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					                   Chapter 1
       Refractory and Insulating Materials




             Metallurgy College of Central
                   South University
            Tel: 13617311503;      8830761
            E-Mail: caogui@mail.csu.edu.cn
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中南大学冶金科学与工程学院 曹       Chapter 1 Refractory and Insulating Materials
              回转窑(Rotary kilns)
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中南大学冶金科学与工程学院 曹   Chapter 1 Refractory and Insulating Materials
 Contents of Chapter 1 Refractory and Insulating Materials
 1.1 Introduction
 1.2 Properties, constitutes and categories of refractory materials
 1.2.1 Categories of refractory materials
 1.2.2 Constitutes of refractory materials
 1.2.3 Properties of refractory materials
 1.3 Refractories production and properties
 1.3.1 Aluminosilicate refractories
 1.3.2 Silica refractory bricks
 1.3.3 Magnesite refractory bricks
 1.3.4 Miscellaneous carbonaceous refractory bricks
 1.3.5 Cements of refractories
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中南大学冶金科学与工程学院 曹                   Chapter 1 Refractory and Insulating Materials
1.4 Size of refractories
1.5 Water-cooling and hang slag protection
1.5.1 Water-cooling hang slag
1.5.2 Water jackets
1.5.3 Hot hang slag protection
1.6 Insulating Materials
1.6.1 Introduction
1.6.2 Insulating Brick Manufacture
1.6.3 Properties and Applications of Insulating Materials

References
Problems
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中南大学冶金科学与工程学院 曹                  Chapter 1 Refractory and Insulating Materials
1.1 Introduction
1. Definition of refractory materials: Refractoriness(℃) ≥1580℃,
inorganic nonmetallic materials, a reasonable thermal-shock
resistance, slag resistance, refractoriness-under-load and high hot
strength.
2. Application: Various furnaces and kilns, 60~70% refractory
materials consumed in metallurgical industry.
3. Examples: a 1513m3 blast furnace needed 3000t refractory
materials; a 210m3 reverberatory furnace needed 1500t refractory
materials; open-hearth: 45~60kg refractory materials per ton steel;
2~5kg refractory materials per ton crude copper.
4. Demands of refractory materials for metallurgy furnaces: ①
Refractoriness: 1000~1800℃; ② High-temperature strength:
refractoriness-under-load; ③ A high thermal-shock resistance; ④
slag resistance; ⑤ Thermal expansion allowance; ⑥ Size tolerance
requirement and occasionally maximum warpage.
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中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials
1.2 Properties, constitutes and categories of refractory materials
1.2.1 Categories of refractory materials
1. According to their chemical mineral constitutes, refractory
materials are commonly grouped into ① those containing mainly
aluminosilicates; ② those made predominately of silica; ③ those
made of magnesite, dolomite, or chrome ore, termed basic
refractories (because of their chemical behavior); and ④ a
miscellaneous category usually referred to as special refractories.
2. According to their refractoriness, refractory materials are
commonly grouped into ① general refractory materials:
refractoriness: 1580~1770℃; ② advanced refractory materials:
refractoriness: 1770~2000℃; ③ special refractory materials:
refractoriness: above 2000℃.
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中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
1.2.2 Constitutes of refractory materials
1. Chemical constitutes: main components and assistant components
included additives and impurities.
2. Example: Silica refractory bricks. They are made from crushed and
ground quartzite(≥93% SiO2) to which about 2% lime(CaO) has been
added to assist in bonding, both before and after firing. The quality of
silica refractory bricks is to a great extent determined by the amount
of Al2O3 impurity, even small amounts having deleterious effect on
refractories. High-grade silica brick contains less than 0.6% Al2O3,
and even the standard grade contains less than 1%. The outstanding
characteristic of silica is its ability to withstand high loads at elevated
temperatures, for example, as a sprung-arch roof 30 or 40 ft wide
over an open hearth. The hearth may be operated within 50 of the
melting point of silica.
3. Mineral constitutes: main crystallized phases and matrix.
4. Chrome refractory bricks are made from chrome ore, a complex
mineral containing oxides of chromium, iron, magnesium, aluminum,
and other oxides crystallized in the spinel structure. These crystals
are usually embedded in a less refractory matrix called gangue.
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中南大学冶金科学与工程学院 曹                  Chapter 1 Refractory and Insulating Materials
1.2.3 Properties of refractory materials

1. Physical properties of refractory materials
                           V 1 V 2 V 3
⑴ Porosity:             P               100%
                                V
                              V       V
⑵ Apparent porosity: Pa          2        3
                                               100%
                                      V




              Fig 1.1 Pore types in refractory products
              1-sealed pores 2-open pores 3-run-through pores
                                                                              8
中南大学冶金科学与工程学院 曹                   Chapter 1 Refractory and Insulating Materials
                                          G        G
⑶ Absorbing water percentage: Paw                       100%
                                              aw
                                               G

⑷ Permeability to air: The rate of flow of gas in milliliters per second
through one square centimeter of the material under a pressure
gradient of one centimeter head of water, per centimeter thickness.
It is related with run-through channel-type pores and gas pressure;
lower, better.
                   m                          3
⑸ Bulk density: ρ              kg m
                   V
                       m
            
⑹ Density: ρ                                           kg m         3

               V  (V1 V             2   V 3 )
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
2. Mechanical behavior of refractory materials
⑴ Compressive strength(N·cm-2):
   ① general refractory materials>1000~1500 N·cm-2;
   ② advanced refractory materials>2500~3000 N·cm-2.
⑵ Hot compressive strength(N·cm-2) is important for refractories, but
most materials become plastic and flow at elevated temperatures.
Therefore, the rate of flow at a given temperature under a given load
is a more important design criterion.
⑶ Abrasion resistance: Although wear in furnaces is more often due
to slag attack than abrasion there are locations such as reheating-
furnace hearths, the blast-furnace stack, and blast pipes, where high
abrasion resistance at relatively low temperatures.
⑷ Transverse breaking strength.
                                       σ
⑸ Modulus of rupture (E):         E                    N  cm      2
                                      ΔL/L                                 10
中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
                                 Transverse breaking strength
                                    1-白云石砖;2-高铝砖;
                                    3-叶蜡白云石砖;4-镁砖;
                                    5-硅砖;6-铬砖;
                                    7-熟料砖;8-不烧镁铬砖;
                                    9-直接结合镁铬砖;
                                    10-再结合镁铬砖




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中南大学冶金科学与工程学院 曹   Chapter 1 Refractory and Insulating Materials
3. Thermal properties of refractory materials
⑴ Thermal expansion (m): This property is of direct importance in
that adequate expansion allowance should always be made in furnace
structures, but it is equally important in that it shows up peculiarities
in expansion, e.g. the cristobalite change in a silica bricks, which may
have a marked effect on thermal-shock resistance.
                       L1  L 0                    1
                  β 
                   m                         C
                      L 1 (t t0 )
⑵ Thermal conductivity (λ) determines the amount of heat that will
flow through a furnace wall under given conditions, and a knowledge
of this property is essential to furnace design.
⑶ Specific heat(Cp): The specific heat of refractories is rarely
determined, mainly because for a given type of material it is relatively
constant (see Table 1.1).
                                                                            12
中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
         Table 1.1 Average specific heat (Cp)
            of refractory materials(kJ·kg-1·K-1)

 Temperature /℃      25~600    25~1000         25~1200           25~1400

      Clay
                     0.921       0.963           0.996             1.022
 refractory bricks
    Magnesite
                     0.883       0.942           0.971             1.000
 refractory bricks
      Silica
                     1.130       1.193           1.214               —
 refractory bricks

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中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials
4. Performance peculiarities of refractory materials
⑴ Refractoriness (℃): This property is determined according to the
softening temperature or the pyrometric cone equivalent (PCE), the
number of the standard pyrometric cone which deforms under heat
treatment in the same manner as the fireclay. Thus, the minimum
PCEs for low, intermediate, high, and superduty fireclays are 19, 29,
31/32, and 33, respectively.
⑵ Refractoriness-under-load: Although the subject of considerable
development and standardization, the RUL test is tending to be
replaced both with manufacturers and users by the hot modulus of
rupture test, which is considered to give results at least as relevant to
practice and with far less effort.
⑶ Slag resistance: The furnace designer and operator go to
considerable trouble to see that bricks do not fail due to such
avoidable causes as inadequate thermal-expansion allowance or
excessive rates of heating or cooling. Spalling still occurs, but is
usually a minor factor in furnace wear compared with slag attack.
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
       Refractoriness

                                   Refractoriness-under-load
                                                                    15
中南大学冶金科学与工程学院 曹         Chapter 1 Refractory and Insulating Materials
⑷ Thermal-shock resistance: It is the ability of a specimen to
withstand, without cracking, a difference in temperature between one
part and another. For example, if a red-hot brick in dropped into cold
water, it is likely to shatter since the outside cools and contracts while
the center is still hot. This cracking is often referred to as thermal
spalling, the term spalling meaning any cracking off of large pieces
of brick. Whether or not a given specimen cracks under heat shock
depends not only on the material of which it is made, but also on its
size and shape and on the test conditions, for example, whether it is
dropped into water or into still air at the same temperature.
⑸ Permanent dimensional change on reheating (length or volume):
Even if a brick is capable of withstanding normal loading at
operating temperatures it can cause serious trouble due permanent
growth or shrinkage.
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
1.3 Refractories production and properties
1.3.1 Aluminosilicate refractories
1. Main components: SiO2, Al2O3
2. Assistant components: Fe2O3, K2O, Na2O, TiO2, CaO.
3. According to the total Al2O3 content, high alumina bricks, clay
bricks and semisilica bricks can be produced from aluminosilicate
refractories.




  Fig 1.2 Phase diagram for
   the system Al2O3—SiO2

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中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
1.3.2 Silica refractory bricks
1. Main components: SiO2≥93%.
2. Assistant components: 2% CaO, 0.5~1% Al2O3, Fe2O3, TiO2.




                        Fig 1.3 SiO2 anamorphosis
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中南大学冶金科学与工程学院 曹                  Chapter 1 Refractory and Insulating Materials
                  Table 1.2 SiO2 anamorphosis

     Crystal       Anamorphosis        Volume change (%) Melting point(℃)
                     β- Quartz
     Quartz                                   ±0.82                   1600
                     α- Quartz
                   β- Cristobalite
   Cristobalite                                ±2.8                   1728
                   α- Cristobalite
                    γ- Tridymite
   Tridymite                                  ±0.28
                    β- Tridymite                                      1670
                                              ±0.20
                    α- Tridymite




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中南大学冶金科学与工程学院 曹                    Chapter 1 Refractory and Insulating Materials
      Table 1.3 Properties of silica refractory bricks


                Index                   grade 1        grade 2
          SiO2 content (%)               ≥94.5          ≥93
          Refractoriness(℃)              ≥1710         ≥1690
     Refractoriness-under-load(℃)        ≥1640         ≥1620
        Apparent porosity(%)              ≤23            ≤26
    Thermal-shock resistance, times      1~2            1~2
            Volume change               growth         growth



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中南大学冶金科学与工程学院 曹           Chapter 1 Refractory and Insulating Materials
1.3.3 Magnesite refractory bricks
1. Main components: MgO≥80%.
2. Magnesite refractories are basic refractories, which is so named
because magnesium carbonate mineral was for many years the sole
raw material. Since world war Ⅱ sea water has become a significant
source of magnesium oxide refractory, and such material is often
called sea-water magnesite. In any case, the raw material is calcined
to form a material largely magnesium oxide, MgO; about 5% iron
oxide is usually added before calcining.
3. Properties of general magnesite refractory bricks:
  ① refractoriness: >2000℃;
  ② refractoriness-under-load: 1500~1550℃, not for roof or arch;
  ③ thermal-shock resistance(water cool): 2~3 times;
  ④ Thermal expansion: obvious;
  ⑤ slag resistance: basic;
  ⑥ thermal conductivity: excellent.
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中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials
1.3.4 Miscellaneous carbonaceous refractory bricks
1. Carbon refractory bricks: Carbon, generally in the form of graphite,
is used for such equipment as crucibles and as stopper nozzles in
ladles for steel casting. A potentially very large use of carbon is in
blocks for construction of blastfurnace hearths.
2. Graphite refractory bricks: Graphite has very good thermal-shock
resistance and moderate electrical conductivity, does not melt but
rather sublimes as a significant rate only at temperatures well above
3000℃, is quite inert chemically, and is wet by very few molten
materials. Its main disadvantage, common to all nonoxide materials
at high temperatures, is that it oxidizes; since the products are all
gaseous, they offer no protection against further oxidation.
3. Silicon carbide refractory bricks: SiC is used for many refractory
shapes, its outstanding properties being good thermal and electrical
conductivity (it is used to make electric heating elements for
furnaces), good heatshock resistance, strength at high temperatures,
and abrasion resistance.
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中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
      Table 1.4 Properties of the carbonaceous refractory bricks

                                           Graphite clay
     Name            Carbon bricks                           Silicon carbide bricks
                                              bricks
                   Metallurgical coke,                            Artificial SiC
                                          Graphite, clay;
 Raw materials      petroleum coke,                           bond(metal, cermet);
                                           C:30~90%
                    anthracite, pitch                             SiC:30~90%
 Refractoriness        High;                  About
                                                                   ≮1770℃
      (℃)          3500℃,sublime              2000℃
 Slag resistance      Excellent                 Good                  Good
 Thermal-shock
                          Good                Better                  Good
   resistance
                                           Electrode,c
 Applications      Furnace lining                              Stopper, retort
                                             rucible

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中南大学冶金科学与工程学院 曹                    Chapter 1 Refractory and Insulating Materials
1.3.5 Cements of refractories
     Cements are an intimate mixture of a metal and a nonmetal, for
example, Al2O3 and chromium. Although the nonmetal may be an
oxide, it is more commonly a carbide or nitride (as in cemented
tungsten carbide).
      In certain positions, e.g. open-hearth-furnace roofs, silica bricks
are laid dry. Where cement is used, e.g. in back and front walls, the
composition must be such as to withstand the operating temperature.
Thus for use in open-hearth furnaces above stage level its
refractoriness should be comparable with that of the fired bricks. This
is best achieved by fine grinding of a good-quality quartzite or
ganister, and the addition of a minimum of clay to give plasticity,
together, where necessary, with a small amount of organic bond such
as sulphite lye. The use of higher, though still quite small, amounts of
clay can lead to failure of a vertical wall due to softening of the
jointing material at the hot face.
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
         Table 1.5 General cements of refractories

         Bricks       Cements      Cements components          Remark
                                       Clay: 100%;
          Clay          Clay         400~600L(water)/
                                       m3(clay dried)
                                       Silica: 100%;
         Silica         Silica       400~600L(water)/
                                      m3(silica dried)
                                 Magnesite: 100%;
       Magnesite      Magnesite        halogen         wet build
                                water(d=1.25):suitable
                               Magnesite dried: 100%;
    Aluminomagnesite Magnesite                        dry build
                               Fe2O3 powder: suitable


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中南大学冶金科学与工程学院 曹              Chapter 1 Refractory and Insulating Materials
1.4 Size of refractories
   Size of currency refractory bricks(GB2992-82).
   Example: brick number: Ts-65, symbol: S3075k,
b×a/a1×c=300×75/55×225, cuniform brick, high×superior
width/below width×length: 300mm, 75mm, 55mm and 225mm.
1.5 Water-cooling and hang slag protection
1.5.1 Water-cooling hang slag
    The lower of the temperature of the contact interface between
refractory lining and fused slag in the high temperature metallurgical
furnaces, the slower of the losing of refractory bricks.
    While the exterior of refractory lining is cooled and kept
invariableness, the temperature of the fused slag is lowered. When
the temperature of the fused slag is lower than the softening
temperature, a compact slag layer is formed on the refractory lining
to prevent the slag attack further.
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
1.5.2 Water jackets
     Water jackets or water tanks are absolutely necessarily
equipment for water-cooling hang slag in the high temperature
metallurgical furnaces. Water jackets can be made from armor plate
or copper.
1.5.3 Hot hang slag protection
      Hot hang slag protection is artificially performed that fused slag
layer is formed on the refractory lining of the high temperature
metallurgical furnaces to prevent the slag attack.
     There are two kinds of the hot hang slag protection:
     ① hang slag protection;
     ② spatter slag protection.
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中南大学冶金科学与工程学院 曹                  Chapter 1 Refractory and Insulating Materials
1.6 Insulating Materials

1.6.1 Introduction

1. Principle of insulating materials

   Insulating Materials derive their low thermal conductivity from
their pores, while their heat capacity is determined almost entirely by
the solid component. The insulating effect is principally the result of
achieving a series of air spaces between an alternate series of solid
boundaries. Other things being equal, the more pores present, and the
less solid, the lower will be the conductivity. Such correlations as
were noted in other chapters between porosity and conductivity are
therefore to be expected.
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中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
2. Classification of insulating materials

  Insulating bricks are often described simply as low-, medium-, or
high-temperature.

⑴ low-temperature insulating bricks: operating temperature<900℃,
e.g. , diatomite bricks, asbestos bricks.

⑵ medium-temperature insulating bricks: operating temperature
900~1200℃, e.g. , vermiculite bricks, lightweight clay bricks.

⑶ high-temperature insulating bricks: operating temperature >
1200℃, e.g. , lightweight high alumina bricks, ceramic-fibre.
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中南大学冶金科学与工程学院 曹                  Chapter 1 Refractory and Insulating Materials
1.6.2 Insulating Brick Manufacture
   The methods employed in producing insulating brick are so
extensive that only a brief summary of the position can be made.
1. Diatomite Insulating Bricks
   The manufacturing methods used as follows:
① sawing into blocks directly from the face of the deposit, to give a
‘natural’ grade
② heating natural-grade blocks to about 950℃ to make them suitable
for use up to 800℃
③ moulding, light pressure, or extrusion, of wet diatomaceous earth
with or without clay additions followed by firing to suitable
temperature
④ addition of combustibles, e.g. ground cork, charcoal, or sawdust,
to a diatomaceous earth batch
⑤ bonding of precalcined diatomite granules with plastic clay
followed by firing to a relatively high temperature.
                                                                          30
中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials
2. Lightweight Clay Insulating Bricks
   The production of insulating bricks from materials of a fireclay
type is carried out by a number of different methods. These have
been summarized as follows:
① incorporation of natural or synthetic lightweight materials, such as
diatomite, expanded vermiculite, or raw kyanite
② inclusion of materials which are later removed by combustion or
sublimation, more usually the former
③ production of a cellular structure by mechanical beating using a
frothing agent
④ formation of gas bubbles in a semifluid medium by chemical
reaction
⑤ miscellaneous methods.
                                                                          31
中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials
3. Lightweight High Alumina Insulating Bricks
   It has been demonstrated both by research workers and by
production plants that excellent insulating bricks can be
manufactured from a sillimanite-type base. Thus Salmang reported
the production of bricks varying in porosity from 45% to 63%, while
Clews reported results on sillimanite bricks made by adding
anthracite, or paper pulp, as combustibles, or using aluminum and
acid to get froth. A high firing temperature, of the order of 1400℃, is
required to get the best properties in the product. As will be seen
from the data given under ‘Properties’, insulating materials of even
higher alumina content are now available, culminating in bubble
alumina having a maximum operating temperature of 1815℃. The
conductivity of such bricks, however, is several times that of low-
temperature insulation, due in part to a higher bulk density, and
possibly large pore size, but also to the conductivity of alumina being
high compared with that of fireclay.
                                                                           32
中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
1.6.3 Properties and Applications of Insulating Materials
1. Properties of insulating materials
⑴ Porosity(%), >50%
⑵ Bulk density(kg/m3): 500~1000kg/m3
⑶ Thermal conductivity: small
⑷ Cold-crushing strength: low.
2. Applications of Insulating Materials
⑴ Insulation should increase production by avoiding loss of heat
⑵ Insulation should save of furnace fuel economies(40~60%)
⑶ Insulation should improve conditions for operators
⑷ Insulation should make furnace or kiln lighter.

                                                                            33
中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
       Table 1.6 Properties of some insulating bricks

    Properties      Diatomite Bricks Lightweight Clay Lightweight High
                                         Bricks        Alumina Bricks
   Refractoriness      <1200               <1670                <1750
       (℃)
   Bulk density          >0.5              >1.0                    0.8
     (g/ml)
    Modulus of          <35                <30                     <30
  rupture (N/cm2)
   Maximum safe          ≤900              ≤1300                 ≤1350
  temperature (℃)



                                                                            34
中南大学冶金科学与工程学院 曹                 Chapter 1 Refractory and Insulating Materials
                     References
[1] Duffy, J. I. Rothenberg, G. B. Refractory materials :developments.

   Park Ridge; New York; p.1~366. (81.55088/D858 )
[2] Chesters J. H. Refractories: production and properties. Carriton
    House Terrace, London, p.1~553. (81.55/C525)

[3] 曹刿. Pyrometallurgy Equipment, 火法冶金设备(英文版).
   中南大学教材科, P1~90. 2005.
[4] 唐谟堂, 何静. 火法冶金设备. 中南大学出版社, P1~339. 2003



                                                                           35
中南大学冶金科学与工程学院 曹                Chapter 1 Refractory and Insulating Materials
                         Problems

 8.1 Reverberatory furnace for producing matte with 100000

 ~150000 ton per year will be constructed. Select the types of

 refractory materials and calculate the amounts of the refractory

 materials (t/tmatte).


 8.2 State the main properties of refractory materials and how to

 produce insulating Materials.

                                                                          36
中南大学冶金科学与工程学院 曹               Chapter 1 Refractory and Insulating Materials    End

				
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