Mechanism Of Discoloration Research Articles

Failure Analysis of the Solder Discoloration After Vacuum Sintering of Power Chips

In this paper, the discoloration of the solder after the vacuum sintering of the power chip is analyzed. The morphology and composition of the discoloration area were characterized and analyzed by the metallographic microscope, SEM, EDS and XPS, and the discoloration mechanism was studied. The analysis results show that the main components of the color-changing solder are C, O, Pb, Sn, Ni, Ag, and Au, which are the normal components of the solder after vacuum sintering. The reason for color-changing is the oxidation of the Sn element, and the different thickness of oxide shows different colors. The discoloration solder was treated with formic acid, and the solder returned to bright silver-white. The test further confirmed that the discoloration was caused by metal oxidation. The problem of solder discoloration is solved by optimizing the process to reduce the sintering time and vacuum defoaming time.

Bio-Based Pentamethylenediamine-Derived Semiaromatic Copolyamide: Controllable Synthesis and Discoloration Mechanism

Bio-Based Pentamethylenediamine-Derived Semiaromatic Copolyamide: Controllable Synthesis and Discoloration Mechanism

Two new Zinc (II)-viologen coordination polymers: Syntheses, structures, and photochromic behaviors

The self-assembly of Zn (II) ions with monosubstituted viologen ligand 1-(3-carboxybenzyl)-4,4’-bipyridinium chloride (m-Hbcbpy·Cl) and 1,3,5-benzenetricarboxylic acid (H3BTC) under solvothermal conditions results in two coordination polymers, namely, {[Zn(bcbpy)Cl2]·H2O}n(1) and {[Zn(bcbpy)(HBTC)H2O]·2H2O}n(2). Due to the formation of viologen radicals, the two compounds exhibit a triple photochromic behavior to sunlight, UV light and blue light through electron transfer, and the sequence of light response time is 1 > 2. Photochromic mechanisms and the relationships between structures and properties have been discussed adequately. And using time-dependent density functional theory (TDDFT) to study the discoloration mechanism of compounds 1 and 2. More importantly, compound 1 can be deposited on filter paper and displays potential applications as an inkless printing material. In addition, the capabilities of compound 2 to act as anti-counterfeiting materials for QR codes have also been investigated.

Transcriptome analysis reveals chrysanthemum flower discoloration under high-temperature stress.

Temperature is an important environmental factor affecting plant anthocyanin synthesis. High temperatures are associated with decreased anthocyanin pigmentation in chrysanthemum. To reveal the effects of high temperature on anthocyanin biosynthesis in chrysanthemum, ray florets of the heat-sensitive cultivar “Nannong Ziyunying” (ZYY) were subjected to RNA sequencing. A total of 18,286 unigenes were differentially expressed between the control and treatment groups. Functional annotation and enrichment analyses of these unigenes revealed that the heat shock response and flavonoid pathways were significantly enriched, suggesting that the expression of these genes in response to high temperature is associated with the fading of chrysanthemum flower color. In addition, genes related to anthocyanin synthesis and heat shock response were differentially expressed under high-temperature stress. Finally, to further investigate the molecular mechanism of discoloration under high-temperature stress and facilitate the use of marker-assisted breeding for developing novel heat-tolerant cultivars, these results were used to mine candidate genes by analyzing changes in their transcription levels in chrysanthemum.

An allochroic organic cage for efficient volatile organic compounds sensor and capture both in gaseous and aqueous phase

Environmental security caused by volatile organic compounds (VOCs) such as air and water pollution seriously endangering global human health. Removing VOCs with porous adsorption materials is very effective, but there are still many challenges. Herein, an allochroic amine porous organic cage containing phenolphthalein moiety is designed by a simple method. The amine cage shows excellent uptake capacity toward various VOCs both in the gaseous and aqueous phases, accompanied by an obvious allochroic response. A high dichloromethane vapor uptake capacity of up to ∼3000 mg g−1 is obtained with remarkable regeneration cycle performance. The allochroic response to VOCs and discoloration mechanism were further investigated and revealed a structural change related to a revisable break-reform of a weak C–O bond. The inner relationships between adsorption behavior and allochroic phenomenon are also discussed.

Flexible, infrared adjustable, thermal radiation control device based on electro-emissive PANI/Ce4+ thin films inspired by chameleon

Electrochromic materials (ECMs) with reversible change ability are widely concerned as environmental stealth materials that can actively adjust their color and infrared (IR) emissivity. Chameleon is the master of camouflage in the environment, inspired by the discoloration mechanism of chameleon's pigment capsule, we fabricated biomimetic film with superb IR thermal radiation regulation ability, in which polyaniline (PANI) and cerium ion (Ce4+) were used to simulate the skin receptor and pigment capsule in chameleon's skin respectively. In the wavelength scope of 8 ∼ 14 μm, the IR emissivity’s change (△ε) of the film from emeraldine-salt state (ESs) to leucoemeraldine-base state (LBs) is as high as 0.58. Beyond that, we use an integrated rolling thermal packaging process to assemble the films into electro-emissive devices (EEDs) with excellent cycle endurance, flexibility and IR thermal radiation management capabilities. This work provides a new strategy for the preparation of reliable IR thermal radiation control materials and devices.

Transcriptome and metabolome changes in Chinese cedar during cold acclimation reveal the roles of flavonoids in needle discoloration and cold resistance

Cryptomeria fortunei growth and development are usually affected by low temperatures. Despite the evergreen nature of this species, most needles turn yellowish-brown in cold winters. The underlying discoloration mechanisms that cause this phenomenon in response to cold acclimation remain poorly understood. Here, we measured the pigment content and ultrastructure of normal wild-type (Wt) and evergreen mutant (GM) C. fortunei needles and performed integrated transcriptomic and metabolomic analyses to explore potential discoloration mechanisms. The results showed that the needle chlorophyll content of these two genotypes decreased in winter. Wt needles showed greater decrease in the chlorophyll content and local destruction of chloroplast ultrastructure and contained larger amounts of flavonoids than GM needles, as shown by metabolomics analysis. We subsequently identified key differentially expressed genes in the flavonoid biosynthesis pathway and observed significantly upregulated flavonol synthase expression in Wt needles compared with GM needles that significantly increased the anthoxanthin (flavones and flavonols) content, which is likely a key factor underlying the difference in needle color between these two genotypes. Therefore, flavonoid metabolism may play important roles in the cold resistance and needle discoloration of C. fortunei, and our results provide an excellent foundation for the molecular mechanism of C. fortunei in response to cold stress.

Blackening Mechanism and Mechanical Properties Variation of Zirconia Ceramic Induced by Active Metal Brazing

Blackening of zirconia (ZrO2) ceramics often occurs in active metal brazing, however, its discoloration mechanism and induced variation in mechanical properties remain unclear. Herein, ZrO2 ceramic and Ti are successfully brazed by Ag–Cu–Pd filler in vacuum along with the blackening phenomenon. In the brazed joints, the reaction layers of TiO2 + Ti3(Cu, Pd)O are formed adjacent to ZrO2, indicating that partial oxygen in ZrO2 is taken by active Ti in the liquid filler that dissolved from the Ti substrate. Furthermore, the height of the blackened ZrO2 ceramic near the brazing seam is in line with the amount of Ti content added to the filler, which infers that bulk‐sized black ZrO2 can be efficiently obtained by the interfacial reaction between Ti and ZrO2. Additionally, the black ZrO2 is having abundant Zr3+ defects and more tetragonal phase content than the original ZrO2. The formation of Zr3+ defects results in the blackening of ZrO2, while the phase transformation leads to reduced hardness, improved impact toughness, and enhanced wear resistance of black ZrO2. Thus, this blackening phenomenon of ZrO2 ceramics provides a new way to tune the mechanical properties of ZrO2.

A novel multifunctional Cd (II) coordination polymer based on viologen: photochromic, photocontrolled fluorescence and amines detection

• A novel multifunctional Cd-viologen coordination polymer has been synthesized. • The photochromic mechanism of 1 was investigated experimentally and theoretically. • Compound 1 has the ability to detect amines. • The photo-controlled luminescence properties of 1 has been explored. A novel coordination polymer, named [Cd(HCOO)(pbpy) 0.5 (bdc)(H 2 O)]·3H 2 O ( 1 ), based on a new flexible viologen ligand 1,1′-[1,4-phenylenebis(methylene)]-bis(4,4′-bipyridinium) dichloride ( pbpy·2Cl ), Cd(NO 3 ) 2 ·4H 2 O and terephthalic acid (H 2 bdc) was synthesized. Compound 1 has good photosensitive activity and can also respond to sunlight at room temperature. And using time-dependent density functional theory (TDDFT) to study the discoloration mechanism of compound 1 . Attractively, 1 has the ability to select and detect amines due to the electron-deficient properties of pbpy·2Cl . In addition, photocontrolled luminescence properties of 1 , during the coloration-decoloration process, has been researched.

Discoloration Mechanisms of Natural Rubber and Its Control.

Color is an important indicator for evaluating the quality of natural rubber (NR). Light-colored standard rubbers are widely used in high-grade products and have high economic value. This paper first introduces the history and test standards of the standard light-colored rubber. The origin of color deepening in NR processing, color substances, and its biosynthetic pathway are reviewed. Then, the discoloration mechanism of NR is studied from the perspectives of enzymatic browning (caused by polyphenol oxidase and polyphenols) and non-enzymatic browning (including Maillard reaction and lipid oxidation). Finally, the strategies to control the discoloration of NR will be described.

Development of Oxygen Radical Sensor for Atmospheric Non-Equilibrium Microwave Discharge Plasma Jet

Presently, an atmospheric-pressure non-equilibrium microwave discharge plasma jet is expected to be applicable in the sterilization and disinfection equipment for dental implants. However, since the atmospheric-pressure plasma is in non-equilibrium state, there have been no simplified means established to measure basic properties of the plasma. We successfully developed a radical sensor, a simplified tool for detecting oxygen radicals released from plasma by using polyester fiber as base material, and methylene blue as dye. When this sensor detects an oxygen radical, the color of the radical sensor changes from blue, the original color, to white. In this report, we are going to explain the results of the experiments in the fabrication process to verify the behavior of this radical sensor. We combined polyester fiber, the base material of the radical sensor, and methylene blue, the dye, to prototype the radical sensor and used it in our experiments. The radical sensor features the mechanism in which the color changes from blue to white when plasma-irradiated. We used the angle meter to measure the hydrophilicity level and verified the etching effects of the oxygen radicals on the base material in order to clarify this discoloration mechanism. From this result, we found out that the hydrophilicity varied greatly as the flow rate of the oxygen gas used as plasma gas changed and that the color-changing mechanism was due to the adsorption effect of the oxygen radicals. We also used X-ray photoelectron spectroscopy (XPS) to analyze the components to further understand the adsorption effect of the oxygen radicals and clarified that the oxygen radicals accounted for the color-changing mechanism of the radical sensor.

Gemological Characteristics and Discoloration Mechanism of Color-Chang Pyrope-Spessartine Garnet

Gemological Characteristics and Discoloration Mechanism of Color-Chang Pyrope-Spessartine Garnet

Proteomic Changes in Sarcoplasmic and Myofibrillar Proteins Associated with Color Stability of Ovine Muscle during Post-Mortem Storage.

The objective of this study was to investigate the proteomic characteristics for the sarcoplasmic and myofibrillar proteomes of M. longissimus lumborum (LL) and M. psoasmajor (PM) from Small-tailed Han Sheep. During post-mortem storage periods (1, 3, and 5 days), proteome analysis was applied to elucidate sarcoplasmic and myofibrillar protein changes in skeletal muscles with different color stability. Proteomic results revealed that the identified differentially abundant proteins were glycolytic enzymes, energy metabolism enzymes, chaperone proteins, and structural proteins. Through Pearson’s correlation analysis, a few of those identified proteins (Pyruvate kinase, Adenylate kinase isoenzyme 1, Creatine kinase M-type, and Carbonic anhydrase 3) were closely correlated to representative meat color parameters. Besides, bioinformatics analysis of differentially abundant proteins revealed that the proteins mainly participated in glycolysis and energy metabolism pathways. Some of these proteins may have the potential probability to be predictors of meat discoloration during post-mortem storage. Within the insight of proteomics, these results accumulated some basic theoretical understanding of the molecular mechanisms of meat discoloration.

The effects of cellulose nanofibers compounded in water-based undercoat paint on the discoloration and deterioration of painted wood products

Cellulose nanofibers (CNFs) have many potentials as filler to improve the properties of the other materials. We have developed the novel paints containing CNFs, and which controlled the discoloration of wood products. To clarify the discoloration mechanism of wood panels using an undercoat paint containing CNFs, prepared by an integrated process from Cryptomeria japonica, the composites and films made of CNFs and acryl resin that was a raw material for the paints were prepared. Observation of the surface of the CNFs/acryl resin composite film by atomic force microscopy showed that the fibers and the resin were uniformly mixed. The composite film prevented light transmittance in the ultraviolet (UV) light region, as well as oxygen gas permeation. The permeability coefficient of the oxygen gas decreased to 60% with the addition of 1.5 wt% of CNFs to the acryl resin. The addition of CNFs also increased the breaking stress by approximately 1.5 times compared with the acryl resin film. Electron spin resonance (ESR) analysis after UV irradiation resulted in the lowest radical formation of a piece of wood wrapped in the CNFs/acryl resin composite compared with the acryl-coated specimen and the wood as it was. Therefore, the CNFs composite film shielded the UV rays and oxygen more effectively than the original acryl resin, making it difficult for these factors to reach the wood’s surface, and thus, perhaps suppressing the generation of radicals from the wood. These actions would suppress the production of coloring substances caused by the radicals, resulting in the suppression of discoloration. Furthermore, the increase in the film’s strength by the addition of CNFs would have enhanced the stability of overall the paints with a CNF-containing undercoat. These effects might have contributed not only to the prevention of discoloration but also to the prevention of the occurrence of minute cracks caused by various weather deterioration factors.

Discoloration and Degradation of Bamboo under Ultraviolet Radiation

Light is one of the most adverse factors for bamboo deterioration and causes surface degradation and discoloration. The study was carried out to initiate efficient and effective photodiscoloration to modify and enrich bamboo colors that may be applied to bamboo dyeing. Different types of bamboo samples commonly used in the industry were studied experimentally under two types of ultraviolet (UV) light. Effects of light sources, radiation time, and distances on discoloration and discoloration mechanism were systematically studied. For both UV 313 and high-pressure mercury light, the bamboo surface turned red-yellow, and color parameters including Δ E , Δ a , Δ b , and C rapidly increased first and then stabilized for long time, while Δ L showed a similar trend, except for the final decrease. Compared with UV 313, high-pressure mercury lamp light was highly efficient and took less time to induce discoloration. Heat treatments darkened the bamboo color and slowed down photodiscoloration, and the higher temperature led to more photostability. The color change of bamboo scrimber under UV radiation was less and slower than that of untreated bamboo due to high density and heat treatment, and the dark carbonized scrimber changed less than that of the light carbonized scrimber. Relatively high contents of isovanillin, syringaldehyde, β-hydroxypropiovanillone, p-hydroxybenzaldehyde, and syringic acid were identified by GC-MS, and syringaldehyde, 2,6-dimethylbenzoquinone, and 3-hydroxy-4-methoxybenzoic acid were identified by HPLC-MS from a bamboo discoloration layer after high-pressure mercury lamp radiation. These products all contained a conjugated double bond and were conjectured to be degraded from lignin or aromatic extracts. Particularly, 2,6-dimethylbenzoquinone which contained a cyclohexenedione structure without benzene rings, was more chemically stable than other conjugated double bonds with benzene rings, and was supposed to be the final product (chromogenic group) during bamboo photodegradation. Untreated or light-colored bamboo under high-energy UV light initiated highly efficient and effective photodiscoloration, and UV light is recommended for being applied to industrial bamboo dyeing. Compared with traditional chemical dyeing, the photoinduced dyeing method has no chemical addition and is easy to operate and environmental-friendly.

Identification of microRNAs and their target genes related to needle discoloration of evergreen tree Chinese cedar (Cryptomeria fortunei) in cold winters.

Comparative analysis of miRNAs and their gene targets between the evergreen and yellowish-brown Cryptomeria fortunei phenotypes in cold winters suggests a possible role of miRNA-regulated pathways in needle color. Cryptomeria fortunei (Chinese cedar) is a conifer tree of considerable economic, ornamental and ecological importance. Despite the evergreen nature of C. fortunei, most needles turn yellowish- or reddish-brown in winter. The roles of microRNAs (miRNAs) in regulating pigment biosynthesis in color-leafed plants have been widely investigated. However, whether or not an miRNA-mediated staged discoloration mechanism exists in evergreen C. fortunei is currently unknown. In this study, we deciphered the microRNAs landscape in overwintering C. fortunei needles using high-throughput sequencing. A total of 517 known and 212 novel miRNA mature/star sequences, including 233 differentially expressed miRNAs, were identified. Based on integrated transcriptome and miRNA analysis, 2702 target unigenes of the miRNAs were predicted and these targets were significantly enriched in pigment-related biosynthesis pathways. A miRNA-target pigment biosynthesis regulatory network was then constructed, and its module miRNA (ath-miR858b, aly-miR858-3p, cme-miR828 and novel33_mature)-MYBs (v-myb avian myeloblastosis viral oncogene homolog) appeared to be a key factor regulating needle discoloration in C. fortunei. These miRNA-MYBs were further confirmed by degradome sequencing. Overall, these findings provide new insight into the posttranscriptional regulatory mechanism of leaf/needle discoloration in gymnosperms and may contribute to the miRNA-mediated genetic improvement of evergreen C. fortunei needles.

Theoretical investigation of fluorescence changes caused by methanol bridge based on ESIPT reaction* *Project supported by the National Basic Research Program of China (Grant No. 2019YFA0307701), the National Natural Science Foundation of China (Grant No. 11874180), the Young and Middle-aged Scientific and Technological Innovation Leaders and Team Projects in Jilin Province (Grant No. 20200301020RQ).

The different fluorescence behavior caused by the excited state proton transfer in 3-hydroxy-4-pyridylisoquinoline (2a) compound has been theoretically investigated. Our calculation results illustrate that the 2a monomer in tetrahydrofuran solvent would not occur proton transfer spontaneously, while the 2a complex in methanol (MeOH) solvent can undergo an asynchronous excited state intramolecular proton transfer (ESIPT) process. The result was confirmed by analyzing the related structural parameters, infrared vibration spectrum and reduced density gradient isosurfaces. Moreover, the potential curves revealed that with the bridging of single MeOH molecular the energy barrier of ESIPT was modulated effectively. It was distinctly reduced to 4.80 kcal/mol in 2a-MeOH complex from 25.01 kcal/mol in 2a monomer. Accordingly, the ESIPT process induced a fluorochromic phenomenon with the assistant of proton-bridge. The elucidation of the mechanism of solvent discoloration will contribute to the design and synthesis of fluorogenic dyes as environment-sensitive probes.

Electrospun cationic nanofiber membranes for adsorption and determination of Cr(vi) in aqueous solution: adsorption characteristics and discoloration mechanisms.

In this study, a novel cationic nanofiber membrane with various functional groups, good structural stability, and high adsorption capacity of Cr(vi) is presented. This nanofiber membrane is prepared by electrospinning a mixed aqueous solution of a cationic polycondensate (CP) and polyvinyl alcohol (PVA). With the aid of PVA, CP can be smoothly electrospun without using any organic solvents, and the cross-linking between CP and PVA improves the stability of membrane in acidic solution. Chemical and morphology characterization reveals that the CP/PVA membrane is composed of interwoven nanofibers that contain numerous cationic groups. Due to its high cationicity and hydrophilicity, the CP/PVA membrane shows great affinity for HCr2O7− and Cr2O72−. Adsorption experiments indicate that the CP/PVA membrane can remove Cr(vi) from simulated wastewater rapidly and efficiently in both batch and continuous mode. Besides, the presence of most coexisting ions will not interfere with the adsorption. Due to the redox reaction between the CP/PVA membrane and adsorbed Cr(vi), the CP/PVA membrane exhibits distinct color change after Cr(vi) adsorption and the discoloration is highly dependent on the adsorption amount. Therefore, in addition to serving as a highly efficient adsorbent, the CP/PVA membrane is also expected to be a convenient and low-cost method for semi-quantitative determination of Cr(vi) in wastewater.

Studies on the photofading of alizarin, the main component of madder

Natural dyes have been the focus of textile industry for their environmental protection properties. However, some limitations such as poor photostability has limited their wide application, and the researches of the discoloration mechanism of fabric with natural dye are relatively limited. As one of the most important natural dye, madder has been widely used in textile field. Herein, as the main pigment of madder, alizarin was selected as the model natural dye to explore the photo-fading progress of alizarin-dyed fabrics. The photodegradation progress of alizarin was explored by UV, HPLC, HPLC-MS and Datacolor (computer color matching system). When exposed to light, alizarin could be oxidized into colorless small molecules through ·OH radical-mediated route, and finally resulting in the fading of alizarin. In addition, the influence of pre-mordant and the liquid rate has also been studied. These results provide us a good insight into the photo-fading progress of natural dyes, and our work could help to open the way to further studies aiming at improving the photostability of natural dyes or developing new photo-stable dyes.

Adsorption mechanisms of pigments and free fatty acids in the discoloration of shea butter and palm oil by an acid-activated Cameroonian smectite

Discoloration mechanism of shea butter and palm oil was studied by the adsorption of pigments and free fatty acids onto a Cameroonian clay. Adsorbent characterization was performed using ICP-AES, FTIR, SEM, N2 gas adsorption and CEC. The adsorbent is a microporous swelling clay of smectite type. Discoloration depends on temperature and the equilibrium time decreases with increase in temperature. Among pseudo-first, pseudo-second order and intra-particle diffusion kinetics models studies, pseudo-second order was the best applicable to describe pigments and free fatty acids adsorption, suggesting that discoloration of the two oils occurs in two steps: the transfer of pigments and free fatty acids from the oil to the clay surface, followed by the interaction between adsorbates and the surface. The lower values of activation energies and validation of the Temkin isotherm model indicate a physisorption process influenced by mass transfer. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Temkin isotherms models. Amongst them, Freundlich was the best model to describe adsorption in both cases, indicating the existence of heterogeneous adsorption sites on clay surface. The most appropriate model for pigments adsorption was Freundlich while Temkin model was the most appropriate for the adsorption of free fatty acids suggesting that pigments and free fatty acids are not adsorbed on the same type of sites.