TW202000344A - Metal powder, production method therefor, and sintering temperature prediction method - Google Patents

Abstract

One of the problems addressed by the present invention is to provide a metal powder that comprises metal particles in which the concentration and distribution of sulfur are controlled, and a production method therefor. The provided method for producing the metal powder comprises generating a metal chloride gas by chlorinating a metal with chlorine, and generating metal particles by reducing a gaseous metal chloride in the presence of a gas containing sulfur. The reduction is done such that the bulk concentration of sulfur in the metal particles is between 0.01 wt% and 1.0 wt%, inclusive, and such that the local concentration of sulfur at a position 4 nm from the surface of the metal particles is at least 2 at%. The bulk concentration and local concentration are estimated by using an inductively coupled plasma atomic emission spectrometer and an energy-dispersive X-ray spectroscopic analyzer provided on a scanning transmission electron microscope, respectively.

Description

Metal powder and its manufacturing method, as well as sintering temperature prediction method

One of the embodiments of the present invention relates to metal powder and its manufacturing method. Or, one of the embodiments of the present invention relates to a method of quality control of metal powder, a method of estimating characteristics of metal powder, or a method of predicting sintering temperature.

Aggregates containing fine metal particles (hereinafter referred to as metal powders) have been used in various fields, and metal powders of metals such as copper, nickel, and silver that exhibit high conductivity have been widely used as, for example, stacked ceramic capacitors (MLCC) The original materials of electronic components such as internal electrodes. MLCC already has a stack of ceramic layers containing dielectric materials and internal electrodes containing metals as the basic structure. The stack is formed by applying the dispersion liquid containing the dielectric material and the dispersion liquid containing the metal powder alternately and then heating, and sintering the dielectric material and the metal powder. For example, Patent Document 1 or 2 has disclosed a method for controlling the sintering characteristics of metal powder during heating.

"Patent Literature" "Patent Document 1": Japanese Patent Publication No. H11-80816 "Patent Document 2": Japanese Patent Publication No. 2014-189820

One of the embodiments of the present invention, one of the problems is to provide a metal powder containing metal particles whose concentration or distribution of sulfur is controlled and a method of manufacturing the same. Or, one of the embodiments of the present invention, one of the problems is to provide a metal powder with a high sintering start temperature and a manufacturing method thereof. Or, one of the problems of one of the embodiments of the present invention is to provide a metal powder with a small variation in sintering start temperature and a method for manufacturing the same. Alternatively, one of the problems of one of the embodiments of the present invention is to provide a method for quality control of metal powder, a method for estimating characteristics of metal powder, or a method for predicting sintering temperature.

One of the embodiments related to the present invention is metal powder. The metal powder contains: metal and metal particles containing sulfur. The total concentration of sulfur in the metal particles is 0.01% by weight or more and 1.0% by weight or less, and the local concentration of sulfur in the metal particles at a position of 4 nm from the surface is 2% by atom or more. The total concentration and the local concentration are estimated by an energy-dispersive X-ray spectrometer equipped with an inductively coupled plasma luminescence spectroscopic analysis device and a scanning transmission electron microscope, respectively.

One of the embodiments related to the present invention is a method of manufacturing metal powder. This method includes generating a gas of metal chloride by chlorination of a metal through chlorine, and generating metal particles by reducing metal chloride, which is a gas, in the presence of a gas containing sulfur. The reduction is performed in such a manner that the total concentration of sulfur of the metal particles becomes 0.01% by weight or more and 1.0% by weight or less, and the local concentration of sulfur of the metal particles at a position of 4 nm from the surface becomes 2% by atom or more. The total concentration and the local concentration are estimated by an energy-dispersive X-ray spectrometer equipped with an inductively coupled plasma luminescence spectroscopic analysis device and a scanning transmission electron microscope, respectively.

One of the embodiments related to the present invention is a method for predicting the sintering temperature of metal powder. This method involves measuring the local concentration of sulfur in the metal particles selected from the metal powder at 4 nm from the surface. The local concentration of sulfur is measured using a scanning transmission electron microscope equipped with an energy-dispersive X-ray spectrometer.

Hereinafter, various embodiments of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in various forms without departing from the gist thereof, and the interpreter is not limited by the description of the implementation forms of the following examples.

In order to make the description more clear, the drawings are compared with the actual state, although the width, thickness, shape, etc. of each part are schematically indicated, but in the end they are only an example, not to limit the interpreter of this disclosure. In this specification and the drawings, elements that have the same functions as those already explained about the drawings that have already appeared may be marked with the same symbols, and redundant descriptions may be omitted.

<First Embodiment>

In this embodiment, the structure and characteristics of the metal powder, which is one of the embodiments related to the present invention, are described.

1. Structure

An aggregate of multiple metal particles in a metal powder system. The metal particles include metal and sulfur. The metal system is selected from nickel, copper, silver, etc., typically nickel. The number average particle size of the metal powder may be 50 nm or more and 400 nm or less, 100 nm or more and 300 nm or less, or 100 nm or more and 250 nm or less. In other words, the average value of the particle diameters of a plurality of (eg, 600) metal particles selected from the metal powder must fall within the above range as the number average particle diameter of the metal powder. As the above-mentioned number average particle size, for example, the metal particles contained in the metal powder can be observed through a scanning electron microscope, and the particle size of a plurality of particles (for example, 600) can be measured, and the average value can be used. The particle size is the diameter of the smallest circle of inscribed particles.

The metal powder contains sulfur. Specifically, the total concentration of sulfur in the metal powder is 0.01% by weight or more and 1.0% by weight or less, or higher than 0.01% by weight and 0.6% by weight or less, or 0.15% by weight or more and 0.6% by weight or less, or 0.16% by weight % Or more and less than 0.6% by weight. In other words, the average value of the total concentration of sulfur in a plurality of metal particles (for example, the number corresponding to 0.5 g) of metal powder falls within the above-mentioned range. The so-called total concentration of sulfur here refers to the proportion of the weight of sulfur in the weight of metal particles. The total concentration of sulfur of one metal particle selected from the metal powder, or the average of the total concentration of sulfur of a plurality of metal particles, is calculated as the total concentration of metal powder.

The total concentration of sulfur can be measured by inductively coupled plasma luminescence spectrometry. For example, it can be measured using an inductively coupled plasma luminescence spectrometer (SPS 3100) manufactured by SII NanoTechnology Co., Ltd. To exemplify a specific measurement method, first dissolve the metal powder with an acid, and then perform ICP emission spectroscopic analysis at a measurement wavelength of 182.036 nm to obtain the total concentration of sulfur.

The metal particles contain sulfur not only near the surface, but also relatively away from the surface toward the inside of the particles. Specifically, although the concentration of sulfur decreases from the surface of the metal particles as it approaches the inside, the concentration of sulfur at the position of 4 nm from the surface (hereinafter, the concentration of sulfur at the specific position of the metal particles is referred to as a local concentration) It is 2 atomic% or more. In addition, the concentration of sulfur at a position of 4 nm from the surface may be 4 atomic% or less. The average value of the local concentration of sulfur in a plurality of (for example, 10) metal particles selected from the metal powder at the above-mentioned position falls within the above-mentioned range.

In addition, a position having a local concentration of one-half of the local concentration of sulfur on the surface of the metal particles (hereinafter referred to as halved depth) may exist within a range of 2 nm or more and 4 nm or less from the surface. That is, the average value of the halved depth of a plurality of (eg, 10) metal particles selected from the metal powder must fall within the range already described above.

The local concentration of sulfur described above can be estimated by, for example, an energy dispersive X-ray spectrometer (STEM-EDS: Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscope) provided in a scanning transmission electron microscope . To exemplify a specific measurement method, first disperse the metal powder in the resin and cure the resin. After that, a cross-section polisher (CP) was used to expose the cross-section, and a focused ion beam (FIB) was used to produce a thin-film sample that was sampled by a plane. The thickness of the sample is about 100 nm, whereby the metal particles can be formed into a thin film with this thickness. After that, the obtained thin film is subjected to EDS measurement on a straight line passing through the center of the metal particles, thereby obtaining a local concentration. As conditions for EDS measurement, for example, conditions of acceleration voltage 200 kV, probe diameter 1 nm, pitch width 3 nm, and measurement time per point of 15 seconds can be selected.

2. Features

The metal powder containing metal particles has a high overall concentration of sulfur, and the widespread distribution of sulfur in the surface layer of the metal particles, and has a high sintering start temperature, such as in the range of 600 ℃ or more . In addition, the sintering start temperature may be 700°C or lower. Based on the above characteristics, the local concentration of sulfur in the surface layer portion of the metal particles is measured. If the local concentration satisfies the conditions described above, the metal powder for the aggregate of metal particles can be judged to have high sintering Starting temperature. Therefore, with this embodiment, an effective method for estimating the characteristics of the metal powder can be provided.

As shown in the examples, the widespread distribution of sulfur and the high overall concentration are related to the high sintering start temperature of the metal powder, which is implied. In addition, if the total concentration of sulfur is the same, it is advantageous from the viewpoint of wide distribution of sulfur (the presence of sulfur in the surface layer to the depth) and improvement of the sintering start temperature. If this is used, the sintering start temperature of the metal powder can be estimated or estimated by measuring the distribution or overall concentration of sulfur in the surface layer. For example, by STEM-EDS analysis of any metal particles selected from metal powders, it can be estimated that the local concentration of sulfur in the metal particles at a position of 4 nm from the surface is 2 atomic% or more. The sintering temperature of the metal powder containing the metal particles is above 600°C. In other words, with this embodiment, even if the metal powder is not sintered, the sintering behavior of the metal powder can be estimated by measuring the sulfur concentration of the surface layer, and an effective method for managing the quality of the metal powder can be provided .

As described above, in the case of using metal powder as a raw material for the internal electrode of MLCC, for example, the dispersion liquid containing the dielectric substance and the dispersion liquid containing the metal powder are alternately coated and then fired. In the dispersion liquid containing the dielectric substance, it contains the oxide powder of Ba or Ti series or the polymer material, solvent, dispersant, etc. functioning as the binder. In the dispersion liquid containing the metal powder, it is not only the metal powder Also contains binders or solvents, dispersants, etc. During firing, these binders, solvents, and dispersants will evaporate or decompose, and at the same time, oxide powder or metal powder will sinter to give the dielectric film and internal electrodes, respectively. Generally, the sintering starting temperature of the dielectric is higher than the sintering starting temperature of the metal powder, so the sintering of the metal powder will start first during firing. As a result, a gap is generated between the dielectric and the internal electrode during firing, and peeling may occur between the internal electrode and the dielectric film due to the gap, which may cause a decrease in the characteristics or yield of the MLCC.

On the other hand, the metal powder related to the present embodiment exhibits a high sintering start temperature, so sintering will start at a temperature closer to the sintering start temperature of oxide powder and the like. As a result, high adhesion can be ensured between the internal electrode and the dielectric during firing, and peeling can be suppressed. Therefore, the metal powder can be used as a raw material for providing various electronic components with excellent characteristics.

As described above, according to the present embodiment, the sintering behavior of the metal powder can be estimated even without sintering. Therefore, it is possible to provide a quality control method for manufacturing metal powder with high reliability as an electrode material for MLCC.

<Second Embodiment>

In this embodiment, an example of a method for manufacturing metal powder will be described.

The metal powder system is manufactured using the gas phase method. That is, it is produced by reducing "steam of metal chloride obtained by chlorinating metal (hereinafter also referred to as chloride)" or "steam obtained by heating metal chloride" in the presence of sulfur-containing gas. . However, since high-purity chloride vapor can be obtained and the supply amount of chloride vapor can be stabilized, it is preferable to generate chloride vapor by chlorination of metal. The device (chlorination furnace) for chlorinating the metal may be a well-known one, so the description is omitted.

FIG. 1 is a schematic cross-sectional view of a reduction device 110 which is a device for reducing chloride. The reduction device 110 has a function of guiding sulfur into metal particles while reducing chloride to produce metal powder. The reduction device 110 includes a reduction furnace 112 and a heater 114 for heating the reduction furnace 112 as a basic structure. The first conveying pipe 116 is connected to the reduction furnace 112, and the gas of metal chloride can be introduced into the reduction furnace 112 through the intermediate. The reduction furnace 112 is further provided with a first gas introduction tube 118 for supplying hydrogen, hydrazine, ammonia, methane or the like as a reducing gas. A reducing gas supply source (not shown) is connected to the first gas introduction pipe 118. The valve 120 is installed in the first gas introduction pipe 118, whereby the supply amount of the reducing gas can be controlled.

The first conveying pipe 116 is provided with a second gas introduction pipe 122 for supplying sulfur-containing gas. The second gas introduction pipe 122 is mediated by a valve 124 and a sulfur-containing gas supply source (not shown) is connected, and the supply amount can be adjusted by the valve 124. With this configuration, the reducing gas can be brought into contact with the mixed gas of the chloride gas and the sulfur-containing gas. The first gas introduction tube 118 and the second gas introduction tube 122 may be further connected to an inert gas (inert gas) supply source, whereby the inert gas as the carrier gas can be mixed to supply the reducing gas or the sulfur-containing gas to the reduction炉112. With this configuration, the mixed gas of the chloride gas and the sulfur-containing gas can be supplied to the reduction furnace 112. Although not shown, the second gas introduction pipe 122 may be connected to the reduction furnace 112, and the chloride gas and the sulfur-containing gas may be separately supplied to the reduction furnace 112 instead of being connected to the first delivery pipe 116.

In the reduction furnace 112 heated by the heater 114, the chloride is reduced by the reducing gas, thereby generating metal particles, and introducing sulfur derived from the sulfur-containing gas to the metal particles. In addition, the chloride gas is preferably introduced by a producer of a chlorination furnace, which is not shown in the figure, instead of being separated separately. By constructing this type, chlorination and reduction can be carried out continuously, and metal powder can be efficiently produced.

The reduction furnace 112 is further provided with a third gas introduction pipe 126 useful for supplying cooling gas to the reduction furnace 112. The third gas introduction tube 126 is preferably provided at a position away from the first delivery tube 116. For example, when the first conveying pipe 116 is provided above the reduction furnace 112, the third gas introduction pipe 126 is provided below the reduction furnace 112. As the cooling gas, an inert gas such as nitrogen or argon can be used, and a supply source (not shown) of these gases is connected to the third gas introduction pipe 126. The flow of cooling gas can be controlled by valve 128. By supplying cooling gas, the growth of metal particles formed in the reduction furnace 112 can be controlled. The metal powder system is conveyed to the separation device or the recovery device by the cooling gas through the second conveying pipe 130, and is separately separated and purified.

During the reduction, the reduction furnace 112 is heated by the heater 114, and the first conveying pipe 116 and the second gas introduction pipe 122 lead the metal chloride gas and the sulfur-containing gas into the reduction furnace 112, and the first gas is introduced at the same time. The tube 118 supplies reducing gas into the reduction furnace 112. The heating temperature of the reduction furnace 112 is preferably lower than the melting point of the metal, for example, selected from the range of 800°C to 1100°C. In this way, the metal produced in the reduction furnace 112 can be made into solid metal particles and taken out. The amount of reducing gas supplied to the reduction furnace 112 is adjusted using the valve 120 to be stoichiometrically equal to or slightly surplus to the supplied metal chloride.

The sulfur-containing gas is a gas containing a component selected from hydrogen sulfide, sulfur dioxide, or sulfur halide. Examples of sulfur halide include _Sn Cl ₂ (n is an integer of 2 or more), SF ₆ , SF ₅ Cl, and SF ₅ Br. Among them, sulfur dioxide, which is easy to handle, is preferred. The flow rate of the sulfur-containing gas is adjusted using the valve 124 to be 0.01% by weight or more and 1.0% by weight or less with respect to the metal powder produced from the chloride per unit time supplied to the reduction furnace 112.

By adopting the method described above, the total concentration and local concentration of sulfur can be controlled within the range described in the first embodiment, and it can be manufactured not only near the surface, but also at a high concentration in the interior away from the surface Sulfur metal particles, and metal powder containing metal particles.

『Examples』

1. Example 1

In this embodiment, an example of applying the manufacturing method described in the second embodiment to manufacturing metal powder is disclosed.

In the chlorination furnace, nickel and chlorine gas are reacted to generate nickel chloride gas, the reduction furnace 112 is heated to 1100°C, and the nickel chloride gas is made to contain sulfur from the first conveying pipe 116 connected to the chlorination furnace The gaseous mixture of sulfur dioxide gas and nitrogen gas is introduced into the reduction furnace 112 at a flow rate of 2.8 m/sec (1100°C conversion). At the same time, hydrogen gas is introduced into the reduction furnace 112 from the first gas introduction pipe 118 at a flow rate of 2.2 m/sec (1100° C. conversion). As the cooling gas, nitrogen gas is used and supplied from the third gas introduction pipe 126. The obtained nickel powder (number-average particle size 190 nm) was purified using a generator (not shown) or the like. The total sulfur concentration of the obtained nickel powder was 0.15% by weight.

As Comparative Example 1 relative to this Example 1, nickel powder produced by subjecting nickel powder obtained by reduction of nickel chloride in the absence of sulfur-containing gas to sulfur treatment was used, and its sulfur concentration was measured . The nickel powder of Comparative Example 1 was produced by producing nickel powder without introducing sulfur-containing gas into the reduction furnace 112 in the above-mentioned embodiment, and then performing the following post-processing.

That is, for the slurry obtained during the purification of nickel powder (number average particle size 190 nm) produced in the absence of sulfur-containing gas, the sulfur content ratio relative to nickel powder is 0.15% by weight Aqueous thiourea solution was added and stirred for 30 minutes. Thereafter, the slurry was dried with an air flow dryer, thereby obtaining the nickel powder of Comparative Example 1.

For the nickel powders of Example 1 and Comparative Example 1, the local concentration of sulfur was measured from the surface in the depth direction using STEM-EDS. The measurement was performed using a scanning transmission electron microscope (JEM-2100F manufactured by JEOL Ltd.) equipped with an energy dispersive X-ray spectrometer (JED-2300T manufactured by JEOL Ltd.). The results obtained are disclosed in Table 1 and Figure 2.

"Table 1"

As shown in Table 1 and FIG. 2, it can be seen that the local concentration of sulfur on the surface of the nickel powder of Comparative Example 1 is higher than that of the nickel powder of Example 1, but it increases with the depth from the surface - That is, as it gets closer to the inside - it decreases sharply. In contrast, the nickel powder of Example 1 can be confirmed that although the local concentration of sulfur on the surface is low, the reduction rate in the depth direction is small, and sulfur is also distributed inside the nickel powder. In Example 1, the halving depth is 3.2 nm.

From these results, it can be seen that by using the manufacturing method related to the embodiment of the present invention, it is possible to obtain metal powder with sulfur distributed deeper.

2. Example 2

In this Example 2, the effect of the total concentration of sulfur on the sintering start temperature was studied. Using the same method as in Example 1, the flow rate of the sulfur-containing gas was changed from 1.7 m/sec to 2.2 m/sec (1100°C conversion) to prepare nickel powder having various total concentrations of sulfur. Similarly, using the same method as Comparative Example 1 described in Example 1, the concentration or addition amount of the thiourea aqueous solution was changed to prepare nickel powder having various total concentrations of sulfur as Comparative Example 2. The measurement of the total sulfur concentration was carried out in the same manner as in Example 1.

The measurement of the sintering start temperature was performed by a scanning electron microscope (SU-5000 manufactured by Hitachi High-Technologies Corporation) equipped with a heating stage (Murano 525 heating stage manufactured by Gatan Corporation). To exemplify a specific method, first, the metal powder is formed into particles of ø5 mm×1 mm, joined to a heating table, and guided into a scanning electron microscope. The heating stage was gradually raised from room temperature to 800°C, while being observed with a scanning electron microscope. As the temperature rises, the metal particles start to sinter, but the temperature at which more than half of the nickel powder in the field of view is sintered is set as the sintering start temperature. The results are shown in Figure 3.

In Comparative Example 2, it can be seen that as the overall concentration of sulfur increases, the sintering start temperature increases. However, as also described in Example 1, in the metal powder of Comparative Example 2, since the sulfur is not distributed into the metal particles at a high concentration, there is an upper limit on the total concentration of sulfur. Because of this, the overall concentration of sulfur is about 0.2% by weight at the maximum, and the sintering starting temperature stays at about 500°C to 600°C.

On the other hand, it can be seen that the nickel powder of Example 2 has a higher sintering start temperature than Comparative Example 2. In addition, in Example 2, the sulfur is distributed inside the nickel particles. Therefore, if compared with the nickel powder of Comparative Example 2, a higher total sulfur concentration can be achieved. For example, in the second embodiment, metal powder with an overall sulfur concentration of more than 0.2% by weight, or even an overall sulfur concentration of 0.3% by weight or more can be obtained. Because of this, the sintering start temperature of the nickel powder of Example 2 can reach more than 600°C and also reach about 700°C. In addition, it can be seen that when the total sulfur concentration is the same, by applying the manufacturing method of this embodiment, a nickel powder with a higher sintering start temperature can be produced.

The point to be noted here is that in Example 2, if the total concentration of sulfur becomes 0.15 wt% or more, the sintering start temperature is 600°C or more, or even more than 600°C can be achieved with a high probability. Therefore, by making the total concentration of sulfur in the metal powder more than 0.15% by weight, even if the total concentration of sulfur changes significantly, it does not show an effect on the sintering start temperature, which can effectively suppress the sintering start temperature. change. In other words, with the manufacturing method of this embodiment, it is possible to provide metal powder with a small variation in sintering start temperature.

According to the embodiment of the present invention, those who have ordinary knowledge in the technical field to which the present invention pertains can add, delete, or change design elements appropriately, or can add, omit, or change conditions of processes, as long as they have the gist of the present invention. That is included in the scope of the present invention.

Even if it is other operational effects that are different from the operational effects brought about by the above-described embodiments, those who are clear from the description in this specification or who have general knowledge in the technical field to which the present invention belongs Those who are easy to predict are self-understood as those facilitated by the present invention.

110‧‧‧reduction device 112‧‧‧reduction furnace 114‧‧‧ Heater 116‧‧‧The first delivery pipe 118‧‧‧The first gas inlet tube 120‧‧‧Valve 122‧‧‧ 2nd gas inlet tube 124‧‧‧Valve 126‧‧‧ 3rd gas inlet tube 128‧‧‧Valve 130‧‧‧ 2nd delivery pipe

<FIG. 1>: A schematic cross-sectional view of a reduction furnace of a metal powder manufacturing apparatus according to one embodiment of the present invention. <FIG. 2>: A graph showing the state of sulfur concentration of metal particles contained in metal powders of Examples and Comparative Examples. <FIG. 3>: A graph showing the relationship between the sintering start temperature of the metal powder and the total concentration of sulfur in Examples and Comparative Examples.

Claims (9)

A metal powder comprising: metal particles containing metal and sulfur having an overall concentration of 0.01% by weight or more and 1.0% by weight or less; wherein the local concentration of sulfur in the metal particles at a position of 4 nm from the surface is 2 atomic% Above; the total concentration and the local concentration are estimated by an energy-dispersive X-ray spectrometer equipped with an inductively coupled plasma luminescence spectroscopic analysis device and a scanning transmission electron microscope, respectively. The metal powder according to claim 1, whose number average particle diameter is 50 nm or more and 400 nm or less. The metal powder according to claim 1, wherein the sintering start temperature of the metal powder is 600°C or higher. The metal powder according to claim 1, wherein the metal is nickel, copper or silver. A method of manufacturing a metal powder, comprising: generating a gas of metal chloride by chlorination of a metal through chlorine; and by reducing the aforementioned metal chloride which is a gas in the presence of a gas containing sulfur Generation of metal particles; wherein the reduction is such that the total concentration of sulfur of the metal particles becomes 0.01% by weight or more and 1.0% by weight or less, and the local concentration of sulfur of the metal particles at a position of 4 nm from the surface becomes 2% by atom or more The total concentration and the local concentration are estimated by an energy-dispersive X-ray spectrometer equipped with an inductively coupled plasma luminescence spectroscopic analysis device and a scanning transmission electron microscope, respectively. The method according to claim 5, wherein the aforementioned reduction is performed without separate separation of the aforementioned metal chloride. The method according to claim 5, wherein the sulfur-containing gas system includes sulfur dioxide gas. A method for predicting the sintering temperature of a metal powder, which includes: measuring the local concentration of sulfur in the metal particles selected from the metal powder at a position of 4 nm from the surface, wherein the local concentration of sulfur is used with energy dispersion Type X-ray spectrometer scanning electron microscope to measure. The prediction method according to claim 8, further comprising: measuring the total concentration of sulfur in the metal powder, wherein the total concentration of sulfur is the scanning penetration provided with the energy dispersive X-ray spectrometer Electronic microscope to measure.

Images