Broadly defined synthesis and properties of phase change materials

Phase change materials are currently used in numerous applications such as sensor, memory, detector, etc. due to change in properties when external stimuli are applied. Over the past few decades, nanostructured phase change materials have shown enhanced properties and characteristics compared to the conventional bulk phase change materials. Transition metal chalcogenides are reported to undergo thermally triggered phase transitions, yet there is still significant room for improvements for nanostructured FeTe2. Also, two-dimensional MXenes are reported to have multiple phases due to change in the surface chemistry. This thesis proposes solution phase synthesis and properties of FeTe2 nanostructures with different Te vacancy concentrations and synthesis of nanostructured Ti3C2Tx MXenes. Te nanowires were first synthesized in the reactor with ethylene glycol solvent and Fe precursor was injected to form FeTe2. The morphology changed from flakes to necklace structure as the concentration of iron precursor changed from the stoichiometric ratio to the iron-rich, respectively. These materials were washed and sintered into a nanocomposite disk using spark plasma sintering. To study the properties of the FeTe2 nanocomposite disk, Seebeck coefficient measurement was applied on the nanocomposite disk within certain temperature range. Phase transitions from p-type to n-type conduction were observed at phase transition temperatures. Phase transition temperature changed with sintering time and initial molar ratio between Fe and Te. The longer sintering time and excess Fe injection during solution phase synthesis resulted in higher Te vacancy in FeTe2 and decrease in phase transition temperature. Two disks with different phase transition temperatures were integrated into one disk using spark plasma sintering. I-V characteristic measurement was applied to the integrated disk while heating. As temperature increased, p-n junction was formed as one side of the disk with the lower phase transition temperature changed to n-type and the other side of the disk with the higher phase transition temperature still remained p-type. I-V characteristic measurements were conducted while heating and cooling and reversible switching behavior was observed. MAX bulk disk was synthesized from TiH2, Al, and TiC powders by spark plasma sintering. The disk was ground into fine powders and a 325-mesh sieve was used to ensure the particle sizes to be small for effective etching. To produce MXene, MAX powders were etched with concentrated hydrofluoric acid to remove Al between Ti3C2 layers

Composition Modulation of Ag_2Te Nanowires for Tunable Electrical and Thermal Properties

In this article, we demonstrated that composition modulation of Ag_2Te nanowires can be achieved during the self-templated transformation of Te nanowires into Ag_2Te nanowires during solution phase synthesis, which provides a mean to tune the carrier density of the Ag_2Te nanowires. Both nearly stoichiometric and Ag-rich nanowires have been synthesized, which give rise to p-type and n-type Ag_2Te nanocomposites after hot press, respectively. The electrical and thermal properties of the two kinds of samples have been measured. Theoretical modeling based on the near-equilibrium Boltzmann transport equations has been used to understand the experimental results. We found that ZT of the heavily doped n-type sample reaches 0.55 at 400 K, which is the highest ZT value reported for Ag_2Te at the same temperature mainly due to the reduced thermal conductivity by the nanostructures. Theoretical analysis on the carrier transport shows that the power factor is also very well optimized in the doped Ag_2Te sample considering the reduced carrier mobility by the nanostructures

Broadly defined synthesis and properties of phase change materials

Phase change materials are currently used in numerous applications such as sensor, memory, detector, etc. due to change in properties when external stimuli are applied. Over the past few decades, nanostructured phase change materials have shown enhanced properties and characteristics compared to the conventional bulk phase change materials. Transition metal chalcogenides are reported to undergo thermally triggered phase transitions, yet there is still significant room for improvements for nanostructured FeTe2. Also, two-dimensional MXenes are reported to have multiple phases due to change in the surface chemistry. This thesis proposes solution phase synthesis and properties of FeTe2 nanostructures with different Te vacancy concentrations and synthesis of nanostructured Ti3C2Tx MXenes. Te nanowires were first synthesized in the reactor with ethylene glycol solvent and Fe precursor was injected to form FeTe2. The morphology changed from flakes to necklace structure as the concentration of iron precursor changed from the stoichiometric ratio to the iron-rich, respectively. These materials were washed and sintered into a nanocomposite disk using spark plasma sintering. To study the properties of the FeTe2 nanocomposite disk, Seebeck coefficient measurement was applied on the nanocomposite disk within certain temperature range. Phase transitions from p-type to n-type conduction were observed at phase transition temperatures. Phase transition temperature changed with sintering time and initial molar ratio between Fe and Te. The longer sintering time and excess Fe injection during solution phase synthesis resulted in higher Te vacancy in FeTe2 and decrease in phase transition temperature. Two disks with different phase transition temperatures were integrated into one disk using spark plasma sintering. I-V characteristic measurement was applied to the integrated disk while heating. As temperature increased, p-n junction was formed as one side of the disk with the lower phase transition temperature changed to n-type and the other side of the disk with the higher phase transition temperature still remained p-type. I-V characteristic measurements were conducted while heating and cooling and reversible switching behavior was observed. MAX bulk disk was synthesized from TiH2, Al, and TiC powders by spark plasma sintering. The disk was ground into fine powders and a 325-mesh sieve was used to ensure the particle sizes to be small for effective etching. To produce MXene, MAX powders were etched with concentrated hydrofluoric acid to remove Al between Ti3C2 layers.</p

IgA nephropathy in a laboratory worker that progressed to end-stage renal disease: a case report

Background: IgA nephropathy (IgAN) is the most common form of glomerulonephritis, a principal cause of end-stage renal disease (ESRD) worldwide. The mechanisms of onset and progression of IgAN have not been fully revealed, and epidemiologic studies have yielded diverging opinions as to the role of occupational exposure to organic solvents in the initiation or worsening of IgAN. As the authors encountered a laboratory worker with IgAN that progressed to ESRD, we present a case report of IgAN progression due to dichloromethane exposure along with a review of literature. Case presentation: A 41-year-old male laboratory worker began to experience gross painless hematuria after two years of occupational exposure to toluene. Although clinical follow-up was initiated under the impression of IgAN based on clinical findings, the patient continued to work for four more years in the same laboratory, during which he was in charge of laboratory analysis with direct exposure to a high concentration of dichloromethane without proper protective equipment. During that time, his renal function rapidly worsened and finally progressed to ESRD 10 years after the first clinical symptoms. The result of exposure assessment through reenactment of his work exceeded the occupational exposure limit for dichloromethane to a considerable degree. Conclusions: The causal association between occupational solvent exposure and IgAN is still unclear; therefore, this case report could be used as a basis to support the relevance of occupational solvent exposure to IgAN and/or its progression. Early intervention as well as close monitoring of laboratory workers exposed to various organic solvents is important to prevent or delay the progression of glomerulonephritis to ESRD in the occupational setting.OAIID:RECH_ACHV_DSTSH_NO:T201619409RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A074611CITE_RATE:0FILENAME:Min2016AOEM_IgA nephropathy in a laboratory worker that progressed to end-stage renal disease a case report.pdfDEPT_NM:보건학과EMAIL:[email protected]_YN:NFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/5d11c631-71db-49a5-9483-20d55ae03dfc/linkY

Additional file 1: Table S4. of The association of relational and organizational job stress factors with sleep disorder: analysis of the 3rd Korean working conditions survey (2011)

Odds ratio of selected variables and Sleep disorder. (XLSX 14 kb

Method for Synthesis of Tetrabenzoporphyrin Precursor for Use in Organic Electronic Devices

We developed a new synthetic method for bicyclo[2.2.2]­octadiene (BCOD)-fused porphyrin (<b>1</b>), a tetrabenzoporphyrin (TBP, <b>2</b>) precursor that is well-known as a good material for use in organic electronic devices. The newly developed method synthesizes the BCOD-fused pyrrole intermediate (which is the most important intermediate in synthesizing BCOD-fused porphyrin) in a simpler and easier manner than other existing methods, and thus, the new method can efficiently synthesize the TBP precursor

Synthesis of core/shell nanocrystals with ordered intermetallic single-atom alloy layers for nitrate electroreduction to ammonia

10.1038/s44160-023-00258-xNature Synthesi