Zircon ZrSiO4 Research Articles

Theoretical and experimental study for compost based on Zircon ZrSiO4

Theoretical and experimental study for compost based on Zircon ZrSiO4

Structural Construction of Binders Based on Orthophosphoric Acid and Refractory Materials

The formation of phosphate binders in systems based on orthophosphoric acid and the most common refractory fillers in foundry technology (quartz dust, zircon ZrSiO4, and kyanite‐sillimanite Al2SiO5) has not been previously studied. The phase composition of these inorganic binders was studied, and the formation of silicon SiP2O7 and zirconium ZrP2O7 pyrophosphates was confirmed. The study by differential thermogravimetric analysis in the temperature range of 20–1000°С established the fact that the formed binders are thermally stable and do not emit harmful gaseous substances. The obtained results of the studied binders make it possible to develop new environment‐friendly core mixtures of thermal hardening.

A new high thermal shock resistant onelayer glass–ceramic coating for industrial and engineering applications

Purpose: A new high thermal stability single layer glass–ceramic coating system designing for applied on various grade of steel alloy has been developed in this work. Design/methodology/approach: The thermal shock resistance, thermal conductivity and thermal expansion of the coating system were evaluated by using suitable standard tests. Some crystalline agents (Lithium oxide Li2O, Titanium oxide TiO2, Zircon ZrSiO4 and Feldspar CaO∙Al2O3∙2SiO2) were add at constant ratio 6% to coating system to evaluate their effects on the resultant coatings. Findings: The results indicate the suitability of these coatings for protection of metal substrate. Also the results show that the properties of resultant coating were hardly affected by composition and concentration of crystalline agent. Research limitations/implications: Coating with lithium oxide has the lowest thermal expansion, which means the highest thermal shock resistance. While, values of thermal conductivity were too close for all types of coating. Originality/value: Generally, the resultant coating properties have been enhanced in all cases; this is associated with the introduce the crystalline agent which lead to the formation of a complex network of crystalline phases.

Fracture toughness of Al2O3/ZrSiO4 coatings obtained by multi-chamber gas-dynamic accelerator

In the current work the research of fracture toughness of Al2O3/xZrSiO4 composite coatings have been realized using automatic system for microhardness analysis. Al2O3/xZrSiO4 (x = 0, 3, 25 wt. %) coatings were produced from a mixture of cheap raw materials (alumina and zircon ZrSiO4) on the surface of stainless steels by a new multi-chamber gas-dynamic accelerator. It has been experimentally established that adding of ZrSiO4 increases fracture toughness of alumina coatings.

Molecular dynamics study of self-radiation damage in mineral matrices

Mechanisms of radiation damages in minerals promising for the utilization of highly active radioactive waste (zircon ZrSiO4, monazite LaPO4, orthophosphate YbPO4, lakargiite CaZr0,8Sn0,1Ti0,1O, and Gd2Zr2O7 and Gd2Ti2O7 compounds with the pyrochlore structure) are studied by the computer simulation using the molecular dynamics method. The formation of a damaged region in the structures under study is considered along with the recovery (relaxation) processes in these structures. The number of Frenkel pairs and antistructural defects that form in the structure of these minerals after the pass of the knocked out thorium atom is calculated by the molecular dynamics method. A parameter is proposed that characterizes the mineral tendency to amorphization under the effect of the radiation damage. The obtained results show that one of the main factors determining the radiation stability of minerals is the crystal structure type, compounds with the monazite structure being more radiationally stable than compounds with the zircon structure. It is found that the Gd2Zr2O7 compound and lakargiite have a weaker tendency to amorphization than other minerals such as zircon, monazite, and orthophosphate YbPO4. A high radiation stability of the studied Gd2Zr2O7 compound as well as a solid solution of the composition CaZr0.8Sn0.1Ti0.1O3 makes it possible to propose them as a possible matrix for the utilization of highly active radioactive waste.

Atomistic Computer Simulation of the Mixing Properties of Zircon ZrSiO4 — Monazite LaPO4 and Zircon ZrSiO4 — Xenotime YPO4 Solid Solutions

Atomistic Computer Simulation of the Mixing Properties of Zircon ZrSiO4 — Monazite LaPO4 and Zircon ZrSiO4 — Xenotime YPO4 Solid Solutions

Specific features of the initial stages of the aluminothermic reduction of zirconium from ZrO2

The phase composition of the products of the low-temperature stage of the reaction of ZrO2 with aluminum is studied. The influence of charge compacting and particle size of the reagents is revealed. The onset temperatures for the reaction of zirconium oxide (TsrO-1 and TsrO-S trade marks) and aluminum (APZh and PA-4 trade marks) are determined by differential scanning calorimetry. A high dispersity of ZrO2 and the presence of zircon ZrSiO4 in zirconium oxide (TsrO-S) are found to provide a decrease in the onset temperatures for the reaction. Intermetallic compound ZrAl3 is predominantly formed at the low-temperature stage of the reaction of ZrO2 with aluminum. Zirconium is reduced from ZrO2 by aluminum stage by stage through the formation of lower oxides ZrO and Zr3O. Suboxide AlO is detected in the products of reaction of ZrO2 with aluminum. The heat flow rates are estimated, according to which the reduction of zirconium from ZrO2 by aluminum is formally characterized by the first order, and the activation energy is E = 160–170 kJ/mol.

Structural, Microstructure, Mechanical and Electrical Properties of Porous Zr4+-Cordierite Ceramic Composites

Zirconium-cordierite ceramic composites have been synthesized by a co-precipitation method using MgCl2·6H2O, NaAlO2, Na2SiO3·5H2O, and ZrOCl2·8H2O as starting materials. XRD, FT-IR, and SEM techniques were employed to study the effect of zirconium on the crystal structure and microstructure of the samples. XRD results revealed that spinel MgAl2O4 and t-ZrO2 phases were predominant in the samples with low Zr4+ content (10 wt.%), whereas zircon ZrSiO4 was predominant with high Zr4+ content (≥15 wt.%). The densification behavior was improved from 30.4 to 44.6% of the theoretical density (2.6 g/cm3) at 15 wt.% of Zr4+. However, microhardness of the sintered samples was enhanced from 7.1 to 7.5 GPa with increasing the Zr4+ dose from 0 to 25 wt.%. On the other hand, the gradual increase in Zr4+ content from 0 to 25 wt.% led to suppression in the electrical resistivity (ρ) from 16.6 to 2.8 × 109 Ω/cm, respectively. In addition, the dielectric permittivity (e) of the pure cordierite was decreased with Zr4+ ion addition. The maximum dielectric permittivity (e) at low frequencies (10 MHz) was 18.7 at 10 wt.% Zr4+ content, whereas at high frequencies (1 GHz) it was 38.8 at 15 wt.% Zr4+ content.

Zr complexation in high pressure fluids and silicate melts and implications for the mobilization of HFSE in subduction zones

Field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble HFSE (i.e., Ti, Zr, Nb and Hf) by high pressure fluids, probably via complexation with polymerized alkali–silica dissolved species and halogens (F and Cl). Here we investigate the complexation of Zr in subduction-related fluids (aqueous fluids and hydrous haplogranite melts) up to 800°C and 2.4GPa using X-ray absorption spectroscopy (XANES and EXAFS) in a hydrothermal diamond anvil cell and provide evidence for the formation of Zr–O–Si/Na polymeric species in alkali-(alumino)silicate fluids at high pressure. Zr4+ speciation in dilute fluids (2.5wt% HCl) is dominated by 8-fold-coordinated [Zr(H2O)8]4+ hydrated complexes at room conditions and no evidence for extensive Zr–Cl complexation in the fluid was found up to 420°C, as confirmed by ab initio XANES calculations of various ZrO8−xClx clusters. The addition of Na and Si dissolved species (from 35 to 60wt% dissolved Na2Si2O5, NS2) into the fluid favors the formation of alkali-zirconosilicate clusters Zr–O–Si/Na similar to those found in vlasovite (Na2ZrSi4O11), with Zr4+ in octahedral coordination with oxygen (Zr–O distance=2.09±0.04Å) and ∼6 Si (Na) second neighbors (Zr–Si/Na distance=3.66±0.06Å). This coordination environment also dominates Zr speciation in F-free and F-bearing NS2 and haplogranite glasses and high pressure hydrous haplogranite melts (15.5–33wt% dissolved H2O) in the investigated pressure–temperature range. The XAS analyses, assisted by ab initio XANES calculations, are not conclusive concerning the extent of Zr–F complexation in hydrous granitic melts. Alkali-zirconosilicate Zr–O–Si/Na clusters such as those identified in this study may explain the enhanced solubility of zircon ZrSiO4 (and other HFSE-bearing minerals) in alkali-aluminosilicate-bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the mobilization of HFSE in subduction zones. Fluid–rock interactions and/or P/T variations as fluids migrate through the mantle wedge could affect the stability of these complexes, triggering the precipitation of HFSE-bearing accessory phases that are eventually recycled into the mantle, contributing to the dispersion of HFSE. These processes provide a possible explanation for the characteristic HFSE depletion recorded in arc magmas.

High-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air

The high-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air has shown their high corrosion resistance. A five-stage nonisothermal oxidation mechanism is established for the samples when heated at a rate of 20°C/min: 1) oxygen adsorption–desorption; 2) formation of ZrO2 and B2O3 oxides; 3) formation of α-SiO2 cristobalite and ZrSiO4 zircon; 4) formation of amorphous SiO2; and 5) formation of upper protective borosilicate film with ZrSiO4 inclusions at less than 40 wt.% SiC. It is shown that small ZrSi2 admixtures (<6–8 wt.%) substantially slow down the oxidation of the ceramics in initial heating stages due to diffusion-hindered formation of ZrO2 and B2O3. The 67.3 wt.% ZrB2–26 wt.% SiC–6.7 wt.% ZrSi2 ceramics are characterized by the highest corrosion resistance since their upper scale layer represents borosilicate glass stabilized with ZrO2 (tetragonal) inclusions.

Mechanical properties and electronic structure of zircon: Ab inito FLAPW-GGA calculations

Calculations of the mechanical properties and electronic structure of zircon ZrSiO4 using the first-principle FLAPW-GGA method are performed. It is established that a parameter limiting the mechanical stability of the crystal is the shear modulus G. According to Pugh’s criterion, ZrSiO4 lies on the boundary of the brittle-ductile transition, and this material is extremely sensitive to different disordering effects that, in principle, can contribute both to its brittleness and to improvement of flexibility.

Electronic structure of Pu3+ and Pu4+ impurity centers in zircon

Using a fully relativistic DV cluster method, we study the electronic structure of a large fragment of the crystal lattice of zircon ZrSiO4 with a plutonium dopant atom replacing a Zr4+ zirconium atom. Three possible states of the impurity center are considered: Pu4+ (isovalent substitution), Pu3+ (non-isovalent substitution), and Pu3+ with an oxygen vacancy in the nearest environment that provides charge compensation. Relaxation of the ZrSiO4 crystal lattice near a defect is simulated using a semi-empirical method of atomic pair potentials (GULP program). An analysis of overlap populations and effective charges on atoms shows that the chemical bonding of plutonium with a matrix is covalent, while isovalent substitution yields a more stable system than a Pu3+ impurity. In the presence of vacancies the structure of chemical bonding is intermediate with respect to substitutions Pu4+ → Zr4+ and Pu3+ → Zr4+.

Photoreduction processes and nanocluster formation induced by a CO2 laser on silicate surfaces

The photoreduction processes stimulated either the cw (power density 105–106 W/cm2) or pulsed (pulse energy 3–4 J, pulse duration 200 ns, effective laser spot diameter 1 mm) radiation of a CO2 laser on the surfaces of fused and crystalline quartz, as well as of natural silicates (nepheline KNa3[AlSiO4]4, rhodonite CaMn4[Si5O15], and zircon ZrSiO4), are studied. The X-ray emission analysis of irradiated surfaces showed that the laser irradiation of these materials leads to the sublimation of silicon oxides and the enrichment of surfaces with constituent metal elements. Laser radiation also stimulates the formation of silicon and metal nanoclusters on irradiated surfaces. The appearance of these nanoclusters is confirmed by both photoluminescence and X-ray emission studies of irradiated surfaces.

Formation of nanoclusters on the surface of silicates, induced by the radiation of a CO_2 laser

This paper discusses photochemical transformations caused by the action of radiation, both continuous and from a pulsed CO2 laser, on the surface of silicates (nepheline KNa3[AlSiO4]4, rhodonite CaMn4[Si5O15], zircon ZrSiO4, etc.). It was established by means of x-ray-emission analysis of a laser-irradiated surface that the action of laser radiation on these materials results in selective sublimation of silicon oxides, as well as enriching the surface with inclusion elements. The action of laser radiation also leads to the appearance on the irradiated surface of silicon and metallic nanoclusters, and this was confirmed by means of both photoluminescence and x-ray-emission studies of the laser-irradiated surface.

Electronic structure of a uranium impurity center in zircon

The electronic structure of a large fragment of the crystal lattice of zircon ZrSiO4 with a uranium impurity atom replacing the zirconium atom was investigated using the completely relativistic discrete variation (DV) cluster method. The results are compared with the data of a similar calculation of the ideal ZrSiO4 crystal. An analysis of the overlap populations and effective charges on the atoms of the matrix and impurity showed that chemical binding of uranium with the environment is covalent, and the electron density redistribution caused by this substitution changes not only the impurity and the nearest environment, but also the atoms of the next coordination spheres.

First-principles investigation of high-κdielectrics: Comparison between the silicates and oxides of hafnium and zirconium

Using density-functional theory, we investigate the structural, vibrational, and dielectric properties of Hf and Zr oxides and silicates which have drawn considerable attention as alternative high-kappa materials. For the silicates, we consider hafnon HfSiO4 and zircon ZrSiO4; while for the oxides, we study the cubic and tetragonal phases of HfO2 and ZrO2. Special emphasis is put on the analysis of the differences and similarities between Hf and Zr in these materials. In particular, we discuss the Born effective charge tensors, the phonon frequencies at the Gamma point of the Brillouin zone, and the dielectric permittivity tensors. Our study reveals very similar properties of Hf and Zr compounds, which are essentially related to the chemical homology of Hf and Zr.

Effect of Layer-by-Layer Electric-Spark Alloying on the Properties of an Electrolytic Coating of the System Ni – B

The effect of layer-by-layer electric-spark alloying on the tribological parameters of a composite electrolytic coating of the system Ni – B is studied. It is shown that layer-by-layer electric-spark alloying with intermetallic TiAl and a composite AlN – ZrB2 halves coating wear and prevents transfer of coating material to the counterbody. The reason for this is formation of a graded structure for the surface layer including zircon ZrSiO4 and intermetallic TiAl. The latter is responsible for formation of β-tialite during tribological oxidation acting as a solid lubricant.

Compressibility and high presussure chemistry of metamict Zircon ZrSiO4

Compressibility and high presussure chemistry of metamict Zircon ZrSiO₄

Preliminary Evaluation of Thermodynamic Mixing Properties and Miscibility Limits for Cubic Dioxide (Zr, M)O2 and Zircon (Zr, M)SiO4 Solid Solutions (M = An4+, Ln4+)

Cubic zirconia ZrO2 and zircon ZrSiO4 are considered as perspective crystalline form for immobilization of U, Pu and other radionuclides [1, 2]. The present study was undertaken to determine temperature dependence of solid solution limits in these compounds using thermodynamic theory of solid solutions and available equilibrium data. Thermodynamic mixing properties has been evaluated by means of the relationship between Margules parameter W and interatomic distances R in end-members AX and BX of a solid solution (A1−xBx)XW = α(ΔR/R)2where ΔR = R(BX) - R(AX), R = (1−x) R(AX) + x R(BX), α is a constant for isotypic isostructural compounds. According to the Urusov's energetic theory of enthalpy of mixing [3] such relationships exist between parameters W, AR and R of solid solutions with similar bonds between isomorphous atoms and their neighbors

Preparation of radiation damaged ceramic powders by ion bombardment

Abstract Ceramic powders can be prepared in a radiation damaged condition by bombardment with 1 to 4 MeV ions of Ne, Ar, Kr or Xe. The powder particle sizes are chosen to correspond to the ion beam penetration but are found to be considerably greater than the calculated ion ranges for powders becoming metamict. A monolayer of powder particles of sizes up to about 5 μm is sedimented onto long strips of metal foil with an area density of about 1 mg-cm-2. The ion beam is rastered to irradiate an area as the foil rotates on a drum through the beam. Alternately, monolayers of powder particles can be prepared by the use of a very-thin layer of rubber cement. By these techniques, plates can be prepared for irradiation in the ion beam and also for direct insertion into an X-ray diffractometer. Gram amounts of irradiated material can be collected in a few hours for studies such as powder X-ray diffraction, SEM, Differential Scanning Calorimetry and density measurements. Thus, zircon ZrSiO4 becomes non-crystalline ...