Stannous Research Articles

Quality Assessment of a Traditional Makeup Foundation Sbdaj in Kurdistan-Iraq

The use of Sbdaj, the ancient and traditional mineral foundation, is a popular practice in Kurdistan Region Iraq. The research work is confined to a comparative analysis of traditional foundations (Sbdaj) and modern foundations (Vichy). The analytical tests were performed for heavy metals and major contents using X-ray fluorescence and inductively coupled plasma spectra after sample preparation in two different ways. Also, the UV spectrum and FT-IR spectroscopy of the Sbdaj foundation and Vechi Sunscreen have been taken. The revealed peaks of Infrared absorption of Sbdaj foundation are (3378; 2960; 2854; 1637; 1261; 1092; 1054; 799; 657) cm-1, which allowed identifying the stretching band of (hydroxyl, methyl, carbonyl, silica group, ester ) respectively, while obtained IR spectra for Vichy foundation (3392; 2959; 2856; 1639; 1409; 1261; 1044; 843; 673) cm-1 that identify the stretching and bending of (hydroxy, methyl, ester, methyl, silica, ether) respectively, that returns to the ingredients used in these foundations. The Contents of major (SiO2, Al2O3) and trace elements (Pb, W, Nd, I, Sn, Cu, Ni, and Cl) were able to be determined by (XRF). (ICP-OES) used for identifying the presence of )Pb, Sb, Cd, Sr, Se, As, Zn, Ni, Mn, Cr, V, and Ti(. The overall mean concentrations of heavy metals in Sbdaj varied between (0.194 to 62235.18 ppm). 0.194 ppm for Cd and 62235.18 ppmfor Pb. The levels found in Sbdaj are more than the suggested safe limit for skin protection. The UV- absorption spectrum shows that Sbdaj contains blocking components that absorb UV radiations. It exhibits the same absorption band (318 nm) as the Vichy Sunblock.

Experimental and theoretical research on improving the gas sensitivity of ethanol based on Bi-doped ZnSn(OH)6

The wider band gap of ZnSn(OH)6 (ZHS) leads to higher resistance and low sensitivity to gases, and doping is one important way of reducing resistance and improving gas sensitivity. In this paper, cubic ZHS and Bi-doped ZHS were successfully prepared by hydrothermal method and analyzed by XRD, SEM, TEM and XPS, respectively. The results are as following: XRD pattern of the samples are consistent with ZHS standard card, and the XRD characteristic peak shifts to the left after Bi doping; the size of the cubic particle decreases greatly; Zn, Sn, O and Bi elements are evenly distributed. The replacement of Sn with Bi will form a displacement impurity, and insert a shallow donor impurity level at the bottom of the conduction band. As a result, the carrier concentration increases while the band gap width and material resistance decreases. Therefore, the performance of the sensor is greatly improved.

Enhancing Wettability of Cu3P/Cu Systems through Doping with Si, Sn, and Zr Elements: Insights from First Principles Analysis

Explaining the wetting mechanism of Cu-P brazing materials and Cu remains challenging. This fundamental research aims to reveal the wettability mechanism of Si, Sn, and Zr doping on the interfacial bond strength of the Cu3P/Cu system through the first principles study. We carried out several sets of calculations to test the validity of the result; included in the work are those used to establish the interfacial structure and to analyze the effect of doping on the wettability. Specific analysis was carried out in terms of three aspects: the work of adhesion (Wad), the charge density difference, and the density of states (DOS). The calculated results show that doping with Si, Sn, and Zr elements can effectively improve the wettability within the CuP/Cu interface with very high accuracy, and is particularly effective when doped with Zr. These results provide an insightful theoretical guide for enhancing the CuP/Cu system's wettability by adding active elements.

Reducing Exact Two-Component Theory for NMR Couplings to a One-Component Approach: Efficiency and Accuracy.

The self-consistent and complex spin-orbit exact two-component (X2C) formalism for NMR spin-spin coupling constants [ J. Chem. Theory Comput. 17, 2021, 3874-3994] is reduced to a scalar one-component ansatz. This way, the first-order response term can be partitioned into the Fermi-contact (FC) and spin-dipole (SD) interactions as well as the paramagnetic spin-orbit (PSO) contribution. The FC+SD terms are real and symmetric, while the PSO term is purely imaginary and antisymmetric. The relativistic one-component approach is combined with a modern density functional treatment up to local hybrid functionals including the response of the current density. Computational demands are reduced by factors of 8-24 as shown for a large tin compound consisting of 137 atoms. Limitations of the current ansatz are critically assessed for Sn, Pb, Pd, and Pt compounds, i.e. the one-component treatment is not sufficient for tin compounds featuring a few heavy halogen atoms.

Mechanism of Fe removal by Sn addition in Al-7Si-1Fe alloy

Excess impurity Fe will form various intermetallic compounds in Al-based alloys, such as α-Al8Fe2Si and β-Al5FeSi, which greatly reduce the elongation of alloys. Therefore, Fe removal is a promising approach for high performance Al-based alloy. In this paper, we propose an effective method for the Fe removal from Al-7Si alloys by adding Sn. Based on the thermodynamic calculations, the element Sn was selected for Fe removal. The microstructure of Fe-rich compounds and Fe content in alloy were compared by optical microscope (OM), scanning electron microscopy (SEM) and inductively coupled plasma generation spectrometer (ICP). It was observed that the reduction of Fe content in Sn can reach 33.8%, comparable to the level of adding B. More Fe-rich compounds deposited at the bottom after addition of Sn. However, the phase type and morphology of Fe-rich compound were unchanged. The β-Sn attached to the β-Al9Fe2Si2 which was determined by transmission electron microscopy (TEM), and a coherent interface between β-Sn and β-Al9Fe2Si2 phase was observed with the orientation of (0 0 1)[1 1 0]β-Sn∥(2 2 0)[0 0 1]β-Al9Fe2Si2. It deduced that the attached β-Sn with larger density than alloy would lead to more deposition of β-Al9Fe2Si2. This study provides an insight into the preparation of high-performance Al-Si alloy by removing Fe from secondary Al alloy with Sn addition.

Efficient and low-damage machining of Ti6Al4V: laser-assisted CBN belt grinding

ABSTRACT This study introduces a new method for efficient and low-damage machining of Ti6Al4V: laser-assisted CBN belt grinding. The impact of laser power and grinding depth on the machining behavior of the material is investigated, the elemental distribution and chemical state of the ground surface are analyzed, and the removal mechanism of laser-assisted CBN belt grinding is described. The results show that increasing laser power will improve processing efficiency, enhance plastic material removal, and improve surface quality; the tangential grinding force is decreased by 63.5% and the normal grinding force is decreased by 72.6% at the maximum laser power; a large amount of Ti and N are present on the ground surface, and they are present in the form of TiN compounds. This study is a guide to the research on efficient and low-damage machining of hard-to-process materials like titanium alloys.

Effect of B addition on microstructures and properties of Cu-15Ni-8Sn alloy

The effect of B addition on microstructures and properties of as-cast, solution-treated and aged Cu-15Ni-8Sn alloy was systematically investigated in the present study. It is found that the micron-scale Ni6.67SnB2 phase is identified in as-cast microstructure for B-containing Cu-15Ni-8Sn-xB alloys. Moreover, it is suggested the segregation of Sn element at grain boundary could be alleviated to a certain degree with B addition. After being solution-treated at 850 °C for 4 h, the Ni6.67SnB2 phase is still existed in the matrix, thereby resulting in a significant influence on the microstructures and properties during subsequent aging process. Results demonstrate that, during aging treatment at 400 °C, the transformation of DO22 ordered phase into L12 ordered phase can be increasingly inhibited with increase of B content and completely prevented for 0.3 and 0.5 wt% B addition. Additionally, the appropriate B addition (0.04, 0.08, 0.1 wt%) could remarkably suppress the formation and growth of the discontinuous precipitation. Nevertheless, with excess B addition (0.3, 0.5 wt%), the discontinuous precipitation is instead promoted. More importantly, alloys with appropriate B addition (0.04, 0.08, 0.1 wt%) could also maintain the peak hardness without deterioration as long as 18 h during the aging process, which suggests the tremendous enhancement of softening resistance. It is believed that the suppression of discontinuous precipitation by Ni6.67SnB2 phase should be responsible for such enhancement of softening resistance. It is anticipated that the current work could provide guidance for the multi-component design of high-performance Cu-Ni-Sn alloy.

Sb-doped SnS2 nanosheets enhance electrochemical reduction of carbon dioxide to formate

Electrocatalytic carbon dioxide (CO2) is a forward-looking strategy to convert renewable energy into fuel. Herein, we show that the novel Sb-doped SnS2 nanosheets were synthesized by a simple hydrothermal method for efficient electroreduction of CO2, and the atomic ratio of Sb/Sn was controllable. The introduction of Sb significantly enhanced the current density and Faradaic efficiency for formate products compared to pristine SnS2 nanosheets. When the Sb content was 1%, the Sb-SnS2 nanosheets achieved a remarkable Faradaic efficiency of 90.86% for formate products at −1.1 V vs. RHE. The experimental results showed that 1% Sb-doped SnS2 nanosheets changed the electronic structure of the Sn element, allowing the catalyst to reconfigure to generate Sn0 during the electrochemical reaction, while the singlet tin had a synergistic effect with Sn4+, making it easier to transport electrons on the surface and promoting the activation process of CO2, which is a key factor to improve the electroreduction performance of CO2.

Trace Elements in Soy-Based Beverages: A Comprehensive Study of Total Content and In Vitro Bioaccessibility.

Soy-based beverages are one of the most consumed plant-based beverages, which have been used as a substitute for dairy products. Soy is a source of several nutrients (vitamins, minerals, and phenolic compounds, etc.) and its consumption is usually associated with several benefits, such as the prevention of cardiovascular diseases, cancer, and osteoporosis. However, non-essential trace elements can be found in these beverages. Thus, a comprehensive study concerning trace elements Al, As, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sb, Se, Sn, Sr, and Zn in soy-based beverages was proposed. In vitro digestion allowed to simulate the gastrointestinal juice (bioaccessibility) and the Caco-2 cells culture model was applied for the bioavailability assay. Trace elements measures were performed by inductively coupled plasma optical emission spectrometry (ICP OES). Multivariate analysis classified soy-based beverages according to their soy source (isolate protein, hydrosoluble extract, and beans); Al, Cu, Fe, Mn, Sr, Se, and Zn bioaccessible fractions corresponded to approximately 40%-80% of their total content, and soy-based beverages were found to be a good Fe, Se, and Zn source. However, our results showed risk exposure assessment from daily consumption of one glass of soy-based beverage can contribute to 3.5% and 0.9% of Al Provisional Tolerable Weekly Intake (PTWI) for children and adults, respectively.

Experimental characterization of tool wear morphology in milling of Al520-MMC reinforced with SiC particles and additive elements Bi and Sn

Combining aluminium as a soft, lightweight, and low-strength material with reinforcing elements may lead to fabricating materials with excellent abrasion resistance and a high strength-to-weight ratio. However, these fabricated materials are classified as difficult to cut materials due to elevated tool wear size. According to the literature, limited studies were reported on the effects of various reinforcing elements on the machinability of Al520-MMC, mainly tool wear morphology and size. Therefore, in the course of this study, Al520-MMCs were fabricated with various reinforcing elements, such as silicon carbide (SiC), bismuth (Bi), and tin (Sn) particles. No similar work was found in this regard. Accordingly, as an originality of this work, besides fabricating new MMcs, the experimental characterization of tool wear morphology was conducted when milling Al520-MMCs with various reinforcing elements. Despite the reinforcing elements used, higher tool flank wear was observed under dry machining. Furthermore, knowing that Al520-MMC is a soft metal, the built-up edge (BUE) was observed under all lubrication modes and cutting speeds. Additionally, abrasion was found in all cutting conditions used. Therefore, it could be stated that the reinforcing elements and cutting speed had the most significant effects, and the lubrication mode had minimal impact on the wear size. Compared with the recorded values of tool flank wear in machining Al520 + 10% SiC, the flank wear was reduced by around 50% when Bi and Sn were used in the matrix structure. In other words, using bismuth (Bi), and tin (Sn) particles may lead to better tool life.

Chemical Insights into the Formation of Colloidal High Entropy Alloy Nanoparticles.

Nanoparticles of high entropy alloys (HEAs) have distinct properties that result from their high surface-to-volume ratios coupled with synergistic interactions among their five or more constituent elements, which are randomly distributed throughout a crystalline lattice. Methods to synthesize HEA nanoparticles are emerging, including solution approaches that yield colloidal products. However, the complex multielement compositions of HEA nanoparticles make it challenging to identify and understand their reaction chemistry and the pathways by which they form, which hinders their rational synthesis. Here, we demonstrate the synthesis and elucidate the reaction pathways of seven colloidal HEA nanoparticle systems that contain various combinations of noble metals (Pd, Pt, Rh, Ir), 3d transition metals (Ni, Fe, Co), and a p-block element (Sn). The nanoparticles were synthesized by slowly injecting a solution containing all five constituent metal salts into oleylamine and octadecene at 275 °C. Using NiPdPtRhIr as a lead system, we confirmed the homogeneous colocalization of all five elements and achieved tunable compositions by varying their ratios. We also observed heterogeneities, including Pd-rich regions, in a subpopulation of the NiPdPtRhIr sample. Halting the reaction at early time points and characterizing the isolated products revealed a time-dependent composition evolution from Pd-rich NiPd seeds to the final NiPdPtRhIr HEA. Similar reactions applied to FePdPtRhIr, CoPdPtRhIr, NiFePdPtIr, and NiFeCoPdPt, with modified conditions to most efficiently incorporate all five elements into each HEA, also revealed similar Pd-rich seeds with system-dependent differences in the rates and sequences of element uptake into the nanoparticles. When moving to SnPdPtRhIr and NiSnPdPtIr, the time-dependent formation pathway was more consistent with simultaneous coreduction rather than through formation of reactive seeds. These studies reveal important similarities and differences among the pathways by which different colloidal HEA nanoparticles form using the same synthetic method, as well as establish generality. The results provide guidelines for incorporating a range of different elements into HEA nanoparticles, ultimately providing fundamental knowledge about how to define and optimize synthetic protocols, expand into different HEA nanoparticle systems, and achieve high phase purity.

Auto‐encoder neural network incorporating x‐ray fluorescence fundamental parameters with machine learning

AbstractWe consider energy‐dispersive x‐ray fluorescence (XRF) applications where the fundamental parameters method is impractical such as when instrument parameters are unavailable. For example, on a mining shovel or conveyor belt, rocks are constantly moving (leading to varying angles of incidence and distances) and there may be other factors not accounted for (like dust). Neural networks do not require instrument and fundamental parameters but training neural networks requires XRF spectra labeled with elemental composition, which is often limited because of its expense. We develop a neural network model that learns from limited labeled data and also benefits from domain knowledge by learning to invert a forward model. The forward model uses transition energies and probabilities of all elements and parameterized distributions to approximate other fundamental and instrument parameters. We evaluate the model and baseline models on a rock dataset from a lithium mineral exploration project. Our model works particularly well for some low‐Z elements (Li, Mg, Al, and K) as well as some high‐Z elements (Sn and Pb) despite these elements being outside the suitable range for common spectrometers to directly measure, likely owing to the ability of neural networks to learn correlations and nonlinear relationships.

Effects of Hypervalent Bismuth on Electronic Properties of the Azobenzene Tridentate Ligand and Roles of Lewis Acidity in Controlling Optical Properties.

Organobismuth compounds have been studied in various fields, including electronic states, pnictogen bonds, and catalysis. Among them, one of the unique electronic states of the element is the hypervalent state. So far, many issues regarding the electronic structures of bismuth in hypervalent states have been revealed; meanwhile, the influence of hypervalent bismuth on the electronic properties of π-conjugated scaffolds is still vailed. Here, we synthesized the hypervalent bismuth compound, BiAz, by introducing hypervalent bismuth into the azobenzene tridentate ligand as a π-conjugated scaffold. The influence of hypervalent bismuth on the electronic properties of the ligand was evaluated from optical measurements and quantum chemical calculations. The introduction of hypervalent bismuth revealed three significant electronic effects: first, hypervalent bismuth shows position-dependent electron-donating and electron-accepting effects. Second, BiAz can have a larger effective Lewis acidity than the hypervalent tin compound derivatives reported in our previous research. Finally, the coordination of dimethyl sulfoxide transformed the electronic properties of BiAz, similar to the hypervalent tin compounds. The data from quantum chemical calculations showed that the optical properties of the π-conjugated scaffold were able to be changed by introducing hypervalent bismuth. To the best of our knowledge, we first demonstrate that the introduction of hypervalent bismuth should be a new methodology for controlling the electronic properties of π-conjugated molecules and developing sensing materials.

The non-destructive investigation of a late antique knob bow fibula (Bügelknopffibel) from Kaiseraugst/CH using Muon Induced X-ray Emission (MIXE)

A knob bow fibula (Bügelknopffibel) of the Leutkirch type, which typologically belongs to the second half of the 4th and early 5th century CE, was excavated in 2018 in the Roman city of Augusta Raurica, present-day Kaiseraugst (AG, Switzerland). This was analyzed for the first time for its elemental composition by using the non-destructive technique of Muon Induced X-ray Emission (MIXE) in the continuous muon beam facility at the Paul Scherrer Institute (PSI). In the present work, the detection limit is 0.4 wt% with sim1.5 hours of measurement time. The fibula was measured at six different positions, at a depth of 0.3–0.4 mm inside the material. The experimental results show that the fibula is made of bronze, containing the main elements copper (Cu), zinc (Zn), tin (Sn) and lead (Pb). The compositional similarities/differences between different parts of the fibula reveal that it was manufactured as two “workpieces”. One workpiece consists of the knob (13.0±0.6 wt% Pb), bow (11.9±0.4 wt% Pb) and foot (12.5 ± 0.9 wt% Pb). These show a higher Pb content, suggesting a cast bronze. The spiral (3.2 ± 0.2 wt% Pb), which is part of the other workpiece, has a comparatively lower Pb content, suggesting a forged bronze.

Fabrication of novel oxochalcogens halides of manganese and tin nanocomposites as highly efficient photocatalysts for dye degradation and excellent antimicrobial activity

The dark brown and white crystals of manganese and tin (Mn2Se3Cl2O7 and SnSe3O4Cl) have been synthesized by solid-state reaction at 450 C. The morphology and the elemental analysis of newly synthesized compounds were studied by SEM and EDX Analysis. SEM analysis reveals that the particle size for Mn2Se3Cl2O7 was found to be 0.2–2.5 μm and for SnSe3O4Cl 2.0–6.0 μm. The EDX studies showed the presence of Mn, Se, O, Cl, and Sn elements. Powdered XRD confirmed the presence of a new phase present in these compounds. Under UV-vis irradiation, the kinetics of methylene blue (MB) degradation catalyzed by produced nanoparticles were monitored. The dye degradation efficiency was estimated, and results reveals that after 150 min of irradiation, almost 75% of the dye was degraded in the presence of Mn compound while 71% degradation was shown by Sn compound. Both composites display antimicrobial activity against Staphylococcus aureus and Escherichia coli with a maximum value of 34.5 mm. The maximum antimicrobial activity shown by Mn-incorporated nanocomposites estimated at 32.5 mm was against Gram-positive bacteria and 26.4 mm against Gram-negative bacteria. Similarly, the maximum antifungal activity shown by Sn incorporated estimated at 33.9 mm was compared to Gram-positive bacteria and 27.8 mm against Gram-negative bacteria.

Study on the impact erosion wear resistance and damage evolution of TiN films under different impact cycles

Depositing TiN coating is an effective way to improve the erosion resistance of titanium alloy. However, few studies have been carried out to analyze the damage process of TiN coated specimens. In this study, a TiN coating was prepared on the Ti6Al4V by employing a filtered cathodic vacuum arc. The erosion performance and damage evolution of TiN coating were investigated, accompanied by varying the impact cycles from 500 to 10,000. The change of peak impact force and energy absorption rate with increasing impact numbers were analyzed. A white-light interferometer was used to characterize the 3D surface topographies of the damaged surface. Scanning electron microscopy and energy dispersive spectrometer were used to observe the state of the eroded surface. The results show that the sand is embedded in the substrate with the increase of impact numbers. With decreasing the number of impacts, the energy absorption rate of the TiN coating increased rapidly, while the peak impact force decreases rapidly. The formation of impact pits, plow grooves, micro-cutting, brittle spalling, and cracks can be regarded as the wear mechanisms of the samples under sand erosion.

Biogeochemical Features of the Formation of the Holocene Sediments in Lake Dukhovoe at the Stage of Early Diagenesis in Eastern Baikalia

Abstract —A 6-meter core of the Holocene sediments in Lake Dukhovoe is studied. The material composition of the core is heterogeneous and has clear bedding. Lacustrine sediments are represented by the upper 293 cm. Each bed of the sediments is subjected to microbiological analysis. A high total number of heterotrophic bacteria is revealed in the upper (0–15 cm) and deeper (110–150 cm) sapropel intervals. Sulfate-reducing bacteria are identified only in Chrysophyceae cysts. The CaO/Fe2O3 ratio shows the degree of “carbonate content” of bottom sediments. It is low in the lake sapropel (0.2), which indicates the geochemical specificity (carbonate-free sapropel). Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr, and Cr concentrations in sapropel are within the average concentrations for the Earth’s crust, shale, and oceanic pelagic clays, while U and Mo concentrations exceed them. Phytoplankton is enriched in phosphorus (biogenic element) and chalcophile elements (Zn, Cd, Sn, Sb, Hg, Pb, and Cu), which characterize the pollution of the modern atmosphere of the Baikal region. Diagenetic processes result in the transformation of the pore waters, namely an increase in mineralization as compared to lake water, an increase in the concentrations of biogenic components (HCO3-, NH4+, NO3-, and PO43-) and a decrease in SO42-. Pyrite framboid accumulations are revealed in organomineral sediments below the horizon of 200 cm, and iron phosphates represented by vivianite are identified in sapropel.

Discrimination of Pb-Zn deposit types using sphalerite geochemistry: New insights from machine learning algorithm

Due to the combined influences such as ore-forming temperature, fluid and metal sources, sphalerite tends to incorporate diverse contents of trace elements during the formation of different types of Lead-zinc (Pb-Zn) deposits. Therefore, trace elements in sphalerite have long been utilized to distinguish Pb-Zn deposit types. However, previous discriminant diagrams usually contain two or three dimensions, which are limited to revealing the complicated interrelations between trace elements of sphalerite and the types of Pb-Zn deposits. In this study, we aim to prove that the sphalerite trace elements can be used to classify the Pb-Zn deposit types and extract key factors from sphalerite trace elements that can discriminate Pb-Zn deposit types using machine learning algorithms. A dataset of nearly 3600 sphalerite spot analyses from 95 Pb-Zn deposits worldwide determined by LA-ICP-MS was compiled from peer-reviewed publications, containing 12 elements (Mn, Fe, Co, Cu, Ga, Ge, Ag, Cd, In, Sn, Sb, and Pb) from 5 types, including Sedimentary Exhalative (SEDEX), Mississippi Valley Type (MVT), Volcanic Massive Sulfide (VMS), skarn, and epithermal deposits. Random Forests (RF) is applied to the data processing and the results show that trace elements of sphalerite can successfully discriminate different types of Pb-Zn deposits except for VMS deposits, most of which are falsely distinguished as skarn and epithermal types. To further discriminate VMS deposits, future studies could focus on enlarging the capacity of VMS deposits in datasets and applying other geological factors along with sphalerite trace elements when constructing the classification model. RF’s feature importance and permutation feature importance were adopted to evaluate the element significance for classification. Besides, a visualized tool, t-distributed stochastic neighbor embedding (t-SNE), was used to verify the results of both classification and evaluation. The results presented here show that Mn, Co, and Ge display significant impacts on classification of Pb-Zn deposits and In, Ga, Sn, Cd, and Fe also have relatively important effects compared to the rest elements, confirming that Pb-Zn deposits discrimination is mainly controlled by multi-elements in sphalerite. Our study hence shows that machine learning algorithm can provide new insights into conventional geochemical analyses, inspiring future research on constructing classification models of mineral deposits using mineral geochemistry data.

Analysis of Tin Stock Investment Projections during the Covid-19 Pandemic

Indonesia and other countries in the world are still experiencing the Covid-19 pandemic and continue to struggle for the country's health and economic recovery. The government along with all elements of society are tackling the impact of Covid-19 by implementing 3M (wearing masks, washing hands, maintaining distance), implementing health protocols, vaccination programs and implementing Large-Scale Social Restrictions (PSBB). The community collaborates on advances in smartphone technology with PSBB activities in their daily activities. With the advancement of technology platforms, it is very easy for people to transact in the stock investment mechanism and have an impact on people's lives.
 99% of Indonesia's tin mineral potential is in the Bangka Belitung Archipelago Province, while the rest is in the Riau Islands, Riau and West Kalimantan. The economic condition of the Bangka Belitung Islands province is still supported by the mining and quarrying sector, especially tin mining and the tin processing industry, in line with Irawan's study. So the tin stock investment instrument is still one of the instrument models that can be used during the Covid 19 pandemic. In the world of stock investment, there are two types of analysis known, namely fundamental analysis and technical analysis. Technical analysis attempts to test historical data in predicting stock prices in order to buy or sell an investment instrument.
 Keywords: Covid 19, Stocks, Tin, Investment

High sensitivity for detecting trace Sn2+ in canned food using novel covalent organic frameworks

Tin (Sn) element plays a vital role in the human body, and its detection is a mandatory inspection item for canned food. The application of covalent organic frameworks (COFs) in fluorescence detection has received extensive attentions. In this work, we designed a kind of novel COFs (COF-ETTA-DMTA) with high specific surface area (353.13 m2/g) by solvothermal synthesis using 2,5-dimethoxy-1,4-dialdehyde and tetra (4-aminophenyl) ethylene as precursors. It shows fast response time (about 50 s), low detection limit (228 nM) and good linearity (R2 = 0.9968) for the detection of Sn2+. Via coordination behavior, the recognition mechanism of COFs toward Sn2+ was simulated and verified by the small molecule with the same functional unit. More importantly, this COFs was successfully applied to identify Sn2+ in solid canned food (luncheon pork, canned fish, canned red kidney beans) with satisfactory results. This work provides a new approach for determining metal ions with COFs taking the advantage of their natural rich reaction set and specific surface area, improving the detection sensitivity and capacity.