Bewise Inc. www.tool-tool.com Reference
source from the internet. Selenium (pronounced
/sɨˈlɛniəm/si-LEN-ee-əmor
/sɨˈliːniəm/si-LEE-nee-əm)
is a
chemical
element with the
atomic number 34,
represented by the
chemical symbol Se,
an
atomic mass of 78.96. It is a
nonmetal,
chemically related to
sulfurand
tellurium, and
rarely occurs in its elemental state in nature.
Isolated
selenium occurs in several different forms, the most stable of which is a
dense purplish-gray semi-metal (
semiconductor)
form that is structurally a trigonal polymer chain. It conducts
electricity better
in the light than in the dark, and is used in
photocells (see
section
Allotropesbelow). Selenium also exists in many non-conductive forms: a black
glass-like allotrope, as
well as several red crystalline forms built of eight-membered
ring molecules,
like its lighter cousin sulfur.
Selenium is found in economic
quantities in
sulfideores such as
pyrite,
partially replacing the sulfur in the ore matrix. Minerals that are
selenide or selenate compounds are also known, but are rare. The chief
commercial uses for selenium today are in glassmaking and in chemicals
and
pigments. Uses in
electronics,
once important, have been supplanted by
silicon semiconductor
devices.
Selenium salts are toxic in large amounts, but trace
amounts of the element are necessary for cellular function in most, if
not all, animals, forming the active center of the enzymes
glutathione
peroxidase and
thioredoxin
reductase (which indirectly reduce certain oxidized molecules in
animals and some plants) and three known
deiodinase enzymes
(which convert one
thyroid hormone to another). Selenium requirements in plants differ by species, with
some plants, it seems, requiring none.
Selenium (
Greek σελήνη
selene meaning
"Moon") was discovered in 1817 by
Jöns Jakob
Berzelius,who found the element associated with
tellurium (named for
the Earth). It was discovered as a byproduct of
sulfuric acid production.
It came to medical notice later because of its
toxicity to humans working in industry. It was also recognized as an
important veterinary toxin. In 1954, the first hints of specific
biological functions of selenium were discovered in
microorganisms.
Its essentiality for mammalian life was discovered in 1957. In the
1970s, it was shown to be present in two independent sets of
enzymes. This was
followed by the discovery of
selenocysteine in
proteins. During the 1980s, it was shown that selenocysteine is encoded
by the
codon TGA.
The recoding mechanism was worked out first in
bacteria and then in
mammals (see
SECIS element).
Growth
in selenium consumption was historically driven by steady development
of new uses, including applications in rubber compounding,
steel alloying, and
selenium
rectifiers. Selenium is also an essential material in the drums of
laser printers and copiers. By 1970, selenium in rectifiers had largely
been replaced by
silicon,
but its use as a photoconductor in plain-paper copiers had become its
leading application. During the 1980s, the photoconductor application
declined (although it was still a large end-use) as more and more
copiers using organic photoconductors were produced. At the current
time, the largest use of selenium worldwide is in glass manufacturing,
followed by uses in chemicals and pigments. Electronics use, despite a
number of continued applications, continues to decline.
In the
late 1990s, the use of selenium (usually with
bismuth) as an additive
to
plumbing brasses to meet no-lead
environmental standards became important. At present, total world
selenium production continues to increase modestly.
Selenium
occurs naturally in a number of inorganic forms, including
selenide,
selenate, and
selenite. In
soils, selenium most often occurs in soluble forms such as selenate
(analogous to sulfate), which are leached into rivers very easily by
runoff.
Selenium has a biological role, and it is found in
organic compounds such as dimethyl selenide,
selenomethionine,
selenocysteine,
and
methylselenocysteine.
In these compounds selenium plays a role analogous to that of sulfur.
Selenium
is most commonly produced from
selenide in many
sulfide ores, such as those of
copper,
silver, or
lead. It is obtained as a
byproduct of the processing of these ores, from the
anode mud of copper
refineries and the mud from the
lead chambersof
sulfuric acidplants. These muds can be processed by a number of means to obtain free
selenium.
Natural sources of selenium include certain
selenium-rich soils, and selenium that has been
bioconcentrated by certain plants. Anthropogenic sources of selenium include coal
burning and the mining and smelting of sulfide
Structure of trigonal selenium
Native
selenium is a rare mineral, which does not usually form good crystals,
but, when it does, they are steep rhombohedrons or tiny acicular
(hair-like) crystals.Isolation of selenium is often complicated by the
presence of other compounds and elements.
Most elemental selenium
comes as a byproduct of
refiningcopper or producing
sulfuric acid.
Industrial
production of selenium often involves the extraction of
selenium dioxidefrom residues obtained during the purification of
copper. Commonly,
production begins by oxidation with
sodium carbonateto produce selenium dioxide. The selenium dioxide is then mixed with
water and the solution is
acidifiedto form
selenous
acid (
oxidationstep). Selenous acid is bubbled with
sulfur dioxide (
reduction step) to give
elemental selenium.
Elemental selenium produced in chemical
reactions invariably appears as the amorphous red form: an insoluble,
brick-red powder. When this form is rapidly melted, it forms the black,
vitreous form, which is usually sold industrially as beads. The most
thermodynamically stable and densest form of selenium is the
electrically conductive gray (trigonal) form, which is composed of long
helical chains of selenium atoms (see figure). The conductivity of this
form is notably light-sensitive. Selenium also exists in three different
deep-red crystalline monoclinic forms, which are composed of Se
8molecules, similar to many allotropes of sulfur. However, selenium does
not exhibit the unusual changes in viscosity that sulfur undergoes when
gradually heated.
Selenium has six naturally occurring
isotopes, five of which
are stable:
74Se,
76Se,
77Se,
78Se,
and
80Se. The last three also occur as
fission products,
along with
79Se,
which has a
half-lifeof 295,000 years. The final naturally occurring isotope,
82Se,
has a very long half-life (~10
20 yr, decaying via double
beta decay to
82Kr),
which, for practical purposes, can be considered to be stable.
Twenty-three other unstable isotopes have been characterized.
See
also Selenium-79for more information on recent changes in the measured half-life of
this long-lived fission product, important for the dose calculations
performed in the frame of the geological disposal of long-lived
radioactive waste.
Although it is toxic in large doses, selenium is an essential
micronutrient for
animals. In plants, it occurs as a bystander mineral, sometimes in
toxic proportions in
forage(some plants may accumulate selenium as a defense against being eaten
by animals, but other plants such as
locoweed require
selenium, and their growth indicates the presence of selenium in soil).
It is a component of the unusual
amino acids selenocysteine and
selenomethionine.
In humans, selenium is a
trace element nutrient that functions as
cofactorfor
reduction of
antioxidant enzymes
such as
glutathione
peroxidases and certain forms of
thioredoxin
reductase found in animals and some plants (this enzyme occurs in
all living organisms, but not all forms of it in plants require
selenium).
The
glutathione
peroxidase family of enzymes (GSH-Px) catalyze certain reactions
that remove reactive oxygen species such as
hydrogen peroxideand organic
hydroperoxides:
2 GSH + H2O2----GSH-Px → GSSG + 2 H2O
Selenium also plays a role in the functioning of the
thyroid gland and in
every cell that utilizes thyroid hormone, by participating as a
cofactorfor the three known
thyroid hormone deiodinases, which
activate and then deactivate various thyroid hormones and their
metabolites. It may inhibit
Hashimotos's
disease, in which the body's own thyroid cells are attacked as
alien. A reduction of 21% on TPO antibodies was reported with the
dietary intake of 0.2 mg of selenium.
Dietary selenium comes from
nuts, cereals, meat, fish, and eggs.
Brazil nuts are the
richest ordinary dietary source (though this is soil-dependent, since
the Brazil nut does not require high levels of the element for its own
needs). In descending order of concentration, high levels are also found
in
kidney,
tuna,
crab, and
lobster.
The
human body's burden of selenium is believed to be in the 13-20 milligram
range.
Although selenium is an essential
trace element,
it is toxic if taken in excess. Exceeding the
Tolerable
Upper Intake Level of 400 micrograms per day can lead to selenosis
This 400 microgram Tolerable Upper Intake Level is based primarily on a
1986 study of five Chinese patients who exhibited overt signs of
selenosis and a follow up study on the same five people in 1992. The
1992 study actually found the maximum safe dietary Se intake to be
approximately 800 micrograms per day (15 micrograms per kilogram body
weight), but suggested 400 micrograms per day to not only avoid
toxicity, but also to
avoid creating an imbalance of nutrients in the diet and to account for
data from other countries. The Chinese people who suffered from selenium
toxicity ingested selenium by eating corn grown in extremely
selenium-rich stony coal (carbonaceous
shale). This coal was
shown to have selenium content as high as 9.1%, the highest
concentration in coal ever recorded in literature. A dose of selenium as
small as 5 mg per day can be lethal for many humans.
Reference
ranges for blood tests, showing selenium in purple in center
Symptoms
of selenosis include a garlic odor on the breath, gastrointestinal
disorders, hair loss, sloughing of nails, fatigue, irritability, and
neurological damage. Extreme cases of selenosis can result in
cirrhosis of the
liver,
pulmonary
edema, and death. Elemental selenium and most metallic
selenides have
relatively low toxicities because of their low
bioavailability.
By contrast,
selenatesand
selenitesare very toxic, having an oxidant mode of action similar to that of
arsenic trioxide. The chronic toxic dose of selenite for human beings is
about 2400 to 3000 micrograms of selenium per day for a long time.
Hydrogen selenideis an extremely toxic, corrosive gas. Selenium also occurs in organic
compounds such as dimethyl selenide,
selenomethionine,
selenocysteineand
methylselenocysteine,
all of which have high
bioavailability and are toxic in large doses.
Nano-size
selenium has equal efficacy, but much lower toxicity.
On April
19, 2009, twenty-one
poloponies began to die shortly before a match in the United States Polo
Open. Three days later, a pharmacy released a statement explaining that
the horses had received an incorrect dose of one of the ingredients used
in a vitamin compound, with which the horses had been injected. Such
vitamin injections are common to promote recovery after a match. The
pharmacy did not initially release the name of the specific ingredient
due to ongoing law-enforcement and other investigations. Analysis of
inorganic
compounds of the vitamin supplement indicated that selenium
concentrations were ten to fifteen times higher than normal in the
horses'
blood
samples and 15 to 20 times higher than normal in their liver
samples. It was later confirmed that selenium was the ingredient in
question.
Selenium
poisoning of water systems may result whenever new agricultural
runoff courses through normally dry undeveloped lands. This process
leaches natural soluble selenium compounds (such as selenates) into the
water, which may then be concentrated in new "wetlands" as the water
evaporates. High selenium levels produced in this fashion have been
found to have caused certain congenital disorders in wetland birds.
Selenium
deficiency is relatively rare in healthy, well-nourished individuals.
It can occur in patients with severely compromised
intestinal function,
those undergoing
total
parenteral nutrition, and also on advanced-aged people (over 90).
Also, people dependent on food grown from selenium-deficient soil are
also at risk. However, although
New Zealand has low
levels of selenium in its soil, adverse health effects have not been
detected.
Selenium deficiency may only occur when a low selenium
status is linked with an additional stress such as chemical exposure or
increased oxidant stress due to vitamin E deficiency.
There are
interactions between selenium and other nutrient such as
iodine and
vitamin E. The
interaction is observed in the
etiology of many
deficiency diseases in animals and pure selenium deficiency is in fact
rare. The effect of selenium deficiency on health remains uncertain, in
particular, in relation to
Kashin-Beck
disease.
Cancer Several studies have
suggested a possible link between cancer and selenium deficiency. One
study, known as the NPC, was conducted to test the effect of selenium
supplementation on the recurrence of skin cancers on selenium-deficient
men. It did not demonstrate a reduced rate of recurrence of skin
cancers, but did show a reduced occurrence of total cancers, although
without a statistically significant change in overall mortality.The
preventative effect observed in the NPC was greatest in those with the
lowest baseline selenium levels.In 2009 the 5.5 year SELECT study
reported that selenium and vitamin E supplementation, both alone and
together, did not significantly reduce the incidence of
prostate cancer in 35,000 men who "generally were replete in selenium at baseline". The
SELECT trial found that vitamin E did not reduce prostate cancer as it
had in the Alpha-Tocopherol, Beta Carotene (ATBC) study, but the ATBC
had a large percentage of smokers while the SELECT trial did not.. There
was a slight trend toward more prostate cancer in the SELECT trial, but
in the vitamin E only arm of the trial, where no selenium was given.
Dietary
selenium prevents chemically induced carcinogenesis in many rodent
studies. It has been proposed that selenium may help prevent cancer by
acting as an
antioxidantor by enhancing immune activity. Not all studies agree on the
cancer-fighting effects of selenium. One study of naturally occurring
levels of selenium in over 60,000 participants did not show a
significant correlation between those levels and cancer. The SU.VI.MAX
study concluded that low-dose supplementation (with 120 mg of ascorbic
acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 µg of selenium, and
20 mg of zinc) resulted in a 30% reduction in the incidence of cancer
and a 37% reduction in all-cause mortality in males, but did not get a
significant result for females.However, there is evidence that selenium
can help chemotherapy treatment by enhancing the efficacy of the
treatment, reducing the toxicity of chemotherapeutic drugs, and
preventing the body's resistance to the drugs. Studies of cancer cells
in vitro showed that chemotherapeutic drugs, such as Taxol and
Adriamycin, were more toxic to strains of cancer cells grown in culture
when selenium was added.
In March 2009, Vitamin E (400 IU) and
selenium (200 micrograms) supplements were reported to affect gene
expression and can act as a tumor suppressor. Eric Klein, MD from the
Glickman Urological and Kidney Institute in Ohio said the new study
“lend credence to the previous evidence that selenium and vitamin E
might be active as cancer preventatives”.In an attempt to rationalize
the differences between epidemiological and
in vitro studies and
randomized trials like SELECT, Klein said that randomized controlled
trials “do not always validate what we believe biology indicates and
that our model systems are imperfect measures of clinical outcomes in
the real world”.
HIV/AIDS Some research has
indicated a geographical link between regions of selenium-deficient
soils and peak incidences of
HIV/
AIDS infection. For
example, much of
sub-Saharan
Africa is low in selenium. However,
Senegal is not, and also
has a significantly lower level of AIDS infection than the rest of the
continent. AIDS appears to involve a slow and progressive decline in
levels of selenium in the body. Whether this decline in selenium levels
is a direct result of the replication of HIV or related more generally
to the overall malabsorption of nutrients by AIDS patients remains
debated.
Low selenium levels in AIDS patients have been directly
correlated with decreased immune cell count and increased disease
progression and risk of death. Selenium normally acts as an
antioxidant, so low
levels of it may increase oxidative stress on the immune system leading
to more rapid decline of the immune system. Others have argued that
T-cell associated genes encode selenoproteins similar to human
glutathione
peroxidase. Depleted selenium levels in turn lead to a decline in
CD4
helper T-cells,
further weakening the immune system.
Regardless of the cause of
depleted selenium levels in AIDS patients, studies have shown that
selenium deficiency does strongly correlate with the progression of the
disease and the risk of death.
Tuberculosis Some
research has suggested that selenium supplementation, along with other
nutrients, can help prevent the recurrence of tuberculosis.
Diabetes
A well-controlled study showed that selenium intake is
positively correlated with the risk of developing
type 2
diabetes. Because high serum selenium levels are positively
associated with the prevalence of diabetes, and because selenium
deficiency is rare, supplementation is not recommended in well-nourished
populations such as the U.S.
Mercury Experimental
findings have demonstrated a protective effect of selenium on
methylmercury toxicity, but epidemiological studies have been inconclusive in linking
selenium to protection against the adverse effects of methylmercury.
Chemistry Selenium is a catalyst in many chemical
reactions and is widely used in various industrial and laboratory
syntheses, especially
organoselenium
chemistry. It is also widely used in structure determination of
proteins and nucleic acids by X-ray crystallography (incorporation of
one or more Se atoms helps with
MADand
SADphasing.)
Manufacturing and materials use The
largest use of selenium worldwide is in
glass and
ceramic manufacturing,
where it is used to give a red color to glasses,
enamels and
glazes as well as
to remove color from glass by counteracting the green tint imparted by
ferrous impurities.
Selenium is used with
bismuth in
brasses to replace more
toxic
lead. It is also
used to improve abrasion resistance in
vulcanized rubbers.
Electronics
Because of its
photovoltaic and
photoconductiveproperties, selenium is used in
photocopying,
photocells,
light meters and
solar cells. It was
once widely used in
rectifiers.
These uses have mostly been replaced by silicon-based devices, or are
in the process of being replaced. The most notable exception is in power
DC
surge
protection, where the superior energy capabilities of selenium
suppressors make them more desirable than
metal oxide
varistors.
Sheets of amorphous selenium convert
x-ray images to patterns
of charge in
xeroradiographyand in solid-state, flat-panel x-ray cameras.
Photography Selenium is used in the
toning of
photographic prints, and it is sold as a toner by numerous
photographic manufacturers including
Kodak and
Fotospeed.
Its use intensifies and extends the tonal range of black and white
photographic images as well as improving the permanence of prints.
Early
photographic
light
meters used
seleniumbut this application is now obsolete.
The substance loosely
called
selenium
sulfide (approximate formula SeS
2) is the active
ingredient in some anti-dandruff shampoos.The selenium compound kills
the scalp fungus
Malassezia,
which causes shedding of dry skin fragments. The ingredient is also
used in body lotions to treat
Tinea versicolordue to infection by a different species of
Malassezia fungus.
Nutrition Selenium is used widely in
vitamin preparations and
other
dietary
supplements, in small doses (typically 50 to 200 micrograms per day
for adult humans). Some livestock
feeds are fortified with
selenium as well.
Selenium may be measured in blood, plasma,
serum or urine to monitor excessive environmental or occupational
exposure, confirm a diagnosis of poisoning in hospitalized victims or to
assist in a forensic investigation in a case of fatal overdosage. Some
analytical techniques are capable of distinguishing organic from
inorganic forms of the element. Both organic and inorganic forms of
selenium are largely converted to monosaccharide conjugates
(selenosugars) in the body prior to being eliminated in the urine.
Cancer patients receiving daily oral doses of selenothionine may achieve
very high plasma and urine selenium concentrations.
Main
article:
Evolution
of dietary antioxidants Over three billion years ago,
blue-green algae were the most primitive oxygenic photosynthetic
organisms and are ancestors of multicellular eukaryotic algae. Algae
that contain the highest amount of antioxidant selenium, iodide, and
peroxidase enzymes were the first living cells to produce poisonous
oxygen in the atmosphere. It has been suggested that algal cells
required a protective antioxidant action, in which selenium and iodides,
through peroxidase enzymes, have had this specific role.Selenium, which
acts synergistically with iodine, is a primitive mineral antioxidant,
greatly present in the sea and prokaryotic cells, where it is an
essential component of the family of
glutathione
peroxidase (GSH-Px) antioxidant enzymes;
seaweeds accumulate high
quantity of selenium and iodine. In 2008, a study showed that iodide
also scavenges reactive oxygen species (ROS) in algae, and that its
biological role is that of an inorganic antioxidant, the first to be
described in a living system, active also in an in vitro assay with the
blood cells of today’s humans."
From about three billion years
ago, prokaryotic selenoprotein families drive selenocysteine evolution.
Selenium is incorporated into several prokaryotic selenoprotein families
in bacteria, archaea and eukaryotes as selenocysteine, where
selenoprotein peroxiredoxins protect bacterial and eukaryotic cells
against oxidative damage. Selenoprotein families of GSH-Px and the
deiodinases of eukaryotic cells seem to have a bacterial
phylogenetic origin. The selenocysteine-containing form occurs in species as diverse
as green algae, diatoms, sea urchin, fish and chicken. Selenium enzymes
are involved in utilization of the small reducing molecules
glutathione and
thioredoxin. One
family of selenium-containing molecules (the
glutathione
peroxidases) destroy peroxide and repair damaged peroxidized cell
membranes, using glutathione. Another selenium-containing enzyme in some
plants and in animals (
thioredoxin
reductase) generates reduced thioredoxin, a dithiol that serves as
an electron source for peroxidases and also the important reducing
enzyme
ribonucleotide
reductase that makes DNA presursors from RNA precursors.
At
about 500 Mya, plants and animals began to transfer from the sea to
rivers and land, the environmental deficiency of marine mineral
antioxidants (as selenium, iodine, etc.) was a challenge to the
evolution of terrestrial life. Trace elements involved in GSH-Px and
superoxide dismutase enzymes activities, i.e. selenium,
vanadium,
magnesium,
copper, and
zinc, may have been lacking
in some terrestrial mineral-deficient areas.Marine organisms retained
and sometimes expanded their seleno-proteomes, whereas the
seleno-proteomes of some terrestrial organisms were reduced or
completely lost. These findings suggest that, with the exception of
vertebrates, aquatic
life supports selenium utilization, whereas terrestrial habitats lead to
reduced use of this trace element Marine fishes and vertebrate thyroid
glands have the highest concentration of selenium and iodine. From about
500 Mya, freshwater and terrestrial plants slowly optimized the
production of “new” endogenous antioxidants such as
ascorbic acid (Vitamin C),
polyphenols(including flavonoids),
tocopherols, etc. A
few of these appeared more recently, in the last 50–200 million years,
in fruits and flowers of angiosperm plants. In fact, the angiosperms
(the dominant type of plant today) and most of their antioxidant
pigments evolved during the late
Jurassic period.
The
deiodinase
isoenzymesconstitute another family of eukaryotic selenoproteins with identified
enzyme function. Deiodinases are able to extract electrons from iodides,
and iodides from iodothyronines. They are, thus, involved in
thyroid-hormone regulation, participating in the protection of
thyrocytesfrom damage by H
2O
2 produced for thyroid-hormone
biosynthesis.About 200 Mya, new selenoproteins were developed as
mammalian GSH-Px enzymes.
Chalcogen
compounds
Selenium forms two oxides:
selenium dioxide(SeO
2) and
selenium trioxide(SeO
3). Selenium dioxide is formed by the reaction of
elemental selenium with oxygen:
Se8 + 8 O2
→ 8 SeO2It is a
polymeric solid that
forms monomeric SeO
2 molecules in the gas phase. It dissolves
in water to form
selenous
acid, H
2SeO
3. Selenous acid can also be made
directly by oxidising elemental selenium with
nitric acid:
3 Se + 4 HNO3 → 3 H2SeO3 + 4 NO Saltsof selenous acid are called
selenites. These include
silver selenite (Ag
2SeO
3) and
sodium selenite (Na
2SeO
3).
Hydrogen sulfidereacts with aqueous selenous acid to produce
selenium
disulfide:
H2SeO3 + 2 H2S
→ SeS2 + 3 H2OSelenium disulfide
consists of 8-membered rings of sulfur atoms with selenium replacing
some of the sulfur atoms. It has an approximate composition of SeS
2,
with individual rings varying in composition, such as Se
4S
4and Se
2S
6. It has various applications, including
use in shampoo as an anti-
dandruff agent, an
inhibitor in polymer chemistry, a glass dye, and a reducing agent in
fireworks.
Unlike
sulfur, which forms a stable
trioxide,
selenium trioxide is unstable and decomposes to the dioxide above 185
°C:
2 SeO3 → 2 SeO2 + O2
(ΔH = −54 kJ/mol) Selenium trioxide may be synthesized by
dehydrating
selenic
acid, H
2SeO
4, which is itself produced by the
oxidation of selenium dioxide with
hydrogen peroxide:
SeO2 + H2O2 → H2SeO4Hot, concentrated selenic acid is capable of dissolving gold,
forming gold(III) selenate.
Selenium reacts with
fluorine to form
selenium
hexafluoride:
Se8 + 24 F2 → 8 SeF6Unlike its sulfur counterpart,
sulfur
hexafluoride, however, SeF
6 is more reactive and is a
toxic pulmonary irritant. It can cause
frostbite and severe
irritation on contact with skin.
Other selenium
halides include SeF
4,
Se
2Cl
2, SeCl
4, and Se
2Br
2.
Selenium dichloride (SeCl
2), an important reagent in the
study of selenium chemistry, may be prepared in pure form by reacting
elemental selenium with
SO2Cl2in
THF solution. Some of the selenium oxyhalides, such as SeOF
2, are
useful as nonaqueous solvents.
Like oxygen and sulfur, selenium
forms
selenides with
metals. For example, reaction with
aluminum forms
aluminum selenide:
3 Se8 + 16 Al → 8 Al2Se3Other selenides include
mercury selenide(HgSe),
lead
selenide (PbSe), and
zinc selenide (ZnSe). An important selenide is
copper
indium gallium selenide (Cu(Ga,In)Se
2), a
semiconductor.
Selenium
does not react directly with
hydrogen; so
hydrogen selenide,
the analogue of hydrogen sulfide and water, is prepared by first
reacting selenium with a metal to produce a selenide, and then
protonating the
selenide anion with an acid to produce H
2Se.
Tetraselenium
tetranitride, Se
4N
4, is an explosive orange
compound analogous to
S4N4It can be synthesized by the reaction of SeCl
4 with [((CH
3)
3Si)
2N]
2Se
in
dichloromethanesolution at −78 °C.
Selenium reacts with
cyanides to yield
selenocyanates.For
example:
8 KCN + Se8 → 8 KSeCN 歡
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不同要求，我們有能力達到非常卓越的客戶需求品質，這是現有相關技術無法比擬的，我們成功的滿足了各行各業的要求，包括：精密HSS DIN切削刀具、協助客戶設計刀具流程、DIN or JIS 鎢鋼切削刀具設計、NAS986 NAS965 NAS897 NAS937orNAS907 航太切削刀具,NAS航太刀具設計、超高硬度的切削刀具、醫療配件刀具設計、複合式再研磨機、PCD地板專用企口鑽石組合刀具、粉末造粒成型機、主機版專用頂級電桿、PCD V-Cut刀、捨棄式圓鋸片組、粉末成型機、航空機械鉸刀、主機版專用頂級電感、’
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銑刀與切斷複合再研磨機、銑刀與鑽頭複合再研磨機、銑刀與螺絲攻複合再研磨機等等。我們的產品涵蓋了從民生
刀具到工業級的刀具設計；從微細刀具到大型刀具；從小型生產到大型量產；全自動整合；我們的技術可提供您連續生產的效能，我們整體的服務及卓越的技術，恭
迎您親自體驗！！ BW
Bewise Inc. Willy Chen willy@tool-tool.com bw@tool-tool.com www.tool-tool.com
skype:willy_chen_bw mobile:0937-618-190 Head &Administration Office
No.13,Shiang Shang 2nd St., West Chiu Taichung,Taiwan 40356 http://www.tool-tool.com /
FAX:+886 4 2471 4839 N.Branch 5F,No.460,Fu Shin North Rd.,Taipei,Taiwan
S.Branch No.24,Sec.1,Chia Pu East Rd.,Taipao City,Chiayi Hsien,TaiwanWelcome to BW
tool world! We are an experienced tool maker specialized in cutting
tools. We focus on what you need and endeavor to research the best
cutter to satisfy users’ demand. Our customers involve
wide range of industries, like mold & die, aerospace, electronic,
machinery, etc. We are professional expert in cutting field. We would
like to solve every problem from you. Please feel free to contact us,
its our pleasure to serve for you. BW product including: cutting tool、aerospace tool .HSS DIN Cutting tool、Carbide end mills、Carbide cutting tool、NAS Cutting tool、NAS986 NAS965 NAS897 NAS937orNAS907 Cutting Tools,Carbide end mill、disc milling cutter,Aerospace
cutting tool、hss
drill’Фрезеры’Carbide drill、High speed steel、Compound Sharpener’Milling cutter、INDUCTORS FOR PCD’
CVDD(Chemical Vapor Deposition
Diamond )’PCBN
(Polycrystalline Cubic Boron Nitride) ’Core drill、Tapered end
mills、CVD Diamond
Tools Inserts’PCD
Edge-Beveling Cutter(Golden Finger’PCD V-Cutter’PCD Wood tools’PCD Cutting tools’PCD Circular Saw Blade’PVDD End Mills’diamond tool. INDUCTORS FOR PCD .POWDER FORMING MACHINE
‘Single Crystal
Diamond ‘Metric
end mills、Miniature
end mills、Специальные
режущие инструменты ‘Пустотелое сверло
‘Pilot reamer、Fraises’Fresas con mango’
PCD (Polycrystalline
diamond) ‘Frese’POWDER
FORMING MACHINE’Electronics cutter、Step drill、Metal cutting saw、Double margin drill、Gun barrel、Angle milling cutter、Carbide burrs、Carbide tipped cutter、Chamfering tool、IC card engraving cutter、Side cutter、Staple Cutter’PCD diamond cutter specialized in
grooving floors’V-Cut
PCD Circular Diamond Tipped Saw Blade with Indexable Insert’PCD Diamond Tool’Saw Blade with Indexable Insert’NAS tool、DIN or JIS tool、Special tool、Metal slitting saws、Shell end mills、Side and face milling cutters、Side chip clearance saws、Long end mills’
end mill grinder’drill grinder’sharpener、Stub roughing end mills、Dovetail milling cutters、Carbide slot drills、Carbide torus cutters、Angel carbide end mills、Carbide torus cutters、Carbide ball-nosed slot drills、Mould
cutter、Tool manufacturer. Bewise Inc. www.tool-tool.com よ
うこそＢｅｗｉｓｅ Ｉｎｃ.の
世界へお越し下さいませ、先ず御目出度たいのは新たな 情報を受け取って頂き、もっと各産業に競争力プラス展開。弊社は専門なエンド・ミルの製造メーカーで、客先に色んな分野のニーズ、 豊富なパリエーションを満足させ、特にハイテク品質要求にサポート致します。 弊社は各領域に供給
できる内容は： （１）精密
ＨＳＳエンド・ミルのＲ＆Ｄ （２）Carbide Cutting tools設計（３）鎢鋼エンド・ミ
ル設計 （４）航空エ
ンド・ミル設計 （５）超高硬度エンド・ミル （６）ダイヤモンド・エンド・ミ
ル （７）医療用品エ
ンド・ミル設計 （８）自動車部品＆材料加工向けエンド・ミル設計弊社の製品の供給調達機能は： （１）生活産業～ハイテク工業までのエンド・ミル設計（２）ミクロ・エ
ンド・ミル～大型エンド・ミル供給 （３）小Ｌｏｔ生産～大量発注対応供給 （４）オートメーション整備調達 （５）スポット対応～流れ生産対応 弊社
の全般供給体制及び技術自慢の総合専門製造メーカーに貴方のご体験を御待ちしております。 Bewise
Inc. talaşlı imalat sanayinde en fazla kullanılan ve üç eksende (x,y,z)
talaş kaldırabilen freze takımlarından olan Parmak Freze imalatçısıdır.
Çok geniş ürün yelpazesine sahip olan firmanın başlıca ürünlerini
Karbür Parmak Frezeler, Kalıpçı Frezeleri, Kaba Talaş Frezeleri, Konik
Alın Frezeler, Köşe Radyüs Frezeler, İki Ağızlı Kısa ve Uzun Küresel
Frezeler, İç Bükey Frezeler vb. şeklinde sıralayabiliriz. BW специализируется в
научных исследованиях и разработках, и снабжаем самым
высокотехнологичным карбидовым материалом для поставки режущих /
фрезеровочных инструментов для почвы, воздушного пространства и
электронной индустрии. В нашу основную продукцию входит твердый карбид /
быстрорежущая сталь, а также двигатели, микроэлектрические дрели, IC
картонорезальные машины, фрезы для гравирования, режущие пилы,
фрезеры-расширители, фрезеры-расширители с резцом, дрели, резаки форм
для шлицевого вала / звездочки роликовой цепи, и специальные нано
инструменты. Пожалуйста, посетите сайт www.tool-tool.com для
получения большей информации. BW is specialized in
R&D and sourcing the most advanced carbide material with high-tech
coating to supply cutting / milling tool for mould & die, aero space
and electronic industry. Our main products include solid carbide / HSS
end mills, micro electronic drill, IC card cutter, engraving cutter,
shell end mills, cutting saw, reamer, thread reamer, leading drill,
involute gear cutter for spur wheel, rack and worm milling cutter,
thread milling cutter, form cutters for spline shaft/roller chain
sprocket, and special tool, with nano grade. Please visit our web www.tool-tool.com
for more info.
