Composite zircon ceramics based on raw materials activated by ammonium bifluoride

The results of studies of the synthesis processes of baddeleyite-zircon ceramics based on fluorinated plasmadissociated and natural zircon are presented. It was found that to obtain densely sintered ceramics based on fluorinated natural zircon, the introduction of CaO is required to stabilize free ZrO2 in the composition of the ceramics. The introduction of Y2O3 into the composition of ceramics based on plasma-dissociated zircon makes it possible to reduce the sintering temperature from 1600 to 1500 °C. It is difficult to obtain ceramics based on plasmadissociated zircon with a high degree of fluorination due to the formation of an excessive amount of ZrF4.

THE EFFECT OF PH AND CALCINATION TEMPERATURE ON THE ZrO2 PHASE FORMATION FROM NATURAL ZIRCON SAND OF KERENG PANGI

In this research ZrO2 has been synthesized from Kereng Pangi zircon sand in Central Kalimantan through alkali fusion-coprecipitation method. Firstly, zircon sand (ZrSiO4) was purified to reduce impurities by magnetic separation, cleaned using an ultrasonic cleaner, soaked/leached with HCl 2 M for 12 hours and leached with HCl at 60 ºC for 3 hours. Secondly, alkali fusion was done with KOH as an alkali. This product was then washed by water and dried before leached with HCl 30% at 90 ºC for 30 minutes to precipitate and seperate Silica from Zircon. ZrO2 filtrate (ZrOCl2) precipitated with NH4OH at pH 4, pH 7, and pH 10 forms Zr(OH)4 gel. Zr(OH)4 gel was dried and characterized by DTA-TGA, which was then followed by calcination based on DTA TGA results at temperature ranges of 550 ºC - 700 ºC to produce ZrO2. XRD results show that single tetragonal phase of ZrO2 is formed in all variations of pH precipitation and calcination temperature. An analysis using MAUD software show that crystal size reduces as the increase in precipitation of pH. The crystal size results are 110 nm, 66 nm and 48 nm at pH 4, pH 7 dan pH 10 at 700 ºC, respectively. Moreover, XRF results show that ZrO2 with purity is at around 95.8 % at pH 4 and 96.3 % at pH 7 and pH 10.

PHASE FORMATION PROCESSES AT LOW-TEMPERATURE FLUORINATION OF ZIRCONIUM SILICATE

Zirconium silicate ceramics is widely used in different fields of engineering. One of the most actual problem of zircon ceramics is the requiring of high temperatures for its sintering. Perspective method for activation of silicate materials with the aim of intensification of synthesis and sintering processes is the low-temperature fluoridation with the ammonium hydrofluoride. In accordance with that, processes occurring during the interaction of plasma dissociated zircon and natural zircon with ammonium hydrodifluoride were studied. It was established that plasma dissociated zircon actively interacts with ammonium hydrofluoride in the solid phase. Natural zircon because of its chemical inertness reacts with ammonium hydrofluoride only when latter melts. The main product of fluorinating is ammonium hexafluorosilicate. By-products are ammonium hexafluorozirconate and ammonium heptafluorozirconate. Their quantity increases with the content of ammonium hydrofluoride in mixtures. Kinetic equation of reaction between zircon and ammonium hydrofluoride is k×τ = 1-(1-α)1/n. Activation energy of plasma dissociated zircon and natural zircon fluorinating reactions are 13.9 and 32.7 kJ/mol, respectively. Order of reactions (n) are 2.0 and 1.5, respectively. Thermal treatment of fluorinated materials at 400 °C leads to ammonium hexafluorosilicate sublimation and thermal dissociation of ammonium fluorozirconates to zirconium fluoride and fluorozirconate intermediates. It was established that low-temperature fluoridation of zircon makes possible to regulate chemical composition of minerals. Materials obtained by ammonium hydrofluoride treatment of plasma dissociated and natural zircon can be potentialy used in the functional zircon and zirconia-zircon ceramics technology.

Characterization of the potential reference material SA02 for micro-beam U–Pb geochronology and Hf–O isotopic composition analysis of zircon

In the present work, a natural zircon megacryst SA02 (exact provenance unknown) is investigated as a new potential reference material for U–Pb geochronology and Hf–O isotopic composition analysis via micro-beam methods.

Identification of Multiple Rare Earths and Other Associated Elements in Zircon by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS), which is a powerful technique for the detection of minor and trace elements in a sample, has been used to analyze the enriched zircon mineral collected from the beach sands of southern Bangladesh. In addition to zirconium, a large number of rare earth elements viz. cerium, lanthanum, praseodymium, neodymium, ytterbium, gadolinium, dysprosium, erbium, samarium, europium, holmium and yttrium and other associated elements like hafnium, niobium, tantalum, magnesium, calcium, sodium, titanium and iron along with non-metals like phosphorus and silicon were detected in the enriched zircon samples by the LIBS technique. To the best of our knowledge, this is the first time that multiple rare earth elements have been identified in natural zircon by LIBS. Journal of Bangladesh Academy of Sciences, Vol. 44, No. 1, 59-68, 2020

Diametral Tensile Strength and Hardness Evaluation of Prototype Composite Based on Natural Zircon Sand Using Geopolymerization Method with Coupling Agent Variation

The widely use of dental composite triggers a lot of research to synthesize composite made from natural sources. One of the natural sources that could be used as a filler of composite is natural zircon sand from Indonesia. The physical properties of dental composite, such as Diametral Tensile Strength (DTS) and hardness could be affected by the filler of the composite. The aim of this research is to determine the value of diametral tensile strength and hardness of prototype composite with natural zircon sand-based filler by using geopolymerization method with various coupling agents. The procedures began from synthesizing Zirconia-Alumina-Silica filler from natural zircon sand using geopolymerization method with two different coupling agents, 3-mercapto propyltrimethoxysilane (3-MPTS) and 3-aminopropyltriethoxysilane (3-APTS), which then mixed with resin matrix to form composite resin, some of the samples were then subjected to a DTS test using Lloyd Universal Testing Machine (5.6 N initial load) until a crack/fracture was formed while some of them was subjected to a hardness test using Vickers Hardness Tester. The results showed the average DTS of dental composite using MPTS coupling agent was 13.78 MPa, while the average DTS of dental composite using APTS coupling agent was 8.90 MPa, and the average hardness result of dental composite coated by 3-MPTS was higher (20.68 VHN) than composite coated by 3-APTS (18.02 VHN). This difference could be affected by filler particle composition, filler surface area and also coupling agent variation. In conclusion, the tensile strength of the prototype resin composite sample group with the natural zircon sand filler using MPTS coupling agent was higher than the APTS coupling agent group.

Particle Size Analysis of the Synthesised ZrO2 from Natural Zircon Sand with Variation of pH Deposition Using Alkali Fusion-Coprecipitation Method

Zirconia (ZrO2) is one of the refractory ceramic materials that have applications in several fields. The aim of this study was to synthesis ZrO2 from natural zircon sand collected from Kereng Pangi, Central Kalimantan with a variation of pH deposition using alkali fusion co-precipitation method. The synthesized ZrO2 began with the preparation process involved magnetic separation, milling, and leaching with HCl. Furthermore, the alkali fusion process was used KOH solution and heated in an electrical furnace at 700°C for 3 h whereas the co-precipitation process was carried out using a filtrate mixed with the NH4OH solution to reach a pH variation between 3–11 and then precipitated for 12 h. The precipitates were dried in an oven and then calcined at 800°C for 3 h. The structure of synthesized ZrO2 was characterized using XRD and the particle sizes were measured using particle size analyzer (PSA). The XRD analysis showed that the identified phase of zirconia powder is tetragonal with a crystal size in nanometer size. Result of PSA measurement revealed that the crystal size decreased in the range pH of 3 - 7, but increased in the range pH of 7 - 11. The biggest powder particle size could be achieved at 260 nm with pH 7 whereas the smallest size was at 143 nm occurred at pH 3.

Cathodoluminescence of synthetic zircon implanted by He+ ion

He+ ion implantation at 4.0 MeV, equivalent to energy of α particles from natural radioactive nuclei 238U and 232Th, has been conducted for undoped synthetic zircon. The cathodoluminescence (CL) of implanted samples was measured to clarify the radiation-induced effects. Unimplanted synthetic zircon shows pronounced and multiple blue emission bands between 310 nm and 380 nm, whereas the implanted samples have an intense yellow band at ~550 nm. The blue emission bands can be assigned to intrinsic defect centers formed during crystal growth. The yellow band should be derived from induced-defect centers by He+ ion implantation, which might be related to the metamicitization originated from a self-induced radiation in natural zircon. The yellow band may be separated into two emission components at 1.96 eV and 2.16 eV. The emission component at 2.16 eV is recognized in both unimplanted and implanted samples, and its intensity increases with an increase in the implantation dose. The CL of zircon can be used as the geodosimeter.