Composites based on zirconium dioxide and zirconium hydrophosphate containing graphene-like additions for removal of U(VI) compounds from water

2020 ◽  
Vol 10 (12) ◽  
pp. 4591-4602
Author(s):  
O. V. Perlova ◽  
Yu. S. Dzyazko ◽  
A. V. Palchik ◽  
I. S. Ivanova ◽  
N. O. Perlova ◽  
...  
2021 ◽  
Vol 12 (1) ◽  
pp. 18-31
Author(s):  
O. V. Perlova ◽  
◽  
I. S. Ivanova ◽  
Yu. S. Dzyazko ◽  
M. O. Danilov ◽  
...  

Unlike ion-exchange resins, inorganic sorbents possess high selectivity towards heavy metal ions and stability against ionizing radiation. However, sorption on these materials is rather slow. Moreover, sorption capacity strongly depends on the solution pH. In order to improve sorption properties of inorganic ion-exchangers, composites containing advanced carbon materials are obtained. Regularities of sorption of U(VI) compounds from low-concentrated aqueous solutions (up to 0.1 mmol dm–3 of uranium) on hydrated zirconium dioxide and zirconium hydrophosphate are considered. The sorbents were modified with partially unzipped multiwalled carbon nanotubes (PUMWCNTs). Sorption isotherms were obtained and analyzed. They obey Dubinin-Radushkevich model indicating sorption sites, a size of which is comparable with that of ions being sorbed. As found, the sorption mechanism is ion exchange. The effect of the solution pH on the sorption rate of U(VI) ions and capacity of inorganic ion-exchangers and their composites has been considered. Carbon additions increase sorption capacity of zirconium dioxide and zirconium hydrophosphate, when the initial pH of one-component solution is 3–4 and 5–7 respectively. Under these conditions, U(VI)-containing cations are removed from the solution practically completely. The rate of sorption obeys the model of chemical reaction of pseudo-second order, when uranium is removed from one-component solution. PUMWCNTs slow down sorption on zirconium dioxide and accelerate it on zirconium hydrophosphate. The dependence of the pseudo second order equation constants on the pH of U(VI) solutions was analyzed. The reaction of the first order occurs, when the solution contains also Ca2+ and Mg2+ ions. Regeneration was carried out using HNO3 and NaHCO3 solutions: the rate-determining stage of desorption is particle diffusion. It has been shown that one-component ZHP can be regenerated with a NaHCO3 solution practically completely. The most suitable solution for U(VI) desorption from ZHP-PUMWCNTs composite is a 1 M HNO3 solution.


Author(s):  
R.A. Ploc

Samples of low-nickel Zircaloy-2 (material MLI-788-see(1)), when anodically polarized in neutral 5 wt% NaCl solutions, were found to be susceptible to pitting and stress corrosion cracking. The SEM revealed that pitting of stressed samples was occurring below a 2000Å thick surface film which behaved differently from normal zirconium dioxide in that it did not display interference colours. Since the initial film thickness was approximately 65Å, attempts were made to examine the product film by transmission electron microscopy to deduce composition and how the corrosion environment could penetrate the continuous layer.


2020 ◽  
Author(s):  
I. F. Zakirov ◽  
Yu. V. Ivanova ◽  
A. V. Shak

2021 ◽  
Vol 270 ◽  
pp. 115200
Author(s):  
S. Idrissi ◽  
S. Ziti ◽  
H. Labrim ◽  
L. Bahmad

2021 ◽  
pp. 100750
Author(s):  
N. Sundar ◽  
S. Ananda Kumar ◽  
P. Keerthana ◽  
S. Johan Stanley ◽  
G. Ananda Kumar

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3102
Author(s):  
Rini Behera ◽  
Lora Mishra ◽  
Darshan Devang Divakar ◽  
Abdulaziz A. Al-Kheraif ◽  
Naomi Ranjan Singh ◽  
...  

The objective of the present study was to evaluate the one-year clinical performance of lithium disilicate (LD) and zirconium dioxide (ZrO2) class II inlay restorations. Thirty healthy individuals who met the inclusion criteria were enrolled for the study. The patients were randomly divided into two study groups (n = 15): LD (IPS e.max press) and ZrO2 (Dentcare Zirconia). In the ZrO2 group, the internal surfaces of the inlays were sandblasted and silanized with Monobond N (Ivoclar, Leichsteistein, Germany). In the LD group, the internal surfaces of the inlays were etched with 5% hydrofluoric acid. The ceramic inlays were cemented with self-cure resin cement (Multilink N). Clinical examinations were performed using modified United State Public Health Codes and Criteria (USPHS) after 2 weeks, 4 weeks, 6 months and 1 year. The one-year survival rate was evaluated. In total, one failure was observed in the ZrO2 group. The survival probability after 1 year for the ZrO2 inlays was 93%, and for the LD inlays was 100%, which was statistically insignificant. The differences between both groups for most USPHS criteria (except for colour match) were statistically insignificant. Within the imitations of the present study, the lithium disilicate- and zirconia dioxide-based inlays exhibited comparable clinical performances. However, the colour and translucency match was superior for the lithium disilicate restorations.


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