Fabrication of micro gear wheels by micropowder injection molding

The micropowder injection molding technology was investigated to fabricate the microsized gear wheels on a conventional injection molding machine. The feedstock comprised of carbonyl ferrum powder and a wax-based thermoplastic binder. Microinjection molding was fulfilled at about 423 K under 100 MPa. The heating system was applied to the die to improve the fluidity of the feedstock and subsequently the cooling system was used to enhance the strength of the green compacts after injection by decreasing the temperature of the die. The gear wheels were realized successfully with their addendum circle diameter ranging from 800 to 200 um and with the center hole as small as 60 um.

Influence of α-Al_2O_3 Micropowder Addition on Properties of Corundum Dry Ramming Mix

In order to improve the service life of corundum lin- ing.for induction Jitrnace, corundum dry ramming mix was prepared using brown corundum, fu.sed magnesia, and α-Al2O3 micropowder as main starting materials, mul the it!fluence of α-Al2O3 micropowder additions （0, 1% , 2%, and 3%, in mass） on properties of corundum dry ramming re.ix was investigated. The results show that after heat treating at 1 600 ~C , with the in-crease of α-Al2O3 addition, the permanent change in di- mensions on heating of the specimens decreases firstly and then increases, bulk density increases, apparent po- rosity decreases, and the crushing strength declines first- Iv and then enhances; when the addition of α-Al2O3 is 2 mass% , the termanent change in dimensions on heating of the specimens i.s relatively small and the crushing .strength decrease.s to 22.8 MPa. The XRD attd SEM reults show that after .firing at 1 600 for 3 h sin, all granular magnesium aluminate spinel form. and is welldistributed, which enhances the density.

Effects of Four Kinds of Alumina Micropowder on Properties of Al_(2)O_(3)-C Refractories

In order to further improve the strength and the thermal shock resistance of Al_(2)O_(3)-C materials for steel ladle slide gates,the effects of four kinds of alumina micropowders(unimodal activated alumina micropowder 07RAL,unimodal activated alumina micropowder 15RA,bimodal activated alumina micropowder 22RABL,and calcined alumina micropowder 40CA)on the density,the strength and the thermal shock resistance of Al_(2)O_(3)-C materials were studied.The results show that the density,the strength and the thermal shock resistance of Al_(2)O_(3)-C materials can be improved with the introduction of activated alumina micropowders.Among them,the specimen with bimodal activated alumina micropowder shows the best comprehensive performance,especially the hot modulus of rupture.Its actual application results in steel mills show that the average service life of the Al_(2)O_(3)-C slide plates prolongs,and the problems of cast hole reaming,plate oxidation,roughening and cracking during the use of slide plates are obviously improved.

Effect of SiO2 Micropowder Addition on Properties of Alumina-magnesia Based Wet Gunning Mix for Working Layer

The magnesia - alumina based wet gunning mix was prepared using tabular corundum aggregates,fused mag- nesia aggregates, tabular corundum micropowder, silica mieropowder and pure calcium ahuninate cement as the main starting materials. Effects of silica micropowder ad- ditions （0, 0. 2% , 0. 5% , 1.0% , 1.5% , 2. 0% , and 2.5%, by mass, the same hewinafier） on properties oJ the gunning mix were researched. The results show that when ttze silica micropowder addition is i. 0% -2. 0% , the gunning mix has good .flou,ability and pumpability. Adding 2.5% silica micropowder, the nepheline forms at 1 600 ℃, which will reduce the high. temperature proper- ties of ntagnesia -ahtmina wet gunning mix. The intro- duction qf silica micropowder has obvious effects on cold mechanical properties of the gunning mix. For the speci- tnens dried at 110 ℃ , the strength increases slightly with the silica micropowder addition increasing. For the specimens heat-treated at 1 600 ℃ for 3 h, the strength in- creases nutrkedlv with the silica micropowder addition in- creasing. When keeping the water addition and particle size di, stribution constant, the residual linear expansion rate qf the specimen with 1.5% of silica micropowder is the lowest, ltot modulus tf rupture at 1 450 ℃ .for 0. 5 h oJ the specimens decreases gradually with the increase of silica fame addition. A small amount of silica micropow- der is beneficial for the slag penetration resistance.

Rheological and Sintering Properties of Two Kinds of Corundum-spinel Micropowders

For the proper use of micropowders in castables,slurries and fired samples were prepared with two kinds of corundumspinel micropowders(D and G).The effects of the solid content and disperser WSM-R1 on the rheological properties of the slurries were studied.The sintering properties and the slag corrosion resistance of the fired samples were also researched.The results show that:the slurries all show pseudoplastic rheological characteristics.With the same solid content,the slurry with micropowder G has higher initial viscosity than that with micropowder D.Disperser WSM-R1 significantly reduces the initial viscosity of the two slurries and plays a more obvious dispersing effect on the slurry with micropowder G.The fired sample with micropowder G has higher bulk density,lower apparent porosity and better corrosion resistance than that with micropowder D.

Coating metals on micropowders by magnetron sputtering

Magnetron sputtering was used to coat various metals on micropowder surfaces. By using this method, the fine particles are better dispersed and can therefore be coated more homogeneously. The micro-powders used include cenospheres from fly ash of coal-burning electric power plants （diameter 40-200 μm and particle density 0.7 ± 0.1 g/cm^3）, as well as carborundum particles of different sizes. Aluminum, silver, copper, cobalt and nickel were used as the coating metals. Tests showed that the coated metal film was compact adhering tightly on the base powders, and the coated powders possess adequate flow properties.

PERFORMANCE OF PULVERIZED SLAG SUBSTITUTED CEMENT

The Portland cement is equivalently substituted by slag micropowders with various specific areas. The workability, activity and acid-corrosion resistance of the slag-substituted cements are investigated, the activation of gypsum is discussed also the porosity and pore distribution of mortars of the slag micropowders cement are determined by mercury intrusion porosimetry.

Influencing Factors of Properties of Castables for Hot Blast Stove Pipes

In order to prolong the service life of castables for hot blast stove pipes,effects of SiO2 micropowder addition and aggregate kind on properties of castables for hot blast stove pipes,and properties of silica sol bonded castables were researched using homogenized bauxite,andalusite particles,andalusite fines,white fused corundum fines,α-Al2O3 micropowder,pure calcium aluminate cement,SiO2 micropowder,and silica sol as starting materials. The results show that：（1） as SiO2 micropowder addition increases,the shrinkage rate of fired specimens increases; BD increases firstly,reaches the highest at 4 mass%,and then decreases; CMOR and CCS of all specimens increase gradually; so the appropriate SiO2 micropowder addition is 4 mass%;（2） the specimens with bauxite aggregate have better CCS and volume stability,but specimens with andalusite aggregate have better thermal shock resistance;（ 3） for castables for hot blast stoves using silica sol as binder,the addition of pure calcium aluminate cement can decrease the linear change rate after treatment at 1 400℃ and can slightly enhance CCS and CMOR,but has very little influence on AP and BD; and the introduction of citric acid worsens the thermal shock resistance of specimens.

THE PREPARATION OF HIGH－PURITY，ULTRAFINE AND MONODISPERSED TITANIUM DIOXIDE POWDER FROM TITANIUM TETRACHLORIDE BY HYDROLYSIS OF TITANIUM ALKOXIDES

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