore, the effect of RHA average particle size and percentage on concrete workability, fresh density, superplasticizer (SP) content and the compressive strength were also investigated. Although grinding RHA would reduce its average particle size (APS), it was not the main factor controlling the surface area and it is thus resulted from RHA's multilayered, angular and microporous surface. Incorporation of RHA in concrete increased water demand. RHA concrete gave excellent improvement in strength for 10% replacement (30.8% increment compared to the control mix), and up to 20% of cement could be valuably replaced with RHA without adversely affecting the strength. Increasing RHA fineness enhanced ...