Nickel Oxide Nanopowder (NiO NP) Bookmark

(nickel oxide nanopowder)

**What:** Nickel oxide nanopowder consists of extremely fine particles of nickel(II) oxide (NiO), typically ranging from 1 to 100 nanometers (nm) in size. This nanoscale dimension dramatically alters its properties compared to bulk nickel oxide.

**Key Properties:**
* **High Surface Area:** Massive surface area per unit mass, crucial for catalytic and sensing applications.
* **Semiconductor Behavior:** Exhibits p-type semiconducting properties with a wide band gap (~3.6-4.0 eV).
* **Catalytic Activity:** Highly effective catalyst for various chemical reactions, including fuel cell electrodes and pollutant decomposition.
* **Electrochromic:** Changes color reversibly upon electrochemical oxidation/reduction (used in smart windows).
* **Magnetic:** Exhibits antiferromagnetic or weak ferromagnetic behavior depending on particle size and structure.
* **Gas Sensing:** Sensitive to various gases (like CO, NO2, H2) due to surface reactions altering conductivity.
* **Thermal Stability:** Generally stable at high temperatures.

**Synthesis Methods:**
* Chemical Precipitation
* Sol-Gel Processing
* Hydrothermal/Solvothermal Synthesis
* Thermal Decomposition
* Spray Pyrolysis
* Electrochemical Methods

**Primary Applications:**
1. **Electrodes:** Cathode material in Ni-based batteries (Ni-Cd, Ni-MH), supercapacitors.
2. **Catalysts:** Oxidation catalysis, steam reforming, photocatalysis for environmental cleanup.
3. **Gas Sensors:** Detection of toxic and combustible gases.
4. **Electrochromic Devices:** Smart windows, displays.
5. **Magnetic Materials:** Components in data storage, ferrofluids.
6. **Ceramic Pigments:** Colorants (often black/grey).
7. **Electronic Devices:** Potential in transistors, varistors.
8. **Antimicrobial Coatings:** Limited but researched use.

**Safety & Handling:**
* **Toxicity:** Nickel oxide nanoparticles are considered hazardous. Inhalation is the primary exposure risk. Classified as carcinogenic (Category 1B) and mutagenic (Category 2) under EU CLP. Handle with extreme caution.
* **PPE:** Essential to use appropriate personal protective equipment (PPE): NIOSH-approved respirator (N95 minimum, often higher required), nitrile gloves, lab coat, safety goggles.

(nickel oxide nanopowder)

* **Environment:** Work within a certified fume hood or glove box. Avoid generating dust. Store sealed in clearly labeled, appropriate containers. Follow strict disposal regulations for hazardous nanomaterials.
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Tungsten oxide, specifically WO3, possesses fascinating properties when interacting with hydrogen gas. This interaction underpins its significant role in hydrogen detection and sensing technologies. Tungsten oxide is a semiconductor material. When exposed to hydrogen gas at elevated temperatures, typically above 150°C, a remarkable change occurs. Hydrogen molecules dissociate on the oxide surface. The resulting hydrogen atoms inject electrons into the conduction band of the tungsten oxide. This process effectively reduces the oxide, forming tungsten bronze compounds like HxWO3. The most visually striking consequence is a dramatic color change. Pristine tungsten oxide is often pale yellow or transparent, but upon hydrogen exposure, it turns deep blue. This electrochromic effect provides a simple, visual indicator for hydrogen presence. Beyond color change, the electron donation significantly alters the material’s electrical resistance. Tungsten oxide exhibits a substantial decrease in electrical resistance upon hydrogen exposure. This measurable change forms the basis for highly sensitive chemiresistive hydrogen gas sensors. These sensors are crucial for safety in hydrogen fuel applications, leak detection in industrial settings, and various research environments. The sensitivity and selectivity of WO3-based sensors can be further enhanced through nanostructuring, doping with catalysts like platinum or palladium, or forming composites. While primarily valued for sensing, tungsten oxide’s interaction with hydrogen is also relevant in catalysis, particularly in hydrogenation reactions, and in advanced electrochromic devices for smart windows. Its ability to reliably and reversibly respond to hydrogen makes tungsten oxide a key functional material in the expanding hydrogen economy.

(tungsten oxide hydrogen)

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Tungsten Oxide Blue: The Chameleon Material

(tungsten oxide blue)

Not all tungsten oxide is yellow. Introduce tungsten oxide blue, scientifically WO₃-x, where ‘x’ signifies oxygen vacancies. This slight deviation from the stoichiometric WO₃ formula unlocks fascinating properties, most visibly its characteristic blue or deep violet color.

The blue hue arises directly from its unique structure. Missing oxygen atoms create oxygen vacancies. These vacancies trap electrons within the material’s crystal lattice. When light hits WO₃-x, these trapped electrons readily absorb specific wavelengths in the yellow and red parts of the visible spectrum. This absorption leaves the complementary blue/violet light to be reflected or transmitted, giving the material its striking appearance.

Beyond its color, tungsten oxide blue is an electrochromic powerhouse. Electrochromism allows a material to reversibly change its color or opacity when a small electrical voltage is applied. Applying a voltage injects ions (like H⁺ or Li⁺) and electrons into the WO₃-x structure. This injection changes its optical properties, typically causing it to switch from its colored state to a transparent or bleached state. Reversing the voltage reverses the process.

(tungsten oxide blue)

This reversible color change makes tungsten oxide blue incredibly valuable for smart window applications. Smart windows using WO₃ can dynamically control the amount of light and heat entering a building, enhancing energy efficiency and occupant comfort. Its electrochromic nature also lends itself to applications in energy storage, particularly in lithium-ion batteries, where it can function as an electrode material benefiting from its ability to intercalate ions. It’s a material where color science meets practical energy solutions.
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Sodium Tungsten Oxide: The Versatile Tunable Material

(sodium tungsten oxide)

Sodium tungsten oxide, often denoted NaWO₃, is an intriguing inorganic compound belonging to the family of tungsten bronzes. These materials exhibit a characteristic metallic luster and electrical conductivity, distinguishing them from typical metal oxides. Its structure is based on the perovskite framework, where sodium atoms occupy cavities within a lattice primarily formed by corner-sharing WO₆ octahedra.

A key feature of sodium tungsten oxide is its non-stoichiometric nature. The sodium content (x in NaₓWO₃) is variable, allowing precise tuning of its electronic and optical properties. This tunability makes it exceptionally valuable for research and applications. As the sodium concentration increases, the material undergoes a dramatic transition from a transparent insulator to a reflective metal, accompanied by a striking color change – often deep blue to golden yellow.

This electrochromic behavior is perhaps its most famous attribute. Sodium tungsten oxide can reversibly change its optical properties, especially its coloration, in response to an applied electrical voltage. This makes it a prime candidate for smart windows that dynamically control light and heat transmission in buildings, enhancing energy efficiency. Thin films of NaₓWO₃ are central to this technology.

(sodium tungsten oxide)

Beyond smart windows, sodium tungsten oxide shows promise in thermoelectric applications for converting heat directly into electricity, and as a catalyst or catalyst support. Its ability to intercalate ions also sparks interest for battery research. Ongoing studies explore its potential in gas sensing, photovoltaics, and advanced electronic devices. Its unique blend of tunable electronic structure, optical properties, and stability continues to drive innovation across materials science and engineering fields.
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Ammonium tungsten oxide generally refers to ammonium paratungstate (APT), a key compound in tungsten chemistry and industry. Its chemical formula is often represented as (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O or (NH₄)₁₀W₁₂O₄₁·5H₂O, signifying its complex polyatomic structure. APT appears as white or slightly yellow crystalline solids, typically in fine powder form.

(ammonium tungsten oxide)

Its primary significance lies as an essential intermediate in tungsten metal and tungsten carbide production. The compound is industrially produced by digesting tungsten ore concentrates (like wolframite or scheelite) in alkaline solutions, followed by precipitation using ammonium salts. This purification step effectively isolates tungsten from impurities.

A critical property of APT is its behavior upon heating. When calcined under controlled conditions, it undergoes thermal decomposition. This process involves losing ammonia and water molecules, ultimately transforming into tungsten trioxide (WO₃), a crucial precursor for tungsten powder reduction. The purity and particle size of the resulting WO₃, and thus the final tungsten powder, are heavily influenced by the starting APT characteristics.

(ammonium tungsten oxide)

Beyond metal production, APT finds use as a catalyst precursor in various chemical reactions, particularly in petroleum refining and oxidation processes. Its decomposition products or derived tungsten compounds exhibit catalytic activity. Research also explores modified ammonium tungsten oxides (like ammonium tungsten bronzes) for applications in electrochromic devices, where their ability to change color with applied voltage is exploited for smart windows and displays. Handling requires care as APT can decompose to release ammonia gas under certain conditions. Its stability and solubility properties make it a fundamental material in the tungsten value chain.
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Tungsten trioxide, WO3, is a versatile inorganic compound. It appears as a yellow crystalline solid or powder. Key properties include semiconductor behavior and electrochromism, meaning it changes color reversibly under electrical charge. This makes it essential for smart windows that dynamically control light and heat. WO3 is also highly insoluble and stable under many conditions. Its photocatalytic activity is valuable for environmental applications like breaking down pollutants. WO3 effectively senses gases like nitrogen dioxide and ammonia, changing electrical resistance upon exposure, crucial for air quality monitors. Research explores WO3 in batteries, particularly cathodes for lithium-ion systems, and in photoelectrochemical cells for solar water splitting to produce hydrogen fuel. Nanostructured WO3 enhances surface area, boosting performance in sensing and catalysis. Future potential lies in optimizing nanostructures and composites for energy storage, conversion, and advanced electrochromic devices. Tungsten trioxide remains a key material for smart technologies and sustainable solutions.

(tungsten 6 oxide)

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Lithium tungsten oxide, often denoted as LixWO3 or LiyWO3+z, represents a class of materials within the tungsten bronze family. Its significance stems primarily from its electrochemical properties, making it relevant for energy storage research, particularly lithium-ion batteries. The structure is typically a distorted perovskite framework derived from WO3, where lithium ions can intercalate into the tunnels and cavities.

(lithium tungsten oxide)

The material exhibits interesting characteristics. It can achieve reasonably high theoretical specific capacities, potentially exceeding 200 mAh/g depending on the specific composition and structure. Lithium insertion/extraction occurs at relatively low voltages, often below 1.5 V vs. Li/Li+, which can be advantageous for certain cell configurations. This low voltage operation is linked to the reduction/oxidation of tungsten ions (W⁶⁺ ↔ W⁵⁺) during cycling.

However, lithium tungsten oxide faces significant challenges hindering widespread commercial battery use. A major issue is its electronic conductivity, which is generally poor in the pristine state. While lithium insertion improves conductivity, it often remains insufficient for high-rate applications without conductive additives or nanostructuring. Lithium-ion diffusion within the crystal lattice can also be slow, limiting power density. Furthermore, structural changes during deep lithium insertion can lead to capacity fading over cycles.

(lithium tungsten oxide)

Synthesis typically involves solid-state reactions, heating mixtures of lithium and tungsten precursors (like carbonates or oxides) at high temperatures (700-1000°C). Precise control over stoichiometry and crystal structure is crucial for optimizing performance. Despite the challenges, research continues due to its unique properties. It serves as a model system for studying intercalation chemistry and finds niche applications in electrochromic devices due to its color changes upon lithium insertion. Its stability compared to some other anode materials also attracts interest for specialized battery designs.
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Tungsten trioxide WO3 is a critical inorganic compound with unique properties driving diverse applications. It typically appears as a yellow crystalline solid or powder. WO3 is a wide bandgap semiconductor around 2.6-2.8 eV. Its electrical conductivity changes significantly with temperature and gas exposure making it a key material in chemiresistive gas sensors for detecting pollutants like NOx NH3 H2S and O3. Synthesis methods include calcining ammonium paratungstate or direct oxidation of tungsten metal. WO3 exhibits fascinating chromic properties. It is electrochromic meaning its optical transmission and color change reversibly upon charge insertion extraction under an applied voltage. This powers smart windows for energy saving. It also shows photochromism darkening under UV light. Photocatalysis is another major area. WO3 acts as a photocatalyst under visible light for applications like water splitting to produce hydrogen and degrading organic pollutants in water treatment. Its bandgap allows it to absorb a portion of the visible spectrum. Nanostructured WO3 like nanowires nanorods and nanoflowers enhances surface area improving performance in sensing electrochromic devices and photocatalysis. Thin films are crucial for electrochromic windows and displays. WO3 is also used in fireproofing fabrics as a pigment in ceramics and paints and historically in x-ray screens phosphors. Its stability non toxicity and tunable properties through doping or nanostructuring ensure its continued importance in advanced materials science for energy environmental and electronic technologies.

(wo3 tungsten)

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Tungsten oxide, chemical formula WO3, is a versatile inorganic compound. Commonly appearing as a yellow powder or crystalline solid, it’s an n-type semiconductor with a bandgap around 2.6-2.8 eV. Its properties make it crucial in several advanced technologies. A primary application is in electrochromic devices. WO3 thin films change color reversibly from transparent to deep blue upon lithium ion insertion and extraction. This principle is used in smart windows that dynamically control light and heat transmission in buildings, enhancing energy efficiency. WO3 is also a key material in gas sensors. Its electrical conductivity changes significantly upon exposure to specific gases like nitrogen oxides (NOx), ammonia (NH3), or hydrogen sulfide (H2S). This sensitivity allows for the detection of pollutants and hazardous gases in environmental monitoring and industrial safety. Furthermore, WO3 exhibits photocatalytic activity under visible light irradiation. It can degrade organic pollutants in water and air, contributing to environmental remediation efforts. Research also explores its potential in photocatalytic water splitting for hydrogen fuel production. The material is stable, relatively non-toxic, and can be synthesized in various nanostructured forms (nanoparticles, nanowires, nanorods) to enhance its surface area and reactivity. These nanostructures improve performance in sensing and catalysis. Tungsten oxide is also investigated for use in batteries, particularly as a cathode material in lithium-ion systems, and in solar cells. Ongoing research focuses on optimizing its nanostructure, doping it with other elements to modify its bandgap and electronic properties, and developing efficient composite materials to further boost its performance across all application areas, solidifying its role in sustainable technologies.

(tungsten oxide wo3)

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Tungsten carbide oxidation presents a significant challenge limiting its high-temperature applications. This hard, wear-resistant material excels in cutting tools, dies, and wear parts, but exposure to oxygen at elevated temperatures triggers degradation.

(tungsten carbide oxidation)

The oxidation process begins noticeably around 400-500°C. Atmospheric oxygen reacts chemically with the tungsten carbide grains. The primary reaction is WC + 5/2 O2 → WO3 + CO2. This forms tungsten trioxide (WO3), a voluminous, brittle oxide, and carbon dioxide gas.

This reaction has detrimental consequences. The formation of WO3 creates significant internal stresses due to its larger molar volume compared to WC. This leads to cracking and spallation of the oxide layer. Crucially, the escaping CO2 gas creates pores and voids within the material structure. This combination of oxide formation and gas evolution causes severe material loss, surface pitting, and a catastrophic disintegration phenomenon known as “pest oxidation” at certain temperatures, destroying structural integrity.

Oxidation significantly accelerates tool wear mechanisms like flank wear and crater wear in machining applications. It reduces hardness and strength, leading to premature failure. The rate increases dramatically with rising temperature.

(tungsten carbide oxidation)

Mitigation strategies are essential. Applying protective coatings (like Al2O3, TiAlN, TiCN) creates a barrier against oxygen diffusion. Alloying with elements forming stable oxides (e.g., chromium) can improve inherent oxidation resistance. Careful control of the cobalt binder phase chemistry and microstructure also plays a role. Limiting operating temperatures below the critical oxidation threshold remains the simplest, though often impractical, defense. Understanding and managing tungsten carbide oxidation is vital for extending component life in demanding environments.
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