- Summary, What
must be known,
-
- On this page :
- Ceramics Technology :
Boron and compounds
- Toxicology :
Boron and Ceramics.
- Version Française :
- Technologie
Céramique : Bore et composés
- Toxicologie :
Bore et céramique
-
-
|
Ceramics technology : Boron
and Compounds
|
- 1)
Commercial Boron Compounds used mainly in Ceramics :
-
- Commercial
borax (or sodium
tetraborate) in the hydrated form (also called borax
decahydrate), formula 2B2O3.Na2O.10H2O, molecular mass
381.43, is used to introduce B2O3 (boric anhydride)
and Na2O in fritted compounds, it is also used to
produce Boric acid (H3BO3) and other compounds.
-
- 100g of Borax decahydrate
brings 36.4g of boric anhydride and 16.2g of Na2O.
-
- This product is soluble in
water and acids. It begins to melt in its water of
crystallization under the action of heat and gives
boric acid partially by hydrolysis (H3BO3) which
volitilizes according to the following reaction:
- B4O7 2- + 7 H2O <--
--> 2 OH- + volatile 4H3BO3 --^
- This reaction can cause
difficulties to ensure the presence of Boron (boric
Anhydride : B2O3) in amounts wanted in recipes during
firing or fritting. Boron losses are thus inevitable.
Any heating leading to the fusion of hydrated borax
involves this trouble.
- That is why that for
fritting it is often preferable to use anhydrous borax Na2B4O7 (molar mass 201.27, melting
point approximately 740°C), with which risks of
Boron losses are less.
-
- 100g of anhydrous Borax
bring 69.2g of B2O3 and 30.8g of Na2O.
-
- Boric
acid (1/2
(B2O3.3H2O)), molar mass 61.84, allows to introduce
B2O3 alone in a recipe. It is the unique compound
allowing to introduce only boric anhydride.
- It is soluble in water and
melts at low temperature (starting from 172°C).
It is a synthetic product, pure, and of precise
composition.
-
- 100g of boric acid bring
56.2g of B2O3.
-
- These water-soluble
compounds must be introduced into glazes in the form
of frits. It is thus advisable to get " Ad hoc " frits
to carry out glaze recipes necessary for production.
-
-
- 2) Boric
Anhydride (B2O3 ) :
-
- This product does not exist
in this form in a free state, it is brought into frits
by borax (if Na2O is necessary) or by boric acid.
-
- Boron is a glass-former,
i.e. it allows the construction of a vitreous matrix
by formation of a triangular assembly with oxygen (a
cation related to three atoms of oxygen) and that its
ionic potential is relatively high (higher than 7).
The ionic potential being the ratio of the valence of
the cation (3 for boron) on the value of its ionic ray
(0.20Å for boron), this one has a value of
3/0.20 = 15 for boron.
- Boric Anhydride (B2O3)
classified as an acidic oxide, appears thus with
silicon, titanium and zirconium (SiO2, TiO2, ZrO2) in
the classification established by the formula of
Seger.
-
-
- B2O3 is an energetic glazes
fluxing oxide, in the case of additions smaller than
12% (*) it lowers their dilation coefficient (more
strongly than silica) and brings good elasticity to
them which favors their adhesion to earthenware
clays.
- In large amounts , B2O3
tends to make glazes milky, especially if they contain
much CaO.
- B2O3 in small amounts lowers
the viscosity of glazes and makes them more brilliant
and more transparent. It also reduces their surface
tension and lowers their point of softening. The
substitution for alkaline oxides by B2O3 in small
amounts improves the mechanical properties of glazes
and lowers their dilation (*).
- B2O3 also improves
resistance to acids, and hardness of glazes.
-
-
- Boron containing alkaline
glazes, developed to replace leaded glazes are not
toxic.
- They also make it possible
to fire above1150°C, temperature at which leaded
glazes start to strongly vaporize.
- The main oxides present in
alkalino-boric glazes are: CaO, Na2O, K2O, Al2O3,
SiO2.
- But in general, a better
fusibility is achieved by increasing the number of
basic oxides in the formula, one can also find in
these: ZnO, BaO and MgO.
-
- (*) Anomaly of Boron
:
- In a silicates medium,
boron in the presence of alkaline oxides (Na, K, Li =
oxides of the R2O group) forms BO4 groups
(co-ordination number 4) or BO3 groups (co-ordination
number 3) according to the molar ratio R2O/B2O3. The
formation of BO4 groups causes a reinforcement of the
glass structure and the dilation coefficient drops,
while the formation of BO3 groups involves an increase
in the latter..
- The effect of boron on
the decrease of dilatation does not follow a linear
law, its action increases, passes by a maximum, then
decreases according to the alkalinity of the glass. In
practice, one notes that boron lowers in a linear way
the dilation coefficient of an alkalino-boric glaze
for additions up to 12-15 % mol of B2O3, then beyond
that, there is a return behind with an increase in
this coefficient.
-
-
- 3) A few
formulas :
-
-
- Examples of Boric Glazes
:
-
- Cone 02a (1060°C)
:
-
-
|
K2O 0.25
|
AL2O3 0.25
|
SiO2 2.50
|
|
CaO
0.65
|
-
|
B2O3 0.45
|
|
ZnO
0.10
|
-
|
-
|
-
- Cone 4a (1160°C)
:
-
-
|
Na2O 0.25
|
AL2O3 0.40
|
SiO2 3.20
|
|
K2O 0.25
|
-
|
B2O3 0.50
|
|
CaO
0.20
|
-
|
-
|
|
BaO
0.30
|
-
|
-
|
-
- Examples of
alkalino-boric frits :
-
- Frit
A :
-
-
|
Na2O 0.302
|
AL2O3 0.168
|
SiO2 2.200
|
|
K2O 0.088
|
-
|
B2O3 0.600
|
|
CaO
0.532
|
-
|
-
|
|
BaO
0.076
|
-
|
-
|
-
- Frit
B :
-
-
|
Na2O 0.264
|
AL2O3 0.418
|
SiO2 4.703
|
|
K2O 0.132
|
-
|
B2O3 0.963
|
|
CaO
0.594
|
-
|
-
|
|
MgO
0.013
|
-
|
-
|
-
- Frit
C :
-
-
|
Na2O 0.400
|
AL2O3 0.300
|
SiO2 5.000
|
|
CaO
0.300
|
-
|
B2O3 1.000
|
|
MgO
0.250
|
-
|
-
|
|
ZnO
0.050
|
-
|
-
|
-
- 4) Eutectics
with boron compounds :
-
- The melting properties of
boron are due partly to the many possible eutectics
from the compounds present in the glazes. Here is a
table which summarizes the most known cases,
classified by ascending order of melting points
temperature :
-
-
|
Eutectic
Compounds
|
Formula
|
Melting Point
|
|
Boric Anhydride
|
B2O3
|
294 °C
|
|
Thallium
Metaborate
|
TlO2, B2O3-
|
350 °C
|
|
PbO/B2O3/SiO2
|
PbO, 0.238 B2O3,
0.780 SiO2
|
485 °C
|
|
Lead Oxide, Boric
Anhydride
|
2.303 PbO, B2O3
|
493 °C
|
|
Lead Oxide, Boric
Anhydride
|
2 PbO, B2O3
|
497 °C
|
|
Lead Oxide, Boric
Anhydride
|
5 PbO, 4 B2O3
|
548 °C
|
|
Lead Oxide, Boric
Anhydride
|
4 PbO, B2O3
|
565 °C
|
|
K2O, B2O3, SiO2
|
K2O, 2.11 B2O3, 2.85
SiO2
|
630 °C
|
|
Sodium Metaborate
and Lithium Metaborate
|
1.43 (Na2O-B2O3),
Li2O-B2O3
|
640 °C
|
|
Anhydrous
Borax
|
Na2O, 2B2O3
|
741 °C
|
|
Barium Oxide, Boric
Anhydride
|
BaO, 0.64 B2O3
|
750 °C
|
|
Lead Oxide, Boric
Anhydride
|
PbO, 2B2O3
|
768 °C
|
|
Na2O, B2O3, SiO2
|
Na2O, 1.29 B2O3,
0.78 SiO2
|
790 °C
|
|
Sodium Metaborate,
Sodium Metaphosphate
|
Na2O-B2O3,
Na2O-P2O5
|
800 °C
|
|
Lithium Metaborate,
Lithium Metasilicate
|
Li2SiO3, 4.66
(Li2O-B2O3)
|
802 °C
|
|
Sodium Metaborate,
Sodium Metasilicate
|
Na2SiO3, 1.52
(Na2O-B2O3)
|
815 °C
|
|
Sodium and Potassium
Metaborates
|
K2O-B2O3, 1.24
(Na2O-B2O3)
|
855 °C
|
|
Cadmium
Metaborate
|
CdO, B2O3
|
875 °C
|
|
Potassium Metaborate
and Potassium Metaphosphate
|
KBO2, KPO3
|
885 °C
|
|
Strontium Diborate
and Strontium Metaborate
|
SrO, 1.58 B2O3
|
890 °C
|
|
Strontium
Diborate
|
SrO, 2 B2O3
|
930 °C
|
|
Cuprous
Sesquiborate
|
3 Cu2O, 2 B2O3
|
950-1000 °C
|
|
Sodium
Metaborate
|
Na2O, B2O3
|
965 °C
|
|
Potassium
Metaborate
|
K2O, B2O3
|
968 °C
|
|
Cupric
Metaborate
|
CuO, B2O3
|
980 °C
|
|
Strontium,
Metaborate, Strontium Pyroborate
|
SrO, 0.71 B2O3
|
980 °C
|
|
Magnesium
Metaborate
|
MgO, B2O3
|
988 °C
|
|
Calcium Metaborate,
Calcium Diborate
|
2 CaO, 3B2O3
|
990 °C
|
|
Barium
Pyroborate
|
2 BaO, B2O3
|
1000 °C
|
|
Calcium
Diborate
|
CaO, 2B2O3
|
1025 °C
|
|
Barium Metaborate
|
BaO, B2O3
|
1050 °C
|
|
Calcium Metaborate
and Calcium Pyroborate
|
CaO, 0.83 B2O3
|
1060 °C
|
|
Calcium
Metaborate
|
CaO, B2O3
|
1095 °C
|
|
Strontium
Metaborate
|
SrO, B2O3
|
1100 °C
|
|
Strontium
Pyroborate
|
2 SrO, B2O3
|
1115 °C
|
|
Calcium
Pyroborate
|
2 CaO, B2O3
|
1215 °C
|
|
Magnesium
Pyroborate
|
2 MgO, B2O3
|
1340 °C
|
-
- Links
: (Boron compounds supplier) http://www.etimine.com/
-
-
Article written by : Smart.Conseil
/ Septembre 2002.
-
-
-
|
Toxicology : BORON and
Ceramics
|
-
-
- SOURCES :
-
- -Boric acid (BO3H3),
- -Sodium tetraborate, anhydrous or
Anhydrous Borax (Na2B4O7), these two materials are
used in the manufacture of boron frits.
-
- -
Sodium tetraborate, decahydrate or Borax or
Decahydrate Borax (Na2B4O7.10H2O),
- -Ulexite (NaCaB5O9.8H2O),
- -Colemanite (2CaO.3B2O3.5H2O),
- -Gerstley Borate (North America), see
our comprehensive report on this site :
- -Boron frits,
- -Lead-boro silicate.
-
- General information :
-
- The
natural forms include boric acid and the borates.
-
- Boric
Acid, Borates, Boron Oxide :
-
- Since
these products have similar metabolism and toxicity,
we will discuss them together
-
- I-
Boric Acid :
-
- Boric
acid (H3BO3, CAS # 10043-35-3) has a pH of 4 in a
saturated aqueous solution. It has antibacterial and
antifongic properties, hence it is used as a
colourless disinfectant for the skin and the mucous
membranes, ocular, oto-rhino-laryngologeal and
vaginal.
- European standards have set authorized
concentrations of boric acid at 0.5% for oral hygiene
products and at 5% for talcs and cosmetics.
- It is
used in the nuclear industry, for its capacity to
absorb neutrons, for control and emergency regulation
of reactions.
-
- II-Borates :
-
- Borates, among which sodium borate or
borax, are also used in :
- -the
glass industry, ceramics, enamels,
- -the
manufacture of cosmetics, paints, dyes,
- -the
treatment of leather and wood,
- as:
- -fertilizers,
- -weedkillers, insecticides
- -retardings of combustion
-
- III-Boron Oxide :
-
- Boron
oxide, B2O3 CAS# 1303-86-2, formed by the thermal
fusion of boric acid, is used in the glass industry.
-
- Toxicological properties
:
-
- I-
Absorption :
-
- A-Digestive absorption :
- Digestive absorption is fast and
almost complete; the blood peak is located at the
second hour.
-
- B-Cutaneous absorption :
- These
products are little absorbed by a healthy or slightly
scarified skin. Skin absorption by a seriously injured
or burned skin can be significant and be the source of
intoxication in the case of a local treatment
containing boron.
-
- C-Differences of preparation
:
- There
is a significant difference of absorption between the
hydrated forms (< 1%) and the gel forms (20%).
-
- II-Distribution :
-
- The
distribution in the body is ubiquitous; the
concentration in body fluids is identical to that of
the plasma.
- There
are however two exceptions: the bone, where it
concentrates (two to three times the plasmatic
levels), and the fat tissue where one finds only 20%
of the plasmatic levels. There is no active transfer
between the blood compartment and tissues.
-
- III-Bio-transformation :
-
- In
the body, borates are metabolized to boric acid which
remains unchanged.
-
- IV-Excretion :
-
- Whatever the route of entry, excretion
is mainly urinary (80 to 85% of the absorbed amount)
in the form of boric acid, and less in the form of
borates. Small amounts are found in the feces and
perspiration.
- Although not properly evaluated, its
half-life of elimination is less than 20 hours. In the
case of massive ingestion, elimination is biphasic,
50% in 12 hours and 50% in 1 to 3 weeks.
-
- V-Acute Intoxication :
-
- A-Oral Lethal Dose (LD) :
- In
man, the oral LD may be estimated in the following
manner :
- 1-Newborn= 1 to 3 g.
- 2-Child= 5g.
- 3-Adult= 15 to 20 g.
-
-
- B-Latency Period :
- whatever the route of intoxication, a
delay of a few hours precedes symptomatology.
-
- C-Clinical Findings :
- 1-Digestive disorders : nausea,
vomiting, abdominal pains.
- 2-Neurological disorders : headaches,
tremors, agitation, convulsions, hallucinations.
- 3-Severe intoxication : coma,
collapse, metabolic acidosis, cyanosis, fever and
respiratory depression.
- 4-Renal impairment : tubular necrosis
may occur (oliguria and proteinuria, possibly anuria).
- 5-Cutaneous disorders (after a few
days) : extensive desquamative dermatitis beginning
with erythema involving the palms of the hands, the
soles of the feet and the buttocks, with the
possibility of a secondary generalization (formation
of bubbles, massive exfoliation), similar to Ritter’s
syndrome (exfoliative dermatitis of the newborn).
Alopecia may be observed.
-
- Death
occurs due to infections, shock, neurological
complications, the autopsy showing renal tubular
necrosis, cerebral oedema, hepatitis and
gastro-enteritis.
-
- D-Laboratory Findings :
- The
intoxication is confirmed by measuring boron in blood,
which is detectable below 1µg/L. by many
techniques:
-
- 1-In
adults:
- a-toxic effects are observable from 15
to 20 mg/L. of blood boron,
- b-signs of severity are seen as low as
40 mg/L,
- c-the
presence of more than 40 mg/L. suggests a serious
intoxication,
- d-the
evolution may be fatal for concentrations equal to 500
mg/L.
-
- 2-In
newborns :
- a-toxic effects have been observed for
blood boron levels as low as 4 mg/L.
-
- E-Mortality :
- In
studies dating from the 50s, mortality is estimated at
more than 50%; it relates primarily to accidental
intoxications in children.
- As
from the 80s, in an American series, intoxications are
generally asymptomatic (88.3%), and never fatal. This
difference may be explained by a better way of dealing
with these intoxications.
-
- F-Treatment :
- Above
all, treatment is aimed at purifying (skin and mucous
membranes wash, gastric wash, hemodialysis, peritoneal
dialysis ), and symptomatic.
-
- G-Skin Irritation :
- 1-Borax: is a severe eye irritant.
- 2-Boron and borates: are not or only
slight skin irritants.
- 3-Boron oxide: causes slight
irritation of the skin and mucous membranes (skin
irritation, ocular irritation, nosebleed, dryness of
the mouth, the throat and the nose, pharyngeal pain,
sputum, cough), disappearing at the end of exposure
without pulmonary impairment, nor long-term effect.
-
-
- VI-Chronic Intoxication :
- In
man, the repeated inappropriate use of boric acid has
caused, particularly in children, chronic
intoxications characterized primarily by
cutaneo-mucous, hair and nails disorders.
-
- -dermatosis,
- -conjunctivitis,
- -red
coloured tongue,
- -cracks of the lips,
- -
loss of hair,
- -digestive disorders,
- -neurological disorders
-
- These
effects are close to those observed at the time of
acute intoxication and are related to boron
accumulation in the body. These disorders are usually
reversible at the cessation of its use; they are
enhanced by the presence of a pre-existing kidney
insufficiency.
- Workers exposed to dust of borates or
boron oxide present signs of rhinitis, conjunctivitis
or cough. In the long run, no pulmonary impairment has
been found.
- In
the case of chronic intoxication, blood boron levels
are frequently higher than 30 mg/L.
-
- Effects on reproduction
:
-
- A-Experimentally :
- Animal experimentation has revealed
disorders of reproduction related to boric acid and
borax exposure. These were testicular and fertility
effects.
- The
mechanism of this toxicity is not completely
elucidated. In the female rat, an increase in the
number of spontaneous abortions and a fall in the
number of litters were observed.
- A
study relating to development shows that boric acid
causes birth defects in three (3) species studied
(rat, rabbit, mouse).
-
- B-In Man :
- A
previous study carried out in Russia with exposure
levels varying from 20 to 83 mg/m3 at 50% of the
studied workstations i.e. 2 to 8 times the currently
allowed exposure limit, showed a reduction of sexual
activity and a deterioration of the quality of the
sperm
- In
the USA, these results were not confirmed in a study
of 542 workers whose average exposure was 19.7
mg/m3.
-
- As
far as birth defects in man are concerned, there does
not seem to be any case reported in the
literature.
-
- Carcinogenesis and Mutagenesis
:
-
- A-Experimentally :
- 1-Boric acid has not caused genetic
mutations nor chromosomal abnormalities in a series of
in vitro experiments on bacteria or eucaryotic cells.
- 2-In
the rat and in the mouse, no carcirogenic effect due
to boric acid has been found during a 2 year
experiment.
-
- B-In man :
- Epidemiologic studies have also been
negative.
-
- Exposure Limits :
-
- I-Gerstley Borate :
- VEMP
(Quebec) : 5 mg/m3
-
- II-Boron oxide :
- A-IDLH (Immediate danger to life and
health) 2,000 mg/m3
- B-VEMP : 10mg/m3
-
- III-Sodium tetraborate, anhydrous or
Anhydrous Borax (Na2B4O7) :
- VEMP
: 1 mg/m3
-
- IV-Sodium tetraborate, decahydrate or
Borax or Decahydrate Borax :
- VEMP
: 5 mg/m3
-
- Prevention :
-
- Laws
on Occupational Health and Safety aim at the
elimination of hazards at the source.
- When
engineering methods and modifications of working
methods are not able to sufficiently reduce the
exposure to these substances, the wearing of personal
protective gears may become necessary. These
protective gears must be in conformity with
regulation.
-
-
-
-
-
-
-
-
-
- References :
-
- 1-CSST-Quebec, Repertoire
Toxicologique, 2002
- 2-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R., last
edition.
- 3-Potterycrafts-MSDS, United Kingdom,
avril 2002.
- 4-Sax’s Dangerous Properties of
Industrial Materials, Lewis C., last
edition.
- 5-Bore et ses composés,
Encyclopédie Médico-Chirurgicale,
Toxicologie-Pathologie Professionnelle, M. Falcy, mai
2002.
- 6-Clay and Glazes for the Potter,
Rhodes Daniel, 1973.
-
-
-
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