Boron oxide structure. It is also called boric oxide or boria.

The results show that the composite material has Aug 1, 2017 · B2O3/SiO2 substitution in 55S4. The material was first reported in 1940, [1] with a modified synthetic procedure published in 1955, [2] however, the material's structure had remained unknown for nearly a century. A quantum molecular dynamics procedure was used to Nov 1, 2019 · Request PDF | Effects of boron oxide composition, structure, and morphology on B4C formation via the SHS process in the B2O3–Mg – C ternary system | This study investigates the formation of Skin that becomes contaminated with boron oxide should be promptly washed or showered with soap or mild detergent and water to remove any boron oxide. Yuanzheng Yue, Jincheng Du, in Encyclopedia of Materials: Technical Ceramics and Glasses, 2021. 1021/JP972157S Corpus ID: 96077853; Boron Oxide Oligomer Collision-Induced Dissociation: Thermochemistry, Structure, and Implications for Boron Combustion May 1, 2024 · Boron doping can improve oxidation resistance due to the crack-healing effects of boron oxide. Here, by optimizing the doping content and annealing temperature, we obtained boron-doped LLO materials Li1. Among them, B 4 C is the superior one for its chemical and physical properties such as hardness, electrical and thermal conductivity, and heat capacity, all of which depend extremely on its structure [[1], [2], [3], [4]]. The positive effect of Structure models for boron oxide glass and molten boron oxide are reviewed. By means of the small-angle X-ray scattering (SAXS) technique, studies were made of vitreous B2O3 and binary alkali borate glasses containing lithium, sodium, potassium, rubidium and cesium oxides in … Aug 29, 2017 · An extraordinary variety of polyhedral boron–hydrogen clusters is now known; one example is the B 12 H 12 2− ion, which has a polyhedral structure similar to the icosahedral B 12 unit of elemental boron, with a single hydrogen atom bonded to each boron atom. Indeed, in recent years there have been serious chal­ lenges to previous structure concepts for both crystalline and glassy borates. }, author={Minh Tho Nguyen and Myrna H. Borosilicate glass is an important glass type produced widely on the industrial scale and finds many technological applications from lab and kitchen ware, lighting and optics, display, to nuclear waste disposal and biomedicine. Typical effects of long-term boron deficiency are stunted, misshapen growth; vegetable ‘brown heart’ and sugar beet ‘dry rot’ are among the disorders due to boron deficiency. 5 or less, the Na+1 ions are attracted primarily by the borate network; therefore, the ternary glasses can be viewed as A new study of the structure of vitreous boron oxide has been made under greatly improved conditions. nocx. 05. The boron-oxide-added bSAO and pSAO without boron oxide also exhibited no obvious diffraction peaks shift (Figs. Aug 1, 2018 · Raman spectra of boron trioxide at the same pressure (upper); the boron oxide is the α-B 2 O 3 phase (hexagonal structure) under 2. J. 6b03056 Corpus ID: 206421397; The Effect of Boron Doping on Structure and Electrochemical Performance of Lithium-Rich Layered Oxide Materials. 2020. 4) - (6. It is never found as the free element (Cotton et al. It is not surprising therefore that boron nitride and carbon exhibit similarity in their crystal structure. 7) and Crystalline boron formed a protective coating of boron oxide between 600 and 1100°C, and after 24 hours in this temperature range 16–19% of the boron was oxidized to B 2 O 3. 4 C (8. Mater. 5-15 mol%) ordered mesoporous bioactive glasses Apr 1, 2009 · Due to the intrinsic electron-deficiency of boron and the large difference of electronegativity between boron and oxygen, boron oxide clusters exhibit exotic bonding characteristics and novel Aug 12, 2022 · The article surveys the most recent achievements starting with the boron doping mechanism, mainly focused on doping in semiconductor materials such as Si, Ge, graphene, carbon nanotube, or other 2D materials. @article{Liu2016TheEO, title={The Effect of Boron Doping on Structure and Electrochemical Performance of Lithium-Rich Layered Oxide Materials. At higher temperatures, boron reacts with all nonmetals, except tellurium and the noble gases, and with nearly all metals; it oxidizes to B 2 O 3 when heated with concentrated Name: boron oxide (B2O3) Formula: B 2 O 3: Molar Mass: 69. Its valence electron shell is 2s 2 2p 1, so it has three valence electrons. Dixon}, journal Boron oxide, B 2 O 3, like SiO 2 has the ability to dissolve metallic oxides to form borates and glasses which are difficult to crystallize. . • Thermal conductivity reaches as high as 3. Jul 20, 2016 · Polyanion doping shows great potential to improve electrochemical performance of Li-rich layered oxide (LLO) materials. 3,4 on oxide B2O3 and boron suboxide B6O are well known and cribed in the literature. 3). B2O3 doped (0. 2Mn0. These doped Boron trioxide or diboron trioxide is the oxide of boron with the formula B 2 O 3. Oct 10, 2019 · Herein, a novel approach to resolve this challenge by inserting boron nitride nanosheets (BNNSs) into the ZnO-based device structure is reported. The hybrid structure with double switching layer device can combine memristive functions—nonvolatile bipolar memory, multilevel switching, and neuromorphic functionalities—simulating biological Feb 24, 2022 · Here, we demonstrate a borophene oxide analogue as a fully inorganic liquid with a layered structure and extraordinary thermal stability, suggesting that it is a candidate for use in optical Nov 23, 2019 · Boron nitride is one of the leading materials used to obtain refractory composites (along with SiC, Si 3 N 4, AlN, B 4 C). In an attempt to answer these questions various properties of boron oxide will be compared with Jun 21, 2007 · To rationally design and explore a potential energy source based on the highly exothermic oxidation of boron, density functional theory (DFT) was used to characterize small boron clusters with 0−3 oxygen atoms and a total of up to ten atoms. 016 Corpus ID: 225859148; Synergistic effect of graphene oxide and boron-nitrogen structure on flame retardancy of natural rubber/IFR composites Dec 1, 2022 · Boron oxide containing bioactive glasses were found to remain the bioactivity of the base silicate based bioactive glasses and with additional enhanced antibacterial properties [55]. As the temperature increases, the α-B 2 O 3 changes into an amorphous phase (900 °C, 1050 °C, 1200 °C, 1350 °C). As boron and oxygen are elements of the p block of the periodic table, and even more heads of their respective groups, the electronegativity difference between them is not very high; therefore, B2O3 is expected to be covalent in nature. Nov 1, 2001 · The result concerning the structure of vitreous boron oxide is a convincing corroboration of the boroxol ring model. Jun 18, 2024 · Visit ChemicalBook To find more Boron oxide(1303-86-2) information like chemical properties,Structure,melting point,boiling point,density,molecular formula,molecular weight, physical properties,toxicity information,customs codes. @article{Nguyen2009ThermochemistryAE, title={Thermochemistry and electronic structure of small boron and boron oxide clusters and their anions. At last,Boron oxide(1303-86-2) safety, risk, hazard and MSDS, CAS Boron oxide may refer to one of several oxides of boron: Boron trioxide (B 2 O 3, diboron trioxide), the most common form; Boron monoxide (BO) Boron suboxide (B 6 O) Boron oxide & boric acid combined: 20% is used in textile glass fibers; 19% as a flux in enamels, frits, & glazes; 9% in glasses; 1% as a herbicide; 51% in misc applications, including use as a catalyst in oxidation of hydrocarbons, as a conditioning agent, & in manufacture of other boron compounds (1969) Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure. It is also called boric oxide or boria. The mechanical and dielectric properties of pyrolytic, hot-pressed (hexagonal and turbostratic modification) and reactive sintered boron nitride are presented. Note the primitive cell may appear less symmetric than the conventional cell representation (see "Structure Type" selector below the 3d structure) Feb 12, 2001 · Boron and nitrogen are neighbours of carbon in the periodic table - in combination boron and nitrogen have the same number of outer shell electrons - the atomic radii of boron and nitrogen are similar to that of carbon. Jun 28, 2024 · Boron, chemical element that is a semimetal essential to plant growth and of wide industrial application. Oct 7, 2017 · Despite numerous studies conducted on the properties and structure of B 2 O 3. The increased presence of boron suboxide may not find enough time to diffuse through the surface coat and react with the carbon core. Therefore, the presence of boron oxide species on the surface increases. Sep 1, 2022 · Request PDF | Effects of boron oxide on the structure, properties and bioactivities of bioactive glasses: A review | Borate and boron oxide containing bioactive glasses have drawn attention A new study of the structure of vitreous boron oxide has been made under greatly improved conditions. 4). D. The experimental unit cell parameters a = b = 4. 13BxO2 (x = 0. 3 bioactive glasses with 5 mol% of SrO has been synthesized and characterized to understand their structure and bioactivity as a function of composition by combining experimental and computer simulation techniques. Furthermore, the boron oxide overlayer on Ni NPs was selectively The current work presents the smallest boron oxide species with a hexagonal boroxol ring, establishes an analogy between bor on oxides and the 3,5-dehydrophenyl cation, and enriches the chemistry of borons oxide and boronyls. You can also browse global suppliers,vendor,prices,Price,manufacturers of Boron oxide(1303-86-2). Raman spectrometry, X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR) were utilized to characterize the structural changes THE accepted structure of boron nitride, proposed by Hassel1 and Brager2,3, is that of graphite with the carbon atoms replaced by boron and nitrogen atoms, and is designated structure type B. 37 Å Apr 25, 2022 · Boron oxide clusters have structural diversity and unique chemical bonding, and recent literature has shown that boronyl complexes dominate boron-rich oxide clusters. M. The structures, vibrational frequencies, and stabilities were calculated for each of these clusters. Within the near distance range, the model correlation function coincides very well with the experimental distance correlation function (Fig. Employees who handle boron oxide or non-aqueous liquids containing boron oxide should wash their hands thoroughly with soap or mild detergent and water before eating, smoking or using toilet Quantity Value Units Method Reference Comment; Δ f H° gas-284. Boron carbide with a rhombohedral phase comes in a wide variety of compositions ranging from B 10. The first three ionization energies of boron, however, are much too high to allow formation of compounds containing the B3+ ion; thus, in all its compounds boron is covalently bonded. Grant and David A. 617: Additional Names: boracic anhydride: boric acid anhydride: boric anhydride: boric acid (HBO2), anhydride Sep 1, 2022 · DOI: 10. It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. 06) with comprehensively improve … Feb 6, 2017 · B2O3/SiO2 substitution in 55S4. Jan 1, 2018 · A hybrid network structure of boron nitride and graphene oxide is formed. It is also shown that this boron oxide can be reduced A structure of some interest in connection with boron oxide is the structure of cesium enneaborate, Cs20"9 B20316), the borate with the highest molar fraction of boron oxide. SnO 2 forms in the P4 2 /mmm space group crystalizing in the rutile structure. Using Rh Kα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4πsinθ/λ = 20 Å−1, and a rigorous interpretation was obtained in terms of pair functions. Boron oxide clusters offer intriguing molecular models for the electron-deficient system, in which the boronyl (BO) group plays a key role and the interplay between the DOI: 10. Applications General Aspects. The glass coating can be applied by using viscous sintering of glass powders, which is also known as the enameling method, but they can also be formed using other Aug 1, 2007 · Due to the intrinsic electron-deficiency of boron and the large difference of electronegativity between boron and oxygen, boron oxide clusters exhibit exotic bonding characteristics and novel Structure models for boron oxide glass and molten boron oxide are reviewed. May 17, 2024 · The treatment of boron in fracturing backflow fluid is a widely studied issue in oil and gas resource extraction. The layered structure of hexagonal boron nitride, the covalent type of crystalline bond, and the ability not to be wetted by most metals and oxides limit the methods for producing dense ceramics based on it [1,2,3,4,5]. Find boron oxide and related products for scientific research at MilliporeSigma Apr 1, 2022 · These glass compositions are also the archetypes of multicomponent boron-containing oxide glasses. Amorphous boron oxidized at a greater rate than crystalline boron between 600 and 1000°C, and after 24 hours 22–26% of the boron was oxidized to B 2 O 3. In this work, the material of canola straw-derived biochar composite graphene oxide (BC@GO) was produced and used for boron removal. 12 in Dec 18, 1997 · DOI: 10. However, simulations of boron oxide (B 2 O 3)-containing oxide glasses pose a challenge due to the lack of reliable empirical potentials. the structure of boron oxide and simple borates Technical Report · Sat Oct 01 00:00:00 EDT 1960 OSTI ID: 4078358 Jan 1, 2016 · The low-temperature carbothermal nitridaton of boron oxide (B2O3) was induced by the networked carbon structure prepared from a condensed boric acid (H3BO3)-poly(vinyl alcohol) (PVA) product. A counterexample in boronyl chemistry is presented in this work. 3(b). 3 on the Structure and Viscosity of CaO–SiO 2 –B 2 O 3 ‐based Jan 9, 2020 · This work evaluates the impact of boron incorporation into bioactive glasses on their biokinetic, mechanic and structural properties. Boron (B) is a chemical element with an atomic number 5 that belongs in the Period 2 and Group 13 in the periodic table. 7 GPa and 750 °C conditions. Using global structural searches, electronic structure calculations, and chem Mar 17, 2023 · Therefore, it was confirmed that the core-shell structure observed was composed of a metallic Ni(0) core and a boron oxide shell. Jun 1, 2020 · DOI: 10. Apr 15, 2020 · Introduction. 3 bioactive glasses with 5 mol% of SrO has been synthesized and characterized to understand their structure and bioactivity as a function of composition by combining Boron monoxide (BO) is a binary compound of boron and oxygen. The main component of the vitreous B 2 O 3 network, the planar boroxol ring, breaks up when the temperature increases. 2022. 621; CAS Registry Number: 12045-60-2; Information on this page: Vibrational and/or electronic energy levels; References; Notes; Other data available: Gas phase thermochemistry data; Options: Switch to calorie-based units Boron carbide was discovered in the 19th century as a by-product of reactions involving metal borides, but its chemical formula was unknown. It is a low-abundant metalloid that is a poor electrical conductor at room temperature. 00 W m −1 K −1, 10-fold higher than that of pure PEG. To explore the optimal boron doping content in PyC interphase, structure characters and mechanical properties of C 128−x B x (x = 8, 20, 32, 44, 64) were simulated by ab-initio Sep 6, 2021 · The effect of boron doping on structure and electrochemical performance of lithium-rich layered oxide materials. Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. However, under lower temperature, a tiny layer of B2O3 can be The most stable crystalline form is the hexagonal one, also called h-BN, α-BN, g-BN, and graphitic boron nitride. 100118 Corpus ID: 252507908; Effects of boron oxide on the structure, properties and bioactivities of bioactive glasses: A review @article{Lu2022EffectsOB, title={Effects of boron oxide on the structure, properties and bioactivities of bioactive glasses: A review}, author={Xiaona Lu and Jincheng Du}, journal={Journal of Non-Crystalline Solids: X}, year={2022}, url Nov 1, 1995 · Boron Oxide Oligomer Collision-Induced Dissociation: Thermochemistry, Structure, and Implications for Boron Combustion. That is, one of boron’s 2s electrons is promoted to a 2p orbital, giving the outer electron configuration 2s12p2; the Jun 19, 2021 · An extraordinary variety of polyhedral boron–hydrogen clusters is now known; one example is the B 12 H 12 2− ion, which has a polyhedral structure similar to the icosahedral B 12 unit of elemental boron, with a single hydrogen atom bonded to each boron atom. Kriz; Structure of Crystalline Boron Oxide, The Journal of Chemical Physics, Volume 48, Issue 11, 1 June 1968, Pages 5277–5278, http Solubility Equations of Boron Compounds under Coolant Conditions in VVER-Type Reactor Plants. 14. The Journal of Physical Chemistry A 1997 , 101 (51) , 9935-9941. 81 g/mol. Apr 7, 2022 · The structural and bonding properties of a boron oxide B 5 O 6 − cluster has been studied using computer global structure searches and quantum chemical calculations, revealing a perfectly planar C 2v (1 A 1) global minimum geometry. Mar 4, 2010 · The results extend previous observations on the growth mechanism for boron oxide clusters: (i) The low spin electronic state is consistently favored. The third electron will go on another side of the symbol: \[\mathbf{\dot{Be}}\mathbf{:}\nonumber \] Again, it does not matter on which sides of the symbol the electron dots are positioned. This structure has two three-dimensional inter- locking, twin networks based on B--O bonds16). H 2 O system [22,23,24,25] such as thermal dehydration of boron compounds as well as multiple methods for the production of boron oxide, few exact studies have been done on the kinetics of boric acid dehydration. Bray, H. 1999). 737 Å and c = 3. However, due to their complicated structural nature and particularly boron coordination change with composition and thermal history, atomistic simulations of these glasses lag behind the more extensively studied silicate glasses. ‒%C). Hexagonal boron nitride (point group = D 3h; space group = P6 3 /mmc) has a layered structure similar to graphite. Matus and Vu Thi Ngan and Daniel J. Interfaces 8 , 18008–18017 (2016). 186 Å were determined using X Boron is the 51st most common element found in the earth’s crust and is found at an average concentration of 8 mg/kg (Cotton et al. 345) have coaxed boron into a more confined setting and made a boron analog of carbon monoxide as a triply bonded BO anion that was stabilized by coordination to a platinum center. Controversy remained as to whether or not the material had this exact 4:1 stoichiometry, as, in practice the material is always slightly carbon-deficient with regard to this Jan 2, 2024 · Chemsrc provides Boron oxide(CAS#:1303-86-2) MSDS, density, melting point, boiling point, structure, formula, molecular weight etc. However, hypothesizing an analogy with the superstructures Based on lithium aluminosilicate glass, the composition of glass was optimized by replacing SiO2 with B2O3, and the influence of glass composition on structure and performance was studied. Boron trichloride is also made from boron oxide, but in the presence of carbon, (6. 8 at. 1021/jp811391v Corpus ID: 12822109; Thermochemistry and electronic structure of small boron and boron oxide clusters and their anions. ACS Appl. 621; CAS Registry Number: 12045-60-2; Information on this page: Gas phase thermochemistry data; References; Notes; Other data available: Vibrational and/or electronic energy levels; Options: Switch to calorie-based units Jun 27, 2022 · The next atom is boron. Sep 1, 2019 · A review of the literature is presented, including a description of the crystal structure and morphological features of graphite-like hexagonal boron nitride, as well as the preparation of materials based on it. Contrary to other phases, which are semiconductors , this phase is a metal and becomes a superconductor with a critical temperature increasing from 6 K at 160 GPa to 11 K at 250 GPa. Two structural networks coexist when < 1/3 and metastable phase separation (liquation) occurs in such a glass on heating, with formation of microscopic volumes of different composition of high silica and sodium borate content. Sep 4, 2021 · Boron oxide or boric anhydride is an inorganic compound whose chemical formula is B2O3. Kline, P. Boron oxide Displaying lattice parameters for primitive cell; note that calculated cell volumes are typically overestimated on average by 3% (+/- 6%) . [47] Boron oxide. The most common oxide of boron is boron trioxide, $\ce{B2O3}$, which is the anhydride of boric acid: (OH)3}$, which is suggestive of its structure) instead reacts Mar 1, 2022 · The well-known undoped allotropic forms of boron, , α, b, g and tetragonal t-form, are superhard. Natural boron exists in 2 stable isotopes however pure boron is hard to prepare due Apr 7, 2023 · Besides, some BO 4 units were converted to BO 3 units, increasing the fraction BO 3 units in the glass structure. }, author={Jiatu Liu and Shuangbao Wang and Zhengping Ding and Ruiqi Zhou and Qingbing Xia Boron Oxide plays a key role in numerous glasses of high technological importance, yet its role in glass structure is far from clear. Mar 30, 2009 · DOI: 10. Boron hydrides are gases of the composition B n H n + 4 and B n H n + 6, are known as boranes. 54Ni0. arabjc. 13Co0. where γ Na 2 O and γ B 2 O 3 are the molar fractions of sodium and boron oxides in the glass. 3(c) with Fig. Using Rh Kα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4πsinθ/λ = 20 A−1, and a rigorous interpretation was obtained in terms of pair functions. Formula: B 2 O; Molecular weight: 37. It was not until the 1930s that the chemical composition was estimated as B 4 C. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10 −6 K −1 at 20 °C), making them more resistant to thermal shock than any other common glass. This paper reports development of a set of conditions boron oxide forms a three- or two-di- mensional coordinative structure [2B3+, 302-],, or a molecular structure [ { (B3+)z(Oz-)3) and in the latter case whether x equals 1,2, or more. Here is possible scenario: as B 2 O 3 doping increases, numerous boron atoms exist in the glass structure, which need extra oxygen atoms to form units. Boric anhydride | B2O3 | CID 518682 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety Dec 1, 2023 · This is due to the uncontrollable partial pressure increase of boron sub-oxide. Each boron is triangularly surrounded Sep 17, 2018 · Molecular dynamics and related atomistic computer simulations are effective ways in studying the structures and structure–property relations of glass materials. 1016/j. 4–15 wo crystalline Boron oxide. \[ \text{B}_2\text{O}_3 \text{ + 3 C + 3 Cl}_2 \rightarrow \text{2 BCl}_3 \text{ + 3 CO}\] Many of the trihalides are readily prepared by either the direct reaction of the metal with the appropriate halogen, (6. Using Rh Kα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4πsinθ/λ = 20 Å −1, and a rigorous interpretation was obtained in terms of pair functions. ‒%C) to B 4 C (20 at. 3(a) and 3(d)). The product formed easily in room temperature solution from a precursor substituted with a silyl group on the oxygen and a bromide on the boron and exhibited Jul 1, 2018 · The oxide layer of boron particle is generally regarded as a two-layer structure the inner layer is B2O3 and the outer is (BO)n. The models are discussed with reference to spectroscopic data, diffraction data and other physical properties for boron oxide. Boron is a nonmetal and is typically found in nature bound to oxygen. Frequently used doping methodologies are discussed, including ion implantation and solid-phase doping, mainly focused on recent developing techniques of monolayer doping. A new study of the structure of vitreous boron oxide has been made under greatly improved conditions. Nov 1, 2001 · To explain this unusual temperature coefficient of the surface tension, a change in the boron oxide structure while raising the temperature was proposed in this study. (ii) The most stable structure of a neutral boron monoxide B(n)O is obtained either by condensing O on a BB edge of a B(n) cycle, or by binding one BO group to a B(n-1) ring. • Light-to-electric energy conversion is realized. 04 and 0. • The shape-stability of the composite PCM is greatly enhanced. They are easily oxidized with considerable energy liberation and have been studied for use as rocket fuels. Articles of Boron oxide are included as well. 1999; Jansen 2003). Jun 28, 2024 · Boron - Compounds, Uses, Properties: In its compounds boron shows an oxidation state of +3. Jan 1, 2008 · The results indicate that: (1) for a sodium oxide to boron oxide ratio of 0. 37 A Jun 22, 2021 · Bulk rutile SnO 2. 51: kJ/mol: Review: Chase, 1998: Data last reviewed in June, 1968: Quantity Value Units Method Reference Comment Borosilicate Glasses. Elemental boron is chemically inert at room temperature, reacting with only fluorine and oxygen to form boron trifluoride, BF 3, and boric oxide, B 2 O 3, respectively. Each boron is triangularly surrounded by 3 oxygen atoms with a B–O distance of 1. 6), or the acid, (6. Thereby, the oxygen ions in BO 4 units before are now serving to new boron atoms Oct 14, 2021 · Boron chloride oxide | BClO | CID 141024 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities The boron-oxide-added aSAO with larger grains adjusted the diffraction peak shifts to higher diffraction angles, comparison of Fig. 1021/acsami. 1 In 2016,2 two re boron modifications were discovered, namely, Ï„-B and ofen, a two-dimensional (2D) allotropic boron modification. Then, a series of characterization and batch adsorption experiments were conducted on the material. There are over 200 minerals containing boron oxide; however, only four boron-containing minerals (borax, kernite Mar 6, 2018 · The combined comprehensive structural characterization of material 3 validates the proposed model for material 3 as being a hybrid molecular boron oxide material that consists of a cross-linked Guitar slide made of borosilicate glass. It has a molar mass of 26. jb lh cm mu zq qc qf ne xv uw